A roof prism (also called a Dach prism, as Dach is German for roof) is in general any kind of reflective optical prism containing a section where two faces meet at a 90° angle. Reflection from the two faces returns an image that is flipped laterally across the axis where the faces meet.
A single Porro prism is the simplest type of roof prism, though in its most common application (the double-Porro configuration in binoculars) it is not used as a roof prism.
Other common roof prisms are the Abbe–Koenig prism, the Amici roof prism, the Schmidt–Pechan prism and the roof pentaprism.
