How To Photograph Star Trails
With a Digital SLR Camera
This tutorial will cover all aspects of photographing star trails, from planning, setup, and composition, to determining exposure values, and finally to post-processing.
Thanks for taking the time to check out this page. I'm naming this article "How to Photograph Star Trails", but more accurately it should be called "How I Photograph Star Trails.” I’m sure there are plenty of people who do things differently than me. If you have any feedback, suggestions, questions, or comments about anything on this page, please feel free to contact me, or leave a comment at the bottom of the page. I encourage discussion of the topic. This will be a live working document and I'll update it as I continue to learn new and/or better ways to perfect my system. Please feel free to share and/or link to this document if you'd like.
The idea of photographing star trails first piqued my interest a few years ago when we moved to our new home in Ponte Vedra, outside the Jacksonville city lines, and far from the light of the city. I noticed when I was standing in our backyard that I could see so many more stars than when we were living in the city. Being the photographer/experimenter that I am, I thought, "Wouldn't it be awesome to see how these stars move over a long period of time in ONE photograph". I had seen some star trail shots before, but I'd never attempted one. My first few tries were disasters, but each time I added a small piece to the puzzle, until I got to the point where I was making images that I was satisfied with. Hopefully by sharing my experience here with you, it will give you a leg up and help you avoid some of the mistakes that I made.
For me I've found that the best way to photograph star trails with a digital camera is to shoot multiple exposures, and combine them later with software. That is the method I'll be explaining in this tutorial.
Before I get started, I want to point out that I am going to assume that you know the basic relationship between ISO, Shutter speed, and Aperture. I will try and explain it a bit, but it is really a whole lesson in itself. If you are unclear on this, I highly recommend the book Understanding Exposure by Bryan Peterson. For me, it has been the hands down most important item I've ever purchased for my photography.
Things you might need:
1. Something to keep your lens from fogging up if it's cold outside. I like to use those hand warmer things that you use when you are skiing. I just use some Gaffers tape to wrap them around the lens. They do a fantastic job.
2. The moon in the New Moon phase. (This is desirable, but sometimes not absolutely necessary)
3. A Battery Grip. With a battery grip you can shoot with two batteries. With two batteries you can shoot twice the amount photos before you run out of power.
1. Check the weather to be sure you are going to have a dry and clear evening. Here in Florida those nights don't come very often in the spring and summer, but all the time in the late fall and winter. I'm sure out west they happen all the time.
2. If you are shooting in your backyard, or any other property that is artifically irrigated, **make sure the sprinklers are NOT set to run** Unfortunately, I learned this lesson the hard way.
3. Determine how long you want your exposure to be. Obviously if you want longer trails you will need to extend the amount of time you make exposures of the stars. To help you out, I put together a handy photo below that shows star trail lengths over 3 different intervals. If you want to see even more, you can click on my gallery, 9 Star Trail Exposure Lengths In order to do this, you can check out the images below to help you determine how long of an exposure you will need to get the effect you desire. Since I've done most of my star trail photography in my backyard, I've been able to set the camera up and go inside to watch TV. Normally I'll just fall asleep on the couch and go pick up the camera after I wake up in the middle of the night. If you plan to employ this strategy, I want to strongly reiterate the importance of Steps 1 and 2. I would hate to get an email from someone blaming me for letting it rain on your camera! :)
4. Put your camera on your tripod, and attach your wired shutter release. Bring it to a place outside where you would like to photograph the stars. (click the photo on the left to view a higher resolution version)
Composing the Image:
Focus: The first thing to do is establish focus. Basically, point the camera at a bright star or anything that is far away but bright, and half-press the shutter until it locks focus. Once you are satisfied with the focus, carefully turn off the auto-focus feature (you will usually find this on the lens). Then you won't have to worry about focus anymore. Just be careful not to change the focus by accidentally moving the focus ring or zoom ring on your lens. Also, when you are finished shooting your star trails, don’t forget to switch the lens back to auto-focus.
Compose: Once you have set up your tripod and established your focus point, you will need to compose your image. Obviously, the stars are the main ingredient for this project, but I've found that it's always desirable to have something from Earth in the foreground of the photo to give perspective to the star trails. I've done this mostly in my backyard, so the pine trees behind our yard have been my foreground for the most part. If you are interested in capturing the "circle" around the North Star, then you will need to know how to find it. This site has a good explanation on how to find the North Star. As you can see from my photos, our backyard faces the north. I've always loved the swirl effect that results from having the north star in the frame, but, to my surprise, my most popular star trails photo has been the one facing east, with my house as the foreground. The only explanation I can think of for this is not only does it add perspective, but it also adds "life" to the photo. That may be something worth considering when composing your photograph as well.
Focal Length: The kit lens that comes with most consumer level DSLRs generally has a focal length range of around 18mm to 55mm. I've found that I prefer the wider the focal length the better. So if you are using the kit lens, first try it at 18mm, then experiment at other focal lengths if you like. I shot most of my star trails images at 18mm - UNTIL I discovered ultra wide lenses. A while back I purchased a 10-20mm lens by Sigma, and it really gave the images a whole new dimension. I love the 10mm focal length so much that I also purchased the Canon 10-22mm lens, and kept the Sigma as a backup. Since then, Canon has released a more "affordable" ultra wide with a focal length of 10-18mm. Check out the image above, I shot it at 10mm. Compare it to the image at the top of this page, which I shot from the same place at 18mm. Can you see the difference? Whenever I shoot star trails now, I use one of my ultra wides, and at 10mm. In fact, I use the Canon 10-22mm in all kinds of situations - it might just be the most used lens in my collection. The ultra wides give a look to photos that you just cannot get with a "normal" zoom, and I highly recommend picking one up.
The Moon: If the moon is in the sky, make sure it is A) not in the frame, and B) not going to move into the frame during the course of the shot! Obviously the moon adds light pollution to the sky, but as long as it's out of the frame (preferably as far from the frame as possible) you can still record the star trails successfully. Just remember that any light that is in the area (the moon, streetlights, city lights) will decrease the amount of stars that you will see in your photo, so you will want to try your best to keep it to a minimum. You can see this by comparing my backyard shots to any that I've done elsewhere, where there is more light.
Here is an example of how light pollution can affect a photo of star trails. The first photo shows one hour's worth of exposures in my backyard; the next is one hour's worth of exposures over the St. Johns river, facing toward downtown Jacksonville:
Determining your Exposure value:
Before I explain how to determine your exposure, I want to explain the basic premise of how I shoot all these images. In the "things you need" section, I wrote that you need a Wired Shutter Release with a mechanism to lock the shutter button down. Have you ever used the Sports setting on your DSLR? Or put the camera in burst mode? You hold the shutter button down and the camera just fires off photo after photo, without ever releasing the shutter button. This is precisely what you will be doing here, except on a longer, larger scale. Each shot will be a 30-second exposure.
Test Photos: It’s a good idea to take a few test shots and tweak the settings until the image you see on the LCD (the foreground as well as the stars) is exposed the way you are looking for. The first thing you will need to do is put your camera into "Manual" mode. This is normally the "M" on the dial at the top of your camera. The three settings that you will be concerned with when determining your exposure will be ISO, Shutter speed, and Aperture. As I said above, these all relate to each other. When one of these is adjusted, another one might need to be adjusted to compensate. Here is basically what you will be trying to achieve for each of these settings:
Aperture: Quick story: The first time I tried shooting star trails with my DSLR, I figured I could do it with one super long exposure. So I set up the camera and tripod in the backyard, fired off a few test shots, and found a composition where a good exposure would be 1 minute at f4 and ISO 200. Using the knowledge that I gained from the Understanding Exposure book, I calculated that I could get the same exposure by increasing it to 64 minutes, but changing to f/22 and ISO 100. I changed the settings, started the exposure with my wired shutter release, and went inside to watch TV. 64 minutes later I came back outside and stopped the exposure. When I viewed the photo on the computer, I learned two very important things:
1. The photo was very noisy and there were TONS of random colored dots all over the photo (I later learned these were called hot pixels). If you leave the shutter open too long on a digital camera, you will get more noise and hot pixels, which result from the digital sensor working overtime collecting all of the information in your photo. Remember that, unlike a film camera, your sensor is a piece of electronics that can (and will) heat up if you leave it running too long. This is why for me the best way to photograph star trails with a digital camera is to shoot multiple exposures, and combine them later on the computer. I have yet to determine what the longest acceptable exposure is, but if I ever experiment with that, I will definitely let you know. Most likely, each camera will have a different threshold, and each person will have a different opinion on what is acceptable.
2. The second issue that I noticed was that the star trails were VERY faint, almost to the point that you could not even see them. The lesson I learned here is that your aperture (aka f-stop) needs to be as close to "wide open" as possible. Which means you want your f/stop to be the lowest number possible. (f/2.8, f/4, f/5.6...). I do not recommend going any smaller than f/5.6. I'm sure the photo will be fine, but for each stop down of aperture, the less amount of stars and light intensity you are going to capture. Think of it this way: at the beginning of a 30 second exposure, a star will have an entirely different footprint in your frame than at the end of the exposure. Since it is moving so quickly, you want to be able to capture as much light as possible at each position that it is in (wider aperture = more light into the sensor at any given moment).
If you find that an aperture of f/5.6 is still causing your foreground to be overexposed, then I would suggest finding a different place to shoot from. Conversely, if your aperture is as wide open as possible, and your foreground is still underexposed, I recommend bumping up your ISO, but not too high (see "ISO" below for more details).
Shutter speed: For this method, the shutter speed needs to be exactly 30 seconds. The only reason for this is because 30 seconds is the longest shutter speed that you can set your camera to before switching to "bulb". If your camera goes higher, then you can go higher. And trust me it would be nice to do longer exposures, so you can have fewer photos to work with. I just haven't put the time into exploring other options as of yet. Again, remember that there will be a noise threshold for longer shutter speeds. Some things that might be worth exploring are intervalometers if there are any available for your camera, or tethering to a computer. I've tried intervalometers with so-so luck but haven't been able to perfect it yet. With my cameras and the intervalometers that I've used, the shortest interval between shots I'm able to get is 3 seconds, which to me is way too long, especially when facing the east or west when stars "move" the fastest. If I become more successful with this method or any other method I discover, I'll be sure to update this section.
ISO: I like to use the lowest ISO necessary to achieve the exposure I need. A general rule of thumb that I like to use is if your camera was manufactured in 2009 or after, start at ISO 200 and experiment up from there, but try to cap it at 800. If you have an older camera, start at ISO 100 and go from there, but try not to go beyond 400. The reason for this is you want as little noise as possible in your photos. Noise is increased as the shutter speed increases, and also as the ISO increases, so since you are shooting 30 second exposures, I figure why not strive to have the lowest ISO possible in order to get the shot you want.
When determining your exposure, don't depend on what the camera says is a "proper" exposure. You can use that as a starting point, but you may want to go lighter or darker depending on how you want your final product to look. This is the beauty of using manual. Also, remember that none of my recommendations are hard-fast rules. Photography is an art. If you need to bump your ISO to 800 or 1600 or even higher to get the exposure you want, or if you need to stop down to f/8 or f/11, give it a try. You never know, it could be the exact ingredient you need to make the image you had hoped to make.
*****A Tip For Taking Test Photos***** Taking test shots at 30 seconds each can take a lot of time. One trick that I use is changing my shutter speed to 4 seconds, so I can take more test shots in a short period of time. That is *3 stops* faster than 30 seconds, so I will need to compensate for those 3 stops by bumping my ISO up by 3 stops (e.g. from 100 to 800). Otherwise each test shot will take 30 seconds! Once I have the exposure where I want it, I change the shutter speed back to 30 seconds, and the ISO back down 3 stops, and take one last exposure at 30 seconds. If it looks good, then I know I'm ready to begin.
OK, now you have composed your image, and determined your exposure values. This is the easy part. Press the button on your shutter release, lock it down, and watch the camera do its work. If you are at home this is easy because you can go inside and get a snack, watch TV, take a nap, or whatever. If you are not, make sure you have something to occupy yourself with in order to pass the time. Also if you are in a public place, make sure you are set up in a place where nobody else will accidentally disturb your setup. One wrecked exposure in the middle of 250 exposures will greatly decrease the amount of photos you can use in your final product.
JPG vs. RAW: While it’s not absolutely necessary to shoot in RAW, I highly recommend it for one main reason: white balance. I’ve found that when I point the camera to the sky at night, it never registers the white balance the way I ultimately like it. Each shot is different with many factors playing into the colors in the night sky. For my taste, it would take too long to test white balance ranges in camera when I can do it one time on the computer with software, after the photos are finished. It’s nice knowing that I can test the entire range of white balance after the fact, and create the colors that are most appealing to me for each individual shot.
Converting to JPG: If you are shooting JPG, you can skip this step; otherwise read on. Once I have the RAW files on the computer, I open them up in my RAW editor of choice (for me, I use Adobe Lightroom) and choose one of the early photos to edit. I'll do the normal exposure adjustments, and adjust sharpness up, and use the white balance slider back and forth until I find the exact color that most appeals to me. I don't go so extreme that the colors are completely unrealistic, but I do give myself some creative license. Once I have the photo the way I like it, I copy the recipe and paste or sync it to the rest of the photos in the set. Airplanes: If you are shooting anywhere near civilization, you will most likely have some shots with airplane trails in them. I like to use the clone tool in Photoshop to remove the airplanes. If it was a busy night, this could take a while, but your final product will look much better if you take the time to remove them. If there are a lot of airplanes on any particular night, sometimes I'll go ahead and render the star trails photo, and then decide which airplane trails are most offensive and just remove those. It's always best to go back to the original photos to remove the airplane trails, and then re-render the star trails photo. I have, however, discovered that if I decide to make a time lapse video of the photographs, then I like to leave the airplanes in for them. I think they have a very cool "shooting star" effect. Again, just my taste; you may think differently.
Most of my star trails shots I’ve rendered using an app called startrails.exe. It was created for the soul purpose of combining images for star trails. I'm sure there are other good apps out there. If anyone has any other good ones they recommend, let me know and I'll give it a try.
Startrails.exe will also build a time-lapse video of your photos , which I have not tried that feature yet with this software.
To start, just click "File >> Open Images" and choose your images. Then choose "Build >> Startrails", and it will begin combining all of your images.
Here is what it looks like when it is processing. Notice that it will continually show you the photo as it is being rendered. That's a neat feature.
There you have it! ... I hope you found this guide useful. As I had said above, I encourage feedback so that I can improve, and please feel free to email me or comment below with any other questions or comments. Enjoy shooting your star trails, and please send me a copy of your photo if you try. If I get enough, I'll create a gallery with others' names and photos and link to it from here.
And remember the most important lesson of all in photography: Have Fun! You are going to make mistakes. Don’t worry, everyone does; just remember that each mistake you make leads you to becoming a better photographer!