Re: outdated glasses? (longish)

[P3D Gregory J. Wageman <gjw@xxxxxxxxxx>]

John R caught the following mistakei in my post:

>>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.

Indeed.  Such glasses would extinguish at 90 degrees to each other.

>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.

That's what I originally wrote, but then I though I had found a way to
simplify it.  It seems I forgot the old advice: "Make thinks as simple
as possible, but no simpler." :-)

	-Greg W.


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