9 out of 10 points and recommendedexcellent color correction, very robust, smooth mechanicslens cap difficult to attach with lens hood attached
I tested this lens with my Canon 400D and had direkt comparison with a Nikon 18-70 lens.reviewed July 24th, 2007 (purchased for $489)
The Sigma did beat the Nikon lens in many respects but I was not completely satisfied.
The Sigma 18-50 provides very sharp images in the middle part of the picture all the way up to f/2,8.
The outer parts of the picture, though, seem to be of worse quality than the Nikon which, in contrast, is not 100% sharp in the middle (f/2,8 - 4)
My Sigma seems to perform better at 18-30mm than at 50mm (weird!?) where the images are a bit blurry towards the edges (f/2,8 - 4)
Best results with aperture set at approx 6,7 - 9,5 - sharp images right to the edge.
Closing the aperture to 13 and down to 22 does worsen the image quality again.
Other positive impressions: No ghosts on nighttime shots in a city with so many bright light sources.
Edges darken very little when the aperture is set at 2,8.
Very good overall performance for a Zoom lens! Highly recommended.