Patent ID: 7035193

Claim:
An objective lens for recording data to and/or reproducing data from first and second optical discs, the first optical disc having a recording density higher than that of the second optical disc, a first light beam being used for the first optical disc, a second light beam being used for the second optical disc, the second light beam having a wavelength longer than that of the first light beam, the objective lens comprising at least one surface including a plurality of annular zones divided by steps, the steps having functions of phase shifting a wavefront of light passing through the plurality of annular zones so that a beam spot formed at a converging point of an average wavefront of the wavefront phase shifted by the steps is used for recordation and/or reproduction for the first and second optical discs, the plurality of annular zones of the at least one surface including at least one annular zone structure, the at least one annular zone structure including: first and second annular zone groups each of which has at least three steps for phase shifting the wavefront in a first direction; and a first return step which is a step formed at a boundary between the first and second annular zone groups, the first return step phase shifting the wavefront in a second direction opposite to the first direction, wherein an absolute value |Δψ1| of a phase shifting amount of the first light beam given by the first return step satisfies a condition: 6π<|Δψ1|<14π (1), wherein the absolute value Δψ1| of the phase shifting amount of the first light beam given by the first return step is smaller than larger one of an absolute value of a sum of phase shift amounts given by the first annular zone group and an absolute value of a sum of phase shift amounts given by the second annular zone group.