Image-pickup optical system

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.