Re: outdated glasses? (longish)

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Wed, 3 Sep 1997 14:59:43 -0500
>From: "P3D Gregory J. Wageman" <gjw@xxxxxxxxxx>
>Subject: Re:  outdated glasses? (longish)

>...The most commonly-available polarizing glasses use linear polarizers,
>with the axes of polarization being 90 degrees to each other (obviously),
>and at a 45 degree angle from vertical, like this: \ /.

>>Is that why I'm not seeing the stereo effect with the older glasses?
>>Or is this because the older glasses have all lost their polarization?

>That's easy enough to test.  Take two pairs of glasses and put them
>lens-to-lens.  The paired polarizers which are now crossed, should be
>nearly opaque.  If they're not, then they're no longer polarizing.  This
>is true whether they're circular or linear.

That would be true for one lens horizontally polarized and the other
vertically polarized, but is it true when they're both at 45 degrees to
the vertical as you depicted? Seems to me they'd still be parallel.

  ----+  +----
      O  O
   -> O  O ->
  ----+  +----

If you rotate one pair with respect to the other, and can't find any
angle for which there is near complete extinction (opacity), then they're 
probably not polarizing correctly.

John R


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