Patent ID: 6429972
Filing Date: 2002-08-06
Classification: G02B

Abstract:
A diffractive lens having an optical axis, comprising:a lens surface having a peripheral portion, and a diffractive relief provided on the lens surface, wherein the diffractive relief is shaped in annular zones, and wherein following conditional formulas (1) and (2) are satisfied: hiâˆ’1&lE;hiâ€ƒâ€ƒ(1) x=f(hâˆ’hti)+Sâ€ƒâ€ƒ(2) â€ƒwhere i is a suffix showing an ordinal number of each of the diffractive annular zones obtained by counting each diffractive annular zone in such a manner that a diffractive annular zone including the optical axis is counted as a first diffractive annular zone and other diffractive annular zone are counted respectively in consecutive order from the optical axis toward the peripheral portion; h is a distance between a point on the diffractive relief and X axis in a direction perpendicular to X axis, wherein X axis locates on the optical axis; x is a distance between the point and H axis in a direction parallel to X axis, wherein H axis is perpendicular to X axis at an original point predetermined on X axis; hi is a distance from X axis to a border between i-th diffractive annular zone and (i+1)-th diffractive annular zone which are counted from the optical axis in the above manner, provided that h0=0; f(h) is a function of h to obtain a shape of the diffractive relief; hti is a constant in which at least one of hti is not zero; and S is a term characterizing an aspherical surface, and wherein f(h) is a following conditional formula (3): f&af;(h-hti)=(h-hti)2/rti1+1-(h-hti)2/rti2+xti-rti(3)â€ƒwhere rti is a constant and xti is a constant.