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Note that the times are approximate, and vary between different films and ASA numbers, but the table shows in general how the exposure time is adjusted. In photography , reciprocity is the inverse relationship between the intensity and duration of light that determines the reaction of light-sensitive material.
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.
A developable photographic latent image forms when crystals of silver halide in an emulsion layer are exposed to light. The initial nucleation phase is chemically and thermodynamically unstable; it is thus temperature sensitive, and involves the production of one, or very few silver atoms as sub-latent image specks in each silver halide crystal.
Exposure is a combination of the length of time and the illuminance at the photosensitive material. Exposure time is controlled in a camera by shutter speed, and the illuminance depends on the lens aperture and the scene luminance. Slower shutter speeds (exposing the medium for a longer period of time), greater lens apertures (admitting more ...
The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinner than common window glass. They were heavily used in the late 19th century. With the spread of photographic film, the use of plates declined through the 20th.
Structurally, collodion wet plates are held together with a specific emulsion type, made using a silver halide mixture in gelatin. Fluctuations in RH can strain the adhesive emulsion, causing the gelatin to expand and contract. The strain from incorrect RH can also cause the emulsion to crack or separate along the plates' edges. [10]
For example, starting with an exposure of 1/60 at f /16, the depth-of-field could be made shallower by opening up the aperture to f /4, an increase in exposure of 4 stops. To compensate, the shutter speed would need to be increased as well by 4 stops, that is, adjust exposure time down to 1/1000.
Contact print of a photo film cut in pieces, used for reviewing and selecting images for the final print. Photo by Paolo Monti, 1975. Contact printing is a simple and inexpensive process. Its simplicity avails itself to those who may want to try darkroom processing without buying an enlarger.