A roof prism is a reflective optical prism containing a section where two faces meet at a 90° angle. These two 90° faces resemble the roof of a building, giving this prism type its name.
Reflection from the two 90° faces returns an image that is flipped laterally across the axis where the faces meet.
Characteristic for a roof prism is that the beam is split in half, with one half of the beam hitting first one face then the other face, while it is invert for the other half of the beam.
Therefore, a roof prism can be used only with some distance to focal planes, or the "edge" of the roof would introduce slight distortions. Furthermore, the angle between the two faces
has to be very close to 90°, or image quality would be degraded.
60/40 scratch and dig
|Roof Angle Tolerance|
±3 arc minutes
|Surface Flatness||λ/4 @632.8nm|
|Clear Aperture||> 80%|
|Protective Beve||<0.25mm x 45°|
Note: Custom sizes and coatings are available upon request.