Focal length: A refracting telescope has a main lens, or objective lens, and a second lens, the eyepiece (see Figure 3.55). For a given magnification M of the telescope, the focal length Fo of the...

Focal length: A refracting telescope has a main lens, or objective lens, and a second lens, the eyepiece (see Figure 3.55). For a given magnification M of the telescope, the focal length Fo of the objective lens is a linear function of the focal length Fe of the eyepiece. For example, a telescope with magnification M = 80 times can be constructed using various combinations of lenses. The following table gives some samples of focal lengths for telescopes with magnification M = 80. Here focal lengths are in centimeters.

stant of proportionality is M. Use this relation to write a formula for Fo in terms of Fe and M.

c. Solve the equation you obtained in part c for M and thus obtain a formula for magnification as a function of objective lens focal length and eyepiece focal length.

d. To achieve a large magnification, how should objective and eyepiece lenses be selected?