How stereo works
People see depth partly because their two eyes view the world from slightly different positions, about six to seven centimeters apart in most adults. The brain compares the two views and uses the differences to judge distance. A stereoscopic camera imitates this by taking two photographs from points a similar distance apart. When each eye is shown only its own picture, the brain reconstructs a sense of depth. Everything in stereo photography, from the Victorian parlor to modern headsets, is a variation of this idea.
The stereoscope before the camera
The stereoscope was invented before photography could supply the pictures. In 1838, the English scientist Charles Wheatstone described a viewing device that used angled mirrors to present a different drawing to each eye. He showed that pairs of flat images could be fused into one three-dimensional impression. When photography arrived, it was a natural source of such pairs. The first stereo photographs in the early 1840s were made by taking two exposures from slightly different positions or with two cameras side by side. Some sources note that Wheatstone had calotype stereo pairs made for him, though details of the earliest examples are not firmly documented.
Brewster, the lens stereoscope and the Great Exhibition
The Scottish scientist David Brewster developed a lens-based stereoscope around 1849, which was smaller and more convenient than Wheatstone’s mirror design. He also described a camera with two lenses to take stereo pictures simultaneously. A French instrument maker, Jules Duboscq, produced Brewster’s stereoscopes commercially, and examples were shown at the Great Exhibition in London in 1851, where Queen Victoria is reported to have taken an interest. The device quickly became fashionable.
The Victorian craze
In the 1850s and 1860s, stereo cards became one of the most popular forms of photography. Companies such as the London Stereoscopic Company, founded in 1854, sold cards of landscapes, monuments, foreign cities, comic scenes and portraits. Viewing a stereo card gave many people their first sense of faraway places in depth. In 1861, the American physician and writer Oliver Wendell Holmes designed a simple hand-held viewer and chose not to patent it, which helped it spread. Stereo views were often kept in parlors, sold door to door and used for teaching geography.
Twin-lens stereo cameras were made for this market, and photographers also used single-lens cameras that were moved sideways between exposures, which only works for still subjects. Two lenses allowed people to be photographed without blurring or mismatches between the pair.
Twentieth-century revivals
Interest in stereo declined as the century turned, but it returned in several waves.
View-Master. Introduced in 1939, the View-Master viewer used small color transparencies on a circular reel. It became a common toy and tourist souvenir, and variants of it were also used in military training.
Stereo cameras of the 1950s. After the war, cameras such as the Stereo Realist (from 1947) took pairs of color slides on 35mm film, viewed through special viewers or projected. A small community of enthusiasts built up around them.
3D film. In the early 1950s, studios released films in stereoscopic 3D, with Bwana Devil in 1952 widely cited as the start of the boom. Two projectors and polarizing glasses were typical. The first wave faded within a few years, partly because projection was difficult to keep in synchronization. Later waves included the 1980s and the 2009 release of Avatar, which was shot with purpose-built twin-camera rigs and encouraged many theaters to install digital 3D projectors.
Digital stereo cameras
Digital technology made stereo easier to capture and process. In 2009, Fujifilm released the FinePix Real 3D W1, a compact camera with two lenses and two sensors and a screen that showed 3D without glasses. Other makers produced 3D camcorders and cameras around 2010, when 3D television was being promoted. Consumer interest was limited, and many of these products were short-lived, partly because viewing 3D on flat-screen displays often required glasses and gave some viewers headaches.
From two views to depth maps
Modern “3D cameras” often work differently from the twin-lens design. Depth cameras measure the distance to each point in the scene, producing a depth map in addition to a normal image. Methods include:
- Projecting a pattern of infrared light and measuring how it distorts, as the Microsoft Kinect did in 2010.
- Timing how long light takes to travel to an object and back.
- Using two close-set lenses to calculate depth from the difference between views, which is how many dual-camera smartphones estimate depth for blurred-background portraits.
Apple added a lidar sensor to some devices in 2020 to improve depth measurements. These sensors are also used for augmented reality, and for 3D scanners that capture the shape of objects and rooms, sometimes by methods such as laser triangulation. Stereo imaging underlies VR headsets too, since a headset shows each eye a slightly different image.
Notes on accuracy
Dates for the earliest stereo daguerreotypes and calotypes vary, and some accounts credit different people with early twin-lens cameras. The overall story, in which stereo photography tracks a repeating cycle of enthusiasm and fading, is well documented, but exact dates and claims of the first 3D camera should be treated as approximate.