Celestron C11 SCT Disassembly

Learn how to completely disassemble and then reassemble a Celestron SCT. Whether you have a 6", 8", 9.25", 11" or 14" SCT you will be able to do the same with you telescope once you watch this video. The video goes through step by step so that you know exactly how to do this for yourself. The whole process was intended for several improvements to the C11 which we will go into detail about in another video. During the process of disassembling this video we think we discovered a flaw in the Celestron motorized focuser which can contribute to mirror flop. In a separate video will will show the problem and two different ways to fix it.
This is the companion video to two other videos on the C11:
1. Celestron 11" SCT Modifications: To be released soon
2. Celestron Motorized Focuser • Celestron Motorized Fo...
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[@smsandel]

Good video. Save most of your headaches by using anti-seize lubricant on all threaded connections. Most of these threads are aluminum to aluminum direct contact and the simplest preventative for stuck threads is anti-seize lubricant.

[@seansmith908]

Great video, you know its a real shame that the manufacturers don't provide some videos from their repair and support departments. Seeing how they get these scopes back into shape would be amazing for those that can't afford to send them in.

[@astronomytipsreviewswithcu740]

I agree fully.

[@Rich-hy2ey]

Not just cost. It's always a risk shipping an SCT.

[@RobertKarlBerta]

i have worked on many Celestron SCTs from 8" to 14" with complete dissassembly to assembly with many tweaks. Word to the newbies....it is actually fairly easy to do BUT you do need to take your time and use extreme care. Generally the service is necessary when the corrector plate comes slightly loose so it Rotates in place. The corrector plate and mirror are indexed to each other....in other words they must be put back at the stock orientation for best performance. I recommend that every owner of a SCT when new....use a Pentel permanent fine tip marker marker to mark a spot on the very edge of the mirror with a dot that is lined up with a given orientation of the mirror. I usually mark the 3:00 postion when standing in front of the scope and looking directly at the corrector plate. If you have a Hyperstar or Fastar capable version there will be a keyed slot that the secondary goes in to ensure the correct indexing. That slot will be at the 3:00 position so now you see why I use that point as the reference point. In addition the corrector, if it comes loose, can move a bit out of perfect alignment. The corrector, mirror, and secondary mirror need to be perfectly centered and indexed for best performance. You can actually see if it is centered by standing in front of the scope and looking into the scope. You should see all the reflections, cleaerances, etc. and it is very easy to visually center everything. I actually don't like removing the scopes outer tube from the rear casting. I know how to remove the secondary to gain access. Generally I figure if I am going to this much trouble I want to make sure the secondary, corrector plate and especially the Fastar/Hyperstar secondary holder is solid and centered. Once you are sure the scope optics are aligned and solid....you need to do a GOOD colimation. This is easy to do if you learn how to do it...and it is worth learning as it takes just a few minutes and the performance of your SCT will never be good without a good colimation. I have met people who say that their scope was never colimated and that it doesn't need it. I say give me a few minutes and I will check it out. Usually they are so far out (and poor performance) that when I am done they are amazed. I have two 11" and one 8" SCT and manage an observatory with a 14". All four scopes are really great optically. About 8 years ago I did a demonstration to a large meeting of three clubs where I dissassembled one of the 11" scopes and went through the entire process. Took me about an hour even with Q&A. Generally though I don't recommend going though any of this unless your scope has a major issue such as a loose corrector plate. I recommend that you send it to Celestron for service. As far as dust on the corrector plate, in the scope, etc. It won't make ANY difference and you have a lot more chance of making it worse if you screw up.

[@astronomytipsreviewswithcu740]

Good input!

[@repairengineer]

I agree, I just took my C11 apart and as long as you mark the corrector and put it back this isn't a big deal. Just don't scratch the parts. If your scopes are like mine and not bran new then be careful and go for it.

[@tubedude54]

This looks helpful. I have a 2001 or 2 Nexstar 11 that I need to remove the corrector plate and put a gasket on the secondary holder to tighten it up. What I have read is that C put a gasket that holds the corrector plate in position and that it pretty much 'cements' itself over time to the plate so that it will not be popping out like yours did. The instructions on how to do it is to use an applicator to dab alcohol on the edge so it soaks into the gasket which hopefully will loosen it. I will see since I'm going to be doing it in the next day or so. Hope it all works out!

[@deep_space_dave]

Excellent video, thanks! You did everything the correct way and I really like how you demonstrated that! I recently had to remove my corrector plate off my C6 as I had a mishap when removing my HyperStar and the center baffle came loose! I took the opportunity to clean the inside of the corrector plate and realized I had a film on it. I carefully cleaned the film (was not mold!) and put everything back and miraculously the SCT was still collimated! But now my images were brighter than ever (no I didn't rub off the coatings LOL) even brighter then when I got the scope new! I think these things come from the factory with bad QA and I have no idea what this thick grease they use or what they use to clean the components but it is definitely not high quality. The only suggestion I would make is if you live in a cold climate, use a grease that is still viscous at lower temps. Thanks again! Clear Skies!

[@newforestobservatory9322]

There is absolutely no need to remove the corrector plate if your Hyperstar is stuck to the secondary mirror holder. Simply remove the Hyperstar from its holder leaving the Hyperstar holder stuck to the secondary mirror holder. There is now a hole (where the Hyperstar was) giving you access to the backside of the corrector plate. Stick one hand through the hole and grab hold of the threaded plastic ring on the backside of the corrector plate and use your other hand to unscrew the secondary mirror holder. I have done this at least half a dozen times with no need to remove the corrector plate.

[@astronomytipsreviewswithcu740]

Great tip. Wish I knew this years ago. If one does remove the corrector plate I suggest taking the opportunity to replace the slippery gasket that Celestron supplies with a sticky one like those available from Starizona.

[@vk3dgn]

Thanks, very informative! I'd be removing my watch and any jewellery before doing this kind of work.

[@DaveSwenson]

Very informative video - nice job Curtis. Looking forward to more from Dave! BTW: I hate Birch trees - messiest trees around!

[@tullyfisher]

You are a brave man! I would most probably never do that myself. - Very informative video! 👍🏼 cs

[@astronomytipsreviewswithcu740]

Dave is the brave one since it was his C11 that we disassembled. This was nothing. Wait until you see the follow up video showing how Dave drilled into the baffle tubes to add nylon screws. I am working on finalizing that video and will post it soon

[@peterberbee]

I like Kyrtox grease for many applications. However, I would not use it on a telescope. The problem is that if it gets on a optical surface, it sticks. There are exotics Kyrtox solvents available. I'm not sure they are optical surface safe. Anyway, ordinary synthetic grease works fine for this application and it can be removed with common solvents. Thanks for the video. I enjoy seeing how various telescopes are taken apart.

[@mycarolinaskies]

As an added upgrade for Celestron tubes, epoxy the interior OTA nuts in place, then you can remove the rear assembly bolts without having to remove the corrector. It's something Celestron should have done from the beginning. The debris inside and dirtiness of the primary mirror is symptomatic of not using proper filtering on the vent holes, I hope that will be part of the upgrade process.

[@Greebstreebling]

Great to see how it comes apart. I must admit I would not expose my primary mirror in the ways shown here - far too much chance of accidental damage.

[@astronomytipsreviewswithcu740]

You just have to be careful like Dave was with his.

[@houstonderk]

Reading through some other posts about mirror flop and tightening the front mirror locknut after finding it loose, did you notice that on yours when pulled apart? Most of the topics I see this have the retainer nut with the 2 holes for a spanner wrench but seems the newer edges have a ring with no holes in them.

[@markdeslauriers241]

I too had to tear apart my C6 because the nuts that hold the focuser rod to the mirror assembly came loose. I also have the Celestron electronic focuser. Th eend one is welded on but the inside nut was loose allowing the rod to just spin. That black grease was nasty.

[@shaneskaalerud3371]

6:40 I’m guessing a Q-tip or something like a small brush would help take those little tree specs out?

[@domeguy5107]

I just watched your video and was fascinated by it. I noticed that on the outside baffle there were two set screw holes. did you put them in to stop the mirror slop, if so what type of screw did you use and what size?

[@douglasthompson9482]

Thank you for the video. I am having trouble collimating my Meade 8” sct. Any thoughts….would like to do this during the day as the weather is poor this winter.

[@astronomytipsreviewswithcu740]

I don't see how you can do it during the day. Wouldn't we all love to do that. There are lots of on line tutorials on collimating an SCT. Hopefully you can find the one that helps.

[@jackfrost4033]

I had to remove and replace 4 screws in the primary housing to replace the red dot finder and install the starsense undoing the screws was easy, putting them back in was more difficult especially towards the end with significant forcing is this abnormal?

[@astronomytipsreviewswithcu740]

Dave did not have any trouble with any of the screws.

[@timpatton3948]

Thanks for this. My Hyperstar got stuck on my c 11 and I had to remove the corrector plate as well. I have a problem with my c 8 and the Celestron focuser. When I hit the calibration button it was taking a long time to calibrate so I looked outside to see what was going on. Just as I stepped outside I heard a loud twang. I looked inside and the nut that joins the mirror cradle to the rod on the focuser mechanism striped and came off. I thought this was kind of bizarre. It looks like a little brass nut. The threads are floating around in the case . I didn't know the focus motor would keep turning when it came to the end. I need to take it apart and see what the deal is. The rod may be bent a little.

[@astronomytipsreviewswithcu740]

Sorry to hear that. Let us know how it turns out.

[@KrzysPioro]

Well done! Its that Krytox GPL205?

[@astronomytipsreviewswithcu740]

Thanks! There is a link to the Krytox down below the video. Check it out.

[@kingdomofme3681]

I'm wanting to buy a Celestron c6. I am wondering if I can get new optics like mirrors and the focuser later down the line in case I want to upgrade it or if something breaks after warranty. Do you know if this is possible?

[@astronomytipsreviewswithcu740]

Celestron can support you after warranty but it fan get pretty expensive to pay for shipping to southern CA and the cost of the parts and labor. There is no mirror upgrade that you can do, but you certainly can use one of many mirror upgrade options like the motorized mirror from Celestron or a focuser from one of many other companies which attach to the optical port.

[@kingdomofme3681]

@@astronomytipsreviewswithcu740 alright, so Celestron will support my product as long as I pay them after the warranty? If that's the case, then that's great.

[@shaneskaalerud3371]

18:26 What is a mirror flop? My guess would be the mirror moved or is not in the right place as it should be when moving your telescope in and out of the house I’m assuming because of winter rain bad weather.

[@astronomytipsreviewswithcu740]

Mirror flop is the name given when the mirror shifts slightly when the telescope moves across the night sky. Although the shift is slight mechanically, optically it is significant and undesirable when taking astro photos.

[@mycarolinaskies]

Mirror movement is the shift as the primary mirror to baffle alignment shifts by microns between the top to bottom inner and outer baffles. Because the fit between the two is 'interference' there is always a small gap. Think about two tubes nested together, in order for the outer tube to slide that gap needs to exist. A permanent fix used by Meade is actually a redesign to include crayford style roller bearings which apply constant low pressure. I'm assuming the fix in this case is using nylon bolts to apply slight pressure while still alowing enough slippage between the tubes. We will see that in the next installment I believe.

[@astronomytipsreviewswithcu740]

@@mycarolinaskies You have the right idea but we will show that in the 3rd installment. I am anxious to discuss the Celestron motorized focuser problem and fix in the next installment. May take a week to get it edited and up since I am traveling this week.

[@starhopper457]

What did you use to remove the old grease on the baffle tubes?

[@astronomytipsreviewswithcu740]

Dave used a rag to wipe off the bulk of the grease and then some isopropyl alcohol to remove any residue

[@starhopper457]

@@astronomytipsreviewswithcu740 Thank you Sir! I am looking at having to do this exact cleaning with an older Meade 8" SCT.

[@astronomytipsreviewswithcu740]

@@starhopper457 Good luck.

[@Endymion4242]

Why not remove the primary mirror before taking off the back? Scary to work near the mirror to hold those nuts.

[@astronomytipsreviewswithcu740]

Just need to take your time and watch what you are doing and should not be an issue. I suppose you could remove the mirror by disconnecting the focuser, the locking knobs if it is an Edge and removing the baffle tube retaining ring and then pulling the mirror out. To each their own but I think folks are much too timid about the mirror. Just use common sense when taking the scope apart, have a nice clean large padded surface to work on and take your time. After all, folks clean these all the time which requires even more handling than what Dave had to do.

[@SimonT65]

What a great video, very thorough! I don't suppose that you would consider doing a follow up with how you collamated using the Hotech would you? I'm struggling to get the three laser dots to align on the reflector in the rear cell. I believe my corrector is out of alignment.

[@astronomytipsreviewswithcu740]

Thanks. The initial alignment is by far the hard part of using the HoTech. There are several videos on this already. Once you get it you will have less trouble from there on. Good luck.

[@cosmoscarl4332]

No flocking way!🤪

[@shaneskaalerud3371]

1:23 For number seven what kind of knife? Kidding aside a butter knife? Lol

[@lharris828]

It was not like that with my c11 ota! The focus for was deep inside after defocusing and the internal screw was locked. The manufacturer told me that it was locktited in! Not like you show.

[@astronomytipsreviewswithcu740]

Sorry, but I do not follow what you are saying. Maybe try again and I will get your point.

[@lharris828]

@@astronomytipsreviewswithcu740 focus all the way in and then all the way out. The focus rod - with the screw end - can be brought outwards. However, with mine it stops deep inside the focus barrel so it cannot be unscrewed. Celestron confirm that the inaccessible screw is glued in!!

[@shaneskaalerud3371]

2:18 I’m sorry but there’s no sound at the moment. And I’m assuming you’re trying to say be careful of taking that piece out.

[@astronomytipsreviewswithcu740]

Yep

[@BariumCobaltNitrog3n]

2023 and people are still making silent movies. I'm sure I'm the only one who doesn't enjoy seeing every single screw come out (what they do nobody knows) in total silence, and learning more about the neighbor's trees than how the telescope functions. I was hoping to see how the focuser is attached and how it works. Wish me luck.

[@denodan]

Why don't you, instead of taking out the corrector plate, just unscrew the whole from assembly in one go like you do to the primary as you just unscrew the back