Lens system and imaging apparatus having a lens at each side of an intermediate image which move in synchronization during focusing

1. A lens system that comprises a first optical system and forms an intermediate image that is formed inside the first optical system by light from an input side, into a final image on an output side,

wherein the first optical system includes a combination of lenses as follows:

a first lens with positive refractive power that is disposed at a position closest to the intermediate image, on the input side of the intermediate image, compared to any other lens in the lens system, wherein the first lens moves during a focusing;

a second lens with negative refractive power that is disposed at a position closest to the intermediate image, on the output side of the intermediate image, compared to any other lens in the lens system, wherein the second lens moves in synchronization with the first lens during the focusing; and

a third lens with positive refractive power that is disposed at a position closest to the second lens, on the output side of the second lens, compared to any other lens in the lens system, wherein the third lens does not move in synchronization with the first lens during focusing.

2. The lens system according to claim 1 ,

wherein the first optical system further includes a fourth lens with positive refractive power that is positioned on the output side of the third lens and moves during focusing.

3. The lens system according to claim 2 ,

wherein a focal length f 1 of a first subsystem that includes the first lens and the second lens, a focal length f 3 of another subsystem that includes the fourth lens, and a focal length f of the first optical system satisfy the following conditions:

−200 mm< f 1<−90 mm;

90 mm< f 3<200 mm; and

190 mm< f< 300 mm.

4. The lens system according to claim 1 ,

further comprising a second optical system that is disposed on an output side of the first optical system and includes a zooming system.

5. The lens system according to claim 4 ,

wherein a focal length fwf in a state focused at an infinity distance at a wide angle end of the lens system, a focal length fwn in a state focused at a shortest distance at the wide angle end of the lens system, a focal length ftf in a state focused at an infinity distance at a telephoto end of the lens system, and a focal length ftn in a state focused at a shortest distance at the telephoto end of the lens system satisfy the following conditions:

|1− fwf/fwn|< 0.005; and

|1− ftf/ftn|< 0.005.

6. The lens system according to claim 4 ,

wherein a distortion dwf in a state focused at an infinity distance at a wide angle end of the lens system, a distortion dwn in a state focused at a shortest distance at the wide angle end of the lens system, a distortion dtf in a state focused at an infinity distance at a telephoto end of the lens system, and the distortion dtn in a state focused at a shortest distance at the telephoto end of the lens system satisfy the following conditions:

| dwn−dwf|< 1.0%; and

| dtn−dtf|< 1.0%.

7. An imaging apparatus comprising:

the lens system according to claim 1 ; and

an imaging device disposed at a position where the final image of the lens system is formed.

8. The lens system according to claim 1 ,

wherein the second lens moves together with the first lens with a constant air gap between the first lens and the second lens during the focusing.

9. A lens system that comprises a first optical system and forms an intermediate image that is formed inside the first optical system by light from an input side of the first optical system, into a final image on an output side of the first optical system,

wherein the first optical system includes:

a first lens with positive refractive power that is disposed on the input side of the intermediate image and closer to the intermediate image than any other lens on the input side of the intermediate image, wherein the first lens moves during a focusing; and

a second lens with negative refractive power that is disposed on the output side of the intermediate image and closer to the intermediate image than any other lens on the output side of the intermediate image, wherein the second lens moves in synchronization with the first lens during the focusing; and

a third lens with positive refractive power that is disposed on the output side of the second lens and closer to the second lens than any other lens on the output side of the second lens, wherein the third lens does not move in synchronization with the first lens during focusing.

10. The lens system according to claim 9 wherein:

the first lens has a concave surface facing the intermediate image and the second lens has a concave surface facing the intermediate image, such that the concave surface of the first lens faces the concave surface of the second lens.

11. The lens system according to claim 9 ,

wherein the first optical system further includes a fourth lens with positive refractive power that is positioned on the output side of the third lens and that moves during focusing.

12. The lens system according to claim 9 ,

wherein the third lens has a convex surface facing the output side.

13. The lens system according to claim 1 wherein:

the first lens has a concave surface facing the intermediate image and the second lens has a concave surface facing the intermediate image, such that the concave surface of the first lens faces the concave surface of the second lens.

14. The lens system according to claim 13 ,

wherein the third lens has a convex surface facing the output side.