A roof prism (also called a Dach prism or Dachkanten prism, from the German: "Dachkante", lit. roof edge) is a reflective optical prism containing a section where two faces meet at a 90° angle. These two 90° faces resemble the roof of building, giving this prism type its name. Reflection from the two 90° faces returns an image that is flipped laterally across the axis where the faces meet.
Characteristic for a roof prism is that the beam is split in half, with one half of the beam hitting first one face then the other face, while it is invert for the other half of the beam. Therefore a roof prism can be used only with some distance to focal planes, or the "edge" of the roof would introduce slight distortions. Furthermore the angle between the two faces has to be very close to 90°, or image quality would be degraded.
The simplest roof prism is the Amici roof prism, with other common roof prism designs being the Abbe–Koenig prism, the Schmidt–Pechan prism and probably the best known being the roof pentaprism pictured here. A porro prism is not a roof prism, contrary to popular notion, as the two 90° faces usually don't meet in a Porro prism and therefore don't form a roof edge.
Read more about Roof Prism: Phase Correction
Other articles related to "roof prism, roof, prism, roof prisms, prisms":
... This must be suppressed by multilayer phase-correction coatings applied to one of the roof surfaces to avoid unwanted interference effects and a loss of contrast in the image ... In a roof prism without a phase correcting coating s-polarized and p-polarized light each acquire a different geometric phase as they pass through the upper prism ... distribution perpendicular to the roof edge as compared to that along the roof edge ...
... Dielectric coatings are used in Schmidt-Pechan roof prism to cause the prism surfaces to act as a dielectric mirror ... index materials deposited on the roof prism's reflective surfaces ... coating increases reflectivity from the prism surfaces by acting as a distributed Bragg reflector ...
... In binoculars with Schmidt-Pechan roof prisms, mirror coatings are added to some surfaces of the roof prism because the light is incident at one of the prism's glass-air boundaries at an ... Schmidt-Pechan roof prism use aluminium mirror coating (reflectivity of 87% to 93%) or silver mirror coating (reflectivity of 95% to 98%) is used ... Porro prism binoculars and roof prism binoculars using the Abbe-Koenig roof prism typically do not use mirror coatings because these prisms reflect with 100% reflectivity using total internal reflection in the prism ...
... In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of reflection prism used in optical instruments to alter the orientation of an image ... consists of a block of glass shaped as a right geometric prism with right-angled triangular end faces ... In operation, light enters the large rectangular face of the prism, undergoes total internal reflection twice from the sloped faces, and exits again through the large rectangular face ...
Famous quotes containing the words prism and/or roof:
“Neither can I do anything to please critics belonging to the good old school of projected biography, who examine an authors work, which they do not understand, through the prism of his life, which they do not know.”
—Vladimir Nabokov (18991977)
“A shudder in the loins engenders there
The broken wall, the burning roof and tower”
—William Butler Yeats (18651939)