Angular Resolution Calculator

About this calculator

This calculator applies the Rayleigh criterion, θ = 1.22·λ/D, to find the smallest angular separation a telescope (or any circular-aperture optical instrument) can resolve between two point sources, where λ is the light's wavelength and D is the aperture diameter — the 1.22 constant comes from the position of the first dark ring in the Airy diffraction pattern produced by a circular opening. A larger aperture or shorter wavelength gives finer resolution, which is why large observatory mirrors can separate close double stars that small telescopes blur together.

Amateur and professional astronomers evaluating what a telescope can realistically show, optical engineers designing camera lenses or microscopes, and physics students studying diffraction-limited optics use this. Enter the wavelength of light and the aperture diameter to get the angular resolution.