A range finder is an instrument for remote measurement of distance. Radar and sonar provide non-optical range finders. Optical range finders – used in cameras for correct focusing, and in military applications – are of two types. Coincidence range finders measure the angles formed from each end of a base line to the object viewed, and calculate the distance by trigonometry. The images from each optical path are made to coincide. Stereoscopic range finders are stereo binoculars which are adjusted until the stereo image formed by reticles in the eyepieces appears to be at the same distance as the object.