3D viewing in the early 20th century. Photo by William Fraser
Seeing double: 3D in vintage stereographs
Humans have two eyes for a good reason. Viewing the same scene from two close but very slightly different locations creates an impression of depth. The brain, processing visual data from each eye, builds a scene in which it's easy to determine which elements are near and which are far away. We can learn to interpret a two-dimensional image - like a painting or a photograph - as representing depth of field, but of course it is never the same as viewing the real item or scene with two eyes. In the 1830s when photography was…