Canon Speedlite Transmitter ST-E3-RT Review

Canon Speedlite Transmitter ST-E3-RT Review

Canon Speedlite transmitter ST-E3-RT - view showing top LCD display
Canon Speedlite Transmitter (radio) ST-E3-RT


Introduced in March 2012 the Canon ST-E3-RT is a compact radio transmitter which sits on the camera’s hotshoe and can control other RT radio wireless enabled speedlites such as the Canon 600EX ii-RT, 600EX-RT, 430EX iii-RT and even some third party speedlites such as the Yongnuo YN600EX-RT II or the YN968EX-RT.

Using a Canon ST-E3-RT as a master controller on your camera has the advantage of being much smaller and lighter than using a speedlite. As you would expect from Canon this controller supports all the features of the Canon speedlite system including Manual, E-TTL II and Multi (strobe) modes, high speed sync, first and second curtain sync, flash exposure compensation and flash exposure bracketing etc. The ST-E3-RT can control up to 5 groups and 15 speedlites using 15 radio channels and 10,000 wireless IDs.

Canon ST-E3-RT display in radio mater mode

The first thing that you notice when looking at the ST-E3-RT is that the display, menu and control layout looks exactly like that of a Canon 600EX-RT. So if you’ve used this speedlite before you’ll immediately feel right at home.

The only complaints that I have about the controller are (1) the price – it’s almost the same price as a Canon 430EX III-RT speedlite and (2) Canon have decided not to include an infra-red autofocus assist lamp. They included one on the ST-E2 optical master but I guess they think the more recent Canon cameras are much more capable at focussing in low light conditions and don’t need it. I personally don’t agree and I still miss this very useful feature and considering that the Yongnuo YN-E3-RT II retails at around a third of the price and includes a very powerful AF assist lamp I think Canon have made a mistake omitting this feature.

Guide Price

£319 / US$285 (updated 05 March 2021)

Wex (UK) / Amazon (UK) / B&H Photo (US) / Adorama (US) / Amazon (US)


The Canon ST-E3-RT Speedlite Transmitter is compatible with the Canon 600EX ii-RT, 600EX -RT and the 430EX iii-RT (basically any Canon Speedlite with an “RT” in the name). It’s also compatible with the Yongnuo YN600EX-RT II, the YN968EX-RT and the YNE3-RX receiver. This transmitter does not have optical transmission so it cannot be used with the earlier Canon 580EX II, 430EX II or the more recent 470EX-AI

Canon ST-E3-RT radio controller mounted on top of an EOS 5D camera

Canon ST-E3-RT Specification

Flash Head Tilt & Swivel

Fixed head, no swivel.

Manual Exposure

Manual / output settings: Yes – 1/1- 1/128
Manual steps: 1/3 stop increments

ETTL Exposure

Canon E-TTL/ E-TTL II with flash exposure compensation (FEC), flash exposure lock (FE lock) and flash exposure bracketing (FEB) 

Wireless Communication

Radio Wireless (RF) 2.4GHz
Uses Canon’s 2.4GHz RT radio system.
Transmitter maximum range approximately: up to 30m
No. of groups: 5 (A, B, C, D & E) up to 15 units
No. of channels: Auto, 15 channels and 10,000 wireless IDs
Master/Slave: Master only

Optical Wireless
No, this is a radio transmitter only.

Auto-Focus (AF) Assist 

No AF assist.

Front view of the ST-E3-RT Canon radio flash trigger

Other Features

High speed sync (HSS): Yes
Second-curtain flash sync: Yes
Modelling flash: Yes (fired with camera’s depth-of-field preview button)
Colour temperature info communication: Yes
Remote shutter release: Yes
Custom function: 8 (3 personal functions) 
Flash settings from camera menus (with compatible cameras only): Yes
External flash exposure sensor (S1, S2): No
PC terminal: No

Batteries & Recycling Time

Battery: 2 x AA batteries (alkaline or rechargeable Ni-MH)

Build Quality

Dust and water resistance: Yes
Mounting foot material: Metal
Size: 67.4 x 61.5 x 77.4mm (2.7 x 2.4 x 3.0″)
Weight: 110g/3.9oz (excluding batteries)


Yongnuo YN-E3-RT II – this is the updated version of the Yongnuo radio transmitter that looks and functions exactly the same as the Canon controller but costs much less. This version will now work with some of the more recent Canon speedlites and cameras. The earlier version has a few compatibility issues with canon equipment released after 2016.

Canon ST-E3-RT Manual

Canon ST-E3-RT manual download pdf format
Canon ST-E3-RT Manual pdf format (opens external link to Canon official website)

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Page last checked and updated 05 March 2021