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 lens unit, the second lens unit, the third lens unit, and the fourth lens unit are arranged in that order from an object side to an image side,
• wherein the zoom lens performs zooming by changing distances between the lens units,
• wherein the first lens unit includes two or less lenses and the second lens unit consists of a negative lens and a positive lens in that order from the object side to the image side, and
• wherein the following condition is satisfied:
• −1.3<m1/√{square root over ((fw·fT))}<−0.8
• where fw and fT are focal lengths of the entire zoom lens at a wide-angle end and a telephoto end, respectively, and m1 is an amount of movement of the first lens unit in an optical axis direction during zooming from the wide-angle end to the telephoto end, the amount of movement m1 being positive when the first lens unit moves toward the image side and negative when the first lens unit moves toward the object side.