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Binoculars

2007 Schools Wikipedia Selection. Related subjects: Engineering

   Porro-prism binoculars with central focusing
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   Porro-prism binoculars with central focusing

   Binocular telescopes, or binoculars, (also known as field glasses) are
   two identical or mirror-symmetrical telescopes mounted side-by-side and
   aligned to point accurately in the same direction, allowing the viewer
   to use both eyes ( Binocular vision) when viewing distant objects. Most
   are sized adequate to be held using both hands although there are much
   larger types.

   Unlike a monocular telescope, binoculars give users a three-dimensional
   image: the two views, presented from slightly different viewpoints to
   each of the viewer's eyes, merge to produce a single perceived view
   with a sensation of depth, allowing distances to be estimated.
   Binoculars are also more comfortable for viewing, as they negate the
   need to close or obstruct one eye to avoid confusion. It is also easier
   and more comfortable to steadily hold and move a pair of binoculars
   than a single tube, as the two hands and the head form a steady
   three-point platform.
   A typical Porro prism binocular design
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   A typical Porro prism binocular design

Optical design

   Galilean binoculars
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   Galilean binoculars

Galilean binoculars

   Almost from the invention of the telescope in the 17th century the
   advantages of mounting two of them side by side for binocular vision
   seems to have been explored . Most early binoculars used Galilean
   optics; that is they used a convex objective and a concave eyepiece
   lens. The Galilean design has the advantage of presenting an erect
   image but has a narrow field of view and is not capable of very high
   magnification. This type construction is still used in very cheap
   models and in " opera glasses".

Porro prism binoculars

   Double Porro prism design
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   Double Porro prism design

   Named after Italian optician Ignazio Porro who patented this image
   erecting system in 1854 and later refined by makers like Carl Zeiss in
   the 1890's , binoculars of this type use a Porro prism in a double
   prism Z-shaped configuration to erect the image. This feature results
   in binoculars that are wide, with objective lenses that are well
   separated but offset from the eyepieces. Porro prism designs have the
   added benefit of folding the optical path so that the physical length
   of the binoculars is less than the focal length of the objective and
   wider spacing of the objectives gives better sensation of depth.

Roof prism binoculars

   Abbe-Koenig "roof prism" design
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   Abbe-Koenig "roof prism" design

   Binoculars using Roof prisms may have appeared as early as the 1880s in
   a design by Achille Victor Emile Daubresse . Most roof prism binoculars
   use either the Abbe-Koenig prism (named after Ernst Karl Abbe and
   Albert Koenig and patented by Carl Zeiss in 1905) or Schmidt-Pechan
   prism (invented in 1899) designs to erect the image and fold the
   optical path. They are narrower, more compact, and more expensive than
   those that use Porro prisms. They have objective lenses that are
   approximately in line with the eyepieces.

Porro vs. Roof prisms

   Aside from the difference in price and portability noted above these
   two designs have effects on reflections and brightness. Porro-prism
   binoculars will inherently produce an intrinsically brighter image than
   roof-prism binoculars of the same magnification, objective size, and
   optical quality, as less light is absorbed along the optical path.
   However, as of 2005, the optical quality of the best roof-prism
   binoculars with up-to-date coating processes as used in Schmidt-Pechan
   models is comparable with the best Porro glasses, and it appears that
   roof prisms will dominate the market for high-quality portable
   binoculars in spite of their higher price. The major European optical
   manufacturers (Leica, Zeiss, Swarovski) have discontinued their Porro
   lines; Japanese manufacturers (Nikon, Fujinon, etc.) may follow suit.

Optical parameters

   Binoculars are usually rated by objective diameter, magnifying power,
   and field of view. The diameter of the objective lenses determines the
   light-gathering power and the theoretical resolving power of the
   binoculars. The ratio of the focal lengths of the objective and the
   eyepiece gives the linear magnifying power (expressed in "diameters").
   It is customary to categorise binoculars by the magnification × the
   objective diameter in mm; e.g. 7×50. A magnification of factor 7, for
   example, produces an image as if one were 7 times closer to the object.
   The resulting “field of view” is measured in the width viewed at factor
   1000 (in meters or feet).

   The magnification required depends upon the application, but with the
   major proviso that large magnifications give an image much more
   susceptible to shake when hand-held. A larger the magnification also
   leads to a smaller the field of view. Binoculars with lower
   magnification may well show more detail because they can be held
   steadily and the larger fields of view can contribute to a more natural
   viewing experience. For general hand-held use, subject to shake, 7 to 8
   diameters is a good compromise between power and image steadiness for
   most people. Binoculars of 7×30 or 8×30 power are good for daytime use.
   For general night use, a 50 mm objective gives maximum brightness;
   objective diameter must be increased for higher magnifications at
   night.

   Binoculars concentrate the light gathered by the objective into a beam,
   the exit pupil whose diameter is the objective diameter divided by the
   magnifying power. For maximum effective light-gathering and brightest
   image, the exit pupil should equal the diameter of the fully dilated
   human eye—about 7 mm, reducing with age. Light gathered by a larger
   exit pupil is wasted. The current trend favors models with 5 mm exit
   pupil, such as 10x50 or 8x40, while 7x50 is falling out of favour. For
   daytime use an exit pupil of 3 mm—matching the eye's contracted
   pupil—is sufficient. However, a larger exit pupil makes alignment of
   the eye easier and avoids dark vignetting to intrude from the edges.

Optical coatings

   U.S. Navy binoculars
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   U.S. Navy binoculars

   Since binoculars may have 16 air-to-glass surfaces, with light lost at
   every surface, optical coatings can significantly affect their image
   quality. When light strikes an interface between two materials of
   different refractive index (e.g., at an air-glass interface), some of
   the light is transmitted, some reflected. In any sort of image-forming
   optical instrument (telescope, camera, microscope, etc.), ideally no
   light should be reflected; instead of forming an image, light which
   reaches the viewer after being reflected is distributed in the field of
   view, and reduces the contrast between the true image and the
   background. Reflection can be reduced, but not eliminated, by applying
   optical coatings to interfaces. Each time light enters or leaves a
   piece of glass; about 5% is reflected back. This "lost" light bounces
   around inside the binoculars, making the image hazy and hard to see.
   Lens coatings effectively lower reflection losses, which finally
   results in a brighter and sharper image. For example, 8x40 binoculars
   with good optical coatings will yield a brighter image than uncoated
   8x50 binoculars. Light can also be reflected from the interior of the
   instrument, but it is simple to minimize this to negligible
   proportions.

   A classic lens-coating material is magnesium fluoride; it reduces
   reflections from 5% to 1%. Modern lens coatings consist of complex
   multi-layers and reflect only 0.25% or less to yield an image with
   maximum brightness and natural colors. For roof-prisms, anti-phase
   shifting coatings are sometimes used which significantly improve
   contrast. The presence of a coating is typically denoted on a pair of
   binoculars by the following terms:
     * coated optics: one or more surfaces coated.
     * fully coated: all air-to-glass surfaces coated. Plastic lenses,
       however, if used, may not be coated.
     * multi-coated: one or more surfaces are multi-layer coated.
     * fully multi-coated: all air-to-glass surfaces are multi-layer
       coated.

   Phase-corrected prism coating and dielectric prism coating are recent
   (in 2005) effective techniques for reducing reflections.

Mechanical design

Focusing and adjustment

   Binoculars to be used to view objects that are not at a fixed distance
   must have a focusing arrangement. Traditionally, two different
   arrangements have been used to provide focus. Binoculars with
   "independent focus" require the two telescopes to be focused
   independently by adjusting each eyepiece, thereby changing the distance
   between ocular and objective lenses. Binoculars designed for heavy
   field use, such as military applications, traditionally have used
   independent focusing. Because general users find it more convenient to
   focus both tubes with one adjustment action, a second type of binocular
   incorporates "central focusing", which involves rotation of a central
   focusing wheel. 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). 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 also "focus-free or "fixed-focus" " binoculars. They have a
   depth of field from a relatively large closest distance to infinity,
   and perform exactly the same as a focusing model of the same optical
   quality (or lack of it) focused on the middle distance.

   Zoom binoculars, while in principle a good idea, are general considered
   not perform very well.

   Most modern binoculars have hinged-telescope construction that enables
   the distance between eyepieces to be adjusted to accommodate viewers
   with different eye separation. This adjustment feature is lacking on
   many older binoculars.

Image stabilization

   Shake can be much reduced, and higher magnifications used, with
   binoculars using image-stabilization technology. Parts of the
   instrument which change the position of the image may be held steady by
   powered gyroscopes or by powered mechanisms driven by gyroscopic or
   inertial detectors, or may be mounted in such a way as to oppose and
   dampen sudden movement. Stabilization may be enabled or disabled by the
   user as required. These techniques allow binoculars up to 20× to be
   hand-held, and much improve the image stability of lower-power
   instruments. There are some disadvantages: the image may not be quite
   as good as the best unstabilized binoculars when tripod-mounted, and
   stabilized binoculars contain more advanced technology to go wrong, and
   to become obsolete. They are also more expensive, heavier, and battery
   life tends to be short. Stabilization is not suitable when tracking
   moving objects.

Alignment

   A well-collimated pair of binoculars, when viewed through human eyes
   and processed by a human brain, should produce a single circular,
   apparently three-dimensional image, with no visible indication that one
   is actually viewing two distinct images from slightly different
   viewpoints. Departure from the ideal will cause, at best, vague
   discomfort and visual fatigue, but the perceived field of view will be
   close to circular anyway. The cinematic convention used to represent a
   view through binoculars as two circles partially overlapping in a
   figure-of-eight shape is not true to life.

   Misalignment is remedied by small movements to the prisms, often by
   turning screws accessible without opening the binoculars, or by
   adjusting the position of the objective via eccentric rings built into
   the objective cell. Alignment is usually done by a professional
   although instructions for checking binoculars for collimation errors
   and for collimating them can be found on the Internet.

Applications

   Coin-operated binoculars
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   Coin-operated binoculars

General use

   Hand-held binoculars range from small 3x10 Galilean opera glasses, used
   in theaters, to glasses with 7 to 12 diameters magnification and 30 to
   50 mm objectives for typical outdoor use. Porro prism models
   predominate although bird watchers and hunters tend to prefer, and are
   prepared to pay for, the lighter but more expensive roof-prism models.

   Many tourist attractions have installed pedestal-mounted, coin-operated
   binoculars to allow visitors to obtain a closer view of the attraction.
   In the United Kingdom, 20 pence often gives a couple of minutes of
   operation, and in the United States, one or two quarters gives between
   one-and-a-half to two-and-a-half minutes.

Military

   Naval ship binoculars
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   Naval ship binoculars

   Binoculars have a long history of military use. Galilean designs were
   widely used up to the end of the 19th century when they gave way to
   porro prism types. Binoculars constructed for general military use tend
   to be more heavily ruggedized than their civilian counterparts. They
   generally avoid more fragile center focus arrangements in favour of
   independent focus. Prism sets in military binoculars may have redundant
   aluminized coatings on their prism sets to guarantee they don’t lose
   their reflective qualities if they get wet.

   There are binoculars designed specifically for civilian and military
   use at sea. Hand held models will be 5x to 7x but with very large prism
   sets combined with eyepieces designed to give generous eye relief. This
   optical combination allows the user to see through them even when they
   are pitching and vibrating in relationship the viewers eye without the
   image vignetting or going dark. Large permanently mounted models with
   large objectives operating at higher magnification are also used.

   Very large “binocular” naval rangefinders (up to 15 meters, weight 10
   tons, for ranging World War II naval gun targets 25 km away), have been
   used, although late-20th-century technology made this application
   redundant.

Astronomical

   Binoculars are widely used by amateur astronomers; there wide field of
   view making them useful for comet and supernova seeking (giant
   binoculars) and general observation (portable binoculars).

   Of particular relevance for low-light and astronomical viewing is the
   ratio between magnifying power and objective lens diameter. A lower
   magnification facilitates a larger field of view which is useful in
   viewing large deep sky objects such as the Milky Way, nebula, and
   galaxies, though the large exit pupil means some of the gathered light
   is wasted. The large exit pupil will also image the night sky
   background, effectively decreasing contrast, making the detection of
   faint objects more difficult except perhaps in remote locations with
   negligible light pollution. Binoculars marketed for specifically for
   astronomical use will tend to have higher magnification combined with a
   larger aperture objective because the diameter of the objective lens
   determines the faintest star you can see.

   Much larger binoculars have been made by amateur telescope makers,
   essentially using two refracting or reflecting astronomical telescopes,
   with mixed results. A very large example in the professional
   astronomical world, although not one that would normally be called
   binoculars, is the Large Binocular Telescope in Arizona, USA, which
   produced its "First Light" image on October 26, 2005. The LBT comprises
   two 8-meter reflector telescopes. While certainly not intended to be
   held to the eyes of a viewer, it uses two telescopes to view the same
   object, giving additional information due to the larger field of view
   that results from the separation of the objective mirrors.

Manufacturers

   Some notable binocular manufacturers as of 2005:

   1. European brands
     * Leica GmbH (Ultravid, Duovid, Geovid: all are Roof)
     * Swarovski Optik (SLC, EL: all are Roof; Habicht: Porro, but to be
       discontinued)
     * Zeiss GmbH (FL,Victory, Conquest: all are Roof; 7x50 BGAT/T: Porro,
       15x60 BGA/T Porro, discontinued)
     * Eschenbach Optik GmbH (Farlux, Trophy, Adventure, Sektor...; some
       are Roof, some are Porro)
     * Docter Optik (Nobilem: Porro)
     * Optolyth (Royal: Roof; Alpin: Porro)
     * Steiner GmbH (Commander, Nighthunter: Porro; Predator, Wildlife:
       Roof)
     * Russian Military Binoculars (BPOc 10x42 7x30, BKFC series)

   2. Japanese brands
     * Canon Co. (I.S. series, Porro variants?)
     * Nikon Co. (High Grade series, Monarch series,RAII, Spotter series:
       Roof; Prostar series, Superior E series, E series, Action EX
       series: Porro)
     * Fujinon Co. (FMTSX, MTSX series: Porro)
     * Kowa Co. (BD series: Roof)
     * Pentax Co. (DCFSP/XP series; Roof, UCF series: Inverted Porro;
       PCFV/WP/XCF series: Porro)
     * Olympus Co. (EXWPI series: Roof)
     * Minolta Co. (Activa, some are Roof, some are Porro)
     * Vixen Co. (Apex/Apex Pro: Roof; Ultima: Porro)
     * Miyauchi Co. (Specialized in over-sized Porro binocualars)

   P.S. Many of the above are OEM products of Kamakura or Chinese
   manufacturing plants.

   3. Chinese brands

   In the early years of the 21st century, some mid-priced binoculars have
   become available in the internal Chinese market. A few of them are said
   to be comparable both in performance and in price to some of the better
   brands, with the great majority of them being inferior.
     * Sicong (from Xian Stateoptics. Navigator series: Roof; Ares series:
       Porro)
     * WDtian (from Yunnan State optics, all Porro)
     * Yunnan State optics (MS series: Porro)

   4. American brands
     * Bushnell Performance Optics
     * Leupold & Stevens, Inc.
     * Vortex Optics

   5. Russian brands
     * Yukon Advanced Optics

     * Baigish
     * Kronos

   Retrieved from " http://en.wikipedia.org/wiki/Binoculars"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
