Dove Prisms

Dove prisms have an unusual and very interesting characteristic — if you look through the prism and rotate it around a longitudinal axis, the image rotates through an angle twice as much as the prism. Optimized performance with input collimated light. Coated dove prisms feature a protected aluminum coating with black Krylon paint on the diagonals and are ideal for displaced retroreflection.

As the dove prism is rotated about its own long axis, the orientation of its image rotates at twice the angular displacement. Thus, an image can be rotated through 180° by rotating the dove prism through only 90° .

Nevertheless, the dove prism is simply one section of a right-angle prism

A collimated beam of light directed into the prism through one inclined face will be refracted toward the base, where total internal reflection inverts the beam and directs it out through the second inclined face

Because the two inclined faces are symmetrically angled with respect to the base, the output beam travels the same trajectory as the input beam; there is no deviation or displacement of the beam.

Engineers use dove prisms to invert an image or to provide continuous control of the orientation of an inverted image. Limitations are related to its size (it must be rather long compared to its aperture) and to its aberrational effects upon beams that are converging or diverging. Collimated beams are preferred because they do not experience aberration as they pass through the prism.