Half-Penta prisms or Semipentaprisms are used to deviate the line of sight by 45° without inverting or reverting the image. The beam is reflected twice in the prism, with one reflection happening at less than the critical angle, therefore the prism requires aluminized and over-coated with Inconel and black paint for this surface to be usable in practice. Combining a Half-Penta Prism with a corresponding size Schmidt roof prism cerates a Pechan prism pair. The Pechan prism pair will invert or revert the image while not deviating the line of sight.
These prisms are fabricated from N-BK7 etc
They can be AR coated on the incidence face.