The Unexposed Emulsion Density of a Photographic Layer^*

* Communication No, 2113-H from the Kodak Research Laboratories.

Abstract

The unexposed density of a photographic layer (denoted by the symbol Δ) is defined as the logarithm (to the base 10) of the ratio of intensities just within the top and bottom of an emulsion layer illuminated with monochromatic radiation. On the assumption that light is thoroughly diffused within the layer it can be shown that

$$\Delta ={\log }_{10}\frac{\left(1-S\right)+\left(R-S\right)\left(1+r\right)/\left(1-r\right)}{T\left(1+r\right)/\left(1-r\right)}$$

where R and T are the reflexion and transmission factors of the layer, S the fraction of incident radiation reflected without entering the layer, and r is the internal reflexion factor at the air-gelatin and air-support interfaces for diffuse radiation. The main purpose of this paper is to compare values of Δ deduced from the above formula with those obtained by direct experimental means, and to illustrate variations of Δ with coating weight, grain size and wavelength. The variations of reflexion and transmission factor with these parameters are also discussed in general terms. It is shown that the agreement between Δ values determined directly and those deduced from the formula is quite good, except when the number of grains per unit area is becoming small, in which case the calculated values are too low. An explanation of this discrepancy is advanced and experimental confirmation presented.

Notes

* Communication No, 2113-H from the Kodak Research Laboratories.