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From: testarne@media-lab.media.mit.edu.MEDIA.MIT.EDU (Thad Starner)
Newsgroups: sci.virtual-worlds
Subject: Re: Polarized light 3D systems: info wanted
Message-ID: <1991May31.035906.25600@milton.u.washington.edu>
Date: 30 May 91 21:32:39 GMT
References: <1991May15.232536.27134@milton.u.washington.edu> <1991May17.
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  The only response I can give to Dick until I run a few more tests is
to give some more info:

According to the Tektronics Stereoscopic manual (1988), there is "a
limit [I assume of time "on" per iteration] of about 20msec for the
left eye state, which limits the lower rate at which the Modulator can
be used to about 20 Hz." 

Also:

"The Pi-cell is the fastest large area liquid crystal effect switching
from non-driven to driven in .2 msec and from driven to non-driven in
approximately 2 msec.  To enable a 120 Hz vertical refresh rate, the
cell is electrically split into top and bottom segments.  Multiplexed
2:1 from a PROM it is possible to achieve an acceptable contrast ratio
with flicker free operation."

This info supports your driven/relax hypothesis.  

As far as the color-dependent variation in the extinction ratios, I
assumed that this included phosphor characteristics since the header
to the stats I gave was

"Optical Performance (P4 phosphor and Tek Stereo glasses):"

and there were other mentions of assumptions of 1.5msec decay
phosphor.  The extinction ratios seem to be the most dependent on the
phosphor values, so I believe that this is where the assumption comes
in (though ave light transmission is also related).

As far as the pure shutter effects on the extinction ratios, I'm
curious myself. 

Can anyone think of a good fast way of testing this, or does anyone know?  

About asymmetry effects - it is possible that Tektronics made their
driver so that this is taken into account.  If I have time I'll put a
scope on it.  If not the direct modes on the modulator should allow you
to design a circuit to compensate.

Flicker- I didn't notice it after a while, but of course as soon as
someone brought it to my attention I would see it.  I did get a
monstrous headache while getting the system up, but that was mainly my
own fault due to problems with depth reversal and incorrect views.
The final system I used for an extended period of time with no ill
effects except an increased sensitivity to depth information ("Wow!
I've been sitting in front of the stereoscopic for so long I see
everything in 3D!").

I'll post more info as I do more tests.  

If people are really curious and are in the area, call me up and I'll
show it to you.



                                                Thad