Zoom lens and image pickup apparatus equipped with same

1. A zoom lens comprising, in order from the object side:

a first lens unit having a negative refractive power;

a second lens unit having a positive refractive power; and

a third lens unit having a positive refractive power, wherein

the first lens unit comprises a negative lens and a positive lens, and

the negative lens in the first lens unit is a biconcave lens, the first lens unit and the second lens unit move in such a way as to vary the distance between the first lens unit and the second lens unit, and

the zoom lens satisfies the following conditional expression expressions (1), (4) and (11):

Σd 13 /f t <0.4 0.37  (1)

|m 2G |/f w >4.6  (4), and

d 1m /I h <0.2  (11)

where Σd 13 is the total sum of the thickness of the lenses included in the first to third lens units of the zoom lens on the optical axis, and f t is the focal length of the entire zoom lens system at the telephoto end, f w is the focal length of the entire zoom lens system at the wide angle end, m 2G is the amount of shift of the second lens unit on the optical axis during zooming from the wide angle end to the telephoto end, and d 1m is the thickness of the negative lens in the first lens unit on the optical axis, and I h is the largest image height of the zoom lens on an image pickup surface of the zoom lens.

2. The zoom lens according to claim 1 , wherein the zoom lens satisfies the following conditional expression (2):

Σd/f t <0.45   (2)

where Σd is the total sum of the thickness of all the lenses included in the zoom lens on the optical axis.

3. The zoom lens according to claim 1 , wherein the first lens unit and the second lens unit move in such a way as to vary the relative distance between the first lens unit and the second lens unit during zooming and the zoom lens satisfies the following conditional expressions expression (3) and (4):

f 1 /f w <−2.5   (3), and

|m 2G |/f w >4.6   (4),

where f 1 is the focal length of the first lens unit, and

f w is the focal length of the entire zoom lens system at the wide angle end,

and m 2G is the amount of shift of the second lens unit on the optical axis during zooming from the wide angle end to the telephoto end.

4. The zoom lens according to claim 1 , wherein the zoom lens satisfies the following conditional expressions (5), (6), (7), and (8):

1.70<n 1nd <1.80   (5)

50<ν 1nd <60   (6)

1.60<n 1pd <1.70   (7), and

20<ν 1pd <30   (8),

where n 1nd is the refractive index of the negative lens in the first lens unit with respect to the d-line, ν 1nd is the Abbe constant (n 1nd −1)/(n F1 −n C1 ) of the negative lens in the first lens unit with respect to the d-line, n C1 is the refractive index of the negative lens in the first lens unit with respect to the C-line, n F1 is the refractive index of the negative lens in the first lens unit with respect to the F-line, n 1pd is the refractive index of the positive lens in the first lens unit with respect to the d-line, ν 1pd is the Abbe constant (n 1pd −1)/(n F2 −n C2 ) of the positive lens in the first lens unit with respect to the d-line, n c2 is the refractive index of the positive lens in the first lens unit with respect to the C-line, and n F2 is the refractive index of the positive lens in the first lens unit with respect to the F-line.

5. The zoom lens according to claim 1 , wherein the zoom lens satisfies the following conditional expressions (3a), (9), and (10):

−3.0<f 1 /f w <−2.5   (3a),

2.05<f 2 /f w <2.20   (9), and

3.9<f 3 /f w <5.2  (10),

where f 1 is the focal length of the first lens unit, f 2 is the focal length of the second lens unit, and f 3 is the focal length of the third lens unit, and f w is the focal length of the entire zoom lens system at the wide angle end.

6. The zoom lens according to claim 1 , wherein the negative lens in the first lens unit is a biconcave lens, the first lens unit and the second lens unit move in such a way as to vary the distance between the first lens unit and the second lens unit, and the following conditional expression (11) is satisfied:

d 1m /I h <0.2  (11),

where d 1m is the thickness of the negative lens in the first lens unit on the optical axis, and I h is the largest image height of the zoom lens on an image pickup surface of the zoom lens.

7. The zoom lens according to claim 1 , wherein the zoom lens satisfies the following conditional expression (12):

f t /f w >4.5   (12),

where f w is the focal length of the entire zoom lens system at the wide angle end.

8. The image pickup apparatus comprising:

a zoom lens according to claim 1 ; and

an image pickup element disposed on the image side of the zoom lens and having an image pickup surface that receives an image formed by the zoom lens.