Roof-prism binocularsAn instrument with an arrangement of its prisms which greatly reduces weight and bulk, thus recommending good quality examples of this type to birdwatchers. They may also be called 'Dialyt-type' binoculars after the trade name which the Carl Zeiss company uses for its roof-prism range. Instruments which have the traditional prismatic arrangement are called porro-prism binoculars. See page 91.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver