# Why we take objective of short focal length and eye piece of long focal length in a compound microscope?

I think compound microscope will also work if focal length of eyepiece is kept smaller than that of objective lens. I am just a beginner in physical optics. I understand ray diagram of compound microscope. Kindly explain in an easy way.

Theoretically speaking, there is no problem at all which of the focal lengths is greater as the formula for magnification is given by:- $$M = \frac{D}{f_e-1}\left[\frac{v}{f_O}-1\right]$$ Therefore whether $f_O > f_e$ or $f_O < f_e$, you can still acheive magnification.