Canon extension tubes
LEE BEEL
Technique Extension tubes
Move closer
Increasing the distance between the lens and the sensor or film
reduces the focusing distance. That’s how macro lenses do it. But
you can get similar results by fitting an extension tube.
Right and opposite
Shooting square to
the subject overcomes
some of the problems
with the limited depthof-field in close-up
photography. Much of
the dragonfly is sharp in
both photographs. They
were taken using the EF
12 and EF 25 extension
tubes mounted
together on an EF 70200mm f2.8L IS USM
lens. The main light is
from a Speedlite fired
through a diffuser to
avoid hotspots on the
delicate wings. Slow
shutter speeds pick up
the ambient light.
Right 1/15 second at
f16, ISO 400.
Opposite 1/10 second at
f16, ISO 100.
Both with EOS 5D Mk II.
Extension tubes work by increasing
the lens extension – the physical distance
between the front element of the lens and the
film or digital sensor.
An extension tube is simply a light-tight
tube that fits between the camera body and
lens. The extension of the lens is increased,
the minimum focusing distance decreases,
and you can get closer to your subject for
greater magnification.
LEE BEEL
If you are serious about macro photography,
you probably own a macro lens. They are the
tool of choice for photographers who want to
get close to their subjects, but do not want to
compromise on image quality, ease of use or
performance.
However, the performance of macro lenses
comes at a price – the cost of the lens. But
what if you would like to dabble in macro or
close-up photography without the expense of
buying a macro lens? Is there any way to get
in closer and obtain increased magnification
with the range of lenses you already own?
Extension tubes could be the solution you
are looking for. The principle is very simple.
When it comes to close-up photography, your
lenses are limited by how close to the subject
they can focus. The closer the focusing
distance, the further the front element needs
to be from the sensor plane. This distance is
called extension – the greater the extension
the closer you can get to the subject.
Canon extension tubes
Canon makes two extension tubes, the EF
25 II and EF 12 II. They have a length of
25mm and 12mm respectively. The EF 25
II gives more extension, and therefore
greater magnification, but it is
more expensive. You can also
use the two together for even
more extension. Canon doesn’t
recommend this (it says data
transfer may be affected), but it
worked for us.
The EF 25 II and EF 12 II
extension tubes were introduced
in September 2004 at the same time as the
EOS 300D camera and EF-S lenses. Prior to
this date, Canon sold the EF 25 and EF 12
extension tubes. They are identical to the
newer versions except in one respect – you
cannot use them with EF-S lenses.
These Mark I versions have long
been discontinued, but you
may be able to find them on
the second-hand market. If
you do not use EF-S lenses
they could be an economical
alternative.
Above Canon
extension tube EF 25
II fitted between an
EOS camera and an EF
50mm f1.8 lens.
Current extension tubes EF 25 II and EF 12 II
Discontinued extension tubes EF 25 and EF12
46 |47
Technique Extension tubes
48 |49
Extension tubes in action
The magnification formula
There is a formula for working out how much
magnification extension tubes will give you:
magnification = extension/focal length
Every lens has an effective extension.
Canon does not make this figure available, but
we can work it out once we know the focal
length and magnification of a lens, figures
that Canon do publish. Let’s take Canon’s EF
50mm f1.8 II lens, as an example. We know
the focal length (50mm) and Canon gives
the magnification as 0.15x (this is at the
minimum focusing distance of 45cm). From
these figures a little algebra reveals that the
effective extension built into the lens is 7.5mm
(extension = magnification x focal length).
We use the phrase ‘effective’ extension
because the focal length of the lens can
change slightly at different focusing distances.
Adding the EF 25 II extension tube to
the lens gives a total extension of 32.5mm.
To work out the magnification, just divide
the extension (32.5mm) by the focal length
(50mm) to give a figure of 0.65x.
It’s much easier to judge magnification with
some practical examples. The photos on the
right show how much magnification you can
obtain with certain focal lengths.
Magnification and focal length
The above equation also helps to explain the
effect that extension tubes have on lenses
of different focal lengths. Using simplified
figures, we can see that the additional
magnification of a 50mm lens used with the
EF 25 II extension tube is 0.5x (25/50). Fit the
same extension tube to a 100mm lens and
Minimum focusing distances
Tube magnification
Lens
Extension tubes
17-40mm f4L
at 40mm
50mm f1.4
85mm f1.8
70-210 f4L IS
at 210mm
None
28cm
45cm
85cm
120cm
EF12 / EF12 II
23cm
27cm
51cm
102cm
EF25 / EF25 II
22cm
22cm
41cm
90cm
EF12 + EF25 or
EF12 II + EF25 II
N/A*
21cm
37cm
62cms
* Lens cannot focus on the subject at this extension.
Extension
tubes
EF12
EF25
EF12 II
EF25 II
Lens
compatibility
Approximate
retail price*
EF, TS-E lenses
discontinued
EF, EF-S, TS-E
lenses
£71.99
12mm
24-100mm
£99.99
25mm
50-150mm
Extension
minimum focus
of lens
with EF 12 II
extension tube
with EF 25 II
extension tube
with EF 12 II and
EF 25 II tubes
Above EF 17-40mm f4L lens at a focal length of 40mm. The front lens element
was less than 3cm from the stamps for the third photo and has cast a shadow. It
is not possible to focus with both tubes attached.
Recommended
focal lengths
12mm
24-100mm
25mm
50-150mm
Above EF 50mm f1.4 lens
* Varies by dealer.
Unsuitable
lenses
The EF 14mm, and
EF 15mm lenses are
unsuitable for the EF12/
EF12 II extension tubes.
These lenses, plus the
EF 20mm and EF 24mm
are unsuitable for the
EF25/EF25 II extension
tubes. Zoom lenses at
these focal lengths are
also unsuitable.
the magnification drops to 0.25x (25/100). So
the longer the focal length, the less effect is
gained from adding extension tubes. This
explains why extension tubes are more useful
with lenses of shorter focal lengths.
Does this mean that you can use the EF 25
II extension tube with a 24mm lens for 1.0x
magnification? Unfortunately not, because the
minimum focusing distance is greater than the
distance from the camera’s sensor plane to
the subject required for 1:1 magnification. You
cannot focus on the subject – only on a point
somewhere behind it.
Above EF 85mm f1.8 lens
Left The effectiveness
of adding extension
tubes depends on the
focal length of the lens.
The shorter the focal
length, the greater the
effect. The 17-40mm
lens has the greatest
magnification, but
with a gap of less than
3cm between the lens
element and the subject
when used with the EF
25 II, it is impractical
to use at this high level
of magnification as the
lens blocks the light.
The 50mm and
85mm lenses give
more practical
working distances and
good magnification,
especially when the
two extension tubes are
combined.
The 70-200mm
lens does not benefit
as much from the
extension tubes. If you
have this focal length
lens, the 500D or
250D close-up lenses
will give you greater
magnifications.
All photos taken
with an EOS 40D.
Above EF 70-200mm IS f4L lens at a focal length of 200mm
Crop factor effect
Magnification is determined by the focal
length and the extension of the lens.
From this we can see that the crop factor
of the camera you use is not even a
consideration. However, in practice, the
crop factor does make a difference to the
apparent magnification. This is because
at a magnification of, say 1x, an object
that measures 36mm by 24mm will be
reproduced at life size on a full-frame
camera. An APS-C camera, on the other
hand, will only record the central part of
the object, an area of approximately 15 x
22.5mm (the exact sensor size varies by
model). Compare the two images side by
side and it appears that the photo taken
with the APS-C size camera has greater
magnification. This means that an APS-C
camera appears to get you closer to your
subject than a full-frame camera.
Right The top picture
shows the image
captured by a full-frame
sensor. The white
rectangle shows the
area seen by an APS-C
sensor. (Assuming
the same lens is used
on each camera to
take the picture.)
Both images have the
same magnification.
However, if you want
both images to fill the
same print area, the
APS-C image has to be
enlarged more than the
full frame image. The
result is that th APS-C
camera appears to give
greater magnification.
EF 12 TUBE
Above This photo was taken with
the same 85mm lens focused at its
minimum focus setting, and with the
EF 12 extension tube fitted. However,
instead of focusing at 85cm, the
lens can now focus at a distance of
approximately 53cm from the subject.
EF 25 TUBE
Above The 85mm lens was focused
at its minimum focusing distance.
With the EF 25 extension tube fitted,
the photographer could move within
39cm of the subject.
NO TUBE
Above This photo was taken with an
EF 85mm f1.8 lens on an EOS 40D.
The lens was set to its minimum
focusing distance of 85cm. This
photo is as close as the photographer
can get with this lens.
Right The EF 25 and EF 12 extension
tubes were combined, giving a total
extension of 37mm. The 85mm lens
was set to its minimum focusing
distance, enabling a sensor plane to
subject distance of 34cm.
EF 12 + EF 25 TUBE
Technique Extension tubes
50 |51
Focus stacking
The solution
Focus stacking is a technique which can be
used to achieve front-to-back sharpness in
close-up images with shallow depth-of-field.
Depth-of-field
Depth-of-field is determined by three factors:
• the focal length of the lens
• the aperture
• the distance between the lens and subject.
Of the three, the third factor has the greatest
affect on depth-of-field. The closer your lens
is to your subject, the less depth-of-field
you have. When shooting close-up or macro
photography with extension tubes, depth-offield may be so limited that you cannot obtain
front to back sharpness even at f16 or f22.
This holds true regardless of focal length.
Diffraction
Another problem is diffraction. Diffraction
is a kind of lens distortion that starts to
appear at small apertures, such as f16 and
f22. Diffraction degrades image quality – look
closely at the same image taken with the same
lens at apertures of f8 and f22 and you might
see a significant difference in image quality.
The image taken at f22 may have more depthof-field, but appears to be less sharp than the
image taken at f8 because of diffraction.
Above A different part
of the flower is in focus
in each of the photos.
The focus stacking
technique blends them
all together to create a
new image comprising
the sharp zones in each
photo (see main image).
Focus stacking involves taking several photos,
all at the same aperture (ideally f8 or f11 –
the sharpest settings for most lenses) each
with a slightly different point of focus. The
first image is focused towards the front of
the subject, the next a little further back, and
so on. The aim is the have every part of the
subject in focus in at least one of the images.
You then blend the images using dedicated
software to create a photo with back-to-front
sharpness. Adobe Photoshop CS4 and CS5,
have an auto-blending function for focus
stacking. If you use Windows, CombineZM
is a free program that does the same. It’s
available from:
http://hadleyweb.pwp.blueyonder.co.uk/
CZM/News.htm.
Helicon focus is a program available for
both Mac and PC users at:
www.heliconsoft.com.
Licenses start from $30US, and you can
download the program and try it for 30 days
without any restrictions.
We tested Adobe Photoshop CS4 and
Helicon Focus. Both programs worked
flawlessly – Helicon Focus was much quicker
and easier to use, but cropped tighter into the
image than Photoshop CS4.
Focus stacking in Photoshop
1 If you shot the photos in RAW,
process them identically in Digital
Photo Professional (DPP) or other
RAW conversion software.
4 Go to Tools > Photoshop > Load
files into Photoshop layers. This loads
the selected photos into Photoshop
CS 4 and combines them into a single
file with each photo in its own layer.
Helicon Focus
Helicon Focus is very easy to use.
Start by clicking the Add Images
button to load your photos and clear
any other images already there. Press
the Render button (you can play with
focus parameters, but the default
ones worked fine for us) and then the
Saving button to save the image once
the blending process has finished.
without focus stacking
with focus stacking
As far as we know, focus
stacking is exclusive to digital
photography. Unlike many other
digital techniques, it does not
appear to be an implementation
of a film technique. It is not the
answer to every depth-of-field
issue, but it will solve a few
tricky problems.
2 DPP users: Go to File > Batch
Process and save the images in the
JPEG format in a new folder (set
Image quality to 10).
5 The photos need to be aligned.
Each photo is slightly different, as at
such close lens-to-subject distances
the effective focal length of the lens
changes when you focus on different
points. To fix this, go to Select >
All layers then Edit > Auto-Align
Layers... Select ‘Auto’ and press OK.
Photoshop aligns the layers.
3 Open Adobe Bridge, navigate
to the new folder and select all the
images (Edit > Select all).
6 To blend the sharp parts of the
layers together, go to Edit > AutoBlend Layers, Select ‘Stack Images’
and tick ‘Seamless Tones and
Colours’ then press OK. It will take a
few minutes. When done, go to Layer
> Flatten Image to flatten the layers
and then save the photo.
Focus stacking tips
• Use a tripod and cable release
to keep the camera in the same
position for every shot. Be
careful not to jog the tripod.
• Avoid camera shake caused by
camera vibration at slow shutter
speeds by enabling the mirror
lock-up in the Custom Functions
menu.
• Take two exposures at each
setting when using slow shutter
speeds as insurance against any
spoilt by camera shake.
• Use ISO 100 for maximum image
quality and colour saturation, or
a high ISO like 1600 or 3200 for a
grainy effect caused by noise.
• Use the Quick Control screen,
if your camera has it. It is much
easier to see your aperture,
shutter speed and ISO settings
here than on the LCD panel on
top of the camera.
• If you have more than one EOS
camera, try using the one with
fewer megapixels. This produces
smaller files, which are easier
for your computer to handle,
particularly if you are blending
a lot of photos or have a slow
computer.
• Shoot RAW + JPEG, and make
sure that you set the Picture
Style, white balance, aperture and
shutter speed manually. Shoot
each photo at the same ISO,
aperture and focal length. If your
settings are accurate, you can
blend the JPEG files straight out of
the camera, and you have the RAW
files as insurance in case you need
to tweak any settings afterwards.
Technique Extension tubes
52 |53
Rodel Manabat Case studies
May-lin Joe
Tube pros and cons
The big advantage of extension tubes is that
they can be used with nearly any lens. They
can also be used in combination with closeup lenses (covered in the July–September
2010 issue), or with a macro lens, for even
greater magnifications.
Light loss
There is one major disadvantage – adding
an extension tube reduces the amount of
light reaching the film or digital sensor.
This means that you need to increase the
exposure by increasing the ISO, using a
slower shutter speed or setting a wider
aperture. Light loss can be as much as two
stops at higher magnifications – although
you always have the option of using offcamera Speedlites so that you can use low
ISOs and small apertures. Both Lee Beel
and Rodel Mandabat, whose photos appear
in this article, use Speedlite flashes with
diffuses fitted to them for this reason.
Of course, much of the time you might
not be aware of this light loss. Unless you
are using the manual shooting mode, the
camera’s through-the-lens metering system
will automatically adjust the exposure values
to give correct exposure. However, it will
reduce your creative options for smaller
apertures or faster shutter speeds.
Focus shift
I have always been fascinated by macro
subjects, especially insects. I used to own
an EF 100mm f2.8 Macro lens, but it was
rather frustrating not being able to take the
shots I had in mind. So I sold my macro lens
and changed my set up to a more compact
solution. I now use an EF 12 II extension tube
with an EF 24-70mm f2.8L lens. It is easier,
quick to change and a great combination with
a fast aperture lens. It is a bit heavier than
the 100mm f2.8 Macro lens, but it serves a
dual purpose – a general walk around lens
and a good macro option (by attaching the
extension tube).
I like taking close-up and macro shots of
plants, leaves, flowers, petals, butterflies,
water droplets and insects – anything with
symmetry, lines and interesting texture.
Most of the time I use my EF 12 II tube with
my EF 24-70mm f2.8L. I normally shoot at the
70mm focal length. Using the rule of thumb
for calculating magnification (magnification
= extension/focal length), at 70mm the
magnification is 12mm/70mm = 0.17x.
I set the focusing to manual or automatic
depending on the subject. If the subject is
moving (such as insect, flower, plant, droplets
on leaves) then it is better to focus manually.
If your subject is fixed you can mount your
camera on a tripod, set autofocus and use
The photos on this
page were taken using
an EF 24-70mm lens set
to 70mm and fitted with
an EF12 II extension
tube. The depth-offield is very narrow
but Rodel has used
this limitation to great
creative effect.
Above EOS 40D, EF
24-70mm f2.8L lens
with EF 12 II Extension
tube, ISO 100, f2.8, 1/40
second.
Right EOS 40D, EF 2470mm f2.8L lens with
EF 12 II Extension tube,
ISO 400, f2.8, 1/200
second.
a shutter release cable to minimize camera
shake. I prefer to use a wider aperture (f2.8 to
f4) to draw attention to only a portion of the
subject. I use selective focusing from the 9
autofocus points of my camera. If there is too
much movement in the subject AI focusing is
of great advantage.
Flash is important. I used to ignore
using the camera’s built-in flash, but after
colleagues showed me the advantage of using
flash it has now become part of my set-up. I
also use a Speedlite 580EX II with a Stofen
OmniBounce diffuser.
Both Rodel and
May-lin can be
found online at
Flickr. You can
view their galleries
at www.flickr.
com/photos/
rodjbman71 and
www.flickr.com/
photos/mayj
respectively.
For my water droplet photos I use an
EF 100mm Macro lens with an EF 25 II
extension tube and manual focus to get the
biggest, clearest droplet possible. I always
use a tripod and work with natural light.
I shoot my water drop shots indoors as
it’s usually somewhat breezy where I live,
but I have good light from large windows.
I set up the flower with the background
positioned between 6 to 12 inches behind
it, depending on the desired result.
I place the water droplet on the petal
with a syringe and adjust the background
so that I can see it in the drop. It can be
a little time consuming, even frustrating,
to get a drop to a nice shape and make
it stay in place. The droplet has to be
positioned to get an unobscured view of
the background.
Sometimes I use printed matter such
as gift wrap or greeting cards to produce
the refracted image in the water droplet.
Designs with bright clear colours give the
clearest refractions. The image will be
inversed in the water drop. I position the
background sheet upside down so that
the design shows the right way up in the
refraction. I also like to use flowers – again
the brightest coloured flowers make the
clearest images.
Another disadvantage occurs when you
use extension tubes with zoom lenses. If
you change the focal length of the lens, the
focusing distance changes as well, and you
need to refocus. You can get around this by
selecting the focal length you want to use
first (normally the longest) before focusing.
You don’t have this problem if you are
using a prime (fixed focal length) lens.
Telephoto lenses
Extension tubes work best with lenses that
have a focal length of between 35mm and
150mm. Below 35mm, you may need to
get so close to your subject to focus that it
becomes impractical. With longer telephoto
lenses, the increase in magnification is so
slight that using extension tubes may not
be useful. Canon’s 250D or 500D close-up
lenses will get you much closer.
Image quality
While Canon’s double element close-up
lenses, the 250D and 500D, are high quality
close-up lenses that have a minimal effect
on image quality, less expensive close-up
lenses can degrade image quality quite
badly. Extension tubes contain no glass and
so have little impact on image quality.
Above The
effectiveness of
adding extension
tubes depends on
two factors – the
focal length of
the lens and the
minimum focusing
distance. The shorter
the lens, and the
closer its minimum
focal distance, the
greater the level of
magnification will be
gained from adding
an extension tube.
Third party
EOS-fit extension
tubes are made by
other companies and
are less expensive
than those from
Canon. However, the
build quality can be
inferior and we have
not come across any
that are compatible
with EF-S lenses.
Canon extension
tubes maintain full
electrical contact
between the camera
body and lens, so
that you can stop
down the aperture
and, if you want to,
use autofocus. It
is possible to buy
extension tubes for
under £10, but the
catch is that they
have no electrical
contacts. You cannot
stop down your
lens and use a small
aperture as EF lenses
do not have manual
aperture rings. This
means that you will
be limited to using
your lens at its widest
aperture, unable to
increase the depthof-field.
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