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Holography Glossary


first practical and commercial photographic process, introduced by Louis Daguerre in 1839. The sensitive material comprised silver iodide, deposited on a polished silver plated copper base. A positive image was produced by camera exposure and mercury "development", which turned light struck halides gray-white. The image was made permanent by immersing the plate in a solution of sodium chloride.
Daylight enlarger 
early type of enlarger using light from a hole in a window to provide illumination of the negative.
reducing an exposed emulsion's sensitivity to light. This can be done by the application of dyes or by using oxidation agents
chemical bath containing reducing agents, which converts exposed silver halide to black metallic silver, making the latent image visible.
process of converting exposed silver halide to a visible image. The term is also used in non-silver halide processes, for example, dichromated gelatin where image formation is a completely different mechanism, but the end result is similar.
abbreviation of diazonium compounds, which decompose under the action of intense blue or ultraviolet radiation, forming an image in an azo dye.
Dichroic filters 
produced by metallic surface coatings on glass to form colors by interference of light. Used in high quality color enlarger heads.
Dichroic fog 
purple-green bloom usually seen on negatives and caused by the formation of silver in the presence of an acid.
Diffraction Efficiency 
a measure of performance for a diffraction grating or hologram. Diffraction efficiency is the ratio of optical power diffracted by the grating to the power incident. More simply, it is the percentage of light diffracted. In holography, higher diffraction efficiencies are preferred, yielding brighter holograms.
reduction in the strength of a liquid by mixing it with an appropriate quantity of water.
Dimensional stability 
substance's ability to remain unchanging in size when subjected to processing and drying.
Dish development 
method of development used for processing single sheet, cut film or paper by immersing in a shallow dish of developer and agitating by rocking the dish.
Documentary photography 
taking of photographs to provide a record of social and political situations with the aim of conveying information.
control of exposure in photographic printing achieved by reducing exposure to specific areas of the paper. Typically, a small disk mounted on the end of a thin wire would be wiggled over an area to be lightened during enlargement. (Many photographers simply used their fingers as the "dodge.") Less light meant a lighter area and the wiggling helped blend the lightened area smoothly with the area around it.
Dry down 
refers to the amount a print darkens after drying.
Dry mounting 
method of attaching prints to mounting surfaces by heating shellac tissue between the mount and the print.
Dye destruction process 
method of producing a colored image by partially bleaching fully formed dye layers incorporated in the sensitive material.
Dye-image monochrome films 
black & white negative films designed for color processing.
Dye sensitizing 
defined as all silver halides used in black & white emulsions are sensitive to blue light. Early photographic materials possessed only this sensitivity.
Dye transfer print 
method of producing color prints via three color separation negatives. Negatives are used to make positive matrices, which are dyed in subtractive primaries and printed in register.
picture structuring which relates to a sense of movement and action.