Question

11. A real image of a distant object is formed by a planoconvex lens on its principal axis. Spherical aberration

• A. is absent
• B. is smaller if the curved surface of the lens faces the object
• C. is smaller if the plane surface of the lens faces the object
• D. is the same whichever side of the lens faces the object

Answer 1

Answer: (B)

is smaller if the curved surface of the lens faces the object

Answer 2

In general spherical aberration is minimum when the total
deviation produced by the system is equally divided on all
refracting surfaces. A planoconvex lens is used for this
purpose. In order that the total deviation be equally divided
on two surfaces, it is essential that more parallel beam (or the
incident and refracted) be incident on the convex side. Thus,
when the object is far away from the lens, incident rays will
be more parallel than the refracted rays, therefore, the object
should face the convex side,but if the object is near the lens,
the object should face the plane side. This has been shown in
figure.