how do we discuss chromatic abberation?

Chinmaya Lal Thakur, 13 years ago

Grade:12

1 Answers

suryakanth AskiitiansExpert-IITB

105 Points

13 years ago

Dear Chinmaya,

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.

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).

These two types have different characteristics, and may occur together. Axial CA occurs throughout the image, and is reduced by stopping down (this increases depth of field, so though the different wavelength focus at different distances, they are still in acceptable focus). Transverse CA does not occur in the center, and increases towards the edge, but is not affected by stopping down.

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