There are some frightening online postings regarding attempts by other users to collimate the AT8RC telescope. Hmmm. This does not sound good. So, I dug out and read the manufacturer instructions. My takeaway? DO NOT mess with the primary mirror screws! Check. From my readings, those who have, managed to truly make it worse and then spent many hours, days, and other tools to get it back. This should be simple, why is everyone making it sound so hard?
The Astro-Tech collimation instructions emphasize use of a Chesire eyepiece with a light source. This kind of eyepiece has a mirror with a center hole, and the mirror is tilted precisely in a 45 degree angle such that you can visually inspect the appearance of concentric rings with an external light source. Well, my vision ain't what it used to be, so I used my Orion LaserMate Deluxe collimator which is a chesire piece with a laser as your external light source. Brilliant. Much better than my visual acuity.
Removed the extension rings and put the focuser assembly directly to the back of the scope. Turned on the laser collimator. Surprise! The secondary was not in collimation. The return beam point was off center by at least one of the LaserMate's target rings. Out comes the Allen wrench. Took a few minutes to figure out the "loosen-tighten" pattern on the secondary adjustment bolts, then fairly quickly centered beam point and tightened alignment screws. Cool.
Next step in collimation, the star test. Results will be in the next post.