Patent ID: 7551335

Claim:
An optically variable element comprising: a surface portion having an interface which forms an optically effective structure, with respect to a reference surface the optically effective structure at least one of projects and is set back therefrom, wherein the optically effective structure has at least one free-form surface appearing three-dimensionally to a viewer, wherein the free-form surface is formed by a partial region of the interface, which is of a lens-like configuration and which produces a magnification or reduction effect and which forms a free-form element, wherein the free-form element includes a grating structure having grating lines substantially following contour lines of the free-form surface, wherein the grating structure includes grating grooves with first and second opposed flanks, the first flanks extending parallel to each other and substantially parallel to a normal to the reference surface, the second flanks disposed at an oblique angle with respect to the normal to the reference surface, wherein the oblique angle of each of the second flanks either increases or decreases progressively away from a central region of the free-form surface towards an edge thereof, thereby changing the spacing of the grating lines from the central region toward the edge.