4. Consider a concave spherical mirror with radius of curvature R=20 cm and diameter D=10 cm, immersed in water (n=1.33).
(a) Find the focal length of the mirror and the position of the paraxial image point P′ when the object point P is placed at the center of curvature of the mirror.
(b) Evaluate the optical path length for the path PAP', where point A is on the mirror at a distance rho from the axis. Compute the aberration function I(rho) and the maximum transverse aberration in the paraxial image plane.
(c) Compare this image to the corresponding image for a similar parabolic mirror.