| 摘要 |
<p>Provided is an objective lens for an endoscope, suitable for a compact high pixel density image-capturing element which matches laser treatment and having a simple configuration. Also provided is an endoscope using the objective lens. An objective lens (1) for an endoscope comprises, in sequence from the object side, a front group (FG), an aperture stop (S), and a back group (BG). The front group (FG) comprises, in sequence from the object side, a negative first lens (L1) which has a concave surface facing the image side, a positive second lens (L2) which has a convex surface facing the object side and also has a flat surface or a concave surface facing the image side, and a filter (FL). The back group (BG) comprises, in sequence from the object side, a positive third lens (L3) which has a convex surface facing the object side and a joined lens (E45) which is composed of a flat-convex lens or a double-convex lens (L4) and of a negative meniscus lens (L5). The objective lens (1) for an endoscope satisfies the following conditional formula (1): (1)... n3 > -?3/12 + 5.5, where n3 is the refractive index of the third lens (L3), and ?3 is the Abbe number of the third lens (L3).</p> |
