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 ?
Therefore, lack of binocularity, per se, cannot be the cause of latent nystagmus.
Thus, sensitivity to motion in depth requires binocularity, but not necessarily stereopsis.
These findings, which are all assessments of binocular function, suggest that binocularity is not a major factor in predicting reading difficulties.
2) An early interruption to binocularity, typically from infantile esotropia syndrome, often results in three clinical signs which persist throughout life, even if the visual axes are surgically straightened.
This series of articles aims to explore eye movements and binocularity in terms of the motor function, binocular alignment and the consequences of misalignment of the visual axes.
Enhanced binocularity of the progressive zones "provides perfect vision and increased visual comfort through real-time optimisation".
The tests include reading tests, LogMAR reading test, LogMAR near charts, task images (books and newspapers), binocular vision tests (fixation disparity, binocularity, suppression, steropsis), Duochrome (dots, letters, rings), Amsler (positive and negative contrast, draw directly on charts) and fixation targets.