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FunctionThe Dove prism was invented by H. W. Dove in the mid-19th century. It resembles a truncated right-angle prism sitting on its hypotenuse face. Light entering the prism parallel to the hypotenuse face will be reflected internally at that face and will emerge parallel to its incident direction. One of the incident parallel rays will emerge along a continuation of its incident direction, and if the prism is rotated about that ray through some angle, the image rotates through twice that angle.
Dove prisms are used as image rotators and image reflectors. Without rotation along the long axis of the prism, the image emerges upside down.