Stereoscope
The stereoscope was the first device to show photographs with the illusion of three dimensions. Ordinarily, a camera only shows images in two dimensions, but two different cameras used simultaneously can simulate two eyes, if the lenses of the cameras are the right distance apart. Thus, when the resulting photographs are viewed together, the image appears to have depth.
The first stereoscopes were developed in France in the early nineteenth century as an offshoot of the intense research on light and optics that was happening. The stereoscope was modified in 1849 by Sir David Brewster, who had invented the kaleidoscope some thirty-five years earlier. The improved stereoscope featured a system of lenses and prisms that would overlap the two photographs without straining the viewer's eyes.
Like the kaleidoscope, the stereoscope was a popular success; marketed as "refined amusement," it found its way into the drawing rooms of high-minded audiences everywhere, offering views of famous landmarks and faraway vistas. Brewster even advertised its properties as an educational tool, claiming its three-dimensional images showed the nuances of art and nature that textbooks and lectures could not.
Modern inventors have taken Brewster's stereoscope-with its handle, slide, and screened-lens prisms--and have incorporated several improvements. The most common modern stereoscope is housed in a plastic casing with two holes for viewing, and is most familiar as a child's toy that uses slides on a paper disc to display three-dimensional vignettes from popular cartoons and television shows.
The first stereoscopic camera was invented in 1859 by noted physician and essayist Oliver Wendell Holmes (1841-1935). Dubbed the stereopticon, Holmes' device replaced the two cameras previously required with one camera bearing two lenses and yielding two negatives. Though the stereo camera saw brief periods of popularity among amateur photographers, its use dwindled until the early 1950s, when filmmakers became intrigued by the idea of three-dimensional movies. In 1952 producers unveiled the first 3-D motion picture projector, which utilized a system not unlike Holmes' stereopticon. Moviegoers donned special glasses, often with red and green lenses, that would overlap the two images on the screen to create the illusion of depth.
The IMAX format of ultralarge-frame film projected on a 80-ft-high screen has been adapted to 3-D. The IMAX camera contains two objective lenses separated by the approximate interocular distance of the human eye. Each lens records on a separate film strip, one for the right eye, one for the left. When the film is shown, both films are screened simultaneously.
To isolate the images so that the left eye sees the left-eye film strip and the right eye sees the right-eye film strip, IMAX 3-D designers use the phenomenon of polarization. Polarization controls the oscillation properties of a lightwave; certain types of filters will admit light polarized in one direction, but will block light polarized in the other. When the movie is shown, filters apply a distinct polarization to the left eye and to the right eye film strips. Viewers in turn wear special glasses with polarizing filters matched to the projector such that the left lens of the glasses only admits the images for the left eye, and the right lens only admits images for the right eye. The result is an amazingly realistic illusion of three-dimensionality, without the headaches associated with the red and green glasses of the 50's.
In addition to its entertainment applications, stereoscopic technology is frequently used in medical research, as well as topographical surveys.
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