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Transmission Densitometer for Color Films
By K. G. MACLEISH
The need for unification of density measurements made in numerous and widely separated laboratories led to the development of the Eastman Electronic Densitometer, Type 31 A. This densitometer reads diffuse ^densities of color films from 0.0 to 4.1 through narrow-band color filters, with a standard deviation of ±1% among different instruments. The construction and performance of the densitometer are described.
J. HE BEHAVIOR of a photographic image in an optical system, such as a projector or a printer, can be described in terms of the fraction of the incident radiation transmitted by selected portions of the image. In practice it is convenient to use the negative logarithm of this fraction, a number which is referred to as the density of the material. It is well recognized that density, so defined, is not in general a property of the material alone, since its value depends on the optical configuration of the illuminating and receiving systems.1 Thus different density-measuring instruments, or densitometers, may be quite at variance with one another in their readings on identical samples.
Of the many different types of transmission densitometers employed by the
Presented on April 30, 1953, at the Society's
Convention at Los Angeles by K. G. Mac
leish, Camera Works, Eastman Kodak Co.,
Rochester, N.Y.
(This paper was received on April 27,
1953.)
Eastman Kodak Company, each is considered more or less satisfactory for the specific kinds of measurement to which it is adapted. The need, however, for coordination of sensitometric results throughout the organization has made it imperative that each laboratory have available a precision densitometer of some one type, to which all measurements may be referred. Moreover, it is highly desirable that this standard instrument be versatile, sensitive, rugged, and generally suited for use both in research and in process control. None of the densitometers available prior to 1948 seemed to meet all these requirements; the decision was therefore made to undertake the development of a new densitometer having the desired characteristics. The resulting instrument, which is the subject of this paper, has been designated as the Eastman Electronic Densitometer, Type 31 A.
To date, about seventy Type 31 A densitometers have been placed in service in Kodak plants and laboratories
696
June 1953 Journal of the SMPTE Vol. 60