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| David Jonsson... |
 Posted: Thu Nov 19, 2009 5:33 am |
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Hi
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
David |
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| HVAC... |
| Posted: Thu Nov 19, 2009 12:13 pm |
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"David Jonsson" <davidjonssonsweden at (no spam) gmail.com> wrote in message
news:069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com...
[quote]Hi
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
[/quote]
Well, of course in ANY infrared telescope, cooling
is essential. |
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| Saul Levy... |
| Posted: Thu Nov 19, 2009 12:31 pm |
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Mainly in the telescope only the INSTRUMENT is cooled.
The rest is just GOOD DESIGN!
Satellites have MORE cooling.
Saul Levy
On Thu, 19 Nov 2009 12:13:46 -0500, "HVAC" <harlowcampbell at (no spam) gmail.com>
wrote:
[quote]"David Jonsson" <davidjonssonsweden at (no spam) gmail.com> wrote in message
news:069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com...
Hi
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
Well, of course in ANY infrared telescope, cooling
is essential.[/quote] |
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| David Jonsson... |
| Posted: Thu Nov 19, 2009 2:29 pm |
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On Nov 19, 6:31 pm, Saul Levy <saulle... at (no spam) cox.net> wrote:
[quote]Mainly in the telescope only the INSTRUMENT is cooled.
The rest is just GOOD DESIGN!
Satellites have MORE cooling.
Saul Levy
On Thu, 19 Nov 2009 12:13:46 -0500, "HVAC" <harlowcampb... at (no spam) gmail.com
wrote:
"David Jonsson" <davidjonssonswe... at (no spam) gmail.com> wrote in message
news:069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com....
Hi
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
Well, of course in ANY infrared telescope, cooling
is essential.
[/quote]
I mean traditional telescopes. Thermal disturbance would mainly be in
infrared but I assume also in less amount in shorter visible
wavelenghts?
How would one calculate the thermal disturbance on a lens in a optical
telescope?
David |
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| Saul Levy... |
| Posted: Thu Nov 19, 2009 7:37 pm |
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You can see at high magnification the thermal waves going by.
Like optical errors in a telescope they are measured in wavefront
errors.
Saul Levy
On Thu, 19 Nov 2009 16:29:17 -0800 (PST), David Jonsson
<davidjonssonsweden at (no spam) gmail.com> wrote:
[quote]On Nov 19, 6:31 pm, Saul Levy <saulle... at (no spam) cox.net> wrote:
Mainly in the telescope only the INSTRUMENT is cooled.
The rest is just GOOD DESIGN!
Satellites have MORE cooling.
Saul Levy
On Thu, 19 Nov 2009 12:13:46 -0500, "HVAC" <harlowcampb... at (no spam) gmail.com
wrote:
"David Jonsson" <davidjonssonswe... at (no spam) gmail.com> wrote in message
news:069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com...
Hi
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
Well, of course in ANY infrared telescope, cooling
is essential.
I mean traditional telescopes. Thermal disturbance would mainly be in
infrared but I assume also in less amount in shorter visible
wavelenghts?
How would one calculate the thermal disturbance on a lens in a optical
telescope?
David[/quote] |
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| Dan Birchall... |
| Posted: Fri Nov 20, 2009 2:56 am |
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davidjonssonsweden at (no spam) gmail.com (David Jonsson) wrote:
[quote]I mean traditional telescopes. Thermal disturbance would mainly be in
infrared but I assume also in less amount in shorter visible
wavelenghts?
[/quote]
In the case of terrestrial telescopes, there are 2-3 temperatures you'd
be concerned with:
1. The temperature of the outside air,
2. The temperature of the air inside the dome (if you have a dome), and
3. The temperature of your mirror.
All of those temperatures should be as similar as possible; if there
are significant differences, you'll get thermal disturbance that will
impact your seeing. You definitely _don't_ want to make your telescope
unnaturally cooler than the surrounding air.
Our scope has sensors all over the place; glancing at about 30 of them
right now during operations, almost everything is between -1 and +1
celsius, which is pretty good.
--
djb at (no spam) | Dan Birchall, Night Operation Assistant, Subaru Telescope/NAOJ.
naoj | Views I express are my own, obviously not those of my employer.
..org | I only wear black so much because I can't find anything darker. |
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| Odysseus... |
| Posted: Fri Nov 20, 2009 4:02 am |
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In article
<069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com>,
David Jonsson <davidjonssonsweden at (no spam) gmail.com> wrote:
[quote]I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
[/quote]
Cooling is used in astrophotography, but I can't see any point to
cooling a lens. As Dan said, you generally want the whole instrument to
be at uniform temperature, in equilibrium with the air, to minimize
convection currents in the optical path.
In the day of film, astronomical cameras were often cooled to take long
exposures with hypersensitive emulsions; nowadays high-end cameras have
cooled sensors to reduce noise.
--
Odysseus |
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| Saul Levy... |
| Posted: Fri Nov 20, 2009 11:20 am |
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The atmosphere is usually the worst offender.
It's a REAL MESS in most places.
Saul Levy
On Fri, 20 Nov 2009 09:02:49 GMT, Odysseus
<odysseus1479-at at (no spam) yahoo-dot.ca> wrote:
[quote]In article
069f42a1-72b9-4691-b513-b63c3d996289 at (no spam) m26g2000yqb.googlegroups.com>,
David Jonsson <davidjonssonsweden at (no spam) gmail.com> wrote:
I assume that security intelligence gathering is more evolved than
astronomy. I read about a method used in surveillance satellites where
they cooled the lens in telescopes to get better pictures. Is this
method used in astronomy too? Are there any calculations on how much
disturbance the heat in a glass lens or reflecting mirror causes?
Cooling is used in astrophotography, but I can't see any point to
cooling a lens. As Dan said, you generally want the whole instrument to
be at uniform temperature, in equilibrium with the air, to minimize
convection currents in the optical path.
In the day of film, astronomical cameras were often cooled to take long
exposures with hypersensitive emulsions; nowadays high-end cameras have
cooled sensors to reduce noise.[/quote] |
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| David Jonsson... |
| Posted: Sun Nov 22, 2009 8:36 am |
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Thanks for all replies.
What about space telescopes then? I can imagine that they are only in
use on the dark side of Earth where temperature is low?
David |
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| Saul Levy... |
| Posted: Sun Nov 22, 2009 5:06 pm |
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Sats. spend about HALF their time in sunlight, David!
They are INSULATED and have TEMPERATURE CONTROLS.
Saul Levy
On Sun, 22 Nov 2009 10:36:42 -0800 (PST), David Jonsson
<davidjonssonsweden at (no spam) gmail.com> wrote:
[quote]Thanks for all replies.
What about space telescopes then? I can imagine that they are only in
use on the dark side of Earth where temperature is low?
David[/quote] |
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| Odysseus... |
| Posted: Sun Nov 22, 2009 6:22 pm |
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In article
<019a16a1-d5a7-45dd-847a-c929fc750fae at (no spam) p35g2000yqh.googlegroups.com>,
David Jonsson <davidjonssonsweden at (no spam) gmail.com> wrote:
[quote]What about space telescopes then? I can imagine that they are only in
use on the dark side of Earth where temperature is low?
[/quote]
No: that wouldn't be practical. Above the atmosphere "seeing" is more or
less perfect regardless of temperature -- there's no convection or
conduction to speak of -- so heat-management isn't much of an issue for
the optics. It's impossible for an orbiting satellite to remain in the
Earth's shadow; in low Earth orbit there's only shade for about half an
hour at a time, alternating with an hour of sunshine. Moreover solar
panels are much handier than nuclear power-plants.
Instead, space telescopes (like many other satellites) are wrapped in
reflective insulating material to mitigate the effects of radiation &
thermal cycling on the workings. The infrared cameras have powerful
cryogenics for their sensors. (Hubble started out with an 'ice-block'
made of nitrogen, but it boiled away earlier than expected, so was
replaced with a 'freezer' on the third service mission.) Of course the
operators take care not to let an instrument point toward the Sun.
--
Odysseus |
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| G=EMC^2 Glazier... |
| Posted: Mon Nov 23, 2009 3:55 pm |
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David Cold lens here in Florida would make it wet. I an drinking a cold
can of Bud and my hands a dripping Get the picture Bert |
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