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Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography , it consists of silver halide crystals dispersed in gelatin . The emulsion is usually coated onto a substrate of glass , films (of cellulose nitrate , cellulose acetate or polyester ), paper, or fabric.
Light can be considered to be a stream of discrete photons, and a light-sensitive emulsion is composed of discrete light-sensitive grains, usually silver halide crystals. Each grain must absorb a certain number of photons in order for the light-driven reaction to occur and the latent image to form. In particular, if the surface of the silver ...
Apart from the widely employed factors such as log-exposure, density, opacity and transmission, sensitometric control of film for television transmission is also particularly concerned with contrast ratios. The definition of contrast ratio is therefore re-stated as follows : 'The ratio between the opacities of the darkest and lightest points in ...
Outside of this range, it becomes necessary to increase the exposure from the calculated value to account for this characteristic of the emulsion. This characteristic is known as reciprocity failure. The film manufacturer's data sheets should be consulted to arrive at the correction required, as different emulsions have different characteristics.
Hence, if an excited molecule transfers its energy to a sensitizer thus exciting it, longer and easier to quantify light emission is often observed. The color (that is, the wavelength), brightness and duration of emission depend upon the sensitizer used. Usually, for a certain chemical reaction, many different sensitizers can be used.
The science of photography is the use of chemistry and physics in all aspects of photography. This applies to the camera, its lenses, physical operation of the camera, electronic camera internals, and the process of developing film in order to take and develop pictures properly.
To explain this in graphical form you may have a graph on Log exposure energy versus fraction of resist thickness remaining. The positive resist will be completely removed at the final exposure energy and the negative resist will be completely hardened and insoluble by the end of exposure energy. The slope of this graph is the contrast ratio.
Photographic emulsions were originally coated on thin glass plates for imaging with electron microscopes, which provided a more rigid, stable and flatter plane compared to plastic films. [7] Beginning in the 1970s, high-contrast, fine grain emulsions coated on thicker plastic films manufactured by Kodak, Ilford and DuPont replaced glass plates.