How To Create Star Trail Images

With today’s digital cameras it is surprisingly easy to create star trails photographs. At the highest level, all you do is run a sequence of night star shots through a star trails program and enjoy the result. As is often the case, the challenges come in the details.

You’ll need to capture images covering 30 to 60 minutes or more. A sturdy tripod is essential. You can trigger exposures manually, but that’s tedious and not fun to do for an hour at night. Ideally you’ll have a remote trigger that can lock down to fire off sequential shots, or even better, an intervalometer which takes shots at certain intervals which you define.

You’ll need to focus your lens on an object at infinity, and leave the focus mode set to manual so it won’t hunt for focus in the dark. The focus ring of your lens probably continues past that point to compensate for differences as temperatures fluctuate, so note where this is, or if your lens has continuous focus ring with no visible scale, focus your camera during the day, switch it into manual, and carefully tape the focus ring with removable painter’s masking tape.

You’ll want to take sequential shots close together so the star trails to be continuous, so turn off your camera’s long exposure noise reduction.

You’ll also want a consistent exposure, so put your camera in manual exposure mode.

Cameras have different sensitivity to light, and the moon phase and local light pollution can affect your exposure, so you’ll need to run some tests to determine what settings to use for your individual shots.

With no moon in perfectly dark skies I use f/2.8 at ISO 6400 for 30 seconds. Don’t have f/2.8 or ISO 6400? No problem, lengthen your exposure time. If you have f/4.0 and ISO 1600, you’ll double the time for the aperture and then another 4X for the two stop loss in sensitivity to 1600, so your exposure time could be 4 minutes. Your actual time will often be less due to some ambient light from the moon or light pollution. Take lighter and darker shots to ensure that you’ve identified an exposure which isn’t too bright or too dark.

Once you have the basic exposure figured out, take that exposure over and over until you reach 30 to 45 minutes or more total. Leave as little time as possible between shots.

For this example I used about 80 shots of 30 seconds each, covering 40 minutes. I used the free StarStaX software (www.StarStaX.net) in “lighten” mode, where the lightest pixels are kept as images are merged, creating the trails as the stars move from frame to frame.

Unfortunately in Yosemite Valley the cars driving by also create lasting light trails. To remove them, there’s also a “darken” mode which keeps the darkest pixels, eliminating the car headlights.

This also eliminates the star trails, but by using layers in Photoshop and blending that center portion of the darkened sequence into the lightened star trails sequence to get a star trails image without the car lights.

So what else can the free StarStaX software be used for?  You can use it for quickly and easily layering any landscape images where you want the brightest portions to come through, like bringing multiple lightning strikes into one image:

Go give it a try!