Penta prism has two important properties. The first is that as the image is deviated by 90 degrees it is neither inverted nor reversed. The second is that the penta-prism is a constant deviation prism, meaning that the same exact 90-degree deviation angle applies to all rays transmitted by the useful aperture regardless of the angles between these rays and the optical axis. The deviation is thus independent of the prism orientation, making the penta-prism especially important in application in which prism orientation can’t be precisely controlled. This prism is commonly used in optical tooling, alignment, range finding, surveying, and other instrumental applications. Specifications Material: CDGM H-K9L, grade A fine annealed Dimension tolerance: ±0.2mm 90° angle deviation: Better than 5 arc seconds Flatness: Lambda/2 @632.8nm Surface quality: 60-40 Reflectivity: R > 95% per surface @ 630 - 680nm