Patent ID: 8508836

Claim:
An image pickup optical system, comprising: a plurality of lenses and an aperture stop; wherein the plurality of lenses consists of five lenses, the image pickup optical system comprising in order from an object side: the aperture stop; a first lens having a positive refracting power; a second lens having a negative refracting power; a third lens; a fourth lens having a positive refracting power; and a fifth lens having a negative refracting power, wherein the image pickup optical system has a fixed focal length, and at least one of surfaces of the fifth lens has an inflection point, and the image pickup optical system satisfies the following conditional expressions −1.27< r 8/ f<− 0.25 0.36< f 4/ f≦ 0.98 where, f denotes a focal length of the overall image pickup optical system, f4 denotes a focal length of the fourth lens, and r8 denotes a paraxial radius of curvature of an object side surface of the fourth lens.