Circular Aperture — Airy Rings

Light passing through a circular aperture spreads into the Airy pattern — a bright central disk surrounded by concentric rings — computed here from the exact Bessel-function form I(u) = [2·J₁(u)/u]². This is the diffraction limit that caps the resolving power of every lens, telescope and eye (the Rayleigh criterion). Students vary the aperture diameter a, screen distance D and wavelength λ, and switch to an Enhanced exposure to reveal the faint outer rings. First dark ring at sinθ₁ = 1.22 λ/a.