Image Recording in Electron Microscopy

Abstract

Three properties of any recorder are of primary importance in electron microscopy: (1) its spread function, (2) its signal-to-noise characteristics (or, detective quantum efficiency, DQE), and (3) its sensitometric curve shape. Photographic materials are found to have spread functions that are not limiting under normal conditions. The remaining two factors are investigated by analysis of mathematical models and comparison with experimental results. Most photographic materials are found to be near-perfect detectors, in that they record the input signal without appreciable loss and do not seriously add to the input noise. They have similarly shaped curves of density vs electron exposure. It is shown that to optimize the recording step in electron microscopy, it is advantageous to be able to select speed–granularity combinations at will, if DQE can be kept high. Variations in the processing of a commercial photographic plate are found to accomplish this effect.