A rangefinder is a device that measures distance from the observer to a target.

Techniques

Some devices use active methods to measure (such as ultrasonic ranging module, laser rangefinder, radar distance measurement); others measure distance using trigonometry (stadiametric rangefinders and parallax, or coincidence rangefinders). Older methodologies that use a set of known information, usually distances or target sizes, to make the measurement, have been in regular use since the 18th century.

Applications

Applications include surveying, navigation, to permit focus in photography, choosing a golf club according to distance, and correcting aim of a projectile weapon for distance.

Golf

A rangefinder camera is a camera fitted with a rangefinder, typically a split-image rangefinder: a range-finding focusing mechanism allowing the photographer to measure the subject distance and take photographs that are in sharp focus. Most varieties of rangefinder show two images of the same subject, one of which moves when a calibrated wheel is turned; when the two images coincide and fuse into one, the distance can be read off the wheel. Older, non-coupled rangefinder cameras display the focusing distance and require the photographer to transfer the value to the lens focus ring; cameras without built-in rangefinders could have an external rangefinder fitted into the accessory shoe. Earlier cameras of this type had separate viewfinder and rangefinder windows; later the rangefinder was incorporated into the viewfinder. More modern designs have rangefinders coupled to the focusing mechanism, so that the lens is focused correctly when the rangefinder images fuse; compare with the focusing screen in non-autofocus SLRs. Accessory rangefinders, often fitting into the camera's accessory shoe, could be used with cameras with rangefinder not built in.