Zoom lens and image pickup apparatus including the same

A zoom lens, comprising:

• 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 first, second, third, and fourth lens units are arranged in order from an object side to an image side, respectively,
• wherein, during zooming from a wide-angle end to a telephoto end, the first lens unit moves along a locus that is convex toward the image side, the second lens unit moves along a locus that is convex toward the image side in a zoom range from the wide-angle end to an intermediate zoom position and along a locus that is convex toward the object side in a zoom range from the intermediate zoom position to the telephoto end, and the third lens unit moves such that the distance between the third lens unit and the second lens unit at the telephoto end is smaller than that at the wide-angle end, and
• wherein, when f1 is a focal length of the first lens unit and ft is a focal length of the entire lens system of the zoom lens at the telephoto end, a following condition is satisfied:
• 0.3<f1/ft<1.1