Except for coorner cube prisms,DIGCO supplies roof prisms and porro prisms for binoculars,too

A roof prism is a reflective prism containing a section where two faces meet at a 90° angle, resembling the roof of a building and thus the 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.

A Porro prism is not a roof prism contrary to popular notion, as the Porro prism's two 90° faces usually don't meet and therefore don't form a roof edge.

but both are key for binoculars as core optics as follows,