Question

The length of an astronomical telescope for normal vision is _______.

• A. $-\frac{f_o}{f_e}$
• B. $-f_o\times f_e$
• C. $\frac{f_e}{f_o}$
• D. $f_o+f_e$

Answer 1

The correct option is D $f_o+f_e$

To get a magnified image of an object at infinity the image formed by objective lens will beat focus and if we want maximum magnification then the image formed by objective should be at focus of the eye piece.

Hence length of telescope =$f_o+f_e$.

Here $f_o$ and $f_e$ are focal length of objective and eyepiece lens respectively.