The star test is always the best if done right. If you get a good star test at 50x per inch you are in great shape, but you have to use high power. At lower powers unless the star is precisely centered you may not get accurate results. Be sure to examine a slightly defocused star on both sides of focus for symmetry and concentricity. The image of the diagonal, if applicable, should be centered. Clear Skies Don Colton -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com]On Behalf Of Richard Tenney Sent: Tuesday, August 12, 2003 11:35 AM To: Visit http://www.utahastronomy.com for the photo gallery. Subject: [Utah-astronomy] Lasers and collimation questions The (holographic) laser collimator I use (Laser Max) gets my 16-inch close enough for my taste, only takes a minute to do, and has saved me from having to center-dot my mirror. The times that I've done a star test afterwards has shown a good pattern. Is the star test the best confirmation of collimation, or does the cheshire do a better job? It would be interesting some time to line up a few different scopes of various focal lengths, try different lasers, and compare collimation results with traditional collimation tools and star testing (along with one or more of you collimation pros!). Maybe I've been kidding myself all this time... -Rich --- Chuck Hards <chuckhards@yahoo.com> wrote:
This thread was started merely to gather information on the green laser as a star-pointer, Don, but I agree with you completely. Manual collimation, with a star-test for tweaking is the best way to go, but many folks either can't get the knack or don't want to take the time. Some just like gadgets.
The collimators that project a grid are a step in the right direction. Rich and I used one on my 10" last year, and while it was close, a star-test later revealed that collimation was in fact off by about 1/10" at the image plane. While this may be satisfactory for visual use at low to medium powers, it is totally unacceptable for a "fast" Dob, imaging of any kind, or high-magnification viewing.
Chuck
--- "Don J. Colton" <djcolton@piol.com> wrote:
In my experience I have found lasers worse than useless for collimating Newtonians. See the June 2002 issue of Sky and Telescope for an explanation of the problems. As a test I set up a Newtonian telescope with the diagonal offset almost an inch in the wrong direction and by tilting the diagonal and adjusting the main mirror the laser converged as it is supposed to do; but the star images were terrible. A sight tube, Chesire and autocollimator are far superior for collimation.
Several times I have seen laser collimated telescopes that were dramatically out of collimation with shadow of the secondary far off to one side.
I have not tried the new holographic lasers that project a pattern so I can't comment on them.
Clear Skies Don Colton
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