The process through which people perceive depth comes from the brain's ability to merge the two slightly different projections of the world onto the retinas; this process is known as stereopsis and is the fundamental principle on which 3D movies and pictures are based. Thus, by devising a system in which the separate viewpoints get to each eye, a movie can be projected onto a screen with the perception of depth by viewers.
Some Methods of Projecting 3D Movies
There are several methods to project a 3D movie onto a screen, among them are anaglyph and polarization. These methods have their advantages and limitations and new ways are being sought to overcome these limitations to make the experience as enjoyable as possible for the viewer. While the polarization technique overcomes some of the limitations of anaglyph, the view must keep their head level or else the projection from the one eye "bleeds” through the other thus destroying the 3D effect. To overcome this limitation, circular polarization is used.
Spinning Electric Field Vectors
Light is an electromagnetic wave, which mean it has both electric and magnetic field vectors (Griffiths). Typically, this electric field vector just points in one direction. In the case of circular polarization, the tip of the electric field vector, at a fixed point, describes a circle as time progresses. While this may seem complex, it is not. The polarization of a light wave describes the effect of light on an electron. So, a horizontally polarized light source will induce an electron to oscillate in a left to right direction. A circularly polarized light source will induce an electron to move in a circle. (See Figure 1).
A linearly polarized light wave can be described as being either horizontally or vertically polarized. A circularly polarized light source is described as either being of right-handed/clockwise polarization or left-handed/counter-clockwise polarization. Physicists use the term “curl” to describe how a vector twists and this can best be described by making a fist while sticking out the thumb as if “thumbing a ride”.
When someone points their right thumb against the direction of wave propagation and makes a fist with, or “curls”, the other fingers, the direction they curl in is counter-clockwise, see Figure 2. Similarly, if the same thing is done with the left hand, the fingers curl in the clockwise direction, see Figure 3. It is for this reason that a right-handed curl is known as counter-clockwise and left-handed curl is known as clock-wise.
RealD 3D Glasses
The RealD system is similar to the polarizing system in that glasses with polarizing filters are used. The main difference between the two systems is that in the case of RealD, circularly polarized light is projected onto the screen and circularly polarizing filters are used in the glasses. This overcomes the limitation of needing to keep the head level and allows a viewer to watch a movie in a posture that is more comfortable to them.
Disadvantages
Movies that use polarized light suffer from a loss of screen brightness due to absorption by the polarizing filters. However, as the ambient and reflected light in a theater is reduced by the 3D glasses, this is not an issue as the perceived loss in contrast is not great.
One complaint that all 3D movies suffer from has to do with complaints of nausea and headaches from movie goers. This is probably due to rapid scene cuts with different depths, something that directors generally try to avoid while filming their movies. Thus, as 3D movies become more prevalent, new techniques will have to be explored for a new breed of film-makers to tell their story.
Works Cited
Griffiths, David J. Introduction to Electrodynamics. Upper Saddle River, N.J.: Prentice Hall, 1999. Print.
David Latchman - David is a self-avowed science geek and coffee addict who is curious about the world around him.
