COLLIMATOR

Col″li‐ma′tor (?), n. 1. 1. (Astron.) A telescope arranged and used to determine errors of collimation, both vertical and horizontal. Nichol.
2. 2. (Optics) 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.