The formula of magnification power and resolving power of a telescope is, $M.P. = \frac{f_0}{f_e} \& R.P.=\frac{a}{ 1.22 \lambda }$. A large aperture(a) of the objective lens provides better resolution so, the good quality of the image is formed, and also it gathers more light. The larger the objective, the lighter the telescope collects and increases the brightness of the image and large focal length enhances the magnifying power of the telescope.