Pentaprism

A pentaprism (also pentagonal prism ) is a five -sided optical prism. Of the five areas are used as two internal reflection surfaces. A light beam is deflected typically 90 °. And an exit surface to the light passing therethrough - as is common with a reflection prism - vertically taken to avoid chromatic dispersion of wavelength-dependent diffraction of the light. The reflective surfaces are mirror-coated, since the light of total reflection fall on it to steep. The double reflection a transferred image remains true to side.

The general application is the deflection of light to form an image remains true to side.

A pentaprism with non- mirrored surfaces can be used to observe the Sun. At each reflecting surface leaving about 96 % of the light, the prism, remain so in the end ( and heat ), only 0.16 % of the original amount of light for observation. For visual observation that is still too much, a lichtschwächendes filter ( neutral density filter or polarizing filter ) must be set before.

A variant of the pentaprism is the Roof pentaprism (sometimes short roof prism ) which produces an upright, but reversed image. In this, a mirror surface is replaced by two mutually perpendicular surfaces. These need not be mirrored, because you can use the total reflection. The roof prism and penta prism is often used in the viewfinder of SLR cameras ( pentaprism viewfinder ). This gives a laterally correct and upright image, because the image on the ground glass of the camera upright, but is reversed to see. With binoculars roof prism and penta prism is used, for example, along with a 90 ° deflecting half cube prism. Besides the Geradsichtigkeit is achieved by means of the fourth reflection, that the image is mirrored.

A special feature of the pentaprism is that the exit angle of the light beam is always 90 ° to the incident angle. Thus, the optical component is invariant with respect to disturbances ( tilting of the prism ).

• Reflection prism
• Camera technology