RE: Filters for EIR - adding a Polarizer

["Editor - P.O.V. Image Service" <editor@xxxxxxxxxxxxxxx>]

Sarah Morgan  wrote:

> Helmut,
> How does the polarizer affect the wavebands you pick up on your Heliopan
> filter (I believe its a #29?)?

OK, the Polarizer will generally affect only  visible light and that more so
towards the blue end of the spectrum... It simply limits light that is not
polarized in a particular direction from entering the lens...

What that means in practice with standard color emulsions is that you have
increased color saturation to the emulsion...  Predominantly through the reduction
in overall levels of light which to the film will be reproduced as white or light
blue...

The reduction in this ("background noise") light results in an apparent increase
in color separation and saturation...

That said, let's jump to HIE and EIR...

With HIE, and a #29, or #25 filter, the removal of the additional "white" light in
skies moves the reproduction of the sky more firmly into the Blue realm, giving a
darker blue sky..  However, the Red filter blocks most blue light, meaning..  A
very dark sky on any emulsion..  On HIE, this also happens, but to a somewhat
lessened effect, given the same filtration..  It will increase the separation
between clouds and sky..

Now that we understand what's happening, let's jump to EIR...


To understand, look at the explanation by Michel Wurtz of EIR color imaging at:

 CoCam: Infrared Photography: Michel Wurtz - Colour Infrared
http://www.cocam.co.uk/CoCamWS/Infrared/EIR/eir.htm

We are going to again be decreasing the amount of stray "white light"  in the
image..

So, we will, of course increase our color separation in EIR images, just as in
standard color images..

But, as our polarized sky becomes "blacker / bluer" the sky will become darker..
With a yellow filter, a sky (where it is not obscured by clouds) will become bluer
on the EIR image (after filtering it is a dark green subject)..  With an orange
filter, expect the sky to simply become blacker...

However, as the polarizer will not effect IR light anywhere near as strongly as
that of visible light (as a result of the longer IR wavelengths being able to more
easily move past the polarizer), we should see something interesting..  Our
Magentas, Yellows, Reds and Whites should become noticeably brighter in our final
images (overall exposure of those colors will increase when compared to the
baseline average across the film, as IR will remain constant with a decrease in
the overall visible light component)...  This also means, one may wish to increase
your ISO rating of the film for in camera metering, as the unmetered IR light will
be a greater % of your new overall exposure...

You may also see some apparent  shift towards the yellow/red/magenta in your
image..

Now for the real fun...  Think I'm going to try using some of those Cokin color
shifting polarizers with the film...  The Polarizers that when used with another
polarizer shift things Red and Yellow, or Blue and Red, etc. with a roll of EIR..

Those filters give bizarre enough effects with visible light tuned emulsions...

Will probably run the tests on the Great Falls in Paterson, NJ, the next time I
get a sunny day..  If anyone is interested in the results, I will put up a page
with some samples....

Keith


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