a nice story about a radical new design for phone camera lenses.
The story explains how a 'new' technology is becoming available. It's SO cool that you will one day (not quite yet) be able to take photos with
your cell camera that might rival a DSLR camera with a big Nikon lens.
Wow, that's pretty neat, right? The new lens will be able to actively focus, act like a big macro lens that can do wide angles, close ups and act as
a telephoto lens. On top of which, the quality will be incomparable. Since the lens is a big problem with small cameras, this is a boon to
Scientists have developed a super-thin lens that can function either as a convex or a concave lens with the flick of a switch. It means a scene can
either be magnified or viewed at wide angle.
It could provide a new generation of small lenses used in devices such as mobile phones and tablet computers, allowing keen photographers to capture
images that previously required expensive SLR lenses.
Sounds really promising! A new day will dawn for cell phones and tablets!
Now...what else. Hm.
Welp, if you've ever paid attention to the weirder bits of my posts I do occasionally drop the oblique reference to Current Actual Military/Gubmint
Stuff into them. They're not usually that blatant, which irritates BFFT and mbkennel (sorry).
Back in maybe 2007, I started popping occasional references to this technology into posts, and I suppose none of you are NRO/NGIA employees (heh) as
my 'who amongst you will respond to this?' trolling got bupkes as a reaction for the last five years. So. The question you ought to ask is - this
sounds miraculously good. What sort of chicanery might it be turned to? And that gets us, gentle reader, into the odd and arcane arts of Orbital
Sparrow and Rayleigh and Dawes! Oh my!
A popular meme in the world at large, and certainly on conspiracy web sites goes something like this:
"My uncle, who works for the FBI, says that satellites are so good that we can read the letter in your hand if you open it at the mailbox" or "we
can read dates off of coins on the ground" or whatnot.
There's an issue with optical lensing. And that problem is, the lenses are not infinitely large. You wouldn't think that would be a problem, would
you? But it's true - the lack of infinite aperture actually is like an error in the lens. What you get as a result of this is an effect called
diffraction, which sets an upper limit on the amount of information that can pass through the lens, or, in short, a lens of a given aperture (size)
cannot resolve details smaller than a certain size (angular resolution, literally), given a particular color of light. It doesn't matter if the lens
is made by magical Keebler elves in a hollow tree so that every atom in the lens is exactly where design would have it. It doesn't matter if the air
is crystal clear. It doesn't matter. For any finite lens, the resolution at a fixed distance is limited by the aperture and the wavelength.
If you google around for this, you'll want to look for "telescope", "modulation transfer function", "resolution" and "aperture" among other
things. This has actually been known for a long time - the late 19th century scientist Lord Rayleigh was one of the first to point this out, so you
will see the problem often discussed as "Rayleigh's Criterion" or "Rayleigh's limit". Other people have refined the thing, so you'll also see
Sparrow's Limit and Dawe's limit, and occasionally something called an "Airy disk". Some of these are more applicable to stellar imaging than
ground imaging, but it's still all the same issue - a finite lens has limits on its performance. The reading on this varies from mind-numbingly
mathematical to overly simple - choose your poison.
So, how do TPTB, in this case pretty much entirely the NRO/NGIA with the occasional CIA surprise, deal with this? Well, they can't, at least not with
optical imaging. Rayleigh sets a physical bar against reading the dates on coins, newspapers, or counting hairs on Uncle Fred's head. You can use
better optics, to get as close to the limit as possible. You can use BIGGER optics - remember the larger the aperture, the smaller the resolution for
a fixed orbital height. So a big lens or mirror means a finer-grained image. But you've got to get the damned thing into orbit, so something like
Hubble is about as big as you can get.
And, in fact, the Hubble's mirror is, oddly, about the size of the main mirror on a KH-11. Or so I'm told.
But it's just damned tough to make them much larger AND get them into orbit. Big is heavy, and fragile.
So what's another way? Well, you can contrive to make a faux aperture by combining a number of smaller telescopes. If you had an array of mirrors (or
lenses), each small in itself, you could, if all went well, put their images together so that the aperture looked like the size of the array, not the
size of the mirrors making it up. That's great in theory - you see it done a LOT in ground based radio telescopes. But it's tough to do with optics.
Not that you CAN'T do it, but the accuracy of positioning the individual mirrors in the array is a function of the wavelengths involved. For radio,
that can be meters off and still be ok. For light, the spacing has to be to fractions of a wavelength of light. And remember, the shorter the
wavelength of light, the better you can resolve details, so these two things work against each other. You want it short for details, but short is
tough for mirror positioning.
Not that this has stopped them. One way to make this work better is to tether a group of sats, usually three, and spin the crap out of them so that
the tethers are really rigid. Then you use micropositioners to adjust the spacings, and voila! an aperture as big as the three sats at the ends of the
tethers, made of three much smaller mirrors. This isn't perfect either, because tiny perturbations like going in and out of direct sunlight, or
gravitational anomalies caused by masscons below, most particularly if you ever have to reposition/retask the group, just takes FOREVER to compensate
for, so optical satellite clusters that do this go on and off line constantly as they fall out of perfect alignment and have to recalibrate. Also,
it's just not quite as good as a real mirror of that size, so you can't get the maximum resolution or light gathering capability a huge mirror or
lens would provide. But it's better than a poke in the eye.
(continues on page 2 - maybe this is a good test for tldr!)