collimator

Plural: collimators

Noun

• 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
• An optical device that generates a parallel beam of light. Often used to compensate for laser beam divergence.
• A similar device that produces a parallel beam of particles such as neutrons.
• A small telescope attached to a larger one, used to point it in the correct general direction.