Optical prism
CVI Melles Griot

Prisms are blocks of optical material with flat, polished sides that are attached at precisely controlled angles to each other. Prisms may be used in an optical system to deflect or deviate a beam of light. They can invert or rotate an image, disperse light into its component wavelengths, and be used to separate states of polarization.

The orientation of prism determines its effect on a beam of light or image. A viewer looks through a prism at an object and sees a virtual image. This image may be displaced from the original object, or, in the case of a dove prism, may coincide with the object. Furthermore, image orientation may differ from the object, as shown in the drawings below.

Prisms will introduce aberrations when used with convergent or divergent beams of light. Using prisms with collimated or nearly collimated light will help minimize aberrations. Conjugate distances that include prisms should be long.