Re: Fwd:

[George L Smyth <GLSmyth@xxxxxxx>]

Helmut Faugel TE wrote:
> 
> On Tue, 18 Aug 1998, George L Smyth wrote:
> > I rather doubt that the images would impart anything special.  I would imagine
> > that the boiler would not be as hot as a soldering iron, so it will not emit
> > infrared radiation in the recordable range.
> 
> If I remeber it in the right way IR-film can only record thermal radiation
> form objects which are hotter than 400 degree Celsius. In G. Spitzings
> book about IR-photography there is picture of a soldering iron recorded
> on Ektachrome IR with a lens stopped down to f/5.6 and some (10 ?) minutes
> exposure time in total darkness. So even if your object is very hot it
> take a long time to record a picture, and it is nearly impossible to derive
> the surface temperature from such a picture.

Actually, the temperature is 250C.  At 500C the object will become self-luminous
and recordable with normal panchromatic film.  The belief that infrared film can
record heat is only partially true - it can if hot enough, as noted in the
soldering iron reference.  However, magazines like Shutterbug that make the
claim that heat from a person's body can be recoeded with IR film merely
perpetuates the half-understood myth.

george

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