In this chapter, we investigate image imperfection, which results mainly from the phase errors in image‐forming waves. The phase error, especially in the exit pupil plane, is conventionally called aberration. (Apodization is the word for describing the corresponding amplitude error.) Aberration is generally expressed in polynomials. We first focus on the aberration of optical systems with axial symmetry and study the effects of Seidel aberrations, the lowest‐order aberrations that degrade the image contrast. We then consider the aberration of general optical systems by introducing Zernike polynomials.
The orthogonality of Zernike polynomials sheds light on the method of minimizing the aberration when optimizing an optical system.
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