| 摘要 |
There is provided an objective lens used for an optical information recording/reproducing device for recording information to and/or reproducing information from two types of optical discs, by selectively using one of two types of substantially collimated light beams including first and second light beams. When wavelengths of the first and second light beams are respectively represented by λ1 (nm) and λ2 (nm), λ1<λ2 is satisfied. The objective lens includes a first optical element, and a second optical element made of material different from that of the first optical element. The first and second optical elements are cemented via a cementing surface. Further, the objective lens is configured to satisfy a condition: 0.006 < { ( nR 2 - nR 1 ) - ( nB 2 - nB 1 ) } ×   [ { ( k 2 r 2 3 ) + 8 × A 42 } × f 1 3 + 2.29 ] < 0.038 . ( 1 )
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