April 6th, 2007

Elvis Costello

These 3-D glasses

So Wikipedia says that the Disney Digital 3-D process uses circular polarized light, with the left and right images using opposite rotations. This much makes sense; it's a great way to prevent ghosting. But how do the glasses themselves work?

I have a working hypothesis: the lenses have two layers. The front layer is a quarter-wavelength plate, which converts the circular polarized light to linear polarized, and the back layer is an ordinary polaroid filter. The two quarter-wavelength plates are of opposite handedness, but the polaroid filters go in the same direction.

This explains everything I've discovered so far:

- why, when I held them up to a window last night, they appeared to be polarized in the same direction;
- why they behave differently when I'm wearing them than when I'm looking through them the wrong way (for instance, if I wear them, look at my plasma computer screen and tilt my head, nothing happens except the color balance goes a little wonky, but if I look through them the wrong way and tilt my head 45 degrees to the left, my screen goes black);
- why, when I wear them and look in a mirror, each eye can see the other but not itself (which creates a weird shimmering effect if I look with both eyes open);
- why, when I wear them, I look like Elvis Costello.

Wait, scratch that last one (although I do!)

Update: My dad came home, I showed him what I'd figured out, and indeed he confirmed that while these glasses are an amazing technological marvel to the moviegoing public, to a physicist they are simply a pair of circular polarizers of opposite handedness that you look through backwards.
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