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Photo Accessories

Speedlite Transmitter ST-E3-RT: a Radio Wireless flash transmitter


For photographers wanting to use remote Canon Speedlite flashguns with Radio transmission, rather than Optical transmission, the ST-E3-RT is the ideal solution, offering a range of up to 30 metres and control of up to five remote flash groups.

Who is it for?

Professional photographers are more frequently choosing to use portable Speedlite flashguns when working on location because they are lightweight and battery-powered. The Canon Speedlite Transmitter ST-E3-RT acts as a wireless master in the new Canon Radio Wireless flash control system and will therefore find favour among all photographers; both advanced enthusiasts and professionals working with flash and embracing the strobist movement.

The ST-E3-RT will especially be of interest to portrait and commercial shooters, though the 30m range and the ability to trigger a remote camera will also prove interesting to wildlife photographers who are looking to experiment with remote camera setups. Wedding and social photographers will also enjoy the ability to hide flashguns behind subjects or within a scene, without needing a line-of-sight connection between the transmitter and remote Speedlites.

Key features


  • Wireless Radio slave transmitter
  • Radio camera remote control shooting function
  • Dot matrix LCD display
  • Weather-sealed to match EOS-1D X
  • Powered by 2x AA batteries

Compatible with the Speedlite 600EX-RT flashgun, the ST-E3-RT is a first for the EOS System – a 2.4GHz radio transmission frequency to control Slave flashguns. This radio transmission removes two of the potential pitfalls with optical transmission, namely the limited range and the need for a line-of-sight connection between the Master and Slave. It also allows the use of up to five groups of Slave Speedlites, rather than three, with up to three flashguns in each group, for a total of 15 slaves.

Using the Radio transmission, the range is extended to around 30m and Slave flashguns can be hidden behind obstacles or subjects without fear that they may not fire. So that you know when remote flashguns are ready to fire, the display on the top of the transmitter will show a flash ready symbol when using the wireless Radio transmission settings.

When used with an EOS-1D X or EOS 5D Mark III DSLR, the radio wireless settings allow very complex flash setups with the Group Firing Mode. This mode allows you to set different flash modes for each of the five firing groups, so Group 1 and 2 may be E-TTL, Group 3 and 4 set to Manual, and Group 5 using Auto external metering with the built-in thyristor. With earlier camera models, the maximum number of groups is reduced to three and the remote Speedlites in each group will switch to E-TTL automatically.

As part of the Radio triggering functions, the ST-E3-RT transmitter can also be used to trigger the camera wirelessly. When using the transmitter mounted on either the EOS-1D X or the EOS 5D Mark III, the trigger control will be sent through the hotshoe contacts of the camera. With earlier models, the accessory cable, SR-N3 attaches to the side of the flashgun and plugs into the N3 connector on the side of the camera. This allows you to trigger a camera remotely from up to 30 metres away, without needing any further bulky accessories.

Following on from the simple radio camera triggering, there is also a Linked shooting function. Using an ST-E3-RT you can trigger up to 15 Slave cameras fitted with either Speedlite 600EX-RT or ST-E3-RT units. In this arrangement you can capture images from several different views at once. In Linked shooting, the Master flash will only trigger the camera. It will not transmit metering information to the flashguns, so these settings will need to be made on each flash individually.

Although it is compatible with all digital EOS cameras, when used with the EOS-1 Series cameras since the EOS-1D Mark III and EOS-1Ds Mark III, the extra weather sealing on the transmitter and the strengthened hotshoe mount mate perfectly to retain the all-weather performance of these cameras. The body weather sealing of the transmitter matches that on the EOS-1D X for use in a wider range of environmental conditions.

The hotshoe mount has also been modified to minimise dust and dirt on the hotshoe that may cause transmission errors. As the hotshoe lock is used, it causes the contacts to be wiped clean, preventing build-up of dirt and dust. The pressure of the locking foot has also been changed – it is now a variable pressure switch to ensure correct contact between the camera and transmitter.

Mounted on the EOS-1D X or the EOS 5D Mark III, the ST-E3-RT allows access to not just the standard flash control screen in the camera menu, but also a Flash Quick Control screen that shows all active flash settings at a glance. As with previous Speedlite models mounted on recent EOS cameras, the flash settings can be made both from the transmitter itself, or from within the Flash function settings in the camera menu.

To make settings easier to understand when using the flash rather than the camera menu, the screen is now a 172x104-dot LCD panel. This allows more information to be displayed more clearly, at any given time, and makes the menus easier and quicker to navigate.


  • 2.4GHz Radio transmission

    Not relying on an optical signal, the Radio transmission feature allows the ST-E3-RT to act as a wireless master at up to 30m and with no line-of-sight connection between it and a remote Speedlite 600EX-RT.

  • Channel Scan

    The 2.4GHz Radio transmission allows longer range, non-line-of-sight control of Speedlite 600EX-RT flashguns. To ensure the best communication and minimum interference from other radio signals, the ST-E3-RT features a Channel Scan function that will test the signal strength on each of the 15 available channels. Once completed, it will automatically set the channel with the best signal-to-noise ratio.

FLASH MODES
Auto exposure control E-TTLII/E-TTL/TTL
High speed sync (FP) Yes
Manual / output settings Yes - 1/1-1/128
Manual steps 1/3 step
Strobe / output settings Yes - 1/4-1/128
Frequency -500Hz
FLASH-RELATED FUNCTION
FE lock Yes
Flash exposure compensation Yes
Flash exposure bracketing Yes
Second-curtain flash sync No
Modelling flash Yes
Colour temperature info communication No
WIRELESS FLASH
Transmitter Yes
Transmission type Radio
Transmitter Max range approx. Indoors: 30m
Outdoors: 30m
Slave No
No. of groups 5
No. of channels 15
Remote Shutter Release Yes
AF ASSIST
AF-assist beam No
POWER SOURCE
Battery 2 x AA batteries
External power supply No
CONSTRUCTION
Dust and water resistance Yes
Mounting foot material Metal
MISC.
Custom function 8 (3 personal functions)
PC terminal No
Compatible accessories SPEEDLITE 600EX-RT
Dedicated flash bracket No
DIMENSIONS & WEIGHT
Size (W x H x D), mm 67.4 x 61.5 x 77.4¹
Weight (Excluding batteries), grams 110g
Size (W x H x D), mm ¹ Except for the dust and water prevention adaptor
* Time taken to recharge flash after full discharge using Alkaline AA batteries.
** With Compatible cameras only.