Zoom lens and image pickup apparatus
View Patent ↗A zoom lens has first to fifth lens groups G 1 to G 5 having positive, negative, positive, positive, and negative refractive power, in order from an object side. The first lens groups G 1 includes a prism L 2 for bending a light path. Zooming is performed by adjusting a focal length by linear movement of the second lens group G 2 and fourth lens group G 4 and compensating an image surface position by nonlinear movement of the fifth lens group G 5 . Focusing is performed by moving the fifth lens group G 5.
1. A zoom lens comprising, in order from the object side:
a first lens group having a positive refractive power and including an optical element for bending a light path;
a second lens group having a negative refractive power;
a third lens group having a positive refractive power;
a fourth lens group having a positive refractive power; and
a fifth lens group having a negative refractive power, and wherein:
zooming is performed by moving the second, fourth, and fifth lens groups and focusing is performed from an infinitely distant object to a closely located object by moving the fifth lens group towards an image surface side.
2. The zoom lens according to claim 1 , wherein, when zooming, a focal length is changed by linear movement of the second and fourth lens groups, and a compensation is made by nonlinear movement of the fifth lens group as to deviation of an image surface position in conjunction with the focal length change.
3. The zoom lens according to claim 1 , further comprising movement means for moving the second and fourth lens groups, and wherein the movement means comprise a single motor and a transfer mechanism for transferring a driving force of the motor to each of the second and fourth lens groups as straight linear motion of different moving directions and distances.
4. The zoom lens according to claim 3 , wherein the transfer mechanism comprising:
a shaft having a first male thread and a second male thread having a threading direction and a lead amount different from the first male thread formed thereon, and rotating in conjunction with rotations of the motor;
a first movable body threadably mounted by the first male thread of the shaft and physically connected to the second lens group; and
a second movable body threadably mounted by the second male thread of the shaft and physically connected to the fourth lens group.
5. The zoom lens according to claim 1 , wherein of the relationship 2.2<|D 2 /D 4 |<5.0, wherein a stroke from a short focal length end to a long focal length end of the second lens group is D 2 and a stroke from a short focal length end to a long focal length end of the fourth lens group is D 4 , is satisfied.
6. The zoom lens according to claim 1 , wherein of the relationship nd2>1.78, vd2<26.5, wherein a refractive index of the optical element for bending a light path is nd2 and its Abbe number is vd2, is satisfied.
7. The zoom lens according to claim 1 , wherein the fifth lens group consists of one single lens having a negative refractive power.
8. The zoom lens according to claim 7 , wherein either an object side or an image surface side of the single lens of the fifth lens group is aspheric.
9. The zoom lens according to claim 7 , wherein the single lens of the fifth lens group satisfies of the relationship vd5≦30.0 when the Abbe number of a line d is vd5.
10. An image pickup apparatus including a zoom lens comprising, in order from an object side:
a first lens group having a positive refractive power and including an optical element for bending a light path;
a second lens group having a negative refractive power;
a third lens group having a positive refractive power;
a fourth lens group having a positive refractive power; and
a fifth lens group having a negative refractive power, wherein zooming is performed by moving the second, fourth, and fifth lens groups, and focusing is performed from an infinitely distant object to a closely located object by moving the fifth lens group towards an image surface side.