Re: polarizer and IR (Re: Focusing/Best time of day)

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

On  6 Aug 96 at 17:41, N. Remi Shih wrote:

> 
> >Look up in the sky before shooting next time.  Is the sky a washed out
> >blue, or is it a deep blue color.  If it's the former, then forget it,
> >if the latter then shoot in that direction.  That's right, look around
> >and you'll see a difference in the sky's color.  Midday, it'll be
> >difficult to get that dark sky, but early/late is a different story.
> >
> Will put a polarizer help darken the sky?  Will it bounce out the IR...

In addition to all other answers, I'd like mention that polarizers
loose their effect beyond 800nm. You can even use two crossed
polarizers as a dark IR filter; they cross polarize visible light
(ie block it), but let IR pass unaffected. So shooting with very dark 
IR filters *and* a polarizer is sortof fooling yourself. 
Guenter Spitzing even proved in an experiment with Ektachrome IR that 
cross polarized water reflections appeared as red on film, simply 
because only visible reflection was 'killed', and IR shows as red on 
EI. 
This is not said that polarizers can't be useful with lighter IR 
filters, just don't expect to see the same effects on film as you see 
through the filter with your eye.

I have been experimenting with special IR polarizers, but I am still
not sure if they are worth the price and hassle (they only come in
foil, unmounted; and the best are hideously expensive).

--
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. 7