A rangefinder camera is one with a double (stereoscopic) viewfinder, allowing the photographer to judge the focusing distance. The rangefinder shows a double image, and lining up the two images of the object to be focused on more or less accurately gauges its distance. Older cameras may display the focusing distance and require the photographer to transfer the value to the lens focusing ring; most recent designs are coupled rangefinders - that is, the focus is adjusted both in the rangefinder and in the objective lens by the same control.
The most famous rangefinder cameras are the Leica M-series. The latest of these is the M7, which is the first of the series to feature automatic exposure. Other current models include the Contax G1 and G2, the Voigtlander Bessa R and R2, and the Hasselblad Xpan. Russian Leica copies like the Zorki and Fed brands are fairly common in the used market. These all take 35mm film; there are also medium-format rangefinders like the Mamiya 7, the Pentax 67 and the Fuji G-series.
Rangefinder cameras are less commonly used than single-lens reflex models. SLRs are usually more technically advanced, with more system options, and have the advantage that the image is seen through the same lens through which it is photographed.
Since the user looks through a viewfinder some distance from the lens and sees an image which is slightly different from the image which will be recorded on the film framing becomes inaccurate at close range. Rangefinder cameras will typically work best in taking pictures of objects far away, such as landscapes, where the difference between the viewer and the lens will not have as great of an effect. For closeup photography, the rangefinder camera is inappropriate, as the image recorded may be significantly different from what the viewer sees.
However, rangefinders do have several advantages. Since there is no moving mirror, as used in SLRs, the shutter response is very fast and quiet. The lack of a mirror also allows lenses to project deep into the camera body, and so higher quality wide-angle lenses are possible. (Voigtlander's 12mm is the widest-angle non-fisheye lens in general production.) The focusing system is more accurate with standard and wide-angle lenses (whereas an SLR is more accurate with telephotos). Since the cameras are simpler, build quality is generally higher - while most Leicas are treasured and protected from the slightest scratch, they are nonetheless capable of withstanding considerable abuse. These qualities make rangefinders ideal for action-grabbing candid shots and street photography.