Most astronomers agree that the best way to collimate reflective optics is to observe a star through the scope, examine the concentricity of its diffraction rings on either side of focus, and adjust the optics until the rings are perfectly concentric. Collimation using a star in this way is even more sensitive to minor optical misalignments than using a laser to collimate the scope. Many advanced amateur astronomers with very large aperture scopes will do a final collimation tweak on a star even after
collimating their scope with a laser.
The Astrozap artificial star is designed to provide a steady, stable reference light source to be used in lieu of an actual star for this type of precise collimation. It allows you to collimate your scope without worrying about your mount’s polar alignment, star drift, or seeing conditions. The battery-operated Astrozap artificial star is a very bright, pinpoint source of light with a consistent brightness level equal to that of a first magnitude star. It will produce beautiful diffraction rings when defocused in any eyepiece.
The Astrozap artificial star can be used at star parties to provide a collimating star for everyone’s use. It never moves, so there are no tracking or centering issues to worry about, as there are with a real star. This makes it ideal for collimating a Dobsonian-type non-driven scope. Over the short star-to-scope distances it is used, it is unaffected by atmospheric disturbances so you can get an accurate collimation under any seeing conditions.
How far the artificial star should be from the telescope depends on the telescope. For an 8” Schmidt-Cassegrain, the recommended distance is approximately 100 feet. The minimum distance should be no less than 50 feet. The further away from the scope, the better, until you start losing contrast in the eyepiece. Indoor use is a possibility, although it is recommended that you do the collimation with the scope in the field to avoid the chance of knocking the scope out of collimation during transport to your observing site.
Collimation, in its simplest terms, is the proper alignment of the mirrors or other optical surfaces in a telescope. A telescope that is out of collimation, with its optics not at the correct angles to the light path, typically will not perform as well as a smaller telescope that is in collimation (even one as much 25 to 50% smaller in aperture). So, even if you put considerable extra money into buying a larger telescope, you won’t get the all optical benefits you paid for unless that larger scope is properly collimated. Also, no telescope will reach a truly sharp focus at high powers unless its collimation is perfect. Careful collimation is well worth the time and effort.
One of the feature images below shows the diffraction rings of the Astrozap artificial star using an optical system that is both in and out of collimation. The photos were taken with an 8” Schmidt-Cassegrain using a modified webcam at prime focus. The image on the left shows the properly-collimated scope. The image on the right shows the same scope out of collimation. The artificial star distance was approximately 50 feet from the telescope. Even though this picture was taken on a 95° summer day just before dusk, note the complete lack of any atmospheric disturbance in the shape of the rings.
The Astrozap artificial star features an 18,000 millicandela output ultra-white LED focused on a 100 micron precision laser-drilled stainless steel aperture. This gives a pinpoint of light with brightness level equivalent to a 1st magnitude star. It is powered by two user-replaceable AA batteries. The artificial star is housed in a lightweight but rugged plastic body, with the protectively-recessed light-emitting aperture at one end and a simple on/off switch at the other. There are no adjustments that need to be made to operate the artificial star. Simply turn it on. The artificial star has three rubber feet so it can be mounted on a table or uneven surface, such as a tree trunk or the top of a stone wall. It can also be attached to a standard photo tripod using the 1/4”-20 thread adaptor built into the bottom of the unit.
The procedure for collimating your particular telescope should be outlined in its manual. Please read the instructions there first. It will tell you the location of the collimation screws and any cautionary notes concerning collimation adjustments.