Penta Prism

Penta Prism is a Five –Side prism, It has two important properties ,First the image is neither inverted nor reverse while deviated by 90 degree. Secondly, It is a constant deflection device ;i.e all the transmitted rays are deviated by the same exact 90 degree. Slight movement of the prism does not effect the true right angle. 
It is commonly used in Plumb Level, Surveying, Alignment, Range finding and Optical Tooling. The reflecting surfaces of this Prism must be coated with a metallic or dielectric coating. The standard Penta Prism reflecting surfaces are coated with aluminum with Black Paint.