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Proposed Telescope Focuses Light Without Mirror Or Lens
A team of scientists from Observatoire Midi Pyrénées in Toulouse, France have been working with an unusual technique for focusing light. It takes advantage of diffraction - the bending of waves when they encounter an obstacle in their path - to focus light as it passes through a foil sheet with precise holes in it. The scientists suggest that an orbital 30-meter imager could resolve planets the size of Earth within 30 light-years. In addition, the foil is much lighter than traditional materials, and thus easier to transport.
"A Fresnel imager with a sheet of a given size has vision just as sharp as a traditional telescope with a mirror of the same size, though it collects just 10% or so of the light. It can also observe in the ultraviolet and infrared, in addition to visible light. The imager can take very detailed images with high contrast, which is great for 'being able to see a very faint object in the close vicinity of a bright one.'"
Great, but will it get build before I'm dead?
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Hmm, a large flat surface with holes in it.
It looks like launching one of these babies would require solutions to the same technical problems as solar sails, ie stowing & unfolding once in orbit.
Would it be possible to have the sheet do double duty, acting as both a Fresnel "lens" and a means of propulsion for the spacecraft? That might be a neat way of getting the instruments to a good location.
Make a sphere with a central axis. Place the fresnel lens on the surface of the sphere. Rotate the sphere about the center (where the focal point is.) No more formation flying, etc. Since you don't need any part of the sphere but the place where the fresnel lens is, just create a radius - lens at one end, focal point at the other end. Use a track to adjust the focal point distance from the foil. Rotate the entire assembly to re-point. No formation flying. Precision alignment all the time. Slow adjustment means good fuel economy.
It seems to me that this is a great excuse for a foil-making plant in space. Imagine a veewwwwy large foil sheet. Then think of the available resolution. This is better than a dispersed array.
Well, one can hope. :-)
I've fallen off your lawn, and I can't get up.
"anoptikon"
I think it would be clear to anyone who examines it, the idea clearly has some holes in it.
I don't know about angles, but it's fear that gives men wings. -Max Payne
.. when I didn't have my glasses handy and still wanted to look at something in particular.
I would form a small hole by curling my index then look through it for visual correction to my myopea.
I was thinking hey neat till I read this in the article.
For one thing, the light comes to a focus far away from the foil sheet - with distances measured in kilometres, which means the camera and other instruments have to be mounted on a separate spacecraft. The instrument spacecraft would have to stay precisely aligned with the foil sheet, to within a millimetre or so.
Certainly not impossible, and still exciting, but this isn't going to be a mainstream or amateur tool any time soon.
Looks like there also may be a related patent to get past...
http://www.patentstorm.us/patents/6375326-claims.html
These posts express my own personal views, not those of my employer
According to TFA the slotted lens would be much lighter but also MUCH MUCH larger than traditional setups. Also, the distance between the lens and the camera is so large that a second spacecraft is needed. Trying to maintain the alignment of two spacecraft would be difficult at best. Now consider that they would need to fire thrusters and move one of them every time they need to focus on a different object. How much fuel would be used up just looking at 10 different objects? I would expect a lot. Add to this what micro-meteors and the random castaway screw driver would do to the foil over time and you can see some real limitations to this. Not saying it's impossible, just that they need to work out some ways around the obvious problems.
are you an old geezer, or a young whippersnapper? Or are you somewheres inbetween?
Has there been a severe rationing of mod-points recently?
Perhaps the mod-point crisis is related to the credit-crisis?
So basically they're building A HUGE FRAKKIN' PINHOLE CAMERA. Frankly I find it strange that they would build a telescope that only collects 10% of the light, as this might present problems for planet finding. Not to mention that huge sheets of foil tend to crinkle and are susceptible to micro-meteoroids. But, if they could make it cheap enough, they could launch a bunch of them and do "brute force astronomy."
I think you are missing a big point here. We're not talking about a solid sheet like a sail, but rather, a sheet which is X% holes, and for which the exact geometric arrangement of the holes is critical for the physics to work. Looks to me like one has even started to think about how it can survive the stresses of being launched at multiple G's.
Canon has been using the same principle in a couple of lenses for some time now. The lenses themselves are pretty damn expensive but well regarded; I hope the telescope meets similar success.
Also forgot to add: the efficiency of transmission is better as the percentage of holes gets bigger, i.e., as it gets more fragile.
In the first 8 years of the 21st century I have witnessed an almost feverish acceleration of astronomer attention on the discovery of "exoplanets" - planets around stars other than our own Sun. Already some solar systems very similar to our own have been discovered and some tentative measurements of the atmospheric content of these planets is underway. I believe it is only a matter of months or years before an oxygen-rich "earth-like" planet is discovered. Prognosticator of prognosticators that I am, I'll even go so far as to suggest a date: before the end of 2012.
But who cares when it happens, if it does happen, what then? What next? Will there be any debate that the concentration of oxygen implies that life is present on this newly discovered world? Will it take the imaging of an exoplanet to "prove" that life exists elsewhere in the universe? Will it take more?
And finally, will anyone care? Not the geeks. Not the astronomers or the scientists or the science fiction writers, but the average person on the street. At the time of writing, each exoplanet discovery is treated to an orgy of poorly understood journalism. It seems the idea of "planets around other stars" is something the mainstream audience can understand just enough and goes well to fill that slot in the news between the sports and the weather. Will this fad wear off by the time the startling discovery of exoplanet life is made? Or worse yet, will such an amazing discovery get exactly the same amount of coverage as the average exoplanet discovery gets now?
Ultimately the whole thing could be a terrible disappointment. Imagine, for a moment, that not only do astronomers discover life on an exoplanet but they actually discover intelligent life on an exoplanet. Pretty little pictures of roads and factories, ships at sea, planes and rockets in flight. Some serious questions would need to be directed towards the SETI program.. as it seems highly unlikely that a modern society could exist without emanating some signals that SETI should have picked up. Maybe a thorough search of the archives will reveal that many possible signals from that part of the sky were ignored accidentally.
In any case, now that we know they're there, how do we go about contacting them? Should we? Who gets to decide? Is that a pointless question as there's just no way to stop someone from sending a signal if they want to? And then there's the long long wait for the signal to get there and maybe no-one is listening or maybe the signal is too corrupted or just not decipherable by an alien mind. Decades may pass with no message returned. The general public will lose interest. Can you imagine?
How we know is more important than what we know.
This looks good on the drawing board but making a real-world example is going to require some very fancy engineering. Building larger scale structures in space isn't as easy as many think; there's gravitational gradients, solar wind and more out there. Forces that are tiny - but when these tiny forces are applied (unevenly) to a large structure the total forces can be very impressive (and destructive).
IANAL, but at least from a technical point of view, the patent you cite seems to have little to no relevance here:
1) It deals with using a Fresnel lens, not a zone plate,
2) It's main point is using, for a single imaging, one Fresnel lens twice via having two separate optical paths through it.
Looks like it might possibly be an interesting patent, but it's not connected with the idea for this telescope (unless the Fresnel lens cited in the article, which corrects the chromatic aberation of the zone plate, is used in the fashion cited in patent, which doesn't seem likely to me).
Canon has been using the same principle in a couple of lenses for some time now. The lenses themselves are pretty damn expensive but well regarded; I hope the telescope meets similar success.
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The logistics of maneuvering two satellites (kilometers apart) to stay aligned would be daunting. More research needs to be done to decrease the focal length.
What you want to look for is not a planet with X, Y or Z in terms of chemical components in the atmosphere, but evidence of a dynamic equilibrium actively maintained by a minimum of two opposing negative feedback loops that involve highly unstable components in the atmosphere. Since there will be day and night, and seasons, different points on the planet will register different prevailing feedback loops. These conditions cannot arise in a wholly inorganic environment. An inorganic environment may be chaotic (the atmospheres of Saturn and Jupiter, for example) or very basic (as in the case of the surface of Pluto) but the systems are relatively basic. They are simple chemical systems, passively reacting to the occasional direct strike by a comet, but there is nothing metastable or unstable about any of those examples. If anything, they are remarkable in their stability.
It is planets whose chemistry should be violently unstable but are actively held in dynamic equilibrium that are interesting. Those have processes that are in the realms of what we would consider living matter, and outside the realms of the non-living.
What about intelligent life? First define intelligence, and then secondly prove there's any on Earth. If we don't know what we're looking for, or how to recognize it if we find it, then such a search is futile. I regard SETI as more of a research lab for advanced theories into digital signal processing. It won't be useful until the one kilometer array is active, and the planned closures in Britain inclclude key parts of that array. We also need very very powerful signals processing - a million channels, or even half a billion, isn't much. We don't even know if we want the radio or optical spectrums. So, two arrays - one radio, one optical - at a kilometer diameter and, oh, say a trillion channels being monitored and analyzed with rather better signals theory than SETI@Home use. When will this happen? Never. That, then, is the earliest alien intelligence can be passively detected by us.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
From the article: "It does not require a large primary mirror or lens, though it does use a smaller secondary mirror and lens."
So it *DOES* use a LENS AND MIRROR to focus light. Honestly, when will journalists, and scientists, stop making claims that are obviously NOT true?!?
Knowing Google's lust for data collection, the Soviet Union is still alive and well inside the psyche of Sergey Brin....
It's good and all to look at the stars, but when is mankind ever going to reach them?
If each mistake being made is a new one, then progress is being made.
Heh. That's not even freaking close to "A HUGE FRAKKIN' PINHOLE CAMERA."
;)
It's actually closer to Fresnel lens, sorta. Well, not really, but just to get the idea started that you can use something very thin to the same effect as a bulky normal lens or telescope. This one actually a Fresnel zone plate It uses light Interference to act more like a lens, although it is really just a special pattern of lots and lots of pinholes.
If you will, it's closer to the double-slit experiment in light interference that surely you must still remember from school. Behind the panel with the slits, light gets to act funny: you get zones that get more light, and zones which gets less. Photons bend their paths in certain (statistically) predictable ways.
It turns out that if you use some carefully calculated concentric circles as slits, you can actually get the light interfering in such a way, that it's actually focused like with a lens. Essentially those dark and bright bands turn into just one bright dot at the right distance. Well, having concentric holes in a thin foil is kinda hard, but these guys figured out that you can use lots and lots and lots of pinholes instead.
Anyway, even the most summary read of TFA or even the summary would have provided the hint that it's about lots of holes and interference. Which should have been plenty of hint that it's nothing like a pinhole camera. Unless, of course, you actually built a camera with sieve-like Fresnel zone plates before and mistakenly called it a pinhole camera. But I'm fairly sure that you didn't
A polar bear is a cartesian bear after a coordinate transform.
Light pressure is going to make that alignment problem about 10x worse.
The article makes it sound like only a 30-meter "Fresnel" optics can allow to resolve an earth-size object within 30 light-years.
The fact is that any conventional 30-meter telescope can resolve an earth-size object within 30 light-years (circa 6000Angstrom in wavelength). Spatial resolution can be determined by the ratio of wavelength to diameter of the optics:
6000A / 30m ~ 2e-8 radian ~ 0.004 arcsec.
So a 30m telescope can resolve an object in angular size of 0.004arcsec at 6000Angstrom.
At the distance of 30 light-years, the earth-size object looks like
6400km / 30lyr ~ 2e-8 radian ~ 0.004 arcsec.
So that's that. This telescope doesn't give us any special resolving power per optics size. So the advantage is merely its light weight.
Since the precise alignment of holes is required for this optics to work, I can see why this project got kicked out by ESA. It's probably too premature to attempt in deploying this kind of precision engineering in space today.
You would still have to protect the foil sheet somehow from micro particles & space junk punching extra holes in it ruining the focus....
They're already widely used down here on Earth.
This one-off controversy about when the millenium started is getting a little old, no?
...
Yeah, I know, "no one likes a math geek"
Why settle for a piddling 30 meters? Saturn's rings have a certain zone-plate like flavour to them. With a few artificial shepherd moons to tweak the periodic intervals, weought to get some sort of an interference pattern. The focal length will be huge so the rings don't have to be flat...
Actually, this is pretty silly, but it might be possible to make a partially self-assembling zone plate out of a massive central body and a carefully seeded orbiting cloud of black dust, edge-on to the sun. You might be able to get a refractive zone plate using orbiting gas, but you would have to control the optical retardation, where black is just black and if it is black in the right places, then it might work.
For another fun sort of lens, see http://en.wikipedia.org/wiki/Luneberg_lens
"... the dark side of the Moon"?
Got Brain Damage, have we?! I see the pigs are on the wing again!
I mean sure, there is always a DSOTM, but the pesky thing is always moving!
BTW, who reckons that Waters' recent errant flying pig was a deliberate stunt; a reprise of the simimar incident in London in 1976 (IIRC); and NOT an accident?
"Absorbing your worst..."
make the foil into a parabolic shape to reflect light to a camera instead of cutting holes in it to defract light to a camera much further away?
The question of whether a computer can think is no more interesting than the question of whether a submarine can swim.
IT occurs to me that is the focal length is THAT long we could put these very large systems in space and have a smaller GROUND based detector.
Simply put the thing in GEO orbit and point it at a receiving station. This will dramatically increase the "lense" size.
Of course you will get some interference from the atmosphere but this can be activly compensated.
O RLY?! I suppose they haven't considered how unbearably LONG 30 light years is. I'm certainly not prepared to wait that long. Besides, we'll all be dead in 30 light years, what with the Hopi prophecy foretelling the end of time, and all.
While I'm here, let me get this out of the way, save us some time:
(joke) ------------->
(you)----> O__O
Please stop stalking me, bro.
You have to love simple solutions to big problems. I have a question for any expert- is the same phenomenon the reason people with blurry vision squint? I noticed at my last eye exam... my left eye is weak, and besides memorizing the test a little by going right eye first, I passed the left eye test by lining up the letters very close to the edge of the device I was looking through to make them less blurry. It appeared to be refraction, but could it also just be something related to decreasing the amount of light (is that related to astigmatism)? I don't wear glasses (and don't want to), so I apologize for any lack of common knowledge.
the reason people build huge, $$ mirrors is to collect more photons - there just ain't a lot of photons from things a gazillion (or so) lightyears away.
So, you really want to maximize the number of photons you collect; one way to do this is larger surface area (in a conventional mirror)
I think (but don't know) that # photons scales with radius ^2
If the fresnel thingy is 10% efficient that would appear to be a problem
Here we are with all this technology and we're studying the galaxy with nothing more than a glorified pinhole camera.
I read Slashdot for the headlines, because the headlines, unlike the articles, are usually original and never duplicated
Zero Image makes excellent pinhole cameras and they also have a special zone plate accessory. Follow this link to learn more about the technique and how it looks like on photographs: http://www.zeroimage.com/web2003/EntryPage/entryFrameset.htm
-You could spin the foil to keep it stretched. Might need some extra weight attached to the edges. This would make it difficult to steer.
-The holes will probably cause some distortions in the surface from uneven distribution of stress. Maybe it would be better to replace holes with clear patches of film, just selectively deposit the silver film in some areas only. You would lose some portions of the spectrum based on what your film was not transparent to.
-The focus problem is maybe the largest. I wonder if there's some way to get around the limitation of need to be exactly at a single plane for focus -- some kind of holographic capture within a 3-D block of "film", with later recovery of an image through post-processing.
Overall, I like this idea a lot.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
If it is up there, I take my point away :)
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Then you're stuck looking in the same direction (straight up) all the time, that's sort of a waste.
horror vacui
not necessarily, you could construct the receiver to rotate a few degrees, maybe even 10-15 degrees in any direction wouldn't be unreasonable. Then you have a telescope with similar ranges of other large systems.
Have you tried looking at what a 30 meter telescope would cost to build on Earth? (The largest one we have is about 11 meters).
.. and God forbid there is some space assembly required?
Now after you price it out, how about launching it to space
You used the figure 6400km for Earth, which is its approximate radius, not diameter. The calculation goes a bit more like this, at interesting wavelengths from mid-infrared (say, ~5000nm) to mid-ultraviolet (~200nm). We'll use the approximation you used: wavelength / aperture = radians (resolved).
mid-infrared:
(5e-6)m / 30m = 1.67e-7 radians
optical:
(5e-7)m / 30m = 1.67e-8 radians
mid-ultraviolet:'
(2e-7)m / 30m = 6.67e-9 radians
What is the angular diameter of Earth at 30 light years? (I'm not sure how you figure 6400km / 30ly is 2e-8 radians; that arithmetic is off by 3 orders of magnitude.)
12,700km / 30 ly 4.5e-11 radians
This is too small to be resolved, and by quite a bit. Even Jupiter has only 1/13th the minimum resolvable diameter at this distance. So no, a "normal" 30m aperture could not hope to resolve an Earth-sized feature at 30ly, or even one 100 times larger.
Let's compare this to Betelgeuse, which has been imaged in ultraviolet from Earth (er, very close to it!), well enough to resolve large- and medium-scale photosphere detail:
(4.38e11)m / 430ly = 1.08e-7 radians
But the Hubble's aperture is 2.4 and not 30 meters!
2.4 * 1.08e-7 = 259nm
So with mid-ultraviolet (or shorter), you can image the star and big details from a single 2.4m objective. That's because Betelgeuse has such a HUGE diameter (of the photosphere). Anything that's small enough to avoid stellar fusion is absolutely minuscule by comparison.
They're using a different type of effect: Fresnel diffraction. They're probably using the Fraunhofer approximation because of the large focal length involved, but the article doesn't say and I haven't read their publication.
Speaking of which, this seems to be an earlier paper of theirs on this very subject, published in 2006:
http://arxiv.org/abs/astro-ph/0510383
Might be worth a read.
refer to my original post, thx
Please stop stalking me, bro.
...with a thyroid condition?
...Lorenzo / I'm into kinky crustaceans. I just discovered internet praWn.
nt
Hey, pinhole cameras are making a comeback!