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Evolution Secondary Mirror Loose?

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#1 TonyMan

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Posted 11 September 2019 - 11:47 AM

A guy from my club said he felt my Evolution 8" needed collimation the other night. Before we did anything I decided to order Bob's Knobs for it. When I took the scope out of the case and was looking at the way the secondary is connected on the corrector, I noticed I could turn the assembly fairly easy by  hand. This doesn't sound right to me, but I could be wrong.

 

Has anyone else seen this? I'm not sure how one would go ahead with tightening it. Would I have to remove the collector itself?

 

 

Thanks

 


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#2 Gary Z

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Posted 11 September 2019 - 12:04 PM

OUCH....sorry to hear,

 

 

Are the collimation screws tight?  If all the screws are loose, I can see the secondary mirror becoming loose, but normally, when adjusting these screws, only one at a time should be messed with at small increments.  I realize you stated that before you guys touched anything, but was there some sort of collimation attempt earlier?  Now, if you have not touched these screws, and they are tight and your secondary mirror assembly is loose, that's certainly not good. How old is your Evo Mount and scope?  If under warranty, call Celestron, but if you or anyone has messed with these screws, corrector plate or secondary mirror, well, that "possibly" could void the warranty.....but still worth calling. 

 

Was this scope dropped?  I'm just trying to think about what would cause the secondary mirror assembly to be loose, should nothing else be accomplished that might contribute to this.  I've had my C8 on numerous road trips, about 3 collimations, where one was after installing Bob's Knobs. I've been using this orange C8 since 2014.  I had Celestron replace the SCT due to the primary mirror flaking. 


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#3 TonyMan

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Posted 11 September 2019 - 12:30 PM

The scope is 3 years old, so I believe it’s out of warranty.

 

I’m afraid I didn't explain myself fully. We ever attempted collimation, he just said he feels it needs collimating. It has never been collimated since I purchased it. I wanted to order Bob’s Knobs so was examining the secondary assembly to make sure I was ordering the right ones when I discovered the looseness.

 

Based on your comments I believe action is required. The guy from my club is a lot more experienced than me, so I feel I should get in contact with him for assistance in straightening this out and installing the new screws.

 

Thanks


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#4 Gary Z

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Posted 11 September 2019 - 12:35 PM

I did a search on what can cause the secondary mirror assembly to be loose.  it is worth looking into as well as you having your more experienced fellow looking at it.  https://www.cloudyni...dary-on-my-sct/

 

Gary


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#5 TonyMan

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Posted 11 September 2019 - 01:41 PM

Thanks, I’ll talk to him. Kinda sounds like we may have to take the corrector plate off to resolve!


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#6 Noah4x4

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Posted 11 September 2019 - 01:54 PM

Is the entire assembly is physically loose, or are you merely turning the outer ring that holds the secondary mirror?  

 

If you remove this ring, you will see that the secondary mirror has a tiny grub screw that fits into a slot. This is used to affix the mirror in its correct position without needing collimation after using Hyperstar. Might this screw have fallen out? Is that why the mirror is rotating?

 

If the principle ring that is affixed to the corrector plate is rotating (e.g. the entire assembly), then you have a more significant problem. But let's eliminate these other minor possibilities first.



#7 GoFish

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Posted 11 September 2019 - 02:02 PM

This is an aggravating problem. A few things I will offer from experience:

  • Preserve the “clock” angles of the corrector plate and the secondary holder
  • A good way to do this is to use blue painters tape to mark relative positions of corrector, secondary holder, and the end of the OTA
  • Maintain the present centering of the corrector with respect to the end of the OTA as established by the 4 little grub screws 
  • Maintain the in/out shimming of the corrector as set by any fiber shims. 

A good long term fix for this problem for me was to replace the fiber gasket on the secondary holder with a sorbothane gasket. Available from Starizona. 

 

https://starizona.co...n-kit-c8-gasket

 


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#8 TonyMan

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Posted 11 September 2019 - 02:27 PM

I'm turning the outer ring on the secondary, what I would call the housing. See the pic, and excuse my shaky drawing.

Attached Thumbnails

  • Secondary.jpg


#9 Michael_Swanson

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Posted 11 September 2019 - 07:33 PM

That portion is a threaded ring that removes and allows you to pull the secondary out, insert a HyperStar lens assembly, and image at f/2.  When you turn it, is the secondary itself (for example, the "fastar" label) turning as well?  If so, these two articles at my website should help:

https://www.nexstars...ondaryTurns.htm

https://www.nexstars...ctorRemoval.htm

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com


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#10 TonyMan

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Posted 11 September 2019 - 08:33 PM

Michael - will check that in the morning - it's night, I need to move the care to access the scope case, and the skunks are on the move! Once I felt it would turn I was afraid to do anything else for fear I'd really screw something up.

 

Now I'm mildly embarrassed because I found your website some time ago, read some stuff, and haven't gone back in a while. I will check those articles out and report back tomorrow on the status of the movement.

 

Thanks much!


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#11 TonyMan

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Posted 12 September 2019 - 12:47 PM

Well, perhaps things aren't as bad as I though. I checked turning the assembly and yes, the whole thing including the Celestron logo turned. However, I then turned it clockwise and about 1/4 of a turn it felt like it was getting tighter. About another 1/8 of a turn and it would go no further. I the tried counter clockwise and just the outside ring turns and I could take the ring off. I put it back on and now feel like it was probably a tad loose originally and hopefully now its secure. I'll have to wait for a clear night to check the collimation and work on installing the Bob's Knobs.

 

Thanks for all the help. I now have a much better understanding of how this assembly id constructed.



#12 Michael_Swanson

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Posted 12 September 2019 - 07:44 PM

You may still want to read this article as I discuss rotational orientation and how I went about tightening the secondary holder so it wouldn't rotate in the future:

https://www.nexstars...ctorRemoval.htm

 

That said, no big worries unless it comes loose again.

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com


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#13 TonyMan

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Posted 12 September 2019 - 08:57 PM

Oh yes, I intend to. I scanned through it yesterday, just didn't give it a good thorough reading.Things like this I typically read a couple of times to insure I've understood the content.

 

Thanks again for the help!



#14 MikeMiller

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Posted 18 September 2019 - 09:00 PM

It is interesting this topic is here this week. Tonight I took my EdgeHD 8 out for its yearly deep cleaning. I have not used my hyperstar more than once in the last year so this was the first time in a while that the secondary has been removed.

 

I noticed that the little set screw that is supposed to prevent the secondary from rotating around managed to get pushed in all the way. This allowed the secondary to rotate to all kinds of wrong positions.

 

I used a small allen wrench to unthread it back to it's usual position so when it was placed in the notch, it will no longer turn.

 

I don't recall if it was misalligned before I removed the secondary, but the position of the set screw would have allowed it to be completely wrong.

 

I do see that now it is properly oriented, that on mine the fastar logo in the center of the secondary does line up with the text on the outer edge of the secondary. I don't know if this is always the case, but if the word "fastar" is upside down, you may need to remove it and check if you have the same problem that I did.


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#15 Noah4x4

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Posted 18 September 2019 - 11:47 PM

I "lost" the tiny grub screw that aligns my secondary mirror. Then having frantically spent two days trying to determine its size to replace it, fortunately, I found it. I am grateful that I have artificial grass where I erect my telescope so that it wasn't trodden into soil and lost forever. It is funny how you can spend hours looking for a "lost" item like this then easily spot it 24 hours later. A magnet on a string might have helped. But I digress.....

 

A sensible tip.....

 

My point is that Hyperstar users might be wise to affix this tiny grub screw with a drop of Loctite or Superglue. It performs no function except sit in a slot to ensure no collimation is required when reinstalling your secondary mirror, so it can be permanent affixed once correctly positioned. 


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#16 Michael_Swanson

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Posted 18 September 2019 - 11:56 PM

That screw normally is fixed with Loctite but it sounds like either Celestron changed that practice or a batch escaped the factory without it.

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com


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#17 Clouzot

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Posted 19 September 2019 - 01:49 AM

That small grub screw has been turning freely on my XLT C925 (bought new in 2018) since the very first day. No trace of Loctite as far as I can see...and it eventually set itself free. Fortunately, it fell into the Hyperstar holder when I was removing the secondary mirror assembly, and I heard it immediately...!



#18 Michael_Swanson

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Posted 19 September 2019 - 09:39 PM

Maybe now it is supposed to thread in tight and bottom out with still enough protruding to do the job?  But from Mike Miller's post, it sounds like it will thread in too far...

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com



#19 MikeMiller

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Posted 19 September 2019 - 10:06 PM

Maybe now it is supposed to thread in tight and bottom out with still enough protruding to do the job?  But from Mike Miller's post, it sounds like it will thread in too far...

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com

I wonder if I managed to shear off the bolt at some point. Though the end that sticks out does not look broken.



#20 Noah4x4

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Posted 19 September 2019 - 11:33 PM

Maybe now it is supposed to thread in tight and bottom out with still enough protruding to do the job?  But from Mike Miller's post, it sounds like it will thread in too far...

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com

When I reinstalled mine in my Evolution 8" (after it fell out), I noted that was infinitely adjustable - hence the grub screw hole is clumsily drilled deeper than the length of the screw. It could therefore potentially protrude nil or (almost) its full length. It could be that the OP has his screwed in too deeply.

 

Mine was also extremely loose fitting. No evidence of Locktite or other adhesive. Hence ALL Hyperstar users are advised to check and apply a drop of Locktite. Lose this grub screw and you might have some difficulty in replacing. Its absence in a Fastar system will mean that your secondary mirror will freely rotate and lose collimation. 




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