Zoom lens and image pickup apparatus including the same
A zoom lens includes, in order from an object side toward an image side, a first lens unit having a positive refractive power, a 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. The second lens unit, the third lens unit, and the fourth lens unit are moved during zooming. A position of the third lens unit at a telephoto end is closer to the object side than a position of the third lens unit at a wide-angle end. The focal length of the zoom lens at the wide-angle end, the difference in the position of the second lens unit on an optical axis between that at the wide-angle end and that at the telephoto end, and the focal length of the second lens unit are set appropriately.
1. A zoom lens comprising, in order from an object side toward an image side:
a first lens unit having a positive refractive power;
a 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,
wherein the second lens unit, the third lens unit, and the fourth lens unit are moved during zooming,
wherein a position of the third lens unit at a telephoto end is closer to the object side than a position of the third lens unit at a wide-angle end, and
wherein the zoom lens satisfies the following conditional expressions:
−3.2< f 2/ fw<− 2.0
3.5<| m 2/ f 2|<5.1
1.0<(β3 t/β 3 w )×(β4 t/β 4 w )<5.0
where fw denotes a focal length of the zoom lens at the wide-angle end, m2 denotes a difference with respect to an image plane in positions of the second lens unit on an optical axis between that at the wide-angle end and that at the telephoto end, f2 denotes a focal length of the second lens unit, β3 w and β3 t denote lateral magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, and β4 w and β4 t denote lateral magnifications of the fourth lens unit at the wide-angle end and at the telephoto end, respectively.
2. The zoom lens according to claim 1 , further satisfying the following conditional expression:
2.5<β2 t/β 2 w< 25.0
where β2 w denotes lateral magnification of the second lens unit at the wide-angle end and β2 t denotes lateral magnification of the second lens unit at the telephoto end.
3. The zoom lens according to claim 1 , further satisfying the following conditional expression:
0.1<| m 3/ m 2|<0.5
where m3 denotes a difference with respect to the image plane in positions of the third lens unit on the optical axis between that at the wide-angle end and that at the telephoto end.
4. The zoom lens according to claim 1 , wherein an image formed by the zoom lens is moved in a direction perpendicular to the optical axis by moving the entirety or part of the third lens unit in a direction nonparallel to the optical axis.
5. The zoom lens according to claim 1 , wherein the second lens unit includes, in order from the object side toward the image side, a negative lens component, another negative lens component, and a positive lens component.
6. The zoom lens according to claim 1 , wherein the third lens unit includes, in order from the object side toward the image side, a positive lens component, another positive lens component, and a negative lens component.
7. The zoom lens according to claim 1 , wherein an image circle of the zoom lens at the wide-angle end is smaller than an image circle of the zoom lens at the telephoto end.
8. An image pickup apparatus comprising:
a zoom lens; and
an image pickup device that receives an image formed by the zoom lens, wherein the zoom lens comprises in order from an object side toward an image side:
a first lens unit having a positive refractive power;
a 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,
wherein the second lens unit, the third lens unit, and the fourth lens unit are moved during zooming,
wherein a position of the third lens unit at a telephoto end is closer to the object side than a position of the third lens unit at a wide-angle end, and
wherein the zoom lens satisfies the following conditional expressions:
−3.2< f 2/ fw<− 2.0
3.5<| m 2/ f 2|<5.1
1.0<(β3 t/β 3 w )×(β4 t/β 4 w )<5.0
where fw denotes a focal length of the zoom lens at the wide-angle end, m2 denotes a difference with respect to an image plane in positions of the second lens unit on an optical axis between that at the wide-angle end and that at the telephoto end, f2 denotes a focal length of the second lens unit, β3 w and β3 t denote lateral magnifications of the third lens unit at the wide-angle end and at the telephoto end, respectively, and β4 w and β4 t denote lateral magnifications of the fourth lens unit at the wide-angle end and at the telephoto end, respectively.