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Cost of cleaning/collimating old C8?

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#1 khobar

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Posted 24 September 2020 - 10:44 PM

I have a C8 I bought used here (or Astromart, I forget) I've had about 20 years, and I'm wondering how much it would cost to have it overhauled. 

 

The corrector is quite hazy, lots of dust but also a glar that doesn't come off with air. Images are somewhat mushy - could be seeing perhaps, but stars are never pinpoints. I've done only a limited check on collimation - I'm sure it would benefit from more accuracy.

 

This C8 does not have "Starbright" coatings, or whatever, as near as I can tell. I'm not sure it has any coatings at all after all this time. Certainly don't see any color on the glass, but that might be meaningless.

 

Thoughts?

 

Thanks in advance.

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#2 macdonjh

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Posted 25 September 2020 - 12:31 PM

khobar,

 

Neither cleaning nor collimating a C8 is difficult.  Perhaps do the work yourself?


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#3 KTAZ

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Posted 25 September 2020 - 12:57 PM

My first concern would be the age of the tube. Its current market value is pretty low, so I also recommend you do the cleaning yourself. The cost of the materials is pretty low, but the cost of sending it back to Celestron would be more than the scope is worth.

 

https://www.youtube....cMk&app=desktop

 

I'd do that first. Once you have the corrector off and have cleaned the primary mirror, you can inspect the mirror much better. On a scope that old, without modern coatings, it is possible that the primary and/or secondary mirrors could have taken on some oxidation over the years. If you see nothing, reassemble, collimate, and star test. If you see excessive oxidation, you can turn it into a cool office trash can (but I'd still collimate and star test it first...might be good enough for your purposes?).

 

EDIT; If you do take on the cleaning, be sure to check the retaining ring that holds the mirror against the sled. These have been known to shrink/desiccate over the years and you may need to tighten it up to reduce any resulting image shift and/or mirror flop.


Edited by KTAZ, 25 September 2020 - 12:59 PM.


#4 khobar

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Posted 25 September 2020 - 01:38 PM

Thank you.

 

I could clean it myself - the value is low so there's not too much at stake. Biggest concern really is collimation. I know the mechanics, but I wonder, can Sharpcap or PHD2 help during the star test? A laser collimator for a Newt probably isn't much use.

I will keep an eye out for the retaining ring. And since this scope does have fairly significant mirror shift, is there something I could for to address that, too?



#5 Jaimo!

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Posted 25 September 2020 - 02:02 PM

Thank you.

 

I could clean it myself - the value is low so there's not too much at stake. Biggest concern really is collimation. I know the mechanics, but I wonder, can Sharpcap or PHD2 help during the star test? A laser collimator for a Newt probably isn't much use.

I will keep an eye out for the retaining ring. And since this scope does have fairly significant mirror shift, is there something I could for to address that, too?

I use a camera when star testing, prevents the need to go look through the eyepiece...  Use a fast exposure with high gain, potentially 2x2 bin.



#6 Bean614

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Posted 25 September 2020 - 06:25 PM

I'm  not sure I'm understanding this.   You haven't collimated your scope in 20 years? Is there a reason for that? 


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#7 khobar

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Posted 25 September 2020 - 08:01 PM

I'm  not sure I'm understanding this.   You haven't collimated your scope in 20 years? Is there a reason for that? 

That is correct. As for why, the collimation has *looked* okay for as much as I use it - I didn't want to risk mucking it up. I generally use my 80mm APO for deep sky, and the SCT kinda sits in a corner in its protective bag. But the weather has become tolerable enough to do the planets, and I now know being out of collimation even a little can make a huge difference in clarity and contrast. Hence my interest in having a pro do it. However, the cleaning could cost up to $200, and the collimation another $150. Plus shipping. Yikes.

 

So, tonight I'll do a star test.

Jaimo! - I had a camera in mind - thanks! 

 



#8 KTAZ

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Posted 25 September 2020 - 08:16 PM

If you can get your hands on a camera and a barlow, MetaGuide will help you with the collimation at night (but you need patience to get a star centered).

If not, there is a 2 step process you can use to collimate during the day that works very well.

#9 Bean614

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Posted 25 September 2020 - 09:48 PM

That is correct. As for why, the collimation has *looked* okay for as much as I use it - I didn't want to risk mucking it up. I generally use my 80mm APO for deep sky, and the SCT kinda sits in a corner in its protective bag. But the weather has become tolerable enough to do the planets, and I now know being out of collimation even a little can make a huge difference in clarity and contrast. Hence my interest in having a pro do it. However, the cleaning could cost up to $200, and the collimation another $150. Plus shipping. Yikes.

 

So, tonight I'll do a star test.

Jaimo! - I had a camera in mind - thanks! 

 

If you send away the scope for collimation, it will NOT arrive back to you collimated after shipping!  it sounds like you're very fearful of collimation, but truly, doing it yourself is the ONLY way to ensure that your scope is showing you the best it can.  Spending $150 to have an SCT Collimated, and then shipped(!) to you, is a complete waste of money.  Have you considered a refractor?  I'm not being facetious here--- If you own a Newtonian Reflector,  a Maksutov or Schmidt Cassegrain, Collimation IS part of the Ownership experience.  Think about this:  You have NEVER seen what your SCT is capable of showing you, ever.  A Refractor pretty much stays collimated for life, save for an occasional (every 5 years???) tweak.  Think about it...



#10 davidc135

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Posted 26 September 2020 - 07:35 AM

One more vote for doing it yourself.

I'd consider firstly; a quick clean of the outside of the corrector plate using 'Zeiss wipes' or plain tissues and propyl alcohol, without removing the corrector. If the mirrors are in a half decent state I'd look at an out of focus Polaris etc to get an idea of the present state of collimation.

 

If it happens that the shadow of the secondary mirror is obviously off centre when the out of focus star is mid field it should only take 5 minutes to greatly improve things. You can get by with (I'm assuming with Celestron) an Allen key and a low and high power eyepiece even in not so good seeing. It may not be perfect but should be made pretty good.

 

If there's a positive result after this quickie clean and adjustment it's likely worthwhile undertaking a more thorough cleaning/collimation.

 

Following collimation a simple star test will also tell you if the optics are reasonably well corrected or not.

 

David



#11 macdonjh

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Posted 26 September 2020 - 07:02 PM

That is correct. As for why, the collimation has *looked* okay for as much as I use it - I didn't want to risk mucking it up. I generally use my 80mm APO for deep sky, and the SCT kinda sits in a corner in its protective bag. But the weather has become tolerable enough to do the planets, and I now know being out of collimation even a little can make a huge difference in clarity and contrast. Hence my interest in having a pro do it. However, the cleaning could cost up to $200, and the collimation another $150. Plus shipping. Yikes.

 

So, tonight I'll do a star test.

Jaimo! - I had a camera in mind - thanks! 

 

Shoot, I'll do it for half that...

 

Do you have an astronomy club in your area?  I'm sure a club member can teach you how to collimate your scope.  A friend in my club helped me learn in five minutes.




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