The online computery journal thingy of a turtle - These 3-D glasses

Apr. 6th, 2007

02:43 pm - These 3-D glasses

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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.

Current Mood: geekygeeky
Current Music: Buddy Holly - It's So Easy
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Comments:

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From:normanrafferty
Date:April 6th, 2007 09:44 pm (UTC)
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Wow, I almost wanna see this movie just to see the glasses work.
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From:kinkyturtle
Date:April 6th, 2007 10:26 pm (UTC)
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It's amazing! You can tilt your head as far as you want and not see any ghost images (of course, tilt your head too far, and instead of a 3-D image, it'll look like you're watching a movie with a droopy eye.)

Disney calls the system "Disney Digital 3-D", although that's just a name they've gotten a license to slap onto an existing system called Real D.
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From:quasiskunk
Date:April 6th, 2007 10:08 pm (UTC)
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I dunno about the technical aspects, but I <3 Elvis Costello too!
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From:hartree
Date:April 7th, 2007 01:23 am (UTC)
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Oh, those wacky physicicsts.

(Good deduction, KT. I'm impressed! :)
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From:kinkyturtle
Date:April 7th, 2007 09:11 am (UTC)
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I learned about polarized light back in college and managed to dredge enough of it back up to figure it out!
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