Retrofocus-type objective for an endoscope

Claim 2

A retrofocus-type objective for an endoscope comprising a first lens component comprising a negative lens, a stop, a second lens component comprising a positive meniscus lens arranged to be concave toward the object side, a third lens component comprising a positive lens, a fourth lens component comprising a cemented doublet consisting of a positive lens and a negative lens, and a fifth lens component comprising a positive lens in the order from the object side, said retrofocus-type objective being arranged to be focused by advancing said third lens component and said fourth lens component and, moreover, to fulfill the conditions (1) and (2) shown below: ##EQU3## where reference symbol f 1 represents the focal length of the first lens component, reference symbol f 2 represents the total focal length of the second through the fifth lens components, and reference symbol f a represents the focal length of the lens system as a whole when focused on an object at a short distance, said objective further satisfying the following conditions: D/f.sub.a <0.7 (3) where reference symbol D represents the airspace between the first and second lens components, and further fulfilling the conditions (4), (5) and (6) shown below: ##EQU4## where reference symbol r 1 represents the radius of curvature of the surface on the object side of the first lens component, reference symbol r 4 represents the radius of curvature of the surface on the object side of the second lens component, reference symbol r 6 represents the radius of curvature of the surface of the object side of the third lens component, and reference symbol r 10 represents the radius of curvature of the surface on the image side of the fourth lens component.

Claim 3

A retrofocus-type objective for an endoscope according to claim 1 having the following numerical data: ______________________________________ r.sub.1 = 2.6667 d.sub.1 = 0.1994 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.3493 d.sub.2 = 0.4274 r.sub.3 = ∞ (stop) d.sub.3 = 0.1083 r.sub.4 = -1.0188 d.sub.4 = 0.4387 n.sub.2 = 1.51633 ν.sub.2 = 64.15 r.sub.5 = -0.6439 d.sub.5 = 0.1673 (variable) r.sub.6 = 2.9248 d.sub.6 = 1.1453 n.sub.3 = 1.51633 ν.sub.3 = 64.15 r.sub.7 = -2.0177 d.sub.7 = 0.1766 r.sub.8 = 1.4803 d.sub.8 = 1.2137 n.sub.4 = 1.51633 ν.sub.4 = 64.15 r.sub.9 = -1.0849 d.sub.9 = 0.7123 n.sub.5 = 1.84666 ν.sub.5 = 23.78 r.sub.10 = 5.3578 d.sub.10 = 0.7729 (variable) r.sub.11 = 3.6279 d.sub.11 = 0.4217 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ ______________________________________ f.sub.a = 1.0, NA = -0.00972, image height = 0.54986 f.sub.1 /f.sub.a = -0.8017, f.sub.2 /f.sub.a = 1.1698 D/f.sub.a = 0.5356, r.sub.1 /f.sub.a = 2.6667 r.sub.4 /f.sub.a = -1.0188, R = 1.89 ______________________________________ object distance magnification d.sub.5 d.sub.10 ______________________________________ 14.2450 -0.059 0.7123 0.2279 1.5385 -0.563 0.1673 0.7729 ______________________________________ where, reference symbols r 1 through r 12 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 11 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 6 respectively represent refractive indices of respective lenses, and reference symbols ν 1 through ν 6 respectively represent Abbe's numbers of respective lenses.

Claim 4

A retrofocus-type objective for an endoscope according to claim 1 having the following numeral data: ______________________________________ r.sub.1 = 2.8409 d.sub.1 = 0.1988 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.3615 d.sub.2 = 0.4257 r.sub.3 = ∞ (stop) d.sub.3 = 0.1705 r.sub.4 = -1.0429 d.sub.4 = 0.4372 n.sub.2 = 1.51633 ν.sub.2 = 64.15 r.sub.5 = -0.6563 d.sub.5 = 0.1705 (variable) r.sub.6 = 2.4944 d.sub.6 = 1.0228 n.sub.3 = 1.51633 ν.sub.3 = 64.15 r.sub.7 = -2.2139 d.sub.7 = 0.1763 r.sub.8 = 1.4502 d.sub.8 = 1.2104 n.sub.4 = 1.51633 ν.sub.4 = 64.15 r.sub.9 = -0.9766 d.sub.9 = 0.5683 n.sub.5 = 1.84666 ν.sub.5 = 23.78 r.sub.10 = 3.6813 d.sub.10 = 0.767 (variable) r.sub.11 = 2.7899 d.sub.11 = 0.4207 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ ______________________________________ f.sub.a = 1.0, NA = -0.00985, image height = 0.54830 f.sub.1 /f.sub.a = -0.825, f.sub.2 /f.sub.a = 1.1045 D/f.sub.a = 0.5962, r.sub.1 /f.sub.a = 2.8409 r.sub.4 /f.sub.a = -1.0429, R = 1.49 ______________________________________ object distance magnification d.sub.5 d.sub.10 ______________________________________ 14.2045 -0.058 0.7102 0.2273 1.53409 -0.566 0.1705 0.7670 ______________________________________ where, reference symbols r 1 through r 12 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 11 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 6 respectively represent refractive indices of respective lenses, and reference symbols ν 1 through ν 6 respectively represent Abbe's numbers of respective lenses.

Claim 5

A retrofocus-type objective for an endoscope according to claim 1 having the following numerical data: ______________________________________ r.sub.1 = 3.6957 d.sub.1 = 0.1989 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.3701 d.sub.2 = 0.4676 r.sub.3 = ∞ (stop) d.sub.3 = 0.1272 r.sub.4 = -1.4476 d.sub.4 = 0.3888 n.sub.2 = 1.51633 ν.sub.2 = 64.15 r.sub.5 = -0.6918 d.sub.5 = 0.1708 (variable) r.sub.6 = 3.2891 d.sub.6 = 0.6936 n.sub.3 = 1.51633 ν.sub.3 = 64.15 r.sub.7 = -2.0554 d.sub.7 = 0.4029 r.sub.8 = 1.5486 d.sub.8 = 1.2372 n.sub.4 = 1.51633 ν.sub.4 = 64.15 r.sub.9 = -1.0511 d.sub.9 = 0.3899 n.sub.5 = 1.84666 ν.sub.5 = 23.78 r.sub.10 = 19.7115 d.sub.10 = 0.7667 (variable) r.sub.11 = 3.7001 d.sub.11 = 0.6818 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ ______________________________________ f.sub.a = 1.0, NA = -0.00966, image height = 0.54830 f.sub.1 /f.sub.a = -0.8131, f.sub.2 /f.sub.a = 1.1386 D/f.sub.a = 0.5948, r.sub.1 /f.sub.a = 3.6959 r.sub.4 /f.sub.a = -1.4476, R = 2.82 ______________________________________ object distance magnification d.sub.5 d.sub.10 ______________________________________ 14.20454 -0.060 0.7101 0.2274 1.53409 -0.561 0.1708 0.7667 ______________________________________ where, reference symbols r 1 through r 12 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 11 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols n 1 through n 6 respectively represent refractive indices of respective lenses, and reference symbols ν 1 through ν 6 respectively represent Abbe's number of respective lenses.

Claim 6

A retrofocus-type objective for an endoscope according to claim 1 having the following numerical data: ______________________________________ r.sub.1 = 1.9989 d.sub.1 = 0.1714 n.sub.1 = 1.51633 ν.sub.1 = 64.15 r.sub.2 = 0.3480 d.sub.2 = 0.4689 r.sub.3 = ∞ (stop) d.sub.3 = 0.1389 r.sub.4 = -1.2988 d.sub.4 = 0.3433 n.sub.2 = 1.6968 ν.sub.2 = 55.52 r.sub.5 = -0.6881 d.sub.5 = 0.1694 (variable) r.sub.6 = 52.6913 d.sub.6 = 0.5319 n.sub.3 = 1.6968 ν.sub.3 = 55.52 r.sub.7 = -1.8710 d.sub.7 = 0.2159 r.sub.8 = 2.3843 d.sub.8 = 0.9709 n.sub.4 = 1.7130 ν.sub.4 = 53.84 r.sub.9 = -0.8613 d.sub.9 = 0.4555 n.sub.5 = 1.78472 ν.sub.5 = 25.71 r.sub.10 = 1.8834 d.sub.10 = 0.7814 (variable) r.sub.11 = 1.4427 d.sub.11 = 0.7476 n.sub.6 = 1.51633 ν.sub.6 = 64.15 r.sub.12 = ∞ ______________________________________ f.sub.a = 1.0, NA = -0.00959, image height = 0.55682 f.sub.1 /f.sub.a = -0.8458, f.sub.2 /f.sub.a = 1.2798 D/f.sub.a = 0.6078, r.sub.1 /f.sub.a = 1.9989 r.sub.4 /f.sub.a = -1.2988, R = 1.82 ______________________________________ object distance magnification d.sub.5 d.sub.10 ______________________________________ 14.27755 -0.057 0.7377 0.2130 1.54198 -0.533 0.1694 0.7813 ______________________________________ where, reference symbols r 1 through r 12 respectively represent radii of curvature of respective lens surfaces, reference symbols d 1 through d 11 respectively represent thicknesses of respective lenses and airspaces between respective lenses, reference symbols. n 1 through n 6 respectively represent refractive indices of respective lenses, and reference symbols ν 1 through ν 6 respectively represent Abbe's numbers of respective lenses.