Binoculars

A binocular (from Latin, bi-, "two-", and oculus, "eye") is a hand-held tool used to make distant objects appear closer by passing the image through two adjacent series of lenses, and erecting prisms. The prisms revert the image by the principle of total internal reflection of the incoming light. Binoculars display images right side up instead of inverted as astronomical telescopes do. The prisms can be arranged in a dog-leg double Porro configuration, the traditional arrangement, which results in a wide set of binoculars. The objective lenses are not aligned with the eyepieces, and the prisms reflect the light along a Z-shaped path to the eyepiece. "Roof prism" binoculars (using either an Abbe-Koenig or Schmidt-Pechan design) have the objective lenses in line with the eyepieces and are therefore narrower than those which use the porro configuration. By definition, the magnified images are available to both eyes of the observer.

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Current models of binoculars can be so powerful that they are better described as two small telescopes pointing in the same direction, with the two oculars arranged so that it is possible to look through them with both eyes. Most binoculars have a mechanism for changing the distance between the oculars to adapt to different users, and a dioptre adjustment is often employed on one eyepiece (usually the right) to make up for any difference in focus of the two eyes. The normal dioptre setting ranges from 56-72mm.

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The optical characteristics are described by two numbers separated by "x", for example "7x50". The first number is the magnifying power, the second is the diameter of the objective lens (the one further from the eye) in millimeters.

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Binoculars range from small 3x10 models, often used in theaters, to average 7x50 or 10x50 for amateur outdoor use, to large 20x80 or even 20x140 "galaxy" models. The largest models are more like telescopes, as their high magnifying power means a static mounting is necessary, otherwise natural small hand movements would be amplified and make viewing difficult. For this reason a practical limit on standard hand-held binoculars is put at 9x or 10x.

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This limitation can be avoided by the use of the image-stabilized binoculars supplied by a number of manufacturers. With the use of electrical or mechanical image stabilization, binoculars up to 20x can be hand-held. The image of more moderate (8x-10x) power binoculars is also significantly improved with this technique. However, it does come with some drawbacks.In reality the images produced are usually a little bit blurrer than the best traditional models.

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Of particular interest in astronomical use is the ratio between magnifying power and objective lens diameter. Due to the way binoculars work, the resulting ratio is the diameter of the final exit pupil on the oculars. For example, a 10x50 binocular produces a 5 mm exit pupil (objective size divided by the magnifying power). For maximum efficiency, this image should match the diameter of the eye's pupil, which in dark environments grows to about 7mm. This ratio is also a measure of the brightness of the image: the larger the exit pupil, the brighter the image reaching the eye. Thus 10x50 and 8x40 binoculars have the same brightness, although the latter has a smaller magnification. An exit pupil larger than the diameter of the user's eye pupil is therefore inefficient.

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Different optic types also affect relative brightness. A Porro prism binocular will produce a brighter image than a roof prism binocular of the same magnification and objective size. The quality of the glass and optical coatings will also affect the apparent brightness.However, with the advance of the phase-correction prism coating and later dielectic prism coating, the optical quality of a few premium roofies are at least on par with most premium Porro glasses. The current market trend is that, in the realm of portable binocular, roofies will dominate the market.

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Binoculars have the advantage over telescopes and monoculars of the same diameter by enabling the use of both eyes at the same time, which provides a better experience for the observer, partly due to the stereoscopic effect, allowing the user to judge and follow movements more easily. It is therefore much easier to follow fast-moving objects such as aircraft, water skiers or race horses with binoculars than with a telescope.

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Binoculars are widely used by amateur astronomers. Their wide field of view enabling their use in comet hunting and general observation.

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As a tribute to binoculars, a telescope currently being constructed in Arizona, USA, consisting of two 8-meter mirrors, is called the Large Binocular Telescope.

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Tool: A tool is a device that provides a mechanical or mental advantage in accomplishing a task....

Lenses: REDIRECT Lens...

Prism: Prism commonly means:...

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