60 by 60 Optical Glass Binoculars

The prisms reinvert, or erect, the inverted image supplied by the objective of each telescope. They prescribe a folded path for the light rays, allowing a shorter overall length for the instrument. When the prisms used are of the Porro type (see optics: Reflecting prisms), they also provide better depth perception at greater distances by allowing the two objectives to be set farther apart than the eyepieces