Pentaprism

A variant of this prism is the roof pentaprism which is commonly used in the viewfinder of single-lens reflex cameras.

This lateral inversion 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 90°, which laterally reverses the image back to normal.

Reflex cameras with waist-level finders (viewed from above), including many medium format cameras, display a laterally reversed image directly from the focusing screen which is viewed from above.

The same optical paths can be realized with three mirrors, in an arrangement called the pentamirror.

The pentaprism is typically much heavier, but only has one entrance and one exit, providing a notably superior optical performance.

A pentaprism.
A perspective drawing showing a roof pentaprism commonly used in a single lens reflex camera (SLR). The image is flipped laterally by the prism.
An image as seen through a roof pentaprism. This is looking in through the eyepiece plane.
Double pentaprism as used in surveying.
Hensoldt roof pentaprism binoculars