Variable magnification optical system and image pickup apparatus using the same

A variable magnification optical system having a plurality of lens elements, comprising in order from an object side:

• a first lens unit having a positive refractive power;
• a second lens unit having a negative refractive power;
• a third lens unit having a positive refractive power;
• and
• at least one lens unit, wherein
• an aperture stop which determines an optical axial light beam is positioned between an image-side surface of the second lens unit and an image-side surface of the third lens unit, and
• at a time of zooming from a wide angle end to a telephoto end,
• the second lens unit moves from the object side to an image side, and
• at least one of the lens units positioned on the image side of the aperture stop moves, and
• a second predetermined positive lens element satisfies the following conditional expressions (1) and (2), and
• a second predetermined negative lens element satisfies the following conditional expressions (3) and (4), and
• the second lens unit includes in order from the object side, a first sub-lens unit having a negative refractive power, a second sub-lens unit having a negative lens element, and a third sub-lens unit having a negative lens element, and
• at least one of the second sub-lens unit and the third sub-lens unit includes a positive lens element, and
• the following conditional expressions (5) and (6) are satisfied:
• 0.520<(θg,F)G2p<0.610 (1),
• 0.680<(θC,t)G2p<0.900 (2),
• 0.520<(θg,F)G2n<0.560 (3),
• 0.750<(θC,t)G2n<0.900 (4),
• −0.25<fG21/fG22<0.90 (5), and
• −0.70<fG21/fG23<0.40 (6)
• where,
• fG21 denotes a focal length of the first sub-lens unit,
• fG22 denotes a focal length of the second sub-lens unit,
• fG23 denotes a focal length of the third sub-lens unit,
• (θg, F) G2p denotes a partial dispersion ratio of the second predetermined positive lens element,
• (θC, t) G2p denotes a partial dispersion ratio of the second predetermined positive lens element,
• (θg, F) G2n denotes a partial dispersion ratio of the second predetermined negative lens element,
• (θC, t) G2n denotes a partial dispersion ratio of the second predetermined negative lens element,
• (θg,F)=(ng−nF)/(nF−nC),
• (θC,t)=(nC−nt)/(nF−nC),
• where,
• ng denotes a refractive index for a g-line,
• nF denotes a refractive index for an F-line,
• nC denotes a refractive index for a C-line,
• nt denotes a refractive index for a t-line, and
• the second predetermined positive lens element is all positive lens elements in the second lens unit,
• the second predetermined negative lens element is the negative lens element in the second sub-lens unit and the negative lens element in the third sub-lens unit, and
• the lens element is a lens having a medium of a refractive index higher than 1 filled between an object-side surface and an image-side surface, and having no refracting surface between the object-side surface and the image-side surface.