The resolving power of a telescope depends on

Explanation

Rayleigh's criterion for minimum resolution : Two over-lapping diffraction patterns due to two point sources are acceptably (or just) resolved if the centre of the central peak of one diffraction pattern is as far as the first minimum of the other pattern.

The sharpness of the central maximum of a diffraction pattern is measured by the angular separation between the centre of the peak and the first minimum. It gives the minimum resolvable angular separation or the angular limit of resolution.
Two overlapping diffraction patterns due to two point sources are not resolved if the angular separation between the central peaks is less than the minimum resolvable angular separation. They are said to be just separate, at resolved, if the angular separation between the central peaks is equal to the minimum resolvable angular separation. They are said to be well resolved if the angular separation between the central peaks is more than the minimum resolvable angular separation as shown in the figure.