SHOOTING TECHNIQUESThe quickest method for immediate star images is using the high-ISO method. With this technique, your end goal is to freeze the stars in place and capture the Milky Way. Start with these settings: ISO 3200, ƒ/4 at 25 seconds. This should let in enough light that you'll get some spectacular results very fast. Remember to check your focus.
If you're using a wide-angle lens like a 20mm or wider, the stars shouldn't show movement during this exposure. Use the "500 rule" to make sure the stars are frozen—500 divided by the focal length of your lens equals the longest exposure you can have before the stars will show movement. For example, if I'm using a 20mm lens, 500 divided by 20 is 25; I can set an exposure of 25 seconds and not have star movement. The Milky Way is one of my favorite subjects for this technique. On a dark night with clear skies, the Milky Way will appear as a hazy white line running across the sky. If you can't find the Milky Way, try using a smartphone app like Star Chart or Google Sky Map.
After you've photographed the Milky Way and stars without movement in the night sky, how about trying star trails? Star-trail photography involves leaving your exposure open for an hour or longer to capture star movement through the night sky. The camera settings are similar except your exposure needs to be set at "Bulb" and your ISO will be lower. Also, use a cable release with a locking mechanism so you can lock the shutter open for as long as you need.
To really capture star rotation, try these settings: ISO 100, ƒ/2.8 for 1 hour using a wide-angle lens like a 20mm. Remember, the wider the lens, the more night sky and star trails you can capture. Don't worry if a plane flies through your shot or meteors fall from the sky; these items will add interesting streaks in the final shot. It's very important to have your long-exposure noise reduction on for this shot. Your results will look a lot less noisy using in-camera noise reduction.
Another star-trail technique is stacking a series of short exposures to create one star-trail shot. The advantage here is, you're using shorter exposures with less noise to create the final image, but this will require more postprocessing to get the final shot. StarStaX software can help you stack images together. A sample exposure here might be ISO 3200, ƒ/4 at 25 seconds for numerous frames. One important point: Make sure your noise reduction is off or the processing time might exceed the interval time you want to use between shots.