Patent ID: 7253973

Claim:
An image-pickup optical system comprising: a first lens unit having positive optical power; an aperture stop; and a second lens unit; wherein the first lens unit, the aperture stop, and the second lens unit are disposed this in order from the object side to the image side of the image-pickup optical system, wherein the image-pickup optical system includes a diffractive optical element which is disposed closer to the object than the aperture stop and is disposed at a position satisfying, 0.1 <φdo/φf <0.7, where φf represents the beam effective diameter of the lens disposed closest to the object in the image-pickup optical system and φdo represents the beam effective diameter of the diffractive optical element, wherein the image-pickup optical system includes a lens which is provided, the lens being composed of a material satisfying, 0.5<θgF<0.6 and 75<νd, where νd represents the Abbe number and θgF represents a partial dispersion ratio, and wherein the lens is disposed at a position satisfying, 0.2<φdo/φa<1.5, where φa represents the beam effective diameter of the lens.