Sigma has been on quite a run lately, producing camera lenses with ambitious apertures and impressive edge-to-edge sharpness. The 50mm F1.4 EX DC HSM ($499 direct)($599.95 at Amazon) is an older design, and not quite up to the company's recent standards. It's sharp in the center, but edges are a bit soft, even when the aperture is narrowed. The lens is available for Sigma, Nikon, Canon, Pentax, and Sony cameras, and it doesn't offer a significant price advantage over its competition. Our Editors' Choice 50mm lens is still the Nikon AF-S Nikkor 50mm f/1.4G($406.95 at Amazon), and is the clear choice if you're considering this lens for a Nikon system; but if you shoot with another camera system, you may want to consider this Sigma lens.

The lens measures 2.7 by 3.3 inches (HD) and weighs about 1.1 pound. It's got an internal focus motor and a big 77mm front element. The lens can focus as close as 17.7 inches, which is in line with the other 50mm f/1.4 lenses that we've tested. A reversible petal-style lens hood and a soft carrying case are included. There's no optical stabilization system, which is also typical for this type of lens; Sony and Pentax owners will benefit from the in-camera stabilization that those cameras provide. Alpha shooters will want to consider this as an alternative to the Sony 50mm f/1.4, which uses a screw-drive focus system that is noticeably noisier than the Sigma's internal focus motor. Sony cameras that use full-time Live View for fast video autofocus will benefit from this, and if you have an APS-C body like the Alpha 77($700.00 at Amazon), the lack of edge sharpness that we saw on a full-frame camera isn't a concern.

I used Imatest to check sharpness when paired with the full-frame Canon EOS 6D($1,999.99 at Amazon). At f/1.4 it delivers impressive sharpness at the center areas of the frame, but edges are very soft. Our evaluation looks at a center-weighted score that considers the entirety of the frame; the cutoff for an acceptably sharp photo is 1,800 lines per picture height. The lens does better that, notching 1,959 lines on the test, but outer row of test squares is downright blurry at 838 lines. It's a disappointing result, especially when you consider that the Canon EF 50mm f/1.4 USM($349.00 at Amazon) managed a comparable 1,874 lines at f/1.4, with an edge score of 1,341 lines using the same test camera.

Stopping the lens down improves the score marginally; at f/2 the overall score is 2,140 lines, and at f/2.8 it improves to 2,173 lines; edges are around 1,000 lines at both of these settings. Narrowing the aperture to f/4 improves sharpness to 2,317 lines with edges that land just shy of 1,200 lines. Edge performance finally gets to an acceptable level at f/5.6; the overall score is 2,472 lines there, with edges that hover around 1,650 lines. At f/8 the lens sings; the overall score is 2,600 lines and edges top 2,100 lines. But the Canon lens gets sharper faster. It hits 2,466 lines at f/4 with edges that resolve 1,750 lines; at f/5.6 its sharpness is rated at 2,739 lines with ultra-sharp edges that resolve 2,321 lines. Our Editors' Choice Nikon lens is even better; its sharpness is 1,955 lines at f/1.4, with edges that are just shy of 1,800 lines. The Sigma shows 1.5 percent barrel distortion, which is just enough to mention—straight lines are going to show a bit of an outward curve in your photos, but it's easily corrected in software. Both the Nikon and Canon 50mm f/1.4 lenses show 1.6 percent.

On a full-frame camera, the Sigma 50mm F1.4 EX DC HSM is a bit of a disappointment. Imatest shows that it's quite sharp in the center, but the edges just can't keep up. How often this affects real-world performance will depend on your photographic style. If you like to frame in-focus subjects towards the center of the frame, the shallow depth of field that you'll get when shooting at wider apertures perfectly disguises this shortcoming. And if you've got an APS-C camera, the unsharp edges are going to be cropped out of your photos due to the smaller image sensor size. Sony shooters, especially those with APS-C cameras, should take a close look at this one as it offers an internal focus motor, and Pentax shooters who don't want to drop $800 on the weather-sealed DA* 55mm f/1.4 should also consider this as a less-costly alternative. But Canon shooters are better off with the 50mm f/1.4 USM, and if you're rocking a Nikon D-SLR you'll be happy to know that the AF-S Nikkor 50mm f/1.4G is an excellent performer. It impressed us enough to earn our Editors' Choice award.

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