Patent ID: 7768716

Claim:
A zoom optical system comprising: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; and a third lens unit having a positive refractive power which are arranged in order from an object side, at least the first and second lens units being moved to change spaces between the lens units, thereby varying magnification, wherein the first lens unit includes a double-concave negative lens, the second lens unit includes a positive lens and a negative lens in order from the object side, the third lens unit includes a positive lens, a total number of lens units included in the zoom optical system is three, a total number of lenses included in the zoom optical system is four, and the following condition is satisfied: −5.0<( r 5+ r 6)/( r 5− r 6)<2.0 (1) wherein r 5 denotes a radius of curvature of an image-side surface of the positive lens in the second lens unit on an optical axis, and r 6 denotes a radius of curvature of an object-side surface of the negative lens in the second lens unit on the optical axis.