| 摘要 |
PURPOSE:To obtain a condenser lens for an optical disc by which a substantial working distance is obtained even at F=3mm. in an aspherical plastic lens of one group and one element by satisfying prescribed conditions and providing a flat part on the outside circumferential edge of the effective diameter on the aspherical face. CONSTITUTION:The conditions (1) 0.3<d/f<0.65, (2) 0.6<(C0+2C1).(n-1)f<1 are satisfied where (d) is designated as the thickness of the lens, (f) the focal length of the lens, (n) the refractive index of the lens at 800nm wavelength, C0 the reference curvature of the aspherical phase and C1 the coefft. of the secondary aspherical phase, in an aspherical face plastic lens of one group and one element constituted of the aspherical face of which the 1st face and the 2nd face both have positive refracting power. A plane part is provided at both ends 2' of the 1st face or the 2nd face 2 of the plastic lens 1, then even if a deviation arises in the fitting between a holder 3 and the lens, the influence thereof on the aberration performance is eliminated simply by moving both in parallel. |
