The Loxia 2.8/21 ($1,499) is the third in the Zeiss series of manual focus lenses for Sony's mirrorless camera system. It covers an ultra-wide field of view when paired with a full-frame model, and a more moderate wide angle when used with an APS-C model like the Alpha 6000 ($398.00 at Amazon) . Photographers are certain to appreciate its image quality, and videographers will be happy with the manual focus ring and clickless aperture control. If you have a penchant for compact primes and prefer manual focus, the Loxia is a good choice. But Sony shooters who prefer autofocus will undoubtedly prefer the Vario-Tessar T* FE 16-35mm F4 ZA OSS ($1,249.99 at Dell) , an Editors' Choice winner, to capture the world in an ultra-wide perspective.

Design
The Loxia ($1,499.00 at Amazon)  is small at just 2.8 by 2.4 inches (HD), but heavy for its size at 13.9 ounces. The heft is due to its construction. The barrel is all metal, and the design incorporates an o-ring at the lens mount to prevent dust and moisture from entering the camera at that point. The lens uses 52mm front filters, a characteristic shared with the Loxia 35 ($1,299.00 at Amazon) and the Loxia 50 ($949.00 at Amazon) . A lens hood is included.

The manual focus ring is metal, unlike the rubber rings used on lenses in the manual focus Zeiss Milvus series for SLR cameras, and features a ridged texture. It turns about 180 degrees to move from the 9.8-inch focus distance to infinity, with a hard stop at each end. The long throw allows for precise adjustment, and there is a printed depth of field scale in meters and feet, along with markings for f/4, f/8, f/16, and f/22. With a lens this wide, scale focus is quite practical.

The aperture ring sits at the base of the lens. It's fairly narrow, but is also marked with a ridged texture. It can be adjusted in third-stop increments, or set to continuous (clickless) control using an included tool—you'll need to twist a screw on the mount to do so. Videographers generally prefer apertures without detents so that the iris can be controlled smoothly while recording, where photographers are used to lenses that click in place at certain f-stops. One of the few bad things I have to say about the Loxia is in regards to the aperture ring. It's just a bit narrow, and I found it difficult to grip and turn it without inadvertently turning the focus ring at the same time.

There's no optical stabilization. That isn't a big concern for photographers—it's not that hard to hold a camera steady when shooting at 21mm. Videographers who are interested in using the lens on a handheld system should consider pairing it with a body with built-in stabilization, like the Sony Alpha 7S II ($1,998.00 at Amazon) , to avoid jittery footage.

Image Quality
I used Imatest to see just how sharp the Loxia is when paired with the 36-megapixel Alpha 7R ($629.99 at Amazon) . At f/2.8 it scores 3,098 lines per picture height on a center-weighted sharpness test, which is much better than the 1,800 lines we like to see in an image. Performance is strong through most of the frame, though the center is markedly crisper (3,622 lines) than the edges (2,366 lines).

Stopping down to f/4 boosts the average score to 3,282 lines, and improves the edges to about 2,500 lines. At f/5.6 the lens manages 3,495 lines (with edges that touch 3,000), and peak performance is achieved at f/8—3,601 lines. Beyond that diffraction robs a bit of quality; sharpness dips to 3,376 lines at f/11, 3080 lines at f/16, and 2,257 lines at f/22.

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I also checked to see how the lens does with capturing images that are evenly illuminated across the frame. I used an Expodisc 2.0 to capture an even white image and ran those results through Imatest's Uniformity test. There is some darkening of the corners at f/2.8, about 2EV, which is noticeable. Stopping down to f/4 dropped that to a much more reasonable 1EV—slightly dimmer than the center, but not distracting. At narrower apertures, f/5.6 all the way through f/22, the corners displayed a 1.4EV drop when compared with the center of the frame.

The lens shows some distortion, though it's not drastic. You can expect about 1.2 percent, which you'll have to look for carefully to notice. Its pattern is mustache, which resembles barrel distortion at the center of the frame, but straightens out toward the edges.

Conclusions
Like the other two lenses in the series, the Loxia 2.8/21 is for manual focus devotees only. But appealing to a niche audience isn't a bad thing, and the mechanical feel of a true manual focus lens certainly trumps the electronic focus systems offered by autofocus lenses for Sony's mirrorless system. For those who appreciate it, using the Loxia nets rewards—it's incredibly sharp, shows very little distortion for a lens of this type, and is also quite compact. It's a fine alternative to our Editors' Choice, the larger (but autofocusing) Vario-Tessar T* 16-35mm F4 ZA OSS.

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