| 摘要 |
PROBLEM TO BE SOLVED: To obtain a wide-angle retrofocus type objective lens for an endoscope capable of being applied to side vision and excellently correcting transverse chromatic aberration by satisfying specified conditions. SOLUTION: This lens is constituted of a front group diverging lens group, a brightness diaphragm, a positive lens and a rear group converging lens group including a bonding lens obtained by bonding a positive lens and a negative lens in order from an object side. It satisfies conditions|R1 /R2|<=1, R1 >0, 0.64<|fa /fb|<1.45,νa /νb and na /nb . In the expressions, R1 and R2 express the radius of curvature of the surfaces on the object side and an image side of the positive lens positioned just behind the diaphragm in the rear group converging lens group. fa and fb , na and nb , andνa andνb express the focal distances of the positive lens and the negative lens of the bonded lens in the rear group converging lens group, respectively.
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