Zoom lens and image pickup apparatus having the same

An image pickup apparatus comprising a zoom lens, wherein the zoom lens comprises in order from an object side to an image 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 zooming;
• a third lens unit having a positive or negative refractive power which moves during zooming;
• an aperture stop;
• and
• a fourth lens unit having a positive refractive power which does not move for zooming,
• wherein, in the fourth lens unit, a front group is a lens system including a lens face which satisfies a relationship of
• h_bar_i/h_i≦0.06,
• among lenses in an optical path from the aperture stop to an image plane, and a rear group is a lens system other than the lens system of the front group, where h_i is an incidence height from an optical axis of an on-axis ray of an i-th lens, which is a thin lens, in paraxial tracking and h_bar_i is an incidence height from an optical axis of an off-axis main light beam of the i-th lens in the paraxial tracking, and wherein the zoom lens satisfies the following conditional expressions:
• 0.420<dLm/d<0.710,
• 0.630<θLm<0.690,
• 2.16×10−3<(θRfn−θRfp) / (νRfp−νRfn)<3.10×10−3, and
• 0.17<φRb/φRf<0.61,
• where a partial dispersion ratio of a material of a positive lens Lm formed of a material having a highest partial dispersion ratio, which is contained in the rear group, is represented by θLm,
• a distance from the aperture stop to the image plane is represented by d,
• a distance from the aperture stop to the positive lens Lm is represented by dLm,
• an average value of Abbe constants of materials of positive lenses contained in the front group is represented by νRfp,
• an average value of partial dispersion ratios thereof is represented by θRfp,
• an average value of Abbe constants of materials of negative lenses contained in the front group is represented by νRfn,
• an average value of partial dispersion ratios thereof is represented by θRfn,
• a refractive power of the front group is represented by φRf, and
• a refractive power of the rear group is represented by φRb.