P3D Re: Ortho and TDC

[Tom Hubin <thubin@xxxxxxxxx>]

Michael Georgoff wrote:

<snip>

> Maybe I'll do some reading about mirrors...  If I bounce light around
> enough, I may be able to be an projectionist and still see ortho.  Sorta
> like a gigantic Project-or-View...  Gee whiz, I assumed that the
> projectionist could get ortho out of the deal somehow, kinda like a Kenner
> Give-A-Show Projector, only more fun...

Hello Michael,

A word of warning about mirrors. Silver mirrors alter the polarization
very little at any angle of incidence. But they may be expensive.

Aluminum mirrors will mess up the polarization except under certain
conditions. At nearly normal incidence any polarization will be
preserved. Although you get the mirror image. This should not be a
problem.

Usually angles of incidence near 45 degrees will trash the polarization
You will find that the linear polarization incident on the mirror will
generally exit as elliptical polarization. This will give you a lot of
crosstalk (some call it ghosting) in the images. 

If you make all of the reflections so that the linear polarization of
the incident light is either in the plane of reflection or perpendicular
to the plane of reflection then the light exiting will also be linear.
This means that the mirrors cannot simply reflect up or down or left or
right. They must reflect up-and-left or up-and-right or down-and-left or
down-and-right. 

Try this experiment. 

First, the standard arrangement as a control. Mount a stereo slide and
project it at your screen. Look at the screen with your 3d polarized
glasses. Shut off one lamp or block one beam at a time and verify that
each eye cannot see the image intended for the other eye. If there is a
lot of crosstalk then you need to fix your projector before you try the
rest of the experiment.
  
Now rotate the projector 90 degrees and aim it at a mirror. Rotate the
mirror 45 degrees so that the images are on the screen. As before,
project just one image and look at it with each eye. There will be lots
of crosstalk if the mirror is not silver. Very little crosstalk if the
mirror is silver.

Tom Hubin
thubin@xxxxxxxxx
AO Systems Design



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