| 摘要 |
An objective lens for an endoscope includes a first lens group having one negative lens, a second positive lens group having at least one positive lens, and a third positive lens group having a cemented lens consisting of one positive lens and a negative lens adhered thereto. The objective lens satisfies the requirements defined by the following relationships: theta g,d<-2.223x10-3x nu d+1.365; and, -1.2<f1/f<-0.8, wherein theta g,d=(ng-nd)/(nF-nC), ng represents the refractive index of the glass material of the first lens at the g-line, nd represents the refractive index of the glass material of the first lens at the d-line, nF represents the refractive index of the glass material of the first lens at the F-line, nC represents the refractive index of the glass material of the first lens at the C-line, nu d represents the Abbe number of the glass material of the first lens, f1 represents the focal length of the first lens, and f represents the focal length of the whole lens system.
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