For an astro newbie, collimating your SCT can be fairly intimidating. The process doesn’t really sound that complex. But . . .
Last Saturday night was one of the best nights for astrophotography after weeks of clouds and rain. I was determined to not let it go to waste. Beginning the preparations just before sunset it wasn’t long until I had everything ready. PoleMaster, Starsense, focus; done, done and done. Then I starting thinking about that little nagging, less than perfect, shape I was seeing in my stars after stacking. No problem. Just take a few minutes tweaking the collimation and then move on to astro bliss. Right? Wrong!
While I could spend a few paragraphs describing how my donut shapeshifted into something that looked more like a crab from Neptune than a donut I will instead spare you the horror of it all. I ended up throwing in the towel fearful I had turned my expensive telescope into an expensive ‘thing’. I was just going to tweak it. I went to bed having wasted the night.
Next morning I got up and began watching every Youtube video I could find about collimating a SCT. Read forums. I reviewed all those tools and procedures. Found a guy who would fix it for $475 plus shipping. Of course after it was shipped back the first thing you would want to do is collimate it. Hmm? Then I remember reading “Of course if you have an SCT you do not need any of those tools”.
I am the proud owner of an artificial star which was purchased for just such a task. So I stripped everything off my OTA, removed it and the mount from the pier and brought it all into the house and set it up on its original tripod. Found the furthest line-of-sight through my house and carefully placed my artificial star in view of the SCT.
Step 1: I turned my OTA vertical with the secondary mirror pointed straight down. I tightened all three of Bob’s knobs so the mirror was fairly level and down against its own housing.
Step 2: I unscrewed ONE of the knobs while counting the turns (albeit partial turns) and then divided that count by 2 and screwed it back in by the result. Repeat for the other two knobs one at a time.
Step 3: Find, focus and center the artificial star. Defocus forming the airy disk i.e. la donut.
(Note: Upon completion of steps 1 – 3 the crab was dead. I now had a donut. Far from perfect but I felt like I once again had an expensive telescope and not just an expensive thing.)
Step 4: Hold a pen (or stick or finger) in front of the aperture lined up with one of the adjusting screws and look through the eyepiece to discover its location. Do this with each screw and note the screw that is nearest the narrow part (wall) of the donut.
Step 5: Using ¼ turns (or less), turn that screw clockwise. Turn the other two screws counterclockwise the exact same amount (or as close as humanly possible)
Step 6: Repeat step 5 again and again while re-centering the donut each time. Re-centering is critical and must be done before each adjustment. Else the crab from Neptune may return.
After following this procedure I achieved a donut so symmetrical I seriously could not see the slightest deviation.
And of course now the clouds and rain are back in the forecast. Ya gota truely love this hobby or you will end up in a padded cell playing with your toes.
Hope this helps someone. Clear skies and moonless nights.
Edited by HumblePie, 02 June 2020 - 10:07 PM.