posted by Rudi .
A simple camera telephoto lens consists of two lenses. The objective lens has a focal length f1 = +41.7 cm. Precisely 36.1 cm behind this lens is a concave lens with a focal length f2 = -13.9 cm. The object to be photographed is 4.06 m in front of the objective lens. How far behind the concave lens should the film be placed?