Number of Quanta Required to Form the Photographic Latent Image as Determined from Mathematical Analysis of the H and D Curve*

Abstract

One method of approach which has been used to determine the number of quanta utilized by a photographic grain in acquiring a latent image is through mathematical analysis of the characteristic (H and D) curve of the emulsion. For the most part, the theoretical investigations of this problem have been based on the fundamental assumption that a fixed, minimum number of quanta are required for the production of a just developable latent image, this minimum number being assumed to be the same for every grain. Analyses based on this assumption have all led to the conclusion that a small number of quanta (1 to 4) are involved in latent-image formation. A study of the method of treatment of the exposure problem outlined above is presented here in order to show to what extent the conclusion about the number of quanta used rests on experimental fact and to what extent it is dependent upon the fundamental assumptions made in the analysis. It is shown that the conclusion of a small number of quanta arrived at is directly dependent upon the basic assumption that all grains have the same inherent sensitivity, and therefore may be considered valid in just so far as this assumption is found to be in accord with experimental fact.