A pentaprism redirects a beam through a right angle using two reflecting faces whose planes meet at . In the meridional section their combined action is a rotation, preserving the relevant image-top direction as the beam turns. It does not by itself perform the additional lateral reversal of a roof pentaprism; the latter has an extra reflecting face.
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A pentaprism is an optical device used primarily in cameras, especially single-lens reflex (SLR) cameras. It serves to invert and revert the image captured by the camera's lens so that when you look through the viewfinder, the image appears right-side up and correctly oriented, matching the way we perceive objects in reality. The pentaprism is made up of five polished surfaces, which allow light entering from the camera lens to be reflected within the prism before reaching the eyepiece.