Roof prism folding binoculars

Pentaprism pentaprism is an optical prism with five reflecting surfaces, which can deflect the incident light by 90 °. The incoming light is reflected twice in the prism to change the direction by 90 °, which will not only not invert, but also change the partial chirality of the image. The ordinary right angle prism will invert the image and change the partial chirality.

The reflection inside the prism is not caused by total reflection, because the angle of the incident light at the time of reflection is less than the critical angle, that is, the minimum angle of total reflection, so both reflecting surfaces should be plated as reflecting mirrors; The incident and outgoing surfaces should be coated with anti reflection film to reduce reflection. Although the fifth surface is not used, the included angle with the two reflecting surfaces is an obtuse angle (greater than the internal angle of a right angle).