Large aperture wide angle lens system employing an aspherical surface

Claim 2

A large aperture wide angle lens which employs one aspheric surface comprising: a first lens group having a negative refractive power overall and including at least one convex lens, a second lens group having an overall positive refractive power and including at least a concave lens and a convex lens, and a third lens group of the retro-focus type having an overall positive refractive power in which a meniscus concave lens with a convex plane thereof faces an image side and is located nearest to said second group, a diaphragm interposed between said second and said third groups, at least one surface of the lenses in said third group at the rear of said diaphragm being aspheric, said aspheric surface being formed in a shape defined by X and Y which are obtained when Y is varied in the following equation: ##EQU8## wherein X represents an axis taken along the direction along which a light beam proceeds on the optical axis, Y is an axis to be perpendicular to said X - axis, Ri is the paraxial curvature radius at the vertex of the aspheric surface, Ni designates the refractive index of the medium in front of the aspheric surface, Ni' designates the refractive index of the medium at the rear of the aspheric surface, and f represents the focal distance of the overall lens system, the following conditions being satisfied by the wide angle lens; ##EQU9## wherein L represents the overall length of the lens system, f 1 designates the focal distance of the first group, f II is the focal distance of the second group and f III is the focal distance of the third group.

Claim 3

A large aperture wide angle lens as in claim 1 in which said aspheric surface is located at the image side of the meniscus concave lens in said third group.

Claim 4

A large aperture wide angle lens as described in claim 2 specially satisfying the following formulas: ##EQU10## wherein R I convex represents the radius of curvature at the image side of the convex lens in the group I while R II convex expresses the radius of curvature at the image side of the convex lens in group II.

Claim 5

A large aperture wide angle lens which employs one aspheric surface comprising: a first group having negative refractive power; a second group having positive refractive power; a third group having positive refractive power said three groups being arranged in sequence from the object direction to form a retro-focus type lens having a diaphragm interposed between said second and said third groups said first group being composed of a meniscus concave lens having a convex surface facing the object direction, a convex lens, and a meniscus concave lens having a convex surface facing the object direction, said second group having a biconvex lens and a concave lens and said third group having a meniscus concave lens composed of a concave lens and convex lens and with its convex plane facing the image side, at lease one surface of the lenses in said third group being aspheric and having a shape which is given by X and Y obtained when Y varies as in the following formulas: ##EQU11## wherein Xrepresents an axis along the direction of the light beam on the optical axis, Y is an axis perpendicular to the X - axis, Ri designates the paraxial curvature radius at the vertex of the aspheric surface, Ni is the refractive index of the medium in front of the aspheric surface while Ni' denotes the refractive index of the medium at the rear of the aspheric surface, and f is the focal distance of the whole lens system.

Claim 6

A large aperture wide angle lens which employs one aspheric surface comprising: a first group having negative refractive power; a second group having positive refractive power; a third group having positive refractive power said three groups being arranged in sequence from the object direction to form a retro-focus type lens having a diaphragm interposed between said second and said third groups said first group being composed of a meniscus concave lens having a convex surface facing the object direction, a convex lens, and a meniscus concave lens having a convex surface facing the object direction, said second group having a biconvex lens and a concave lens and said third group having a meniscus concave lens composed of a concave lens and convex lens and with its convex plane facing the image side, at lease one surface of the lenses in said third group being aspheric and having a shape which is given by X and Y obtained when Y varies as in the following formulas: ##EQU11## wherein Xrepresents an axis along the direction of the light beam on the optical axis, Y is an axis perpendicular to the X - axis, Ri designates the paraxial curvature radius at the vertex of the aspheric surface, Ni is the refractive index of the medium in front of the aspheric surface while Ni' denotes the refractive index of the medium at the rear of the aspheric surface, and f is the focal distance of the whole lens system.

Claim 7

A large aperture wide angle lens as in claim 4, in which said aspheric surface is a surface at the image side of the meniscus concave lens in said third group III.

Claim 8

A large aperture wide angle lens as in claim 5, wherein said second group is composed of a biconvex lens disposed toward the object direction and the biconcave lens disposed at the image side.

Claim 9

A large aperture wide angle lens as in claim 5, wherein said second group is composed of the biconcave lens disposed toward the object direction and the biconvex lens disposed toward the image direction.

Claim 10

A large aperture wide angle lens as in claim 5, wherein, substantially, ______________________________________ [f = 24.5 F 1.4 ω = ± 42°] f = 24.5 F:1.4 ω = ± 42° ______________________________________ R.sub.1 = 50.193 D.sub.1 = 1.500 N.sub.1 = 1.58913 V.sub.1 = 61.1 R.sub.2 = 22.569 D.sub.2 = 11.000 R.sub.3 = 428.240 D.sub.3 = 4.000 N.sub.2 = 1.58913 V.sub.2 = 61.1 R.sub.4 = -102.530 D.sub.4 = 2.000 R.sub.5 = 44.584 D.sub.5 = 3.000 N.sub.3 = 1.80518 V.sub.3 = 25.4 R.sub.6 = 152.276 D.sub.6 = 1.500 N.sub.4 = 1.58913 V.sub.4 = 61.1 R.sub.7 = 18.288 D.sub.7 = 10.437 R.sub.8 = 28.795 D.sub.8 = 7.000 N.sub.5 = 1.71300 V.sub.5 = 54.0 R.sub.9 = -39.264 D.sub.9 = 0.200 R.sub.10 = -117.870 D.sub.10 = 1.500 N.sub.6 = 1.58921 V.sub.6 = 41.1 R.sub.11 = 35.370 D.sub.11 = 10.681 R.sub.12 = -15.854 D.sub.12 = 1.000 N.sub.7 = 1.80518 V.sub.7 = 25.4 R.sub.13 = 99.094 D.sub.13 = 4.500 N.sub.8 = 1.77250 V.sub.8 = 49.6 R.sub.14 = -33.487* D.sub.14 = 0.150 R.sub.15 = -133.553 D.sub.15 = 5.000 N.sub.9 = 1.77250 V.sub.9 = 49.6 R.sub.16 = -25.530 D.sub.16 = 0.150 R.sub.17 = -79.919 D.sub.17 = 6.000 N.sub.10 = 1.77250 V.sub.10 = 49.6 R.sub.18 = -27.816 ______________________________________ wherein the asterisked (*) surface is an aspheric surface and wherein ______________________________________ Coefficient of aspheric surface Y X ______________________________________ B = 0.20647 × 10.sup..sup.-4 0 0 C = 0.36845 × 10.sup..sup.-7 1.225 0.02237 D = -0.80225 × 10.sup..sup.-10 2.450 0.08899 E = 0.52622 × 10.sup..sup.-13 3.675 0.19841 4.900 0.34804 6.125 0.53406 7.350 0.75115 8.575 0.99244 9.800 1.24937 11.025 1.51179 12.250 1.76822 13.475 2.00625 14.700 2.21315 f.sub.I = -43.614 f.sub.II = 44.702 f.sub.III = 33.572 Back focus = 36.500 ______________________________________

Claim 11

A large aperture wide angle lens as described in claim 5, wherein, substantially, ______________________________________ [f = 24.5 F 1.4 ω = ± 42°] f = 24.5 F:1.4 ω = ± 42° ______________________________________ R.sub.1 = 51.399 D.sub.1 = 1.500 N.sub.1 = 1.58913 V.sub.1 = 61.1 R.sub.2 =23.989 D.sub.2 = 10.500 R.sub.3 = 146.244 D.sub.3 = 4.000 N.sub.2 = 1.58913 V.sub.2 = 61.1 R.sub.4 = -123.350 D.sub.4 = 2.000 R.sub.5 = 36.242 D.sub.5 = 3.000 N.sub.3 = 1.80518 V.sub.3 = 25.4 R.sub.6 = 179.177 D.sub.6 = 1.500 N.sub.4 = 1.58913 V.sub.4 = 61.1 R.sub.7 = 16.966 D.sub.7 = 8.297 R.sub.8 = -37.872 D.sub.8 = 1.500 N.sub.5 = 1.59720 V.sub.5 = 35.6 R.sub.9 = 102.608 D.sub.9 = 0.200 R.sub.10 = 31.802 D.sub.10 = 5.500 N.sub.6 = 1.71300 V.sub.6 = 54.0 R.sub.11 = -39.227 D.sub.11 = 11.972 R.sub.12 = -15.730 D.sub.12 = 1.000 N.sub.7 = 1.80518 V.sub.7 = 25.4 R.sub.13 = 131.434 D.sub.13 = 5.742 N.sub.8 = 1.77250 V.sub.8 = 49.6 R.sub.14 = -34.176 * D.sub.14 = 0.150 R.sub.15 = -159.831 D.sub.15 = 5.000 N.sub.9 = 1.77250 V.sub.9 = 49.6 R.sub.16 = -25.585 D.sub.16 = 0.150 R.sub.17 = -60.981 D.sub.17 = 5.500 N.sub.10 = 1.77250 V.sub.10 = 49.6 R.sub.18 = -27.134 ______________________________________ wherein the asterisked (*) surface is an aspheric surface and wherein ______________________________________ Coefficient of aspheric surface Y X ______________________________________ B = 0.21699 × 10.sup..sup.-4 0 0 C = 0.35319 × 10.sup..sup.-7 1.225 0.02191 D = -0.92699 × 10.sup..sup.-10 2.450 0.08714 E = 0.61850 × 10.sup..sup.-13 3.675 0.19412 4.900 0.34012 6.125 0.52111 7.350 0.73157 8.575 0.96445 9.800 1.21115 11.025 1.46170 12.250 1.70517 13.475 1.93029 14.700 2.12630 f.sub.I = -60.406 f.sub.II = 50.558 f.sub.III = 33.911 Back focus = 36.500 ______________________________________

Claim 12

A large aperture wide angle lens as described in claim 5, wherein ______________________________________ [f = 24.5 F 1.4 ω = ± 42°] f = 24.5 F:1.4 ω = ± 42° ______________________________________ R.sub.1 = 58.377 D.sub.1 = 1.500 N.sub.1 = 1.58913 V.sub.1 = 61.1 R.sub.2 = 22.505 D.sub.2 = 10.000 R.sub.3 = 85.255 D.sub.3 = 4.500 N.sub.2 = 1.58913 V.sub.2 = 61.1 R.sub.4 = -101.797 D.sub.4 = 2.000 R.sub.5 = 61.083 D.sub.5 = 1.500 N.sub.3 = 1.58913 V.sub.3 = 61.1 R.sub.6 = 19.598 D.sub.6 = 8.139 R.sub.7 = 26.570 D.sub.7 = 3.000 N.sub.4 = 1.80518 V.sub.4 = 25.4 R.sub.8 = 62.807 D.sub.8 = 7.960 N.sub.5 = 1.58913 V.sub.5 = 61.1 R.sub.9 = -36.357 D.sub.9 = 0.200 R.sub.10 = -177.303 D.sub.10 = 1.500 N.sub.6 = 1.60562 V.sub.6 = 43.7 R.sub.11 = 36.089 D.sub.11 = 9.669 R.sub.12 = -14.680 D.sub.12 = 1.000 N.sub.7 = 1.80518 V.sub.7 = 25.4 R.sub.13 = 43.066 D.sub.13 = 5.500 N.sub.8 = 1.77250 V.sub.8 = 49.6 R.sub.14 = -34.315 * D.sub.14 = 0.150 R.sub.15 = -86.111 D.sub.15 = 4.500 N.sub.9 = 1.77250 V.sub.9 = 49.6 R.sub.16 = -27.367 D.sub.16 = 0.150 R.sub.17 = -288.678 D.sub.17 = 6.000 N.sub.10 = 1.77250 V.sub.10 =49.6 R.sub.18 = -27.467 ______________________________________ wherein the asterisked (*) surface is an aspheric surface and wherein ______________________________________ Coefficient of aspheric surface Y X ______________________________________ B = 0.18703 × 10.sup..sup.-4 0 0 C = 0.33568 × 10.sup..sup.-7 1.225 0.02183 D = -0.46676 × 10.sup..sup.-10 2.450 0.08689 E = 0.23254 × 10.sup..sup.-13 3.675 0.19386 4.900 0.34042 6.125 0.52305 7.350 0.73691 8.575 0.97552 9.800 1.23068 11.025 1.49228 12.250 1.74832 13.475 1.98497 14.700 2.18683 f.sub.I = -40.346 f.sub.II = 40.756 f.sub.III = 31.880 Back focus = 36.500 ______________________________________