Zoom lens and image pickup apparatus

An apparatus comprising:

• a zoom lens;
• and
• a sensor configured to receive an optical image formed by the zoom lens,
• wherein the zoom lens includes four or more lens units including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power,
• wherein a distance between adjacent lens units varies during zooming from a wide-angle end to a telephoto end,
• wherein the first lens unit moves during zooming,
• wherein a distance between the first lens unit and the second lens unit widens during zooming from the wide-angle end to the telephoto end,
• wherein a distance between the second lens unit and the third lens unit narrows during zooming from the wide-angle end to the telephoto end,
• wherein the first lens unit consists of three or less lenses,
• wherein the second lens unit consists of, in order from the object side to the image side, a first single lens as a spherical lens having a negative refractive power, a cemented lens in which a lens having a negative refractive power and a lens having a positive refractive power are cemented, and a second single lens as a spherical lens having a negative refractive power, and
• wherein following inequalities are satisfied:
• 1.35≤|f2|/skm≤5.00
• 3.1≤d21/d22≤6.0
• 48≤νBC≤80
• 3.5≤|f1/fw|≤10.0
• where skm represents a minimum value of a back focus in an entire zoom area of the zoom lens, f2 represents a focal length of the second lens unit, d21 represents a distance on an optical axis between a lens surface on the image side of the first single lens and a lens surface on a most object side of the cemented lens, and d22 represents a distance on the optical axis between a lens surface on a most image side of the cemented lens and a lens surface on the object side of the second single lens, and νBC represents an average value of an Abbe numbers for a d-line, f1 represents a focal length of the first lens unit, and fw represents a focal length of the zoom lens at the wide-angle end.