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What Are Binoculars?
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models. Many different abbreviations are used for binoculars, including glasses, binos and bins.
Unlike a (monocular) telescope, binoculars give users a three-dimensional image: for nearer objects the two views, presented to each of the viewer's eyes from slightly different viewpoints, produce a merged view with an impression of depth. There is no need to close or obstruct one eye to avoid confusion, as is common with monocular telescopes. The use of both eyes also significantly increases the perceived visual acuity (resolution), even at greater distances where depth perception is not apparent.
Hand-held binoculars range from small 3 x 10 Galilean opera glasses, used in theaters, to glasses with 7 to 12 diameters magnification and 30 to 50 mm objectives for typical outdoor use.
Many tourist attractions have installed pedestal-mounted, coin-operated binoculars to allow visitors to obtain a closer view of the attraction. In the United Kingdom, 20 pence often gives a couple of minutes of operation, and in the United States, one or two quarters gives between one-and-a-half to two-and-a-half minutes.
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