Rangefinder Cameras
The distance from the camera to the subject is the most important factor when focusing an image, and a rangefinder camera achieves sharp focus with a device that measures this distance: a rangefinder.
This rangefinder is usually coupled to the focusing mechanism of the camera (coupled rangefinder). The backward and forward movement of the lens as it focuses is communicated by a lever to adjust the rangefinder optics, allowing you to focus accurately on a subject in the viewfinder simply by operating the focusing lever of the lens.