In detail: The Canon lens has a slightly larger range of focal lengths (10-22) and is by approx. 2/3 stop brighter. Looking at the distortion, so the Canon is indeed in the middle area much better, but it cuts at 10mm from significantly worse. Regarding the vignetting, the two lenses give nothing and achieve nevertheless good to very good results. The test results in terms of sharpness is excellent for both of lenses - even if the sigma is usually a little better. You can see on the chromatic aberrations of the two lenses so the Sigma has the nose slightly ahead, but also the Canon is pretty good here.
The Sigma lens is processed first class - because Canon can still cut a slice and at the speed of the auto focus, there is no appreciable difference. Both have manual intervention in the very fast autofocus and both lenses can be used only on Crop cameras (GNTB. EOS 20D, 30D, 300D and 350D).
The other alternatives in the market (the Sigma 12-24, the Tamron 11-18 and Tokina 12-24) fare worse - particularly in the area of chromatic aberrations where all clearly recognizable color edges left in the picture, although the Tokina otherwise exemplary results with delivered. That leaves the decision to take that objective to clarify the question whether the 2mm longer focal length and 2/3 stops in the exposure really justify yet very significant price difference. For me, no way, and so I came to this objective with which I am very satisfied.
