>Max, > >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. >
Thanks for your comment.
I noticed the specular reflection in the initial tests so in the second batch of the tests I tried to avoid them by arranging the camera-subject-flash angles. I originally shot just the wall and the results were similar.
In the tests, I changed the mode on the flash to TTL (no BL) when shooting with the SC-28 connection.
I will do some more tests to investigate this further.