Binoculars or field glasses are two refracting telescopes mounted side-by-side and preachily aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Each monocular part of a binocular is a single compact (or shortened) refracting telescope, which is made shorter by folding the optical path as it is focussed through the system.
Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models. Unlike a (monocular) telescope, binoculars give users a three-dimensional or stereoscopic image. Each eyepiece presents a slightly different aspect image to each viewer’s eyes, and the parallax allows the visual cortex to generate an impression of depth.
Perspective Research Centre 
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