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Orchid XP v8 wrote:
>>>>> (I'm guessing that due to the absurdly long wavelength, most
>>>>> objects would be too blurry to see.)
>>>>
>>>> Indeed, that's kind of the point. That's why you can listen to the
>>>> radio indoors.
>>>
>>> You can see light indoors too. Not because it has a short wavelength,
>>> but because certain substances do not absorb it.
>>
>> That's why you can listen to the radio in the dark.
>
> I'm not sure what you're talking about, but I know what I'm talking
> about: Different materials absorb different wavelengths.
I'm being sarcastic, is all.
> There are
> materials that absorb visible light, and others that let visible light
> pass through it unaltered.
Yes.
> Presumably the same thing applies to *every*
> wavelength - which ought to include radio waves. You can listen to radio
> indoors because not all of your house is made of metal (AFAIK the only
> thing that absorbs radio waves).
I'm pretty sure a couple kilometers of concrete would do the trick too.
> That's nothing to do with the size of a
> radio wave, it's to do with what materials do or don't absorb it.
It has to do with both. Any amount of non-conductive surface smaller
significantly than a radio wave is unlikely to absorb it, unless you happen
to be very unlucky in the choice of your sizes. The reason that far fewer
materials absorb radio waves is that they're very long and hence low energy.
You need a substance where the electron gap bands are very close together
(like free electrons in a conductor's surface) to capture radio waves.
> Now, what kind of a picture you could make with a "light" having a 2 Km wavelength,
I have no idea.
http://universe.chimons.org/contents/Radio.jpg
--
Darren New, San Diego CA, USA (PST)
Yes, we're traveling together,
but to different destinations.
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Invisible wrote:
> John VanSickle wrote:
>
>> I always knew that UV was bad for your skin!
>
> Notice how freckly she looks in UV though. That melanin really does mop
> up UV very effectively, eh? (Compare to how apparently freckle-less her
> skin appears under normal conditions.)
Those aren't good freckles, if they only show up in a UV filter. UV
photography is a good way to spot skin damage from too much UV exposure.
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Invisible wrote:
> http://en.wikipedia.org/wiki/File:UV_Vis_IR_Portrait.jpg
>
> I wonder how much of the difference is due to the wavelength, and how
> much is due to how the camera responds to it.
That's actually a really cool picture. I assume that the shorter/longer
wavelengths are what accentuates her wrinkles in the ultraviolet and
smooths them in the infrared, but I'm surprised the effect is so visible
at those length scales. Maybe subsurface scattering is playing a large
role in this.
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> Now, what kind of a picture you could make with a "light" having a 2 Km
> wavelength, I have no idea. I vaguely gather that there's some sort of
> relationship between the wavelength of something and the size of object
> you can see with it. (Hence electron microscopes have better resolution
> than light microscopes, for example.)
The issue is diffraction. Once the objects get to the same scale as the
wavelength then things get blurry. For example normal light goes through
your doorway in straight lines, if something is geometrically obscured by
the wall, the light from it won't reach you (directly at least). However if
your "light" has a wavelength of 1 metre (or your "doorway" has a width of
100 nm) then you'll be able to see things that are geometrically "blocked"
by absorbing materials. This is because the wave will diffract as it goes
through the gap.
IOW I suspect if light had 2 km wavelength then everything would be a big
blur.
http://en.wikipedia.org/wiki/Diffraction
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>> Now, what kind of a picture you could make with a "light" having a 2
>> Km wavelength, I have no idea.
>
> http://universe.chimons.org/contents/Radio.jpg
Well, yes, they have various radio telescopes. But I wonder... these
images are in colour, but does the colour actually represent different
wavelengths? Or is it just the intensity of radiation being recieved?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On 4/2/2010 5:40 AM, Orchid XP v8 wrote:
> Mike Raiford wrote:
>
>> Interestingly, UV imaging can also be used in forensics to find
>> evidence of an injury after the bruise has faded in visible, it will
>> show up in UV wavelengths for quite some time.
>
> If you believe NCIS and so forth, UV makes blood and other bodily fluids
> glow bright green. (I never did figure out why...)
>
Only if treated with Luminol, the I think it's more of a dull blue....
>> Eventually I plan on buying an inexpensive P&S modified to capture UV,
>> visible and IR. Its UV capability is one of the reasons. I've always
>> wanted to capture what my eyes cannot.. .
>
> I've been watching Richard Hammond's Invisible Worlds. Some very cool
> stuff, but unfortunately the cool stuff is only on screen for, like, 2
> seconds, and then we get Hammond chattering some more.
I hope that show is available in the States soon, I've been following
the guy who did the UV Photography's blog for quite some time.
> I'd love to do the whole trip with time-lapse photography, high-speed
> photography, UV and thermographs, etc. In fact, I've often wondered what
> the world would look like if you would see radio waves. (I'm guessing
> that due to the absurdly long wavelength, most objects would be too
> blurry to see.) I've even wondered what the world would look like if you
> could see sound.
Interesting thought. Not sure how to build a detector for radio waves,
though (in terms of forming an image on a plane ...) it's exceedingly
difficult to detect thermal IR, I can only imagine the difficulty in
focusing radio waves onto a plane.
> (Eyes and ears both detect waves. Eyes detect only three frequency
> bands, but with ludicrous spatial resolution. Ears detect waves with
> rubbish spatial resolution, but insane frequency resolution.)
>
It's amazing when you look at how your auditory system works. Your brain
essentially gets the Fourier transform of what you're listening to. Also
interesting how color vision interpolates between 3 broad bands of
wavelengths to give the perception of a huge amount of hues. Though,
because there's only really 3 different frequencies detected, you get
some metameric failure for certain colors. Different frequency spectrum,
but they look identical. A good example of this is when you photograph
something whose color is in the violet end of the spectrum. Our red
receptors are a little sensitive to the very short wavelengths of
visible light, giving us the perception of purple. The red elements on
most digital cameras' Bayer arrays don't usually have the same ability
to pass the short wavelengths, giving certain dyes and flowers a more
blue color than what your eyes perceive.
It's fascinating how we process information from our world. I've often
wondered why we perceive blue as-- well-- BLUE, rather than red. I'd
love to know what the world would look like if I had tetrachromatic or
even pentachromatic vision. Some of the subtleties of some colors would
definitely be more obvious. Fun stuff.
--
~Mike
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On 4/12/2010 1:17 PM, Orchid XP v8 wrote:
>>> Now, what kind of a picture you could make with a "light" having a 2
>>> Km wavelength, I have no idea.
>>
>> http://universe.chimons.org/contents/Radio.jpg
>
> Well, yes, they have various radio telescopes. But I wonder... these
> images are in colour, but does the colour actually represent different
> wavelengths? Or is it just the intensity of radiation being recieved?
>
depends... sometimes it is colored by wavelength, sometimes just a scale
of intensity. In the case of that image, it looks like intensity mapping.
--
~Mike
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On 4/5/2010 10:51 AM, Kevin Wampler wrote:
> That's actually a really cool picture. I assume that the shorter/longer
> wavelengths are what accentuates her wrinkles in the ultraviolet and
> smooths them in the infrared, but I'm surprised the effect is so visible
> at those length scales. Maybe subsurface scattering is playing a large
> role in this.
Right. the UV light does not penetrate as deep, so will reveal more
surface detail. IR on the other hand penetrates deeper, giving the skin
the milky appearance.
--
~Mike
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>> If you believe NCIS and so forth, UV makes blood and other bodily fluids
>> glow bright green. (I never did figure out why...)
>
> Only if treated with Luminol, the I think it's more of a dull blue....
Yes, you never get to see that...
>> I've been watching Richard Hammond's Invisible Worlds. Some very cool
>> stuff, but unfortunately the cool stuff is only on screen for, like, 2
>> seconds, and then we get Hammond chattering some more.
>
> I hope that show is available in the States soon, I've been following
> the guy who did the UV Photography's blog for quite some time.
The other problem, of course, is that I missed it while it was on TV, so
I had to watch it on BBC iPlayer. So it's very blury. (Oh, and I watched
two episodes but seem to have somehow missed the rest...)
>> I'd love to do the whole trip with time-lapse photography, high-speed
>> photography, UV and thermographs, etc. In fact, I've often wondered what
>> the world would look like if you would see radio waves.
>
> Interesting thought. Not sure how to build a detector for radio waves,
> though (in terms of forming an image on a plane ...) it's exceedingly
> difficult to detect thermal IR, I can only imagine the difficulty in
> focusing radio waves onto a plane.
Presumably you need some sort of shielding to block out waves except
through a specific opening, and then use magnets to focus the waves that
come through the opening?
Alternatively, just don't bother trying to focus it at all. You'd still
get *something*, if not a sharp images.
> It's fascinating how we process information from our world. I've often
> wondered why we perceive blue as-- well-- BLUE, rather than red. I'd
> love to know what the world would look like if I had tetrachromatic or
> even pentachromatic vision. Some of the subtleties of some colors would
> definitely be more obvious. Fun stuff.
Apparently most mammals see only 2 wavelengths. Humans and a few
primates have a duplicate gene that mutated very slightly, yielding a
new pigment that responds to a very slightly different wavelength band,
giving us 3-colour vision. (Go look at the CIE spectrum diagrams. The
"red" and "green" wavelengths are quite close together, but "blue" is a
mile away.)
Apparently mad scientists tried introducing the mutant gene into mice.
Normally mice see only 2 wavelengths, but these genetically-engineered
mice see the same 3 bands that we do. And, as best as the scientists can
tell, their brains were able to process this new information. Just
adding the new pigment was all that was necessary for the brain to adapt
and use it.
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Am 29.04.2010 14:34, schrieb Mike Raiford:
>> I'd love to do the whole trip with time-lapse photography, high-speed
>> photography, UV and thermographs, etc. In fact, I've often wondered what
>> the world would look like if you would see radio waves. (I'm guessing
>> that due to the absurdly long wavelength, most objects would be too
>> blurry to see.) I've even wondered what the world would look like if you
>> could see sound.
>
> Interesting thought. Not sure how to build a detector for radio waves,
> though (in terms of forming an image on a plane ...) it's exceedingly
> difficult to detect thermal IR, I can only imagine the difficulty in
> focusing radio waves onto a plane.
It's being done, not only for IR, but also for radio/microwave.
Thermal IR cameras are pretty well established as equipment for e.g.
police helicopters to search for or track people (particularly at night).
Modern jet fighter planes like the F22 Raptor are also equipped with
electronics that can detect the direction of both IR and radar (i.e.
microwave) emitters, to warn the pilot of potential threats. And AFAIK
they're not limited to a single emitter, but can detect multiple at once.
Sound "images" are common for sonar systems. And ultrasound imaging
devices, for that matter.
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