Patent ID: 7561499

Claim:
A light focusing optical system comprising: a diffraction element and lens with which light for recording to and/or reproducing from a plurality of optical recording media of different kinds is focused onto the optical recording media, said diffraction element including two elements in physical contact, said two elements in contact along a boundary surface, wherein said diffraction element has at least first and second diffractive surfaces; said first diffractive surface diffracts light whose wavelength is 630 nm or more and 670 nm or less to perform aberration correction on an optical recording medium whose cover layer on which light is incident has a thickness of approximately 0.6 mm; and said second diffractive surface diffracts light whose wavelength is 400 nm or more and 415 nm or less to perform aberration correction on an optical recording medium whose cover layer on which light is incident has a thickness of approximately 0.1 mm or approximately 0.6 mm, one of said first and second diffractive surfaces is the boundary surface, a surface of one of the two elements being an aspheric surface with a negative refractive power.