Do amateur adaptive optics work in the visible waveband and are they good for visual astronomy

[kingsbishop]

Hello I’m wondering if adaptive optics work on visual observing or if there is something like that in development?

[Nik271]

I doubt it, for adaptive optics you will need a composite miror made of several parts and this puts you in the realm of big expensive professional research telescopes, and they have no time for visual. 

Live luckly imaging is more likey to be in development, I think this is perfectly possible nowadays and will be a big selling point for planetary observers.

[pipnina]

On 24/11/2022 at 04:28, kingsbishop said:

Hello I’m wondering if adaptive optics work on visual observing or if there is something like that in development?

I imagine any adaptive optics system that works for imaging will work for visual observing too. However the cost of such systems is still very high, far out of the reach of us mortals. I think I have seen telescopes with adaptive secondaries before, but they were "ask for quote" price!

[vlaiv]

It would be useless for amateur observing needs.

Problem is that seeing is both time and direction dependent. Each point in the sky has its own wavefront aberration and is in principle different to any other point in the sky.

To be precise - there is very small "window" around a point that has same / similar aberration - something like few arc seconds in radius - and this is zone that adaptive optics works in.

Such system can't even correct field large enough for planetary observation (in visible light) - it is mostly used for stellar sized objects.

 

[vlaiv]

Here is a bit more on this:

Quote

isoplanatic angle
 

Another parameter of importance in adaptive optics is the isoplanatic angle, http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/theta.gif₀. Suppose that there are two stars close together on the sky. What angle would these two stars have to be separated by in order for them to pass through approximately the same turbulent region of the atmosphere? Figure 62 shows that this can be estimated from the angle over which the turbulence pattern is shifted by a distance of only r₀, in which case the beams from the two stars would share a substantial fraction of the turbulent region (shaded in yellow). Assuming that the turbulent layer is at an altitude h above the telescope, the isoplanatic angle is hence given by

http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/theta.gif₀ = r₀ / h.

At a good observing site on a typical night, h = 10 km and r₀ = 10 cm at http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/lambda.gif₀ = 500 nm. Hence http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/theta.gif₀ = 10^-5 radians, which is ~2". Detailed arguments lead to a more accurate version of this equation: http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/theta.gif₀ ~ 0.314 r₀ / h. The isoplanatic angle determines the area on the sky over which adaptive optics correction is effective. The dependence of http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/theta.gif₀ on r₀ implies that much wider fields (and hence more extended objects) can be corrected with adaptive optics in the infrared than in the optical, making the technique much more attractive in the infrared. The increased isoplanatic angle in the infrared also means that many more natural guide stars are available, as discussed below.

taken from :

http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/phy217_tel_adaptive.html

 

[Astronomist]

Check this out- very cool but probably useless for visual, not to mention obscenely expensive.

https://planewave.com/product/hartsci-clearstar-adaptive-optics/

[tooth_dr]

1 hour ago, Astronomist said:

Check this out- very cool but probably useless for visual, not to mention obscenely expensive.

https://planewave.com/product/hartsci-clearstar-adaptive-optics/

Seems to work only work outside the visible spectrum in the IR region, so definitely not suitable for visual, but a cool product on the euromillions win list of stuff to buy. 

[kingsbishop]

On 27/11/2022 at 09:12, vlaiv said:

It would be useless for amateur observing needs.

Problem is that seeing is both time and direction dependent. Each point in the sky has its own wavefront aberration and is in principle different to any other point in the sky.

To be precise - there is very small "window" around a point that has same / similar aberration - something like few arc seconds in radius - and this is zone that adaptive optics works in.

Such system can't even correct field large enough for planetary observation (in visible light) - it is mostly used for stellar sized objects.

 

If it only corrects a small part then why don’t you use higher magnification?

[vlaiv]

5 hours ago, kingsbishop said:

If it only corrects a small part then why don’t you use higher magnification?

From the text I linked, isoplanatic angle is calculated to be 2" in visible light.

To put this into perspective, here is image of Jupiter as it would appear under high magnification with marked area of 2"x2":

Yellow dot is area corrected. In fact - at this scale, it is even less than that - about a single pixel, but I was not able to mark it that small with the tool I was using.

This is with x300 magnification.

Rest of the image would be "normally blurred" (or even a bit more than normally as it would be affected by deformed mirror - mirror would be deformed to correct just that tiny yellow patch, but it would cause additional blur for the rest of the image where deformation does not match the seeing).

[Nik271]

At the current state this technique is useful for imaging of  stars systems, even exoplanets, accretion discs and neighbourhoods of black holes. No good for visual observation. I think the development of the telescope left visual observing a long time ago, mid 20th century perhaps. That's fine with me, still plenty of fun to be had looking at the sky.

[kingsbishop]

On 28/11/2022 at 18:14, vlaiv said:

From the text I linked, isoplanatic angle is calculated to be 2" in visible light.

To put this into perspective, here is image of Jupiter as it would appear under high magnification with marked area of 2"x2":

Yellow dot is area corrected. In fact - at this scale, it is even less than that - about a single pixel, but I was not able to mark it that small with the tool I was using.

This is with x300 magnification.

Rest of the image would be "normally blurred" (or even a bit more than normally as it would be affected by deformed mirror - mirror would be deformed to correct just that tiny yellow patch, but it would cause additional blur for the rest of the image where deformation does not match the seeing).

But can’t it do the whole planet because the whole planet is bright enough for it to work?

[vlaiv]

2 minutes ago, kingsbishop said:

But can’t it do the whole planet because the whole planet is bright enough for it to work?

It has nothing to do with brightness - it has to do with how atmosphere and light behave.

Here is simplified diagram:

Single point in the sky is effectively at infinity as far as we are concerned, so incoming light from that point that hits our telescope is effectively "parallel". For this reason - any point in the sky will actually have "a pillar" of light that is as wide as telescope aperture, but all these pillars will be at slightly different angle.

For example - Jupiter is about 45 arc seconds in diameter - that means that one side of it is "at an angle" of 45 arc seconds to the other side (or these pillars are at that angle).

Because atmosphere is causing turbulence - any two pillars that are at an angle will first pass thru same piece of atmosphere (bottom part of image) and then slowly diverge as they go up in atmosphere. At some point they will pass thru completely separate pieces of atmosphere.

For small angle - pillars will pass thru same piece of atmosphere for the most part - for large angle - they will quickly diverge and become separate.

As soon as you have two different parts of atmosphere act on light beams - they will be distorted differently. Adaptive optics can correct for either one or the other - but can't do both.

In reality - there is infinite number of such pillars (for every point in the sky) and only group of them that are really close together - and pass thru same piece of atmosphere, can be corrected at the same time. This is isoplanatic angle that was mentioned before - maximum angle that can separate two pillars that will have mostly the same distortion.

It is very small - few arc seconds, while Jupiter is x20 larger than that in diameter - so only very small segment can be corrected (in visible light) at any given moment. Rest of the image will be blurry.

Due to nature of light - small telescopes can't even resolve image that is so small - 2" in diameter (or if you will they can cover it up with 10 or so pixels - and no more resolution than that).

[kingsbishop]

3 hours ago, vlaiv said:

It has nothing to do with brightness - it has to do with how atmosphere and light behave.

Here is simplified diagram:

Single point in the sky is effectively at infinity as far as we are concerned, so incoming light from that point that hits our telescope is effectively "parallel". For this reason - any point in the sky will actually have "a pillar" of light that is as wide as telescope aperture, but all these pillars will be at slightly different angle.

For example - Jupiter is about 45 arc seconds in diameter - that means that one side of it is "at an angle" of 45 arc seconds to the other side (or these pillars are at that angle).

Because atmosphere is causing turbulence - any two pillars that are at an angle will first pass thru same piece of atmosphere (bottom part of image) and then slowly diverge as they go up in atmosphere. At some point they will pass thru completely separate pieces of atmosphere.

For small angle - pillars will pass thru same piece of atmosphere for the most part - for large angle - they will quickly diverge and become separate.

As soon as you have two different parts of atmosphere act on light beams - they will be distorted differently. Adaptive optics can correct for either one or the other - but can't do both.

In reality - there is infinite number of such pillars (for every point in the sky) and only group of them that are really close together - and pass thru same piece of atmosphere, can be corrected at the same time. This is isoplanatic angle that was mentioned before - maximum angle that can separate two pillars that will have mostly the same distortion.

It is very small - few arc seconds, while Jupiter is x20 larger than that in diameter - so only very small segment can be corrected (in visible light) at any given moment. Rest of the image will be blurry.

Due to nature of light - small telescopes can't even resolve image that is so small - 2" in diameter (or if you will they can cover it up with 10 or so pixels - and no more resolution than that).

What I mean is because Jupiter is light around the whole disk of the planet adaptive optics can detect the atmosphere distortion around the whole disk of the planet by using the planet as a guide star and then if it is light around the whole planet then shouldn’t the adaptive optics be able to see the distortion around the whole planet?

[robin_astro]

Simple affordable tip tilt adaptive optics are available (which moves the whole field to follow the seeing which is effectively image stabilisation or fast guiding) This can be effective for small apertures where the atmospheric turbulence scale is larger than the aperture so in bad seeing can potentially reduce the PSF of star images in long exposures beyond what traditional guiding can achieve. I have not heard of anyone using this type of system visually but in any case it would only stabilise the image, not improve the sharpness of planetary detail. 

Cheers

Robin

[vlaiv]

1 hour ago, kingsbishop said:

What I mean is because Jupiter is light around the whole disk of the planet adaptive optics can detect the atmosphere distortion around the whole disk of the planet by using the planet as a guide star and then if it is light around the whole planet then shouldn’t the adaptive optics be able to see the distortion around the whole planet?

Well, no.

First - it is much easier to quantify distortion if there is single point of light - like a star (artificial or real).

As soon as you have extended object - all points of it act as individual stars and distortions start to overlap so it is hard to say what the distortion is - even if it is uniform.

Other issue is that distortion ceases to be uniform over such large area so there is really no single distortion covering jupiter - there is bunch of different distortions, and whichever you pick to use - other parts of jupiter won't be corrected (as it is different distortion).

[vlaiv]

3 minutes ago, robin_astro said:

Simple affordable tip tilt adaptive optics are available (which moves the whole field to follow the seeing which is effectively image stabilisation or fast guiding) This can be effective for small apertures where the atmospheric turbulence scale is larger than the aperture so in bad seeing can potentially reduce the PSF of star images in long exposures beyond what traditional guiding can achieve. I have not heard of anyone using this type of system visually but in any case it would only stabilise the image, not improve the sharpness of planetary detail. 

Cheers

Robin

That is effectively just compensating for mount performance. Over such large field, tilt component of seeing is random and averages to 0, so what is left is just due to mount.

It is beneficial for long exposure/as guiding aid, but, as you pointed out - it would not improve planetary detail (nor stabilize scintillation for that matter).

[robin_astro]

1 hour ago, vlaiv said:

That is effectively just compensating for mount performance. Over such large field, tilt component of seeing is random and averages to 0, so what is left is just due to mount.

This is to improve planetary visual views so the field is not very wide as planets are small (a few tens of arcsec). The fast bulk movement of the planet when viewing at high magnification  in poor seeing is significant and obvious even  with a static mount and this first order movement could be corrected using a tip tilt adaptive optics system working on the planet image via a beam splitter.  Potentially in principle the same technique could even be used to correct the next order field distortion to keep the planet round using a deformable mirror or lens and if you had a system which observed the planet using conventional lucky imaging to continuously produce an optimised image of the planet you could even use that to fully correct the visual view, though that would need a fast computer and a fully deformable corrector and (deep pockets!)

Of course none of this is useful for planetary imaging as you need a high speed imaging system to do this so it is easier to use these images for conventional  lucky imaging post processing

Cheers

Robin

Edited November 29, 2022 by robin_astro
typo

[kingsbishop]

Hello i am wondering there are 2 adaptive optics products I have my eye on that are still in development and I want to know if either of them work in the visible waveband and are they good for visual astronomy

 

is the MATX Adaptive optics kit good for visual astronomy and do they work in the visible waveband?

 

is the AO-2 and AO-5 adaptive optics by Don Bruns good for visual astronomy and do they work in the visible waveband?

 

If not are there any other amateur adaptive optics in development that work in the visible waveband and are good for visual astronomy?

 

 

[Cornelius Varley]

20 hours ago, kingsbishop said:

Hello i am wondering there are 2 adaptive optics products I have my eye on that are still in development and I want to know if either of them work in the visible waveband and are they good for visual astronomy

 

is the MATX Adaptive optics kit good for visual astronomy and do they work in the visible waveband?

 

is the AO-2 and AO-5 adaptive optics by Don Bruns good for visual astronomy and do they work in the visible waveband?

 

If not are there any other amateur adaptive optics in development that work in the visible waveband and are good for visual astronomy?

 

 

Haven't you asked these questions in your other similar threads? It might be better just to concentrate your questions in one of the other threads rather than repeating the same questions.

[Cornelius Varley]

Threads merged.

[kingsbishop]

On 28/11/2022 at 18:14, vlaiv said:

From the text I linked, isoplanatic angle is calculated to be 2" in visible light.

To put this into perspective, here is image of Jupiter as it would appear under high magnification with marked area of 2"x2":

Yellow dot is area corrected. In fact - at this scale, it is even less than that - about a single pixel, but I was not able to mark it that small with the tool I was using.

This is with x300 magnification.

Rest of the image would be "normally blurred" (or even a bit more than normally as it would be affected by deformed mirror - mirror would be deformed to correct just that tiny yellow patch, but it would cause additional blur for the rest of the image where deformation does not match the seeing).

But why are there no images in the visible light for uranus and neptune or the moons of Jupiter, Saturn, uranus and neptune or pluto if the isoplanatic angle is small enough for visible observing on those tiny objects why are they all in infarred?

[andrew s]

The eye brain system is very good at selecting moments of good seeing. That's how our visual forebears managed to see such fine details on the moon and planets.

Not withstanding a few deluded missteps by some observers. 

Regards Andrew 

[vlaiv]

2 hours ago, kingsbishop said:

But why are there no images in the visible light for uranus and neptune or the moons of Jupiter, Saturn, uranus and neptune or pluto if the isoplanatic angle is small enough for visible observing on those tiny objects why are they all in infarred?

I have no idea. We would need to ask scientists working on large telescopes if there is any particular reason for this.

It might be that instruments fitted to large telescopes simply don't record visible light, or that for scientific work - IR data is equally good or even better at revealing what is of interest.

Atmosphere is much more stable in IR part of the spectrum (refraction of light depends on wavelength and shorter wavelengths are bent more than longer - hence rainbow) and maybe its simply not worth spending time on visible part of spectrum.

Nowadays 99% of scientific work in astronomy is done outside of visible spectrum

[ollypenrice]

8 hours ago, andrew s said:

 

Not withstanding a few deluded missteps by some observers. 

Regards Andrew 

Missteps into the canal, from memory...

Splosh!

lly