Adding the Third Dimension

Two girls appear in a stereo photograph taken in 1853. When seen through a stereoscope like the one at right, which used a pair of lenses to magnify the two images, the slightly different views merged and the girls stood out in relief. This viewer is an ornate affair on a stand most were inexpensive hand-heId models. 

By the early 1860s a new photographic fad was sweeping Europe and America: stereoscopic photographs. These were pictures in pairs, viewed through a twin-lens device called a stereoscope, which made each pair merge into a sin­gle view that seemed startlingly three dimensional, like a perfectly detailed model of the actual scene. Almost ev­ery middle-class household boasted dozens, sometimes hundreds, of these pictures. Family and friends gathered in the parlor to gape at each new set the pyramids of Egypt, Parisian street scenes, the wonders of Peking, views of the Holy Land-all of them seeming to spring to life in vivid perspective before the eyes of the viewer.

Stereo photography was based on a long-k-nown phenomenon of vision: that the eyes receive two slightly different views of a scene, which the brain trans­lates into a single image having three dimensions. Thus a pair of pictures supplying slightly different views to each eye created the illusion of depth when seen through the stereoscope. Among the first to make a camera spe­cifically designed for the job was an English optical intrument maker named John B. Dancer, who in 1856 patented a device that took two pictures simultaneously through lenses set slightly apart. 

A box on a box, Dancer's device combines a stereo camera atop a platestoring magazine. The camera has two lenses mounted 2,5 inches apart, about the distance between the pupils of a person's eyes. In front of each lens is a revolving disk with holes of different diameters, one of which was selected to provide the aperture size needed for the correct exposure. In front of the disks is a doubleended paddle used as a shutter; turned by hand, it uncovered the lenses for focusing and taking picture . 

With Dancer's magazine-loading system the photographer could prepare the camera in advance for a series of stereo pictures by stacking 'plates in the arewer of the box below the camera. Once he·had tocusedhls subject on a ground-glass screen at the back of the camera, the ohotoqrephet replaced the screen with a plate-cflanging back (a). He then turned a knob (b) to operate a gear that moved the plate- carrying drawer iorwerd. As" a plate came into position, its number appeared in the window (c) on the camera's side. He lowered a rod (d), screwed it into a threaded hole (e) on the top of the plate and pulled the plate up into picture­taking position. After exposure was made the plate was lowered, the rod unscrewed and raised, and the drawer moved forward to bring a fresh plate into position for the next picture.