Does my Canon dRebel fully support the 600EX II-RT and ST-E3-RT?

Question

Will using a Canon T3i as a body with the 600EX II-RT & ST-E3-RT limit the transmitter or speedlite from full potential use? Does this body fully support the external equipment?

Answer 1

Does this body fully support the external equipment?

The EOS Rebel T3i/600D fully supports the capability of the Canon ST-E3-RT other than being able to only use two groups instead of the three supported by the transmitter when used with other Canon models that support 3 groups.

The Canon ST-E3-RT, however, does not fully support the capabilities of the EOS Rebel T3i/600D.

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Based on what little information the EOS Rebel T3i/600D Instruction Manual provides, it appears that Canon includes a more or less full external flash control menu under [Shooting (red) tab 1 → flash control → external flash func. setting] and [Shooting (red) tab 1 → flash control → external flash C.Fn setting]. This menu is used to control external flashes directly attached to the camera's hot shoe as well as off camera flashes controlled by either a directly connected "master" flash or by a wireless optical or radio transmitter.

There are at least three limits imposed by Canon when using the EOS Rebel T3i/600D with external speedlights controlled by using the camera's menu via the radio-based ST-E3-RT or the previous optical-based ST-E2. The first two are the case with all current Canon cameras, the other is only the case with Canon cameras released prior to 2012 (which includes your EOS Rebel T3i/600D). Each of these limits can be circumvented by using a Yongnuo YN-E3-RT transmitter instead of the Canon ST-E3-RT.

Full Group control

None of the menus built into the various Canon bodies allow for fully independent group control of external flashes via the camera's menu with a Canon controller, either the radio based ST-E3-RT or the older ST-E2. The controls on both ST units also limit fully independent group control. This, however, can be circumvented by using the Yongnuo YN-E3-RT instead of the Canon ST-E3-RT. The Yongnuo "clone" allows one to fully control each group independently of the others.

From a YN-E3-RT announcement at Flash Havoc:

Group Mode functionality is a big advantage in the Canon RT system, as it allow access to 5 groups (instead of just 3), but most importantly it allows the mixture of ETTL and Remote Manual groups used at the same time, which can’t otherwise be done without access to the Group Mode. Any group can be set to set to ETTL / Manual / External Auto / or OFF. Flash Exposure compensation (FEC) can also be set by group, which is generally much more intuitive than Canon’s old ratio selection.

Even with a compatible external flash on the camera's hot shoe controlling off camera flashes the Rebel T3i/600D can only control up to two groups. Many other Canon models allow only three groups. With the controls on the YN-E3-ST you can set five groups fully independently of each other. You can use different modes, such as E-TTL or Manual Power, for each group. You can also set each group to different FEC values (for each group set to E-TTL) or manual power levels (for each group set to manual power) without having to use Canon's A:B C ratio settings.

2nd Curtain Sync

Canon does not allow second-curtain sync when using external flashes controlled by the ST-E3-RT (or the optical ST-E2). The option is greyed-out in the camera's flash control menu. Using a YN-E3-RT the controller can be used to set second-curtain sync. When second-curtain sync has been enabled via the YN-E3-RT controller, the new setting is accurately reflected on the camera's control panel! Of course with most Canon cameras, any shutter time shorter than 1/30 second results in first-curtain sync even if second-curtain is selected via the camera's menu. But at longer shutter times it can be quite useful!

Sync speed

Canon cameras released prior to 2012 have a shortest sync speed of one stop slower than the camera's rated X-sync when using the ST-E3-RT. Even though your EOS Rebel T3i/600D is capable of 1/200 second X-sync with hotshoe mounted flashes, using the ST-E3-RT will limit you to shutter times of 1/100 second or slower. Again, the YN-E3-RT removes this limit and allows you to use the 1/200 X-sync that your camera is capable of using.

Other benefits of the YN-E3-RT that the ST-E3-RT lack are:

• A USB port that allows firmware updates to the flash controller
• An AF Assist emitter on the front of the controller
• Control Canon RT compatible flashes from the YN-E3-RT in manual mode when shooting with a NON-Canon camera.

For additional reading regarding the differences between the Canon ST-E3-RT and the Yongnuo YN-E3-RT:
Yongnuo YN-E3-RT vs. Canon ST-E3-RT
YN-E3-RT – Adds GR Group Mode for Pre 2012 Cameras!
YongNuo YN-E3-RT – Now Available!
YN-E3-RT – Adds Remote Manual for NON Canon Cameras!
Yongnuo YN-E3-RT vs Canon ST-E3-RT Speedlite Wireless Tra...

Answer 2

Will using a Canon T3i as a body with the 600EX II-RT & ST-E3-RT limit the Transmitter or Speedlite from full potential use?

Yes.

But it may not matter if you don't need those features.

Does this body fully support the external equipment?

Yes and No. It does support the equipment and is compatible, but cannot do all the features in the ‑RT system.

It is a pre-2012 body (i.e., was introduced before the RT gear hit the market), and therefore does not support all the new features that were introduced with the -RT system. Group ID codes, Gr mode (where you can individually assign groups as M or TTL and turn groups on and off), and using the flash as your shutter remote with an ST-E3-RT on-camera, etc. are not something this camera body's menus and hotshoe can do.

It can do pretty much everything you can do with the optical wireless system, though. You can still control three groups (if not five) in Manual or in TTL with ratios. And you should have HSS, TTL, and remote power control over radio.