Re: polarizing filters with b&w infrared

[Scott Donkin <photos@xxxxxxxxxx>]

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.


Cya...

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Topic No. 5