The prisms of binoculars, lengthen the light path between the objective lens and the eyepiece—thereby increasing the magnification the lens system can provide—without increasing the length of the binoculars.There are two types of prisms used in the binoculars.
1.) Porro-prism binoculars, the most common type, use an offset prism arrangement.
2.)Roof-prism binoculars are more compact because they use prisms with complex shapes to eliminate the offset arrangement; however, they are more difficult to manufacture.