Additive color:  A way to produce colors of light by mixing light of the three additive primary colors - red, green, and blue. Varying proportions of the additive primaries can be combined to create light of all other colors, including white, which is a mixture of all wavelengths.

Albumen:  Egg white; used in early photographic emulsions as a coating for papers.  Also used for glass plates.

Alkali: a substance with a pH above 7.  Developers are usually alkaline solutions.

Ambient light: see available light

Ambrotype:  a collodion wet-plate process in which the emulsion was coated on a glass plate.   The negative image produced was visible as a positive image when the glass was backed with a dark material.

Aperture:  the size of the lens opening through which light passes.  The relative aperture is measured as the focal length of the lens divided by the diameter of the aperture; this is expresses as an f-number: f/8, f/11, etc.

Aperture-priority: a mode of automatic exposure in which the photographer selects the aperture and the camera sets the shutter speed that will produce the correct exposure.

Archival processing:  processing of film and paper designed to protect the print or negative as much as possible from premature deterioration caused by chemical reactions.

Artificial light:  light from an electric lamp, a flash bulb, or electronic flash.  Often describes lights the photographer has set up to illuminate a scene

Automatic focus:  a system by which the camera adjusts its lens to focus on a given area.  Abbreviated AF

Av abbreviation for aperture value.  Used on some camera information displays as a shortened way to refer to aperture settings (f-stops)

Available light the light that already exists where a photograph is to be made, as opposed to light brought in by the photographer.  Often implies a relative dim light.  Also called ambient light or existing light


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