COLLIMATOR, a lens (q.v.) placed at a distance equal to its focal length from the luminous object under examination; the rays proceeding from the lens are thus rendered parallel. Collimation (adjustment of the distance between the collimator and the luminous object) is necessary in order that a sharp spec trum (see SPECTROSCOPY) may be obtained when the light is dis persed by a prism (q.v.) or by a grating.