>I think I'm missing something. I get the feeling that iTT does >not consider the individual outputs of the groups? IOW, if you >had two groups set to 0 "compensation", the shot >would be one stop overexposed? > >I always assumed it was calculating based on each group >illuminating the same subject whether it was or not. It >doesn't make sense that the exposure is set for each group >independently. With 3 groups, you could be as much as 1.58 >stops over.
No, I know from experience that images with overlapping flashes on the subject will not normally be overexposed. In fact, I usually have to increase compensation to get proper exposure.
I think I know why.
The question has been asked many times here on Nikonians and other forums as to why, when using a single flash wirelessly in TTL, it always underexposes. I think the system assumes you may have multiple flashes and that overlap and overexposure could be always be a possibility, so it underexposes each group intentionally by a stop or so.