Stereoscopes

A stereoscope is a viewing device that creates the illusion of three-dimensional depth by presenting two offset images to the eyes. Each image corresponds to a slightly different viewpoint, and the brain fuses the two inputs into a single, depth-rich image.

History and development: The concept was demonstrated by Charles Wheatstone in 1838 with a pair of mirrors that directed two photographs to the viewer’s eyes. In 1849, David Brewster introduced a rival prism-based design that offered greater comfort and magnification. The late 19th and early 20th centuries saw mass production of stereo cards containing paired photographs, known as stereographs or stereoviews, becoming a popular form of home entertainment and education.

Mechanism and construction: Stereoscopes generally fall into two main families. Mirror stereoscopes use angles and mirrors to deliver two images from a card placed on a table or stand, one to each eye. Prism stereoscopes, or lens-based viewers, use prisms or lenses to direct each image to the corresponding eye, often with slight magnification and adjustable focus. More compact “pocket” and tabletop models have been produced for hobbyists, collectors, and professional use.

Uses and legacy: Historically, stereoscopes were used for photography, cartography, education, medicine, and archaeology, among other fields. Today, while digital 3D displays and virtual reality have largely supplanted traditional viewers, stereo viewers and stereoview cards remain of interest to collectors, museums, and researchers, and modern devices continue to adapt the basic principle for digital formats.