9 out of 10 points and recommendedvery resistant against ghosting and flare, very sharp in the centersoft edges at 10 and 12mm unless stopped down to F5.6-8
Contrast is very good at all settings.reviewed December 10th, 2009 (purchased for $740)
The lens is very resistant to flare and ghosting, much better than the competitors. I compared it to various Nikon and Tokina super wide zooms.
AF (HSM) is accurate, fast and quiet and the build quality is very good. The MF ring is well dampened and feels comparatively precise and accurate.
Sharpness in the center is very good, the borders are also fine but the edges tend to be soft at 10mm and 12mm unless the lens is stopped down to F5.6-8.
At 17mm and 20mm the edges catch up nicely and the lens can be used wide open without problems.
All in all the Nikkor DX 12-24 or the Tokina DX 11-16 are sharper near the edges but the Sigma wins in terms of contrast, resistance against flare and ghosting and AF performance.
In comparison the AF performance of the Tokina was really a problem, especially at 16mm and the Nikon didn't autofocus very well at 12mm.
Both the Nikon and the Tokina are much more difficult to focus manually due to focus shifts when changing the focal length.
Watch out for sample variatons! My first sample of the Sigma 10-20 was decentered and had to be exchanged. The second sample is fine.