Originally posted by pbo ...and I never noticed any kind of pre-flash
Ditto here. When I use either 360 or 540 mounted to my K20D and shoot in P-TTL mode, and I don't notice any pre-flash and usually the exposure is spot-on, although I have the flash compensated at +0.7.
I know the technical description of how P-TTL works does say there is a pre-flash followed almost instantaneously, by the secondary camera-directed flash, yet I have not seen any unusual amount of closed-eyes on my subjects so far.
Lately I've been playing with these two flashes together in Manual Mode in reduced intensity, triggered wireless by the on-board flash of my K20D, with/without diffusers, and bouncing off the walls and ceiling. I've gotten to a stage where I usually get the exposure within one stop the first time.