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Abstract
It is shown theoretically that there is a simple relation between speed, emulsion coating weight and granularity for films exposed directly to X-rays, and it is suggested that emulsion coating weight becomes less important when metal intensifying screens are used. These theories are tested by exposing a wide range of films to 45-kV X-rays directly and to 180-kV X-rays and 60Co r-rays in the presence of lead screens. A broad connection between speed and granularity is observed at all energies. This becomes more sharply defined at higher energies, since emulsion coating weight appears to have less influence when metal screens are used, particularly with 60Co r-rays.
The granularities are measured in a way that emphasizes the lower frequencies to which the eye is most sensitive and should correlate well with the visual impression of graininess. Visual ranking experiments confirm this view.