Patent ID: 7715286

Claim:
An optical pickup projecting a collected beam onto a recording surface of an optical storage medium to retrieve recorded information by means of an intensity of reflection from the recording surface, said pickup correcting a first spherical aberration in an optical system by producing at correcting means a second spherical aberration which cancels the first spherical aberration, said pickup being characterized in that: the correcting means is capable of producing at least two second spherical aberrations of different magnitudes by means of a collected beam spot on the recording surface of the optical storage medium so that the magnitudes are ¼ or more of a wavelength λ in differences between maximum of measurement values and minimum of the measurement values or 1/14 or more of a wavelength λ in standard deviation; and said pickup comprises control means which: causes the correcting means to produce the at least two second spherical aberrations of different magnitudes; calculates an optimal magnitude of aberration correction for the first spherical aberration through a numeric evaluation based on an evaluation value of a reference signal obtained by receiving reflection of intensities in the presence of the spherical aberrations of such magnitudes; and controls the correcting means to carry out correction using the optimal magnitude of aberration correction.