Chromatic Aberration and Resolving Power in Electron Microscopy

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Abstract
Contrast difficulties in the observation of fine detail in thin specimens may be overcome by employing dark‐field observation. This introduces the added complication, however, that the imaging electrons are now inhomogeneous, having experienced a most probable energy loss of the order of 20 volts. The present calculations of the effect of chromatic aberration and diffraction show that with an objective aperture smaller than the ``optimum aperture,'' and centered optics, such inhomogeneities do not appreciably affect the resolution, even in the extreme case that the electrons are uniformly distributed in energy.