Roof prism
Appearance
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c8/Roof-pentaprism.png/220px-Roof-pentaprism.png)
A roof prism 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 Amici roof prism, the Abbe-Koenig prism, the Schmidt-Pechan prism, and the roof pentaprism.