Patent ID: 8526124

Claim:
An optical system comprising: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; and a third lens unit having a positive or negative refractive power, the first, second, and third lens units being disposed in order from an object side to an image side, wherein the first lens unit is configured by a first partial lens unit and a second partial lens unit each having a positive refractive power, wherein the first partial lens unit is configured by a positive single lens, the first partial lens unit having at least one aspherical surface, wherein the second partial lens unit is configured by a positive lens and a negative lens, the second partial lens unit having a diffraction optical surface of a diffraction optical element that is rotationally symmetric with reference to an optical axis, wherein the second lens unit is a focus lens unit that is movable in a direction of the optical axis, and wherein the following condition is met: 0 <βasph< 2.0, where βasph is a paraxial lateral magnification of a partial optical system between a final surface of the optical system and a lens surface that is on the image side, adjacent to an aspherical surface disposed closest to the object side when the optical system is focused at infinity.