Question

Why eyepiece of a telescope is of short focal length while objective is of large focal length ?

Answer 1

Focal length of objective $=f_0$
Focal length of eyepiece$=f_e$
Magnification $=\frac{f_0}{f_e}$.
When the focal length of eyepiece decreases the magnification increases. We get a bigger and clearer image of the object viewed.