Patent ID: 6445511
Filing Date: 2002-09-03
Classification: G02B

Abstract:
An inner-focus-type lens comprising three lens groups of positive, negative and positive refractive power, respectively, in order from the object side, as follows:a first lens group formed of four lens elements of positive, positive, negative and negative refractive power, respectively, in order from the object side; a second lens group having at least one each of a positive lens element and a negative lens element, said second lens group being moved along the optical axis in order to focus the inner-focus-type lens; and a third lens group that includes a stop nearest the object side, and at least one each of a positive lens element and a negative lens element; wherein the following conditions are satisfied: 0.61/f<0.7 âˆ’1.02/f0.73/f<1.6 â€ƒwhere f1 is the focal length of the first lens group, f is the focal length of the inner-focus-type lens when focused at infinity, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.