This page will contain videos about Binocular, as they become available.BinocularsBinocularsBinocular telescopes, or binoculars, are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, one to be viewed through each of the user's eyes. By contrast, relatively small single-tube telescopes are often called "monoculars". The advantages of a binocular over a monocular telescope are:
The most commonly seen binoculars are of a size to be held by hand, and contain optical elements to fold the optical path so that the physical length of the binoculars is less than the focal length of the lenses. The folding of the optical path allows the separation between the objective lenses to be increased, allowing larger lenses to be used and giving a better sensation of depth. All practical binoculars display an erect image, obtained either by using simple Galilean optics ("field glasses", "opera glasses"), or by using optical prisms both to erect the image and to fold the optical path. Larger binoculars become uncomfortable and difficult to hold steady, and are mounted on tripods or other supports. Very large binoculars with a very wide separation (up to 15 meters, weight 10 tonnes, for ranging Second World War naval gun targets 25km away) have been used for accurate rangefinding, although late twentieth century technology made this application redundant. An extreme example, although not one would that normally be called binoculars, is the Large Binocular Telescope in Arizona, USA, which produced its "First Light" image on 26 October 2005. The LBT comprises two 8-meter reflector telescopes. While not intended to be held to the eyes of a viewer (!), the use of two telescopes to view the same object gives additional information due to the larger field of view that results from the separation of the objective mirrors. Prismatic binocularsBinoculars with prisms to shorten the optical path and erect the image may have double Porro prism design which gives a Z-shaped optical path. This results in a set of binoculars which is wide, with objective lenses which are well-separated but offset from the eyepieces. Binoculars which use roof prisms (either the Abbe-Koenig or Schmidt-Pechan designs) are narrower, more compact, lighter, and more expensive than those which use Porro prisms. They have objective lenses which are approximately in line with the eyepieces. Design detailsBinoculars to be used to view objects which are not at a fixed distance must have a focussing arrangement. In some cases the two telescopes are focused independently by changing the distance between ocular and objective lenses. It is more convenient for the viewer to focus both tubes with one action (usually rotation of a central focussing wheel), and for one of the two eyepieces to be adjustable to compensate for differences between the viewer's eyes (usually by rotating the eyepiece in its mount). Once this adjustment has been made for a given viewer, the binoculars can be refocussed on an object at a different distance by using the focusing wheel to move both tubes together without eyepiece readjustment. The distance between the eyepieces on most binoculars can be adjusted to accommodate viewers with different eye separation. Optical parametersOptical layout of a binocular with a double-Porro designThe diameter of the objective lenses determines the light-gathering power and the ultimate resolving power of the binoculars. The ratio of the focal lengths of the objective and the ocular lenses gives the linear magnifying power (expressed in "diameters"). It is customary to categorise binoculars by the magnification × the objective diameter in mm; e.g. 7×50. The magnification required depends upon the application, but with the major proviso that large magnifications give an image much more susceptible to shake when hand-held. The objective lens needs to be large enough to give acceptable resolution in all circumstances, but must be larger for low-light and night use. The field of view depends upon the optical construction of the binoculars. Simple Galilean binoculars have the disadvantage of a narrower field of view—this is the reason for the prevalence of the more complex optical arrangements used. For general hand-held use, subject to shake, 7 diameters is a good compromise between power and image steadiness for most people. 7×30 is good for daytime use. For general night use, a 50mm objective gives maximum brightness for 7 diameters magnification; objective diameter must be increased for higher magnifications at night. Hand-held binoculars range from small 3x10 Galilean opera glasses used in theaters, to glasses with 7 to 12 diameters magnification and 30 to 50mm objectives for typical outdoor use. Larger models with objectives of up to about 150mm are used on supports, typically for amateur astronomy. Much larger binoculars have been made by dedicated amateur astronomers, essentially using two refracting or reflecting astronomical telescopes, with results claimed to be impressive. Of particular relevance for low-light and astronomical viewing, as against astrophotography, is the ratio between magnifying power and objective lens diameter. Binoculars concentrate the light gathered by the objective into a beam, the exit pupil whose diameter is the objective diameter divided by the magnifying power. For maximum effective light-gathering and brightest image, the exit pupil should equal the diameter of the fully dilated human eye—about 7mm, reducing with age. Light gathered by a larger exit pupil is wasted. However, for viewing stars and small astronomical objects, a large exit pupil will mostly image the night sky background, effectively decreasing contrast, making the detection of faint objects more difficult except perhaps in remote locations with negligible light pollution. A large exit pupil facilitates viewing larger objects such as nearby galaxies, though. The current trend favours models with 5mm exit pupil, such as 10x50, or 8x40; 7x50 is falling out of favour. For daytime use an exit pupil of 3mm—matching the eye's contracted pupil—is sufficient. Optical constructionU.S. Navy binocularsWhen light strikes an interface between two materials of different refractive index (e.g., at an air-glass interface), some of the light is transmitted, some reflected. In any sort of image-forming optical instrument (telescope, camera, microscope, etc.), ideally no light should be reflected; instead of forming an image, light which reaches the viewer after being reflected is distributed in the field of view, and reduces the contrast between the true image and the background. Reflection can be reduced, but not eliminated, by applying optical coatings to interfaces; this is of great importance for any optical instrument with multiple interfaces. Light can also be reflected from the interior of the instrument, but it is simple to minimise this to negligible proportions. Phase-corrected prism coating and dielectric prism coating are recent (in 2005) effective techniques for reducing reflections. When light traverses an optically transmissive material, some light is absorbed. This reduces brightness, and is also undesirable, although less of a problem than reflections in most cases. (The advanced naval binocular rangefinders of the mid-twentieth century had perhaps 150 glass elements; absorption of light would have been significant.) Different optical construction affects reflections and brightness. A Porro prism binocular will inherently produce an intrinsically brighter image than a roof prism binocular of the same magnification, objective size, and optical quality, as less light is absorbed along the optical path. However, as of 2005, the optical quality of the best roof-prism binoculars with up-to-date coating processes as used in Schmidt-Pechan models is comparable with the best Porro glasses, and it appears that roof prisms will dominate the market for high-quality portable binoculars in spite of their higher price. The major European optical manufacturers (Leica, Zeiss, Swarovski) have discontinued their Porro lines; Japanese manufacturers (Nikon, Fujinon, etc.) may follow suit. When buying binoculars of lower price, Porro prism binoculars can be expected to give more image quality for money. Image stabilisationShake can be much reduced, and higher magnifications used, with binoculars using image stabilisation technology. Parts of the instrument which change the position of the image may be held steady by powered gyroscopes or by powered mechanisms driven by gyroscopic or inertial detectors, or may be mounted in such a way as to oppose and dampen sudden movement. Stabilisation 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 unstabilised binoculars when tripod-mounted, and stabilised binoculars contain more advanced technology to go wrong, and to become obsolete. They are also more expensive, heavier, and battery life tends to be short. Stabilisation is not suitable when tracking moving objects. MaintenanceIf the binoculars are not collimated properly, i.e., if the images from the two tubes are not properly aligned, then they will give poor results and can be uncomfortable and tiring to use. This may be due to poor manufacturing quality control (more likely with cheaper binoculars) or to a shock (being dropped) or drift over time. If the binoculars are basically sound, this can be remedied by small movements to the prisms, often by turning screws accessible without opening the binoculars. While it is inadvisable for the non-expert to try to repair quality instruments, collimation by the owner may be justified for maladjusted binoculars which are not good enough to merit the expense of professional attention. Instructions for checking binoculars for collimation errors, and for collimating them, can be found on the Internet (search for collimation binoculars and the model). A well-collimated pair of binoculars should produce, when viewed through human eyes and processed by a human brain, a single circular, apparently three-dimensional, image, with no visible indication that we are actually viewing two distinct images from slightly different viewpoints. Departure from the ideal causes, at best, vague discomfort and visual fatigue, but the perceived field of view will be close to circular anyway. The cinematic convention to represent a view through binoculars as two circles partially overlapping in a figure-of-eight shape is not true to life. Choosing binocularsNaval ship binocularsIdeally a pair of binoculars will produce two uniformly sharp images, each of perfect quality, with no errors of geometry or colour-correction and no internal reflections. The two images will be identical (apart from the slightly different viewpoint), with no differences in size, orientation, aberrations, etc. Real binoculars depart to a greater or lesser extent from the ideal. All binoculars should be accurately aligned and collimated, comfortable to use, and robust. Roof-prism models will be lighter and more compact for a given size, but more expensive than equivalent Porro models. Hermetically sealed binoculars filled with dry gas (usually nitrogen) will not be susceptible to clouding due to condensation at low temperatures; this will also help to prevent mildew, although air may leak in over a period of years if the binoculars are not overhauled. Completely waterproof (submersible) binoculars are available. All binoculars should be reasonably free from reflections. Fully multi-coated (FMC) models should be better in this respect than others. For roof-prism models, phase coating is better. The magnification and objective diameter must be chosen to suit the requirement, remembering that higher magnification exaggerates shake when hand-held, and that larger objective lenses increase the weight and size. For general-purpose use, 8x40 is a good combination. 7x50 is brighter for night use. Larger objective diameters have better light-gathering power, and can view fainter objects for astronomical use. If more compact binoculars are required, smaller objectives may be used at some loss of performance and increase in price. Image stabilisation much improves image steadiness and allows the use of higher magnification in hand-held applications. The trade-off is that compared to unstabilised binoculars of the same parameters, stabilised binoculars are more expensive, larger and heavier, less reliable due to their complexity, more subject to obsolescence, and consume batteries. Zoom binoculars, while in principle a good idea, do not perform very well. Some binoculars (and cameras) claim to be "focus-free". This is an example of marketing departments making a virtue of necessity. Such models would have been called "fixed-focus" in more honest times: they have a depth of field from a relatively large closest distance, to infinity, and perform exactly the same as a focussing model of the same optical quality (or lack of it) focussed on the middle distance. Binoculars of the same make and model may vary from unit to unit, although hopefully less so for the more highly priced models from quality manufacturers, so the experienced user may benefit from trying several samples. By the same token, many cheaper types of generally mediocre quality but basically sound design may have a few exceptionally good units. Some reputable binocular manufacturers as of 2005: 1. European Brands
2. Japanese Brands
P.S. Many of the above are OEM products of Kamakura or Chinese manufacturing plants. 3. Chinese Brands In the early years of the 21st century some mid-priced glasses have become available on the internal Chinese market. A few of them are said to be comparable both in performance and in price to some of the better brands; the great majority of them are inferior.
Binoculars are widely used by amateur astronomers, their wide field of view making them useful for comet and supernova seeking (giant binoculars) and general observation (portable binoculars). The major market is amongst bird watchers and hunters, who mostly prefer, and are prepared to pay for, the lighter but more expensive roof-prism models. This page about Binocular includes information from a Wikipedia article. Additional articles about Binocular News stories about Binocular External links for Binocular Videos for Binocular Wikis about Binocular Discussion Groups about Binocular Blogs about Binocular Images of Binocular |
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The major market is amongst bird watchers and hunters, who mostly prefer, and are prepared to pay for, the lighter but more expensive roof-prism models. 3. Peter Berkowitz's Democratizing The Constitution. Many of the above are OEM products of Kamakura or Chinese manufacturing plants. However, both books' historical premises and practical prescriptions have been challenged, for example by Prof. P.S. Having established this premise of what liberty is, and argued that the Framers intended to maximize active liberty over the modern liberty, Breyer argues a predominantly Utilitarian case for Judges making rulings which give effect to the democratic intentions of the Constitution. Japanese Brands. Breyer terms this "modern liberty." The second Berlinian concept — to Berlin, "positive liberty" - is the "freedom to participate in the government;" In Breyer's terminology, this is the titular "active liberty," which he believes the Judge should champion. 2. But what is liberty? Breyer refers the reader to Isaiah Berlin’s Two Concepts of Liberty. The first Berlinian concept, being what most people understand by liberty, is "freedom from government coercion;" Berlin termed this negative liberty and warned against its dimunition. European Brands. Breyer argues that the Framers of the Constitution set out to establish a democratic government involving the maximum liberty for its citizens. 1. Breyer's recent book, Active Liberty: Interpreting Our Democratic Constitution, deals with his judicial philosophy at greater length, emphasizing his belief in judicial deference to democratic decision-making. Some reputable binocular manufacturers as of 2005:. Breyer has also demonstrated a consistent pattern of deference to Congress, voting to overturn congressional legislation at a lower rate than any other Supreme Court justice since 1994.[4]. By the same token, many cheaper types of generally mediocre quality but basically sound design may have a few exceptionally good units. However, Breyer is also deferential to the interests of law enforcement and urges that the Court be deferential to legislative judgments in its First Amendment rulings. Binoculars of the same make and model may vary from unit to unit, although hopefully less so for the more highly priced models from quality manufacturers, so the experienced user may benefit from trying several samples. He has also urged that the Supreme Court cite international law in its decisions. Such models would have been called "fixed-focus" in more honest times: they have a depth of field from a relatively large closest distance, to infinity, and perform exactly the same as a focussing model of the same optical quality (or lack of it) focussed on the middle distance. He has consistently voted in favor of abortion rights, which is one of the most controversial areas of the Supreme Court's docket. This is an example of marketing departments making a virtue of necessity. While somewhat moderate, Breyer most frequently sides with Justices John Paul Stevens, David Souter and Ruth Bader Ginsburg, generally acknowledged as being the "liberal" wing of the court. Some binoculars (and cameras) claim to be "focus-free". He has said that while some of his colleagues "emphasize language, a more literal reading of the text, history and tradition," he prefers to consider the "purpose and consequences" of the text.[3]. Zoom binoculars, while in principle a good idea, do not perform very well. On the bench, Breyer generally takes a pragmatic approach to constitutional issues, interested more in producing coherence and continuity in the law than in following doctrinal, historical or textual strictures. The trade-off is that compared to unstabilised binoculars of the same parameters, stabilised binoculars are more expensive, larger and heavier, less reliable due to their complexity, more subject to obsolescence, and consume batteries. Although Chief Justice Roberts joined the Court in September of 2005, the duties of the junior Justice never fall upon the Chief Justice, who is considered primus inter pares -first among equals. Image stabilisation much improves image steadiness and allows the use of higher magnification in hand-held applications. The junior Associate Justice on the Court is expected to take on duties such as opening and closing the door at private conference meetings and fetching coffee [2]. If more compact binoculars are required, smaller objectives may be used at some loss of performance and increase in price. Breyer was also the second longest-serving "junior justice" in the history of the Court, close to surpassing the record set by Justice Joseph Story of 4,228 days (from February 3, 1812 to September 1, 1823); Breyer fell 29 days short of tying this record, which he would have reached on March 1, 2006, had Justice Samuel Alito not joined the Court on January 31, 2006. Larger objective diameters have better light-gathering power, and can view fainter objects for astronomical use. Senate in an 87 to 9 vote and took his seat August 3, 1994. 7x50 is brighter for night use. Breyer was confirmed by the U.S. For general-purpose use, 8x40 is a good combination. Clinton nominated him as an Associate Justice of the Supreme Court on May 17, 1994, to fill the vacancy left after the retirement of Harry Blackmun in 1994. The magnification and objective diameter must be chosen to suit the requirement, remembering that higher magnification exaggerates shake when hand-held, and that larger objective lenses increase the weight and size. In 1993 President Bill Clinton considered him for the seat which ultimately went to Ruth Bader Ginsburg. For roof-prism models, phase coating is better. On the sentencing commission, Breyer played a key role in reforming federal criminal sentencing procedures, producing the Federal Sentencing Guidelines, which were formulated to increase uniformity in sentences for criminal cases. Fully multi-coated (FMC) models should be better in this respect than others. He also served as a member of the Judicial Conference of the United States between 1990 and 1994 and the United States Sentencing Commission between 1985 and 1989. All binoculars should be reasonably free from reflections. His nomination to the Court of Appeals was the last judgeship approved by the Senate in the Carter administration. Completely waterproof (submersible) binoculars are available. From 1980 to 1994, he served as a Judge on the United States Court of Appeals for the First Circuit and as its Chief Judge from 1990 to 1994. Hermetically sealed binoculars filled with dry gas (usually nitrogen) will not be susceptible to clouding due to condensation at low temperatures; this will also help to prevent mildew, although air may leak in over a period of years if the binoculars are not overhauled. Breyer was a visiting professor at the College of Law in Sydney, Australia and later at the University of Rome. Roof-prism models will be lighter and more compact for a given size, but more expensive than equivalent Porro models. Both remain extremely important in the law of administration and bureaucracies. All binoculars should be accurately aligned and collimated, comfortable to use, and robust. While there, he authored two highly influential books on deregulation: Breaking the Vicious Circle: Toward Effective Risk Regulation and Regulation and Its Reform. Real binoculars depart to a greater or lesser extent from the ideal. At Harvard, Breyer was known as a leading expert on administrative law. The two images will be identical (apart from the slightly different viewpoint), with no differences in size, orientation, aberrations, etc. Breyer stayed at Harvard Law School until 1994, and he also served as a professor at Harvard's Kennedy School of Government from 1977 to 1980. Ideally a pair of binoculars will produce two uniformly sharp images, each of perfect quality, with no errors of geometry or colour-correction and no internal reflections. Breyer became an assistant professor, law professor, and lecturer at Harvard Law School starting in 1967, the same year he married Joanna Hare, a psychologist and member of the British aristocracy with whom he now has three children (Chloe, Nell, and Michael). The cinematic convention to represent a view through binoculars as two circles partially overlapping in a figure-of-eight shape is not true to life. Kennedy of Massachusetts, and helped pass a airline deregulation legislation in the United States that closed the Civil Aeronautics Board. Departure from the ideal causes, at best, vague discomfort and visual fatigue, but the perceived field of view will be close to circular anyway. He worked closely with the chairman of the committee, Senator Edward M. A well-collimated pair of binoculars should produce, when viewed through human eyes and processed by a human brain, a single circular, apparently three-dimensional, image, with no visible indication that we are actually viewing two distinct images from slightly different viewpoints. Senate Committee on the Judiciary from 1974 to 1975 and served as chief counsel of the committee from 1979 to 1980. Instructions for checking binoculars for collimation errors, and for collimating them, can be found on the Internet (search for collimation binoculars and the model). Breyer was a special counsel to the U.S. While it is inadvisable for the non-expert to try to repair quality instruments, collimation by the owner may be justified for maladjusted binoculars which are not good enough to merit the expense of professional attention. Attorney General for Antitrust from 1965 to 1967 and an assistant special prosecutor on the Watergate Special Prosecution Force in 1973. If the binoculars are basically sound, this can be remedied by small movements to the prisms, often by turning screws accessible without opening the binoculars. He was a special assistant to the Assistant U.S. This may be due to poor manufacturing quality control (more likely with cheaper binoculars) or to a shock (being dropped) or drift over time. Breyer served as a law clerk to Associate Justice Arthur Goldberg during the 1964 term. If the binoculars are not collimated properly, i.e., if the images from the two tubes are not properly aligned, then they will give poor results and can be uncomfortable and tiring to use. [1]. Stabilisation is not suitable when tracking moving objects. Breyer is the older brother of federal district judge Charles Breyer. They are also more expensive, heavier, and battery life tends to be short. After graduating from Lowell, Breyer went on to receive a Bachelor of Arts in philosophy from Stanford University, a Bachelor of Arts from Magdalen College at the University of Oxford as a Marshall Scholar, and a Bachelor of Laws (LL.B) from Harvard Law School. There are some disadvantages: the image may not be quite as good as the best unstabilised binoculars when tripod-mounted, and stabilised binoculars contain more advanced technology to go wrong, and to become obsolete. At Lowell, he was a member of the Lowell Forensic Society and debated regularly in high school debate tournaments, including against future Harvard Law School professor Lawrence Tribe. These techniques allow binoculars up to 20× to be hand-held, and much improve the image stability of lower-power instruments. In 1955, Breyer graduated from Lowell High School. Stabilisation may be enabled or disabled by the user as required. At age 12, he was awarded Eagle Scout. Parts of the instrument which change the position of the image may be held steady by powered gyroscopes or by powered mechanisms driven by gyroscopic or inertial detectors, or may be mounted in such a way as to oppose and dampen sudden movement. Breyer was born to a middle-class Jewish family in San Francisco, California, on August 15, 1938. Shake can be much reduced, and higher magnifications used, with binoculars using image stabilisation technology. . When buying binoculars of lower price, Porro prism binoculars can be expected to give more image quality for money. Supreme Court. The major European optical manufacturers (Leica, Zeiss, Swarovski) have discontinued their Porro lines; Japanese manufacturers (Nikon, Fujinon, etc.) may follow suit. Since 1994 he has served as an Associate Justice of the U.S. However, as of 2005, the optical quality of the best roof-prism binoculars with up-to-date coating processes as used in Schmidt-Pechan models is comparable with the best Porro glasses, and it appears that roof prisms will dominate the market for high-quality portable binoculars in spite of their higher price. Stephen Gerald Breyer (born August 15, 1938) is an American attorney, political figure, and jurist. A Porro prism binocular will inherently produce an intrinsically brighter image than a roof prism binocular of the same magnification, objective size, and optical quality, as less light is absorbed along the optical path. ISBN 140003003X. Different optical construction affects reflections and brightness. Vintage. (The advanced naval binocular rangefinders of the mid-twentieth century had perhaps 150 glass elements; absorption of light would have been significant.). My Life. This reduces brightness, and is also undesirable, although less of a problem than reflections in most cases. Clinton, Bill (2005). When light traverses an optically transmissive material, some light is absorbed. Phase-corrected prism coating and dielectric prism coating are recent (in 2005) effective techniques for reducing reflections. Light can also be reflected from the interior of the instrument, but it is simple to minimise this to negligible proportions. Reflection can be reduced, but not eliminated, by applying optical coatings to interfaces; this is of great importance for any optical instrument with multiple interfaces. In any sort of image-forming optical instrument (telescope, camera, microscope, etc.), ideally no light should be reflected; instead of forming an image, light which reaches the viewer after being reflected is distributed in the field of view, and reduces the contrast between the true image and the background. When light strikes an interface between two materials of different refractive index (e.g., at an air-glass interface), some of the light is transmitted, some reflected. For daytime use an exit pupil of 3mm—matching the eye's contracted pupil—is sufficient. The current trend favours models with 5mm exit pupil, such as 10x50, or 8x40; 7x50 is falling out of favour. A large exit pupil facilitates viewing larger objects such as nearby galaxies, though. However, for viewing stars and small astronomical objects, a large exit pupil will mostly image the night sky background, effectively decreasing contrast, making the detection of faint objects more difficult except perhaps in remote locations with negligible light pollution. Light gathered by a larger exit pupil is wasted. For maximum effective light-gathering and brightest image, the exit pupil should equal the diameter of the fully dilated human eye—about 7mm, reducing with age. Binoculars concentrate the light gathered by the objective into a beam, the exit pupil whose diameter is the objective diameter divided by the magnifying power. Of particular relevance for low-light and astronomical viewing, as against astrophotography, is the ratio between magnifying power and objective lens diameter. Much larger binoculars have been made by dedicated amateur astronomers, essentially using two refracting or reflecting astronomical telescopes, with results claimed to be impressive. Larger models with objectives of up to about 150mm are used on supports, typically for amateur astronomy. Hand-held binoculars range from small 3x10 Galilean opera glasses used in theaters, to glasses with 7 to 12 diameters magnification and 30 to 50mm objectives for typical outdoor use. For general night use, a 50mm objective gives maximum brightness for 7 diameters magnification; objective diameter must be increased for higher magnifications at night. 7×30 is good for daytime use. For general hand-held use, subject to shake, 7 diameters is a good compromise between power and image steadiness for most people. Simple Galilean binoculars have the disadvantage of a narrower field of view—this is the reason for the prevalence of the more complex optical arrangements used. The field of view depends upon the optical construction of the binoculars. The objective lens needs to be large enough to give acceptable resolution in all circumstances, but must be larger for low-light and night use. The magnification required depends upon the application, but with the major proviso that large magnifications give an image much more susceptible to shake when hand-held. 7×50. It is customary to categorise binoculars by the magnification × the objective diameter in mm; e.g. The ratio of the focal lengths of the objective and the ocular lenses gives the linear magnifying power (expressed in "diameters"). The diameter of the objective lenses determines the light-gathering power and the ultimate resolving power of the binoculars. The distance between the eyepieces on most binoculars can be adjusted to accommodate viewers with different eye separation. Once this adjustment has been made for a given viewer, the binoculars can be refocussed on an object at a different distance by using the focusing wheel to move both tubes together without eyepiece readjustment. It is more convenient for the viewer to focus both tubes with one action (usually rotation of a central focussing wheel), and for one of the two eyepieces to be adjustable to compensate for differences between the viewer's eyes (usually by rotating the eyepiece in its mount). In some cases the two telescopes are focused independently by changing the distance between ocular and objective lenses. Binoculars to be used to view objects which are not at a fixed distance must have a focussing arrangement. They have objective lenses which are approximately in line with the eyepieces. Binoculars which use roof prisms (either the Abbe-Koenig or Schmidt-Pechan designs) are narrower, more compact, lighter, and more expensive than those which use Porro prisms. This results in a set of binoculars which is wide, with objective lenses which are well-separated but offset from the eyepieces. Binoculars with prisms to shorten the optical path and erect the image may have double Porro prism design which gives a Z-shaped optical path. . While not intended to be held to the eyes of a viewer (!), the use of two telescopes to view the same object gives additional information due to the larger field of view that results from the separation of the objective mirrors. The LBT comprises two 8-meter reflector telescopes. An extreme example, although not one would that normally be called binoculars, is the Large Binocular Telescope in Arizona, USA, which produced its "First Light" image on 26 October 2005. Very large binoculars with a very wide separation (up to 15 meters, weight 10 tonnes, for ranging Second World War naval gun targets 25km away) have been used for accurate rangefinding, although late twentieth century technology made this application redundant. Larger binoculars become uncomfortable and difficult to hold steady, and are mounted on tripods or other supports. All practical binoculars display an erect image, obtained either by using simple Galilean optics ("field glasses", "opera glasses"), or by using optical prisms both to erect the image and to fold the optical path. The folding of the optical path allows the separation between the objective lenses to be increased, allowing larger lenses to be used and giving a better sensation of depth. The most commonly seen binoculars are of a size to be held by hand, and contain optical elements to fold the optical path so that the physical length of the binoculars is less than the focal length of the lenses. The advantages of a binocular over a monocular telescope are:. By contrast, relatively small single-tube telescopes are often called "monoculars". Binocular telescopes, or binoculars, are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, one to be viewed through each of the user's eyes. Yunnan State optics (MS series: Porro). WDtian (from Yunnan State optics, all Porro). Navigator series: Roof; Ares series: Porro). Sicong (from Xian Stateoptics. (Specialized in over-sized Porro binocualars). Miyauchi Co. (Apex/Apex Pro: Roof; Ultima: Porro). Vixen Co. (Activa, some are Roof, some are Porro). Minolta Co. (EXWPI series: Roof). OLympus Co. (DCFSP/XP series; Roof, UCF series: Inverted Porro; PCFV/WP/XCF series: Porro). Pentax Co. (BD series: Roof). Kowa Co. (FMTSX, MTSX series: Porro). Fujinon Co. (High Grade series, Monarch series,RAII, Spotter series: Roof; Prostar series, Superior E series, E series, Action EX series: Porro). Nikon Co. series, Porro variants?). (I.S. Canon Co. Russian Military Binoculars (BPOc 10x42 7x30, BKFC series). Steiner (Commander, Nighthunter: Porro; Predator, Wildlife: Roof). Optolyth (Royal: Roof; Alpin: Porro). Docter Optik (Nobilem: Porro). Zeiss GmbH (FL,Victory, Conquest: all are Roof; 7x50 BGAT/T, 15x60 BGA/T:Porro, but to be discontinued). Swarovski Optik (SLC, EL: all are Roof; Habicht: Porro, but to be discontinued). Leica GmbH (Ultravid, Duovid, Geovid: all are Roof). it is easier and more comfortable to steadily hand-hold and move a pair of binoculars than a single tube—the two hands and the head form a steady 3-point platform. it is more comfortable to use both eyes for viewing, without the need to close or obstruct one eye to avoid confusion. it gives a 3-dimensional image with depth: the two distinct views presented from slightly different viewpoints to each of the viewer's eyes merge to produce a single perceived view with a sensation of depth, allowing distances to be estimated. |