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Dirk Bruere at NeoPax
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 Posted: Fri Oct 10, 2008 4:46 am Post subject: Liquid Mirrors |
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.... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
--
Dirk
http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff |
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Mark Thorson
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| Posted: Fri Oct 10, 2008 5:08 am Post subject: Re: Liquid Mirrors |
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Dirk Bruere at NeoPax wrote:
[quote]
... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
[/quote]
It would distort as it froze, water would collect on the surface,
and it will oxidize. |
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Mark Thorson
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| Posted: Fri Oct 10, 2008 5:15 am Post subject: Re: Liquid Mirrors |
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Dirk Bruere at NeoPax wrote:
[quote]
... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
[/quote]
It occurs to me that it could be designed to view off-axis.
You could run an electric current through the mercury, and
use a big magnet to throw the parabola off axis. Or forget
gravitation, and aim using magnetism alone to maintain the
parabola. Use a fine-grain electrode structure, and maybe
you don>t have to spin it. Just distort the surface into
a parabola, with real-time corrections for atmospheric
distortion and any other non-linear effects. |
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Dirk Bruere at NeoPax
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| Posted: Fri Oct 10, 2008 5:27 am Post subject: Re: Liquid Mirrors |
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Mark Thorson wrote:
[quote]Dirk Bruere at NeoPax wrote:
... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
It would distort as it froze, water would collect on the surface,
and it will oxidize.
[/quote]
Well, I doubt the water and oxidize bit if done under dry nitrogen.
And is it impossible to have a liquid that did not distort as it froze?
--
Dirk
http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff |
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Dirk Bruere at NeoPax
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| Posted: Fri Oct 10, 2008 5:28 am Post subject: Re: Liquid Mirrors |
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Mark Thorson wrote:
[quote]Dirk Bruere at NeoPax wrote:
... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
It occurs to me that it could be designed to view off-axis.
You could run an electric current through the mercury, and
use a big magnet to throw the parabola off axis. Or forget
gravitation, and aim using magnetism alone to maintain the
parabola. Use a fine-grain electrode structure, and maybe
you don>t have to spin it. Just distort the surface into
a parabola, with real-time corrections for atmospheric
distortion and any other non-linear effects.
[/quote]
It it is simpler to create a flat mirror then reflect off that into the
spinning liquid.
--
Dirk
http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff |
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N:dlzc D:aol T:com (dlzc)
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| Posted: Fri Oct 10, 2008 5:30 am Post subject: Re: Liquid Mirrors |
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Dear Dirk Bruere at NeoPax:
"Dirk Bruere at NeoPax" <dirk.bruere@gmail.com> wrote in message
news:6l7jedFb18tjU1@mid.individual.net...
[quote]... for telescopes.
Cheap, but can only point straight up as any tilt
destroys the parabola. So why not freeze it in
place?
[/quote]
It is done this way with glass. leaving only a final polish
necessary (usually) to capture "vibration rings" from the drive
and supports.
David A. Smith |
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N:dlzc D:aol T:com (dlzc)
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| Posted: Fri Oct 10, 2008 5:33 am Post subject: Re: Liquid Mirrors |
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"Dirk Bruere at NeoPax" <dirk.bruere@gmail.com> wrote in message
news:6l7jedFb18tjU1@mid.individual.net...
[quote]... for telescopes.
Cheap, but can only point straight up as any
tilt destroys the parabola. So why not freeze
it in place?
[/quote]
.... really should append some links...
http://mirrorlab.as.arizona.edu/SOMLBrochure.pdf
http://query.nytimes.com/gst/fullpage.html?res=9406E1DF1439F931A25751C0A963948260&sec=health&spon=&pagewanted=all
http://www.universityscience.ie/pages/scimat_Mirror_Mirror.php
David A. Smith |
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Terry
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| Posted: Sat Oct 11, 2008 5:00 am Post subject: Re: Liquid Mirrors |
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On Fri, 10 Oct 2008 00:46:38 +0100, Dirk Bruere at NeoPax
<dirk.bruere@gmail.com> wrote:
[quote]... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
[/quote]
Done. A long time ago. Check "Amateur Telescope Making" book 1,
Albert Ingalls. Mercury was used, back when it wasn>t as toxic... I
think it was in the 1930s.
There>s also mention of a magnesium oxychloride mirror, made by mixing
solutions of ???, pouring into a mold, and rotating until stiff.
Best -- Terry |
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Fred Kasner
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| Posted: Sat Oct 11, 2008 5:03 am Post subject: Re: Liquid Mirrors |
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Dirk Bruere at NeoPax wrote:
[quote]... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
[/quote]
You could spin it at high speed and produce the necessary liquid surface
for reflection and focusing.
FK |
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Martin Brown
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| Posted: Mon Oct 13, 2008 2:17 pm Post subject: Re: Liquid Mirrors |
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Terry wrote:
[quote]On Fri, 10 Oct 2008 00:46:38 +0100, Dirk Bruere at NeoPax
dirk.bruere@gmail.com> wrote:
... for telescopes.
Cheap, but can only point straight up as any tilt destroys the parabola.
So why not freeze it in place?
Done. A long time ago. Check "Amateur Telescope Making" book 1,
Albert Ingalls. Mercury was used, back when it wasn>t as toxic... I
think it was in the 1930s.
[/quote]
Mercury is still used for this. Metallic mercury isn>t quite that bad
once the surface has matured with a very thin oxide layer on it.
There are some scary pictures of people stood next to one of them
without any PPE.
http://www.astro.ubc.ca/lmt/lzt/index.html
A large zenith telescope isn>t all that much of a handicap if you can
have a swathe of sky to look at sufficient to keep it occupied.
[quote]
There>s also mention of a magnesium oxychloride mirror, made by mixing
solutions of ???, pouring into a mold, and rotating until stiff.
[/quote]
And there was a SciAm article about making your own epoxy resin based
parabolic mirror almost good to long IR wavelengths. The spin method is
also used now to rough out some glass blanks.
In general any phase change either physical or chemical cure released
heat and/or changes volume so distorts the figure. You also have special
problems supporting a thin mirror other than when it is facing
vertically. Engineers for radio astronomy have a structural design that
always distorts under gravity to remain a parabola with a slight change
in focal length depending on the altitude of the object. They are now
being used at optical wavelengths as the techniques cross over.
Regards,
Martin Brown
** Posted from http://www.teranews.com ** |
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