Following my recent acquisition of an F4, I just got an SB24. It worked great except that I could not get the low light autofocus light to operate. I returned the SB24 and just bought a new one from a different source. This one exhibits the same behavior. I also have an SB23, which has no such problem. The red lines are quite bright and the F4 has no trouble, but I don't even see lines with the SB24. Is there some trick here that I'm missing or does the problem seem to be with the F4? Joel
