One of these things is eliminated when the tangential and sagittal surfaces lie on the Petzval surface.
The Strehl ratio of intensities is used when these things are present. The function for these things can be expanded in terms of a complete set of polynomials orthogonal over the interior of the unit circle; that set of polynomials is named for Zernike. One of these things is eliminated when the tangential and sagittal surfaces lie on the Petzval surface. For a rotationally symmetric system, five of these things, of third-order, are described by the Seidel coefficients. These things arise because the basic trigonometric functions are truncated after one term in their Taylor series in the paraxial approximation, which is not valid. Those third-order ones include coma and astigmatism. For 10 points, identify these departures from ideal optics that come in spherical and chromatic types.
The Strehl ratio of intensities is used when these things are present.
optical aberrations [or geometrical aberrations]