Photosensitive Material

Topics: X-ray, Photographic film, Sensitometry Pages: 4 (799 words) Published: February 11, 2013
Photosensitive materials (x-ray films) are used to record the invisible x-ray image. It is required to reproduce all the characteristics of the invisible image in visible form .The films ability to do so depends on its sensitometric properties.

Sensitometer:
Measures films sensitivity to light; shows the range of densities on an image. Sensitometry:-
The scientific study of the response of photosensitive material to different levels of exposure. How is it done?
Producing a sensitometric strip and plotting a characteristic curve.

sensitometer (optical step wedge) and densitometer are used to measure film's response to light
Response of exposure & How is it manifested
The response is the change that takes place, after exposure to electromagnetic radiation (light or x-rays), in the photosensitive emulsion on the film
The response of the film to exposures is manifested as a degree of blackening produced after chemical processing Witch is quantified by:- •Transparency
Opacity
Optical Density (OD(
The optical density describes how much a certain area of the film is opaque to light incident upon it . In Radiography the degree of film blackening is quantitatively indicated by the term ‘Optical Density witch is expressed as a number that is actually a logarithm, using the common base 10. Photographic density is defined by

D = log 10 Io / I
D = density.
IO= light incident on a film
. I = light transmitted by the film
Densitometer
is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or photographic film, due to exposure to light. Optical density is a result of the darkness of a developed picture and can be expressed absolutely as the number of dark spots (i.e., silver grains in developed films) in a given area, but usually it is a relative value, expressed in a scale. According to the principle of

operation of the densitometer, one
can have:...
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