adj. denoting radiation, especially light, of the same frequency or wavelength.
n. (in optics) a defect in the image formed by an optical device (e.g. a lens). In chromatic aberration the image has coloured fringes as a result of the different extent to which light of different colours is refracted. In spherical aberration, the image is blurred because rays from the object come to a focus in slightly different positions: the rays passing through more peripherally are bent more than those passing through centrally. This occurs even with monochromatic light.... aberration
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