Long, swirling star trail photography is on the bucket list of many photographers. In the film days, this required leaving your shutter open for one continuous exposure on the order of hours and hoping that everything would turn out just right. In the digital era, many photographers rely on a process known as stacking to take a large number of individual frames and combine them into the final image. This article will lay out how to capture incredible star trail photographs and combine them using the free program StarStaX.
Shooting Your Individual Star Trails Photographs
Many detailed posts have been written about how to capture individual photographs for star trails stacking, so this article will only provide a quick overview. Check out the linked posts at the end of this article for additional details.
For equipment, you will need your camera, a fast wide angle lens, a sturdy tripod, a remote shutter release, and a full battery or two. A red headlamp or flashlight as well as a folding chair can also come in handy. I recommend a wide angle lens, like 18 mm (or wider), so that you can capture a larger expanse of the sky. A fast lens (one with a wide aperture, like f/1.8) is also preferred so that you can capture more light with each frame. (Most of the photographs in this article were shot at 18 mm and f/3.5 on my Tamron 18-270 mm lens.)
Choose your location and timing carefully. Capturing star trails around the time of the new moon is preferable, so that bright moonlight does not wash out all the stars from the sky. You also want to get as far from artificial lights as possible. You can use the web site Dark Sky Finder to look for possible dark sky locations near you. Once you have chosen a location, you can use the web site Clear Dark Sky to check their 48 hour forecasts about the potential for clear sky in a given location.
Once you are on location, spend some time choosing your final composition. Think about a position that will provide an interesting foreground – an unique tree, a geologic formation, or a body of water – as well as an expansive view of the night sky. If you want an image of the stars swirling around a complete circle, then be sure to include the North Star in your viewfinder (in the Northern Hemisphere). If you want extremely long swirls in less time, then compose for a view farther away from the North Star.
Shoot one photograph with your widest aperture and a fairly high ISO value for 30 seconds. (The image above was shot at 30 seconds, f/3.5, and ISO 6400.) Your image will be quite noisy, but you should get a strong sense for your overall composition.
Once you have your composition nailed down, you want to dial in your final settings using manual mode. Choose your widest aperture (like f/1.8 or f/3.5), a 30 second shutter speed, and a mid-range ISO like 800-1600. (Newer cameras have less noise at higher ISO values, but you may want to use an ISO of 400 or 800 with an older or entry-level camera.) Turn off the autofocus and use manual focus to focus on infinity.
Before you start shooting, cover your lens with a lens cap or piece of black paper and shoot a few frames. These will be your dark frames when you process the images in StarStaX. Dark frames allow the program to subtract digital noise and hot pixels from your final image.
Use your remote shutter release to lock down your shutter. As soon as your camera finishes taking the first 30 second picture, it will start taking the next, and so on. Then pull out your folding chair, sit back, and enjoy the wait. An hour’s worth of shots is a good goal to aim for. The more photographs that you take for your stack, the longer and more defined your final star trails will be.
Once you have finished capturing your shots, remember to take a few dark frames again at the end. Leave your settings the same but cover the lens with the lens cap and shoot a couple more frames.
Preparing Photographs for Stacking
Depending on your photographs and the end result you are envisioning, you may want to do some post-processing on your individual frames before loading them into StarStaX. Whether you use Lightroom, Photoshop, or another post-processing software, you will want to apply a similar treatment to all your images if you choose to do any corrections, such as adjusting the white balance or fixing the colors.
You may also need to do some quick editing of individual shots, especially if you were shooting at a location with unwanted stray light. In the photographs below, you can see that this frame captured the light from passing cars on the far side of the lake. The quickest solution to problems like these is to open these individual frames in Photoshop, set the brush tool to black, and paint over any unwanted light.
You can see a big difference in the foreground between these two stacks of the same individual star trails. Painting out the stray light trails in those few individual pictures allows for a more seamless and less distracting foreground, once you stack all the photographs together.
Alternatively, you can choose one frame in Lightroom or Photoshop and make any adjustments needed until the non-sky portions of your image are just right. Then, after creating your star trails in StarStaX, you can combine your ideal foreground with your stacked sky using layers and masks in Photoshop.
Stacking Your Star Trails Photographs Using StarStaX
StarStaX was developed by Markus Enzweiler and is available as a free download for Windows, Mac, and Linux computers. (Screen shots courtesy of the Windows 0.60 version.) After downloading and opening the program, the first thing you need to do is load your individual photographs by going to File -> Open Images or hitting the Open Images button. You may select JPEG, TIFF, bitmap, or PNG file types. After selecting your star trails shots, you need to load your dark frames by going to File -> Open Dark Frames or hitting the Open Dark Frames button.
Once you have both types of files loaded, it is time to run your first stack. The default options are a good starting point: try lighten mode and check the button for subtract dark frames, if you have uploaded some. Click Edit -> Start Processing or the Start Processing button. The amount of time it will take the program to complete the stacking will vary based on your computer and the number of individual photographs, but it should be on the order of a few minutes at most.
After the program has finished stacking your images, click File -> Save As or the Save button and save your stacked image. Stacks will not save automatically. You can use the zoom tools to look more closely at your stack and see if the results match your expectations.
You may notice that there are some gaps in your star trails, which result from the time between one photograph ending and another beginning. In that case, you may want to run the stack again. Your individual photographs and dark frames are still loaded, so just change the blending mode to Gap Filling and start processing your files again.
After your gap filling version has finished processing, there are a few options you can use to adjust the amount of gap filling applied. Click the Images tab and experiment with the different sliders to minimize the appearance of any gaps. Click the 1:1 button to zoom into the pixel level, as in the image below, to see the impact of the Gap Filing sliders.
Want a really unique shot? Run the stack again in either Lighten or Gap Filling and click the checkbox for Comet Mode. Your final star trails will each take on the appearance of a streaking comet.
Now You Try
Now that you have the basic idea, you need to find a great location and give it a try! Do not feel discouraged if you are far from any suitable dark sky locations. You might be surprised at what you can capture even under less than ideal settings.