Leica chose its first prime lens for the T mirrorless camera system wisely. The Leica Summicron-T 23mm f/2 ASPH. ($1,850) matches the field of view and light gathering capability of the quintessential Leica optic, the 35mm Summicron that has adorned many of its full-frame digital and 35mm rangefinder cameras. This new Summicron is an autofocus lens that covers a smaller APS-C image sensor, but it's quite compact and can focus closer than its M-mount cousins. And, while it doesn't deliver quite the impeccable performance that its price would dictate, it's a solid prime lens option for the T system, and one that does a better job capturing images with a shallow depth of field than the Vario-Elmar-T 18-56mm f/3.5-5.6 zoom that is also available for the T.

The lens measures just 1.5 by 2.5 inches (HD) and weighs a mere 5.4 ounces. That's noticeably smaller than the Sony Carl Zeiss 24mm f/1.8 ($1,098.00 at Amazon) lens (2.4 by 2.5 inches, 7.9 ounces) that's available for the competing E-mount camera system. The Summicron covers an almost identical field of view and gathers almost as much light, so its size is certainly worth noting. Using the included hood almost negates the svelte form factor, as it essentially doubles the height of the lens. But it is reversible for storage, which will save a bit of room in your camera bag.

The Summicron utilizes 52mm front filters; that's the same size that the Vario-Elmar-T employs, so you can share one set between the two lenses. The lens barrel is all metal, and there's a manual focus ring with a ridged design. Close focus is capable to about 1 foot (0.3-meter), but as you near the close end of the focus range, the T (Typ 701) ($1,398.24 at Amazon) narrows the iris—at the closest distance the Summicron's maximum aperture is f/2.8. While the logic behind this isn't clear, my guess is that the lens doesn't perform optimally at close distances without being stopped down.

The Fujifilm X100S , which features an APS-C sensor and a fixed 23mm f/2 lens, captures images with a very soft look at close distances at f/2; stopping it down to f/2.8 delivers a sharp image in the same shooting scenario. If that's the same case with the Summicron, I would have preferred that Leica make f/2 available and simply noted that you should narrow the iris to f/2.8 for optimal results in close-focus situations. The other side of the argument, and the one that Leica chose to agree with if it is indeed a sharpness issue, is that you don't want to have to concern yourself with the focus distance and adjust the aperture along with it when actually out shooting in the real world.

I used Imatest to check and see just how the lens performs when paired with the 16-megapixel T. At f/2 it betters the 1,800 lines per picture height we want to see on a center-weighted sharpness test, but not by much. It scores 1,837 lines, and the middle third (1,759 lines) and outer edges (1,440 lines) are both on the soft side. Stopping down to f/2.8 improves the overall score to 2,240 lines, with numbers that approach 2,000 lines through most of the frame. There is still a little bit of softness at the very edges (1,549 lines), but that's forgivable.

At f/4 the lens delivers very even performance across the frame, with a center-weighted score of 2,125 lines. The very edges of the frame are sharp here as well, showing 1,813 lines. The lens is sharpest at f/5.6 (2,144 lines). There's no sign of barrel distortion in images. If you shoot in JPG, there is some evidence of purple and yellow color fringing near the edges of the frame when shooting. It definitely gives edges a fuzzy feel at f/2, but lessens as you stop down. Interestingly enough, it's not visible in Raw DNG images once they've been imported into Lightroom. That means that the software knows to look for the color fringing and remove it automatically. Lightroom is included with the T, and even you shoot in JPG you can use the software to remove the unwanted colors from images with a few clicks.

If you're a prime lens shooter and have made the decision to go with the T system, the Leica Summicron-T 23mm f/2 ASPH. is the only game in town. It's a good lens, but some issues with sharpness at its maximum aperture and color fringing (if you're a JPG shooter) keep it from being a great one. It's performance doesn't quite live up to its asking price that, while a bargain compared with a full-frame M-mount 35mm Summicron ($3,195), is on the high side for a mirrorless lens. But Leica products command premium prices, and if you're smitten enough with the T's industrial design, and you're willing to pay the cost of entry to enter the T system, this is a solid lens option, especially for M-mount 35mm Summicron devotees.

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