1.25" (31.7mm) Collimator

This is the classical tool for collimating newtonian reflectors.

Light is reflected into the telescope through the 45° angled surface. When looking through the small porthole of the Chesire you will see the separate optical components and the reflections thereon. A perfectly aligned telescope will have all reflections centered in each other.

A crosshair at the front end of the collimator helps you identify where the center is.