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Equipment Discussions >> Reflectors

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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Questions about mirror refiguring
      #6328707 - 01/22/14 03:43 PM

I'm considering getting my 12" newtonian mirror refigured later this year. I see that Swayze Optical and opticewavelabs.com do this, are there any others? Lockwood Custom Optics appears to be for high end, much larger mirrors.

Based on the images at http://www.opticwavelabs.com/refiguring.php, I would tentatively say that my mirror is roughly 3/4 wave, ASSUMING those images are valid for a 12" mirror. In any case, that is approximately the level of detail I get visually on Jupiter in the best moments of very good seeing. Though I have not used filters.

I think that my 6" mak-newt mirrror has better contrast for its size.


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nirvanix
Carpal Tunnel


Reged: 06/07/07

Loc: Saskatoon, SK
Re: Questions about mirror refiguring new [Re: sneutrino]
      #6328725 - 01/22/14 03:53 PM

Are you sure your primary is mounted properly - chiefly that the clips are not tightened down hard on the mirror? Is the center spot exactly centered? Checking these require taking the mirror out of the tube. If the above two aren't the problem, are you certain of your collimation procedure accuracy? Do you let the scope cool for a couple of hours? Have you done a star test to rule out a poor quality secondary?
If you've seen to all of the above then you could be a good candidate for a refigure.


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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: Questions about mirror refiguring new [Re: sneutrino]
      #6328729 - 01/22/14 03:55 PM

Quote:

I'm considering getting my 12" newtonian mirror refigured later this year.... Lockwood Custom Optics appears to be for high end, much larger mirrors.



I have refigured quite a few 10" and 12" mirrors. I do have a bit of a wait time right now, though.

Recently I have seen some mirrors in that size range with poor anneals. That's the wild card - if the glass is well-annealed, the figure will be stable. If it is not, the figure might change over time, and refiguring is a bit of a gamble. To test the anneal, the coating must be stripped so that one can see through the glass.

The type and quality of glass depends on manufacturer, timing, and luck. More recent mirrors are more likely to be made from cheaper, lower-quality glass with poorer anneal. Older mirrors are more likely to be Pyrex, which is good.


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Questions about mirror refiguring new [Re: sneutrino]
      #6328756 - 01/22/14 04:05 PM

send out the primary and secondary, Ed Jones does testing for free.

I heard Owl wasn't excepting any work till march.


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backwoody
Pooh-Bah


Reged: 01/08/07

Loc: Idaho USA
Re: Questions about mirror refiguring new [Re: Pinbout]
      #6329054 - 01/22/14 06:19 PM

Another option is www.lightholderoptics.com

John Lightholder made my excellent primary, and also tests and refigures mirrors.


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photiost
scholastic sledgehammer
*****

Reged: 12/14/06

Loc: Montreal, Canada
Re: Questions about mirror refiguring new [Re: backwoody]
      #6329106 - 01/22/14 06:38 PM

Make sure you have a good secondary.

If possible get that checked as well.


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Questions about mirror refiguring new [Re: nirvanix]
      #6329238 - 01/22/14 07:38 PM

Quote:

Are you sure your primary is mounted properly - chiefly that the clips are not tightened down hard on the mirror? Is the center spot exactly centered? Checking these require taking the mirror out of the tube. If the above two aren't the problem, are you certain of your collimation procedure accuracy? Do you let the scope cool for a couple of hours? Have you done a star test to rule out a poor quality secondary?
If you've seen to all of the above then you could be a good candidate for a refigure.




Mirror clips are fine/loose. Not 100% confident on the mirror donut center. Mirror cooling is OK, I have used a large box fan on the back of the mirror for 3 hours. Body heat is ruled out as well (stepping away and returning to the eyepiece).

For secondary collimation I use a laser, and rotate the laser in the focuser and watch the orbit of the laser on the primary mirror (unfortunately, the laser spot moves). I note the position of the center of the orbit, and place that orbit center at the center of the mirror.

For primary collimation I use a barlowed laser and this agrees with the cheshire.

I have not done a whole lot of star tests (e.g. at 500x), but when I have, the seeing is so bad that I can't really do the test. I will try this again when there is good seeing.


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sneutrino
super member


Reged: 08/08/09

Loc: San Jose, CA
Re: Questions about mirror refiguring new [Re: Mike Lockwood]
      #6329251 - 01/22/14 07:41 PM

Quote:

The type and quality of glass depends on manufacturer, timing, and luck. More recent mirrors are more likely to be made from cheaper, lower-quality glass with poorer anneal. Older mirrors are more likely to be Pyrex, which is good.




I'm fairly sure it is Pyrex, it is an orion xx12i from ~2005/2006 and the current online instruction manual pdf says it is Pyrex.


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nirvanix
Carpal Tunnel


Reged: 06/07/07

Loc: Saskatoon, SK
Re: Questions about mirror refiguring new [Re: sneutrino]
      #6329308 - 01/22/14 08:24 PM

Quote:



I have not done a whole lot of star tests (e.g. at 500x), but when I have, the seeing is so bad that I can't really do the test. I will try this again when there is good seeing.




A bad secondary will likely show up as a out of round star test and if you rotate the primary the orientation of the lopsidedness won't change,


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Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Questions about mirror refiguring new [Re: sneutrino]
      #6329558 - 01/22/14 10:53 PM

Forgive me.. I mean no offense.

Just looking at a picture and saying that your mirror is only "X" wave because it does not look like the picture tells you absolutely noting about the quality of the mirror.

A big mirror can take hours and hours to cool, and thermal currents or seeing can greatly affect the performance.

I would not be so quick to jump to refiguriong until you try to make an assessment of the quality using a star test or Ronchi Grating (if the mirror is as bad as you think, it should be easy to see using a Ronchi grating).

Do some homework.

Download the program "Aberrator 3.0" and put in the specs on your scope.

It is an easy program to use.

Then, use the program to try to model what you see when you defocus the telescope.

In particular, look at the Spherical Aberration and compare the size of the secondary shadow when you have about 10 waves of defocus (and Aberrator will show you what 10 waves of focus looks like).

Or find someone on the forum that lives near you that will check it, or go to a local club or something.

But don't just assume that your mirror is as bad as you say it is because you see a blurry picture of Jupiter somewhere that says this is what a bad scope looks like.

Not the post is incorrect, but if the scope is not cooled or seeing is not good, or the scope is not in good collimation, a good scope can put up a blurry image.

And you could have a simple problem like a pinched mirror or bad mirror cell.

Do some howework would be my suggestion..

Otherwise, you might send in a mirror and get back a great mirror, only to see the exact same soft image....


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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: Questions about mirror refiguring new [Re: sneutrino]
      #6329582 - 01/22/14 11:12 PM

Quote:

I'm fairly sure it is Pyrex



That's good.

Advice about checking the secondary is also good, I usually insist on this. I find about 1/3 of them have a problem.

If you see round stars up to high power, that is good. If not, I have another article about that: Why Aren't My Stars Round?

As the previous post suggests, learn as much as you can, it will be beneficial in the future.


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Tristan
sage


Reged: 06/07/11

Loc: NC
Re: Questions about mirror refiguring new [Re: Mike Lockwood]
      #6329887 - 01/23/14 05:40 AM

Another one to consider is Gordon Waite (Waite Research). He did my 12" and I have been very happy with it.

Clear skies,


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Tristan
sage


Reged: 06/07/11

Loc: NC
Re: Questions about mirror refiguring new [Re: Tristan]
      #6331379 - 01/23/14 08:08 PM

If you want to see the before and after of the refigure you can go to this link

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