Adaptive optics for a small telescope

In article , Gleb wrote:
1. To be mounted in 1.25 inch ocular socket (2" socket??). To be used with
telescopes with diameter in the range 25cm to 1m.

I wouldn't waste effort trying to make the kit fit into a 1.25" form
factor - most serious amateurs (if you're talking about metre scale
telescopes, then you're talking about quite seriously committed amateurs) will
have taken the plunge to use 2" eyepieces etc.

On the other hand we have little experience with astronomy and therefore any
advice would help.

Odd. I can't think of any other field than astronomy with a real need
for AO. Might just be my lack of imagination though.

3. The system will require an additional laptop computer to run the AO and
will add to the complexity of the telescope setup.

Will it? The AO would need to be operating while your imager is
accumulating photons, but that accumulation does not really need the active
participation of the computer. While you're reading the imager though, you
don't really need the AO to be operating. Do you?

--
Aidan Karley,
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233

Aidan Karley wrote:
In article , Gleb wrote:

On the other hand we have little experience with astronomy and therefore any
advice would help.

Odd. I can't think of any other field than astronomy with a real need
for AO. Might just be my lack of imagination though.

Long range surveillance cameras and spotting scopes are two that come to
mind. The scintillation distortion looking horizontally though 1000
meters of air in the daytime is often worse than looking at stars though
100km of atmosphere vertically at night. Bigger optics don't help much
for daytime observation as the telescopes are neither limited by photon
rate or the telescope's optical characteristics.

While there wouldn't be bright stars in the field for reference, a low
power near IR laser "collimated" though the same deformable mirror could
illuminate a point in the image plane being viewed. Something under
5mw should do for a distance of 500 to perhaps 2000 meters horizontally
aginst an object of modest albedo like a rock, tree, or building.
It could also provide autofocusing as a side benefit. The AO sensor
could be filtered to only see the laser wavelength, leaving the rest of
the band for the surveillance camera (perhaps also near IR) or a visual
observer. Scintillation is somewhat wavelength dependent, but I'd still
expect a considerable improvment in image quality.

3. The system will require an additional laptop computer to run the AO and
will add to the complexity of the telescope setup.

Will it? The AO would need to be operating while your imager is
accumulating photons, but that accumulation does not really need the active
participation of the computer. While you're reading the imager though, you
don't really need the AO to be operating. Do you?

To be of real use the update rate of the deformable mirror has to be as
fast as the major components of scintillation are changing. In windy
conditions video frame rates of 30 or 60 times per second are none too
fast. It takes a healthy computer to analyze each frame, compute the
motions for all of the actuators and set them in well under 1/60 second.

For a computer which has nothing else to do than read a CCD only one
computer would be needed. If it also has to keep a telescopes altitude
and azimuth servos correct, run an autoguider, and still allow the
telescope operator to play video games it might take two.

There definitely is a market for this. There are people who will spend
$30 000+ for an APO imaging setup (OTA, mount, camera, etc.) and twice
that for an RC. There are two pieces of advice I can offer:
First, keep the final cost of the system under $10 000.
Second, you should try to make it work with F8 systems because most off
the shelf Ritcheys are in this range. If it only woks with F10 or
longer then you will exclude most of your prime market.

Please state what APO and OTA stand for.
RC I suppose means Ritchey Chretien?

To be of real use the update rate of the deformable mirror has to be
as
fast as the major components of scintillation are changing. In windy
conditions video frame rates of 30 or 60 times per second are none
too
fast. It takes a healthy computer to analyze each frame, compute the

motions for all of the actuators and set them in well under 1/60
second.

For a computer which has nothing else to do than read a CCD only one
computer would be needed. If it also has to keep a telescopes
altitude
and azimuth servos correct, run an autoguider, and still allow the
telescope operator to play video games it might take two.

the AO system for Gemini north uses a 400Mhz IBM Power PC processor.
just to give you a benchmark that is about as powerfull as a $150
Playstation 2. to handle every computer controlled operation (including
AO) an astronomer is going to use can be easily handled by a standard
PC of last year.

Gaspard de la Nuit wrote:


There definitely is a market for this. There are people who will
spend
$30 000+ for an APO imaging setup (OTA, mount, camera, etc.) and
twice
that for an RC. There are two pieces of advice I can offer:
First, keep the final cost of the system under $10 000.
Second, you should try to make it work with F8 systems because most
off
the shelf Ritcheys are in this range. If it only woks with F10 or
longer then you will exclude most of your prime market.

Please state what APO and OTA stand for.
RC I suppose means Ritchey Chretien?

APO is short for apochromatic refractor. It is similar to a regular
refractor except it uses exotic glass types to reduce chromatic
aberration.
OTA stands for Optical Tube Assembly. In other words just the telescope
tube with the optics in it. "OTA only" is used to denote a
telescope without mount or eyepieces. Generally if you see a telescope
sold as "OTA only" it does not include a finder scope either. This
is how higher end telescopes are sold because typically when an amateur
finally decides to upgrade he or she already owns a mount and a
collection of eyepieces.

Ian Anderson
www.customopticalsystems.com

On a sunny day (Mon, 21 Mar 2005 08:00:18 -0500) it happened DustyMars
wrote in :

In article ,
says...
I consider designing a low-cost AO system for a small telescope. It
seems we have all necessary resources: we produce deformable mirrors and
wavefront sensors, we also produce closed-loop AO systems with up to 59
channels, so integration wouldn't be too complicated as all structural parts
are available.

On the other hand we have little experience with astronomy and therefore any
advice would help.

The preliminary tech requirements:

1. To be mounted in 1.25 inch ocular socket (2" socket??). To be used with
telescopes with diameter in the range 25cm to 1m.

2. Aberration free afocal mirror system, transparent in the visible and
near IR and fully operational even with AO switched off. To achieve this,
we'll use a system with a field of a couple of mm (in the primary focus)
for a foacl ratio of 1/10. The field and F# are compromized to reduce the
complexity of the optics, but the field will be limited anyway by the
anisoplanatism of the AO and the F# must be small for a HR imaging

3. To have al least 19 degrees of freedom (depending on the seeing can be
good to correct up to ~13 Zernike terms to about 10% of the uncorrected
value). 37 degrees of freedom is also possible but I'm not sure a small
scope really will collect enough light to correct that many terms in real
time.

4. To operate on a natural star with magnitude of at least 4 (with a 25cm
telescope), using 50% of light for running the AO and 50% for registration.

5. To be easy in setting up and running. To use single +12V power supply
and three cables connecting the system with the deformable mirror
controller and the dedicated control laptop PC.

6. The total weight of the optical correction unit mounted to the telescope
not to exceed 1kg. Mirror controller incl power supply - also 1 kg, add some
extra for cables and laptop.


The system is supposed to provide a diffraction-limited imaging in a rather
bad seeing conditions. It will allow stable imaging of bright objects such
as stars, double stars and planets. Another advantage of using such a
system is that it will correct the aberrations of the telescope, improving
the quality of optics, for instance making the period of mirror cooling also
available for observations. In fact, correction of the static aberrations
can be done on a bright star once, and then the system can be used in
static correction mode.

The project is technically feasible (although quite expensive in its
development stage), but I still have my doubts regarding its usefulness:

An interesting article on the practical application of Adaptive optics
can be found he
http://www.journals.uchicago.edu/AJ/...90240/brief/99
0240.abstract.html
I have been wondering if somehow fluid lenses could be used for adaptive
optics in a telescope.
Then you could use electical voltages to change lens properties locally.
http://www.heise.de/newsticker/resul...einze%20Linsen
It is a German article, in short it describes a lens formed by a layer of oil
on a layer of some other fluid, with an electical field applied.
These lenses are extremely small, a French company has already made a zoom
objective for a cellphone camera with this technology.
http://www.varioptic.com/en/
It uses less power then a mechanical construction.
I wonder if a big one could be made....

Jan Panteltje wrote:

I have been wondering if somehow fluid lenses could be used for adaptive
optics in a telescope.
Jan,

I don't think actuation is a critical problem, more like others have
said, AO for astronomy is light starved and needs to be high speed.

Steve

On a sunny day (Mon, 21 Mar 2005 17:14:42 +0000) it happened Steve
wrote in
:

Jan Panteltje wrote:

I have been wondering if somehow fluid lenses could be used for adaptive
optics in a telescope.
Jan,

I don't think actuation is a critical problem, more like others have
said, AO for astronomy is light starved and needs to be high speed.
Yes, I think fluid lenses have the high speed, maybe it could be build
in the eyepiece... integrated with a chip to activate it?
As to the light losses, OK, did I see f2.8 to f1.4 on a site?

Steve

On Mon, 21 Mar 2005 14:03:07 GMT, Jan Panteltje
wrote:

I have been wondering if somehow fluid lenses could be used for adaptive
optics in a telescope...

The most basic AO correction is for image shift (usually called
tip/tilt). Any system needs to address this, and it isn't obvious how
fluid lenses could do so.

Beyond that, there are many high order corrections. While this can
involve a change in focus, which a variable lens could correct for, the
corrections are typically achieved by altering the wavefront over
multiple zones- something a single lens can't do.

The usual actuator for AO is a flexible mirror, and this is not the
difficult part of the problem. A flexible mirror can be made quite
inexpensively these days, especially if there were some high volume
application.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On a sunny day (Mon, 21 Mar 2005 18:33:31 GMT) it happened Chris L Peterson
wrote in
:

On Mon, 21 Mar 2005 14:03:07 GMT, Jan Panteltje
wrote:

I have been wondering if somehow fluid lenses could be used for adaptive
optics in a telescope...

The most basic AO correction is for image shift (usually called
tip/tilt). Any system needs to address this, and it isn't obvious how
fluid lenses could do so.

Beyond that, there are many high order corrections. While this can
involve a change in focus, which a variable lens could correct for, the
corrections are typically achieved by altering the wavefront over
multiple zones- something a single lens can't do.

The usual actuator for AO is a flexible mirror, and this is not the
difficult part of the problem. A flexible mirror can be made quite
inexpensively these days, especially if there were some high volume
application.
I was under the impression (could be wrong of cause) that in these fluid
lenses the curvature is set by a voltage gradient.
That would mean that if you had several electrodes, you could control
curvature locally perhaps.
Transparent metallized pattern on bottom container concected to output
electrodes of a chip?
These things only take a few volt.
Who knows what the future will bring.