Zoom image pickup optical system

a) Field of the Invention A zoom image pickup optical system including, in order from the object 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 fourth lens unit having positive refractive power, in which at least the second lens unit and the fourth lens units are moved along an optical axis to change a magnification, in which the third lens unit includes at least two lens components, in which the fourth lens unit includes at least two lens components, and in which radii of curvature on at least one of pairs of surfaces of the third lens unit and the fourth lens unit such as an image side surface of a most image side lens component in the third lens unit and an object side surface of a most object side lens component in the fourth lens unit which correspond to each other with regard to an airspace between the third lens unit and the fourth lens unit have different signs.