Patent ID: 7426170

Claim:
An objective lens for use in an optical pickup apparatus at least reproducing and/or recording information using a light flux with a wavelength λ 1 emitted by a first light source for a first optical disc having a protective substrate with a thickness t 1 and reproducing and/or recording information using a light flux with a wavelength λ 2 (1.5×λ 1 ≦λ 2 ≦1.7×λ 1 ) emitted by a second light source for a second optical disc having,a protective substrate with a thickness t 2 (0.8×t 1 ≦t 2 ), the objective lens comprising: a diffractive structure formed on at least one optical surface of the objective lens, wherein each of the light flux with the wavelength λ 1 and the light flux with the wavelength λ 2 enters the objective lens, an optical system magnification m 1 of the objective lens for the light flux with a wavelength λ 1 and an optical system magnification m 2 of the objective lens for the light flux with a wavelength λ 2 have different signs and values from each other, and the diffractive structure has a positive diffractive action.