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600 ex-rt Groups firing at a different time- Please help


Hello everyone,

   First time on the forum and I really appreciate the assistance. I own 5 600 ex-rt's and I have them divided as follows:


Master, 2 speedlites into Group A, 2 speedlites into Group B.


I have them all on ETTL and have double-checked to ensure all of my settings are correct. The problem I am having is when I test fire them Group A fires and then Group B fires approximately a half-second later. 


Is this normal? I have read the manual closely to verify they are on the correct settings for simultaneous firing, but I am obviously missing something.


Thank you, Bill 


Rising Star

I found your scenario interesting so I tried to duplicate it the best I could with what I had.  My test was a ST-E3-RT as the master, 1 - 600 in Group A and 1 - 600 in Group B.  Both of mine fired the test flash exactly the same time.  I did use ETTL and messed with exposure comp some but no matter what I did, they fired the exact same time.  Maybe there is a difference in our C. F settings. 


I have

C. Fn-02 set to 2 (both buttons, can't image this would make any difference anyway)

C. Fn-07 set to 0 (1/32)


I don't think any other custom functions should make a difference.  Are all your 600s set up the exact same way? 


One difference you have is the AF assist beam on the master where I don't have that of course on the ST-E3.  But I don't see how that would effect the test flash anyway


I am curious to see what your findings are.  Please keep us posted

Well I continued to test them this morning and I was still not able to find a solution. However, when i changed all of them to Group A they fired at the exact same time. Maybe it has to do with the way I test them. I normally just set them on a table and lay the two A's to the left and the 2 B's to the right. They are also next to each other. I also cleared them to ensure I had not changed the settings acccidentally, but still to no avail. 

    The other thing I noticed is when I set all of them to manual it seemed they were a lot brighter then when they are on ETTL. Is that because the sensor on them on ETTL lowers the flash strength whereas on manual they fire always at full strength unless you change the settings?

     I am doing a test shoot with them in a  week or so in a ballroom. This should give me an opportunity to see how they work in a real world situation instead of while they are on my desk.

   Its all so weird. I find it hard to believe that my 600's are the only ones which do this. 


Keif, how are you testing this? By pressing the test button by any chance? If so, it's designed to fire each group in delay of 1 second.

Diverhank's photos on Flickr

Thank you so much! Yes by using the test I am such a dumb as#.  Thanks!!


The only thing I can think of is that your slave group B flashes have gone into sleep mode and took a while to wake up? Try pressing the master test/pilot button to wake them all up before firing...

Diverhank's photos on Flickr
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