It's not a particularly feature-rich lens -- aside from the manual/auto focus switch there's a distance readout window for the manual focus and focal-length indicators for the zoom ring, but that's about it. I know it's rare to have optical image stabilization in wide-angle lenses (and many manufacturers will tell you it's unnecessary), but I really would like it. If you shoot video without a rig, it's essential. Of course, this isn't an issue for Sony bodies that use sensor-shift stabilization. It's also supported by Sigma's optional USB dock, which allows you to manage and configure lenses and firmware updates.
My coarse metric for performance when shooting stills is the profanity factor, as in how often I find myself epitheting "Why are you so [expletive deleted] slow??" I don't remember cursing the lens out at all; it kept up with my primary test camera, the 7D, pretty well. This isn't a noisy lens for video autofocus, but it is a slightly slow mover in conjunction with continuous AF. The manual-focus ring has a nice feel for gradual focus, however.
|Mounts||Canon EF-S (tested), Nikon DX, Sigma, Sony A|
|Focal range||18-35mm (28.8 - 56 equivalent on Canon; 27 - 52.5 on Nikon and Sigma)|
|Aperture range||f1.8 - f16|
|Minimum focus distance||11 inches (from focal plane)|
|Angle of view||Approximately 76.5 - 44.2 degrees (depending on focal length)|
|Elements||17 elements in 12 groups; 1 aspherical with Special Low Dispersion (SLD) glass|
|Minimum length||3.1 inches|
|Maximum length||4.8 inches|
Its image quality is generally excellent. There's some aberration (fringing) on both sides at 18mm and in the center at 35mm f1.8, but at 18mm it's quite sharp in the center from wide open to f11, and as expected gets a little soft at f16; at 35mm it's sharp from f2.0 to just under f16 as well. The edge-to-edge sharpness at both ends looks good, too. Its nine-bladed aperture renders beautiful out-of-focus areas, and I didn't see any vignetting. For 35mm shooting, the company's full-frame 35mm 1.4 DG HSM lens is a little sharper, but if you need the flexibility of a zoom it's worth the convenience trade-off.
Sigma has been producing some really nice lenses, and as its PR folks will attest, they've had to pry this lens out of my possession; I really like almost everything about it. This is the type of lens that makes you feel like your APS-C body has gotten a full-frame upgrade.