Camera and Tripod Astrophotography

     You might be surprised to find out that you can do astrophotography without a telescope. But yes, it's true; all you need to take a picture of the sky is a camera and tripod, and perhaps a cable release to trigger the camera. Of course, your pictures will be limited to wide-field and not close-up views of the sky, because magnified views (through a long focal length lens, for example) will probably have trails in them (more on this later), and even if your aim is to photograph trails, you won't capture very many with a close-up view. So what are the subjects you can photograph? Well, practically any constellation is good game. Also up for grabs are the Milky Way, planetary and lunar conjunctions, and even some bright comets. You can even capture some deep-sky objects such as bright nebulae and star clusters, but not in close-up detail. Photographing from a dark, non-light-polluted site will help you capture deep-sky objects and the Milky Way, but this is not a necessity for constellations, the moon, and planets.

     So let's say you've got your camera, tripod, and cable release ready and want to take a picture of the sky…what should you do?

     Well, first of all find what you're photographing! If you're an experienced sky-watcher then this should not be very difficult. If it's a constellation you're after, for example, you'll know where to look. For those not as experienced (and for special events such as conjunctions), there are many aids you can use to figure out what will appear in the sky and where. These include sky charts, magazines, websites, and software such as Stellarium or Starry Night.

     The next step is to focus your camera on the sky. To ensure the best focus, point your camera at the brightest star or planet in the sky, and use that to focus. It is important to realize that setting the camera's lens to "infinity" won't necessarily be the best focus for the sky. The best focus is usually very close to the "infinity" setting, but you'll probably want to take several test shots of the bright star or planet to find the best focus. Take a short exposure around a few seconds, and see what you get. Re-adjust the focus and take another test image, and repeat this until you get the best focus. You'll find that as you go closer to the best focus, the star's image will become smaller, and as you move away from proper focus, the star's image will become bigger, and it will form a disc which is larger and larger the further away from focus you are. If your camera has live-view focusing, you may not need the test shots as a bright star will probably appear on the camera's preview screen. With both test shots and live-view focusing, the best focus is when the star you're focusing on appears smallest.

     The next step, once you've focused, is to center your object of interest in the camera's viewfinder, which can in fact be a bit challenging. The reason is that with many cameras, the image in the camera's viewfinder can be quite dim. The solution is, like with focusing, to take a few test shots. While your camera is pointed where you think it's right, take your first test shot. Then, use this test image to re-position your camera until you get the object positioned where you want it. This isn't too hard to do, and I think you'll find this method will work quite well.

     Of course, if you're photographing something bright like the moon or even planets, you'll find focusing and positioning through the viewfinder (or live view) easy enough that you probably won't need test shots. The test-shots method described above is mainly for focusing and positioning dim objects.

     So now that you've got your subject front and center, you're ready to take your picture! The next step is to figure out what settings to use on your camera in terms of ISO, f-ratio and exposure time. There is no set rule to this, but understanding what the parameters mean will guide you. Try a high ISO and low f-ratio for dim objects such as the Milky Way, but be aware that this will introduce noise and lower the contrast of your image. If you don't want trails in your image, maximum exposure times will be around 20-30 seconds for a 50mm lens. This time will be smaller if you're using a larger focal-length lens or if you're photographing far from the celestial pole (Polaris in the North). You can increase this time by using small focal length lenses and photographing close to the celestial pole. Still, the maximum time you can expose with any lens or sky-coordinate will probably not be more than 2 minutes.

     So that's it! Now you should be ready to take astrophotos with only a camera and tripod! Below are some pictures that I took using camera and tripod photography:

Cassiopeia between two trees. Film SLR camera, 15 second exposure:

Cassiopeia from a dark site. Notice the much greater amount of stars that appears! Cassiopeia has been outlined. This is a combination of several 30 second exposures (the combination, called "stacking", was done to reduce the noise in the image; I will explain stacking in a future post). ISO was 1600. 18mm focal length, f/5.6.

The moon and Venus at sunset. A simple 1.3 second exposure at ISO 400. 23mm focal length, f/8.

Thanks for reading :)

and clear skies!