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Lambda Research Optics, Inc. - DFO
Photonics Dictionary

coincidence rangefinder

An optical instrument used to determine the distance to a target being viewed. Two similar optical systems view the target via 45° mirrors at the ends of a fixed baseline. One system creates the top half of the image while the other creates the bottom. Viewing the split image through a common eyepiece, one of the 45° mirrors is rotated to achieve coincidence of the two image halves. The angle of mirror rotation is proportional to the target distance.
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