One of the things I get asked most frequently regarding my night photography is how are my star trail images created? Star trails is a term in photography used to describe very long exposures of the stars in which their movement across the sky can be seen in the resulting photo as “trails” of light. The stars themselves are not actually moving, of course, but they appear that way to us due to the rotation of the Earth. For this reason, the north star, Polaris, is often used as a focal point in these images. Relative to our position in space, and being situated in the northern hemisphere in the world (in North America), Polaris always appears at a fixed point in the sky and this is why the star can be used for navigation. Star trails in photos where the camera is facing north will appear in a circular pattern around the north star as seen in the photograph above, because the star is fixed and the Earth rotates about the north/south axis.
Digital photography has made the creation of star trail images much easier and accessible to anyone with a digital camera capable of shooting in manual mode, a wide angle lens and a sturdy tripod. Digital allows us to take a series of photographs over a long period of time and combine them in software on the computer, this is how I got started. However, in the days of analog film, if one wanted to take a 1 hour star trail photo the only option available was setting the camera on a tripod for a single 1 hour exposure and hope for the best. Film speed, sensor heat, grain; all factors that needed to be considered, a single moment of a bright light entering the frame could ruin a night’s work, and if you wanted a well lit foreground – forget about it.
All of that is solved with multiple single exposures in digital photography. Layering in software makes it possible to combine multiple exposures, control noise more effectively through shorter exposures, discard frames that may have been ruined for some reason, edit out unwanted elements such as jet trails and shoot for as long as battery power will allow.
There are several methods that can be used to accomplish this, some cameras even come with stacking modes built-in. There are programs that will stack photos for you as well, such as StarStax. While I appreciate these methods and have used them myself, they mostly rely on JPEGs, which have limited editing potential. I prefer to use Adobe Lightroom and Photoshop so that I can control all aspects of editing and get the most out of my photos while shooting in RAW. This is the method I will be describing in this post!
The good thing about choosing a location for star trails is that it doesn’t have to be in the darkest places. Interesting, colorful photos can be produced right on the edge of city lights. As long as there are no street lights in the immediate vicinity. The only other thing to watch for is the moon phase. The moon can provide foreground lighting but it’s best to shoot when the moon is not in the sky or if the moon is at crescent phase and won’t be passing directly into the frame of your shot. For tips on foreground lighting check out the article I wrote on the subject!
I like to find interesting foreground objects that are oriented in some way that lines up with the north star to create interesting compositions with the circular arrangements of the star trails.
Sometimes, the parallel lines created near the east/west axis of the earth can create interesting patterns as well.
Recently, I wrote a couple blog posts about how I shoot time-lapse photography and we will be using the same methods for shooting that I describe in that article. In fact, when I shoot star trail images, I often shoot for the duel purpose of making a time-lapse of the resulting images in addition to the star trail photo. I would also suggest looking at the article I wrote on Milky Way photography for tips on shooting at night, such as using a hand warmer around the lens to combat dew formation and how to focus the camera at night.
When shooting for star trails, the camera settings will be the same as shooting any other night sky image, except you will be shooting at intervals over a long period of time. You will need a camera capable of shooting in manual mode on a stable tripod with a wide angle lens. Unlike Milky Way photography, the lens aperture does not have to be super wide. For example, when shooting the milky way, typically an aperture wider than f/3.5 is needed in order to gather as much light to get as many stars in the shot as possible. For star trails, the goal is not always to get as many stars exposed as possible but to create a pleasing composition. Less light and less stars will result in more distinct and separate trails, rather than dominating and filling the image completely with star light.
Here is a good starting point for the exposure settings: ISO 1600, f/2.8 (if shooting wider than f/4 increase the ISO to 3200), and 30 secs per shot. Experimenting with the ISO and aperture settings is a good way to get a feel for the type of star trail photo you want to produce.
Most tutorials will instruct you to set the lens focus to the infinity marker, but true infinity focus is rarely on that marker. A better way to focus at night is to use live view to zoom in on a very bright star, and manually focus using the focus ring on the lens. Alternatively, you can set your desired aperture ahead of time and auto-focus on a distant mountain or other object in the landscape during daylight hours. This is a fairly reliable method but is not always accurate and the focus ring is prone to being moved before setting up to shoot. Once you have focus, be sure to turn off Autofocus on the camera body AND lens, even if using back button AF to ensure that it doesn’t change during the shoot. Additionally, you can always tape the focus ring in place if you are extra cautious. Do a test shot to check your focus and exposure settings.
Shoot in RAW rather than JPEG in order to get the most out of your photos in editing. White balance doesn’t matter when shooting in RAW. It can be kept on Auto-WB, which is what I often do. However, it can be set for “Daylight” to produce naturally lit conditions or “Flourescent” for something that looks more like what we might see with the naked eye.
Cover the viewfinder with something opaque like black tape. Outside light can leak into the sensor during long exposures and covering the viewfinder will prevent this.
Turn off all in-camera noise reduction, both High ISO NR and Long Exposure NR, if you’re camera has these options. Turn off the LCD screen previews to save battery power. Next, the camera needs to be set to shoot at intervals. Some cameras have a built-in interval mode, but you can also buy an intervalometer that functions as a remote trigger. The intervals will need to be set 2 or 3 seconds longer than the exposure time. For 30 second exposures, the interval will be 33 seconds. The amount of total time shooting will depend on how long you want the trails to be, for example the photo shown at the beginning of this article with the bridge was shot over 4 hours and the image of the fire tower above was 15 minutes. In general, 15 minutes or 20-40 shots will be the minimum amount needed.
Another way to shoot star trails without an intervalometer is to shoot in continuous drive mode with a wired remote shutter. Most wired remotes have a button that allows the remote to stay depressed so the camera will continue to trigger the next shot until the remote is reset.
Now the waiting begins! Keep the surrounding lights to a minimum. Read a book by lamp-light, warm up in the vehicle if it’s nearby, see how far you can walk in the dark without tripping and falling flat on your face, or just look up and enjoy the night sky until shooting is finished!
After shooting all night you will probably be anxious to edit the photos and see the result! I will briefly cover the editing process here, but I go in depth in a video where I process a star trail photo from the beginning to end exclusively for subscribers at the $10 level to my Patreon only!
Load the RAW files into Lightroom as you normally would.
Edit the exposure settings with the first photo in the sequence. Usually I make simple adjustments, maybe bumping the Exposure up slightly, along with the blacks and whites. White balance can be set to around 4400-5000K, which tends to give a darker, bluer look.
Next, copy the develop settings and paste them to all the photos in the sequence.
Inevitably, planes and helicopters will cross your frame while shooting and create ugly criss-cross patterns across your star trails. These can be edited out by painting them over with a dark brush in Photoshop, however, there’s another method that I like to use in Lightroom that is nondestructive to the photos. Create an adjustment brush selection with the Exposure, Whites, Blacks, and Shadows slider set all the way to the left at -4, with feathering at 0 and flow at 100%. Scan all your images for jet trails and paint over them with the brush. This essentially has the same effect as painting with a black brush over the trails in Photoshop. This is tedious work but well worth doing and will greatly clean up the final image, in my opinion.
Now, select all photos, right click -> edit in -> open as layers in Photoshop. Loading the layers will take a long time, so this is a good time to step away.
Note: In Photoshop, unless this has changed in recent versions, only 200-300 layers can be loaded at once. If your sequence contains more than this amount of shots, you will have to repeat the following steps with 200 photos at a time and merge the resulting images each time.
Once everything is loaded in Photoshop, go to the layers panel and select all the layers. Still within the layers panel, go to the blending mode dropdown box and select “lighten.” This will retain only the lightest parts of each successive layer in the stack, essentially masking out anything dark (which is why we painted black over the jet trails with the adjustment brush tool in LR).
Right click on one of the layers with all the layers still selected and select “merge layers” to combine all the photos into one.
At this point, the star trail image is complete and you can apply any additional editing you wish! I prefer to add a curves adjustment layer to increase the contrast between the lights and darks, and sometimes making additional tweaks with the color.
Closing Photoshop will bring up the save menu, save the file and it should bring it back into Lightroom automatically, where you can make final edits.