How to do Star Trail Photography

Methodist Church

I don’t know that I can say my photography is famous (in fact I’m certain of it), but if there is one thing people identify me with, it is my star trail pictures from in and around Cades Cove in the Great Smoky Mountains National Park.  I got bitten by the bug quite some time ago, and frankly it is now my favorite form of photography.  There is just something about being out in the park after dark, hoping for clear skies and trying to think creatively.  I’ve done a few presentations on star trail photography and have been asked many times to write a howto on the subject… so here ya go!  Before we begin, I’ll admit that this is a very long read.  This is everything I’ve learned over the past several years though, so if this is something you’re excited about, dig in.

What is star trail photography?

If you’ve followed along on my photography blog you’ve no doubt seen star trail photos… quite honestly you may be sick of them!  The above image is an example, but what exactly are you looking at?  Well we all know that the earth is spinning, and as the earth turns the stars move across the sky.  Star trail photography illustrates this movement in the night sky with a long exposure (or many long exposures) photo that allows the stars to streak in the sky.  What you’re seeing is not a meteor shower as I have been asked before; this happens every single night… it just isn’t perceivable to the human eye.

How do you photograph star trails?

There are two main ways to capture star tails: 1) with a single, super long exposure 2) with multiple moderately long exposures, stacked together using special software.  Depending on your camera and patience level, there really may only be one option.  I personally find that, at least with the grade of cameras I can afford, one really long shot just isn’t feasible.  Below is an illustration of the difference between the two methods, taken using a Canon XSi.

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The image on the left is a single, 45 minute exposure.  So literally you put your camera on a tripod, set it to bulb, and hold the shutter open using a cable release for 45 minutes.  The image on the right was taken on an equally clear night, using the same camera, and also for 45 minutes, but using the stacking method.  See the difference?  The single exposure is terrible.  These consumer grade cameras just weren’t meant to have the shutter open that long.  It’s noisy, it’s grainy,  it’s muddy… it’s hideous.  Aside from the quality being awful, there are a few other things I don’t personally like about a single frame shot.  At the end of the shot I decided to play with light painting the cabin to have it stand out a little more.  As you can see, it didn’t work out very well.  The unfortunate thing about that experiment is it totally wasted 45 minutes worth of time.  Once you do it… there is no going back.  Not so using the image stacking method.  Also note that there is a ton of movement in the trees.  While this may also have shown up using the stacking method, there is at least a chance it would not have, and very definitely would have produced a sharper image.  You can see in the second image, that while there is a little bit of movement in the trees, it isn’t nearly as pronounced.

Star trails using the stacking method

Okay, so what is the stacking method?  Basically what you do is take a series of consecutive, 30-ish second exposures over some long amount of time.  The “long amount of time” I reference is totally up to you and depends on how long you want the trails to be going through your sky.  I happen to like 45 minutes worth of stars; some like much longer… I find it distracting (all the images you will find on this site are approximately 45 minutes).  So, at the end of 45 minutes and assuming you took 30 second exposures, you’ll end up with about 90 images (30 second exposures equals about 2 per minute over a 45 minute period).  To accomplish this series of shots, you can do one of two things.

1) You can set your camera up to take consecutive images (generally signified by three squares stacked on themselves and under normal shooting scenarios, if you held the shutter button down it would just rattle off photos) and then using a cable release, hold the button down for the length of time desired.  Most shutter releases have a lock on them so you can push the button in and lock it in place.  Next, put your camera in manual mode and dial in the appropriate exposure (more on this in a minute), and then let the camera do its thing.  An intervalometer can also accomplish the same task, but is not necessary for star trails.

2) If your camera is compatible, you can load Magic Lantern on it and not have to use a cable release.  Outside of not having to use a cable release, the process looks exactly the same.  Set your camera on manual mode with the appropriate settings and then tell Magic Lantern to “take pictures like crazy”, which will cause the camera to continuously take picture after picture until you tell it to stop.  This is a “techie” sort of task, so I’d recommend you proceed with extreme caution unless you’re comfortable with the process outlined on their website.

I guess there is a third way, which would be to just sit there and push the button over and over, but I wouldn’t recommend this as you’ll inevitably shake the camera and mess up the image.

Properly exposing your star trail image

Above I mention that you should select an appropriate setting for your camera in manual mode, and then let it go to town taking pictures.  So what are those appropriate settings?  Well that depends on the look you’re going for, and frankly takes a little playing with to dial in the look you’re after.  What *I* generally do is start with my aperture around f/3.5 and the exposure set at 30 seconds and then let the scene dictate what my ISO is.  I’ve shot as low as ISO 400 on a REALLY bright night and as high as ISO 1600 on a really dark night.  On average, I would say I shoot around ISO 800 and I really don’t like going much higher than ISO 1250 because my camera starts to suck past that (I’m shooting with a Canon 60D these days).  You’ll have to play with your camera and see where it performs best to know when to call it quits.  Also, depending on the scene, you may want it mostly black, as with the silhouette shot of the Methodist Church in Cades Cove at the top of this article.  One thing to note though, the stacking process does lighten the image a bit, so if the individual frames are a hair dark, you’ll probably be fine.  HOWEVER, it is easier to darken an image in post process than it is to lighten one, especially when you’re talking about night images that won’t be blown out.

As an example, check out the two images below.  The camera settings for the first shot were the same settings I used for the consecutive images in the stack.  See how much lighter the field and mountains are?  Part of this is due to the snow on the ground, which helps lighten the entire scene, but part of it is from the inherent lightening of the stacking process.  Images without snow are generally not as dramatic.

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One final thing to consider are exposures longer or shorter than 30 seconds.  I mention else where about the possibility of using a single frame from this process as a standalone image.   I have found myself out and about and then realize halfway through my star trail image that the Milky Way is directly overhead and I end up liking that single shot better than the stacked image.  The problem with going longer than 30 seconds is that the stars will definitely be “ovaled”, which doesn’t look right.  Truth be told though, even at 30 seconds the stars aren’t perfect pin points.  Look closely at the stars in the image above and you’ll see what I mean.  Well, turns out there is a science to figuring out how long of an exposure you can have without ovaling the stars.  The best explanation I’ve found is here.  I say all this to say, it is at least something you should consider.  I stick to 30 seconds most of the time, just in case… and sometimes I back it down to 20 seconds for this very reason.  Play with it though, and if it isn’t concerning to you and you have an intervalometer or you have Magic Lantern, you could always go longer for better exposure in each image, and let the stars do what they may.

Focusing in the dark

This is one that stumps a lot of people right off the bat.  I’ll make it easy on you though; almost all of my images are focused just shy of infinity.  If your lens has the markings on it, you’ll see what looks like an L laid over on its side just next to the infinity symbol.  Set your camera to the point of the leg on the sideways L.  If you don’t have the markings on your lens, spin the focus ring (this will obviously need to be done in manual focus mode) to infinity and then twist it back just a hair.  This is definitely something you can experiment with.   If your subject is close to being in focus at infinity and you want to dial it in a little better, I generally shine all my flashlights at the main subject to help with focusing.  Be careful about getting too far away from infinity though, the stars will start to go wonky in the sky.

Subsequently, I also use the flashlight method for getting the angle of my camera just right.  There is nothing more annoying than getting home with an awesome star trail photo… that’s crooked.  Not that you can’t straighten it in post processing, but you start losing sky when you do.  Just a thought.

Stacking images for a star trail photograph

Alright, so you’ve dialed in your exposure and setup the shot and now you’re left with a bunch of images.  Now it is time to stack those images into a single star trail image.  Before I go any further, some of you are already thinking about post processing… hold your horses for just a second; I’ll get to that.  For now, lets stack your unprocessed images.  If you shot in RAW (more on this too), don’t do any lens corrections or any adjustments… just output them as JPG to a single folder and start from there.

There are several different ways to actually stack these images.  I started off using a program call Startrails from www.startrails.de.  It’s free software, does a fine job, and doesn’t require any other software.  If you’re a Photoshop user, however, I’d recommend the free stacking script from Art in Nature Photography’s website (the scripts are located here).  With both software packages, you aim the program at a folder and it does the rest.  The only “problem” with the Startrails application is that it leaves “gaps” in the star trail (illustrated below).  The Photoshop script does not do that.  Frankly the only time you would ever notice this is if you print the image to a huge size, or zoom in on your computer to the maximum.   Under normal viewing circumstances, these gaps would not be noticeable.  Like a blemish in a diamond that only the owner knows is there… it got on my nerves, so I switched to using the script.

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Everything else.

Okay, so that’s the basics and will get you started making fun star trail images.  What follows are the nuanced things that you will likely care about once you’ve done a few star trail images and you want to perfect the process.  I’ve also included answers to questions I commonly get.

RAW vs JPG

I almost hate having this discussion because people get so hung up on it… BUT here is my take as it pertains to star trail images.  When I started shooting star trails I only shot in JPG.  I originally did this because I was not comfortable with RAW images at the time.  I have switched now to solely shooting in RAW for a couple reasons.  1) You can push a RAW image around a little more than you can a JPG… ESPECIALLY when they are as dark as the ones you may end up with shooting at night.  I also like being able to adjust the white balance substantially.  2) When I go out, I generally have a star trail image in mind, but occasionally I’ll end up with a single frame image that I just like better.  As an example, if the Milky Way were to cross the sky and be particularly brilliant, I may toss the star trail image and just stick with that.  Why does it matter?  See #1.  You can push the image around a little more and since my camera can’t climb the ISO ladder very far, I end up really having to push Milky Way images around a lot to really get the stars to pop.  So… really just one reason.

Post Processing Workflow

I personally do about half of my post processing before the stack and the other half afterwards.  I always start by importing the RAW images in to Lightroom.  As I mentioned at the beginning, make sure you don’t do any lens corrections before the stack.  The reason is that you will get funky concentric circles in the image from where the software removed the barreling.  See the images below.  In the top one, look at the mountains on the right-hand side of the image and you’ll see what I’m talking about.  The second image did not have lens corrections done prior to the stack.

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Its subtle, but it drove me nuts until I figured it out.  What I will do prior to the stack though is adjust the white balance.  Don’t be too heavy handed here as you can always adjust a little more after the stack.  I tend to like my images a little cool (I like the sky to have a blue-ish tint), but I’ll try to just get it neutral before the stack, and then cool it off a little more afterwards.  I will also dial in a touch of clarity, just to make the stars sharper.  From there I export.  Next, I start the labor of love of removing all the planes from my images.  I detest plane light trails in my star trail images, so I literally go one by one and remove the lines.  This can take a while… but to me, it’s worth it.  Some people like them, it’s totally up to you.  After clearing the planes out, I’ll do the stacking process mentioned above.  After the stack, I pull the final image back in to Lightroom and do whatever else I feel the image needs.  Usually that involves more color correction.  Especially here in the Eastern United States, we get a lot of light pollution which leads to some funky colors in your night sky (another reason I like to really cool my images off).  Good luck.

Moon or No Moon

A lot of people assume that when you want to get a star trail image, you should go on a moonless night.  I personally prefer to shoot on a night where there is at least a little bit of a moon.  The reason why is that it provides some lighting in the rest of the scene that you just can’t get otherwise.  I generally prefer a sliver of a moon, however the image below I actually shot on a full moon night.

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Now, it is definitely true that you will get less stars in your sky the brighter the moon is.  Compare this image with any other image here and you’ll notice that right away… especially the one with the snow on the ground, which was shot on a totally moonless night.  I would submit to you though, that the stars in the sky shouldn’t be the main attraction to the image, but a supporting role.  In light of that, to me, the number of stars isn’t as important.  Play around with it and you’ll get a feel for it.  If you do shoot when there is a moon in the sky, ensure that the moon doesn’t end up in your shot.  It might sound neat, but it just ends up being this giant scar in the sky.  This can be particularly frustrating when you’re not paying attention to which direction your camera is facing and you end up having the moon rise / set right in your image!

Composition

A lot of people start out shooting star trails by just aiming their camera straight up and letting it run.  There is certainly nothing wrong with this for learning purposes, I’ve frankly done it myself.  I would offer though that you’ll never get a compelling image doing that.  I am certainly no expert on composition, however I would suggest to you that a star trail image should be just as compelling during the day with nice lighting as it would at night with no lighting.  I find the most interesting images are not just a spiral of stars in the sky, but something to look at that the stars just happen to be spiraling over.  Get creative!  I will say this though, when it comes to star trail images you might compose the image with a little more sky than normal, which I feel is fine.  I have also been known to put myself in my images, just for something different.  People often ask if I stood there for the entire 45 minutes!  That’s the nice thing about the stacking method, you can get your shot, and then play with the last several frames and edit in whatever you like!  In the end, the shot is yours, so do what makes you happy.

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Getting the circle in the stars

While this may be obvious to some, if you are wanting to have a full circle of stars in your sky, you will need to be able to locate the North star (assuming you’re in the Northern hemisphere that is).  The North star is the innermost circle in the spiral and the star that will travel the least in your image.  Some people can just look at the sky and pick it out, I always need a little help.  If you have a smartphone or tablet, there are applications out there to assist.  Since I use Android, my personal favorite is the Google Sky Map.  It is a free utility and very useful.  If you’ve got an Apple device, search around and I’m sure you can find a usable one.  Once loaded, just pull your device out and aim it at the sky and turn around until you locate it.  I will make one comment on this.  While I do like images that have the North star in them, I don’t feel it is necessary.  Also, like any other thing in photography, avoid having the center of the circle dead center in the sky.

Getting in the Park after dark

Many people often ask me how I get into Cades Cove after dark.  Well… I walk or I ride my bike.  For Cades Cove anyway, the road is just closed to cars after dark.  You are free to walk in or ride your bike in.  I have passed numerous Rangers on my way in over the years, and they all just wave and carry on… so there is no reason to hide in the bushes when you see them coming!  Just be respectful of the Park and its rules and don’t damage any of our heritage while you’re in there.  If I ride my bike in, I always park it on the road and then walk to the cabins, just like I would do during the day.  Cades Cove is an amazing place after dark… oh… and you’ll have the whole place to yourself!

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Have questions or think of something I left out?  Send me a message from the Contact Page and I’ll add it in the article!

–Dan Thompson