On Necessary Measurements for the Characterization and Optimum Use of Photographic Materials for Scientific Purposes

Abstract

The measurements most often made and quoted in connexion with photographic materials relate to the mean response to light. For any radiation detector, such responsivity characteristics are important where cost or environment severely limit the level of technology that can be applied; for example, respectively, in commercial darkrooms or in rocket missiles. In other circumstances responsivity is mainly a matter of convenience. The quality of the results is then limited in practice, as it always is in principle, by signal-to-noise relations. Knowledge of the properties, often called detectivity characteristics, which define these relations is therefore needed for the rational use of the material. The definition and use of the quantities called noise-equivalent quantum efficiency and noise-equivalent quantum storage are recalled. For any condition of exposure they represent abstractions from the sinusoidal response factors (acceptance factors) and granularity spectra. More subtle abstractions are able to give realistic figures of merit for lens-emulsion combinations under prescribed constraints and conditions of use. Different requirements lead to different figures of merit, but these are found to be nearly equivalent to each other over a wide range of conditions. These concepts lead to a definite solution to the ultimate sensitivity “challenge”, uncertain only in so far as the conditions laid down are defective.