Re: Polarization single lamp twin projector.

[T3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>]

Jose Lunazzi wrote

>A single glass plate polarizes 100% the 28% of reflected light,
>remaining not entirely polarized 72% of transmitted light(I can make the
>calculation available to whom wants it, since it is one excercise of my
>optics course, already typed). Reflectivity is 15% at the external
>surface and same at internal surface, so that transmission of the
>unpolarized part is 28 % (not 22,5 %).

I see that you corrected this in your next post

>It would be interesting to know why the Anderton system was not kept
>nowadays, because if some residual of unpolarized light remain after the
>plates, this could be eliminated by a polarizer sheet.

I do not see any reason to keep the Anderton system system nowadays
because of the weight and delicate nature of the glass plates if you are
going to have to eliminate residual unpolarised light after the plates
with a polaroid sheet you may just as well just have the sheet. Personally
I am suprised that Anderton's system did not do better until the invention
of polaroid would have made it obsolete so perhaps it did not work that
well although it had good reports.  The last of these seems to have been in
1898. There were a couple of red/green anaglyph systems introduced in the
UK after Anderton's polarised system in 1893.
 By Newton and Co 1896 and Theodore Brown about 1905 which seems a strange
thing to do if Anderton's was a success. Also in 1896 an advert by Anderton
and Wright
(who was involved in Newton and Co and their anaglyph system) for Anderton's
metallic screen made no mention of stereo projection just the superior
light reflection for normal projection as most modern adverts for such
screens would do.  An advert for Theodore Brown's system had the words 
"ordinary screen" written on the screen in the illustration. This may have
a reference to Anderton's system which would have required the metallic
screen. If you are referring to a modification of Anderton's system to
produce a polarising beamsplitter, that might be worth while if it can be
made to work.  Anderton himself did not even attempt that as far as I know.

>Just using the previous values I calculated that 6 plates allows for 10%
>of unpolarized light (20% of one polarization) and proportion between
>both polarized beams would be 1/0.8 .
>The angle between both beams would be 66 degrees, a mirror at the
>reflected beam could make them parallel.  Aluminum reflective coating,
>f.ex., absorbs 18% of the light and balance between intensities woulb be
>equal. Total absortion: 20% , distributed within the mirror and the
>polarizer sheet.  The ghost image would be 5 times less than with the
>ordinary system.

I know of a text book which suggests between 5 and 15 plates depending on
the material and its refractive index and another which suggests 24 as
being the optimum for glass demonstrating this by a graph. Anderton it seems
used about 30.

 P.J.Homer


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End of TECH-3D Digest 200
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