posted by Danny .
Telephoto lenses allow one to "zoom in" on distant objects, making them bigger. A particular telephoto lens consists of a combination of two thin lenses having focal lengths of f1=20 cm and f2=−8 cm, respectively. The lenses are separated by a distance of d=15 cm. Determine the image size in cm on the film plane, located at the back focal point of the lens system, of a distant object subtending an angle of α=2∘ at the camera.