Diver's Face Mask Having Aspheric, AFOCAL Lens System Providing Unit Magnification for use as a Window Between Air and Water
Patent, filed 20 Jul 1998, patented 7 Dec 1999
DEPARTMENT OF THE NAVY WASHINGTON DC
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A lens system is adaptable to face masks for divers and camera windows and assures improved viewing characteristics underwater, including unit magnification and substantially perspective distortion-free viewing over a wider field of view. The system includes a first lens having a concave outer face contacting water and a concave inner face contacting a gas filled interior. A second lens spaced apart from the first lens in the interior has a convex outer surface and a flat inner surface. The concave outer face and concave inner face of the first lens and the convex outer surface and flat an inner surface of the second lens are coaxially aligned and optically oriented to afocally process and transmit light passing through them to a nodal point in the interior. At least one of the outer face, concave inner face, convex outer surface and inner surface defines an aspheric curve. A pair of such lens systems may be mounted in a face mask structure or a single modified lens system having a flat outer face may be mounted in a case for an underwater camera.