Patent ID: 7920341

Claim:
An optical system comprising, in order from the object: a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power; at least one of the first lens group, the second lens group, the third lens group, and the fourth lens group has at least one A lens which satisfies the following conditional expressions: 1.85000<nA −0.92 <fA/fG<− 0.10 where nA denotes a refractive index of a medium of the A lens at d-line in which wavelength λ=587.6 nm, fA denotes a focal length of the A lens, and fG denotes a focal length of the lens group having the A lens; and a lens group or a portion of a lens group in the optical system being shifted as a vibration reduction lens group in a direction perpendicular to the optical axis for correcting an image blur upon generating a camera shake, and the vibration reduction lens group includes the A lens.