Re: polarizing filters with b&w infrared

[Michael Creem <creem@xxxxxxxxxxxx>]

Scott Donkin wrote:
> 
> At 08:50 PM 08/11/96 +0000, you wrote:
> 
> >|So, for the pic you mention, which was shot with a Pola filter and #25,
> >|there WILL be some polarizing affects, simply because the #25 allows a =
> >slice
> >|of the visible spectrum through (from about 590nm).
> >
> >Depending on which post you're referring to, there is some confusion
> >here.  The publication in question shows six otherwise identical
> 
> Actually, I meant my comments to be most general.
> 
> The fact remains that standard Poal filters have a reduced effect on IR
> wavelengths, that's all.
> 
> >Based on my experience, however, it appears that if you were using the
> >new Ilford film, whose reach into the IR is limited, and you want dark
> >skies, the use of a polarizer in addition to the red filter could be
> >very effective.
> 
> But that is the key to it...
> 
> You are using a film with a filter combination that limits it's window from
> 590nm (the cut off from the visible region of the #25) to, what (?) 750nm
> for the Ilford film?  In other words, you are shooting a LOT of visible
> light in this scenario.
> 
> Have you tried using an 87 filter, in combination with the Pola, AND this
> Ilford film?  This would give you a window of about 720nm to 750nm: pure IR.
> Your results would be markedly different!
> 
> Oh... and note that I am assuming the Ilford film drops off at 750nm, as I
> have not used that brand of IR stock.  If it only runs out at 720nm, then
> try the above using an 89B instead of the 87.
> I have a Calumet flyer that says that SFX "up to 740nm" Michael

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End of INFRARED-PHOTOGRAPHY Digest 118
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