Bauernfeind_prism
A Bauernfeind prism is a type of reflecting prism used to deviate a beam of light by 45° to 60°, depending on its construction, while neither flipping nor rotating the image.[1] It is named for its inventor, the German expert of geodesy Karl Maximilian von Bauernfeind.[2]
The beam is reflected twice in the prism, with one reflection happening at less than the critical angle. Therefore, the prism requires a reflective coating for this surface to be usable in practice.
A Bauernfeind prism with 45° beam deviation is also known as a half-penta prism or semipentaprism.[3][4] A Bauernfeind prism is used together with a Schmidt roof prism to form a Schmidt–Pechan prism.