Adaptive optics for a small telescope

On Mon, 21 Mar 2005 18:47:47 GMT, Jan Panteltje
wrote:

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.

I can certainly believe it is possible to make a fluid lens where
complex spatial changes in curvature can be controlled. But the current
technology seems limited to essentially changing the simple curvature of
a meniscus.

_________________________________________________

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

"Chris L Peterson" wrote in message
...
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.


The flexible mirror, by itself, if useless unless coupled with actuators that
can deform it, a computer to drive the actuators based on some measurements of
the wavefront distortion, and a means to take those measurements. For amateur
use this probably means something quite a bit smaller and far more economical
than what the professionals use. Whether such a device can be made small enough
and economical enough is one question. Whether enough amateurs will use it is
another.

As I see it, you might invent a telescope whose primary, probably a mirror, can
do it, but its utility might be questionable, depending on the method chosen to
measure the wavefront distortion, but an add-on to an existing system doesn't
seem to be practical. Then there's the question of the economics of it all.

This has been the trend for decades now. The professionals come up with some
idea for their requirements. Some amateurs with enough resources to try it for
themselves find a more economical way to do it, but there is either not enough
interests in the possibilities or enough amateurs with the right resources to
copy the attempt. If both of these problems are overcome, then it starts making
significant inroads into the amateur community. Autoguiding, CCD imaging, even
webcams which can be seen as fast data takes ala scintillation imagers (but used
for different purposes and goals) were done via this route. Not everything has
flowed in this direction of course, because the requirements of the
professionals don't necessarily overlap with those of the amateur, but some
have.
--
Sincerely,
--- Dave
----------------------------------------------------------------------
It don't mean a thing
unless it has that certain "je ne sais quoi"
Duke Ellington
----------------------------------------------------------------------

IMHO,

A.O. Has never been closer to the reach of Amateur Astronomy.
As the industrial push for A.O. continues, the possibility of lower cost
components has already become evident with sites like Ebay where
I have seen tip/tilt and DMs for sale.

For Astronomy, Location, location, location, location.
You use AO with your best telescope at the best site.
Best results in a photon limited system comes from systems that need
the least static corrections (optics) and have the lowest optically
significant turbulence. AO can't make a bad site good.

We did some seeing measurements two months ago at the VATT and had
seeing from 0.5 to 1.5 arc seconds most of the time. 80 or 90 percent of
the seeing was near the telescope. (under 1 Km) We are not ready to say
how much was at the telescope/dome level but I suspect from a few
percent to all at times.

This means:
Speeds are not as high as the upper layers
Iso patch size is larger than in an upper layer dominated case

D.O.D. ie star wars did R and D using AO for various applications and
produced high order non photon limited systems with as high a bandwidth
as they could because the were tracking bats out of hell.

Mt Wilson has such a mirror, 256 elements ? and on the Hooker (100")
can go down to 12 th ? depending on the color of the star.

You need a big scope to go to faint.

The Old Mt Wilson AO system used a custom TEC CCD
and a lot of DSP boards not to mention 256 Hv amplifiers.

These systems used a wave front detector, usually a Shack/Hartmann
that breaks the light in to sub pupils used to control the tip/tilt of
each region buy the displacement transducer near the sub pupils. The
Reconstructor takes the wavefront signals and produces mirror control
signals. Faster is better as you are in a control loop.

All of the above is simplified by measuring and controlling the mirror
curvature. F. Roddier is the man to read the works of to understand all
about it. The re constructor for a curvature system is a diagonal matrix
making it fast. My first system was analog the computer just
watched the loop, taking data.

Curvature mirrors are being made for optical communications and as the
volume goes up the prices go down. These are low voltage pizo bimorph
mirrors and could be made cheap if you knew how. (i don't)

That leaves the detector and that's the rub. To work well it needs to
be noiseless with high Q.E. not to mention a fast readout time.

We used APD detectors and kHZ readout rates =$$$
and a fiber fed lens array (low fat) and that is another trick.

CMOS based sensors are in a fast lane to low noise performance.
It may be possible to obtain cmos sensors with machine vision processors
integrated in the near future.

I would start by using a bimorph to correct the static mirror errors
first. You would have a knob for tip/tilt, defocus, astigmatism X any Y
etc. That would allow people like me with aging eyes to be able to enjoy
not wearing glasses at the eyepiece.

When a detector comes along then go for it. While you are waiting you
could play with non photon limited bright systems. For vibration these
systems need to be fast with a large tip/tilt range. With a laser beacon
or possibly with techniques used in solar adaptive optics one could make
a daytime horizontal path system.

One last comment (Whew)

See Hardy and Wallner SPIE Vol 2201 Adaptive Optics in Astronomy
(1994) pp 77-87

"Wavefront compensation using active lenses"

Using two lenses that you tip/tilt and dispalce will correct
eight Zernike terms. They tell all.


Clear dark steady and closed loop.

Dan

Babcock's proposed (1953) Eidophor used a mirror covered with a film of oil
scanned by an electron beam to change the local slope.

It was never implemented, however.

Marc Reinig
UCO Lick Observatory
Laboratory for Adaptive Optics

"Jan Panteltje" wrote in message
news:1111413792.625bb338adab5b3084454285a3190639@t eranews...
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....

Adaptive optics for a small telescope?

"Babcock's proposed (1953)
Eidophor used a mirror covered
With a film of oil
Ccanned by an electron beam
To change the local slope.

It was never implemented,
However."

~ Marc Reinig
UCO Lick Observatory
Laboratory for Adaptive Optics

"Renigging?
Truth, redress, forthcoming?"
~ Twittering

Adaptive optics for a small telescope?

"Babcock's proposed (1953)
Eidophor used a mirror covered

With a film of oil
Scanned by an electron beam
To change the local slope.

It was never implemented,
However."

~ Marc Reinig
UCO Lick Observatory
Laboratory for Adaptive Optics

"Reneging?
Truth, redress, confession, forthcoming?

Annus Horribilis ~ A year of great unhappiness
Or misfortune."
~ Twittering

Vulgaris
Vulgate
Vulgar Latin
Vulgarity

Vulture!

Vying ~
Flying

Steve wrote:

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.

IIRC the rest of AO (usually implemented as a deformable mirror, not a
lens) is an artificial star created with a laser, and used with
detectors and a serious computer to correct for atmospheric distortions.

The FAA seems to be a bit nervous these days about lasers being shot
into the sky...

--
Pat O'Connell
[note munged EMail address]
Take nothing but pictures, Leave nothing but footprints,
Kill nothing but vandals...

Why not search for a cure to prostate problems first, and go back to
outfitting dog sleds with J12 Pratt & Whittney engines? !?


Gleb wrote:

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:

1. Small field and ability to work on only bright objects will limit the
usability to very bright double stars and planets. Are (amateur) astronomers
really interested in this?

2. Although we plan to have it transparent, the system will limit the field
of view and reduce the amount of light available for observation. The light
loss will be compensated by the resolution gain, but the effect can be
limited or even negligible for a small telescope.

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

4. It can be quite expensive, especially in the beginning, though if there
is a market, the price can be very acceptable.

I would appreciate any comments on the above mentioned topics.

Gleb Vdovin
OKO Tech
PO Box 581, 2600 AN Delft, The Netherlands
http://www.okotech.com

Marc Reinig wrote:

Babcock's proposed (1953) Eidophor used a mirror covered with a film of oil
scanned by an electron beam to change the local slope.

It was never implemented, however.

? Eidophors were invented by Fischer in 1939 and the first one
demonstrated in 1943. There was one still in use in a lecture theatre at
my university in the late 1970's.

There is a picture of the prototype online at:
http://www.cinephoto.co.uk/eidophor_1.htm

Regards,
Martin Brown

Marc Reinig
UCO Lick Observatory
Laboratory for Adaptive Optics

"Jan Panteltje" wrote in message
news:1111413792.625bb338adab5b3084454285a3190639@t eranews...

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....