If you're a space geek like me, you know that this has been a great season. Not only did we get to witness the extraordinary transit of Venus across the sun in June, but we also enjoyed a spectacular annular solar eclipse in May. And more recently, NASA announced that one of the Voyager probes has finally left the solar system for interstellar space.
Such events turn my attention to astrophotography. Some time ago, I told you how to shoot the moon, and I've also explained the basics of shooting star trails by using very long exposures. This week, I'll focus on shooting star trails by taking lots of relatively short exposures and then combining the results.
Astrophotography for Beginners
You have a lot of ways to capture the beauty of the night sky with a camera, but shooting star trails is among the easiest, mainly because you can do it with almost any camera. There's something magical about these kinds of photos, because they reveal the mathematical precision of the cosmos generally hidden from the naked eye--it's easy to see that the earth spins under a blanket of stationary stars.
Photo courtesy of Flickr user Moyan_Brenn
To take a star-trail photo like this one, all you need is a camera with a manual exposure mode; such a camera will let you dial in the shutter speed and aperture setting independently. To make things easier, you'll want either a remote shutter release that you can lock (so that the camera takes photo after photo with no intervention from you) or an "intervalometer" mode, in which you can schedule the camera to take a set of photos automatically. Check your camera's menu or user guide to see whether it has such a mode.
Taking the Shots
Ready for some astro action? Get started while there's still a little light left in the sky. Set your camera on a tripod, and compose the shot so that it includes something interesting aside from the stars. You might want to include some buildings, for example, or an unusual arrangement of trees or mountains. Including even a simple group of trees, as in the photo here, is better than just pointing the camera straight up into the empty sky.
Check your camera's settings, too. Since you're going to combine a large number of shots into a single photo, make each shot a brief exposure to minimize digital noise. Set the ISO to 400 or 800, and open the aperture all the way, to f/4 or the smallest f-number your camera supports. Finally, set the shutter speed to 30 seconds.
If you have an intervalometer mode, tell your camera to take one photo every 30 seconds for several hours. (You might need to make that every 31 or 32 seconds, since some cameras "miss" every other shot if the shutter speed is exactly the same as the shooting interval.)
If you don't have an intervalometer, attach a remote shutter release to your camera and be ready to lock it down so that every time one exposure is completed, it will automatically start the next, until you choose to unlock it.
That's everything you need for the setup. I like to start shooting before the sky is completely black--you'll find that if even a few of your photos capture a deep-blue twilight sky, it will add a rich color to your completed photo. Now just start shooting, and leave the camera alone for several hours. How long is long enough? You can get a nice photo with 75 or 100 photos, but the longer you can shoot the sky, the longer the trails will be. Try for 300 photos.
Stacking the Exposures
Thankfully, taking the photos is the hard work; stacking them together is not much more complicated than the process for making a panorama in an application such as Windows Live Photo Gallery. You'll need a specialized star-trail stacking program; I recommend two, both of which are easy to use and free. Startrails is a good choice because it can not only stack your photos but also make an animation of the stars rotating in the sky. StarStax is a similar program, but it lacks the animation option.
To use Startrails, for example, simply download the program and copy the folder to a location on your PC (the program requires no other installation). Run Startrails by double-clicking the icon in the program folder.
Select File > Open, and choose all of the photos from your star shoot. Then, click Build > Startrails. A few minutes later (it might take a while on a slower PC, or if you have hundreds of photos), you'll end up with a completed photo that you can save to your PC.
Hot Pic of the Week
This week's Hot Pic: "Hong Kong at Night" by Paul Bild, Vancouver, British Columbia
Paul says: "I took this photo with a Canon Digital Rebel XS and a Tamron wide-angle 17-50mm lens while taking a cruise to Asia. While stopped in Hong Kong, I found myself on a pedestrian bridge between two buildings. I placed the camera on the side wall, and took the shot using the camera's self-timer. I corrected the white balance from the RAW image, and I used my photo editor's Perspective Correction tool to correct the wide-angle architectural distortion."
This week's runner-up: "Eagle" by Karl Rudlaff, Waterford, Michigan
Karl says that he shot this photo with a Nikon D200 while on a recent trip to Alaska. "We were on a small boat at the time, so I had to shoot hand-held."
Visit the Hot Pics Flickr gallery to browse past winners.