I bought the lens a year ago for my Canon EOS 60D. Initial tests confirmed other results: at maximum aperture, in particular at 10 mm, very strong compromising sharpness in the corners, which I find downright mushy. After a year in use, it was not only the corners at full aperture, but the entire left side of the picture, the focus was unacceptable for me (found when viewing holiday photos). So for Sigma-Service posted (only purchase Occupied settled because I had no other documents). Within a week (including post 10 days) repaired under warranty. Renewed testing of the adjusted lens provided no change to the new state: weak to very weak in terms of sharpness at smaller focal length and large aperture, dimmed good imaging performance (minimum aperture 8) and longer focal lengths. The fact that the Sigma brings a strong barrel distortion and is not exactly high speed, I do not consider as a weakness, it turns out but directly from the nature of the objective and the technical data. The autofocus was always sufficiently accurate in my tests. Processing a total fine. Conclusion: for the optical power three stars, an extra star for the good Sigma Service. PS: All my purely subjective impression without any claim to universality. Update (April 2014): Here it came after a holiday the disillusionment many images just in the edge region (this time more right) again a muddy appearance that is unacceptable to me. It seems increasingly at objects that are at least about 20 meters, to attract attention. As an illustration 100% Crops from the center and the right edge of the image (ISO 100, f7.1, 1/640 s, 14 mm). Due to the weak optical power depreciation on two star.
