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#1
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why no true high resolution systems for "jetstream" seeing?
While it's true that webcams are doing wonders for certain types of seeing,
in many areas of the US during the Wintertime, the jetstream is constantly overhead and even a webcam cannot undo this blurring. I keep reading about these new adaptive optics scopes, like the new pro scope used for solar imaging, which also incorporate speckle imaging and reconstruction- why nothing for amateurs? Couldn't blurring of frames (caused by high jetstreams) be deblurred or "reconstructed" so blurring is minimized. With computers and the power they possess these days, I'm surprised there aren't programs that can do this or maybe jetstream effects still can't be truly nullified. Thanks, Frank |
#2
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why no true high resolution systems for "jetstream" seeing?
On Sat, 07 Jan 2006 16:16:24 GMT, "Frank Johnson"
wrote: While it's true that webcams are doing wonders for certain types of seeing, in many areas of the US during the Wintertime, the jetstream is constantly overhead and even a webcam cannot undo this blurring. I keep reading about these new adaptive optics scopes, like the new pro scope used for solar imaging, which also incorporate speckle imaging and reconstruction- why nothing for amateurs? Couldn't blurring of frames (caused by high jetstreams) be deblurred or "reconstructed" so blurring is minimized. With computers and the power they possess these days, I'm surprised there aren't programs that can do this or maybe jetstream effects still can't be truly nullified. It simply isn't possible to do much along these lines with amateur systems. Adaptive optics requires a reference object very close to the target, and in almost all cases that object (if one exists at all) is going to be dim. For this reference to be useful, you need to collect enough photons to get out of the noise. Since detectors are already nearly 100% efficient, the only way to get enough light is with a large aperture. Adaptive optics starts becoming practical as apertures get in the range of a meter, and larger is better. Obviously, this is well outside what most would consider amateur optics. The lack of available reference stars is another problem for amateurs. Professional observatories can address this by making their own, using lasers to excite atoms high in the atmosphere. But aside from cost, shining such lasers at the sky requires special permits that pretty much preclude their use by amateurs. Finally, adaptive optics wouldn't provide much benefit to most amateurs because it can only correct the field over a few arcseconds- much smaller than typical observing or imaging fields. It is more a scientific tool for examining very small zones at high resolution than something useful for improving the aesthetics of an image or view. Adaptive optics would really only be useful for most amateurs for observing (or imaging) very small (or small areas) and very bright objects- the Sun, Moon, and brighter planets. Right now, adaptive optics are expensive enough to produce that there probably isn't enough market for so limited a device to justify development. That might change in the future, but don't expect to see anything useful for deep sky observing- ever. What may come around, assuming that low readout noise cameras become generally available, is software that selects high quality short frames and stacks them automatically. This is done already with planets, of course, but doesn't work with dim objects. Unfortunately, as the size of the field increases, the number of useable high resolution frames decreases. It might take several hours to collect a few minutes worth of data. Deconvolution techniques can help to reconstruct distorted images, but there is no certain way to determine just where any given photon came from. Deconvolution is a sort of educated guess, but it frequently produces invalid data- and there is no getting around that problem. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#3
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why no true high resolution systems for "jetstream" seeing?
"Chris L Peterson" wrote in message ... On Sat, 07 Jan 2006 16:16:24 GMT, "Frank Johnson" What may come around, assuming that low readout noise cameras become generally available, is software that selects high quality short frames and stacks them automatically. This is done already with planets, of course, but doesn't work with dim objects. Unfortunately, as the size of the field increases, the number of useable high resolution frames decreases. It might take several hours to collect a few minutes worth of data. The professionals are catching up with the amateurs in this area http://news.bbc.co.uk/1/hi/sci/tech/4456988.stm Robin |
#4
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why no true high resolution systems for "jetstream" seeing?
On Sat, 7 Jan 2006 18:08:37 -0000, "Robin Leadbeater"
wrote: The professionals are catching up with the amateurs in this area http://news.bbc.co.uk/1/hi/sci/tech/4456988.stm Thanks for the link. "Lucky imaging"; great name! Sounds like a good amateur project, looking for previously unknown doubles. Perfect for this technique because the sources are bright, and the field is small. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#5
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why no true high resolution systems for "jetstream" seeing?
"Chris L Peterson" wrote in message ... On Sat, 07 Jan 2006 16:16:24 GMT, "Frank Johnson" wrote: While it's true that webcams are doing wonders for certain types of seeing, in many areas of the US during the Wintertime, the jetstream is constantly overhead and even a webcam cannot undo this blurring. I keep reading about these new adaptive optics scopes, like the new pro scope used for solar imaging, which also incorporate speckle imaging and reconstruction- why nothing for amateurs? Couldn't blurring of frames (caused by high jetstreams) be deblurred or "reconstructed" so blurring is minimized. With computers and the power they possess these days, I'm surprised there aren't programs that can do this or maybe jetstream effects still can't be truly nullified. It simply isn't possible to do much along these lines with amateur systems. Adaptive optics requires a reference object very close to the target, and in almost all cases that object (if one exists at all) is going to be dim. For this reference to be useful, you need to collect enough photons to get out of the noise. Since detectors are already nearly 100% efficient, the only way to get enough light is with a large aperture. Adaptive optics starts becoming practical as apertures get in the range of a meter, and larger is better. Obviously, this is well outside what most would consider amateur optics. The lack of available reference stars is another problem for amateurs. Professional observatories can address this by making their own, using lasers to excite atoms high in the atmosphere. But aside from cost, shining such lasers at the sky requires special permits that pretty much preclude their use by amateurs. Finally, adaptive optics wouldn't provide much benefit to most amateurs because it can only correct the field over a few arcseconds- much smaller than typical observing or imaging fields. It is more a scientific tool for examining very small zones at high resolution than something useful for improving the aesthetics of an image or view. Adaptive optics would really only be useful for most amateurs for observing (or imaging) very small (or small areas) and very bright objects- the Sun, Moon, and brighter planets. Right now, adaptive optics are expensive enough to produce that there probably isn't enough market for so limited a device to justify development. That might change in the future, but don't expect to see anything useful for deep sky observing- ever. What may come around, assuming that low readout noise cameras become generally available, is software that selects high quality short frames and stacks them automatically. This is done already with planets, of course, but doesn't work with dim objects. Unfortunately, as the size of the field increases, the number of useable high resolution frames decreases. It might take several hours to collect a few minutes worth of data. Deconvolution techniques can help to reconstruct distorted images, but there is no certain way to determine just where any given photon came from. Deconvolution is a sort of educated guess, but it frequently produces invalid data- and there is no getting around that problem. Hi, yes, I already pretty much understand the current techniques involving adaptive optics. I myself have experimented on Jupiter by using one of its moons as a PSF. Then I tried to apply max ent to Jupiter only to end up with a very noisy and artifact prone result. As you said, there simply might have not been enough signal to work with. There *is* a phenomenon I've noticed with my setup on nights when seeing is plagued with an overhead jetream: because my tracking isn't perfect, I make small drive corrections during capture to keep a chosen planet centered in the field. Sometimes when I've adjusted the tracking, there will be moments while the drive corrector is engaged where the planet I'm imaging suddenly becomes clear. When I let go of the corrector, the blurs caused by the overhead jet return but for a few moments there were clear frames. One might suspect a sort of vibration as the reason, but I have noticed this with several different mount/ scope combinations and I think it has something to do with maybe "catching up with" or "matching" jetstream winds for a moment (a second) while the planet is being moved back to the center of field. I still search for a CCD camera with very high sensitivity, rapid frame captures and very low noise. The webcam is ok, but falls short in the noise and sensitivity department. Commercial CCD cams, although much less noisy, can't capture nearly as many frames per time as a webcam and are much more expensive. I recently read here about meteor CCD cameras possibly offering the best signal to noise ratios and sensitivity, but it's tough finding anyone currently using those. Frank _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#6
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why no true high resolution systems for "jetstream" seeing?
On Sat, 07 Jan 2006 16:46:24 GMT, Chris L Peterson wrote:
It simply isn't possible to do much along these lines with amateur systems. Adaptive optics requires a reference object very close to the target, and in almost all cases that object (if one exists at all) is going to be dim. For this reference to be useful, you need to collect enough photons to get out of the noise. Since detectors are already nearly 100% efficient, the only way to get enough light is with a large aperture. Adaptive optics starts becoming practical as apertures get in the range of a meter, and larger is better. Obviously, this is well outside what most would consider amateur optics. Hi Chris, Most of your original reply is accurate and useful, but your comment on the aperture size follows a common misconception. Large apertures do not collect more photons for an adaptive optics system; the only photons that count are those in a subaperture about the diameter of r0, typically 20 cm. Larger aperture telescopes require more subapertures. The only way to get more photons in the subaperture are 1) wait for good seeing, when you can get by with larger subapertures; 2) go to longer IR wavelengths, even to 10 microns, where r0 is always larger than visible light; 3) use a laser guide star. (Longer integration periods in good seeing also help collect more photons.) Solution 1) is not useful for a world-class observatory, since every night is too valuable to waste; solution 2) is used by some observatories, but then the resolution lambda/D is not very good; solution 3) is pretty expensive, but its getting better, and is probably the ultimate solution. The amatuer solution is to look at only very bright, very small targets. There are very few of these, limiting the market. I recall a few years ago, that some observers were able to detect craters on Mercury, on a side that was not imaged by the space probes, by using a million short exposure images, and looking for the higher resolution "lucky shots". So, there is opportunity for useful work in this area. Don Bruns |
#7
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why no true high resolution systems for "jetstream" seeing?
Chris L Peterson wrote:
It simply isn't possible to do much along these lines with amateur systems. Adaptive optics requires a reference object very close to the target, and in almost all cases that object (if one exists at all) is going to be dim. For this reference to be useful, you need to collect enough photons to get out of the noise. Since detectors are already nearly 100% efficient, the only way to get enough light is with a large aperture. Adaptive optics starts becoming practical as apertures get in the range of a meter, and larger is better. Obviously, this is well outside what most would consider amateur optics. Wouldn't you need good coherence at one-meter scales for that? Isn't the Fried parameter shorter than that most of the time? -- Brian Tung The Astronomy Corner at http://astro.isi.edu/ Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/ The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/ My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html |
#9
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why no true high resolution systems for "jetstream" seeing?
If you're willing to pay the hefty price there are plenty of cameras on
the market. Andrea T. |
#10
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why no true high resolution systems for "jetstream" seeing?
Frank Johnson wrote: While it's true that webcams are doing wonders for certain types of seeing, in many areas of the US during the Wintertime, the jetstream is constantly overhead and even a webcam cannot undo this blurring. I keep reading about these new adaptive optics scopes, like the new pro scope used for solar imaging, which also incorporate speckle imaging and reconstruction- why nothing for amateurs? Hi: At the _moment_ (things could change), the effective systems are expensive and difficult for amateurs to implement. For example, the most effective and versatile adaptive optics require an artificial star to be projected via a high power laser. Good way to ensure a visit to your backyard by the Black Helicopters. ;-) Peace, Rod Mollise Author of _Choosing and Using a Schmidt Cassegrain Telescope_ Like SCTs and MCTs? Join the SCT User Mailing List. http://www.groups.yahoo.com/group/sct-user ============================ See my home page at http://skywatch.brainiac.com/astroland/index.htm for further details! ============================ For Uncle Rod's Astro Blog See: http://journals.aol.com/rmollise/UncleRodsAstroBlog/ |
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