Flash Photography with Canon EOS Cameras

Flash Photography with Canon EOS Cameras
Flash Photography with Canon EOS Cameras - Part I.
Copyright © 2001-2004 NK Guy
Version 1.6. March 11, 2004.
The invention and subsequent automation and miniaturization of electronic flash
revolutionized photography. If you’re a photographer you’re no longer tied to
available light. A reliable and portable light source is immediately at your disposal if
you choose.
But flash photography has always been a very difficult technique to master on any
camera system. It’s easy to take a snapshot of your friends in a restaurant and get
that hideously blown-out rabbit-in-the-headlights look from built-in automatic flash.
But using electronic flash well - achieving natural-looking images - is quite tricky.
This is in large part, of course, because the human eye can’t fully discern the effects
of a flash burst at the time an image is taken - the brief pulse of light is just too
short for us to process. And you can’t even see the flash if you’re looking through the
viewfinder of an SLR camera anyway, as the mirror will have been raised for the
duration of the flash. It’s also because small light sources mounted close to the lens
produce a very unnatural form of light.
So you have to read manuals and experiment. But with film-based photography
there’s a long lag time in the feedback loop - you have to take your film in to be
processed before you see what worked and what didn’t. Taking notes can be
cumbersome because of the highly automated nature of modern flash. Even
professionals don’t rely entirely on their experience and flash meters and do test
shots with a Polaroid instant film back in studio flash situations. Digital photography
has one of the benefits of shortening this feedback loop considerably, but that
doesn’t really help those of us who still use film.
So, here’s some information that may help you understand some of the mysteries of
flash photography with Canon EOS camera equipment. Much of the information
presented herein is fairly general in nature and thus covers similar flash systems
used by other manufacturers, but much is very specific to Canon EOS products.
Note that this document covers Canon EOS products, including digital EOS cameras.
Canon’s PowerShot series of digital cameras can use Speedlite EX-series flash units,
but since they aren’t EOS cameras there are significant differences in the way they
Table of Contents
Part I - Flash Photography with Canon EOS Cameras.
Existing documentation.
Top Ten Frequently Asked EOS Flash Questions.
1 - My camera already has a built-in flash. Do I need an external one? If so, what
2 - I’m not happy with my flash photos. The lighting always looks harsh and
3 - Are my friends possessed by demonic powers? Their eyes are glowing an evil red!
4 - I took a flash photo and there’s a curved shadow at the bottom of the photo.
5 - I took two flash photos in rapid succession and the second one is totally dark.
6 - I’ve put a diffuser or reflector on my flash. Do I have to compensate for this
7 - I tried to take a flash photo and the camera wanted a really slow shutter speed.
8 - I tried taking a flash photo and the camera wouldn’t let me set a very high
shutter speed.
9 - I took a flash photo and the background is pitch black or very dark.
10 - My camera meters in P and Av modes very differently when I have a flash
turned on.
Flash metering systems used by Canon EOS.
Controlling flash exposure.
Flash metering principles.
TTL (through the lens) flash metering.
Refinements to TTL flash, including Canon AIM.
A-TTL (advanced TTL).
Limitations of A-TTL.
E-TTL (evaluative TTL).
Limitations of E-TTL.
Canon EF lenses with distance data for E-TTL II.
FP (focal plane) flash mode.
TTL and E-TTL and EOS film cameras.
TTL and E-TTL and EOS digital cameras.
Type A and type B bodies.
Disabling E-TTL.
EOS system compatible flash units.
Internal flash.
Basic (PIC) modes and external flash units.
Canon external flash unit types.
Nomenclature of external flash units.
Older Canon Speedlite flash units.
Hotshoe flashes.
Handle-mount (grip) flash.
Macro flash.
Third-party flash units.
Other flashes.
Which flash unit should I buy?
Part II - EOS flash photography modes.
Subject and Background in flash photography.
Fill flash.
Fill flash ratios.
Auto fill reduction.
Slow shutter sync.
X-sync (flash sync) speed.
Maximum X-sync speed and EOS bodies.
EOS flash photography confusion.
Program (P) mode flash.
Tv (shutter priority) mode flash.
Av (aperture priority) mode flash.
Manual (M) exposure mode flash.
Multiple flash units.
Metering patterns for the background when using flash.
Flash metering patterns.
Do not focus and recompose.
Flash terminology.
Strobe and flash.
Inverse square law.
Guide number.
Exposure values (EV).
Dedicated or non-dedicated flash units.
Shoe mount.
The redeye effect.
Redeye reduction.
The first curtain sync problem.
Second-curtain sync.
Colour temperature theory.
Colour temperature and film.
Colour temperature and flash photography.
Colour filters.
Limitations of filters.
Wratten numbers.
Trigger circuit voltage.
Slave flashes.
Flash meters.
Flash sync trivia.
Part III - Common EOS flash features.
Bounce flash - swivel and tilt.
Zooming flash heads.
Flash head coverage.
AF assist light.
Camera-specific notes on AF assist lights.
Flash exposure compensation (FEC).
Which bodies/flash units have FEC.
List of which bodies/flash units have FEC.
Faking flash exposure compensation.
Flash exposure lock (FEL).
Flash exposure bracketing (FEB).
Enabling second curtain sync.
List of which flash units and camera bodies have second-curtain sync.
Range warning.
Manual flash.
Flash exposure level.
Rapid-fire mode.
Stroboscopic flash.
Setting stroboscopic flash.
Flash exposure confirmation.
Wireless remote control.
List of wireless-capable flash units and cameras.
Modelling flash.
Save Energy (SE) mode.
High-voltage connector.
PC terminals/sockets.
Custom functions on flash units.
Test flash (manual firing).
Manual flash triggering for light painting.
Flash safety.
Extension cords.
Flash diffusers.
Flash brackets.
External battery packs.
Flash extenders
Power source options for external flash units.
Standard AA non-alkaline (zinc carbon) cells.
Standard AA alkaline cells.
Rechargeable nickel-cadmium (NiCad) cells.
Lithium AA cells.
Rechargeable nickel metal hydride (NiMH) cells.
External battery pack.
Flash tips.
Quality of light.
General flash photography.
Shooting indoors in a small space.
Shooting outdoors or indoors in a large space.
Links to other useful documents.
Disclaimer and copyright.
Existing documentation.
Learning more about flash photography with EOS cameras is hard as there’s
relatively limited information available on the topic. Canon’s manuals tend to be
fairly short, and not much information has been published about the flash algorithms
used by EOS cameras. There’s a brochure on the topic - Canon’s “Flash Work,” but
unlike the excellent and similarly titled book “Lens Work,” the flash brochure does
not go into much detail. Hove/Silver Pixel Press published a book on the Canon
Speedlite 540EZ flash unit, which also briefly described other Canon flash units sold
at the time, but the book is now apparently out of print.
Canon USA did publish two technical booklets on the subject in the early 1990s - the
“Canon Speedlite Reference Guide” and the smaller “Canon EOS Speedlite System.”
However, these are now out of print and don’t cover E-TTL technology. The Speedlite
Reference Guide is a very useful resource for learning more about TTL and A-TTL
flash, however. Many thanks to Brett Cheng for mailing me a copy!
When the Elan II (EOS 50) was released, Canon USA’s Chuck Westfall provided some
valuable information that Mark Overton wrote up in the form of an FAQ. This
document is very useful, but somewhat terse - it doesn’t cover a lot of the
terminology and background. It also deals primarily with one camera/flash
combination - the Elan II and the Speedlite 380EX. So I decided to write a somewhat
more detailed account of how EOS flash works.
The document you are currently reading is, however, extremely long and detailed.
So if you want a quick précis of EOS flash technology you should probably consult
the Westfall/Overton FAQ on Bob Atkins’ Web site.
Finally, please note that I have no particular insight into or access to the mysterious
ways of Canon’s flash engineers. I wrote this document partly because I thought it
might be helpful to others and partly because explaining something is a great way to
learn something yourself. But there may, of course, be technical errors in this
document. If you spot any errors or ambiguous or vague sections, Please send
Top Ten Frequently Asked EOS Flash Questions.
Before we start, however, I’d like to provide quick answers to the top ten Frequently
Asked EOS Flash Questions, since they come up an awful lot.
1) My camera already has a built-in flash. Do I need an external one? If so,
what kind?
This question crops up all the time on discussion forums, much to the irritation of
oldtimers. And their irritation usually arises for two simple reasons. First, they’re
grumpy cantankerous curmudgeons and second, the question is sort of meaningless
without knowing what your photographic requirements and interests are.
It’s very much like asking, “Which car should I buy?” The answer depends on your
needs and budget. But here’s a brief overview of what you should consider.
If you just want something to take snapshots with, a built-in popup flash is probably
sufficient. It can’t produce much light and so doesn’t have a lot of range, but then
friends in restaurants aren’t going to be very far from you. It has a harsh quality, but
for snapshots most people don’t seem to mind much. And internal flash units are
convenient - you can’t lose them unless you lose the whole camera, and they don’t
add any additional weight or bulk.
However, if you want to get into more advanced photography you’ll probably want
either to buy a good external flash unit or else eschew flash as often as possible and
rely more on available light. As noted above, the light from an internal flash unit is
very harsh, whereas external units let you soften the light by bouncing it off of walls
or ceilings, or attaching light-softening diffusers. Most importantly, an external flash
unit can be taken off the camera - either with an extension cord or wireless. This is
important since on-camera flash provides unnatural head-on lighting.
At this point it’s largely a matter of how much you want to spend and how much
weight you want to carry around. Please consult the “which flash?” section of this
document for more details.
Nonetheless, remember that flash is no panacea for photographic lighting problems.
It’s obviously a valuable tool, but often the best way to ruin a nice picture is to blast
tons of light onto the scene with a flash unit. Available light photography forces you
to slow down and consider the light around you, which ultimately can help you
become a better photographer.
2) I’m not happy with my flash photos. The lighting always looks harsh and
Flash is like that. Basically, soft lighting is light which originates from a large area.
Portable camera flashes, by contrast, have very small light-producing areas and,
therefore, produce very hard-edged light with pronounced shadows. Flash units also
tend to be mounted right next to the camera lens, producing an unnatural look. How
often do you see the world illuminated by light emanating from your head? You don’t
- unless you’re wearing a caving helmet. Light tends to come from overhead sources
- the sun, ceiling lamps, etc.
The easiest way to soften the lighting in your flash photos is to bounce the light from
the flash unit off a large white surface. Walls and ceilings work for this, as do
portable folding reflectors. You can also buy diffusers that attach to your flash that
help a little bit as well. For more information have a look at the section on quality of
3) Are my friends possessed by demonic powers? Their eyes are glowing an
evil red!
This is the “redeye” effect; a common problem with the internal flash units built into
cameras. It’s caused by the light from the flash unit reflecting off the red blood
vessels lining the interior of the eye. The light shines back into the camera, resulting
in the famous red glow.
The easiest way to minimize the risk of redeye is to use an external flash unit rather
than a built-in flash. The problem is fully explained in the redeye section of this
document, as is the related problem of greeneye in cats and dogs.
If, however, your friends’ eyes glow an evil red in real life and not just in your flash
photos of them then you’re reading the wrong document and probably should do a
Web search on exorcism.
4) I took a flash photo and there’s a curved shadow at the bottom of the
You’re using the camera’s internal flash and you also have a very large lens installed
or a lens with a big lens hood. Either way, something is blocking the light from the
internal flash.
To fix the problem you could try a different lens, zoom wider if the lens is extended
(ie: shorten the lens if it’s a zoom lens), remove the lens hood or use an external
flash unit. It’s also possible that you’re too close (a metre or less) to the subject.
5) I took two flash photos in rapid succession and the second one is totally
All flash units take a number of seconds to charge up between flash bursts. Some
flash units have “rapid-fire” abilities which let them fire the flash even if the internal
capacitor is not yet fully charged - but others don’t.
So if your second photo is dark it probably means that your flash unit lacks rapid-fire
capabilities. You have to wait for the unit to charge up fully (and the pilot light on the
back of the unit goes on) before taking the second photo. However, if your flash does
have rapid-fire capabilities then you probably took the second photo too quickly and
the flash unit hadn’t enough time to recharge to an adequate power level.
Note that different types of batteries charge up the flash at different speeds, so if
this is a consistent problem you should look into your battery options.
6) I’ve put a diffuser or reflector on my flash. Do I have to compensate for
this somehow?
Diffusers of any kind obviously reduce the amount of light that your flash unit
produces. You’ll find a similar effect if you bounce the light from your flash unit off a
wall or into a photographic umbrella.
However, so long as you’re using automated (TTL, A-TTL or E-TTL) metering then
the camera will compensate automatically. There is no need to adjust anything.
You’ll have decreased range, but you shouldn’t have any exposure problems unless
you’re too far away from the subject and the decreased range now means you’re out
of range. Diffusers can easily cost you at least half your flash range, depending on
the type.
7) I tried to take a flash photo and the camera wanted a really slow shutter
This occurred because you are trying to take a flash photo in low-light conditions and
the camera is in Av (aperture priority) mode or the night PIC (icon) mode if your
camera has it.
In Av, night and Tv (shutter speed priority) modes the camera meters for ambient
(existing) light and fills in the foreground subject using the flash. It does not assume
that the primary light source is the flash, and therefore the shutter speed it sets is
the same as it would set if you weren’t using flash at all.
In low light this results in slow shutter photography. If the shutter speed is very long
you will, therefore, need a tripod to avoid motion blur during the exposure.
Alternatively you can switch to full auto (green rectangle) or Program (P) mode,
which automatically expose for the flash-illuminated subject and not the background.
These modes try to ensure that the shutter speed is high enough to let you handhold
the camera without a tripod. The drawback of P and basic modes is that photos
taken in dimly lit areas usually end up with black or poorly lit backgrounds.
8) I tried taking a flash photo and the camera wouldn’t let me set a very
high shutter speed.
Each camera model has a top shutter speed that can be used with flash. This is
known as its flash sync or X-sync speed, and varies from 1/90 sec on low-end
cameras to 1/250 on pro cameras. (1/500 sec on the digital 1D)
If you have a newer camera and an EX series flash you can use FP mode to
circumvent this limit - see the FP section for more details.
9) I took a flash photo and the background is pitch black or very dark.
This is the flip side of question 7. In P (program) mode and all flash-using PIC (icon)
modes except for night mode (if your camera has it) the camera uses the flash as
the primary light source for the foreground subject.
If the ambient light levels are low, therefore, the background will turn out very dark.
This is because the flash is not illuminating the background and the shutter speed is
too short to expose adequately for background areas.
Remember that the light from any battery-powered flash is somewhat limited. You
can’t expect a small flash unit to light up the Grand Canyon or Eiffel Tower. You can
only reasonably expect it to light up people standing in the foreground or close
backgrounds such as room interiors.
To avoid this problem of black backgrounds you will need to take a photo in Av, Tv or
M modes, as mentioned in question 7. If the ambient lighting is very low you may
need a tripod to avoid motion blur for the time required to expose the background
adequately. Using fast film (eg: ISO 800) and wide lens apertures (the smaller the f
stop you can get on your lens) will help bring up the background as well.
10) My camera meters in P and Av modes very differently when I have a
flash turned on.
That’s how EOS cameras are designed to work. P, Av, Tv and M modes all meter for
flash in different ways. See the section on “EOS flash confusion” for details. Here’s
the short version, which repeats some of the points made in previous FAQ questions.
Keep in mind that the camera meters for ambient (existing) light conditions and flash
illumination independently.
P (program) mode keeps the shutter speed between 1/60 sec and the maximum
flash sync speed your camera can handle. It does this so that you shouldn’t need a
tripod, even if light levels are low. It then tries to illuminate the foreground using
Av (aperture priority) and Tv (shutter speed priority) modes set the shutter speed or
aperture to expose for the existing light conditions correctly. They then fill in the
foreground using flash. If light levels are low you will need a tripod to avoid blur.
M (manual exposure) mode lets you set both aperture and shutter speed to be
whatever you want. The camera then automatically controls the illumination of the
foreground subject using flash.
Flash metering systems used by Canon EOS.
Electronic flash has come a long way since Harold “Doc” Edgerton, an American
researcher and inventor, made modern electronic flash photography a reality in
1931. But simple or complex, the basic principle of electronic flash remains the same
- you charge up a capacitor (or “condenser”) with electricity and then release the
stored energy in a brilliant split-second burst of light from a flash bulb - a glass tube
filled with inert gases.
The light output changes instantly in response to the presence or absence of power
being delivered to the tube, so the primary form of control you have over the light
output is duration of the electrical pulse, which is switched off by a component called
a “thyristor.” Old-fashioned manual flashes require you to calculate the distance to
the subject and then set the flash duration time yourself; a cumbersome and errorprone process. Modern flash units automate this process completely through the use
of computer-controlled electronics.
Controlling flash exposure.
In regular photography you have two basic ways by which to control the amount of
ambient (available) light entering the camera and exposing the film. You can adjust
the shutter speed, which affects the duration of the exposure since ambient light is
essentially constant in this context. And you can adjust the lens aperture - the
physical diaphragm on most lenses which governs the quantity of light that enters
the lens. (you can also use different lenses, add filters to the lens and so on, but
we’re talking about the fundamental issues here)
However, flash photography is quite different since it involves split-second bursts of
light. A key point to remember in flash photography is that the shutter speed of the
camera normally does not have any bearing on flash exposure - an exception being
FP mode, mentioned later. Light from a continuous source is affected by shutter
speeds, but flash bursts are so brief - in the milliseconds - that a mechanical shutter
mechanism has no way of limiting the amount of light from a flash unit that hits the
film. Shutter speed only affects the amount of ambient light.
You therefore have four basic ways to control how much light from a flash unit
exposes the film.
First, you can adjust the lens aperture. However, lens apertures also affect
the amount of ambient light striking the film as well, so it would obviously be
hugely inconvenient if that were the only option at our disposal.
Second, you can adjust the distance from the flash unit to the subject. Light
falloff follows known physical laws and so can reliably be calculated, but of
course it’d be very inconvenient if you had to move the flash unit around all
the time just to adjust flash exposures. That sort of thing is fine in a studio
setting, but not for casual or photojournalist photography. Additionally,
altering flash unit/subject distances affects the relative size of the flash light
source, which results in different qualities of light (hard vs soft).
Third, you can put various diffusers or light baffles between the flash unit and
the subject, which would be a nuisance to carry around and deal with.
Fourth, you can adjust the duration of the flash pulse as mentioned above,
which thereby affects the intensity of the light produced. And this is the
primary method of control we use for electronic flash.
So that’s what flash metering is really all about, in a nutshell. You need to adjust the
duration of the flash pulse so you can expose the film correctly and achieve your
photographic goal. Determining what this flash duration should be is not an easy
thing to do, however, and so camera makers over the years have come up with
various automated systems to do it.
Flash metering principles.
Flash metering has very different requirements from normal ambient light metering
for the reasons outlined above. Ambient light metering is performed well in advance
of the shutter opening. EOS cameras, for example, activate the internal light meter
when you press the shutter release button down halfway. But the subjectilluminating flash pulse, however, occurs after you press the shutter release all the
way. That means that the flash pulse appears after the mirror has flipped up
(blocking the ambient light meter) and the shutter has opened.
There are thus two basic ways you can meter for flash automatically. First, you can
measure the flash pulse as it is being emitted or second, you can send out a lowpower test pulse (preflash) of known brightness first and base your light calculations
on that data before the shutter opens.
These two flash metering methods are used by Canon’s automated flash metering
systems. TTL and A-TTL flash use the former and E-TTL the latter. Flash units
capable of E-TTL also support FP mode flash. Here’s an explanation of these
TTL (through the lens) flash metering.
As noted above, the earliest electronic flashes required the photographer to perform
distance calculations by hand. Later, the first generation of automatic electronic flash
units relied upon external sensors to determine the flash exposure setting. These
sensors, mounted on the front of the flash unit, simply recorded the flash bulb’s
light, reflected back from subject, and cut off the power when enough light for a
satisfactory exposure was determined. The venerable Vivitar 283 still sold today
works this way, in fact.
Of course, such external sensors were easily fooled. The sensor might, for example,
cover more or less area than the lens currently in use. So Olympus pioneered
through-the-lens flash metering in the mid 1970s with the OM2. Canon later included
TTL flash metering in their T90 camera a decade later, and added the feature as
standard with the EOS line of film cameras. It’s for this reason that the Canon T90 is
the only non-EOS camera capable of using Canon’s TTL system.
TTL flash metering works by measuring the pulse of flash-generated light bouncing
back off the subject and entering the lens. It actually measures this light reflecting
off the surface of the film itself, in realtime, by using an off the film (OTF) sensor.
The light from the flash bulb is quenched when the sensor determines enough light
has been produced to achieve a satisfactory flash exposure to get a mid-toned
For those interested, the OTF sensor is buried deep in the camera body, and is
visible if you put the camera in bulb mode (ie: flip up the mirror and open the
shutter) and open the camera back. It’s a small lens pointing back at a 45° angle
towards where the film surface would be, and is located at the bottom of the camera
in the ridged black area right in front of the shutter curtain. The rectangular or crossshaped hole or holes immediately in front of it are the autofocus sensors.
The TTL sequence of operation is as follows:
When the shutter release is depressed halfway the current ambient light
levels are metered by the camera as usual. Shutter speed and aperture are
set by the camera or user depending on the current mode - P, Av, Tv or M. In
P mode the camera sets the shutter speed to a value between 1/60 and Xsync. In the other modes it meters normally. (except on certain cameras
which have a custom function that can lock the camera to X-sync in Av mode)
When the shutter release is pressed all the way the camera flips up the mirror
and opens the shutter, exposing the film.
The flash unit sends power to the flash tube, illuminating the scene. The start
time of the flash triggering depends on whether first or second curtain sync
has been set.
Duration of the flash pulse is determined by the OTF sensor, which meters for
an average scene. If the photo is being taken under bright lighting conditions
(10 EV or brighter), auto fill reduction is applied. (unless it has been disabled
by a custom function, as is possible on some bodies) This can reduce the flash
output by anywhere from 0.5 to 1.5 stops.
As soon as the flash unit determines that the foreground subject has been
adequately lit - by this realtime measurement of reflected flash light - it cuts
off the power to the flash tube and the light from the flash unit is immediately
The shutter stays open for the full duration of the shutter speed time.
The mirror flips down and the shutter closes. If the flash unit has a flash
exposure confirmation light and if the flash metering was deemed adequate
then the light glows.
One note - since the sensor records light reflecting off the surface of the film
itself it will of course react differently to film with very different reflective
properties. According to B&H’s Henry Posner on the EOS list, all cameras with
TTL flash are calibrated to work with the emulsion characteristics of typical
colour print film and there may, therefore, be very subtle differences in flash
metering when you use slide film. Since slide film has very narrow exposure
tolerances (latitude) this might be an issue for you.
Cameras which support TTL flash:
The T90 and all EOS film cameras except the EF-M. The digital D30, D60, 1D,
1Ds, 10D, 300D/Digital Rebel/Kiss Digital and 1D mark II cameras do not
support TTL.
Flash units which support TTL flash:
All “E’ series Speedlites plus the 300TL: 160E, 200E, 220EX, 300EZ, 380EX,
420EZ, 420EX, 430EZ, 540EZ, 550EX, 480EG, MR-14EX, MT-24EX and 300TL.
Refinements to TTL flash, including Canon AIM.
TTL metering is more reliable than systems which rely on external sensors, but it can
still be fooled. For example, a highly reflective subject or a subject in white
surroundings can result in a lot of light reflecting back, so the resulting picture may
well be underexposed as the camera quenches the flash too soon. An off-centre
subject poses similar problems. Another issue is that the flash metering occurs while
the shutter is open, so the camera can’t accurately factor flash in with ambient light
Canon refined TTL control on their multiple focus point cameras by adding a feature
they call AIM, (“Advanced Integrated Multi-point Control System”) which is basically
multiple-segment flash metering. This lets the camera bias the flash exposure to the
currently selected focus point, thereby increasing the chances of getting accurate
flash exposure for off-centre subjects.
The AIM system means that it’s best to rely on selecting off-centre focus points for
flash photography rather than using the centre point and then recomposing the
image. (unless you use flash exposure lock, explained below) For more information
on AIM consult the flash metering patterns section. Note that older EOS cameras
with multiple-segment flash metering didn’t use the term “AIM” in their
documentation - Canon came up with the marketing term sometime in the mid 90s so the fact your multiple focus point camera doesn’t mention AIM doesn’t mean it
hasn’t got it.
Nikon improved their TTL flash metering system by incorporating subject distance
into flash calculations - their “3D” system. This system determines distance
information by reading the current focussing distance from the lens. Canon did not
incorporate a similar distance-data system in their flash technology until 2004, with
the introduction of E-TTL II. However, while distance data is valuable, it’s important
to keep in mind that distance data isn’t very useful when using a flash in bounce
mode or when using any diffusion system in which the light from the flash unit does
not travel directly to the subject, since both cases increase the flash to subject
distance over the lens to subject distance.
A-TTL (advanced TTL).
Canon’s first step in altering flash exposure design was the creation of A-TTL, or
“advanced through the lens” flash metering, which was introduced with the T90
camera and continued on to the EOS series of film cameras.
A-TTL flash units (300TL and EZ series Speedlites only) send out a brief burst of light
during the metering phase. (ie: when the shutter release button is pressed halfway)
This preflash is recorded by an external sensor on the front of the flash and used to
determine a reasonable aperture to ensure adequate depth of field, particularly at
short distances. The flash unit then sends out the actual scene-illuminating flash
once the shutter has opened.
The A-TTL sequence of operation is as follows:
When the shutter release is depressed halfway the current light levels are
metered by the camera. In P and Tv modes the ambient aperture value is
determined and stored, but not set. In Av and M modes the ambient aperture
value is user-set.
The flash unit fires a preflash (either near-infrared light from a front-mounted
secondary flash bulb or white light from the main flash bulb, depending on
the flash unit and operating mode) in conjunction with the ambient light
metering, in order to determine the approximate distance from the flash to
the main subject. In P mode only, the correct aperture value to expose the
main subject is then calculated.
In P mode only, the two aperture values (ambient and flash) are compared
when the shutter release is fully depressed. The camera typically sets the
smaller of the two apertures, particularly if the distance to the subject is
determined to be fairly close. In Av and M modes the aperture is determined
by the user setting and in Tv mode the aperture is determined by the ambient
light meter settings.
If the photo is being taken under bright lighting conditions (10 EV or
brighter), auto fill reduction is applied. (unless it has been disabled by a
custom function, as is possible on some bodies) This can reduce the flash
output by anywhere from 0.5 to 1.5 stops.
Finally, the camera flips up the mirror and opens the shutter, exposing the
The flash unit then sends out the actual scene-illuminating flash. The start
time of the flash pulse depends on whether first or second curtain sync has
been set. Duration of the flash pulse is determined by the standard OTF
sensor - exactly the same as TTL flash.
The shutter stays open for the full duration of the shutter speed time.
The mirror flips down and the shutter closes. If the flash unit has a flash
exposure confirmation light and if the flash metering was deemed adequate
then the light glows.
Camera bodies which support A-TTL:
All EOS bodies which support TTL (see above).
Flash units which support A-TTL:
Speedlites 300EZ, 300TL (T90 only), 420EZ, 430EZ, 540EZ.
Limitations of A-TTL.
Sadly A-TTL, despite its name, is of rather limited value. For one thing, use of A-TTL
in bounce mode on some flash units such as the 420EZ and 430EZ results in blinding
flashes of white light from the main bulb each time you press the shutter halfway,
which can be very annoying to human subjects. Although these flash units use a
small separate A-TTL tube to flash fairly discreet near-infrared red light during the
preflash stage when the head is pointed straight on, they flash the main flash tube
(white light) instead when the flash head is tilted or swivelled.
If that weren’t enough, the preflash isn’t even really used by most EOS cameras
when it’s in Av, Tv or M modes, since unlike P mode you aren’t setting aperture
automatically for flash metering purposes. And, unlike E-TTL, the A-TTL preflash is
never used for actual flash metering. The original purpose of the A-TTL preflash in
those modes was to provide information to the flash out of range warning light in
early EOS cameras - the 630, RT and 1. Canon had to drop that whole system for
patent reasons by the late 80s, but the A-TTL preflash in non-P mode still lives on as
a kind of useless appendix in most A-TTL flash units.
It’s interesting to note that the 540EZ flash avoids these problems simply by ditching
A-TTL in bounce mode altogether and reverting to TTL. In fact, the 540EZ doesn’t
use A-TTL for Av and Tv modes either, unlike the earlier flash units. Presumably by
that point Canon decided that most 540EZ buyers weren’t going to be 630, RT and 1
owners as well.
Since the A-TTL sensor is on the front of the flash unit - behind a recessed plastic
lens and not inside the camera, metering through the camera lens, it’s conceivable
that a very heavy filter on the lens might result in some metering problems since the
filter doesn’t cover the sensor as well. And, speaking of the flash-mounted sensors,
be sure not to block it with your hand or anything for the same reason. Some flash
diffusers can also present a problem in that the light spilling downwards from the
diffuser can enter the A-TTL sensor inadvertently.
Finally, despite the additional complexity of the preflash circuitry, A-TTL simply ends
up setting a pretty small aperture most of the time, to assure wide depth of field,
which isn’t always what you want.
In short, A-TTL adequately assures reasonable flash exposure and depth of field in a
point and shoot fashion in P mode. It isn’t so useful for more subtle or complex
lighting techniques and isn’t useful at all in Av, Tv and M modes.
E-TTL (evaluative TTL).
With the Canon Elan II/50 camera in 1995, Canon introduced another form of flash
technology - E-TTL, for “evaluative through the lens” flash metering. E-TTL fires a
low-power preflash of known brightness from the main bulb to determine correct
flash exposure. It measures the reflectance of the scene with the preflash, then
calculates proper flash output to achieve a midtoned subject, based on that data. It
uses a preflash, but doesn’t suffer from A-TTL’s drawbacks for two reasons.
First, the E-TTL preflash occurs immediately before the shutter opens and not when
the shutter release is pressed halfway. Unlike the A-TTL preflash, therefore, the ETTL preflash is actually used to determine flash exposure and isn’t fired during the
ambient (existing) metering stage. Some users may be surprised to learn that E-TTL
actually fires a prefire flash before the main flash at all. Using regular settings the
process happens so quickly that the preflash is difficult to notice, though you might
catch glimpse of it before the mirror blackout - an exception being second-curtain
Second, the preflash light is analyzed by the same evaluative metering system that
the camera uses to meter ambient light. This means it meters through the lens and
is harder to fool than external sensors, isn’t confused by bounced light and does not
read anything off the surface of the film. For what it’s worth, unlike the TTL flash
meter, the E-TTL metering sensor cannot be seen by the curious - it’s hidden away
up in the pentaprism (or roof mirror in low-end EOS cameras) housing.
E-TTL is also generally superior to TTL and A-TTL when it comes to fill flash. The ETTL algorithms are usually better at applying subtle and natural fill flash light to
daylight photographs. E-TTL exposure is also linked to the current AF focus point,
which in theory results in finer-grained exposure biasing than most multiple-zone
TTL flash sensor systems.
The usual E-TTL sequence of operations, not counting the optional flash exposure
lock (FEL) feature or wireless operation, is as follows:
When the shutter release is pressed halfway the current ambient light levels
are metered by the camera as usual. Shutter speed and aperture are set by
the camera or user depending on the current mode - PIC (icon) modes or P,
Av, Tv or M.
When the shutter release is pressed all the way the flash unit immediately
fires a low-power preflash from the main flash tube. (ie: white light)
The reflected light from this preflash is analyzed by the same evaluative
metering system that the camera uses for metering ambient light levels. The
appropriate power output (ie: flash duration) of the flash is determined and
stored in memory. The entire sensor area is evaluated and compared to the
ambient metering, and the area around the active focus point is emphasized.
If you are in manual focus mode then either the central focus point or
averaged metering is used.
If the photo is being taken under bright lighting conditions (10 EV or
brighter), auto fill reduction is applied (unless it has been disabled by a
custom function, as is possible on some bodies) and the flash output is
decreased by anywhere from 0.5 to 2 stops. However, the E-TTL auto fill
reduction algorithm has never been published to my knowledge, so nobody
outside Canon knows exactly how it works.
The mirror flips up and the shutter opens, exposing the film - or sensor chip if
it’s a digital camera.
The flash tube is then fired at the previously determined power level to
illuminate the scene. Start time of the flash burst depends on whether first or
second curtain sync has been set. The OTF sensor in the camera, if present, is
not used in E-TTL mode.
The shutter stays open for the full duration of the shutter speed time.
The mirror flips down and the shutter closes. If the flash unit has a flash
exposure confirmation light and if the flash metering was deemed adequate
then the light glows.
Camera units which support E-TTL:
All type A EOS cameras (see below).
Flash units which support E-TTL:
All EX series Speedlites: 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
Limitations of E-TTL.
One drawback of E-TTL is that the preflash can cause people who blink quickly to be
photographed mid-blink - what EOS list member Julian Loke has referred to as the
BEETTL syndrome, for “blinking eye E-TTL.” The preflash normally occurs an
extremely brief period of time before the main flash, but when using second-curtain
sync with slow shutter there’s enough time for rapid blinkers to react to the preflash.
This apparently can also be a problem for nature photographers who photograph
Another problem is that the use of preflash can trigger studio slave flash units which
work by detecting the light from the triggering camera - analogue optical slaves. This
results in flash exposure going very wrong, since the optical slave is triggered too
soon. The preflash can also confuse handheld flash meters, making manual flash
metering very difficult.
More abstractly, E-TTL is a very automated system and isn’t well documented for the
user. For instance, as noted above, Canon have never published details on the E-TTL
auto fill reduction algorithm. It takes a bit of experimenting to figure out how the
system is likely to respond. And there’s relatively little user selection or choice in
operation modes. Most flash units don’t, for instance, let you manually choose TTL,
A-TTL or E-TTL flash metering at will.
E-TTL has also been a problem for a lot of digital users (see TTL and E-TTL and
digital EOS cameras below) because of the way E-TTL flash metering is performed.
Some of these issues are addressed by E-TTL II, which is described in the next
Finally, not every E-TTL feature is supported by every type A body and E-TTL flash
unit. Some wireless E-TTL features and other functions such as the modelling light,
for example, require both newer type A EOS bodies like the EOS 3 or EOS 30 and
flash units like the 550EX or 420EX. Part III of this article describes which features
are available for which combinations of camera body and flash unit.
Introduced in 2004 with the EOS 1D mark II digital camera and the EOS Elan
7N/EOS 30V/7S film camera, E-TTL II is an improved version of regular E-TTL which
includes two key innovations.
Improved flash metering algorithms.
First, E-TTL II examines all evaluative metering zones both before and after the ETTL preflash goes off. Those areas with relatively small changes in brightness are
then weighted for flash metering. This is done to avoid the common E-TTL problem
of highly reflective materials causing specular highlights in a flash-illuminated image
and throwing off the flash metering. Normally E-TTL II uses evaluative algorithms for
its flash metering, but the EOS 1D mark II has a new custom function (CF 14-1) that
lets you use centre-weighted averaging rather than evaluative metering for flash
metering if you prefer.
Distance data incorporated into some calculations.
Second, E-TTL II can use distance data when it’s available. Many EF lenses (see list
in next section) contain rotary encoders that can detect the current focus distance.
For example, if your camera is focussed on an object 4 metres away then the lens
will send this approximate focus distance data to the camera body.
Under certain conditions the distance data is factored into the calculations for
determining proper flash output. This is particularly useful if you use the focus and
recompose method without setting FEL - the new system can help minimize flash
metering errors under these conditions. Canon describe the new system as
essentially metering flash data across a flat plane rather than a point.
Up until now distance data hasn’t really been used much by EOS cameras. Some PIC
(icon modes) apparently incorporate distance data into their exposure calculations,
but that’s really been about it. E-TTL II is the first really useful application of this
information that Canon have implemented, and is obviously very similar to the
fashion in which Nikon have long relied on distance data for their flash metering
Cases in which distance data is not used.
Distance data is not always used by E-TTL II. There are three very significant cases
in which distance data is not used, aside from the obvious case when it isn’t available
because the lens doesn’t provide it. These three conditions are bounce flash, macro
flash and wireless E-TTL flash.
When you’re using bounce flash (ie: when the flash unit’s head is in basically any
position other than full-on straight) then there is no way for the camera to know the
distance the light took to reach the subject from the flash. Light will be scattered off
walls or ceilings or reflectors and won’t travel directly to the subject. Since bounce
flash is a common technique to improve the quality of a flash-illuminated scene it
means that the primary advantage of E-TTL II in this situation is just better
evaluative flash metering.
The other two conditions are similar. With macro flash you’re too close to the subject
for the lens to determine useful information, and with wireless E-TTL flash the
camera will have no idea where the flash units are positioned in relation to the
subject. Note that E-TTL II can still use distance data if the flash unit is connected to
a camera via an Off-Camera Shoe Cord. (there was some confusion about this early
on, but Canon USA’s Chuck Westfall has confirmed it) This means that users of flash
brackets won’t be left out, though it does mean that if you position the flash unit
closer to or further from the subject than the camera, or if you point the flash unit
away from the lens axis while keeping the flash head locked in a straight ahead
position, then you might throw off the flash metering slightly. You can’t directly
disable the use of distance data if the lens has it, though in this case you could take
the simple precaution of setting the flash head to a very slight off-centre bounce
position that would disable distance data while not significantly altering the flash
To summarize, there are two important points to keep in mind. First, E-TTL II does
not require any changes to either the flash units or lenses used with an E-TTL II
camera - the changes are all basically internal to the camera body. And second,
while E-TTL II does use distance data when it’s available and when it’s appropriate
(eg: when using direct non-bounce flash), it doesn’t prevent you from using older
Camera units which support E-TTL II:
EOS 1D mark II, EOS 30V/33V/7S/Elan 7N/Elan 7EN.
Flash units which support E-TTL II:
All EX series Speedlites: 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
Canon EF lenses with distance data for E-TTL II.
The following lenses are capable of returning distance data for use with those
cameras which can use them. This list was published by Canon USA’s Chuck Westfall
in March 2004 and is reasonably comprehensive, though does have a few omissions.
Note that most of the lenses with distance data capabilities contain ring USM focus
motors. In fact, the first three lenses with distance encoders were introduced in 1990
along with the EOS 10/10S - the 35-135mm 4-5.6 USM, 70-210mm 3.5-4.5 USM,
and 100-300mm 4.5-5.6 USM. It’s also not clear what the resolution is of a typical
lens distance decoder. Photos I’ve seen of the decoder rings (not quite like children’s
toys in a cereal packet) in one lens suggest that the distance data is fairly
approximate, with each combination of distance contacts returning a certain distance
I have no information as to whether any third-party lenses compatible with the EF
lens mount are capable of returning distance data.
EF 14mm 2.8L USM
EF 20mm 2.8 USM
EF 24mm 1.4L USM
EF 28mm 1.8 USM
EF 35mm 1.4L USM
MP-E 65mm 2.8 1-5x Macro
EF 85mm 1.8 USM
EF 100mm 2 USM
EF 100mm 2.8 Macro USM
EF 100mm 2.8 Macro (discontinued)
EF 135mm 2L USM
EF 180mm 3.5L Macro USM
EF 200mm 2.8L II USM
EF 200mm 2.8L USM (discontinued)
EF 300mm 2.8L IS USM
EF 300mm 4L IS USM
EF 300mm 4L USM (discontinued)
EF 400mm 2.8L IS USM
EF 400mm 4 DO IS USM
EF 400mm 5.6L USM
EF 500mm 4L IS USM
EF 600mm 4L IS USM
EF 1200mm 5.6L USM
16-35mm 2.8L USM
17-35mm 2.8L USM (discontinued)
17-40mm 4L USM
20-35mm 3.5-4.5 USM
24-70mm 2.8L USM
24-85mm 3.5-4.5 USM
28-70mm 2.8L USM (discontinued)
28-80mm 3.5-5.6 USM (discontinued)
28-105mm 3.5-4.5 USM (discontinued)
28-105mm 3.5-4.5 II USM
28-105mm 4-5.6 USM
28-105mm 4-5.6
28-200mm 3.5-5.6 USM
28-200mm 3.5-5.6 (discontinued)
28-300mm 3.5-5.6L IS USM
35-135mm 4-5.6 USM (discontinued)
70-200mm 2.8L IS USM
70-200mm 2.8L USM
70-200mm 4L USM
70-210mm 3.5-4.5 USM (discontinued)
70-300mm 4.5-5.6 DO IS USM
90-300mm 4.5-5.6 USM
90-300mm 4.5-5.6
100-300mm 4.5-5.6 USM
100-400mm 4.5-5.6L IS USM
EF-S 18-55mm 3.5-5.6 USM (Japan only)
EF-S 18-55mm 3.5-5.6
If your lens doesn’t appear on the list above then it may not have distance data
capabilities. Here are a few current lenses in the EF lineup which don’t have distance
data. Note the 50mm 1.4 USM and the 85mm 1.2L USM are in this list.
15mm 2.8 fisheye
24mm 2.8
28mm 2.8
35mm 2.0
50mm 1.4 USM
50mm 1.8 II
85mm 1.2L USM
135mm 2.8 SF
28-80mm 3.5-5.6 II
28-90mm 4-5.6 II USM
28-90mm 4-5.6 II
35-80mm 4-5.6 III
55-200mm 4.5-5.6 II USM
75-300mm 4-5.6 IS USM
75-300mm 4-5.6 III USM
75-300mm 4-5.6 II
80-200mm 4.5-5.6 II
FP (focal plane or high speed sync) flash mode.
Synchronizing flash exposure with both curtains of focal plane shutters was as much
of a problem in the days of single-use flash bulbs as it is today with electronic flash
units. For that reason flash bulbs designed to work with focal plane shutters were
developed. Such bulbs produced light quite rapidly and sustained their light output
for the full duration of the shutter opening. They were called FP bulbs.
With E-TTL Canon introduced an implementation of an electronic FP flash mode,
which is a way of circumventing the X-sync limitation in certain cases, and another
flash technology pioneered by Olympus. FP flash lets you take flash photos at any
shutter speed you like, and works by pulsing the flash bulb at an extremely high rate
- 50 KHz - simulating constant light at the cost of total light output. FP stands for
“focal plane,” by analogy to the old FP flash bulbs, though Mark Overton memorably
refers to it as “fast pulse” mode in his FAQ, since that’s exactly how it works today.
This mode is useful for shooting with fill flash outdoors with wide apertures. Normally
you can’t shoot outdoors and use fill flash unless you stop down the lens or use very
slow film. However, changing film is a nuisance and stopping down the lens increases
the depth of field. If you’re shooting a portrait, say, you probably want to blur the
background and the only way to do this is to shoot with a wider aperture. But the
wider aperture lets in more light, and you can’t compensate by increasing the shutter
speed if you then bump up against the camera’s X-sync limit.
FP mode flash solves this problem by letting the shutter speed exceed the X-sync
limit and reach the camera’s maximum shutter speed (usually 1/2000 or 1/4000 sec)
instead. The primary drawback is that pulsing the light causes a reduction in overall
light output and thus range.
When you have FP mode engaged you typically get about a third less range than you
would if you were shooting with normal flash. With a powerful flash unit like the
550EX this may not be a big problem, particularly if your flash subject is fairly close
to you. But this loss of range could be a serious impediment if you’re using a smaller
flash unit (eg: the tiny 220EX), if the subject is far away, or if you’re using slow film.
Of course, if you’re using FP mode simply for a little fill flash (rather than relying on
it to illuminate your subject) then this loss of range shouldn’t be a huge problem.
Note an important point - FP mode does not help you freeze motion; the name
“high-speed sync” is a bit misleading in this regard. Normal flash photography is very
good at freezing motion on film, since the flash burst is so incredibly brief. However
when you use FP mode flash, the flash unit pulses the light output to simulate a
longer-duration burst of light. Since the flash burst is no longer particularly brief you
can’t freeze motion as easily, even with high shutter speeds. The mode is called
high-speed sync since it lets you synchronize flash exposure with high shutter
speeds, not that it lets you take high-speed photographs.
Since Canon’s FP mode is tied in with E-TTL technology it’s only available when using
EX-series flashes attached to A-type bodies. There are two exceptions to the “type A
gives you FP flash” rule. First, the type B EOS 1N body can be reprogrammed by
Canon at great expense to support FP mode but cannot support any other feature
associated with E-TTL even when so reprogrammed. And second, the digital SLRs
with built-in flash (10D, 300D, etc) support FP mode on external flash units but have
E-TTL compatible internal flashes which cannot support FP mode.
FP mode is indicated on type A cameras and flash units by a small lightning bolt
symbol and the letter H, for “high speed sync.”
Camera units which support FP mode flash:
All type A EOS cameras plus the EOS 1N if reprogrammed as above.
Flash units which support FP mode flash:
All EX series Speedlites: 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
TTL and E-TTL and EOS film cameras.
All film-based Canon EOS cameras at the time of writing support TTL flash metering the one exception being the oddball Canon EF-M, which was a manual-focus camera
that could accept EF-mount lenses but which lacked both autofocus and TTL flash
circuitry as a cost-saving measure. (you had to buy an optional flash unit with an
external sensor, the Speedlite 200M, if you wanted to do flash photography with the
EF-M) All film-based EOS cameras with built-in flashes rely solely on TTL for flash
exposure control of those internal flash units.
Canon cameras designed prior to the Elan II/EOS 50 of 1995 don’t support E-TTL.
With the release of this camera Canon divided their camera bodies into two types - A
and B. Type A bodies are bodies which support E-TTL, FEL and FP flash technologies.
Type B bodies are bodies which do not.
With flash units it’s easy - if the name of the flash unit ends with the letter X (eg:
550EX, MT-24EX) then it’s an E-TTL unit. If it ends with anything else (eg: 430EZ,
480EG) then it is not.
However, there are three points of note here. First, Canon continued designing and
selling type B bodies for many years after the introduction of the Elan II/EOS 50,
such as the EOS 3000 and venerable EOS 5/A2, so the date you bought your camera
won’t determine if it’s a type A or B body. Second, since Canon came up with the
whole A/B naming convention in 1995, older cameras are obviously not described as
being “type B” in their manuals. And third, type A simply means support for E-TTL,
FEL and FP mode - it doesn’t mean that the camera necessarily supports other recent
flash features such as wireless flash ratios or modelling flash.
So the upshot of all this is the following:
First, all EX-series (ie: E-TTL capable) flash units also support TTL metering
and automatically revert to TTL metering when used with an older type B
camera body. However, no EX-series flash units support A-TTL metering.
Second, since all EOS film cameras (both type A and type B) support both TTL
and A-TTL metering they can all use E-series flash units in TTL mode and EZseries flash units in A-TTL mode. All EOS digital cameras support either E-TTL
or both E-TTL and E-TTL II (see below).
Third, if both the camera and flash unit support E-TTL (ie: the camera is a
type A body and the flash an EX series) then they will use E-TTL unless
specifically overridden (see “disabling E-TTL” below).
TTL and E-TTL and EOS digital cameras.
All current Canon digital cameras with hotshoes - both the interchangeable-lens SLR
cameras and the point and shoot digital cameras - support E-TTL (or both E-TTL and
E-TTL II) and do not support either TTL or A-TTL. Even Canon digital cameras with
internal popup flashes are E-TTL only. (though if you want to use flash with a nonEOS camera you should probably check out Kevin Bjorke’s page for its limitations.
Canon have also written a letter to D30 users concerning proper use of EX flash
Since digital bodies lack film they can’t use regular off the film flash sensors for TTL
metering. The mirrorlike surface of a CMOS or CCD imaging chip has very different
reflective properties from film. Besides, Canon have clearly switched to E-TTL, only
supporting TTL for back compatibility with older products.
This means that only Canon EX flash units or third-party flash units with E-TTL
support can be used with Canon’s current lineup of digital cameras. Older E and EZ
flash units will not work correctly - no automatic through the lens metering is
possible. You can get manual-capable EZ flash units like the 540EZ to fire in manual
flash mode but this requires external flash metering.
Unfortunately, E-TTL has been a particular problem for digital EOS users. Many users
report serious problems with wildly varying exposure when using an E-TTL flash unit
with their Canon DSLRs, particularly the D30 and D60. Some of these problems stem
from the users focussing and recomposing and failing to use the flash exposure lock
(FEL) feature, which sets the wrong area around which the flash will meter. But
many problems can’t be blamed on this. The main problem appears to stem from the
way in which E-TTL on these bodies biases flash exposure heavily to the focus point.
For more information please consult the section on E-TTL flash metering patterns.
For this reason some digital EOS users have given up on E-TTL and gone back to the
old-style autoflash units. Others routinely set their lens to manual focus once focus
has been achieved, since the camera uses a centre-weighted average metering
pattern for flash metering when in manual focus.
Still, at least with digital you have a rear-panel preview and histogram, so you can
tell right away if a flash photo failed to work. And Canon are aware of the problem.
The EOS 10D has revised E-TTL algorithms which rely on centre-weighted average
metering for E-TTL flash, even if the lens is set to autofocus mode. And E-TTL II,
introduced with the EOS 1D mark II, analyzes all metering zones before and after
the preflash for improved flash metering.
Note that this applies to the wholly Canon-designed generation of digital SLRs - the
D30 onwards. It’s not clear how the first generation of Canon digital SLRs (developed
in conjunction with Kodak), the long-discontinued EOS DCS1, DCS3 and D2000
cameras, support flash. It seems the DCS cameras theoretically support TTL, albeit
poorly, and the D2000 and D6000 support E-TTL as well, but Canon’s Web site
doesn’t really go into much detail.
Type A and type B bodies.
While Canon have officially divided their camera bodies into types A and B there are
subvariants of type A cameras. Specifically, the first generation of type A cameras
does not have support for wireless E-TTL flash ratios and modelling flash; the second
generation does. There is also a third generation which supports E-TTL II.
Type A bodies
Support for E-TTL flash, FEL and FP mode:
Elan II(E), EOS 50(E)/55
D2000, D6000 (digital)
IX, IX 7, IX Lite, IX 50 (APS)
Rebel G/500N/New EOS Kiss, Rebel G II
Rebel 2000/EOS 300/Kiss III, Kiss IIIL
300V/Rebel Ti/Kiss 5
3000N/Rebel XS N/EOS 66
3000V/Rebel K2/Kiss Lite
As above plus support for wireless E-TTL flash ratios and modelling flash:
Elan 7(E)/EOS 30/33/7
D30, D60 and 10D (digital)
1D and 1Ds (digital)
300D/Digital Rebel/Kiss Digital (digital)
As above plus support for E-TTL II:
EOS 1D mark II (digital)
EOS Elan 7N/Elan 7EN/EOS 30V/33V/7S
Type B bodies
Support for TTL and A-TTL only:
EOS 600 series - 600, 620, 630, 650, RT
EOS 700, 750, 800
EOS 10/10S/10QD
First generation Rebel series - Rebel, Rebel S, EOS 1000 and all 1000 variants, Rebel
II, Rebel X, XS/EOS 500/Kiss
EOS Elan/100
EOS A2(E)/5
EOS 3000/88, 5000/888
EOS DCS3, DCS1 (first generation digital)
Disabling E-TTL.
There are times when TTL metering may be more desirable than E-TTL. A common
example is a studio setting where analogue optical slave units can be fooled by the
E-TTL preflash. The 550EX, MR-14EX and MT-24EX let you disable E-TTL via a
custom function, but they’re the only Canon Speedlites with this ability. All other EX
flash units (220EX, 380EX, 420EX) will always operate in E-TTL mode when mounted
to an E-TTL-capable camera, even if the camera is also capable of supporting TTL
and even though they’ll work in TTL mode just fine on a type B camera.
One way around this is to buy Canon’s Hot Shoe Adapter for wired multiple-unit
flash. This adapter works only in TTL mode, so putting an E-TTL flash unit onto an
HSA will force it to work in TTL only. This is a pretty expensive approach, however.
Another option is to tape over one of the data contacts in the hotshoe. Covering the
lower left contact (the left contact out of the hotshoe’s group of four that’s closest to
the back of the camera when looking at the camera from the top) will disable all ETTL functionality. (though it’ll also disable second-curtain sync along with FP flash
and FEL) For more details have a look at this article on EOSDoc.
Note that digital EOS cameras will not fire the flash if the flash is in TTL mode. Digital
EOS cameras work with E-TTL or E-TTL II flash only and support neither TTL nor ATTL.
EOS system compatible flash units.
This document is concerned primarily with two types of flash technologies built by
Canon for use with their EOS cameras - the pop-up integral flash units built into
most low and midrange EOS cameras and the external shoe-mounted Speedlite flash
units which can be attached to any EOS camera.
I do not discuss studio flash units (large flash units for studio photography, usually
powered by AC current and not batteries, and called “studio strobes” in North
America) in any detail here. Here’s a good brief introduction to a typical monolight
studio flash, if you’re interested.
Internal flash.
Most low to mid-range Canon EOS cameras contain integral flash units, built into the
top housing that contains the camera’s prism or mirror. Some are motorized and pop
up immediately in all basic (PIC or icon) modes except sports and landscape if the
camera thinks you need flash, or upon the touch of a button if you’re in an advanced
(creative zone) mode. Others require the user to lift up the flash manually. One
camera, the 10/10s, has a motorized flash unit which both pops up and retracts
mechanically, for those interested in trivia.
These internal flash units are useful for quick snapshots and the like, but aren’t
usually useful for quality photography for a number of reasons. First, they’re very
small and offer very low output levels - low guide numbers such as 11 or 13.
Second, they’re located quite close to the lens axis and so are very likely to cause
the redeye effect when photographing people. Third, since they don’t extend very far
above the top of the camera body their light is easily partially blocked by large
lenses or lenses with large lens hoods. And fourth, they don’t offer any tilt or swivel
options and generally have coverage areas of only 28mm or 35mm at the wide end.
However, since they’re built-in they’re obviously eminently portable and handy at a
moment’s notice. They’re useful for applying a touch of fill flash when outdoors. And
they recharge very rapidly as they use the camera’s lithium battery as a power
source. This latter can be a bit expensive, though, as using the built-in flash runs
down the camera battery alarmingly quickly.
No EOS camera lets you use the internal flash when an external flash unit is
mounted on the hotshoe. In fact, external flash units physically prevent the internal
flash from being raised. Additionally, EOS cameras with motorized internal flashes
have small electrical switches built into the hotshoe which detect the presence of a
device and disallow internal flash popup. So the internal flash won’t rise
automatically if anything’s in there - even, say, a hotshoe-mounted spirit level or
something else non-electrical. These switches, incidentally, have been known to
stick, rendering the internal flash inoperable.
None of the professional EOS cameras (1, 1v, 3, etc) have built-in flash units, for the
reasons listed above and possibly also because of the difficulty of waterproofing a
popup flash mechanism. All EOS film cameras use TTL only for internal flash control.
At time of writing the only EOS cameras to use E-TTL for internal flash unit control
are those digital EOS cameras with built-in flash (D30, D60, 10D, 300D/Digital
Rebel/Kiss Digital), though their internal flash units do not support FP mode.
Cameras with internal flash units:
Please consult the flash coverage list.
Basic (PIC) modes and external flash units.
Older EOS cameras, such as the 10/10s and Elan/100, have PIC (“programmed
image control” or icon) modes that don’t handle external flash units correctly. The
PIC modes which use flash when necessary (all but landscape and sports) are
designed to use the internal flash and are optimized for its characteristics. Check
your manual to see if your camera fits in this category - probably pre 1995 or so.
Newer EOS cameras, such as the Elan II/EOS 50 or Elan 7/EOS 30, can use an
external flash unit with the PIC modes. But nonetheless for best control you’re better
off using one of the “creative” zone modes anyway - P, Av, Tv or M. Remember that
there are significant differences in the way each of these four modes handle flash
Because the full auto (green rectangle) and PIC modes afford very little control over
the way the camera works I primarily discuss how flash works with the “creative”
zone modes.
Canon external flash unit types.
There are three basic types of external flash units considered here - standard
hotshoe flashes, handle flashes and macro flashes. (as noted above, studio flashes of
the kind that require household AC power are not discussed in this document)
For a complete list of Canon’s EOS flashes over the years check out Dave Herzstein’s
comprehensive EOS flash page.
Nomenclature of external flash units.
Canon have made a number of flash units compatible with EOS cameras. The naming
system is fairly logical - they’re given names such as “Speedlite 550EX”. Here’s what
the parts of the name mean:
Speedlite is the product name for all Canon flash devices. (versus
“Speedlight” for Nikon)
550 is the maximum guide number - output rating of the flash in metres multiplied by 10 to make it sound cooler. (I very much doubt that Canon
marketing measure things in decimetres)
E means it works with EOS cameras.
X means that it supports E-TTL flash technology. At time of writing only flash
units which end in the letter X support E-TTL.
Flash units which end with “Z”, such as the 430EZ, are flash units with zooming
motors and support for A-TTL but not E-TTL. The 480EG flash has a built-in grip.
Flashes end in “E” only, such as the 200E, are basic models with neither zooming
heads nor E-TTL support.
Although this naming system is very reasonable it does mean it’s easy to confuse
different models which happen to have identical guide numbers. For example, the
420EZ and 420EX flash units are very different indeed. The former was top of the
line for its time, but supports only TTL and A-TTL and is now quite dated. The latter
is considered a midrange flash unit in today’s lineup, and although is technologically
much more sophisticated as it supports both E-TTL and wireless flash slave mode, it
lacks stroboscopic mode and has no manual controls.
Older Canon Speedlite flash units.
Older Canon Speedlite flash units which lack the letter E in their product name were
not designed for EOS cameras. There were Speedlite A models (eg: 199A) for old Aseries Canons such as the A1 and AE1 and Speedlite T models (eg: 277T) for Tseries Canons such as the T50 (but not the T90) and various other special-purpose
You can put these older flashes on your EOS camera and they’ll trigger OK when you
take a photo, but they can’t use modern automated flash metering. So you have to
either use them in auto mode if they have such a setting (set your camera to a
shutter speed up to the camera’s X-sync), dial in manual power and calculate the
flash distance yourself if they have manual controls or else expect the flash to fire at
full power.
I don’t know if all earlier Speedlite products have safe triggering voltages or not. The
list maintained by Kevin Bjorke on his Web site suggests that T series flash units are
OK and most A series and older flash units are in a grey zone, but you should
probably check for yourself.
The one exception is the 300TL flash unit. It was designed for the old Canon T90
camera, and its more advanced features (such as its versions of FEL and secondcurtain sync) are not supported by EOS cameras. However it can be used with EOS
cameras as a basic TTL flash unit even though it lacks an E designation.
Hotshoe flashes.
Canon sell and have sold a number of different standard hotshoe flash units, which
can be divided into three basic categories. Have a look here for a brief comparison of
E and EZ (ie: non-EX) flash units.
Basic flash units - 160E*, 200E, 220EX.
These small devices have very limited power output - you could think of them as
little flash units for those cameras which lack built-in flash. The 160E and 200E
support TTL only, but the 220EX supports both TTL and E-TTL. They do not zoom,
swivel or tilt, but are extremely compact and lightweight. The tiny 160E is the only
Canon flash unit which does not use four AA cells - it uses a lithium 2CR5 battery
instead. That means that it’s very small and light, but expensive to operate as
lithium batteries are very costly.
Midrange units - 300EZ*, 380EX*, 420EX.
These flash units have more power and have zooming flash heads but no manual
controls. The 300EZ supports TTL and A-TTL and the EX units support TTL and ETTL. When it comes to flash heads, the 300EZ neither tilts nor swivels, the 380EX
tilts only and the 420EX both tilts and swivels. The 420EX can also serve as a slave
unit in wireless E-TTL flash.
The high-end units - 420EZ*, 430EZ*, 540EZ, 550EX.
These are of course the largest and most powerful flash units of the standard type.
They support the most advanced Canon flash technology at the time they were
introduced; TTL and A-TTL in the case of the EZ units and TTL and E-TTL in the case
of the 550EX. They also have both manual controls and tilt and swivel flash heads.
Of these the 420EZ is the most limited - it has no flash exposure compensation, for
* Discontinued product at time of writing.
Handle-mount (grip) flash.
Canon still make one large flash unit of this type, the 480EG. It’s basically a flash
bracket with a massive heavy-duty flash attached to the side. The camera sits on the
bracket and is held in place via the tripod mount. This type of handle flash is
sometimes jokingly referred to as a “potato masher” flash unit.
The 480EG is a high-output flash unit meant for press or wedding photographers, but
hasn’t been updated in some time and is a TTL-only flash (no A-TTL or E-TTL
support). Nowadays people usually just buy flash brackets and put a regular 550EX
flash unit on them for this sort of application. This setup also lets you mount the
flash unit vertically above the lens rather than to the side only, like the 480EG. But if
you want the sheer light output you can’t beat the 480EG or similar flash units from
manufacturers such as Metz.
The 480EG is also the most powerful flash unit that Canon make, even though its
advertised guide number is only 48 and thus seemingly lower than flash units like
the 540EZ or 550EX. This is because the 480EG’s flash head does not zoom and
cannot, therefore, automatically concentrate light output when used with longer focal
lengths - it can just blast the same amount of light regardless of lens zoom setting.
See the sections on guide numbers and zooming flash for a more detailed
The unit does, however, ship with a wide-angle attachment and a telephoto
attachment which can be clipped on and used to diffuse or concentrate the unit’s
light output. (the telephoto attachment gives the unit a guide number of 68 at
135mm, so you may occasionally see the 480EG being misleadingly described as a
flash unit with a guide number of 68) The 480EG has twin bulbs, a slave connector
and full tilt and swivel capabilities, but it does not support second-curtain sync or
exotic features like stroboscopic flash.
Interestingly, it also has an old-style external auto flash sensor built in. So if you
have an older pre-EOS camera that doesn’t support TTL metering - or if you want to
avoid TTL metering altogether for some reason - you can still use it. You can even
use the optional Synchro Cord 480 to link the flash to a camera via a PC socket.
Macro flash.
Canon sell three flash units for macro (closeup) photography. Two, the TTL-only ML3 flash and the E-TTL MR-14EX flash, are ring-shaped flashes designed to fit directly
around the end of a macro lens. The other, the luxurious and hugely expensive E-TTL
MT-24EX “macro twin lite,” contains two small flash heads on the end of a pair of
short swivelling arms which can be adjusted independently and which can also be
clipped to a ring that fits macro lenses. The MT-24EX flash heads can even be
detached and mounted separately on other mounts, since each head includes a shoe
mount and a standard 1/4-20 tripod mount. Both the MR-14EX and the MT-24EX can
control slave flash units in wireless E-TTL mode, which is very handy - you use the
macro flash units (the two tubes are assigned to groups A and B) to illuminate the
foreground and then use slaved Speedlites (assigned to group C) to illuminate the
background. Note that the older and long-discontinued ML-2 macro ring lite flash
supports TTL, but only with the T90 camera - Canon states that it cannot meter TTL
reliably with EOS cameras.
Macro flashes are specifically designed for closeup photography, and let you take
shadowless photos of small objects. Additionally, since each macro flash has two
independent flash tubes you can adjust the lighting ratio between them, for more
directional lighting. Unfortunately, only newer-model mid to high end type A cameras
support ratio control.
It was trendy for a while in the 1990s to take fashion photos with large ring flashes
to get a flat shadowless look to the models, but macro flashes aren’t really powerful
enough to do this sort of thing well. (though the MT-24EX is bright enough to be
used for this in closeup portrait setups if you really want to)
For some bizarre reason people consistently mistype “macro” as “marco,” as if the
flash unit type were of Italian provenance. Please note that it’s not.
Third-party flash units.
A number of manufacturers other than Canon build flash units that can be used with
EOS cameras. Here’s a bit of information on them.
Note that one problem with third party flashes is that Canon have not published the
data protocols used by its cameras, lenses and flashes. So any flash unit designed to
be compatible with EOS TTL, A-TTL or E-TTL flash metering has been reverseengineered based on the behaviour of existing products. It’s quite possible that
Canon will release a future camera that uses some modification to the protocol and
your flash won’t work with it.
This may or may not be a big issue for you, but it’s worth keeping in mind as it has
been a problem in the past. For instance, the EOS 30/Elan 7 does not work with
some Metz adapters and the EOS 300V/Rebel Ti/Kiss 5 doesn’t work with any Metz
adapters - see the note below.
Another common problem involves AF assist lights. As far as I know no third party
flash unit is capable of illuminating the AF assist light when a focus point other than
the centre point is selected when used with multiple focus point cameras.
Achiever, a Hong Kong third-party manufacturer of flash units, point and shoot
cameras and various sundry other products like paper shredders, list a number of
flash units that they say work with EOS cameras.
I understand that their products are all TTL only. But useful feature lists of their
products aren’t published on their site at all, so who knows?
Metz, a respected German maker of flash units, sell quite a few “Mecablitz” flashes
that work with EOS cameras by means of an adapter system. Photozone list some of
them - the 54MZ-3, 50MZ-5, 40MZ-3, 40MZ-1, 40MZ-3i, 40MZ-1i, 40MZ-2, 40AF-4
and 32MZ-3 - and describe their features. The Metz range is, in fact, much more
extensive than Canon’s, and Metz offers features that Canon do not - such as flash
units with memory settings, built-in secondary reflectors, clip-on coloured filters and
audio warning signals.
Metz’s Web site has an excellent listing of which features are available with which
Canon cameras and what adapters are required, though some of the vocabulary has
been translated rather literally from German and may be unfamiliar. A “lighting
control indicator” is what Canon call a “flash exposure confirmation” light, for
example. An “AF measuring beam” is the confusing name for the “AF assist light” or
“AF auxiliary light.”
Note that some users of Metz products have reported that the SCA3101 adapter,
which works using TTL with older Canon-compatible bodies, will not work with the
Elan 7/EOS 30. Even though the Elan 7/EOS 30 supports TTL on Canon flashes you
must apparently use the SCA3102 Metz adapter. So you’re best off consulting the
Metz site and, preferably, doing some testing of your own before buying. Note also
that Metz have a wireless flash triggering system, but it’s not compatible with
Finally, I understand that Metz have acknowledged that none of their flash units with
the SCA3102 adapter currently work correctly with the new EOS 300V/Rebel Ti/Kiss
5 camera, owing to changes in the design of the flash shoe electronics.
Sigma, Japanese maker of many third-party lenses, build six flash units compatible
with Canon EOS. Two are TTL - the EF-430 ST and the EF-500 ST, and two are E-TTL
- the EF 430 Super and the EF-500 Super. The DG models are E-TTL units designed
to be compatible with digital EOS cameras. Some of these flash units are listed on
The EF-500 Super and the EF-500 Super DG are particularly well regarded by a lot of
EOS users, since feature-wise they’re nearly identical to Canon’s 550EX, which costs
twice as much. The Sigma units are not built as sturdily as the Canon, but it’s hard
to argue with the price. They even have wireless capabilities compatible with Canon’s
system and has the ability to operate as an optical slave. For more information on
EF-500 Super, specifically how it compares with the 550EX, please consult the brief
article co-authored by Jim Strutz and myself.
German photo accessory marketer Soligor sell a few Canon-compatible flash units;
likely rebranded products. Their Web site lists some details. The flashes appear to be
TTL only.
Sunpak, a Japanese marketer of photo products, sell the TTL-only AF4000 and
AF5000 flash units. Finding useful information on the massively amateur-looking
Tocad America Web site, their US distributor, is pretty hopeless, though. Good luck.
American camera accessory and snapshot camera marketer and designer (they don’t
build products) Vivitar sell the 283 and 285HV flash units. These are self-contained
flashes that rely entirely on their built-in flash sensors - they don’t support TTL
metering of any kind. In fact, Vivitar apparently pioneered the autoflash concept with
the 283, which is probably the best-selling flash unit of all time.
283s and 285s are relatively cheap and commonly used by photo professionals as
remote flashes triggered by optical slaves and so on. You should be aware, however,
that older models have a very high trigger voltage that can damage EOS cameras.
Newer models are fine, but check first before attaching any such flash unit to your
camera, just to be sure.
Vivitar also sell a number of EOS-compatible flashes, some of which are said to be
rebranded Sigma products. There’s a list of their flash units on their Web site, and
several are said to be Canon compatible, though TTL only. Their Web site is pretty
uninformative, so you’re basically on your own there.
Other flashes.
Finally, any electronic flash unit that mounts on a camera hotshoe and which has a
trigger voltage of less than 6 volts will fit an EOS camera and will be fired when you
take a photo. However, it won’t work with any form of TTL flash metering. See the
section on “Older Canon Speedlite flash units” for details.
Which flash unit should I buy?
This question obviously comes down to your light output and feature needs, your
budget and your weight and size requirements. Here are a few notes to help you
make a decision. If you don’t know whether your camera is a type A or type B
model, consult this list. All flash units marked with an asterisk are discontinued
I have a type B camera with no plans to buy a type A camera in the future.
You should probably stick with an E or EZ series flash unit, since buying an EX unit
means you’re paying for features you can’t use. Also, since EZ units are mostly
discontinued you can get a used unit fairly cheaply.
The 200E, but only if you need something really tiny for occasional
close-range fill flash work. Particularly if your camera lacks a built-in
flash unit. I’d avoid the 200E if size and weight are not critical, as it’s
got feeble output, doesn’t tilt or swivel and lacks flash exposure
compensation buttons for use on older EOS cameras which lack FEC
If you want a reasonably powerful and feature-complete unit for cheap
then the 430EZ* is your best bet.
If you want the best you can buy in terms of features and output then
the 540EZ is for you. This unit gives you slightly more output and flash
exposure confirmation compared to the 430EZ. It also doesn’t
generate irritating flashes of white light each time you press the
shutter release halfway when in creative zone modes other than P.
Not recommended:
The 160E* offers little unless size and weight are a really serious
issue. The 160E uses a 2CR5 lithium battery, which is a costly way to
power a flash unit. However it’s this small lithium cell which explains
the incredibly tiny size of the 160E.
The 300EZ* is a fixed unit which can neither swivel nor tilt - get a
430EZ instead. The 430EZ is larger and heavier, but more flexible than
the 300EZ.
The 420EZ* isn’t a bad unit but lacks convenient flash exposure
compensation buttons. The 430EZ has these plus an external battery
socket and doesn’t cost much more.
I have a Canon digital camera, a type A camera, or a type B camera but plan
to buy a type A camera soon.
If you have a type A camera you’re best off buying an EX-series (E-TTL capable)
flash to take full advantages of the newer features. All EX-series flash units will work
fine in TTL mode with type B cameras as well - the only missing feature being A-TTL,
which is fairly useless anyway. Finally, if you have a digital Canon camera such as a
D60 or PowerShot then you don’t have a choice - you must get an EX-series flash
unit as the earlier models won’t work.
The 220EX, but only if you need something really tiny and lightweight
for occasional close-range fill flash work. Particularly if your camera
lacks a built-in flash unit. However, I’d avoid the 220EX if size and
weight are not critical, since it doesn’t produce much light and doesn’t
tilt or swivel.
The 420EX is great for general-purpose fully-automatic flash
photography. It can also serve as a wireless E-TTL slave. However it
lacks manual controls and only supports flash exposure compensation
(FEC) on midrange and pro EOS bodies (ie: those cameras with
custom functions).
The top of the line 550EX flash is quite powerful and can do anything a
portable flash unit can be expected to do, but it’s very large and both
costs more and weighs more than a brand new low-end EOS camera.
However it can serve as an E-TTL wireless master, has manual controls
and works in stroboscopic mode.
Not recommended:
The 380EX* can tilt but can’t swivel. It also can’t be used as a wireless
slave. Unless money is a serious concern and you find a 380EX on sale
for a really good price I’d get the 420EX instead, since the 420EX
usually doesn’t cost much more.
I have specialized requirements:
Macro photography with a type B body: the ML-3*.
Macro photography with a type A body: the MR-14EX.
Macro photography with a type A body and a huge budget: the MT-24EX.
News or wedding photography for which massive light output is important and subtle
control is not: the 480EG. Though Metz offer many high-powered grip models which
offer more control over the Canon unit.
What about third party units?
A number of companies other than Canon sell EOS-compatible flash units. The vast
majority, however, are TTL only. There is also a small risk of compatibility problems
with both current and future EOS camera bodies.
If you’re satisfied with TTL operation (particularly if you have a type B camera with
no plans to upgrade to a type A) and you’ve tested the flash unit to ensure that it
works with your existing camera body, then an inexpensive third party unit may be
the way to go if you’re on a tight budget. But I can’t offer any recommendations for
such cheap units because there are so many different brand names which sell them.
Many of these units are actually the same basic product, rebadged and sold by
different distributors. So if a cheap third-party product is of interest to you I’d
recommend you go to your local camera shop and look around.
There are some better units worth considering as well. Metz make a wide range of
well-featured and powerful flash units with interchangeable adapter modules
(including an E-TTL capable module for type A cameras), and Sigma sell the popular
EF 500 Super, which supports E-TTL and wireless E-TTL operation.
On to Part II.
- NK Guy, tela design.
Disclaimer and copyright:
This site is copyright © 2001-2004 NK Guy, tela design. This information is provided
with neither warranties nor claims of accuracy or completeness of any sort. Use this
information at your own risk. All trademarks mentioned herein belong to their
respective owners.
I wrote this document in the hope that others in the Internet community might find it
useful or interesting. However, I don’t think it’s reasonable for anyone else to earn
money from - or take credit for - my work.
Therefore you may copy and print this document for your own personal use. You
may not, however, reprint or republish this work, in whole or in part, without prior
permission from me, the author. Such republication includes inclusion of this work in
other Web sites, Web pages, FTP archives, books, magazines or other periodicals,
CD-ROM and DVD-ROM compilations or any other form of publication or distribution.
Please do not frame this site within another.
Please send feedback if you find this article to be of interest or value or if you have
any comments, corrections or suggestions.
Please also consider making a donation to help defray some of the costs of building
and maintaining this site. Thanks!
Thanks to Jim Strutz, Mark Overton, Gerard Maas, Steve Dunn, Julian Loke, Lewis
Macdonald and Martijn Stol for valuable suggestions to this document. Any errors or
omissions are purely my own, however.
Back to Photo notes.
Flash Photography with Canon EOS Cameras - Part II.
Copyright © 2001-2004 NK Guy
Version 1.6. February 11, 2004.
Back to Part I.
EOS flash photography modes.
The four main Canon EOS “creative” zone modes (P, Tv, Av and M) each handle flash
metering in very different ways. These differences are probably one of the primary
sources of confusion in the world of Canon EOS flash photography.
Here are a few important terms and concepts that you need to know before
understanding how these confusing points originate.
Subject and Background in flash photography.
The typical flash photograph is assumed to have two basic regions. The foreground
or subject is the area around the autofocus metering point - perhaps a person.
Background ambient lighting is just everywhere else.
This is an important distinction because all portable flash units have a limited range.
As noted in the FAQ section, you can’t expect a small flash unit on your camera to
illuminate the Eiffel Tower or the Grand Canyon or even a large space such as a
ballroom. The camera, therefore, handles the subject and background metering
differently and independently.
Fill flash.
Flash photography takes on two very basic forms. In regular flash photography, the
flash is the primary light source for the photo. Flash metering is done for the
foreground subject, and the background is metered by the camera’s regular
exposure metering system. This can lead to the background being underexposed and
dark if ambient light conditions are low. This is how most people think of flash - as a
way of taking photos in dark places.
However, flash can also be used in bright locations or in daylight to lighten shadows,
reduce the harsh contrast of full sunlight or brighten up dull images without being
the primary light source for the photo. This is called “fill flash.” And it’s often a
source of surprise for non-photographers, who don’t expect to see photographers
using flash units outdoors on sunny days on in brightly lit settings. In such situations
the fill flash is being used as a sort of portable reflector - shining a little extra light in
certain areas.
A typical example might be a person who’s wearing a hat outdoors on a sunny day.
Hat brims often cast dark shadows over the subject’s face, and a little flash can
lighten up this shadow nicely. A backlit subject is another common use for fill flash you can’t simply crank up the exposure compensation to expose the subject correctly
as then the background lighting would be too strong. Or perhaps you want a little
sparkle of light reflecting back from a person’s eyes - the “catchlight.” Sometimes
wildlife photographers use flash units at great distances from their quarry for the
same reason - they aren’t using the flash to illuminate the animal but to provide a
lively catchlight to the eyes.
In all these cases you are, from the point of view of the camera, using two light
sources at the same time. There’s ambient lighting, which is all the available light
around you - reflected light from the sun or artificial light sources. And there’s the
light from the flash unit, which is supplementing this existing light. As always,
ambient light levels hitting the film are governed by the lens aperture and shutter
speed and flash levels are governed by flash metering. By adjusting the output of the
flash unit you’re essentially adjusting the ratio between flash-illuminated and
ambient light-illuminated scene.
In fact you could argue that the two cases I present above - flash as primary light
source and ambient light as primary light source - are an artificial distinction and
that all flash photography is fill photography in a sense; just that in the first case the
ambient lighting is so low as to be insignificant, whereas in the second case it’s the
reverse. This is true enough, but I think the distinction is useful to make, particularly
in terms of the way full auto and P modes work versus Tv, Av and M modes.
Unlike certain other camera systems (particularly Nikon), Canon EOS cameras
always default to fill flash mode when the camera is in Tv, Av and M modes. They
also perform fill flash in P mode if ambient light levels are high enough. There’s no
separate switch or pushbutton to engage fill flash. For details have a look at the
section on EOS flash photography confusion below.
Fill flash ratios.
The “fill flash ratio” is commonly described in terms of the ratio of ambient light plus
fill flash combined, compared to the fill flash alone. Canon EOS gear, however,
usually lets you adjust the fill flash in terms of stops of flash output, in either 1/2 or
1/3 stop increments. What’s the relationship between the two ways of describing fill
A ratio of 1:1 would mean that the flash unit is the sole source of light (0
ambient + 1 flash) and therefore you wouldn’t have a fill flash situation.
A 2:1 ratio would mean that the ambient light and flash are at the same level
(1 ambient + 1 flash). That basically means 0 stops of compensation given a
fairly flat-lit scene, and usually results in rather unnatural looking fill flash.
A ratio of 3:1 means that there is twice as much light from the ambient
source as the flash (2x ambient plus 1 of flash). Such a ratio requires a -1
stop fill flash setting on the flash unit, since each stop means a doubling or
halving of the amount of light.
A ratio of 5:1 means that there is four times as much light from the ambient
source as the flash (4x ambient plus 1 of flash). This is a -2 stop difference.
Typically photographers use between 1 and 2 stops of fill flash to lighten
shadows without creating a phoney flash-illuminated look.
However, the term “ratio” is confusing and seems to mean different things to
different people. Sometimes people talk about a 1:1 ratio when the ambient and fill
lights are of equal intensity. So a 2:1 ratio might mean -1 stop fill flash and 4:1
would mean -2 stop fill flash. In this case they’re talking more about the light output
than they are about the reflected light.
The concept of ratios works well in studio situations where you have total control
over the lighting. You can turn off the main light and measure the fill lighting with a
meter, you can move lights around to vary their strength, etc. But if you’re taking a
candid photo outdoors you have no such control. You can hardly turn off the sun,
and automated TTL flash is going to have its own ideas as to what constitutes correct
For those reasons I prefer not to deal with ratios at all for non-studio flash
photography but just in terms of the number of stops compensation used by the
flash. Note that the term “ratio” is also used in flash photography in conjunction with
multiple flash setups, particularly multiple wireless units in the case of wireless E-TTL
Auto fill reduction.
Also called “automatic reduction of flash output” in some Canon documentation.
Canon EOS cameras automatically use regular flash exposure with no compensation
when ambient light levels are low - 10 EV or lower. However, when ambient light
levels are brighter - 13 EV or higher - the camera will switch to fill flash mode and
reduce the flash unit’s output level. It does so in TTL mode by dropping flash output
by 1.5 stops. Between 10 and 13 EV the camera will smoothly lower the flash unit’s
output by half a stop for each EV.
E-TTL flash works in a similar fashion, though apparently flash output will be lowered
by as many as 2 stops when ambient lighting is bright. Canon have not, however,
divulged their secret E-TTL fill reduction algorithm, so it’s total guesswork exactly
how it works. Apparently, though, the algorithm compares the brightness level of
each zone both before and after the preflash, in part to compensate for highly
reflective areas.
Some mid to high end EOS cameras allow you to disable this auto fill reduction by
means of a custom function. See the section on flash exposure compensation for
details. Note that any flash compensation you may apply manually is in addition to
this auto fill flash reduction, unless of course you’ve disabled it via a custom
Slow shutter sync.
There are two basic ways in which a camera can take a flash photo when light levels
are low. The camera can either use a short shutter speed to minimize camera motion
blur and have the flash blast out enough light to illuminate the foreground objects
whilst leaving the background dark, or the camera can extend the shutter time to
allow more of the background to show up and flash-illuminate the foreground
subject. This latter technique is called slow sync, slow shutter sync or “dragging” the
It’s only possible in Tv, Av and M modes - you can’t use it in P mode or most of the
PIC (icon) modes. The one exception is the night scene PIC mode on many EOS
cameras, which uses slow shutter exposure with first-curtain flash.
A typical example is a tourist snapshot of someone standing in front of a famous
landmark at night. If you keep the shutter speed fast then you’ll have a nice flashilluminated photo of your friend against a pitch black backdrop, unless the landmark
is extremely brightly lit or unless you’re using very fast film. However, by slowing
down the shutter speed you can take a photo of the person standing against a
properly exposed background.
The drawback is obvious, of course. By slowing the shutter speed you’re going to
need a tripod to avoid blur induced by camera movement, especially with long
shutter speeds like 1/15 second or slower.
Sometimes slow shutter sync is used to provide a dynamic motion effect in flash
photos. A photo taken with flash and a slow shutter speed can provide an interesting
mix of flash-illuminated subject and ambient-light-illuminated motion blur. The effect
is difficult to predict, but can be very striking and exciting when it works.
Take my photo of fire performers for example - the flash freezes the motion of the
performers but the slow shutter captures the swirling motion of their fire chains.
Have a look at the discussion of colour temperature theory to find out why the righthand flash-illuminated performer has a bluish tinge to his skin whereas the rest of
the photo is illuminated with very yellow-orange light. Steve Mirarchi also has some
interesting examples on his Photo.net article on concert photography.
X-sync (flash sync) speed.
Timing is critical for flash photography. The burst of light from a flash unit is
extremely brief (in milliseconds), and must occur when the shutter is fully open. If
the flash burst occurs when the shutter is still opening or closing then the shutter
itself may prevent the entire image area from being fully exposed.
Modern SLR camera shutters are equipped with a pair of moving curtains which wipe
across the opening to the image area. They travel vertically because the travel
distance is less than if they travelled horizontally, and there are two curtains to make
fast shutter speeds possible. At high shutter speeds the opening is actually an open
slit between the two curtains, travelling the height of the image area.
This presents a problem with flash photography. If you have only a slit exposed at
the time the flash happens to go off then you won’t be able to illuminate the entire
image area with the flash burst. An electronic flash burst is always much briefer than
the fastest shutter speed motion that the shutter mechanism can achieve.
Different cameras have different shutter designs - some are faster than others. But
each camera will have a maximum shutter speed at which a flash burst will expose
the full image area of the film. This maximum flash-compatible shutter speed is
called “X-sync speed.” X-sync and flash sync are the same thing on modern
cameras, since they all use electronic flash.
Maximum X-sync speed and EOS bodies.
1/90 second.
All low-end Canon EOS cameras. These are cameras of the Rebel series in North
America (eg: Rebel G, Rebel 2000), the Kiss series in Japan (eg: EOS Kiss, Kiss III),
and the EOS three-digit series (eg: EOS 300, 500 but not the EOS 100, 600 series or
750/850) and all EOS four-digit series (eg: EOS 1000, 3000) elsewhere.
Note, however, that some users report that their Rebel/EOS three/four-digit cameras
are actually physically capable of attaining a 1/125 second X sync. That is, the
shutter mechanism can sync that fast but the camera’s computer has been
deliberately programmed not to allow flash sync at speeds faster than 1/90 second.
It’s not clear why Canon did this. One theory is that it was an intentional move on
Canon’s part to cripple their low-end cameras for marketing reasons. (ie: so that
they compete less with midrange models) Another theory is that this was done
because of flash duration tolerances - Canon decided to play it safe and ensure that
their low-end shutters always can record a full flash burst.
Either way you can’t override the camera’s programming and perform flash sync with
any dedicated flash unit which meters through the lens. But if you’re using an
externally triggered flash with an optical slave or adapter cable you may be able to
take advantage of this higher sync speed if your camera falls into this category (nondedicated flash units do not communicate with the camera concerning flash exposure
and thus the programmed 1/90 sec limit is not an issue). Unfortunately empirical
testing is the only way to find out.
1/125 second.
Mid-range EOS cameras. These are EOS two-digit cameras (eg: EOS 10 and 50) and
the Elan series in North America (eg Elan II, Elan 7). Most of the first generation EOS
cameras (600, 630, 650, 750 and 850) also have a 1/125 sync, as does the original
Elan/EOS 100.
1/200 second.
Semi-pro EOS cameras. These are the single-digit EOS cameras that aren’t in the 1
series - the EOS 3 and 5 (A2 in North America). The digital D30 and D60 also have
an X-sync of 1/200 sec as does, surprisingly enough, the APS IX. (apparently the
smaller physical dimensions of the IX shutter allow it to reach a higher X-sync speed)
1/250 second.
Top of the line professional EOS cameras - the EOS 1, 1N, 1V, 1Ds and 1D mark II.
The one odd one out is the EOS 620, an old camera from the late 80s which
nonetheless could sync at 1/250 sec as well.
1/500 second.
The digital 1D camera has a startling 1/500 sec X-sync and a 1/16 000 sec top
shutter speed. This is because both X-sync and shutter speed are normally handled
electronically by the CCD and not by a mechanical shutter. The 1D does have a
mechanical shutter but it’s used for bulb mode. Note, however, that the CMOS-based
1Ds has a top X-sync speed of 1/250 like the 1V upon which it’s based - the higher
X-sync speed of the 1D derives from its use of a CCD image sensor.
All EOS cameras will deliberately prevent you from exceeding the X-sync value for
shutter speed when you’re using non-FP flash.
Note the first exception - if you have an E-TTL flash on a type A body with FP mode
flash enabled you’re fine. You can exceed X-sync at the cost only of lowered flash
output. But there is a possible second exception, and that is if you’re using third
party flash gear, particularly studio flash units that use optical slaves or generic flash
units. Such a setup likely won’t notify the camera properly of your use of flash, so be
EOS flash photography confusion.
The main area of confusion in EOS flash photography is the fact that P, Tv, Av and M
modes handle flash illumination differently, especially when ambient light levels are
not bright. Here’s a summary of how the modes basically work when you have a
flash unit turned on. This summary assumes that you do not have FP mode flash
enabled if that option is available to your particular camera and flash unit
Shutter speed
Lens aperture
Automatically set from 1/60 sec to the
camera’s maximum X-sync speed.
Automatically set
according to the camera’s
built-in program.
You can set any shutter speed between Automatically set to
30 seconds and the camera’s maximum match the shutter speed
X-sync speed.
you have set.
Automatically set between 30 seconds
and the camera’s maximum X-sync
speed to match the lens aperture you
have set.
You can set any shutter speed between You can set any lens
30 seconds and the camera’s maximum aperture you like.
X-sync speed.
You can set any lens
aperture you like.
And here are the details:
Program (P) mode flash.
The overriding principle of Program (P) mode in flash photography is that the camera
tries to set a high shutter speed so that you can hold your camera by hand and not
rely on a tripod. If that means the background is dark, so be it.
Program mode operates in one of two modes, depending on the ambient (existing)
light levels.
1) If ambient light levels are fairly bright (above 13 EV) then P mode assumes you
want to fill-flash your foreground subject. It meters for ambient light and uses flash,
usually at a low-power setting, to fill in the foreground.
2) If ambient light levels are not bright (below 10 EV) then P mode assumes that you
want to illuminate the foreground subject with the flash. It sets a shutter speed
between 1/60 sec and the fastest X-sync speed (see above) your camera can attain.
The aperture is determined by the camera’s built-in program.
Because the camera tries to keep the shutter speed at a reasonable speed for
handholding the camera you will end up with dark or black backgrounds if you take a
flash photo in P mode when ambient light levels are not bright.
On most if not all EOS cameras, P mode is not shiftable when flash (internal or shoemounted Speedlite) is used. Note also that DEP mode cannot work correctly with
flash - its metering settings basically revert to P mode if you try it.
Tv (shutter priority) mode flash.
In this mode the camera lets you change the shutter speed. It then automatically
chooses an aperture setting to expose the background correctly. Flash duration
(flash output) is determined by the flash metering system. In other words, the
camera always works in fill flash mode when it’s in Tv mode - it always tries to
expose the background adequately, unlike P mode.
If the maximum aperture value of your lens starts flashing in the viewfinder it means
the background of the scene you’re shooting is too dimly lit. If you want to try and
expose the background then you should decrease the shutter speed to compensate.
Otherwise the camera will just try and expose the foreground with flash and the
background will come out dark. Naturally at slower shutter speeds you’ll need to use
a tripod to avoid blurring caused by camera shake.
As always, the camera will prevent you from exceeding its built in X-sync speed
unless FP mode is available to you and engaged. If the minimum aperture value of
your lens starts flashing then your scene is too brightly lit. You must then either
engage FP mode if it’s available or perhaps put a neutral density filter on the camera
or use slower film. Or turn off flash altogether and simply use a reflector of some
type to bounce ambient light onto the subject.
The 420EZ and 430EZ flash units will operate in A-TTL mode in Tv mode, but the
540EZ works only in TTL mode. Note also that some people have reported that in
this mode their type A camera bodies underexpose the background by up to a stop
when light levels are low and an E-TTL flash unit is engaged. If this is the case try
testing by comparing the aperture setting with M mode, which does not do this. You
may need to apply exposure compensation if this effect exists on your camera and is
Av (aperture priority) mode flash.
Av mode lets you set the depth of field by specifying the lens aperture. The camera
then chooses a shutter speed ranging from 30 seconds to the camera’s X-sync
speed, in order to expose the background correctly. If that means the shutter speed
is some really low value so that you need to use a tripod to avoid camera-shake blur,
so be it. In dark conditions, therefore, Av mode works in slow sync mode.
Flash duration (flash output) is determined by the flash metering system. Like Tv
mode the camera always works in fill flash mode when in Av mode.
There is one exception to this. A number of EOS cameras have a custom function
you can set to ensure that the shutter speed in Av mode when using flash is locked
to the X-sync speed. The EOS 10/10s and Elan II/EOS 50, for example, have such a
custom function, which lets your camera behave more like P mode when in Av mode.
However this custom function will only lock the camera to X-sync in Av mode and will
not choose a shutter speed from 1/60 sec to X-sync, the way P mode does.
As always, the camera will prevent you from exceeding its built in X-sync speed
unless FP mode is available to you and engaged. If the shutter speed value of 30"
flashes in the viewfinder then there isn’t enough light to expose the background
correctly and you’ll need a larger aperture or faster film. If the camera’s X-sync
flashes in the viewfinder then you’ll need to decrease the lens aperture, engage FP
mode if it’s available or use slower film.
The 420EZ and 430EZ flash units will operate in A-TTL mode in Av mode, but the
540EZ works only in TTL mode. Note also that some people have reported that in
this mode their type A camera bodies underexpose the background by up to a stop
when light levels are low and an E-TTL flash unit is engaged. If this is the case try
testing by comparing the shutter speed setting with M mode, which does not do this.
You may need to apply exposure compensation if this effect exists on your camera
and is undesirable.
Manual (M) exposure mode flash.
In manual exposure mode you specify both the aperture and shutter speed, and your
exposure settings will determine how the background (ambient lighting) is exposed.
The subject, however, can still be illuminated by the automatic flash metering
system since the flash can automatically calculate flash output levels for you. This is
a marked contrast to the olden days, when photographers would carry around little
flash exposure tables with them in order to work out manual flash settings.
This is how flash works in manual mode. Note that we’re talking about the manual
exposure mode setting only, which can use automatic TTL flash metering (it will not
use A-TTL metering in manual exposure mode). Also, we aren’t talking about setting
the output of the flash manually - that’s manual flash and a different topic
Set your camera to M for manual exposure mode.
Set the aperture and shutter speed to expose the background correctly.
Press the shutter button down halfway if your flash has a rear-panel LCD
(liquid crystal display). The flash coupling range will appear in the flash unit’s
LCD. This range is the distance that can safely be covered by the flash.
If your lens has a distance scale you can check the current focussing distance
to ensure that the distance to your subject falls within this range. Otherwise
you’ll have to estimate.
If the “flash ready” lightning bolt symbol appears in the viewfinder you can
press the shutter all the way to take the photo. The flash’s TTL or E-TTL
system will determine the flash exposure level of the subject.
If your flash lacks a rear-panel LCD you won’t have a preview of the flash coupling
range, of course. Also, LCD-equipped flash units will not calculate the flash coupling
range if you’re using bounce flash, and the coupling range will not necessarily be
correct if you have a diffuser on the flash head.
Some Speedlite flashes, such as the 540EZ and 550EX, can display the coupling
range in either feet or metres, depending on which measurement system has been
set by the small switch in the battery compartment. Others, such as the 430EZ, are
hardwired to one measurement system or the other, depending on where the flash
was sold. US market flashes used feet and all other countries on the planet* had
only metre flashes available to them.
* Trivia note - even countries such as Canada and the UK which are officially metric
but which are nonetheless full of people who still use imperial measurements. Also
Yemen, Rwanda, Burundi and Burma, which used to stand proudly with the USA as
the planet’s only officially non-metric countries and which have now given up and are
switching over to metric. Liberia is the only holdout I can find, and even there it’s
only the government - apparently businesses and schools use metric.
Multiple flash units.
As noted above, the basic problem with balancing ambient light and shutter speed
requirements is that the output from a flash unit is only sufficient to illuminate the
foreground, unless you’re in a small interior space in which you can bounce the light.
If you’re in a larger space or an area in which you can’t bounce light effectively you
could consider using multiple flash units - a unit or two for subject illumination and
another unit or two for the background. Such a setup gives you increased range and
affords more control over the lighting.
There are three common ways to do this - wired, optical slaves and wireless.
Wired multiple flash.
With a wired system you buy the necessary connecting cords and adapters to hook
up more than one unit to your camera. Each flash unit fires simultaneously when you
take a photo, and you can use TTL metering or configure the output for each flash
unit manually (assuming the unit in question has the ability to have its output set
manually). For details check out the extension cord section.
Optical slave multiple flash.
With optical slaves you position your various flashes - big AC-powered studio flash
units or small battery-powered units - around the scene and connect tiny optical
sensors to each one. These sensors respond to a flash being fired and trigger their
own flash units immediately. For more information have a look at the slave flash
Wireless multiple flash.
Finally, you can use a wireless control system to trigger your flashes. A number of
companies manufacture radio remote systems that let you do this - the Pocket
Wizard Multimax and the Quantum Radio Slave being popular products. These third
party systems have a long range and can be used in conjunction with optical slave
units if necessary.
The most recent option is Canon’s own wireless E-TTL, which lets you set up multiple
Speedlite flash units and trigger them remotely using light pulses. (ie: this system
does not use radios) The Canon system essentially requires E-TTL and supports all
associated features - FP flash, FEL and so on. On certain camera bodies, ratio control
between different flash units and modelling flash is also available. For more
information consult the wireless E-TTL section.
Metering patterns for the background when using flash.
EOS cameras have different metering patterns, depending on the model. These
metering patterns include evaluative (varying number of zones from 3 to 35), partial
(from 6.5% to 10.5%, sometimes centred around the active focus point), centreaveraged and spot. When you aren’t using a flash these metering patterns are used
for metering the subject of a photo.
However, in flash photography the camera needs to meter for the background and
not the subject, so the metering pattern should change when possible. This varies
from camera to camera.
EOS cameras with single zone ambient metering such as the T90 and the original
Rebel/1000 cameras use centre-weighted average metering for TTL and A-TTL flash.
EOS cameras with multiple metering zones for ambient metering use the outer
segments of their evaluative metering sensor for TTL and A-TTL flash. (their
evaluative sensors are divided into patterns depending upon the number of zones
and the segments closest to the edge of the frame are selected)
Note that most EOS cameras with partial metering buttons won’t use the outer
evaluative zones for ambient metering when the button is pressed. Instead they use
partial metering patterns for ambient light metering in flash photography as well.
The T90, EOS 1, 700, 750 and 850 are exceptions - they do not let you switch to
partial metering for flash.
Unfortunately, the way in which E-TTL meters ambient lighting has not been publicly
documented by Canon, so far as I know.
Flash metering patterns.
As above, information on flash metering patterns is fairly scarce, particularly for ETTL flash.
TTL and A-TTL flash metering patterns:
The flash metering pattern is determined by the type of flash sensors built into the
camera. If the camera has only one focussing point then it will have a single zone
flash sensor. Flash metering is conducted using this sensor in a centre-weighted
averaging pattern.
If the camera has multiple focussing points then it will have multiple zones; what
Canon call their AIM system. The number of flash metering zones depends on the
camera model. For instance, the EOS 10/10s has three focussing points and three
flash metering zones, and flash metering uses whichever corresponding
autofocussing point or points are active. However, the EOS 5/A2 uses the same
sensor as the 10/10s so it too has 3 flash metering zones even though it has 5
autofocus points. The Elan II/EOS 50 has 3 AF focussing points and a 4 segment/3
zone flash sensor. (this latter means that the flash sensor has 4 segments but it
chooses two consecutive segments, yielding 3 possible zones)
These multiple zone flash sensors let the camera bias the flash exposure to the
currently selected AF point. When you focus manually the camera does not bias any
flash zone but chooses the central zone instead.
Note that the A2/5 is somewhat different from other multiple AF point cameras in
that it will only bias flash exposure correctly to the nearest AF point if that point was
manually selected. In automatic and ECF modes it apparently always chooses the
centre zone.
E-TTL flash metering patterns:
The camera uses its evaluative metering system to meter the flash output, based
upon the preflash. When in autofocus mode most EOS bodies which do not use E-TTL
II bias flash metering toward the currently selected AF point, but always in an
evaluative mode pattern - they don’t use spot or partial metering patterns. When in
manual focus mode it appears that at least some EOS bodies switch to centreweighted averaging.
Note, however, that this biasing of E-TTL metering to the active point is potentially
problematic, since it means that the flash metering is done in almost a spot-metering
fashion. Many user complaints regarding flash metering problems in E-TTL mode
appear to be linked to this issue. If the camera happens to be over a dark object, for
example, flash metering can be considerably overexposed, and vice-versa. The
standard answer to this problem is to use FEL and meter off something mid-toned,
but this is clearly not a solution for rapid-shooting situations such as weddings and
sports. Another approach is to set the camera lens to manual focus, since the body
apparently switches to centre-weighted average metering in that mode, but that’s
obviously not a useful answer much of the time either.
Users of the digital D30 and D60 have been particularly unhappy with E-TTL flash
metering. The 10D apparently reduces this problem by defaulting to a centreweighted averaging metering pattern in E-TTL, even when the lens is set to
E-TTL II addresses this problem by altering flash metering considerably. It examines
each evaluative metering zone before and after the E-TTL preflash. It then calculates
the weighting for each zone independently, biasing against those zones with high
reflectivity in the preflash. This means that E-TTL II does not have a flash metering
pattern as such, since it’s calculated dynamically.
Note that since I’ve been unable to find definitive published statements from Canon
on this topic it isn’t as authoritative as it could be. Please contact me if you have
further information about E-TTL flash metering.
Do not focus and recompose.
The fact that the camera biases flash exposure to the nearest focus point, if the
camera has multiple focus points, is important to keep in mind. If you’re in the habit
of using the old “focus, lock AE and recompose image” technique, be sure not do this
when taking flash photos.
Flash metering occurs after ambient light metering, so in this case you’re locking AE
but not flash metering, and therefore recomposing messes up your flash metering.
Instead, select the focus point that’s closest to your subject in order to bias flash
exposure to that area.
There are two exceptions to this rule, however. First there are type A bodies which
support FEL. You can use FEL in such situations to lock flash exposure to a given
area of your photo before recomposing. Second, cameras with support for E-TTL II
are supposedly less vulnerable to this problem because they can include distance
data in flash metering.
Flash terminology.
Here are a number of other terms and concepts related to EOS flash photography
and flash photography in general. For more information on the principles of
electronic flash, check out Toomas Tamm’s page.
Strobe and flash.
We have a little UK/US terminology problem here. In the UK a “strobe” is something
which emits blinking pulses of light whereas in the US a “strobe” is any electronic
flash unit, whether it fires once or continuously.
We also have the additional confusion that arises from “flash” having four meanings a verb meaning to produce a pulse of light, a flash of light, flash-based photography
in general and a flash-producing device. Finally, we have “Speedlite” and
“Speedlight,” which are the tradenames used by Canon and Nikon respectively for
their series of electronic flash units.
So. In this document I adopted the following convention:
I don’t use the word “strobe” at all in order to minimize confusion.
I refer to electronic devices designed to emit pulses of light for photographic
purposes as “flash units” if there’s any possibility for ambiguity with any other
meaning of the word. Yes, that leaves me vulnerable to crappy adolescent
jokes. Oh, well.
I refer to electronic flash units that are emitting pulsating flashes of light as
Finally, speaking of UK/US stuff, I’ve used the antiquated convention of
referring to corporations in plural form (as groups of people) rather than
independent entities. Since everyone assumes I’m just making a grammatical
error rather than a feeble ideological point I might change that...
Inverse square law.
Light dropoff from a light source always seems very rapid. Consider a campfire at
night - a pool of light surrounded by darkness. Or a flashlight (electric torch in the
UK) being shone into the night sky - a bright bar of light that rapidly fades to
nothing. You might think that when you double the distance from a light source you
get half as much light, but it doesn’t work like that - you actually get just a quarter
as much light.
Space is three dimensional, so imagine a sphere drawn around a light source that’s
producing photons. As you get further away from the light source this imaginary
sphere increases in size. The surface area of the sphere also increases, but it’s being
illuminated by the same amount of light - the same number of our photons. It’s not a
simple 1:1 relationship - the sphere is not twice as large when you get twice as far
from it.
The actual relationship between distance from the light source and size of the
imaginary sphere can be described mathematically as the inverse square law. It
states that light output is proportional to the inverse square of the distance. (ie:
divide 1 by the distance, then square the result) So if you double the distance you
get 1/2 2, or one quarter as much light. If you quadruple the distance you get 1/4 2,
or only one sixteenth as much light.
All light sources follow this rule, which is why light from a flash unit tends to drop off
in intensity pretty rapidly. It also explains why you don’t necessarily gain much more
flash range when you buy a moderately more powerful flash unit, and why
foreground objects are much more brightly illuminated by your camera-mounted
flash unit than distant objects.
Guide number.
The maximum distance range of a flash unit is indicated by its guide number. If you
use automatic flash metering you may never have to deal with guide numbers at all,
except when you’re shopping for a flash unit and want to know how powerful each
one is. But guide numbers are critical for all manual flash work.
The guide number is used in flash calculations to determine the appropriate aperture
required to cover a certain distance or vice-versa. Note that technically the guide
number describes the distance coverage of a flash, not its actual power output as
such. Because of the inverse square law of light falloff, a flash unit has to have four
times the power output in order to throw light twice as far.
To find the aperture (f stop number) required to take a photo of a subject you divide
the flash unit’s guide number by the distance to the subject. To find the maximum
distance that can be reasonably illuminated using the current aperture setting you
divide the guide number by the f stop number. In each case it’s the distance from
the flash to the subject that’s important, not the distance from the camera to the
subject. These two distances may be the same with on-camera flash, but not with
off-camera flash or when using bounce flash.
f-stop number = GN / distance
distance = GN / f-stop number
Canon’s guide numbers are measured in metres and are for ISO 100 film. Their
Speedlite product names, for example, include the highest guide number of the flash
(which is the guide number for the flash when on maximum zoom in the case of
zooming flashes) multiplied by 10 - eg: 550EX. Note, however, that Canon USA
express guide numbers in feet in their material, so always double-check the
measurement system. For example, US advertising material says that the Elan 7’s
built-in flash has a guide number of 43, which sounds quite remarkable until you
realize that that translates to a metric guide number of 13. (the built-in flash units in
EOS cameras typically have a guide number of 12 or 13 unless they have a zoom
I refer solely to metric guide numbers in this document. Here are approximate metric
conversion values:
1 metre = 3.3 feet
1 foot = 0.3 metres
An important point is that the guide number is rated for ISO 100 film. So if you’re
using film of a different speed you have to factor that in to your calculations. Once
again the math is based on the inverse square law - quadruple the film speed and
you double the guide number. Thus the maximum range possible with your flash unit
increases when you use faster film. Here’s a quick way to do the conversion if you
want to avoid thinking about square roots:
Film speed doubles: GN x 1.4
Film speed halves: GN x 0.7
Another thing to remember when comparing flash units is that zooming flash heads
affect the advertised guide number. For instance, the 480EG flash contains more
powerful flash tubes than the 540EZ, even though the former has a guide number of
48 and the latter a maximum guide number of 54. This is because at 35mm
coverage the 540EZ’s guide number is only 36. However, the 540EZ’s zooming head
can concentrate the unit’s light output at longer focal lengths, whereas the 480EG’s
non-zooming head essentially wastes light by illuminating areas not covered by
lenses with focal lengths longer than 35mm, except when an optional lens is
installed. Such flash extenders, which can concentrate the light to a tighter area and
thus throw light even further distances, are available as add-on accessories for other
flash units as well.
As noted above, the guide number does not describe the amount of light output as
such. Flash unit capacity is also described in terms of light output units such as beam
candlepower seconds (BCPS) or effective candlepower seconds (ECPS) or in terms of
energy capacity units such as joules or watt-seconds. None of these measuring
systems are commonly used with portable electronic flash units, so I’m not going to
cover them here. They also measure different things and are, therefore, not
convertible or interchangeable units.
Finally, a fair bit of subjectivity goes into determining the guide number, which is
presumably why it’s called a “guide.” After all, how is an “adequately exposed”
subject determined? Guide values are, therefore, not a very reliable way to compare
flash units built by different manufacturers. Particularly since manufacturers tend to
be wildly and cheerfully optimistic when it comes to assigning guide numbers to their
Exposure value (EV).
The sensitivity of camera gear at autofocussing or determining correct exposure
metering is rated in terms of EV - exposure value - for a given lens type and film
Since the amount of light hitting the surface of film is determined by exposure time
(shutter speed) and lens aperture, exposure values are simply combinations of
shutter speeds and apertures. For example, f4 at 1/30 sec has an EV of 9, which is
the same EV as f2 at 1/125. Toomas Tamm has a complete EV table on his Web site.
Both speed/aperture combinations let the same amount of light hit the film - the only
differences between the two are depth of field and type of motion recorded. Depth of
field decreases as the aperture increases and subject motion blur increases as
shutter speed decreases.
However, it’s only meaningful to compare exposure values when they’re rated for the
same film speed. Canon rate EV values in their documentation for a standard 50mm
f1.4 lens using ISO 100 film.
Dedicated or non-dedicated flash units.
In the olden days of electronic flash, when the flash sensor was self-contained in the
flash unit itself, the flash trigger controlled by the camera was the only control the
camera had over the flash. The output level and shutoff time were both determined
by the flash unit itself since two-way communications between camera and flash unit
were not possible. For this reason a lot of generic flashes were sold and basically
worked the same way on every manufacturer’s camera.
However, by the 1980s camera makers started designing dedicated flash systems
which would only work with their own cameras, in order to achieve more precise
control over the final results. (and also probably to sell more of their product by
discouraging third-party sales) Canon’s Speedlite flash units are, therefore,
dedicated flash units since they can communicate digitally with EOS cameras. They
can work on other cameras in the most basic of ways, but advanced through the lens
metering and other features reliant on two-way communication will not work on
cameras built by another manufacturer.
Some makers of third party flash units, such as Metz and Sigma, get around the
dedicated interface problem by figuring out the camera system-specific protocols and
either building generic units with custom flash adapters designed to work with
specific camera makes or else building different flash models for each camera make.
Shoe mount.
Most SLRs today have a squarish slide-in socket on the top of the prism or mirror
housing which accommodates external flash units. These are called hotshoe mounts “hot” because they contain a flash-triggering electrical contact. (though it should be
noted that no modern camera lacks this contact, so this term exists now for historical
reasons) Despite the dramatic name the contacts do not carry any significant
electrical current when a flash unit is not installed, so there’s no risk of electrocution
from a hotshoe.
EOS cameras have shoe mounts containing 4 additional small contacts in addition to
the large central flash-triggering contact. These small contacts carry digital signal
data, proprietary to the Canon EOS system, to the flash. They aren’t compatible with
flashes made by Nikon, Pentax, Minolta, etc.
Another Canon feature is the presence of a small hotshoe locking pin on most EOS
flashes. This pin extends out when the tightening wheel is rotated, fitting into a small
hole on most EOS bodies and preventing the flash from sliding accidentally out from
the shoe. The pin is spring-loaded so the flash will still fit in hotshoes which lack the
locking pin hole.
Note that the plastic shoe of external flash units isn’t quite as sturdy as it should be.
It’s a bad idea to pick up a camera and flash by the flash unit. Pick up the camera
body to be on the safe side.
The redeye effect.
Redeye, the common bane of snapshots, occurs when the light from the flash unit
bounces off the blood vessels lining the retina of a person’s eye and makes it back to
the camera. The result is the familiar evil satanic glowing red eye effect that shows
up disconcertingly often with point and shoot cameras. It happens a lot in restaurant
and living room photos because the low ambient light levels mean that the subject’s
pupils tend to be dilated fairly wide to let in more light. The problem doesn’t occur in
daylight partly because the pupil of the eye contracts and reflects less light and
partly because the relative brightness of flash illumination to ambient light is much
lower during the day.
The problem of redeye is intensified the further you are from your subject and so
becomes very apparent when shooting portraits using telephoto lenses. The greater
the distance from the subject the further you have to lift the flash away from the
lens to eliminate redeye. This is because it’s an issue of how narrow the angle
between the subject-flash and subject-lens distances is. The smaller this angle whether because you’re a long way away from the subject or because the flash is too
close to the lens or both - the greater the chance of redeye. Built-in flash units,
located very near to the lens, are thus extremely likely to cause redeye.
Interestingly enough, flash photography of cats and dogs can involve a similar, but
slightly different, problem. Cats and dogs have a reflective membrane in their eyes
called the tapetum lucidum, which helps their night vision. The tapetum reflects light
from a flash unit very efficiently, and tends to colour it green, yellow or blue. The
membrane also explains why the eyes of animals like cats or deer by the side of the
road at night are clearly visible as brilliant points of light. Humans lack this layer and
so we don’t have tapetal reflections.
Redeye reduction.
There are a number of ways of dealing with redeye. The first, and generally most
effective, way is to move the flash as far away as possible from the lens or point the
flash head away from the subject (ie: bounce the light). As noted above, the closer
the flash source is to the lens axis the worse redeye is going to be. So if you detach
the flash unit from the camera and lift it up in the air a short distance you’re likely to
reduce redeye considerably. This is one reason why wedding and news
photographers tend to mount their flash units on external metal brackets attached to
the camera itself - flash brackets. And bounce flash eliminates redeye by definition.
One drawback with moving the flash, aside from the inconvenience of moving the
flash unit, involves low-light photography. When light levels are low the pupil of the
eye will dilate to let in more light, just like a lens diaphragm. If you take a photo of a
person with flash their irises don’t have enough time to react to the burst of light, so
their pupils will remain dilated. The result is a photo of someone with huge pupils, as
if they were on drugs.
Another way of reducing redeye (and also minimizing the huge pupil problem) is to
have the subject look at a bright light shortly before taking the flash photo. This
usually sort of works because the person’s pupils will contract in response to the
bright light, reducing the amount of light reflected back from the retina to the
camera. For this reason many EOS cameras have bright white lamps built into them
which the photographer can illuminate at will.
On some EOS cameras, such as the Elan/100 or Elan II/50/55, the redeye reduction
lamp is mounted in the built-in flash housing and cannot work with external flash
units. On other cameras, such as the D30, the redeye reduction lamp is mounted
lower on the body and also works with external flashes. On other bodies the redeye
reduction lamp won’t work with external flash units even though it’s body mounted.
However, redeye reduction lamps aren’t so useful with external flash units anyway,
as they tend to be raised fairly high off the lens axis and are often used in a bounce
mode which spreads light across a wide area. And if the subject is some distance
away the redeye lamp won’t be of much use. It’s for this reason that no Speedlite
external flash unit has any form of redeye reduction lighting system - it’s really just
a feature for point and shoots and built-in flash.
The downside to redeye reduction lights is quite severe - people tend to look stunned
and glazed after staring at an intensely bright light for a few seconds. Stunned and
glazed or evil and satanic - with onboard flash photography, the choice is yours!
You can also colour over the redeye with a black pen on the final prints or scan the
image into a computer and use an image editing program to correct the redeye, but
obviously these are rather clumsy ways to solve the problem.
The first curtain sync problem.
As noted in the section on X-sync, Canon EOS cameras (and basically all SLRs) have
two moving “curtains” in the shutter mechanism. The first curtain opens the shutter
and the second curtain closes it.
Let’s say you take a flash photo of a static object combined with a long shutter
speed. Normally the shutter opens, the flash fires, time passes and then the shutter
closes. Now let’s say you’re taking a photo of a moving object. The object is
illuminated enough to leave light trails recorded on the film as the object moves
along. But if you fire the flash immediately after the shutter opens then you’ve got a
bit of a problem, since the light trails will appear to be moving in front of the flashilluminated object. The object will actually sort of look like it’s moving backwards.
Second-curtain sync.
To solve the first-curtain sync problem mentioned above, and to get the light trails
looking like they’re following behind the moving object as they should, you need to
fire the flash right before the shutter closes. This is called second curtain or rear
curtain sync flash since the flash is fired about 1.5 milliseconds before the second
curtain of the shutter starts to close. The result is a photo which expresses motion
nicely - it will show light trails following the moving object. The Canon T90/Speedlite
300TL was apparently the first camera/flash combination to support this feature.
The drawback to second curtain sync is that it can make it harder to take a photo if
you’ve got a really long shutter period. With first curtain sync you can see the
moving object in the viewfinder and can thus trigger the shutter at the exact
moment. But with second curtain sync you a) can’t see the moving object when the
shutter is open, because with SLRs the mirror flips up out of the way and b) you
have to predict accurately whether or not the object will still be in the frame at the
end of the exposure period. For these two reasons EOS cameras ship with first
curtain sync as the default.
There’s one minor issue to be aware of if you use E-TTL flash with second-curtain
sync. The E-TTL preflash occurs prior to the shutter opening, and so the flash will
visibly fire twice when you’re using long shutter speeds and second-curtain. (the
preflash always fires before the shutter opening - it’s just that with a long shutter
speed and second curtain sync, the time delay between the two flashes is increased
and thus more noticeable)
This delay between preflash and subject-illuminating flash usually doesn’t have any
negative side-effects, but there are two cases in which it might be a problem. First, if
the subject is moving then the preflash metering obviously won’t be right for the
final exposure - FEL may be required. And second, the preflash might confuse human
subjects if they’re expecting just one flash. They might assume you’ve taken the
photo and walk off or look away from the camera.
See the section on how to enable second-curtain sync, if it’s available on your
particular camera and flash combination.
Colour temperature theory.
(nb: this section gets pretty detailed, but it’s a useful basis for understanding colour
shifts in photography)
The human eye (or, more accurately, the brain) is extremely adaptable. If you look
at a sheet of white paper in a room lit only by an overhead incandescent tungsten
lamp, the paper will look white. If you carry the same sheet of paper outdoors and
look at it in sunlight it’ll still look white. But tungsten light and sunlight produce very
different types of light - tungsten light is orange in tone whereas sunlight is quite
This is because they are light sources of different colour temperatures - so called
because they represent the colour of light produced by a theoretical “black body”
object that’s heated to a certain temperature, measured in degrees Kelvin. (Kelvin is
similar to the Celsius scale but uses absolute zero, -273°C, as the starting point
rather than the freezing temperature of water) Note that some of the terminology is
a bit confusing here. In colloquial English we say that reddish light is “warmer” than
bluish light. But in terms of the colour temperature model, light becomes more blue
as the colour temperature increases. Note also that we’re talking about a
photographic colour temperature model, which by dealing just with red and blue light
is a huge simplification of the colour temperature model used by physicists.
Regular incandescent tungsten light has a theoretical colour temperature of about
3200 degrees Kelvin, though household bulbs are often a bit lower at about 2900°K.
(they go down in colour temperature as they age or when supplied with lower
voltages, such as from a dimmer circuit) Tungsten halogen bulbs (usually just called
“halogens” even though they have tungsten filaments just like regular incandescent
bulbs) and non daylight-corrected photoflood bulbs are usually slightly higher,
sometimes reaching 3400°K. The light from a candle flame is quite low in
temperature, hovering at around 1400-2000°K.
Daylight has a colour temperature of between 5000°K and 6000°K; often given as
5500°K for the midday sun. Naturally these values can vary. Just as regular light
bulbs drop in colour temperature, as noted above, the colour of daylight varies at
different times of the day and because of different weather conditions. In fact,
natural light can vary from around 2000°K at sunset to over 20 000°K in blue
evening shade. Skylight, or the sun’s light scattered by the atmosphere, is extremely
blue in colour.
Normally the human brain compensates for these differences in colour temperature
automatically. One of the few times they become really noticeable is when you
encounter both types of light at, for example, dusk. If you’re outside looking at the
windows of a building you’ll see that the tungsten light of a household lamp looks
quite orange-yellow in tone and the sky and your surroundings look quite blue.
Colour temperature and film.
Colour temperature isn’t a purely theoretical issue. It’s a real problem for colour
photography, because film records light as it sees it, does not offer interpretation
and cannot automatically adapt. So film has to be formulated from the start to
assume a certain colour temperature is white.
This is what is meant by “daylight” film and “tungsten” film - they’re film types
designed to assume that daylight and regular tungsten light bulbs are white,
respectively. You’ll get weird colour shifts if you shoot with the wrong type of film. A
tungsten-lit room shot on daylight film will look quite orange and a daylight-lit room
shot on tungsten film will look quite blue. So it’s important to use film which matches
your lighting conditions. It’s not normally essential to be absolutely precise about
this, but pros who need exact colour will buy expensive colour meters to determine
the exact type of colour in a given scene.
Colour casts also occur from lighting types other than incandescent tungsten bulbs.
Other forms of artificial light yield strange colour casts on daylight film as well. Most
fluorescent lamps tend to result in a somewhat greenish tinge unless a special
magenta filter is put over the lens, though there are significant colour differences
between manufacturers. (indeed there are now daylight-balanced fluorescent bulbs
which avoid this problem) High pressure mercury and sodium lamps used for
industrial lighting result in somewhat unpredictable colour casts depending on the
formulation of the bulbs being used. Note that the term “colour temperature” does
not technically apply to fluorescent and high-pressure lamps. However, approximate
equivalent colour temperature numbers are often supplied by manufacturers as a
convenience. Finally, daytime colour temperature varies throughout the day and
depending on weather conditions. A snowy evening can be very blue and a dusty
sunset very orange.
Colour temperature issues are one area in which digital photography has a significant
advantage over chemical-based photography. Most good digital cameras let you set
the white balance - the assumed white point - of your subject at will. The EOS 1D,
D30, D60 and 1Ds cameras all let you use auto white balance settings or preset
settings for common lighting situations. This sort of adjustment isn’t possible with
film-based photography since the colour temperature balance (white balance
information) is permanently built into the film emulsion chemistry at time of
manufacture and cannot be altered afterwards. All you can really do with film is to
put filters in front of the lens to cut out certain wavelengths of light or perform
various filtration tricks in the darkroom when printing - or scan the pictures and alter
them in a computer.
Colour temperature and flash photography.
Since most photography is done with the sun as a light source, most film is balanced
for daylight. Until recently, in fact, tungsten-balanced film was only widely available
as slide/transparency film (as two types - the rare tungsten A and the more common
B, which have slightly different colour temperatures - 3400°K and 3200°K
respectively). And for that reason flash units also have bulbs designed to produce
light approximating midday sunlight in temperature. However, since sunlight is more
blue than tungsten, light from a camera flash will look quite blue compared to the
orange-yellow light of indoor tungsten light.
This difference in colour temperature is particularly noticeable with slow shutter sync
photography. If you take a photo indoors using slow shutter sync with flash and
daylight-balanced film, you’ll get a normally coloured subject with strange orangeyellow fringing. This results from the subject being illuminated brightly by the
daylight-balanced flash and then any motion blur from the slow shutter being
illuminated dimly by tungsten light.
You can also exploit these differences in colour temperature to achieve certain
effects. For example, shooting with flash and tungsten-balanced film can yield bluetinged results. Or you could take a photo of someone outdoors with tungsten film
and an orange tungsten-light compensation filter on the flash head. The result would
be a normal coloured person with a cold, bluish background.
Colour filters.
There are specific filters you can use to perform this type of colour temperature
conversion when you take a photo; the type of filter depending on the kind of effect
you want to achieve. You might want to balance the light of a flash unit to match
ambient lighting, for example. Or you might want deliberately to make the two types
of lighting very different in colour for creative effect.
You can put the filters in different places. For instance, if you want to affect the look
of the entire scene you could put a filter over the lens. To affect the output of a
specific lamp you could buy a gel filter and put it over the lamp only. Or you could
tape a filter or coloured diffuser over your flash unit’s head to affect just the light it
A great way to alter the light colour from a flash unit on the cheap is to go to a
theatrical lighting store and ask for a Lee or Rosco gel swatch booklet. This is a little
bound collection of gel filter samples - each coincidentally just large enough to cover
the lens of a typical flash unit. The booklet lists the exact properties of each gel, and
quite often you can get one for free.
This sort of colour temperature conversion can go in either of two ways, of course. If
we want to go from yellow-orange light (tungsten) to blue light (daylight) we want a
cooling filter. To go the other way we want a warming filter. As noted earlier these
are somewhat confusingly named since cooling involves an increase in colour
temperature and vice-versa, but the names reflect ordinary casual usage of the
words and not colour temperature theory. Naturally, cooling filters are blue and
warming filters orange-amber (light orange-yellow filters are sometimes called
Limitations of filters.
One important thing to remember about filters is that they cannot shift colours over
along the spectrum, as it were. All a filter does is simply prevent certain wavelengths
of light passing through - hence the name. So by definition colour-correction filters
always cut the amount of light entering the lens.
Filters can change the colour of white light since white light consists of colours from
across the spectrum, as Newton discovered with his famous prism experiments. But
if you’re taking a photo of a scene illuminated by, let’s say, pure red light you can’t
simply slap a filter on the lens to make everything a different colour. Filters can’t add
light of any wavelengths or convert incoming light to a different wavelength.
Taking photos of scenes illuminated by yellow-orange sodium and mercury vapour
streetlights is a real problem for this reason. Such lamps produce light of very
narrow spectral bands. You can’t alter this light much by putting a filter on your lens,
since filtering out the yellow light doesn’t leave much else.
This problem of filtration limits your colour-correction choices considerably when
dealing with chemical-based photography. There are ways of doing colour alteration
in the darkroom, but they’re expensive and cumbersome. So again, moving your
images into the digital realm has real advantages. Once your photo is inside a
computer you can alter the colours as much as you like.
Colour temperature of light is usually measured in degrees Kelvin. But another unit
you often see in photography is the mired, for “micro reciprocal degrees,” and
pronounced “my-red.” To obtain the mired value for a colour temperature simply
divide 1 million by the colour temperature. So, for instance, 5500°K is the same as
182 mired, since 1 000 000 / 5500 = 182.
Mireds are commonly used for converting light from one colour temperature to
another using a colour conversion filter. For example, let’s say we want to take a
photo using electronic flash but we have tungsten film in our camera. So we need to
tape a coloured gel over the flash head. The question is, what kind?
Let’s assume the light from the flash unit is 5500°K and the tungsten film wants
3200°K light. These are 182 mired and 312 mired respectively, so the difference we
want to make up is about +130 mired, our mired shift value. (a positive number is a
warming filter; a negative number a cooling)
Now we consult a gel filter catalogue or swatch book (as noted above, available from
theatrical lighting shops) and see what the closest filter to a +130 mired shift is. If
we went with Rosco we could buy a “Roscosun CTO” gel that performs a +167 mired
shift. Or if we went with Lee Filters we could go with a “Full C.T. Orange” gel to get
+159. Neither gel is precisely the same as our calculation, but they’re close enough
for print film, where you can always do some adjustment in the lab. And when using
slide film you might want to overcompensate on the side of warm like this anyway,
unless you’re deliberately looking for a cool blue look. But this is all assuming the
flash unit actually has a colour temperature of 5500°K - it’s probably slightly higher.
Of course, lots of filter companies simply specify the colour temperature conversion
range so you can avoid the whole conversion to mireds altogether if you’re just doing
a simple tungsten to daylight conversion, say. But the mired model is useful for more
complex colour conversion tasks where multiple filters are involved.
Wratten numbers.
Many filter companies follow the Wratten series of numbers to describe their colour
conversion products. Frederick Wratten was a British inventor who developed a fairly
arbitrarily-numbered series of colour filters a century ago. His company was bought
by Kodak in 1912, though Wratten-branded filters are now sold by Tiffen.
80 series: blue-coloured cooling filters. For daylight film with tungsten light
Typical light
source to be
mired shift
Old flash bulbs
85 series: yellow/amber-coloured warming filters. For tungsten film with
Typical use
mired shift
Converting type A
tungsten film
Converting type B
tungsten film
These filters are fairly dark and cost 1 stop (80 series) to 2/3 stop (85 series) of
There are also more subtle and commonly used filters for cooling and warming, such
as the 81 warming filters and 82 cooling filters. These filters aren’t used for colour
conversion but for less extreme applications - minimizing unwanted colour casts. For
example, an 81B is useful for reducing the blue cast of daylight film shot in the
German manufacturers use their own system in which KB is a cooling (blue) filter
and KR is a warming (orange) filter.
Trigger circuit voltage.
Old flash units - both studio and hotshoe-mount - used pretty high voltages between
the camera and the flash - often from 25 to 250 volts. This is because the flash units
were fired by simple switches - electrical contacts.
Modern cameras, however, rely on electronic circuitry rather than electric switches.
This allows for more flexibility and the possibility for computerization, but the circuits
can’t withstand high trigger circuit voltages (anything above 6 volts, in the case of
EOS cameras, according to Canon) and can be damaged by units with high trigger
Note that this 6 volt limit does not necessarily apply to PC sockets. Canon states that
its 1D digital camera, for example, is capable of withstanding trigger voltages of up
to 250 volts when firing flash units with its PC socket. The 6 volt limit applies to the
camera hotshoe only. Unfortunately Canon doesn’t always state what trigger voltage
the PC sockets on all of its PC-socket-equipped cameras can withstand, so if this
information is not supplied in the manual you should probably contact Canon.
Anyway. If you intend to connect an old flash to your EOS camera’s hotshoe be
absolutely sure that its trigger voltage does not exceed 6 volts. You can measure this
with a voltmeter. Various accessories, such as the Wein Safe-Sync HS hotshoe unit,
can be used to protect the camera from these high voltages if you want to use such
a flash. Even safer are optical triggers, since there are no physical connections
between the camera and flash unit at all.
Note that the damage to the camera can be subtle and cumulative - simply hooking
up the flash and seeing if it works is no guarantee that the high voltage isn’t slowly
damaging your camera’s flash circuit - arcing and pitting connectors and breaking
down internal components. (of course, Canon is probably being a bit conservative
with its 6 volt limit, so you might not be taking a huge risk if the voltage of your
flash unit is a tiny bit over) Note also that the power supply used by the flash is
irrelevant - it has no bearing on the trigger voltage. Many Canon Speedlite flash
units, for example, can use high voltage battery packs but they still have low trigger
voltages. And portable battery-powered flash units may require 6 volts in battery
power but nonetheless may step up the trigger voltage considerably.
An additional problem is that some older flash units have reversed polarity. EOS
cameras all have a negative ground and a positive centre pin on the hotshoe itself,
though some pro models have polarity-detecting PC connectors that can work with
either type of flash unit.
Finally, some flash units have all-metal hotshoes. This can be a problem if they
inadvertently short out any of the four small data contacts on EOS cameras. If you
have such a camera you could cover up the contacts with electrical tape or use a PC
cord adapter so the flash unit doesn’t plug directly into the camera’s hotshoe mount
at all. The same applies if your flash unit has a really large central contact. EOS
cameras have fairly small hotshoe central contacts with four tiny data contacts below
it. If your flash unit’s hotshoe contact is so large that it shorts out any of the data
contacts you may damage your camera.
The old Canon EOS FAQ also has a great deal of information on the subject of trigger
voltages, and Kevin Bjorke maintains a comprehensive table of trigger voltages for
various flash units.
Slave flashes.
Slave flashes are simply self-contained flash units which respond to external triggers
of some kind. They’re frequently used in studio situations. For example, you might
have a multiple-flash setup - one flash to illuminate the subject and another unit or
two to illuminate the background separately.
Many slave flashes are triggered by light: optical slaves. They have small sensors
built in or attached that detect the light pulse from another flash unit and then
trigger immediately themselves. Since they respond so rapidly, the time delay
between the trigger flash and the slave flashes going off does not affect the exposure
of the photo. The Wein Peanut, a tiny and inexpensive accessory, is a popular optical
trigger that’s basically compatible with most flash units out there. (though ironically
not entirely compatible with a lot of Canon Speedlites - see further down in this
section for details)
Since the sensors watch for flash bursts, you use one flash unit as the triggering
flash - typically the built-in flash unit on your camera or an external unit connected
to the camera’s hotshoe or PC connector. The triggering flash can be set to a low
power output so that it doesn’t affect the scene if you want - optical slaves are
usually sensitive enough. The slaves are also usually sensitive to infrared energy, so
another popular trick is to tape an infrared filter gel over the internal flash unit. This
lets you trigger the flash units with a burst of energy that’s invisible to the human
eye and to most types of film.
Canon E-TTL flash metering poses a problem for optical slave setups, since standard
analogue optical slaves are likely to be triggered by the flash unit’s metering preflash
rather than the actual flash. And since the slave flash requires time to recharge it
may not have enough power to fire in response to the actual flash. The usual
solution to this is to switch over to regular TTL flash in lieu of E-TTL. There are two
problems to this approach, however. For more details have a look at the section on
disabling E-TTL mode. The other option is to use FEL to trigger the slaves once, then
wait for them to recharge and then take the photo. (or use FEL to trigger the slaves,
immediately use FEL again, before the studio units recharge, to set the correct flash
exposure lock and then take the photo) This can be rather inconvenient, however.
Standard optical slaves are also a problem outside the controlled environment of the
studio. They’re a real nuisance in wedding photography when, for instance, Uncle
Charlie’s point and shoot camera flash triggers your optical slaves. Situations like
that call for expensive radio-controlled wireless systems or, if battery-powered slaves
have enough power output for your needs, Canon’s E-TTL wireless system. An
alternative is the new generation of optical slaves, such as the Wein Digital Smart
Slave products, which are capable of distinguishing between a preflash and a
genuine scene-illuminating flash and only respond to the latter.
A significant problem with multiple slave flash photography (at least, one which
doesn’t rely on automated metering like Canon’s wireless E-TTL) is that it’s difficult
to preview or visualize the final result without a lot of testing and experience. Usually
each flash unit has to have its output set manually. In fact, unless you’re replicating
a predetermined lighting formula that works for you or you’re configuring a fairly
simple one or two flash setup with a light meter, I’d say that it’s pretty well a
requirement that you have a Polaroid back for your film camera or a digital camera
to do this sort of thing well. Digital is particularly beneficial here since you can take
dozens of test photos at no cost and determine exactly how the various flash units
are illuminating your scene, where the shadows fall, etc.
However, using cheap optical slave flash units can be an affordable way to set up
your own studio. Buy a few old battery-powered Vivitar 283s or second-hand studio
units, slap some cheap optical triggers onto them and you’re in business.
Canon do not build any flash units specifically intended for use as studio equipment.
However, you can buy hotshoe adapters - optical or wired - to turn any flash you
want into a slave, and the 480EG can be slaved via the optional Synchro Cord 480.
Hotshoe adapters aren’t always reliable with every camera and flash unit
combination, so it’s worthwhile doing some testing first. In particular, a lot of people
have reported problems with small optical slaves not being able to trigger Canon
Speedlite flash units more than once without the flash being turned off and turned on
again between each shot. The Ikelite Lite-Link is one device designed to work with
Canon flash units that apparently does not have this problem. It also has a sort of
simulated TTL feature - it can cut the light from the slave flash as soon as the master
flash has quenched its light, rather than simply firing at full power.
Finally, Canon state in their literature that a sync speed of perhaps 1/60 or 1/125 is
required for studio flash. There are two reasons why they suggest speeds this low,
even if the camera’s capable of higher flash sync with TTL-metering portable
Speedlite flash units. First, many older studio units take quite a while to attain full
brightness or have slight colour shifts depending on the flash duration. And second,
the triggering delay (the time that elapses between the camera triggering the flash
and the flash unit actually firing) with slaved studio flash units is often longer than
the very brief and known triggering time with TTL flash units.
For these reasons you’re probably best off doing a series of tests with a new slaved
flash unit setup at different shutter speeds to determine what the top shutter speed
for your configuration is going to be. Particularly with optical and radio slave units or
older flash units.
Note that Canon do sell a number of flash units that can serve as slave units in a
wireless E-TTL setup - see the section on wireless E-TTL for details.
Flash meters.
Regular light meters cannot measure the split-second burst of light from a flash unit.
For that you need a specialized flash meter, though of course many devices can
meter for both ambient and flash light.
These are useful in studio situations, when you’re using flash units that don’t have
any TTL or E-TTL capabilities. You might, for example, have a large studio flash unit
bouncing light onto the subject by means of a flash umbrella. You could use the
handheld flash meter to determine accurately the correct flash output settings to
expose the subject properly.
Since this article deals primarily with automated through-the-lens metered flash I
don’t deal with flash meters. There are many other online resources and books to
help you learn more about flash metering, however.
Flash sync trivia.
I haven’t been able to find out why shutter sync with electronic flash is referred to as
“X” sync. Some random reason lost in the mists of time, no doubt. Really old
cameras also had M-sync connectors, which were designed for non-electronic single-
use flash bulbs (the kind of bulbs which contain a metal filament or piece of metal
wool which burns out).
Unlike electronic flash, which achieves maximum brightness almost instantaneously,
old electric flash bulbs required a longer period of time to reach maximum
brightness. So with “M-sync” the shutter opening was delayed by 20 ms or so after
the bulb was fired, to provide adequate time for the light output to build. No EOS
camera has M-sync capabilities, since hardly anybody uses electric flash bulbs these
days. Apparently the M stood for “medium” speed flash bulbs.
On to Part III.
Back to Part I.
- NK Guy, tela design.
Disclaimer and copyright:
This document is copyright © 2001-2004 NK Guy, tela design. This information is
provided with neither warranties nor claims of accuracy or completeness of any sort.
Use this information at your own risk. All trademarks mentioned herein belong to
their respective owners.
I wrote this document in the hope that others in the Internet community might find it
useful or interesting. However, I don’t think it’s reasonable for anyone else to earn
money from - or take credit for - my work.
Therefore you may copy and print this document for your own personal use. You
may not, however, reprint or republish this work, in whole or in part, without prior
permission from me, the author. Such republication includes inclusion of this work in
other Web sites, Web pages, FTP archives, books, magazines or other periodicals,
CD-ROM and DVD-ROM compilations or any other form of publication or distribution.
Please do not frame this site within another.
Please send feedback if you find this article to be of interest or value or if you have
any comments, corrections or suggestions.
Please also consider making a donation to help defray some of the costs of building
and maintaining this site. Thanks!
Back to Photo notes.
Flash Photography with Canon EOS Cameras - Part III.
Copyright © 2001-2004 NK Guy.
Version 1.6. February 11, 2004.
Back to Part II.
Common EOS flash features.
Here are some features found on various Canon EOS Speedlite flash units. Note that
not every flash has every feature, and some features only work in conjunction with
certain camera bodies.
Bounce flash - swivel and tilt.
Many of Canon’s external flash units have the ability either to tilt or both tilt and
swivel the flash head independently of the flash body. The 430EZ, for example, lets
you tilt the head from 0° (straight on) to 90°. Left swivel goes from 0° to 180° facing backwards! Right swivel only goes from 0° to 90°. There are click stops at
various detent positions, and a spring-loaded bounce latch keeps the flash head
pointed head-on.
Tilt and swivel let you bounce (reflect) the flash unit’s light off walls, ceilings,
reflectors, etc, in order to soften the light. Non-bounced flash light tends to be fairly
harsh, since it originates from a relatively small area. This harsh light tends to result
in unflattering photos of people, for reasons outlined in the quality of light section.
Bounce flash softens light nicely, but does have some disadvantages. For one, you
obviously can’t bounce flash outdoors unless you carry a reflector or something with
you - it’s most immediately useful in interior spaces. Some interiors, in fact, aren’t
much good either if they have really dark surfaces or high ceilings. Another
drawback is that coloured surfaces (such as painted ceilings or walls) can end up
tinting the light from the flash, resulting in unwanted colour shifts. Relying on ceiling
bounce flash can sometimes result in unattractive shadows appearing under the eyes
and nose - some photographers elastic-band an index card around the back of
vertically-pointing flash heads in order to bounce a little bit of light forward to
minimize this problem. And finally, bouncing the light obviously reduces the amount
of light hitting the subject and this costs about half your range. For this reason you
may want to use faster film or larger lens apertures when using bounce flash.
Low-end flash units which lack tilt and swivel heads can also be used for bounce
flash - you simply attach an Off-Camera Shoe Cord 2 and then you can point the
flash unit in any direction you like. Note, however, that this technique doesn’t work
well with flash units that rely on external sensors such as A-TTL devices since the
sensors will be recording the light bouncing back from the reflective surface and not
the subject.
You probably won’t want to use bounce flash in manual flash mode. You can do it,
but you have to perform the flash calculations manually, as described in the section
on manual flash.
Flash units which neither tilt nor swivel:
Speedlites 160E, 200E, 220EX, 300EZ, ML-3, MR-14EX, MT-24EX*.
Flash unit which tilt only:
Speedlite 380EX.
Flash units which both tilt and swivel:
Speedlites 300TL, 420EZ, 430EZ, 540EZ, 420EX, 550EX, 480EG.
Flash units with an additional downward tilt for macro shots:
Speedlites 540EZ, 550EX.
* The MT-24EX macro flash unit has independently movable swivelling arms with
detachable heads. So it’s not fixed, but it doesn’t tilt or swivel in the way that shoemount Speedlites do. As a macro flash it’s not meant for illuminating rooms with
bounced light, though it can be used for lighting small spaces.
Zooming flash heads.
Canon’s mid to high-end external flash units contain small motors which move the
flash bulb closer to or further away from the clear plastic screen at the front. This
allows the flash to alter the coverage area of the light emitted from the unit - the
closer the bulb is to the screen, the wider the coverage angle and vice versa. It also
means that the flash’s light output can be concentrated for greater distances and
used more efficiently. (ie: you aren’t wasting light by illuminating areas not covered
by longer focal-length lenses)
Typically the zooming motor covers the range used by 24 to 80mm lenses or 24 to
105mm, and does so in several fixed steps matching popular prime lens focal
lengths, such as 24-28-35-50-70-80mm. (continuous zooming control to arbitrary
focal lengths is not supported) Remember that a flash unit’s upper zoom limit doesn’t
prevent you from using the flash with longer lenses. All it means is that the zoom
can’t concentrate its light beyond a certain point for more efficient coverage of a
narrower area. At least, not without a flash extender accessory. The reverse is not
true for the wider end, however. If you use, for example, a flash unit with 24mm
coverage at the wide end with a 17mm lens you’ll get a kind of vignetting effect
(darkening of the edges) since the flash will not be able to illuminate the entire
coverage area of the wide angle lens.
Some zooming flashes have manual controls that allow you to override the automatic
zoom setting by pressing a button. Others are only automatic - they zoom to a
setting near to the current lens focal length when you press the shutter halfway.
Canon flash units usually default to a 50mm zoom setting when in bounce mode and
to 35mm when no EF-compatible lens is attached.
For some strange reason camera bodies with image areas less than that of 35mm
film (APS cameras and most EOS digital cameras) do not compensate for the
cropping factor of their image areas. So you are, in effect, wasting light when taking
a photo using such a camera body and a zooming flash unit, since areas outside the
edges of the picture will be illuminated. This isn’t a huge issue, but it does seem a bit
odd that no compensation was built in. Perhaps Canon were concerned that this
could lead to confusion, since turning a zoom lens on such a body would result in the
flash head zooming to a different focal length on its LCD screen.
Remember that the flash head will zoom to the nearest zoom setting that is less or
equal to that of the focal length of your attached lens. So if you have a 100mm lens
attached, say, and the flash unit can zoom to either 80mm or 105mm, then it will
automatically go to 80mm only. It will not narrow the light cone down any further by
zooming to 105mm, as you would risk getting darkening around the edges of the
picture if it did.
Wireless-capable units with zooming heads (420EX and 550EX) will zoom to 24mm
when in wireless slave mode. The 420EX has no manual zoom controls and so always
shoots at 24mm. However, the 550EX’s manual zoom controls are very useful in
wireless mode since they let you set up your slave units around the scene, override
the default zoom setting and adjust the coverage angles for each unit independently.
They aren’t so commonly used outside a wireless context but they allow you, for
example, to create a sort of spotlight/vignetting effect by narrowing the flash
coverage down to a tighter circle than that required by the focal length of the lens.
(an intentional use of the problem outlined above) You can also use manual controls
to adjust the zoom setting so that you can work with manual lenses which don’t
transmit focal length information to the camera.
All Canon flash units which have names ending in Z, such as the 540EZ, contain
zooming flash motors. However, some later E-TTL flashes such as the 420EX and
550EX also have zooming heads, so Z Speedlites aren’t the only ones with the
Two EOS cameras, the Elan/100 and the A2/5, have three-position zoom motors
built into their internal flash units. It’s this zoom capability that explains why the
Elan/100’s built-in flash has a maximum guide number of 17 at 80mm. When the
flash isn’t zoomed out it has a guide number of 12; typical for a camera’s built-in
flash. Canon have not carried this feature through to any later bodies, however.
Presumably the expense and bulk of the zooming mechanism were deemed to
outweigh the benefit of improved guide numbers.
The primary disadvantages of a zooming flash unit are that the zoom motor makes a
loud buzzing noise when adjusting coverage angles and that the flash head has to be
larger to accommodate the motor.
Flash units with motorized zooming heads:
300EZ, 420EZ, 430EZ, 540EZ, 380EX, 420EX, 550EX.
Flash head coverage:
Flash units.
Flash unit with 28mm fixed coverage (no zoom motor):
Speedlite 220EX.
Flash units with 35mm fixed coverage (no zoom motor):
Speedlites 160E, 200E*, 480EG**.
Macro flash units (no zoom motor):
Speedlites ML-3, MR-14EX, MT-24EX.
Flash unit with hand-operated four-position 24-85mm (24-35-50-85mm) zoom head
(no zoom motor):
Speedlite 300TL.
Flash unit with automatic-only four-position 28-70mm (28-35-50-70mm) zoom
Speedlite 300EZ.
Flash units with automatic six-position 24-80mm (24-28-35-50-70-80mm) zoom
coverage with manual override:
Speedlites 420EZ, 430EZ.
Flash units with automatic-only six-position 24-105mm (24-28-35-50-70-105mm)
zoom coverage; no manual override:
Speedlites 380EX, 420EX.
Flash units with automatic seven-position 24-105mm (24-28-35-50-70-80-105mm)
zoom coverage with manual override:
Speedlites 540EZ, 550EX.
* The 200E can be augmented by an optional accessory clip-on adapter (Wide
Adapter 200E) which extends its 35mm flash coverage to 28mm.
** The 480EG ships with two accessory clip-on lenses which can be used to alter its
default 35mm coverage. The Wide Panel 480EG-20 takes you to 20mm and the Tele
Panel 480EG-135 takes you to 135mm.
Cameras with fixed 35mm internal flash coverage, GN 12:
EOS 750 (first EOS camera to sport a built-in flash), 700, 10/10s, Rebel S/1000F,
EOS 5000/888.
Cameras with fixed 35mm internal flash coverage, GN 14:
EOS Rebel II S/1000FN*.
Cameras with fixed 28mm internal flash coverage, GN 12:
Rebel X/EOS 500/Kiss, Rebel 2000/EOS 300/Kiss III, EOS Kiss III L, EOS 300V/Rebel
Ti/Kiss 5 (high profile), Rebel G/EOS 500N/New Kiss, EOS 3000/88, 3000N/66.
Cameras with fixed 28mm internal flash coverage, GN 13:
EOS Elan II(E)/50/55, Elan 7(E)/30/33, Elan 7N(EN)/30V/7S.
Cameras with automatic-only three-position 28-80mm (28-50-80mm) internal flash
zoom coverage, GN 12 or 13 to 17:
EOS Elan/100 (GN 12-17), A2(E)/5 (GN 13-17).
Cameras with fixed 22mm** internal flash coverage, GN 11 or GN 10:
EOS IX/IX E (GN 11), IX Lite/50/7 (GN 10).
Cameras with fixed 18mm** internal flash coverage, GN 12:
EOS D30, D60.
Camera with fixed 18mm** internal flash coverage, GN 13:
EOS 10D.
Camera with fixed 18mm** internal flash coverage, GN 13, high profile:
300D/Digital Rebel/Kiss Digital.
Cameras with no internal flash:
EOS 650, 620, 850, 600/630, 1, RT, Rebel/1000, Rebel II/1000N, Rebel X, 1N,
1NRS, 3, 1V, 1D, 1Ds, 1D mark II.
* Seems odd that this particular low-end camera should have a higher guide number
than all other EOS cameras with built-in flash, but that’s what the Canon camera
museum claims.
** Note that these coverage areas are related to the dimensions of the image area APS film for the IX cameras and the sensor chip for the D30, D60 and 10D digital
cameras. All have smaller image areas than 35mm film. The digital cameras would
have a 28mm coverage area if they were 35mm cameras, for example.
AF assist light.
It’s very hard for cameras based on passive autofocus mechanisms (this includes all
EOS cameras except the manual-focus EF-M) to focus when it’s dark, since they rely
on contrast between light and dark areas. For this reason many EOS cameras have a
built-in light that automatically illuminates in low light situations to help the
autofocus system to work. On some cameras this is a relatively discreet patterned
red light from a bright red LED (light emitting diode), on some it’s an irritating bright
white incandescent light and on others it’s an even more irritating pulse of the builtin flash. (for a list of these cameras please see the next section)
All of Canon’s Speedlite flash units for EOS cameras have patterned red AF assist
lights - sometimes called AF auxiliary lights in older Canon manuals - built in. These
are clear red panels on the front which use one or two high-brightness LEDs to
project red circles of light striped with dark lines, in order to give the camera a highcontrast pattern to focus on. Red is chosen in part because high-output red LEDs are
readily available, but also because red light does not cause the pupils of the eye to
dilate as much as does white light. The red light is sometimes described as being
“near infrared,” though it is in fact visible.
An important thing to remember is that the AF assist light works only if your camera
is in One-shot mode - it will not illuminate in AI Servo or in any icon AE mode which
employs AI Servo, such as the Sports mode. This is because the camera is constantly
focussing and refocussing when in AI Servo mode, in order to track subject motion.
Also, if you have a camera body with multiple focussing points and your flash unit’s
AF assist light isn’t lighting up in low light it’s probably because the AF light on the
flash you happen to be using cannot cover your currently selected (ie: non-centre)
focussing point. Many flash units have AF assist lights which can only illuminate the
area around the central point. Switch to the central focussing point and the flash
unit’s AF assist light should start working. Two exceptions are noted in the next
section - the A2(E)/5 and the 10/10s.
As for the coverage area of these AF lights and multiple focus points, the coverage
varies but depends in part on when the flash was introduced. For example, the
430EZ flash was introduced when Canon’s cameras all had one focussing point only,
and so the 430EZ’s AF assist light cannot cover all the focussing points built into,
say, the Elan 7/EOS 30. The 420EX, however, has an AF assist light which covers all
7 points used by the newer camera. There is a full list below.
The maximum range of the AF assist light varies from unit to unit, but is typically a
distance of around 5-10 metres from flash unit to subject. Flash units which cover
more than one focus point have lower AF assist ranges for outer points. The MR14EX and MT-24EX macro ring light flashes have small white incandescent bulbs for
modelling and focussing rather than red AF assist LEDs. The Macro Twin Lite MT24EX can be configured so that pressing the shutter release halfway turns these
lamps on. The MR-14EX requires a press of the controller-mounted “lamp” button to
enable the lamps.
Flash units with 1 (central) point AF assist light coverage:
Speedlites 160E, 200E, 220EX, 300EZ, 380EX, 420EZ, 430EZ.
Flash unit with 5 point AF assist light coverage:
Speedlite 540EZ.
Flash unit with 7 point AF assist light coverage:
Speedlite 420EX.
Flash units with 45 point (area) AF assist light coverage:
Speedlites 550EX, ST-E2. (see the note below concerning the EOS Elan 7/30/33/7)
Flash units with white incandescent focus assist bulbs:
Macro Speedlites MR-14EX and MT-24EX.
Flash units with no AF assist lights:
Speedlites 480EG, 300TL.
Camera-specific notes on AF assist lights.
The EOS 5/A2/A2E and 10/10s: these older cameras never activate the AF assist
lights on external flash units - they will only illuminate the camera body’s built-in AF
assist light. The reason for this limitation is because the camera bodies have multiple
selection points and the flash units sold at the time could not cover all of the points.
The 10/10s is also unusual in that its external two focussing sensors look for
horizontal lines and not vertical lines, whereas many flash units project only vertical
striped lines.
Sadly, this restriction was pretty short-sighted, since later Speedlite flash units
handily cover all the focus points of multiple focus point cameras, but these older
camera bodies still doggedly rely on the body AF light only - even if the central focus
point is the only one selected. And the body’s AF assist light can be blocked by larger
lenses or lens hoods. Luckily, the body’s AF assist light has a reasonable range - only
slightly shorter than most external flash units.
The EOS 300/Rebel 2000, EOS 30/Elan 7 and other EOS cameras which lack a red AF
assist light on the body: you can always use the AF assist light on a flash unit if you
want to avoid the irritating main flash pulses used by your camera as an AF assist
light. Some of the smaller Speedlite flashes are quite compact and can easily be
packed in a camera bag, though the tiniest don’t cover multiple focussing points,
limiting you to the central point. The ST-E2 transmitter covers all 45 of the EOS 3’s
focussing points, all of the D30/D60 points, and 5 of the 7 points of the Elan 7/EOS
30/33/, so it’s a better bet for most newer cameras if all you want is AF assist. A
rather unfortunate and inconvenient (and expensive, in the case of the ST-E2) way
to deal with the camera’s shortcomings, but there you go. The EOS 30/33/Elan
7/EOS 7 is most suitable for use with an external flash unit’s AF assist light, since
this camera has a custom function which disables the external flash while
maintaining the operation of the AF assist.
The EOS D30/60: the primary weakness of these otherwise excellent digital cameras
is their weak autofocus performance, particularly in dim light. Many D30/60 users
advocate carrying an ST-E2 wireless flash transmitter and using its AF assist light to
help the camera focus in low-light situations. Other users carry a 550EX set to TTL
mode. In TTL mode the 550EX will not fire but the AF assist light will still work.
These are somewhat expensive options. You could always use one of the tiny and
inexpensive Canon flash units like the 160E or 200E for this, but their AF assist lights
cover only the central focussing point of the D30/60.
The Elan 7/EOS 30/33/7: this camera has 7 focussing points - five in a row and one
point above and one point below the row. However, the Speedlite 550EX flash unit
and ST-E2 unit predate the Elan 7/EOS 30/33/7. So, although they cover all 45
points of pro cameras they do not adequately cover the upper and lower AF points on
the Elan 7/EOS 30/33/7. This is because they project horizontal patterns across the
area read by the upper and lower AF points of the Elan 7/30/33/7, but these points
want vertical patterns. At time of writing the 420EX is the only flash unit which
adequately illuminates these upper and lower AF sensors.
Cameras with red patterned (LED) body-integral AF assist lights:
EOS 10/10s, A2/A2E/5, Elan/100, Elan II/IIE/50/50E/55.
Cameras with bright white incandescent body-integral AF assist lights:
EOS Rebel XS/500/Kiss, EOS 3000/88, EOS 3000N/66/Rebel XS N, D30, D60.
Cameras which fake AF assist by pulsing the internal flash unit:
EOS Rebel 2000/EOS 300/Kiss III, Kiss IIIL, EOS Elan 7/30/33/7, EOS Rebel
Ti/300V/Kiss 5, EOS 10D, EOS 300D/Digital Rebel/Kiss Digital.
Cameras with no body-integral AF assist lights:
EOS 650, 620, 700, 750, 850, RT, 1, Rebel/EOS 1000, Rebel S II/1000FN/1000S,
Rebel X, EOS 5000/888, Rebel G/500N/New Kiss, IX, IX Lite, 1N, 1N HS, 3, 1V, 1D,
1Ds, 1D mark II.
Flash exposure compensation (FEC).
There are times when you may want to adjust the total flash output from a flash unit
above or below what the assumed mid-tones that the camera thinks you probably
want. For example, a scene that’s mainly white or mainly dark will fool automated
sensors, so you may want to override the flash unit. This is flash exposure
compensation; referred to as “fill-in ratio control” or “flash level control” in older
Canon material.
As noted in the section on fill flash, a common application for flash is lightening
shadows and toning down the high-contrast nature of full sunlight. Adding a subtle
catchlight in someone’s eyes is another. For cases like this you might want to dial in
an additional minus stop or two of flash compensation over the camera’s built-in
flash program since you don’t want to blast out a ton of fill flash that will wash out
the subject’s face or cast flash shadows. Or perhaps you want to take a harshly lit
flash photo, like old paparazzi photos from the days of non-electronic bulb flash. You
could then dial in additional flash compensation. Yet another common situation is
overriding the default flash controls in situations that are hard for the flash system to
meter. Wedding photos of a man in a black tuxedo in a large room or a woman in a
white dress next to a white cake are typical examples.
FEC is adjustable in half or one-third stop intervals, depending on the camera and
flash. You can apply both positive (more light from the flash) or negative (less)
compensation, usually by up to three stops. Remember that, on cameras which have
it, FEC is completely independent from regular exposure compensation on your
camera. (cameras which lack FEC simply adjust flash and ambient compensation
simultaneously) It’s quite possible to, for instance, apply plus 1 stop FEC and dial in
minus two stops exposure compensation at the same time. Just like regular light
metering, one stop represents a doubling or halving of light output. Altering FEC
means altering power output, not distance. (see the section on guide numbers for
more information)
As noted earlier, EOS bodies automatically apply by default auto fill reduction under
brighter ambient lighting conditions. So it may not be necessary to dial in any FEC if
you just need fill flash - particularly if you’re using E-TTL rather than TTL. E-TTL is
generally agreed to have improved and more subtle fill flash when ambient light
levels are bright. You’ll probably want to run some tests to see how your camera and
flash combination works for you. Remember that any FEC you apply manually will be
in addition to any auto fill reduction that the camera may apply.
However, most pro and semi-pro EOS cameras have a custom function that can
disable automatic fill flash reduction if you desire. This is useful when shooting
backlit objects, where you don’t want fill flash reduction.
Cameras which disable auto fill flash reduction with custom function 10:
EOS D30, D60.
Cameras which disable auto fill flash reduction with custom function 14:
EOS 1N, 1NRS, 3, 1V, 1D, 1Ds, 10D, 1D mark II.
Camera which disables auto fill flash reduction with custom function 16:
EOS 5/A2(E).
Which bodies/flashes have FEC.
Flash exposure compensation may or may not be available to you, depending on
which camera body and flash you have. Most midrange EOS cameras support FEC for
internal flashes, but most low-end EOS cameras do not. Also, remember that FEC
will not work in the basic (PIC) metering modes - just P, Tv, Av and M modes.
For FEC to work with an external flash you need one of the following two cases:
either both a camera capable of supporting FEC on external flash units and a
flash unit capable of receiving FEC commands, or
any EOS camera except the 620, 650, 750 or 850 and an external flash unit
with FEC switches built in - the Speedlites 430EZ, 540EZ, 550EX, MR-14EX or
The next section has a comprehensive list of which cameras and flash units have
which features.
For instance, let’s say you have an Elan 7/EOS 30 with a Speedlite 420EX external
flash. In this case you can use the FEC controls built into the camera to control the
flash exposure levels on the external flash.
Or let’s say you have an original Elan/EOS 100 with a Speedlite 540EZ external flash.
In this case you can’t use the camera’s on-board FEC controls, because the Elan/100
is the only EOS camera with FEC controls that can’t send FEC signals to external
flashes. But the 540EZ happens to have controls that let you set the FEC levels
directly on the flash itself, so you’re fine.
However, if you have, say, a Canon Rebel G and a Speedlite 380EX then you’re out
of luck. The Rebel G can’t send out FEC commands to a flash, and the 380EX lacks
external FEC controls. You can’t directly adjust the flash exposure settings
independently of the exposure metering. You can only fake FEC by altering the ISO
Some bodies display the FEC setting in the viewfinder and others only display it in
the top-deck LCD. If your flash unit has its own FEC controls you can look at the
flash unit’s rear panel LCD for the current FEC setting. Also, remember that if your
flash unit has FEC controls then its settings will override those of the camera’s
custom function setting, if it has one.
List of which bodies/flashes have FEC.
Camera bodies which do not support any kind of FEC even with flash units
with external FEC controls:
EOS EF-M, 650, 620, 750 or 850.
Camera bodies which only support FEC when used with an external Speedlite
flash unit which has FEC controls:
EOS 600/630, RT, 700, 1, 10/10s, all EOS 1000 series cameras, all EOS Rebel
series cameras, all EOS Kiss series cameras, 300, 300V, 500, 500N,
5000/888, 3000/88, 3000N, IX Lite/IX 50/IX 7, EOS 300D/Digital Rebel/Kiss
Camera body which supports FEC on the internal flash but not on external
flash units unless they have external FEC controls:
EOS Elan/100.
Camera bodies which support FEC on internal flash units and can also control
FEC on any external Speedlite flash unit:
EOS 5/A2(E), Elan II(E), 50(E)/55, IX, Elan 7(E), 30/33/7, D30, D60, 10D.
Camera bodies which lack internal flash units but which can control FEC on
any external Speedlite flash unit:
EOS 1N, 1NRS, DCS 1/3/5, D2000, D6000, 3, 1V, 1D, 1Ds, 1D mark II.
Camera bodies with a flash exposure level scale on the right side of the
EOS 1N, 1V, 1D, 1Ds, 1D mark II.
Flash units with external FEC controls:
Speedlites 430EZ, 540EZ, 550EX, MR-14EX, MT-24EX.
Faking flash exposure compensation.
It’s possible to fake FEC if your camera and flash combination lacks the ability. It
basically involves fiddling with your camera’s manual ISO (film speed) override. You
can’t simply adjust exposure compensation because doing so affects both ambient
exposure settings and flash exposure settings simultaneously.
The workaround is thus to do the ambient metering first and locking it into place by
going into manual metering mode. This puts both the shutter speed and aperture
under your direct control. Once that’s done you can manually alter the ISO setting of
the camera (if your camera supports this, as the vast majority of EOS cameras do).
If you lower the film speed rating you’re essentially tricking the camera into
producing more flash output - halving the ISO results in one stop more flash output.
If you raise the film speed rating then the camera will produce less flash output doubling the ISO results in one stop less flash output.
The drawbacks to this technique are obvious and threefold. First, it’s rather fiddly
since altering ISO isn’t a commonly changed thing and thus the interface isn’t the
easiest to use. Second, you have to be certain to set the ISO value back to its
correct setting when you’re done or else you risk messing up the exposure settings
for the rest of the roll. And third, you can’t really use it if your camera lacks manual
ISO controls altogether.
Flash exposure lock (FEL).
EOS cameras (type A) which support E-TTL also support flash exposure lock when
used with EX flash units. This feature lets you lock flash settings in, then optionally
recompose the image before taking the final photo. This allows you to adjust the
flash settings in certain difficult to meter cases. Canon first introduced FEL in 1986
with their T90 camera and 300TL flash, but dropped the feature with the first EOS
cameras. It wasn’t until 1995, with the introduction of the Elan II(E)/50/55 and ETTL, that FEL made its return.
FEL works by issuing a preflash when the AE lock button or, if the camera has one,
when the FEL button is pressed. (on most EOS cameras the AE lock and flash
exposure features are tied together, but top of the line EOS cameras have separate
FEL buttons which allow you to set AE lock and FEL independently) The camera then
stores flash exposure data, biased towards either the current focus point or the
central focus point, for a 16 second period or for as long as you keep the shutter
release pressed halfway. During this time you can recompose the photo or you can
adjust the aperture and shutter speed (overriding AE lock, which is set when you
press the AE lock button, if you like).
FEL is thus useful for taking photos in which the subject is not covered by one of the
focus points or photos containing reflective surfaces which can fool flash metering or
certain cases in which the subject is moving. It’s also useful for scenes in which you
want to bias the flash exposure to something other than the current focus point. A
major drawback with FEL is that the E-TTL preflash occurs when the AE lock or FEL
button is pressed, which can confuse your photographic subjects who may think that
the photograph is already taken.
If you lock focus on a scene and recompose you will likely have poor flash metering,
since E-TTL biases flash metering to the current focus point. Use FEL instead to avoid
this problem.
Some cameras have a custom function (CF 8 on the Elan II(E)/EOS 50/55 and Elan
7(E)/EOS 30/33/7) which lets you specify whether you want partial metering and FEL
tied to the central focus point - the default - or to the active focus point instead.
Cameras that support FEL:
All type A bodies.
Cameras with separate FEL buttons:
EOS 3, 1V, 1D, 1Ds, 1d mark II.
Flash units which support FEL with type A bodies:
All EX series flash units.
The T90 and the 300TL flash unit support FEL, but only with each other. Their FEL
protocols are not compatible with E-TTL, and so putting an EX series flash unit on a
T90 will not give you FEL.
Flash exposure bracketing (FEB).
Recent high-end EOS flashes - the 550EX, MR-14EX and MT-24EX - support flash
exposure bracketing. It’s a function of the flash unit - the Canon “Flash Work”
brochure says that these recent high-end flash units can do FEB on any EOS camera
except the 650, 620, 750, 850 - and EF-M.
This is a similar concept to auto-exposure bracketing (AEB), only instead of changing
ambient exposure settings you shoot a series of three photographs with normal,
positive flash compensation and negative flash compensation. You can apply the
bracketing value in half, third or full stop values.
Enabling second curtain sync.
This depends very much on the camera and flash unit that you’re using. Early on,
Canon put control for this feature on the flash unit. Later they switched to putting
control for this feature on the camera body. So whether you have second-curtain
sync available to you depends on a complicated set of permutations.
Many mid to high end Canon flash units, listed below, have a button or switch which
lets you enable second curtain sync. It’s usually marked with a triple triangle ( >>>
) symbol or the word SYNC. For instance, on the 430EZ and 540EZ you press the +
and - buttons together simultaneously to turn on second-curtain sync. When you do
so a triple triangle symbol appears in the LCD. On the 300EZ and 300TL there’s a
small slide switch - left is first-curtain sync and right is second-curtain.
Most midrange and professional EOS bodies from the A2(E)/5 onwards have a
custom function that lets you specify whether you want first or second curtain flash.
The exception is the original Elan/100, which had a custom function that can only
control the internal flash and not external flash units. In the case of a camera with a
custom function and an external flash unit which has a second curtain switch it
appears the physical switch on the flash takes priority, though this may vary from
model to model.
Low-end EOS cameras, such as the 1000 series or Rebel series, do not have any
custom functions and so cannot control second curtain sync options directly. So to
take advantage of second curtain sync on such cameras you must have an external
flash which has externally-available controls to operate it.
Second-curtain sync cannot be used with any EOS camera in a PIC (icon) mode - you
have to be set in P, Av, Tv or M modes. And you can’t set second-curtain sync in
stroboscopic mode or FP mode, since that wouldn’t make any sense. Finally, secondcurtain sync requires a dedicated Speedlite flash unit - it isn’t supported on flash
units connected via a PC socket.
List of which flash units and camera bodies have second-curtain sync.
Note: verifying this information is difficult, since it’s not listed on all product specs,
and I don’t have access to every camera and flash unit that Canon have ever built. I
believe this list is accurate, but please let me know if there are any errors.
Flash units which do not support second-curtain sync:
Speedlites 160E, 200E, 480EG, ML-3.
Flash units with external second-curtain sync controls:
Speedlites 300EZ, 420EZ, 430EZ, 540EZ, 540EZ, 550EX, MR-14EX, MT-24EX.
Flash units which can use second-curtain sync when used with any EOS body that
has a second-curtain sync custom function other than the Elan/100:
Speedlites 220EX, 380EX, 420EX, 550EX, MR-14EX, MT-24EX.
Camera bodies which cannot support second-curtain sync in any form:
EOS EF-M, 750, 850.
Camera bodies which lack custom functions altogether and so support second-curtain
sync only when used with flash units with external controls:
EOS 650, 620, 700, all EOS 1000 series cameras, all EOS Rebel series cameras, all
EOS Kiss series cameras, 300, 300V, 500, 500N, 5000/888, 3000/88, 3000N, the IX
Lite/IX 50/IX 7*, IX**, EOS 300D/Digital Rebel/Kiss Digital.
Camera bodies with custom functions but which lack a custom function to enable
second-curtain sync:
EOS 600, 630, 1, 1N, 1NRS, RT, 10/10S.
Camera body which has a second-curtain sync custom function that works on the
internal flash but not on external units:
EOS Elan/100.
Camera bodies with custom functions that enable second-curtain sync on both
internal flash and on compatible external flash units:
EOS A2(E)/5, Elan II(E)/50(E)/55, Elan 7(E)/30/33/7, D30, D60, 10D.
Camera bodies with custom functions that enable second-curtain sync on compatible
external flash units but which lack internal flash:
EOS 3, 1V, 1D, 1Ds, 1D mark II.
The T90 camera and the 300TL flash unit support second-curtain sync, but only with
each other.
* I haven’t been able to find out if the IX Lite/50/7 camera supports second-curtain
sync with flash units that have external controls, but since it’s based around Rebelstyle technology it seems unlikely that such support would have been removed.
** The Westfall/Overton FAQ states that the IX can use second-curtain sync with
380EX flash units, which lack external second-curtain sync controls. The Canon
“Flash Work” brochure, however, isn’t clear on this.
Range warning.
The first type of range warning applies only to the 630, 1 and RT cameras. All other
EOS cameras lack this kind of range warning for patent reasons. If the foreground
subject is too close to or too far from the flash to be illuminated by it, it’s said to be
“out of coupling range.” If the subject is too far away then both the shutter speed
and aperture values will blink in the viewfinder display. If it’s too near then the
distance display will blink.
The second type of range warning is built into the FEL feature with type A bodies. If
the lightning bolt icon in the viewfinder blinks when you set FEL then you know that
you don’t have enough flash output to illuminate the subject correctly.
Manual flash.
High-end Canon flash units can also work in full manual mode, which lets you set the
flash output by hand rather than relying on an automated system like TTL or E-TTL.
Note that manual flash metering is not the same thing as the camera’s manual
exposure (M) mode, which is used for ambient (non flash) light metering. Though
having said that, you usually put the camera into manual exposure mode when using
manual flash metering, so it can be very confusing.
Traditionally, manual flash units required the user to perform calculations by hand in
order to use them. However, Speedlites with manual controls and rear LCD panels
can perform these calculations for you. This is how you do it.
Set the camera to either Av (aperture priority) or M (manual exposure) mode.
You can set the camera to other “creative” zone modes if you want, but the
aperture symbol will flash to indicate a problem and the picture’s flash
metering will probably be out.
Set the flash to manual mode. On the 430EZ and 550EX, for example, you
press the mode button on the flash. The flash mode (TTL or A-TTL) will switch
to M.
Press the plus or minus button to set the correct flash intensity. 1/1 means
full power, 1/2 means half power and so on. Different flash models support
different numbers of flash intensity - the full list is below.
Press the shutter button halfway. The flash will display the current aperture
and a distance setting. On the 430EZ this distance setting will be a number of
metres or feet, depending on whether you bought the flash anywhere in the
world but the US or the US. On the 540EZ and 550EX the distance
information is shown on a little scale, and the unit type can be changed by a
small switch in the battery compartment.
If you’re in Av mode the shutter speed will be the camera’s X-sync speed and
you can manually set the aperture. In M mode you can set the shutter speed
to any value from 30 seconds to the camera’s X-sync and the aperture to
anything within the lens range.
Adjust the settings so that the distance information on the flash matches the
number on the distance scale on the lens you’re using. If the lens lacks a
distance scale then you’ll have to estimate or measure the distance.
Once everything’s set correctly you can press the shutter release all the way
to take the photo, assuming the “flash ready” lightning bolt is displayed in the
The flash can’t help you in bounce mode - you have to perform the calculations
manually by measuring the flash to subject distance. Remember that in bounce
mode it’s not the distance from the flash to the subject that’s important - it’s the
distance that the light actually has to travel from the flash to the reflecting surface
and then to the subject. You also have to factor in the light loss from the reflecting
surface, which can only really be done by experience or judicious use of a flash
meter. Also don’t forget that the flash unit’s guide number is measured in metres
and for ISO 100 film. If you want to use feet and/or film of a different speed you will
need to do some additional arithmetic.
Flash units with manual controls:
Speedlites 420EZ, 430EZ, 540EZ, 550EX, 480EG, MR-14EX, MT-24EX, 300TL.
Two levels of manual power - MHi (full power) and MLo (1/16):
Speedlite 300TL.
Five levels of manual power - full power to 1/16:
Speedlite 480EG.
Six levels of manual power - full power to 1/32:
Speedlites 420EZ, 430EZ.
Seven levels of manual power - full power to 1/64:
Speedlites MR-14EX, MT-24EX.
Eight levels of manual power - full power to 1/128:
Speedlites 540EZ, 550EX.
Flash exposure level.
The most recent high-end Canon cameras have the ability to display the flash
exposure level in the viewfinder. When you press the FEL button near the shutter
release a sliding scale will appear in the viewfinder on the right side. Typically this is
done with a grey card filling the spot metering circle.
The flash exposure level will be displayed on the far right bar of this scale. You can
then adjust the output on the flash unit manually to match the standard exposure
Cameras with viewfinder flash exposure level scale:
EOS 3, 1V, 1D, 1Ds.
Rapid-fire mode.
Electronic flashes work by charging up a capacitor with electricity, then releasing the
stored-up power in a split-second burst of light. This charging process, the “recycle
time,” takes up to a few seconds on larger units - which can be a problem if you
need to take several flash photos in fairly rapid succession, such as at a wedding.
Many EOS flashes have the ability to be triggered even if not fully recharged, on the
theory that there are times when you’re better off being able to take a photo without
a full flash charge available (ie: at a lower guide number than maximum) than
having the flash not fire at all. Flash units capable of this feature have a two-colour
flash ready (“pilot”) light. If the light is red then the flash is fully charged. If it’s
green then the flash is only partially charged but will still fire anyway if you take a
It can be quite frustrating using a flash unit without rapid-fire, in fact. It’s all too
easy to take two photos in succession only to find that the second one didn’t trigger
the flash and so is totally underexposed.
Rapid-fire mode will not work if the camera is in continuous film winding mode, if the
flash is in manual mode at full or half power or if the camera is in stroboscopic flash
mode at a fairly fast setting. The 430EZ does not work in rapid-fire mode if an
external battery pack is used.
Flash units with rapid-fire capabilities:
Speedlites 160E, 300EZ, 420EZ, 430EZ, 540EZ, 550EX, 480EG.
Flash units with no rapid-fire capabilities:
Speedlites 200E, 220EX, 380EX, 420EX, ML-3, MR-14EX, MT-24EX, 300TL.
Stroboscopic flash.
In flash photography the term “stroboscopic” refers to a photographic technique
whereby a number of brief pulses of light are emitted during the course of a
photographic exposure. The result can capture, for instance, half a dozen steps of a
dancer in motion. Each step would be recorded on the same frame of film, like a
multiple exposure. Here’s a less than thrilling example that I took as a test - a bit
poorly done, since the foreground was underexposed because of insufficient flash
output, but you get the idea.
To take a stroboscopic photo you need to have a very dark background that doesn’t
reflect much light. If you have a bright background you’ll find that the multiple pops
of light from the flash will build up cumulatively to overwhelm the foreground
subject. You’ll probably also need to experiment a fair bit to determine the ideal
number of light pulses to cover your action appropriately and the output settings
required to expose the subject correctly. You’ll probably want to use negative (print)
film and not slide film for such a photo, since the former has much wider exposure
Setting stroboscopic flash.
High-end Canon hotshoe flash units have a stroboscopic mode, activated by pressing
the mode button until MULTI is displayed on the rear LCD panel.
You can then enter the firing frequency in hertz (ie: the number of flashes per
second) and the power output setting. The 5xx flashes also let you specify the actual
number of stroboscopic light flashes as well. The 4xx flashes don’t, so you have to
calculate that number from the time period the shutter is kept open and the number
of flashes per second you’ve set. The maximum firing frequency of the flash varies
from flash model to model, but it ranges from 5 to 199 Hz. Power settings also vary the 430EZ and 540EZ, for example, cannot use stroboscopic flash at full or half
power - only 1/4 power and down.
Naturally there’s a relationship between these settings - you can’t fire many times at
higher power settings if the firing frequency is high, for example, since the flash
needs time to recharge. The flash manual includes a table showing the maximum
number of flashes you can expect at different power settings and firing frequencies.
There is a risk of overheating and damaging the flash bulb if you pulse the bulb too
much, but the flash units have cutoff mechanisms that prevent this from occurring.
Once you’ve set the flash settings you can put the camera into M (manual exposure)
mode and determine how long the shutter should be kept open in order to cover the
full field of action for your photo. You can also set the proper aperture. As you do
this the flash will display the coupling range on its rear-panel LCD. (press the shutter
release halfway if the coupling range information is not displayed) Adjust the power
output and aperture so that the coupling range matches the focus distance.
Stroboscopic flash won’t work with the EOS EF-M, 750 and 850 cameras.
Flash units with stroboscopic capabilities:
Speedlites 420EZ, 430EZ, 540EZ and 550EX.
Stroboscopic ranges:
Speedlite 420EZ: 1-5 Hz.
Speedlite 430EZ: 1-10 Hz.
Speedlite 540EZ: 1-100 Hz.
Speedlite 550EX: 1-199 Hz.
Flash exposure confirmation.
Not to be confused with flash exposure compensation. Some Nikons have a very
handy feature - a small LED which illuminates in the viewfinder to indicate that the
flash believes you had enough light to exposure your subject correctly.
Unfortunately, for patent reasons no Canon camera bodies have such a feature.
The closest thing in the Canon world can be found on many flash units, not camera
bodies. Most Speedlite flash units have a small LED which lights up for two or three
seconds, post-exposure, to confirm that there was sufficient light from the flash to
illuminate your subject correctly. This is a nuisance since you have to lift your head
and peer at the flash back in order to see this light, but I guess at least it’s there.
Keep in mind one important limitations of this feature - the LED will glow even if the
image was overexposed. It only checks to see that the photo was not underexposed
owing to being out of range. So having this LED light up is no guarantee of a
perfectly exposed flash photograph.
Flash units with flash exposure confirmation:
Speedlites 480EG, 540EZ, ST-E2 remote transmitter, ML-3 ring flash and all EX flash
Wireless remote control.
There are a number of third-party (ie: non-Canon) systems for controlling flash units
from a distance such as products from Wein and PocketWizard. However, the newest
E-TTL Canon flash units are also capable of being triggered remotely without wires,
much like Minolta’s pioneering wireless flash system. These wireless E-TTL units work
as master or slave units.
And yes, it’s kind of unfortunate that the terms “master” and “slave” are used in this
context. Unfortunately the terminology is pretty common in the world of hardware
engineering to mean a system with a controlling device and a responding device, the
grim political and social overtones of the words notwithstanding. However, to
minimize confusion I’ll use the terms since Canon use them.
How wireless E-TTL works.
Canon’s wireless E-TTL system employs brief digitally-encoded pulses of light (either
visible or infrared, depending on the master unit used) to transmit commands from a
master flash unit to a slave unit or multiple slaves. Since the system relies on digital
messages in the light pulses it’s immune to the problem that regular optical slave
flash units have - that of being triggered accidentally in response to other flash units
firing. (unless you’re near other photographers who are also using Canon wireless
flash units, of course)
Wireless E-TTL doesn’t use radio signals like most third party systems, so you can’t
trigger flashes remotely from great distances, such as the other side of a sports
arena. But it’s ideal for quick, portable and flexible flash setups in smaller spaces.
Canon chose light-controlled wireless rather than radio partly because it’s cheaper to
implement and partly to avoid the regulatory nightmare of getting licensing approval
for radio transmitters from every country in which Canon sell photographic gear.
Canon’s wireless system requires at least two wireless-capable flash units in order to
work. A master flash unit is attached to the camera’s hot shoe (either directly or
using the Off-Camera Shoe Cord) and the slave flash unit or units are set up to
illuminate the scene as desired. Unfortunately no current EOS camera can use its
internal flash unit as a wireless E-TTL master; convenient as that would be. Hopefully
future EOS camera bodies will have this ability - it shouldn’t require additional
hardware to implement, and it'd be very handy. You would then, for example, be
able to walk around with a camera in one hand and a flash in the other without any
bulky transmitter units or cumbersome cords.
As noted above, the master unit sends command signals to the slave units by using
pulses of visible light or infrared, so each slave must be positioned such that the
wireless sensor on its front can see these pulses. When shooting indoors with many
light-reflecting surfaces (walls, ceilings, etc) the slave should be able to detect the
master’s control signals even if the two units aren’t set up to point at one another,
but outdoors or in an un-reflective indoor setting the slave unit’s front-mounted
sensor must be able to see the front of the master unit, which can be a little
inconvenient. It may help to remember that many Canon flash units, such as the
420EX and 550EX, have rotating heads, so it’s possible to have the flash head
pointing in a very different direction from the body of the unit. You can also put the
master unit on an off-camera shoe cord rather than mounting it directly to the
camera body if you need to point it in a certain direction.
Command transmission distance depends partly on the angle at which the master is
transmitting relative to the slave and whether you’re using the units indoors or
outdoors. In addition the 550EX, which uses visible white light from the large main
flash tube to send data, has greater range than the ST-E2, which uses a smaller
flash tube covered by a plastic filter so it emits only invisible infrared energy.
The 550EX has an official transmission range of 8-10 metres (25-30 feet) when used
outdoors, with horizontal coverage of roughly 80° and vertical of about 60°,
assuming that the flash head is set to its 24mm setting. Naturally you can adjust the
flash head zoom setting manually to a tighter coverage than that if you want - or
wider if you use the flip-down 17mm panel, though at the cost of dramatically
decreased range. There’s conflicting data about the ST-E2. Canon USA’s spec sheet
claims that the ST-E2 has the same range as the 550EX, which appears to be
incorrect. Canon USA’s Chuck Westfall has said that the ST-E2 actually has a range
of about 3.5-5 metres (12-15 feet) when used outdoors, with coverage of about 40°
horizontal and 30° vertical.
The control pulses from the master unit to the slave or slaves are sent at varying
points in the period between the camera’s shutter release being fully pressed down
and the shutter opening. The wireless E-TTL control sequence works as follows:
Photographer presses the shutter release button halfway.
Ambient light metering of the scene is conducted.
Photographer presses the shutter release all the way.
The master flash unit sends a wireless signal to all slave units in group A,
instructing them to issue a low-power preflash.
Any slave units in group A fire a preflash and the camera records this light
output using its evaluative meter.
The master flash instructs group B slaves to issue a preflash.
Any slave units in group B fire a preflash and the camera records this light
The master flash instructs group C slaves to issue a preflash.
Any slave units in group C fire a preflash and the camera records this light
The camera calculates what the final flash output for the scene should be,
based on both the preflash data from each slave group (if any) and the userdefined group ratios/flash exposure compensation settings.
The camera flips up the mirror and opens the shutter.
The master flash instructs all slave units to fire simultaneously.
All slave units fire at whatever level the master unit has told them to.
Naturally if the master flash unit is flash-capable (ie: not an ST-E2) and is
configured to fire then it too will do so.
The camera flips down the mirror and closes the shutter.
There are of course differences in the timing of some of these events if AE
lock, flash exposure lock (FEL) and/or second-curtain sync are used, but that
is the basic flowchart. Naturally these command pulses and prefires occur at
an extremely rapid rate. They’ll register with the human observer but occur
far too quickly to mean anything to a human.
Using wireless E-TTL.
You can specify one of four different data channels for flash control, and each flash
unit can be put into one of three groups. The four channels are there so that up to
four cameras can use wireless E-TTL in the same physical location without conflicting
with each other, and the three groups are there so that independent flash output
ratios can be specified (though only with certain cameras; see below). When wireless
mode is used with any type A body you have full E-TTL metering, FP mode, FEL and
other E-TTL features.
There is no coded limit to the number of slave flash units which can be in each
group. This is because there is no two-way communication between master and
slave units - each slave simply sits there and awaits commands, and the master only
knows what slave units exist in terms of whatever light they produce during the
prefire stage. So you can set up as many slave units as your space and budget can
accommodate. The only issue here is the SE (save energy) feature, which will cause
slave units to switch to an energy-saver mode after a certain period of time. (see the
SE section for details)
You can check whether your slave flashes are within transmission distance or not by
pressing the test (“pilot”) button on the master flash unit. The camera will instruct all
the slave units to emit a flash of light. First the A group units will flash, then the B
and then the C. If your camera has modelling flash capabilities (see list in next
section) you can use that feature as well, giving you a quick preview of the final
The 550EX, when used as a master unit, can have its main tube disabled, so it can
control the slaves without contributing any camera-mounted light to the scene. In
addition, flash units with zooming flash heads (the 550EX and 420EX) automatically
zoom out to 24mm coverage when in wireless flash slave mode, though it’s possible
to override the zoom setting manually in the case of the 550EX.
You can use Canon’s wireless flash units with older type B bodies, but only if you set
the flash output settings manually, (where possible - the 420EX has no flash
exposure compensation pushbuttons and so can fire only at full power) which isn’t
particularly convenient. In other words, Canon’s wireless system works only with ETTL and does not work with either TTL or A-TTL flash metering.
A number of recent mid to high-end type A camera bodies - see full list in next
section - are capable of supporting varying light ratios between flash groups. (ie: this
is unrelated to fill flash ratios with single flash units) Each slave flash can be in one
of three groups - A, B or C. If your camera is ratio-capable you can then specify the
ratio of light produced by flash units in groups A and B. This A:B ratio can be set
from 1:8 to 1:1 to 8:1 in half-stop increments, which yields a total of 13 stops. The
550EX is also capable of specifying flash compensation for a third and completely
independent group - group C. Compensation of group C is adjusted from -3 to +3
stops relative to the A:B ratio, in 1/3 increments.
Note that if you’re using a 550EX as a wireless master unit (either on-camera or
connected to it using the off-shoe camera cord) then it defaults to group A. If you
want to control the ratio of slave unit output to master unit output be sure to put the
slave units into group B.
The two Canon EX macro units - the MR-14EX and the MT-24EX - also support
wireless flash capabilities. The flash units can both serve as master units in wireless
E-TTL setups, though not in the way one might expect. One of the two flash tubes on
the macro unit is assigned to the A group and the other to the B group (the tubes
are marked on the flash unit) and you can use the macro unit controller to specify
the output ratio between the two tubes if you have a ratio-capable camera. You can
then assign other slave flash units to group C and adjust flash exposure
compensation of these units relative to the two macro unit tubes. You can also use a
custom function on the flash to control slaves in groups A and B, but they are linked
to the internal tubes.
Unfortunately, the first generation of type A (E-TTL capable) bodies support wireless
E-TTL but do not support wireless E-TTL ratio control - all flash units on the same
channel will fire at the same power when used with such cameras. However, if you’re
using a 550EX as a slave there is a partial workaround for this - you can specify flash
exposure compensation manually using the flash unit’s push buttons.
One interesting side benefit of wireless E-TTL’s ability to control multiple flash units
is simplifying high-speed photography. If you want to use flash to freeze rapid
motion (water droplets, insects, hummingbirds, etc) you often have real range
problems, since short duration flash pulses are also effectively low output pulses. If
you’ve only got one flash unit at your disposal this limits the range the camera can
be from the light source. However, with E-TTL you can set up a battery of slave
units, each at the same distance from the subject, and fire them simultaneously at
low power. An expensive solution, to be sure, but one which affords a fair bit of
ST-E2 wireless transmitter.
Another interesting component of Canon’s wireless flash system is the ST-E2
transmitter. This compact unit fits onto a camera’s hotshoe and can control external
wireless Speedlite flash units, but can’t produce any scene-illuminating white light.
The ST-E2 contains a small flash bulb, which it uses to send the control signals to
other flash units, but the bulb is covered by a filter so that most of its light output is
invisible infrared (IR) energy. Since the human eye can’t detect IR, the ST-E2 is
more discreet in operation than the 550EX when controlling slave units.
Although fairly small and portable, the ST-E2 can’t transmit its control signals as far
as, and its coverage angle is more narrow than, the 550EX. The ST-E2 is capable of
about half the range of the 550EX, in fact, at about 3-5 metres (see coverage details
above). This basically limits its usefulness to indoor photography in small rooms or
studios. Unlike the 550EX the ST-E2 supports only groups A and B and A:B ratio
control - it unfortunately cannot control group C. The ST-E2 also does not support
flash exposure bracketing (FEB).
On a more positive front, the ST-E2 also contains a red AF assist light, which makes
it a popular accessory for owners of EOS cameras which lack true AF assist lamps notably the Elan 7/EOS 30/33/EOS 7 and D30 and D60 cameras.
Drawbacks of wireless E-TTL.
On the whole, wireless E-TTL is a powerful and flexible system with a few drawbacks.
First, the wireless control pulses can inadvertently trigger analogue optical slave
units and flash meters; a problem suffered by E-TTL in general. Both the white light
pulses from the flash units (wireless signals are sent as preflashes from the main
flash tube) and the infrared pulses from the ST-E2 control unit are sufficiently bright
to cause problems with such equipment. Second, another side effect of the light
pulses is you must ensure that the various units are correctly positioned so they can
see each other, and that the receiving sensors on the front of each slave flash unit
are not covered by anything. This also limits the working range compared to radiocontrolled wireless units. Third, portable battery-powered flash units are still fairly
low-powered compared to studio units and thus not suitable for a lot of complex
flash arrangements or larger areas. Fourth, the ST-E2 unit cannot control group C
slaves. And finally and most inconveniently, buying a bunch of Canon flash units is a
fairly expensive proposition.
List of wireless-capable Canon flash units and cameras.
Master-capable flash units:
The Speedlite 550EX and the ST-E2 transmitter both have the ability to act as a
master (control) unit. The MR-14EX and MT-24EX macro flashes can also serve as
masters, but only with slave units in group C or with slave groups A and B linked to
the internal tubes and other slave units in group C (see above).
Slave-capable flash units:
Speedlites 420EX and 550EX can both act as a slave flash when using wireless ETTL. The MR-14EX and MT-24EX can also act as slave flashes, with the two flash
bulbs on each unit assigned to slave groups A and B.
Flash units with no support for wireless E-TTL:
The earlier EX flash units - 220EX and 380EX - cannot operate in Canon’s wireless
mode. No TTL-only or A-TTL flash units (all E and EZ units) can operate in Canon’s
wireless mode.
Non-Canon wireless-capable flash units:
Metz also build a wireless flash system, but it’s not compatible with Canon’s
implementation. Sigma, however, make at least one flash unit (the EF 500 Super)
that’s designed to be compatible with Canon’s wireless protocol.
Camera bodies with support for basic wireless E-TTL:
All type A cameras.
Camera bodies with additional support for flash ratios and wireless modelling light:
EOS 3, 1V, Elan 7/7E/EOS 30/33/EOS 7, D30, D60, 1D, 1Ds, 10D, 1D mark II.
Modelling flash.
Large studio flash units frequently have incandescent tungsten bulbs built in
alongside the main flash tube or tubes. These constant-light bulbs cast light on the
subject in much the same way as the actual flash bulb would, only much more dimly.
This constant light is known as a modelling light, as it allows you to preview the flash
effect in a rough fashion - or at least see where the flash shadows and reflections are
likely to fall.
The Canon modelling flash feature lets you simulate the effect of the flash going off
before you take the picture - particularly useful for previewing wireless E-TTL flash
ratios. It works by pulsing the flash rapidly (at 70 Hz) for a second, much like in FP
mode. This obviously drains the batteries and can overheat the flash unit if triggered
repeatedly, so it’s best used sparingly. Pressing the depth of field preview button
fires the modelling light, but you can turn this off with a custom function if you find it
annoying. The 420EX must be in slave mode for the modelling light to work.
You need both a camera and a flash unit which can support modelling flash to use
the feature. The camera must be in a creative zone mode for this feature to operate
- modelling flash will not work in the PIC modes. Note also that Canon’s ring flashes
also contain small white incandescent bulbs for focus assist and modelling purposes.
Camera bodies which support modelling flash:
EOS 3, Elan 7/EOS 30/EOS 7, 1V, 1D, 1Ds, D30 and D60, EOS 300V/Rebel Ti/Kiss 5,
Flash units which support modelling flash:
Speedlites 420EX, 550EX, MR-14EX and MT-24EX.
Save Energy (SE) mode.
Most EOS flashes go into low-power or SE mode (called “Energy Conservation
Control” in some Canon material) after a predetermined period of time - usually 90
seconds or 5 minutes - in order to minimize battery drain. Some flash units are
always in SE mode when powered on. However, since it can be annoying to have
your flash unit turn itself off in the middle of setting up a shot some flash units have
a three-position switch - off, on and SE. The ability to override SE mode is very
important for wireless flash applications.
Pressing the shutter release button down halfway will wake up the flash and
recharge it. If you’re using the intervalometer on an EOS 10/10s, a 600-series
camera with the Technical Back E, an EOS 1 or 1N with the Command Back E1 or an
EOS 1v, 3, D2000, D30 or D60 with the TC-80N3 timer/remote controller, the
camera will wake up the flash unit a minute or so prior to taking a photo in order to
give it time to recharge.
Note that there is still battery drain associated with the SE mode. If you’re going to
leave the flash off for more than an hour or so you’re probably best off turning it off
altogether. Some more advanced flash units like the 550EX have custom functions
which allow you to adjust various power-down time intervals.
No power switch at all:
Speedlite 160E. (unit charges up when you press the shutter halfway)
No SE function:
Speedlites 480EG, 200E.
90 second SE timeout:
Speedlites 380EX, 420EX*, 430EZ, 540EZ, 550EX*, MR-14EX, MT-24EX.
5 minute SE timeout:
Speedlites ML-3, 300EZ, 420EZ, 300TL.
SE override capabilities (3 position power switch):
Speedlites 540EZ, 550EX*, MR-14EX, MT-24EX, 300TL.
* These flash units behave differently when they’re used off-camera in wireless slave
mode. Here the SE timeout is extended to 10 minutes for the 420EX and 60 minutes
for the 550EX (unless custom function 4 is set on the 550EX, in which case it’s 10
minutes). Pressing the master unit’s test button or activating FEL on the camera will
wake up a slumbering flash.
High voltage connector.
Speedlites 430EZ, 540EZ, 550EX, MR-14EX, MT-24EX and 480EG have high voltage
connectors which allow you to connect large-capacity external battery packs. See the
battery pack section for details.
PC terminals/sockets.
Many older flash units and most studio flash units support PC connectors, which are
simply electrical connectors and wires used to connect cameras and flash units. They
just carry a trigger current and do not carry digital data communications of any kind
such as metering information.
All semi-pro and high-end EOS cameras have a built-in PC socket. Lower and
midrange EOS cameras generally don’t have PC sockets. However you can cheaply
buy small adapters which plug into the camera’s hotshoe mount which convert to PC
cables, so this normally isn’t a huge limitation. None of Canon’s standard flash units
can be triggered via a PC cable without a hotshoe adapter for the flash unit. Only the
480EG can connect to a PC connector via the optional Synchro Cord 480.
The PC here stands for “Prontor/Compur,” two manufacturers of leaf shutters used in
older and large format cameras. It does not stand for “personal computer” in this
context, and so a camera with a PC socket cannot be hooked up to a computer
through it. Some of Canon’s material refer to it as a “German” socket.
Finally, be aware that many studio flash units use very high trigger voltages, which
can damage your camera. Canon recommends that trigger voltages of 6 volts or less
only be used with the camera’s hotshoe. The PC socket has better high-voltage
protection on at least some models, however. The EOS 1D, for example, should not
be used with flash units which have a trigger voltage of greater than 250 volts. I
don’t have information on every PC-equipped EOS camera model, so please consult
the manual which came with your camera. (assuming the manual says anything - the
D30 manual does not list a safe voltage, so you may need to ask Canon)
EOS cameras with PC sockets:
EOS 1, 1N, 1NRS, 5/A2/A2E, 3, 1V, 1D, 1Ds, D30, D60, 10D, 1D mark II.
Custom functions on flash unit.
The most recent high-end E-TTL Canon flash units - standard hotshoe flash unit
550EX and ring lights MR-14EX and MT-24EX - have custom functions, much like mid
and high end Canon camera bodies. These “functions” (settings or parameters,
really) allow you to alter the default behaviour of the flash units in certain ways.
For example, custom function 3 on the 550EX and MR-14EX lets you switch from ETTL to TTL flash metering.
Test flash (manual firing).
If you want to fire the flash manually simply press the illuminated pilot light on the
back of the unit. The flash unit will fire a test burst, whether on-camera or not.
Flash units which lack a manual fire button:
Speedlites 160, 200, possibly others.
Manual flash triggering for light painting.
A fun way of taking interesting photos in the dark is to trigger a flash unit manually
whilst leaving the shutter open - sometimes called “open flash.” For example, you
could set your camera on a tripod, open the shutter by putting the camera into
“bulb” mode, and then walk around the scene with a flash unit, painting the scene
with light. Coloured gels can be taped over the flash head as well, to illuminate the
photo with different colours of light.
Canon Speedlites with manual controls or old flash units with manual metering are
ideal for this - you can take the device off the camera shoe, dial in the appropriate
manual flash setting (full power, say, or 1/2 power or 1/16 or whatever) and then
trigger the flash by hand. You do this on most Speedlite flash units by pressing the
illuminated pilot light on the back of the device - other flash units should have similar
manual trigger buttons. If you wear dark clothing and point the flash away from you
you shouldn’t even appear in the photo. You can’t rely on your camera’s light meter
to help you meter the scene, so this sort of thing is largely a trial and error process.
It’s helpful to keep the flash the same rough distance from the area to be illuminated
for each flash burst.
If you have an E-TTL (type A) camera with an EX series flash unit you can even take
advantage of FEL to meter
Naturally you don’t have to use flash unit to do this. People often take outdoor night
scenes using high-powered floodlamps or indoor photos with small flashlights
(electric torches) or blinky light toys. And it doesn’t have to be used purely for fun or
unusual photographs. Here’s a photo, for example, that was primarily illuminated by
the full moon and small kerosene lamps. However I had a portable incandescent
flashlight with me which I used to brighten up shadow areas. Sort of a really slow fill
Finally, on a somewhat related topic, it’s possible to do high-speed photography such as photos of a balloon being burst with a pin - using ordinary flash gear. You
build or purchase a sound trigger, set up your subject in a pitch-black room, open
the camera shutter and let the sound trigger fire the flash. Flash units are capable of
extremely brief light bursts, particular at low power settings - remember that power
output on portable flash units is determined by the duration of the pulse. There’s a
lot of useful information on how to do this at http://www.hiviz.com/.
This is sort of a feature; albeit an undesirable one. But flash units always make
various kinds of noise. There’s usually a high-pitched whistling whine which increases
in frequency as the unit is charged up. This is caused by an oscillator circuit, used to
convert DC to AC so that the device can generate the high voltages needed to charge
the capacitor. Some flash units, like the 540EZ and the 550EX, have multiplex
circuits which make particularly noticeable humming/clicking sounds when powered
on. All flash units also make a soft popping sound when fired.
The other thing you can hear on zooming flash units is the hollow rattling buzz of the
small electric motor used to move the flash bulb inside the flash head. This is also
totally normal.
Flash safety.
Finally, and this isn’t really a flash unit feature as such but just something that
doesn’t really fit in anywhere else, I’d like to remind you about the need to keep
flash safety in mind.
Electronic flash technology involves extremely high voltages - literally thousands of
volts. The amperage is fairly low, but nonetheless some of the internal components
of any flash unit still have quite a high-voltage kick to them if they’ve been charged
up recently. And it takes a bit of time for this high voltage energy to drain out of the
flash unit’s capacitors. Even cheap disposable cameras with built-in flash units can
shock you if they’re disassembled.
So. Don’t expose your flash unit to rain or liquids if you can avoid it. And don’t open
up the device and monkey around with the innards unless you know what you’re
doing and have drained the capacitors by grounding them. You could literally get a
nasty shock - which could be deadly if you have a heart condition.
However, as long as you don’t dismantle your flash unit or pour lemonade into it you
shouldn’t have any problems.
As with any photographic endeavour there are all kinds of add-on accessories you
can buy for use with your flash unit.
Extension cords.
There are two extension cord systems which allow you to move the flash away from
the camera for more complex flash setups.
The Off Camera Shoe Cord 2.
The OCSC 2 is a simple coiled cord with sockets on either end that lets you attach a
flash unit to your camera’s hotshoe and move the flash independently of the camera,
up to a distance of about 60 cm (2 feet). This cord, though expensive, preserves all
flash functions including E-TTL if it’s available, and is useful for mounting a Speedlite
flash to a flash bracket.
It’s pretty short, however. You can connect two of them together if you need more
distance, but Canon do not recommend this practice since the electrical impedance
(internal resistance) changes. I’ve heard from other users that worked just fine for
them, so you might want to experiment to see if it works reliably for you. Note also
that there was the original Off Camera Shoe Cord (no numeric designation) which
lacked a locking hotshoe pin. Despite reports to the contrary online, it appears that
the two cords are both fully compatible with EOS cameras except for the note below.
The OCSC 2 has problems with some earlier EOS models. For one thing, it’s not fully
compatible with the EOS 600, 630 and RT and may behave unpredictably on those
cameras. More excitingly, when used on the 10/10s camera the cord can generate
more radio-frequency interference than is permitted by US, Canadian and German
regulatory agencies. Using a 10/10s camera with an OCSC 2 in those countries
makes you an RF outlaw!
Multiple TTL flash.
There’s also the camera-mounted TTL Hot Shoe Adapter 3, which runs off a small
lithium CR-2025 battery. This adapter connects with various dramatically costly
accessories - 60cm and 3 metre connecting cords, the tripod-mount-equipped OffCamera Shoe Adapter OA-2 for connecting Speedlites to cords and a TTL distributor
that lets you hook one camera up to 3 flash units.
The cords must be used in conjunction with the Hot Shoe Adapter 3 and the Camera
Shoe Adapter and connect together using mini-DIN style connectors - they don’t use,
say, PC connectors or anything like that. Note: there was also the original Hot Shoe
Adapter (no numeric designation), which worked only with the T90 and does not
work with EOS cameras, and the Hot Shoe Adapter 2, which does work with EOS
This system works with TTL only - A-TTL and E-TTL are not supported. In fact, a
whole slew of flash features are not supported if you use the TTL Hot Shoe Adapter 3
cable system. You can’t use A-TTL or E-TTL, there is no preflash, second-curtain sync
does not work, the DEP mode will not work, program shift won't work, automatic
flash head zooming is disabled (though manual zooming works if the flash supports
it), the aperture and coupling range data is not displayed on flashes with LCD panels
and the AF assist light does not work. These features are all disabled because their
control signals a) are all sent down one line and b) would result in contradictory
instructions from multiple flash units. (though as a side note this device can be used
for disabling E-TTL features if you like)
You can’t automatically adjust lighting ratios between the individual flash units in TTL
multiflash mode - all flashes will fire at the same time and shut off at the same time.
There are four awkward workarounds for this problem. First, you could move
individual flash units closer to and further from your subject. Second, you could stick
neutral density filters or diffusers on the flash heads. Third, you could use manual
zoom controls, if available, to zoom the flash head since that reduces the light output
on wider lens settings. And fourth, you can use manual controls, if available, to
adjust light output of each unit individually. However any flash set to manual will
disable TTL flash for all of the flash units. You can’t shoot a multiple flash photo with
a mixture of manual flash and TTL autoflash.
The TTL Hot Shoe Adapter 3 cord system is really only useful for older (type B)
bodies and compatible flashes. In fact, the cord system doesn’t work at all on E-TTL
only cameras like the digital 1D, 1Ds, D30 and D60. The new wireless system
supported by the latest E-TTL flash units is considerably more flexible (it supports
ratios on certain cameras, for example) and convenient (no wires to trip over or limit
your placement of slave units).
Flash diffusers.
A number of manufacturers, such as StoFen and Lumiquest, sell various attachments
you can clip or tape onto the head of your flash unit. These diffusers usually cost a
couple stops of light, easily halving your flash range, but can soften and tame the
harsh light of a flash considerably under certain circumstances - see the quality of
light section for more information on how they work. There are two basic types small light redistributors and large panels.
Small diffusers are of the StoFen Omnibounce variety - milky white (or green or
yellow) plastic open-ended boxes which fit snugly over the head of the flash unit.
These small diffusers redistribute the flash unit’s light output so there’s more light
scattering around and bouncing off walls and ceilings and so on. This type of diffuser
is, therefore, good for bouncing light around small interior spaces or for doing macro
(closeup) photography without a macro flash. It’s not so good if you’re shooting
outdoors or in dark interior spaces, where there’s nothing off which to bounce the
light. In such situations you’re simply cutting down your usable range, wasting
power (and thus batteries and thus money) and increasing flash cycle time by using
a small diffuser. It’s also not recommended for use in spaces where the walls or
ceilings are painted bright colours, as the light bouncing off those surfaces will have
a colour cast to it.
The other type of diffuser, such as the Lumiquest ProMax, is a big white stick-on
panel. These diffusers essentially enlarge the light output area of the flash, softening
the edges of shadows. Unlike small diffusers these larger accessories aren’t so reliant
on white surfaces off which to bounce light and thus are of more value outdoors or in
large banquet halls and so on. However, they’re really meant for relatively closerange shooting - they won’t help much when taking pictures at a distance and indeed
will hinder, as they cut the range of your flash unit by at least half and again,
wasting batteries and increasing flash cycle times.
Note that Speedlites 540EZ and 550EX also include flip-down panels that serve as
wide-angle flash diffusers and which increase flash coverage to 18 or 17 mm,
respectively. Such panels are important for wide-angle photography since flash units
aren’t typically designed to cover huge areas. Fisheye lenses in particular represent a
bit of a problem, since they have such wide coverage (nearly 180° diagonal for
15/16mm fisheyes and nearly 180° vertical for 8mm fisheyes) and so some
experimenting with diffusers would be required for successful flash-illuminated
fisheye photography.
Be careful if you’re using A-TTL flash. A-TTL relies on an external sensor on the front
of the flash unit, behind a recessed transparent lens. Certain types of flash diffusers
can either block this sensor or reflect light down from the flash head to the sensor.
Either way the sensor will get confused, which can lead to problems with your flash
metering. Make sure the diffuser doesn’t block the sensor. In the case of StoFen’s
Omnibounce accessory, for example, follow the instructions and tilt the flash head
upwards by 45 degrees or so.
Another important thing to remember is that you do not have to adjust flash
compensation when using a diffuser in any automatic flash metering mode that
works through the lens (TTL, A-TTL or E-TTL) - just put the diffuser on the flash unit
and shoot away. The camera will adjust automatically for the stop or two that the
diffuser costs you, up to the limits of the flash unit’s light output. Of course, if you
plan on shooting in manual flash metering mode you’ll need to factor in the reduced
light output yourself through testing.
Finally, don’t think you have to spend the money on these accessories. You can
always just slap together a homemade flash diffuser out of a white translucent milk
jug or tracing paper or thin fabric or whatever else you have lying around. A
common trick is to angle the flash unit vertically, then use an elastic band to wrap an
index card around the back of the flash head. This provides some forward light in
addition to the light bouncing off the ceiling. The expensive accessories are mainly
just more convenient and professional-looking.
Flash brackets.
As noted above, the large metal brackets from companies such as Stroboframe and
Newton, and designed for mounting external flash units to a camera, are commonly
used by wedding photographers and the press for reducing the risk of the redeye
effect. However they also serve other purposes as well.
By raising the flash up above the lens you also reduce ugly flash shadows cast onto
walls behind a subject. The shadows still occur; they’re simply lowered down below
the subject and thus may not appear in the final picture. Many flash brackets also
have rotating attachments which allows you to keep the flash centred above the lens
at all times rather than having it on the side when you take photos in portrait
orientation rather than landscape.
The primary drawbacks of flash brackets are that they’re very large and cumbersome
and that they make you look like you’ve got a huge gigantic camera rig - which can
frighten your human subjects or make them feel much more self-conscious than they
would normally.
Another drawback involves AF assist lights. If you raise the flash off the camera you
may find that the assist light on the flash unit no longer lines up correctly with the
camera’s focus points, thanks to simple geometry. Ironically this isn’t a problem for
A2/5 and 10/10s users, because those cameras never activate the AF assist light on
external flash units.
External battery packs.
Most of Canon’s high-end flash units have sockets on the side which can
accommodate external high-voltage (270 volts) battery packs. These packs have two
basic functions - they speed up the flash’s recycle time between shots to a second or
two (critical for news or wedding photography) and extend the time you can go
between changing batteries. They’re also useful in cold weather (battery
performance always drops precipitately at freezing temperatures) since you can stuff
the pack inside your jacket to keep the cells warm if necessary.
The Compact Battery Pack E requires 6 regular AA alkaline, NiCad or NIMH cells, but
the newer Compact Battery Pack CP-E2 can also accept lithium AA cells. Either
compact pack can be attached to the bottom of a camera using the tripod mounting
screw. The much larger Transistor Pack E can use either 6 regular C cells (with
Battery Magazine - lithium cells are not compatible) or nickel-cadmium rechargeable
cells (with Ni-Cd Pack) and obviously has much greater capacity than the smaller
Compact pack.
A number of other companies also sell high-power battery packs compatible with the
Canon Speedlite high-voltage connector. These products include Quantum
Instruments’ Turbo (lead-acid) and Turbo Z (NiCad), Lumedyne’s Cycler and
Dynalite’s Jackrabbit.
Unfortunately, the packs are all fairly heavy, bulky and inconvenient, (especially the
huge Transistor Pack E and third party products) and require that the flash unit be
tethered to the battery pack via a coiled cord. Note also that the flash unit will not
work with an external pack if the flash unit’s internal AA batteries are dead or
missing - the high-voltage power is used solely for recharging the unit’s capacitors,
not for powering its control circuitry.
A number of manufacturers also sell generic battery packs (such as the Quantum
Bantam) which can be connected to most AA-powered EOS flash units - even those
which don’t have special power sockets. They work by replacing the AA batteries with
a plastic shell and running a cord to the power pack. However, as they aren’t highpower they can’t speed up the recycle time as dramatically - they’re more useful for
extending the number of shots you can accomplish between battery changes.
Keep in mind that portable flash units were not designed for continuous high-power
use. You can damage your flash if you fire too many high-power bursts in a short
period of time; something an external battery pack may let you do. So try not to fire
flash bursts for longer than a few seconds, especially at full power manual or small
aperture TTL firing. Remember that smoke emerging from your flash unit is
shorthand for “stop immediately.”
Flash units with high-voltage sockets:
Speedlites 430EZ, 540EZ, 550EX, 480EG*, MR-14EX and MT-24EX.
* The Compact Battery Packs are not recommended for use with the 480EG.
Flash extenders.
If you’re doing nature photography of wild animals or are stalking wild celebrities for
a tabloid and need to use flash photography across great distances, you might
consider a flash extender, such as the Better Beamer. These accessories are simply
plastic Fresnel lenses you can attach to your flash unit’s head with tape or velcro.
They concentrate the light much like a zooming head and give you an extra couple
stops of light, at the cost of coverage area. They’re only really useful, therefore,
when using very long telephoto lenses - say, 300mm or so or longer. Michael
Reichmann’s “Luminous Landscape” Web site has some example photos of how this
works, and Arthur Morris’ “Birds as Art” site sells them.
I’ve also seen the term “flash extender” refer to devices which let you mount your
external flash unit higher up off the camera hotshoe, but that’s something different
Power source options for external flash units.
Most Canon external flash units run off four standard AA (LR6) alkaline cells, though
one - the tiny and discontinued Canon 160E - used instead a small 2CR5 lithium
battery of the type used by many EOS cameras. Here are some power source options
for the AA type of flash.
Remember that all batteries can leak. If they do you’ll find your beloved flash unit
full of a corrosive liquid that will damage or even destroy it. It’s wise to remove any
cells from your flash if you aren’t planning on using it for some length of time - a few
weeks or whatever.
Note also that some flash units can behave erratically when battery power is low.
Normally weak batteries just result in long recycle times, but on the 430EZ at least
low batteries can result in strange behaviour - the flash triggering randomly, the
zoom motor buzzing at odd intervals, etc. So if your flash unit suddenly starts acting
strangely try changing the batteries. This can also happen if the flash unit isn’t firmly
seated in the hotshoe or if the contacts are dirty or corroded.
Standard AA non-alkaline (zinc carbon) cells.
Pros: Available for next to nothing.
Cons: Don’t last very long at all and can’t be recharged. They also have fairly high
internal resistance and so it takes a few extra seconds for the flash unit to recharge
between shots.
Standard AA alkaline cells.
Pros: Alkalines are cheaply and readily available anywhere. They store a fair bit of
power and let you go a reasonably long time between replacements.
Cons: Last much longer than carbon zinc cells but otherwise have the same
disadvantages. Recycle time to full power can range from 6-20 seconds, depending
on how new the cells are.
Rechargeable nickel-cadmium (NiCad) cells.
Pros: Relatively inexpensive, rechargeable hundreds of times. They have a fairly low
internal resistance and so decrease the recycle time the flash unit will take to
recharge to full power to 4-6 seconds. NiCads also have better cold-weather
performance than alkalines - their performance suffers when the temperature drops
below freezing, but not as badly.
Cons: Don’t store as much juice as alkalines, so you have to switch batteries much
more often. NiCad cells are also hazardous household waste (heavy metals) and
should not be thrown into the regular garbage system. NiCad cells drain flat (“selfdischarge”) within a few weeks after charging.
Lithium AA (FR6) cells.
Pros: A fairly new development, these are lithium cells built to an AA shape. They
store a lot of power, have long shelf lives, and recharge the flash at roughly the
same rate as alkalines.
Cons: Really expensive and not rechargeable. Steep death curves - they’ll work fine
and then suddenly run out of power unexpectedly. Most importantly, only the latest
Canon Speedlites can use them. Older models are not compatible with lithium AA
cells owing to power issues, and might be damaged by them. The 540EZ and all EX
series flash units can safely use lithium cells; all other flash units cannot.
Rechargeable nickel metal hydride (NiMH) cells.
Pros: Affordable and rechargeable hundreds of times. Higher capacity (1600 mAH)
cells have similar capacities to alkaline cells. Not as hazardous to the environment as
NiCads. Have a similar recycle time to full charge as NiCads - around 4-6 seconds.
Cons: Require different chargers from commonly available NiCad chargers. Can selfdischarge in a couple of weeks.
External battery pack.
Pros: High-power packs can decrease recycle time to a second or two, letting you
shoot flash photos more rapidly. Store a lot of power and so mean you don’t have to
change batteries as often.
Cons: Large, bulky packs linked to the flash via coiled cords. High-power battery
packs work only with a handful of high-end flash units with the necessary power
socket. Third-party battery packs are required for use with other Canon flash units,
but don’t have as rapid recycle times.
Flash tips.
Here is a handful of tips and potential pitfall areas. To begin with, however, a brief
discussion about the quality of light (the kind; not a value judgement) involved in
flash photography.
Quality of light.
I’m sure we’ve all had the experience - getting a roll of film back from the lab, only
to find that the photos are all harshly lit and disappointing. How is that the
professionals get such wonderful looking photos? Well, there are many reasons for
this, but since this is an article about flash photography I’m going to discuss just one
very common reason why amateur photographs can look terrible - flash.
The problem comes down to the quality of light. For a professional-looking photo of a
person you generally want very soft light; light which lacks distinct shadows. Hard
light, by contrast, tends to produce sharp-edged shadows, emphasizes facial
blemishes and generally looks very unflattering.
The difference between hard and soft lighting essentially comes down to the relative
size of the light source compared to the subject. Soft lighting is light which originates
from a large area. Think of an overcast day, when the sun’s light is filtered through
clouds covering the entire sky - shadows are very soft. By contrast, a stage spotlight
will cast a perfectly sharp circle.
And so this is the crux of the matter. Portable camera flashes are essentially
designed to work like spotlights and have pretty small light-emitting areas - just a
few square centimetres. This is partly for portability reasons and partly because flash
units are designed to achieve the maximum distance range possible, by
concentrating their light output with a reflector and lens. Any softening of the light
necessarily involves a reduction in efficiency and range. So the light from a flash unit
is, therefore, very hard-edged and harsh. Sometimes you want light like that - for
illuminating glittery objects and emphasizing specular highlights. But for many things
you don’t.
The easiest way to soften the lighting in your flash photos is to bounce the light from
the flash unit off a large white surface. White walls and ceilings work very well for
this, as do large portable folding reflectors. You can also buy diffusers that attach to
your flash that can help as well, either by distributing the light in more directions so
the light can bounce off walls and ceilings, or by increasing the light-producing area
somewhat. Remember that coloured surfaces will add a colour cast to the light something you should always be aware of when bouncing light in interior spaces. A
blood-red wall is going to reflect red light onto your subject.
Studio flash units (the big kind that plug in the wall) are frequently used with
photographic umbrellas or softboxes to give the light source a larger surface area.
Umbrellas are large folding umbrellas lined with white or silver, off which the light
from the flash unit is bounced. (ie: the flash unit is mounted in the middle of the
umbrella facing away from the subject, and the light bounces outwards) Softboxes
are large boxes with reflective interiors and diffused white fabric front panels.
Portable battery-operated flash units don’t really have the power required to
illuminate large studios when used with umbrellas and large panel diffusers. But if
you’re on a budget and working in a smaller space, a photo umbrella - or even a
regular umbrella painted silver on the inside and taped to a stand - can be a handy
tool. So can directing the light from your flash unit through a simple frame with thin
white fabric stretched over it. Experiment to find out what works for you. Here again,
incidentally, digital cameras have a huge advantage - you can move things around
and experiment constantly and get immediate feedback on the screen as to whether
the new configuration works or not.
Remember that it’s the relative size of the light source compared to the subject
that’s important. A huge softbox a long way away from a subject has the same kind
of hard light as does a small diffused flash close up. So placing the diffused
lightsource close to the subject is important as well. In studio situations softboxes
are often positioned just outside the frame of the image area.
General flash photography tips:
Remove any lens hoods when using an internal flash. If you don’t you’ll
probably notice a dark crescent-shaped flash shadow at the bottom of your
Don’t stand closer than a metre or so (3 feet) to your subject unless you have
a macro flash. You’ll get similar shadowing at the bottom of the photo. An
external unit with a small diffuser can help, though.
If the tilt/swivel head is not set straight on, double-check its position if you
switch from landscape to portrait orientation or vice-versa. If the head is
pointing the wrong way for the current orientation you might end up with ugly
flash shadows, or half your photo might be properly exposed for flash and the
other half not at all.
If you’re shooting in vertical (portrait) orientation and you have a shoemounted flash, be absolutely certain that your left hand is not holding the
lens or in a position that could block light from the flash unit.
If your camera has more than one focussing point do not use the old “focus,
lock AE and recompose image” trick when taking flash photos. Instead, select
the focus point nearest to your subject in order to bias flash exposure to that
area. The exception to this rule is type A bodies which support FEL. You can
use FEL in such situations to lock flash exposure to a given area of your photo
before recomposing.
If you need to shoot a number of flash photos in rapid succession consider
using NiMH (nickel metal hydride), NiCad (nickel cadmium) or lithium (if your
flash can handle them - many models cannot) batteries instead of regular
alkalines. The internal resistance of these batteries is lower and thus the
recharge time is faster. Note, however, that NiCad batteries can’t store as
much power as alkaline batteries so you’ll have to replace them more often.
Another alternative is an external battery pack, though they tend to be large
and cumbersome.
Tips on shooting indoors in a small space:
Use bounce flash off a low ceiling or a wall to soften the light. Unless the walls
or ceiling are painted in strong colours, in which case you’ll probably want to
avoid bounce flash unless you want to tint the light.
If you don’t bounce the flash try using a small flash diffuser to break up the
directionality of the light.
Be sure you aren’t shooting towards something reflective, like a glass window
or mirror. Flash glare will bounce off the glass and look like an ugly mess. It
will also throw off the flash metering, underexposing the photo.
Tips on shooting outdoors or indoors in a large space:
Don’t use bounce flash if outdoors or if the ceilings are too high or too dark or
are painted in colours that will tint the light of the flash. Keep the flash
straight on. If you tilt the flash, for example, you’ll find the upper half of the
image to be brightly lit and the lower half dark. This looks awful. The one
exception is if you have a large flash diffuser installed.
You probably won’t want to use a small flash diffuser as it’ll just cut the useful
range of the flash. Small diffusers are light redistributors and thus most
useful when there are nearby white surfaces off which the flash will bounce,
softening the light. Large flash diffusers are mildly useful in that they spread
the source of the flash unit’s light over a larger area, softening shadows,
though the cost in range may not be worth it.
When photographing people at great distances in low-light conditions
remember that the risk of redeye in the photos goes up. This is particularly
apparent when taking closeups of people using a telephoto lens from a long
way away. (typical example - you’re zooming in with a long lens to get a
child’s face during a school concert in a dimly lit gymnasium and the photo
ends up looking like a choir of young Satans) Try to separate the flash as far
as possible from the camera - even a large flash on a shoe mount won’t be
adequate distance.
Links to other useful documents.
Chuck Westfall/Mark Overton “EOS Flash FAQ”.
Dave Herzstein’s “EOS Speedlites Comparison Table”.
Canon EOS FAQ Version 2.4. Section 3: Flash. (very useful, but no longer updated)
PhotoZone flash technology FAQ.
Discharge Graphs of Electronic Flash.
Toomas Tamm’s “Electronic Flash Information”.
Kevin Bjorke’s “PowerShot flash photography”. (discussion of flash photography with
Canon digital cameras but more generally applicable)
Moose Peterson’s “the TTL Flash System”. (Nikon oriented, but has some general
Kodak Flash Photography. (a series of pages with helpful beginner material)
Cybaea “Colour Temperature and Colour Correction Defined and Explained”.
Kelvin scale. (includes a list of colour temperatures)
Photodo’s “Take the lights (sic) temperature and avoid colour casts”. (interesting
description of colour meters and colour temperature)
Photo.net: A-TTL and E-TTL. What is the difference?
Photo.net: Elan IIe and 380 ex fill flash.
Canon “Flash Work” brochure. (online edition from Canon Malaysia)
Vincent Laforet - “Show me the Light.” (brief writeup on Canon E-TTL wireless flash.
Scroll down 2/3 of the page to find the article)
Photography Tips - guide numbers.
Sam’s Strobe FAQ. (total geek information - extremely detailed notes on the
electronics found in flash units)
Back to Part II.
- NK Guy, tela design.
Disclaimer and copyright:
This document is copyright © 2001-2004 NK Guy, tela design. This information is
provided with neither warranties nor claims of accuracy or completeness of any sort.
Use this information at your own risk. All trademarks mentioned herein belong to
their respective owners.
I wrote this document in the hope that others in the Internet community might find it
useful or interesting. However, I don’t think it’s reasonable for anyone else to earn
money from - or take credit for - my work.
Therefore you may copy and print this document for your own personal use. You
may not, however, reprint or republish this work, in whole or in part, without prior
permission from me, the author. Such republication includes inclusion of this work in
other Web sites, Web pages, FTP archives, books, magazines or other periodicals,
CD-ROM and DVD-ROM compilations or any other form of publication or distribution.
Please do not frame this site within another.
Please send feedback if you find this article to be of interest or value or if you have
any comments, corrections or suggestions.
Please also consider making a donation to help defray some of the costs of building
and maintaining this site. Thanks!
Back to Photo notes.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF