range finder

also n.
Any of various optical, electronic, or acoustical instruments used to determine the distance of an object from the observer.

rangefinder range'find'er adj.

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An optical instrument for measuring distance, usually from its position to a target point. Light from the target enters the optical system through two windows spaced apart, the distance between the windows being termed the base length of the rangefinder. The rangefinder operates as an angle-measuring device for solving the triangle comprising the rangefinder base length and the line from each window to the target point. Rangefinders can be classified in general as being of either the coincidence or the stereoscopic type.

In coincidence rangefinders, one-eyed viewing through a single eyepiece provides the basis for manipulation of the rangefinder adjustment to cause two images or parts of each to match or coincide. This type of device is used, in its simpler forms, in photographic cameras. The basic optical arrangement is shown in the illustration, where M₁ and M₂ are a semitransparent mirror and a reflecting mirror, respectively. When coincidence is obtained, that is, when the target T is seen in the same apparent position along either path, the rangefinder equation for the range D is satisfied:

Simple coincidence rangefinder. A is a right angle; L = convergence angle at target T.

Stereoscopic rangefinders are entirely different, although externally they resemble coincidence rangefinders except for the fact that they possess two eyepieces. It is essentially a large stereobinocular fitted with special reticles which allow a skilled user to superimpose the stereo image formed by the pair of reticles over the images of the target seen in the eyepieces, so that the reticle marks appear to be suspended over the target and at the same apparent distance.

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n. an instrument for estimating the distance of an object, especially for use with a camera or gun.

See the Introduction, Abbreviations and Pronunciation for further details.

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Dansk (Danish)
n. - afstandsmåler

Français (French)
n. - télémètre

Deutsch (German)
n. - Entfernungsmesser

Ελληνική (Greek)
n. - (τεχνολ.) τηλέμετρο

Italiano (Italian)
telemetro

Português (Portuguese)
n. - telêmetro (m)

Русский (Russian)
дальномер

Español (Spanish)
n. - telémetro

Svenska (Swedish)
n. - avståndsmätare

中文（简体）(Chinese (Simplified))
测距仪

中文（繁體）(Chinese (Traditional))
n. - 測距儀

한국어 (Korean)
n. - 거리 측정기

日本語 (Japanese)
n. - 距離計, 測距儀

עברית (Hebrew)
n. - ‮מד-טווח - מכשיר להערכת מרחק של עצם כדי לצלמו או לירות בו‬

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range finder	Range Finder 200
Leica 1200 Range Finder	bushnell golf range finder