Zoom lens and image pickup apparatus including the same

An image pickup apparatus, comprising:

• a zoom lens comprising in order from an object side:
• a first lens unit having a positive refractive power which does not move for zooming;
• a second lens unit having a negative refractive power which moves during varying magnification;
• a third lens unit having a positive refractive power which moves during varying magnification;
• and
• a fourth lens unit having a positive refractive power which does not move for varying magnification,
• wherein the third lens unit moves toward an image side and then toward the object side when varying magnification from a wide angle end to a telephoto end, and
• wherein the zoom lens satisfying the following relationships:
• −3.2<f1/f2<−1.0;
• −0.55<f2/f3<−0.20;
• and
• −0.7<1/β3w<0.5,
• where f1 is a focal length of the first lens unit, f2 is a focal length of the second lens unit, f3 is a focal length of the third lens unit, and β3w is a lateral magnification of the third lens unit at the wide angle end when a ray enters from infinity;
• and
• a solid-state image pick-up element for receiving an image formed by the zoom lens.