Lenses capable of close-up photography

Claim 2

A lens system capable of focusing continuously from infinite distance to close distance comprising, in the order from the object side, a converging first lens group disposed at a fixed distance from an image plane, a diverging second lens group disposed movably along the optical axis thereof for focusing, and a converging third lens group disposed at a fixed distance from the image plane, said diverging second lens group maintaining paraxial rays exiting therefrom substantially parallel throughout all the range of focusing, said first, second and third lens groups satisfying the following condition formulae:

Claim 3

0<f 1 /|f 2 |<1.4 1.6≦f.sub.3 /|f.sub.2 |≦2.2 wherein, f 1 , f 2 and f 3 are focal lengths of said converging first lens group, diverging second lens group and converging third lens group, respectively.

Claim 4

0<f 1 /|f 2 |<1.4 1.6≦f.sub.3 /|f.sub.2 |≦2.2 wherein, f 1 , f 2 and f 3 are focal lengths of said converging first lens group, diverging second lens group and converging third lens group, respectively.

Claim 5

A lens system according to claim 1 wherein said system satisfies the following condition: 1.6≦(f.sub.3 /R)≦4.2 wherein, R is the diameter of the image circle of said lens system.

Claim 6

A lens system according to claim 1 wherein said system satisfies the following condition: 1.6≦|βmin|≦4 wherein, βmin is the minimum lateral magnification in the reversed direction of said first lens group.

Claim 7

A lens system according to claim 1 wherein said converging lens group comprises two positive lens components at least one of which has surfaces cemented together and wherein said two positive lens components satisfy the following conditions: -0.25 <(r.sub.b +r.sub.a)/(r.sub.b -r.sub.a)<+0.15 +0.5<(r.sub.d +r.sub.c)/(r.sub.d -r.sub.c)<+1.5 wherein, r a and r b are curvature radii of front and rear surfaces of the front positive lens component, respectively; and r c and r d are curvature radii of front and rear surfaces of the rear positive lens component.

Claim 8

A lens system according to claim 1 wherein said diverging second lens group comprises a cemented concavo-concave lens which satisfies the following condition: -0.5<(r.sub.8 +r.sub.6)/(r.sub.8 -r.sub.6)<0 wherein, r 6 is the curvature raius of surface at the object field side of said concavo-concave lens; and r 8 is that at the image field side of the same.

Claim 9

A lens system according to claim 1 wherein said third lens group comprises a meniscus lens component composed of a positive lens and a negative lens cemented together with its convex surface facing toward the object side, a negative meniscus lens component with its convex surface facing toward the image side and a positive lens component arranged in this order as viewed from the object side.

Claim 10

A lens system according to claim 1 and as specified by the following data of lens elements: ______________________________________ f∞ = 121.168 F-number 4 ______________________________________ r d nd νd ______________________________________ 1 161.530 1.5000 1.80518 25.5 2 43.284 10.0000 1.71300 53.9 3 -181.654 .2000 1.0 4 73.861 5.5000 1.71300 53.9 5 -1704.595 d.sub.5 = Variable 1.0 6 -108.243 4.7000 1.78470 26.1 7 -34.631 2.3000 1.69680 55.6 8 49.671 d.sub.8 = Variable 1.0 9 26.350 13.6000 1.71300 53.9 10 250.000 2.9000 1.72342 38.0 11 27.045 25.7 1.0 12 -15.884 2.4000 1.78470 26.1 13 -21.077 .1000 1.0 14 70.700 4.7000 1.62280 56.7 15 -123.414 1.0 M 0 -0.504 -1.002 d.sub.0 ∞ 295.169 175.712 d.sub.5 0.925 16.141 31.167 d.sub.8 36.408 21.192 6.166 Bf 58.798 58.798 58.798 f.sub.1 60.484 f.sub.1 /|f.sub.2 | 1.15 f.sub.2 -52.5 f.sub.3 /|f.sub.2 | 2.0 f.sub.3 105.173 f.sub.3 /R 2.43 R 43.28 β min 2.0 ______________________________________ Diaphragm plane is 1.8 before r.sub.9. wherein, data are arranged in the order of lens surface as viewed from the object side, and f 1 , f 2 and f 3 have the same meanings as defined in claim 2; r is the radius of curvature of lens surface; d is the thickness at the center of lens and air spacing; nd is the refractive index of lens; νd is Abb's number; M is the photographic magnification of the total system; d 0 is the distance from the object to the first surface, that is, working distance; R is the diameter of image circle; and Bf is back-focus.

Claim 11

A lens system according to claim 1 and as specified by the following data of lens elements: ______________________________________ f∞ = 162.0 F-number 4 ______________________________________ r d nd νd ______________________________________ 1 240.000 7.0000 1.71300 53.9 2 -179.034 .1800 1.0 3 110.000 11.7000 1.71300 53.9 4 -92.000 1.5000 1.80518 25.5 5 552.084 d.sub.5 = Variable 1.0 6 -148.000 4.5000 1.78470 26.1 7 -49.474 2.0000 1.69680 55.6 8 72.112 d.sub.8 = Variable 1.0 9 34.350 17.4594 1.71300 53.9 10 320.945 3.7230 1.72342 38.0 11 34.066 27.345 1.0 12 -20.865 3.0811 1.78470 26.1 13 -27.057 .1284 1.0 14 90.763 6.0338 1.62280 56.9 15 -153.699 1.0 M 0 -0.501 -1.000 d.sub.0 ∞ 412.0 250.5 d.sub.5 2.351 27.351 52.351 d.sub.8 55.903 30.903 5.903 Bf 79.515 79.651 79.559 f.sub.1 90.0 f.sub.1 /|f.sub.2 | 1.2 f.sub.2 -75.0 f.sub.3 /|f.sub.2 | 1.8 f.sub.3 135.0 f.sub.3 /R 3.12 R 43.28 β min 1.8 ______________________________________ Diaphragm plane is 1.215 before r.sub.9. wherein, data are arranged in the order of lens surface as viewed from the object side, and f 1 , f 2 and f 3 have the same meanings as defined in claim 2; r is the radius of curvature of lens surface; d is the thickness at the center of lens and air spacing; nd is the refractive index of lens; νd is Abbe's number; M is the photographic magnification of the total system; d 0 is the distance from the object to the first surface, that is, working distance; R is the diameter of image circle; and Bf is back-focus.

Claim 12

A lens system according to claim 1 and as specified by the following data of lens elements: ______________________________________ f∞ = 106.25 F-number 4 ______________________________________ r d nd νd ______________________________________ 1 162.000 .3868 1.80518 25.5 2 41.950 9.2456 1.71300 53.9 3 -142.482 .1849 1.0 4 66.000 5.0850 1.71300 53.9 5 1678.852 d.sub.5 = Variable 1.0 6 -88.300 4.0051 1.78470 26.1 7 -29.511 1.9599 1.69680 55.6 8 443.347 d.sub.8 = Variable 1.0 9 20.450 10.9929 1.71300 53.9 10 202.077 2.3441 1.72342 38.0 11 21.393 17.5 1.0 12 -12.348 1.9399 1.78470 26.1 13 -17.036 .0808 1.0 14 55.000 1.5000 1.71300 53.9 15 30.500 6.5000 1.50137 56.5 16 -42.981 1.0 M 0 -0.500 -1.000 d.sub.0 ∞ 263.0 156.9 d.sub.5 11.184 25.9 40.616 d.sub.8 35.581 20.865 6.149 Bf 46.256 46.297 46.269 f.sub.1 55.921 f.sub.1 /|f.sub.2 | 1.25 f.sub.2 -44.737 f.sub.3 /|f.sub.2 | 1.9 f.sub.3 85.0 f.sub.3 /R 1.96 R 43.28 β min 1.9 ______________________________________ Diaphragm plane is 0.765 before r.sub.9. wherein, data are arranged in the order of lens surfaces as viewed from the object side, and f 1 , f 2 and f 3 have the same meanings as defined in claim 2; r is the radius of curvature of lens surface; d is the thickness at the center of lens and air spacing; nd is the refractive index of lens; νd is Abbe's number; M is the photographic magnification of the total system; d 0 is the distance from the object to the first surface, that is, working distance; R is the diameter of image circle; and Bf is back-focus.