Zoom lens

Claim 2

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group consisting of, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group consisting of, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, the axial separation between said 4-1-3rd lens and said 4-1-4th lens and the axial separation between said 4-2-1st lens and said 4-2-2nd lens being smaller than the axial separation between said 4-1-4th lens and said 4-2-1st lens, and said 4-1-2nd lens and said 4-1-3rd lens being axially separated from each other.

Claim 3

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 4

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 5

9<|R IV3 /R IV5 |<1.35 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.4<R.sub.IV7 /f.sub.W <1.9 0.9<RI.sub.IV10 /f.sub.W <1.3 1.1<|R.sub.IV12 /R.sub.IV13 |<2 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.45 0.14<D.sub.IV4 /f.sub.W <0.27 0.8<D.sub.IV8 /f.sub.W <0.9 0.23<D.sub.IV10 /f.sub.W <0.5 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial lens thickness or air separation, and f W is the shortest focal length of the entire system of said zoom lens.

Claim 6

9<|R IV3 /R IV5 |<1.35 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.4<R.sub.IV7 /f.sub.W <1.9 0.9<RI.sub.IV10 /f.sub.W <1.3 1.1<|R.sub.IV12 /R.sub.IV13 |<2 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.45 0.14<D.sub.IV4 /f.sub.W <0.27 0.8<D.sub.IV8 /f.sub.W <0.9 0.23<D.sub.IV10 /f.sub.W <0.5 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial lens thickness or air separation, and f W is the shortest focal length of the entire system of said zoom lens.

Claim 7

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 8

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 9

7<|f T /f II |<6.1 0.18<R.sub.II2 /f.sub.T <0.22 1.75<|R.sub.IV3 /R.sub.IV5 |<1.95 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.7<R.sub.IV7 /f.sub.W <1.9 1.15<R.sub.IV10 /f.sub.W <1.3 0.15<D.sub.IV4 /f.sub.W <0.25 0.95<D.sub.IV18 /f.sub.W <1.15 0.12<D.sub.IV10 /f.sub.W <0.15 wherein R IIi is the radius of curvature of the i-th lens surface counting from front in said 2nd lens group, D IIi is the i-th axial lens thickness or air separation in the 2nd lens group, f II is the focal length of said 2nd lens group, R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens group, and f W and f T are the shortest and longest focal lengths of the entire system of said zoom lens.

Claim 10

7<|f T /f II |<6.1 0.18<R.sub.II2 /f.sub.T <0.22 1.75<|R.sub.IV3 /R.sub.IV5 |<1.95 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.7<R.sub.IV7 /f.sub.W <1.9 1.15<R.sub.IV10 /f.sub.W <1.3 0.15<D.sub.IV4 /f.sub.W <0.25 0.95<D.sub.IV18 /f.sub.W <1.15 0.12<D.sub.IV10 /f.sub.W <0.15 wherein R IIi is the radius of curvature of the i-th lens surface counting from front in said 2nd lens group, D IIi is the i-th axial lens thickness or air separation in the 2nd lens group, f II is the focal length of said 2nd lens group, R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens group, and f W and f T are the shortest and longest focal lengths of the entire system of said zoom lens.

Claim 11

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 12

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 13

9<|R IV3 /R IV5 |<1.2 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.5<R.sub.IV7 /f.sub.W <1.7 0.8<R.sub.IV10 /f.sub.W <1.0 1.3<|R.sub.IV12 /R.sub.IV13 |<1.7 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.4 0.05<D.sub.IV4 /f.sub.W <0.2 0.55<D.sub.IV8 /f.sub.W <0.85 0.16<D.sub.IV10 /f.sub.W <0.24 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens groups, and f W is the shortest focal length of the entire system of said zoom lens.

Claim 14

9<|R IV3 /R IV5 |<1.2 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.5<R.sub.IV7 /f.sub.W <1.7 0.8<R.sub.IV10 /f.sub.W <1.0 1.3<|R.sub.IV12 /R.sub.IV13 |<1.7 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.4 0.05<D.sub.IV4 /f.sub.W <0.2 0.55<D.sub.IV8 /f.sub.W <0.85 0.16<D.sub.IV10 /f.sub.W <0.24 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens groups, and f W is the shortest focal length of the entire system of said zoom lens.

Claim 15

A zoom lens according to claim 4, further satisfying the following condition: 3.0<|R.sub.IV4 /R.sub.IV5 |<4.6.

Claim 16

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions: ##EQU2## wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation, N IVi is the refractive index of the glass of the i-th lens element, and f IV is the focal length of said 4th lens group.

Claim 17

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions: ##EQU2## wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation, N IVi is the refractive index of the glass of the i-th lens element, and f IV is the focal length of said 4th lens group.

Claim 18

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 19

A zoom lens comprising: four lens groups, said four lens groups being, from front to rear, a 1st lens group having a positive refractive power and movable for focusing, a 2nd lens group having a negative refractive power and movable for changing the image magnification, a 3rd lens group having a negative refractive power and movable for compensating for the shift of an image plane resulting from the change of the image magnification, and a 4th lens group having two lens groups, or, from front to rear, a 4-1st lens group and a 4-2nd lens group, and having a positive refractive power as a whole, said 4-1st lens group having, from front to rear, a bi-convex 4-1-1st lens having a strong refractive power at the rear, a bi-convex 4-1-2nd lens having a strong refractive power at the front, a 4-1-3rd lens of negative refractive power turning its concave surface toward the front, and a 4-1-4th lens of positive refractive power turning its convex surface toward the front, and said 4-2nd lens group having, from front to rear, a 4-2-1st lens of negative refractive power turning its concave surface toward the rear, a bi-convex 4-2-2nd lens having a strong refractive power at the rear, and a 4-2-3rd lens of positive refractive power having a strong refractive power at the front and turning its convex surface toward the front, satisfying the following conditions:

Claim 20

9<|R IV3 /R IV5 |<1.35 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.4<R.sub.IV7 /f.sub.W <1.9 0.9<R.sub.IV10 /f.sub.W <1.3 1.1<|R.sub.IV12 /R.sub.IV13 |<2 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.45 0.14<D.sub.IV4 /f.sub.W <0.27 0.8<D.sub.IV8 /f.sub.W <0.9 0.13<D.sub.IV10 /f.sub.W <0.5 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens group, and f W is the shortest focal length of the entire system of said zoom lens.

Claim 21

9<|R IV3 /R IV5 |<1.35 (where R.sub.IV3 >0, R.sub.IV5 <0) 1.4<R.sub.IV7 /f.sub.W <1.9 0.9<R.sub.IV10 /f.sub.W <1.3 1.1<|R.sub.IV12 /R.sub.IV13 |<2 (where R.sub.IV12 <0, R.sub.IV13 >0) 1.15<R.sub.IV13 /f.sub.W <1.45 0.14<D.sub.IV4 /f.sub.W <0.27 0.8<D.sub.IV8 /f.sub.W <0.9 0.13<D.sub.IV10 /f.sub.W <0.5 wherein R IVi is the radius of curvature of the i-th lens surface counting from front in said 4th lens group, D IVi is the i-th axial thickness or air separation in said 4th lens group, and f W is the shortest focal length of the entire system of said zoom lens.