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 Which of the following statements are correct regarding spherical aberration :

1. It can be completely eliminated    
2. If can’t be completely eliminated but it can’t be minimised by allowing either paraxial or marginal rays to hit the mirror    
3. It is reduced by taking large aperture mirrors    
4. none of the above