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SCT Telescope Collimation (With NO fancy tools)

Dylan O'Donnell

66,498 views

Being out of collimation is not fun. Trying to collimate an SCT telescope can cause serious mental anguish. So instead of reading the instructions, you should watch this video first so you know what you're doing. Disclaimer: I don't know what I'm doing.

Shout out to High Point Scientific who know what they're doing.
https://bit.ly/3oW0PMx

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Celestron 11" Edge HD Telescope
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Celestron RASA 8" F2 Telescope
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Intro Music - "Moving the Ocean (Aerologic Edit)" by Blastculture.
Slow City by Enzo Orefice (via Storyblocks)
Lofi - Aces by STÉ (via Storyblocks)
Learning to Fly by Michele Nobler (via Storyblocks)
... and something guitar thingy I just made up.

20 Comments

@DylanODonnell Creator 3 years ago (edited) Pinned

Thanks for watching! And thanks also to @MarkusSchierz and @jesuspineiro1622 for reminding me that if you want to dial collimation in perfectly, you should recenter the star as well after each adjustment. Lots of love for Bob's Knobs too which I understand .. it's a great product. I found they didn't hold collimation for as long as the factory screws in the past and local stockists didn't have the zinc plated options I need in this case.

Also .. you should loosen opposite screws first and then tighten target screw. I do this a bit in the video but don’t say so explicitly.

And yes.. do be careful waving your PP around the scope glass in the dark :)

@robertlowenthal689 2 years ago

This video was a lifesaver for my C9.25 Edge HD. I replaced the stock screws with Bob’s Knobs and messed up the collimation to the point where I had no idea where the secondary was pointing (my fault, not Bob’s). I felt hopeless and had no idea how to fix it. After watching your video, I removed the secondary mirror and adjusted it using a screwdriver shaft as a feeler gauge. I got it close enough that I was able to collimate the telescope in about 5 minutes. I hadn’t realized that I only needed to move the screws by a fraction to adjust collimation. Thank you!!!

@FlankerOneTwo-n3m 3 years ago

Thanks for the video! I replaced the Philips head screws on my EdgeHD secondary holder with M3 hex head screws, as I find that the long arm of the hex wrench makes it much easier to reliably make small adjustments, rather than aiming a pointed screwdriver towards my corrector plate and trying to guess how much I turned it the round grip. Much less prone to slip as well. One additional note is that collimation on a defocused secondary shadow is still relatively rough collimation, and is more an indicator of mechanical centering of the secondary mirror relative to the primary optical axis. However, because the SCT secondary is spherical and therefore has no optical axis of its own, centering is actually neither required nor sufficient for exact collimation (centering is extremely important for Hyperstar however, as it has a very strong optical axis). To dial in exact collimation, it is still desirable to actually examine the Airy disk and rings of an exactly focused, centered star. This after all is what the image is composed of, but the problem is that seeing often makes this difficult. I've found that the best solution for me is to use Metaguide (free) - its live stacking and high frame rate make examination of the Airy disk and first ring feasible under most reasonable seeing conditions, and the coma detection feature is much more sensitive than I can detect by eye. Lucky imaging on planets is where you'll really see the difference, as the scope is then (hopefully) diffraction limited rather than seeing limited and typically much more highly sampled. I'd be interested to hear your thoughts on it if you decide to give it a try!

@brandonrunyon 3 years ago

I fixed my collimation by buying an esprit. Also, happy to see your kid out and about.

@billbean5912 2 years ago

Best collimation video I’ve ever seen. Thank you.

@joedenisco6033 3 years ago

Dylan, That was priceless. The thin side needs to be tightened to PUSH it away from edge. Very easy to remember!
Thank You, and I really appreciate all the advice you give to the community.
Joe D

@meadmaker4525 3 years ago

Great video, but I kinda feel like Celestron needs to maybe go back to the drawing board and design a better mounting plate for that secondary mirror. No reason they can't machine a plate that mounts the mirror at perfect "zero" once the screws are installed, without mirror flop or lopsided attachment. As it stands, it's EXTREMELY fiddly and more than a little delicate. Can't understand why they left it the way it is, but maybe there's something I don't know.

@robertsipes7391 3 years ago

First off, I think it is great that no matter what string of short clips you use in the intro to Star Stuff, that you include the one where you chuck the can toward the observatory dome. I must say, from the beginning days of your channel, that one has always been my favorite. I have said that the day Dylan O'Donnell leaves that clip out of his intro, that will be the day he has lost his soul for astrophotography. Oh well, I have a 2008 Celestron CPC1100 that needs collimation. Thanks for sharing and thanks for being Dylan. I hope your family is doing well also.

@aaronwmorris 3 years ago

Meade SCTs are a bit different. Celestron secondary mirrors pivot on the central axis bump as you showed, but Meade secondaries use springs for tension instead of the central axis. A Meade SCT can be returned to the flat collimation by finger tightening all 3 screws all the way in (per the manual).

@rosscayley8773 3 years ago

Nice Dylan. Another really quick and easy way Ive found for 'roughing in' an SCT collimation thats way off (especially easy with Bobs knobs) is to view the symmetry of the secondary vs the primary (and vs the baffle tube) by looking directly down the optical axis from the objective side, in daylight. By adjusting the viewing distance you can vary the relative size of the secondary and its obstruction of the primary, so that any asymmetry becomes obvious as an uneven 'ring' of primary mirror showing around the secondary. Its really easy and intuitive to adjust until it looks even, and you can do it during the day. It works so well that, in my experience, the subsequent star test becomes more a confirmation of good collimation than an additional step.

@k-d-n 3 years ago

Instead of a star, I always use a powerful flashlight covered in tinfoil, with the smallest hole you can possible make with a needle. This way you don't need the mount, and you can collimate your telescope indoors.

@Photomanguru 3 years ago

Thank you so much for taking the time to make this top quality instructional video, I stopped looking for answers after I saw this. Keep up the GREAT work!

@jeffbennett4461 7 months ago

After hours of struggle, I think I beat my collimation issue. I used my own stuff modeled after your video. I did it! Im so darn proud of myself right now!!!!!! My stars were looking weird, so I decided to try the first collimation moon this scope from the factory. I decided at the same time to install set of Bob's knobs. I tried collimation using the installed screws, but it was almost impossible. I finally got it. WHEW, what a journey down a rabbit hole. When you have to take the secondary mirror out and re-install it by measuring the level with a micrometer. It was a journey, but now it's all running perfectly (hope), stars are razor sharp, focus routine is ending at 99-100%, really unbelievable. Now I know it was out a bit, but more importantly I know how to do it.

I just wanted you know how happy I am right now. This was a big hill for me. I considered tossing some very expensive gear in the trash. Thankfully, I calmed down.
Thank you again

@MakeAMark 3 years ago

Hey Dylan -- one of the most useful videos out there for SCT users. Thanks for digging in on this. I know there are a lot more subtleties to collimation, as pointed out in some comments, but this video really is helpful.

@allenbaylus3378 2 years ago

got stuck before - bobs knobs - on my Meade 8 inch SCT.
The star kept on moving out of the view on my ASIAIR - I will try again - I only wish it wasn't winter temps outside now.

It's always inspiring to see other people do this with success.

@MarkusSchierz 3 years ago

Great video. However i think you forgot to recenter the star after your adjustments. For my c8 that makes a difference.

@steppen57 3 years ago

I am so scared of collimating my C8. I checked the collimation just a couple of nights ago, and it looked fine. But I will likely come back to this video. You make it look so darn easy. Thank you for this very instructional video. Love the closing as usual.

@astrojudebob 3 years ago

Thank you for the video. Perfect timing. I was going to collimate on the next clear night.

@deep_space_dave 3 years ago (edited)

Ah I miss those days when I had an SCT as collimation was so easy. Now I'm a masochist with a RASA and it's dredded tilt 🙂 One piece of advice though, after getting your out of focus star, do a counter clockwise turn of the focuser to level out the mirror as it likes to flop around. Collimation will be more accurate that way. This was the most clear and complete video on SCT collimation, so well done Dylan! BTW Bob's Knobs are cool but I heard that the regular screws hold collimation better. Thanks for the video and clear skies!

@amritseecharan848 3 years ago

One of your best videos so far. Very very clear instructions. I image from Trinidad, and would like to share my images with you. Jupiter and Saturn are looking better every passing day