Aberration compensating apparatus and method

An aberration compensating apparatus for compensating an aberration occurring in a light beam, said light beam being applied to a recording medium and reflected by said recording medium through an optical path of an optical system, comprising:

• a liquid crystal unit including a first electrode layer having a plurality of divisional electrodes electrically separated from each other in the same plane and a second electrode layer, and a liquid crystal element provided between said first and second electrode layer which provides a light beam passing therethrough with a phase change when an electric field is applied;
• a detector for receiving the reflected light beam through said liquid crystal unit to generate a detection signal;
• a voltage generator for generating voltages to be applied to each of the plurality of divisional electrodes;
• and
• a controller for performing compensation control for said aberration by changing the applied voltages to each of the divisional electrodes with reference to an applied reference voltage to a predetermined divisional electrode of said first electrode layer,
• wherein said controller determines the applied reference voltage based on an amplitude change of said detection signal when the applied voltage to each of the plurality of the divisional electrodes are changed.