Principles of stereo viewing
When we look at the world around us, our brain takes two slightly different images - one from each eye - and combines them to make one image with depth. This is sometimes called stereo or 3D vision. To see depth in a flat image - stereo viewing - requires the eye to be given two pictures, each one slightly different, which mimic the usual input to each eye and fools the brain into converting two flat pictures into one single image with the appearance of depth.
The principle was first described by Euclid, who showed that the left and right eyes see slightly different views. Artists experimented with stereo drawings, and in 1838 Sir Charles Wheatstone invented a bulky stereoscope (which required drawings for viewing) but it wasn't until after the invention of photography that stereo views became relatively simple to produce. By 1870, the boom in stereoscopes and stereo cards was well under way.
This 3-D picture card is of Brunig Station, Switzerland
Millions of cards were sold. Victorian and Edwardian stereo cards, which have two pictures mounted side by side, are now very collectable, and a reasonable collection can be built up quickly and relatively cheaply.
The popularity and use of side-by-side 3-D prints did not end with the Edwardian era but continued until well into the twentieth century.
During the war 3-D aerial reconnaisance pictures were taken which were then examined using a table-mounted viewer.
Vistascreen viewers were made in the early 1960s in red or cream plastic. They are very simple folding viewers which take stereo cards.
Vistascreen picture cards
Weetabix gave away Vistascreen picture cards and there was a promotional Weetabix viewer. The Weetabix cards are on cheaper card and are usually of poorer quality.
There are other ways of producing two images for the brain to process.
Anaglyphs are pictures printed in two colours which are slightly offset. Viewing the pictures through coloured glasses gives one colour for each eye and a seemingly 3-D image results. Usually the two colours are red and green or red and blue. This was the technique used to produce cinema films in 3-D.
Anaglyph packaging and red/green filters for Swatch watch
Anaglyph Swatch watch strap and face. Viewed through red/green filters, this will appear 3-D.
Anaglyph pictures still used sometimes; for example, there is a "3-D" Swatch watch with red/green filters in the packaging.
There is also the Minoru webcam which uses the same technique. The camera has two lenses at a separation which is approximately that of the human eyes. Software converts the two images into anaglyphs. Viewers need red/blue glasses to see the 3-D effect. The resulting films are compatible with YouTube.
The View-Master Stereomatic uses polarised light to create two images. Special glasses are required to view the 3-D image. A silvered screen has to be used for projection to polarise the light.
The View-Master System
The two main components of the View-Master system are the View-Master viewer and the View-Master reel. Projectors, cameras, reel storage boxes and other accessories were also made but it is the viewer and the reel which are the foundation of the system.
Yellowstone National Park reel, showing the pictures arranged in opposite pairs
The View-Master reel contains fourteen pictures arranged around the rim of the reel. This gives seven stereo pairs of images. The pictures are on transparency film and therefore require a light source behind them to illuminate the image.
The Thunderbirds set from the 1980s (reissued) showing a viewer and reels
The disc is inserted into a special viewer and the result is a spectacular stereo effect. Although lighted viewers were made, the majority of viewers do not need batteries. They need to be held up to a light source - a window is good. Diffusers help provide even illumination. The viewers have two eyepieces and a lever to move the reel on to the next image.
A View-Master reel from the America's Scenic Wonders Reel Pak issued in 1970 - Farmlands and Forests.
More than a billion reels have been sold since the introduction of View-Master. Although marketed - mainly - as a toy, View-Master is widely collected by adults and children.