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I have 2 3d portraits of my father that were taken in Paris around 1945. He said he was seated on the center of a semi-circular track that the camera moved on to take multiple exposures that were somehow merged to yield these glass plate portraits that have some 3d depth to them. Does anyone know anything about this technique? Are these portraits worth anything beyond their sentimental value?

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Stereo still photography was popular near the turn of the last century. Two images were taken; one mimics a right eye view and the other a left eye view. The difference in these two views is call “parallax”. The fact that people with normal vision, morph double eyed vision into a single minds-eye image is the core of our ability to see depth (3D).

3D cameras make two images; the parallax shift is about the same as the separation of the human eyes, about 45mm. However, making two images with a greater separation enhances the 3D illusion.

The oldest method to view was a wooden hand-held device that that held the two images and a simple double magnifier arrangement. This viewer isolated the two images and resented the viewer with two images each to the appreciate eye. In the 1940’s a company called Stereo Realist made 3D camera and 3D viewer that was most cleaver.

Another arrangement was to make the two pictures, either separately or simultaneously with the camera. The viewpoint is the correct parallax. These are then printed on photo paper as two images superimposed. These prints appeared to be a spoiled double exposure. The print is then overplayed with a transparent plastic sheet embossed using a pattern of lens-like shapes. The overlay is called “lenticular”.

The two images and the lenticular overlay were carefully made. The lenticular overlay directs the light to the observer in such a way that the left image is shielded from the right eye and the vice versa. In other words, the left eye receives the correct image as does the right eye. Thus the eye/brain combination creates a mental image that is 3D.

It was possible but to mount a camera on a mechanical support that moved the camera during the exposure. The resulting image seemed to be indistinct and blurry. When overlaid with a lenticular cover glass or plastic, a 3D image is envisioned.

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