I recently purchased this lens on ebay as i was after a lens i could use in low light situations at an affordable price.
After reading reviews on here and a few other sites, coupled with the fact that it was a DG lens designed specificaly for digital cameras, i didnt think there would be a compatability issue with my 40D or my 10D.
At first this seemed to be the case but after a few test shots it became apparent that unless shooting at 40mm the camera and lens were not communicating, and although you could dial in a smaller aperture on the camera the lens was staying wide open,resulting in over exposed images.
A few more test shots at 40mm resulted in an err 01 on my 40D and a err 99 on my 10D.
The lens appears to focus and work fine at f2.8 but just doesnt like to be told to close the apperture down in anyway.
I havent seen any other posts on here regarding this issue and infact some have used a 10D with this lens no problem, so i do know if this is an isolated case or if anyone else has had this problem with this particular lens.
I contacted Sigma, but alas as it is now dis-continued they will not offer a repchipping service.
So i guess i shall just have to keep using it at f2.8 perhaps i should have spent the money on canons 50mm f1.8 instead.