Large aperture zoom optical system and image pickup apparatus

A large aperture zoom optical system, comprising, successively from an object side to an image side:

• a first lens group having a positive refractive power;
• a second lens group having a negative refractive power;
• a third lens group having a positive refractive power;
• a fourth lens group having a negative refractive power;
• and
• a fifth lens group having a positive refractive power,
• wherein the fifth lens group is fixed, and at least the second lens group, the third lens group and the fourth lens group are moved toward the image side at the time of zooming from a wide angle end to a telephoto end,
• wherein the third lens group comprises a single lens element,
• wherein the third lens group is moved toward the image side at the time of focusing from an object at an infinite distance to an object at a short distance for focusing, and
• wherein the single lens element of the third lens group meets the following conditional expression (1):
• 0.2<(R1+R2)/(R1−R2)<0.75 (1)
• where
• R1:
• a curvature radius of an object-side surface of the single lens element, and
• R2:
• a curvature radius of an image-side surface of the single lens element.