Will an image be clearer through a telescope if the lenses have a shorter or longer focal length?

My sis needs it for a science report :)Will an image be clearer through a telescope if the lenses have a shorter or longer focal length?
For a given lens diameter (aperture), less precision is needed in grinding the lens if the focal length is longer. Therefor, it is more expensive to get the same clarity with a shorter focal length. If you pay the same money for two lenses, the one with the longer focal length probably makes a sharper image. However, the cost of the whole telescope may be more because it needs a longer tube.





You get more magnification by having an objective lens with a long focal length and an ocular lens with a short focal length.





Most astronomical telescopes use a mirror instead of an objective lens because mirrors don't have as many kinds of aberrations as lenses do.