OBJECTIVE LENS FOR OPTICAL PICKUP DEVICE, OPTICAL PICKUP DEVICE, AND OPTICAL INFORMATION RECORD/PLAY DEVICE

摘要

Disclosed is an objective lens wherein an effective diameter f1 (mm) when a first optical disc is in use satisfies formula (1), wherein it is possible to ensure an adequate working distance when a third optical disc is in use by increasing the number of annular sections and increasing the paraxial power of the diffraction. It is further possible to increase efficiency of usage of light that passes through a central region by minimizing the step difference dt (nm) of a first optical path difference giving structure such that formula (2) is satisfied, and it is possible moreover, to shift a light focus location of a third light beam that passes through the central region without superpositioning an optical path difference giving structure having an aperture stop function in the central region, thereby allowing the step difference dt of a second optical path difference giving structure to be minimized such that the formula (2) is satisfied as a result: 1.9 = f1 = 3.0 (1); dt < 5.0 × ?1/(n1-1) (2); wherein n1 is the refraction of the objective lens on a first wavelength.