Patent ID: 8730593

Claim:
An image pickup optical system comprising, in order from an object side to an image side: a first lens unit that does not move for focusing and has a positive optical power; a second lens unit that moves during focusing; an aperture diaphragm; and a third lens unit that does not move for focusing, wherein the image pickup optical system includes a diffractive optical element, and an optical element NLF made of a solid material on the object side of an intersection between a paraxial chief ray and an optical axis, and wherein the following conditional expressions are satisfied where f is a focal length of an entire image pickup optical system in focusing upon an infinitely distant object, f 1 is a focal length of the first lens unit, Fno is an F-number of the entire image pickup optical system in focusing upon an infinitely distant object, d 1a is a distance from a lens surface vertex of the first lens unit closest to an object to a lens surface vertex of the first lens unit closest to an image, f DOE is a focal length only by a diffraction component of the diffractive optical element, f NLF is a focal length of the optical element NLF, and Δθg FNLF is a partial dispersion ratio difference of a material of the optical element NLF: 4.0 <f 2 /( f 1 ×Fno×d 1a )<10.0; 20 <f DOE ×f NLF /f 2 <1000; and 0.0272 <Δθg FNLF <0.3000.