EOS 40d with 550ex flash

Hi, just wondering if anyone has had a similar problem when using a 550ex on a 40d.
When using in one shot mode, the flash works fine, however once the drive is set to 3fps or 6.5fps the pilot light on the 550 goes out and the flash does not fire at all (not even one frame).
I also have a 420ex which does not exhibit this problem and happily fires away.

Your 420EX will fully charge and fire at 3-6.5 fps? I'd check that again

I have no doubt the 420EX will shoot at 6.5 fps if the amount of power used for each shot is low enough. The 550EX should, too.

At 1/8 power, my 580EX II will do 5 fps for 10 shots. This is enough power for 20 feet at f/5.6 ISO 400.

I have not heard of the behavior you describe with the 550EX. Check to see if there might be a custom function on the flash that allows for continuous shooting.

Curtis N wrote in post #6602061
I have no doubt the 420EX will shoot at 6.5 fps if the amount of power used for each shot is low enough. The 550EX should, too.

At 1/8 power, my 580EX II will do 5 fps for 10 shots. This is enough power for 20 feet at f/5.6 ISO 400.

I have not heard of the behavior you describe with the 550EX. Check to see if there might be a custom function on the flash that allows for continuous shooting.

Well how about that. With a fresh set of Eneloops, cranking the ISO up a bit, and using f/2.8, I can take about 5 rapid fire shots in a row with my 20D/420EX. No go if the batteries aren't fresh though.

Strange problem for sure. I just put my 550EX on my 20D, turned them all on, got a red light on the flash, moved the 20D to continuous and I was able to shoot flash (the flash would not keep up but it did fire several times).

My 550 and 40D work fine together, but i've never tried doing that.

Sorry - can't simulate your problem.
Could possibly be Flash Custom Function settings. Here are my CF settings for the flash:
F1 - 1
F2 - 0
F3 - 0
F4 - 1
F5 - 0
F6 - 0

Maybe batteries? It's amazing what a fresh set of batteries will do.

The only thing you should be experiencing when switching from ONE SHOT to AI SERVO, is the beam being emitted from the flash will not emit on AI SERVO.

Thanks samnz,

Turns out it was a bad batch of rechargeables, works fine with all other sets.
I was starting to worry as the flash unit has served me well the past few years.