Material: Grade A BK7 or fused silica optical glass
Similar to a right-angle prism, but the hypotenuse is
  replaced by a total internal reflection (TIR) roof
Beam enters through the side face deflected by 90° with
  the image inverted and reversed 
Widely used in telescopes, viewing systems and
  rangefinders

Roof Prism Specifications

Dimension Tolerance:+0.0, - 0.2mm
Flatness: λ/2 at 632.8nm
Surface Quality: 60-40 scratch and dig
Clear Aperture: >80%
Bevel: 0.2 mm to 0.5 mm x 45o
Angular Deviation Tolerance: +/- 3'
Coatings: Protective Al coatings on the roof surface or/and
              AR coating with R<0.2% on side faces
              available upon request