Coincidence rangefinder

A coincidence rangefinder or coincidence telemeter is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object. There are subtypes split-image telemeter, inverted image, or double-image telemeter with different principles how two images in a single ocular are compared. Coincidence rangefinders were important elements of fire control systems for long-range naval guns and land-based coastal artillery circa 1890–1960. They were also used in rangefinder cameras.

A stereoscopic rangefinder looks similar, but has two eyepieces and uses a different principle, based on binocular vision. The two can normally be distinguished at a glance by the number of eyepieces.