Why Airy disc formula has 1.22 in front of it?Does it depend on aperture diameter?Thanks
The factor 1.22 is there because an Airy disc is comprised of a Bessel function:
the 'diameter' of the first dark ring is equal to 1.22*l/d, where l is the wavelength of light and d the diamater of the entrance pupil. If the aperture was not circular, the factor 1.22 would be different, reflecting the difference in far-field diffraction pattern.
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