A Hollow Penta Mirror (HPM) is a five-sided mirror assembly that reflects incoming light at a fixed 90° angle, using two precisely aligned flat mirrors inside a rigid, hollow structure.

The Hollow Penta Roof Assembly (HPRA) is a constant deviation device developed by PLX to duplicate, with advantages, the performance of a penta prism. Unlike a solid prism that is limited in transmission through glass, the new device utilizes front surface reflectance, and thus is unlimited in wavelength transmission. By modifying the coating, polarization of the exiting beam can be precisely controlled. The device enables incoming parallel light to be deviated at 90° with great accuracy. Like the solid prism, the assembly is an invariant, and thus permits movements such as rotation without compromising either the basic 90° deviation or its inherent accuracy.

PLX HPRA’s are available in two configurations:

TYPE A (“PM” unit) is a combination of two flat mirrors mounted at 45°. In an imaging system the unit will produce an unchanged image of an object.

TYPE B (“PR” unit) is a combination of a roof mirror assembly and a flat mirror, mounted at 45°. In an imaging system, the unit turns the image at 90°, and a mirror image is displayed.