Question

Two converging lenses with focal lengths 5 cm and 30 cm are placed 35 cm apart. Rays from a very distant object are impinged on the lens system parallel to the principal axis. What is the refractive power of the combination of these two lenses?
What you have is a confocal telescope. The focal point of both lenses is a common point between them. For such an optical system, the magnification is the ratio of the focal lengths, or in this case 6. Not very powerful.

It is not called "refractive power" in any optics textbook I have ever seen, but fashions change.

Related Questions

Two converging lenses with the focal lengths of 40 cm and 20 cm are 10 cm apart. a 2.0-cm-tall obje... Two plus lenses have focal lengths in the ratio 3:1. When placed together in close contact the focal... Two converging lenses are separated by 50 cm, and have focal lengths of f1 = 20 cm and f2 = 10 cm,...