Objective lens system for an endoscope

Claim 2

An objective lens system for an endoscope comprising a first lens component arranged as a positive meniscus lens concave toward the object side, a second lens component arranged as a positive lens, a third lens component arranged as a positive cemented doublet consisting of a positive lens element and a negative lens element cemented together, a fourth lens component arranged as a positive cemented doublet consisting of a positive lens element and a negative lens element cemented together, a fifth lens component arranged as a negative cemented doublet consisting of a negative lens element and a positive lens element cemented together, and a sixth lens component arranged as a negative cemented meniscus doublet consisting of a positive lens element and a negative lens element cemented together and arranged to be concave toward the image side, said objective lens system for an endoscope being arranged to fulfill the conditions (1), (2) and (3) shown below: 0.05/f≦(n.sub.4 -n.sub.5)/r.sub.8 ≦0.08/f (1) 0.03/f≦(n.sub.6 -n.sub.7)/r.sub.11 ≦0.06/f (2) 0.1/f≦(n.sub.9 -n.sub.8)/r.sub.14 ≦0.15/f (3) where, reference symbol f represents the focal length of the lens system as a whole, reference symbols n 4 and n 5 respectively represent refractive indices of the lens elements on the object side and image size in the third lens component, reference symbols n 6 and n 7 respectively represent refractive indices of the lens elements on the object side and image side in the fourth lens component, reference symbols n 8 and n 9 respectively represent refractive indices of the lens elements on the object side and image side in the fifth lens component, reference symbol r 8 represents the radius of curvature of the cemented surface in the third lens component, reference symbol r 11 represents the radius of curvature of the cemented surface in the fourth lens component, and reference symbol r 14 represents the radius of curvature of the cemented surface in the fifth lens component.

Claim 3

An objective lens system for an endoscope according to claim 1 further fulfilling the conditions (4), (5) and (6) shown below: ν.sub.4 -ν.sub.5 ≧55 (4) ν.sub.6 -ν.sub.7 ≧50 (5) ν.sub.9 -ν.sub.8 ≧50 (6) where, reference symbols ν 4 and ν 5 respectively represent Abbe's numbers of the lens elements on the object side and image side in the third lens component, reference symbols ν 6 and ν 7 respectively represent Abbe's numbers of the lens elements on the object side and image side in the fourth lens component, and reference symbols ν 8 and ν 9 respectively represent Abbe's numbers of the lens elements on the object side and image side in the fifth lens component.

Claim 4

An objective lens system for an endoscope according to claim 2 further fulfilling the conditions (7) and (8) shown below: -5.0f≦r.sub.13 ≦-3.0f (7) 1.1f≦r.sub.18 ≦1.4f (8) where, reference symbol r 13 represents the radius of curvature of the surface on the object side of the fifth lens component, and reference symbol r 18 represents the radius of curvature of the surface on the image side of the sixth lens component.

Claim 5

An objective lens system for an endoscope according to claim 3 having the following numerical data: ______________________________________ f = 1.0, NA = 0.5, β = -27.42X, IH = 1.3435 ______________________________________ r.sub.1 = ∞ d.sub.1 = 1.385 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = ∞ d.sub.2 = 1.7313 r.sub.3 = -3.7978 d.sub.3 = 0.7756 n.sub.2 = 1.755 ν.sub.2 = 52.33 r.sub.4 = -2.5512 d.sub.4 = 0.1662 r.sub.5 = 7.9003 d.sub.5 = 1.662 n.sub.3 = 1.497 ν.sub.3 = 81.61 r.sub.6 = -4.9723 d.sub.6 = 0.4571 r.sub.7 = 6.8767 d.sub.7 = 1662 n.sub.4 = 1.43389 ν.sub.4 = 95.15 r.sub.8 = -3.4598 d.sub.8 = 0.6925 n.sub.5 = 1.64769 ν.sub. 5 = 33.80 r.sub.9 = -6.7756 d.sub.9 = 0.4155 r.sub.10 = 3.9211 d.sub.10 = 1.2742 n.sub.6 = 1.497 ν.sub.6 = 81.61 r.sub.11 = -5.464 d.sub.11 = 0.554 n.sub.7 = 1.74077 ν.sub.7 = 27.79 r.sub.12 = 10.0734 d.sub.12 = 1.2881 r.sub.13 = -4.0748 d.sub.13 = 0.4155 n.sub.8 = 1.71736 ν.sub.8 = 29.51 r.sub.14 = 1.8283 d.sub.14 = 0.831 n.sub.9 = 1.497 ν.sub.9 = 81.61 r.sub.15 = 7.9155 d.sub.15 = 0.1385 r.sub.16 = 2.1662 d.sub.16 = 1.3158 n.sub.10 = 1.7618 ν.sub.10 = 27.11 r.sub.17 = -1.795 d.sub.17 = 0.8033 n.sub.11 = 1.6935 ν.sub.11 = 53.23 r.sub.18 = 1.2922 ##STR10## ##STR11## ##STR12## ν.sub.4 -ν.sub.5 = 61.35 r.sub.13 = -4.0748 ν.sub.6 -ν.sub.7 = 53.82 r.sub.18 = 1.2922 ν.sub.9 -ν.sub.8 = 52.1 ______________________________________ where, reference symbols r 1 through r 18 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 17 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, reference symbol β represents the magnification, and reference symbol IH represents the image height.

Claim 6

An objective lens system for an endoscope according to claim 3 having the following numerical data: ______________________________________ f = 1.0, NA = 0.5, β = -30.828X, IH = 1.5461 ______________________________________ r.sub.1 = ∞ d.sub.1 = 2.391 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = ∞ d.sub.2 = 1.5462 r.sub.3 = -4.4486 d.sub.3 = 0.8927 n.sub.2 = 1.755 ν.sub.2 = 52.33 r.sub.4 = -3.3053 d.sub.4 = 0.1914 r.sub.5 = 8.2555 d.sub.5 = 1.9128 n.sub.3 = 1.49782 ν.sub.3 = 66.83 r.sub.6 = -5.2121 d.sub.6 = 0.526 r.sub.7 = 6.5355 d.sub.7 = 1.9128 n.sub.4 = 1.43389 ν.sub.4 = 95.15 r.sub.8 = -3.662 d.sub.8 = 0.797 n.sub.5 = 1.65016 ν.sub.5 = 39.39 r.sub.9 = -7.9534 d.sub.9 = 0.4781 r.sub.10 = 4.323 d.sub.10 = 1.4665 n.sub.6 = 1.497 ν.sub.6 = 81.61 r.sub.11 = -5.534 d.sub.11 = 0.6377 n.sub.7 = 1.74077 ν.sub.7 = 27.79 r.sub.12 = 12.0791 d.sub.12 = 1.7534 r.sub.13 = -3.905 d.sub.13 = 0.4781 n.sub.8 = 1.71736 ν.sub.8 = 29.51 r.sub.14 = 1.6997 d.sub.14 = 0.9555 n.sub.9 = 1.497 ν.sub.9 = 81.61 r.sub.15 = 4.7794 d.sub.15 = 0.1572 r.sub.16 = 2.0721 d.sub.16 = 1.5129 n.sub.10 = 1.7618 ν.sub.10 = 27.11 r.sub.17 = -2.3009 d.sub.17 = 0.9227 n.sub.11 = 1.6935 ν.sub.11 = 53.23 r.sub.18 = 1.3757 ##STR13## ##STR14## ##STR15## ν.sub.4 -ν.sub.5 = 55.76 r.sub.13 = -3.905 ν.sub.6 -ν.sub.7 = 53.82 r.sub.18 = 1.3757 ν.sub.9 -ν.sub.8 = 52.1 ______________________________________ where, reference symbols r 1 through r 18 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 17 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, reference symbol β represents the magnification, and reference symbol IH represents the image height.

Claim 7

An objecitve lens system for an endoscope according to claim 3 having the following numerical data: ______________________________________ f = 1.0, NA = 0.5, β = -40X, IH = 1.4176 ______________________________________ r.sub.1 = ∞ d.sub.1 = 2.006 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = ∞ d.sub.2 = 0.9168 r.sub.3 = -3.4978 d.sub.3 = 0.6996 n.sub.2 = 1.72916 ν.sub.2 = 54.68 r.sub.4 = -2.3121 d.sub.4 = 0.1337 r.sub.5 = 7.486 d.sub.5 = 1.1114 n.sub.3 = 1.497 ν.sub.3 = 81.61 r.sub.6 = -4.8326 d.sub.6 = 0.403 r.sub.7 = 5.9694 d.sub.7 = 1.4327 n.sub.4 = 1.43389 ν.sub.4 = 95.15 r.sub.8 = -3.2278 d.sub.8 = 0.4307 n.sub.5 = 1.64769 ν.sub.5 = 33.8 r.sub.9 = -5.5916 d.sub.9 = 0.4042 r.sub.10 = 3.934 d.sub.10 = 1.2198 n.sub.6 = 1.497 ν.sub.6 = 81.61 r.sub.11 = -5.3503 d.sub.11 = 0.4952 n.sub.7 = 1.74077 ν.sub.7 = 27.79 r.sub.12 = 9.0002 d.sub.12 = 1.1745 r.sub.13 = -4.3317 d.sub.13 = 0.1855 n.sub.8 = 1.71736 ν.sub.8 = 29.51 r.sub.14 = 1.7362 d.sub.14 = 0.7429 n.sub.9 = 1.497 ν.sub.9 = 81.61 r.sub.15 = 14.1672 d.sub.15 = 0.1337 r.sub.16 = 2.0963 d.sub.16 = 1.1649 n.sub.10 = 1.7618 ν.sub.10 = 27.11 r.sub.17 = -1.7501 d.sub.17 = 0.7362 n.sub.11 = 1.16935 ν.sub.11 = 53.23 r.sub.18 = 1.2259 ##STR16## ##STR17## ##STR18## ν.sub.4 -ν.sub.5 = 61.35 r.sub.13 = -4.3317 ν.sub.6 -ν.sub.7 = 53.82 r.sub.18 = 1.2259 ν.sub.9 -ν.sub.8 = 52.1 ______________________________________ where, reference symbols r 1 through r 18 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 17 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 11 respectively represent refractive indices of respective lenses, reference symbols ν 1 through ν 11 respectively represent Abbe's numbers of respective lenses, reference symbol β represents the magnification, and reference symbol IH represents the image height.