Zoom lens and image pickup apparatus and image pickup system having the same

An image pickup apparatus comprising:

• a zoom lens;
• and
• an image sensor configured to receive light of an image formed by the zoom lens,
• wherein the zoom lens includes, in order from object side to 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, during zooming from a wide-angle end to a telephoto end, the first lens unit is arranged to move, the distance between the first lens unit and the second lens unit increases, the distance between the second lens unit and the third lens unit decreases, and the distance between the third lens unit and the fourth lens unit decreases,
• wherein the second lens unit consists of a first lens having a negative refractive power and a second lens having a positive refractive power, the second lens being disposed on the image side of the first lens, and
• wherein a following conditional expression is satisfied:
• −0.3<f2/ft<0.0
• where f2 represents a focal length of the second lens unit and ft represents a focal length of the zoom lens at the telephoto end.

An image pickup system comprising:

• a zoom lens;
• and
• a controlling unit configured to control the zoom lens during zooming,
• wherein the zoom lens includes, in order from object side to 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, during zooming from a wide-angle end to a telephoto end, the first lens unit is arranged to move, the distance between the first lens unit and the second lens unit increases, the distance between the second lens unit and the third lens unit decreases, and the distance between the third lens unit and the fourth lens unit decreases,
• wherein the second lens unit consists of a first lens having a negative refractive power and a second lens having a positive refractive power, the second lens being disposed on the image side of the first lens, and
• wherein a following conditional expression is satisfied:
• −0.3<f2/ft<0.0
• where f2 represents a focal length of the second lens unit and ft represents a focal length of the zoom lens at the telephoto end.