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Achromatic Lens
An achromatic lens or achromat is a lens (optics), lens that is designed to limit the effects of chromatic aberration, chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus on the same plane. Wavelengths in between these two then have better focus error than could be obtained with a simple lens. The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of Dispersion (optics), dispersion. Typically, one element is a negative (Lens (optics)#Types of simple lenses, concave) element made out of flint glass such as F2, which has relatively high dispersion, and the other is a positive (Lens (optics)#Types of simple lenses, convex) element made of Crown glass (optics), crown glass such as BK7, which has lower dispersion. The lens elements are mounted next to each other, often cemented together, and shaped so that the chromati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromatic Aberration Lens Diagram
Diatonic and chromatic are terms in music theory that are used to characterize Scale (music), scales. The terms are also applied to musical instruments, Interval (music), intervals, Chord (music), chords, Musical note, notes, musical styles, and kinds of harmony. They are very often used as a pair, especially when applied to contrasting features of the Common practice period, common practice music of the period 1600–1900. These terms may mean different things in different contexts. Very often, ''diatonic'' refers to musical elements derived from the modes and transpositions of the "white note scale" C–D–E–F–G–A–B. In some usages it includes all forms of heptatonic scale that are in common use in Western music (the major, and all forms of the minor). ''Chromatic'' most often refers to structures derived from the chromatic scale in 12-tone equal temperament, which consists of all semitones. Historically, however, it had other senses, referring in Ancient Greek mus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barrister
A barrister is a type of lawyer in common law jurisdiction (area), jurisdictions. Barristers mostly specialise in courtroom advocacy and litigation. Their tasks include arguing cases in courts and tribunals, drafting legal pleadings, jurisprudence, researching the law and giving legal opinions. Barristers are distinguished from solicitors and other types of lawyers (e.g. chartered legal executives) who have more direct access to clients, and may do transactional legal work. In some legal systems, including those of Anglo-Dutch law, South Africa, Stockholm Institute for Scandinavian Law#Scandinavian Law, Scandinavia, Law of Pakistan, Pakistan, Law of India, India, Law of Bangladesh, Bangladesh and the Crown Dependencies of Law of Jersey, Jersey, Guernsey#Politics, Guernsey and the Manx Law, Isle of Man, ''barrister'' is also regarded as an honorific. In a few jurisdictions barristers are usually forbidden from "conducting" litigation, and can only act on the instructions of ano ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refraction
In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and Wind wave, water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. Optical Prism (optics), prisms and Lens (optics), lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength of light,R. Paschotta, article ochromatic dispersion in th, accessed on 2014-09-08 and thus the angle of the refraction also varies correspondingly. This is called dispersion (optics), dispersion and causes prism (optics), prisms and rainbows to divide white light into its constituent spectral ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the center (geometry), ''center'' of the sphere, and the distance is the sphere's ''radius''. The earliest known mentions of spheres appear in the work of the Greek mathematics, ancient Greek mathematicians. The sphere is a fundamental surface in many fields of mathematics. Spheres and nearly-spherical shapes also appear in nature and industry. Bubble (physics), Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is spherical Earth, often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres rolling, roll smoothly in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radius
In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is the line segment or distance from its center to any of its Vertex (geometry), vertices. The name comes from the Latin ''radius'', meaning ray but also the spoke of a chariot wheel.Definition of Radius at dictionary.reference.com. Accessed on 2009-08-08. The typical abbreviation and mathematical symbol for radius is ''R'' or ''r''. By extension, the diameter ''D'' is defined as twice the radius:Definition of radius at mathwords.com. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abbe Number
In optics and lens design, the Abbe number, also known as the Vd-number or constringence of a Transparency (optics), transparent material, is an approximate measure of the material's dispersion (optics), dispersion (change of refractive index versus wavelength), with high values of ''Vd'' indicating low dispersion. It is named after Ernst Abbe (1840–1905), the German physicist who defined it. The term Vd-number should not be confused with the Normalized frequency (fiber optics), normalized frequency in fibers. The Abbe number, V_\mathsf d\ , of a material is defined as : V_\mathsf d \equiv \frac, where n_\mathsf C, n_\mathsf d, and n_\mathsf F are the refractive indices of the material at the wavelengths of the Fraunhofer lines, Fraunhofer's C, d, and F spectral lines (656.3 nanometre, nm, 587.56 nm, and 486.1 nm respectively). This formulation only applies to the visible spectrum, human vision. Outside this range requires the use of different spectral lines. Fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Dispersion
Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Sometimes the term chromatic dispersion is used to refer to optics specifically, as opposed to wave propagation in general. A medium having this common property may be termed a dispersive medium. Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, and in gravity waves (ocean waves). Within optics, dispersion is a property of telecommunication signals along transmission lines (such as microwaves in coaxial cable) or the Pulse (signal processing), pulses of light in optical fiber. In optics, one important and familiar consequence of dispersion is the change in the angle of refraction of different colors of light, as seen in the spectrum produced by a dispersive Prism (optics), prism and in chromatic aberration ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apochromat
An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses. The prefix ''apo-'' comes from the Greek preposition ''ἀπό-'', meaning free from or away from. Explanation Chromatic aberration is the phenomenon of different colors focusing at different distances from a lens. In photography, chromatic aberration produces soft overall images, and color fringing at high-contrast edges, like an edge between black and white. Astronomers face similar problems, particularly with telescopes that use lenses rather than mirrors. ''Achromatic'' lenses are corrected to bring ''two'' wavelengths into focus in the same plane – typically red (~0.590 μm) and blue (~0.495 μm). ''Apo''chromatic lenses are designed to bring ''three'' colors into focus in the same plane – typically red (~0.620 μm), green (~0.530 μm), and blue (~0.465 μ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peter Dollond
Peter Dollond (2 February 1731 – 2 July 1820) was an English inventor of optical instruments. He was the son of optician John Dollond. He is known for his successful optics business, and for the invention of the apochromat. Biography Dollond was born in Kensington. Working together with his father and subsequently with his younger brother and nephew ( George Dollond) he successfully designed and manufactured a number of optical instruments. He is particularly credited with the invention of the triple achromatic lens - i.e., apochromatic lens - in 1763, still in wide use today, though known as the Cooke triplet after a much later 1893 patent. Peter Dollond worked at first silk weaving with his father, but his father's passion for optics inspired him so much that in 1750 Peter quit the silk business and opened an optical instruments shop in Kennington, London. After two years, his father gave up silk, too, and joined him. Dollond telescopes, for sidereal or terrestrial us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Achromatic Telescope
The achromatic telescope is a refracting telescope that uses an achromatic lens to correct for chromatic aberration. How it works When an image passes through a lens, the light is refracted at different angles for different wavelengths. This reflects focal lengths that are dependent on the color of the light. So, for example, at the focal plane an image may be focused at the red end of the spectrum, but blurred at the blue end. This effect is particularly noticeable the further an object lies from the central axis of the telescope. The image of a star can appear blue on one side and orange on the other. Early refracting telescopes with non-achromatic objectives were constructed with very long focal lengths to mask the chromatic aberration. An Achromatic telescope uses an achromatic lens to correct for this. An achromatic lens is a compound lenses made with two types of glass with different dispersion. One element, a ''concave'' lens made out of Flint glass, has relatively high ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
George Bass (optician)
George Bass was an optician known to have made an achromatic doublet around 1733. The specifications for the lens elements were given by Chester Moore Hall. According to Hoyle,Fred Hoyle, ''Astronomy; A history of man's investigation of the universe'', Rathbone Books Limited, 1962, Hall wished to keep his work on the achromatic lenses a secret and contracted the manufacture of the crown and flint lenses to two different opticians, Edward Scarlett and James Mann.- A review of the events of the invention of the achromatic doublet with emphasis on the roles of Hall, Bass, Jesse Ramsden Jesse Ramsden Fellow of the Royal Society, FRS FRSE (6 October 1735 – 5 November 1800) was a British mathematician, astronomy, astronomical and scientific instrument maker. His reputation was built on the engraving and design of dividing engine ..., John Dollond and others. They in turn sub-contracted the work to the same person, George Bass. He realized the two components were for the sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Dollond
John Dollond (30 November 1761) was an English optician, known for his successful optics business and his patenting and commercialization of achromatic doublets. Biography Dollond was the son of a Huguenot refugee, a silk-weaver at Spitalfields, London, where he was born. He followed his father's trade, but found time to acquire a knowledge of Latin, Greek, mathematics, physics, anatomy and other subjects. In 1752 he abandoned silk-weaving and joined his eldest son, Peter Dollond (1731–1820), who in 1750 had started in business as a maker of optical instruments; this business went on to become Dollond & Aitchison. His reputation grew rapidly, and in 1761 he was appointed optician to the king. In 1758 he published an "Account of some experiments concerning the different refrangibility of light", describing the experiments that led him to the achievement with which his name is specially associated, the discovery of a means of constructing achromatic lenses by the combinati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
