Roof prisms have two secions that meet at 90°. Amici-Roof Prisms rotate a beam by 90° and at the same time invert the beam of light, providing a true image that is not inverted. This makes the amici roof prism appropriate for use in telescope eyepieces.
The reflecting faces of Amici-Roof Prisms generally rely on Total Internal Reflection but can be coated to increase the range of angles over which the prism will work. It is also important for Roof Prisms that the 90°angle between the two faces is very accurate to 90°, or image quality will be affected.
Other common designs of roof prism are the Abbe–Koenig prism, the Schmidt–Pechan prism, which are both used in endoscope applications.