Explanation

A simple astronomical (Keplerian) telescope uses two convergent (convex) lenses: a large-aperture, long-focal-length objective that collects light and forms a real inverted image, and a short-focal-length eyepiece that magnifies that image. The combination with a divergent eyepiece belongs to Galileo's terrestrial telescope, not the astronomical telescope. The magnifying power of such a telescope equals the ratio of the focal lengths of the objective and the eyepiece.