I just bought myself a 1DIII to use as my primary sports-shooting body. I've already got a 7D, which does a great job, but I know the focus-capture speed is better, and the frame rate is higher, and they're pretty reasonable now, plus it operates a lot like the 7D, so no huge learning curve.
Running through my various lenses with the 1DIII, I see that I'm getting vignetting with my Sigma 10-20 and 17-70 lenses. I can pretty much eliminate it by changing the aspect ratio to 4:5, and it doesn't concern me much, as it's normally used with a 70-200L, a 100-400L, or a 100mm prime, but I'd like to know if this is common? The APS-H sensor certainly contributes to the vignetting, but I'm wondering if there's something about the Sigma construction that helps create the vignetting?