I actually have no trouble using my Cheshire after dark. I took a white piece of paper & taped it over the outside opening. Then I shine my red flashlight on the paper. The paper diffuses the light enough to create an evenly illuminated background to see the centerspot edges. In the book that came with the collimation tools "Perspectives on Collimation" they actually recommend you re-collimate every 1-2 hours to compensate for thermal variations as the mirror cools. It seems hard to believe that slight thermal variations would make enough of a difference as to affect collimation, am I wrong on this? --Paul ---------- From: Josephine Grahn Sent: Tuesday, August 12, 2003 7:13 PM To: Visit http://www.utahastronomy.com for the photo gallery. Subject: RE: [Utah-astronomy] Lasers and collimation questions Don et al., I highly suggest that people read and spend some serious time at the Mel Bartels website. It will clear up a lot of misconceptions, and get you well on your way to a properly collimated scope. http://zebu.uoregon.edu/~mbartels/kolli/kolli.html It's best to use a sight tube to get you very close on the diagonal orientation. Then a simple (non-holographic) laser can be used to fine tune diagonal orientation and for adjusting the tilt of the primary. Perhaps once or twice in six years that we've tried, has the seeing been good enough to tweak the collimation of our 16" scope at adequately high power; and never good enough for the 24". Lasers are great for collimation because they can be used at night; but the assumption is made that the mechanical center of the mirror is the optical center. A Cheshire is a great tool, but not convenient if you want to tweak collimation after dark. A laser is a worthwhile addition to your toolkit. I hate to see people leaving with the idea that lasers can't do the job, they can do an excellent job. Jo Grahn _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy