ViewMaster Design and Function
The ViewMaster design and concept has a history dating back to 1911, but it wasn't until the mid-1960s that the ViewMaster caught on as a toy for children. It was around this time that the photographic slides used in the ViewMaster began to be focused more on cartoon characters and toys than on scenic landscapes.
The modern ViewMaster is a lightweight, hand-held device made mostly out of plastic. It resembles a pair of magnifying binoculars in appearance. There are two eyepieces on one side and an opaque plastic panel on the other side to allow light to shine through the inner chamber. In the space between the eyepieces and the opaque panel, there is a round rotary disc that is designed to hold ViewMaster slide discs. A lever on the side of the ViewMaster turns this rotary disc, allowing the user to rotate the slide discs and align new slide images with the eyepieces.
Each ViewMaster slide disc is a round piece of thick paper with fourteen small windows punched out. These windows are filled with small celluloid image slides. There are seven pairs of images, with each pair including two slightly different angles on the same image.
The ViewMaster allows users to see objects that appear in 3-D through a technique called stereoscopy, or stereoscopic imaging. Stereoscopy works by presenting the left and right eyes of humans with slightly different images. While this does not create actual three dimensional images, stereoscopic images can trick the brain into recognizing depth perception.
To make a picture of a turtle appear in 3-D in a ViewMaster, two pictures are taken of the turtle simultaneously. The positioning and angling of the cameras are similar to the positions and angles of the eyes in the human head. Therefore, these two images, when taken together and viewed independently with each eye, recreate human binocular vision.
The images are made into slides and placed next to each other on a ViewMaster slide disc. When the slides are viewed in the ViewMaster, the left eye is only seeing the image taken from the left perspective while the right eye only sees the image taken from the right perspective. When the brain organizes these images for the viewer, the experience of real depth perception is recreated.
The concepts that make the ViewMaster work are the same ones that enable our own binocular vision system to allow us to perceive and judge depth. Since humans' eyes are spaced slightly apart, they both see different things at the same time. Yet we actually "see" only one unified image. This is because the two distinct images captured by each eye are correlated together in the brain.
When the brain correlates images, it tells us how near or far they are. When the difference between two images of the same object is great, that object is close. When the difference between two images of the same object is slight, that object is far away. If you look closely at two ViewMaster image slides from the same pair, you will see that the same principles apply to the images that appear closer and farther away.