Lens adjustment for Canon EOS Digital?

I have a Canon EOS Digital camera (8 mp XT version). For legal purposes, I need to take photos close to what the eye actually sees. It has a 1.6X focal length magnifier. I have been told that the lens needs to be set on 50 or 55mm but this is for 35mm SLR's. My lens on my camera is the stock one (18-55). What does it need to be set on?