Photography, History of Photography.

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. Traditional photography uses the action of light to cause changes in a film of silver halide crystals in which development converts exposed silver halide to (nonsensitive) metallic silver. Following exposure in a camera or other device, the film or plate is developed, fixed in a solution that 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 emulsion-coated material, and a similar sequence of processing steps is followed. Digital photography captures images directly with an electronic photosensor. See also Photographic materials.

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 record-keeping. 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 high-quality reproduction in quantity. Industrial photography includes the generation and reproduction of engineering drawings, high-speed 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. 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 teaching through visual education. See also Printing; Schlieren photography.

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.