Welcome to The Sound of Science from WNIJ and NIU STEAM. It’s a weekly series explaining important STEM concepts. Today’s hosts are Jeremy Benson and Newt Likier.

Today’s question comes from Damon, who wants to know, “how do 3D movies work?”

Most movies have 2 spatial dimensions, the length and height of the screen. But 3D movies add a third dimension, depth.

We perceive depth when our eyes each see a slightly different perspective on what we’re looking at. The closer the object is to us, the greater the difference in those perspectives. This means that to experience a movie in 3D, both of our eyes need to be seeing their own version of what’s happening.

One way to do this is called an analglyph. Which uses red and blue tinted glasses. Two versions of an image are superimposed over each other, and colored lenses filter the light that reaches each eye.

Analglyphs don’t preserve the original colors of the image though. Another method people have tried is called an Active Shutter System. In this method, the film is cut so that each frame alternates between the left and right viewpoint. Special glasses are then synchronized with the projector, allowing one eye to see while an alternating shutter blocks the other.

This method never really caught on. Most 3D movies we see nowadays are shown using RealD 3D. Which utilizes polarizing lenses and special projectors to create true color 3D images.

Light moves as a wave, and the direction it’s waving is called its polarization. Light can be polarized in any direction and can even rotate. Polarizing sunglasses work by blocking light that’s not waving in the right direction. In 3D glasses one of the lenses is polarized to only allow clockwise rotating light, while the other only allows counterclockwise.

The projector then shows alternating frames from the left and right perspectives. A filter switches the direction of the light’s polarization for each frame, allowing each eye to see its own perspective.

This is one we could definitely go even more in-depth on, but I think we’re just about out of time.

Remember to send us your questions at niusteam@niu.edu or on Facebook at NIU STEAM.

This has been the Sound of Science on WNIJ, where you learn something new every day.