Scanning electron microdensitometry.

Diffraction arid partial coherence cause errors in the measurement of small-scale photographic detail by microdensitometers and projection systems. The optical imaging nonlinearities can be avoided by scanning the silver distribution with a narrow beam of energetic electrons and counting the secondary quanta that are excited. It is found that the number of low energy (secondary) and high energy (backscattered) electrons emitted from various emulsion types as well as the characteristic Ag x-ray fluorescence are measures of the local silver concentration. A mechanism for the secondary electron contrast, which is only in part due to surface relief, is proposed. Spatial frequencies up to 2280 1p/mm have been retrieved by such scanning electron beam probes.