The Carl Zeiss Biogon T* 2,8/25 ZM ($1,201 list)( at Amazon) is a wide-angle lens for use with M-mount rangefinder cameras. If you don't have a Leica digital or another 35mm rangefinder available, the lens can also be paired with mirrorless cameras like the Sony Alpha 7. Its field of view is appealing to shooters who feel that a 21mm lens is just a bit too wide and that a 28mm is not wide enough.

Like the entirety of Zeiss's ZM line, this Biogon has a metal lens barrel with a manual focus ring with a long throw, tight tolerance, and smooth operation. The focus ring has a small finger grip to make focus more comfortable, and the aperture ring can be set from f/2.8 all the way down to f/22 in third-stop increments. The 25mm lens measures 2.8 by 2.1 inches (HD), weighs 9.2 ounces, and supports 46mm front filters. There's no lens hood included, but you can add if desired. Zeiss sells two hoods that are compatible with the lens, one circular and one square; each sells for $84. There's a printed depth of field scale on the barrel, with marks down to f/16; the wide-angle field of view is well suited for scale focusing.

Unless you're using the lens with a Live View camera, you'll need to guess distances when focusing to its minimum 0.5-meter setting: Leica rangefinders only offer rangefinder coupled focusing to 0.7 meters. They also lack 25mm frame lines, so you'll have to use the 28mm lines and frame loosely or invest in an external finder. The Leica M8, which uses a smaller APS-H image sensor, has a set that approximate the 24mm field of view, which is close enough to use a 25mm lens without an external finder.

I used Imatest to check the distortion characteristics of the lens when paired with the full-frame Leica M (Typ 240)($2,969.00 at Amazon). It shows about 1.1 percent barrel distortion, which is just barely noticeable in field conditions. At f/2.8 the center-weighted sharpness is an impressive 2,213 lines per picture height, much better than the 1,800 lines we require for a photo to be called sharp. There's some drop-off at outer edges of the frame—they show just 1,070 lines. That's a low enough number to show some visible fuzziness.

But narrowing the aperture to f/4 largely takes care of that issue. The center-weighted score jumps to 2,806 lines and edges improve to a decently sharp 1,580 lines. At f/5.6 the lens approaches the 3,000 line mark and edges top 2,200 lines. You'll get the best performance at f/8, where the lens manages an amazing 3,122 lines with edges that hover around 2,600 lines.

If you're in the market for a wide-angle rangefinder lens, the Carl Zeiss Biogon T* 2,8/25 ZM is a good performer and a good value. It's a little less than half the price of the Leica Elmar-M 24mm f/3.8 ASPH., and captures about twice the light at its maximum aperture. The optics of the Biogon aren't perfect: You'll have to stop down a little bit to capture images that are crisp from corner to corner and there is just a slight bit of distortion. But even at $1,200 it's a bargain compared with Leica lenses, and its compact design and smooth manual focus action can't be matched by less expensive SLR lenses of similar focal lengths.

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