collimate

v. t. [ imp. & p. p. Collimated; p. p. & vb. n. Collimating. ] [ See Collimation. ] (Physics & Astron.) To render parallel to a certain line or direction; to bring into the same line, as the axes of telescopes, etc.; to render parallel, as rays of light. [ 1913 Webster ]

Collimating eyepiece, an eyepiece with a diagonal reflector for illumination, used to determine the error of collimation in a transit instrument by observing the image of a cross wire reflected from mercury, and comparing its position in the field with that of the same wire seen directly. --
Collimating lens (Optics), a lens used for producing parallel rays of light. [ 1913 Webster ]