A disadvantage of the astronomical telescope for terrestrial use (for example, at a football game) is that the image is inverted. A Galilean telescope uses a converging lens as its objective, but a diverging lens as its eyepiece. The image formed by the objective is behind the eyepiece at its focal point so that the final image is virtual, erect, and at infinity.

(a) Show that the magnifying power is M = –fo/fe, where fo is the focal length of the objective and fe is that of the eyepiece (which is negative).

(b) Draw a ray diagram to show that the final image is indeed virtual, erect, and at infinity.