Chapter 18, Problem 59A

To determine

To explain: The reason for using achromatic lens in precision optical instruments.

Explanation of Solution

Introduction:

The focal length of a lens is governed by the refractive index of the material from which the lens is made up of. For the increase of wavelength, most of the material shows decrease in its refractive index. Hence there will be variation in the refractive index of the lens with the wavelength of light. Because of this variation in refractive index, it is not possible for a lens to focus light rays of all the wavelengths to a common focal point. This leads to a deception in an image of the object seen through a lens and is called chromatic aberration.

If a lens is used in an optical instruments, there will be distortion in the image produced due to the chromatic aberration. In order to minimize this chromatic aberration, achromatic lens is used in high precision optical instruments. Achromatic lens is the combination of lenses that made from different materials.