Human vision or the way in which we visually perceive things is a complex process. Our brain acts much like a sensor for the photographic lens to process the information gathered by the eyes to formulate the visual imagery. During the process, the brain uses different kinds of visual cues (perspective, scale, overlapping of objects), to assess the relative distance of the object from the viewer and its dimensional depth. The disparity in perspective between objects seen separately through left and right eye is the paramount feature that creates an illusion of depth. Stereoscopy is the process by which an illusion of depth is created in a flat image (photograph or a painting), by presenting slightly different images to the left and right eyes, making the experience similar to how we see things in reality.
1. Wheatstone Stereoscope
In 1828, Sir Charles Wheatstone invented the earliest type of stereoscopes which consisted of a pair of mirrors, each set at an angle of 45 degrees to the viewer’s eyes, reflecting two slightly different images for the left and right.
Fig 1. Charles Wheatstone Mirror Stereoscope
2. Brewster Lenticular Stereoscope
David Brewster implemented the idea of using lenses to view dissimilar images as one creating the illusion of depth. The relatively smaller, handheld lenticular stereoscope thus developed came to be known as Brewster Stereoscope.
Fig 2. Brewster Lenticular Stereoscope