A Bauernfeind prism is a type of reflecting

prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentary ...

used to deviate a beam of light by 45° to 60°, depending on its construction, while neither flipping nor rotating the image. It is named for its inventor, the German expert of

geodesy Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...

Karl Maximilian von Bauernfeind Karl Maximilian von Bauernfeind (28 November 1818 – 3 August 1894) was a German geodesist and civil engineer. Education At the age of 18, Bauernfeind studied under Georg Ohm at the Polytechnic School in Nuremberg. Two years later, he stud ...

. The beam is reflected twice in the prism, with one reflection happening at less than the

critical angle Critical angle may refer to: *Critical angle (optics), the angle of incidence above which total internal reflection occurs *Critical angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference lin ...

. Therefore, the prism requires a

reflective coating Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. The ' ...

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. A Bauernfeind prism is used together with a

Schmidt roof prism Schmidt may refer to: * Schmidt (surname), including list of people with the surname * Schmidt (singer) (born 1990), German pop and jazz singer * Schmidt (lunar crater), a small lunar impact crater * Schmidt (Martian crater), a crater on Mars * ...

to form a

Schmidt–Pechan prism A Schmidt–Pechan prism is a type of optical prism used to rotate an image by 180°. These prisms are commonly used in binoculars as an ''image erecting system''. The Schmidt–Pechan prism makes use of a roof prism section (from the German: ...

Applications

The Bauernfeind prism is commonly used in

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

tubes and in geodesy to deviate the path to the

eyepiece An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The ...

in order make the device more ergonomic. More recent applications are glasses that deflect the viewing angle either downwards (for relaxed reading or watching TV), or upwards (as in

belay glasses Belay glasses are eyeglasses with Porro prism, prismatic lenses that are used by belaying, belayers in rock climbing to avoid the neck strain commonly associated with belaying. Belaying involves a person standing on a stable platform below a rock ...

for watching a climber while belaying).

References

{{DEFAULTSORT:Bauernfeind Prism Prisms (optics)