| 摘要 |
PROBLEM TO BE SOLVED: To shorten the overall length of the above objective lens, to reduce its outside diameter and to well correct various aberrations inclusive of chromatic aberration while satisfying the basic requirements of the objective lens of an endoscope that its visual field angle is wide by forming the lens on the extreme image side in the fourth lens group of a meniscus lens having a concave face on the image side. SOLUTION: This endoscopic objective lens is composed, successively from an object side, a first lens group 11 having negative refracting power as a whole, a second lens group 12 having positive refracting power as a whole, a third lens group 13 having positive refracting power as a whole and the fourth lens group 14 having negative refracing power as a whole. The lens on the extreme image side in the fourth lens group 14 is formed of the meniscus lens having the concave face on the image side. Further, the conditions 0<=f/ra <0.7, 0<=|f/rb|0.7(rb <0) are satisfied. In the equations, (f) is the focal length over the entire system of the objective lens, ra is the radius of curvature on the extreme image side of the second lens group and rb is the radius of curvature on the extreme object side of the third lens group.
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