H-α (hydrogen-alpha) at 656 nm (nanometers) is deep red in color and the most popular narrowband filter. Hydrogen is ubiquitous in the cosmos and is present in emission nebula (North American, Pelican), planetary nebula (Dumbbell, Ring), Wolf-Rayet objects (Crescent, Thor’s Helmet) and supernova remnants (Veil). Many imagers like to present just a black-and-white H-α image of an object. It is has a beauty all by itself, like an Ansel Adams photo. However, most imagers blend their H-a data into their red RGB data to enhance structural detail while maintaining a “natural” look. Therefore, the H-α filter should be your first narrowband addition to your LRGB filters. The basic imaging set of 5 filters becomes LRGBH-α.
Astrodon H-α filters have a center bandwidth of 656.3 nm