Retrofocus type lens system

Claim 2

A retrofocus type lens system comprising, in the order named from an object side: a first lens group having a negative refracting power; and a second lens group having a positive refracting power, said second lens group being constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing; said rear group having an aspherical surface, said aspherical surface having a shape in which a negative surface refracting power is increased from a lens vertex to a periphery thereof, so that said aspherical surface corrects variations in coma and curvature of field when said rear group is moved to perform close distance focusing, said negative surface refracting power being defined as a difference between an incident angle and an exit angle of an arbitrary ray incident on an arbitrary point of a refracting surface.

Claim 3

A retrofocus type lens system according to claim 1, wherein said rear group is moved to the object side in performing close distance focusing.

Claim 4

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein the aspherical surface of said aspherical lens satisfies the following condition: ##EQU16## where f: focal length of entire system AS-S: difference between aspherical surface AS at outermost position of effective diameter of spherical surface and reference spherical surface S having predetermined radius of curvature of vertex along optical axis.

Claim 5

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein the aspherical surface of said aspherical lens satisfies the following condition: ##EQU16## where f: focal length of entire system AS-S: difference between aspherical surface AS at outermost position of effective diameter of spherical surface and reference spherical surface S having predetermined radius of curvature of vertex along optical axis.

Claim 6

A lens system according to claim 3, characterized by the following data: Focal length: f=20.442 F-number: 2.8 Field angle: 2ω=94° ______________________________________ Radius of Central Refractive ABBE curvature thickness · index number No. r Distance d n ν ______________________________________ 1 37.995 5.000 1.51860 70.08 G.sub.1 2 95.859 0.100 3 23.281 1.400 1.80458 25.49 4 10.195 5.000 5 36.935 1.200 1.71300 53.97 6 12.047 3.200 7 146.392 3.200 1.80458 25.49 8 -56.052 1.300 1.74810 52.28 9 10.566 5.000 1.67270 32.16 10 -35.743 0.100 G.sub.2F 11 39.235 3.300 1.67270 32.16 12 597.045 1.500 13 -36.762 3.200 1.58267 46.46 14 -14.665 2.600 15 -32.150 3.500 1.77279 49.44 16 -10.048 1.100 1.79504 28.61 17 52.115 1.000 18 59.969 3.000 1.51860 70.08 19 -20.708 d.sub.19 = variable 20 -50.000 1.200 1.49108 57.57 G.sub.2R 21 ⊚ -50.000 1.200 22 -38.396 4.000 1.51860 70.08 23 -17.634 Bf = variable ______________________________________ r.sub.21 Aspherical surface (⊚) Bf 37.981 ˜ 40.406 d.sub.19 3.623 ˜ 1.252

Claim 7

A lens system according to claim 3, characterized by the following data: Focal length: f=20.537 F-number: 2.89 Field angle: 2ω=95° ______________________________________ Radius of Central Refractive ABBE curvature thickness · index number No. r Distance d n ν ______________________________________ 1 40.684 5.350 1.48749 70.24 G.sub.1 2 134.136 0.100 3 25.122 1.500 1.79504 28.61 4 10.858 5.350 5 38.293 1.300 1.67025 57.58 6 12.480 3.200 7 251.347 2.150 1.80458 25.49 8 -100.595 0.550 9 -375.019 1.400 1.74810 52.28 10 13.494 5.350 1.67270 32.16 G.sub.2F 11 -51.750 0.100 12 40.944 3.500 1.67270 32.16 13 606.477 1.100 14 -26.965 3.400 1.59507 35.51 15 -15.776 2.700 16 -37.264 3.750 1.78797 47.53 17 -16.451 1.200 1.78470 26.07 18 98.285 1.050 19 174.298 3.200 1.50137 56.46 20 -19.483 d.sub.20 = variable 21 ⊚ -80.075 1.800 1.49108 57.57 G.sub.2R 22 -80.074 1.255 23 -73.455 6.000 1.69680 55.61 24 -14.371 1.600 1.71736 29.48 25 -26.293 Bf = variable ______________________________________ r.sub.21 Aspherical surface (⊚) Bf 38.596 ˜ 40.932 d.sub.20 3.377 ˜ 1.041

Claim 8

A lens system according to claim 3, characterized by the following data: Focal length: f=20.43 F-number: 2.84 Field angle: 2ω=94° ______________________________________ Radius of Central Refractive ABBE curvature thickness · index number No. r Distance d n ν ______________________________________ 1 40.829 5.350 1.48749 70.24 G.sub.1 2 134.005 0.100 3 25.199 1.500 1.79504 28.61 4 10.862 5.350 5 38.806 1.300 1.67025 57.58 6 12.467 3.200 7 262.298 2.150 1.80458 25.49 8 -100.528 0.550 9 -375.086 1.400 1.74810 52.28 10 13.868 5.350 1.67270 32.16 G.sub.2F 11 -51.061 0.100 12 41.413 3.500 1.67270 32.16 13 602.176 1.100 14 -27.056 3.400 1.59507 35.51 15 -15.804 2.700 16 -38.208 3.750 1.78797 47.53 17 -16.474 1.200 1.78470 26.07 18 103.533 1.050 19 152.349 3.200 1.50137 56.46 20 -20.336 d.sub.20 = variable 21 -80.000 1.800 1.49108 57.57 G.sub.C 22 ⊚ -80.001 d.sub.22 = variable 23 -83.420 6.000 1.69680 55.61 G.sub.f 24 -14.454 1.600 1.71736 29.48 25 -27.124 Bf = variable ______________________________________ r.sub.22 Aspherical surface (⊚) d.sub.20 3.3105 ˜ 1.1060 d.sub.22 1.5974 ˜ 1.4814 B.sub.f 38.1052 ˜ 40.4905

Claim 9

A lens system according to claim 3, characterized by the following data: Focal length: f=20.54 F-number: 2.89 Field angle: 2ω=94° ______________________________________ Radius of Central Refractive ABBE curvature thickness · index number No. r Distance d n ν ______________________________________ 1 40.684 5.350 1.48749 70.24 G.sub.1 2 134.136 0.100 3 25.122 1.500 1.79504 28.61 4 10.858 5.350 5 38.293 1.300 1.67025 57.58 6 12.480 3.200 7 251.347 2.150 1.80458 25.49 8 -100.595 0.550 9 -375.019 1.400 1.74810 52.28 10 13.494 5.350 1.67270 32.16 G.sub.2F 11 -51.750 0.100 12 40.944 3.500 1.67270 32.16 13 606.477 1.100 14 -26.965 3.400 1.59507 35.51 15 -15.776 2.700 16 -37.264 3.750 1.78797 47.53 17 -16.451 1.200 1.78470 26.07 18 98.285 1.050 19 174.298 3.200 1.50137 56.46 20 -19.483 d.sub.20 = variable 21 ⊚ -80.075 1.800 1.49108 57.57 G.sub.C 22 -80.074 d.sub.22 = variable 23 -73.455 6.000 1.69680 55.61 G.sub.f 24 -14.371 1.600 1.71736 29.48 25 -26.293 Bf = variable ______________________________________ r.sub.21 Aspherical surface (⊚) d.sub.20 3.3766 ˜ 1.1576 r.sub.22 1.2553 ˜ 1.1386 B.sub.f 38.5960 ˜ 40.9320

Claim 10

A retrofocus type lens system comprising, in the order named from an object side: a first lens group having a negative refracting power; and a second lens group having a positive refracting power, said second lens group being constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing: said rear group having an aspherical surface, said aspherical surface having a shape in which a positive surface refracting power is decreased from a lens vertex to a periphery thereof, so that said aspherical surface corrects variations in coma and curvature of field when said rear group is moved to perform close distance focusing, said positive surface refracting power being defined as a difference between an incident angle and an exit angle of an arbitrary ray incident on an arbitrary point of a refracting surface.

Claim 11

A retrofocus type lens system comprising, in the order named from an object side: a first lens group having a negative refracting power; and a second lens group having a positive refracting power, said second lens group being constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing: said rear group having an aspherical surface, said aspherical surface having a shape in which a positive surface refracting power is decreased from a lens vertex to a periphery thereof, so that said aspherical surface corrects variations in coma and curvature of field when said rear group is moved to perform close distance focusing, said positive surface refracting power being defined as a difference between an incident angle and an exit angle of an arbitrary ray incident on an arbitrary point of a refracting surface.

Claim 12

A retrofocus type lens system according to claim 8, wherein said rear group is moved to the object side in performing close distance focusing.

Claim 13

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein said lens system satisfies the following conditions when a focal length of said movable rear group is given by f 2R and an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on a lens surface, closest to the object side of said rear group is given by α: ##EQU17## where f: focal length of entire system α: value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of rear group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula α.sub. : angle formed between paraxial ray incident on frontmost lens surface and optical axis h: incident height of paraxial ray incident on frontmost lens surface.

Claim 14

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein said lens system satisfies the following conditions when a focal length of said movable rear group is given by f 2R and an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on a lens surface, closest to the object side of said rear group is given by α: ##EQU17## where f: focal length of entire system α: value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of rear group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula α.sub. : angle formed between paraxial ray incident on frontmost lens surface and optical axis h: incident height of paraxial ray incident on frontmost lens surface.

Claim 15

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein said rear group comprises a correction group including said aspherical lens for correcting aberrations and a focusing group which is moved relative to said correction group and has a focusing function, and satisfies the following conditions when a moving distance of said correction group is given by l c , a moving distance of said focusing group is given by l f , an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on said correction group is given by α c , and an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on said focusing group is given by α f : ##EQU18## where α c : value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of correction group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula α f : value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of correction group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula f: focal length of entire system α.sub. : angle formed by optical axis and paraxial ray incident on frontmost lens surface of said first lens group h 1 : incident height of paraxial ray incident on frontmost lens surface of first lens group f c : focal length of correction lens group f f : focal length of focusing lens group l c : focusing moving distance of correction group in rear group of second lens group l f : focusing moving distance of focusing group in rear group of second lens group.

Claim 16

A retrofocus type lens system comprising a first lens group having a negative refracting power and a second lens group having a positive refracting power in the order named from an object side, wherein said second lens group is constituted by a front group having a positive refracting power and a rear group which has a positive refracting power and is movable along an optical axis to perform focusing, and said rear group has an aspherical surface, said aspherical surface having a shape in which the negative surface refracting power is increased from a lens vertex to a periphery thereof, and which corrects variations in aberrations, and wherein said rear group comprises a correction group including said aspherical lens for correcting aberrations and a focusing group which is moved relative to said correction group and has a focusing function, and satisfies the following conditions when a moving distance of said correction group is given by l c , a moving distance of said focusing group is given by l f , an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on said correction group is given by α c , and an angle formed by an optical axis and a paraxial ray from an infinity object point along the optical axis and incident on said focusing group is given by α f : ##EQU18## where α c : value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of correction group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula α f : value obtained by calculating angle formed between optical axis and paraxial ray from infinity object point along optical axis and incident on a lens surface closest to object side of correction group, using α 1 =0 and h 1 =f as initial values of the paraxial ray tracing formula f: focal length of entire system α.sub. : angle formed by optical axis and paraxial ray incident on frontmost lens surface of said first lens group h 1 : incident height of paraxial ray incident on frontmost lens surface of first lens group f c : focal length of correction lens group f f : focal length of focusing lens group l c : focusing moving distance of correction group in rear group of second lens group l f : focusing moving distance of focusing group in rear group of second lens group.