Few technological advances have impacted astronomy as much as the digital revolution. That’s been true in the professional realm since the 1980s, and it’s been true for amateur astrophotographers like us since the turn of the millennium. Perhaps nothing illustrates this seismic shift more vividly than comparing historic photographs of the Moon with their more modern counterparts.
For instance, take the great lunar crater Clavius, imaged in the 1950s with what was then the world’s largest telescope, the 200-inch Hale telescope at Palomar Observatory. If you compare that shot with a corresponding image taken in 2005 using a standard 14-inch consumer scope and one of the first commercially available CCD cameras, the differences in resolution, sharpness, and dynamic range between the two are striking.
So, what are some of the tools and methods for cutting-edge lunar imaging now available to those with telescopes suitable for amateurs (6 to 14 inches)? Apart from good optics and a solid mount, most practitioners can employ any number of excellent webcam models or laptop computers (with appropriate image-capture software), as well as sophisticated image-stacking and processing software. In addition, for close-up, high-resolution imaging of select lunar features, quality Barlow lenses or Powermates — which both extend focal lengths — are essential, as are atmospheric dispersion correctors and, typically, near-infrared filters to minimize the effects of less-than-perfect seeing conditions.
Shooting from his home near Brussels, Belgium, one of this article’s authors, Leo Aerts, routinely uses a custom-built Opticon 10-inch f/15 “planetary” Schmidt-Cassegrain (with only a 25 percent central obstruction) and a Celestron 14-inch f/11 scope, both on movable Losmandy G-11 equatorial mounts. The telescopes are stored in his home garage and wrapped in thermal insulating material to prevent overheating during daytime hours.
Although Aerts has used many older model webcams, including several DMK CCD models, they operated at relatively low capture rates of 30 to 60 frames per second (fps). His current favorite cameras are ZWO CMOS models, an ASI 178MM with a 2.4 micrometer (µm) pixel size, and an ASI 290MM with 2.9 µm pixels. These models perform very well up to 150 to 250 fps, with low levels of noise and high infrared sensitivity. Aerts also routinely uses an AstroTechniek atmospheric dispersion corrector, especially when his target is below 40° high in the humid Belgian skies. These handy optical devices have two rotatable prisms made of silicate glass, which can be adjusted to introduce a degree of native chromatic aberration that counteracts that of our atmosphere.