Shooting Out Your Back Door

Jack Kramer

Well, that's not literally shooting out your back door; we're talking about taking uncomplicated, fairly quick photographs of the night sky from your backyard. There is a major difference between this venue and what you might photograph from a dark sky site. First of all, we live under an umbrella of light pollution that makes long exposure photographs impractical. However, many people are surprised to discover that some interesting results can be achieved from their backyards with a single lens reflex camera mounted on a stationary tripod.

Exposures of up to 15 seconds will allow you to capture objects such as stars or planets without them showing any trailing. For these exposures, you would use about a 50mm lens set to its widest (lowest f stop). A wider field lens allows longer exposures, and a telephoto will require that the exposure be shorter in order to avoid trailed images. An object lower in the sky moves "faster" than an object at the zenith, so this also will affect how long your exposures can be. Use the "bulb" shutter setting. Even cameras with electronic shutters work just fine with these relatively short exposures without running down the battery by keeping the shutter open for an extended period. (That's a feature that makes the old mechanical shutter cameras desirable for long exposure work.) The faster the speed of your film, the shorter your exposures can be. A fairly fast film with a speed of at least ISO 400 will net you quite a few stars -- including many that are barely visible to the naked eye. If the moon or a bright planet is included in the shot, it will usually be over-exposed; if they're your primary target, then drastically shorten your exposure. As the exposures become longer and/or you use a faster film, the sky background becomes appreciably lighter due to the cumulative effect of light pollution. The advantage of a slower film is that it normally has a finer grain, and this allows a more pleasing image if you decide to show off your work with a large print. Also, be sure to use a cable shutter release so as not to cause vibrations by touching the camera.

With the forthcoming increase in solar activity, we can expect more northern lights. These can be captured with a 10 second exposure on film as slow as ISO 200. Obviously, a faster film will allow you to shorten your exposures and "freeze" some of the fast-moving auroral streamers. Be sure to bracket your exposures by taking several of different length.

If you take slides to show at a club meeting, don't worry too much about a bright background. Because of the distance to the screen, the projected image will be fainter than you might expect. It's more important that the star, planet, or aurora images be as "dense" (i.e.: bright) as possible, and what looks like a bright sky background through your slide viewer will project surprisingly dark. Print negatives generally do not convert very well to the slide format; they often come out looking more grainy than the print, with a lighter sky background.

Having given this a try, you will then be able to add "astrophotographer" to your resume!