Stereoscopy is a technique to create the illusion or perception of depth when viewing stereoscopic images. Humans have two eyes and the small perspective differences between the left and right eye are interpreted by the brain as “depth” and so we experience a three-dimensional world.
With stereoscopy it is possible to simulate this process. The most popular way to create stereoscopic images is with a camera. With a regular camera, a photo is taken and then the position of the camera is shifted slightly to take a second photo. The distance between both positions is the stereo baseline.
The result is two nearly identical photos with only a slight difference in perspective caused by the two different camera positions. The two pictures are called a stereo pair.
A stereo camera has two lenses and the lenses are mounted at some distance from each other. The distance is comparable to the distance between the two eyes of a human (about 6,5cm). With a stereo camera, the two images can be shot simultaneously, without having to move the camera position.
A developed stereo photo is called a stereoview. There are several ways to view a stereoview in 3D. This website focuses on the most commonly used method that fits the themes and time period of this website: by using a stereoscopic viewer, better known as a stereoscope. The stereoview is placed in the stereoscope and viewed through two lenses. The viewer now sees the image in 3D.
Stereo photography is still practiced in the digital age, but today it is a photography niche. However, it had two major waves of popularity between 1851 and 1930.