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One 600EX-RT added a 600EX II-RT flash firing 1 sec apart not together when triggered by ST-E3-RT


Slave 600EX-RT set to CH A and slave 600EX II-RT set to CH B when triggered by Master ST-E3-RT. Flash CH A fires first then 1 sec. later CH B fires. can not get then to fire together. ST-E3-RT not connected to camera.

How do fix to fire together or maybe it is user error.



How is the ST-E3-RT the master if not on the camera?   Since both versions of the 600 series can use radio wireless, why not have the ST-E3-RT on your camera?  You can then have both flashes in the same group.  Or in different groups if you'd like to control them independently.


Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers

Thank you for your input. The ST-E3-RT is on the camera. Taken off for testing. When in the same group the both fire as expected, together. I do not understand why in different groups, the A group fires and the B group delays fire for about a sec.

What settings do you have in each group?  Perhaps one is set to first curtain and the other to second curtain?


Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers

Thank you for your input. I do not see on the screen a way to set up first and second curtains. I do not know what that even means. Also, I would have had to do this on both speedlites. When I switch the speedlites making the other A and the other B the effect of the delay is the same. The B group is delayed by 1 sec. All on screen information between the 2 speedlites looks the same.


If you are pressing the test button on the ST-E3-RT, then the expected behaviour is to trigger each group in sequence. Te idea being that you can see if a specific group is triggered or not. It was more of a problem when using optical wireless, but the behaviour is the same when pressing the test button when using radio. 

If you are using E-TTL, the way the system works is to get each group of lights to send out a pre-flash, so with two groups there would be two pre-flashes. Then the camera looks at the pre-flash metered results for each group and works out the appropriate power for A and B groups, then instructs both groups to fire at the correct power when the shutter is open. 

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