The aperture and focal length of the objective of telescope are large, why?

The aperture and focal length of objective of microscope are small, why ?

The aperture of the objective lens of a telescope is made large so as to

The aperture of the objective lens of a telescope is made large so as to

The aperture of objective lens of a telescope is made large so as to

why should objective of a telescope have larger focal length ?

The focal length of the objective lens of a telescope is 50 cm If the magnification of the telescope is 25, then the focal length of the eye-piece is