94 replies to this topic

[CharlesC]

Is there Adaptive Optics equipment available to amateurs?

 

 

[mclewis1]

SBIG AO series ... been around for a few years.

 

https://www.sbig.com...daptive-optics/

[gdd]

Here is one from Orion which can be used with other cameras:

http://www.telescope.../61/p/53076.uts

 

Gale

[Eddgie]

Is there Adaptive Optics equipment available to amateurs?

 

The optics the others are referring to are not the same thing that many people used to mean when talking about "Adaptive Optics," and I am not sure the equipment they are referring is the same thing that you were thinking about.

 

The optics mentioned above are often referred to as "Active Optics" as well as "Adaptive Optics."

 

Must of us heard the term "Adaptive Optics" in the context of optics that could correct for seeing.  This technology typically used a reference laser beamed into the sky and mirror warping on the primary to deform the primary or the primary mirror segments to attempt to adapt the mirror to the aberrated wavefront entering the aperture. In other words, they improved the aberrations resulting from seeing.

 

The "Active Optics" are more accurately referred to at "Tip/Tilt High Speed Guiding."  This technology is really geared more to reducing the effect of vibrations on the mount, or minute tracking errors, or lower order atmospheric shift (low frequency wavering in the atmosphere that causes the star to move around, and not the kind of aberration that comes from the more normal seeing where the star is fuzzed up or the diffraction rings are flaring and breaking.

 

From the web page: These AO systems use a tip-tilt transmissive element to correct for image wander due to low order local atmospheric effects and for correction of mount errors, wind vibration and other erratic motion of the optical system that is otherwise too fast for an autoguider or telescope drive corrector to respond to effectively.

 

So, if you are looking to correct image wander, these devices mentioned are all you need.

 

If you are looking for adaptive optics that correct wave-front aberrations, these systems don't do that.  They only correct for image wander.

Edited by Eddgie, 24 November 2014 - 12:18 AM.

[WebFoot]

When I imaged with my Meade fork-mounted scopes, I was able to completely compensate for the mount wobbles with the SBIG AO-7.

 

Marketed as an "adaptive optics" system, it's nothing at all like a "real" adaptive optics system.  Instead, It's just a fast guider, using a mirror to subtly adjust the light path as many as 30/Hz.  It's an amazing tool.

 

So, yes, there are very effective tools, called "adaptive optics" out there, for imaging, but they're not really adaptive optics as exist at, say, Mt. Palomar.

 

Mark

[gdd]

 

Is there Adaptive Optics equipment available to amateurs?

 

The optics the others are referring to are not the same thing that many people used to mean when talking about "Adaptive Optics," and I am not sure the equipment they are referring is the same thing that you were thinking about.

 

The optics mentioned above are often referred to as "Active Optics" as well as "Adaptive Optics."

 

Must of us heard the term "Adaptive Optics" in the context of optics that could correct for seeing.  This technology typically used a reference laser beamed into the sky and mirror warping on the primary to deform the primary or the primary mirror segments to attempt to adapt the mirror to the aberrated wavefront entering the aperture. In other words, they improved the aberrations resulting from seeing.

 

The "Active Optics" are more accurately referred to at "Tip/Tilt High Speed Guiding."  This technology is really geared more to reducing the effect of vibrations on the mount, or minute tracking errors, or lower order atmospheric shift (low frequency wavering in the atmosphere that causes the star to move around, and not the kind of aberration that comes from the more normal seeing where the star is fuzzed up or the diffraction rings are flaring and breaking.

 

From the web page: These AO systems use a tip-tilt transmissive element to correct for image wander due to low order local atmospheric effects and for correction of mount errors, wind vibration and other erratic motion of the optical system that is otherwise too fast for an autoguider or telescope drive corrector to respond to effectively.

 

So, if you are looking to correct image wander, these devices mentioned are all you need.

 

If you are looking for adaptive optics that correct wave-front aberrations, these systems don't do that.  They only correct for image wander.

 

The SBIG and Orion "adaptive optics" works more like the image stabilization in consumer cameras. The closest thing we have to adaptive optics for the typical amateur is the "lucky imaging" technique used for solar system imaging, only instead of reforming the wavefront before it hits the sensor post processing infers what image could result in a multitude of unique frames. But faint DSO's do not provide enough information on subexposures only a small fraction of a second long. However there are extremely low noise cameras available that will do 1-2 second DSO subexposures which is a step in the right direction.

 

Gale

[freestar8n]

I'm not sure where the idea that this is "active optics" comes from - because the fast tip/tilt corrections are adjusting for the wavefront just as much as other aberration terms such as defocus.  "Active optics" refers to very slow adjustments of the optical system caused by flexure - such as the supports for the mirror segments.  The timescale there is more like minutes rather than 10 Hz of a typical amateur adaptive optics system.

 

If you look at the Fried work on long exposure vs. short exposure imaging - the key difference is the motion of the star spot caused by wavefront tilt.  That's an important part of seeing that causes the stars to swell - and it has a fast Zernike term just like other terms in adaptive optics.  You could call it tip/tilt adaptive optics or first order adaptive optics - but I would not call it active optics.

 

Even though I think it really is a form of adaptive optics - in practice when amateurs use it, a key benefit they may get in their images is just from tighter guiding and better correction of their mounts.  So even though the technology is fast - it may be that the main benefit people get from it is just better correction of guiding issues rather than atmospheric ones.

 

Frank

[gdd]

I think the idea that active or adaptive optics corrects for seeing is that the problem of atmospheric turbulence is usually mentioned. Turbulance changes more than the position of the image or overall focus, it change different parts of the image differently and simultaneously. I took a video of sunspots. They are not only jiggling around but morphing from one shape to another, sometime in the same location you would see one spot, then two, then none, all in a fraction of a second. The explanations need to say what the mirror deformations are correcting for.

 

Gale

[freestar8n]

Yes - and a key part of turbulence is the fast tip/tilt of the wavefront. It is a real part of seeing just like the other distortions of the wavefront - and adaptive optics is there to correct for it. A professional observatory would use active optics to make very slow changes in the mirror supports - and it would use adaptive optics for fast changes in tip/tilt, focus, spherical - and any other aberrations it can cancel. It just happens the amateur stuff only corrects for tip/tilt - but it is still fast, important, and in the realm of adaptive optics.

Frank

[freestar8n]

And to answer the OP's question - the only adaptive optics for amateur astro I know about are from SBIG, Orion, and StarlightXpress.

Frank

[Corsica]

You may want to have a look at:

 

http://www.cloudynig...t/#entry6450432

[jeff.bottman]

Its exactly analogous to Canon image stabilizing binoculars, as I understand.  They are not marketed as 'Adaptive' binoculars!

[Lucullus]

Aren't amateur adaptive optics and guiding actually real adaptive optics in the professional sense, just with the limit of being able to only correct tip/tilt? If we look at Zernike polynomials https://www.google.c...zernike&imgrc=_ tip & tilt are just first order aberrations, but nevertheless, it's the first step in professional adaptive optics. Professionals simply correct for higher terms, too, as well as chaotic atmospheric seeing. In this sense, amateur, as well as active mirror optics are adaptive optics, too, but correcting just the very first orders of Zernike aberrations. Or am I wrong?

[ram812]

You may want to read Claire Max's (unclassified now) report from Lawrence Livermore National Laboratory in Ca. that her and her team 30 some years ago found a way to precisely measure and remove a stars twinkle. It works by shining a laser in the sky to create an artificial star and then "Jiggling" the telescope's primary mirror to the same amount,thus eliminating the twinkling effect. Basically a "Laser Guide Star". Lick Observatory was where it first was used, I believe. Hope this helps, not really what small telescopes would use without big bucks! Ralph

[Oberon]

Aren't amateur adaptive optics and guiding actually real adaptive optics in the professional sense, just with the limit of being able to only correct tip/tilt? If we look at Zernike polynomials https://www.google.c...zernike&imgrc=_ tip & tilt are just first order aberrations, but nevertheless, it's the first step in professional adaptive optics. Professionals simply correct for higher terms, too, as well as chaotic atmospheric seeing. In this sense, amateur, as well as active mirror optics are adaptive optics, too, but correcting just the very first orders of Zernike aberrations. Or am I wrong?

 

No, you are right.

[Lucullus]

Right?! It's not the Zernike polynomials fault that the first order (Tip/Tilt) doesn't require a Laser Guide Star to be corrected and higher orders, as well as chaotic seeing need one. Linguistically, active as well as classically understood adaptive optics could be summarised below the title "adaptive optics", and the first Zernike term as "pseudo-adaptive" or so. I'd love to hear jhayes_tucson's opinion on this.

[Alph]

Right?! It's not the Zernike polynomials fault that the first order (Tip/Tilt) doesn't require a Laser Guide Star to be corrected and higher orders, as well as chaotic seeing need one. Linguistically, active as well as classically understood adaptive optics could be summarised below the title "adaptive optics", and the first Zernike term as "pseudo-adaptive" or so. I'd love to hear jhayes_tucson's opinion on this.

FWIW

Laser guide stars are insensitive to the image motion (tip-tilt). One needs to have a natural guide star to correct for the tip-tilt image motion. A simple tip-tilt mirror or sometimes active optics are used for tip-tilt corrections.

Hope this explains confusion about active optics and tip-tilt mirrors (Amateur A/O units)

[freestar8n]

There is no need to redefine these terms. Adaptive optics refers to fast corrections to correct atmospheric aberrations of the star - and tip/tilt are perfectly normal Zernike aberration terms arising from atmospheric turbulence. Active optics refers to much slower corrections of the optics and mechanics of the telescope system - e.g. flexure of the components or slumping of the mirror in its cell. That is the way R. N. Wilson uses these terms. I have only seen fast tip/tilt corrections referred to as "active" optics in amateur discussions that are disconnected from the literature.

Yes - simple tip/tilt adaptive optics used by amateurs are very different from the elaborate systems in use professionally. But it's still a form of adaptive optics - and not active optics.

There is another term to watch out for - and that is scintillation or twinkling. Those terms refer to changes in flux from a star - and are very different from aberrations of the wavefront. The wavefront could be arriving perfectly and with no distortion - but if the intensity is changing then there is scintillation or twinkling. Seeing and scintillation are different things with different atmospheric causes.

Frank

[Jon Isaacs]

A year or two back , I purchased a 6 inch Starblast that had been advertised on my local Craigslist.  As it turned,  the seller had used the scope to demonstrate the feasibility of  measuring the straightness of railway rails.  The Seller was Dr. Donald Bruns who recently retired from a career in optical design.  From what I gathered,  Don had worked for one of those small companies that work for various branches of the US government where a top secret clearance is mandatory. 

 

I spent a most interesting hour in conversation.  In any event, Don is an active amateur astronomer and his retirement,  he was once again turning his efforts towards adaptive optics for the amateur.  

 

http://www.stellarpr...tive/AO5lit.htm

 

Don's system is a true adaptive optics system that has millisecond response.   In answering my questions, he said the Orion and Sbig systems we're meant to correct guiding errors. 

 

I scanned Dr. Baudat's article in his link and Don's conclusions were inline with Dr. Baudat's.  Of primary interest to me was the very small field of view that can be corrected,  a corrected radius of 4 arc-seconds for the field of view comes to mind.. I think many are probably like me,  I thought the field would much larger,  at least an arc-minute. 

 

Dr.  Bruns is a member of CloudyNights...   Maybe he will see this thread and take the opportunity to provide an updated progress report. 

 

Jon

[freestar8n]

The claim is that if a system only corrects for tip/tilt errors - it is active optics and not adaptive optics. That is false since it is counter to professional usage. Ironically, I don't know of any amateur system that actually uses active optics - in the sense the term is used professionally. It would need to be a system that makes slow corrections to the mechanics or the mirror support in response to changing load. I don't know any amateur system that does that.

If you read the descriptions of amateur adaptive optics devices by sbig or sx - etc. - they clearly claim and intend to correct for seeing. They may also be correcting for guiding/mount errors - and that is likely the case when corrections are as slow as 1Hz or so. But when they are operating at 20Hz and the seeing is neither perfect nor terrible - there is no reason they shouldn't correct for exactly the same tip/tilt errors that are being removed by professional adaptive optics systems - which often rely on a specific separate stage designed for just that component.

So some things are certain: fast tip/tilt corrections are adaptive optics and not active optics. Also, the various amateur products are "meant" to correct for fast seeing.

Now there is a separate question of whether they really are achieving that goal of reducing the impact of seeing motion. That is hard to answer because it is difficult to separate small mount errors from seeing errors. If the system is correcting for tip/tilt errors due to turbulence, the region of correction should get worse as you move away from the guidestar. The distance need not be arc-seconds - it could be many arc-minutes depending on the nature and frequency of the turbulence. But I don't know of any amateur images that have shown that drop off at all - but I also don't know anyone who has really looked into it carefully. That would be "proof" to me that it is truly correcting for seeing - and although I haven't seen such proof - there is no fundamental reason that fast tip/tilt alone shouldn't be able produce such a result.

In my guiding work I look at it from the other side - that indeed the main benefit of such systems is to provide rapid corrections of mount errors. So I emphasize that much of the benefit of AO can be realized just by tighter and lower latency corrections with the mount itself - and by studying the guidestar at video rates. But that doesn't mean that an additional level of correction at the 10-20Hz range wouldn't begin to correct for true seeing effects.

Frank

[sixela]

Or am I wrong?

No, you're not. Even in professional scopes, the first kinds of adaptive optics were also merely tip/tilt correctors. That they've gone beyond just that more recently doesn't change the name that was used for that class of optics.

[Lucullus]

@#17: If the star flux over the integration time of an adaptive optics system is enough to make out the star and the tip/tilt motion is non-zero between two integration times, there is no reason whatsoever why adaptive optics should be insensitive to tip/tilt. But longer integration times than several hundred Hz just makes it much easier. Moreover, as the LGS imitates a natural star and goes through the very same telescope optics as the other photons, a LGS of course is sensitive to tip/tilt - it is influenced by the very same mirror bendings as the photons coming from beyond the atmosphere. The differences of LGS and astro photons lie beyond the gravity-bending telescope optics in the individual instrument sections like wavefront sensor, CCD, spectrographs, polarimeters etc. where LGS photons and astro photons have different purposes. But to summarise, the big telescope optics influences all incoming photons in the same way.

Edited by Lucullus, 12 December 2016 - 08:14 AM.

[Jon Isaacs]

If you read the descriptions of amateur adaptive optics devices by sbig or sx - etc. - they clearly claim and intend to correct for seeing. They may also be correcting for guiding/mount errors - and that is likely the case when corrections are as slow as 1Hz or so. But when they are operating at 20Hz and the seeing is neither perfect nor terrible - there is no reason they shouldn't correct for exactly the same tip/tilt errors that are being removed by professional adaptive optics systems - which often rely on a specific separate stage designed for just that component.

 

So some things are certain: fast tip/tilt corrections are adaptive optics and not active optics. Also, the various amateur products are "meant" to correct for fast seeing

 

 

The question is not what they intend to do but rather what they actually do and whether they are actually fast enough to make a significance. 

 

From what I can gather,  the SBig units seem to operate at 10 Hz.   

 

Jon

[freestar8n]

The question is not what they intend to do but rather what they actually do and whether they are actually fast enough to make a significance. 
 
From what I can gather,  the SBig units seem to operate at 10 Hz.   
 
Jon

I was responding to what you had said earlier:

Don's system is a true adaptive optics system that has millisecond response.   In answering my questions, he said the Orion and Sbig systems we're meant to correct guiding errors.

You used the word, "meant" - which to me implies intent. I'm saying they are meant to correct for seeing motion.

I think they all operate at a range of speeds - limited by the brightness of the star and the guide camera. Certainly as low as 1Hz and I think as high as 20Hz. But even 10 Hz should freeze a lot of seeing motion under the right circumstances. And under those circumstances the field that would be corrected could be very large - unlike the field when correcting for very high order turbulence aberrations - which could be only a few arc-seconds.

There are people all over the world collimating with MetaGuide because it can freeze out star motion and reveal the Airy pattern even when there is mediocre seeing. Although this doesn't involve actual mechanical motion - it does just rely on tip/tilt corrections of the star image at similar rates of 10-60Hz. Even at the low frequencies around 10 Hz you can see a dramatic reduction in the star size in realtime - on the display. So as long as the mechanical devices can do the same thing at about the same speed - the fwhm in the images should be noticeably reduced.

Frank

[noisejammer]

It might be appropriate to note that the dominant terms in a Taylor expansion are usually first order. Who really cares if the source of image jiggle is the atmosphere or the mount? 

 

I used my AO-7 / ST-8XE combination when doing photometric measurements of cataclysmic variables. It was mounted on my LX200/12 - but I'd already replaced the drives to provide near arc-sec tracking. Since the mount performance was comparable with the resolution of my camera, presumably the AO-7 would be working against atmospheric smearing of the image.

 

With the AO-7 active and locked to a bright, field star (10 Hz or higher) I found that I was able to perform excellent, high cadence photometry on 16.5^m targets; without it I could get acceptable performance to around 14^m and maybe 15^m on a good night.

 

The main problem with the AO-7 is that its active sensor is mounted adjacent to the primary imaging sensor. This means correction bandwidth is lost when a filter is inserted... generally a bad thing because the filter means the target is dimmer too.