| 摘要 |
PROBLEM TO BE SOLVED: To provide an objective lens for recording or reproducing information to/from an optical information recording medium, which can cope with high numerical aperture and short wavelength, which is made light in weight and inexpensive and whose axial chromatic aberration is excellently compensated; to provide a condensing optical system capable of effectively compensating the fluctuation of spherical aberration caused on the respective optical surfaces of an optical pickup device caused by the change of the oscillation wavelength of a laser beam source, the change of temperature and humidity and errors in the thickness of the transparent base plate of the optical information recording medium with simple constitution and the optical pickup device; and to provide an objective lens, the condensing optical system and the optical pickup device for recording or reproducing information to a plurality of optical information recording media whose transparent base plates are different in thickness. SOLUTION: This objective lens for recording and/or reproducing information to/ from the optical information recording medium is a single lens having zonal diffraction structure at least, on one surface, having at least one aspherical surface, and formed of plastic material, and satisfies and of following expressions. NA>=0.7, λ<=500 nm, 5.0<=fD/f<=40.0, 0.03<=λ×f×Σ(ni/(Mi×Pi2))<=0.70. |
