Two photos, a few inches apart
A stereocard is two photographs of the same scene, taken from spots about as far apart as your eyes, and mounted side by side on a stiff card, usually around 3½ by 7 inches.
Side by side they look identical. Compare them closely and you'll see that nearby things shift more between the two views than faraway things do. That shift is called parallax, and it's all your brain needs to rebuild depth.
One photo per eye
You looked at the card through a stereoscope: two lenses set eye-width apart, with a divider between them, so your left eye saw only the left photo and your right eye saw only the right one.
The lenses let your eyes relax as if they were looking into the distance, and your brain did the rest, fusing two flat pictures into one scene you could look into.
From parlor craze to headset
- 1838
Charles Wheatstone explains how two slightly different views make depth, and builds a mirror stereoscope. Photography barely exists yet, so the first stereo pictures are drawings.
- 1849
David Brewster swaps the mirrors for lenses, which makes a stereoscope small enough to hold.
- 1851
Brewster's viewer, built in Paris by Jules Duboscq, is shown at the Great Exhibition in London and becomes a sensation.
- 1854
The London Stereoscopic Company is founded, with the slogan “No home without a stereoscope.”
- 1861
Oliver Wendell Holmes designs a cheap handheld viewer and chooses not to patent it. His design is the one most people picture today.
- 1892
The Keystone View Company starts in Meadville, Pennsylvania. It grows into the biggest name in the business, and its card sets end up in classrooms across America.
- 1939
View-Master debuts, and stereo pairs move from cards to paper reels.
- 2024
Apple Vision Pro goes on sale, and phones start capturing spatial photos. The stereoscope becomes a headset, and the card becomes a file.
Where the red and cyan come from
The other old way to see stereo was to print both views on top of each other in two colors, then look through glasses with a colored filter over each eye, so each eye only picks up its own view. Wilhelm Rollmann described the idea in 1853. It came back as the 3D movies of the 1950s and comic books with paper glasses.
That's what the offset in our wordmark is about: red for the left eye, cyan for the right.
See depth without a headset
Thousands of old cards are online
Libraries have scanned huge collections of 19th- and early 20th-century stereocards. Many are in the public domain.
The same idea, in your pocket
A headset is a stereoscope with a screen inside, and a spatial photo is a stereocard you took on your phone. Stereocard is a place to share them, open to anyone with a headset and a browser.