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单词 photography
释义
photography

Physics
  • The process of forming a permanent record of an image. Traditionally photography has used specially treated film or paper. In normal black-and-white photography a camera is used to expose a film or plate to a focused image of the scene for a specified time. The film or plate is coated with an emulsion containing silver salts and the exposure to light causes the silver salts to break down into silver atoms; where the light is bright dark areas of silver are formed on the film after development (by a mild reducing agent) and fixing. The negative so formed is printed, either by a contact process or by projection. In either case light passing through the negative film falls on a sheet of paper also coated with emulsion. Where the negative is dark, less light passes through and the resulting positive is light in this area, corresponding with a light area in the original scene. As photographic emulsions are sensitive to ultraviolet and X-rays, they are widely used in studies involving these forms of electromagnetic radiation. See also colour photography; digital camera.


Science and Technology
  • The creation of a durable image by recording electromagnetic radiation either electronically, to form an image consisting of discrete units (pixels) stored on a computer or other electronic device, or by exposing a photosensitive material coating a film or glass photographic plate. A film or plate produces an analogue image; an electronic device produces a digital image. The camera that captures the image consists of a system of lenses, which focus the radiation emitted or reflected from the subject on to a sensitive surface for a specified time. An exposed film or plate must be developed, by processing it chemically. This produces a negative image, in which dark areas are pale, light areas dark, and colours are reversed. Further chemical processing produces a positive image, leaving the negative undamaged so that it may be used many times. A digital image must be viewed on a monitor and can then be printed.

    Mike Allaby


Chemistry
  • The process of forming a permanent record of an image on specially treated film or paper. In normal black-and-white photography a camera is used to expose a film or plate to a focused image of the scene for a specified time. The film or plate is coated with an emulsion containing silver salts and the exposure to light causes the silver salts to break down into silver atoms; where the light is bright dark areas of silver are formed on the film after development (by a mild reducing agent) and fixing. The negative so formed is printed, either by a contact process or by projection. In either case light passing through the negative film falls on a sheet of paper also coated with emulsion. Where the negative is dark, less light passes through and the resulting positive is light in this area, corresponding with a light area in the original scene. As photographic emulsions are sensitive to ultraviolet and X-rays, they are widely used in studies involving these forms of electromagnetic radiation. See also colour photography.


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