Zoom lens and image pickup apparatus including the same

An image pickup apparatus, comprising:

• a camera;
• and
• a zoom lens;
• wherein the zoom lens includes, in an order from an object side:
• a first lens unit having positive refractive power which does not move for varying magnification;
• a second lens unit having negative refractive power which moves in an optical axis direction during varying magnification;
• a third lens unit which moves in the optical axis direction during varying magnification;
• and
• a fourth lens unit having positive refractive power which does not move for varying magnification, wherein:
• the fourth lens unit comprises, in an order from the object side, a first sub lens unit having positive refractive power, and a second sub lens unit having positive refractive power;
• the first sub lens unit and the second sub lens unit are separated by a largest air interval in the fourth lens unit;
• the second sub lens unit comprises at least one refracting optical element having positive refractive power;
• the following conditions are satisfied:
• −2.100×10−3×vdm+0.693<θgFm;
• and
• 0.555<θgFm<0.900,
• where “θgFm” and “vdm” represent a partial dispersion ratio and an Abbe constant of the refracting optical element, respectively, provided that:
• vdm=(Nd−1)/(NF−NC);
• and
• θgFm=(Ng−NF)/(NF−NC),
• where “Ng”, “NF”, “Nd”, and “NC” represent refractive indices for a g-line, an F-line, a d-line, and a C-line, respectively;
• and
• the third lens unit, the first sub lens unit, and the second sub lens unit each satisfy the following conditions for lenses except the refracting optical element having positive refractive power included in the second sub lens unit:
• 1.5×10−5<Σi,j(φpij×(dn/dT)pij)/Σiφi<3.0×10−5
• (i=3, 4a, 4b) (j=1, 2, . . . , Spi);
• and
• −4.0×10−5<Σi,j(φnij×(dn/dT)nij)/Σiφi<−2.5×10−5
• (i=3, 4a, 4b) (j=1, 2, . . . , Sni),
• where “φpij” represents refractive power of a j-th lens having positive refractive power from the object side in an i-th lens unit, “φnij” represents refractive power of a j-th lens having negative refractive power from the object side in the i-th lens unit, “φi” represents refractive power of the i-th lens unit, “(dn/dT)pij” represents a coefficient of refractive index variation due to temperature variation (an average value in a range of −20° C. to 40° C.) in air on an e-line of the j-th lens having positive refractive power other than the refracting optical element among lenses having positive refractive power from the object side in the i-th lens unit “(dn/dT)nij” represents a coefficient of refractive index variation due to temperature variation (an average value in a range of −20° C. to 40° C.) in the air on the e-line of the i-th lens having negative refractive power from the object side in the i-th lens unit “Spi” represents a number of lenses having positive refractive power in the i-th lens unit other than the refracting optical element, and “Sni” represents a number of lenses having negative refractive power in the i-th lens unit.