Patent ID: 7755852

Claim:
An optical element molding method, comprising: heating and pressing a molding material plural times when molding an optical element having a radius of curvature R smaller than r, wherein r denotes a radius of a sphere having the same volume as the optical element to be molded, wherein the optical element has at least one convex surface, and a shape of the optical element is expressed by the following expression which is defined in a coordinate system in which an optical axis of the optical element is defined as a Z axis and a plane which is tangential to a vertex of the convex surface and which is perpendicular to the optical axis is defined as an X-Y plane, an X axis being orthogonal to the Z axis and a Y axis being orthogonal to the Z axis and the X axis: Z L (ρ)= Cρ 2 /(1+√{square root over (1 −KC 2 ρ 2 )})+Σ B i ρ i (1) where Z L (ρ) denotes a length of a perpendicular line being drawn from a point, which is on the convex surface and which has a distance ρ from the optical axis, to the tangential surface, ρ denotes the distance from the optical axis and is expressed by √{square root over (x 2 +y 2 )}, C denotes a curvature of the convex surface and is expressed by 1/R R denotes a radius of curvature of the convex surface, K denotes a constant, B i denotes an i-th order aspheric coefficient, and i denotes a natural number equal to or larger than three, a shape of a surface of the sphere is expressed by the following expression which is defined in a coordination system in which a central axis of the sphere is defined as a Z axis and a plane which is tangential to a vertex of the surface of the sphere and which is perpendicular to the central axis is defined as an X-Y plane, an X axis being orthogonal to the Z axis and a Y axis being orthogonal to the Z axis and the X axis: Z P (ρ)= cρ 2 /(1+√{square root over (1 −c 2 ρ 2 )}) (2) where Z P (ρ) denotes a length of a perpendicular line being drawn from a point, which is on the surface of the sphere and which has a distance ρ from the central axis, to the tangential surface, ρdenotes the distance from the central axis and is expressed by √{square root over (x 2 +y 2 )}, c denotes a curvature of the surface of the sphere and is expressed by 1/r, and r denotes the radius of the sphere, and ΔZ 0 which is expressed by Z L0 -Z P0 is equal to or larger than 25 μm, where ρ B0 is ρ that satisfies the following expression: dZ L (ρ)/ dρ=dZ P (ρ)/ dρ (3) Z L0 is expressed by Z L (ρ B0 ), and Z P0 is expressed by Z P (ρ B0 ).