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space telescope design using artificial guide stars

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Jamie M
Guest

Thu Jan 10, 2019 2:45 pm   



On 1/10/2019 2:03 AM, Martin Brown wrote:
Quote:
On 09/01/2019 19:01, Jamie M wrote:


That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

There was a time when this was done for hard X-rays before narrow
angle glancing incidence imaging was possible.

Hi,

That is a stationary mask pattern that was used which is integral to the
X-ray telescope.

At least one was proposed (not sure if it was ever built) that consisted
of a 1-D quadratic residue mask in front of a wider block of detectors.
The spinning satellite would then image the object in radial slices.

They were all big blocks of scintillator with photomultiplier detectors.
The initial design was complete rubbish designed at Saclay in France
where they put their atomic bomb makers out to grass.

http://adsabs.harvard.edu/abs/1983A%26A...120..150D

It was actually for gamma-rays.

They tried to use maximum entropy to tart up the results but basically
as published the thing lacked adequate discrimination and had ghosts.

Imagine if you replace the stationary coded aperature mask pattern with
a transparent LCD screen, ie like this one:

https://www.youtube.com/watch?v=wxjZu7F2GfI

If a space rated version is put in space, between an optical telescope
and the object being viewed, it could have the effect of vastly
improving the resolving power of the telescope by cycling the pixels
from transparent to opaque in a repeatable pattern. Also optionally
colour filtering could be done if using a monochrome CCD on the
telescope.

It wouldn't make a blind bit of difference to the resolving power of the
telescope which is determined fundamentally by the longest baseline that
it correlates photons over (typically diameter of its optics).

The distance from the telescope to the LCD coded aperature depends on
how wide the LCD is and the pixel size, and the angular resolution of
the telescope, but it would be effective over a large range of distances.

The aperture would have to introduce a uniform phase delay if it was to
work at all. Mainly coded apertures allow you to alter the depth of
field after taking the image data but when everything you are looking at
is effectively at infinity this is not an advantage in astronomy and
merely degrades signal to noise with no benefits at all.


Hi,

Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)

pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)

If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active at a
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.

It would be a lot more efficient to use an actual telescope and a higher
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.

There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.

The brightness seen by the telescope would be reduced compared to not
using the LCD, due to small transmission loss through the transparent
screen, as well as the percentage of masked pixels. Noise floor
considerations on the telescope would be a limit to resolving power,
since even a single pixel telescope with sufficient light detection
could resolve with an LCD coded aperture.

cheers,
Jamie











>

Jamie M
Guest

Thu Jan 10, 2019 2:45 pm   



On 1/9/2019 8:50 PM, Jasen Betts wrote:
Quote:
On 2019-01-09, Jamie M <jmorken_at_shaw.ca> wrote:


Imagine if you replace the stationary coded aperature mask pattern with
a transparent LCD screen, ie like this one:

https://www.youtube.com/watch?v=wxjZu7F2GfI

you'd have to make it optically flat and deal with diffraction
artifacts from the grid.


I think it would only need to be optically flat enough so that the
light from the LCD hits somewhere on the telescope, ie +-0.0001 degree?
(depends on the aperture of the telescope and distance to the LCD)

As since the LCD aperture is software controlled the error in
optical flatness can be compensated for as long as some part of
the telescope gets hit by the light from the LCD.

cheers,
Jamie

Martin Brown
Guest

Fri Jan 11, 2019 11:45 am   



On 10/01/2019 12:51, Jamie M wrote:
Quote:
On 1/10/2019 2:03 AM, Martin Brown wrote:

The aperture would have to introduce a uniform phase delay if it was
to work at all. Mainly coded apertures allow you to alter the depth of
field after taking the image data but when everything you are looking
at is effectively at infinity this is not an advantage in astronomy
and merely degrades signal to noise with no benefits at all.

Hi,

Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)

pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)

If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active at a
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.


Congratulations. You have reinvented the pinhole camera.

Quote:
It would be a lot more efficient to use an actual telescope and a higher
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.

There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.


You really are utterly clueless. The incident wavefronts must remain
coherent through the optical chain to make a diffraction limited image.

The moon dark side occulting stars and radio sources has in the past
been used as a means to determine their position. Back in the days when
radio telescopes all had very poor resolution. These days star positions
are known so well it is used by amateurs to determine the heights of
mountains at the lunar limb in grazing occultations.

A very lucky occultation of a fairly bright star by Titan gave the first
hints that it had an atmosphere in 1989. There is a video of it (link
seems to have vanished). A diffraction peak at mid eclipse was predicted
but it was way brighter than expectations from a pure geometrical disk.
The atmosphere boosted the signal.

https://astrotalkuk.org/episode-14titan/

Looking for microlensing by compact objects passing in front of distant
stars is an active area of research.

--
Regards,
Martin Brown

Jamie M
Guest

Fri Jan 11, 2019 2:45 pm   



On 1/11/2019 1:52 AM, Martin Brown wrote:
Quote:
On 10/01/2019 12:51, Jamie M wrote:
On 1/10/2019 2:03 AM, Martin Brown wrote:

The aperture would have to introduce a uniform phase delay if it was
to work at all. Mainly coded apertures allow you to alter the depth
of field after taking the image data but when everything you are
looking at is effectively at infinity this is not an advantage in
astronomy and merely degrades signal to noise with no benefits at all.

Hi,

Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)

pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)

If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active at a
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.

Congratulations. You have reinvented the pinhole camera.


Hi,

A pinhole lens camera has a single small aperture and projects the image
onto a CCD, not sure how you confuse that with the 4 pixel coded
aperture I described.

Quote:

It would be a lot more efficient to use an actual telescope and a higher
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.

There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.

You really are utterly clueless. The incident wavefronts must remain
coherent through the optical chain to make a diffraction limited image.


Assuming the waveform isn't coherent is just ignoring the main idea of
using a variable coded aperture to effectively increase angular
resolution of a telescope, in favour of irrelevent details. Here is a
simple fix if you are too lazy to imagine a sufficiently flat LCD
masking screen to keep phase error low enough:

Replace the transparent LCD with a laser cut stainless steel sheet, with
concentric cutouts in the same idea as a DVD optical disc. The cutouts
will pass the light from the star with no impact on the light as
it is travelling through free space. Rotate the stainless steel sheet
on its axis, axially between the telescope and the object(s) being
imaged to have the effect of creating a repeatable variable coded
aperture.

cheers,
Jamie


Quote:

The moon dark side occulting stars and radio sources has in the past
been used as a means to determine their position. Back in the days when
radio telescopes all had very poor resolution. These days star positions
are known so well it is used by amateurs to determine the heights of
mountains at the lunar limb in grazing occultations.

A very lucky occultation of a fairly bright star by Titan gave the first
hints that it had an atmosphere in 1989. There is a video of it (link
seems to have vanished). A diffraction peak at mid eclipse was predicted
but it was way brighter than expectations from a pure geometrical disk.
The atmosphere boosted the signal.

https://astrotalkuk.org/episode-14titan/

Looking for microlensing by compact objects passing in front of distant
stars is an active area of research.


Jamie M
Guest

Sat Jan 12, 2019 11:45 pm   



Hi,

I think if using a spinning disc with cutouts for the variable
coded aperture, to have an optimal placement of cutouts, I think
2D golomb rulers, or Costas array's would work:

https://en.wikipedia.org/wiki/Costas_array

https://www.researchgate.net/publication/307851185_Simulation_and_Analysis_of_Optimum_Golomb_Ruler_Based_2D_Codes_for_OCDMA_System

cheers,
Jamie



On 2019-01-11 5:41 a.m., Jamie M wrote:
Quote:
On 1/11/2019 1:52 AM, Martin Brown wrote:
On 10/01/2019 12:51, Jamie M wrote:
On 1/10/2019 2:03 AM, Martin Brown wrote:

The aperture would have to introduce a uniform phase delay if it was
to work at all. Mainly coded apertures allow you to alter the depth
of field after taking the image data but when everything you are
looking at is effectively at infinity this is not an advantage in
astronomy and merely degrades signal to noise with no benefits at all.

Hi,

Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)

pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)

If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active at a
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.

Congratulations. You have reinvented the pinhole camera.

Hi,

A pinhole lens camera has a single small aperture and projects the image
onto a CCD, not sure how you confuse that with the 4 pixel coded
aperture I described.


It would be a lot more efficient to use an actual telescope and a higher
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.

There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.

You really are utterly clueless. The incident wavefronts must remain
coherent through the optical chain to make a diffraction limited image.

Assuming the waveform isn't coherent is just ignoring the main idea of
using a variable coded aperture to effectively increase angular
resolution of a telescope, in favour of irrelevent details.  Here is a
simple fix if you are too lazy to imagine a sufficiently flat LCD
masking screen to keep phase error low enough:

Replace the transparent LCD with a laser cut stainless steel sheet, with
concentric cutouts in the same idea as a DVD optical disc.  The cutouts
will pass the light from the star with no impact on the light as
it is travelling through free space.  Rotate the stainless steel sheet
on its axis, axially between the telescope and the object(s) being
imaged to have the effect of creating a repeatable variable coded
aperture.

cheers,
Jamie



The moon dark side occulting stars and radio sources has in the past
been used as a means to determine their position. Back in the days
when radio telescopes all had very poor resolution. These days star
positions are known so well it is used by amateurs to determine the
heights of mountains at the lunar limb in grazing occultations.

A very lucky occultation of a fairly bright star by Titan gave the
first hints that it had an atmosphere in 1989. There is a video of it
(link seems to have vanished). A diffraction peak at mid eclipse was
predicted but it was way brighter than expectations from a pure
geometrical disk. The atmosphere boosted the signal.

https://astrotalkuk.org/episode-14titan/

Looking for microlensing by compact objects passing in front of
distant stars is an active area of research.



Jamie M
Guest

Tue Jan 15, 2019 8:45 am   



Hi,

A recently developed technology called COACH using coded apertures for
optical telescopes (coded aperture correlation holography)

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-11-12430

https://www.sciencedaily.com/releases/2019/01/190104104030.htm

cheers,
Jamie





On 2019-01-12 2:04 p.m., Jamie M wrote:
Quote:
Hi,

I think if using a spinning disc with cutouts for the variable
coded aperture, to have an optimal placement of cutouts, I think
2D golomb rulers, or Costas array's would work:

https://en.wikipedia.org/wiki/Costas_array

https://www.researchgate.net/publication/307851185_Simulation_and_Analysis_of_Optimum_Golomb_Ruler_Based_2D_Codes_for_OCDMA_System


cheers,
Jamie



On 2019-01-11 5:41 a.m., Jamie M wrote:
On 1/11/2019 1:52 AM, Martin Brown wrote:
On 10/01/2019 12:51, Jamie M wrote:
On 1/10/2019 2:03 AM, Martin Brown wrote:

The aperture would have to introduce a uniform phase delay if it
was to work at all. Mainly coded apertures allow you to alter the
depth of field after taking the image data but when everything you
are looking at is effectively at infinity this is not an advantage
in astronomy and merely degrades signal to noise with no benefits
at all.

Hi,

Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)

pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)

If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active
at a
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.

Congratulations. You have reinvented the pinhole camera.

Hi,

A pinhole lens camera has a single small aperture and projects the image
onto a CCD, not sure how you confuse that with the 4 pixel coded
aperture I described.


It would be a lot more efficient to use an actual telescope and a
higher
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.

There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.

You really are utterly clueless. The incident wavefronts must remain
coherent through the optical chain to make a diffraction limited image.

Assuming the waveform isn't coherent is just ignoring the main idea of
using a variable coded aperture to effectively increase angular
resolution of a telescope, in favour of irrelevent details.  Here is a
simple fix if you are too lazy to imagine a sufficiently flat LCD
masking screen to keep phase error low enough:

Replace the transparent LCD with a laser cut stainless steel sheet, with
concentric cutouts in the same idea as a DVD optical disc.  The cutouts
will pass the light from the star with no impact on the light as
it is travelling through free space.  Rotate the stainless steel sheet
on its axis, axially between the telescope and the object(s) being
imaged to have the effect of creating a repeatable variable coded
aperture.

cheers,
Jamie



The moon dark side occulting stars and radio sources has in the past
been used as a means to determine their position. Back in the days
when radio telescopes all had very poor resolution. These days star
positions are known so well it is used by amateurs to determine the
heights of mountains at the lunar limb in grazing occultations.

A very lucky occultation of a fairly bright star by Titan gave the
first hints that it had an atmosphere in 1989. There is a video of it
(link seems to have vanished). A diffraction peak at mid eclipse was
predicted but it was way brighter than expectations from a pure
geometrical disk. The atmosphere boosted the signal.

https://astrotalkuk.org/episode-14titan/

Looking for microlensing by compact objects passing in front of
distant stars is an active area of research.





Guest

Tue Jan 15, 2019 10:45 am   



On Tuesday, 15 January 2019 08:34:15 UTC+1, Jamie M wrote:
Quote:
Hi,

A recently developed technology called COACH using coded apertures for
optical telescopes (coded aperture correlation holography)

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-11-12430

https://www.sciencedaily.com/releases/2019/01/190104104030.htm


So you re-developed interferometry. Good job.

The huge mirrors are not there to increase resolution but to get more light to the sensor.

Bye Jack

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