Autocollimator

The autocollimator consists of an alignment telescope that is mounted on a stand, and there is an illuminated target that is projected through the telescope at a focusable distance. There is also a mirror or a steel block placed at the base of the collimator below the telescope. The image from the illuminated target reflects off of the mirror, and goes back through the telescope to reach the eye.  The base could be aligned via a tilt stage to be perpendicular to the optical axis of the telescope, and the target could be focused through the eyepiece. At this point, the telescope is said to be focused at infinity. When a photographic lens is placed on a platform at a specific distance above the mirror, the autocollimator could be utilized to check the infinity focus of the lens. It can also be used to check the perpendicularity of the lens to the mirror, film gate or image sensor.