I once owned 4 Canon F1s, and tested the shutter speeds on all of them. Although the speed dial cranks up to 1/2000/sec, NONE of them had actual speeds higher than 1/500. I think I recall that you needed some sort of accessory to use those higher speeds, one that replaced the viewfinder and hooked into the body through that little door on the front to the left of the lens mounting breech. If you were shooting at F/2.8 and 1/000sec or faster, you were overexposing your film and increasing your grain.

Pete Gomena