Image pickup optical system and image pickup apparatus
An image pickup optical system according to the present invention includes: a first lens group having a positive power; a second lens group having a negative power; a third lens group having a positive power; and a fourth lens group having a positive power which consists of a front group with a negative power and a rear group with a positive power. The first lens group moves to the object side and a distance between each neighboring lens groups changes, for varying power of the image pickup optical system. One group of the front group and the rear group in the fourth lens group consists of one lens which moves substantially perpendicular to an optical axis for a shake compensation. The image pickup optical system fulfills the predetermined conditional formula according to a focal length of the first lens group.
1. An image pickup optical system for forming a light flux from an object into an optical image on an image pickup element, the image pickup optical system comprising, in order from an object side thereof:
a first lens group having a positive power;
a second lens group having a negative power;
a third lens group having a positive power; and
a fourth lens group having a positive power which consists of, in order from the object side, a front group with a negative power and a rear group with a positive power,
wherein the first lens group moves to the object side and a distance between each neighboring lens groups changes, for varying a power of the image pickup optical system from a wide-angle end to a telephoto end,
one group between the front group and the rear group in the fourth lens group consists of one lens which moves substantially perpendicular to an optical axis for a shake compensation, and
the image pickup optical system fulfills following conditional formulas:
5 <f 1 /fw <20,
0.01 <f 3 /f 4<0.6,
where f 1 is a focal length of the first lens group,
fw is a focal length of the image pickup optical system at the wide-angle end,
f 3 is a focal length of the third lens group, and
f 4 is a focal length of the fourth lens group.
2. The image pickup optical system of claim 1 ,
wherein the fourth lens group fulfills a following conditional formula:
−3 <f 4 n/f 4 p <−1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.
3. The image pickup optical system of claim 1 ,
wherein the other group which is not used for the shake compensation in the fourth lens group consists of one lens.
4. The image pickup optical system of claim 1 ,
wherein the third lens group comprises a plurality of lenses including a lens closest to an image side which has an aspheric surface.
5. The image pickup optical system of claim 1 ,
wherein the first lens group consists of a negative lens and a positive lens, in order from the object side.
6. An image pickup optical system for forming a light flux from an object into an optical image on an image pickup element, the image pickup optical system comprising, in order from an object side thereof:
a first lens group having a positive power;
a second lens group having a negative power;
a third lens group having a positive power;
a fourth lens group having a positive power which consists of, in order from the object side, a front group with a negative power and a rear group with a positive power, and
a fifth lens group arranged at an image pickup element side of the fourth lens group,
wherein the first lens group moves to the object side and a distance between each neighboring lens groups changes, for varying power of the image optical system from a wide-angle end to a telephoto end,
one group between the front group and the rear group in the fourth lens group consists of one lens which moves substantially perpendicular to an optical axis for a shake compensation, and
the image pickup optical system fulfills a following conditional formula:
5 <f 1 /fw <20,
where f 1 is a focal length of the first lens group, and
fw is a focal length of the image pickup optical system at the wide-angle end.
7. The image pickup optical system of claim 1 ,
the image pickup optical system fulfills a following conditional formula:
6 <f 1 /fw <15.
8. The image pickup optical system of claim 1 ,
wherein the fourth lens group fulfills a following conditional formula:
−2.5 <f 4 n/f 4 p <−1.1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.
9. The image pickup optical system of claim 1 ,
wherein the image pickup optical system fulfills a following conditional formula:
0.1 <f 3 /f 4 <0.6,
where f 3 is a focal length of the third lens group, and
f 4 is a focal length of the fourth lens group.
10. An image pickup apparatus comprising:
the image pickup optical system of claim 1 ; and
an image pickup element for receiving a light flux guided by the image pickup optical system.
11. The image pickup apparatus of claim 10 ,
wherein the fourth lens group in the image pickup optical system fulfills a following conditional formula:
−3 <f 4 n/f 4 p <−1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.
12. The image pickup apparatus of claim 10 ,
wherein the other group which is not used for the shake compensation in the fourth lens group in the image pickup optical system consists of one lens.
13. The image pickup apparatus of claim 10 ,
wherein the image pickup optical system further comprises a fifth lens group arranged at an image pickup element side of the fourth lens group.
14. The image pickup apparatus of claim 10 ,
wherein the image pickup optical system fulfills a following conditional formula:
6 <f 1 /fw <15.
15. The image pickup apparatus of claim 10 ,
wherein the fourth lens group in the image pickup optical system fulfills a following conditional formula:
−2.5 <f 4 n/f 4 p <−1.1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.
16. The image pickup apparatus of claim 10 ,
wherein the image pickup optical system fulfills a following conditional formula:
0.1 <f 3 /f 4<0.6,
where f 3 is a focal length of the third lens group, and
f 4 is a focal length of the fourth lens group.
17. The image pickup optical system of claim 1 ,
wherein the fourth lens group fulfills a following conditional formula:
−2.193 <f 4 n/f 4 p <−1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.
18. The image pickup optical system of claim 6 ,
wherein the image pickup optical system fulfills a following conditional formula:
0.01 <f 3 /f 4<1,
where f 3 is a focal length of the third lens group, and
f 4 is a focal length of the fourth lens group.
19. The image pickup optical system of claim 18 ,
wherein the first lens group consists of a negative lens and a positive lens, in order from the object side.
20. The image pickup optical system of claim 10 ,
wherein the fourth lens group fulfills a following conditional formula:
−2.193 <f 4 n/f 4 p <−1,
where f 4 n is a focal length of the front group, and
f 4 p is a focal length of the rear group.