Real-D 3D Glasses: Videos
To showcase the polarization effects of glasses used for 3D movies, a pair of Real-D 3D glasses used in Famous Players cinemas were obtained for simple tests. These can easily be repeated with a pair from any Real-D cinema. Important in these tests is the fact that light from an LCD screen is linearly polarized, as seen in the simple polaroid videos.
The Real-D glasses are designed to work with circularly polarized light, a polaroid with a coating on one side acting as a wave retarder, converting the incident circularly polarized light to linearly polarized light. When viewing the linearly polarized light from the laptop through the glasses, the light first hits the wave retarder and becomes circularly or elliptically polarized; the polaroid behind the coating has no effect on the light, only dimming it. Rotation of the glasses has no effect except for mild colour changes, likely due to a wavelength-dependent defect in the glasses (they do have to be mass-produced after all). However, if the glasses are flipped upside-down, the light hits the polaroid first and the glasses act purely as a linear polarizer. This can be seen in the video below.
Video: Real-D glasses, when held regularly, only cause slight colour changes in the linearly polarized laptop light, but when held backwards, act as linear polarizers.
Perhaps a bit more interesting is what happens using two pairs of Real-D glasses held in series. When the pair is held back-to-back, the two linear polarizers are in contact; light is linearly polarized after hitting the first, and with the proper rotation is completely blocked in all four combinations. However, if the glasses are held front-to-front, the light is first linearly polarized, then circularly polarized by the wave retarder. The second wave retarder will linearly polarize the light once again. Depending on the combination, the light will either be completely blocked are pass entirely through the second linear polarizer. If the two lenses are built to accept the same circular polarization, light will pass through; if they accept opposite polarizations, all light will be blocked. This can be seen in the video below.
Video: Real-D 3D glasses held in series, depending on the orientation, have varying effects, acting as linear polarizers, becoming transparent or fully blocking light.
© Copyright 2010, Jeffery Dech, John Donohue, and Ryan Woodman