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I photograph oil paintings with cross polarization and find that linear
polarizers on the lens and the lights are the only combination that works
for me.
Jerry McCollum
steven T koontz <sko...@mindspring.com> wrote in article
<3567940B...@mindspring.com>...
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d^b * "Lie to me."
=\_/= *** * "Yes, it's terribly simple. The good guys are always
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********** distinguished by their pointy horns or black hats. And
** *** we always defeat them and save the day. No one ever
* * dies, and everybody lives happily ever after."
,+ ,+ "Liar." -Buffy the Vampire Slayer
http://suba01.suba.com/~lovecats/index.htm (photography)
In article <6kct7m$ck2$1...@gte1.gte.net>,
> I think you need to use a regular plane polarizer on the camera. There
> is
> no "cross" polarization on a circular polarizer in this application,
> at
> least that's been my experience. If you check your ciircular polarizer
> by
> holding it up against the light polarizers (looking at a white
> backgropund)
> you should find that no amount of rotation brings you to extinction.
> It's
> the same throughout the rotation.
>
> I photograph oil paintings with cross polarization and find that
> linear
> polarizers on the lens and the lights are the only combination that
> works
> for me.
>
> Jerry McCollum
Circular Polarizers consist of a linear Polarizer and an attached
quarter-wave plate, the latter side facing the film. If the (linear)
polarizers on the lamps and the polarizing part of the circular
polarizer face each other and are cross polarized the result is
identical to two linear polarizers in crossed positions. Only if the
filter is mounted the wrong way, i.e. the quarter-wave plate facing
outward, the crosspolarization is lost.This is easily shown when one
makes the test described by you, i.e. looking through the polarizer at
the lamp polarizers. Only if the male filter thread (the lens side) of
the filter faces your eye, you get extinctinction, not if the front side
faces your eye.
This is actually the purpose of using a circular polarizer, to avoid any
crosspolarizing effects between the image-forming light and polarization
effects in the camera (i.e. due to reflection on beamsplitters, prisms
etc. - this is usually not an issue with view cameras).
If you see any differences between a linear poalrizer and a correctly
mounted circular one, they may be due to quality differences of the
polarizers.
Arne Croell