The Sigma 17-70mm has a DxO Mark Score of 15. This makes it the 5th best APS-C zoom lens tested on the Canon EOS 7D. However if you look at the scores in detail, for sharpness it ranks number 3, ahead of any canon APS-C lens. This does exclude all of the immensely good lenses designed to cover full frame 35mm but they generally have a price tag to match the larger format. The score of 15 overall and of 9 P-Mpix for sharpness makes this a very serious contender. Distortion and vignetting at 0.4% and 0.7EV are at the lower end of the range of scores in this group, transmission differs from the stated value by just under 0.5EV which is on a par with other lenses of this type and chromatic aberration is well controlled, better than most.