Patent ID: 7613096

Claim:
A converging optical element for use in an optical pickup apparatus reproducing and/or recording information on a first optical disc having a protective substrate with a thickness t 1 (mm) using a first light flux with a wavelength λI (nm) emitted by a first light source, reproducing and/or recording information on a second optical disc having a protective substrate with a thickness t 2 (mm) using a second light flux with a wavelength λ 2 (nm) emitted by a second light source, and reproducing and/or recording information on a third optical disc having a protective substrate with a thickness t 3 (mm) using a third light flux with a wavelength λ 3 (nm) emitted by a third light source, the converting optical element comprising: a phase structure arranged on at least one surface of the converging optical element, wherein the thicknesses t 1 , t 2 and t 3 satisfy t 1 ≦t 2 <t 3 , when m 3 is an optical system magnification of the converging optical element for an effective light flux which is necessary for recording or reproducing information on the third disc and f 3 is a focal length of the converging optical element for the third light flux, the focal length f 3 satisfies 0.01 <|m 3|×( t 3− t 1)/ f 3<0.03, and the converging optical element satisfies 0.03< |SC max|/ f< 0.05 where SCmax is an amount of an offence against sine condition on an edge of an effective diameter of the converging optical element when the pickup apparatus reproduces or records information on the third disc using a finite coniugated system, and f is a focal length of the converging optical system for a light flux emitted by one of the first to third light sources and passing through a position which is on a principal plane of the converging optical element and is located away from the optical axis by a distance H in a perpendicular direction to the optical axis.