Optical Instruments: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Optical Instruments. Understanding the underlying formula is key to arriving at the correct answer below:

Magnification $m = \frac{f_o}{f_e}$. The objective acts as an object for the eyepiece at distance $u = -(f_o + f_e)$. Using lens formula $\frac{1}{v} - \frac{1}{u} = \frac{1}{f_e}$, we get $v = \frac{f_e(f_o+f_e)}{f_o}$. Magnification of this image is $\frac{I}{L} = \left|\frac{v}{u}\right| = \frac{f_e}{f_o}$, so the telescope magnification is $\frac{L}{I}$.