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Ceramic Mirrors

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#26 luxo II

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Posted 25 October 2020 - 06:03 PM

FYI Scopes with SiC mirrors exist, as a commercial product - here https://apertureos.c...ucts/small-sat/

 

Shudder to think what these cost, but it would be really interesting to see one on the field one day.



#27 MellonLake

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Posted 25 October 2020 - 06:22 PM

Yep... I know they are out there (really out there as in space), which means the technology works and has major advantages!  I am more interested in if it can be moved into consumer telescopes or ATM.  This technology will probably come to terrestrial telescopes at some point because it will make bigger mirrors cool faster, remain more dimensionally stable and maybe even lighter. 

 

Oh, and I did not want to hijack your thread.   

 

And if any one just wants to try grinding a 5" mirror (pretty thin but would probably still work)(thicker and larger is available from China)

https://www.ortechce...carbide-plate/ 



#28 hakann

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Posted 25 October 2020 - 08:57 PM

There are many companys that sell ceramics optics but the customers is using them in space or where weight on each kg is very critical vs the costs so for this aplication money is not the object.
They will work and they can be very stiff and very light but if we see or focus as I said above to plano design for AMT or visual use.
We fight the costs or if we get it cast ( material itself would not be high ) but who will do that for a ’resonable price’ ?
And how to grind it less MRF ?
Then the ’clad’ costing will also cost as the material will not get as good as we like the smothness.
-Ok, lets say technology get us there or a wallet is kind to us or if one wil on Lotto..
At the moment you get many Zerodur mirrors or multiple Quartz or a bunch in Pyrex from source that we know can make us happy on tolerance.
Decent parabola and smothness that test good in the classic test.
What I say here, where is the gain in the EP use a SiC ?
Yes, they get out heat way faster, they is stiffer so theoretical they sag less so all this is all good.
But if one has a good optician ( or by own hands = still possible ) and a correct cell and will wait some ( use fans ) it might be way better.
As I visited 3 companys as Zygo discuss this I know their tolerance.
It is total impossible to talk to this company’s on ATM tolerances ( ak’a 1/8 or 1/10 and ask for visual test ) as they will just shake their heads and say one is a to get real.
They will do what industry has for std, the diffraction limit.
I know it’s all good but ask here on CN on that - they will laughter.
But has any of this optics ever hit a pro latest Zygo IF ?
I was to test my CZO 18” at a aerospace company ( for fun ) but when I has the price it was twice what Carl sold it to me at, and optics would not be better in the EP.
What I learned was aerospace must hold what’s told in documents and not ’trust me’, but we are in hobby to watch a faint galaxy ( for fun ) and we are Ok if we are Ok in the EP.
And if not get very big like 1 meter or so we has a fair price get there.
Ok we will not get any document but we don’t pay for that either.
Plus a document in our world don’t mean anything anyway.

I’ll bean over this many times at CN and it’s a dead road as so few or non of this optics will ever come out to public.
But I can say from own experiance bigger optics can be real good from the ATM industry.
The best I ever look into was a 25” Newton in a thicker plano in Sital at f/4.5 from Lomo. For me a game changer.
It was 40K Euros 15 years ago but now I think it’s x3 and get bigger and faster Lomo will be very expensive and their market is not for AMT really anyway.

If, I say if the Chinese ( who else... ) might sell commercial SiC optics/telescopes their market will never be bigger Newts, or if, what will the gain be in the EP ?

How will this mirrors be done by ATM, and if, how to be polished ?

Overall the visual astronomy is a small group, and each year the sky get worse.

I might think if this happends it might be bigger ( now I’mean maybe 16” ) for astro photo.
But to this day few cast cellulars in Pyrex hits the market ( to expensive for most ) and is the gain if any worth it ?
This photo guys take nice picture in telescope not expensive att all, and of cource made in China.

Edited by hakann, 25 October 2020 - 09:13 PM.


#29 mark cowan

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Posted 25 October 2020 - 10:42 PM

Yep... I know they are out there (really out there as in space), which means the technology works and has major advantages!

Advantages for micro-gravity requirements, not so much for terrestrial use.



#30 MellonLake

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Posted 26 October 2020 - 06:15 AM

Ok, I get it too expensive to manufacture.



#31 mark cowan

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Posted 26 October 2020 - 03:58 PM

No not expense - the advantages don't scale down to terrestrial use and needs - compared to the difficulty (hence expense) of manufacture, to make them widely adoptable.   More like bragging points than pivotal. :shrug:



#32 arcainemachinest

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Posted 04 November 2020 - 06:24 AM

consider casting the slip and then putting it in a vacuum chamber to degas it? we used to do this when casting rubber pull a 29 inch vacuum and slowly release the vacuum 2 times and hold it for 10 min the 3rd time very slowly let the air back in.


  • Augustus, Earthbound1 and MellonLake like this

#33 Earthbound1

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Posted 22 November 2020 - 01:32 AM

Glad to see this topic being revisited. Been on hiatus, but still have dreams of commercially produced SiC mirrors for the masses and other goodies. There's an older thread here on CN with this very topic that I've read before. I'll see if I can find it and post a link here. As an aside, even a rudimentary vacuum system made from a Hoover, a Shop Vac or a Dirt Devil coupled with some gentle knocking on the container of slurry should remove a good bit of the air and ensuing porosity, even if it's not completely air tight. When mixing investment for lost wax casting we mix it then quickly vacuum it properly, while rapping on the side of the plexiglass "bell" to expedite the release of air in the bowl underneath, then pour it into the flasks and re-vacuum it before the 20 minute working time is gone and it starts to set up. Once in the flasks, due to the fragile nature of the wax sprues we don't knock on the table of the vacuum casting machine, letting the vacuum pull any remaining trapped air out. Sometimes a few miniscule "balls" after pouring the molten metal, due to unreleased tiny bubbles are present, but usually not. Cheers, clear skies, some cloudy nights and lots of stellar views! - Chip

Edited by Earthbound1, 22 November 2020 - 02:31 AM.



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