Stereoscope

Stereoscope, pronounced STEHR ee uh skohp, is an optical viewing device that makes photographs seem to have three dimensions. An ordinary camera sees things only in a flat plane, and not in the round, the way our eyes usually see things. But two cameras set slightly apart can work like our eyes. They can photograph the same object at the same time. These two photographs are then mounted side by side and viewed through a combination of lenses and prisms called a stereoscope. The two views then enter the eyes without strain, and the resulting mental image appears to have three dimensions. The stereoscope user sees everything in the round.

A stereoscope with a cabinet of pictures was once a common item. The old-style stereoscope consisted of a rack and handle, a slide, and a pair of screened lens-prisms. The present-day stereoscope is a plastic box with two viewing holes. One popular type has picture slides mounted in a cardboard or plastic disk.

Today, stereoscopes are employed extensively in aerial surveys to map out land elevations. Astronomers use a special type of stereoscope for finding small planets. It is possible to mount two stereophotographs side by side and view them without prisms. The effect is a good picture in the round, but it causes eyestrain.

In 1952, producers introduced "three-dimensional" motion-picture projection. Some types used a large, curved screen and a new kind of sound projection to produce a three-dimensional effect. Others used a stereoscopic principle. Persons watching the film wore special eyeglasses so that each eye saw only the view meant for it. The mental image that resulted had three dimensions.

Contributor: Jack Feinberg, Ph.D.Phys., Prof., Physics Department, Univ. of Southern California.

Stereoscope

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