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C5 and the secondary alignment issues....

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#1 Jeff Lee

Jeff Lee

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Posted 12 January 2020 - 12:56 PM

Have bought a used C5 (circa 2000) I noticed that it had a small amount of what looks like RTV or harder sealant on the corrector's retaining ring. It has the silver phillips head screws. From what I've found on the web those C5 that had the issue had black phillips head screws and no drop of sealant on the corrector's retaining  ring (added by Celestron to help cure the issue?).

 

Was there ever any formal announcement of this issue and if so what were the year(s)  of scopes that had the issue. Mine seems to be centered very well but have not had it out yet.

 

I would think getting the corrector off with that hard sealant in place might be a real chore but since mine has clean mirror and inside corrector I guess that's an issue for a later day.

 

Anyone know the real story on this?


Edited by Jeff Lee, 12 January 2020 - 01:57 PM.


#2 JMP

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Posted 12 January 2020 - 02:02 PM

I can only tell you my story. I picked up a G5 version about the same time that Sky and Telescope mentioned the corrector centering issue in a review of the Nexstar 5. I measured carefully and sure enough mine was off center by about .040" so I centered the corrector. This made the view worse!

 

Yes, the corrector is smaller than the holder. And Celestron did not put in cork shims for centering. Saved on labor costs I suppose.

 

Eventually I was able to determine that the optical axis was not quite centered in the tube. When carefully collimated on a star I could look into the front and see that the secondary was not centered. By trial and error I was able get the secondary centered on the axis and collimated on a star at the same time. My "diamond ring" pic was taken with this scope. I wound up with the secondary offset slightly from the physical center, just about where the factory put it.

 

So be careful of trying to fix something that may not be broken-

 

JMP


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#3 Jeff Lee

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Posted 12 January 2020 - 03:45 PM

I agree. Just wanting to have the back story in case the need arises.




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