Penta Prisms The Optical Penta Prism can deviate an incident beam without inverting or reversing to 90 degree. The deviation angle of 90 degree is independent of any rotation of the prism about axis parallel to the line of intersection of the two reflecting faces. It is commonly used in Plumb Level, Surveying, Alignment, Range Finding and Optical Tooling. The reflecting surfaces of the prism must be coated with a metallic or dielectric coating. The standard Penta Prism reflecting surfaces are coated with aluminum or enhanced aluminum. The main material ofpenta prisms are as follows: BK7 glass and all catalog optical glass, UV Fused Silica, Corning 7980, JGS1, Sapphire crystal, Quartz crystal, Germanium (Ge) monocrystal, etc.