How Do 3D Movies Work

Barco's DP-2000 Cinema Projector
which can show Real D

I just saw Hugo, which is the best 3D movie since Avatar.


Everyone can see that the Real D system uses polarized glasses, but if you look back at the projector, there is only one lens showing only one image on the screen. (Review what polarized light means here.)

How are they putting two different images on the screen at the same time with just one set of optics? The answer is that the images are switching back and forth at 144 times/sec. So the images are flickering faster than your eye can see it. Movie frames change just 24 times a second, so in a 3D projector each frame is shown three times to each eye.


Another part of the secret is the screen; the screen must not change the polarization of the light. One way to do this is to coat the screen with silver -- like in the old days of Hollywood, the silver screen is coming back! If you used a glass coated screen, the polarization might shift, and blur the effect. There are cheaper alternatives like aluminium coatings and pearlescent coatings.

Real D's web site studiously avoids any discussion of their technology or the specs of their equipment. This is because Real D just licenses technology, the projectors are made by other companies like Sony and Kodak. There are some Real D patents, and they relate to the technology for switching polarizations.

Critics, most notably my DW, say that 3D movies are darker.  3D movies are darker due to the absorption of the filters. A projector system designed for 3D would simply use a larger lamp to attain the target brightness that the theater owner wants.  If a theater owner is upgrading a theater for the premiere of a new 3D movie, s/he will buy a machine that will provide the best experience he can afford. As always you get what you pay for.

It might pay to shop around for a better theater if you find 3D movies too dark.