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Actinograph
An actinograph is an instrument for measuring or estimating the amount of light available, in terms of its ability to expose photographic film. That is, it measures the ''actinic'' or ''chemical'' intensity of light, as opposed to radiometric or photometric amount of light. The earliest actinographs were 24-hour recording devices, using a rotating cylinder of photographic paper exposed through a wedged-shaped slit to record a graph of actinic light during the period of a day; hence the ''graph'' suffix in ''actinograph''. Such devices were developed and described by Robert Hunt, secretary of the Royal Cornwall Polytechnic Society in 1845, as an improvement on T. B. Jordan's 1839 ''Heliograph''. In 1888, Ferdinand Hurter and Vero Charles Driffield patented a device for estimating the actinic power of sunlight and for computing exposure times and apertures for cameras, based on the plate speed, time of day, time of year, and latitude. These were slide rules, not measuring in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Actinograph 1846
An actinograph is an instrument for measuring or estimating the amount of light available, in terms of its ability to expose photographic film. That is, it measures the ''actinic'' or ''chemical'' intensity of light, as opposed to radiometry, radiometric or photometry (optics), photometric amount of light. The earliest actinographs were 24-hour recording devices, using a rotating cylinder of photographic paper exposed through a wedged-shaped slit to record a graph of actinic light during the period of a day; hence the ''graph'' suffix in ''actinograph''. Such devices were developed and described by Robert Hunt (scientist), Robert Hunt, secretary of the Royal Cornwall Polytechnic Society in 1845, as an improvement on T. B. Jordan's 1839 ''Heliograph''. In 1888, Ferdinand Hurter and Vero Charles Driffield patented a device for estimating the actinic power of sunlight and for computing exposure times and apertures for cameras, based on the film speed, plate speed, time of day, ti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slide Rule
The slide rule is a mechanical analog computer which is used primarily for multiplication and division, and for functions such as exponents, roots, logarithms, and trigonometry. It is not typically designed for addition or subtraction, which is usually performed using other methods. Maximum accuracy for standard linear slide rules is about three decimal significant digits, while scientific notation is used to keep track of the order of magnitude of results. Slide rules exist in a diverse range of styles and generally appear in a linear, circular or cylindrical form, with slide rule scales inscribed with standardized graduated markings. Slide rules manufactured for specialized fields such as aviation or finance typically feature additional scales that aid in specialized calculations particular to those fields. The slide rule is closely related to nomograms used for application-specific computations. Though similar in name and appearance to a standard ruler, the slide rule is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Actinometer
Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyranometers, pyrheliometers and net radiometers. An actinometer is a chemical system or physical device which determines the number of photons in a beam integrally or per unit time. This name is commonly applied to devices used in the ultraviolet and visible wavelength ranges. For example, solutions of iron(III) oxalate can be used as a chemical actinometer, while bolometers, thermopiles, and photodiodes are physical devices giving a reading that can be correlated to the number of photons detected. History The actinometer was invented by John Herschel in 1825; he introduced the term ''actinometer'', the first of many uses of the prefix ''actin'' for scientific instruments, effects, and processes. The actinograph is a related device for estimating the actinic power of lighting for photography. Chemical actinometry Chemical actinometry inv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hurter And Driffield
Ferdinand Hurter (1844–1898) and Vero Charles Driffield (1848–1915) were nineteenth-century photographic scientists who brought quantitative scientific practice to photography through the methods of sensitometry and densitometry. Among their other innovations was a photographic exposure estimation device known as an actinograph. See also * H&D speed numbers, originally described in 1890, for film speed Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to describe the relation ... measurements References External links A brief history of Hurter and Driffield by Ron Callender in ''Encyclopedia of Nineteenth-century Photography'' 2008 pp.732-4 History of photography {{photo-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photographic Film
Photographic film is a strip or sheet of transparent 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, and resolution of the film. 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 very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to ultraviolet light, X-rays, gamma rays, and high-energy particles. Unmodified silver halide crystals are sensitive only to the blue part of the visible spectrum, producing unnatural-looking rendition ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiometry
Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. The fundamental difference between radiometry and photometry is that radiometry gives the entire optical radiation spectrum, while photometry is limited to the visible spectrum. Radiometry is distinct from quantum techniques such as photon counting. The use of radiometers to determine the temperature of objects and gasses by measuring radiation flux is called pyrometry. Handheld pyrometer devices are often marketed as infrared thermometers. Radiometry is important in astronomy, especially radio astronomy, and plays a significant role in Earth remote sensing. The measurement techniques categorized as ''radiometry'' in optics are called ''photometry'' in some astronomical applicati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power. In modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. Photometry and the eye The human eye is not equally sensitive to all wavelengths of visible light. Photometry attempts to account for this by weighting the measured power at each wavelength with a factor that represents how sensitive the eye is at that wavelength. The standardized model of the eye's response to light as a function of wavelength is given by the luminosity function. The eye has different responses as a function of wavelength when ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robert Hunt (scientist)
Robert Hunt (6 September 1807 – 17 October 1887) was a British mineralogist, as well as an antiquarian, an amateur poet, and an early pioneer of photography. He was born at Devonport, Plymouth and died in London on 17 October 1887. Life and work Early life Hunt's father, a naval officer, drowned while Robert was a youth. Robert began to study in London for the medical profession, but ill-health caused him to return to settle in Cornwall. In 1829, he published ''The Mount’s Bay; a descriptive poem ... and other pieces'' but received little critical or financial success.Alan Pearson, 'Hunt, Robert (1807–1887)’, Oxford Dictionary of National Biography, Oxford University Press, 200 Retrieved 16 Jan 2011/ref> In 1840, Hunt became secretary to the Royal Cornwall Polytechnic Society at Falmouth. Here he met Robert Were Fox, and carried on some physical and chemical investigations with him. Career He was appointed Professor of Mechanical Science, Government School o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Royal Cornwall Polytechnic Society
The Royal Cornwall Polytechnic Society (commonly known as The Poly) is an educational, cultural and scientific charity, as well as a local arts and cinema venue, based in Falmouth, Cornwall, England, United Kingdom. The Society exists to promote innovation in the arts and sciences. History In 1832 the Fox family. a prominent Quaker business family of Falmouth, founded the Cornwall Polytechnic Society, to promote the ideas and inventions of the workers in their Perran Foundry. This was the first use of the word ‘ Polytechnic’ (meaning "of many arts and techniques") in Britain. In 1835 King William IV bestowed Royal Patronage on the Society, at the request of Davies Gilbert and it changed its name from the Cornwall Polytechnic Society to the Royal Cornwall Polytechnic Society. In the same year the Polytechnic Hall was built, at 24 Church Street, Falmouth, being originally used for “objects connected with the sciences, arts and literature”, but not for theatrical pu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Klaus Hentschel
Klaus Hentschel (born 4 April 1961) is a German physicist, historian of science and Professor and head of the History of Science and Technology section in the History Department of the University of Stuttgart. He is known for his contributions in the field of the history of science. Life and work Born in Bad Nauheim, Hentschel from 1979 to 1985 studied physics, philosophy, science, history and musicology at the University of Hamburg. He completed his studies in philosophy in 1985 with the master's examination, and a study in physics in 1987. After some studies in the United States, among others in Boston on a DAAD, he in 1989 received his PhD at the University of Hamburg. His thesis was entitled "Interpretationen und Fehlinterpretationen der speziellen und der allgemeinen Relativitätstheorie durch Zeitgenossen Albert Einsteins" (Interpretations and misinterpretations of the special and general relativity theory by Albert Einstein's contemporaries). After graduation Hentschel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferdinand Hurter
Ferdinand Hurter (15 March 1844 – 12 March 1898) was a Swiss industrial chemist who settled in England. He also carried out research into photography. Early life Ferdinand Hurter was born in Schaffhausen, Switzerland, the only son of Tobias Hurter, a bookbinder, and his wife Anna Oechslein.N. J. Travis (2004) ‘Hurter, Ferdinand (1844–1898)’, rev., ''Oxford Dictionary of National Biography'', Oxford University PressRetrieved on 10 July 2007 His father died when Ferdinand was aged only two and his mother worked as a nurse to support him and his sister Elizabeth. She later married her late husband's half-brother, David, and Ferdinand developed a strong relationship with his stepfather. After education at the local Gymnasium (school), Gymnasium he became an apprentice to a dyer in Winterthur before moving to Zürich to work in a silk firm. He then attended Zürich Polytechnic before going to Heidelberg University. Here he studied chemistry under Robert Bunsen and ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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