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Missing cork shim on a Meade 12 OTA.what to do?

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#1 Bill Barlow

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Posted 25 August 2014 - 11:28 AM

I recently pulled the front corrector from my newly acquired used Meade 12 ACF OTA to clean it up a bit and noticed that one of the cork shims that holds the corrector in place in the front cell was missing.  I'm sure the seller had no idea this was going on.  I noticed that this allowed the corrector lens to move around a bit and not stay firmly in place.  Can this shim be replaced with something similar?  I assume this corretor movement might affect the alignment of the primary and secondary mirrors a bit as I noticed when I checked collimation the other night the in-focus rings were perfect but the out-focus rings were off a bit.  Saturn was kind of blurry but as the night went on, the images of globular star clusters at medium and high powers was pretty good.  How would you check primary and secondary mirror alignment without and laser or other collimation tools?  Do I need to send this to someone like Company 7 to have it done properly?  Is there anyone else I could contact if necessary?  Thanks for any help/feedback.

 

Bill



#2 rmollise

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Posted 25 August 2014 - 12:35 PM

Sure...anything will work. Including paper.



#3 Erik Bakker

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Posted 25 August 2014 - 12:36 PM

I noticed this with my C5 and simply cut an identical small small piece of cork from a wine-cork. Works very well with a noticeable improvement in the alignment of the optics. Of course the cork was taken from a bottle of first-class French wine  ;)


Edited by Erik Bakker, 25 August 2014 - 12:40 PM.


#4 Bill Barlow

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Posted 25 August 2014 - 01:28 PM

Thanks for the help.  I have some sturdy cardboard boxes that I could possibly cut a small 1/2" x 1/4" piece and try to see if that works out.  I'm not a wine drinker, only beer. so I guess a piece of cork is out.

 

Bill



#5 Erik Bakker

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Posted 25 August 2014 - 02:11 PM

[.....]  I'm not a wine drinker, only beer. so I guess a piece of cork is out.

 

Bill

Bill, in that case paper or cardboard will have to do. Cardboard may be difficult to cut thin and sturdy enough. In that case a folded piece of paper could work well too. Just experiment until you have something that works for you. Can't go wrong here.


Edited by Erik Bakker, 25 August 2014 - 02:11 PM.


#6 Bill Barlow

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Posted 25 August 2014 - 04:19 PM

So once I get a replacement shim, and re-seed the front corrector and re-attach the corrector retaining ring, is there a way to see if the primary and secondary are aligned close enough to not affect the views once the optics are collimated?  When I checked the collimation last Saturday, Poisson's spot was directly centered in the secondary shadow on both in and out of focus diffraction rings.

 

Bill



#7 amicus sidera

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Posted 25 August 2014 - 04:56 PM

Step 1: Obtain cork sheet of appropriate thickness at local craft store.

 

Step 2: Cut cork shim to dimensions matching existing shims, and place into position

 

Step 3: Use telescope.

 

 

You're welcome.  :)



#8 Ed Holland

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Posted 26 August 2014 - 03:42 PM

Hardware stores might also carry cork gasket material, or even easier, a piece trimmed from stick-on cork pads that they are very likely to carry.

 

Best of luck :)



#9 Bill Barlow

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Posted 26 August 2014 - 04:09 PM

Thanks for all the suggestions.  I will try and find something similar to use and install it so the corrector lens won't move around and throw off my optical alignment and collimation.

 

Bill








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