PrismaticHaving prisms, namely angular pieces of glass which deflect rays of light. Prisms are used in binoculars and in some telescopes and their use reduces the bulk and weight of the instrument. There are two arrangements, producing porro-prism binoculars and roof-prism binoculars.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver