Thanks also Arnie for sharing your experience. With respect to controlling the 1/1, 1/2, 2/3, 1/3 output ratio between the built-in flash and the off-camera 360 as described by the 360's manual, I do not think it will work between the two off-camera 360's. That is, setting one 360 to 1/3 and the other 360 to 2/3 will not give you a 1/3 - 2/3 ratio between the two off-camera flashes. Both off-camera flashes might be set identically to 1/3 or 2/3 to yield a collective 3 against the built-in flash's 1 or 2, but there is no way for the camera to know that you have two wireless 360's out there(unless I'm mistaken). The two off-camera flashes operate as if only one were there, as far as I can guess.
I tried it with two 360ftz as slaves (Wireless and P-TTL) and the built-in flash as the controller, setting one 360 at 1/3 and the other one at 2/3, and it worked! I scraped my test pictures but can easily reproduce the results.
I just tried to reproduce the results in a more controlled way than the last (and first) time and I could not see a difference between 1/3 and 2/3. I guess my previous setting was not stable enough. I was replacing the flashes approximatively at the same place after changing their settings and my subject was tricky: a pale spruce top of a musical instrument with light stricking at a low angle.
Sorry for the false expectations.
I now understand that the ratio can only be between the master and the slave (or slaves as a group) as Mark had understood.
There still are two way to influence the respective output of the 2 slave flashes: their distance from the suject and neutral density filter (or gel) over one flash.
Andre
