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SENSITOMETRY
Its History and Present Day Application in the Motion Picture Industry
Emery Huse*
I
BEFORE entering into a discussion of sensitometry it would be well first to go back quite a few years and call to mind the beginnings of photography, in which sensitometry plays a part.
Although it was first observed in the early part of the eighteenth century that silver salts were darkened by light, no real use was made of these findings for the purpose of making pictures until Wedgewood published a paper entitled "An Account of a Method of Copying Paintings on Glass and on Making Profiles by the Agency of Light upon Nitrate of Silver." This paper appeared in the year 1802. Wedgewood conceived the idea of making silhouettes by using paper treated with silver nitrate which would darken in the light. Also Wedgewood was one of the first to try to take photographs in the "camera obscura." The camera obscura was nothing more than a camera consisting of a box with a lens at one end and a ground glass at the other. Wedgewood, of course, removed the ground glass and put his prepared paper in its place but did not achieve any great success due to the low sensitivity of his material.
Later Sir Humphrey Davey succeeded in making photographs by sunlight with the aid of a microscope. It is generally conceded that this method of Davey's gave the first pictures made by means of a lens on a photographic material.
It was quite some time later before development, as we now know of it, and fixation were discovered. This work was advanced considerably by Fox Talbot in the middle of the nineteenth century and his work was succeeded later by the wet collodion process, which is still in existence and is used by photo engravers.
The difficulties of the wet collodion plates disappeared with the coming of the gelatin emulsion process. The first gelatin emulsions were made in 1871 by Dr. Maddox. Naturally, further experimentation was carried on in the succeeding years until during the latter part of the nineteenth century George Eastman's continual experiments to substitute a light, flexible support for the heavy and easily damaged glass were successful and film as we know it today became a reality. Eastman's experiments, in conjunction with Thomas Edison, paved the way for the present day cinematography.
II
The Beginnings of Sensitometry Sensitometry literally means a measure of sensitivity. As early as 1848 Claudet devised an instrument for determining the speed of the daguerreotype plate, which instrument was termed a "photo
* (West Coast Division, Motion Picture Film Department, Eastman Kodak Company)
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