The Voigtlander Ultron 21mm F1.8 ($1,149) captures an ultra-wide field of view when paired with a full-frame rangefinder or mirrorless camera, and also manages to capture a lot of light. When set to its f/1.8 aperture, its center sharpness is excellent with some softness at the edges of the frame. It can also lock on to subjects just a half meter (about 20 inches) away, which makes a shallow depth of field possible. When stopped down, the edges sharpen considerably, which is a must for landscape shooters. Its an excellent value, especially when compared with the $7,650 Leica Summilux-M 21mm f/1.4 ASPH. 

The Ultron ($1,149.00 at Amazon)  can focus as close as 0.5-meter, which is beyond the 0.7-meter capability of most rangefinder cameras. If you're pairing it with the Leica M (Typ 240) ($2,969.00 at Amazon) you can use an EVF or Live View to confirm focus when you move in closer, and you won't have any concern about the limitation when using a camera with full-time Live View like the Sony Alpha 7 . If you're using the lens with a film rangefinder or a body without Live View like the Leica M Monochrom ( at Amazon) you'll just have to guess at the focus when you get closer to 0.7-meter.

It's a rangefinder lens, so the Ultron is manual focus only. Its construction is all metal, with a large knurled focus ring and a physical aperture ring with half-stop clicks from f/1.8 all the way down to f/22. The focus ring turns smoothly, but it's appropriately tight. There's a printed depth of field scale on the barrel with markings for f/1.8 and f/4 through f/11 at full-stop increments. The lens is on the large size; it measures 3.6 by 2.7 inches (HD), weighs 14.5 ounces, and supports 58mm front filters. The metal lens hood is built into the barrel. It's noticeably bigger than Voigtlander's compact Color-Skopar 21mm F4 (1.1 by 2.1 inches, 4.8 ounces), but the Ultron captures more than four times the light at its widest aperture.

I used Imatest to check the sharpness and distortion characteristics of the lens when paired with the full-frame Leica M (Typ 240). At f/1.8 it manages a score of 2,150 lines per picture height on a center-weighted sharpness test. That's better than the 1,800 lines that we require to call an image sharp, but performance is not even across the frame. The center third is tack sharp (3,012 lines), but the middle third is on the soft side (1,559 lines) and the outer edges are fuzzy (529 lines).

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Stopping down to f/2 doesn't improve things, but at f/2.8 the average score jump to 2,541 lines. The center (3,510 lines) and middle third (1,892 lines) show a lot of detail, but the outer edges (617 lines) are still a bit muddy. At f/4 the average score jumps to 3,006 lines, with outer edges that hit 1,095 lines. If you're shooting for sharp edges, you'll be happy with the results at f/5.6, they show 1,782 lines with an overall average of 3,274 lines. The lens is at its best at f/8—its average score is 3,128 lines and even the very outer edges top 2,200 lines. The Ultron shows more detail from edge to edge than the Zeiss Biogon T* 2,8/21 ZM ; its edge resolution at f/11 lags behind that of the Ultron set at f/8.

The lens is extremely well corrected for distortion, it shows none at all. But it does show purple color fringing in high contrast areas. Whether it's tree branches against a sky or light coming in through window panes, it's evident. The effect lessens as you stop down, but it's still there at f/4. It's easy enough to fix in Lightroom—I found that dialing in a setting of 4 on the Defringe tool eliminated even the worst instances—but is a concern if you don't like to edit images. In the first image of Grand Central Terminal, the purple has been removed in Lightroom, but the crop above shows how it looks without editing. This is a tough situation for almost any lens, but the Leica Super-Elmar-M 18mm f/3.8 ASPH. captured the image, under identical conditions, without showing any sort of color fringing.

If you're in the market for a wide-angle lens for a rangefinder or mirrorless camera, the Voigtlander Ultron 21mm F1.8 is an excellent way to go. Its center is very sharp, even wide open, and most of the frame shows a lot of detail at f/2.8, with edge-to-edge crispness available at f/5.6. The lens is an absolute bargain when compared with Leica's 21mm Summilux, which costs more than $7,000 and has similar light-gathering capability. It's bigger than similar lenses that capture a comparable amount of light, so you may opt for the Voigtlander 21mm Color-Skopar or the Zeiss C Biogon 4,5/21 ZM ( at Amazon) if a compact design is more important than a wide aperture.

Thanks to Photo Village, Voigtlander's U.S. distributor, for loaning us this lens for review.

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