| 摘要 |
PURPOSE: To obtain an endoscopic objective lens which is wide in visual field angle, short in the overall length of the lens, long in back focus and excellent in optical performance. CONSTITUTION: This endoscopic objective lens is composed, successively from an object side, of a first divergent lens 11, a brightness diaphragm, a second convergent lens 12 and a third convergent lens 13 consisting of a combined lens of a positive lens and a negative lens or the negative lens and the positive lens and satisfies the following conditions:ν1 >45, -0.8<f/f1 <-0.5, 0.8<|r6 /f|<2.0,|ν3 -ν4|>25, 0.4<d2 /f<1.2, 1.5<LD/f<2.5, -10<r3 /f<-1.0, whereν1 : the Abbe number of the first divergent lens 11, f f1 : the focal length of the entire system and the first divergent lens 11, r6 : the radius of curvature of the combined face of the third convergent lens 13, d2 : the central thickness of the second convergent lens 12, LD: the focal length of the first divergent lens 11 and the third convergent lens 13, r3 : the radius of curvature of the object side face of the second convergent lens 12.
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