Pentaprism
= Pentaprism
{wiki}
A <pentaprism> redirects a beam through a right <angle> using two reflecting faces whose planes meet at $45^\circ$. In the meridional section their combined action is a $90^\circ$ 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.