Re: Myth of Heat exposing IR film

[Andrew Davidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

Bertha,

> discussion.  I explained that IR is a very broad spectrum of which film
> records a small bit but I couldn't remember that it is near IR the film
> records and far IR that produces heat until I got home and checked my 
> references.

You have this right. An object would have to be at over 300 degrees C to start
to give off energy with a wavelength such that infrared sensitive films could
start to detect it and form an image of it. While normally "we" only use
something like Kodak's high speed infrared film, there are (or were) special
purpose films (made by Kodak in particular but also other manufacturers I
think) that have been used for astronomical purposes in particular that are
sensitive beyond the range of this film.

> that emitted both near and far IR, thus the confusion.  But I wonder, was or
> is there some special application, eg. military or scientific, that
> incorporates some IR technology that has caused this confusion or is it just a

Any imaging technology these days that is based on formaing images by long-ir
wavelengths (and sometimes also "simple" photon or light amplification) devices
such as used for surveilance and night vision systems is dubbed "infrared".

The Gulf War had a lot to do with this. It was the first time that THERMAL
imagers were widely used by the military. Planes identified hot spots on the
desert floor at night by the residual heat of tank engines and kaboomm ...
gone.

Photographic film, on the other hand, is nowhere near as sensitive to thermal
radiation. One could argue this out logically by simply stating that the mere
act of holding the film casette in one's hands would expose or fog the film ...
which does not happen.

And ... the "aura" or "glow" we sometimes see in photos of human subjects, is
mostly due to overexposure and halation. There is no "glow" around the subject
... it is merely a photographic effect ... usually one we try to avoid.

BTW, if you want to read about this and other aspects of infrared and
ultraviolet and technical photography in general you could check out a bunch of
introductory or overview articles at: http://www.rit.edu/~andpph/articles.html
 
regards

Andy  o o  0 0 o . o  Davidhazy, Imaging and Photo Tech
       \/\/\/\/\/\/          http://www.rit.edu/~andpph
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