Chapter 25, Problem 11Q

To determine

Which surface to face the object when a Plano convex lens is used to form image of an object at infinity. Show using ray diagrams.

Answer to Problem 11Q

Solution:

The curved surface should face the object.

Explanation of Solution

Given:

It is given that in a thin lens spherical aberration is minimized when rays bend equally at the two surfaces.

The curved surface should face the object.

When the flat surface of the lens faces the object and the rays areparallel to the optical axis, there will be no bending occurring at the first surface and as the ray moves to the second (curved)all the bending will occur at this surface. Hence bending will not be equal on the two surfaces in this case of flat surface facing the object and ray parallel. The bending at the two surfaces may be equal (or at least less different)if the curved surface faces the object. See the figure below

Figure 1

When the parallel rays from the distant object come above or below the optical axis with the flat surface facing the object, then the first bending is actually away from the axis. In this case also, bending at both the surfaces can be equal (or at least less different)when the curved surface face the object. As shown in the figure below.

Figure 2