The Sony DT 16-50mm F2.8 SSM ($799.99) may be available as a kit lens with the Sony Alpha 77 II ($1,198.00 at Amazon) camera, but its fixed f/2.8 aperture and wide-angle field of view separate it from more common lenses like the DT 18-55mm f/3.5-5.6 SAM II ($79.99 at Amazon) . It's pretty sharp throughout its zoom range, but it doesn't quite measure up to some others that are available for the Sony system, notably the Sigma 17-70mm F2.8-4 DC Macro OS HSM and our Editors' Choice, the Sigma 18-35mm F1.8 DC HSM ($598.00 at Amazon) .

The lens is fairly large, measuring in at 3.5 by 3.2 inches (HD). It weighs 1.3 pounds, uses 72mm front filters, and includes a reversible lens hood. It covers a field of view which matches that of a 24-75mm lens on a full-frame camera, and its maximum aperture is a constant f/2.8 throughout that range. It can focus as close as 12 inches, which translates to a maximum 1:5 magnification ratio. That puts it a bit behind the Sigma 17-70mm ($322.18 at Amazon) , which can capture images with 1:3 life size magnification.

There aren't a lot of controls on the lens, just a manual zoom ring and a manual focus ring, both with ridged rubber finishes. A locking switch can keep the lens from zooming, which will prevent the barrel from drifting during transport or when the camera is hanging from your neck or at your side. There's no optical stabilization built into the lens; Sony includes stabilization in its camera bodies instead.

I used Imatest to check the sharpness and distortion characteristics of the lens when paired with the 24-megapixel Alpha 77 II. At 16mm f/2.8 the lens records 2,377 lines per picture height, a better score than the 1,800 lines per picture height that we use to mark an image as sharp. Our testing methodology uses a center-weights scoring method, but we do look at how the lens performs at its edges as well. Imatest shows a 1,719-line edge score at 16mm f/2.8, which is pretty good. There's some improvement at f/4 (2,623 lines), at f/5.6 (2,689 lines), and at f/8 (2,706 lines). If you want to stop down, they improve to 1,815 lines at f/5.6 and 1,940 lines at f/8.

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At 24mm the sharpness is about the same; the lens shows 2,289 lines at f/2.8 and improves to 2,657 lines at f/4. Edges are a little soft (1,735 lines) at f/2.8, but are tack sharp (2,247 lines) at f/4. At 35mm the overall sharpness is still good at f/2.8 (2,123 lines), but quality at the edges drops off quickly (1,405 lines). Stopping down to f/4 bumps the overall sharpness to 2,640 lines, and edges jump to 1,792 lines.

At the maximum zoom (50mm) the lens is again sharp in the center, which gives it a center-weighted score of 2,055 lines, but edges hover around 1,000 lines and the area of the frame between the center and outer edges is also a bit soft (1,656 lines). The lens is a lot better at f/4, with a 2,552-line center-weighted score that carries throughout the frame. Edges are still an issue, showing just 1,393 lines, and even at f/5.6 they only improve to 1,676 lines. Distortion is a nonissue through most of the zoom range, but at 16mm there's quite a bit—about 2.7 percent barrel distortion. That makes straight lines appear to curve outward, but it can be corrected via software. Lightroom includes a lens profile that will compensate for distortion with a single click.

Despite some issues with edge performance when zoomed in and distortion at the wide end, the Sony DT 16-50mm F2.8 SSM represents a significant upgrade over the more pedestrian 18-55mm f/3.5-5.6 zoom that is bundled with entry-level Sony SLRs. At $800 it's on the pricey side, especially when you can get the Sigma 17-70mm F2.8-4 DC Macro OS HSM, a lens that covers a longer zoom range and can focus at closer distances, for $500. Our Editors' Choice zoom, the Sigma 18-35mm F1.8 DC HSM, doesn't cover as much of a range, but it's impeccably sharp and captures more than twice the light as the Sony 16-50mm, for the same asking price.

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