For those of you who are obsessive about technical details, love to tweak technology without manuals or directions, and have a very high frustration tolerance, astrophotography may be for you. My experience has shown that most photographers of the enthusiast and above level are technofiles, with a keen affinity toward precision gadgets, be it cameras, iPads, or watches. Enter the astrograph, a telescope designed at least in part for astrophotography, and the motorized equatorial mount, which together take the need for precision to absurd new heights. Pixel peeping is not only recommended for developing the craft of astrophotography, but is pretty much a requirement. Discovering that the smallest stars in my photographs are 3×4 pixels instead of 3×3 pixels, in other words that my stars aren’t round, is cause for many nights worth of tweaking and heading scratching. In the sport of astrophotography, an improvement of 1 pixel is considered a success. If you usually don’t have the patience to use a tripod for your landscapes, you can stop reading now, because your shiny new telescope will simply end up on eBay. Now that I’ve scared off the run and gun photographers, let’s get down to a few things that I’ve learned by trial and error, with an emphasis on error.
There are essentially three main challenges to astrophotography, your subject is usually small, always in motion, and very dim. In other words, astrophotography is hard because of the precision required to get round stars with the long exposures needed for dim, highly magnified celestial objects. The earth spins on its axis and creates an apparent motion of the heavens. To stop that motion in a photograph, so as not to have star trails, you need either a very short exposure or the ability to exactly counter the earth’s rotation with a telescope mount that tracks in precisely opposite direction and speed. The only celestial objects that are bright enough to use short exposures are the sun, moon, and to some extent a couple of planets. Pretty much everything else needs tracking. While the motion of the stars to the unaided eye is imperceptible over a few seconds, like watching the hour hand of a clock, the high magnification of a telescope also magnifies that motion. With long focal length telescopes and no tracking mount, the stars will zoom out of view in a few seconds, leaving streaks across your photographs as evidence of their passing. As the telescope focal length and corresponding magnification increases, so does the requirement for precision tracking and precision optics. Likewise, the cost of the system quickly increases to the point where you could buy a new car instead. I decided to get in at the moped level.
The image of Andromeda Galaxy is a single 5 minute exposure at ISO 800. The image was heavily processed to bring out the relatively limited image data found in a single frame. Andromeda, like almost all celestial objects, will benefit from stacking multiple long exposures. Through stacking, image noise, which results from high ISOs and long exposures, can be averaged out and subtracted from the stacked image files. This leaves cleaner image data that is not lost in background noise and results in better detail and color. You can expect an imaging session of several hours to include only a couple of subjects. Most of the time is spent acquiring a series of sub frames, or subs, of each subject for eventual stacking and processing.