Here’s the quick version from 1905 Supervisor Neil Cramer:
That right there is a Stereoscope! It’s a device that has its lenses tilted slightly (like binoculars) so that when looking through it, you see one image. Specifically, the cards next to it depict the same photograph-well almost the same one. It’s the same picture, but what happens is that the photographer takes a picture, then moves a step to the left or right to take another, then when they’re put side by side and viewed through a device, say a Stereoscope, the image appears to be in 3D.
It’s early 3D entertainment!
Here’s the long version from a resource made by Artifacts Curator Benita Hartwell:
Stereo cards, along with their stereoscope viewers, formed one of the most popular forms of domestic media in the nineteenth century. From the 1850s on, stereoscopes were available in hand-held and cabinet-style viewers.
The stereo card takes advantage of the fact that human vision is stereoscopic. Each eye views the world from slightly different locations. The pair of images found on a stereo card is photographed from slightly different positions. When the card is placed in a viewer, the right eye sees the right image, the left eye the left image. The brain interprets the two images as one, as well as the depth of the images, which produces the “magical” impression of a three-dimensional image.
The earliest stereo cards were produced by local photographers in vacation destinations, who photographed sights for tourists. Soon, larger companies started producing sets on a variety of topics. By 1858, the London Stereographic Company could already boast of more than 100, 000 different views on offer. Fictional and fantastical scenes (or tableaux) were popular, especially those that featured horror, melodrama, humour, and sentiment. Scenes from exotic locations that one might never visit also proved a hit. There were also stereo cards that verged on pornography “ some stereoscopes came with a locked drawer to enable a gentleman to keep his risqué stereo cards hidden.
Photographers of stereo cards had to ensure the scenes the depicted did not look boring when viewed. In particular, they had to pay attention to the depth of the scene when organizing the structure of a photograph to be taken. This led stereo card photographers to produce images unlike any other produced in the field of photography.