1.
Aperture
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In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of a system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, a wide aperture admits uncollimated rays, resulting in a sharp focus only for rays coming from a certain distance. This means that a wide aperture results in an image that is sharp for things at the correct distance, the aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane. In the human eye, the pupil is the aperture, an optical system typically has many openings or structures that limit the ray bundles. In general, these structures are called stops, and the stop is the stop that primarily determines the ray cone angle. In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the stop or the opening itself. For example, in a telescope, the stop is typically the edges of the objective lens or mirror. One then speaks of a telescope as having, for example, note that the aperture stop is not necessarily the smallest stop in the system. Magnification and demagnification by lenses and other elements can cause a large stop to be the aperture stop for the system. In astrophotography, the aperture may be given as a measure or as the dimensionless ratio between that measure and the focal length. In other photography, it is given as a ratio. Sometimes stops and diaphragms are called apertures, even when they are not the stop of the system. The word aperture is used in other contexts to indicate a system which blocks off light outside a certain region. In astronomy, for example, a photometric aperture around a star usually corresponds to a window around the image of a star within which the light intensity is assumed. The aperture stop is an important element in most optical designs and its most obvious feature is that it limits the amount of light that can reach the image/film plane. This can be unavoidable, as in a telescope where one wants to collect as much light as possible, or deliberate
2.
Pinhole (optics)
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A pinhole is a small circular hole, as could be made with the point of a pin. In optics, pinholes with diameter between a few micrometers and a hundred micrometers are used as apertures in optical systems, pinholes are commonly used to spatially filter a beam, where the small pinhole acts as a low-pass filter for spatial frequencies in the image plane of the beam. A small pinhole can act as a lens, focusing light and this effect is used in pinhole cameras. This effect is used in pinhole occluders, which are used by ophthalmologists, orthoptists and optometrists to test visual acuity. The same principle has also applied as an alternative to corrective lenses
3.
Camera obscura
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The surroundings of the projected image have to be relatively dark for the image to be clear, so many historical camera obscura experiments were performed in dark rooms. The term camera obscura also refers to constructions or devices that use of the principle within a box. Camerae obscurae with a lens in the opening have been used since the second half of the 16th century, before the term camera obscura was first used in 1604, many other expressions were used including cubiculum obscurum, cubiculum tenebricosum, conclave obscurum and locus obscurus. Rays of light travel in straight lines and change when they are reflected and partly absorbed by an object, retaining information about the color, lit objects reflect rays of light in all directions. The human eye itself works much like a camera obscura with an opening, a biconvex lens, a camera obscura device consists of a box, tent or room with a small hole in one side. Light from a scene passes through the hole and strikes a surface inside, where the scene is reproduced, inverted and reversed. The image can be projected onto paper, and can then be traced to produce an accurate representation. In order to produce a reasonably clear projected image, the aperture has to be about 1/100th the distance to the screen, many camerae obscurae use a lens rather than a pinhole because it allows a larger aperture, giving a usable brightness while maintaining focus. As the pinhole is made smaller, the image gets sharper, with too small a pinhole, however, the sharpness worsens, due to diffraction. Using mirrors, as in an 18th-century overhead version, it is possible to project a right-side-up image, another more portable type is a box with an angled mirror projecting onto tracing paper placed on the glass top, the image being upright as viewed from the back. There are theories that occurrences of camera obscura effects inspired paleolithic cave paintings and it is also suggested that camera obscura projections could have played a role in Neolithic structures. Perforated gnomons projecting an image of the sun were described in the Chinese Zhoubi Suanjing writings. The location of the circle can be measured to tell the time of day. In Arab and European cultures its invention was later attributed to Egyptian astronomer. Some ancient sightings of gods and spirits, especially in worship, are thought to possibly have been conjured up by means of camera obscura projections. In these writings it is explained how the image in a collecting-point or treasure house is inverted by an intersecting point that collected the light. Light coming from the foot of a person would partly be hidden below. Rays from the head would partly be hidden above and partly form the part of the image
4.
Ibn al-Haytham
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Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham, also known by the Latinization Alhazen or Alhacen, was an Arab Muslim scientist, mathematician, astronomer, and philosopher. Ibn al-Haytham made significant contributions to the principles of optics, astronomy, mathematics and he was the first to explain that vision occurs when light bounces on an object and then is directed to ones eyes. He spent most of his close to the court of the Fatimid Caliphate in Cairo and earned his living authoring various treatises. In medieval Europe, Ibn al-Haytham was honored as Ptolemaeus Secundus or simply called The Physicist and he is also sometimes called al-Baṣrī after his birthplace Basra in Iraq, or al-Miṣrī. Ibn al-Haytham was born c.965 in Basra, which was part of the Buyid emirate. Alhazen arrived in Cairo under the reign of Fatimid Caliph al-Hakim, Alhazen continued to live in Cairo, in the neighborhood of the famous University of al-Azhar, until his death in 1040. Legend has it that after deciding the scheme was impractical and fearing the caliphs anger, during this time, he wrote his influential Book of Optics and continued to write further treatises on astronomy, geometry, number theory, optics and natural philosophy. Among his students were Sorkhab, a Persian from Semnan who was his student for three years, and Abu al-Wafa Mubashir ibn Fatek, an Egyptian prince who learned mathematics from Alhazen. Alhazen made significant contributions to optics, number theory, geometry, astronomy, Alhazens work on optics is credited with contributing a new emphasis on experiment. In al-Andalus, it was used by the prince of the Banu Hud dynasty of Zaragossa and author of an important mathematical text. A Latin translation of the Kitab al-Manazir was made probably in the twelfth or early thirteenth century. His research in catoptrics centred on spherical and parabolic mirrors and spherical aberration and he made the observation that the ratio between the angle of incidence and refraction does not remain constant, and investigated the magnifying power of a lens. His work on catoptrics also contains the known as Alhazens problem. Alhazen wrote as many as 200 books, although only 55 have survived, some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew, the crater Alhazen on the Moon is named in his honour, as was the asteroid 59239 Alhazen. In honour of Alhazen, the Aga Khan University named its Ophthalmology endowed chair as The Ibn-e-Haitham Associate Professor, Alhazen, by the name Ibn al-Haytham, is featured on the obverse of the Iraqi 10, 000-dinar banknote issued in 2003, and on 10-dinar notes from 1982. The 2015 International Year of Light celebrated the 1000th anniversary of the works on optics by Ibn Al-Haytham, Alhazens most famous work is his seven-volume treatise on optics Kitab al-Manazir, written from 1011 to 1021. Optics was translated into Latin by a scholar at the end of the 12th century or the beginning of the 13th century
5.
Solar eclipse
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As seen from the Earth, a solar eclipse is a type of eclipse that occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks the Sun. This can happen only at new moon when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy, in a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured, if the Moon were in a perfectly circular orbit, a little closer to the Earth, and in the same orbital plane, there would be total solar eclipses every month. However, the Moons orbit is inclined at more than 5 degrees to the Earths orbit around the Sun, Earths orbit is called the ecliptic plane as the Moons orbit must cross this plane in order for an eclipse to occur. In addition, the Moons actual orbit is elliptical, often taking it far away from Earth that its apparent size is not large enough to block the Sun totally. The orbital planes cross each other at a line of nodes resulting in at least two, and up to five, solar eclipses occurring each year, no more than two of which can be total eclipses. However, total solar eclipses are rare at any particular location because totality exists only along a path on the Earths surface traced by the Moons shadow or umbra. An eclipse is a natural phenomenon, nevertheless, in some ancient and modern cultures, solar eclipses have been attributed to supernatural causes or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of its explanation, as the Sun seems to disappear during the day. People referred to as eclipse chasers or umbraphiles will travel to locations to observe or witness predicted central solar eclipses. For the date of the next eclipse see the section Recent, during any one eclipse, totality occurs at best only in a narrow track on the surface of Earth. An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon. A hybrid eclipse shifts between a total and annular eclipse, at certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth and this phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as an eclipse, because the umbra passes above the Earths polar regions. Partial eclipses are virtually unnoticeable in terms of the suns brightness, even at 99%, it would be no darker than civil twilight. Of course, partial eclipses can be observed if one is viewing the sun through a darkening filter, the Suns distance from Earth is about 400 times the Moons distance, and the Suns diameter is about 400 times the Moons diameter. Because these ratios are approximately the same, the Sun and the Moon as seen from Earth appear to be approximately the same size, about 0.5 degree of arc in angular measure
6.
Giambattista della Porta
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Giambattista della Porta, also known as Giovanni Battista Della Porta was an Italian scholar, polymath and playwright who lived in Naples at the time of the Scientific Revolution and Reformation. Giambattista della Porta spent the majority of his life on scientific endeavors and he benefited from an informal education of tutors and visits from renowned scholars. His most famous work, first published in 1558, was entitled Magiae Naturalis, in this book he covered a variety of the subjects he had investigated, including the study of, occult philosophy, astrology, alchemy, mathematics, meteorology, and natural philosophy. He was also referred to as professor of secrets, Giambattista della Porta was born at Vico Equense, near Naples, to the nobleman Nardo Antonio della Porta. He was the third of four sons, second to survive childhood, having an older brother Gian Vincenzo, Della Porta had a privileged childhood including his education. His father had a thirst for learning, a trait he would pass all of his children. He surrounded himself with distinguished people and entertained the likes of philosophers, mathematicians, poets, the atmosphere of the house resembled an academy for his sons. The members of the circle of friends stimulated the boys, tutoring and mentoring them. It is possible that his fathers interest and influence in providing a well-rounded education helped to turn della Porta into the Renaissance man that he was to become. As well as having talents for the sciences and mathematics, all the brothers were also interested in the arts. Despite their interest none of them possessed any sort of talent for it and they were all accepted into the Scuola di Pitagora, a highly exclusive academy of musicians. Apparently the pure impressiveness of their intellect was enough to allow three tone-deaf mathematicians into a school for the musically gifted, the status of the family as a symbol of knowledge and intellectual growth surely helped in their acceptance as well. More aware of their social position than the idea that his sons could have professions in science, Nardo Antonio was raising the more as gentlemen. Therefore, the boys struggled with singing, as that was considered an accomplishment of gentlemen. They were taught to dance, ride, to part and perform well in tournaments and games. The training gave della Porta, at least earlier in his life, a taste for the aspects of his privileged living. This kind of lifestyle, the façade and showmanship involved in presenting ones self carried with Giambattista throughout his life, in 1563, della Porta published De Furtivis Literarum Notis, a work about cryptography. In it he described the first known digraphic substitution cipher, charles J. Mendelsohn commented, He was, in my opinion, the outstanding cryptographer of the Renaissance
7.
Magia Naturalis
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Magia Naturalis is a work of popular science by Giambattista della Porta first published in Naples in 1558. Its popularity ensured it was republished in five Latin editions within ten years, with translations into Italian, French, Dutch, Natural Magic is a fine example of pre-Baconian science. Its sources include the ancient world learning of Pliny the Elder, Natural Magic was translated and published in English in 1658. Natural magic White magic Natural Magic online Natural Magick From the Collections at the Library of Congress
8.
Photography
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Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic sensor, this produces an electrical charge at each pixel. A negative image on film is used to photographically create a positive image on a paper base, known as a print. The word photography was created from the Greek roots φωτός, genitive of φῶς, light and γραφή representation by means of lines or drawing, several people may have coined the same new term from these roots independently. Johann von Maedler, a Berlin astronomer, is credited in a 1932 German history of photography as having used it in an article published on 25 February 1839 in the German newspaper Vossische Zeitung. Both of these claims are now widely reported but apparently neither has ever been confirmed as beyond reasonable doubt. Credit has traditionally given to Sir John Herschel both for coining the word and for introducing it to the public. Photography is the result of combining several technical discoveries, later Greek mathematicians Aristotle and Euclid also independently described a pinhole camera in the 5th and 4th centuries BCE. Daniele Barbaro described a diaphragm in 1566, wilhelm Homberg described how light darkened some chemicals in 1694. The fiction book Giphantie, published in 1760, by French author Tiphaigne de la Roche, the discovery of the camera obscura that provides an image of a scene dates back to ancient China. Leonardo da Vinci mentions natural camera obscura that are formed by dark caves on the edge of a sunlit valley, a hole in the cave wall will act as a pinhole camera and project a laterally reversed, upside down image on a piece of paper. So the birth of photography was primarily concerned with inventing means to capture, renaissance painters used the camera obscura which, in fact, gives the optical rendering in color that dominates Western Art. The camera obscura literally means dark chamber in Latin and it is a box with a hole in it which allows light to go through and create an image onto the piece of paper. Around the year 1800, British inventor Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance and he used paper or white leather treated with silver nitrate. The shadow images eventually darkened all over, the first permanent photoetching was an image produced in 1822 by the French inventor Nicéphore Niépce, but it was destroyed in a later attempt to make prints from it. Niépce was successful again in 1825, in 1826 or 1827, he made the View from the Window at Le Gras, the earliest surviving photograph from nature. Because Niépces camera photographs required a long exposure, he sought to greatly improve his bitumen process or replace it with one that was more practical. With an eye to eventual commercial exploitation, the partners opted for total secrecy, Daguerres efforts culminated in what would later be named the daguerreotype process
9.
David Brewster
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Sir David Brewster KH PRSE FRS FSA FSSA MICE was a Scottish physicist, mathematician, astronomer, inventor, writer, historian of science and university principal. Most noted for his contributions to the field of optics, he studied the double refraction by compression and discovered the photoelastic effect, for his work, William Whewell dubbed him the Father of modern experimental optics and the Johannes Kepler of Optics. He is well-recognized for being the inventor of the kaleidoscope and a version of the stereoscope applied to photography. He called it the lenticular stereoscope, which was the first portable and he also invented the binocular camera, two types of polarimeters, the polyzonal lens and the lighthouse illuminator. A prominent figure in the popularization of science, he is considered one of the founders of the British Association, in addition, he became the public face of higher education in Scotland, acting as Principal of the University of St Andrews and then Edinburgh between 1837 and 1868. Brewster also edited the 18-volume Edinburgh Encyclopædia, David Brewster was born at the Canongate in Jedburgh, Roxburghshire, to Margaret Key and James Brewster, the rector of Jedburgh Grammar School and a teacher of high reputation. David was the third of six children, two daughters and four sons, James, minister at Craig, Ferryden, David, George, minister at Scoonie, Fife, and Patrick, minister at the abbey church, Paisley. At the age of 12, David was sent to the University of Edinburgh and he was licensed a minister of the Church of Scotland, but only preached from the pulpit on one occasion. Though Brewster duly finished his studies and was licensed to preach. In 1799 fellow-student Henry Brougham persuaded him to study the diffraction of light, the results of his investigations were communicated from time to time in papers to the Philosophical Transactions of London and other scientific journals. A lesser-known classmate of his, Thomas Dick, also went on to become a popular astronomical writer, as early as 1807 the degree of LL. D. In 1821, he was made a member of the Royal Swedish Academy of Sciences. As a reflection of this fame, Brewster portrait was printed in some cigar boxes. Brewster chose renowned achromatic lens developer Philip Carpenter as the manufacturer of the kaleidoscope in 1817. Although Brewster patented the kaleidoscope in 1817, a copy of the prototype was shown to London opticians, as a consequence, the kaleidoscope became produced in large numbers, but yielded no direct financial benefits to Brewster. It proved to be a success with two hundred thousand kaleidoscopes sold in London and Paris in just three months. A much more valuable and practical result of Brewsters optical researches was the improvement of the British lighthouse system, although Brewsters own discoveries were important, they were not his only service to science. He began writing in 1799 as a contributor to the Edinburgh Magazine
10.
William Crookes
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Sir William Crookes OM PRS was an English chemist and physicist who attended the Royal College of Chemistry in London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes tube which was made in 1875, Crookes was the inventor of the Crookes radiometer, which today is made and sold as a novelty item. Late in life, he interested in spiritualism, and became the president of the Society for Psychical Research. Crookes made a career of being a meteorologist and fierce lecture giver at multiple studies and courses, Crookes worked in chemistry and physics. His experiments were notable for the originality of their design and his interests, ranging over pure and applied science, economic and practical problems, and psychiatric research, made him a well-known personality. He received many public and academic honors, Crookess life was one of unbroken scientific activity. William Crookes was born in London, the eldest of 16 siblings and his father, Joseph Crookes, was a tailor of north-country origin, at that time living with his second wife, Mary Scott Lewis Rutherford Johnson. From 1850 to 1854 he filled the position of assistant in the college and it wasnt in organic chemistry which the focus of his teacher, August Wilhelm von Hofmann, might have been expected to lead him towards, but into new compounds of selenium. These were the subject of his first published papers,1851, in 1855 he was appointed lecturer in chemistry at the Chester Diocesan Training College. In 1856 he married Ellen, daughter of William Humphrey of Darlington and they had three sons and a daughter. Married and living in London, he was devoted mainly to independent work, in 1859, he founded the Chemical News, a science magazine which he edited for many years and conducted on much less formal lines than was usual for the journals of scientific societies. In 1861, Crookes discovered an unknown element with a bright green emission line in its spectrum and named the element thallium, from the Greek thallos. Crookes wrote a treatise on Select Methods in Chemical Analysis in 1871. The method of analysis, introduced by Bunsen and Kirchhoff, was received by Crookes with great enthusiasm. His first important discovery was that of the element thallium, announced in 1861, by this work his reputation became firmly established, and he was elected a fellow of the Royal Society in 1863. He developed the Crookes tubes, investigating cathode rays and he published numerous papers on spectroscopy and conducted research on a variety of minor subjects. In his investigations of the conduction of electricity in low pressure gases, he discovered that as the pressure was lowered, as these examples indicate, he was a pioneer in the construction and use of vacuum tubes for the study of physical phenomena. He was, as a consequence, one of the first scientists to investigate what is now called a plasma and he also devised one of the first instruments for studying nuclear radioactivity, the spinthariscope
11.
William de Wiveleslie Abney
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Sir William de Wiveleslie Abney, KCB, FRS was an English astronomer, chemist, and photographer. Abney was born in Derby, England, the son of Edward Abney vicar of St Alkmunds Derby and he attended Rossall School, the Royal Military Academy, Woolwich and joined the Royal Engineers in 1861, with whom he served in India for several years. Thereafter, and to further his knowledge in photography, he became an assistant at the Chatham School of Military Engineering. Abney was a pioneer of technical aspects of photography. His father had been an early photographic experimenter and friend of Richard Keene, Keene became a close friend of William and his brother Charles Edward Abney. Both Abney sons subsequently became members of the Derby Photographic Society in June 1884. His endeavors in the chemistry of photography produced useful photographic products and he wrote many books on photography that were considered standard texts at the time, although he was doubtful that his improvements would have a great impact on the subject. Abney investigated the blackening of a negative to incidental light, in 1874, Abney developed a dry photographic emulsion, which replaced wet emulsions. He used this emulsion in an Egyptian expedition to photograph the transit of Venus across the sun, Abney also introduced new and useful types of photographic paper, including in 1882 a formula for gelatin silver chloride paper. He was elected a Fellow of the Royal Society in 1876, Abney conducted early research into the field of spectroscopy, developing a red-sensitive emulsion which was used for the infrared spectra of organic molecules. He was also a pioneer in photographing the infrared solar spectrum and he became assistant secretary to the Board of Education in 1899 and advisor to that body in 1903. In 1900 he was Director of the Science and Art Department, Abney invented the Abney level, a combined clinometer and spirit level, used by surveyors to measure slopes and angles. He had married twice, firstly Agnes Matilda Smith, and secondly Mary Louisa Mead, W. de W. Abney, Instruction in Photography, London, published by S. Low, Marston & company,1900. A New Developer, Photographic News,1880,24,345, W. de W. Abney and E. R. Festing, Intensity of Radiation through Turbid Media, Proceedings of the Royal Society of London, Volume 40, pages 378–380,1886. W. de W. Abney and E. R. Festing, part III. Proceedings of the Royal Society of London, Volume 50, pages 369–372, 1891–1892. Abney effect Abney, William de Wiveleslie, techniques of Visual Representation in Research and Teaching, Oxford, OUP2002. online preview, search for Abney Elliot, Paul. The Firs,320 Burton Road, Derby, A nineteenth-century house, response, The University of Derbys Online Journal
12.
William Kennedy Dickson
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William Kennedy-Laurie Dickson was a Scottish inventor who devised an early motion picture camera under the employment of Thomas Edison. William Kennedy Dickson was born on 3 August 1860 in Le Minihic-sur-Rance, Brittany and his mother was Elizabeth Kennedy-Laurie who may have been born in Virginia. His father was James Waite Dickson, a Scottish artist, astronomer, James claimed direct lineage from the painter Hogarth, and from Judge John Waite, the man who sentenced King Charles I to death. At age 19 in 1879, William Dickson wrote a letter to Thomas Edison seeking employment with the inventor and that same year Dickson, his mother, and two sisters moved from Britain to Virginia. In 1883 he was hired to work at Edisons Menlo Park laboratory. In 1888, American inventor and entrepreneur Thomas Alva Edison conceived of a device that would do for the Eye what the phonograph does for the Ear. In October, Edison filed a claim, known as a caveat. In March 1889, a caveat was filed, in which the proposed motion picture device was given a name. Dickson, then the Edison companys official photographer, was assigned to turn the concept into a reality, William Dickson invented the first, practical, celluloid film, for this application. He slit a medium format film, which is 70 mm wide, and perforated the resultant 35 mm film. William Dickson and his team, at the Edison lab, then worked on the development of the Kinetoscope for several years, the first working prototype was unveiled in May 1891 and the design of system was essentially finalised by the fall of 1892. The completed version of the Kinetoscope was officially unveiled at the Brooklyn Institute of Arts, the Kinetoscope introduced the basic approach that would become the standard for all cinematic projection before the advent of video. William Dickson and his team, created the illusion of movement, by conveying a strip of perforated film bearing sequential images, over a light source, with a high-speed shutter. William Dickson was the first person to make a film for the Pope, seeking to develop a movie projector system, they hired former Edison employee Eugene Lauste, probably at Dicksons suggestion. In April 1895, Dickson left Edisons employ and joined the Latham outfit, alongside Lauste, he helped devise what would become known as the Latham loop, allowing the photography and exhibition of much longer filmstrips than had previously been possible. The team of former Edison associates brought to fruition the Eidoloscope projector system, with the Lathams, Dickson was part of the group that formed the American Mutoscope and Biograph Company, before he returned permanently to work in the United Kingdom in 1897. William Dickson left Edisons company and formed his own company, that produced the mutoscope and these machines produced moving images, by means of a revolving drum of card illustrations, similar in concept to flip-books, taken from an actual piece of film. They were often featured, at locations, showing sequences of women undressing or acting as an artists model
13.
Thomas Edison
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Thomas Alva Edison was an American inventor and businessman, who has been described as Americas greatest inventor. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and the long-lasting, practical electric light bulb. Edison was an inventor, holding 1,093 US patents in his name, as well as many patents in the United Kingdom, France. Edisons inventions contributed to mass communication and, in particular, telecommunications and these included a stock ticker, a mechanical vote recorder, a battery for an electric car, electrical power, recorded music and motion pictures. His advanced work in these fields was an outgrowth of his career as a telegraph operator. Edison developed a system of generation and distribution to homes, businesses. His first power station was on Pearl Street in Manhattan, New York, Thomas Edison was born in Milan, Ohio, and grew up in Port Huron, Michigan. He was the seventh and last child of Samuel Ogden Edison, Jr. and Nancy Matthews Elliott. His father, the son of a Loyalist refugee, had moved as a boy with the family from Nova Scotia, settling in southwestern Ontario, in a known as Shewsbury, later Vienna. Samuel Jr. eventually fled Ontario because he took part in the unsuccessful Mackenzie Rebellion of 1837 and his father, Samuel Sr. had earlier fought in the War of 1812 as captain of the First Middlesex Regiment. By contrast, Samuel Jr. s struggle found him on the losing side, once across the border, he found his way to Milan, Ohio. His patrilineal family line was Dutch by way of New Jersey and his mother taught him at home. Much of his education came from reading R. G, parkers School of Natural Philosophy and The Cooper Union for the Advancement of Science and Art. Edison developed hearing problems at an early age, the cause of his deafness has been attributed to a bout of scarlet fever during childhood and recurring untreated middle-ear infections. In his later years, he modified the story to say the injury occurred when the conductor, in helping him onto a moving train, Edisons family moved to Port Huron, Michigan, after the railroad bypassed Milan in 1854 and business declined. Edison sold candy and newspapers on trains running from Port Huron to Detroit and he briefly worked as a telegraph operator in 1863 for the Grand Trunk Railway at Stratford, Ontario railway at age 16. He was held responsible for a near collision and he also studied qualitative analysis and conducted chemical experiments on the train until he left the job. Edison obtained the right to sell newspapers on the road, and, with the aid of four assistants, he set in type and printed the Grand Trunk Herald
14.
Phonograph
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The phonograph is a device invented in 1877 for the mechanical recording and reproduction of sound. In its later forms it is called a gramophone. To recreate the sound, the surface is rotated while a playback stylus traces the groove and is therefore vibrated by it. In later electric phonographs, the motions of the stylus are converted into an electrical signal by a transducer. The phonograph was invented in 1877 by Thomas Edison, while other inventors had produced devices that could record sounds, Edisons phonograph was the first to be able to reproduce the recorded sound. His phonograph originally recorded sound onto a sheet wrapped around a rotating cylinder. A stylus responding to sound vibrations produced an up and down or hill-and-dale groove in the foil, in the 1890s, Emile Berliner initiated the transition from phonograph cylinders to flat discs with a spiral groove running from the periphery to near the center. Later improvements through the years included modifications to the turntable and its system, the stylus or needle. The disc phonograph record was the dominant audio recording format throughout most of the 20th century, from the mid-1980s on, phonograph use on a standard record player declined sharply because of the rise of the cassette tape, compact disc and other digital recording formats. Records are still a favorite format for some audiophiles and DJs, vinyl records are still used by some DJs and musicians in their concert performances. Musicians continue to release their recordings on vinyl records, the original recordings of musicians are sometimes re-issued on vinyl. Usage of terminology is not uniform across the English-speaking world, in more modern usage, the playback device is often called a turntable, record player, or record changer. When used in conjunction with a mixer as part of a DJ setup, the term phonograph was derived from the Greek words φωνή and γραφή. The similar related terms gramophone and graphophone have similar root meanings, the roots were already familiar from existing 19th-century words such as photograph, telegraph, and telephone. In British English, gramophone may refer to any sound-reproducing machine using disc records, the term phonograph was usually restricted to machines that used cylinder records. Gramophone generally referred to a wind-up machine, after the introduction of the softer vinyl records, 33 1⁄3-rpm LPs and 45-rpm single or two-song records, and EPs, the common name became record player or turntable. Often the home record player was part of a system that included a radio and, later, from about 1960, such a system began to be described as a hi-fi or a stereo. In American English, phonograph, properly specific to machines made by Edison, was used in a generic sense as early as the 1890s to include cylinder-playing machines made by others
15.
Kinetoscope
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The Kinetoscope is an early motion picture exhibition device. The Kinetoscope was designed for films to be viewed by one individual at a time through a peephole viewer window at the top of the device, a prototype for the Kinetoscope was shown to a convention of the National Federation of Womens Clubs on May 20,1891. The first public demonstration of the Kinetoscope was held at the Brooklyn Institute of Arts, in 1895, Edison introduced the Kinetophone, which joined the Kinetoscope with a cylinder phonograph. Film projection, which Edison initially disdained as financially nonviable, soon superseded the Kinetoscopes individual exhibition model, many of the projection systems developed by Edisons firm in later years would use the Kinetoscope name. An encounter with the work and ideas of photographic pioneer Eadweard Muybridge appears to have spurred Edison to pursue the development of a motion picture system. The Edison facility was very close by, and the lecture was attended by both Edison and his companys official photographer, William Dickson. No such collaboration was undertaken, but in October 1888, Edison filed a claim, known as a caveat. Patent Office announcing his plans to create a device that would do for the Eye what the phonograph does for the Ear. It is clear that it was intended as part of a complete audiovisual system, in March 1889, a second caveat was filed, in which the proposed motion picture device was given a name, Kinetoscope, derived from the Greek roots kineto- and scopos. Edison assigned Dickson, one of his most talented employees, to the job of making the Kinetoscope a reality, the Edison laboratory, though, worked as a collaborative organization. Laboratory assistants were assigned to work on many projects while Edison supervised and involved himself, Dickson and his then lead assistant, Charles Brown, made halting progress at first. An audio cylinder would provide synchronized sound, while the rotating images, when tests were made with images expanded to a mere 1/8 of an inch in width, the coarseness of the silver bromide emulsion used on the cylinder became unacceptably apparent. The first film made for the Kinetoscope, and apparently the first motion picture ever produced on film in the United States, may have been shot at this time, known as Monkeyshines. 1, it shows an employee of the lab in an apparently tongue-in-cheek display of physical dexterity, attempts at synchronizing sound were soon left behind, while Dickson would also experiment with disc-based exhibition designs. The project would soon head off in more directions, largely impelled by a trip of Edisons to Europe. The first motion system to employ a perforated image band was apparently the Théâtre Optique. Reynauds system did not use film, but images painted on gelatine frames. At the Exposition Universelle, Edison would have both the Théâtre Optique and the electrical tachyscope of German inventor Ottamar Anschütz
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Photographic film
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This article is mainly concerned with still photography film. For motion picture film, please see film stock, photographic film is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, the emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a short exposure to the image formed by a camera lens is used to produce only a very slight chemical change. This creates an invisible latent image in the emulsion, which can be developed into a visible photograph. In addition to light, all films are sensitive to ultraviolet, X-rays. Unmodified silver halide crystals are only to the blue part of the visible spectrum. This problem was overcome with the discovery that certain dyes, called sensitizing dyes, first orthochromatic and finally panchromatic films were developed. Panchromatic film renders all colors in shades of gray approximately matching their subjective brightness, by similar techniques special-purpose films can be made sensitive to the infrared region of the spectrum. In black-and-white photographic film there is one layer of silver halide crystals. When the exposed silver halide grains are developed, the silver halide crystals are converted to metallic silver, color film has at least three sensitive layers, incorporating different combinations of sensitizing dyes. Typically the blue-sensitive layer is on top, followed by a filter layer to stop any remaining blue light from affecting the layers below. Next come a green-and-blue sensitive layer, and a sensitive layer. During development, the silver halide crystals are converted to metallic silver. Because the by-products are created in direct proportion to the amount of exposure and development, following development, the silver is converted back to silver halide crystals in the bleach step. It is removed from the film during the process of fixing the image on the film with a solution of ammonium thiosulfate or sodium thiosulfate, fixing leaves behind only the formed color dyes, which combine to make up the colored visible image. Later color films, like Kodacolor II, have as many as 12 emulsion layers, the earliest practical photographic process, the daguerreotype, introduced in 1839, did not use film. The light-sensitive chemicals were formed on the surface of a copper sheet
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Long-exposure photography
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Long-exposure photography captures one element that conventional photography does not, time. The paths of bright moving objects become clearly visible, clouds form broad bands, head and tail lights of cars become bright streaks, stars form trails in the sky and water smooths over. Only bright objects will form visible trails, however, dark objects usually disappear, boats during daytime long exposures will disappear, but will form bright trails from their lights at night. Whereas there is no fixed definition of what constitutes long, the intent is to create a photo that shows the effect of passing time. A 30-minute photo of an object and surrounding cannot be distinguished from a short exposure, hence. Images with exposure times of several minutes also tend to make moving people or dark objects disappear, often adding a serene, when a scene includes both stationary and moving subjects, a slow shutter speed can cause interesting effects, such as light trails. Long exposures are easiest to accomplish in low-light conditions, but can be done in brighter light using neutral density filters or specially designed cameras, when using a dense neutral density filter your cameras auto focus will not be able to function. It is best to compose and focus without the filter, then once you are happy with the composition, switch to manual focus and put the neutral density filter back on. Long-exposure photography is used in a night-time setting, where the lack of light forces longer exposures. Increasing ISO sensitivity allows for shorter exposures, but substantially decreases image quality through reduced dynamic range and higher noise. By leaving the cameras shutter open for a period of time, more light is absorbed. If the camera is stationary for the period of time that the shutter is open. In this technique, a scene is very dark and the photographer or an assistant takes a light source—it can be small penlight—and moves it about in patterns. The light source can be turned off between strokes, often, stationary objects in the scene are illuminated by briefly turning on studio lights, by one or more flashes from a strobe light, or by increasing the aperture. Long exposures can blur moving water so it has mist-like qualities while keeping stationary objects like land, solargraphy is a technique in which a fixed pinhole camera is used to expose photographic paper for an extremely long amount of time. It is most often used to show the path of the Sun across the sky, one example of this is a single six-month exposure taken by photographer Justin Quinnell, showing sun-trails over Clifton Suspension Bridge between 19 December 2007 and 21 June 2008. Part of the Slow light,6 months over Bristol exhibition and this method of solargraphy uses a simple pinhole camera securely fixed in a position which wont be disturbed. Quinnel constructed his camera from an empty drink can with a 0. 25mm aperture, on February 3,2015 a pinhole camera used in a Georgia State University solargraphy art project was blown up by the Atlanta bomb squad
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Charge-coupled device
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A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by shifting the signals between stages within the one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins, in recent years CCD has become a major technology for digital imaging. In a CCD image sensor, pixels are represented by p-doped metal-oxide-semiconductors capacitors, the charge-coupled device was invented in 1969 at AT&T Bell Labs by Willard Boyle and George E. Smith. The lab was working on bubble memory when Boyle and Smith conceived of the design of what they termed, in their notebook. The device could be used as a shift register, the essence of the design was the ability to transfer charge along the surface of a semiconductor from one storage capacitor to the next. The concept was similar in principle to the device, which was developed at Philips Research Labs during the late 1960s. The first patent on the application of CCDs to imaging was assigned to Michael Tompsett, the initial paper describing the concept listed possible uses as a memory, a delay line, and an imaging device. The first experimental device demonstrating the principle was a row of closely spaced metal squares on a silicon surface electrically accessed by wire bonds. The first working CCD made with integrated circuit technology was a simple 8-bit shift register and this device had input and output circuits and was used to demonstrate its use as a shift register and as a crude eight pixel linear imaging device. Development of the device progressed at a rapid rate, by 1971, Bell researchers led by Michael Tompsett were able to capture images with simple linear devices. Several companies, including Fairchild Semiconductor, RCA and Texas Instruments, picked up on the invention, fairchilds effort, led by ex-Bell researcher Gil Amelio, was the first with commercial devices, and by 1974 had a linear 500-element device and a 2-D100 x 100 pixel device. Steven Sasson, an engineer working for Kodak, invented the first digital still camera using a Fairchild 100 x 100 CCD in 1975. The first KH-11 KENNAN reconnaissance satellite equipped with charge-coupled device array technology for imaging was launched in December 1976, under the leadership of Kazuo Iwama, Sony also started a large development effort on CCDs involving a significant investment. Eventually, Sony managed to mass-produce CCDs for their camcorders, before this happened, Iwama died in August 1982, subsequently, a CCD chip was placed on his tombstone to acknowledge his contribution. He was also awarded the 2012 IEEE Edison Medal For pioneering contributions to imaging devices including CCD Imagers, cameras, in a CCD for capturing images, there is a photoactive region, and a transmission region made out of a shift register. An image is projected through a lens onto the capacitor array, once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor. The last capacitor in the array dumps its charge into a charge amplifier, by repeating this process, the controlling circuit converts the entire contents of the array in the semiconductor to a sequence of voltages
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Surveillance
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Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people for the purpose of influencing, managing, directing, or protecting them. The word surveillance comes from a French phrase for watching over, Surveillance is used by governments for intelligence gathering, the prevention of crime, the protection of a process, person, group or object, or the investigation of crime. It is also used by organizations to plan and commit crimes such as robbery and kidnapping, by businesses to gather intelligence. Surveillance is often a violation of privacy, and is opposed by civil liberties groups. Liberal democracies have laws which restrict domestic government and private use of surveillance, authoritarian government seldom have any domestic restrictions, and international espionage is common among all types of countries. The vast majority of computer surveillance involves the monitoring of data, there is far too much data on the Internet for human investigators to manually search through all of it. Computers can be a target because of the personal data stored on them. If someone is able to install software, such as the FBIs Magic Lantern and CIPAV, on a computer system, such software could be installed physically or remotely. The NSA runs a database known as Pinwale, which stores and indexes large numbers of emails of both American citizens and foreigners. Additionally, the NSA runs a program known as PRISM, which is a mining system that gives the United States government direct access to information from technology companies. Through accessing this information, the government is able to obtain search history, emails, stored information, live chats, file transfers and this program generated huge controversies in regards to surveillance and privacy, especially from U. S. citizens. The official and unofficial tapping of lines is widespread. Between 2003 and 2005, the FBI sent out more than 140,000 National Security Letters ordering phone companies to hand information about their customers calling. About half of these letters requested information on U. S. citizens, human agents are not required to monitor most calls. The StingRay tracker is an example of one of these used to monitor cell phone usage in the United States. Once the phone is connected to the device, there is no way for the user to know that they are being tracked. The operator of the stingray is able to extract information such as location, phone calls, and text messages, a lot of controversy surrounds the StingRay because of its powerful capabilities and the secrecy that surrounds it. Mobile phones are commonly used to collect location data
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Pinhead mirror
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A pinhead mirror can be used to create a camera similar to a pinhole camera. Instead of passing through a hole, the light to form the image is reflected by a small disc-shaped mirror. One advantage is that a mirror can be swivelled to scan a scene or project a scene to different locations. Pinhead mirror technology was protected under US patent 4,948,211 - Method and Apparatus for Optical Imaging Using a Small, TH Nilsson The Pinhead mirror, A previously undiscovered imaging device. Applied Optics,25, 2863-2864 TH Nilsson Pinhead mirrors, imaging, computing and the nature of light Pinhole Journal,4, 2-5
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Angle of view
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In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the general term field of view. It is important to distinguish the angle of view from the angle of coverage, typically the image circle produced by a lens is large enough to cover the film or sensor completely, possibly including some vignetting toward the edge. A cameras angle of view not only on the lens. Digital sensors are usually smaller than 35mm film, and this causes the lens to have an angle of view than with 35mm film. In everyday digital cameras, the factor can range from around 1, to 1.6. For lenses projecting rectilinear images of distant objects, the focal length. Calculations for lenses producing non-rectilinear images are more complex and in the end not very useful in most practical applications. Angle of view may be measured horizontally, vertically, or diagonally, for example, for 35mm film which is 36 mm wide and 24mm high, d =36 mm would be used to obtain the horizontal angle of view and d =24 mm for the vertical angle. Because this is a function, the angle of view does not vary quite linearly with the reciprocal of the focal length. However, except for wide-angle lenses, it is reasonable to approximate α ≈ d f radians or 180 d π f degrees. The effective focal length is equal to the stated focal length of the lens. Angle of view can also be determined using FOV tables or paper or software lens calculators, consider a 35 mm camera with a lens having a focal length of F =50 mm. The dimensions of the 35 mm image format are 24 mm ×36 mm, here α is defined to be the angle-of-view, since it is the angle enclosing the largest object whose image can fit on the film. We want to find the relationship between, the angle α the opposite side of the triangle, d /2 the adjacent side, S2 Using basic trigonometry, we find. For macro photography, we neglect the difference between S2 and F. From the thin lens formula,1 F =1 S1 +1 S2, a second effect which comes into play in macro photography is lens asymmetry. The lens asymmetry causes an offset between the plane and pupil positions
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F-number
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The f-number of an optical system such as a camera lens is the ratio of the systems focal length to the diameter of the entrance pupil. It is a number that is a quantitative measure of lens speed. It is also known as the ratio, f-ratio, f-stop. The f-number is commonly indicated using a hooked f with the format f/N, the f-number N or f# is given by, N = f D where f is the focal length, and D is the diameter of the entrance pupil. It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the pupil diameter in terms of f and N. Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images, the brightness of the projected image relative to the brightness of the scene in the lenss field of view decreases with the square of the f-number. Doubling the f-number decreases the brightness by a factor of four. To maintain the same photographic exposure when doubling the f-number, the time would need to be four times as long. Most lenses have a diaphragm, which changes the size of the aperture stop. The entrance pupil diameter is not necessarily equal to the aperture stop diameter, a 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A200 mm focal length f/4 lens has a pupil diameter of 50 mm. The 200 mm lenss entrance pupil has four times the area of the 100 mm lenss entrance pupil, a T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings, a stop can be a physical object, an opaque part of an optical system that blocks certain rays. In photography, stops are also a used to quantify ratios of light or exposure. The one-stop unit is known as the EV unit. On a camera, the setting is traditionally adjusted in discrete steps. Each stop is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/2 or about 0.7071, each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right
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Image resolution
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Image resolution is the detail an image holds. The term applies to digital images, film images. Higher resolution means more image detail, image resolution can be measured in various ways. Resolution quantifies how close lines can be to other and still be visibly resolved. Resolution units can be tied to physical sizes, to the size of a picture. Line pairs are used instead of lines, a line pair comprises a dark line. A line is either a line or a light line. A resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, photographic lens and film resolution are most often quoted in line pairs per millimeter. The resolution of digital cameras can be described in different ways. Resolution is the capability of the sensor to observe or measure the smallest object clearly with distinct boundaries, there is a difference between the resolution and a pixel. A pixel is actually a unit of the digital Resolution depends upon the size of the pixel, usually, with any given lens setting, the smaller the size of the pixel, the higher the resolution will be and the clearer the object in the image will be. Images having smaller pixel sizes might consist of more pixels, the number of pixels correlates to the amount of information within the image. An image of N pixels height by M pixels wide can have any less than N lines per picture height. Other conventions include describing pixels per unit or pixels per area unit. None of these pixel resolutions are true resolutions, but they are referred to as such. Below is an illustration of how the image might appear at different pixel resolutions. An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 =3,145,728 pixels or 3.1 megapixels, one could refer to it as 2048 by 1536 or a 3. 1-megapixel image. Or, you can think of it as a low quality image if printed at about 28.5 inches wide
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Circle of confusion
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In optics, a circle of confusion is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. It is also known as disk of confusion, circle of indistinctness, blur circle, in photography, the circle of confusion is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with image format, but the most appropriate value depends on visual acuity, viewing conditions. Usages in context include maximum permissible circle of confusion, circle of confusion diameter limit, real lenses do not focus all rays perfectly, so that even at best focus, a point is imaged as a spot rather than a point. The smallest such spot that a lens can produce is often referred to as the circle of least confusion, two important uses of this term and concept need to be distinguished, For describing the largest blur spot that is indistinguishable from a point. A lens can precisely focus objects at one distance, objects at other distances are defocused. Defocused object points are imaged as blur spots rather than points, the greater the distance an object is from the plane of focus, such a blur spot has the same shape as the lens aperture, but for simplicity, is usually treated as if it were circular. In practice, objects at different distances from the camera can still appear sharp. The common criterion for “acceptable sharpness” in the image is that the blur spot be indistinguishable from a point. For describing the blur spot achieved by a lens, at its best focus or more generally, the term circle of confusion is applied more generally, to the size of the out-of-focus spot to which a lens images an object point. In idealized ray optics, where rays are assumed to converge to a point when perfectly focused, a more general blur spot has soft edges due to diffraction and aberrations, and may be non-circular due to the aperture shape. Therefore, the concept needs to be carefully defined in order to be meaningful. Suitable definitions often use the concept of encircled energy, the fraction of the optical energy of the spot that is within the specified diameter. Values of the fraction vary with application, in photography, the circle of confusion diameter limit for the final image is often defined as the largest blur spot that will still be perceived by the human eye as a point. Conventions in terms of the measure are also commonly used. The DoF computed using these conventions will need to be adjusted if the image is cropped before enlarging to the final image size, or if the size. Using the “Zeiss formula”, the circle of confusion is sometimes calculated as d/1730 where d is the measure of the original image. For full-frame 35 mm format this comes out to be 0.025 mm, a more widely used CoC is d/1500, or 0.029 mm for full-frame 35 mm format, which corresponds to resolving 5 lines per millimeter on a print of 30 cm diagonal
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Diffraction
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Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of shadow of the obstacle. In classical physics, the phenomenon is described as the interference of waves according to the Huygens–Fresnel principle. These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a wave travels through a medium with a varying refractive index. Diffraction occurs with all waves, including sound waves, water waves, since physical objects have wave-like properties, diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record observations of the phenomenon in 1660. If the obstructing object provides multiple, closely spaced openings, a pattern of varying intensity can result. This is due to the addition, or interference, of different parts of a wave that travel to the observer by different paths, the formalism of diffraction can also describe the way in which waves of finite extent propagate in free space. For example, the profile of a laser beam, the beam shape of a radar antenna. The effects of diffraction are often seen in everyday life and this principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired, the hologram on a credit card is an example. Diffraction in the atmosphere by small particles can cause a ring to be visible around a bright light source like the sun or the moon. A shadow of an object, using light from a compact source. The speckle pattern which is observed when laser light falls on a rough surface is also a diffraction phenomenon. When deli meat appears to be iridescent, that is diffraction off the meat fibers, all these effects are a consequence of the fact that light propagates as a wave. Diffraction can occur with any kind of wave, ocean waves diffract around jetties and other obstacles. Sound waves can diffract around objects, which is why one can hear someone calling even when hiding behind a tree. Diffraction can also be a concern in some applications, it sets a fundamental limit to the resolution of a camera, telescope
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Vignetting
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In photography and optics, vignetting is a reduction of an images brightness or saturation at the periphery compared to the image center. The word vignette, from the root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a portrait which is clear in the center. A similar effect occurs when photographing projected images or movies off a projection screen, vignetting is often an unintended and undesired effect caused by camera settings or lens limitations. However, it is deliberately introduced for creative effect, such as to draw attention to the center of the frame. A photographer may deliberately choose a lens which is known to produce vignetting to obtain the effect, when using superzoom lenses, vignetting may occur all along the zoom range, depending on the aperture and the focal length. However, it may not always be visible, except at the widest end, in these cases, vignetting may cause an exposure value difference of up to 0. 75EV. There are several causes of vignetting and this has the effect of changing the entrance pupil shape as a function of angle. Darkening can be gradual or abrupt – the smaller the aperture, when some points on an image receives no light at all due to mechanical vignetting, then this results in an restriction of the field of view – parts of the image are then completely black. This type of vignetting is caused by the dimensions of a multiple element lens. Rear elements are shaded by elements in front of them, which reduces the lens opening for off-axis incident light. The result is a decrease in light intensity towards the image periphery. Optical vignetting is sensitive to the aperture and can often be cured by a reduction in aperture of 2–3 stops. Unlike the previous types, natural vignetting is not due to the blocking of light rays, the falloff is approximated by the cos4 or cosine fourth law of illumination falloff. Here, the light falloff is proportional to the power of the cosine of the angle at which the light impinges on the film or sensor array. Wideangle rangefinder designs and the designs used in compact cameras are particularly prone to natural vignetting. Telephoto lenses, retrofocus wideangle lenses used on SLR cameras, a gradual grey filter or postprocessing techniques may be used to compensate for natural vignetting, as it cannot be cured by stopping down the lens. Some modern lenses are designed so that the light strikes the image parallel or nearly so
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Laser
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A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term laser originated as an acronym for light amplification by stimulated emission of radiation, the first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light coherently, spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i. e. they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond, Lasers are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a great distance along the beam. A beam produced by a thermal or other incoherent light source has an amplitude and phase that vary randomly with respect to time and position. Lasers are characterized according to their wavelength in a vacuum, most single wavelength lasers actually produce radiation in several modes having slightly differing frequencies, often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously, there are some lasers that are not single spatial mode and consequently have light beams that diverge more than is required by the diffraction limit. However, all devices are classified as lasers based on their method of producing light. Lasers are employed in applications where light of the spatial or temporal coherence could not be produced using simpler technologies. The word laser started as an acronym for light amplification by stimulated emission of radiation, in the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser, this term is now obsolete. A laser that produces light by itself is technically an optical rather than an optical amplifier as suggested by the acronym. It has been noted that the acronym LOSER, for light oscillation by stimulated emission of radiation. With the widespread use of the acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers. The back-formed verb to lase is frequently used in the field, meaning to produce light, especially in reference to the gain medium of a laser. Further use of the laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser
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Brass
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Brass is a metal alloy made of copper and zinc, the proportions of zinc and copper can be varied to create a range of brasses with varying properties. It is an alloy, atoms of the two constituents may replace each other within the same crystal structure. By comparison, bronze is principally an alloy of copper and tin, however, bronze and brass may also include small proportions of a range of other elements including arsenic, phosphorus, aluminium, manganese, and silicon. The term is applied to a variety of brasses. Modern practice in museums and archaeology increasingly avoids both terms for objects in favour of the all-embracing copper alloy. It is also used in zippers, Brass is often used in situations in which it is important that sparks not be struck, such as in fittings and tools used near flammable or explosive materials. Brass has higher malleability than bronze or zinc, the relatively low melting point of brass and its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard, the density of brass is 8.4 to 8.73 grams per cubic centimetre. Today, almost 90% of all alloys are recycled. Because brass is not ferromagnetic, it can be separated from ferrous scrap by passing the scrap near a powerful magnet, Brass scrap is collected and transported to the foundry where it is melted and recast into billets. Billets are heated and extruded into the form and size. The general softness of brass means that it can often be machined without the use of cutting fluid, aluminium makes brass stronger and more corrosion-resistant. Aluminium also causes a highly beneficial hard layer of oxide to be formed on the surface that is thin, transparent. Tin has an effect and finds its use especially in seawater applications. Combinations of iron, aluminium, silicon and manganese make brass wear and tear resistant, to enhance the machinability of brass, lead is often added in concentrations of around 2%. Since lead has a melting point than the other constituents of the brass. The pattern the globules form on the surface of the brass increases the available surface area which in turn affects the degree of leaching. In addition, cutting operations can smear the lead globules over the surface and these effects can lead to significant lead leaching from brasses of comparatively low lead content
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Shim (spacer)
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A shim is a thin and often tapered or wedged piece of material, used to fill small gaps or spaces between objects. Shims are typically used in order to support, adjust for better fit, shims may also be used as spacers to fill gaps between parts subject to wear. Many materials make suitable shim stock, or base material, depending on the context, wood, stone, plastic, metal, or even paper. High quality shim stock can be commercially, for example as laminated shims. Laminated shim stock is stacked foil that can be peeled off one layer at a time to adjust the thickness of the shim, in automobiles, shims are commonly used to adjust the clearance or space between two parts. For example, shims are inserted into or under bucket tappets to control valve clearances, clearance is adjusted by changing the thickness of the shim. In Assembly and Weld Fixtures precision metal shims are used two parts so that the final production parts are created within the product drawings specified tolerances. In carpentry, small pieces of wood may be used to align gaps between larger timbers, in luthiery, shims made of various materials are often used to adjust neck alignment and can be used beneath a nut or saddle to raise the height of either. In masonry, small stones may be used to align or fill gaps between larger bricks or slabs, special CPU shims are used to protect the central processing unit when installing a heat sink. This is accomplished by manual shimming of individual shims, or automatic shimming procedure, to the Point, A Brief History of the Shim
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Aluminium foil
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Aluminium foil, often referred to with the misnomer tin foil, is aluminium prepared in thin metal leaves with a thickness less than 0.2 mm, thinner gauges down to 6 micrometres are also commonly used. In the United States, foils are commonly gauged in thousandths of an inch or mils, standard household foil is typically 0.016 mm thick, and heavy duty household foil is typically 0.024 mm. The foil is pliable, and can be bent or wrapped around objects. Thin foils are fragile and are sometimes laminated to other such as plastics or paper to make them more useful. Aluminium foil supplanted tin foil in the mid 20th century, annual production of aluminium foil was approximately 800,000 tonnes in Europe and 600,000 tonnes in the U. S. in 2003. Approximately 75% of aluminium foil is used for packaging of foods, cosmetics, and chemical products, in North America, aluminium foil is known as aluminum foil. It was popularised by Reynolds Metals, the manufacturer in North America. In the United Kingdom and United States it is, informally, widely called tin foil, metallised films are sometimes mistaken for aluminium foil, but are actually polymer films coated with a thin layer of aluminium. In Australia, aluminium foil is widely called alfoil, Foil made from a thin leaf of tin was commercially available before its aluminium counterpart. Tin foil was marketed commercially from the late nineteenth into the twentieth century. The term tin foil survives in the English language as a term for the aluminium foil. Tin foil is less malleable than aluminium foil and tends to give a slight tin taste to food wrapped in it, tin foil has been supplanted by aluminium and other materials for wrapping food. The first audio recordings on phonograph cylinders were made on tin foil, tin was first replaced by aluminium in 1910, when the first aluminium foil rolling plant, Dr. Lauber, Neher & Cie. was opened in Emmishofen, Switzerland. Neher & Sons, the manufacturers, started in 1886 in Schaffhausen, Switzerland, at the foot of the Rhine Falls. Nehers sons, together with Dr. Lauber, discovered the endless rolling process, in 1911, Bern-based Tobler began wrapping its chocolate bars in aluminium foil, including the unique triangular chocolate bar, Toblerone. By 1912, aluminium foil was being used by Maggi to pack soups, the first use of foil in the United States was in 1913 for wrapping Life Savers, candy bars, and gum. Processes evolved over time to include the use of print, colour, lacquer, laminate, to maintain a constant thickness in aluminium foil production, beta radiation is passed through the foil to a sensor on the other side. If the intensity becomes too high, then the rollers adjust, if the intensities become too low and the foil has become too thick, the rollers apply more pressure, causing the foil to be made thinner
31.
Joseph Petzval
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Joseph Petzval was a mathematician, inventor, and physicist best known for his work in optics. He was born in the town of Zipser Bela in the Kingdom of Hungary, Petzval studied and later lectured at the Institutum Geometricum in Buda. He headed the Institute of Practical Geometry and Hydrology/Architecture between 1841 and 1848, later in life, he accepted an appointment to a chair of mathematics at the University of Vienna. Petzval became a member of the Hungarian Academy of Sciences in 1873, Petzval is considered to be one of the main founders of geometrical optics, modern photography and cinematography. Among his inventions are the Petzval portrait lens and opera glasses and he is also credited with the discovery of the Laplace transform and is also known for his extensive work on aberration in optical systems. In 1801, Joseph Petzvals father married the Zipser-German Zuzana Kreutzmann, who was born in Szepesbéla, Kingdom of Hungary, the couple brought up six children, Gustáv Adolf, who died prematurely, Nestor Aemilianus, Joseph Maximilián, Petrol Baltazár, and three daughters. In 1810, the moved to Késmárk and in 1819 to Leutschau. The entire family shared an aptitude for technology, josephs father worked as a teacher at the evangelical school in Zipser Bela, as well as an organist in Zipser Bela and later in Käsmark. He was also a conductor and a geodesist in Lőcse and he had a reputation as an outstanding musician and composer, who was also gifted mechanically. In 1824, he was awarded two patents, one for improvements to the clock and the other for a polygraph. Petzvals brother, Petrol Baltazár Petzval, was a well-respected mathematician, Joseph Petzval attended elementary school in Kežmarok, and began his secondary school studies in Kežmarok and Pudlein. On October 1,1819, he returned to his family in Leutschau, both in elementary school and high school he ranked among the best in his class in the subjects of Latin and religion, however, he struggled with his Hungarian. Before arriving at Leutschau, he was, interestingly enough, also very weak in mathematics, in Leutschau, however, he clearly improved in this discipline. He was preparing to undergo a repeat class in mathematics, after Petzval finished the book, the child who had been a weak math pupil swiftly became a math genius. After finishing high school, Petzval decided to move to the Institutum Geometricum, before that, he had to complete a two-year Lyceum, which he attended from 1823 to 1825 in Kaschau. When he arrived at Košice in 1823, Petzval was already well-versed in the subjects of Latin, mathematical analysis, classical literature, in addition to his Slovak he was able to speak perfectly in Czech, German and Hungarian. With his fathers assistance, he also learned French and English, after completing the Lyceum, Petzval worked for a year as an educator for Count Almássy in the Heves county. In addition to bringing in some urgently needed money, this also provided him with important social contacts
32.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
33.
Depth of field
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In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, in cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus. Precise focus is possible at one distance, at that distance. At any other distance, a point object is defocused, and will produce a blur spot shaped like the aperture, when this circular spot is sufficiently small, it is indistinguishable from a point, and appears to be in focus, it is rendered as acceptably sharp. The acceptable circle of confusion is influenced by visual acuity, viewing conditions, the increase of the circle diameter with defocus is gradual, so the limits of depth of field are not hard boundaries between sharp and unsharp. For 35 mm motion pictures, the area on the film is roughly 22 mm by 16 mm. The limit of tolerable error was traditionally set at 0.05 mm diameter, while for 16 mm film, where the size is half as large. More modern practice for 35 mm productions set the circle of confusion limit at 0.025 mm, for full-frame 35mm still photography, the circle of confusion is usually chosen to be about 1/30 mm. Many sources propose CoC limits as a fraction of the film format diagonal, the three formats above at fraction 1/1500 would use 0.029,0.056, and 0.017 mm. Traditional depth-of-field formulas and tables assume equal circles of confusion for near and far objects, the loss of detail in distant objects may be particularly noticeable with extreme enlargements. Achieving this additional sharpness in distant objects usually requires focusing beyond the hyperfocal distance, with this approach, foreground objects cannot always be made perfectly sharp, but the loss of sharpness in near objects may be acceptable if recognizability of distant objects is paramount. Other authors have taken the position, maintaining that slight unsharpness in foreground objects is usually more disturbing than slight unsharpness in distant parts of a scene. The combination of length, subject distance, and format size defines magnification at the film / sensor plane. DOF is determined by subject magnification at the film / sensor plane, for a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF, decreasing magnification increases DOF. For a given magnification, increasing the f-number increases the DOF. If the original image is enlarged to make the final image, when focus is set to the hyperfocal distance, the DOF extends from half the hyperfocal distance to infinity, and the DOF is the largest possible for a given f-number. The comparative DOFs of two different format sizes depend on the conditions of the comparison, the DOF for the smaller format can be either more than or less than that for the larger format. In the discussion that follows, it is assumed that the images from both formats are the same size, are viewed from the same distance, and are judged with the same circle of confusion criterion
34.
Infinity
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Infinity is an abstract concept describing something without any bound or larger than any number. In mathematics, infinity is treated as a number but it is not the same sort of number as natural or real numbers. Georg Cantor formalized many ideas related to infinity and infinite sets during the late 19th, in the theory he developed, there are infinite sets of different sizes. For example, the set of integers is countably infinite, while the set of real numbers is uncountable. Ancient cultures had various ideas about the nature of infinity, the ancient Indians and Greeks did not define infinity in precise formalism as does modern mathematics, and instead approached infinity as a philosophical concept. The earliest recorded idea of infinity comes from Anaximander, a pre-Socratic Greek philosopher who lived in Miletus and he used the word apeiron which means infinite or limitless. However, the earliest attestable accounts of mathematical infinity come from Zeno of Elea, aristotle called him the inventor of the dialectic. He is best known for his paradoxes, described by Bertrand Russell as immeasurably subtle, however, recent readings of the Archimedes Palimpsest have found that Archimedes had an understanding about actual infinite quantities. The Jain mathematical text Surya Prajnapti classifies all numbers into three sets, enumerable, innumerable, and infinite, on both physical and ontological grounds, a distinction was made between asaṃkhyāta and ananta, between rigidly bounded and loosely bounded infinities. European mathematicians started using numbers in a systematic fashion in the 17th century. John Wallis first used the notation ∞ for such a number, euler used the notation i for an infinite number, and exploited it by applying the binomial formula to the i th power, and infinite products of i factors. In 1699 Isaac Newton wrote about equations with an number of terms in his work De analysi per aequationes numero terminorum infinitas. The infinity symbol ∞ is a symbol representing the concept of infinity. The symbol is encoded in Unicode at U+221E ∞ infinity and in LaTeX as \infty and it was introduced in 1655 by John Wallis, and, since its introduction, has also been used outside mathematics in modern mysticism and literary symbology. Leibniz, one of the co-inventors of infinitesimal calculus, speculated widely about infinite numbers, in real analysis, the symbol ∞, called infinity, is used to denote an unbounded limit. X → ∞ means that x grows without bound, and x → − ∞ means the value of x is decreasing without bound. ∑ i =0 ∞ f = ∞ means that the sum of the series diverges in the specific sense that the partial sums grow without bound. Infinity can be used not only to define a limit but as a value in the real number system
35.
Haze
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Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. Sources for haze particles include farming, traffic, industry, seen from afar and depending upon the direction of view with respect to the sun, haze may appear brownish or bluish, while mist tends to be bluish-grey. Whereas haze often is thought of as a phenomenon of dry air, however, haze particles may act as condensation nuclei for the subsequent formation of mist droplets, such forms of haze are known as wet haze. The term haze, in literature, generally is used to denote visibility-reducing aerosols of the wet type. Such aerosols commonly arise from complex chemical reactions occur as sulfur dioxide gases emitted during combustion are converted into small droplets of sulphuric acid. The reactions are enhanced in the presence of sunlight, high relative humidity, a small component of wet haze aerosols appear to be derived from compounds released by trees, such as terpenes. For all these reasons, wet haze tends to be primarily a warm-season phenomenon, large areas of haze covering many thousands of kilometers may be produced under favorable conditions each summer. Haze often occurs when dust and smoke particles accumulate in relatively dry air, when weather conditions block the dispersal of smoke and other pollutants they concentrate and form a usually low-hanging shroud that impairs visibility and may become a respiratory health threat. Industrial pollution can result in dense haze, which is known as smog, since 1991, haze has been a particularly acute problem in Southeast Asia. The main source of the haze has been occurring in Sumatra. In response to the 1997 Southeast Asian haze, the ASEAN countries agreed on a Regional Haze Action Plan, in 2002, all ASEAN countries except Indonesia signed the Agreement on Transboundary Haze Pollution, but the pollution is still a problem today. Under the agreement the ASEAN secretariat hosts a co-ordination and support unit, during the 2013 Southeast Asian haze, Singapore experienced a record high pollution level, with the 3-hour Pollution Standards Index reaching a record high of 401. A full list of areas is available on EPAs website. Haze is no longer a domestic problem and it has become one of the causes of international disputes among neighboring countries. Haze migrates to adjacent countries and thereby pollutes other countries as well, one of the most recent problems concerned the two neighboring countries Malaysia and Indonesia. Winds blow most of the fumes across the narrow Strait of Malacca to Malaysia, the 2015 Southeast Asian haze constitutes an ongoing crisis. Haze causes issues in the area of photography, where the penetration of large amounts of dense atmosphere may be necessary to image distant subjects. This results in the effect of a loss of contrast in the subject
36.
Fraunhofer diffraction
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In contrast, the diffraction pattern created near the object, in the near field region, is given by the Fresnel diffraction equation. The equation was named in honor of Joseph von Fraunhofer although he was not actually involved in the development of the theory and this article explains where the Fraunhofer equation can be applied, and shows the form of the Fraunhofer diffraction pattern for various apertures. A detailed mathematical treatment of Fraunhofer diffraction is given in Fraunhofer diffraction equation and these effects can be modelled using the Huygens–Fresnel principle. Fresnel developed an equation using the Huygens wavelets together with the principle of superposition of waves, generally, a two-dimensional integral over complex variables has to be solved and in many cases, an analytic solution is not available. In this case, the incident light is a plane wave so that the phase of the light at each point in the aperture is the same. This is often known as the far field and is defined as being located at a distance which is greater than W2/λ. The Fraunhofer equation can be used to model the diffraction in this case, for example, if a 0. 5mm diameter circular hole is illuminated by a laser with 0. 6μm wavelength, the Fraunhofer diffraction equation can be employed if the viewing distance is greater than 1000mm. A plane wave incident on a lens is focused at a point by the lens, all the rays have the same phase at the point of focus. Thus, if the light is focused with a lens. The diffracted light can be considered to be made up of a set of waves of varying orientation. In each of these examples, the aperture is illuminated by a plane wave at normal incidence. The width of the slit is W, the Fraunhofer diffraction pattern is shown in the image together with a plot of the intensity vs. angle θ. The pattern has maximum intensity at θ =0, and a series of peaks of decreasing intensity, most of the diffracted light falls between the first minima. The angle, α, subtended by these two minima is given by, α ≈2 λ W Thus, the smaller the aperture, the fringes extend to infinity in the y direction since the slit and illumination also extend to infinity. If W < λ, the intensity of the light does not fall to zero, and if D << λ. We can find the angle at which a first minimum is obtained in the light by the following reasoning. Consider the light diffracted at an angle θ where the distance CD is equal to the wavelength of the illuminating light, the same applies to the points just below A and B, and so on. Therefore, the amplitude of the wave travelling in the direction θ is zero
37.
Fresnel diffraction
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In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by passing through an aperture or around an object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation, the near field can be specified by the Fresnel number, F of the optical arrangement. When F ≫1 the diffracted wave is considered to be in the near field, however, the validity of the Fresnel diffraction integral is deduced by the approximations derived below. The multiple Fresnel diffraction at closely spaced periodical ridges causes the specular reflection, some of the earliest work on what would become known as Fresnel diffraction was carried out by Francesco Maria Grimaldi in Italy in the 17th century. In his monograph entitled Light, Richard C and he uses the Principle of Huygens to investigate, in classical terms, what transpires. The result is if the gap is very narrow only diffraction patterns with bright centers can occur. If the gap is made wider, then diffraction patterns with dark centers will alternate with diffraction patterns with bright centers. As the gap becomes larger, the differentials between dark and light bands decrease until a diffraction effect can no longer be detected, in his Optics, Francis Weston Sears offers a mathematical approximation suggested by Fresnel that predicts the main features of diffraction patterns and uses only simple mathematics. The inner zone is a circle and each succeeding zone will be an annular ring. If the diameter of the hole in the screen is sufficient to expose two Fresnel zones, then the amplitude at the center is almost zero. That means that a Fresnel diffraction pattern can have a dark center and these patterns can be seen and measured, and correspond well to the values calculated for them. Analytical solution of integral is impossible for all but the simplest diffraction geometries. Therefore, it is usually calculated numerically, the main problem for solving the integral is the expression of r. Let us substitute this expression in the argument of the exponential within the integral, in order to make this possible, it has to contribute to the variation of the exponential for an almost null term. For applications involving optical wavelengths, the wavelength λ is typically many orders of magnitude smaller than the relevant physical dimensions, the condition for validity is fairly weak, and it allows all length parameters to take comparable values, provided the aperture is small compared to the path length. For the r in the denominator we go one step further and this is valid in particular if we are interested in the behaviour of the field only in a small area close to the origin, where the values of x and y are much smaller than z. In general, Fresnel diffraction is valid if the Fresnel number is approximately 1, the integral modulates the amplitude and phase of the spherical wave
38.
Fire hydrant
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A fire hydrant, also called fireplug, is a connection point by which firefighters can tap into a water supply. It is a component of active fire protection, the user attaches a hose to the fire hydrant, then opens a valve on the hydrant to provide a powerful flow of water, on the order of 350 kPa. This user can attach this hose to an engine, which can use a powerful pump to boost the water pressure. One may connect the hose with a connection, instantaneous quick connector or a Storz connector. A user should take care not to open or close a fire hydrant too quickly, as this can cause a water hammer, which can damage nearby pipes and equipment. The water inside a charged hose line causes it to be heavy and high water pressure causes it to be stiff. When a fire hydrant is unobstructed, this is not a problem, most fire hydrant valves are not designed to throttle the water flow, they are designed to be operated full-on or full-off. The valving arrangement of most dry-barrel hydrants is for the valve to be open at anything other than full operation. Usage at partial-opening can consequently result in considerable flow directly into the surrounding the hydrant. Gate or butterfly valves can be installed directly onto the hydrant orifices to control individual outputs and these valves can be up to 12 inches in diameter to accommodate the large central steamer orifices on many US hydrants. It is good practice to install valves on all orifices before using a hydrant as the caps are unreliable. When a firefighter is operating a hydrant, he or she typically wears appropriate personal protective equipment, such as gloves, high-pressure water coursing through a potentially aging and corroding hydrant could cause a failure, injuring the firefighter operating the hydrant or bystanders. In most jurisdictions it is illegal to park a car within a distance of a fire hydrant. In North America the distances are commonly 3 to 5 m or 10 to 15 ft, the rationale behind these laws is that hydrants need to be visible and accessible in an emergency. To prevent casual use or misuse, the hydrant requires special tools to be opened, vandals sometimes cause monetary loss by wasting water when they open hydrants. Such vandalism can also reduce water pressure and impair firefighters efforts to extinguish fires. Sometimes those simply seeking to play in the water remove the caps and open the valve, providing residents a place to play, however, this is usually discouraged as residents have been struck by passing automobiles while playing in the street in the water spray. In spite of this, some US communities provide low flow sprinkler heads to enable residents to use the hydrants to cool off during hot weather, while gaining some control on water usage
39.
Focal length
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The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a focal length has greater optical power than one with a long focal length. For a thin lens in air, the length is the distance from the center of the lens to the principal foci of the lens. For a converging lens, the length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. For a diverging lens, the length is negative, and is the distance to the point from which a collimated beam appears to be diverging after passing through the lens. The focal length of a lens can be easily measured by using it to form an image of a distant light source on a screen. The lens is moved until an image is formed on the screen. In this case 1/u is negligible, and the length is then given by f ≈ v. Back focal length or back focal distance is the distance from the vertex of the last optical surface of the system to the focal point. For an optical system in air, the focal length gives the distance from the front. If the surrounding medium is not air, then the distance is multiplied by the index of the medium. Some authors call these distances the front/rear focal lengths, distinguishing them from the front/rear focal distances, defined above. In general, the length or EFL is the value that describes the ability of the optical system to focus light. The other parameters are used in determining where an image will be formed for an object position. The quantity 1/f is also known as the power of the lens. The corresponding front focal distance is, FFD = f, in the sign convention used here, the value of R1 will be positive if the first lens surface is convex, and negative if it is concave. The value of R2 is negative if the surface is convex
40.
Shutter (photography)
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A shutter can also be used to allow pulses of light to pass outwards, as seen in a movie projector or a signal lamp. A shutter of variable speed is used to control exposure time of the film, the shutter is so constructed that it automatically closes after a certain required time interval. The speed of the shutter is controlled by a ring outside the camera, focal-plane shutters are mounted near the focal plane and move to uncover the film or sensor. Behind-the-lens shutters were used in cameras with limited lens interchangeability. Shutters in front of the lens, sometimes simply a lens cap that is removed and replaced for the long exposures required, were used in the days of photography. Other mechanisms than the aperture and the sliding curtains have been used. The time for which a shutter remains open is determined by a timing mechanism and these were originally pneumatic or clockwork, but since the late twentieth century are mostly electronic. The reciprocal of time in seconds is often used for engraving shutter settings. For example, a marking of 250 denotes 1/250 and this does not cause confusion in practice. The exposure time and the aperture of the lens must together be such as to allow the right amount of light to reach the film or sensor. Additionally, the time must be suitable to handle any motion of the subject. Usually it must be fast enough to freeze rapid motion, unless a controlled degree of motion blur is desired, most shutters have a flash synchronization switch to trigger a flash, if connected. This was quite a complicated matter with mechanical shutters and flashbulbs which took a time to reach full brightness. Special flashbulbs were designed which had a burn, illuminating the scene for the whole time taken by a focal plane shutter slit to move across the film. These problems were solved for non-focal-plane shutters with the advent of electronic flash units which fire virtually instantaneously. When using a focal-plane shutter with a flash, if the shutter is set at its X-sync speed or slower the whole frame will be exposed when the flash fires, some electronic flashes can produce a longer pulse compatible with a focal-plane shutter operated at much higher shutter speeds. The focal-plane shutter will still impart focal-plane shutter distortions to a moving subject. Cinematography uses a rotary shutter in movie cameras, a continuously spinning disc which conceals the image with a reflex mirror during the intermittent motion between frame exposure
41.
Coded aperture
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Coded Apertures or Coded-Aperture Masks are grids, gratings, or other patterns of materials opaque to various wavelengths of light. The wavelengths are usually high-energy radiation such as X-rays and gamma rays, by blocking light in a known pattern, a coded shadow is cast upon a plane. The properties of the light sources can then be mathematically reconstructed from this shadow. Coded apertures are used in X- and gamma ray imaging systems, imaging is usually made at optical wavelengths by lenses and mirrors. However, for X-rays and γ-rays, lenses and mirrors do not exist, image modulation by apertures is therefore often used instead. The pinhole camera is the most basic form of such a modulation imager, only a tiny fraction of the light passes through the pinhole, which causes a low signal-to-noise ratio. To solve this problem, the mask can contain many holes, in one of particular patterns. Multiple masks, at varying distances from a detector, add flexibility to this tool, specifically the modulation collimator, invented by Minoru Oda, was used to identify the first cosmic X-ray source and thereby to launch the new field of X-ray astronomy in 1965. Many other applications in fields, such as tomography, have since appeared. In a coded aperture more complicated than a camera, images from multiple apertures will overlap at the detector array. It is thus necessary to use an algorithm to reconstruct the original image. In this way an image can be achieved without a lens. Mar 2006 In the news, Sky-high system to aid soldiers
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