More evidence that the star-test is the best method of collimation. June S&T, page 94, "Secrets of Telescope Resolution" by Daniel W. Rickey: "It's important to note that the difficulty of achieving and maintaining collimation increases quickly with decreasing focal ratio. For example, if you use a laser collimator to align the optics of a 200-mm f/4 reflector, the returning beam of light must fall within 0.35mm of it's target, which is much smaller than the central hole in most collimators. However, for a 200-mm f/8 instrument, the returning laser beam must be within a relatively achievable 2.8mm of center. Obviously a laser collimator alone isn't going to be enough for a fast telescope - the alignment must be fine-tuned by star testing." I've seen this quite often, especially with larger, truss-tube Dobs that must be assembled before each use. The resolution is rarely what the aperture is capable of, and often really bad- even when the owner has used a laser to "collimate" the optics. (Those grid-projection types are even less dependable.) These folks should take the time to familiarize themselves with the diagnostic capabilities of diffraction rings. It's well worth the effort, and doesn't take much time once mastered. Another benefit is that you can detect other optical problems besides poor collimation. Strain, surface irregularities, over/under correction, etc. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com