The Variation of Gamma with Wavelength in the Visible Region^*

* Communication No. 1591H from the Kodak Research Laboratories. M.S. received 13 August 1953.

Abstract

Existing theoretical studies of the dependence of gamma on the unexposed emulsion density, ∆, the logarithm of the ratio of intensities at the top and bottom of a multilayer emulsion, are considered from the point of view of predicting in general terms how gamma should vary with wave-length. It has already been demonstrated both theoretically and experimentally that gamma increases as ∆ decreases, and hence gamma should vary with wave-length in an inverse fashion to the variation of ∆ with wave-length.

It is shown that gamma should rise from the violet through the blue, since in this region ∆ decreases while the sensitivity spread of the emulsion grains remains fairly constant. On the simplest assumption there should be a rapid rise of gamma on passage into the optically sensitized region due to a transition from a volume distribution of grain absorptivities to a surface area distribution. Throughout the optically sensitized region the distribution of grain sensitivities should again be sensibly constant, with a lower spread than in the natural sensitivity region, and there should be an inverse relationship between gamma and ∆.

Experimental data are first presented which confirm a basic assumption of many theoretical treatments, namely, the exponential diminution of intensity through an emulsion layer. It is then shown by detailed comparison of γ- and ∆ wave-length curves that the greater part of the irregularity of the former in the visible region arises from the variation of ∆. It is also shown, however, that sudden changes in grain sensitivity distribution between the natural and dye sensitized region can play an important part, and that within the natural sensitivity region of bromo-iodide emulsions variation of grain sensitivity distribution with wave-length due to non-uniform distribution of iodide with grain size may outweigh the effect of ∆ in determining the trend of the y-wave-length curve.

Notes

* Communication No. 1591H from the Kodak Research Laboratories. M.S. received 13 August 1953.