Variable power optical system and image pickup apparatus having the same

An image pickup apparatus comprising a variable power optical system and an imaging sensor,

• wherein the variable power optical system comprises, at least, in order from an object side,
• a first lens group with negative refractive power,
• a second lens group with positive refractive power,
• a third lens group, and
• a fourth lens group with positive refractive power, which is a rearmost lens group from the object side,
• wherein the variable power optical system has a magnification-changing group with positive refractive power, which is one of the second lens group and the third lens group,
• wherein the magnification-changing group comprises, in order from the object side, a first lens element with positive refractive power, a second lens element having a convex shape on the object side, and a third lens element,
• wherein the rearmost lens group includes a positive lens,
• wherein the first lens group is made to keep still in changing magnification from a wide angle end position to a telephoto end position, and
• wherein the following conditions are satisfied:
• 10≦VdLg≦45
• −1.0<(R2a−R2b)/(R2a+R2b)<1.0
• 1.0≦|f1|/IH≦2.8
• where VdLg denotes an Abbe's Number of the positive lens of the rearmost lens group with respect to the d line, R2a denotes a radius of curvature of an object-side surface of the second lens element of the magnification-changing group, R2b denotes a radius of curvature of an image-side surface of the third lens element of the magnification-changing group, f1 denotes a focal length of the first lens group, and IH denotes an image height of the imaging sensor.