Optical system with long focal length and optical apparatus having the same

An optical apparatus comprising:

• a photoelectric conversion element;
• and
• 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, and
• wherein the photoelectric conversion element configured to receive light of an image formed by the optical system.