Most human beings come equipped with two eyes and a binocular vision system.

For objects up to about 6 to 7 meters away, our binocular vision system lets us easily tell with good accuracy how far away an object is.

For example, if there are multiple objects in our field of view, we can automatically tell which ones are farther and which are nearer, and how far away they are. If you look at the world with one eye closed, you can still perceive distance, but your accuracy decreases and you have to rely on visual cues, which is slower.

The binocular vision system relies on the fact that our two eyes are spaced about 5 centimeters apart. Therefore, each eye sees the world from a slightly different perspective, and the binocular vision system in your brain uses the difference to calculate distance. Your brain has the ability to correlate the images it sees in its two eyes even though they are slightly different.

If you've ever used a View-Master or a stereoscopic viewer, you have seen your binocular vision system in action. In a View-Master, each eye is presented with an image. Two cameras photograph the same image from slightly different positions to create these images. Your eyes can correlate these images automatically because each eye sees only one of the images.

In a movie theater, the reason why you wear 3D glasses is to feed different images into your eyes just like a View-Master does. The screen actually displays two images, and the glasses cause one of the images to enter one eye and the other to enter the other eye. There are two common systems for doing this:

Red/Green or Red/Blue 3D Glasses

The red/green or red/blue system is now mainly used for television 3-D effects, and was used in many older 3-D movies. In this system, two images are displayed on the screen, one in red and the other in blue (or green).

The filters on the glasses allow only one image to enter each eye, and your brain does the rest. You cannot really have a color movie when you are using color to provide the separation, so the image quality is not nearly as good as with the polarized system.



Polarization (the one currently used for movies)

At Disney World, Universal Studios and other 3D venues, the preferred method uses polarized lenses because they allow color viewing.

Two synchronized projectors project two respective views onto the screen, each with a different polarization. The glasses allow only one of the images into each eye because they contain lenses with different polarization.