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).

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.
References in periodicals archive ?
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.
NGC 247 shares a binocular field with 3rd magnitude P Ceti.
Which of the following best describes the binocular field of fixation?
Both stars are categorized as small-amplitude, pulsating red giants and sit together in the same, easy-to-locate binocular field.
Visible as a stellar duo to people with good eyesight, Mizar and Alcor will appear in your binocular field as two well-separated bright i stars.
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.
Just to the east, and in the same binocular field as NGC 2451, lies NCC 2477.
Considering the rather sparse nature of the spring stars, a binocular field this rich is something to linger over and enjoy.
Together, association stars fill a binocular field with plenty of sparkle.
The cluster is located about one binocular field south-southwest of 2nd-magnitude Almach, Gamma (y) Andromedae.