| 摘要 |
PURPOSE: To enable inexpensive working and correcting of chromatic aberrations without using embedded lenses and to improve flatness by providing the above objective lens system with first to forth lens groups and constituting the lens system so as to satisfy specific conditions. CONSTITUTION: This objective lens system consists, successively from an object side, a parallel flat plate L11, the first lens group G1 consisting of a lens L12 and positive meniscus lens of which the concave faces are directed to the object side, the second and third lens groups G2, G3 respectively having positive and negative refracting powers as a whole and the fourth lens group G4 having a combined lens of a positive lens and negative lens L42 and having the negative refracting power as a whole. The objective lens system is so constituted as to satisfy the conditions [(Nla'F)/rl(7)0.06,|(N1a.F)/r2|<=10.06, 0.3<|r3 /(NIL-.F)1<0.4, 6<|f12/F1+|f42/F|<9 where the composite focal length of the entire lens system is defined as F, the radii of curvature of the object side face and image side face of the parallel flat plate Lll and the object side concave face of the lens L12 are respectively defined as r1, r2, r3, the refractive index of the parallel flat plate L11 is defined as Nla, the refractive index of the lens L12 as Nib and the focal lengths of the lenses 112, L42 are respectively defined as f12, f42.
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