Although you may have said that the SB-600 must be mounted on the camera for AF-assist, I thought you also had suggested otherwise.
What I want is the SB-600 to fire those red flashes that the camera uses for AF assist when set to AF-S focus mode, and nothing more. For this I assume that the SB-600 is set to AF assist mode, the camera set to AF-S, and the built-in flash to be closed. To take the actual shot, I want no flash.
Is that all there is to it? You had made a reference to setting the built in flash to commander mode, I think (& so did Nikon support days ago), but I read on this forum that the built-in flash does nothing for AF-assist when the SB-600 is mounted (so it might as well remain closed and commander mode is immaterial). I think your context was testing the red patern from the SB-600 in a dark room, vompared top the built-in flash.
I don't even know if the built-in flash can even be used for focus assist, but its range is too short, anyway. From my checking 85 mm with my zoom, I'll be operating at around 25-30 ft from the subject.
Do I understand?
BTW, I was able to stop action at 1/200 (at least, it looks that way, before cropping). I shot everything at 1/200 (speed priority), with the ISO varied manually all over the place.
I'll check the rental prices for the 600 & 800.
I just checked DOF for 85 mm at 30 Ft. At f/1/8, the depth is 2.71 ft, at f/2.0, the dpeth is 3.02, at f/2.8, the depth is 4.23 ft. not much! I used the calculator on Cambridge in colour. NOTE: I used to use DOFMaster. The last time I went there, Kaspersky Internet Security would not let me; said it was trying to load a trojan!