The Quantum Sensitivity of an Emulsion and the Size of the Grains Producing the Dye Image in a Coupler Starved Format

Abstract

The quantum sensitivity of an emulsion was determined by studying the effect that the exposure and development have on the size distribution of the halide grains: the method is sometimes referred to as a residual-size-analysis. The emulsion coatings were partially developed initially in a colour developer followed by further development to fully develop the grains, and a combination of electron microscopy and optical microscopy was used to establish the response of grains of different size within the polydisperse emulsion. The study was facilitated for this emulsion of wide size spread by arbitrarily placing the grains in 12 size classes where adjoining classes differ in projective area by √2. The most sensitive grains were among the largest and required on average 12 absorbed photons before 50% were rendered developable, and there was a notable fall-off in quantum sensitivity as the grain size decreased.

The response characteristics of grains of different size were used to investigate which grains within the emulsion contributed most to the dye image in a coupler-starved colour negative system. It was observed that at the lowest exposures, grains in a single size class may account for as much as 30% of all the grains responding, and that over quite a wide range of exposures, the grains in just the five largest size classes accounted for over 90% of the developed grains.