>After some tests and thinking, I think the Nikon CLS isn't too >dumb when it comes to managing multiple groups. I think it is >safe to say the flash output of a remote group is affected by >the other groups. Or the camera is smart enough to manage the >outputs of all remote groups as a whole so the final exposure >is more likely desirable. > >I covered that in the 4th post of the subject.
I read your discussion about how multiple remote flashes operate.
My results were quite different. Whenever two remote TTL flashes overlapped, the image did increase in brightness by about 0.7 stops(assuming both were set to the same power).
Here are a couple of things I have noticed:
1) Books with shiny covers are not good subjects when you are up close. The reflected specular highlights can cause the flash power to decrease unpredictably. This doesn't make a big difference, but it might partially explain why your test didn't show much brightness increase when you used two overlapping flashes.
2) It's not usually a good idea to use use TTL-BL when on the SC-28 cord. The TTL-BL equations require that the distance from the subject to the camera equals the distance of the subject to the flash. Also, TTL-BL works best when the camera and flash are colocated. The background ambient must be the same for the flash as for the camera. Bright areas in the background (a window allowing outside light for instance) from the camera position will cause the flash power to increase to try to balance with it, but if the flash is not co-located with the camera and pointed in the same direction, its power may be increased drastically trying to balance the area that the camera sees.
3) TTL on the SC-28 cord works normally, as though the flash were mounted on the camera.