Patent ID: 6220704
Filing Date: 2001-04-24
Classification: G02C

Abstract:
A progressive power lens characterized in thatat least one of two refractive surfaces forming a spectacle lens has a progressive refractive surface including a distance portion and a near portion having different focal powers, and a progressive portion having a focal power progressively changed between said distance and near portions;coordinates are defined such that, assuming that said progressive refractive surface of the lens assembled in each of spectacles is viewed from the front side of a user, the horizontal direction is taken as an X-axis; the vertical direction (direction between said distance and near portions) is taken as a Y-axis; the depth direction is taken as a Z-axis; and a progressively change starting point located at the lower end of said distance portion is taken as an origin (x, y, z)=(0, 0, 0);assuming that a coordinate of an original progressive refractive surface is taken as z.sub.p and a coordinate of said progressive refractive surface is taken as z.sub.t, a relationship of z.sub.t =z.sub.p +.delta. is established; andat said distance portion along a main meridian line extending substantially in the Y-axis direction of said progressive refractive surface, said .delta. is given by .delta.=g(r);at said near portion along the main meridian line extending substantially in the Y-axis direction of said progressive refractive surface, said .delta. is given by .delta.=h(r); andat other portions, said .delta. is given by .delta.=.alpha..multidot.g(r)+.beta..multidot.h(r) where .alpha. and .beta. satisfy the relationship of .alpha.+.beta.=1.0, 0.ltoreq..alpha..ltoreq.1, and 0.ltoreq..beta..ltoreq.1; r is a distance from said progressively change starting point and is expressed by r=(x.sup.2 +y.sup.2).sup.1/2 ; and said g(r) and h(r) are each a function depending only on r and satisfy the relationship of g(r).noteq.h(r) and g(0)=0.