Signedunsigned
FunctionA Porro prism is a 45°-90°-45° reflecting prism. Light entering the hypotenuse face of the prism is reflected internally off the other two faces and emerges from the hypotenuse face. Thus a beam of light is diverted 180° and the image is inverted and reverted.
Pairs of Porro prisms are often used in binoculars.
ProvenanceFrom the Science Center Prep Room, Harvard University, courtesy of Prof. Owen Gingerich.