准直透镜

Collimate \Col"li*mate\, 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.

{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.