A telephoto lens consists of two thin lenses, the front converging lens and the rear diverging lens with optical powers Ф1 = + 10 D and Ф2 = – 10 D. Find:
(a) The focal length and the positions of principal axes of that system if the lenses are separated by a distance d = 4.0cm;
(b) The distance d between the lenses at which the ratio of a focal length f of the system to a distance l between the converging lens and the rear principal focal point is the highest. What is this ratio equal to?