What you need:
-Camera (capable of continuous 30-second exposures)
-Remote for the camera (one with a locking button)
-Flashlight (or any light source really...)
Check out my star trail kit on the right
The first time you do it, I'm assuming you are gonna go to where you "think" is dark and shoot. You may get some stars, but if you're like me, you don't see much stars in the suburbs and there is a lot of light pollution. So the next step is going to some place with some woods and your subject will be some tree tops and more stars. That's cool, I did that too, and the shots come out pretty fun, but simple. So now that I told you all this, change up your subject and skip all the simple steps. Shoot some star trails over a campsite, or your new car like I did in the shots below. Choosing your subject and when you want to shoot will be the hardest work when shooting star trails. If you don't want to light paint or have a black background, you need to shoot on a full moon. The moon will act as the night's sun and light your subject. That's how I lit the background for the shoot below, although the car does have some light painting on it.
Set up your camera on the tripod and compose your shot. This is where the flashlight comes in handy. I use live view and the flashlight on my subject to set my focus. Once you are focused and composed (that makes it almost sound very Zen like... haha) plug the remote in and start testing exposures.
I have a rough idea of what my exposure needs to be, and I start with 30" @ f/4 with ISO 800. I chimp a bit and settle on an exposure. Once the exposure is set, lock the remote so that you are continuously shooting 30-second exposures. Now, we play the waiting game. You can wait for as long as you want, but I usually try to keep my star trails to at least a 15 minute minimum. Otherwise the stars don't show enough movement and look rather "interesting" if I say so. One thing you can do while you wait is some light painting. If you want, you can separate the two tasks if you don't want to risk ruining/not getting the shot since you can't review the shots as the camera runs.
Now you've got somewhere between 30 and a few hundred photos of pretty much the same thing. What do you do?!
Well I have an action to do this next task, but you can do it by hand or search the internet to find an action to do it.
If you shot in RAW like I do, now is when you want to do your conversion to the images and apply the same settings to all images.
First step in the post process is to load all your files into Photoshop layers. There is an option for this in Adobe Bridge under tools>Photoshop.Once all the photos are loaded, go through and change the blending modes to lighten. Do this for all but the last layer, starting from the top down. If you start from the top layer, as you go through you will see the trails build layer by layer. Once you have changed all the layers' blending modes, you will end up with the rough image of star trails.
Now you can go through and fine tune the photo like you would with any normal photo.
And that's it. In the end, its a really simple thing to do, its just so time consuming! Leave a comment below if you have any questions, or share the post with anyone you think might like to know how to shoot some star trails! Thanks and I hope you enjoyed my write up!