Imaging optical system and optical apparatus using the same

An optical apparatus having an imaging optical system, the imaging optical system including a variable magnification optical system, the variable magnification optical system comprising, in order from an object side toward an image side:

• a first lens unit with positive refractive power;
• a second lens unit with positive refractive power;
• a third lens unit with negative refractive power;
• a fourth lens unit with positive refractive power, and
• an aperture stop interposed between the third lens unit and the fourth lens unit,
• wherein the variable magnification optical system changes an imaging magnification while keeping a distance between an object and an image constant in the imaging optical system, the imaging magnification is changed by varying spacing between the first lens unit and the second lens unit, spacing between the second lens unit and the third lens unit, and spacing between the third lens unit and the fourth lens unit, and when the imaging magnification is changed, the imaging optical system satisfies the following conditions in at least one variable magnification state:
• |En|/L>0.4 |Ex|/|L/β|>0.4
• where En is a distance from a first lens surface on the object side of the variable magnification optical system to an entrance pupil of the imaging optical system, L is the distance between the object and the image in the imaging optical system, Ex is a distance from a most image-side lens surface of the variable magnification optical system to an exit pupil of the imaging optical system, and β is a magnification of an entire system of the imaging optical system.