A device capable of collimating radiation, as a long narrow tube in which strongly absorbing or reflecting walls permit only radiation traveling parallel to the tube axis to traverse the entire length.
A device that turns incoming radiation, such as light, into parallel beams. Simple collimators consists of a tube having a narrow, variable slit at one end and a convex lens at the other. Radiation entering the tube through the slit exits the lens in the form of parallel beams. Collimators are used to establish focal lengths of lenses and to measure the distance of distant objects whose position is known.