Zoom lens and image pickup apparatus using the same

1. A zoom lens comprising in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a plurality of lens units, wherein

zooming from a wide angle end to a telephoto end is carried out by changing each distance between the lens units, and

the first lens unit comprises in order from the object side to the image side,

a negative lens and a positive lens, and

the negative lens in the first lens unit is a plastic lens which is a single lens of which, an object-side surface and an image-side surface make a contact with air, and

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

5.3 <ft/fw   (1)

n 1 n <1.7  (2)

where,

ft denotes a focal length at the telephoto end of the zoom lens,

fw denotes a focal length at the wide angle end of the zoom lens, and

n1n denotes a refractive index with reference to a d-line of the negative lens in the first lens unit.

2. A zoom lens comprising in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a plurality of lens units, wherein

zooming from a wide angle end to a telephoto end is carried out by changing each distance between the lens units, and

the second lens unit comprises in order from the object side to the image side,

a front-side unit having a negative refractive power which includes a negative lens, and

a rear-side unit which includes a positive lens and a negative lens, and

the second lens unit does not include a lens unit other than the front-side unit and the rear-side unit, and

the negative lens in the front-side unit is a glass lens, and

both the positive lens and the negative lens in the rear-side unit are plastic lenses which are single lenses of which, an object-side surface and an image-side surface are in contact with air, and

the following conditional expression (1) is satisfied:

5.3 <ft/fw   (1)

where,

ft denotes a focal length at the telephoto end of the zoom lens, and

fw denotes a focal length at the wide angle end of the zoom lens.

3. A zoom lens comprising in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a plurality of lens units, wherein

zooming from a wide angle end to a telephoto end is carried out by changing each distance between the lens units, and

the first lens unit comprises in order from the object side to the image side,

a negative lens and a positive lens, and

both the negative lens in the first lens unit and the positive lens in the first lens unit are plastic lenses which are single lenses of which, an object-side surface and an image-side surface make a contact with air, and

the following conditional expression (1) is satisfied:

5.3 <ft/fw   (1)

where,

ft denotes a focal length at the telephoto end of the zoom lens, and

fw denotes a focal length at the wide angle end of the zoom lens.

4. A zoom lens comprising in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a plurality of lens units, wherein

zooming from a wide angle end to a telephoto end is carried out by changing each distance between the lens units, and

both the first lens unit and the second lens unit comprise a plastic lens, and

the second lens unit comprises in order from the object side to the image side,

a front-side unit having a negative refractive power which includes a negative lens, and

a rear-side unit which includes a positive lens and a negative lens, and

the second lens unit does not include a lens unit other than the front-side unit and the rear-side unit, and

the negative lens in the front-side unit is a glass lens, and

both the positive lens and the negative lens in the rear-side unit are plastic lenses which are single lenses of which, an object-side surface and an image-side surface make a contact with air.

5. A zoom lens comprising in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power; and

a plurality of lens units, wherein

zooming from a wide angle end to a telephoto end is carried out by changing each distance between the lens units, and

the first lens unit comprises in order from the object side to the image side,

a negative lens which is a single lens of which, an object-side surface and an image-side surface make a contact with air, and

a positive lens which is a single lens of which, an object-side surface and an image-side surface make a contact with air, and

the second lens unit comprises in order from the object side to the image side,

a front-side unit having a negative refractive power, which includes a negative lens,

a rear-side unit having a positive lens which is a single lens of which, an object-side surface and an image-side surface make a contact with air, and a negative lens which is a single lens of which, an object-side surface and an image-side surface make a contact with air, and

the second lens unit does not include a lens unit other than the front-side unit and the rear-side unit, and

the following conditional expressions (1), (6), and (7) are satisfied:

5.3 <ft/fw   (1)

−0.3 <n 1 n−n 21 n <−0.09  (6)

n 2 p−n 21 n<− 0.09  (7)

where,

ft denotes a focal length at the telephoto end of the zoom lens,

fw denotes a focal length at the wide angle end of the zoom lens,

n1n denotes a refractive index with reference to a d-line of the negative lens in the first lens unit,

n21n denotes a refractive index with reference to the d-line of the negative lens in the front-side unit, and

n2p denotes a refractive index with reference to the d-line of the positive lens in the rear-side unit.

6. An image pickup apparatus comprising:

a zoom lens according to any one of claims 5 to 1 ; and

an image pickup element which is disposed on an image side of the zoom lens, and which has an image pickup surface which picks up an image formed by the zoom lens, and which converts the image picked up to an electric signal.

7. The zoom lens according to claim 3 , wherein

the second unit comprises in order from the object side to the image side

a front-side unit having a negative refractive power which includes a negative lens, and

a rear-side unit which includes a positive lens and a negative lens, and

the negative lens in the front-side unit is a glass lens, and

both the positive lens and the negative lens in the rear-side lens unit are plastic lenses.

8. The zoom lens according to claim 4 , wherein

the positive lens in the rear-side unit is a plastic lens which has an aspheric surface, and

the following conditional expression (5B) is satisfied:

1.64 <n 2 p   (5B)

where,

n2p denotes a refractive index with reference to a d-line of the positive lens in the rear-side unit.

9. The zoom lens according to claim 5 , wherein

the negative lens in the first lens unit and the positive lens in the first lens unit are plastic lenses, and

the following conditional expressions (2) and (3) are satisfied:

n 1 n <1.7  (2)

20<|ν1 n−ν 1 p|< 60  (3)

where,

n1n denotes a refractive index with reference to a d-line of the negative lens in the first lens unit,

ν1n denotes Abbe number with reference to the d-line of the negative lens in the first lens unit,

ν1p denotes Abbe number with reference to the d-line of the positive lens in the first lens unit, and

ν1n<ν1p.

10. The zoom lens according to claim 5 , wherein

the negative lens and the positive lens in the rear-side unit are plastic lenses, and

the following conditional expressions (4) and (5A) are satisfied:

n 22 n< 1.55  (4)

n 2 p <1.7  (5A)

where,

n22n denotes a refractive index with reference to a d-line of the negative lens in the rear-side unit, and

n2p denotes a refractive index with reference to the d-line of the positive lens in the rear-lens unit.

11. The zoom lens according to claim 5 , wherein

the zoom lens comprises in order from the object side to the image side:

the first lens unit having a positive refractive power;

the second lens unit having a negative refractive power;

a third lens unit having a positive refractive power; and

a fourth lens unit, and

the following conditional expression (9) is satisfied:

0.5<(β3 t/β 3 w )/(β2 t/β 2 w )<1.3  (9)

where,

β3t denotes a lateral magnification at the telephoto end of the third lens unit,

β3w denotes a lateral magnification at the wide angle end of the third lens unit,

β2t denotes a lateral magnification at the telephoto end of the second lens unit, and

β2w denotes a lateral magnification at the wide angle end of the second lens unit.

12. The zoom lens according to claim 5 , wherein

the first lens unit comprises in order from the object side to the image side

a negative lens and a positive lens, and

the total number of lenses in the first lens unit is two.

13. The zoom lens according to claim 5 , wherein

the second lens unit comprises in order from the object side to the image side,

a first negative lens, a second negative lens, and a positive lens, and

the total number of lenses in the second lens unit is three.

14. The zoom lens according to claim 5 , wherein

both the negative lens in the first lens unit and the positive lens in the first lens unit are plastic lenses.

15. The zoom lens according to claim 5 , wherein

the second lens unit comprises in order from the object side to the image side

a front-side unit having a negative refractive power which includes a negative lens, and

a rear-side unit which includes a positive lens and a negative lens, and

the negative lens in the front-side unit is a glass lens, and

both the positive lens and the negative lens in the rear-side unit are plastic lenses.

16. The zoom lens according to claim 15 , wherein

the following conditional expressions (6) and (7) are satisfied:

−0.3 <n 1 n−n 21 n <−0.09  (6)

n 2 p−n 21 n<− 0.09  (7)

where,

n1n denotes the refractive index with reference to the d-line of the negative lens in the first lens unit,

n21n denotes the refractive index with reference to the d-line of the negative lens in the front-side unit, and

n2p denotes a refractive index with reference to the d-line of the positive lens in the rear-side unit.

17. The zoom lens according to claim 5 , wherein

the zoom lens comprises in order from the object side to the image side:

the first lens unit having a positive refractive power;

the second lens unit having a negative refractive power;

a third lens unit having a positive refractive power; and

a fourth lens unit, and

the following conditional expression (8) is satisfied:

2.0<β3 t/β 3 w   (8)

where,

β3t denotes a lateral magnification at the telephoto end of the third lens unit, and

β3w denotes a lateral magnification at the wide angle end of the third lens unit.

18. The zoom lens according to claim 17 , wherein

the third lens unit comprises in order from the object side to the image side,

a positive lens and a negative lens, and

the total number of lenses in the third lens unit is two.

19. The zoom lens according to claim 5 , wherein

the zoom lens is a four-unit zoom lens, and comprising in order from the object side to the image side:

the first lens unit having a positive refractive power;

the second lens unit having a negative refractive power;

a third lens unit having a positive refractive power; and

a fourth lens unit having a positive refractive power.

20. The zoom lens according to claim 5 , wherein

the rear-side unit comprises in order from the object side to the image side

a negative lens and a positive lens.

21. The zoom lens according to claim 20 , wherein

both the negative lens in the rear-side unit and the positive lens in the rear-side unit are plastic lenses, and

both an object-side surface of the negative lens in the rear-side unit and an image-side surface of the positive lens in the rear-side unit are aspheric surfaces.

22. The zoom lens according to claim 21 , wherein

both an image-side surface of the negative lens in the rear-side unit and an object-side surface of the positive lens in the rear-side unit are spherical surfaces.