I have the diopter set at -1.5 because that's the way it looks best to me. I use the split prism to focus on something that's pretty flat and has details and then set the diopter to how it looks the sharpest. Is that not correct? I have a Canon 20D and a Canon EOS Rebel GII for 35mm for my portraits and 35mm film. The Rebel doesn't have diopter adjustments and it looks pretty sharp when I focus, the 20D is pretty much the same though it does have diopter but I don't think it's changed from normal. This is the only camera that doesnt' appera correct when I look through it while set as 0. I've got film drying in my bathroom now though so I will break out my lens and check it out pretty soon. I shot something that appeared out of focus at f/2.8 while focused at infinity to see what's up with that. Also, I can't really go through the hassel of sending it back because of how much time it would take and such. Most of my work is stuff that's fairly close to me anyways.