P3D Circular Polarization

["Lawrence A. Haines" <lhaines@xxxxxxxxxxxxxx>]

I would really like to understand circular polarizers.  But the
explanations given so far in this thread are not clear to me.

My father-in-law was a friend of Edwin Land.  I clearly remember
him telling me that Land came to his home one evening in great
jubilation saying that he had in deed created polarized sheets
and showed my father-in-law the results of carefully scribing by
hand on sheets of plastic (I think it was) many very fine and
close parallel lines.  Then he gleefully showed that by rotating
the sheets the light was blocked from passing through.  He had
theorized this result in prior conversations and was delighted to
find that the theory could be proven.  With this description I
have seemingly always clearly understood the basic principle of
poarization which was to force the light waves to pass through in
only one plane not in all directions.  Or to say it another way,
to permit only light waves of one plane to pass through.

When I purchased my first circularly polarized filters I was
confused to understand how they were manufactured.  I thought
that perhaps they consisted of concentric circles, instead of
lines, that would permit only light in those directions to pass
through.  But I noticed that there was some very slight
difference in light intensity (or at least so it seemed) as the
filter was rotated.  I then began to play with the filters. to
try to understand the physical way they were made.  I took two of
them and quickly discovered that when the two were placed on top
of one another they did not block the light at any rotation.  But
at two points of rotation, 180 degrees apart, they did cancel
what appeared to me to be *all* reflected light from leaves, or
water, or what ever.  I was left mystified as to their actual
construction.  Though from then on whenever I used the air on a
stereo camera I was sure to line up the filters the same way on
each lens, using the dots provided on the ring.  This did seem to
take away some but certainly not all of annoying reflections.
And skies were darkened very slightly.

I have wondered from time to time if the scribed lines on
circular polarization (if in fact that is how they are made) are
concentric or spiral.  Now that I hear about a material lain over
the basic circular polarized material I am further confused.
Perhaps this is a subject that is not explainable in simple
physical terms but I do wonder why not.

Larry Haines...


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