Chromatic aberration

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Spherical aberration 3.png Spherical aberration
Lens coma.png Coma
Astigmatism.svg Astigmatism
Field curvature.svg Petzval field curvature
Lens6a.svg Chromatic aberration

In optics, chromatic aberration (CA, also called achromatism or chromatic distortion) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength.

Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point. Since the focal length f of a lens is dependent on the refractive index n, different wavelengths of light will be focused on different positions.

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Types of chromatic aberration

Chromatic aberration can be both axial (longitudinal), in that different wavelengths are focused at a different distance from the lens, different points on the optical axis (focus shift); and transverse (lateral), in that different wavelengths are focused at different positions in the focal plane (because the magnification of the lens also varies with wavelength; indicated in graphs as (change in) focus length). The acronym LCA is used, but ambiguous, and may refer to either longitudinal or lateral CA; for clarity, this article uses "axial" (shift in the direction of the optical axis) and "transverse" (shift perpendicular to the optical axis, in the plane of the sensor or film).

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