Patent ID: 7760444

Claim:
An imaging optical system comprising in order from an object side thereof: a front lens unit having a negative refracting power; an aperture stop; and a rear lens unit having a positive refracting power, wherein the front lens unit having a negative refracting power includes in order from the object side, a first lens having a negative refracting power, and the rear lens unit having a positive refracting power includes in order from the object side, a second lens which is a positive lens, a third lens which is a negative lens, and a fourth lens which is a positive lens, and the imaging optical system satisfies the following conditional expressions (1) and (2) 1.6 <|f G1 |/F A <5 (1) 1.2 <f G2 /F A <5 (2) where, F A denotes a focal length of the overall imaging optical system, f G1 denotes a focal length of the front lens unit having a negative refracting power, and f G2 denotes a focal length of the rear lens unit having a positive refracting power.