From the February 2003 issue

Tips to photograph star trails

Use these tips to perfect one of the easiest forms of astrophotography.
By | Published: February 5, 2003 | Last updated on May 24, 2024
Star Trails Above Arizona
Circumpolar stars trail over cholla cacti in Organ Pipe Cactus National Monument, Arizona.
Eric DeBolt
The idea behind photographing star trails is wonderfully simple. Just take your old mechanical camera, point it skyward, and leave the shutter open. With patience, practice, and attention, you can take some stunning and artistic images. I will try to help you understand the details that matter most, but the practice and patience are up to you.

Many cameras on the market are capable of making nice star-trail photos. The newer and pricier professional cameras with power-saving, time-exposure modes offer advanced flash functions and
incorporate features useful for regular daytime photography. However, if you opt instead for a mechanical camera, you will get a bargain that is also lighter and smaller. But any sturdy mechanical SLR (single-lens reflex) body with a B, or bulb, setting that can accept a cable release will work. The camera shouldn’t require battery power to keep the shutter open. In cold weather lithium batteries can die during a single exposure.

Star Trails in Utah
On this moonlit night, this image was captured using a 35mm lens at f/1.4 during a 11-hour exposure.
Eric DeBolt
Fixed focal-length lenses will nearly always produce sharper, higher contrast trails than zoom lenses will. A high-quality, wide-angle lens will put a dent in your pocketbook. But new equipment buyers should spend the bulk of their money on the lens, because star-trail photos only require the camera shutter to open and close. The cheapest camera body with the finest lens will yield far better results than a discount lens on a professional camera body.

A sturdy tripod is a must, but even the strongest tripod should be weighted down substantially in windy conditions by hanging something heavy from the center post. Set your tripod low with its feet spread wide to ensure a sharp, vibration-free image.

The film you choose merits careful consideration. Different effects can be achieved with small changes in film speed and formulation. Don’t cut corners on the least expensive and most important part of the process; ten dollars a roll for the finest professional slide film is a bargain. Each exposure costs about fifty cents, including processing at the best lab. Generally you will only be able to shoot one exposure per camera per night.

Star Trails in California
The photographer used a 20mm lens at f/4, to capture this 10-hour exposure.
Eric DeBolt
During the long exposures that are necessary for star trails, the highlights will show up but the film will record almost no detail in shadowy areas, so choose slower-speed films to counteract some of this loss. Images shot on faster film yield a sky that is not nearly as dark and too much grain shows next to the star trails. An exposure several hours long at a wide aperture would never work if the bright stars stood still. But Earth turns, and as the stars sweep across the sky they deliver just enough light so as to not overpower any portion of the film or be too faint to be visible. Adjust the aperture for faster or slower film. An ISO 50 film with an aperture at about f/4 is the best choice for the typical star-trail photo. Capturing a close foreground subject in focus demands a greater depth of field, so you might want to try using an ISO 100 film at f/5.6. Slow black-and-white films can produce some stunning images, but the true colors of the stars are hard to pass up. Keep a detailed notebook or journal of your choices to see what works and what doesn’t.

Star Trails Above Utah
Double Arch at Arches National Park, Utah, frames color star trails.
Eric DeBolt
The right place at the right time
Photos taken in urban areas will always come at the cost of the number of visible stars and the depth of black in the background sky, so pick a location far from high populations. In addition, find a place with low humidity. The dry air of a desert allows subtle star colors to record on film. Some of the best locations for astrophotography are mountaintops surrounded by a desert, far from civilization. The state and national parks of the four-corners states — Arizona, Colorado, New Mexico, and Utah — are ideal.

The natural attractions in America’s parks make fascinating foregrounds by interrupting the star trails and creating silhouettes. This can add missing perspective to these nighttime photos. Access to some of the desirable locations in parks may require special consideration; some of the roads and trails are closed from dusk to dawn. The better you learn the terrain during the day, the easier and safer it will be to maneuver and compose the best shots at night.

The arc length of your star trails depends on how much Earth turns while the shutter is open. The best results come from opening the shutter about two hours after dusk and closing it at least one hour before dawn. But this long of an exposure requires extremely dark skies. Six hours is one-fourth of a day, which equals ninety degrees worth of arc. The best shots seem to be closer to one hundred and twenty degrees, or about eight hours. Therefore, winter is the ideal season for star-trail photography because the nights are longest. Just before and after the new moons of winter you might be able to expose for over ten hours. This time of year also means fewer tourists in the parks to spoil your shots, and the cold, crisp air will let you record the subtle hues of dim stars.

Star Trails and Cactus
A lone Saguaro cactus highlights star trails over Mescal, Arizona.
Eric DeBolt
Awareness of the moon’s cycle is critical. To avoid washing out the star trails in bright moonlight, it’s best to shoot on or near a new moon. However, the moon need not be your enemy. With careful timing, you can record its rise or casting an otherworldly light onto subjects that would ordinarily be silhouettes. Try to select camera positions, lenses, and settings in daylight, but be flexible because things can look quite different by starlight alone.

After experimenting with basic photos, you may wish to add some light of your own for a more creative image. Using different color filters on different parts of the foreground with a little bit of moonlight before closing the shutter can bring various moods to your images.

If you can remember all these tips and add your own creative genius to them, you will be taking fantastic star-trail photos your first time out.