A prism is a polyhedron made of transparent materials such as glass, crystal, etc. It is widely used in Optical instrument. Prisms can be divided into several types based on their properties and uses. For example, in spectral instruments, the compound light is decomposed into a "dispersion prism" of the spectrum, and the equilateral Dispersive prism is more commonly used; In Periscope, binoculars and other instruments, changing the direction of light to adjust its imaging position is called "total reflection prism", which generally uses right angle prism.