How do 3D movies work?

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It's time to understand how 3D movies work, since at this point they're never, ever going away. Find out how the Na'vi hair tentacles managed to reach out and spill your Mr. Pibb.

When going to the theater to see a 3D movie, most of us expect to pay a few extra dollars. This is not justifiable economics. If the theaters behaved according to the mechanics of 3D, they would have to choose between two different rates for the movies; either half as much as a regular film, or twice as much. Who wants to take bets on which they'd charge?

It could be argued that 3D movie patrons should only have to pay half what regular movies are worth. Unlike regular movies, 3D films don't deliver a complete product. A regular film is true mindless entertainment. The brain doesn't have to engage, because everything laid out, including the images. A 3D film presents a fractured image, and it's up to the viewer to knit that fracture into a three dimensional image. This usually isn't too taxing for the viewer, because that's what they do every day. Or, at least, most of them. The ones with two eyes.


Those of you who wondered why you were cursed with two eyes every time you tried to chop onions (or walked in on your parents as a child or just wanted to dress up as Leela from Futurama at Halloween) will be happy to know that there was a reason for your suffering. Two eyes, spaced a bit apart, give us two slightly different images of the world. Our brain analyzes the differences between those two images and comes up with a three-dimensional picture. A movie screen obviously can't form actual three dimensional objects. It just presents two different images and allows your brain to do the thing it has always been doing, synthesizing them into one image that looks three dimensional. You've been cheated! Get your money back!

Or go the alternate route and pay twice as much. It makes sense. You've seen two films. In order to get your mind to see two images, the movie theater has to show you two movies, each showing the exact same thing from a slightly different angle.


In the old days, this was done by showing a red and blue version of the movie and giving the audience red and blue glasses. Looking at the red version of the movie through red glass was like the old joke about a blank piece of paper being a picture of a polar bear in a snowstorm. Red on red looks blank, as does blue on blue. Only contrasting colors are visible. Each eye was shown a different angle, and those angles were combine to make a three dimensional image.

A really ugly, awkward, three dimensional image. Old 3D films were more a gimmick than a movie – unlike 3D films today, of course. The color was off and the image was fuzzy. In order for 3D to look good, there had to be a way to show the audience two different movies without using color. The solution was polarized light.


Polarization takes advantage of the wave properties of light. Imagine a jump rope stretched between two people. One person starts shaking the jump rope. The motion travels until it hits the person on the other end of the jump rope. This is how light travels, and just as the first person is able to shake the jump rope in every direction, creating vertical, horizontal, and diagonal waves, light travels in waves that are oriented in every direction.


Polarized light is waves of light all oriented in only one direction. If the two people in the jump rope analogy were to thread the rope through the posts of a picket fence, and the first person were to start shaking the rope horizontally, the motion would get choked off. If they were to shake the rope on a diagonal, the horizontal motion of the rope would be stifled, while the vertical would travel through to the other end. Only a completely vertical motion would make it to the other side of the fence unhindered. This is polarized motion. Light is polarized in much the same way. Polarized lenses are basically lenses that have vertical, diagonal, or horizontal stripes on them which block all light waves coming in at the wrong angle. Unlike red and blue filters, this doesn't affect the color of the light.

Three dimensional movies use polarized light, and special glasses, to create two films, one for each eye. One lens of the glasses allows only vertically polarized light, the other only horizontally polarized light. One frame of a film is shown in vertically polarized light, which gets through to one eye, and the other in horizontally polarized light, which gets through to the other. The brain gets off its gelatinous butt and uses the two images to create a three dimensional picture, and everyone in the theater goes "Ooooooooooh!" Except one bitter, angry person who goes "That is so fake!" Jerk.


[Via Mindspring and]