The fact that various instruments used to determine photographic density yield different results makes it desirable that some one method should be chosen as a standard. This method should produce results which are in keeping with the implications of the Hurter and Driffield definition of photographic density. A study has been made, extending some of the previous work of Tuttle, of the factors responsible for discrepancies between the readings of existing densitometers, and it is concluded that the integrating sphere densitometer is best suited to serve as a standard instrument. The relations existing between its readings and those of other densitometers are given and it it is shown that these relations are valid for a wide range of photographic materials of varying grain size. Toy’s experiments to determine contact printing densities have been repeated with somewhat different results. Certain effects connected with opal densitometers and reported by Bull and Cartwright have been explained. The dependence of photographic density upon orientation of the photographic sample, that is, whether the emulsion side or base side acts as first surface, is shown. Thin metallic films on glass have been suggested to serve as standard densities. It is shown that such films are not suitable for this purpose since their optical properties are quite different from those of the photographic density.
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