Rayleigh Criterion

Rayleigh criterion states that the maximum resolving power of a lens is limited by diffraction to the ratio of the wavelength of the waves to the diameter of the lens' aperture.

\(\theta \approx 1.22\lambda/D\) (considering that \(sin(\theta) \approx \theta\) )

D is the diameter in metres.

The factor 1.22 is derived from a calculation of the postion of the first dark circular ring surrounding the central Airy disc of the diffraction pattern. This number is more precisely 1.32966989.., the first zero of the order-one Bessel function of the first kind \(J_1(x)\) divided by \(\pi\).