Question

What is the magnification of an astronomical telescope whose objective lens has a focal length of 71 cm and whose eyepiece has a focal length of 2.1 cm?

Answer 1

To solve this problem it is necessary to apply the concepts related to optical magnification (is the process of enlarging the apparent size, not physical size, of something.). Specifically the angular magnification of an optical telescope is given by

$M = -\frac{f_o}{f_e}$

Where,

$f_o =$ Focal length of the objective lens in a refractor

$f_e =$ Focal length of the eyepiece

Our values are given as

$f_o =$ 71cm

$f_e =$  2.1cm

Replacing we have

$M = -\frac{f_o}{f_e}$

$M = -\frac{71}{2.1}$

$M = - 33.81$

Therefore the magnification of this astronomical telescope is -33.81