I'm no pro, but it sounds like your background flash (with its white background) is causing the TTL sensor in your camera to shorten the flashes of the TTLed flashes (the SB26 & 28). TTL flash duration is determined by the amount of light hitting the TTL sensor "at" the film plane. The flashes fire until the correct amount of light is detected for your settings, then the flashes stop firing. If that "correct" amount comes from another light source, the TTLed flashes will still be shut down. Don't know what your background slave flash setting was, so this is just a guess. Perhaps others more knowledgeable will provide you with a more accurate answer than my guess -----Original Message----- >------------------------------ > >Date: Sat, 21 Nov 1998 06:10:45 -0500 >From: [EMAIL PROTECTED] >Subject: Flash puzzle [4] > >This one has me stumped. >I did an indoors setup portrait with SB26 and SB28. I set the flashes >for TTL and my 6006 for TTL and Aperture Priority (something I have >rarely if ever do). For a number of shots I used a small slave flash for >a background light, which was on a slave sensor - that is, it would go >off when it saw the other flashes go off. Since the foreground and >background were both white I bracketed exposure compensation and flash >compensation from .5 to 2 stops overexposed. > >Now the above was my intention and I think I did it right. I could have >made a mistake, of course. I could have forgotten to set slow sync. > >We all saw the flashes going off. But when I got the slides back they >were COMPLETELY dark. Here's the bizarre part. In those shots I used it, >the background flash went off and did light the background but >sillouetted the completely dark subject. > >It seems to me that there must somehow have been a mixup timing and that >the flashes went off when the shutter was closed, then the shutter >opened when there was no flash (As I say, I may have forgotten to set >slow synch). But generally if it is a sycronization problem at least a >band of the photo will show. Even stranger and more puzzling: if it was >an out of synch problem how is it that the slave flash - which works by >coming on when the other flashes fire - showed in those pics I used it >on while the flashes that set it off are not giving off any light at >all? > >This is one for the t.v. show STRANGE PHENOMENON. > >Thanks for any help on this, >Richard Davis > >------------------------------
