I just picked up a 24mm 2.8 Canon S.S.C. lens and the aperture is behaving a strangely. When I use it on my A-1 body, the aperture closes down when I take the shot, but doesn't open up again until I cock the shutter. On my FTb body, the aperture closes down as soon as I mount the lens on the body. As I adjust the f-stop ring, the lens closes down or opens up as if I'm using a depth of field preview. Any idea what's up? Thanks.