Re: IR Filter affects

[Randy King <randyk@xxxxxxxxxxxx>]

Willem-Jan Markerink wrote:
> 
> On 20 Aug 96 at 23:30, Randy King wrote:
> 
> > The affect of filters has been discussed, along with the
> > affects of flashes on IR.  It seems that a filter could
> > increase the IR output of a flash unit.  Basically,
> > energy absorbed by the filter would probably be dissipated
> > as IR.  Is this the case?  If so, how significant is it?
> 
> I sincerely doubt that this is the case. All ASA and GN data I posted
> earlier indicate a halvation of the the flash output.
> I believe the only absorption possible is in the form of heat;
> otherwise it would equal a fluorescence effect; ie a 'transformation'
> into a longer wavelength. Like UV light is reflected/transformed in
> visible, would visible light then be transformed into IR.

That's not what I was thinking of, but now that you mention it, it
would seem likely.  However, I doubt you would find these properties
in photographic quality filters.  

> 
> [I believe there is only one (rare?) form of fluorescence that works
> the other way around]

You may be thinking of bioluminescence.  Higher energies would seem
unlikely.  I'd be real interested if you know of one.

> 
> BTW: when starting this list, I was pondering about its name....I was
> temped to call it Infrared- & UV-photography, but thought it might
> scare people off. UV is a rather related field of science, both
> subject- and material-wise (both HIE and IE are highly sensitive in
> UV, even more than for IR!).

It wouldn't have to be fluorescent to work.  Only certain wavelengths
would be absorbed and re-emitted.  Depending on the material, some
absorbed energy would be converted into heat.  Of course, I imagine
that filter manufacturers actively try to avoid this result.  I was
just hoping that someone may have seen something along these lines.
It seems like any dark filter would reemit as black body radiation.  
The energy must go somewhere, and shorter wavelengths seems less
likely making heat/IR more plausible.

just curious
-Randy

------------------------------

Topic No. 19