The Gradation and Inertia of Hurter and Driffield: A Study in Theory

Abstract

In a deep emulsion the shape of the D-Iog E characteristic depends on two quantities, the photon number P, which is determined by the number of photons required to form a development centre, and the ratio K of the absorption cross sections of a silver halide crystal before and after development. The position of the curve on the exposure axis is determined by the mean reaction cross section 8 of the crystals. In a coating a fourth quantity enters, the" opacity before development" of Hurter and Driffield, here called the exposure ratio R of front to back surface.