This week the New York Public Library began offering high-resolution downloads of the more than 187,000 items from its Digital Collections that are in the public domain. They include thousands of stereographs donated by collector Robert N. Dennis, including a few hundred taken in Maryland, a sampling of which can be seen in the slideshow below.
Stereoscopic photography, popular from the mid-19th century through the dawn of the Great Depression, was an early version of 3D, creating the illusion of depth by getting the viewer’s brain to combine two images taken at slightly different angles. The trick was aided by devices known as stereoscopes.
Unless you’re an antique collector, you probably don’t own a stereoscope. While you won’t see exactly what you’d see though a stereoscope, it is possible to perceive depth in flat images without any aid. One approach is cross-viewing, accomplished by focusing both eyes on a space slightly in front of the image. Another is parallel-viewing, accomplished by relaxing both eyes and gazing through the image, as if it isn’t there. A stereoscopic effect can also be approximated by animating an image pair, as in the Patterson Park GIF above, which the NYPL has made easy to do with its Stereogranimator online tool.