aberratsioon

Aberration is the deviation of an image from the ideal produced by an optical system. It occurs when light rays from a point do not converge to a single point after passing through lenses or mirrors, causing blur or distortion. The concept applies to microscopes, cameras, telescopes, and other imaging devices, as well as to observations in astronomy and electron optics.

Geometric or monochromatic aberrations arise from imperfect focusing of light of a single wavelength due to lens geometry. The most common are spherical aberration (edges and center focus at different points), coma (off-axis points appear comet-shaped), astigmatism (tangential and sagittal rays focus at different distances), field curvature (the image plane is curved rather than flat), and distortion (magnification varies with field position without a true blur). Chromatic aberrations result from wavelength-dependent refractive index. Longitudinal or axial chromatic aberration shifts different colours along the optical axis, while lateral chromatic aberration shifts magnification across the image field.

Aberration of light in astronomy refers to the apparent displacement of stars caused by the finite speed of light and the Earth's motion. Discovered by James Bradley in 1729, it produces an annual shift of up to about 20.5 arcseconds and must be corrected for precise astrometry.

Mitigation relies on optical design and fabrication: achromatic and apochromatic lens combinations reduce chromatic aberration; aspheric surfaces, precise spacing, and advanced coatings reduce spherical aberration, coma, and field curvature. More recent developments include diffractive optics and specialized lens elements. In electron optics, aberration correction uses advanced lenses to counteract spherical aberration. Aberration analysis informs both practical instrument design and the interpretation of observational data.