Technology

Stereoscope 

In 1861 Oliver Wendell Holmes created and deliberately did not patent a handheld, streamlined, much more economical viewer than had been available before. The stereoscope, which dates from the 1850s, consisted of two prismatic lenses and a wooden stand to hold the stereo card. This type of stereoscope remained in production for a century and there are still companies making them in limited production currently. It is primarily American, although it is often named "Mexican stereoscope."

Principles

Two separate images are printed side-by-side. When viewed without a stereoscopic viewer the user is required to force his eyes either to cross, or to diverge, so that the two images appear to be three. Then as each eye sees a different image, the effect of depth is achieved in the central image of the three.

Modern use


In the mid-20th century the View-Master stereoscope (patented 1939), with its rotating cardboard disks containing image pairs, was popular first for 'virtual tourism' and then as a toy. 

The History of Stereo Photography

At one time the steroscop eand its basket of view ards were found in every American parlor.  

Pictures

The pictures used in the stereo views where in the form of "stereographs" which were two pictures of the same scene that were slightly offset and mounted side-by-side. In the 1850s the production of stereographs, also called stereograms, was in high gear and a very popular item. Pictures from around the world, of everything from prominent public people to war scenes were made available. One of the main sources was the Keystone View Company who advertised exotic pictures and capitalized on the 3D illusion of stereo viewing. The company advertised the quote of Carl Sandberg, "the best substitute for intelligent travel is intelligent use of stereographs.", to promote the use of stereo viewing as a way to see the world. Being able to see in stereo was not seen as anything other than entertainment until vertical aerial photography came in after WWII.
In 2010, Hasbro started producing a stereoscope designed to hold an iPhone or iPod Touch, called the My3D. In 2014, Google released the template for a papercraft stereoscope called Google Cardboard. Apps on the mobile phone substitute for stereo cards. The underlying technology is otherwise unchanged from earlier stereoscopes.

See Some Examples
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