Patent ID: 7253968

Claim:
An objective lens for use in an optical pickup device, comprising: at least two plastic lenses of a first plastic lens having positive refractive power and a second plastic lens having positive refractive power, wherein the first plastic lens and the second plastic lens are arranged in this order from the light source side; wherein the objective lens satisfies the following expression (1-1): −0.0004<Δ3 SA /( NA 4 ·f ·(1 −m ))<0.0004 (1-1) where Δ3SA (λRMS) represents a rate of change of a third order spherical aberration of the objective lens when the temperature of an entire body of the objective lens uniformly changes, f (mm) represents the focal length of the objective lens for the light flux having wavelength λ, and m represents the magnification of the objective lens.