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.
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.
Hand-held binoculars range from small 3 × 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.
Although technology has surpassed using binoculars for data collection, historically these were advanced tools used by geographers and other geoscientists. Field glasses still today can provide visual aid when surveying large areas.
Birdwatching is a very popular hobby among nature and animal lovers and a binocular is their most basic tool. Typically binoculars with a magnification of 7x to 10x are used.
Hunters commonly use binoculars in the field as a way to see game animals that are too far away to spot with the naked eye. Hunters most commonly use 8x binoculars with light transmission and large enough objectives to gather light in low light conditions.
Many binoculars have a range finding reticle (scale) superimposed upon the view. This scale allows the distance to the object to be estimated if the object's height is known (or estimable). The common mariner 7×50 binoculars have these scales with the angle between marks equal to 5 mil. One mil is equivalent to the angle between the top and bottom of an object one meter in height at a distance of 1000 meters.
Source: Binoculars from Wikipedia
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