# Explain the newer 3D technology

**URL:** <https://boards.straightdope.com/t/explain-the-newer-3d-technology/523286>\
**Category:** Factual Questions\
**Created:** [January 1, 2010, 1:21pm UTC](https://boards.straightdope.com/t/explain-the-newer-3d-technology/523286 "2010-01-01T13:21:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\
**Post date:** [January 1, 2010, 1:21pm UTC](https://boards.straightdope.com/t/explain-the-newer-3d-technology/523286/1 "2010-01-01T13:21:54Z")

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So I saw Avatar in 3D, and we were examining the glasses afterward. I thought that the newer 3D films used polarized light, but I have two problems understanding this.

1. How do you put polarized light off a screen? I was told that reflected light was polarized by the reflection. Is polarized light still in the same orientation because it was polarized first?

2. We showed that if you put a right lens over a left lens, you get black. This didn’t change by rotating them. Other polarized films I’ve seen did.

I know on this board there’s someone who knows, and even possibly someone who did a technical paper on the method. Thanks.

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**Author:** ![yastobaal](https://avatars.discourse-cdn.com/v4/letter/y/258eb7/32.png) [@yastobaal](https://boards.straightdope.com/u/yastobaal)\
**Post date:** [January 1, 2010, 2:38pm UTC](https://boards.straightdope.com/t/explain-the-newer-3d-technology/523286/2 "2010-01-01T14:38:37Z")

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I know the glasses are polarized in spirals one clockwise the other side anti-clockwise. But that’s the limit of my knowledge.

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**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\
**Post date:** [January 1, 2010, 2:39pm UTC](https://boards.straightdope.com/t/explain-the-newer-3d-technology/523286/3 "2010-01-01T14:39:17Z")

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For release in regular theaters, Avatar used the [RealD Cinema](http://en.wikipedia.org/wiki/Real_D_3D#List_of_RealD_released_and_upcoming_films) 3D system, utilizing a single digital projector fitted with a digital circular polarizer. The glasses are passive circular polarized lenses. The system is described in more detail [here (PDF).](http://www.edcf.net/edcf_docs/real-d.pdf) The key appears to be circular polarization, as opposed to linear polarization. The 3D system used in IMax theaters used a different system.