In Chapter 8 the optical transfer function was introduced. It was used first to describe limitations on image quality stemming from diffraction by various shape and size apertures. Such diffraction at aperture edges gives rise to deflection of light incident on such aperture edges. This deflection causes rays incident on aperture edges to take exit paths different from those of rays incident on the middle portions of the aperture. The latter rays behave according to Snell’s law and form the image. The diffracted rays give rise to image blur. In Section 8.9, it was suggested that the transfer function approach can be used to describe image quality in general for an imaging system and for its various components and not only for diffraction-limited imaging.
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