Viewing In 3-D On A Computer Monitor

To view most computer stereo images, you need to look at the left-hand image with your right eye, and at the right-hand image with your left eye (called convergent or cross-eye viewing). Gaze at the stereo pair, keeping your eyes level and cross your eyes slightly. Try to cross your eyes slowly, so that the two images in the centre come together. When they converge or fuse, you will see them as a single 3-D image. The centre image is three-dimensional. 

Another approach. With your head level and about 2.5 feet from the screen, hold up a finger, with its tip about 6 inches in front of your face, and centered between the stereo pair on the screen. Focus on your finger tip. Without focusing on the screen, notice how many images you see there (they will be blurred). If you see four images, move your finger slowly toward or away from you eyes, keeping focused on your finger tip, until the middle pair of images converge. With your finger still in place, partly covering the converged pair, change your focus to the screen. The image partly hidden by your finger should appear three-dimensional. Your finger should still appear single, but blurred. With some practice, you can remove your finger and still keep the screen images converged into a stereo image.

STEREOGRAPHIC PHOTOGRAPHY
STEREOVIEWS ~ STEREOGRAMS ~ STEREOSCOPES

 
A stereogram or stereoview is a flat two-dimensional image viewed in such a fashion as to produce a three-dimensional effect..Stereographic photography was invented almost immediately after photography itself. During the Victorian era photographers were sent out to photograph the world in 3D, and the photographs were reproduced over and over to meet the demand -- manufacturing and assembling the views was big business. .Looking at stereographs was as common in Victorian times as watching TV is today. People would relax in their parlor and be transported around the country and around the world with a box full of stereos and a hand-held or tabletop viewer.
Stereo pictures are taken by means of a camera with two lenses. This provides two separate pictures 2.5 inches apart, about the distance between the eyes. Although the pictures appear the same, they are not. When looked at in a viewer, which has prismatic lenses, your eyes will blend the two views into one and the brain perceives it in three dimensions the same as normal vision. It's estimated that over 7 million different images were commercially produced, and these had runs anywhere from a handful to thousands! The demise of the stereoscope began with the advent of other forms of entertainment media and by the 1940s, about the only type of stereoviewing available was the View Master.
Manufacturing Stereocards

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The Auto-Stereoscope

These state-of-the-art 1893 "Drop Card" machines display a series of stereoview cards. 
The two side-by-side pictures on each card give a spectacular illusion of three dimensions. 

The internal mechanism of the machines features a patented spring-driven clockwork drive which switches on an electrical lighting bulb and sequentially displays the stereoview cards. 

The wooden cabinets are of ornate and well-constructed design.

The Mutoscope -- manufactured by the American Mutoscope and Biograph Companies -- worked on the same principle as a "flip-book." The individual image frames were conventional black-and-white, silver-based photographic prints on tough, flexible opaque cards. Rather than being bound into a booklet, the cards were attached to a circular reel. The reel held about 850 cards, giving a viewing time of about a full minute. The reel with cards attached had a total diameter of about ten inches. 

Some Mutoscopes were coin-operated. The patron viewed the cards through a pair of lenses enclosed by a hood, similar to the viewing hood of a regular stereoscope. The cards were lit electrically, but the reel was driven by means of a geared-down hand crank.

Each machine held single reel and was dedicated to the presentation of a single short subject, described by a poster affixed to the machine. The patron controled the presentation speed but the crank could be turned only in one direction, preventing the patron from reversing and repeating part of the reel. The patron was advised that stopping the crank or slowing it too much would throw the images far enough out of focus to blur them beyond recognition.