The Sony Carl Zeiss Planar T* 50mm f/1.4 ($1,499.99 direct) is the top-end standard-angle prime lens for Sony D-SLR cameras. It's a more expensive version of the older Sony 50mm f/1.4SEE IT, but it's one that's been designed with very little compromise in terms of optical qualities. The Zeiss lens is sharp from edge to edge, even at wide apertures, is very solidly constructed, and features a built-in focus motor. It's also a bit bigger and heavier than the less expensive standard 50mm f/1.4, but if you're in search of image quality above all, its extra size and cost are worth it.

The Planar T* measures 2.8 by 3.2 inches (HD), weighs in at a hefty 1.1 pound, and supports large 72mm filters. The lens barrel is metal, with a large manual focus ring, and a reversible hood is included. The build quality is definitely a step above other lenses. The minimum focus distance is about 1.5 feet (0.45 m); focusing that close at f/1.4 produces a very shallow depth of field, but the magnification is only 0.14x, so don't think of it as a macro lens. The older Sony 50mm f/1.4 is a lot smaller and lighter (1.7 by 2.6 inches, 8 ounces), and is louder when focusing as it uses a screw-drive system. The Planar T* uses an internal focus motor, and is quite snappy to lock on and fire a shot. It does lack optical stabilization, but you won't find that on Sony SLR lenses as a rule, as modern A-mount cameras put stabilization in the body.

I used Imatest to check the optical performance of the lens when paired with the 36-megapixel full-frame Alpha 7R. The LA-EA4 adapter was used to mount the lens on that mirrorless camera. At f/1.4 it records 2,106 lines per picture height, with edges that score 1,755 lines. The overall score betters the 1,800 lines we require for an image to be sharp, and only some softness at the extreme edges of the frame cause the lens to miss that mark from corner to corner. Stopping down to f/2 brings edges up to close to 2,000 lines, and the center-weighted average score to an outstanding 2,597 lines. The lens crosses the 3,000-line mark at f/2.8, and steadily increases until it peaks at 3,500 lines at f/8.

The standard Sony 50mm f/1.4 never got this sharp when we tested it on the full-frame Alpha 99. It did top 2,000 lines at f/1.4, but at its best it managed 2,500 lines at f/8. There is one area where the 50mm f/1.4 bests the Planar: distortion. The Planar T* shows 2.2 percent barrel distortion, which is a little high for a lens of its focal length and aperture; the Sony 50mm f/1.4 shows 1.6 percent, which is more typical of a 50mm f/1.4. Barrel distortion causes straight lines to appear to have a slight outward curve and can be corrected for with ease in software like Lightroom, but it's something to consider when working with the lens.

Aside from the distortion, there's nothing bad to say about the Sony Carl Zeiss Planar T* 50mm f/1.4 from an optical standpoint. It's impressively sharp from edge to edge. It's also quite well built, and the internal focus motor is quiet and speedy. If you demand the most out of your full-frame Sony SLR, it's an excellent prime lens, but it's not an inexpensive one. The older 50mm f/1.4 will still do the job if you're on a budget, and APS-C Sony shooters can consider the 50mm f/1.8 DT lens, which doesn't cover a full-frame image circle, but is available for a low price, under $200.