When we look at any solid object or assemblage of objects using both eyes, each eye observes a slightly different aspect of the scene. Thus, the pictures projected on the retinas of our two eyes are dissimilar, but the visual mechanism in the brain combines the two dissimilar pictures into a single three-dimensional, or âplasticâ impression. This phenomenon is known as binocular stereoscopic vision.
It was early realized that we may divide the process into two separate and distinct stages. We may first photograph the two dissimilar views by means of two cameras situated in the positions occupied by each of our two eyes, and we may then view the two resulting photographs with our two eyes in such a way that the photograph taken by the right-hand camera is viewed only by the right eye, and that taken by the left-hand camera is viewed only by the left eye. When this is done, provided certain necessary conditions are fulfilled, we perceive the same three-dimensional image that we saw when we looked at the original solid objects directly from the camera position.
When the conditions are correctly chosen, the resulting plastic image will appear to be an exact full-scale model of the original object, apparently situated at its original distance from the camera. We speak of this correct type of stereoscopic reproduction as orthostereoscopy.
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