Hey, Got my new DSLR yesterday: brand new D80 with 17-55mm f/2.8 lens. First thing I tried out was experimenting with DOF, as this is something my old point & shoot couldn't handle. I understand how DOF works - aperture, distance to the subject etc. So I set my camera to manual, focal length at 55mm and fiddled with f numbers and shutter time a bit. Distance to subject was variable (0.5 meters to 5 meters). Then I noticed I could just adjust the DOF (I was going for shallow) with the zoom ring in front of my lens, and any adjustments to the aperture and shutter time just had a brighter/darker photograph as a result. Which makes perfect sense of course, since those control the amount of light let in. Anyway, what I'm trying to say is that I'm confused. I thought ap. and shutter time determined the DOF. So what exactly does this zoom do to DOF? I would have figured I'd get a different DOF adjusting shutter and ap. whilst leaving the zoom alone. But all it does is make my picture brighter/darker. Can someone enlighten me please?