Chapter 30, Problem 16A

To determine

To distinguish: Spherical and chromatic aberration and remedy for each.

Explanation of Solution

Introduction:

A lens cannot perfectly form the image of an object. It happens due to a property of lenses which is called aberration and it makes the image blur and distorted.

Aberration is a property of lenses which cause the light to scatter in different regions and prevents it to be focussed at a specific point. Aberrations in lenses are of two types: spherical aberration and chromatic aberration.

Spherical aberration arises when light passes through the edges of a lens is not bought to focus at the centre but at a different place from the centre. It means all the parallel rays incident on the lens do not converge at the same point of the lens after refraction. Spherical aberration can also be caused by the quality of the lens in addition to its design. It can be remedied by covering the edges of a lens which can block out the rays which blur the image.

Chromatic aberration arises when different colours in a light are not focussed by the lens at a single point. This happens because of different speeds of different colours of light as they travel with different speed inside the glass as well as in other mediums too which makes them to converge at different points. It can be corrected by combining lenses made up of different kinds of glass to make it achromatic.

Conclusion:

Hence, spherical aberration is that defect in which a lens cannot focus the image at a single point after refraction and chromatic aberration is the defect in which all colours of light cannot be focussed at a single point after refraction from the lens..