I have this month bought a second-hand Canon EOS-1V body and have a problem with one of the Camera functions. When using the manual exposure mode, the top dial is used to set the shutter and the rear dial for the lens f/stop. The latter is not functioning and I have read through the instructions including the trouble shooting section, but cannot solve this problem. The aperture can be set by pressing the +/- button, but I want the rear dial to work properly. I am wondering if there is something that I am doing wrong and what the cause is. I have contacted the Photographic store where I bought it and will take it back there this weekend if I cannot get it to work. Any ideas what the problem is?