Patent ID: 7872809

Claim:
An optical system, comprising, in order from an object side thereof, a first lens group of negative refracting power, and a second lens group of positive refracting power, and further comprising a cemented lens which has generally positive refracting power and in which three or more lenses including at least one negative lens are cemented together, wherein: said optical system has a zoom ratio of at least 2, and satisfies conditions (11) and (12): | F co /F ci <0.95 (11) 0.05 <D co /D ci <20 (12) where F co is a focal length of the lens located in said cemented lens and nearest to an object side thereof, F ci is a focal length of the lens located in said cemented lens and nearest to an image plane side thereof, D co is an axial thickness of the lens located in said cemented lens and nearest to the object side thereof, and D ci is an axial thickness of the lens located in said cemented lens and nearest to the image plane side thereof.