The Leica APO-Summicron-M 90mm f/2 ASPH. ($3,995) is a short telephoto lens for Leica M rangefinder cameras. It's quite sharp wide open, and enters into incredibly sharp territory when stopped down a bit. Its design is pretty compact when you consider its aperture and focal length, and the all-metal barrel with a convenient integrated hood is just what you'd expect from a Leica lens. Saying that it's not inexpensive is putting it lightly, but in this case you get what you pay for. If you're on a budget and want a lens in this focal range, consider the Zeiss Tele-Tessar T* 4/85 ZM ($987.00 at Amazon) . But, even at its asking price, the APO-Summicron is worthy of being called our Editors' Choice.

The Summicron  is finished in black anodized aluminum, measures 3.1 by 2.5 inches (HD), and weighs about 1.1 pounds. That's on the heavy side for a rangefinder lens, but positively tiny when compared with an SLR lens that delivers comparable performance, like the Zeiss Otus 1.4/85 ($4,490.00 at Amazon) for Nikon and Canon cameras. The Zeiss opens up to f/1.4, capturing twice the light as the Leica, but it measures 4.9 by 4 inches and weighs 2.7 pounds.

Like all M-mount lenses, the APO-Summicron 90mm is a pure manual focus lens without any fancy features like image stabilization. The focus ring occupies a good portion of the barrel, is finished with a ridged texture for better gripping, and is very smooth when turned. There's a printed depth of field scale with markings for f/2, f/5.6, f/11, and f/16. It's useful when shooting at narrower apertures, but the long focal length makes zone focusing a difficult prospect. The physical aperture ring has full-stop markings from f/2 through f/16, but can be set in half-stop increments. The aperture is an 11-blade design, which helps to maintain circular out-of-focus highlights when the lens is stopped down.

The minimum focus distance is 3.3-feet (1 meter), which is typical for a rangefinder lens of this focal length. Shorter lenses like the Summilux-M 50mm f/1.4 ASPH. ($4,395.00 at Amazon) can focus to 0.7-meter with rangefinder coupling. If you want to work closer, the Macro-Elmar-M 90mm f/4 ($3,650) is available—it can focus to about 0.8-meter on its own, and supports 1:2 magnification when paired with the Macro-Adapter-M ($690).

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I used Imatest to check the sharpness that the 90mm manages when paired with the full-frame 24-megpaixel Leica M-P ($5,447.16 at Amazon) . At f/2 the lens scores 2,449 lines per picture height on a center-weighted sharpness test. That's better than the 1,800 lines we use to call an image sharp. It maintains that level of detail through most of the frame, and even though the outer third is a bit weaker in resolution, it still shows 1,971 lines there.

At f/2.8 the score improves to 2,970 lines, and even the edges of the frame do better than 2,500 lines. At f/4 the resolution improves to 3,288 lines, and it peaks at 3,446 lines at f/5.6. Diffraction sets in at f/8 and the score dips to 3,350 lines, but the lens still resolves a lot of detail at f/11 (2,950 lines) and f/16 (2,408 lines). There's no visible distortion to speak of. The Zeiss Tele-Tessar is sharp in its own right, but it's never quite as sharp as the Leica lens—it peaks at 3,271 lines at f/8—and more importantly, it only captures a quarter of the light at its maximum f/4 aperture compared with the APO-Summicron's f/2 setting.

Aside from the money required to call the Leica APO-Summicron-M 90mm f/2 ASPH. your own, there's nothing to complain about with the lens. The maximum f/2 aperture provides excellent control over depth of field, and the lens is very sharp from edge to edge, even when shot wide open. The manual focus action is very smooth, to the point where the lens is a pleasure to use with any M camera, and the integrated retractable lens hood is always available when needed. There are budget alternatives available in this focal range, including the aforementioned Zeiss Tele-Tessar and Leica's own Summarit-M 90mm f/2.4 ($2,350), but if you can afford it, there's no reason not to choose the APO-Summicron, which is why we're making it our Editors' Choice.

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