Patent No. 5,532,777
Issued: July 2, 1996

Patent No. 5,883,662
Issued: March 16, 1999

Inventor: Pieter O. Zanen, 107 Cayuga Heights Road, Ithaca, NY 14850

Stereographic photography is the method of producing images which are apparently three dimensional by recording separate left- and right-eye images. The viewer reconstructs the 3-D image by viewing the two separate 2-D images simultaneously. Stereographic photography has been known since at least the late 19th century, when stereo viewers were a popular parlor accessory.

Such stereo views have historically been created with two lenses on a single camera, spaced apart by approximately the inter-ocular distance of a human head. The Stereo Realist series of 35mm still cameras, popular in the 1950's, are an example of this kind of imaging. Left and right views were recorded simultaneously through two lens/shutter sets on alternate frames of the 35mm film. The later Nimslo system used four lenses for essentially the same approach.

Stereo movies appeared in the 1950's. The images were typically created either using two synchronized cameras, or a two-lens system on a single camera. Similarly, the various Stereo TV systems have typically used two cameras (see Lipton, et al, US Patent 4,583,117) or a single camera with two lenses (Lipton, et al, US Patent 4,523,226).

All of the multiple-camera systems have severe drawbacks, in the added complexity and cost of duplicating the complete camera system and the synchronization of the two separate images (this is especially a problem in film (non-video) applications). In addition, the use of two separate lenses (whether on one camera or two) introduces problems of synchronizing focus and view.

The need for solving this latter problem is real, but not addressed by prior art devices. Simply mounting two cameras side-by-side will allow the taking of the left- and right-eye images, and the cameras can be focused on whatever the subject is (although follow-focus of moving objects is problematic). However, there is more to stereoscopic vision than simply having two eyes. A simple experiment will demonstrate the problem. If one holds up a finger at arms length, and brings it closer and closer to the face, it becomes apparent that your eyes do more than merely focus on the finger as it approaches. You also aim each eye independently, becoming more and more "cross-eyed" as the finger nears the face. Without this adaptation, most 3-D films tended to induce discomfort as the apparent image distance to the view changed, since the camera views would not shift as one's instinct might expect.

The invention comprises an adapter having a set of four mirrors in two pairs located in front of a camera lens. The centers of the four mirrors are all aligned on a common centerline, with the outer two mirrors facing generally outward along the optical axis of the lens and the inner two mirrors facing generally inward into the lens. The centers of the outer two mirrors are spaced apart by an appropriate interocular distance. The two inside mirrors are together large enough to cover the complete viewing area of the lens, each taking half of the lens viewing area. The two outside mirrors are bigger than the inside pair and large enough to cover the viewing area of the inside pair to avoid viewing area reduction.

The convergence of the two outer mirrors is adjustable by swiveling them simultaneously and equally about their centerlines with a ganging mechanism. The two center mirrors may be fixed, or could be adjustable by being swiveled so that one side of each remains in tight contact with the other along the optical axis of the camera lens, and each makes a 45 or lesser angle to the optical axis.

The actuating mechanism for the outer mirrors is connected to a ring that fits tight around the focusing ring of the lens, so a change in focus automatically leads to readjustment of the convergence of the images. The whole assembly is to be housed in a dust and light proof housing that mounts onto the lens.

The apparatus of the invention is also useful in stereo photogrammetry - see related patent 5,828,913

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