More on polarizing

[T3D <vidi@xxxxxxxxxxxxx>]

>I agree, although I do not have figures (values, numbers) with me now,
>polarizers absorb *almost* 50 % of the intensity due to its basic principle.  
>The difference between 50% and the real value is negligible when calculating
>energy.
>
>There is another absortion, natural and independent of polarization,
>much greater than this and that should be indicated also.
>Usually, polarizers with high extintion rate have also a high absortion
>rate (appear darker).

   You are right, you get the polarization by absorbing all the bad stuff.  
In fact a single Dichroic polarizer transmits about 32% and two polararizers 
in the "open" position transmit a little over 20%, but oh what good 
extinction you get!  So, what this says is, you either get good extinction 
(minimal ghosting) and low apparent image brightness, or you get a good 
bright image from the screen with some ghosting.  It's one of those things.  
As far as the Calcite goes, I wouldn't put too much time into it myself......

   As far as other techniques for polarizing light goes, there are polarizing
beamsplitter cubes but those are wavelength sensitive.  They are nice though
because instead of absorbing, they reflect the other polarized light 90 degrees.

This other reflected light is polarized perpendicular to the direct 
transmitted beam.  Very high powered light can be used with these since they 
do not absorb the energy.

John Vala


------------------------------