Rangefinders can be tricky cameras with which to work, especially if you're used to the precise framing that an SLR delivers. The Carl Zeiss Tele-Tessar T* 4/85 ZM ($940 list) pairs well with the compact bodies that Leica shooters are used to, and is a sharp performer to boot, but its focal length adds one more variable to the equation: it doesn't match the projected frame lines. Modern digital rangefinders like the M (Typ 240) omit 85mm lines in favor of a slightly tighter field of 90mm field of view. If you opt to pair this 85mm lens with a digital M you'll likely require some time to get used to this.

This is not a huge deal. Rangefinder framing is never perfectly precise; in fact it varies a bit based on the distance between lens and subject, even when the frame lines perfectly match the focal length of the attached lens. And if a shot requires it—and if your camera supports it—Live View is an option for precise framing. Mirrorless cameras like the full-frame Sony Alpha 7R will always present the actual field of view of the lens via the EVF or rear LCD. In a worst case, if you frame based on the 90mm lines, you'll have to crop your image a bit to get the shot you want.

The Tele-Tessar is fairly compact when you consider its focal length. It measures just 3.7 by 2.1 inches (HD), weighs about 10.9 ounces, and supports 43mm front filters. There's no hood included; Zeiss sells a reversible metal one for $84. It's a worthwhile add-on; I didn't have access to one when reviewing the lens, and did notice that some of my shots lost contrast when shooting with a harsh overhead light between myself and my subject. The aperture ring can be set from f/4 all the way down to f/22 in third-stop increments. There's a depth of field scale that starts at f/8 and has markings down to f/22, but scale focusing a lens of this type isn't practical. It is useful for prefocusing the lens to the ballpark distance between you and your subject before bringing the camera to your eye, however. Like the rest of the ZM line, the physical quality of the lens is impeccable: Its barrel is all metal, and the focus ring is tight enough so that it won't unexpectedly drift.

The lens is able to achieve its compact size due to a rather modest f/4 maximum aperture. Shooting at f/4 isn't a huge deal with a wide-angle like the Distagon T* 4/18 ZM, but you'll need to use shorter shutter speeds to grab a steady shot with an 85mm lens. The general rule of thumb is a to shoot at the reciprocal of the focal length (1/85-second in this case), but I try and keep the camera set at 1/125-second when working with a lens this long. Leica cameras don't have in-body stabilization, and the all-mechanical lens has no stabilization system, so steady hands are required. An f/2.8 aperture would double the amount of light that the lens can gather, and also make a shallower depth of field possible.

Thankfully, even though the Tele-Tessar is limited in its light gathering capability, it's extremely sharp at all apertures, with even sharpness from edge to edge. Imatest shows that it records 2,863 lines per picture height at f/4; we call an image that betters 1,800 lines sharp. At f/5.6 it jumps to 3,132 lines, and peaks at f/8 (3,271 lines). The lens shows absolutely no distortion. And while a wider aperture would allow for a shallower depth of field, it's easy enough to blur the background of photos with the Tele-Tessar, especially when working near the 0.9-meter minimum focus distance.

If you're looking for a short-telephoto lens for your rangefinder (or mirrorless) camera, the Carl Zeiss Tele-Tessar T* 4/85 ZM is worth careful consideration. It's absurdly sharp, but you may find the f/4 aperture to be a bit limiting, and spending close to $1,000 on an 85mm f/4 is a tough pill to swallow, even if it's a lens that is as good of a performer as this one. If you're in want of a similar lens with a wider aperture you can opt for the Leica Summarit-M 90mm f/2.5 ($2,150). Voigtlander, normally a good choice for shooters on a budget, only offers a 90mm f/3.5 APO Lanthar ($589) lens in Leica Thread Mount. That can easily be adapted to M-mount, but doesn't deliver much advantage in light gathering, only in price.