Patent ID: 7170831

Claim:
An method for measuring an astigmatism of an optical pickup which applies a light beam converged by an objective lens to a recording medium, the method comprising: a first step of finding a first position in an advancing direction of the light beam, which first position causes the beam diameter of the light beam to become minimum in a first direction orthogonal to the advancing direction of the light beam; a second step of finding a second position in an advancing direction of the light beam, which second position causes the beam diameter of the light beam to become minimum in a second direction orthogonal to both the advancing direction of the light beam and the first direction; a third step of finding a first distance representing a difference between the first position and the second position in the advancing direction of the light beam; a fourth step of finding a third position in the advancing direction of the light beam, which third position causes the beam diameter of the light beam to become minimum in a third direction orthogonal to the advancing direction of the light beam and inclining 45 degrees from said first direction; a fifth step of finding a fourth position in said advancing direction of the light beam, which fourth position causes the beam diameter of the light beam to become minimum in a fourth direction orthogonal to both the advancing direction of the light beam and the third direction; and a sixth step of finding a second distance representing a difference between said third position and said fourth position in said advancing direction of the light beam, wherein an astigmatism of the optical pickup is measured in accordance with said first distance and said second distance.