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Roof prism is combined with a right angle prism and a totally internally reflecting roof and they are attached by them largest square surfaces. It can invert and reverse an image, also, deflect the image 90o . Therefore, it is often used in terrestrial telescopes, viewing systems and rangefinders. 

Specification for standard Roof prism:
Material: BK7 Grade A optical glass
Dimension Tolerance:+0,-0.2mm
Flatness: λ/4 at 632.8 nm
Surface Quality: 60-40 scratch and dig
Clear Aperture: >80%
Bevel: 0.2 mm to 0.5 mm x 45o
Angle Tolerance: ± 3arcmin