Collimator /(?)/

Col·li·ma·tor

Collimator

n.
  1. A telescope arranged and used to determine errors of collimation, both vertical and horizontal. (Astron.)
  2. A tube having a convex lens at one end and at the other a small opening or slit which is at the principal focus of the lens, used for producing a beam of parallel rays; also, a lens so used. (Optics)