Porro prism
Concise Oxford English Dictionary © 2008 Oxford University Press:
Porro prism /ˈpɒrəʊ/
▶noun a prism in which the light is reflected on two 45° surfaces and returned parallel to the incoming beam, especially as used in a conventional pair of binoculars.
– origin named after the 19th-cent. Italian scientist Ignazio Porro.
'Porro prism' also found in these Oxford entries:
