title: The NAP prism.
abstract: The optics of the NAP prism are described. This is a prism that is produced commercially in "NAP glasses," which are marketed by the Sakura Company of Japan. It deflects a beam through about 90 degrees while keeping the image erect. Rays are both reflected and refracted, leading to some color fringing. The condition for zero color fringing is explored and the corresponding angle of deviation is calculated. The effects of prism apex angles on beam deviation angle and field of view are also investigated. The results show that the requirement for zero color fringing gives a small field of view but if some color fringing is tolerated, a larger field of view can be obtained.
authors.affiliation: Department of Optometry, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Smith
authors.forename: A W
authors.initials: AW
authors.lastname: Johnston
authors.forename: J D
authors.initials: JD
authors.lastname: Maddocks
mesh_terms: D005139:Eyeglasses; D008433:Mathematics; D055095:Optics and Photonics