Spherical aberration in spherical mirrors is a defect which is due to dependence of focal length ‘f’ on angle of incidence ‘ q ’ as shown in figure is given by where R is radius of curvature of mirror and q is the angle of incidence The rays which are closed to principal axis are called paraxial rays and the rays far away from principal axis are called marginal rays As a result of above dependence different rays are brought to focus at different points and the image of a point object is on a point If f_p and f_m represent the focal length of paraxial and marginal rays respectively, then correct relationship is :

1. f_p = f_m    
2. f_p > f_m    
3. f_p < f_m    
4. none of these