I love so much about these new flashes....I am using them on wedding and even portrait work....I have the off camera flash
as a key and use the on camera for control and fill light (with a bounce card). I previously used the 580ex 2 on camera and
a qflash off camera. I am having problems during entrance and aisle shots where there is fairly fast action....the flashes are just not keeping enough for me to squeezed maybe two shots off during an entrance....this is with the flashes both on ettl with a 1000 iso setting and maybe f stop of 5.6...even in a fairly small venue...you just have to wait at least 2-3 seconds before you are ready for the next flash. When I use the 600 on camera and my quantum off camera...it is definitely better, but still not great. I power them with fresh nimh cells and use the canon battery packs also....and it still is not enough...I think the delay is being caused by the radio signal between the remote and on camera flashes as the slave tells the master it is
ready to fire.
Anone else experiencing this?
I believe I have run into what you are describing and found "my" work around to the issue.
At the time that I ran into this I had 3 off camera flashes going (none on camera, using Canon's remote to fire the flashes). And all three flashes were set to eTTL with various power settings for each flash set on the remote (using the new 5-group setting, not the old style ratios).
Anyway, what I believe I ran into is that one of the flashes was set so far away that it was having to push a lot of light resulting in long recycle times for it. And so, even though the two other flashes were doing their job of lighting the scene I was being forced to wait for the 3rd flash to finish recycling before all three flashes could fire.
I have taken four steps to solve this behavior:
1) I make sure I only turn on (on the remote) those flashes that I really need to light the scene. That way if one of the flashes can't keep up, it won't be holding up the recycle times of the other flashes.
2) Custom Function 6 set to 1. Turning "quick flash" on means that the flashes are allowed to fire even if it hasn't finished recycling.
3) Custom Function 12 set to 0: Using both internal and external power sources to recycle the flash to reduce recycle times.
4) Using only Eneloop batteries for the fastest recycle times.
Of the above, I believe #1 is what really solved the problem for me. By not having one flash hold up the entire set, I get quicker / more reliable flashes. The other steps just help improve the recycle times.
I forgot to mention one more thing.
If one of my flashes is being used as a back light, hair light, accent light, etc, then eTTL doesn't really work for that scenario anyway. And so it's important to put that flash into manual mode. This gives correct exposure for that light, but it also avoids the scenario I described above where it might cause the entire set to be slow to recycle.