The Penta Prismsis one of the beam Angle (90°) steering devices. It has two uses: first, no matter what the incident Angle is on the first side, the outgoing light turns the incident light to a certain Angle (90°); The second is that unlike a rectangular prism, the resulting image has neither rotation nor specular reflection. Penta prism is commonly used as a camera viewfinder, image viewing system, or measuring instrument.