Re: outdated glasses?

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

Steven Leddderman asks:

>My question to the group; do the
>polarized lenses in the projector and the glasses have to match? Is that
>why I'm not seeing the stereo effect with the older glasses? 

There is standard (international) orientation convention.  If this
convention is followed in the projection and glasses (and almost all the
glasses and stereo projectors made in the USA follow this convention) then
the pair works.  I don't know of the FED follows the same convention.  I
think I have heard that it does not.  If this is the case, you are advised
to replace the filters in the FED projector with a standard pair (the
filters need to be rotated, usually by 45 degrees, that's all it takes) so
that the regular glasses that you buy today work with the projector.

>Or is this because the older glasses have all lost their polarization? 

Most older pairs that I get (from the 50s) have lost their polarization. 
There is a simple way to check polarization strength:  Pick up two
different pairs and try and cross the lenses in front of a light source
(rotate them until you get the least amount of light going through).  If
the polarization is strong, there should be almost no light going through. 
If it is weak, you should be able to tell, especially comparing with a pair
that you know is good.

>Does one have to buy glasses that are manufactured by the same
>folks as the projector?

Only if the manufacturer does not follow the international convention for
orienting their filters, as it might be the case with the FED projector.

Hope this helps! -- George


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