Abstract

Defocusing effects for amplitude-modulated targets, in coherent imaging systems such as an electron microscope, are theoretically and experimentally studied. A mathematical model is developed that adequately predicts experimental observations. Of specific interest in this study is the apparent image enhancement that occurs with small amounts of change of defocus. It is shown that certain spatial frequencies of an image are selectively destroyed as a function of the amount of defocus and, consequently, that an apparent image enhancement results for certain image details.

© 1973 Optical Society of America

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