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midlife
member


Reged: 09/24/13

Loc: Ohio
New z8, move the center dot new
      #6105790 - 09/28/13 11:51 AM

Good morning, I have a new z8 and the center dot is off quite a bit, among other things with the primary. I have seen a lot of posts on this, and how to center a new one, but how do I remove the current one? Any tips would be great.

Thanks


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SteveG
Post Laureate
*****

Reged: 09/27/06

Loc: Seattle, WA
Re: New z8, move the center dot new [Re: midlife]
      #6106148 - 09/28/13 03:17 PM

With the mirror out of the tube but still in its cell, I use an exacto knife to peel up the edge of the ring. Carefully pluck it off, then reapply at the center spot. Don't worry about scratching the mirror at the center, it does not see any light due to your secondary.

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schluterdude
super member


Reged: 08/05/13

Loc: Centerville, OH
Re: New z8, move the center dot new [Re: SteveG]
      #6106163 - 09/28/13 03:23 PM

If it doesn't want to come off peacefully, you can try letting a small puddle of alcohol sit on it to soften the glue. Acetone will work as well (try the alcohol first though). It will require a new center for though. The small notebook paper "reinforcing" rings work great as a replacement.

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midlife
member


Reged: 09/24/13

Loc: Ohio
Re: New z8, move the center dot new [Re: schluterdude]
      #6106244 - 09/28/13 04:10 PM

I didn't think marring the mirror in the center would matter, but wasn't sure if scratching the coating woukd cause it to want to flake over time. Anyway, I used a toothpick, it left a lot of the adhesive behind. I scratched the adhesive off with the toothpick with a dab of dishsoap, then rinsed the whole thing with distilled water. Thanks for the replys, it is at least a relief to know I wouldn't screw it up!

On the subject of mirrors, is it normal for there to be uncoated spots around the edge protruding onto the mirror surface? I assume it is from the work holders when they deposit the coating. It would be nice if they matched the coating holders to the cell holders so I didn't have five spots instead of 3 of no reflection around the edge.

Edited by midlife (09/28/13 04:22 PM)


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schluterdude
super member


Reged: 08/05/13

Loc: Centerville, OH
Re: New z8, move the center dot new [Re: midlife]
      #6106460 - 09/28/13 06:57 PM

How big are they? Can you take a pic?

Small is normal, and you are right, it's from the work holding they use during coating. How many spots depends on how they hold it. 3-5 seems ok.


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Billytk
Pooh-Bah


Reged: 04/22/12

Loc: Lake Mary, Fl.
Re: New z8, move the center dot new [Re: schluterdude]
      #6106664 - 09/28/13 10:16 PM

Get a "Hot Spot". I hear they are the best.

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Billytk
Pooh-Bah


Reged: 04/22/12

Loc: Lake Mary, Fl.
Re: New z8, move the center dot new [Re: Billytk]
      #6106669 - 09/28/13 10:22 PM

http://catseyecollimation.com/

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midlife
member


Reged: 09/24/13

Loc: Ohio
Re: New z8, move the center dot new [Re: schluterdude]
      #6109048 - 09/30/13 10:55 AM

The the largest uncoated spot is a little smaller than the mirror clips/clamps. There are 3 spots. I rotated the mirror so the largest is under a clamp but the other two are visible.

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schluterdude
super member


Reged: 08/05/13

Loc: Centerville, OH
Re: New z8, move the center dot new [Re: midlife]
      #6109077 - 09/30/13 11:26 AM

Completely normal. They won't impact viewing. If they really bug you, you can choke down the aperture a bit. This also is a "cheater" way of hiding a turned mirror edge...

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midlife
member


Reged: 09/24/13

Loc: Ohio
Re: New z8, move the center dot new [Re: schluterdude]
      #6109231 - 09/30/13 12:44 PM

Turned mirror edge, is that the bevel around the OD? and thanks for the response, I feel better about it now.

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SteveG
Post Laureate
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Reged: 09/27/06

Loc: Seattle, WA
Re: New z8, move the center dot [Re: midlife]
      #6109463 - 09/30/13 03:27 PM

No - the bevel is purposely cut there to prevent the edge from chipping. A turned edge cannot be seen by looking at the mirror, but it is a frequent issue with mass-produced mirrors. Mine is turned up slightly. I have a circular mask that blocks 1/4" of the mirror edge on my scope.

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