Diffractielimiet

Diffractielimiet, also known as the diffraction limit, is the fundamental limit to the resolvable detail in an optical imaging system caused by diffraction of light. It arises from the wave nature of light and the way a finite aperture shapes the image, producing an Airy pattern rather than a perfect point.

In a circular aperture, the Rayleigh criterion gives the smallest resolvable angular separation between two point sources: θ ≈ 1.22 λ / D, where λ is the wavelength and D is the aperture diameter. In object space, a common form is d ≈ 0.61 λ / NA, with NA the numerical aperture, or Abbe's limit d ≈ λ / (2 NA). The exact value depends on the criterion used and the imaging configuration.

The diffractielimiet sets the ultimate resolution of telescopes, microscopes, and cameras using conventional optics. It improves with larger apertures, shorter wavelengths, and higher numerical aperture, and is degraded by optical aberrations, scattering, and refractive effects within the imaging system.

Overcoming the classical limit: Several approaches can surpass the diffraction limit for specific applications. Super-resolution microscopy methods such as STED, PALM/STORM, and SIM can reveal details below the traditional bound. Near-field techniques (NSOM) and computational imaging also contribute to higher effective resolution. In astronomy, adaptive optics mitigates atmospheric blur to approach the diffraction limit of large telescopes.

See also: diffraction, Airy disk, Rayleigh criterion, Abbe limit, numerical aperture, diffraction-limited imaging.