One of the most common questions I get asked when I present one of my star trails is “wow, what is that?” It is an understandable question. Star trails are a view of the world that we can’t see directly. With a camera, the photographer can show hours of time at once, presenting the world in a new way. Here is how to start basic star trail photography.
Star trails capture the perceived motion of the stars overhead through a long period of time from minutes to hours. Because the camera is in a fixed position and the foreground (everything attached to the earth) is stationary, the only thing that moves over time is the stars.
With digital photography, combining many individual frames, rather than taking a single very long exposure, is the best method of making startrails in most situations. The camera is mounted on a tripod and then a series of individual images are captured one after another with as short a break in between as possible. The individual exposures are layered so that only the brighter parts of each additional frame show up. Since the stars are brighter than the background sky, their tracks are drawn in.
Basic Star Trail Photography
The exact process used to capture the frames of a stacked star trail can vary from camera to camera and from situation to situation. The simplest solution and one I’ve used for many star trails works on most cameras including Nikon and Canon dSLRs. You need a camera with manual exposure mode and continual shooting mode (“machine gun” mode). You also need an external remote shutter button.
Unfortunately, not every camera allows these. I’ve used solutions as crude as taping a rock over the shutter button. You can follow this process for basic star trail photography even if you have one of these cameras. You’ll just have to get creative with how to hold the shutter button down.
The basic star trail photography process goes like this:
- Find a scene.
- Frame your shot & focus your camera.
- Determine your exposure.
- Start the star trail and wait.
- Process the photos and combine into a star trail.
Camera Setting for Basic Star Trail Photography
Before you start there are several camera settings to check.
- Make sure “Long Exposure Noise Reduction” is disabled. Many cameras have this feature enabled by default. When you take a long exposure, the camera takes two exposures back to back, one with the shutter open and another with the shutter closed. That means it takes 60 seconds to take a 30 second exposure. That won’t work for a star trail.
- Put your camera in continual shooting mode. Continual shooting mode is normally used for sports or other fast action subjects. You will know you are in continual shooting mode if when you hold down the shutter button, the camera takes multiple pictures back to back. If your camera is set for a long exposure, it will do this slowly, so test in manual with the shutter speed high.
- Switch to manual exposure mode.
- Disable Auto ISO if your camera has it. Auto ISO will try to second guess you, and it will do it wrong. For star trails, disable Auto ISO.
- Set the exposure settings to ISO1600, 30 seconds (shown as 30″ on most cameras), and f/4 or the fastest aperture your lens will go to if slower than f/4.
- Attach your remote shutter release button.
Once the camera settings are adjusted, find and frame your shot. Take individual images and zoom in to check framing and focus. Make sure the camera is taking 30 second exposures, not 1/30 second exposures, which is an easy mistake to make. In addition, you should tweak your exposure as needed.
Starting the Star Trail
Once you are happy with the framing, it is time to start the star trail. To begin the star trail, press and lock the remote shutter release button. This is ussualy done by sliding the lock mechanism forward.
The camera takes a 30 second exposure. Once that is complete, it sees that the shutter button is still depressed and that it is in continual shooting mode. Therefore, it immediately starts another 30 second exposure. This process repeats until you get tired, your run out of battery or some other artificial limit is hit. For example, Nikon’s impose a limit of 100 to 130 frames to protect the shutter from accidental releases in a bag. There is a simple work around, see below.
When you start the star trail, wait and make sure the camera recycles to the next exposure at 30 seconds. If it does not, recheck the camera setup. Common causes are that the camera is not in continual shooting mode or that long exposure noise reduction is still enabled.
With everything working, what you are left with is several tens to hundreds of RAW files.
Processing Basic Star Trail Photography
Back home and after some sleep it is time to process the RAW files and export them as JPGs into a working directory. Then use star trail stacking software such as StarStaX (free) or any of the numerous Photoshop plugins to stack the many images into a single image. This stacking is usually done using a “lighten only” blend mode. The stars move across the frame and are darker than the background sky so they fill in. Once the image is stacked, you can adjust the curves or do other final adjustments and retouches as needed to perfect it.
This basic outline is just a starting point. There are many places where the procedure could diverge to fit a specific situation. The exposure I gave above (ISO1600, 30s, f/4) is a good starting point. The exposure time will need to be shortened if the area has large amounts of light pollution for example. There are numerous intervalometers (computerized remotes that can handle exposures longer than 30s, among other advantages) on the market which can be used along with bulb mode to lengthen the exposure time in very dark areas. And of course, every camera system has its quirks.
Just the Basics
This is a high level overview of the process. Even basic star trail photography is nuance and benefits from careful refinement. Every camera works a little different and there are specific techniques for problems like light pollution. Post processing star trails is a art in and of itself. Start experimenting or take a class or check out my basic star trail photography walk through video. Learning is a lot of the fun.
*Nikon Users: To get around the continuous frame limit, you simple have to release the remote at any point for a split second to reset the counter. You can do this during an exposure without causing a problem for your star trail. It will not be interrupted.
He is a self taught experiential learner who is addicted to the possibilities that new (to him) gear open up. He loves to share the things he has worked out. Andrew started with a passion for landscape and night photography and quickly branched out to work in just about every form of photography. He is an ex-software developer with extensive experience in the IT realm.