Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
The Rayleigh criterion defines the minimum angular separation at which two point light sources can be resolved as distinct. It is determined by the diffraction limit of an optical system.
The Rayleigh criterion is used to determine the resolving power of optical instruments like telescopes and microscopes.
According to the Rayleigh criterion, two sources are considered resolvable when the central maximum of one diffraction pattern coincides with the first minimum of the other.
Mathematically, it is given by $\theta = 1.22 \frac{\lambda}{D}$, where $\theta$ is the angular resolution, $\lambda$ is the wavelength of light, and $D$ is the diameter of the aperture.
The factor 1.22 in the formula arises from calculations involving a circular aperture and Airy disk patterns.
Smaller wavelengths and larger apertures improve resolving power according to this criterion.
A pattern produced by light passing through a circular aperture, consisting of a central bright spot surrounded by rings; it plays a role in determining resolution limits.