Algorithm for determination of the diffraction focus in the presence of small aberrations.
The diffraction focus (or best focus) is calculated for an optical system that contains small aberrations. By assuming that the wave aberration function is known with respect to an arbitrary point in the image region, we obtained simple analytical expressions of the diffraction focus coordinates for any geometry of the pupil. The method can be easily worked out on a computer by ray tracing. A comparison is done with the method that is based on the displacement theorem.
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