Penta Prism is a five-sided prism containing two reflecting surfaces at 45 to each other, and two refracting faces perpendicular to the entering and emerging beams. The deviation angle of 90deg is thus independent of the orientation of the prism, making it especially important in applications in which the prism orientation cannot be precisely controlled. Due to the geometry that total internal reflection cannot be used, the reflecting surfaces must be coated with a metallic or dielectric coating. The standard Penta Prism reflecting surfaces are coated with aluminum or enhanced aluminum. The coated surfaces can be painted black .
The penta prism is a five-sided prism. It reflects light rays through a 90° angle by two reflections and does invert or revert the image. The reflecting surfaces are aluminized. Slight movement of the prism does not affect the true right angle at which light rays are reflected. It also shortens the optical path length of an instrument.
||see the table as follow
||λ/2 @ 632.8nm
||<0.25mm X 45°
||* S1&S2: Single layer MgF2 coating
|* S3&S4: Aluminized and painted black
|30 Sec. Deviation
||10 Sec. Deviation