Experienced planetary observers use 20x to 30x per inch of aperture to see the most planetary detail. Double-star observers go higher, up to 50x per inch (which corresponds to a ½-mm exit pupil). Beyond this, telescope magnification power and eye limitations degrade the view.
What magnification do I need to see the rings of Saturn?
25x
What magnification is best for telescope?
50 times
What magnification do you need to see galaxies?
In practice, the optimum magnification for most objects is somewhere between about 8× and 40× per inch of aperture — toward the low end for most deep-sky objects (star clusters, nebulae, and galaxies) and the high end for the Moon and planets.