Rangefinder

A rangefinder is a camera that focuses by aligning two overlapping images. The photographer looks through a viewfinder window beside the lens, where a small bright patch shows a second view of the scene. Turning the focus ring merges the two images, and when they line up, the subject is sharp. Leica's M series is the most famous example of the design.

Two windows on the front of the camera view the scene from slightly different positions. A system of mirrors and prisms overlays the second view as a small patch in the viewfinder. The focus ring is coupled to this system, so aligning the double image sets the lens to the exact distance of the subject. The method measures distance by triangulation, the same principle surveyors use.

A DSLR shows the scene through the lens, using a mirror and prism, so the photographer sees what the sensor will record. A rangefinder uses a separate viewfinder window beside the lens and focuses by aligning a double image. Rangefinders are smaller and quieter because they have no moving mirror, but framing is approximate and there is no depth of field preview.

Rangefinders are compact, quiet, and fast to operate, which helps a photographer stay unnoticed. The viewfinder shows space outside the frame lines, so subjects can be seen approaching the picture before the shutter fires, and the view never blacks out. Henri Cartier-Bresson shot much of his work on a 35mm Leica rangefinder, and the cameras remain tied to street photography today.

Parallax error is the small framing shift caused by the viewfinder sitting above and beside the lens rather than behind it. At normal distances the difference hardly matters, but up close the picture lands lower and to one side of what the viewfinder showed. Many rangefinders move their frame lines automatically to reduce the error, and framing a little loose leaves room to correct it.

They take practice. Focusing is manual, and the double-image patch works best on subjects with clear vertical edges. Autofocus, zoom previews, and through-the-lens framing are all missing. Most photographers adjust within a few rolls or memory cards, and techniques like zone focusing make a rangefinder as fast as an autofocus camera for street work.

Yes. The Epson R-D1 arrived in 2004 as the first digital rangefinder, and Leica followed with the M8 in 2006. Leica's current M-series bodies pair a digital sensor with the same optical rangefinder mechanism used since the 1950s. Smaller makers such as Pixii also build digital rangefinders, so the design remains in production today.

Only within limits. The focusing patch loses accuracy as focal length grows, so most rangefinder lenses stop at 135mm. Macro work is even harder because the viewfinder cannot frame accurately at close distances and the rangefinder mechanism does not couple that near. Photographers who need long or close-focusing lenses usually pick an SLR or mirrorless camera instead.

A rangefinder-style camera copies the boxy shape and corner viewfinder of a classic rangefinder but focuses electronically. Fujifilm's X100 and X-Pro lines are common examples. They offer the compact body and offset viewfinder experience with autofocus, and some add hybrid viewfinders that switch between optical and electronic views. They contain no true optical rangefinder mechanism.

The optical rangefinder is a precision mechanism that must be assembled and calibrated by hand, and Leica, the main maker, builds in low volumes. Used film rangefinders offer a cheaper entry: fixed-lens models from Canon, Olympus, and Yashica made in the 1960s and 1970s deliver the same focusing experience for far less money.