The Sigma 19mm F2.8 DN ($199 direct) is a wide-angle prime lens that's available for Sony E-mount cameras in the NEX and Alpha families and Micro Four Thirds cameras from Olympus and Panasonic. Due to the different sensor sizes in those bodies its field of view varies based on which version of the lens you buy; the NEX version (which we tested) acts like a 28.5mm lens on a full-frame, and the Micro Four Thirds version is closer to a 38mm. A 28mm on a full-frame camera is a classic wide-angle field of view, but the narrower 38mm angle edges closer to a standard-angle design.
Regardless of which version you buy, you'll get the same compact 1.8 by 2.4 (HD), 5.6-ounce lens; only the mount differs. The barrel is smooth metal that's cool to the touch. The smoothness actually makes manual focus a bit of an odd experience; it's a strange departure when compared with most lenses which feature a textured ring over the manual focus control. It can focus on objects as close as 7.9 inches, supports 46mm threaded filters, and is available in black or silver. A reversible hood and a soft carrying case are included with the lens.
I used Imatest to check the sharpness of the lens when paired with the APS- C Sony Alpha 3000. At f/2.8 it scores 2,045 lines per picture height on our center-weighted test, which is better than the 1,800 lines that we use to call an image sharp. The edges are a bit soft, just around 1,550 lines, but that's typical of compact wide angles. Its edges are still better than those captured by the Sony 16mm f/2.8 prime lens for the NEX system.
Stopping down to f/4 brings up the overall score to 2,105 lines, but doesn't do much at the edges. At f/5.6 we start to see some sharpening there; the overall score is 2,185 line and the edges hit 1,720 lines. Edges are at their best at f/8 (they approach 1,900 lines), but the overall sharpness drops just a bit to 2,165 lines due to some loss of sharpness at the center of the frame. Distortion is a minor issue; the 19mm shows 1.4 percent barrel distortion, which is just slightly noticeable in field conditions. It's something that's easy enough to fix in software if it's detracting from a shot.
We tested the lens on a Sony camera, but Micro Four Thirds shooters will benefit from the smaller sensor: The soft edges that we saw in our tests will be cut off and the lens should provide more even sharpness from edge to edge at wider apertures. But if you've got the money, you're better served with the Olympus M.Zuiko Digital 17mm f1.8, which has a more ambitious aperture and a better manual focus ring. Neither lens has image stabilization; most Olympus bodies have that built-in, but most Panasonic and all Sony NEX bodies lack it. For a wide-angle like this it's not crucial for stills, but it does go a long way for video use.
The Sigma 19mm F2.8 DN is a good lens for mirrorless cameras, but it's not an outstanding one. We haven't yet tested the Sony 20mm f/2.8 for NEX cameras, which is noticeably smaller but also $150 more expensive. The 19mm is light and compact in its own right, and a good value for any shooter who is a fan of that focal length. Micro Four Thirds owners have more options in the 19mm focal range, including the excellent Olympus 17mm lens, an ultra fast (and expensive) 17.5mm f/0.95 lens from Voigtlander, and the Panasonic 20mm f/1.7; they all capture more light than the Sigma, but can't match it on price.
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