Zoom lens and image pickup apparatus having the same

An image pickup apparatus comprising:

• a solid-state image sensor;
• and
• a zoom lens configured to form an object image on the solid-state image sensor,
• wherein the zoom lens comprises, in order from an object side to an image side:
• a first lens unit having a positive refractive power configured not to move for zooming;
• a second lens unit having a negative refractive power configured to move during zooming;
• a third lens unit having a positive refractive power configured to move during zooming;
• and
• a fourth lens unit having a positive refractive power configured not to move for zooming,
• characterized in that the third lens unit includes a positive lens, a negative lens, and a diffractive optical element, and
• that a focal length (fc) of the third lens unit, a focal length (fdoe) of a diffraction portion of the diffractive optical element, a focal length (fW) at a wide angle end of the zoom lens, and a focal length (fT) at a telephoto end of the zoom lens satisfy the following conditions:
• 0.35<fc/√{square root over ((fW·fT))}<0.81, and
• 45<fdoe/fc<300.