Consulting, Publishing, Engineering

3D movies and the science of polarization

I went to see Coraline in the theaters while it was still being shown in RealD 3D – very cool! Not jump at you cool, but like-you-were-really-there cool. If you get a chance you should go see it!

Even the glasses are pretty cool – not the older, cardboard type with one red eye and one blue, but actual plastic frames with polarized lenses. Ever wonder how this new technology works? Turns out it has to do with polarization, a phenomenon used in lots of other applications. There’s a long explanation of the different approaches over on the encyclopedia, including discussion and videos of sunglasses, radar detectors, fish tanks, and more. The relevant bit to movies is this:

One consumer niche application of polarizers is 3D glasses for viewing movies. The original 3D experience crudely separated the two images using color filters; later polarized glasses with polarizers at +45 and -45 degrees allowed full color for both eyes. However, if you tilted your head, you saw double images and the effect was lost and a headache was often the result. Today, RealD provides a new 3D experience. Their technology separates the two pictures into two circular polarizations, left hand and right hand. The glasses that they distribute filter out the unwanted images and work regardless of what angle your head happens to be.

In order to change linearly polarized light to circularly polarized, a quarter-wave retarder is used. This is a media that presents different indices of refraction to the light wave, such that one is retarded (phase shifted) by 90 degrees.

If you want to be a real nerd, bring home your RealD 3D glasses and play with them in front of a mirror. Put on the glasses and close one eye – the open eye remains shaded, but you can see the closed eye clearly! This is because you’re looking OUT through one lens and IN through the other, reversing the polarization of the reflected wave (as the whole thing is reflected back at you through the mirror). If you have two mirrors positioned at a 90 degree angle you can re-reverse the image and you will find that your OPEN eye is the one that you see clearly in the reflection!

Isn’t science fun?

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