Zoom lens and image pickup apparatus equipped with the zoom lens

An image pickup apparatus comprising:

• zoom lens comprising, in order from an object side to an image side, a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power,
• wherein the first lens unit does not move for zooming, at least the second and fourth lens units are moved during zooming, the first lens unit includes at least one positive lens 1i, and the following conditions are satisfied:
• 0.5826<θgF1i+0.001618×(νd1i×36.23)<0.8000,
• 0.040<√(|f2|×m2)/ft<0.095, and
• 1.90<n2na<2.50,
• where vd1i and θgF1i denote an Abbe number and a relative partial dispersion, respectively, of a material of the positive lens 1i, n2na denotes an average refractive index of materials of negative lenses included in the second lens unit, m2 denotes a movement amount of the second lens unit for zooming from a wide-angle end to a telephoto end, f2 denotes a focal length of the second lens unit, and ft denotes a focal length of the entire zoom lens at the telephoto end;
• and
• an image sensor configured to receive an image formed by the zoom lens.