Ojective lens for endoscope

Abstract

An objective lens particularly suitable for use in endoscope, employing a lens system which is composed of four single lenses, namely, composed of, from the object side, a first lens L.sub.1 consisting of a negative lens having the concave surface thereof on the object side, a second lens L.sub.2 consisting of a positive lens having a surface of smaller radius of curvature disposed on the object side, a third lens L.sub.3 consisting of a positive lens having a surface of smaller radius of curvature on the image side, and a fourth lens L.sub.4 consisting of a positive lens. In this lens construction, the respective lenses L.sub.1 to L.sub.4 are adapted to satisfy the conditions of n.sub.1 >1.70, .gamma..sub.1 >40.0, .gamma..sub.3 <42.5, n.sub.5 >1.60, .gamma..sub.5 >50.0, n.sub.7 >1.60, and .gamma..sub.7 >50.0 (where n.sub.1, n.sub.5 and n.sub.7 are refractive indices of the first lens L.sub.1, third lens L.sub.3 and fourth lens L.sub.4 relative to line d, respectively, and .gamma. .sub.1, .gamma..sub.3, .gamma..sub.5 and .gamma..sub.7 are Abbe's numbers of the first to fourth lenses L.sub.1 and L.sub.4, respectively.)

Dependencies are inferred from the claim text.