I tried out my newly purchased 24-70 yesterday in a room where are retirement party was being thrown. The room was lit by recessed lighting and had a window that spanned the entire width of the room with vertical blinds pretty much closed. Even though the blinds were closed, the 2:00 sun was enough to light the room fairly well for people to see but would have been considered dim for a camera I would imagine. I was playing around with the ISO and cranked it up to 2500 to see what the results would be. I was surprised that at f/2.8 in Aperture Priority I was getting shutter speeds as slow as 1/50. I would have thought that it would have been quite a bit faster or am I missing something?