Marine Binoculars 

Captain's Solid Brass Binoculars with Leather Case 6

The marine binocular are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point exactly in the same direction, allowing the viewer to make use of 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 gigantic pedestal mounted military models. Lots of different abbreviations are used for binoculars, including glasses, nocs, noculars, binos and bins.

Unlike a (monocular) telescope, the  marine binocular gives users a three-dimensional picture: for nearer objects the views, introduced to each of the viewer's eyes from slightly different viewpoints, produce a merged view with an impression of depth.

How Binoculars work

Marine BinocularMarine Binocular

Marine Binoculars have a focusing arrangement which changes the distance between ocular and objective lenses. Normally there are two different arrangements used to provide focus, "independent focus" and "central focusing": Independent focus is an arrangement where the two telescopes are focused independently by adjusting each eyepiece. Binoculars designed for heavy field use, such as military applications, traditionally have used independent focusing.

Central focusing is an arrangement which involves rotation of a central focusing wheel to adjust both tubes together. In addition, one of the two eyepieces can be further adjusted to compensate for differences between the viewer's eyes (usually by rotating the eyepiece in its mount).

Because the focal change effected by the adjustable eyepiece can be measured in the customary unit of refractive power, the diopter, the adjustable eyepiece itself is often called a "diopter". Once this adjustment has been made for a given viewer, the binoculars can be refocused on an object at a different distance by using the focusing wheel to move both tubes together without eyepiece readjustment.

There are "focus-free" or "fixed-focus" binoculars that have no focusing mechanism other than the eyepiece adjustments that are meant to be set for the user's eyes and left fixed. These are considered to be compromise designs, suited for convenience, but not well suited for work that falls outside their designed range.

Binoculars can be generally used without eyeglasses by myopic (near-sighted) or hyperopic (far-sighted) users simply by adjusting the focus a little further. Most manufacturers leave a little extra available focal-range beyond the infinity-stop/setting to account for this when focusing for infinity.People with severe astigmatism, however, may still need to use their glasses while using binoculars.

How To Use Marine Binoculars

Captain's Antique Solid Brass Binoculars 6Captain's Antique Solid Brass Binoculars 6"

A lot of binoculars have got adjustable magnification, zoom binoculars, meant to give the user the flexibility of getting a single pair of binoculars with a all-encompassing reach of magnifications, normally from whirling a "zoom" lever. This is achieved through a complicated series of adjustinglenses similar to a zoom camera lense.

This design is noted to be a compromise and even a novilty  since they add bulk, complexness and delicacy to the binocular. The complex optical track in addition  adds to a narrow field of view and a big drop in brightness level. Examples also possess the ability  to match the magnification for both eyes throughout the zoom scope and apply collimation to avert eye strain and tiredness.

Nearly all New binoculars are also adjustable via a hinged mechanisum that enables the distance between the two telescope halves to be corrected to suit viewers with varied eye separation.. Just about all are optimized for the interpupillary distance.

 Lippershey Telescope-Pre Marine Binocular

Floor Standing Brass/Wood Anchormaster Telescope 50Floor Standing Brass/Wood Anchormaster Telescope 50"

The first binoculars were built in December 1608 for the Assembly of the States General of the Netherlands by Hans Lippershey. They was a spectacle maker from Middleburg in Zeeland & had discovered that a convex lens as well as a concave lens could be combined to produce a magnified picture of a distant object - a simple telescope.

Lippershey offered his telescope to the States General on 2nd October 1608, & they requested a version to be used by both eyes, for military purposes. sets of binoculars (meaning roughly 'two eyes') were duly delivered but do not appear to have been a immense success with the military, perhaps because they would have had low magnification & poor picture quality.

Lippershey requested a patent on his invention but it was refused on the grounds that it was not sufficiently novel. Indeed there is some doubt as to whether Lippershey was the first to merge lenses in to a telescope. Definitely by early 1609 little 'spyglasses', which they would call telescopes, were widely on sale in Paris. 

However was seldom made because they require over two times as much work as a telescope, to manufacture exactly matched pairs of lenses & fix them in correct alignment.

Thinking about that lenses had been available for several centuries, it is surprising that no-one had discovered the telescope before 1608. Possibly the reason is that to get useful magnification the eyepiece lens needs to have a short focal length & thus a immense amount of curvature, & lens-grinding know-how was unable to produce such lenses of sufficient quality to yield a clear picture.

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