Stereoscope

Stereoscope is a viewing device designed to present two separate images to the left and right eye, producing the perception of depth. It relies on binocular disparity, the small difference between the two images created by viewing the scene from slightly different positions. The image pair is typically printed side by side on a card; the viewer looks through an optical system that directs the left image to the left eye and the right image to the right eye, enabling a single three-dimensional scene to be perceived.

The concept was developed in the 1830s by Charles Wheatstone, who demonstrated that two offset pictures could be fused by the brain into a 3D image. He built the first stereoscope using mirrors set at 45 degrees. About a decade later, Sir David Brewster refined the design with lenses and prisms, leading to commercial versions that popularized stereoscopic viewing in the late 19th century. Card sets of paired images, known as stereographs, were widely produced for home viewing and education.

There are several forms, including the original mirror stereoscope and prism-based variants, as well as modern digital stereoscopes that render stereo pairs on electronic displays. Although its heyday was the Victorian era, the basic principle underpins contemporary three-dimensional visualization, including virtual reality, 3D cinema, and certain medical imaging techniques.