Game Development Reference
In-Depth Information
Figure 24-8. Circular polarization filter (public domain image by Dave3457; http:// )
First a linear polarizer rotated to 45 degrees accepts incoming light and polarizes as we
discussed earlier. The circular polarization effect is accomplished when a light wave
polarized at 45 degrees hits the filter that accepts both 0- and 90-degree oscillations. As
previously noted, this is called a quarter-wave filter. The resulting combination of 0-
and 90-degree components of the intermediate 45-degree beam results in oscillations
that turn right or left in a regular pattern. Patterns that turn counterclockwise are called
left-handed. Patterns that turn clockwise are called right-handed.
The main benefit is that the lenses create the same pattern regardless of their rotation
about the center of the lens. In other words, if you rotated the assembly shown in
Figure 24-8 , meaning both lenses about the center axis, there will be no change in the
polarization. This reduces the effect of head position on the viewer's ability to fuse the
right and left eye channels, reducing eyestrain and increasing comfort. As a side note,
it is also required for use in digital cameras, as linear polarization would affect the
autofocus and light-metering features of SLRs.
Like anaglyphs, polarized 3D systems also use glasses to separate two channels that are
projected at the same time. The first systems used two projectors, each with a different
linear polarization filter projecting on to the same screen with precise timing. As the
glasses would allow only the correctly polarized light to be seen by either eye, the viewer
perceived binocular disparity. However, the precise timing between the projectors
would be subject to errors that cause eyestrain and binocular rivalry. Newer systems,
including RealD, use an active polarization filter fitted to the projector. However, this
is still classified as a passive system, because the glasses the user has are just normal
passive filters. In this system, there is a single filter that can change its polarization up
to 200 times a second. Every other frame is separately polarized, and binocular disparity
is experienced without the complexity of an additional projector. Although this system
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