Leica's Summilux-M 50mm f/1.4 ASPH. ($3,995) is a familiar lens to many rangefinder photographers. It covers a standard-angle field of view, a bit tighter than the moderate wide-angle captured by another fan favorite, the Summicron-M 35mm f/2 ASPH.. The Summilux is a fine performer, capturing crisp images at its maximum aperture and getting better and better as it's stopped down. It's a solid, but expensive, choice to pair with your Leica rangefinder or mirrorless camera. If you can live with an f/2 optic, our Editors' Choice, the Zeiss Planar T* 2/50 ZM, is a fine budget alternative.

Design
The Summilux is a compact, heavy lens. It measures 2.1 by 2.1 inches (HD), weighs 11.8 ounces, and supports 46mm front filters. It's made from anodized aluminum and available in black or silver, but the silver version costs more—$4,250. A third version of the lens, finished in black chrome, sells for $3,950, but has a slightly different design that omits the focus tab and built-in hood, and reduces the filter size to 43mm. If you like the look of older Leica lenses, it's an alternative, though I prefer the functionality of the model with the integrated, collapsible hood.

If you do opt for the standard version of the lens, you'll find the focus tab quite useful. It juts out from the focus ring and is curved to fit your finger. The lens can be focused from 27.6 inches (0.7-meter) through infinity. The focus ditance is marked in feet and meters, and a corresponding depth of field scale has shows depth of focus at f/2, f/2.8, f/4, f/8, f/11, and f/16.

The aperture ring sits between the focus ring and the collapsible hood. It can be adjusted from f/1.4 through f/16 in half-stop increments. There are 9 aperture blades, and unlike some more modern lenses they are not rounded. When you shoot at f/1.4 or f/2 you'll enjoy smooth out-of-focus highlights behind a scene, but when the lens is used from f/2.8 through f/5.6, the blades form a distinct octagonal shape, and out-of-focus highlights reflect that. At f/8 through f/16 the aperture is once again fairly circular.

Image Quality
I used Imatest to check the performance of the Summilux when used with the 24-megapixel Leica M (Typ 240). At f/1.4 the lens hits the mark for acceptable sharpness, scoring 1,843 lines per picture height on a center-weighted sharpness test. The lens does much better in the central third of the frame (2,514 lines) than it does at the midparts (1,465 lines) or edges (1,189 lines), so you'll want to keep your subject fairly centered when shooting wide open and use depth of field to mask the softness that the lens exhibits as you move away from center.

At f/2 the Summilux improves to 2,048 lines averaged across the frame, but edge quality is about the same. The center resolution jumps to 2,935 lines and the crispest area extends a bit further out. If you're in want of a lens that's sharper from edge to edge at a wide aperture, and don't need an f/1.4 lens, consider instead the inexpensive Zeiss Planar T* 2/50 ZM or the clinically perfect Leica APO-Summicron-M 50mm f/2 ASPH..

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At f/2.8 the Summilux starts to really shine. The average score jumps to 2,731 lines, with a center that hits 3,400 lines and edges that top 2,000 lines. It improves again at f/4, showing 4,200 lines in the center and 2,800 lines at the edges for a weighted average of 3,450 line. The trend continues at f/5.6 (3,686 lines) and you get the sharpest images at f/8 (3,704 lines)—in both cases the edges top 3,100 lines. Diffraction causes a slight drop in image quailty at f/11 (3,227 lines) and a more significant one at f/16 (2,649 lines).

I used an ExpoDisc to shoot flat gray images with the Summilux that can be analyzed for even illumination using Imatest's Uniformity tool. At f/1.4 the Summilux has a noticeable vignette around the edges of the frame. The sides are about 2EV dimmer than the center and corners lag behind by 3EV. It's less of an issue at f/2—sides show only a 1EV drop, but the corners are still noticeably dim, 2EV behind the center. From f/2.8 onward illumination is even at the sides. Corners show a 1EV drop at f/2.8 and f/4, which is barely noticeable in the field, and a negligible 0.5EV dip at narrower apertures.

Barrel distortion, which is generally an issue with fast 50mm designs—the Sony Carl Zeiss Planar T* 50mm f/1.4 for Alpha SLRs shows 2.2 percent, for example—is not a problem here. The Summilux records about 0.7 percent barrel distortion, which is negligible in the field.

Conclusions
The Leica Summilux-M 50mm f/1.4 ASPH. isn't the newest lens on the block, but even after a decade plus, it's an excellent performer. It controls distortion, captures photos that are very crisp in the center at its widest apertures, and gets very sharp from edge to edge when stopped down a bit. The sides are a little dim at f/1.4, but aside from that, there's not a lot to complain about. It's been the go-to fast-50mm option for Leica shooters for some time, and is still an excellent choice for fans of f/1.4 glass. If you can live with a lens that's a stop slower, consider instead the Zeiss Planar T* 2/50 ZM, which earns Editors' Choice honors based on its performance and value—it's less than one-quarter the price of the Summilux.