Penta prism can deviate an incident beam without inverting or reversing to 90. The deviation angle of 90 is independent of any rotation of the prism about an axis parallel to the line of intersection of the two reflecting faces. It is commonly used in Plumb Level, Surveying, Alignment, Rangefinding and Optical Tooling.            

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