Angular Resolution -- from Eric Weisstein's World of Physics

The angular resolution of a lens or mirror of diameter D is given by

where is the wavelength of radiation. It follows from Fraunhofer diffraction around a circular aperture, and the value 1.220 is given by , where is the first zero of the Bessel function of the first kind Eric Weisstein's World of Math .

Airy Disk, Fraunhofer Diffraction--Circular Aperture