Large aperture zoom optical system and image pickup apparatus

1. A large aperture zoom optical system, comprising, successively from an object side to an image side:

a first lens group having a positive refractive power;

a second lens group having a negative refractive power;

a third lens group having a positive refractive power;

a fourth lens group having a negative refractive power; and

a fifth lens group having a positive refractive power,

wherein the fifth lens group is fixed, and at least the second lens group, the third lens group and the fourth lens group are moved toward the image side at the time of zooming from a wide angle end to a telephoto end,

wherein the third lens group comprises a single lens element,

wherein the third lens group is moved toward the image side at the time of focusing from an object at an infinite distance to an object at a short distance for focusing, and

wherein the single lens element of the third lens group meets the following conditional expression (1):

0.2<( R 1+ R 2)/( R 1− R 2)<0.75  (1)

where

R 1 : a curvature radius of an object-side surface of the single lens element, and

R 2 : a curvature radius of an image-side surface of the single lens element.

2. The large aperture zoom optical system according to claim 1 , wherein the single lens element of the third lens group meets the following conditional expression (1A):

0.24<( R 1+ R 2)/( R 1− R 2)<0.70  (1A)

where

R 1 : a curvature radius of an object-side surface of the single lens element, and

R 2 : a curvature radius of an image-side surface of the single lens element.

3. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (2):

0.9< f 5/ fw< 1.4  (2)

where

f 5 : a focal length of the fifth lens group, and

fw: a focal length of an entirety of the zoom optical system at the wide angle end.

4. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (2A):

0.94 <f 5 /fw< 1.37  (2A)

where

f 5 : a focal length of the fifth lens group, and

fw: a focal length of an entirety of the zoom optical system at the wide angle end.

5. The large aperture zoom optical system according to claim 3 , wherein the fifth lens group includes at least one positive lens element that meets the following conditional expression (3):

ν d> 80  (3)

where

νd: an Abbe number of the positive lens element in the fifth lens group.

6. The large aperture zoom optical system according to claim 3 , wherein the fifth lens group includes at least one positive lens element that meets the following conditional expression (3A):

ν d> 81  (3A)

where

νd: an Abbe number of the positive lens element in the fifth lens group.

7. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (4):

0.68 <f 3 /f 5<0.9  (4)

where

f 3 : a focal length of the third lens group, and

f 5 : a focal length of the fifth lens group.

8. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (4A):

0.73< f 3/ f 5<0.87  (4A)

where

f 3 : a focal length of the third lens group, and

f 5 : a focal length of the fifth lens group.

9. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (5):

1< f 1/ f 5<1.9  (5)

where

f 1 : a focal length of the first lens group, and

f 5 : a focal length of the fifth lens group.

10. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression (5A):

1.11< f 1/ f 5<1.70  (5A)

where

f 1 : a focal length of the first lens group, and

f 5 : a focal length of the fifth lens group.

11. The large aperture zoom optical system according to claim 1 , wherein the fifth lens group comprises, successively from the object side to the image side, a first sub lens group having a positive refractive power, a second sub lens group having a negative refractive power, and a third sub lens group having a positive refractive power,

the fifth lens group meets the following conditional expression (6):

−0.6< f 5 b/f 5 a<− 1.2  (6)

where

f 5 a : a focal length of the first sub lens group of the fifth lens group, and

f 5 b : a focal length of the second sub lens group of the fifth lens group, and

the second sub lens group is moved in a direction perpendicular to an optical axis of the zoom optical system for shake correction.

12. The large aperture zoom optical system according to claim 1 , wherein an F-number is smaller than 3.

13. The large aperture zoom optical system according to claim 1 , wherein the large aperture zoom optical system meets the following conditional expression:

TL/ 2 Y′< 6.0

where

TL: a distance on an optical axis from a lens surface closest to an object, and a focal point on the image side at the wide angle end, and

2Y′: a length of a diagonal line from the object to an image pickup surface of a solid-state image pickup element, or a length of a diagonal line from the object to a rectangular effective pixel region of the solid-state image pickup element.

14. The large aperture zoom optical system according to claim 1 , wherein the third lens group and the fifth lens group each includes a resin lens element manufactured by dispersing particles of 30 nm or smaller in diameter.

15. An image pickup apparatus, comprising:

the large aperture zoom optical system of claim 1 ; and

an image pickup element which converts an optical image into an electrical signal,

wherein the large aperture zoom optical system is operable to form an image of an object on a light receiving surface of the image pickup element.