Digital Star Trails: A Step by Step Guide
We all know that the best parts of the shooting day are around sunrise and sunset. But you don’t have to stop when the Sun goes down. Star trails are a really fun way to make some unique images and squeeze a little more photography into your photo safari or vacation. Star trails used to be exclusive to film cameras. The high noise found in long exposures of early digital cameras made digital star trails a mess.
But with modern D-SLRs anyone with a tripod and some patience can create compelling star trails. In this step by step guide I’ll show you how…
Location, Location, Location
Just like with real estate, location is key for star trails. You need a dark area with an open view of the night sky. Any major amount of light pollution or even intermittent car headlights can ruin your image since your camera will be open for minutes or even hours. If you want to capture the “swirl” of stars around the North star (Polaris) you’ll want your view to be to the north. Lighting issues extend to the moon as well. You’re best off on a moonless night or photographing before the moon rises or after it sets. Most weather websites and various downloadable phone applications will give you the data for the moon’s rise and set where you are.
Of course you also need a cloudless night. You might survive a few wisps of clouds but of course since stars are the subject the more you can see of the sky the better. So for example we don’t do star trails on our bear safaris to Alaska in July since it doesn’t really get dark but they’re easy to do in March and November on our trips to Texas and can be really gorgeous in the desert in Southern Africa when we’re on safari there and in Southeast Asia since we’re there in the dry season.
Star Trails with Joshua Tree near Joshua Tree National Park
Nikon D700, Sigma 24-70mm f/2.8 Lens, RRS BH-55 & Gitzo 3541LS
Your Foreground Is Where You Can Shine
The stars themselves will look more or less like the stars in everyone else’s star trail images. Of course you can choose the length of time you use and exactly where you center the image, but star trails all look pretty similar—except for the foreground. That’s where you can make your images unique. For this article I’m using images I photographed while visiting Joshua Tree National Park so I wanted to showcase Joshua Trees. Fortunately I was staying at the excellent Desert Lily B&B near the park so it was easy to head back out after dark to the trees I had scouted during the day and set up my camera.
Other great foregrounds include mountain profiles, a tent with a welcoming light shining from the inside, or really anything that belongs under the stars. However remember that you need to find a way to make your foreground compatible with the long exposure times of your star trails. If it has its own lighting you need to be able to turn it on for just long enough to have it show up in the image but not stay on for so long that it burns out your sky. For the Joshua Trees I simply lit them briefly with a pocket flashlight (using some white light and some red light). You can tweak the white balance setting to help create the mood you want, either blue and moody to match the sky or warmer to help make your foreground stand out.
The Gear You’ll Need
First you’ll need either a recent model D-SLR (with low noise) or a really top of the line compact camera with a relatively large sensor. Next you’ll need a way to leave the shutter open for an extended period—either a locking shutter release or some type of intervalometer (many D-SLRs have one of these fancy timers built in) you can set for large intervals or for many repetitions of shorter intervals. I use a simple manual locking release for my Nikon D700. It screws into the 10-pin connector and when I set the camera to Manual and Bulb I can press the button, slide the lock and then come back when time is up and pop the lock to close the shutter. If your camera timer only goes up to 30 seconds (like many that are built in) you’ll need to shoot a lot of frames and layer them together as we explain later.
Finally you need a good tripod and head that you can use to lock your camera in place for an extended period of time. Personally I like star trails that last at least 30 minutes and prefer ones that are an hour or two. The extreme is doing a full 12 hour circle of the stars which of course requires a completely moonless night with at least 12 hours of darkness. If your camera has long exposure Noise Reduction it will want to double your exposure time by capturing a “dark frame” after your initial image. That’s great for noise but if you are using several images then it’ll create gaps between them so you are better off disabling long exposure noise reduction in that case.
Capturing The Image
Exposing for star trails is actually pretty easy. Place your ISO down at your cameras native ISO value (for most Nikons that is 200) and then use a medium aperture (I used f/6 for these shots, but f/4 or f/8 would have also worked). Remember that if you want your foreground to be in focus or you need to light it separately you’ll want to capture it in a separate frame (with your camera still locked to the tripod).
A more difficult decision is how many images to take. Say you want to show 1/6th of a full star circle (2 hours). You could take one 2-hour image, 2 1-hour images, 4 30-minute images, etc. Your choice depends on how long an exposure your camera can take without unacceptable noise and how much work you’re willing to put into blending the images on your computer.
For my D700 I’ve found about 30 to 45 minutes to work well, so for a two hour star trail I simply used 3 images of about 40 minutes each. You can check your cameras capabilities by taking some long exposures with the lens cap on and seeing how much noise you get.
Finally remember to have your battery fully charged or supply external power to the camera.
Processing Your Images
After all this work you’ll wind up with one or more images of your foreground and of the stars. Below are the 5 images that I used to create the image showcased above:
I use a fairly simple three step workflow to process my star trails:
Step 1—Since I shoot Raw (NEF files in my case) my first step is to open the images in Photoshop. The only adjustment I make here is to the white balance to pick one (generally from 2700K to 3200K) that makes the sky look right. Then I simply Save the files as TIFFs so that I can blend them. If you shoot JPEGs you can skip this step.
Step 2—Rather than manually blend the images in Photoshop I use a handy application called Image Stacker from TawbaWare that for a mere $17 gives you a variety of options for blending your images. For my star trails I simply drag the saved TIFF files onto Image Stacker and use the Brighten mode (which picks the brightest of the pixels from each image to blend) to create a nicely merged output TIFF. If you don’t want to use an extra utility you can closely mimic this behavior by using the Lighten blend mode in Photoshop to create a layer that shows the Lightest pixel from a stack of layers.
Step 3—Even if your camera has great long exposures there will be noise you’ll need to deal with. There are dozens of options for reducing noise but I use a simple 2-step procedure. First I use a general purpose noise reducer (Noise Ninja, nik Dfine and the built-in noise reduction in CS5 Camera Raw or Lightroom all work for this). Next I use Photoshop’s own Dust filter (found under Filters->Noise) with a radius of about 2—as a compromise between degrading the star trails and not removing enough noise.
After those simple steps I’m ready to save out a final image like the ones I’ve resized and used to illustrate this article. That’s all there is to it. The next time you’re not sure what to photograph after dinner head on out to someplace dark and try out your own version of star trails!
You can read more tips about digital photography on our free informational website nikondigital.org or on my personal site, cardinalphoto.com. And of course if you’d like to join me on a safari where we can practice star trails along with everything else we’ll be doing please check out my safari and workshop calendar.—David Cardinal