If you need a wide-angle lens with excellent quality this lens is one to look at. It will also save you quite a few dollars as opposed to getting a first party lens from Sony/Minolta, Nikon, Canon or Pentax.

Sigma 10-20mm 1:4-5.6 EX DC HSM review Sigma 10-20mm 1:4-5.6 EX DC HSM review

Chromatic aberration is a bit higher than in the previous version of the Sigma 10-20mm. While the ƒ/4-5.6 version, wide open at 10mm wasn't bad in the corners, the ƒ/3.5 version is fairly high in the corners (~10/100ths of a percent of frame height) at every aperture setting. Average CA performance is also slightly higher. In our testing, we were pleasantly surprised by how sharp this lens was wide open, across its focal length range. It wasn't perfect, and never got really *crisp*, but on the whole did quite a bit better than we had been expecting. At the 10mm end, the center is very sharp, but the corners get a little soft, but the corner softness decreases substantially as you move toward the "tele" end of its range, or as you stop down even a little from wide open. At 10-12mm, the corners don't really flatten out until you get to f/8, and even there, they're not quite crisp. - But they're not far off, to the point that it'll probably take a bit of pixel-peeping to see the softness anywhere at f/8. Like most APS-C lenses, the Sigma 10-20 f/3.5 shows some peripheral shading on APS-C DSLR bodies at its wide open apertures. I'm not a big fan of Sigma's lens finish (others love it), but the rubber-covered zoom and focus rings consume a significant portion of the lens. Good for: Cropped sensor shooters looking for an affordable, well-built super wide-angle zoom lens.as do all the other lenses in this comparison except the Sigma 8-16 which does not accept screw-in filters) and has a 2mm focal length advantage on the long end. D40/D5000/D3100 users note that the Nikon version does not have the AF switch you see in the photo, which isn't an issue with bodies with an AF motor (thus an AF switch), but will make full time MF impossible. You can still override things. 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. I really don't like this lens much, it could just be my copy, but I find the results hit and miss. It is capable of superb images but I find focus and exposure can be really off at times (many times). I read somewhere that it is hard to focus because of pronounced field curvature..maybe thats it. I thought I had a bad copy, but after many photos, I think it's just the way the lens is designed. I much prefer my older, clunky Tamron 11-18, believe it or not, it's much more consistent. I recommend this lens for the zoom range. The other lens I'd also recommend is the Tokina 12-24mm for the zoom range also. I don't like the Tamron 11-18mm or the Tokina 11-16mm (unless you need the speed).

Sigma 10-20mm f/3.5 EX DC HSM Interchangeable Lens Review

While we haven't tested it, the Tokina 10-17mm lens is a fisheye, in case you're not interested in rectilinear lenses.

At PMA 2009, among several new lenses Sigma announced the 10-20mm ƒ/3.5, a constant-aperture version of its ultrawide-angle zoom. The lens is slightly larger and heavier, taking 82mm filters instead of 77mm.

Sigma 10-20mm f/4-5.6 EX DC HSM Lens Review Sigma 10-20mm f/4-5.6 EX DC HSM Lens Review

This lens turned out excellent and I soon got addicted. With an UWA like this you can get shots you never thought were possible. It was decent even for indoor shots despite its rather slow and variable maximum aperture (4-5.6). All in all, a really good choice.In the short distance focusing category, the Sigma 10-20 f/3.5 turns in average performance for this lens class. I like Sigma's center-and-side-pinch lens caps. It is easy to remove the caps even with a lens hood installed. That's why it came by surprise for many when Sigma announced another UWA zoom, with the same zoom range, but a little faster this time: f/3.5 throughout the whole zoom range. The larger aperture of course means the lens itself has become larger and heavier, as well as more expensive than its slower sibling. There is also the risk of a problem that results in the lens and body manufacturers directing blame at each other. Sigma's 10-20mm f/4-5.6 EX DC Lens is, in practicality, a narrower aperture version of the Sigma 10-20mm f/3.5 EX DC HSM Lens.