Prisms are polyhedrons made of transparent materials (such as glass, crystal, etc.). They are widely used in optical instruments. Prisms can be divided into several types according to their properties and uses. For example, in composite instruments, composite light is decomposed into spectra. Dispersion prisms, more commonly used are equilateral prisms; in the periscope, binoculars and other instruments to change the direction of light, thereby adjusting its imaging position called "total reflection prism", generally using right angle prism.