Radio control
Technique Radio-controlled flash
Radio control
Last year, Canon launched the Speedlite 600EX-RT – its first flashgun with wireless
radio communication, rather than the infrared communication of previous models. Is
it possible to add radio communication to earlier models? Gerard Maas investigates.
With the introduction of the Speedlite 600EXRT and the Speedlite Transmitter ST-E3-RT,
Canon combines the flexibility and accuracy
of the E-TTL II flash exposure system with
the reliability and performance of radio
Previous Speedlites with a wireless option
use infrared pulses to control and fire slave
units. This means the slave unit must be in lineof-sight of the master unit. This optical infrared
system works over a distance of only about 15
metres between master and slave and there can
be communication problems in bright sunlight.
With the new RT system, two-way radio
communication between the master unit
and slave units is used to transmit settings
and trigger the flash exposure. Radio
communication increases the working range
to about 30 metres, improves reliability when
working in sunny conditions and does not
require line-of-sight between the master and
slave units.
The radio control operation of the Speedlite
600EX-RT is only fully compatible with EOS
cameras introduced in 2012 – these include the
EOS-1D X, 5D Mark III, 6D and 650D. We assume
that later models will also be fully compatible.
One documented limitation for older bodies is
that the flash synchronisation speed is reduced
by one stop. For example, the EOS 5D Mark II
has a normal synchronisation speed of 1/200
second. However, the maximum shutter speed
with the RT system is 1/100 second. The master
unit (Speedlite 600EX-RT or ST-E3-RT) will show
a warning icon if the shutter speed is too fast.
The new five-group control mode (Gr), where
each group can be given an independent control
mode (E-TTL, Ext.A, Manual) or turned on/off, is
only available on the latest cameras. If you try
to use this mode with older camera models, the
master unit will revert to basic E-TTL the first
time the shutter is released.
The documentation also mentions that highspeed synchronisation (HSS) is only available
for the latest cameras. However, models like the
EOS 5D Mark II and 600D seem to work fine in
HSS mode. Older models, like the EOS 400D,
show a black band at the bottom of the frame.
More important, of course, is that the radio
control system of the Speedlite 600EX-RT is not
compatible with any previous Speedlite. The
600EX-RT can be switched to wireless infrared
operation so that it works with other Speedlites,
but that loses the benefits of radio control. This
article looks at some of the accessories which
help you get round this limitation.
Above and right Radio
control flash makes
location photography easy.
The radio communication
ensures a reliable
triggering even when the
off-camera Speedlite is
not facing the transmitter.
This portrait was taken
in an open field, against
the setting sun. The Tuff
TTL radio trigger (see
page 43) preserves
the full E-TTL exposure
calculation, creating a welllit image with the same
simplicity as when the
Speedlite is on-camera,
but with the added quality
of an off-camera light
Wireless and radio have different meanings in photography
Two heads are often better than
one in flash photography. However,
getting both units to fire at the
same time and with the right power
required cables and adapters in the early days
of Speedlite photography.
It was in 1998 that Canon introduced its
first wireless flashgun – the Speedlite 550EX.
However, the term ‘wireless’ can be a little
confusing. In the UK, ‘wireless’ is an old name
for a radio set which receives broadcast
programs from the likes of the BBC and
commercial stations.
In photography, wireless also means
communication without wires, but not
EOS magazine January-March 2013
necessarily by radio waves.
This is the case with the Speedlite 550EX.
The wireless communication is by optical
transmissions – pulses of infrared radiation. It is
a one-way communication, from the master unit
to the slave.
The Speedlite 600EX-RT, introduced last
year, was the first Canon flashgun with radio
communication. This is two-way – the master
and the slave units can exchange information
with each other.
Canon registered a patent for radio flash in
2010. It has taken so long to arrive because of
restrictions on frequencies which are acceptable
in different parts of the world.
Above The Speedlite
600EX-RT. It uses the 2.4
GHz radio band which
is accepted in most
countries. However, the
Speedlite 600EX – without
radio communication – is
available for countries
where the 600EX-RT
cannot be licenced.
EOS magazine January-March 2013
Technique Radio-controlled flash
Hähnel Tuff TTL wireless flash trigger
Speedlite 600EX-RT system
Left The Speedlite 600EX-RT is fully compatible in radio
control mode with the EOS-1D X, 5D Mark III and 650D.
It can also be used in radio mode with most other EOS
cameras, though with a slightly reduced feature list.
Also available is the Speedlite 600EX, which is a similar
flashgun, but without the radio control mode.
Below The Speedlite Transmitter ST-E3-RT offers radio
control only; it is not compatible with earlier Speedlites.
If you are thinking of buying a new Speedlite,
we’d recommend the 600EX-RT unit – even if it
is your only Speedlite, or you have one or more
earlier models. On its own, you will not be able
to make use of the radio control option – or the
wireless infrared, for that matter – but you will
be ready for future developments. There are
likely to be more radio control units in the future.
In the meantime, you could consider adding
the Speedlite Transmitter ST-E3-RT. This is a
master unit normally used in the hotshoe of the
camera and it can control up to 15 Speedlites
with radio transmission. However, it is just as
good controlling a single off-camera Speedlite
600EX-RT. Put this Speedlite into a large
reflector or softbox and you have an excellent
portable light source which can be used indoors
or out.
If you have a Speedlite with infrared wireless
control – or no wireless option at all – take a look
at the flash accessories on the following pages.
They give you the option of upgrading your
existing Speedlite to radio control.
Price guide Speedlite 600EX-RT: £679.99.
Speedlite Transmitter ST-E3-RT: £309.99.
Master unit
A Speedlite or other
device which can
control the firing and
power output of other
flashguns by infrared or
radio signals. A
Speedlite transmitter
offers all the master
controls without an
integral flashgun. The
built-in flash of some
recent EOS cameras can
act as a master unit.
Slave unit
A Speedlite which can
be controlled remotely
by a master unit. Some
Speedlites can be
used as a master or
slave unit; some only
offer a slave function;
some cannot be used
as part of a Speedlite
wireless system, but
can be used remotely
with one or more of the
accessories featured
on the following pages.
It is usually possible
to have multiple slave
units controlled by one
master unit.
Left The design of the Tuff
TTL transmitter is focused
on ease of use. There are
three controls – on/off,
test and a button to select
high speed sync (HSS)
or second curtain flash
The Hähnel Tuff TTL is a wireless TTL flash
trigger that operates with radio signals.
The transmitter is attached to the camera
hotshoe. The receiver is attached to the foot
of the Speedlite. When you press the camera
shutter button, radio signals are sent from the
transmitter to the receiver. The result is an offcamera flash with the same features and ease
of use as if the Speedlite were attached to the
camera. On-camera flash-related features, such
as flash exposure compensation (FEC) and flash
exposure lock (FEL) continue to work, letting you
adjust the operation of the remote flash from the
Additional remote Speedlites
Tuff TTL supports any number of additional
Speedlites in one setup. Each Speedlite requires
a receiver unit (available as optional extras).
When multiple E-TTL or E-TTL II units are
used, they will all fire at the same power. In this
case, all flashes should be pointing towards the
subject for the best effect. This can be useful in
cases when one unit does not have sufficient
An interesting use of two or more Tuff
receivers is to set secondary Speedlites in
manual power mode. This technique can
be used to light backgrounds or other static
subjects for which the exposure does not vary
from one frame to the next. Use the manual
mode (M) on the Speedlite after connecting it to
the trigger and use the Speedlite controls to set
the required output.
Price guide Hähnel Tuff TTL transmitter
and receiver sells for around £95. Additional
receivers are around £50 (see
When using the camera
‘External Speedlite
Control’ menu there are
certain limitations to
the options that can be
used when the Tuff TTL
transmitter is attached
to the hotshoe.
Working normally
w Flash exposure
w Flash exposure
w E-TTL II metering
w Flash firing [enable/
Can be set but does
not do anything
w Zoom setting (needs
to be set manually on
the Speedlite)
Does not work
w E-TTL mode (leave in
E-TTL II mode)
w Shutter sync.
(select on the Tuff TTL
transmitter unit)
w Wireless settings
(the Tuff TTL units use
their own wireless
communication system)
Speedlite at ground level
With the infrared (IR) communication system
used by previous Speedlites it was very difficult
to work in bright light outdoors. Sunlight
contains a lot of infrared radiation. This is seen
as ‘noise’ by the IR receptors, making it difficult
for transmissions from the master unit to be
read accurately by the slave units. The radio
communication of the RT system eliminates this
problem, providing reliable E-TTL II exposure
even under the harsh sun of the Mediterranean
Using a Speedlite off-camera outdoors poses a
new set of challenges. The way light falls on a
subject has a logic and a reason. To achieve the
best results when using off-camera flash, try to
position it so that the light mimics the position
and qualities of the sun at a particular time of
day – for example, low and golden evening light.
Left To create the smooth highlights in the water, this
image was shot with the EF 70-200mm f2.8L USM lens
at maximum aperture, which gave a shutter speed of
1/4000. In High Speed Sync (HSS) mode, the faster the
shutter speed, the shorter the effective flash range. The
key to a successful photo in this situation was to bring
the flash as close as possible to the subject (above).
EOS magazine January-March 2013
Above A Tuff TTL receiver
unit – this attaches to
the base of a Speedlite.
Several receivers can be
used in multi-flash setups.
Speedlite menu
High speed sync in sunlight
Left An assistant can
be more useful than a
lighting stand, moving
the light around at your
camera. The working range is over 200 metres.
If you add an optional Tuff Studio Light Cable
you can also use the system to trigger studio
flash units – though without the advantage of
TTL flash exposure metering.
Left When using a
Speedlite off-camera,
make sure no direct
light reaches the lens.
This will create flare and
probably fool the camera
into underexposing
the subject. Here, an
attachment has been
used to shield the lens
from the flash.
Left The leaves on the ground give away the autumn
season. This is a time of the year where the sun is low
in the sky, producing warmer directional light. On an
overcast day, you could reproduce that golden autumn
sunlight by adding a CTO filter (tungsten white balance
correction) to the Speedlite and placing it at ground level
towards the side. This creates vibrancy in the colour of
the fallen leaves and creates a warm side light on the
dog. The result resembles the mood of a late autumn
afternoon with the sun going down towards the horizon.
EOS magazine January-March 2013
44 |45
Technique Radio-controlled flash
Hähnel Viper wireless group flash trigger
Far left Hähnel Viper
Transmitter. A Speedlite or
Tuff TTL can be fixed to the
pass-through hotshoe on
top of the transmitter.
Left The Viper receiver
with hotshoe for a
c The Hähnel Tuff TTL (previous page) allows you
to fire more than one Speedlite, but all at the
same power. The Hähnel Viper takes this one
stage further. Full manual settings of up to three
groups (A, B, C) of Speedlites allow you to take
creative control of the light in the scene. Each
group can contain one or more Speedlites.
The Viper radio communication facilitates
this control by centralising all the settings in
the transmitter attached to the hotshoe of your
EOS camera. From this unit you can individually
change the power of each group. All the
Speedlites belonging to a group will then fire
at the given power setting. One of the groups
can be studio flash units if you want to combine
Speedlites and studio flash. (The studio flash
power must be set on the studio flash units.)
The Viper sender unit has a full pass-through
E-TTL contact. Using this feature, you can attach
a Viper transmitter to the camera hotshoe and a
Speedite on top of it. The pass-through feature
means that the Speedlite will operate as if it
were attached directly to the camera hotshoe.
In the meantime, remote Speedlites fitted with
Viper receivers are controlled by the Viper
transmitter at distances over 100 metres. An
unlimited number of receivers will work with one
You can attach a Tuff TTL transmitter to the
Viper transmitter to combine the benefits of both
systems – TTL triggering plus group control. This
could provide an economical alternative if you
want to continue using your existing Speedlites
while saving for a move to radio control with
multiple Speedlite 600EX-RT units.
Price guide Hähnel Viper transmitter and
receiver sells for £159.99. Additional receivers
are £59.99 (see
PocketWizard’s MiniTT1, FlexTT5 and AC3
The Viper system is
compatible with all
recent Speedlites.
w 580EX II
w 430 EX II
Older Speedlites can
still be used with ‘M’
(manual) mode on
the transmitter and
manually setting the
power on the Speedlite.
In this case, the Viper
acts as a remote trigger.
The Viper transmitter
and receivers each run
from two AA batteries
with a working life of
around 120 hours. The
Viper transmitter has
a mini USB socket for
software upgrades or
an external 5 volt power
The LCD on the Viper
transmitter is backlit,
indicating groups A, B
and C on/off, together
with flash power output
EOS magazine January-March 2013
Above PocketWizard
MiniTTL transmitter which
attaches to the camera’s
AC3 ZoneController
The PocketWizard
TTL system offers
a third unit, the AC3
This connects to the
on-camera MiniTT1
Transmitter or
FlexTT5 Transceiver
and enables the independent power and mode
setting of up to three groups of Speedlites.
For each group, the AC3 provides a switch
that can set the group to E-TTL or Manual mode,
or turn it off completely. A responsive analog
wheel lets you set the dial to the desired power
setting for the corresponding group.
The power of a group firing in E-TTL
mode can be controlled using flash exposure
compensation of -3 to +3 stops in 1/3 stop
increments. The exposure compensation is
calculated based on the theoretical ‘correct’
exposure provided by the E-TTL algorithm in the
camera. When a group is set to manual mode,
the -3 to +3 stop scale becomes the absolute
power values for the Speedlite.
Price guide PocketWizard MiniTT1
transmitter sells for around £150. The FlexTT5
transceiver also sells for around £150. The AC3
ZoneController sells for around £62.
Speedlites in groups
Multiple flash
The Hähnel Viper is not a TTL device – it
gives you radio control over three groups of
flashguns using the power dial on the Viper
transmitter to adjust the flash power output
level of the Speedlites in each group. A
flashgun manual override enables you to set
the Viper to manual, allowing the Speedlites
to determine the power. Digital Channel
Matching eliminates the risk of interference
from other wireless products within range.
There is a feeling among many photographers
that you need more than one Speedlite to
take good portraits. While not strictly true, it
certainly helps to have at least a main light
and a background light for indoor portraits.
When working with multiple Speedlites it is
best to start with a single light and then add
the second or additional units, one Speedlite
at a time. The AC3 controller makes this easier
by providing an on/off mode for each channel.
With a flip of your finger you can switch each
light on independently and tune its power by
making an exposure and checking the results
on the camera’s LCD.
Left and below Here three Speedlites arew set on
Viper receivers, operated by a Viper transmitter on the
camera hotshoe. One Speedlite, attached to a Lastolite
Ezybox, was set to group A at 1/4 power setting. The
other two were both set to group B to fire at 1/8 power
and were fitted with a blue filter for a night effect.
Above Speedlite attached
to a Flex TT5 with extender
PocketWizards have a long tradition of
manufacturing excellent radio triggers for
the professional photographer and advanced
enthusiast needing the highest level of control.
The PocketWizard’s E-TTL compatible system,
called ControlTL (Control the Light), consists of
the MiniTT1 and FlexTT5 units.
The MiniTT1 is a lightweight transmitter that
takes the E-TTL signal from the camera hotshoe
and converts it to radio signals that are sent to
the receiver.
The FlexTT5 is the receiving side of the
system. It features a hotshoe to attach a
Speedlite. FlexTT5 units can also act as both a
transmitter and a receiver (called a transceiver).
As with the other E-TTL enabled radio
systems, once the transmitter-receiver
communication is established, the camera
‘thinks’ that it has a flash connected to the
hotshoe and most E-TTL features are fully
Third party radio trigger systems use this
communication to trigger all remote units,
making them participate in the pre-flash stage
of the E-TTL flash exposure evaluation. The
evaluative through-the-lens (E-TTL) system of
EOS cameras makes this possible because it
calculates the flash exposure based on the actual
amount of light contributed by the pre-flash of all
Left Here a metallic wall
made a nice reflective
corner. Colour gels
were placed on two
Speedlites, positioned
on the ground, pointing
towards the corner.
A third Speedlite was
placed inside a Lastolite
Ezybox to create a small
pool of light that would
fall on the model’s face,
but not wash out the
background. All the
Speedlites were in E-TTL
mode and had a FlexTT5
EOS magazine January-March 2013
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