binocular

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binocular,

small optical instrument consisting of two similar telescopestelescope,
traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional optical telescopes, which are the subject of this article, also are used to magnify objects on earth and in astronomy; other types of
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 mounted on a single frame so that separate images enter each of the viewer's eyes. As with a single telescope, distant objects appear magnified, but the binocular has the additional advantage that it substantially increases the range of depth perception of the viewer because the magnified images are seen with both eyes. The frame of a binocular is usually hinged to permit adjustment of the distance between the telescopes. Focusing can be done by means of a wheel on the central axis between the telescopes; turning the wheel changes the distance from the objective lenses of the telescopes to the eyepieces. Separate focusing of each telescope from the eyepiece may be provided in some types of binocular. The term binocular now usually refers to the prism binocular, in which light entering each telescope through its objective lens is bent first one way and then the other by a pair of prisms before passing through one or more additional lenses in the eyepiece. The prisms aid in reducing the length of the instrument and in enhancing the viewer's depth perception by increasing the distance between the objective lenses. Other types of binocular include the opera glass and the field glass; both use Galilean telescopes, which do not employ prisms and which usually have less magnifying power than the telescopes in prism binoculars. A binocular is often specified by an expression such as "7×35" or "8×50"—the first number indicates how many times the binocular magnifies an object and the second number is the diameter of either objective lens in millimeters. The size of an objective lens is a measure of how much light it can gather for effective viewing.

Bibliography

See J. T. Kozak, Deep-Sky Objects for Binoculars (1988).

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binocular

[bī′näk·yə·lər]
(biology)
Of, pertaining to, or used by both eyes.
Of a type of visual perception which provides depth-of-field focus due to angular difference between the two retinal images.
(optics)
Any optical instrument designed for use with both eyes to give enhanced views of distant objects, whose distinguishing performance feature is the depth perception obtainable.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
NGC 247 shares a binocular field with 3rd magnitude P Ceti.
Integrated visual fields provide a rapid estimate of the binocular field without the need for extra examination.
(16) They reported that drivers with severe binocular field loss had significantly higher motor vehicle collision and violation rates compared to those without any field loss.
In addition, there should be no significant defect in the binocular field, which encroaches within 20[degrees] of fixation above or below the horizontal meridian" This article, by means of a case report, discusses the importance of visual fields assessment for meeting the visual standard for driving.
Both stars are categorized as small-amplitude, pulsating red giants and sit together in the same, easy-to-locate binocular field. Just north of Gamma ([gamma]) and Alpha ([alpha]) Delphini lies a pair of 6.2- and 6.8-magnitude stars.
The binocular field of fixation shows the area of eye movement in which bifoveal binocular viewing is maintained.
These disparate worlds--the solar system's smallest and the largest major planets--will remain within 5[degrees] of each other (a binocular field) for the first five evenings of January.
So in his honor, let's enjoy a two-for-one binocular field northwest of Antares that gives us an easy triple star and a much more challenging globular cluster.
First center Megrez in your view, then shift roughly half a binocular field toward Dubhe (a Ursae Majoris).
Just for fun, see if you can squeeze all three clusters into the same binocular field. And for a telescopic challenge seek out little NGC 1907, an 8th-magnitude cluster 1/2[degrees] south of M38.