# Chromatic Aberration in a Lens

﻿ Chromatic Aberration in a Lens

In the study of lens, we always consider that the image obtained is perfect size, contour and color. However, in reality it is not so because when considering rays in reality we need to consider both paraxial as well as marginal rays owing to which a image can never be perfect. This difference between an image formed by a lens and the object in terms of shape, size, color etc. is known as aberration. Now aberration is of two types-monochromatic aberration and chromatic aberration. To understand the latter we need to concentrate on a prism first. A prism splits white light into its seven constituent colors. While violet light suffers maximum deviation and deviates towards the base of the prism while red color suffers the minimum deviation. The refracting angle of a prism is greatest at its center and reduces towards the sides. When white light is incident on the prism, each light is deviated at a different angle and thus they focus at different points on the principal axis. This results in the formation of a blurred and colored image. This defect in image formation is termed as chromatic aberration. Now, a lens is considered to be made up of a number of prisms and hence this prismatic phenomenon of chromatic aberration when shown by the lens is known as chromatic aberration in a lens.
Consider a convex lens on which a beam of white light is incident. Dispersion takes place and the white light is split up into its constituent colors and each of the colors is focused at different positions on the axis. This gives a blurry image. A concave lens also shows a similar phenomenon and forms an unclear image. Chromatic aberration in a lens is again of two types-longitudinal and lateral. Longitudinal aberration is the difference between the focal lengths of violet and red color. Lateral chromatic aberration is the difference in the magnification of the image formed by the red and violet light rays.
WORKS CITED
Banerjee, Vivekanandan. Physics: Ray Optics. New Delhi:S. Chand. 2007.
Welford. W.T. Aberrations of Optical Systems. Bristol: Adam Hilger, 1986.