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VIRTUAL REALITY
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PHOTOGRAPHY From: Encarta 98 Encyclopedia
Historical Development The term camera, as well as the apparatus itself, derives from camera obscura, which is Latin for "dark room" or "dark chamber." The original camera obscura was a darkened room with a minute hole in one wall. Light entering the room through this hole projected an image from the outside on the opposite, darkened wall. Although the image formed this way was inverted and blurry, artists used this device, long before film was invented, to sketch by hand scenes projected by the "camera." Over the course of three centuries, the camera obscura evolved into a handheld box, and the pinhole was fitted with an optical lens to sharpen the image. 18th Century The photosensitivity of certain silver compounds, particularly silver nitrate and silver chloride, had been known for some time before British scientists Thomas Wedgwood and Sir Humphry Davy began experiments late in the 18th century in the recording of photographic images. Using paper coated with silver chloride, they succeeded in producing images of paintings, silhouettes of leaves, and human profiles. These photographs were not permanent, however, because the entire surface of the paper blackened after exposure to light. 19th Century
The earliest photographs on record, known as heliographs, were made in 1827 by French physicist Joseph Nicéphore Niépce. About 1831 French painter Louis Jacques Mandé Daguerre made photographs on silver plates coated with a light-sensitive layer of silver iodide. After exposing the plate for several minutes, Daguerre used mercury vapors to develop a positive photographic image. These photographs were not permanent because the plates gradually darkened, obliterating the image. In the first permanent photographs made by Daguerre, the developed plate was coated with a strong solution of ordinary table salt. This fixing process, originated by British inventor William Henry Fox Talbot, rendered the unexposed silver-iodide particles insensitive to light and prevented total blackening of the plate. The Daguerre method produced an unreproducible image on the silver plate for each exposure made. While Daguerre perfected his process, Talbot developed a photographic method involving the use of a paper negative from which an unlimited number of prints could be made. Talbot had discovered that paper coated with silver iodide could be made more sensitive to light if dampened before exposure by a solution of silver nitrate and gallic acid, and that the solution also could be used in developing the paper after exposure. After development, the negative image was made permanent by immersion in sodium thiosulfate, or hypo. Talbot's method, called the calotype process, required exposures of about 30 seconds to produce an adequate image on the negative. Both Daguerre and Talbot announced their processes in 1839. Within three years the exposure time in both processes had been reduced to several seconds. In the calotype process, the grain structure of the paper negatives appeared in the finished print. In 1847 French physicist Claude Félix Abel Niépce de Saint-Victor devised a method of using a glass-plate negative. The plate, which was coated with potassium bromide suspended in albumin, was prepared before exposure by immersion in a silver-nitrate solution. The glass-plate negatives provided excellent image definition but required long exposures. In 1851 British sculptor and photographer Frederick Scott Archer introduced wet glass plates using collodion, rather than albumin, as the coating material in which light-sensitive compounds were suspended. Because these negatives had to be exposed and developed while wet, photographers needed a darkroom close at hand in order to prepare the plates before exposure and to develop them immediately after exposure. Using wet collodion negatives and horse-drawn mobile darkrooms, photographers on the staff of American photographer Mathew B. Brady took thousands of photographs on battlefield sites during the American Civil War (1861-1865). Because use of the wet collodion process was limited largely to professional photography, various experimenters attempted to perfect a type of negative that could be exposed when dry and that would not require immediate development after exposure. Advances were made by British merchant Richard Kennett, who supplied dry-plate negatives to photographers as early as 1874. In 1878 British photographer Charles Bennett produced a dry plate coated with an emulsion of gelatin and silver bromide, which was similar to modern plates. While experiments were being performed to increase the efficiency of black-and-white photography, preliminary efforts were made to use the coated-plate emulsions to produce natural color images of photographic subjects. In 1861 the first successful color photograph was made by British physicist James Clerk Maxwell, who used an additive-color process. About 1883, American inventor George Eastman produced a film consisting of a long paper strip coated with a sensitive emulsion. In 1889 Eastman produced the first transparent, flexible film support, in the form of ribbons of cellulose nitrate. The invention of roll film marked the end of the early photographic era and the beginning of a period during which thousands of amateur photographers became interested in the new process. 20th Century In the early 20th century, commercial photography grew rapidly, and improvements in black-and-white photography opened the field to individuals lacking the time and skill to master the earlier, more complicated processes. The first commercial color-film materials, coated glass plates called Autochromes Lumière—after the process developed by French inventors Auguste and Louis Lumière—became available in 1907. During this period, color photographs were produced with the three-exposure camera. In the 1920s improvement of photomechanical processes used in printing created a great demand for photographs to illustrate text in newspapers and magazines. The demand for photographic illustrations with printed material established the new commercial fields of advertising and publicity photography. Technological advances, which simplified photographic materials and apparatus, encouraged the widespread adoption of photography as a hobby or avocation by great numbers of people. The 35-millimeter camera, which used small-sized film designed initially for motion pictures, was introduced in 1925 in Germany, and because of its compactness and economy, it became popular with both amateur and professional photographers. During this period, finely powdered magnesium was used by professional photographers as an artificial illuminant. Sprinkled in a trough and fired with a percussion cap, it produced a brilliant flash of light and a cloud of acrid smoke. In the 1930s the photographic flashbulb replaced magnesium powder as a light source. The advent in 1935 of Kodachrome color film and in 1936 of Agfacolor, both of which produced positive color transparencies, or slides, initiated the popular use of color film. Kodacolor negative color film, introduced in 1941, gave further impetus to its widespread use. Many photographic processes that were developed for the military during World War II (1939-1945) were released for general use at the end of the war. These advances included new chemicals for film development and fixing. The perfection of electronic computers greatly facilitated the solution of mathematical problems involved in lens design, and many new lenses became available, including interchangeable lenses for existing camera types. In 1947 the Polaroid Land camera, based on a photographic process devised by American physicist Edwin H. Land, added to amateur photography the appeal of prints that could be developed and finished in the camera immediately after exposure. During the 1950s, new manufacturing processes greatly increased the speed, or light sensitivity, of both black-and-white and color films. Black-and-white film speeds rose from a maximum of about ISO 100 to a theoretical maximum of about ISO 5000, and color film speeds increased tenfold. This decade was also marked by the introduction of electronic devices called light amplifiers, which intensify dim illumination, making possible the recording on photographic film of even the faint light of very distant stars. Such advances in mechanical devices systematically raised the technical level of both amateur and professional photography. A film called Itek RS that uses relatively inexpensive chemicals such as zinc, cadmium sulfide, and titanium oxide instead of the more expensive silver compounds was also introduced in the 1960s. A new technique called photopolymerization made possible the production of contact prints on ordinary, unsensitized paper. For other recent developments, see Special Techniques, above.
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