Leica is a company that's known for small prime lenses, so it's a little surprising that it's launching its new SL camera system with a big zoom lens. But that's exactly what the Leica Vario-Elmarit-SL 24-90mm f/2.8-4 ASPH. ($4,950) is. It covers a longer zoom range than the 24-70mm zoom that is the standard with other systems, but does so using a variable rather than fixed aperture. Even though it's not a straight f/2.8, the lens is a solid performer, delivering crisp images and offering excellent close focus capability. It's a solid lens to pair with the Leica SL (Typ 601).

Design
There's no getting around it, the 24-90mm is a big, heavy zoom. It's noticeably larger than your typical 24-70mm f/2.8 (5.4 by 3.5 inches, HD), is hefty at 2.5 pounds, and supports 82mm front filters. A large, rectangular lens hood is included that gives it the look of a cinema lens with a matte box attached. The lens is styled in a similar manner to its S-mount medium format line. It's all black, with the focal range set in yellow typeface on the barrel. It does telescope out when zooming, and both the zoom ring and manual focus ring are large and finished with a ribbed texture for easy gripping.

The lens itself is sealed against dust and moisture, and includes a gasket at the mount to prevent anything from getting into the camera body. The outer elements of the lens are coated using Leica's AquaDura lens coating. It's a hydrophobic coating, the same that the company uses in its sports optics, so water droplets will slide right off.

The minimum focus distance is 1 foot (0.3-meter) throughout the zoom range. At 90mm that allows for a fairly high magnification. There's no printed depth of scale on the body—that's shown on the top information panel of the SL camera body instead. Likewise, optical stabilization and the focus mode are controlled via the body, so the lens is devoid of control switches and buttons.

As for the variable aperture, it drops in a fairly linear fashion as you zoom, which is as much as you can ask from a lens that doesn't have a fixed f-stop throughout its range. The lens has a maximum f/3.1 aperture at 35mm, narrows to f/3.6 at 50mm, and f/3.9 at 75mm.

Image Quality
I used Imatest to check the sharpness of the lens when paired with the 24-megapixel SL (Typ 601). At 24mm f/2.8, the lens scores 2,115 lines per picture height on our center-weighted sharpness test. That's better than the 1,800 lines we look for in an image. The center third of the frame is the sharpest here, with the middle third (1,818 lines) just crossing the threshold of acceptability and the outer third (1,680 lines) showing some signs of softness. Narrowing the aperture improves performance. At f/4 the center-weighted score improves to 2,379 lines and there's more even performance through most of the frame; the edges still lag behind, but they are reasonably crisp at 1,805 lines. There's more improvement at f/5.6 and f/8; the lens shows about 2,400 lines in both cases, with edges that hover around 1,900 lines. Narrowing the aperture any further diminishes image clarity due to diffraction, although results are still solid (2,166 lines) at f/11, and OK at f/16 (1,877 lines)—but try to avoid f/22 (1,520 lines).

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At 35mm f/3.1, the zoom scores 2,287 lines on the sharpness test. The mid parts of the frame show around 2,000 lines and the edges about 1,900. Performance is roughly the same at f/4, f/5.6, f/8, and f/11. Diffraction takes a toll at f/16, dropping the score to 1,956 lines. There's a sharp dip at f/22, an f-stop you should avoid using at any focal length with this lens unless you absolutely need the extra depth of field that it provides.

The 50mm setting is just shy of halfway through the zoom range, and it's where the lens shows its best overall image quality. At f/3.6 it manages 2,429 lines on a center-weighted sharpness test, with superb center sharpness and excellent marks at the mid parts and edges of the frame. Performance is consistent as you stop down, with a slight drop at f/16 and a more severe one at f/22.