Zoom lens system, imaging device and camera

Abstract

A zoom lens system includes a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power, a fourth lens unit having negative optical power, and a fifth lens unit having positive optical power. A condition of 18.5<f G1 /f W <30.0 (f G1 : a focal length of the first lens unit, f W : a focal length of the entire system at the wide-angle limit) and a condition of 1.1<m 5T /m 5W <2.0 (m 5T is a lateral magnification of the fifth lens unit at the telephoto limit, and m 5W is a lateral magnification of the fifth lens unit at the wide-angle limit) are satisfied.

What is claimed is: 
     
         1 . A zoom lens system, in order from an object side to an image side, comprising:
 a first lens unit having positive optical power;   a second lens unit having negative optical power;   a third lens unit having positive optical power;   a fourth lens unit having negative optical power; and   a fifth lens unit having positive optical power, wherein   in zooming from a wide-angle limit to a telephoto limit at the time of image taking, at least the first lens unit, the second lens unit, and the third lens unit move along an optical axis so that an interval between the first lens unit and the second lens unit at the telephoto limit becomes larger than that at the wide-angle limit, and an interval between the second lens unit and the third lens unit at the telephoto limit becomes narrower than that at the wide-angle limit, an aperture diaphragm is disposed between the second lens unit and the third lens unit, and   the following conditions (1) and (3) are satisfied:
   18.5< f   G1   /f   W <30.0  (1)
 
   1.1< m   5T   /m   5W <2.0  (3)
 
   where   f G1  is a focal length of the first lens unit,   f W  is a focal length of the entire system at the wide-angle limit,   m 5T  is a lateral magnification of the fifth lens unit at the telephoto limit, and   m 5W  is a lateral magnification of the fifth lens unit at the wide-angle limit.   
     
     
         2 . The zoom lens system as claimed in  claim 1 , wherein the fourth lens unit is a focusing lens unit that moves along the optical axis in focusing from an infinity in-focus condition to a close-object in-focus condition. 
     
     
         3 . The zoom lens system as claimed in  claim 1 , wherein, in zooming from the wide-angle limit to the telephoto limit at the time of image taking, the respective lens units move along the optical axis so that the interval between the third lens unit and the fourth lens unit at the telephoto limit becomes larger than that at the wide-angle limit. 
     
     
         4 . An imaging device capable of outputting an optical image of an object as an electric image signal, comprising:
 a zoom lens system that forms an optical image of the object; and   an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein   the zoom lens system is a zoom lens system as claimed in  claim 1 .   
     
     
         5 . A camera for converting an optical image of an object into an electric image signal and then performing at least one of displaying and storing of the converted image signal, comprising:
 an imaging device including a zoom lens system that forms the optical image of the object, and an image sensor that converts the optical image formed by the zoom lens system into the electric image signal, wherein   the zoom lens system is a zoom lens system as claimed in  claim 1 .