illustrate:

"Right angle ridge prism" or "Amish prism", which can rotate and reverse the image and deflect light with 90 ° bending. It is suitable for telescopes and any optical instrument that needs to flip the image from the objective lens, open the right side and bend at 90 ° to maintain the correct visual direction. Pentagonal prism is a pentahedral prism of an image with 90 ° light deviation and right rotation. It has two purposes: first, the outgoing light turns the incident light to a certain angle (90 °) regardless of the incident angle on the first side; Second, unlike a right angle prism, its image has neither rotation nor specular reflection. Pentaprism is commonly used in camera viewfinder, image observation system or measuring instrument.

The characteristic of pentagonal prism is that the light is vertically incident from either side of the 90 ° angle, then reflected by the two sides of the 45 ° angle and emitted from the other side of the 90 ° angle. The incident light and the outgoing light are equal to the 90 ° angle. In this way, the optical axis can be turned 90 ° by using pentagonal prism. Recently, the planarity of a large plane has been measured by using this characteristic of the pentagonal prism [1], that is, when the pentagonal prism rotates around the horizontal axis, the outgoing light sweeps a plane in the vertical plane. On the contrary, when rotating around the vertical axis, the planarity in the horizontal plane can be measured. When using the laser as the light source, a large plane can be swept due to the long range of the laser, This is obviously simple, convenient and high-precision for flatness measurement in housing construction and large-scale engineering construction. Therefore, pentagonal prism is needed more and more.

Pentagonal prism cannot realize internal total reflection according to the critical angle principle. Therefore, the two reflecting surfaces of the prism are generally plated with aluminum film and coated with black paint, and the incident surface and emitting surface are plated with MgF2 single-layer antireflection film

The types and general data are as follows:

Schematic diagram of pentagonal prism