Rear focus conversion lens

Claim 2

A rear conversion lens removably mounted between an objective lens and a camera body for making the combined focal length of the rear conversion lens and the objective lens greater than the focal length of the objective lens, including: a converter barrel; a lens group of negative refractive power movable in said converter barrel along the optical axis for converting a convergent light beam from said objective lens to a less convergent light beam and for condensing the light beam on an image plane in the camera body; and means for moving said lens group of negative refractive power along said optical axis in said converter barrel with respect to said objective lens; focusing to objects from infinity to a short distance being effected by the movement of said lens group of negative refractive power by said moving means, and wherein when said lens group of negative refractive power is moved toward the image side by ΔB(>0) for focusing to the short distance from infinity in-focus state, the magnification β' of the rear conversion lens in the short distance in-focus state is substantially given by the following equation: ##EQU9## where β is the enlargement magnification of the rear conversion lens in the infinity in-focus state, D 0 is the distance from a principal point of the rear conversion lens to an image point of the objective lens and f R is the focal length of the rear conversion lens.

Claim 3

A rear conversion lens according to claim 1, satisfying the following conditions: ##EQU10## where β is the enlargement magnification of the focal length in the infinity in-focus state by said rear conversion lens, ΔB f is the amount of variation in the combined back focal length when focused to from infinity to a predetermined short distance, and f R is the focal length of said rear conversion lens.

Claim 4

A rear conversion lens according to claim 2, satisfying the following conditions: ##EQU11## where Σd is the distance from the foremost lens surface to the last lens surface of said rear conversion lens, B f is the back focal length during the infinity in-focus of said rear conversion lens, d 0 is the object point distance of said rear conversion lens, namely, the distance between the image point of the mounted objective lens and the foremost lens surface of said rear conversion lens, and MB is the flange back of the camera body on which said rear conversion lens is mounted.

Claim 5

A rear conversion lens according to claim 3, wherein said lens group of negative refractive power includes a forward group having, in succession from the object side, a positive lens as a first component having its surface of sharper curvature facing the image side, a biconcave negative lens as a second component, and a positive lens as a third component having its surface of sharper curvature facing the object side, and a rearward group having a negative lens having its surface of sharper curvature facing the object side.

Claim 6

A rear conversion lens according to claim 4, satisfying the following conditions: ##EQU12## where f 1 , f 2 and f 3 are the focal lengths of said positive lens (L 1 ) as a first component, said negative lens (L 2 ) as a second component and said positive lens (L 3 ) as a third component, respectively.

Claim 7

A rear conversion lens according to claim 5, satisfying the following conditions: n.sub.- >1.82 ν.sub.- >35 where n - is the highest refractive index of the negative lens in said lens group of negative refractive power, and ν - is the lowest Abbe number of the negative lens in said lens group of negative refractive power.

Claim 8

A rear conversion lens according to claim 6, wherein the refractive index of each of the positive lenses in said forward group is 1.65 or less and the Abbe number thereof is 40 or less.

Claim 9

A rear conversion lens according to claim 7, wherein numerical data are as follows: ______________________________________ β = 1.60 f.sub.R = -75.3339 d.sub.0 = -36.6054 r.sub.1 = 133.317 d.sub.1 = 2.5 n.sub.1 = 1.59507 ν.sub.1 = 35.5 L.sub.1 r.sub.2 = -51.168 d.sub.2 = 0.5 r.sub.3 = -190.874 d.sub.3 = 1.0 n.sub.2 = 1.84042 ν.sub.2 = 43.3 L.sub.2 r.sub.4 = 24.064 d.sub.4 = 0.5 r.sub.5 = 27.743 d.sub.5 = 4.0 n.sub.3 = 1.59507 ν.sub.3 = 35.5 L.sub.3 r.sub.6 = -109.951 d.sub.6 = 1.5 r.sub.7 = -31.481 d.sub.7 = 1.0 n.sub.4 = 1.84042 ν.sub.4 = 43.3 L.sub.4 r.sub.8 = 2846.347 d.sub.8 = 0.1 r.sub.9 = 37.218 d.sub.9 = 2.5 n.sub.5 = 1.51118 ν.sub.5 = 50.9 L.sub.5 r.sub.10 = 115.703 ______________________________________ F or M 82.5596 -0.100 ______________________________________ D.sub.m ∞ 810.4909 D.sub.c 1.0 6.7412 B.sub.f 44.0080 38.2668 ______________________________________ Σd = 13.6 f.sub.2 = -25.374 f.sub.1 = 62.453 f.sub.3 = 37.636 ΔB.sub.f = 5.7412 ______________________________________ where r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, d 0 represents the distance between the image point by the objective lens and the foremost lens surface of the rear conversion lens, F represents the combined focal length of the rear conversion lens when combined with said objective lens, M represents the combined photographic magnification, D m represents the distance from the foremost lens surface of the objective lens to the object, D c represents the air space during the infinity in-focus of the objective lens and the rear conversion lens, B f represents the back focal length of the composite system of the objective lens and the rear conversion lens, ΔB f represents the amount of variation in the back focal length, β represents the magnification of the rear conversion lens, f R represents the focal length of the rear conversion lens, Σd represents the distance from the foremost lens surface of the rear conversion lens to the last lens surface thereof, and f 1 , f 2 and f 3 represent the focal lengths of the first, second and third components (L 1 , L 2 , L 3 ), respectively, in the forward group of the rear conversion lens.

Claim 10

A rear conversion lens according to claim 7, wherein numerical data are as follows: ______________________________________ β = 1.50 f.sub.R = -87.2348 d.sub.0 = -36.6054 r.sub.1 = 500.000 d.sub.1 = 2.5 n.sub.1 = 1.59507 ν.sub.1 = 35.5 L.sub.1 r.sub.2 = -45.149 d.sub.2 = 0.2 r.sub.3 = -325.888 d.sub.3 = 1.0 n.sub.2 = 1.84042 ν.sub.2 = 43.3 L.sub.2 r.sub.4 = 33.269 d.sub.4 = 0.5 r.sub.5 = 39.693 d.sub.5 = 3.0 n.sub.3 = 1.59507 ν.sub.3 = 35.5 L.sub.3 r.sub.6 = -132.889 d.sub.6 = 2.2 r.sub.7 = -28.526 d.sub.7 = 1.0 n.sub.4 = 1.84042 ν.sub.4 = 43.3 L.sub.4 r.sub.8 = 339.137 d.sub.8 = 0.2 r.sub.9 = 57.000 d.sub.9 = 2.6 n.sub.5 = 1.54814 ν.sub.5 = 45.9 L.sub.5 r.sub.10 = -137.274 ______________________________________ F or M 77.4002 -0.0667 ______________________________________ D.sub.m ∞ 1146.2387 D.sub.c 1.0 5.3935 B.sub.f 41.6888 37.2952 ______________________________________ Σd = 13.2 f.sub.2 = -35.874 f.sub.1 = 69.707 f.sub.3 = 51.697 ΔB.sub.f = 4.3936 ______________________________________ where r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, d 0 represents the distance between the image point by the objective lens and the foremost lens surface of the rear conversion lens, F represents the combined focal length of the rear conversion lens when combined with said objective lens, M represents the combined photographic magnification, D m represents the distance from the foremost lens surface of the objective lens to the object, D c represent the air space during the infinity in-focus of the objective lens and the rear conversion lens, B f represents the back focal length of the composite system of the objective lens and the rear conversion lens, ΔB f represents the amount of variation in the back focal length, β represents the magnification of the rear conversion lens, f R represents the focal length of the rear conversion lens, Σd represents the distance from the foremost lens surface of the rear conversion lens to the last lens surface thereof, and f 1 , f 2 and f 3 represent the focal lengths of the first, second and third components (L 1 , L 2 , L 3 ), respectively, in the forward group of the rear conversion lens.

Claim 11

a rear conversion lens according to claim 7, wherein numerical data are as follows: ______________________________________ β = 1.4142 f.sub.R = -96.9405 d.sub.0 = -36.6054 r.sub.1 = 500.000 d.sub.1 = 2.5 n.sub.1 = 1.61293 ν.sub.1 = 37.0 L.sub.1 r.sub.2 = -44.069 d.sub.2 = 0.5 r.sub.3 = -91.297 d.sub.3 = 1.0 n.sub.2 = 1.84042 ν.sub.2 = 43.3 L.sub.2 r.sub.4 = 32.578 d.sub.4 = 1.0 r.sub.5 = 29.021 d.sub.5 = 4.0 n.sub.3 = 1.59507 ν.sub.3 = 35.5 L.sub.3 r.sub.6 = -132.459 d.sub.6 = 2.0 r.sub.7 = -30.959 d.sub.7 = 1.0 n.sub.4 = 1.87739 ν.sub.4 = 38.1 L.sub.4 r.sub.8 = -72.603 ______________________________________ F or M 72.9734 -0.0333 ______________________________________ D.sub.m ∞ 2173.0891 D.sub.c 1.0 3.5255 B.sub.f 39.7209 37.1952 ______________________________________ Σd = 12.0 f.sub.2 = -28.464 f.sub.1 = 66.191 f.sub.3 = 40.377 ΔB.sub.f = 2.5257 ______________________________________ where r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, d 0 represents the distance between the image point by the objective lens and the foremost lens surface of the rear conversion lens, F represents the combined focal length of the rear conversion lens when combined with said objective lens, M represents the combined photographic magnification, D m represents the distance from the foremost lens surface of the objective lens to the object, D c represents the air space during the infinity in-focus of the objective lens and the rear conversion lens, Bf represents the back focal length of the composite system of the objective lens and the rear conversion lens, ΔB f represents the amount of variation in the back focal length, β represents the magnification of the rear conversion lens, f R represents the focal length of the rear conversion lens, Σd represents the distance from the foremost lens surface of the rear conversion lens to the last lens surface thereof, and f 1 , f 2 and f 3 represent the focal lengths of the first, second and third components (L 1 , L 2 , L 3 ), respectively, in the forward group of the rear conversion lens.

Claim 12

A rear conversion lens according to claim 7, wherein numerical data are as follows: ______________________________________ β = 1.8340 f.sub.R =-57.1288 d.sub.0 =-36.1054 r.sub.1 =1947.195 d.sub.1 =2.5 n.sub.1 =1.59507 ν.sub.1 =35.5 L.sub.1 r.sub.2 =-45.857 d.sub.2 =0.2 r.sub.3 =169.434 d.sub.3 =3.0 n.sub.2 =1.59507 ν.sub.2 =35.5 L.sub.2 r.sub.4 =-31.215 d.sub.4 =1.0 n.sub.3 =1.84042 ν.sub.3 =43.3 r.sub.5 =33.579 d.sub.5 =1.0 r.sub.6 =38.359 d.sub.6 =2.5 n.sub.4 =1.59507 ν.sub.4 =35.5 L.sub.3 r.sub.7 =-227.416 d.sub.7 =2.0 r.sub.8 =-34.862 d.sub.8 =1.0 n.sub.5 =1.84042 ν.sub.5 =43.3 L.sub.4 r.sub.9 =40.000 d.sub.9 =2.5 n.sub.6 =1.59507 ν.sub.6 =35.5 r.sub.10 =420.996 d.sub.10 =0.2 r.sub.11 =38.280 d.sub.11 =2.5 n.sub.7 = 1.46450 ν.sub.7 =65.8 L.sub.5 r.sub.12 =246.419 ______________________________________ F or M 94.6350 -0.1 ______________________________________ D.sub.m ∞ 932.1935 D.sub.c 1.5 5.7491 B.sub.f 44.5671 40.3180 ______________________________________ Σd = 18.4 f.sub.2 = -34.226 f.sub.1 = 75.324 f.sub.3 = 55.352 ΔB.sub.f = 4.2491 ______________________________________ where r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, d 0 represents the distance between the image point by the objective lens and the foremost lens surface of the rear conversion lens, F represents the combined focal length of the rear conversion lens when combined with said objective lens, M represents the combined photographic magnification, D m represents the distance from the foremost lens surface of the objective lens to the object, D c represents the air space during the infinity in-focus of the objective lens and the rear conversion lens, B f represents the back focal length of the composite system of the objective lens and the rear conversion lens, ΔB f represents the amount of variation in the back focal length, β represents the magnifcation of the rear conversion lens, f R represents the focal length of the rear conversion lens, Σd represents the distance from the foremost lens surface of the rear conversion lens to the last lens surface thereof, and f 1 , f 2 and f 3 represent the focal lengths of the first, second and third components (L 1 , L 2 , L 3 ), respectively, in the forward group of the rear conversion lens.

Claim 13

A rear conversion lens removably mounted between an objective lens and a camera body and having a negative refractive power for making the combined focal length of the rear conversion lens and the objective lens greater than the focal length of the objective lens, said rear conversion lens including: a forward group having a plurality of lenses; and a rearward group having at least one lens; said forward group and said rearward group being movable relative to each other along the optical axis, focusing to objects from infinity to a short distance being accomplished by relative movement of said two groups and the relative movement of said two groups being such that the aberration fluctuation occurring when the rear conversion lens is focused to a short distance object can be offset.

Claim 14

A rear conversion lens removably mounted between an objective lens and a camera body and having a negative refractive power for making the combined focal length of the rear conversion lens and the objective lens greater than the focal length of the objective lens, said rear conversion lens including: a forward group having a plurality of lenses; and a rearward group having at least one lens; said forward group and said rearward group being movable relative to each other along the optical axis, focusing to objects from infinity to a short distance being accomplished by relative movement of said two groups and the relative movement of said two groups being such that the aberration fluctuation occurring when the rear conversion lens is focused to a short distance object can be offset.

Claim 15

A rear conversion lens according to claim 12, wherein when the variation rates of the amount of variation ΔD 1 in the spacing between said objective lens and said forward group during in-focus and the amount of variation ΔD 2 in the spacing between said forward group and said rearward group relative to the amount of variation ΔB f in the combined back focal length of said objective lens and said rear conversion lens are α 1 and α 2 , respectively, and α is defined as α=α 1 +α 2 +1, the following condition is satisfied: -0.2<α<2.5

Claim 16

A rear conversion lens according to claim 12, wherein when the variation rates of the amount of variation ΔD 2 in the air space between said forward group and said rearward group and the amount of variation ΔB f in the combined back focal length of said objective lens and said rear conversion lens relative to the amount of variation ΔD 1 in the air space between said objective lens and said forward group during in-focus are γ 1 and γ 2 , respectively, and γ is defined as γ=γ 1 +γ 2 +1, the following condition is satisfied: -0.2<γ<2.5

Claim 17

A rear conversion lens according to claim 12, satisfying the following conditions: 1.3<β<2.5 0.6<|F.sub.2 /f.sub.R |<1.3 where β is the enlargement magnification of the focal length in the infinity in-focus state of said rear conversion lens, f R is the focal length of said rear conversion lens, and F 2 is the focal length of the rearward group in said rear conversion lens.

Claim 18

A rear conversion lens according to claim 15, wherein said forward group and said rearward group are both movable toward the image side to be focused to an object at a shorter distance.

Claim 19

A rear conversion lens according to claim 16, wherein said forward group has at least two positive lenses and at least one negative lens and said rearward group has at least one positive lens.

Claim 20

A rear conversion lens according to claim 17, wherein numerical data are as follows: ______________________________________ β = 1.6 r.sub.1 = 95.0 d.sub.1 = 2.5 n.sub.1 = 1.59507 ν.sub.1 = 35.5 L.sub.1 r.sub.2 = -61.141 d.sub.2 = 0.1 r.sub.3 = 527.908 d.sub.3 = 1.0 n.sub.2 = 1.84042 ν.sub.2 = 43.3 L.sub.2 r.sub.4 = 21.858 d.sub.4 = 0.5 G.sub.1 r.sub.5 = 25.603 d.sub.5 = 3.4 n.sub.3 = 1.59507 ν.sub.3 = 35.5 L.sub.3 r.sub.6 = 1258.061 d.sub.6 = 2.1 r.sub.7 = -32.168 d.sub.7 = 1.0 n.sub.4 = 1.84042 ν.sub.4 = 43.3 L.sub.4 r.sub.8 = 2846.377 d.sub.8 = D.sub.2 r.sub.9 = 36.200 d.sub.9 = 2.8 n.sub.5 = 1.51118 ν.sub.5 = 50.9 L.sub.5 G.sub.2 r.sub.10 = 141.254 ______________________________________ F or M 82.5594 -0.125 ______________________________________ D.sub.0 ∞ 653.070 ΔD.sub.1 = 6.0078 D.sub.1 1.0 7.0078 ΔD.sub.2 = -2.4032 D.sub.2 3.0942 0.6910 ΔB.sub.f = -3.6048 B.sub.f 42.0573 38.4525 ______________________________________ α = 0 γ = 0 f.sub.R = -80.7631 α.sub.1 = -1.667 γ.sub.1 = -0.4 F.sub.1 = -42.5634 α.sub.2 = 0.6667 γ.sub.2 = -0.6 F.sub.2 = 94.368 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α.sub. 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 21

A rear conversion lens according to claim 17, wherein numerical data are as follows: ______________________________________ β = 1.5 r.sub.1 =500.0 d.sub.1 =2.5 n.sub.1 =1.59507 ν.sub.1 =35.5 L.sub.1 r.sub.2 =-47.036 d.sub.2 =0.2 r.sub.3 =-463.574 d.sub.3 =1.0 n.sub.2 =1.84042 ν.sub.2 =43.3 L.sub.2 r.sub.4 =34.683 d.sub.4 =0.5 G.sub.1 r.sub.5 =39.693 d.sub.5 =3.0 n.sub.3 =1.59507 ν.sub.3 =35.5 L.sub.3 r.sub.6 =-132.889 d.sub.6 =2.2 r.sub.7 =-30.669 d.sub.7 =1.0 n.sub.4 =1.84042 ν.sub.4 =43.3 L.sub.4 r.sub.8 =339.135 d.sub.8 =D.sub.2 r.sub.9 =53.193 d.sub.9 =2.2 n.sub.5 =1.54814 ν.sub.5 =45.9 L.sub.5 G.sub.2 r.sub.10 =1724.775 ______________________________________ F or M 77.4001 -0.07 ______________________________________ D.sub.0 ∞ 1093.4527 D.sub.1 1.0 5.1536 ΔD.sub.1 = 4.1536 D.sub.2 1.5 0.6693 ΔD.sub.2 = 0.8307 B.sub.f 40.4817 37.1588 ΔB.sub.f = -3.3229 ______________________________________ α = 0 γ = 0 f.sub.R = -86.4912 α.sub.1 = -1.25 γ.sub.1 = -0.2 F.sub.1 = -46.0755 α.sub.2 = 0.25 γ.sub.2 = -0.8 F.sub.2 = 100.0834 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 22

A rear conversion lens according to claim 17, wherein numerical data are as follows: ______________________________________ β = 1.834 r.sub.1 =200.0 d.sub.1 =2.5 n.sub.1 =1.59507 ν.sub.1 =35.5 L.sub.1 r.sub.2 =-50.776 d.sub.2 =0.2 r.sub.3 =715.233 d.sub.3 =3.0 n.sub.2 =1.64831 ν.sub.2 =33.8 L.sub.2 r.sub.4 =-30.000 d.sub.4 =1.0 n.sub.3 =1.84042 ν.sub.3 =43.3 G.sub.1 r.sub.5 =31.470 d.sub.5 =0.5 r.sub.6 =38.359 d.sub.6 =2.5 n.sub.4 =1.59507 ν.sub.4 =35.5 L.sub.3 r.sub.7 =-239.379 d.sub.7 =D.sub.2 r.sub.8 =-35.298 d.sub.8 =1.0 n.sub.5 =1.87739 ν.sub.5 =38.1 L.sub.4 r.sub.9 =40.0 d.sub.9 =2.5 n.sub.6 =1.64831 ν.sub.6 =33.8 r.sub.10 =-577.176 d.sub.10 =0.2 G.sub.2 r.sub.11 =39.932 d.sub.11 =2.5 n.sub.7 =1.51118 ν.sub.7 =50.9 L.sub.5 r.sub.12 =162.674 ______________________________________ F or M 94.6353 -0.125 ______________________________________ D.sub.0 ∞ 742.0465 D.sub.1 1.0 7.1386 ΔD.sub.1 = 6.1386 D.sub.2 2.8 2.1861 ΔD.sub.2 = -0.6139 B.sub.f 44.9229 39.3984 ΔB.sub.f = -5.5246 ______________________________________ α = 0 γ = 0 f.sub.R = -57.2996 α.sub.1 = -1.111 γ.sub.1 = -0.1 F.sub.1 = 856.7929 α.sub.2 = 0.111 γ.sub.2 = -0.9 F.sub.2 = -51.9250 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represent the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 23

A rear conversion lens according to claim 15, wherein said forward group and said rearward group are both movable toward the object side to be focused to an object at a shorter distance.

Claim 24

A rear conversion lens according to claim 21, wherein said forward group has at least two negative lenses and at least one positive lens and said rearward group has a positive lens having its surface of sharper curvature facing the object side.

Claim 25

A rear conversion lens according to claim 22, wherein numerical data are as follows: ______________________________________ β = 1.4 r.sub.1 =65.785 d.sub.1 =2.9 n.sub.1 =1.59507 ν.sub.1 =35.5 L.sub.1 r.sub.2 =-58.904 d.sub.2 =0.2 r.sub.3 =-161.540 d.sub.3 =1.0 n.sub.2 =1.84042 ν.sub.2 =43.3 L.sub.2 r.sub.4 =27.027 d.sub.4 =1.0 G.sub.1 r.sub.5 =34.584 d.sub.5 =3.3 n.sub.3 =1.59507 ν.sub.3 =35.5 L.sub.3 r.sub.6 =-140.675 d.sub.6 =1.5 r.sub.7 =-37.323 d.sub.7 =1.0 n.sub.4 =1.84042 ν.sub.4 =43.3 L.sub.4 r.sub.8 =339.143 d.sub.8 =D.sub.2 r.sub.9 =38.662 d.sub.9 =2.5 n.sub.5 =1.46450 ν.sub.5 =65.8 L.sub.5 G.sub.2 r.sub.10 =162.687 ______________________________________ F or M 72.9686 -0.1 ______________________________________ D.sub.0 ∞ 807.5721 D.sub.1 0.9766 0.9766 ΔD.sub.1 = 0 D.sub.2 0.6 4.1973 ΔD.sub.2 = 3.5973 B.sub.f 37.9237 43.9179 ΔB.sub.f = 5.9942 ______________________________________ α = 1.6 γ.sup. cannot be f.sub.R = -94.8194 α.sub.1 = 0 γ.sub.1 defined. F.sub.1 = -50.817 α.sub.2 = 0.600 γ.sub.2 F.sub.2 = 108.485 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 26

A rear conversion lens according to claim 22, wherein numerical data are as follows: ______________________________________ β = 1.4 r.sub.1 = 105.531 d.sub.1 = 1.0 n.sub.1 = 1.84042 ν.sub.1 = 43.3 L.sub.1 r.sub.2 = 29.529 d.sub.2 = 0.5 r.sub.3 = 32.727 d.sub.3 = 4.5 n.sub.2 = 1.59507 ν.sub.2 = 35.5 L.sub.2 r.sub.4 = -38.160 d.sub.4 = 1.0 G.sub.1 r.sub.5 = -49.868 d.sub.5 = 1.0 n.sub.3 = 1.84042 ν.sub.3 = 43.3 L.sub.3 r.sub.6 = -72.809 d.sub.6 = 1.5 r.sub.7 = -41.039 d.sub.7 = 1.0 n.sub.4 = 1.84042 ν.sub.4 = 43.3 L.sub.4 r.sub.8 = 116.806 d.sub.8 = D.sub.2 r.sub.9 = 39.085 d.sub.9 = 2.6 n.sub.5 = 1.50137 ν.sub.5 = 56.5 L.sub.5 G.sub.2 r.sub.10 = 119.484 ______________________________________ F or M 72.9734 -0.1 ______________________________________ D.sub.0 ∞ 802.2745 D.sub.1 0.9721 0.9721 ΔD.sub.1 = 0 D.sub.2 0.6 3.1382 ΔD.sub.2 = 2.5382 B.sub.f 38.6414 44.9871 ΔB.sub.f = 6.3429 ______________________________________ α = 1.4 γ.sup. cannot be f.sub.R = -96.8924 α.sub.1 = 0 γ.sub.1 defined. F.sub.1 = -52.7683 α.sub.2 = 0.400 γ.sub.2 F.sub.2 = 114.6142 ______________________________________ where β represents the magnification of the rear conversion lens, r presents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α.sub. 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 27

A rear conversion lens according to claim 22, wherein numerical data are as follows: ______________________________________ β = 1.4 r.sub.1 = 143.302 d.sub.1 = 1.0 n.sub.1 = 1.84042 ν.sub.1 = 43.3 L.sub.1 r.sub.2 = 30.158 d.sub.2 = 0.5 r.sub.3 = 32.727 d.sub.3 = 5.0 n.sub.2 = 1.59507 ν.sub.2 = 35.5 L.sub.2 G.sub.1 r.sub.4 = -38.551 d.sub.4 = 2.5 r.sub.5 = -35.904 d.sub.5 = 1.0 n.sub.3 = 1.84042 ν.sub.3 = 43.3 L.sub.3 r.sub.6 = 116.807 d.sub.6 = D.sub.2 r.sub.7 = 36.215 d.sub.7 = 2.6 n.sub.4 = 1.50137 ν.sub.4 = 56.5 L.sub.4 G.sub.2 r.sub.8 = 83.782 ______________________________________ F or M 72.9734 -0.1 ______________________________________ D.sub.0 ∞ 802.6944 D.sub. 1 0.9721 0.9721 ΔD.sub.1 = 0 D.sub.2 0.6 3.3741 ΔD.sub.2 = 2.7741 B.sub.f 38.9676 45.1322 ΔB.sub.f = 6.1646 ______________________________________ α = 1.45 γ.sup. cannot be f.sub.R = -97.0969 α.sub.1 = 0 γ.sub.1 defined. F.sub.1 = -55.0703 α.sub.2 = 0.450 γ.sub.2 F.sub.2 = 124.9465 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 28

A rear conversion lens according to claim 21, wherein said forward group has two positive lenses and a negative lens and said rearward group has a negative lens.

Claim 29

A rear conversion lens according to claim 26, wherein numerical data are as follows: ______________________________________ β = 1.4 r.sub.1 =500.0 d.sub.1 =2.5 n.sub.1 =1.59507 ν.sub.1 =35.5 L.sub.1 r.sub.2 =-46.392 d.sub.2 =0.5 r.sub.3 =-96.993 d.sub.3 =1.0 n.sub.2 =1.84042 ν.sub.2 =43.3 L.sub.2 G.sub.1 r.sub.4 =31.188 d.sub.4 =1.0 r.sub.5 =28.247 d.sub.5 =4.0 n.sub.3 =1.59507 ν.sub.3 =35.5 L.sub.3 r.sub.6 =-132.460 d.sub.6 =D.sub.2 r.sub.7 =-31.476 d.sub.7 =1.0 n.sub.4 =1.90265 ν.sub.4 =35.8 L.sub.4 G.sub.2 r.sub.8 =-67.136 ______________________________________ F or M 72.9738 -0.1 ______________________________________ D.sub.0 ∞ 787.2736 D.sub.1 1.0 1.0 ΔD.sub.1 = 0 D.sub.2 2.8 3.1212 ΔD.sub.2 = 0.3212 B.sub.f 38.8244 45.2511 ΔB.sub.f = 6.4267 ______________________________________ α = 1.05 γ.sup. cannot be f.sub.R = -95.8404 α.sub.1 = 0 γ.sub.1 defined. F.sub.1 = 218.5363 α.sub.2 = 0.05 γ.sub.2 F.sub.2 = -66.5334 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D 0 represents the distance from the foremost lens surface of the objective lens to the object, D 1 represents the spacing between the objective lens and the rear conversion lens, D 2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B f represents the back focal length of the composite system, f R represents the focal length as the rear conversion lens during infinity in-focus, F 1 and F 2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α.sub. 1 and α 2 represent the variation rates of the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB f , γ 1 and γ 2 are the variation rates of the amount of variation ΔD 2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD 1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD 1 .

Claim 30

A rear conversion lens according to claim 15, wherein said forward group is movable toward the image side to be focused to an object at a shorter distance and said rearward group is stationary.

Claim 31

A rear conversion lens according to claim 28, wherein said forward group has a positive lens and three negative lenses and said rearward group has a positive meniscus lens having its convex surface facing the object side.

Claim 32

A rear conversion lens according to claim 29, wherein numerical data are as follows: ______________________________________ β = 1.4 r.sub.1 =74.260 d.sub.1 =1.0 n.sub.1 =1.84042 ν.sub.1 =43.3 L.sub.1 r.sub.2 =28.691 d.sub.2 =0.5 r.sub.3 =32.727 d.sub.3 =4.5 n.sub.2 =1.59507 ν.sub.2 =35.5 L.sub.2 r.sub.4 =-40.0 d.sub.4 =1.0 G.sub.1 r.sub.5 =-59.815 d.sub.5 =1.0 n.sub.3 =1.84042 ν.sub.3 =43.3 L.sub.3 r.sub.6 =-140.152 d.sub.6 =1.3 r.sub.7 =-42.637 d.sub.7 =1.0 n.sub.4 =1.84042 ν.sub.4 =43.3 L.sub.4 r.sub.8 =105.870 d.sub.8 =D.sub.2 r.sub.9 =40.335 d.sub.9 =2.4 n.sub.5 =1.50137 ν.sub.5 =56.5 L.sub.5 G.sub.2 r.sub.10 =155.251 ______________________________________ F or M 72.9734 -0.1 ______________________________________ D.sub.0 ∞ 749.5993 D.sub.1 1.0 4.8062 ΔD.sub.1 = 3.8062 D.sub.2 1.2 0.5149 ΔD.sub. 2 = -0.6851 B.sub.f 38.0912 38.0912 ΔB.sub.f = 0 ______________________________________ α.sup. cannot be γ = 0.82 f.sub.R = -95.9395 α.sub.1 defined. γ.sub.1 = -0.18 F.sub.1 = -50.9159 α.sub.2 γ.sub.2 = 0 F.sub.2 = 107.9336 ______________________________________ where β represents the magnification of the rear conversion lens, r represents the radius of curvature of each lens surface, d represents the center thickness and air space of each lens, n represents the refractive index for the d-line (λ=587.6 nm), ν represents the Abbe number, the subscript numbers represent the order from the object side, F represents the combined focal length of the rear conversion lens during infinity in-focus when combined with said objective lens, M represents the combined photographic magnification during very short distance in-focus, D.sub.0 represents the distance from the foremost lens surface of the objective lens to the object, D.sub.1 represents the spacing between the objective lens and the rear conversion lens, D.sub.2 represents the spacing between the forward group and the rearward group of the rear conversion lens, B.sub.f represents the back focal length of the composite system, f.sub.R represents the focal length as the rear conversion lens during infinity in-focus, F.sub.1 and F.sub.2 represent the focal lengths of the forward group and the rearward group, respectively, of the rear conversion lens, α .sub.1 and α.sub.2 represent the variation rates of the amount of variation ΔD.sub.1 in the spacing between the objective lens and the forward group of the rear conversion lens and the amount of variation ΔD.sub.2 in the spacing between the forward group and the rearward group of the rear conversion lens, respectively, relative to the amount of variation ΔB.sub.f in the back focal length of the composite system, α represents the variation rate of the amount of variation in the full length relative to ΔB.sub.f, γ.sub.1 and γ.sub.2 are the variation rates of the amount of variation ΔD.sub.2 in the spacing between the forward group and the rearward group of the rear conversion lens and the amount of variation ΔB.sub.f in the back focal length of the composite system, respectively, relative to the amount of variation ΔD.sub.1 in the spacing between the objective lens and the forward group of the rear conversion lens, and γ is the variation rate of the amount of variation in the full length relative to ΔD.sub.1.

Claim 33

A rear conversion lens removably mounted between an objective lens and a camera body for making the combined focal length of the rear conversion lens and the objective lens greater than the focal length of the objective lens, including: a converter barrel; a lens group of negative refractive power movable in said converter barrel along the optical axis for converting a convergent light beam from said objective lens to a less convergent light beam and for condensing the light beam on an image plane in said camera body; and means for moving said lens group of negative refractive power along said optical axis from a first position to a second position with respect to said objective lens; focusing to infinity being effected through said objective lens by moving said lens group of negative refractive power to said first position while maintaining said objective lens in infinity in-focus state, and focusing to a short distance being effected through said objective lens by moving said lens group of negative refractive power to said second position.

Claim 34

A rear conversion lens removably mounted between an objective lens and a camera body for making the combined focal length of the rear conversion lens and the objective lens greater than the focal length of the objective lens, including: a converter barrel; a lens group of negative refractive power movable in said converter barrel along the optical axis for converting a convergent light beam from said objective lens to a less convergent light beam and for condensing the light beam on an image plane in said camera body; and means for moving said lens group of negative refractive power along said optical axis from a first position to a second position with respect to said objective lens; focusing to infinity being effected through said objective lens by moving said lens group of negative refractive power to said first position while maintaining said objective lens in infinity in-focus state, and focusing to a short distance being effected through said objective lens by moving said lens group of negative refractive power to said second position.

Claim 35

A rear conversion lens according to claim 31, wherein focusing to a shorter distance than the short distance to which focusing is attainable by only said objective lens is effected by moving said lens group of negative refractive power from said first position to said second position while maintaining said objective lens in short distance in-focus state.