Patent ID: 7717559
Filing Date: 2010-05-18
Classification: G02C

Abstract:
1. A method for calculating a tilt angle of a spectacle lens that comprises an optical convex surface on an object side of the spectacle lens and an optical concave surface on an eye side of the spectacle lens and is mounted in a spectacle frame in a manner tilting with respect to a forward sight line, the optical convex surface being spherical, the optical concave surface being optically curved according to a prescription, the method comprising: defining a design reference point at an intersection of the optical concave surface and the forward sight line; obtaining: an inter-pupil distance; an edged lens width of the spectacle lens; a front bend angle formed by a line and a plane perpendicular to the forward sight line, the line connecting peripheral edges that oppose to each other across the optical convex surface; a bridge length defined by a dimension between the spectacle lens and a neighboring spectacle lens used together with the spectacle lens; a front curvature defined by a radius of curvature of the optical convex surface; and a center thickness of the spectacle lens; obtaining a formula of a sphere of the optical convex surface of the spectacle lens from the edged lens width, the front bend angle, the bridge length, and the front curvature; while approximating the optical convex surface and the optical concave surface to a plate-shaped prism having parallel object-side surface and eye-side surface, obtaining optical paths of a plurality of light rays that enter the object-side surface of the prism, refract in the prism to go straight to be refracted again by the eye-side surface of the prism to be emitted to the eye side; obtaining one of the plurality of light rays of which optical path after exiting the eye-side surface aligns with the forward sight line; setting the design reference point at the exiting position of the one of the plurality of light rays of which optical path after exiting the eye-side surface aligns with the forward sight line; and calculating an angle formed by a plane perpendicular to the forward sight line and a tangent line at the design reference point, the angle being set as the tilt of the lens.