If fp and fm represent the focal length of paraxial and marginal rays, respectively, then the correct relationship is:

Question

Spherical aberration in spherical mirrors is a defect that is due to the dependence of focal length ‘f’ on the angle of incidence 'θ' as shown in the figure is given by

where R is radius of curvature of mirror and q is the angle of incidence. The rays that are close to the principal axis are called marginal rays. As a result, different rays focus at different points and the image of a point object is not a point.

If f_p and f_m represent the focal length of paraxial and marginal rays, respectively, then the correct relationship is:

Answer 1

The correct option is (B).

Explanation:

Paraxial rays are focused at the geometrical focus F of the mirror. The marginal rays are focused at a point F’ somewhat closer to the mirror.