The deviation angle of 90° 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 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. Sometimes, the coated surfaces are with black painting.
High Precision Penta Prisms
Specifications:
Material:BK7 Grade A or equivalent optical glass
Dimension Tolerance:+0.0, -0.1mm
Clear Aperture: >85% of dimension
Surface Quality:40-20 scratch and dig
Flatness: λ/8 @ 632.8nm
Deviation: ±5 arc seconds
Bevel: 0.25mmx45deg
Coating: Upon requirement