How The Polarizer Film Really Works
Surely when you have seen a 3D movie, possibly the first of your life, you have done something silly like reaching out to catch what comes out, moving away so that a stick does not hit your face or things like that. It is that these films are very well achieved and manage to generate a very realistic depth effect. And the most curious of all is that behind this there is a lot of physics. Not only is the physics of vision or light, but behind the technique that allows this type of film a fundamental method in astronomy: the stellar parallax method.
The way It Works
Your eyes (rather your brain) and astronomers who measure the distance to the stars do something very similar. They take two images from two different, separate places, and thus generate the sensation of depth and it is possible to estimate the distance to distant objects. In other words, with two images taken from different points we can generate a feeling of depth. The linear polarizer film is based on this philosophy.
All the above techniques are the basis for the technology currently used. What happens is that for moving images only anaglyphs were used, which do not offer great quality for movies and animations, due to their lack of depth and colors. To solve this, the technologies we talk about below have been developed.
Currently the most used are polarized glasses, of which there are 2 different types (linear or circular) depending on the method used to filter the images. In both cases these are projected superimposed on the screen and the glasses are in charge of showing each eye the corresponding image.
Linear polarization: Orthogonal filters are used that are oriented in the same way as those of the projector, with which each eye lets through the image that has the same angle as his, which normally oscillates between 45º and 135º. The disadvantage of this system is that the viewer has to maintain static vision and not move, since the effect would be lost until he becomes still again, which can be uncomfortable if the projection is long. In the image you can see how on the left the source emits in various wavelengths, but the filter only allows those that are vertical to pass. Use of 3D polarizer comes up to be useful in this matter.
Circular polarization: Each image rotates in one direction, that is, clockwise or counterclockwise, and each glass covers the image that rotates in the opposite direction to its own by means of circular polarizers mounted in reverse. It has the advantage over linear polarization that the viewer can slightly shake his head and lose only part of the effect for less time. In the image we see the effect of the filter when the image rotates clockwise.
An example of this type of glasses are those used by the RealD system, of which we have spoken previously . We can see that the glasses are not bulky, they simply have polarized lenses: