6/15/2016 Photography ­ AccessScience from McGraw­Hill Education (http://www.accessscience.com/) Photography Article by: Anwyl, Robert D. Formerly, Eastman Kodak Company, Rochester, New York. Walworth, Vivian K. Polaroid Corporation, Cambridge, Massachusetts. Anwyl, Robert D. Formerly, Eastman Kodak Company, Rochester, New York. Anwyl, Robert D. Formerly, Eastman Kodak Company, Rochester, New York. Stanton, Anthony P. Tepper School of Business, Carnegie Mellon University, Pittsburgh, Pennsylvania. Destree, Thomas M. Graphic Arts Technical Foundation, Sewickley, Pennsylvania. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097­8542.510500 (http://dx.doi.org/10.1036/1097­8542.510500) Content Branches and Applications Infrared photography Ultraviolet photography High­speed photography Photomicrography Close­up photography Document copying Microphotography Photographic radiometry Remote sensing Stereoscopic photography Nuclear­particle recording Theory of the Photographic Process Latent image Development After processes Sensitometry and Image Structure Hurter and Driffield curve Sensitometric exposure Development Densitometers Contrast Sensitivity Reciprocity effects Tone reproduction Image structure Photographic Apparatus Recorders and plotters Darkroom equipment Contact and projection printers Color Photography Additive color photography Subtractive color photography One­step color photography Color print processes Color motion pictures http://www.accessscience.com/content/photography/510500 1/32 6/15/2016 Photography ­ AccessScience from McGraw­Hill Education Electronic Devices and Technology Digital Photography Sensors Image capture Digital cameras Bibliography Additional Readings The process of forming stable or permanent visible images directly or indirectly by the action of light or other forms of radiation on sensitive surfaces. Traditionally, photography utilizes the action of light to bring about changes in silver halide crystals. These changes may be invisible, necessitating a development step to reveal the image, or they may cause directly visible darkening (the print­out effect). Most photography is of the first kind, in which development converts exposed silver halide to (nonsensitive) metallic silver. Since the bright parts of the subject normally lead to formation of the darkest parts of the reproduction, a negative image results. A positive image, in which the relation between light and dark areas corresponds to that of the subject, is obtained when the negative is printed onto a second negative­working material. Positive images may be achieved directly in the original material in two principal ways: (1) In reversal processing, a positive image results when the developed metallic silver is removed chemically and the remaining silver halide is then reexposed and developed. (2) In certain specialized materials, all of the silver halide crystals are rendered developable by chemical means during manufacture. Exposure to light alters the crystals so that development will not proceed. As a result, conventional “negative” development affects only the unexposed crystals and a positive image is formed directly. The common materials of photography consist of an emulsion of finely dispersed silver halide crystals in gelatin coated in a thin layer (usually less than 25 micrometers) on glass, flexible transparent film, or paper (Fig. 1). The halides are chloride, bromide, or bromoiodide, depending upon the intended usage. The most sensitive materials, used for producing camera negatives, consist of silver bromide containing some silver iodide; the slow materials used for printing are usually of silver chloride; materials of intermediate speed are of silver bromide or silver bromide and chloride. http://www.accessscience.com/content/photography/510500 2/32 6/15/2016 Photography ­ AccessScience from McGraw­Hill Education Fig. 1 Silver halide crystals, shown highly magnified. (a) Conventional pebblelike crystals. (b) Tablet­shaped crystals, used in some modern emulsions, that absorb light more efficiently, resulting in higher film speed. Following exposure of a sensitized recording material in a camera or other exposing device such as a line­scan recorder, oscillograph, plotter, or spectrograph, the film or plate is developed, fixed in a solution which dissolves the undeveloped silver halide, washed to remove the soluble salts, and dried. Printing from the original, if required, is done by contact or optical projection onto a second emulsion­coated material, and a similar sequence of processing steps is followed. For about 100 years, the results of practical photography were almost exclusively in black and white or, more precisely, shades of gray. With the introduction of the Kodachrome process and materials in 1935 and of a variety of other systems over the succeeding years, a large and increasing fraction of photography has been done in color. In most color photography, development is basically the same as in black­and­white photography, except that the chemical reactions result in the formation of dye images and subsequent removal of the image­forming silver. Both negative and positive (reversal) color systems are employed. A special class of print materials relies on bleachable dyes instead of conventional silver halide processes. See also: Photographic materials (/content/photographic­materials/510400) Branches and Applications The several branches of photography may be grouped according to who takes, processes, and uses the photographs. Within the branches, numerous forms or applications of the photographic art may be distinguished by the exposing conditions and the manner in which the photographic materials, methods, and processes have been designed to optimize the results. The divisions are not always distinct, and the subtleties or strengths of one application are often employed to advantage in another. Amateur photography refers to the taking of photographs by the general public for purposes of recollection, record, or amusement. Historically, the cameras were bulky, film formats were little or no smaller than the prints, and good lighting was required to produce black­and­white photographs of still subjects. Advancements in film technology and sophistication of amateur cameras have enabled the amateur photographer to record color photographs of moving objects on progressively smaller film formats in lightweight pocketable cameras under a wide range of lighting conditions. Processing and printing are provided by commercial photofinishers. Alternatively, the amateur photographer can obtain color prints within minutes by using so­called instant cameras and films which embody their own processing means. Advanced amateurs generally use more costly cameras and a broader range of film materials to produce photographs of esthetic merit for display. They may do their own processing and printing or rely on the assistance of professional finishers. Photography is practiced on a professional level for portraiture and for various commercial and industrial applications, including the preparation of photographs for advertising, illustration, display, and record­keeping. Press photography is for newspaper and magazine illustrations of topical events and objects. Photography is used at several levels in the graphic arts to convert original photographs or other illustrations into printing plates for high­quality reproduction in quantity. Industrial photography includes the generation and reproduction of engineering drawings, high­speed photography, schlieren photography, metallography, and many other forms of technical photography which can aid in the development, design, and manufacture of various products. Aerial photography is used for military reconnaissance and mapping, civilian mapping, urban and highway planning, and surveys of material resources. Microfilming, which is used to store documents and radiographs in significantly reduced space, represents one of several applications of a more general category, microphotography. Biomedical photography is used to reveal or record biological structures, often of significance in medical research, diagnosis, or treatment. Photography is widely applied to preparing projection slides and other displays for http://www.accessscience.com/content/photography/510500 3/32 6/15/2016 Photography ­ AccessScience from McGraw­Hill Education teaching through visual education. Nonamateur uses of photography far exceed the amateur snapshot and home movie fields in volume or commercial significance. See also: Printing (/content/printing/545300); Schlieren photography (/content/schlieren­photography/606400) Photography is one of the most important tools in scientific and technical fields. It extends the range of vision, allowing records to be made of things or events which are difficult or impossible to see because they are too faint, too brief, too small, or too distant, or associated with radiation to which the eye is insensitive. Technical photographs can be studied at leisure, measured, and stored for reference or security. The acquisition and interpretation of images in scientific and technical photography usually requires direct participation by the scientist or skilled technicians. Infrared photography Emulsions made with special sensitizing dyes can respond to radiation at wavelengths up to 1200 nanometers, though the most common infrared films exhibit little sensitivity beyond 900 nm. One specialized color film incorporates a layer sensitive in the 700–900­nm region and is developed