Carl Zeiss Biogon T*2,8/28 ZM ($1,087 on Amazon). A compact wide-angle lens with classic field of vision when used in conjunction with full-frame digital rangefinders like the Leica M (Typ 244). You can use it with mirrorless cameras like the Sony Alpha 7R ($1,654.95 on Amazon). This is a great alternative to Leica Elmarit M 28mm f/2.8 ASPH. Although the Biogon may not be as compact as the Leica equivalent, its edge performance is better if its aperture is a little narrower. However, it is half as expensive.
It measures 2.5 by 2.1 inches (HD), is 8.1 ounces and can support 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. You will need to pay an additional $84 for the Zeiss Biogon metal hood.
The Leica lens comes with a clip-on cap. The Biogon's physical characteristics are undisputed. The barrel of the Biogon is made entirely from metal. Its focus ring has excellent ergonomics. The operation is very fluid and it's tightly sealed so that the unit won't move unexpectedly.
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. While the Zeiss can focus closer to 0.75 meter (0.5 meter), you will need to estimate your focus distance if working close to 0.7 meters. Live View is also available, but Leica rangefinder cameras do not offer coupled focus beyond 0.7 meters.
Imatest was used to test the sharpness of the lens using the full-frame Leica M Typ 240 ($4,999.99 Amazon). Distortion is minimal—it's less than 1 percent, which isn't noticeable in field conditions. The Biogon achieves this at maximum aperture. We are looking for lenses that produce more than 1,800 lines per image height. It produces 2,213 lines at f/2.8 thanks to its excellent mid- and center sharpness. The frame's outer edges are disappointing, showing just 712 lines.
The edges will be sharper if the aperture is reduced to f/4. This improves the quality of the lines to 1,580 lines. Overall, the sharpness increases to 2,806 lines. The Biogon's sharpness is at f/5.6. It scores 3,135 lines in the frame, with edges close to 2,100. 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.
Leica Elmarit M also had edges that were less than the center. At f/2.8, they exceeded 1,300 lines. They improved to 1,879 lines with f/4. And at f/2.8, the edges reached 2,700 lines. While the Leica lens costs twice as much as the Zeiss model, its optical performance at similar apertures is superior.
For rangefinder shooters, the Carl Zeiss Biogon T*2,8/28 ZM offers a reliable wide-angle choice. The Leica Elmarit M 28mm f/2.8 AsPH is a better choice. In terms of sharpness the difference is smaller than at f/2.8. It's still not cheap at $1,100, but it isn't as expensive as the Leica Elmarit, which costs $2,200. You can focus closer and have more control over your aperture with the Biogon. The Biogon is a good choice if you are able to live with a lens not performing at maximum aperture.