Image forming lens system and image pickup apparatus using the same

1. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the rear lens unit includes an image-motion correcting lens unit, and a first predetermined lens unit which is disposed on the object side of the image-motion correcting lens unit, immediately before the image-motion correcting lens unit, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

the first predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the image-motion correcting lens unit, and

the following conditional expressions (1) and (2′) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object.

2. The image forming lens system according to claim 1 , comprising:

an aperture stop;

wherein the first predetermined lens unit which is disposed on the object side of the image-motion correcting lens unit, immediately before the image-motion correcting lens unit, is a lens unit having a positive refractive power, and

positions of both the aperture stop and the lens unit having a positive refractive power are fixed.

3. The image forming lens system according to claim 1 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remain stationary, and

the image-motion correcting lens unit has a positive refractive power and includes a positive lens and a negative lens, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

4. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the rear lens unit includes an image-motion correcting lens unit, and a second predetermined lens unit which is disposed immediately after the image-motion correcting lens unit, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

the second predetermined lens unit has a refractive power having a sign different from a sign of a refractive power of the image-motion correcting lens unit, and

the following conditional expressions (1) and (2′) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object.

5. The image forming lens system according to claim 4 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remain stationary, and

the image-motion correcting lens unit has a positive refractive power and includes a positive lens and a negative lens, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

6. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the rear lens unit includes an image-motion correcting lens unit, and a first predetermined lens unit which is disposed on the object side of the image-motion correcting lens unit, immediately before the image-motion correcting lens unit, and a second predetermined lens unit which is disposed on the image side of the image-motion correcting lens unit, immediately after the image-motion correcting lens unit, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

each of the first predetermined lens unit and the second predetermined lens unit has a refractive power having a sign different from the sign of the refractive power of the image-motion correcting lens unit, and

the following conditional expressions (1) and (2′) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object.

7. The image forming lens system according to claim 6 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remain stationary, and

the image-motion correcting lens unit has a positive refractive power and includes a positive lens and a negative lens, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

8. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the rear lens unit includes a positive lens and an image-motion correcting lens unit having a negative refractive power and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

the following conditional expressions (1) and (2′) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object.

9. The image forming lens system according to claim 8 , wherein the rear lens unit includes in order from the object side,

a lens unit having a positive refractive power includes a positive lens,

the image-motion correcting lens unit having a negative refractive power, and

a lens unit having a positive refractive power.

10. The image forming lens system according to claim 8 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remain stationary, and

the image-motion correcting lens unit has a positive refractive power and includes a positive lens and a negative lens, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

11. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the rear lens unit includes a positive lens and a negative lens, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the following conditional expressions (1) and (2′) are satisfied, and

an image-motion correcting lens unit which satisfies the following conditional expression (5) is included in the image forming lens system:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

0.8<| MG ISback ×( MG IS −1)|<5.0  (5)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object, and

MG IS denotes a lateral magnification of the image-motion correcting lens unit in an arbitrary focused state, and

MG ISback denotes a lateral magnification of an overall optical system between the image-motion correcting lens unit and the image plane, in an arbitrary focused state.

12. The image forming lens system according to claim 11 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remains stationary, and

the rear lens unit includes the image-motion correcting lens unit which has a positive refractive power and includes the positive lens and the negative lens, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

13. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the rear lens unit includes a positive lens and a negative lens, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the following conditional expressions (1), (2′) and (6) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

1.5<|( MG foback ) 2 ×{( MG fo ) 2 −1}|<8.0  (6)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object, and

MG fo denotes a lateral magnification of the focusing lens unit in an arbitrary focused state, and

MG foback denotes a lateral magnification of the overall optical system between the focusing lens unit and the image plane, in an arbitrary focused state.

14. The image forming lens system according to claim 13 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remains stationary, and

the rear lens unit includes the image-motion correcting lens unit which has a positive refractive power and includes the positive lens and the negative lens, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

15. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

the first lens unit includes a 1-1 th sub lens unit on the object side, and a 1-2 th sub lens unit on the image side, and

an air space on an optical axis between the 1-1 th sub lens unit and the 1-2 th sub lens unit is the longest in the first lens unit, and

the 1-1 th sub lens unit has a positive refractive power, and

each of the 1-1 th sub lens unit and the 1-2 th sub lens unit includes a positive lens and a negative lens, and

the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the rear lens unit includes a positive lens and a negative lens, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the following conditional expressions (1), (2′) and (8) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

0.35< D G1 /f G1 <1.3  (8)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object, and

D G1 denotes a distance on the optical axis from a lens surface nearest to an object of the first lens unit up to a lens surface nearest to an image of the first lens unit, and

f G1 denotes the focal length of the first lens unit.

16. The image forming lens system according to claim 15 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remains stationary, and

the rear lens unit includes the image-motion correcting lens unit which has a positive refractive power and includes the positive lens and the negative lens, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

17. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

the first lens unit includes a 1-1 th sub lens unit on the object side, and a 1-2 th sub lens unit on the image side, and

an air space on an optical axis between the 1-1 th sub lens unit and the 1-2 th sub lens unit is the longest in the first lens unit, and

the 1-1 th sub lens unit has a positive refractive power, and

each of the 1-1 th sub lens unit and the 1-2 th sub lens unit includes a positive lens and a negative lens, and

the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the rear lens unit includes a positive lens and a negative lens, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the following conditional expressions (1), (2′) and (9) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

0.1< D G112 f G1 <0.6  (9)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object, and

D G112 denotes a distance on the optical axis between the 1-1 th sub lens unit and the 1-2 th sub lens unit, and

f G1 denotes the focal length of the first lens unit.

18. The image forming lens system according to claim 17 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remains stationary, and

the rear lens unit includes the image-motion correcting lens unit which has a positive refractive power and includes the positive lens and the negative lens, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.

19. An image forming lens system comprising in order from an object side to an image side along an optical axis:

a front lens unit having a positive refractive power; and

a rear lens unit, wherein

the image forming lens system does not include any other lens unit on the optical axis, and

the front lens unit includes in order from the object side to the image side, a first lens unit having a positive refractive power, and a second lens unit having a negative refractive power, and

each of the first lens unit and the second lens unit includes a positive lens and a negative lens, and

the second lens unit is a focusing lens unit, and

the focusing lens unit moves toward an image side along the optical axis at the time of focusing operation from an object at infinity to an object at a close distance, and

the second lens unit is the only lens unit that moves, in the front lens unit, and

the rear lens includes in order from the object side to the image side, a lens unit having a positive refractive power, a lens unit having a negative refractive power, and a lens unit having a positive refractive power, and

the lens unit having a positive refractive power positioned on the object side of the lens unit having a negative refractive power in the rear lens unit includes two sub lens units having a positive refractive power, and

an aperture stop is disposed to be sandwiched between the two sub lens units, and

the following conditional expressions (1) and (2′) are satisfied:

0.5< f FF /f< 1.65  (1)

0≤| f/r G2b |<6.5  (2′)

where,

f FF denotes a focal length of the front lens unit at the time of focusing at an object at infinity,

f denotes a focal length of the image forming lens system at the time of focusing at an object at infinity, and

r G2b denotes a paraxial radius of curvature of a lens surface on the object side of the second lens unit, immediately before the object.

20. The image forming lens system according to claim 19 , wherein

the focusing lens unit is a lens unit which is disposed nearest to the image, in the front lens unit, and

the first lens unit includes all lenses disposed on the object side of the focusing lens unit and remains stationary, and

the rear lens unit includes the image-motion correcting lens unit which has a positive refractive power and includes the positive lens and the negative lens, and

the image-motion correcting lens unit moves in a direction different from a direction of the optical axis to reduce an image motion due to shaking of the image forming lens system, and

all lenses other than the image-motion correcting lens unit included in the rear lens unit remain stationary.