A variant of this prism is the roof pentaprism which is commonly used in the viewfinder of single-lens reflex cameras. In this case, the image needs to be reflected left-to-right, as the prism transmits the image formed on the camera's focusing screen, which is itself reflected by the reflex mirror in the camera body. This reflection is done by replacing one of the reflective faces of a normal pentaprism with a "roof" section, with two additional surfaces angled towards each other and meeting at a 90° angle. This form of the prism changes the handedness of the image.
Read more about this topic: Pentaprism
Famous quotes containing the word roof:
“But whenever the roof came white
The head in the dark below
Was a shade less the color of night,
A shade more the color of snow.”
—Robert Frost (1874–1963)