The Sigma APO 70-200mm F2.8 EX DG OS HSM ($1,259) is a less-expensive professional alternative to similar lenses from Canon, Nikon, and Sony. The stabilized 70-200mm f/2.8 zoom is the go-to lens for many an event shooter, and getting one for under $2,000 is an appealing prospect. For the most part, the Sigma 70-200mm delivers solid performance, but it doesn't offer the impeccable image quality that you'll get from our Editors' Choice Canon EF 70-200mm f/2.8L IS II USM ($998.95 at Amazon) .

The APO 70-200mm ($430.00 at Amazon)  is available for Canon, Nikon, Sigma, and Sony cameras, but because it's an older lens it's not available for the Sigma's mount conversion service. It measures 7.8 by 3.4 inches (HD) and is heavy at 3.2 pounds. There are a couple of toggle switches on the lens barrel: one to change between automatic and manual focus, and the other to adjust the image stabilization mode. It can be turned off, put in Mode 1 for standard shots, or put in Mode 2 for shots where the camera pans along with a moving subject during an exposure. The lens has a narrow manual focus ring and a wide zoom ring. It includes both a hood and tripod collar, and its front element accepts 77mm filters.

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I used Imatest to check the sharpness of the 70-200mm when paired with the full-frame 36-megapixel Nikon D810 ($1,996.95 at Amazon) . At 70mm f/2.8 it scores 2,395 lines per picture height on our standard center-weighted sharpness test, which is well in excess of the 1,800 lines we use to mark a photo as sharp. But edge performance suffers, with the sharpness dropping to 1,386 lines at the periphery of the frame, and there's strong (2.4 percent) barrel distortion. Stopping down to f/4 improves the center-weighted score to 2,998 lines, and edges are a more respectable 1,628 lines. At f/5.6 the lens is sharp from edge to edge, scoring 3,390 lines across the frame with edges that approach 2,400 lines. It's even better at f/8—3,637 lines on average with edges that top 3,000 lines—and at f/11 the overall sharpness score is just a little bit higher, while edges top 3,300 lines.

At 100mm the distortion goes away, and sharpness at f/2.8 improves to 2,714 lines, but edge sharpness is still a little weak at 1,640 lines. Stopping down to f/4 boosts the overall score to 3,287 lines, with tack sharp edges that show 2,231 lines. The lens just gets better as you stop down: 3,590 lines at f/5.6, 3,711 lines at f/8, and 3,623 lines at f/11.

There's about 1 percent pincushion distortion at 140mm, and the lens shows its sharpest results at f/2.8—3,003 lines using the center-weighted metric with edges that fall just shy of 2,700 lines. The lens gets better as the aperture is narrowed: 3,490 lines at f/4, 3,629 lines at f/5.6, 3,673 lines at f/8, and 3,569 lines at f/11.

Distortion stays steady at 200mm, but sharpness drops off dramatically. At 200mm f/2.8 the lens shows just 1,628 lines using our center-weighted method, with edges that are just 1,030 lines. You'll want to stop down to f/4 when zoomed all the way in if the light allows it. That will improve the overall score to 2,500 lines, but you'll still have to deal with fuzzy 1,355-line edges. The overall sharpness is better at f/5.6 (2,895 lines), but edges only sharpen by about 100 lines. You'll need to set the lens to a narrow aperture for the best performance—it's great at f/8 (3,211 lines average, 2,103 lines at the edges) and at f/11 (3,370 lines average, 2,614 lines at the edges).

The Sigma APO 70-200mm F2.8 EX DG OS HSM isn't an optically perfect lens like our Editors' Choice Canon EF 70-200mm f/2.8L IS II USM, but it isn't nearly as expensive. If you're willing to sacrifice some sharpness and distortion control in order to save some money, though, it's a solid option. If you shoot with a Sony camera you'll also get images with more detail with the Sony 70-200mm f/2.8 ($799.99 at Amazon) , but we can't speak to Nikon shooters, as we've not yet been able to get an AF-S Nikkor 70-200mm f/2.8G ED VR II ($2,399.95) in for review. Some more recent Sigma lenses, like the excellent Sigma 18-35mm F1.8 DC HSM ($598.00 at Amazon) for APS-C cameras have offered more performance than you'd expect for your dollar, but this Sigma zoom performs just in line with its budget-minded price point.

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