CAnon 580EX and continuous shooting

[Phuong]

C.Fn-8: Quick flash with continous shooting (0: Disable - 1: Enable)

i was wondering what this custom function on the 580EX really is, so i put my 20D on AI Servo and Continous shooting mode, JPG Fine, then plug the 580EX in, turn C.Fn-8.1 and shot 20 shots, all came out correct exposure.
i did it again, this time with C.Fn-8.0, same results.

i'm pretty confused now. Canon doesn't seem to explain very well these flash custom functions

[Jonathan Wienke]

Repeat the test, with sufficient subject distance such that the recycle time of the flash is longer than the interval between exposures. IIRC, when the flash can recycle faster than the camera can shoot, this function will have no effect, but when the flash can't fully recharge between shots (firing at near-full power), enabling the function will result in low-power flashes instead of no flashes if the flash has not fully recycled from the previous firing.