Re: Weddings & IR flash

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

On 20 Aug 96 at 9:31, Cor Breukel wrote:

> .just to add a little bit; I remember a RIT publication where is stated
> that black E6 film (the first part of your slide film, exposed and
> processed) can be used as a IR filter, it will pass IR light (I checked
> that with a spectrophotometer, it's correct). Th suggestion: tape this
> black film on your strobe: voila a IR strobe!.. But beware, I also recall
> that it caused a exploded flash tube, because of the heat of the strobe
> which could not "move away" (clumsy description, don't no better right
> now) Maybe WJ can fill in...

Well, this heat build-up is mentioned in literature; Guenter Spitzing 
states that his 87C gel showed heat defects after 100 bursts, and I 
think that was over a longer period of time, not within a few 
minutes. I didn't understand the reason for this heat build up, since 
the longer wavelengths (including heat!) can pass....only recently it 
occurred to me that any visible light is *absorbed* by the filter, and 
transformed to heat....voila the reason for heat build-up!
An interference filter (reflecting some wavelenghts instead of 
absorbing) could make the problem even larger, since all heat is then 
reflected back into the flash....8-))

Btw, can you specify your spectrophotometer readings?
I am still a bit confused why one sheet would not be enough....you do 
not 'lift' the cut off wavelenght by 50nm or so, you just halve the 
transmission on any spot on the curve. The only reason for needing 
two sheets must be that the transmission curve of one sheet is too 
whimsical....what does your spectrophotometer read with only one 
sheet?

On a side note, regarding being able to see the flash: according to
Guenter Spitzing (page 23, edition 1992, quoting the German Prof. Dr.
Dr. Schober, an expert on human vision), the human eye can see up to
1000nm, providing sufficient light intensity. But this requires more
than 1000x(!) the intensity that is sufficient for seeing
green/yellow (555nm, for which the human eye is most sensitive). And
a flash just does that, bursting a lot of energy in a fraction of a 
second. 
All this means that even the darkest red filter (that is suitable for 
HIE) will have the flash itself appear as a faint red. Blacking it 
out beyond 1000nm is useless, since HIE doesn't record that. 

This leaves the question: did you try it in front of your flash? How 
dark red was it? I can clearly see my flash through a #87C....



--
Bye,

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The difference 
between men and boys
is the price of their toys

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

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Topic No. 13