There are a couple of things to consider when creating a star trail image; the first is the composition. As with any great scenic photo, it needs to be esthetically pleasing. Having a foreground is usually very beautiful and having water in the scene is an extra plus – the stars can reflect off the surface of the water. The picture shouldn’t just be about the stars, but how they are a part of the scene.
Shoot with your widest lens. If you can get the North Star in your composition, it will make beautiful circles around it. A fisheye lens can give you a 180 degree perspective. Basically, the wider the field of view, the more stars you can capture.
As the Earth spins on its axis, the North Star will stay in one spot (pretty much). The other stars seem to revolve around this focal area. In case you’re not acquainted with the accurate position of the North Star, don’t worry, there are many free star tracking apps for your smart phone.
Shutter Speed: 30 seconds
Take a test shot and see what you get. If your test shot is too bright, reduce the ISO or use a smaller aperture (higher F-number). If too dark, try increasing the ISO. Always leave the shutter speed at 30 seconds. It will be a dark image (obviously), but you should be able to make out the pinpoints of the stars and some of your foreground. When you get a good looking exposure, you’re set.
Make sure your camera is set to manual focus and that the vibration reduction is off. Since your camera will not be moving, focus using the view finder or live view and leave it. Remember to have the star’s focus be priority over the foreground.
OK, so now you have your composition decided. Your shutter speed is set to 30 seconds and you have an f stop of about 3.5 or so. Now use your shutter release. On the DSLRs, they simply plug into the side and you press the button and slide it into the lock position. It’s incredibly simple. You will hear the shutter release and hold for 30 seconds. As soon as the image completes it will automatically click again for the next image. Make sure your tripod can sit undisturbed for a while. How long is up to you. I have tried it, rather unsuccessfully, for about 40 minutes and the trails appeared just not bright enough. My final image here was about 2 hours of 30 second exposures. In the end there were 207 separate images. Invest in a shutter release cable. This one from Canon was about $50. They do make much fancier ones, but for this (and most everything) this one works seamlessly.
Now that you have sat out in the dark listening to your camera click click click for a couple hours you are ready for the fun part.
The Lightroom Method:
Joining a couple hundred pictures may appear as an overwhelming task, yet it is actually pretty easy – begin by editing one picture. In Adobe Lightroom, edit your picture to your liking, usually adjusting shadows and whites, white balance, clarity, and noise reduction.
Make this one image as awesome as can be. To duplicate all of your adjustments to the other images, Right-click on the picture in Lightroom and pick “Settings > Copy Settings” verify all of your adjustments are the ones you have made.
You’ll have to paste these settings over the whole batch of pictures. To do this, select all of of the pictures you will be using, and right-click on them. Then, choose “Create Settings > Paste Settings” and your alterations will show up on the pictures.
There are a couple of ways in Lightroom to copy and paste settings. One, which can be useful when changing settings over many pictures, is to utilize the “sync” component. To do a Sync, select the picture you’ve edited. Do a “select all” by holding “command+a” on a Mac or “control+a” on PC. That will choose all the pictures in the strip. Next click the “sync” button in the lower right of the side panel. Pick all the settings you changed (as above) and click “synchronize”.
Assembling In Photoshop:
You now need to send all of the pictures over to Photoshop in a single layer. Select all images, right-click on them and pick “Edit In > Open as Layers in Photoshop” and wait. This will take a few minutes as Photoshop loads each one as separate layers.
After they have all loaded, it is incredible easy, especially of you have Photoshop Cs6 or newer. Just select the layers in the layers board, and switch the blending mode from “normal” to “lighten”. Easy Peasy! You have trails! This is done by looking at pixels of all layers and showing the brightest pixel. Where your foreground is, the scene stays still, there won’t be any change there.
CS5 or Older
If you have Cs5 or older, don’t worry you can still do this, but it will take a while. You can’t select multiple layers and change the blending mode on all of them together, you must do them individually.
After your trails have been completed, flatten all of the layers together and save. Keep on editing as you see fit, however the star trails are finished!
Stacking Without Photoshop:
If you do not use Lightroom or Photoshop, don’t worry. Perhaps the easiest way to blend the images together is by using a stacking program called Starstax. It is so easy. After you download the free program to your computer, simply drop your pictures in and it does all the enchantment for you, AND even fills in the little holes between each of the exposures. The image at the top of the page was blended using Starstax. I did then import it into Photoshop to bump up the contrast a bit.