An incident beam can be deviated by 90 degree without inverting or reversing through a Penta prism. Penta prism has five sides, four of them polished. Two reflective sides are coated with metal or dielectric HR coating and these two sides can be blackened. The deviation angle of 90deg will not be changed if the penta prism is slightly adjusted, this will be convenient to install it. It is widely used in laser level, alignment and optical tooling.The reflecting surfaces of this prism must be coated with a metallic or dielectric reflective coating.