Patent ID: 8556416

Claim:
A diffractive multifocal lens, having an annular diffraction pattern for exhibiting a light diffraction effect, which is formed concentrically repeatedly on a surface of a lens, wherein a diffraction phase structure of the diffraction pattern has a structure expressed by the following formula: ϕ ⁡ ( ξ ) = { p 1 ⁢ ξ , 0 ≤ ξ < w p 2 ⁡ ( ξ - 0.5 ) - q ⁢ ⁢ π , w ≤ ξ < 1 - w p 1 ⁡ ( ξ - 1 ) , 1 - w ≤ ξ ≤ 1 ( 1 ) wherein each symbol is as follows: ξ indicates a position in a radial direction of the lens in one period of the diffraction pattern, having values from 0 to 1; w indicates a position where a form of the formula of φ(ξ) is changed; φ(ξ) indicates a value (radian) of a phase shift amount of light passing through the position of ξ from the phase of light passing through a reference plane; p 1 indicates a value defining a gradient of a straight line φ(ξ), when satisfying 0≦ξ<w, and 1−w≦ξ≦1; p 2 indicates a value defining the gradient of the straight line φ(ξ) when satisfying w≦ξ<1−w; and q indicates a parallel moving amount over the reference plane of the straight line φ(ξ) when satisfying w≦ξ<1−w.