There was a time, back before zoom lenses were commonplace, when the standard kit lens for a 35mm SLR camera was a fast 50mm lens. Today most D-SLRs ship with a 18-55mm f/3.5-5.6 kit lens, which can't match the optical quality or light-gathering capabilities of a classic 50mm prime lens. Sony's 50mm f/1.4 Prime Lens ($449.99 direct)SEE IT is an important photographic tool in its D-SLR lineup, both for owners of full-frame and APS-C camera bodies. On the former, the lens delivers a classic field of view that can be used to capture many different types of photos. Famed street photographer Henri Cartier-Bresson did most of his work with a 50mm lens.

When used on an APS-C camera the lens delivers a 75mm field of view, which makes it more of a short telephoto than a standard-angle lens. This can make it difficult to use in tight situations, limiting its versatility. However, it does serve as a nice portrait lens on an APS-C camera, as its fast f/1.4 maximum aperture makes it possible to highlight a subject by blurring the background behind it. The lens also matches quite well with the smaller form factor of an APS-C camera—it weighs only half a pound and uses 55mm front filters.

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The lens is quite compact, measuring just 1.7 by 2.6 inches (HD) and weighing a mere 8 ounces. Its compact design allows it to balance well on even compact D-SLRs like the Alpha 57£1999.99 at Amazon UK. A lens hood is included, which protects against flare and increases image contrast, and 55mm filters are supported. The lens is noticeably smaller than Nikon's AF-S Nikkor 50mm f/1.4G, but that lens has an internal focus motor for quiet autofocus—the Sony lens is an older design that requires a noisy screw to drive its focus.

I used Imatest to measure the detail that the lens could capture when attached to the full-frame Sony Alpha 99 camera. It performed quite well at all tested apertures, recording 2,083 lines per picture height at f/1.4, 2,254 lines at f/2, and 2,363 lines at f/2.8. Resolution peaks at just under 2,500 lines at f/8. A score of 1,800 lines is considered to be very sharp, so you should feel confident in using the 50mm at any aperture setting without sacrificing image quality. There is some noticeable barrel distortion, about 1.5 percent, which causes straight lines to slightly curve outward. It can be corrected easily with Lightroom's distortion tool, but should be noted.

The 50mm f/1.4 Prime is priced in line with its competition, and performs well. An internal focus motor would be a nice upgrade if Sony opts to refresh the lens at some point in the future, but would undoubtedly add to its size. The company does sell a lower-priced DT 50mm f/1.8 Mid-Range Prime Lens for around $170, but it only covers the image circle of an APS-C camera—if you shoot with an Alpha 99, 850, or 900, you'll want to spend the extra money to get one that lets you take advantage of your camera's full-frame image sensor.

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