| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective lens for an endoscope of an retro-focus type which is proper and effective even with respect to partial out-of-focus conditions, without having to increase the power of the first lens, while reducing the diameter of the endoscope, that is, while further reducing the diameter of the objective lens for the endoscope. <P>SOLUTION: This objective lens for the endoscope is constituted of a front group of lenses G1, having negative refractive power on the whole and a rear group of lenses G2, having restriction on the brightness and positive refractive power as a whole which are arranged in this order from an object side. The front group of lenses G1 are constituted of the first lens L1, having negative refractive power and a group of second lenses (lenses L2), having a surface which is closest to the image side and directing a concave surface to the image side and having positive refractive power as a whole which are arranged, in this order starting from the object side. This objective lens satisfies the expression (1): ¾f<SB>0</SB>/f<SB>1</SB>¾≤1.1 (where f<SB>0</SB>is the composite focal length of the front group of lenses G1, and f<SB>1</SB>is the focal distance of the first lens L1). <P>COPYRIGHT: (C)2010,JPO&INPIT |
