Diffraction-limited system

An optical system whose resolution is constrained by diffraction at its aperture rather than by aberrations or other imperfections.

Airy disk: The central bright region of the diffraction pattern produced by a circular aperture. Its angular size describes the blur that limits a circular-aperture system.
Optical aperture: An opening or effective boundary that limits the light admitted by an optical system. Its shape and diameter determine the system's diffraction pattern.
Hubble Space Telescope: A space telescope launched in 1990 that observes ultraviolet, visible, and near-infrared light. Corrective optics restored its imaging close to the diffraction limit after a primary-mirror flaw.
Optical aberration: An optical imaging error that causes rays from an object point to fail to converge to a single image point. Aberrations broaden images beyond the diffraction pattern and can become the actual resolution limit.
Point spread function: The image formed by an optical system from an ideal point source. It captures the diffraction pattern and any residual aberrations in the system's image.
Wavelength: The spatial period of a wave, measured between successive points in the same phase. Longer wavelengths generally produce broader diffraction patterns for a fixed aperture.
Adaptive optics: Techniques that adjust optical elements to compensate for changing wavefront distortions. It helps ground-based telescopes approach their diffraction limit despite atmospheric turbulence.
Geometrical optics: An approximation that models light as rays and neglects wave effects such as diffraction. It predicts ideal ray convergence but cannot describe the finite diffraction blur.
Numerical aperture: A measure of the range of light angles an optical system can accept or emit. It expresses how strongly an imaging system can collect light and resolve fine detail.
Optical transfer function: A frequency-domain description of how an imaging system transfers contrast from an object to an image. Its cutoff frequency marks the finest spatial detail transmitted by an ideal system.

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