Special Features:

Prism, risley; 2 wedges mounted in a housing that allows independent, manual rotation; indexed drum dials to provide direct angular readout of each wedge.

Properties:

A transparent item with at least two polished plane surfaces inclined toward each other, designed for use in optical instruments to reflect and/or refract a beam of light. It may have one or more mirrored surfaces for greater reflection. Includes optical wedges used to divert paths of light by refraction, but to a lesser degree. See also beam splitter, optical instrument.