![Binocular_with_8x_magnification_and_42_mm_lens_diameter](https://upload.wikimedia.org/wikipedia/commons/9/90/Binocular_with_8x_magnification_and_42_mm_lens_diameter.jpg)
Binoculars or field glasses are two
refracting telescope
A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...
s mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (
binocular vision
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
) when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from
opera glasses
Opera glasses, also known as theater binoculars or Galilean binoculars, are compact, low-power optical magnification devices, usually used at performance events, whose name is derived from traditional use of binoculars at opera performances. Mag ...
to large
pedestal
A pedestal (from French ''piédestal'', Italian ''piedistallo'' 'foot of a stall') or plinth is a support at the bottom of a statue, vase, column, or certain altars. Smaller pedestals, especially if round in shape, may be called socles. In ci ...
-mounted military models.
Unlike a (
monocular
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocul ...
) telescope, binoculars give users a
three-dimensional image: each
eyepiece
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The ...
presents a slightly different image to each of the viewer's eyes and the
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
allows the
visual cortex
The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
to generate an
impression of depth.
Optical designs
Galilean
![Binoculars (AM 2004](https://upload.wikimedia.org/wikipedia/commons/8/81/Binoculars_%28AM_2004.5.5-3%29.jpg)
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
Convex or convexity may refer to:
Science and technology
* Convex lens, in optics
Mathematics
* Convex set, containing the whole line segment that joins points
** Convex polygon, a polygon which encloses a convex set of points
** Convex polytope ...
objective
Objective may refer to:
* Objective (optics), an element in a camera or microscope
* ''The Objective'', a 2008 science fiction horror film
* Objective pronoun, a personal pronoun that is used as a grammatical object
* Objective Productions, a Brit ...
and a
concave
Concave or concavity may refer to:
Science and technology
* Concave lens
* Concave mirror
Mathematics
* Concave function, the negative of a convex function
* Concave polygon, a polygon which is not convex
* Concave set
* The concavity
In ca ...
eyepiece lens. The Galilean design has the advantage of presenting an
erect image In optics, an erect image is one that appears right-side up. An image is formed when rays from a point on the original object meet again after passing through an optical system. In an erect image, directions are the same as those in the object, in ...
but has a narrow field of view and is not capable of very high magnification. This type of construction is still used in very cheap models and in
opera glasses
Opera glasses, also known as theater binoculars or Galilean binoculars, are compact, low-power optical magnification devices, usually used at performance events, whose name is derived from traditional use of binoculars at opera performances. Mag ...
or theater glasses. The Galilean design is also used in low magnification binocular surgical and jewelers'
loupe
A loupe ( ) is a simple, small magnification device used to see small details more closely. They generally have higher magnification than a magnifying glass, and are designed to be held or worn close to the eye. A loupe does not have an attached h ...
s because they can be very short and produce an upright image without extra or unusual erecting optics, reducing expense and overall weight. They also have large exit pupils, making centering less critical, and the narrow field of view works well in those applications. These are typically mounted on an eyeglass frame or custom-fit onto eyeglasses.
Keplerian
An improved image and higher magnification are achieved in binoculars employing
Keplerian optics, where the image formed by the objective lens is viewed through a positive eyepiece lens (ocular).
Since the Keplerian configuration produces an inverted image, different methods are used to turn the image the right way up.
Erecting lenses
In aprismatic binoculars with Keplerian optics (which were sometimes called "twin telescopes"), each tube has one or two additional lenses (
relay lens) between the objective and the eyepiece. These lenses are used to erect the image. The binoculars with erecting lenses had a serious disadvantage: they are too long. Such binoculars were popular in the 1800s (for example, G.& S. Merz models). The Keplerian "twin telescopes" binoculars were optically and mechanically hard to manufacture, but it took until the 1890s to supersede them with better prism-based technology.
Prism
Optical
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
s added to the design enabled the display of the image the right way up without needing as many lenses, and decreasing the overall length of the instrument, typically using Porro prism or roof prism systems. The Italian optical inventor of optical instruments
Ignazio Porro
Ignazio Porro (25 November 1801 – 8 October 1875) was an Italian inventor of optical instruments.
Porro's name is most closely associated with the prism system which he invented around 1850 and which is used in the construction of Porro prism ...
worked during the 1860s with Hofmann in Paris to produce monoculars using the same prism configuration used in modern Porro prism binoculars. At the 1873 Vienna Trade Fair German optical designer and scientist
Ernst Abbe
Ernst Karl Abbe HonFRMS (23 January 1840 – 14 January 1905) was a German physicist, optical scientist, entrepreneur, and social reformer. Together with Otto Schott and Carl Zeiss, he developed numerous optical instruments. He was also a co-ow ...
displayed a prism telescope with two cemented Porro prisms. The optical solutions of Porro and Abbe were theoretically sound, but the employed prism systems failed in practice primarily due to insufficient glass quality.
= Porro
=
![Double Porro prism](https://upload.wikimedia.org/wikipedia/commons/7/77/Double_Porro_prism.svg)
''Porro prism binoculars'' are named after Ignazio Porro, who patented this image erecting system in 1854. The later refinement by Ernst Abbe and his cooperation with glass scientist
Otto Schott
Friedrich Otto Schott (1851–1935) was a German chemist, glass technologist, and the inventor of borosilicate glass. Schott systematically investigated the relationship between the chemical composition of the glass and its properties. In this wa ...
and instrument maker
Carl Zeiss
Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Carl Zeiss AG. Zeiss gathered a group of gifted practica ...
resulted in 1894 in the commercial introduction of improved 'modern' Porro prism binoculars by the
Carl Zeiss company.
Binoculars of this type use a pair of
Porro prism
In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of ''reflection prism'' used in optical instruments to alter the orientation of an image.
Description
It consists of a block of material shaped like a right geometric ...
s in a Z-shaped configuration to erect the image. This results in wide binoculars, with objective lenses that are well separated and offset from the
eyepiece
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The ...
s, giving a better sensation of depth. Porro prism designs have the added benefit of
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
the
optical path
Optical path (OP) is the trajectory that a light ray follows as it propagates through an optical medium.
The geometrical optical-path length or simply geometrical path length (GPD) is the length of a segment in a given OP, i.e., the Euclidean dis ...
so that the physical length of the binoculars is less than the
focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...
of the objective. Porro prism binoculars were made in such a way to erect an image in a relatively small space, thus binoculars using
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
s started in this way.
Porro prisms require typically within 10
arcminutes ( of 1
degree
Degree may refer to:
As a unit of measurement
* Degree (angle), a unit of angle measurement
** Degree of geographical latitude
** Degree of geographical longitude
* Degree symbol (°), a notation used in science, engineering, and mathematics
...
) tolerances for alignment of their optical elements (
collimation
A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction ...
) at the factory. Sometimes Porro prisms binoculars need their prisms set to be re-aligned to bring them into collimation.
Good-quality Porro prism design binoculars often feature about deep grooves or notches ground across the width of the
hypotenuse
In geometry, a hypotenuse is the longest side of a right-angled triangle, the side opposite the right angle. The length of the hypotenuse can be found using the Pythagorean theorem, which states that the square of the length of the hypotenuse equa ...
face center of the prisms, to eliminate image quality reducing abaxial non-image-forming reflections. Porro prism binoculars can offer good optical performance with relatively little manufacturing effort and as human eyes are ergonomically limited by their
interpupillary distance
Pupillary distance (PD) or interpupillary distance (IPD) is the distance measured in millimeters between the centers of the pupils of the eyes. This measurement is different from person to person and also depends on whether they are looking at near ...
the offset and separation of big (60
+ mm wide) diameter objective lenses and the eyepieces becomes a practical advantage in a stereoscopic optical product.
In the early 2020s, the commercial market share of Porro prism-type binoculars had become the second most numerous compared to other prism-type optical designs.
There are alternative Porro prism-based systems available that find application in binoculars on a small scale, like the
Perger prism
A Perger prism or Perger–Porro prism system is a prism, that is used to invert (rotate by 180°) an image. The special feature of this prism is that, like a traditional double Porro prism system, it manages this with only four beam deflections ...
that offers a significantly reduced axial offset compared to traditional Porro prism designs .
=Roof
=
![Abbe-König prism](https://upload.wikimedia.org/wikipedia/commons/f/f1/Abbe-K%C3%B6nig_prism.svg)
''
Roof prism
A roof prism, also called a Dachkanten prism or Dach prism (from German: ''Dachkante'', lit. "roof edge"), is a reflective prism containing a section where two faces meet at a 90° angle, resembling the roof of a building and thus the name. R ...
binoculars'' may have appeared as early as the 1870s in a design by Achille Victor Emile Daubresse.
In 1897 Moritz Hensoldt began marketing
pentaprism
A pentaprism is a five-sided reflecting prism used to deviate a beam of light by a constant 90°, even if the entry beam is not at 90° to the prism.
The beam reflects inside the prism ''twice'', allowing the transmission of an image through a r ...
based roof prism binoculars.
Most roof prism binoculars use either the
Schmidt–Pechan prism
A Schmidt–Pechan prism is a type of optical prism used to rotate an image by 180°. These prisms are commonly used in binoculars as an ''image erecting system''. The Schmidt–Pechan prism makes use of a roof prism section (from the German: ...
(invented in 1899) or the
Abbe–Koenig prism
An Abbe–Koenig prism is a type of reflecting prism, used to invert an image (rotate it by 180°). They are commonly used in binoculars and some telescopes for this purpose. The prism is named after Ernst Abbe and Albert Koenig.
The prism is ...
(named after
Ernst Karl Abbe
Ernst Karl Abbe HonFRMS (23 January 1840 – 14 January 1905) was a German physicist, optical scientist, entrepreneur, and social reformer. Together with Otto Schott and Carl Zeiss, he developed numerous optical instruments. He was also a co-ow ...
and
Albert König and patented by Carl Zeiss in 1905) designs to erect the image and fold the optical path. They have objective lenses that are approximately in a line with the eyepieces.
Binoculars with roof prisms have been in use to a large extent since the second half of the 20th century. Roof prism designs result in objective lenses that are almost or totally in line with the eyepieces, creating an instrument that is narrower and more compact than Porro prisms and lighter. There is also a difference in image brightness. Porro prism and Abbe–Koenig roof-prism binoculars will inherently produce a brighter image than Schmidt–Pechan roof prism binoculars of the same magnification, objective size, and optical quality, because the Schmidt-Pechan roof-prism design employs mirror-coated surfaces that
reduce light transmission.
In roof prism designs, optically relevant prism angles must be correct within 2
arcsecond
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
s ( of 1 degree) to avoid seeing an obstructive double image. Maintaining such tight production tolerances for the alignment of their optical elements by laser or interference (collimation) at an affordable price point is challenging. To avoid the need for later re-collimation, the prisms are generally aligned at the factory and then permanently fixed to a metal plate.
These complicating production requirements make high-quality roof prism binoculars more costly to produce than Porro prism binoculars of equivalent optical quality and until
phase correction coating
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
s were invented in 1988 Porro prism binoculars optically offered superior resolution and contrast to
non-phase corrected roof prism binoculars.
In the early 2020s, the commercial offering of Schmidt-Pechan designs exceeds the Abbe-Koenig design offerings and had become the dominant optical design compared to other prism-type designs.
Alternative roof prism-based designs like the
Uppendahl prism system composed of three prisms cemented together were and are commercially offered on a small scale.
[PROPERTIES AND PERFORMANCE OF THE NEW LEICA TRINOVID 7X35B (=HERE NAMED RETROVID) COMPARED WITH OLDER LEITZ-LEICA TRINOVIDS AND WITH BINOCULARS FROM BECK, FOTON AND THE NEW KOWA 6,5X32. February 2020 by Dr. Gijs van Ginkel](_blank)
/ref>
File:Binocularp.svg, Binoculars diagram showing a Porro prism design
File:2020 Lornetka Baigish 8x30.jpg, Porro prism binoculars, with distinctive eyepiece/objective axis offset
File:Schmidt-Pechan prism-Binocular.png, Binoculars diagram showing a Schmidt–Pechan roof prism design
File:Prismendoppelfernrohr 1905.jpg, Binoculars diagram showing an Abbe–Koenig roof prism design
File:Vortex Diamonback roof prism binoculars.jpg, Roof prism binoculars, with the eyepiece in line with the objective
The optical system of modern binoculars consists of three main optical assemblies:
* Objective lens assembly. This is the lens assembly at the front of the binoculars. It gathers light from the object and forms an image at the image plane.
* Image orientation correction assembly. This is usually a prism assembly that shortens the optical path. Without this, the image would be inverted and laterally reversed, which is inconvenient for the user.
* Eyepiece lens assembly. This is the lens assembly near the user's eyes. Its function is to magnify the image.
Although different prism systems have optical design-induced advantages and disadvantages when compared, due to technological progress in fields like optical coatings, optical glass manufacturing, etcetera, differences in the early 2020s in high-quality binoculars practically became irrelevant. At high-quality price points, similar optical performance can be achieved with every commonly applied optical system. This was 20–30 years earlier not possible, as occurring optical disadvantages and problems could at that time not be technically mitigated to practical irrelevancy. Relevant differences in optical performance in the sub-high-quality price categories can still be observed with roof prism-type binoculars today because well-executed technical problem mitigation measures and narrow manufacturing tolerances remain difficult and cost-intensive.
Optical parameters
Binoculars are usually designed for specific applications. These different designs require certain optical parameters which may be listed on the prism cover plate of the binoculars. Those parameters are:
Magnification
Given as the first number in a binocular description (e.g., 7×35, 10×50), magnification is the ratio of the focal length of the objective divided by the focal length of the eyepiece. This gives the magnifying power of binoculars (sometimes expressed as "diameters"). A magnification factor of 7, for example, produces an image 7 times larger than the original seen from that distance. The desirable amount of magnification depends upon the intended application, and in most binoculars is a permanent, non-adjustable feature of the device (zoom binoculars are the exception). Hand-held binoculars typically have magnifications ranging from 7× to 10×, so they will be less susceptible to the effects of shaking hands. A larger magnification leads to a smaller field of view and may require a tripod for image stability. Some specialized binoculars for astronomy or military use have magnifications ranging from 15× to 25×.[Martin Mobberley, Astronomical Equipment for Amateurs, Springer Science & Business Media – 2012, pp. 53–55]
Objective diameter
Given as the second number in a binocular description (e.g., 7×35, 10×50), the diameter of the objective lens
In optical engineering, the objective is the optical element that gathers light from the object being observed and Focus (optics), focuses the ray (optics), light rays to produce a real image. Objectives can be a single Lens (optics), lens or mirr ...
determines the resolution
Resolution(s) may refer to:
Common meanings
* Resolution (debate), the statement which is debated in policy debate
* Resolution (law), a written motion adopted by a deliberative body
* New Year's resolution, a commitment that an individual mak ...
(sharpness) and how much light can be gathered to form an image. When two different binoculars have equal magnification, equal quality, and produce a sufficiently matched exit pupil (see below), the larger objective diameter produces a "brighter" [ and ]sharper
A sharper is an older term, common since the seventeenth-century, for thieves who use trickery to part an owner with his or her money or other possessions. Sharpers vary from what are now known as con-men by virtue of the simplicity of their co ...
image.[Alan R. Hale, How to Choose Binoculars – 1991, pp. 54–58] An 8×40, then, will produce a "brighter" and sharper image than an 8×25, even though both enlarge the image an identical eight times. The larger front lenses in the 8×40 also produce wider beams of light (exit pupil) that leave the eyepieces. This makes it more comfortable to view with an 8×40 than an 8×25. A pair of 10×50 binoculars is better than a pair of 8×40 binoculars for magnification, sharpness and luminous flux. Objective diameter is usually expressed in millimeters. It is customary to categorize binoculars by the ''magnification'' × ''the objective diameter''; e.g., ''7×50''. Smaller binoculars may have a diameter of as low as 22 mm; 35 mm and 50 mm are common diameters for field binoculars; astronomical binoculars have diameters ranging from 70 mm to 150 mm.
Field of view
The field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Humans a ...
of a pair of binoculars depends on its optical design and in general is inversely proportional to the magnifying power. It is usually notated in a linear
Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
value, such as how many feet (meters) in width will be seen at 1,000 yards (or 1,000 m), or in an angular value of how many degrees can be viewed.
Exit pupil
Binoculars concentrate the light gathered by the objective into a beam, of which its diameter, the exit pupil
In optics, the exit pupil is a virtual aperture in an optical system. Only rays which pass through this virtual aperture can exit the system. The exit pupil is the image of the aperture stop in the optics that follow it. In a telescope or compoun ...
, is the objective diameter divided by the magnifying power. For maximum effective light-gathering and brightest image, and to maximize the sharpness,[ the exit pupil should at least equal the diameter of the pupil of the human eye: about 7 mm at night and about 3 mm in the daytime, decreasing with age. If the cone of light streaming out of the binoculars is ''larger'' than the pupil it is going into, any light larger than the pupil is wasted. In daytime use, the human pupil is typically dilated about 3 mm, which is about the exit pupil of a 7×21 binocular. Much larger 7×50 binoculars will produce a (7.14 mm) cone of light bigger than the pupil it is entering, and this light will, in the daytime, be wasted. An exit pupil that is too ''small'' also will present an observer with a dimmer view, since only a small portion of the light-gathering surface of the retina is used.] For applications where equipment must be carried (birdwatching, hunting), users opt for much smaller (lighter) binoculars with an exit pupil that matches their expected iris diameter so they will have maximum resolution but are not carrying the weight of wasted aperture.
A larger exit pupil makes it easier to put the eye where it can receive the light; anywhere in the large exit pupil cone of light will do. This ease of placement helps avoid, especially in large field of view binoculars, vignetting
In photography and optics, vignetting is a reduction of an image's brightness or saturation toward the periphery compared to the image center. The word ''vignette'', from the same root as ''vine'', originally referred to a decorative border ...
, which brings to the viewer an image with its borders darkened because the light from them is partially blocked, and it means that the image can be quickly found, which is important when looking at birds or game animals that move rapidly, or for a seafarer on the deck of a pitching vessel or observing from a moving vehicle. Narrow exit pupil binoculars also may be fatiguing because the instrument must be held exactly in place in front of the eyes to provide a useful image. Finally, many people use their binoculars at dawn, at dusk, in overcast conditions, or at night, when their pupils are larger. Thus, the daytime exit pupil is not a universally desirable standard. For comfort, ease of use, and flexibility in applications, larger binoculars with larger exit pupils are satisfactory choices even if their capability is not fully used by day.
Twilight factor and relative brightness
Before innovations like anti-reflective coatings were commonly used in binoculars, their performance was often mathematically expressed. Nowadays, the practically achievable instrumentally measurable brightness of binoculars rely on a complex mix of factors like the quality of optical glass used and various applied optical coatings and not just the magnification and the size of objective lenses.
The twilight factor for binoculars can be calculated by first multiplying the magnification by the objective lens diameter and then finding the square root of the result. For instance, the twilight factor of 7×50 binoculars is therefore the square root of 7 × 50: the square root of 350 = 18.71. The higher the twilight factor, mathematically, the better the resolution of the binoculars when observing under dim light conditions. Mathematically, 7×50 binoculars have exactly the same twilight factor as 70×5 ones, but 70×5 binoculars are useless during twilight and also in well-lit conditions as they would offer only a 0.14 mm exit pupil. The twilight factor without knowing the accompanying more decisive exit pupil does not permit a practical determination of the low light capability of binoculars. Ideally, the exit pupil should be at least as large as the pupil diameter of the user's dark-adapted eyes in circumstances with no extraneous light.
A primarily historic, more meaningful mathematical approach to indicate the level of clarity and brightness in binoculars was relative brightness. It is calculated by squaring the diameter of the exit pupil. In the above 7×50 binoculars example, this means that their relative brightness index is 51 (7.14 × 7.14 = 51). The higher the relative brightness index number, mathematically, the better the binoculars are suited for low light use.
Eye relief
Eye relief {{Short description, Optical instrument
The eye relief of an optical instrument (such as a telescope, a microscope, or binoculars) is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. ...
is the distance from the rear eyepiece lens to the exit pupil or eye point. It is the distance the observer must position his or her eye behind the eyepiece in order to see an unvignetted image. The longer the focal length of the eyepiece, the greater the potential eye relief. Binoculars may have eye relief ranging from a few millimeters to 25 mm or more. Eye relief can be particularly important for eyeglasses wearers. The eye of an eyeglasses wearer is typically farther from the eye piece which necessitates a longer eye relief in order to avoid vignetting and, in the extreme cases, to conserve the entire field of view. Binoculars with short eye relief can also be hard to use in instances where it is difficult to hold them steady.
Eyeglasses wearers who intend to wear their glasses when using binoculars should look for binoculars with an eye relief that is long enough so that their eyes are not behind the point of focus (also called the eyepoint). Else, their glasses will occupy the space where their eyes should be. Generally, an eye relief over 16 mm should be adequate for any eyeglass wearer. However, if glasses frames are thicker and so significantly protrude from the face, an eye relief over 17 mm should be considered. Eyeglasses wearers should also look for binoculars with twist-up eye cups that ideally have multiple settings, so they can be partially or fully retracted to adjust eye relief to individual ergonomic preferences.
Close focus distance
Close focus distance is the closest point that the binocular can focus on. This distance varies from about , depending upon the design of the binoculars. If the close focus distance is short with respect to the magnification, the binocular can be used also to see particulars not visible to the naked eye.
Eyepieces
Binocular eyepieces usually consist of three or more lens elements in two or more groups. The lens furthest from the viewer's eye is called the ''field lens'' or ''objective lens'' and that closest to the eye the ''eye lens'' or ''ocular lens''. The most common Kellner configuration is that invented in 1849 by Carl Kellner. In this arrangement, the eye lens is a plano-concave/ double convex achromatic doublet (the flat part of the former facing the eye) and the field lens is a double-convex singlet. A reversed Kellner eyepiece was developed in 1975 and in it the field lens is a double concave/ double convex achromatic doublet and the eye lens is a double convex singlet. The reverse Kellner provides 50% more eye relief and works better with small focal ratios as well as having a slightly wider field.
Wide field binoculars typically utilize some kind of Erfle configuration, patented in 1921. These have five or six elements in three groups. The groups may be two achromatic doublets with a double convex singlet between them or may all be achromatic doublets. These eyepieces tend not to perform as well as Kellner eyepieces at high power because they suffer from astigmatism and ghost images. However they have large eye lenses, excellent eye relief, and are comfortable to use at lower powers.
=Field flattener lens
=
High-end binoculars often incorporate a field flattener lens in the eyepiece behind their prism configuration, designed to improve image sharpness and reduce image distortion at the outer regions of the field of view.
Mechanical design
Focus and adjustment
Binoculars have a focusing arrangement which changes the distance between eyepiece and objective lenses or internally mounted lens elements. Normally there are two different arrangements used to provide focus, "independent focus" and "central focusing":
* ''Independent focusing'' is an arrangement where the two telescope tubes are focused independently by adjusting each eyepiece. Binoculars designed for harsh environmental conditions and heavy field use, such as military or marine applications, traditionally have used independent focusing.
* ''Central focusing'' is an arrangement which involves rotation of a central focusing wheel to adjust both telescope 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 dioptre
A dioptre (British spelling) or diopter (American spelling) is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m−1. It is normally used to express the optical power of a lens or curv ...
, the adjustable eyepiece itself is often called a ''dioptre''. 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 adjust both tubes together without eyepiece readjustment.
Central focusing binoculars can be further subdivided into:
** ''External focusing'', which focuses binoculars by moving the eyepieces, where the volume of the binoculars always changes. During this process, external air and also small dust particles and moisture can be drawn into or pressed out of the binoculars. It is hard to seal or waterproof such systems and in case the eyepieces are moved by a central focuser shaft and external eyepiece arms bridge construction, this construction can (accidentally) get bent/deformed that can result in disabling misalignment.
** ''Internal focusing'', which focuses binoculars by moving internal mounted optical lenses located between the objective lens group and the prism assembly – or rarely located between the prism assembly and eyepiece lens assembly – within the housing without changing the volume of the binoculars. The addition of a focusing lens reduces the light transmission of the optical system contained in the telescope tube somewhat. Internal focusing is generally considered the mechanically more robust central focusing solution and with the help of an appropriate seal like O-rings air and moisture ingress can be prevented, to make binoculars fully waterproof.
With increasing magnification, the depth of field
The depth of field (DOF) is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image captured with a camera.
Factors affecting depth of field
For cameras that can only focus on one object dist ...
– the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image – decreases. The depth of field reduces quadratic with the magnification, so compared to 7× binoculars, 10× binoculars offer about half (7² ÷ 10² = 0.49) the depth of field. However, not related to the binoculars optical system, the user perceived practical depth of field or depth of acceptable view performance is also dependent on the accommodation ability (accommodation ability varies from person to person and decreases significantly with age) and light conditions dependent effective pupil size or diameter of the user's eyes.
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 hyperfocal distance
In optics and photography, hyperfocal distance is a distance beyond which all objects can be brought into an "acceptable" focus. As the hyperfocal distance is the focus distance giving the maximum depth of field, it is the most desirable distan ...
range (for hand held binoculars generally from about to infinity without performing eyepiece adjustments for a given viewer).
Binoculars can be generally used without eyeglasses by myopic
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...
(near-sighted) or hyperopic
Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, i ...
(far-sighted) users simply by adjusting the focus a little farther. 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, will still need to use their glasses while using binoculars.
Some binoculars have adjustable magnification, ''zoom binoculars'', such as 7-21×50 intended to give the user the flexibility of having a single pair of binoculars with a wide range of magnifications, usually by moving a "zoom" lever. This is accomplished by a complex series of adjusting lenses similar to a zoom camera lens. These designs are noted to be a compromise and even a gimmick
A gimmick is a novel device or idea designed primarily to attract attention or increase appeal, often with little intrinsic value. When applied to retail marketing, it is a unique or quirky feature designed to make a product or service "stand ou ...
since they add bulk, complexity and fragility to the binocular. The complex optical path also leads to a narrow field of view and a large drop in brightness at high zoom. Models also have to match the magnification for both eyes throughout the zoom range and hold collimation to avoid eye strain and fatigue. These almost always perform much better at the low power setting than they do at the higher settings. This is natural, since the front objective cannot enlarge to let in more light as the power is increased, so the view gets dimmer. At 7×, the 50mm front objective provides a 7.14 mm exit pupil, but at 21×, the same front objective provides only a 2.38 mm exit pupil. Also, the optical quality of a zoom binocular at any given power is inferior to that of a fixed power binocular of that power.
Interpupillary distance
Most modern binoculars are also adjustable via a hinged construction that enables the distance between the two telescope halves to be adjusted to accommodate viewers with different eye separation or "interpupillary distance
Pupillary distance (PD) or interpupillary distance (IPD) is the distance measured in millimeters between the centers of the pupils of the eyes. This measurement is different from person to person and also depends on whether they are looking at near ...
(IPD)" (the distance measured in millimeters
330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter.
The millimetre (American and British English spelling differences#-re, -er, ...
between the centers of the pupil
The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black ...
s of the eyes). Most are optimized for the interpupillary distance (typically about 63 mm) for adults. Interpupillary distance varies with respect to age, gender and race. The binoculars industry has to take IPD variance (most adults have IPDs in the 50–75 mm range) and its extrema into account, because stereoscopic optical products need to be able to cope with many possible users, including those with the smallest and largest IPDs.
Children and adults with narrow IPDs can experience problems with the IPD adjustment range of binocular barrels to match the width between the centers of the pupils in each eye impairing the use of some binoculars. Adults with average or wide IPDs generally experience no eye separation adjustment range problems, but straight barreled roof prism binoculars featuring over 60 mm diameter objectives can dimensionally be problematic to correctly adjust for adults with a relatively narrow IPDs. Anatomic conditions like hypertelorism
Hypertelorism is an abnormally increased distance between two organs or bodily parts, usually referring to an increased distance between the orbits (eyes), or orbital hypertelorism. In this condition the distance between the inner eye corners as ...
and hypotelorism
Hypotelorism is an abnormally decreased distance between two organs or bodily parts, usually pertaining to the eye sockets (orbits), also known as orbital hypotelorism.
Causes
It is often a result of fetal alcohol syndrome (FAS), caused by lar ...
can affect IPD and due to extreme IPDs result in practical impairment of using stereoscopic optical products like binoculars.
Alignment
The two telescopes in binoculars are aligned in parallel (collimated), to produce a single circular, apparently three-dimensional, image. Misalignment will cause the binoculars to produce a double image. Even slight misalignment will cause vague discomfort and visual fatigue as the brain tries to combine the skewed images.
Alignment is performed by small movements to the prisms, by adjusting an internal support cell or by turning external set screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distingu ...
s, or by adjusting the position of the objective via eccentric
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
rings built into the objective cell.
''Unconditional aligning'' (3-axis collimation, meaning both optical axes are aligned parallel with the axis of the hinge used to select various interpupillary distance settings) binoculars requires specialized equipment. Unconditional alignment is usually done by a professional, although the externally mounted adjustment features can usually be accessed by the end user.
''Conditional alignment'' ignores the third axis (the hinge) in the alignment process. Such a conditional alignment comes down to a 2-axis pseudo-collimation and will only be serviceable within a small range of interpupillary distance settings, as conditional aligned binoculars are not collimated for the full interpupillary distance setting range.
Image stability
Some binoculars use image-stabilization technology to reduce shake at higher magnifications. This is done by having a gyroscope
A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
move part of the instrument, or by powered mechanisms driven by gyroscopic or inertial detectors, or via a mount designed to oppose and damp the effect of shaking movements. 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, stabilized binoculars also tend to be more expensive and heavier than similarly specified non-stabilised binoculars.
Housing
Binoculars housings can be made of various structural materials. Old binoculars barrels and hinge bridges were often made of brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other with ...
. Later steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
and relatively light metals like aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
and magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
alloys were used, as well as polymers like ( fibre-reinforced) polycarbonate
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
and acrylonitrile butadiene styrene
Acrylonitrile butadiene styrene (ABS) (chemical formula (C8H8)''x''·(C4H6)''y''·(C3H3N)''z'' is a common thermoplastic polymer. Its glass transition temperature is approximately . ABS is amorphous and therefore has no true melting point.
A ...
. The housing can be rubber armored externally as outer covering to provide a non-slip gripping surface, absorption of undesired sounds and additional cushioning/protection against dents, scrapes, bumps and minor impacts.
Optical coatings
Because a typical binocular has 6 to 10 optical elements with special characteristics and up to 20 atmosphere-to-glass surfaces, binocular manufacturers use different types of optical coating
An optical coating is one or more thin layers of material deposited on an optical component such as a lens, prism or mirror, which alters the way in which the optic reflects and transmits light. These coatings have become a key technology in th ...
s for technical reasons and to improve the image they produce.
Lens and prism optical coatings on binoculars can increase light transmission, minimize detrimental reflections and interference effects, optimize beneficial reflections, repel water and grease and even protect the lens from scratches. Modern optical coatings are composed of a combination of very thin layers of materials such as oxides, metals, or rare earth materials. The performance of an optical coating is dependent on the number of layers, manipulating their exact thickness and composition, and the refractive index difference between them. These coatings have become a key technology in the field of optics and manufacturers often have their own designations for their optical coatings. The various lens and prism optical coatings used in high-quality 21st century binoculars, when added together, can total about 200 (often superimposed) coating layers.
Anti-reflective
Anti-reflective interference coatings reduce light lost at every optical surface through reflection Reflection or reflexion may refer to:
Science and technology
* Reflection (physics), a common wave phenomenon
** Specular reflection, reflection from a smooth surface
*** Mirror image, a reflection in a mirror or in water
** Signal reflection, in ...
at each surface. Reducing reflection via anti-reflective coatings also reduces the amount of "lost" light present inside the binocular which would otherwise make the image appear hazy (low contrast). A pair of binoculars with good optical coatings may yield a brighter image than uncoated binoculars with a larger objective lens, on account of superior light transmission through the assembly. The first transparent interference-based coating ''Transparentbelag (T)'' used by Zeiss was invented in 1935 by Olexander Smakula
Olexander Smakula ( uk, Олександр Теодорович Смакула) (1900 in Dobrovody, Austria-Hungary, today Ukraine – 17 May 1983 in Auburn, Massachusetts, USA) was a Ukrainian physicist known for the invention of anti-reflecti ...
. A classic lens-coating material is magnesium fluoride
Magnesium fluoride is an inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs natur ...
, which reduces reflected light from about 4% to 1.5%. At 16 atmosphere to optical glass surfaces passes, a 4% reflection loss theoretically means a 52% light transmission ( = 0.520) and a 1.5% reflection loss a much better 78.5% light transmission ( = 0.785). Reflection can be further reduced over a wider range of wavelengths and angles by using several superimposed layers with different refractive indices. The anti-reflective multi-coating ''Transparentbelag* (T*)'' used by Zeiss in the late 1970s consisted of six superimposed layers. In general, the outer coating layers have slightly lower index of refraction values and the layer thickness is adapted to the range of wavelengths in the visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye wil ...
to promote optimal destructive interference
In physics, interference is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructive ...
via reflection in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. There is no simple formula for the optimal layer thickness for a given choice of materials. These parameters are therefore determined with the help of simulation programs. Determined by the optical properties of the lenses used and intended primary use of the binoculars, different coatings are preferred, to optimize light transmission dictated by the human eye luminous efficiency function variance. Maximal light transmission around wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s of 555 nm (green
Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...
) is important for obtaining optimal photopic vision
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visua ...
using the eye cone cell
Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
s for observation in well-lit conditions. Maximal light transmission around wavelengths of 498 nm (cyan
Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue.
In the subtractive color system, or CMYK color ...
) is important for obtaining optimal scotopic vision
In the study of human visual perception, scotopic vision (or scotopia) is the vision of the eye under low-light conditions. The term comes from Greek ''skotos'', meaning "darkness", and ''-opia'', meaning "a condition of sight". In the human eye, ...
using the eye rod cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in per ...
s for observation in low light conditions. As a result, effective modern anti-reflective lens coatings consist of complex multi-layers and reflect only 0.25% or less to yield an image with maximum brightness and natural colors. These allow high-quality 21st century binoculars to practically achieve at the eye lens or ocular lens measured over 90% light transmission values in low light conditions. Depending on the coating, the character of the image seen in the binoculars under normal daylight can either look "warmer" or "colder" and appear either with higher or lower contrast. Subject to the application, the coating is also optimized for maximum color fidelity through the visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye wil ...
, for example in the case of lenses specially designed for bird watching.
A common application technique is physical vapor deposition
Vacuum deposition is a group of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. These processes operate at pressures well below atmospheric pressure (i.e., vacuum). The deposited layers can r ...
of one or more superimposed anti-reflective coating layer(s) which includes evaporative deposition
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation ...
, making it a complex production process.
Phase correction
In binoculars with roof prisms the light path is split into two paths that reflect on either side of the roof prism ridge. One half of the light reflects from roof surface 1 to roof surface 2. The other half of the light reflects from roof surface 2 to roof surface 1. If the roof faces are uncoated, the mechanism of reflection is Total Internal Reflection
Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...
(TIR). In TIR, light polarized in the plane of incidence (p-polarized) and light polarized orthogonal to the plane of incidence (s-polarized) experience different phase shifts. As a consequence, linearly polarized light emerges from a roof prism elliptically polarized. Furthermore, the state of elliptical polarization of the two paths through the prism is different. When the two paths recombine on the retina (or a detector) there is interference
Interference is the act of interfering, invading, or poaching. Interference may also refer to:
Communications
* Interference (communication), anything which alters, modifies, or disrupts a message
* Adjacent-channel interference, caused by extr ...
between light from the two paths causing a distortion of the Point Spread Function and a deterioration of the image. Resolution and contrast significantly suffer. These unwanted interference effects can be suppressed by vapor depositing a special dielectric coating
A dielectric mirror, also known as a Bragg mirror, is a type of mirror composed of multiple thin layers of dielectric material, typically deposited on a substrate of glass or some other optical material. By careful choice of the type and thickne ...
known as a ''phase-correction coating'' or ''P-coating'' on the roof surfaces of the roof prism. To approximately correct a roof prism for polychromatic light several phase-correction coating layers are superimposed, since every layer is wavelength and angle of incidence specific.
The ''P-coating'' was developed in 1988 by Adolf Weyrauch at Carl Zeiss
Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Carl Zeiss AG. Zeiss gathered a group of gifted practica ...
.[A. Weyrauch, B. Dörband: ''P-Coating: Improved imaging in binoculars through phase-corrected roof prisms.'' In: ''Deutsche Optikerzeitung.'' No. 4, 1988.](_blank)
/ref>
Other manufacturers followed soon, and since then phase-correction coatings are used across the board in medium and high-quality roof prism binoculars. This coating suppresses the difference in phase shift between s- and p- polarization so both paths have the same polarization and no interference degrades the image. In this way, since the 1990s, roof prism binoculars have also achieved resolution values that were previously only achievable with Porro prisms. The presence of a phase-correction coating can be checked on unopened binoculars using two polarization filters. Dielectric phase-correction prism coatings are applied in a vacuum chamber with maybe thirty or more different superimposed vapor coating layers deposits, making it a complex production process.
Binoculars using either a Schmidt–Pechan roof prism, Abbe–Koenig roof prism or an Uppendahl roof prism benefit from phase coatings that compensate for a loss of resolution and contrast caused by the interference effects that occur in untreated roof prisms. Porro prism
In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of ''reflection prism'' used in optical instruments to alter the orientation of an image.
Description
It consists of a block of material shaped like a right geometric ...
and Perger prism
A Perger prism or Perger–Porro prism system is a prism, that is used to invert (rotate by 180°) an image. The special feature of this prism is that, like a traditional double Porro prism system, it manages this with only four beam deflections ...
binoculars do not split beams and therefore they do not require any phase coatings.
Metallic mirror
In binoculars with Schmidt–Pechan or Uppendahl roof prisms, mirror coatings are added to some surfaces of the roof prism because the light is incident at one of the prism's glass-air boundaries at an angle less than the critical angle
Critical angle may refer to:
*Critical angle (optics), the angle of incidence above which total internal reflection occurs
*Critical angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference lin ...
so total internal reflection
Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...
does not occur. Without a mirror coating most of that light would be lost. Roof prism aluminum mirror coating (reflectivity
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
of 87% to 93%) or silver mirror coating (reflectivity of 95% to 98%) is used.
In older designs silver mirror coatings were used but these coatings oxidized and lost reflectivity over time in unsealed binoculars. Aluminum mirror coatings were used in later unsealed designs because they did not tarnish even though they have a lower reflectivity than silver. Using vacuum-vaporization technology, modern designs use either aluminum, enhanced aluminum (consisting of aluminum overcoated with a multilayer dielectric film) or silver. Silver is used in modern high-quality designs which are sealed and filled with nitrogen or argon to provide an inert atmosphere so that the silver mirror coating does not tarnish.
Porro prism
In optics, a Porro prism, named for its inventor Ignazio Porro, is a type of ''reflection prism'' used in optical instruments to alter the orientation of an image.
Description
It consists of a block of material shaped like a right geometric ...
and Perger prism
A Perger prism or Perger–Porro prism system is a prism, that is used to invert (rotate by 180°) an image. The special feature of this prism is that, like a traditional double Porro prism system, it manages this with only four beam deflections ...
binoculars and roof prism binoculars using the Abbe–Koenig roof prism configuration do not use mirror coatings because these prisms reflect with 100% reflectivity using total internal reflection
Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...
in the prism rather than requiring a (metallic) mirror coating.
Dielectric mirror
image:Dielectric mirror diagram.svg, Diagram of a dielectric mirror. Thin layers with a high refractive index ''n''1 are interleaved with thicker layers with a lower refractive index ''n''2. The path lengths ''l''A and ''l''B differ by exactly one wavelength, which leads to constructive interference.
Dielectric coatings are used in Schmidt–Pechan prism, Schmidt–Pechan and Uppendahl prism, Uppendahl roof prisms to cause the prism surfaces to act as a dielectric mirror. This coating was introduced in 2004 in Zeiss Victory FL binoculars featuring Schmidt–Pechan prisms. Other manufacturers followed soon, and since then dielectric coatings are used across the board in medium and high-quality Schmidt–Pechan and Uppendahl roof prism binoculars. The non-metallic dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...
reflective coating is formed from several multilayers of alternating high and low refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
materials deposited on a prism's reflective surfaces. The manufacturing techniques for dielectric mirrors are based on thin-film deposition
A thin film is a layer of material ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many a ...
methods. A common application technique is physical vapor deposition
Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...
which includes evaporative deposition
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation ...
with maybe seventy or more different superimposed vapor coating layers deposits, making it a complex production process. This multilayer coating increases reflectivity from the prism surfaces by acting as a distributed Bragg reflector
A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characteristic ...
. A well-designed multilayer dielectric coating can provide a reflectivity
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
of over 99% across the visible light spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wav ...
. This reflectivity is an improvement compared to either an aluminium mirror coating or silver mirror coating.
Porro prism and Perger prism binoculars and roof prism binoculars using the Abbe–Koenig roof prism do not use dielectric coatings because these prisms reflect with 100% reflectivity using total internal reflection
Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...
in the prism rather than requiring a (dielectric) mirror coating.
Terms
All binoculars
The presence of any coatings is typically denoted on binoculars by the following terms:
* ''coated optics'': one or more surfaces are anti-reflective coated with a single-layer coating.
* ''fully coated'': all air-to-glass surfaces are anti-reflective coated with a single-layer coating. Plastic lenses, however, if used, may not be coated.
* ''multi-coated'': one or more surfaces have anti-reflective multi-layer coatings.
* ''fully multi-coated'': all air-to-glass surfaces are anti-reflective multi-layer coated.
The presence of optical high transmittance crown glass offering relatively low refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
(≈1.52) and low dispersion
Dispersion may refer to:
Economics and finance
*Dispersion (finance), a measure for the statistical distribution of portfolio returns
*Price dispersion, a variation in prices across sellers of the same item
*Wage dispersion, the amount of variatio ...
(with Abbe number
In optics and lens design, the Abbe number, also known as the V-number or constringence of a transparent material, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of ''V'' ind ...
s around 60) is typically denoted on binoculars by the following terms:
* BK7 ( Schott designates it as 517642. The first three digits designate its refractive index .517and the last three designate its Abbe number 4.2 Its critical angle is 41.2°.)
* BaK4 (Schott designates it as 569560. The first three digits designate its refractive index .569and the last three designate its Abbe number 6.0 Its critical angle is 39.6°.)
Roof prisms only
* ''phase-coated'' or ''P-coating'': the roof prism has a phase-correcting coating
* ''aluminium-coated'': the roof prism mirrors are coated with an aluminium coating (the default if a mirror coating isn't mentioned).
* ''silver-coated'': the roof prism mirrors are coated with a silver coating
* ''dielectric-coated'': the roof prism mirrors are coated with a dielectric coating
Accessories
Common accessories for binoculars are:
* neck and shoulder straps for carrying
* binocular harnesses (sometimes combined with an integrated field case) to distribute weight evenly for prolonged carrying
* field carrying cases/side bags
* binoculars storage/travel cases
* rainguards for protecting the eyepieces outer lenses
* (tethered) lens caps for protecting the objectives outer lenses
* cleaning kits to carefully remove dirt from lenses and other surfaces
* tripod adapters
Applications
General use
Hand-held binoculars range from small 3 × 10 Galilean opera glasses
Opera glasses, also known as theater binoculars or Galilean binoculars, are compact, low-power optical magnification devices, usually used at performance events, whose name is derived from traditional use of binoculars at opera performances. Mag ...
, used in theater
Theatre or theater is a collaborative form of performing art that uses live performers, usually actor, actors or actresses, to present the experience of a real or imagined event before a live audience in a specific place, often a stage. The p ...
s, to glasses with 7 to 12 times magnification and 30 to 50 mm diameter objectives for typical outdoor use.
Compact or pocket binoculars are small light binoculars suitable for daytime use. Most compact binoculars feature magnifications of 7× to 10×, and objective diameter sizes of a relatively modest 20 mm to 25 mm, resulting in small exit pupil sizes limiting low light suitability. Roof prim designs tend to be narrower and more compact than equivalent Porro prism designs. Thus, compact binoculars are mostly roof prism designs. The telescope tubes of compact binoculars can often be folded closely to each other to radically reduce the binocular's volume when not in use, for easy carriage and storage.
Many tourist attraction
A tourist attraction is a place of interest that tourists visit, typically for its inherent or an exhibited natural or cultural value, historical significance, natural or built beauty, offering leisure and amusement.
Types
Places of natural b ...
s have installed pedestal-mounted, coin-operated binocular tower viewer
A tower viewer is a telescope or binoculars permanently mounted on a stalk. The device magnifies objects seen through its lenses, allowing users to see farther and more clearly than they could with the naked eye or with less powerful viewing dev ...
s to allow visitors to obtain a closer view of the attraction.
Land surveys and geographic data collection
Although technology has surpassed using binoculars for data collection, historically these were advanced tools used by geographers and other geoscientists. Field glasses still today can provide visual aid when surveying large areas.
Bird watching
Birdwatching
Birdwatching, or birding, is the observing of birds, either as a recreational activity or as a form of citizen science. A birdwatcher may observe by using their naked eye, by using a visual enhancement device like binoculars or a telescope, b ...
is a very popular hobby among nature and animal lovers; a binocular is their most basic tool because most human eyes cannot resolve sufficient detail to fully appreciate and/or study small birds. To be able to view birds in flight well rapid moving objects acquiring capability and depth of field are important. Typically, binoculars with a magnification of 8× to 10× are used, though many manufacturers produce models with 7× magnification for a wider field of view and increased depth of field. The other main consideration for birdwatching binoculars is the size of the objective that collects light. A larger (e.g. 40–45mm) objective works better in low light and for seeing into foliage, but also makes for a heavier binocular than a 30–35mm objective. Weight may not seem a primary consideration when first hefting a pair of binoculars, but birdwatching involves a lot of holding up the binoculars while standing in one place. Careful shopping is advised by the birdwatching community.
Hunting
Hunters commonly use binoculars in the field as a way to observe distant game animals. Hunters most commonly use about 8× magnification binoculars with 40–45mm objectives to be able to find and observe game in low light conditions. European manufacturers produced and produce 7×42 binoculars with good low light performance without getting too bulky for mobile use like extended carrying/stalking and much bigger bulky 8×56 and 9×63 low-light binoculars optically optimized for excellent low light performance for more stationary hunting at dusk and night. For hunting binoculars optimized for observation in twilight, coatings are preferred that maximize light transmission in the wavelength range around 460-540 nm.
Range finding
Some binoculars have a range finding reticle
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscope, ...
(scale) superimposed upon the view. This scale allows the distance to the object to be estimated if the object's height is known (or estimable). The common mariner 7×50 binoculars have these scales with the angle between marks equal to 5 mil. One mil is equivalent to the angle between the top and bottom of an object one meter in height at a distance of 1000 meters.
Therefore, to estimate the distance to an object that is a known height the formula is:
:
where:
* is the ''Distance'' to the object in meters.
* is the known ''Object Height''.
* is the angular height of the object in number of ''Mil''.
With the typical 5 mil scale (each mark is 5 mil), a lighthouse that is 3 marks high and known to be 120 meters tall is 8000 meters distant.
:
Military
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 rugged than their civilian counterparts. They generally avoid fragile center focus arrangements in favor of independent focus, which also makes for easier, more effective weatherproofing. 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.
One variant form was called "trench binoculars", a combination of binoculars and periscope
A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position.
In its simplest form, it consists of an outer case with ...
, often used for artillery spotting purposes. It projected only a few inches above the parapet, thus keeping the viewer's head safely in the trench.
Military binoculars can and were also used as measuring and aiming devices, and can feature filters and (illuminated) reticles.
Military binoculars of the Cold War
The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
era were sometimes fitted with passive sensors that detected active IR emissions, while modern ones usually are fitted with filters blocking laser beams used as weapons. Further, binoculars designed for military usage may include a stadiametric reticle in one eyepiece in order to facilitate range estimation.
Modern binoculars designed for military usage can also feature laser rangefinder
A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...
s, compasses, and data exchange interfaces to send measurements to other peripheral devices.
Very large binocular naval rangefinder
A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography an ...
s (up to 15 meters separation of the two objective lenses, weight 10 tons, for ranging World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
naval gun targets 25 km away) have been used, although late-20th century radar and laser range finding technology made this application mostly redundant.
Marine
There are binoculars designed specifically for civilian and military use under harsh environmental conditions at sea. Hand held models will be 5× to 8× magnification, but with very large prism sets combined with eyepieces designed to give generous eye relief. This optical combination prevents the image vignetting or going dark when the binoculars are pitching and vibrating relative to the viewer's eyes due to a vessel's motion.
Marine binoculars often contain one or more features to aid in navigation on ships and boats.
Hand held marine binoculars typically feature:
* Sealed interior: O-rings or other seals prevent air and moisture ingress.
* Nitrogen or argon filled interior: the interior is filled with 'dry' gas to prevent internal fogging/tarnishing of the optical surfaces. As fungi can not grow in the presence of an inert or noble gas atmosphere, it also prevents lens fungus formation.
* Independent focusing: this method aids in providing a durable, sealed interior.
* Reticle scale: a navigational aid which uses a horizon line and a vertical scale for measuring the distance of objects of known width or height – sometimes an important navigational aid.
* Compass: A compass bearing projected in the image. Dampening helps to read the compass bearing on a moving ship or boat.
* Floating strap: some marine binoculars float on water, to prevent sinking. Marine binoculars that do not float are sometime supplied with or provided by the user as an aftermarket accessory with a strap that will function as a flotation device.
Mariners also often deem an adequate low light performance of the optical combination important, explaining the many 7×50 hand held marine binoculars offerings featuring a large 7.14 mm exit pupil, which corresponds to the average pupil size of a youthful dark-adapted human eye in circumstances with no extraneous light.
Civilian and military ships can also use large, high-magnification binocular models with large objectives in fixed mountings.
Astronomical
Binoculars are widely used by amateur astronomers
Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers m ...
; their wide field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Humans a ...
makes them useful for comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
and supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
seeking (giant binoculars) and general observation (portable binoculars). Binoculars specifically geared towards astronomical viewing will have larger aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane.
An opt ...
objectives (in the 70 mm or 80 mm range) because the diameter of the objective lens increases the total amount of light captured, and therefore determines the faintest star that can be observed. Binoculars designed specifically for astronomical viewing (often 80 mm and larger) are sometimes designed without prisms in order to allow maximum light transmission. Such binoculars also usually have changeable eyepieces to vary magnification. Binoculars with high magnification and heavy weight usually require some sort of mount to stabilize the image. A magnification of 10x is generally considered the practical limit for observation with handheld binoculars. Binoculars more powerful than 15×70 require support of some type. Much larger binoculars have been made by amateur telescope makers, essentially using two refracting or reflecting astronomical telescopes.
Of particular relevance for low-light and astronomical viewing is the ratio
In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...
between magnifying power and objective lens diameter. A lower magnification facilitates a larger field of view which is useful in viewing the Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
and large nebulous objects (referred to as deep sky
A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed fa ...
objects) such as the nebulae
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming region ...
and galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
. The large (typical 7.14 mm using 7×50) exit pupil bjective (mm)/powerof these devices results in a small portion of the gathered light not being usable by individuals whose pupils do not sufficiently dilate. For example, the pupils of those over 50 rarely dilate over 5 mm wide. The large exit pupil also collects more light from the background sky, effectively decreasing contrast, making the detection of faint objects more difficult except perhaps in remote locations with negligible light pollution
Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...
. Many astronomical objects of 8 magnitude or brighter, such as the star clusters, nebulae and galaxies listed in the Messier Catalog
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ''Catalogue des Nébuleuses et des Amas d'Étoiles'' (''Catalogue of Nebulae and Star Clusters'').
Because Messier was only int ...
, are readily viewed in hand-held binoculars in the 35 to 40 mm range, as are found in many households for birding, hunting, and viewing sports events. For observing smaller star clusters, nebulae, and galaxies binocular magnification is an important factor for visibility because these objects appear tiny at typical binocular magnifications.Sky & Telescope
''Sky & Telescope'' (''S&T'') is a monthly American magazine covering all aspects of amateur astronomy, including the following:
*current events in astronomy and space exploration;
*events in the amateur astronomy community;
*reviews of astronomic ...
, October 2012, Gary Seronik, "The Messier Catalog: A Binocular Odyssey" (pg 68)
Some open clusters
An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
, such as the bright double cluster ( NGC 869 and NGC 884) in the constellation Perseus
In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...
, and globular clusters
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member ...
, such as M13 in Hercules, are easy to spot. Among nebulae, M17 in Sagittarius and the North America Nebula
The North America Nebula (NGC 7000 or Caldwell 20) is an emission nebula in the constellation Cygnus, close to Deneb (the tail of the swan and its brightest star). The shape of the nebula resembles that of the continent of North America, complet ...
( NGC 7000) in Cygnus are also readily viewed. Binoculars can show a few of the wider-split binary stars
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
such as Albireo
Albireo is a double star designated Beta Cygni (β Cygni, abbreviated Beta Cyg, β Cyg). The International Astronomical Union uses the name "Albireo" specifically for the brightest star in the system. Although designated ' beta', ...
in the constellation Cygnus.
A number of Solar System objects that are mostly to completely invisible to the human eye are reasonably detectable with medium-size binoculars, including larger craters on the Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
; the dim outer planets Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
and Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
; the inner "minor planets" Ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás ...
, Vesta and Pallas
Pallas may refer to:
Astronomy
* 2 Pallas asteroid
** Pallas family, a group of asteroids that includes 2 Pallas
* Pallas (crater), a crater on Earth's moon
Mythology
* Pallas (Giant), a son of Uranus and Gaia, killed and flayed by Athena
* Pa ...
; Saturn's largest moon Titan; and the Galilean moons
The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...
of Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
. Although visible unaided in pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
-free skies, Uranus and Vesta require binoculars for easy detection. 10×50 binoculars are limited to an apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
of +9.5 to +11 depending on sky conditions and observer experience. Asteroids like Interamnia, Davida, Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
and, unless under exceptional conditions, Hygiea, are too faint to be seen with commonly sold binoculars. Likewise too faint to be seen with most binoculars are the planetary moons, except the Galileans and Titan, and the dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
s Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
and Eris. Other difficult binocular targets include the phases of Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
and the rings of Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
. Only binoculars with very high magnification, 20x or higher, are capable of discerning Saturn's rings to a recognizable extent. High-power binoculars can sometimes show one or two cloud belts on the disk of Jupiter, if optics and observing conditions are sufficiently good.
Binoculars can also aid in observation of human-made space objects, such as spotting satellites in the sky as they pass.
List of binocular manufacturers
There are many companies that manufacturer binoculars, both past and present. They include:
* Barr and Stroud
Barr & Stroud Limited was a pioneering Glasgow optical engineering firm. They played a leading role in the development of modern optics, including rangefinders, for the Royal Navy and for other branches of British Armed Forces during the 20th ce ...
(UK) – sold binoculars commercially and primary supplier to the Royal Navy in WWII
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. The new range of Barr & Stroud binoculars are currently made in China (Nov. 2011) and distributed by Optical Vision Ltd.
* Bausch & Lomb
Bausch + Lomb is an eye health products company based in Vaughan, Ontario, Canada. It is one of the world's largest suppliers of contact lenses, lens care products, pharmaceuticals, intraocular lenses, and other eye surgery products. The compan ...
(US) – has not made binoculars since 1976, when they licensed their name to Bushnell, Inc., who made binoculars under the Bausch & Lomb name until the license expired, and was not renewed, in 2005.
* BELOMO (Belarus) – both porro prism and roof prism models manufactured.
* Bresser (Germany)
* Bushnell Corporation
Bushnell Corporation is an American firm that specializes in sporting optics and outdoor products. It is based in Overland Park, Kansas and is a subsidiary of Vista Outdoor. Bushnell's produces binoculars, telescopes, spotting scopes, riflesco ...
(US)
* Blaser – Premium binoculars
* Canon Inc
is a Japanese multinational corporation headquartered in Ōta, Tokyo, Japan, specializing in optical, imaging, and industrial products, such as lenses, cameras, medical equipment, scanners, printers, and semiconductor manufacturing equipment. (Japan) – I.S. series: porro variants
* Celestron
Celestron is an American company based in Torrance, California, United States, that manufactures telescopes and distributes telescopes, binoculars, spotting scopes, microscopes, and accessories manufactured by its parent company, the Synta Technol ...
* Docter Optics
Noblex, formerly Docter Optics, is a German manufacturer of optics, including binoculars, rifle scopes, spotting scopes, red dot sights, flashlights and reading glasses. Its headquarters are in Eisfeld, Thuringia, Germany, where most of the pr ...
(Germany) – Nobilem series: porro prisms
* Fujinon
Fujinon is a brand of optical lenses made by Fuji Photo Film Co., Ltd, now known as Fujifilm. Fujifilm's Fujinon lenses have been used by professional photographers and broadcast stations as well as cinematography. Fujifilm started manufacture ...
(Japan) – FMTSX, FMTSX-2, MTSX series: porro
* I.O.R.
__NOTOC__
Întreprinderea Optică Română ("Romanian Optical Enterprise"), often abbreviated by the acronym IOR, is a major optics company established in 1936 in Bucharest. IOR produces military and civilian-grade optics and associated equipme ...
(Romania)
* Kazan Optical-Mechanical Plant (KOMZ) (Russia) – manufactures a variety of porro prism models, sold under the trade name ''Baigish''
* Kowa (Japan)
* Krasnogorsky Zavod
Krasnogorsky zavod (russian: Красногорский завод им. С. А. Зверева, , Krasnogorsk Works named after S. A. Zverev) is a Russian factory in Krasnogorsk near Moscow which specializes in optical technology. Part of Shvab ...
(Russia) – both porro prism and roof prism models, models with optical stabilizers. The factory is part of the Rostec#Shvabe_Holding[43Shvabe_Holding_Group.html" ;"title="3.html" ;"title="Rostec#Shvabe Holding[43">Rostec#Shvabe Holding[43Shvabe Holding Group">3.html" ;"title="Rostec#Shvabe Holding[43">Rostec#Shvabe Holding[43Shvabe Holding Group
* Leica Camera (Germany) – Noctivid, Ultravid, Duovid, Geovid, Trinovid: most are roof prism, with a few high end porro prism examples
* Leupold & Stevens, Leupold & Stevens, Inc (US)
* Meade Instruments (US) – Glacier (roof prism), TravelView (porro), CaptureView (folding roof prism) and Astro Series (roof prism). Also sells under the name ''Coronado''.
* Meopta
Meopta - optika, s.r.o. is a Czech Republic based company that manufactures various products mainly in the field of optics. The company was once well-known for its still and movie cameras, although it no longer manufactures such products.
Histo ...
(Czech Republic) – Meostar B1 (roof prism)
* Minox
Minox (pronounced ) is a manufacturer of cameras, known especially for its subminiature camera.
The first product to carry the Minox name was a subminiature camera, conceived in 1922, and finally invented and produced in 1936, by Baltic German ...
* Nikon
(, ; ), also known just as Nikon, is a Japanese multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging products. The companies held by Nikon form the Nikon Group.
Nikon's products include cameras, camera ...
(Japan) – EDG, High Grade, Monarch, RAII, and Spotter series: roof prism; Prostar, Superior E, E, and Action EX series: porro; Prostaff series, Aculon series
* Olympus Corporation
is a Japanese manufacturer of optics and reprography products. Olympus was established on 12 October 1919, initially specializing in microscopes and thermometers. Olympus holds roughly a 70-percent share of the global endoscope market, estimated ...
(Japan)
* Pentax
is a brand name used primarily by the Japanese multinational imaging and electronics company Ricoh for DSLR cameras, lenses, sport optics (including binoculars and rifle scopes), and CCTV optics. The Pentax brand is also used by Hoya Corporation ...
(Japan) – DCFED/SP/XP series: roof prism; UCF series: inverted porro; PCFV/WP/XCF series: porro
* (Germany) – both porro prism and roof prism models
* Steiner-Optik Steiner-Optik (also rendered as Steiner Optics) is a manufacturer of optical equipment for the military, hunting and marine sector. The company is headquartered in Bayreuth, northern Bavaria, and has been part of the Beretta Group since 2008. Stei ...
(Germany)
* PRAKTICA (United Kingdom) for birdwatching, sightseeing, hiking, camping.
* Sunagor (Japan)
* Swarovski Optik
Swarovski Optik is a division of the Swarovski group of companies, manufacturing optical instruments. Its headquarters are located in Absam, Tyrol, Austria.
History
Wilhelm Swarovski, son of the original founder, was born in 1918. In 1935, wit ...
* Takahashi Seisakusho
is a Japanese manufacturer of telescopes and related equipment (such as eyepieces and equatorial mounts) founded in 1932 by Kitaro Takahashi in Tokyo. Originally started as a foundry, Takahashi began manufacturing optical equipment after WWII in ...
(Japan)
* Tasco
Tasco (also known as Tasco Worldwide) sells consumer telescopes. Tasco mainly imports telescopes for amateur astronomers but has expanded into other optical products, such as spotting scopes, microscopes, binoculars, telescopic sights, and other ...
* Vixen (telescopes) (Japan) – Apex/Apex Pro: roof prism; Ultima: porro
* Vivitar
Vivitar Corporation is a manufacturer, distributor, and marketer of photographic and optical equipment originally based in Santa Monica, California. Since 2008, the Vivitar name serves as Sakar International's house brand for digital imaging, o ...
(US)
* Vortex Optics
Vortex Optics is an American manufacturer of special optical equipments for hunting, wildlife watching, outdoor recreation, shooting sports and law enforcement and military. Vortex products include binoculars, spotting scopes, riflescopes, r ...
(US)
* Zeiss Zeiss or Zeiß may refer to:
People
*Carl Zeiss (1816–1888), German optician and entrepreneur
*Emil Zeiß (1833–1910), German Protestant minister and painter
Companies
*Carl Zeiss AG, German manufacturer of optics, industrial measurem ...
(Germany) – FL, Victory, Conquest: roof prism; 7×50 BGAT/T: porro, 15×60 BGA/T: porro, discontinued
See also
* Anti-fog
Anti-fog agents, also known as anti-fogging agents and treatments, are chemicals that prevent the condensation of water in the form of small droplets on a surface which resemble fog. Anti-fog treatments were first developed by NASA during Project ...
* Binoviewer
A binoviewer is an optical device designed to enable binocular viewing through a single objective.
In contrast to binoculars, it allows partially stereoscopic viewing and partially monoculair viewing, this because the eyes and brain still pro ...
* Globe effect
* Lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
* List of telescope types
The following are lists of devices categorized as types of telescopes or devices associated with telescopes. They are broken into major classifications with many variations due to professional, amateur, and commercial sub-types. Telescopes can be ...
* Monocular
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocul ...
* Optical telescope
An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electro ...
* Spotting scope
A spotting scope is a compact high-power telescope optimized for detailed observation of distant objects. They are used as portable optical enhancement devices for various outdoor activities such as birdwatching, skygazing and other naturalis ...
* Tower viewer
A tower viewer is a telescope or binoculars permanently mounted on a stalk. The device magnifies objects seen through its lenses, allowing users to see farther and more clearly than they could with the naked eye or with less powerful viewing dev ...
Notes
References
Further reading
* Walter J. Schwab, Wolf Wehran: "Optics for Hunting and Nature Observation". . 1st Edition, Wetzlar (Germany), 2011
External links
The history of the telescope & the binocular
by Peter Abrahams, May 2002
Glossary of Optical Terms
Binocular Optics and Mechanics Chapter from Binocular Astronomy by Stephen Tonkin
Binocular Astronomy by Stephen Tonkin
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