Dove prisms

A dove prism is used to invert an image and are a truncated right angle prism.  A beam entering one of the sloped faces of a dove prism undergoes total internal reflections and exits the opposite face with a flipped orientation (top to bottom).  A rotated dove prism will also change the state of polarization.  Dove prisms are used in interferometry, astronomy, and pattern recognition.  The name comes from it's inventor, Heinrich Wilhelm Dove.