How to Capture Star Trails
Before you dig too far here, if you haven't read my first post sharing my tips on how to get started on shooting the stars, head over there if you'd like some quick, general information about night sky shooting.
You may have seen some of my images of the night sky where the stars look like huge circles or streaks across the frame. I'm going to show you two methods for achieving this effect and weigh in on what the pros and cons are of attempting one method over the other.
Mackinac Bridge, Michigan: One 4-hour exposure
1. Camera - You'll need a camera that has the capability to do long exposures. Ideally, you'll want one that can open the shutter for 30 seconds, and, for one of these methods, you'll need one with "bulb" mode. If you're buying a camera with the intention of trying this out, most DSLRs can do this without issue. Some compact (point and shoot) cameras either lack long exposure features altogether or only allow for lengths like 15 seconds or shorter, and we need all we can get.
2. Tripod - You could get away with setting your camera on a flat surface, but for the lengths of time we'll need, you're going to want a tripod that allows you to be able to easily interact with your camera without messing up your composition.
3. Extra Batteries or an AC Adapter - For Method 1, you're really going to need a lot of juice to do this, depending on the length of time you want to work with, which usually is also dependent on your focal length of your lens. Try to score at least 3 batteries; one in the camera, one ready, and one on the charger as you swap out. If you want, you can order an AC adapter specific to your camera model and just find an outlet near your shooting location.
4. Intervalometer - This will make sure your camera takes a series of pictures on its own while you wait, or can hold your shutter open for long periods of time. Some cameras, like my D5300, have an internal function for this.
Method 1 - One Long Exposure
To start off easy, this is the method that requires the least effort. All you need to worry about is finding your composition and finding a way to keep your camera powered on during the entire exposure. Regular batteries won't expose long enough for most one-shot star trails, so what you'll need is a way to power your camera alternatively. An AC adapter is what I used for the image I took above. This was taken from the parking lot of the northern viewing point of the Headlands International Dark Sky Park in northern Michigan, and so, because my car was very close to me, all I had to do was use my AC adapter and power it with my car's cigarette lighter converted as an outlet and that gave me all night to expose that image for 4 hours straight without cutting the power and taking multiple shots.
Now, as far as shooting goes, you'll notice that you don't get many chances. You'll need to set your camera to Bulb Mode for anything over your camera's shutter duration limitation (usually 30 seconds) and you'll need that intervalometer or any cheap remote shutter that can hold your shutter open for as long as you need. If you intend to do 30 minutes, an hour, or more, you'll quickly realize that you've got to get the settings right, but it probably won't be perfect. Make sure you shoot in RAW so that you have the best ability to post process and correct for any exposure errors that your file will allow for and that you need. I really needed to do a number on the image above because I over exposed it quite a lot (the bridge put out a light more light than I anticipated). If you aren't shooting toward any light pollution, you shouldn't need to worry as much about overexposing. With that in mind, you can afford to scoot your aperture up a bit if you plan on including some landscape elements in your composition, and, with that, you can shoot your ISO down as well. For the shot above, I set my camera to f/22, ISO 100 and let it expose for 4 hours. It ended up being too much, but I was able to save it nicely in post. You'll need to experiment with different settings depending on your specific scenario, but the benefit to doing star trails this way can result in very clean, near-noiseless images.
- Less post production (no stacking/major file handling/extra programs)
- Less noise (ISO is reduced to balance out exposure)
- Aperture increased means more visual elements are in focus
- Greater chance for "Hot Pixels" (can be managed in post, but I've never had much of an issue)
- Typically requires alternative power solution
- Getting correct exposure requires time and experimenting
Method 2 - Stacking
Stacking is my preferred method because there are more things I can do with a series of hundreds of images than just make one long exposure, but I won't go into that now. Stacking is a great way to do star trails because it gives you much more precision when it comes to making sure your exposure will be correct and that you just generally have more control and have a greater idea for how the image should turn out. Contrary to one long exposure, you do not need an alternative power supply for your camera, but I do recommend having at least 3 batteries so that when your camera dies, you always have one ready and on you to swap it out quickly. If you wait too long to swap your batteries out and your camera sits without taking an image for too long, you will have a gap between your resulting star trails where you have no visual data for when your camera was not operating. Having a ready battery while you're near the camera and can act quickly is what I consider to be a much safer way to make sure you won't have gaps in your trails. Just remember to run in and start charging that battery as you may need it if you end up using all your batteries throughout the ordeal.
Stacked series of 350 images and tree painted on the last frame with 500lm flashlight
Now, the nice thing is that, for star trails, your camera settings do not differ from taking a normal still image of the stars. You can even extend your shutter speed out longer than normal to bring down your ISO because once they are all stacked, it won't have mattered if you captured tiny little stars or if they were streaking slightly. So, once you've got your composition down, your settings right, and your focus perfect, now is where you need that intervalometer to get a series of pictures. If your camera has this function internally, great, use that if you like, but if not, you can purchase a cheap intervalometer online for about $25-$35USD. With your intervalometer plugged into your camera, your can have it command your camera to take a series of images at a specific interval and even control the exposure duration from it as well. This comes in handy especially when you want to expose beyond 30 seconds because you can input any number of seconds you like up to many hours. But, for this, just set it to take a normal image of the stars, but doing so many times.
This is where the focal length of your lens comes into play. If you have a wide angle lens, you'll need take many more images because the stars are traveling shorter distances across your frame in the same time than it would on longer lenses. So, for example, I might only need to take 100 images on my 85mm lens as compared to maybe 500 images on my 11-16mm lens.
Okay, so, once you've got that settled, and you've taken your images, it's time to start stacking.
I use a free program called StarStax to handle my stacking, but first, I always do some quick editing in Adobe Lightroom. This is where I correct my exposure a bit, boost contrast, maybe do some noise reduction and final cropping. Then I highlight all my imported images and sync the settings so they'll all look the same for StarStax to easily and correctly stack the images. Once that's done go ahead and export them from Lightroom.
When you've got StarStax open, all you need to do is click on the left-most icon at the top to load your images. Select all your newly exported images and load them into StarStax. You're almost done - once you've got that, go over to where it shows "Blending Mode" and make sure it's on "Lighten". Comet Mode is fun to play with too as it adds a bit of style to your star trails, but you may choose to leave it off. After that, go up to Edit and click "Start Processing", or the keyboard shortcut "Command/Control - P" or the icon to the right in the first set of icons on the top left.
This process may take a while depending on how many images you've got loaded in, but once it goes through them all, you'll get a final stacked image where you can then go to File and "Save as" and save your final image out.
- Finer control of results
- No need for alternate power source
- Multiple uses for series of images (timelpase, noise reduction, etc...)
- More noise
- May require more batteries than you have
- Many files = lots of storage space needed
- Post process takes longer
Additional Things To Consider
When shooting star trails, know that the earth rotates so that the north star essentially does not move, so, if you aim at the north star, you could really see a difference in your results, and on the contrary, the stars furthest from the north star travel across your composition faster than those toward the north star in the same time frame resulting in a coned shape.
And That's it!
As always, thanks for reading and look for me on Twitter and Instagram @_DavidSargent and find me on Facebook at David Sargent Photography to stay up on all my photography related adventures as they happen.