Porro prism
/ˈpəʊlɐɹˌɔɪd ˈɹɛdʒɪstəd ˈkamɹə/
n
Bedeutung:Dual-prism system (blocks of glass at right angles) found in most binoculars; it diverts the light rays toward the eyepiece to correct the inverted image formed in the objective lens.