SLR owners looking to upgrade lenses often must choose between their camera maker's lenses and less expensive third-party models that often aren't as good. But the solid competence of Sigma's $1,250 APO 70-200mm F2.8 EX DG OS HSM makes this lens a great compromise of high quality and good value.
Sigma's fast telephoto zoom is image-stabilized, optically strong, and sturdily built. I tried the Canon version on a full-frame EOS 5D Mark III, where the zoom range is versatile enough to handle indoor portraiture, outdoor architecture, and plenty more.
There's strong competition here from the big boys in the SLR market. From Nikon, there's the $2,400 Nikkor 70-200mm f/2.8G ED VR II and the new $1,400 AF-S Nikkor 70-200mm f/4G ED VR. From Canon, there's the $1,100 EF 70-200mm f/4L IS and $2,500 EF 70-200mm f/2.8L IS II, both built like tanks and optically superb.
The Sigma 70-200mm is best of both worlds: the wide aperture of the higher-end f2.8 models at the price of the lower-end f4 models. The sharpness isn't quite up to the standard of the in-house telephoto zooms, and you won't get things like in-camera correction of vignetting and chromatic aberration that only work with first-party lenses. But the lens is quite competitive for its price.
I shot everything from dinner parties and speeches, where I appreciated the wide aperture's usefulness in dim light, to nature and architecture scenes, where the lens' sharpness across the whole frame when stopped down came into its own.
Optics are good, with reasonable center-frame sharpness at f2.8 and terrific performance at f8. Vignetting at f2.8 is definitely noticeable, but as with sharpness, it's often mostly a nonissue: you're often shooting wide open to deliberately blur out the background. Distortion is manageable, and chromatic aberration is pleasantly low.
Shooting portraits at f2.8 is a pleasure, with nice bokeh -- the smooth blurring of out-of-focus backgrounds to keep them from being distracting.