Humans have binocular vision which means that we have the ability to see three dimensions or “depth”. Perspective differences between the left and the right eye are interpreted by the brain as depth. Stereoscopy simulates this process. The most common way to achieve this is to take stereo photos with a camera and view the stereoscopic images with a stereoscope.
A normal camera has one lens and creates two-dimensional images. It can be used to take stereo photos by taking the two required photos one after the other and slightly adjusting the position of the camera between the two photos. This is especially useful for subjects that are not moving during the time the two pictures are taken.
A stereo camera has two lenses that are positioned next to each other. When taking a photo, two images are captured on the negative at the same time. A stereo camera is therefore also useful for subjects that move. Both lenses capture one photo and the distance between the two lenses results in small perspective differences between the two images. The developed image is a stereoscopic image, also called stereoview, stereograph or stereogram. It will be displayed three dimensionally when it’s viewed using a stereoscope, also known as stereo viewer.
Stereoscopy was invented by the English scientist Charles Wheatstone. He presented his first stereoscope in 1838. It was a large device that worked with mirrors and could be used for viewing stereoscopic drawings because photography would be invented a year later. David Brewster developed in 1849 a more compact stereoscope based on lenses. This lenticular Brewster Stereoscope initially aroused little interest in Britain. He took his prototype to Paris and interested the French instrument maker Jules Duboscq. Duboscq started making and selling stereoscopes and improved Brewster's design. During the Great Exhibition of 1851 in London, the British Queen Victoria looked through the lenses of a Brewster stereoscope made by Duboscq. She was impressed by the three-dimensional view and her enthusiasm contributed to the popularity of stereoscopy in the 1850s. The first widely applied stereoviews were created by using the daguerreotype photography process.
Most stereoviews were printed on paper and are called stereocards. Stereoviews on glass were particularly popular in France due to the high-quality stereoviews of Ferrier & Soulier. Glass stereoviews are called transparencies, diapositives or just slides.
Rise and fall
The first wave of popularity in stereo photography began in England in 1851 and spread to Europe and the United States. It lasted until about 1870. In England, interest waned but in the United States a second wave started around 1885. Publisher Underwood & Underwood produced stereocards on a very large scale and sold them through convincing marketing.
The peak of the second wave in France was between 1893 and 1920. This was mainly influenced by the innovations of Jules Richard who introduced the compact glass formats 45 x 107mm and 6 x 13cm. With his stereo cameras Vérascope and the affordable Glyphoscope, photography came within reach of amateurs. His Taxiphote was the most advanced stereoscope of its time. Other manufacturers in France, like Gaumont and Mattey, adopted the new formats, but also renowned German camera manufacturers like ICA and Ernemann. They all contributed to the success of stereo photography during the second wave.
The second wave in France coincided with two major eras. La Belle Époque was a period of progress and prosperity in which erotic photography could flourish. This period came to an abrupt end with the outbreak of the First World War in 1914. Stereoviews of this conflict were booming in the early 1920s.
The popularity of stereo photography declined in the 1920s and would only see a brief revival after the Second World War. Today it's a niche in the digital era. Fujifilm introduced in 2009 the first digital 3D camera for the consumer market: the FinePix Reaal 3D W1, followed by the W3 in 2010. Although the camera was more successful than expected, there would be no successor. None of the major camera brands offer a digital stereo camera at this moment but stereo photography is still practiced by a group of enthusiasts.
It's possible to view stereoscopic images without a stereoscope. An example are anaglyphs. An anaglyph consists of two layered images. A red image for the left eye and a cyan image for the right eye. A three-dimensional view is displayed when using special anaglyph glasses, better known as 3D glasses. The advantage of anaglyphs is that they can be displayed on a screen, but in my opinion nothing beats the experience of viewing glass stereoviews using a vintage stereoscope.