Spot diagrams give much information about the image formation of an optical system. In order to evaluate the image qualities of lenses quantitatively, it is shown that the geometric optical response function and the intensity distribution can be calculated directly from the coordinates of the spots. Image evaluation using the geometric optical “Strehl definition” is also discussed.
Furthermore, the relation between wave optics and geometrical optics is considered in the case of partial coherence, and it is deduced that, when the wave aberration function is large compared with the wavelength (more than 2λ), the degree of coherence in the object plane scarcely affects the intensity distribution in the image plane.
KENYō MIYAMOTO, "On a Comparison between Wave Optics and Geometrical Optics by Using Fourier Analysis. III. Image Evaluation by Spot Diagram," J. Opt. Soc. Am. 49, 35-39 (1959)