With the equipment upgrade completed it was now time to collimate the 12″. I proceeded in identical fashion to collimation of my 10″ which you can read here: https://daveandtelescope.wordpress.com/2013/12/24/collimating-the-at10rc/
Now I try to keep things simple and certainly don’t pretend to know more about collimating these optics than the folks who built the thing! They provided instructions which I basically followed. I used the Cheshire eyepiece for visual collimation first. The primary looked as well aligned as visual inspection could ascertain. The secondary mirror was centered but the black dot of the viewing aperture was slightly off center, so as instructed by the manufacturer I adjusted the secondary until the dot was centered. Then I went to the star test with CCDWare’s CCD Inspector (see earlier post, link above). Now once again nowhere does it say to adjust the primary during the star test. ONLY the secondary should be adjusted according to these instructions from Astro-Tech. The vector diagram is provided by them that tells you how to move the star image using the secondary. Now initially the collimation was 15-20 arc sec. By adjusting the secondary repeatedly in small increments I was able to bring it down to under 5 arc sec which is my usual goal. I have had people tell me this doesn’t work for them. I accept that. All I can say is 2 times now with 2 different scopes I have been able to accomplish near perfect collimation with this method, which in summary is:
1) Visual collimation with Cheshire. Check primary alignment first, then secondary. If primary is not aligned then adjust. If primary is aligned then check secondary and adjust accordingly
2) Star test. Align secondary based on measurements from the CCDI program