Posted by Abby on .
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.