SPHERICAL ABERRATION CORRECTION PROPER POSITION SEARCH DEVICE AND SPHERICAL ABERRATION CORRECTION PROPER POSITION SEARCH METHOD

摘要

A focus error amplitude obtainer obtains the amplitude of a focus error signal. An error amplitude difference calculator calculates the error amplitude difference, which is the difference of the amplitude in each different position within a movement range of a spherical aberration correction unit. A proper position search controller performs overall control over a spherical aberration correction unit mobile controller, the focus error amplitude obtainer, and the error amplitude difference calculator. A proper position search controller determines a proper position of the spherical aberration correction unit on the basis of the error amplitude difference.