Chromatic aberration

Chromatic aberration is an image defect in which a lens focuses different wavelengths of light at different positions, producing color fringes or reduced sharpness.

Dispersion (optics): Dispersion is the variation of a material’s refractive index with the wavelength of light. Wavelength-dependent refraction makes different colors focus at different positions.
Refraction: Refraction is the change in a wave’s direction as it passes between materials with different propagation speeds. Lenses refract light, and wavelength-dependent refraction is the basis of this defect.
Spherical aberration: Spherical aberration occurs when rays passing through different zones of a spherical surface focus at different positions. It also blurs images, but does not require different wavelengths to focus differently.
Achromatic doublet: An achromatic doublet combines two lens elements of different glasses to bring two wavelengths to a common focus. It reduces longitudinal color error through compensating dispersion.
Longitudinal chromatic aberration: Longitudinal chromatic aberration is the separation of focal positions for different wavelengths along the optical axis. It produces color-dependent focus shifts in front of or behind the image plane.
Geometric optics: Geometric optics models light as rays, describing image formation through reflection and refraction. Ray diagrams show how separate wavelengths form displaced focal points.
Coma (optics): Coma is an off-axis optical aberration that makes point sources appear comet-shaped. Its asymmetric blur can resemble colored edge defects but has a different optical cause.
Apochromat: An apochromat is an optical system corrected to bring three wavelengths to a common focus with reduced secondary spectrum. It extends chromatic correction beyond the two-color correction of an achromat.
Lateral chromatic aberration: Lateral chromatic aberration is wavelength-dependent image magnification that displaces colors sideways, especially away from the optical axis. It creates colored edge fringes even when colors share a focal plane.
Focal length: Focal length is the distance from a lens’s principal plane to the focus of parallel incoming rays. A wavelength-dependent focal length produces longitudinal color blur.

Linked from 14 pages