Variable focal length optical system

A variable focal length optical system comprising:

• a first lens unit (G1) having a positive refractive power and arranged to be closest to an object;
• a final lens unit (Gb) having a negative refractive power and arranged to be closest to an image,
• said first lens unit (G1) and said final lens unit (Gb) moving to said object side when a focal length of an entire lens system changes from a smallest focal length state to a largest focal length state;
• and
• an aperture stop arranged on said image side of said first lens unit (G1) and on said object side of said final lens unit (Gb),
• wherein said system satisfies the following conditions:
• 0.25<.vertline.fb.vertline./f1<0.45
• 0.7<M1/f1<0.9
• 0.4<.vertline.fb.vertline./Mb<0.5
• D/fw<0.7
• where f1 is the focal length of said first lens unit (G1), fb is the focal length of said final lens unit (Gb), M1 is the moving amount of said first lens unit (G1) to said object side, which is obtained when the focal length of said entire lens system changes from the smallest focal length state to the largest focal length state, Mb is the moving amount of said final lens unit (Gb) to said object side, which is obtained when the focal length of said entire lens system changes from the smallest focal length state to the largest focal length state, D is the distance along an optical axis between a surface of said lens system, which is closest to said object, and said aperture stop in the smallest focal length state, and fw is the focal length of said entire lens system in the smallest focal length state.