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How 3D Movies Work?

The author is a resilient graduate in electrical engineering, and an aspiring professional in the said area.

Most of us have experienced 3D movies already but the way they work is also quite interesting.

The whole system is based on the fact that each of the human eye sees a different image because of the small distance between each eye. The brain then combines and interprets these two slightly different images to give us a three dimensional view of the surrounding.

Most 3D theaters make use of 'stereoscopic' 3D which works with the help of polarized light and a pair of cheap 3D glasses.

A 3d film camera. (Notice the Two lenses.)

A 3d film camera. (Notice the Two lenses.)

3D Video Recording

3D videos are recorded by two camera lenses simultaneously. The distance between two lenses is the same as the distance between our eyes (about 2 inches) each image depicts the image seen by one of the human eye. These two images recorded separately can later be combined with the help of 3D glasses.

A 3D Projector

A 3D Projector

3D Projection

Image from each camera is projected on a silver screen with the help of two projecting lenses. One of the lens has a vertical polarizing filter and the other lens has a horizontal polarizing filter. So light emitted by one of the projector lens is vertically polarized and that emitted from the other is horizontally polarized.

The two images are superimposed on each other, they appear to be blurred pictures to the naked eye but when you wear a pair of polarized glasses or simply Real D glasses these are transformed into 3D pictures.

Some of the new 3D projectors use a single projecting lens to project the image so they work by switching between the image of each camera hundreds of times per second to create the same effect.

In theaters this 3D picture is accompanied with 3D Surround sound which is created by placing different speakers all around the viewers (this is something typical of cinema acoustics).

Polarized light

Polarized Light can be defined as light in which particles oscillate in one single plane only. Where as in ordinary un-polarized light particles oscillate in all planes. (Image below explains this process.)

Polarization of light with the help of polarization filters.

Polarization of light with the help of polarization filters.

How 3D Glasses Work?

3D glasses used to watch stereoscopic 3D movies contain two polarizing filters.

  • One of the glass is coated with a vertical polarization filter – that is all light passing through it is vertically polarized.
  • The other one is coated with a horizontal polarization filter – that is all light passing through is horizontally polarized.

The process is illustrated in the diagram below.

How 3d works in cinemas with polarized light

How 3d works in cinemas with polarized light

In this way each eye will see only one of the images projected on the screen (as discussed above that two images are projected on screen) and the desired 3D effect will be achieved.

A pair of 3D glasses.

A pair of 3D glasses.

Viewers can however not tilt their heads when using linear polarizes because it causes parallax errors and headaches because the brain is unable to interpret the image properly.

Most of the modern stereoscopic glasses contain circular polarizing filters but it is much easier to explain and understand linear polarizes so I decided to go with them.

Role of Human Brain

The visual cortex of the human brain combines and interprets these two separate images from each lens as a single image to give us the perception of depth, just as it combines images from two of eyes in every day life. This way the picture comes close to reality and we can enjoy it to the fullest.

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