On 3/31/2010 6:59 AM, 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.)

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.

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.. .

-- 
~Mike

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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...)

> 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'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.

(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.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Am 02.04.2010 12:40, schrieb Orchid XP v8:

> If you believe NCIS and so forth, UV makes blood and other bodily fluids
> glow bright green. (I never did figure out why...)

Because IIRC they also use some spray that somehow reacts with the blood.

Not sure about other body fluids though.

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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.

-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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Darren New wrote:
> 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.

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
> Darren New wrote:
>> 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.

-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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>>>> (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. There are 
materials that absorb visible light, and others that let visible light 
pass through it unaltered. 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). 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.

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.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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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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