Got interested in this when I managed to photograph some of the recent Perseids meteors as they flared across the skies last month, now hooked! The single biggest problem with trying to photograph the stars is that there are feint, so to do so you need a long exposure time. That's the second biggest problem as the earth is rotating about it's poles which effectively makes the stars rotate so a long exposure gives them all tails especially when you zoom in for a closer look.
Example, bright star next to Milky Way, zoomed right out at 24mm for a wide view, looks OK.........
Now zoom in to 200mm for a closer look and see what happens, all the start grow "tails" due to their movement in relationship to the earth, both pictures taken with a 30second exposure....