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.

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

: When light passes through an aperture (like a telescope lens or a pupil), it does not form a perfect point. Instead, it creates a central bright spot surrounded by concentric rings, known as an Airy pattern . According to the Rayleigh Criterion , two point

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