| 摘要 |
An optical system for an endoscope includes a negative lens-group, an aperture diaphragm and a positive lens-group in this order from an object side, wherein the negative lens-group includes a negative first-lens and a negative second-lens in this order from the object side; and wherein the optical system meets conditional expressions (1) and (2): 0.05<H(100)×(nd01-1)/Rf01<0.38(1) and 0.5<enp/FL<2.5(2), where: H(100) is a height at which a principal ray with a field angle of incidence of 100 degrees falls on a surface on the object side of the first lens; Rf01 is a curvature radius of the surface on the object side of the first-lens; nd01 is a refractive index of the first-lens; FL is a focal length of an entire system; and enp is a distance between an entrance pupil and the surface on the object side of the first lens.
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