Patent ID: 6995909

Claim:
A convex lens for allowing luminous flux from a first light source to converge to a first optical information recording medium having a predetermined thickness and allowing luminous flux from a second light source having a wavelength different from the first light source to converge to a second optical information recording medium which is thicker than the first optical information recording medium, characterized in that said lens comprises: a central area close to the central axis of said luminous flux; a peripheral area far from said central axis; and an intermediate area located midway between said central area and said peripheral area, and the luminous flux converging onto the information recording surface of said first optical information recording medium from said first light source is the luminous flux that has passed through said central area, said intermediate area and said peripheral area, the luminous flux converging onto the information recording surface of said second optical information recording medium from said second light source is the luminous flux that has passed through said intermediate area and said central area, said central area provides only a refraction effect; and said intermediate area is provided with a diffraction grating, characterized in that the diffraction grating of the intermediate area, using diffracted light of the same order, forms luminous flux from the first light source into a reduced wavefront aberration with respect to the first optical information recording medium and forms luminous flux from the second light source into a reduced wavefront aberration with respect to the second optical information recording medium.