# U2 3D - how in the world? **URL:** \ **Category:** Factual Questions\ **Created:** [March 5, 2008, 12:29am UTC](https://boards.straightdope.com/t/u2-3d-how-in-the-world/440109 "2008-03-05T00:29:01Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![beckwall](https://avatars.discourse-cdn.com/v4/letter/b/b487fb/32.png) [@beckwall](https://boards.straightdope.com/u/beckwall)\ **Post date:** [March 5, 2008, 12:29am UTC](https://boards.straightdope.com/t/u2-3d-how-in-the-world/440109/1 "2008-03-05T00:29:01Z")
Or for that matter, any 3D movie. But this U2 movie is spectacular, and I just don’t understand how 3D action works. Are there 2 cameras, 1 regular and 1 adapted for 3D? Is the film different, or is it even “filmed” vs digital? What exactly do the glasses you wear (so very improved since the last time I watched 3D) have to do with the process? Anyway, I recommend the movie, however it does cost extra ($15 at our theater) because “it’s a 3D concert!” (said the ticket seller for the one thousandth time). It wasn’t an IMAX film, BTW. Just projected onto a regular movie screen. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [March 5, 2008, 12:43am UTC](https://boards.straightdope.com/t/u2-3d-how-in-the-world/440109/2 "2008-03-05T00:43:02Z")
Your brain perceives 3D by recognizing particular shapes and colors and assuming they’re the same from eye to eye and then the wider the variance in position relative to how it appears in the other eye, the closer it must be. 3D films work by showing the same image from two angles (two cameras, essentially) separately to each eye so that your brain mistakenly assumes it to be real. (Not all people can be fooled, and so they don’t see it.) The way they show different images to you is by projecting horizontal and vertical light waves each with a separate image. The glasses they give you, then, have polarizing vertically and horizontally in the respective eyes, so only light waves that are in the correct direction can get through. > **[Depth perception](https://en.wikipedia.org/wiki/Depth_perception)** > > Depth perception is the ability to perceive distance to objects in the world using the visual system and visual perception. It is a major factor in perceiving the world in three dimensions. Depth perception happens primarily due to stereopsis and accommodation of the eye. > Depth sensation is the corresponding term for non-human animals, since although it is known that they can sense the distance of an object, it is not known whether they perceive it in the same way that humans do. > Depth percepti... > **[Stereoscopy](https://en.wikipedia.org/wiki/Stereogram)** > > Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word stereoscopy derives from Greek στερεός (stereos) 'firm, solid', and σκοπέω (skopeō) 'to look, to see'. Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope. > Most stereoscopic methods present a pair of two-dimensio... > **[Polarization](https://en.wikipedia.org/wiki/Polarization#Basics:_plane_waves)** > > Polarization or polarisation may refer to: > **[Polarized 3D system](https://en.wikipedia.org/wiki/Polarized_3D_glasses)** > > A polarized 3D system uses polarization glasses to create the illusion of three-dimensional images by restricting the light that reaches each eye (an example of stereoscopy). > To present stereoscopic images and films, two images are projected superimposed onto the same screen or display through different polarizing filters. The viewer wears low-cost eyeglasses with a polarizing filter for each eye. The left and right filters have different polarizations, so each eye receives only the image with t... ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [March 5, 2008, 12:49am UTC](https://boards.straightdope.com/t/u2-3d-how-in-the-world/440109/3 "2008-03-05T00:49:51Z")
3D movies are filmed with special cameras which are actually two cameras. They sit right next to each other, just like the eyes in your head, watching the action at slightly different angles. The two images are recorded (on film or analogue video or digital video, whatever you want) in the regular way. The magic happens when you figure out how to transmit each image separately into each eye of each member of the audience. In olden times, 3D glasses had one red and one green lens. The two pictures were colored red and green and projected onto the screen simultaneously (or sometimes in alternating red/green frames.) The red lens let only red light through, and the green lens only green light. So, your two eyes would see two separate images, one from the “red” camera and one from the “green” camera. Voila, instant binocular vision. Your brain is tricked into seeing a 3D image. Later films took advantage of polarized glasses. Each lens had a [polarization](http://en.wikipedia.org/wiki/Polarization) filter oriented ninety degrees with respect to each other. Similarly, the two images were projected through polarized filters similarly oriented. Each lens only lets through light of its matching polarization. The big advantage here is you get a full-color picture instead of red and green. The IMAX helmets have lenses with simple LCDs inside that alternate very fast (faster than you can see) from opaque to transparent. The IMAX film alternates between showing you the left-eye and right-eye pictures, and the left and right lenses alternate between opaque and transparent, so again each eye sees a different picture. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 5, 2008, 1:59am UTC](https://boards.straightdope.com/t/u2-3d-how-in-the-world/440109/4 "2008-03-05T01:59:57Z")
The above replies are correct, but I understand some (most?) newer 3-D projectors use circular polarization: right-hand circular polarization for one eye, left-hand polarization for the other. That way the glasses work properly even if you tilt your head.