Rangefinder (camera)

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Leica I - 35mm camera (1927) with a rangefinder inserted into the accessory shoe

Rangefinder is a term from photo technology . It is an optical device and it is in the photograph to determine the absorption distance between camera and subject used the used lens to correct distance keen to adjust.


In the early days of photography, the distance was only estimated when taking the picture, at best measured with a tape measure or folding rule . The determined distance was then set on the lens or the front of the camera with the lens shifted so that a sharp image was to be expected. Even today, the distance is often measured by hand when shooting film productions.

It was later on etched or ground focusing screens focused through the lens. After all, the camera position no longer had to be left. However, the process is time consuming and complicated. In low light and low-light lenses, it does not work. Without a calibrated distance scale on the camera or the lens, the recording distance - the value - could not yet be determined.

Measuring and knowing the distance as a value is necessary in many areas of photography, e.g. As the focus range to use an objective or in the infrared photography the focal point to the infrared index to correct. The importance of distance measurement in photography had to be clearly pointed out for the first models offered. A large number of technical variants now exist.

Manual range finder

Simple models work on the principle of the mixed image or sectional image rangefinder . These optical devices are also called telemeter. They are plugged into the camera's accessory shoe or hot shoe . After the measurement has taken place, the distance read on a scale is transferred by hand to the calibrated scale of the lens. Some manufacturers (e.g. Zeiss-Ikon ) made models with an integrated (optical) light meter , or those that showed the correct image section - corresponding to the focal length of the lens . Other designed versions that - depending on the measured distance - automatically changed the measuring angle from the rangefinder to the camera in order to compensate for the parallax . Luxury versions combined the functions of rangefinder, exposure meter and parallax-corrected viewfinder (adjustable to the focal length of the lens used) in one device. Electronic rangefinders work today using infrared runtime methods even in complete darkness. They are often built into a flash unit; but there are also hand models.

Coupled rangefinder

These are built directly into the camera. With none of these variants, the distance does not have to be read and transferred by hand after the measurement; This means that the lens used is brought into focus during the measurement process. It is interesting that some manufacturers have developed rangefinder cameras ( Leica M , Nikon SP , Voigtländer Bessa R and others) in which various interchangeable lenses had to be coupled to the camera's range finder. In the rangefinder designed as a viewfinder, the image section matching the lens could also be seen at the same time.

There are six designs:

Principle of the mixed image rangefinder
Viewfinder view of a camera with a mixed image rangefinder

Mixed image rangefinder

Via a system of e.g. T. partially transparent mirror B , in which an additional prism A is rotatably arranged, two identical image details of the subject C are optically brought to coincide. Often these are reflected directly in the viewfinder.

Inverse mixed image rangefinder

A built-in lamp projects two cones of light onto the motif in moderate ambient light or darkness, which must be brought into line, cf. ( Kalart Focuspot ). At first it was only used in the American military. With the rise in popularity of flash photography after World War II, the civilian version of the Focuspot z. B. on Graflex and Rolleiflex cameras, the distance can be measured by anyone in complete darkness.

Principle of the cross-sectional rangefinder

Cutaway rangefinder

Similar to the mixed image rangefinder, two reflected partial images must be superimposed in the eyepiece in order to obtain a full image with a correct distance measurement. With this system, there is no need for partially transparent mirrors. Here, too, the optical measurement window can be reflected in the viewfinder.

Two-lens reflex camera

The distance measurement is determined via the subjective impression of sharpness by a second identical optical system coupled to the taking lens. As a rule, the image from this second lens was projected upwards onto a screen using a mirror. This means that the picture can be viewed with both eyes and upright, but only reversed. Some manufacturers offered prism attachments in order to be able to assess the image in the correct direction and in the recording direction. The impression of sharpness gained through the viewfinder lens was the indicator on a scale for focusing the camera due to the rigid connection with the taking lens underneath on a common lens board.

Canon AF35M with autofocus via infrared distance measurement (1979)

Distance measurement via infrared transit time method

The time passed by the light emitted by the built-in infrared transmitter is evaluated in the receiver sensor and automatically transferred to the lens and, if necessary, to the built-in flash unit. Some versions work partly in the visible light spectrum and allow the use of autofocus systems in poor lighting conditions.

Distance measurement using ultrasonic transit time method

The distance traveled time of an emitted by the integrated ultrasonic transmitter signal is evaluated in the receiver sensor ( sonar system of Polaroid ) and automatically transferred to the lens. Disadvantage: a pane of glass between the camera and the subject (e.g. window) falsifies the measurement result.

Distance measurement through the taking lens

On the screen in the film plane

In large format cameras, a focusing screen is attached to the film plane and the distance is determined by the impression of sharpness of the image projected onto the focusing screen by the lens. The value can be read on a calibrated scale in the walking floor . On some models, the ground glass must be folded away or moved after the setting for recording. Others can be lifted and the film cassette is simply pushed between the screen and the camera.

Due to their design, large format cameras based on the principle of the optical bench do not offer the possibility of reading a measured value for the set distance.

Via single lens reflex viewfinder systems

Principle of the SLR camera


In the single-lens reflex camera ( English single lens reflex , SLR), the distance is directly through the taking lens 1 through the detour via a flip-up mirror 2 on the screen 5 is set. Roof prisms 7 are often used in order to be able to assess the image upright and the right way round . The viewfinder image can be brightened by a condenser lens or Fresnel disk 6 and enlarged by means of an eyepiece 8 . During the measurement, the film 4 remains covered by the shutter 3 . Optical adjustment aids (cross- sectional image indicator , microprisms ) or electronic indicators (e.g. Nikon F3AF in manual mode) are often used with SLRs to facilitate the fine determination of the distance. In this case, the principle of distance measurement is directly linked to the impression of sharpness on the focusing screen as perceived by the photographer. If necessary, the value can be read off the scale on the lens after the measurement.


With modern SLRs - especially with digital cameras - the distance measurement is usually carried out automatically. In this case one speaks of autofocus . Two designs are currently common:

  • Edge contrast measurement - the electronic recording sensor in the camera is used to electronically evaluate areas of large fluctuations in brightness (edges) to interpret the sharpness until these contrast transitions are at their maximum by adjusting the focus.
  • Phase comparison - with the help of an additional sensor built into the camera based on the triangulation principle . A distinction is made here between simple line sensors and two-dimensional cross sensors.

With the lenses of modern digital SLR cameras, the display window for the determined distance is now saved; therefore one can no longer speak of a classic range finder here. In this case, the camera knows the exact distance measured, but the photographer no longer knows.

See also


  • Michel Auer: Collection M. + M. Except. Une histoire de la photographie. 586 pages with 1550 color illustrations, text in French, 24 cm × 27 cm, 2003
  • H.-D. Abring: From Daguerre to today. Vol. 4. 296 pages with approx. 1200 illustrations, precise descriptions and index, 21 cm × 30 cm, 1997
  • Therese Mulligan, David Wooters: History of Photography - From 1839 to Today. 25 years of bags. Anniversary edition, Taschen-Verlag, 2005, ISBN 3-8228-4775-5
  • Beaumont Newhall : History of Photography. Schirmer, Mosel, Munich 1998/2005, ISBN 3-88814-319-5
  • Hartmut Thiele: Legends and stories of the photo industry. 60 pages, 14.5 cm × 21 cm, 2006

Web links

Commons : Photography  - collection of images


  1. Message No. 28 from E. Leitz-Werke Wetzlar from 1923 on the market launch of the 'Nahdistanzmessers' (4 pages - Claus Walter Collection) ( Memento of the original from February 21, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and still Not checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.picfront.org
  2. ^ Karl Pritschow: Handbook of scientific and applied photography, Volume II, The photographic camera and its accessories . Julius Springer, Vienna 1931, ISBN 978-3-7091-3064-3 , p. 339 ff . ( limited preview in Google Book search).
  3. Voigtländer website ( Memento of the original from September 16, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.voigtlaender.de
  4. Jo Lommen's homepage on the history of the Kalart company