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]

Reflections in a Bauernfeind prism for 60 deg beam deviation. Green side requires reflective coating.

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.

Applications

The Bauernfeind prism is commonly used in microscope tubes and in geodesy to deviate the path to the eyepiece in order make the device more ergonomic.[5]

More recent applications are glasses that deflect the viewing angle either downwards (for relaxed reading or watching TV[6]), or upwards (for watching a climber while belaying[7]).

gollark: My Raspberry Pi is on eternally.
gollark: > running an apionet node on a raspberry pi is almost certainly a terrible ideaWhy?
gollark: The random arduino with some LEDs and buttons I have on my desk.
gollark: Beehive monitoring, if I had beehives to monitor.
gollark: GTech™ is able to *emulate* spatial IO using specially programmed nanobots.

References
  1. Hanno Schmidt (26 May 2009). "6-PRISMA" (PDF). Retrieved 2015-03-22.
  2. Techniklexikon.net. "Bauernfeind-Prisma - Techniklexikon". techniklexikon.net. Retrieved 2015-03-22.
  3. "www.edmundoptics.com/optics/prisms/image-rotation-prisms/half-penta-prisms/3249". edmundoptics.com. Retrieved 2015-03-22.
  4. "VOB Lumex -- Prisms". Archived from the original on 2003-05-10. Retrieved 2015-03-22.
  5. Optik: Physikalisch-technische Grundlagen und Anwendungen, p. 475, at Google Books (in German)
  6. "Prismenbrillen, Liegebrillen, Teleskopspiegel - REHADAT-Hilfsmittel". rehadat-hilfsmittel.de. Retrieved 2015-03-22.
  7. Belay glasses
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