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 (see Coating chapter). Sometimes, the coated surfaces are with black painting.
Specifications：
| Material: |
BK7 Grade A optical glass |
| Dimension Tolerance: |
+/- 0.25mm |
90° Deviation Tolerance:
| Standard series: |
< 30 arc seconds |
| Precision series: |
up to 10 arc seconds |
Flatness:
| Standard series: |
λ/2 at 632.8 nm |
| Precision series: |
up to λ/4 at 632.8 nm |
| Reflectivity: |
R > 95% per face from 630 to 680 nm |
| Surface Quality: |
60-40 scratch and dig |
