Humans have the ability to see three dimensions or “depth”. We have two eyes and small perspective differences between the left and the right eye are interpreted by the brain as depth. Stereoscopy simulates this process by creating the illusion of depth when viewing stereoscopic images made by a stereo camera.
A normal camera has only one lens and creates two-dimensional images. A stereo camera has two lenses that are positioned next to each other. When taking a photo, two images are recorded on the negative at the same time. Both lenses record 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.
Stereoscopy was invented in 1838 by Sir Charles Wheatstone. He designed a first stereoscope for viewing stereographic drawings. It was a large device that worked with mirrors. Sir David Brewster developed in 1849 a more compact stereoscope based on lenses. This type is known as the Brewster stereoscope and was the basis of many stereoscopes that were developed afterwards. During the Great Exhibition of 1851 in London, the British Queen Victoria looked through the lenses of a Brewster stereoscope. She was impressed by the three-dimensional view and her enthusiasm contributed to the popularity of stereoscopy.
Most stereoviews were printed on paper and are called stereo cards. Stereoviews on glass were particularly popular in France. These are called transparencies, diapositives or slides.
It's possible to view stereoscopic images without a stereoscope. 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.
Rise and fall
Stereoscopy was popular from around 1850 to 1950. Popularity slowly declined after the Second World War. The peak in France was between 1890 and 1930. This was mainly influenced by the innovations of Jules Richard who introduced the compact glass formats 45x107mm and 6x13cm. With his stereo cameras Vérascope and the affordable Glyphoscope, stereo photography came within reach of amateurs. The First World War took place in this era and many stereoviews were made during the conflict and sold in the early 1920s.
Today, stereoscopy is 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 small group of enthusiasts.