Re: Bears and Butterflies

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 30 Nov 96 at 0:39, Robert Long wrote:

> Before this list started, Willem and I had a conversation on the
> Usenet about a photography I'd seen a number of years earlier that
> purported to show heat loss from a house.  It had been taken at night
> and looked pretty unreal, with "ectoplasm" oozing from the doors and
> windows.  Willem said it could not have been photographed with regular
> IR film, because film is sensitive to near-IR only, and heat is on the
> far end of the spectrum.  Maybe he's right; maybe the picture was made
> through a night-vision scope.  I just don't remember.  On the other
> hand, there are the iron pictures made on IR film that do show the
> heat.  And, as discussed here earlier, whether a given wavelength
> should be considered as heat depends on what materials we're talking
> about.  Anyone have any further thoughts on whether it might be
> possible--using a long exposure at night, no doubt--to actually
> photograph heat loss on HIE?

Night vision scopes as such are not much more sensitive than HIE 
either; depending on generation it ranges from 800 to 900nm. Quite 
slick to estimate the IR effect on film, by using a dark IR filter, 
but not in any way related to heat.
The ectoplasm you saw was probably multi color, right?
Until recently you needed special cooled cameras to make such images; 
a new heat sensor now even makes it possible to record heat without 
external cooling. I have seen demo tapes from Texas Instrumens, both 
a car-mounted (remote control) unit and a hand held device. The 
latter is also used as field equipment by the military.
The tape I saw was black and white, but with some image processing 
one could address colors to different levels of grey (which were 
direct indication of heat; white was hot, black was cold (reverse was 
also possible of course, for whatever reason)).
 
> More recently I raised a question (and got one specific wrong) on a
> peculiarity of certain pigments that I don't understand.  I once had a
> lot of old lacquer recording blanks that I had to strip to send the
> aluminum substrates off for what today we'd call recycling.  I
> discovered that when you looked through a single layer of the lacquer,
> it looked sort of a characterless blue color.  But when I doubled the
> thickness to two layers it looked deep red (very much like a Wratten
> 29), and when I increased the number of layers above two, the red got
> progressively deeper, but only gradually.  Similarly, there are bulbs
> in the New York subway tunnels that play a similar trick.  At a
> distance, you see a ruby red glint, but when you get close it turns
> out to be a blue bulb.  (That's what I got wrong--I had near and far
> conditions reversed.  And I don't know what the bulbs are there for.)
> I'd be interested in any explanation of these two phenomena.

I found the (Ralleigh) scattering theory quite nice; it basically 
says that you can see red from a longer distance than blue.
I have a list of the various scattering phenomena on my homepage,
extracted from a discussion on the newsgroup sci.optics (highly
recommended for this kind of brain crackers). The original question:
why is the sky blue, when at the same time air is colorless....:-)) 
There is also an air-transmission chart, plotting transmission for 
various wavelengths. Fascinating sharp dips and peaks. See:

http://www.a1.nl/phomepag/markerink/mainpage.htm


--
Bye,

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      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 9