I was going to just write a comment response to Rooo sez, but making an actual post seemed like a better idea. Also, this is an “Idiot’s Guide...” because it’s written by one. If I can take this picture, so can you.
Star trail pictures are fun and not hard to do. The whole process is time-consuming but not difficult.
First, find somewhere to take the picture. It doesn’t have to be the darkest area around, just somewhere with a lot of visible sky and something to use as a foreground to anchor the shot.
Try to shoot with the worst light pollution behind you. If you are on the north side of Atlanta, shooting to the south is pointless. But shooting to the north works a lot better. Even if you can’t really get out of the light pollution, shooting away from it is the way to go.
In most cases, you the widest lens you can and open the aperture up all the way. Make sure you have something to set your focus to infinity on. If you are somewhere with ambient light, this isn’t a problem.
If you are out in the middle of nowhere in the dark, your camera isn’t going to find anything to lock the focus on. You probably won’t have anything to around to get a good manual focus either. If this is the case, go out during the day, set the aperture and set the focus to infinity, tape the focus ring in place, and flip the lens from auto to manual. Painter’s tape works well as it comes off without leaving sticky gunk behind. Now just be extra careful not to accidentally move the focus ring when handling your camera. The tape isn’t perfect. And double check everything after you’ve taped it, just to be sure.
As far as setting go, you’ll probably want to use a 30-second exposure. 30-seconds is usually good as you don’t want to wash out the scene. And 30-seconds is where you also start to really notice the trails in a single shot rather than the stars being fine points.
ISO is going to depend on where you are and your camera. The darker the spot, the lower ISO you can use, but don’t go too low. The shots from the header pic were taken at ISO 1250. I probably could have gone a little higher as noise isn’t as much of an issue with the final result. A little trial and error when you start shooting will get you in the right ISO setting.
Now that you are all set and ready to shoot, you just need to do one more thing: setting the camera to keep shooting. You can use a shutter release cable and lock it into place. The issue with this is that on some cameras, it will stop shooting after 100 continuous frames. 100 might be enough for what you are doing, but it also might not.
Your camera probably has an intervolemeter which will allow you to take as many shots as you’ll have battery power for. It might called “interval shooting” in your camera’s menu. For reasons I can not explain, there is a weird issue with Nikons (not sure about Canons). You’ll need to set the exposure for 32-seconds (30-seconds on the normal shutter speed settings is really 32-seconds because math or something) with an interval of one second between shots. Google how to do this for your exact camera if you don’t already know how. Then set the number of frames to whatever you need. I did 200 for the example.
Now, get out the wild, set up on a tripod or something solid, and let the camera go to work for a few hours. Take a nap, play Flappy Wings, look for meteors, or just gaze with wonder at the stars.
When you get home and look at your pics, they will look something like this.
I really should have gone up a bit in ISO. But whatever...
So you have a ton of RAW images, but what to do first. I dump them all into Lightroom and do little adjustments to all of them at once: lens correction, chromatic aberration, maybe white balance, and maybe a pinch of noise reduction.
Now the fun part, getting rid of airplane trails!
Blah. Find each frame with an airplane trail and methodically use the healing brush to get rid of them. Sometimes, you have to do little bits of a long trail at a time, rather than the whole thing at once. Try to leave bright stars in, too. It’s hateful work. Do your best.
Now save all the files as TIFs. While a few hundred pics are saving, go eat dinner or something, it’s gonna be a while.
Now you are ready to start making trails. Get a program such as StarStax or Sequator (both are free and very good). You could do this in Photoshop, but it takes for-fucking-ever to stack 200 pictures into a smart object. StarStax and Sequator give you the same high-quality result in minutes. There are other programs out there that do this as well, but those two are really good and simple to use.
Using whatever program, follow the instructions and it’ll stack all your pics into something that looks like this. I hadn’t gotten rid of all the airplane trails here (blah).
The stacking gets rid of a lot of the noise you might get from a high ISO, which is great!
Now take the stacked image back to Photoshop or Lightroom or whatever you use and start editing until you are happy. When I finished this one, I wasn’t supper happy with it. It was too bland. Normally, stacking the unedited files as discussed above is the best way to go. But sometimes editing a little before stacking might be the way to go. Remember to edit all of the pics the same by syncing or copying settings if you do this. After messing around a bit, I got them all looking a bit more vibrant before stacking.
After screwing around with trying different setting during the stacking process and doing god-knows-what to the stacked image in Photoshop, I eventually ended up with the header pic.
That should get you started. Play around with different camera settings and even lenses. Shooting at 75mm will get you something very different than 16mm; You’ll get longer trails in each shot because math, so you might not have to sit out in the middle of nowhere for as long.
This rocket launch with star trails was shot with my 50mm (which is really 75mm on my cropped sensor) in the middle of St. Petersburg and all its light pollution.
Again, anyone can do this because this idiot did. Post any questions and I’ll gladly answer them.
Now get out there and shoot!