I'm playing with 17-40 f/4 and thought, "what if I duplicate setting for auto mode in manual mode"? I take a shot (indoor) with auto mode - photo came out 1/60, f/4, not sure what default ISO was I change to "M" mode, pop up the flash, same set up, I left ISO at 400 ... resulting photo was darker. I definitely missed something "Av" does not like 1/60 and f/4 ... again, I'm missing "something". What is auto mode doing that I'm not doing in "M" or "Av"? Thanks.