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From: lance@motcsd.csd.mot.com (lance.norskog)
Newsgroups: sci.virtual-worlds
Subject: Re: Polarized light 3D systems: info wanted
Message-ID: <1991Jun4.032252.4466@milton.u.washington.edu>
Date: 3 Jun 91 23:21:10 GMT
References: <1991May31.040533.27531@milton.u.washington.edu>
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[kilian@poplar.cray.com (Alan Kilian) writes an excellent analysis]

1) 
The Extinction Ratio refers to the ratio between
the number of photons that go through in the dark:clear states.
The Haitex goggles (Nintendo goggles which were never
marketed outside Japan) have an extinction ratio of 1:100, as
does CrystalEyes' low end product.  Their high-end product has
an extinction ratio of 1:300.  You reported that your Sega Goggles
"don't go very dark".  Do you have an extinction ratio rating for them?

2)
The naive scheme is to switch between states based on the vertical
retrace.  It seems that you may want to decouple the square wave
to each lens from being alternate portions of one square wave, and
overlap them a bit, initiating the clear phase just before the 
vertical retrace.  So, the circuit inputs should be the vertical
and horizontal retrace, and a horizontal counter.  The circuit counts
horizontal flybacks and retraces just before the bottom of the screen.

Perhaps the off phase should be initiated right around the
bottom of the screen, so as to cut off dying phosphors because
the colors decay at different rates.

3)
The right solution for large screens (> 500 lines) would seem to be
bifocal shutters.  The top half matches the top half of the screen,
and the bottom shows the bottom of the screen.  This gives tighter
control in matching the scan rate of the screen.

4)
A hacker at Vision Research Group (another LCD shutter vendor)
told me that the control waveforms should come out of a ROM
instead of an analog circuit; this gives better performance somehow.

The next generation of LCD shutter gear should be designed based on
these conclusions: Separate the duty cycle for the two lenses.
Adjust the duty cycles of the lenses for the switching times
of the lens and the phosphor decay times of the colors of the monitor.
For big-screen work, try bifocals.

Lance Norskog
lance@motcsd.csd.mot.com