Just one additional comment about "setting the focus to infinity" is that whether you can do this depends on what type of camera you have. Newer DSLRs that use phase focussing employ lenses that allow focussing to go beyong infinity, so setting the focus all the way to that end will be disappointing. The older film lenses often stopped exactly at infinity which made that setting a bit easier. You will also encounter this problem shooting at a star field. Trying to guess at just where infinity really is, in the dark, is frustrating. Usually there is not enough light to achieve auto focus.

My solution, for stars, is to use a zoom lens (like 18-70 mm) and aim at a planet at full zoom. There will be enough light to achieve auto focus on Jupiter or Venus. Then turn to manual focus and be careful not to touch the focus ring. Set back to wide angle or whatever you want and start shooting. Don't focus on the Moon if you want to get stars in focus, it won't work.

Even easier for fireworks, grab your focus from the first burst, then switch to manual focus to prevent hunting.

Wayne