New Flat Lens Focuses Without Distortion 202
yahyamf writes "Applied physicists at Harvard have created an ultrathin, flat lens that focuses light without the distortions of conventional lenses. 'Our flat lens opens up a new type of technology,' says principal investigator Federico Capasso. 'We're presenting a new way of making lenses. Instead of creating phase delays as light propagates through the thickness of the material, you can create an instantaneous phase shift right at the surface of the lens. It's extremely exciting.'" And by "ultrathin," they mean it — 60 nanometers thin. The big advantage for this technology, aimed at telecommunications signals, is that "the flat lens eliminates optical aberrations such as the 'fish-eye' effect that results from conventional wide-angle lenses. Astigmatism and coma aberrations also do not occur with the flat lens, so the resulting image or signal is completely accurate and does not require any complex corrective techniques."
But... (Score:5, Funny)
Will is make my ass look big?
Re:But... (Score:5, Informative)
Have the cameraman back up, which lessens perspective distortion [stepheneastwood.com]. When taking pictures of people you should always get as far back as possible and zoom in. Staying close and zooming out is bad.
Re:But... (Score:4, Interesting)
depends on the effect you want. sometimes the photographer doesn't wish to be flattering.
i've seen some stunning stuff shot on 16mm film with a 2mm lens up real close. it makes their nose look a metre long and their neck seem far away, but it's often just what you need.
also, real estate pics.
Re:But... (Score:5, Informative)
Perspective distortion was used extensively in the filmimg of LOTR. It's how they made the hobbits look much smaller than the actors actually were.
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the hobbits look like they are of different heights. Sometimes they look waist high, sometimes chest high.
And after they smoke some weed they are high as kites!
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Yes, but only in one wavelength.
Re:But... (Score:5, Funny)
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Quick, seize that name!
oh wait... http://backslashdot.org/ [backslashdot.org]
Re:But... (Score:4, Insightful)
Offtopic??? That was classic, should have at least been modded as Funny.
The problem is that lately all you see for the first half of a discussion is an endless stream of jokes ("classic" and "not so classic"). Believe it or not, most people don't come here for the jokes, they come here for technical discussion.
The problem is that slashdot has the "funny" mod, and as far as comment visibility, treats it the same as the "insightful" or "interesting" mod.
To hack around this shortcoming in the mod system, some mods choose to mod down the jokes to try to improve the S/N ratio.
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Potentially, a post could get alternately modded funny and overrated dozens of times, burning through a pile of karma. I'm a little bit surprised there haven't been coordinated attacks on an individual poster.
Re:But... (Score:4, Informative)
The problem is that lately all you see for the first half of a discussion is an endless stream of jokes ("classic" and "not so classic"). Believe it or not, most people don't come here for the jokes, they come here for technical discussion.
The problem is that slashdot has the "funny" mod, and as far as comment visibility, treats it the same as the "insightful" or "interesting" mod.
To hack around this shortcoming in the mod system, some mods choose to mod down the jokes to try to improve the S/N ratio.
If you don't want to see "Funny" posts, adjust your modifier preferences and give "Funny" a negative value.
I consider troll threads more disruptive than joke threads since they garner more responses. Half the replies in a story might be to such a thread when it is posted near the top.
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The problem is that slashdot has the "funny" mod, and as far as comment visibility, treats it the same as the "insightful" or "interesting" mod.
Going for "funny" used to be dangerous to your karma; "funny" was karma-neutral and any joke risked an "offtopic" or "overrated" or even "troll". Since they changed that I've seen way too many bad jokes and redundant jokes that get modded up anyway.
If I think a joke's not funny, I mod overrated. If it's the same joke that's been told fifteen times in the thread alre
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Actually it was pretty hackneyed and arguably a little sexist
A return to refractive telescopes? (Score:5, Interesting)
Re:A return to refractive telescopes? (Score:5, Informative)
Nope. It's IR and down, and it sounds like it probably only works in a fairly narrow frequency band. It also seems like it's probably going to stay that way, since the feature size determines the frequency it's tuned for. Visible light may require impractically small features.
You could probably build an IR telescope using it, but it would still be a tube, it's just the lens would be very thin (which is likely a problem, rather than an advantage for a large aperture - how do you keep it from flexing? Plus your telescope would probably only work properly in a narrow frequency band (and you'd have to filter out other frequencies).
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Re:A return to refractive telescopes? (Score:5, Informative)
THz is LOWER than near IR in frequency (thus, in the wrong direction). They said "up to" in the article, which I suppose is accurate if you're talking about wavelength, but gives entirely the wrong impression.
Re:A return to refractive telescopes? (Score:5, Informative)
Re:A return to refractive telescopes? (Score:4, Informative)
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Agreed. Lower frequency would be correct.
Comment removed (Score:4, Interesting)
Re:A return to refractive telescopes? (Score:5, Interesting)
"because the temperature difference can distort images during the cooling down phase."
If someone told you that they were either way to credulous or thought you were. You may want to let your camera adjust to the ambient temperature (either cooler or hotter), mostly to avoid condensation, which is a pain to wipe off constantly and will make all your pictures look like you took them in the fog. If you're doing astrophotography you want the sensor to be as cool as possible to decrease the thermal noise. But heating or cooling in a lens on a regular camera doesn't affect the image quality noticeably. Unless of course the lens actually shatters, which I've seen happen, but only growing up in northern Canada.
But if you don't think flexing might be a problem take a piece of plastic wrap, stretch it across a five gallon pail and blow on it. Try and get it tight enough so it doesn't move but also doesn't tear. Now think that this lens is thinner than that.
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Yes, heating and cooling matters when your lenses get to be big enough. It sounds like it's a bigger problem with these flat lenses though. They're more sensitive to temperature differences.
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Then you'd have to take the IOR of the glass/substrate boundary into account which at multiple angles is annoying. I'm not saying it can't be done, just that it makes things more complicated and if your substrate is 60nm thick your glass has to be REALLY pure and flat to avoid distortion.
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An array of small thin flat lenses in the tube could do about the same thing as a big conventional lens. I suspect the new method isn't as stable as conventional lenses, even if you support it with a rigid grid.
Also, if this is SWIR or thereabouts, those cameras and their thick lenses aren't exactly cheap nowadays - it could compete with the traditional IR lens materials pretty easily.
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It might replace some special purpose instruments. The problem is, it's still narrowband, so you wouldn't be able to just stick a new camera on your telescope and look at a different part of the spectrum. You'd probably still be better off with a big mirror and a little lens instead of a refractor.
Re:A return to refractive telescopes? (Score:5, Funny)
Yeah, but then you wouldn't want to make them angry... you wouldn't like them when they're angry.
Really? (Score:3, Insightful)
?
Really? No, REALLY?
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HERLK SMERSH
ERMAHGERD
Re:A return to refractive telescopes? (Score:4, Informative)
IR and down in frequency. So you could make a tiny, easily concealable square to focus infrared rays at someone to irradiate them. Or use a magnifying glass, which is slightly bulkier but has much more light collection capacity.
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Won't do that either. You could cook them with IR though. Or just use a magnifying glass, which would do it faster.
Re:A return to refractive telescopes? (Score:5, Informative)
Re:A return to refractive telescopes? (Score:5, Informative)
No, unfortunately the concept is not generalizable to gamma ray frequencies (or xrays). It involves plasmonic components, which require metals with plasma frequencies above the operating frequency (otherwise the metals stops acting as a metal). There is no metal which would still behave "metallic" at gamma ray frequencies, I believe.
Quite right. More fundamentally, this won't work on any ionizing radiation, as you no longer achieve any cohesive refractive effect when your photons are randomly ejecting electrons via Compton or photo-electric effects, which become the dominant interactions at energies beyond UV.
Re:A return to refractive telescopes? (Score:5, Informative)
Take a look at a spectrum. "Terahertz" is low frequency IR and below: it tops out at far infrared. So this thing is basically good for a good chunk of the IR spectrum and a maybe a little bit of the submillimetre stuff that isn't quite IR. Visible light is too high frequency.
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Isn't that similar to the wavelengths of the "nude scanners" the Department of Fatherland Security (DHS) uses in airports, and now rail and bus terminals, interstate freeways, etc?
Re:A return to refractive telescopes? (Score:4, Informative)
The very same. It's possible these lenses might work well for things like that where regular lenses perform poorly. It's really aimed at telecom though - focusing fibre optic lasers.
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Exactly true. In the visible range, a Fresnell lens is essentially a series of concentric rings of prisms with varying base angle; in the present case the change in shape and size of the metal layer does the same thing. In both cases the lens power is strongly dependent on wavelength.
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But... imagine what a Beowulf cluster of these could do!
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What for? Making a narrowband IR camera with very little light gathering ability?
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Um, yes. THz is a bit of the submillimetre usually considered part of the radio spectrum, and far IR. So it goes from very high frequency radio up to nIR. That does NOT include visible. It's "scalable" i.e. tunable, to anywhere in that frequency range. So it's narrowband - you have to make a new lens if you want to look at a different frequency.
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sort of like a Fresnel lens, only using metamaterials and thus only applicable to a narrow range.
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no (Score:5, Informative)
If we sandwich a few of these with the metasurfaces tuned right, could we build a telescope that is a slab instead of a tube?
Only in limited cases, because it's only applicable from near-infrared to terahertz frequencies. UV and visible band are pretty much all out from the sounds of it.
Also: the lens is very thin. Nothing else is - just the lens. Ie, the objective or sensor still has to be some distance behind it, and I'm sure there are limitations with respect to angles. So you still need a tube - especially if the lens is very large in diameter.
This is fascinating, because it sounds like it is operating as a phased array; they *delay* the light depending on where it strikes on the lens. Wild! Phased arrays work by delaying the signal, thus steering the electromagnetic wave, but that's when you're generating or receiving...not modifying and retransmitting!
However, they're doing it in this case by physical manipulation of the gold/silicon structures at construction time. It's not tuneable afterward.
That's fine for telecom / fiber applications, where you only have a fixed number of specific wavelengths. However, astronomers might not mind being restricted to imaging just that one wavelength or that high in the light spectrum.
Sadly, this limitation also makes it useless for semiconductor lithography, which is UV to x-ray range.
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This technique would seem to operate on only a narrow range of wavelengths. Although it may work at visible wavelengths each lens is tuned to a single wavelength. Optical telescopes need ro refract at least a octive with one lens. This lens would need to be tuned to a single frequency. Not a problem for LASER light, monochromatic. No substtute for standard lenses for imaging.
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The results have been... mixed. They do yield smaller and lighter lenses, but also introduce new distortions of their own. The tradeoff is worth it in most photographic applications, but for precision astronomical work I think the loss of contrast and sharpness may limit its usefulness.
Also note that DO reduces but does n
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That's only a problem for that subset of astronomical work that requires precise pretty pictures - for the rest (such as taking spectrograms), not so much.
It's always been possible (Score:4, Interesting)
Re:It's always been possible (Score:4, Interesting)
why go with such big apertures if you want everything in focus? the beauty of such apertures is you can isolate your subject and blur the tits off everything else in the frame.
sensor dynamic range is increasing all the time - i'd say by the time one of these lenses works for visible light, they'd be unnecessary.
of course, there'd still be a need to focus with one of these - the focal point depends on where the subject is.
Re:It's always been possible (Score:5, Funny)
Re:It's always been possible (Score:5, Funny)
Either I'm taking you too literally, or you're doing it wrong.
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why go with such big apertures if you want everything in focus? the beauty of such apertures is you can isolate your subject and blur the tits off everything else in the frame.
sensor dynamic range is increasing all the time - i'd say by the time one of these lenses works for visible light, they'd be unnecessary.
of course, there'd still be a need to focus with one of these - the focal point depends on where the subject is.
Because sometimes the entire landscape *is* the subject and you want to take the photo without long exposure times which necessitates a tripod.
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Sooner or later you run up against the quantum nature of light.
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why go with such big apertures if you want everything in focus? the beauty of such apertures is you can isolate your subject and blur everything else in the frame.
Note to prospective camera geeks: don't take that at face. Consumer pocket cameras lenses and sensors don't provide that type of blur and the number means different things for different lenses. Besides, the fastest apertures they offered at brick stores a month ago were 3.5 to 3.1. My android phone does about the same --everything is "in focus". The end result is zero "blur" for your average group shots. My advanced point and shoot forces 2.0 whenever it can and has a large sensor... yet its "blur" effect
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Yeah, there's a few factors:
Having a small DoF (lots of blur for out-of-plane stuff) relies on real lens length (a 150mm full frame equivalent P&S might be more like a 25mm DSLR), and a wide apature.
Image quality is ... complicated. If you want to take pictures fast (to minimize motion blur) you need good usable ISO, and a good apature number. Usable ISO will very roughly scale with crop factor, because big sensors tend to be better, but it also depends on other factors.
So all the people winging about t
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Also, small DoF comes from a close subject. That's why all the iPhone bokeh shots are of small subjects (flowers, sushi, other iPhones).
What about chromatic aberrations? (Score:2)
That's really all that matters these days. Everything else can be easily corrected in software. Chromatic aberrations are more difficult to deal with nicely.
-Matt
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maybe we should build a sensor with more than just RGB? like RYGCBM? depending on how much aberration, treating all those channels separately will get you within a subpixel's width of the desired lack of aberration.
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That's really all that matters these days. Everything else can be easily corrected in software. Chromatic aberrations are more difficult to deal with nicely.
-Matt
Nope Matt...
Every optical aberration suppresses the system's Modulation Transfer Function (MTF) fundamentally resulting in a loss of information. Despite what CSI has taught you, you can never fully "correct it in software" after the fact. How well you can do depends primarily on signal to noise ratio (SNR), your detector's linearity calibration, and your prior knowledge of the objects power spectral density (usually just a rough semi-educated guess). Therefore, it's still important to have low-aberratio
Re:What about chromatic aberrations? (Score:4, Interesting)
It's just a giant antenna, minus the feed. Think of a massive yagi array, flattened. Works best in a very narrow spectrum.
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Maybe it could still work for a wider spectral range by stacking several layers at various wavelengths. They are thin, so there could be space for a lot.
interestingly... (Score:5, Informative)
according to this [business-standard.com] report it's not a lens, but a diffraction grating.
From linked article:
"Our flat lens opens up a new type of technology. We're presenting a new way of making lenses. It's extremely exciting," says principal investigator Federico Capasso, professor of applied physics at the Harvard School of Engineering and Applied Sciences (SEAS).
Sorry, matey, it ain't that new, it's just a new application of a well established physical property. I do seem to remember using diffraction gratings to magnify light-bending effects at college in 1992 - specifically to fire an EM pulse at 450nm (near blue part of the visible spectrum) through a sample and use a calibrated* diffraction grating to amplify the signal to a photographic plate. What you end up with, essentially, is a highly magnified image (on the order of millions of times) with a very low distortion, with which you can determine the structure of the sample (be it a crystal lattice, eg. graphite, or a double helix, eg. DNA; each molecule has its own unique diffraction pattern). Generally you would use X-rays as pretty much anything is at least partially transparent to this wavelength, but since we had to use visible light from a very low powered lasing LED, we had to use visible-transparent samples. We got stuck with a quartz crystal. Still interesting physics, though, and some very pretty pictures.
*calibrating a diffraction grating is very simple: all you do is make the spacing between the lines on the plate equal to the wavelength of the light you're using. For far blue, you'd use a 400nm grating, for red 700nm. These are but two of several calibrated plates available.
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This new lens is not just a diffraction grating since it uses sub-wavelength structures to alter the apparent optical density (refractive index) of the material, i.e. metamaterials [wikipedia.org].
Misleading article title and blurb! (Score:4, Informative)
The lens is tuned to a single wavelength of light and was demonstrated with a laser.
It's not apochromatic and not instantly useful to most lensing applications.
The authors say that it could potentially be, in the future. But that often means "give us more funding."
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But ... 3 of them could focus red, green, and blue lasers, and give us big screen images.
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Plasmonic devices=a bit far from any practical use (Score:5, Informative)
Whenever us optical engineers hear about plasmonics, we internally roll our eyes, because metal almost always absorbs far too much light to be useful. Even tens of nanometers of penetration and/or propagation can extinguish almost all of the light. This essentially relegates the entire field to the realm of theoretical curiosities and nothing more. (This work uses 60nm thick gold)
The authors of this paper admit that absorption is their biggest obstacle, as this lens only passes 10% of the incoming light. There are other issues for making this work a reality, but they pale in comparison to the classic brick wall you get when passing light through metal.
Yeah.... but how expensive is it? (Score:2)
Co-author checking in. (Score:5, Interesting)
**MOD PARENT UP** (Score:2)
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There's a type of lens called Beugungslinse in German. I think the english term is diffraction lens. It is similar to a Fresnel lens, but the size of the structures are below the wavelength of visible light. What are the differences between these lenses, diffraction grates and the type of lens you're working on?
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it sounds like you're etching a field of micro-lenses (why do you call them anteneas??) - like grooves on a record, the angles of these grooves are tuned to have a slope which graduates across the array - directing the light in a way that finely matches a convex or concave pattern.
if this is the case, it sounds like much more would be possible - perhaps you could go on to simulate custom glass geometries by modulating the algorithm by which you apply the angles and spacing using some sort of stipplegen??
ver
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As an FYI, many articles that are pay walled can be found on the arxiv pre-print server for free.
Re:Co-author checking in. (Score:4, Informative)
Can it be adapted to be *useful* with visible light? Unclear for a variety of reasons. The first is that shifting to the visible will increase metal losses, so more of the light will simply be absorbed instead of focused. Not that the efficiency isn't an issue already: from the article you can see that with the current design, the maximum attainable efficiency is ~10%, with the rest of the light being absorbed (not that much actually) and scattered somewhere else (this is the big one). In fact the presently demonstrated lens has an even lower efficiency, though scaling it up to the 10% figure is fairly trivial. Anyway, in the visible the 10% figure probably drops with the current design, though some design improvements could likely be made. I don't want to give you an upper bound on the efficiency because frankly I'm not sure. Anyway, do you want a lens that only focuses some percentage (say between 10% and 40% just to have some numbers) of the light and throws away the rest? We've gotten so good at making regular old lenses in the visible, that I'm not so sure. On the other hand go to a different frequency range where good lenses are less common, and all of a sudden the present approach may have some value.
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I'd think that well-performing lenses can be made for the frequencies you cover, as long as sufficiently transparent material is available. Obviously you can take a decent visible-light aspherical lens, scale up the size, select the right material, and voila, you have a lens for RF. So, the question is: what is the frequency range where it's hard to find a material that would pass at least around 10% of the signal, at appropriately selected thickness? Another question: what problems specifically call for le
Its all about latitude... (Score:3)
and I don;t mean those little lines on the globe.
I have been an amateur photographer most of my life. The holy grail of photography, for me, has been to find film or techniques that bring film images as close to the latitude of the human eye. In Film Speak the human eye can handle around 12 to 14 f-stops around a given lighted scene. Which is to say that the information that your retina takes in ( given a central point that has lighted value of n ) can be discriminated 12 to 14 f-stops darker or brighter.
We have all experienced taking a picture of a brightly or darkly lit scene. Sunsets are a great example. We as a viewer can enjoy a sunset and see all the detail ( quite clearly ) around us AND enjoy the sunset. This is one of the hardest, if not impossible, things to do with any camera, digital or otherwise for the simple reason that to correctly expose for the sky ( the sunset ) we will always drastically underexpose everything else around us by a large factor.
I think this can be solved with a digital camera, but not until computing speeds drastically increase and not just by a little bit, but by several orders of magnitude since it would mean that each individual pixel would have to be processed and recorded for the sufficient amount of time to record the detail level in a still shot. So in a Nikon D5100 the sensor has ~16 million pixels. To obtain a shutter speed of 1/125 of a second ( .008 seconds ) each pixel who have to be processed in about 5 pico seconds ( 16 million / .008 = 1 * 5 -10th) and of course faster shutter speeds, well you get the point.
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The issue is not about processing speed, but about sensor manufacturing processes. Your 5 ps figure is correct but meaningless: you don't have to serially "process" pixels like you imply, it'd be useless to do so.
In the current sensors, it's hard to put significant electronics for every pixel without making the pixes less efficient. To have the ultimate sensor, you'd want something like an HP multislope A/D coverter right behind every pixel, so that it wouldn't matter how much light falls on it -- it could
Re:Its all about latitude... (Score:5, Informative)
Best explanation I have found that says it succinctly. I hope it helps.
Dynamic range = difference between highest and lowest(brightest/darkest) value that can be recorded on a medium.
Latitude = The degree of variation allowed above or below a certain setting, derived directly from dynamic range. i.e latitude a film is for a certain exposure, how many stops of headroom it has above and below before you lose details.
And just for fun...
Contrast = the difference between intermediate tonal values within a certain range. Generally, contrast is inversely related to dynamic range. A wider range allows finer graduations and hence lower contrast if desired. Contrast is directly related to the tonal response of the medium and can be visualized as a curve from light to dark. The steeper gradient of the curve, the higher the contrast at that point.
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But when I look at raw pictures of my D800 they have significant information hidden in the dark and bright parts of an exposure and with software it can be brought out, effectively lowering the contrast for the whole picture.
Meaning the limiting factor is the contrast range of the screen or printed media, contrary to our eyes they are not dynamic.
I wonder about chromatic aberration (Score:2)
Speaking as both a photographer and a very near-sighted person, it would be really awesome if these new lenses were also free(r) from dispersion as compared with standard lenses. (Dispersion is responsible for colour separation in a prism. It also causes orange-yellow and blue-violet fringing in simple lenses such as eyeglasses. Cameras use compound lens elements in a clunky and expensive way to address this problem - see http://en.wikipedia.org/wiki/Achromatic_lens [wikipedia.org] )
Cameras would be lighter and more accura
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Those lenses are horrible at chromatic aberration, they are designed for monochromatic light, and there's no trivial way so far to change that. So no dice there.
Interstellar laser (Score:2)
Eye Glasses? (Score:2)
As someone who wears small telescopes on his face on a daily basis, can we please get this technology into eye glasses?
Sure I would still have to wear glasses, but at least they might weigh a bit less than my 1kilo "ultrathins" I currently endure.
20nm sounds great! Though they might have to buffer them up a bit so I don't cut my face or nose off or something by mistake.
Sometimes distortions are good (Score:2)
Now that's what patents are for (Score:2)
Sounds like they actually invented something...
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sandwich of perfectly flat, perfectly transparent glass?
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It's not viable for the visible light spectrum... :-/
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Better Than Glasses (Score:2)
Screw glasses, what about Contact Lenses?
Or what about Intra-ocular lenses?
Or could you just implant metamaterials in your cornea to correct your vision?
Uncomfortable as hell (Score:3, Insightful)
Screw glasses, what about Contact Lenses?
I'm not sure how many people demand perfectly flat contact lenses, but it can't be many...
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Or could you just implant metamaterials in your cornea to correct your vision?
I wonder how many nurses it would take to hold the patient down once they learned of your plan to go after their cornea with an ion-beam rework system?
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Or could you just implant metamaterials in your cornea to correct your vision?
I wonder how many nurses it would take to hold the patient down once they learned of your plan to go after their cornea with an ion-beam rework system?
This is why you inject them with Happy Juice (tm) before telling them the details.
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I'm pretty sure that a distortion-free optical material can only be used to make objective lenses...