How much magnification can I use with my telescope?

 Everyones telescope is different, but a rough rule of thumb is around 30-50X per inch diameter of the main lens/mirror. A good ED refractor may, however, use 100X/inch on bright objects, so this is not a hard rule. You can always increase the power above these limits, but it is pointless if you’re not seeing more. This rule breaks down for larger instruments, as the distortion of the atmosphere limits practical magnification to 300X.