Zoom lens, image pickup apparatus, and image pickup system

An image pickup apparatus comprising:

• a zoom lens;
• and
• an image sensor configured to receive image light formed by the zoom lens,
• the zoom lens comprising a plurality of lens units, the plurality of lens units consisting of, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a rear group including two or more lens units,
• wherein a distance between adjacent lens units changes during zooming from a wide-angle end to a telephoto end,
• wherein the first lens unit is fixed relative to an image plane during zooming from the wide-angle end to the telephoto end,
• wherein the first lens unit includes single lens having negative refractive power closest to an object, and a plurality of lenses having positive refractive powers disposed on the image side of the single lens,
• wherein an air lens is formed by an air gap between the single lens and a lens adjacent to and disposed on the image side of the single lens, and
• wherein the following inequalities are satisfied:
• −0.7<(r112+r111)/(r112−r111)<0.4
• 1.0<f1/(−f2)<4.2
• 0.1<T1/f1<0.65
• where r111 is a radius of curvature of a lens surface on the object side of the single lens, r112 is a radius of curvature of a lens surface on the image side of the single lens, f1 is a focal length of the first lens unit, f2 is a focal length of the second lens unit, and T1 is a distance on an optical axis from a lens surface closest to the object of the first lens unit to a lens surface closest to the image plane of the first lens unit.