I've had my Sigma 17-70 2.8-4 for a couple years, and had it on a 50D then on a 7D for the last year or so. I recently bought a 1DmkIII, and was surprised to find that I now have a vignetting problem with the 1DIII. It wasn't an issue with the 50D nor the 7D.
The 1DmkIII, of course, is a 1.3x crop, as opposed to the prior 2 cameras. I have to go out to the 28mm index mark on the lens to lose the vignetting. How does this work? Shouldn't there be a greater chance of vignetting on the 1.6x crop body? Even closing down the aperture doesn't seem to matter.
What do those of you with the -H sensor use for a wide-to-short zoom? Does your lens/body combo show vignetting?