| 摘要 |
PROBLEM TO BE SOLVED: To provide a simple and compact information pickup device which is capable of reproducing optical disks having different thicknesses of substrates with one optical pickup and has structure having compatibility with other ones and less in power consumption and to provide its objective lens. SOLUTION: This device is provided with a laser beam source and an objective lens 6 converging luminous fluxes from the laser beam source on information recording surface 81, 82 of optical information recording mediums. In this case, as to two kinds of different transparent substrates, when thicknesses of the substrates from surfaces of the lens 6 side to recording surfaces are defined as t1A (mm), t2A (mm), refractive indexes of the substrates n1, n2, distances from recording surfaces to surfaces of the opposite sides t1B (mm), t2B (mm) and image-forming magnifications of lens 6 for incident luminous fluxes on the lens 6 m1, m2 and satisfying t1A≠t2A and/or t1B≠t2B and further the focal length of the lens 6 is define as f (mm), the divergence changing means of an incident light on the lens 6 satisfying an equation, |(m1-m2)f+(1-1/n1)t1 A-(1-1/n2) t2A+t1B-t2B|<0.25(mm) is provided. |
