a small telescope attached to a large telescope to use in setting the line of the larger one
optical device consisting of a tube containing a convex achromatic lens at one end and a slit at the other with the slit at the focus of the lens; light rays leave the slit as a parallel beam
双语例句
There are tens of combinations between the collimators and the filters. 多达几十种的准直器和滤光片的自由组合。
