Polarization in 3D glasses

Hello,

Yesterday we took our daughter to a 3D movie. Being 20 minutes
early and having three pairs of polarizing glasses at hand, I
started experimenting with them to pass the time. I'm not an
expert in optics, and I assumed that one lens polarizes the
light vertically, the other horizontally, but soon I found
something that does not fit this assumption...

It seems that the [degree of (?)] polarization depends on the
direction the light comes through the eyeglasses - i.e. they
polarize if I look through them properly (from "inside-out",
the way they are supposed to be used), but if I turn them the
opposite way (with the earpieces(?) sticking away from me),
they do not seem to polarize at all. Why is this?

After the movie I got pleasantly surprised that the glasses
turned out to be ours to keep (I expected one of those baskets
at the exit). So, I tried some other things and took couple
of pictures to show you what I mean.

Picture 1: Looking through one of the lenses in a mirror.
As I would expect, one lens looks transparent in the
reflection, the other is black:

http://avtanski.com/images/var/polarization1.jpg

Picture 2: Turning the glasses to look from the wrong side
in - both lens reflections look transparent:

http://avtanski.com/images/var/polarization2.jpg

My first questions are:

Q1) Why is this? Is this really some kind of one-way
polarization? How can this be?

Q2) How those polarizing filters work (the "one-way" ones,
assuming this is what they are)?


I noticed similar effects with two pairs of glasses. If I
put on a pair of glasses and look with one eye at a second
pair of glasses the following thing happens:

a) If the second pair of glasses is facing toward me (as if
on the face of a person facing towards me), one lens looks
dark the other is clear (as I would expect). If I rotate
the second pair at 90-degrees (as if the person is still
facing me, but has tilted his head sideways) the
transparent lens stays transparent, and the dark one
becomes slightly reddish, but does not become clear. With
horizontal/vertical polarization I would expect the dark
and transparent lenses to switch places.

b) If the second pair of glasses is facing away from me,
both lenses look transparent and they both stay
transparent even if I turn the second pair at 90-degree
angle.

This begs the last question:

Q3) Is there any other kind of polarization that I don't
know about?

In an hour or so browsing around the net I could not find
anything that can explain what I see. Can I have some
expert help, please?

Regards,

- Alex

.

Relevant Pages

  • Re: Polarization in 3D glasses
    ... It seems that the polarization depends on the ... After the movie I got pleasantly surprised that the glasses ... one lens looks transparent in the ... the second pair at 90-degrees (as if the person is still ...
    (sci.optics)
  • Re: Polarized sun glasses
    ... polarized glasses are for riding and driving. ... through car windows with aftermarket tint film, ... My '49 Chevy had laminated glass as well ... in any orientation and its polarization is invisible to the human eye. ...
    (rec.bicycles.tech)
  • Re: Polarization in 3D glasses
    ... circular polarization with a quarter ... wave film is used. ... and the other lens turns it a more blue hue. ... Turn the glasses round, to point the wrong way, and look through the ...
    (sci.optics)
  • Re: Polarized sun glasses
    ... polarized glasses are for riding and driving. ... Try looking at old VW or other tempered glass windshields. ... in such glass causes all angles of polarization and these interfere ...
    (rec.bicycles.tech)
  • Re: Polarized Instrument Display
    ... the polarization is in the cover glass for the LCD. ... never use polarized sun glasses, ... You either have defective polarization on your glasses or the LX has ... you should be able to see the LCD screens ...
    (rec.aviation.soaring)