The Penta Prism is a five-sided prism, featuring two important properties. Firstly, the image is neither inverted nor reversed while it is deviated by 90°. Seconldy, it’s a constant deflection device, i.e. all the transmitted rays are deviated by the same exact 90°. Slight adjustment of the prism does not affect the true right angle. The reflecting surface of this prism must be coated with reflective coating.
