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Mirror grinding?


Guest Turtleboy
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Guest Turtleboy

Hi again.

Just wondering is it worth while considering buying a second hand Newtonian (assuming it can be had at the right price) if the mirror is pretty much fubarred?

What is involved in refurbishing a mirror? Is it just a case of polishing it / grinding it, or does it then have to be re coated?

Does anyone offer a service doing this and is it cost effective, or is it just easier and cheaper to buy a new mirror.

Does anyone know the approximate cost for say a 10" mirror?

Also how bad can a mirror be before it's totally useless? I understand that any marking is far from a good thing but with a 10" mirror can you getaway with a bit of marking without drastically reducing the usefulness of the scope? For example would a perfect 8" mirror be better at collecting light than a slightly marked 10" mirror?

Sorry if this all seems like daft questions but if you don't know then you don't know. :lol:

Thanks

Martin

Edited by Turtleboy
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Ideally you want a mirror to be as clean and in good a condition as possible but I have seen mirrors that are filthy, even marks and cuts in the mirror and for visual, that is not a problem, you probably wont even notice. Imaging is a different kettle of fish all together.


 


I believe a company called Orion Optics can re-coat mirrors, as for cleaning them it is possible to do if your self, if you are careful and use the right stuff (NOT washing up liquid).


 


Unless the mirror is really, really, really dirty and you don't plan on doing any astro photography then I would leave it.


 


If you do want to clean it, then you have to take the mirror cell out, use Baader wonder fluid I believe and then pour some sort of spirits (not vodka) over it to displace any water.


 


Kheldar has done this recently I believe with his now sold 200P, he should see this soon and advise.


 


EDIT : there should be no reason why you would want to re grind it, as long as it is correct in the first place. And I don't think a pristine 8" would be any better than a dirty 10", but I may be wrong.


Edited by Daz Type-R
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Guest Kheldar

Not me guv' - I don't recommend anyone clean their mirrors :D


 


I think to be honest we need a better description of the condition of the mirror - if the coatings are gone, then it's probably going to be cheaper to buy a new scope full stop :o


Edited by Kheldar
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Not me guv' - I don't recommend anyone clean their mirrors :D

 

I think to be honest we need a better description of the condition of the mirror - if the coatings are gone, then it's probably going to be cheaper to buy a new scope full stop :o

 

Ahh, that's right, you replaced the load springs (or something) on the mirror cell did you not?

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I know that the director of my local observatory used the following cleaning method for the 24" mirror:

Remove mirror from scope and carefully prop up at an angle.

Rinse over the mirror with distilled water with Star Drops in it.

Any stubborn marks were GENTLY wiped without applying any finger pressure with a cotton wool ball whist running the Star Drop mixture down the mirror.

Anything on the mirror that this didn't remove stayed on until the next time it got sent for a new vacuum coating.

I don't know if this method is safe, the chap who used it obviously did!

I'm getting some of the Baader fluid for my optical cleaning.

Edited by angusw2
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I would steer clear of wonder fluid/alcohol based fluids on the primary. Distilled water is the way to go. Dions video is very compressive, see below if you have a spare 28 minutes :)

http://youtu.be/0tRHYSzaRLk

Edit: yep re coating is the way forward for that! Orion optics do do it as Darren said. Have a chat with Philjay he recently fm got his 8 inch mirror recited by them :)

Edited by catman161
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