I'm a little confused about lenses and their circles of coverage. I plan to use a 6x6 roll film back on a view camera. Since I want to use movements I need a lens that covers slightly more than the 80mm (or so) diagonal of the film. Howe ver, if a lens covers more than the diagonal, won't part of the image be cropped off, effectively making my standard lens more like a telephoto? Or are the dif ferences so small relative to the film area that they aren't worth worrying abou t? In order to simplify my lens selection, are there any "rules of thumb" governing how much image circle coverage beyond the film area I'll need in order to allow movements? If the camera allows, for example, a 50mm shift do I simply look for a lens that covers 50mm beyond the film area?