Chapter 25, Problem 14Q

To determine

The aberrations in a simple lens but notin human eye. Why?

Answer to Problem 14Q

Solution:

Spherical aberrations are reduced in human eye while chromatic aberrations are not present.

Explanation of Solution

Spherical aberrations can be present in a simple lens but is reduced in human eye.

To correct this spherical aberration in simple lens combination of many lenses together is used to minimize the bending at each of the surfaces.The eye minimizes the spherical aberration by light bending while it light passes through different parts of the eye such as cornea, aqueous humor, lens, vitreous humor, etc. (each has different refraction index).

The edge of cornea is less curved, and eye lens is less dense at the edge. These two characteristics helps in reduction of spherical aberrationsin the eye since the rays are less bend at the outer edges. Curvature of field happens with non-flat focal plane, the curved retina of our eye helps to fix this distortion. Distortion is due to the difference in magnification at various distances from the optical axis (most common in wide-angle lenses), which is compensated in human eye with the small lens and curved retina.

In case of human eye chromatic aberrations are not present, since the shorter wavelengths are absorbed by the lens. Most of chromatic aberrations occur in the violet and blue wavelength, retina are insensitive to these wavelengths.