Importance

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Abstract

There is disclosed a partially transparent, directional viewing sheet formed of plastic material with convex and concave lenses, preferably lenticular lenses, formed respectively on the front and back surfaces of the sheet, there being intervening spaces with flat or convex arcuate surfaces between the concave lenses which spaces are not transparent to images and may be imprinted with an image that is viewable through the sheet from some directions. Preferably the concave lens focal length is typically about one-half of the focal length of the convex lens. Elliptical cross-section of the lenses may minimize spherical aberration and sharpen the focus. The thickness of the sheet causes focal points of the lenses to substantially coincide. The view through such a sheet in a direction substantially aligned with the optical axis of the lenses is a minimally distorted view of objects spaced from the opposite side of the sheet while off-axis viewing will present the image imprinted on the intervening surfaces between the concave lenses on the back surface of the sheet. Convex surfaces are preferred over flat surfaces, especially for high speed printing in offset printing presses.

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First Claim