|This Article Features Photo Zoom|
We’ve seen a number of outstanding star trail images in the OP Assignments galleries, contest entries and other direct submissions to the magazine. Many of the photos are excellent. The cover image for this issue, photographed by Jeffrey Sullivan, is an example of a brilliantly executed star trail image. Some of the others we’ve seen motivated us to do this short step-by-step Solutions article to explain how to do it right.
Sullivan’s cover image is particularly unique because he has used moonlight to illuminate Yosemite Valley. Many star trail shots show a very dark foreground. By contrast, Sullivan’s shows a brightly lit foreground that has a surreal quality by virtue of the fact that it was lit by moonlight with a long camera exposure. You don’t have to use moonlight, of course, but if you have the chance, the effect can be startling.
Location, Location, Location
The first step is to come up with a place where you can get a good composition. Whether you’re shooting by moonlight or on a very dark night, the foreground elements do matter. You want to create a pleasing composition. A lot of photographers will choose something very close and light it with a flashlight during the exposure to add an element of interest. Whether you do that or not, you still want to have a good horizon line. Jagged mountains or a perfectly flat ocean can work, but think it through, and when you review the image on the LCD, be sure to evaluate the horizon critically.
This issue’s dramatic cover of Yosemite Valley by moonlight with star trails was taken by Jeffrey Sullivan.
Point North…Sort Of
There’s no law saying your star trails have to orbit around a single point, but for your first attempts, we recommend that you point your camera generally north. You don’t need to center the North Star (Polaris) in the frame, but it’s a good idea to have it near the midline of the frame. This is a general rule, and like all rules, it’s made to be broken after you’ve built up some experience.
Lock Everything Down
Nothing could be more obvious. You’re going to have a very long exposure, so you need to lock down the camera with a sturdy tripod and a good head. Positive locking is key. If the camera starts slipping during the exposure, the results will be unacceptable.
If you’re shooting a scene like the one on the cover, just focus at infinity. We suggest you use manual focus mode to keep the camera from trying to hunt. If you’re shooting with something close to the camera, you need to focus carefully to be sure everything from your near object to infinity is sharp.
Resist the temptation to use a high ISO. Keep your camera at ISO 100 or 200. You want to be sure not to generate noise in the shot. Noise in a pure-black sky comes out like colorful pixels. It looks horrible.
Because stars are pinpoints of light, exposure can be confusing unless you’re an amateur astronomer. Instead of writing a treatise about focal ratios and limiting magnitudes, suffice it to say that you want to shoot wide open. A faster focal ratio will let you capture more stars than a slower ratio, but since you probably want to capture as many stars as possible, just go ahead and shoot wide open. Shutter speed is determined by how much of a streak you want to have and how long your DSLR can record a single image before the sensor begins generating noise.
The Earth rotates 360º every 24 hours. To create a star trail that goes 90º (a quarter of a circle in the sky), you want a shutter speed of six hours. Most photographers keep the maximum length of any individual trail to about 15º, which means an exposure of about one hour. Depending on your camera, this may be too long for a clean image. Experiment to see how your camera does.
If an hour is too long, you can shoot a series of shorter exposures and combine them in Photoshop. Since your DSLR is locked down, it’s a fairly straightforward process. You can shoot a series of 10- or 15-minute exposures and let the sensor rest between. Be sure to keep the rest period to less than 30 seconds between exposures or you’ll create gaps in your trails.
In these extremely low-light situations, the key to good results is to experiment. Go out on a clear night and give it a try. You’ll quickly get a feel for how your camera behaves and what the limitations are as far as shutter speed. Star trails are fun to shoot, and they always make an impression.