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Edge HD 800-changing collimation after meridian flip

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#1 HH_ASTRO

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Posted 14 June 2018 - 04:17 AM

Also, my mirrors are locked and everything tightened. This is very frustrating because I am imaging so I cannot automate my setup with having to recollimate my telescope all the time.

Can anyone help?

#2 gnowellsct

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Posted 14 June 2018 - 08:55 AM

Sounds like a loose primary lock nut. #2 choice is secondary movement...or corrector is not snugged in place and you get some side to side movement when you flip. I take it when you say mirror is locked you mean you're using aftermarket focuser? Or are there primary lock screws like on c14. An aftermarket rear focuser would not solve loose lock nut.

Edited by gnowellsct, 14 June 2018 - 08:58 AM.


#3 bobhen

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Posted 14 June 2018 - 09:05 AM

This is probably mirror flop (not mirror shift). The retaining ring on the primary or some other part of the cell probably needs attention or the corrector is shifting. The only thing to do is send it back to Celestron, unless, of course, you are comfortable with tearing apart the scope. They will fix it. If the scope is still under warranty, they will fix it for free.

 

This usually happens to the larger SCTs like C11s and C14s so eliminate all other possibilities before you talk to Celestron.

 

This happened to my new C11 and Celestron fixed it. For the next 15 years that I owned the scope, the scope held collimation really well.

 

Bob


Edited by bobhen, 14 June 2018 - 01:43 PM.


#4 cam1936

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Posted 14 June 2018 - 12:45 PM

The only quick fix is to run the focus from one side of travel to the other a couple times to redistribute the grease on the baffle tube. Not likely to solve the issue unless it is a minor change though. As others have said it is probably the retaining nut. I would send to Celestron if under warranty or fix it myself if not.

#5 HH_ASTRO

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Posted 14 June 2018 - 04:45 PM

The only quick fix is to run the focus from one side of travel to the other a couple times to redistribute the grease on the baffle tube. Not likely to solve the issue unless it is a minor change though. As others have said it is probably the retaining nut. I would send to Celestron if under warranty or fix it myself if not.

I will try this tonight. If it is not fixed I will contact Celestron.

Thanks everyone for the help

#6 gnowellsct

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Posted 14 June 2018 - 08:15 PM

Read the appendix to this document

 

The one thing I would change is that it is pretty easy to do the tightening with a spanner wrench (for rear gear clusters, buy in bicycle shops).  When I wrote that document I was still not happy with having to do that operation near the mirror.  As it happens I discovered a fairly safe way to do it.  You cut out a circular piece of cardboard equal to the diameter of your mirror.  you cut out a center hole just big enough to give access to the primary lock nut.

 

You lay down kim wipes so they totally cover the primary.  Then put the protective cardboard down over the mirror (the baffle will stick through it).  Basically this provides protection for the mirror in case you slip.

 

Then you can tighten the lock nut.

 

I confess the first time one does this it is a hair raising experience but, since I am bald, I no longer have to worry.  I've tightened quite a few lock nuts since then.  

 

Greg N



#7 gnowellsct

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Posted 14 June 2018 - 08:19 PM

The thing is, the chances of your C14 being trashed in transit are non-zero, and in my estimation fairly high.  Whether it's one in ten or one in three I couldn't say.  But it's higher than I would like.  

 

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#8 HH_ASTRO

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Posted 15 June 2018 - 06:57 PM

Read the appendix to this document

The one thing I would change is that it is pretty easy to do the tightening with a spanner wrench (for rear gear clusters, buy in bicycle shops). When I wrote that document I was still not happy with having to do that operation near the mirror. As it happens I discovered a fairly safe way to do it. You cut out a circular piece of cardboard equal to the diameter of your mirror. you cut out a center hole just big enough to give access to the primary lock nut.

You lay down kim wipes so they totally cover the primary. Then put the protective cardboard down over the mirror (the baffle will stick through it). Basically this provides protection for the mirror in case you slip.

Then you can tighten the lock nut.

I confess the first time one does this it is a hair raising experience but, since I am bald, I no longer have to worry. I've tightened quite a few lock nuts since then.

Greg N

Yikes. I would be really afraid of getting a wrench that close to the mirror...
Thanks for this though, I will do this if the scope is out of warranty.

#9 gnowellsct

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Posted 17 June 2018 - 02:33 AM

Yikes. I would be really afraid of getting a wrench that close to the mirror...
Thanks for this though, I will do this if the scope is out of warranty.

Well yes, I too had that fear, which is why I developed a protective layer technique.   And of course you saw the other custom tools that had been made to deal with the same issue. Basically if you have the mirror out and are messing with the tube or whatever you want some kind of protection, so it's wise to plan that in advance.  For the C8 putting the mirror somewhere can be as simple as putting a plastic bowl over it.  But that's just to keep it out of harm and free of dust.  To tighten the primary lock nut you have to get up close and personal.   

 

But look, you got dob owners who pull their mirrors from their rocker boxes at the end of each night's observing.  They too are getting up close and personal with expensive optics.

 

GN



#10 rmollise

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Posted 17 June 2018 - 08:50 AM

I will try this tonight. If it is not fixed I will contact Celestron.

Thanks everyone for the help

That will not likely fix your problem. First thing to check? The secondary. At least one of the collimation screws must be snug.




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