Patent ID: 7593167

Claim:
A three-unit zoom lens system comprising in order from an object side thereof: a first lens unit having a negative refracting power; a second lens unit having a positive refracting power; and a third lens unit having a refracting power, wherein at the time of zooming from a wide angle end to a telephoto end, a distance between the first lens unit and the second lens unit is narrowed, and a distance between the second lens unit and the third lens unit changes, and the second lens unit moves toward the object side at the time of zooming from the wide angle end to the telephoto end, the third lens unit moves to a position of increasing magnification at the telephoto end with respect to a position at the wide angle end, and the first lens unit comprises a biconcave negative lens component nearest to the object, and the biconcave negative lens component is the only negative lens component in the first lens unit, and the second lens unit comprises a cemented lens component which includes three lenses in order from the object side namely, a first positive lens, a negative lens, and a second positive lens, and these three lenses are cemented mutually on an optical axis, and the total number of lens components in the second lens unit is one, and a surface on the image side of the negative lens in the second lens unit is a concave surface, and the negative lens in the second lens unit has an Abbe's number smaller than the Abbe's number of the first positive lens and the second positive lens, and has a refractive index higher than a refractive index of the second positive lens, and the third lens unit comprises a lens component, and the total number of lens components in the third lens unit is one, and the three-unit zoom lens system satisfies the following conditional expressions f t /f w >3.6 (1) 0<( r L11f +r L11r )/( r L11f −r L11r )<1.0 (2) where, F w denotes a focal length of the three-unit zoom lens system, at the wide angle end, f t denotes a focal length of the three-unit zoom lens system at the telephoto end, r L11f denotes a paraxial radius of curvature of a surface on the object side, of the biconcave negative lens element in the first lens unit, and r L11r denotes a paraxial radius of curvature of a surface on the image side, of the biconcave negative lens in the first lens unit, and the lens component is a lens having only two surfaces which make a contact with air on the optical axis, namely a surface on the object side and a surface on the image side, and means a single lens or a cemented lens.