Polarized glasses

Polarized glasses create the illusion of three-dimensional images by restricting the light that reaches each eye, and example of stereoscopy. To present a stereoscopic motion picture, two images are projected superimposed onto the same screen through orthogonal polarizing filters. The viewer wears low-cost eyeglasses which also contain a pair of orthogonal polarizing filters. As each filter only passes light which is similarly polarized and blocks the orthogonally polarized light, each eye only sees one of the images, and the effect is achieved.

Related Topics:
Stereoscopy - Orthogonal - Polarizing

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The difficulty arises because light reflected from a motion picture screen tends to lose a bit of its polarization. Aluminized screens are said to be substantially better than glass bead screens in this respect.

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When stereo images are to be presented to a single user, it is practical to construct an image combiner, using partially silvered mirrors and two image screens at right angles to one another. One image is seen directly through the angled mirror whilst the other is seen as a reflection. Polarised filters are attached to the image screens and appropriately angled filters are worn as glasses. A similar technique uses a single screen with an inverted upper image, viewed in a horizontal partial reflector, with an upright image presented below the reflector, again with appropriate polarizers. Polarizing techniques are most simply used with cathode ray technology, as polarizers are used within ordinary LCD screens for control of pixel presentation - this can interfere with these techniques.

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In 2003 Keigo Iizuka discovered an inexpensive implementation of this principle on laptop computer displays using cellophane sheets http://individual.utoronto.ca/iizuka/research/cellophane.htm.

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In optometry, polarized glasses are used for various tests of binocular depth perception (i.e. stereopsis).

Related Topics:
Optometry - Binocular - Depth perception - Stereopsis

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