Application of the Linfoot quality factors to third order spherical aberration
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The location and the character of the best focus on axis by an optical system with a nominal amount of third order spherical aberration is theoretically discussed in this paper. In order to describe the physical status of the image, three criteria Relative Structural Content, Correlation Quality and Image Fidelity defined by Linfoot and another factor called Sharpness are utilized. The "best" focus is then defined in terms of the maximum value of these criteria. Each criterion plays a different role depending upon the structure of the object. These factors are calculated by Simpson's method from the transfer function previously given by G . Parrent for the various focal setting between marginal and paraxial foci and for different amounts of aberration. Assuming a flat object spectrum the computations indicate that for small aberrations (A < lambda/4) the best focus lies midway between the marginal and paraxial foci irrespective of the quality criterion. For large aberrations (A > 2lambda) the best focus deviates slightly from the mid focus, and the deviation depends upon the particular criterion. These results are compared with other studies in the last section. In particular, the result concerning Correlation Quality is compared with the work done by Kuwahara.
Thesis (M.A.)--Boston University
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