The Carl Zeiss Biogon T* 2,8/28 ZM ($1,087 list) is a compact wide-angle lens that delivers a classic field of view when paired with a full-frame digital rangefinder like the Leica M (Typ 240). It can also be used (via an adapter) with a mirrorless camera like the Sony Alpha 7R. It's an affordable alternative to the Leica Elmarit-M 28mm f/2.8 ASPH.. The Biogon isn't quite as compact as its Leica counterpart, and its edge performance suffers unless its aperture is narrowed a bit, but it sells for about half the price.

The Zeiss measures 2.4 by 2.1 inches (HD), weighs 8.1 ounces, and supports 46mm front filters. It's a bit bigger than the Leica Elmarit—it measures 1.8 by 2 inches, weighs 6.3 ounces, and uses smaller 39mm filters. The Leica lens includes a clip-on hood, but you'll have to spend an extra $84 to get the metal hood for the Zeiss Biogon. There's no arguing with the physical qualities of the Biogon. Its barrel is all metal and its focus ring is ergonomically excellent. It's tight, so it won't drift unexpectedly, but very smooth in operation.

Other differences between the Zeiss 28mm and the Leica Elmarit include the aperture ring—the Zeiss goes from f/2.8 to f/22 in third-stop increments, but the Elmarit's minimum aperture is f/16 and the ring is set to half-stops. The Zeiss focuses a bit closer (0.5 meter), but you'll need to guess the focus distance when working closer than 0.7 meter, or use a camera with Live View, as Leica rangefinder cameras only offer coupled focus to 0.7 meter.

I used Imatest to check the sharpness and distortion characteristics of the lens, using the full-frame Leica M (Typ 240) as the test body. Distortion is minimal—it's less than 1 percent, which isn't noticeable in field conditions. We look for a lens to do better than 1,800 lines per picture height using a center-weighted measurement of a standard SFRPlus test chart, and the Biogon does that at its maximum aperture. At f/2.8 it delivers 2,213 lines thanks to excellent center and mid-way sharpness. But the outer edges of the frame are very disappointing; they show just 712 lines.

Narrowing the aperture to f/4 improves edges to a more respectable 1,580 lines and the overall sharpness to 2,806 lines. At f/5.6 the Biogon is sharp from corner to corner, scoring 3,135 lines across the frame with edges that approach 2,100 lines. And at f/8 it delivers it best performance—3,194 lines across the frame with edges that record about 2,550 lines per picture height. The Leica Elmarit-M also showed edges that were weaker than the center; at f/2.8 the edges topped 1,300 lines; they improved to 1,879 lines at f/4 and were a fantastic 2,700 lines at f/2.8. The Leica lens is twice the price of the Zeiss, but its optical performance is better at comparable apertures.

The Carl Zeiss Biogon T* 2,8/28 ZM is a solid wide-angle option for the rangefinder shooters. It's not quite the equal of the Leica Elmarit-M 28mm f/2.8 ASPH. in terms of sharpness, but if you stop it down a bit the gap between the two lenses is less apparent than it is at f/2.8. At close to $1,100 it's not a budget lens, until you look at the $2,200 sticker price that accompanies the Leica Elmarit. The Biogon also offers the ability to focus a little bit closer, and boasts more precise control over aperture. If you can live with a lens that isn't a perfect performer from edge-to-edge at its maximum aperture, the Biogon will serve you well.