The Sony Carl Zeiss Sonnar T* FE 55mm F1.8 ZA ($999.99 direct) is the first standard-angle prime lens for Sony's full-fame mirrorless camera system. Its maximum f/1.8 aperture isn't as sexy as the more standard f/1.4, but it makes up for slightly less light gathering capability with incredible sharpness and a compact design. The only minor quibble is a lack of optical stabilization, but most prime lenses in the 50mm range aren't stabilized. It's a great lens, with no distortion, but its asking price is a bit higher than comparable lenses for full-frame SLR systems.

The Sonnar measures 2.8 by 2.5 inches (HD) and weighs about 11.2 ounces. Its barrel is metal, with a large manual focus ring, and like the Alpha 7 and Alpha 7R it's sealed against dust and moisture. The front element isn't overly large, it's surrounded by a 49mm filter ring. The lens hood is a petal style, and is reversible so it won't take up extra room in your bag when not in use. The lens can focus on objects as close as 19.7 inches (0.5 meter), so it's by no means a macro. But working that close at a wider aperture will create quite a shallow depth of field, and if you work at f/1.8 you'll also be able to separate your subject from the background when they aren't that close to the lens.

I used Imatest to check and see how well the lens performs on the 36-megapixel Alpha 7R. At f/1.8 it's already incredibly sharp, bettering the 1,800 lines per picture height that we require for an image to be sharp by close to 1,200 lines. Impressively, the edges of the image are nearly as sharp as the center, even at f/1.8. At f/2.8 and f/4 it hovers around 3,300 lines, and at f/5.6 and f/8 it increases to about 3,700. It's not quite as sharp on the 24-megapixel Alpha 7 (at f/1.8 it manages 2,800 lines, but just passes the 3,000 line mark at its best). Distortion is negligible; if you shoot JPG there's none, and Raw images show less than 1 percent of the barrel variety.

The Sony Carl Zeiss Sonnar T* FE 55mm F1.8 ZA would be a fine lens on any camera system. That it's designed for a mirrorless full-frame sensor, shows very little distortion, is compact, and incredibly sharp is a testament to the quality of its optical design. There's very little bad to say about the Sonnar, other than it's a bit more expensive than a typical 50mm f/1.4 SLR lens. But those lenses typically show some softness at the edges at wide apertures, display a bit more barrel distortion, and are a bit larger. The 55mm F1.8 is an example of a lens that's well worth its asking price, and is deserving of our Editors' Choice award.

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