Part of the show Naked Science Questions and Answers
Nigel in Buckinghamshire asked:
How do 3D glasses work, and if you need these 3D glasses to appreciate the effect at the end, how do they produce them in the beginning?
In 3D glasses, one lens is one colour and the other is another colour. Now when they project the film, they have a very powerful projector that projects two images side by side. One of the images is very slightly displaced from the other one. The reason for this is that you've got two eyes looking at the world and so you're getting two images of the world reaching your brain. These are slightly overlapping but separated by a small amount, or by the distance your eyes are apart. On the screen, they're projecting these two images: one in one colour and the other in a slightly different combination of colours. What your glasses do is to screen out the colours of one of the images while allowing the colours of the other image through. When your brain recombines them, it's seeing two different sets of images overlapping each other in just the right way to recreate a three dimensional image. If you shut on eye and move your head from side to side, the world looks slightly different. Things close to you move differently from things far away and that's one of the ways your brain judges how far away things are. The way they make the films is that they have two film cameras maybe six inches apart and that produces the same effect as looking through two different eyes.