Rayleigh Criterion (FRESH × 2026)

: If the sources are closer than this criterion, their Airy discs overlap so much that they appear as a single, elongated blob.

The is the universally accepted standard for determining the diffraction limit of an optical system's resolving power. It defines the minimum angular or spatial separation required to distinguish two point sources as separate entities. 1. The Core Principle Rayleigh Criterion

According to the Rayleigh Criterion , two point sources are considered "just resolvable" when the of one source aligns exactly with the first minimum of the diffraction pattern of the other. : If the sources are closer than this