Zoom lens

Abstract

An inner-focusing zoom lens that includes multi groups of lens pieces, namely, the first lens group or the leading lens group of positive refractivity, the second lens group of negative refractivity, and the remaining trailing groups of positive refractivity, as a whole. At least one group of positive refractivity among the trailing groups includes two or more negative lens pieces, at least one of which is connected on its surface to another lens piece to form a duplicated composite lens so that the junction between two of them functions to diverge incident beams. Assuming now that a sum of the refractivities of all the junctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities that substances before and after the junction of the composite lenses respectively have, R is a radius of curvature of the junction, ft is a focal length of the comprehensive lens optics of the zoom lens at the telephoto end.

1 . A zoom lens comprising at least five groups of lens pieces, namely, a first lens group or the leading lens group of positive refractivity, a second lens group of negative refractivity, a third lens group of positive refractivity, a fourth lens group of positive refractivity, and a fifth lens group of negative refractivity all arranged in this order on the closest to the photoshot subject foremost basis, or comprising at least six groups of lens pieces, namely, a first lens group or the leading lens group of positive refractivity, a second lens group of negative refractivity, a third lens group of positive refractivity, a fourth lens group of positive refractivity, a fifth lens group of positive refractivity, and a sixth lens group of negative refractivity all arranged in this order on the closest to the photoshot subject foremost basis, wherein
 the first lens group at least includes one negative lens piece and two or more positive lens pieces, and the first lens group provides optical properties as expressed by the following formulae:
   40 <vd 1<55  (2)
 
   20 <vd 2<35  (3)
 
   
       where vd1 is an Abbe number of the negative lens piece(s) in the first lens group, and vd2 is the Abbe number of the positive lens piece(s) in any one of the lens groups of positive refractivity succeeding to the first lens group. 
     
     
         2 . In an inner-focusing zoom lens that does not conduct the floating focusing and that comprises multi groups of lens pieces, namely, the first lens group or the leading lens group of positive refractivity, the second lens group of negative refractivity, and the remaining trailing groups of positive refractivity, as a whole,
 the second lens group includes a meniscus negative lens having its convex surface faced toward the photoshot subject, and a composite lens having negative and positive lens pieces connected to one another, and the second lens group provides optical properties as expressed by the following formulae:
   1 <R/f (wide)<8  (4)
 
   2ω(wide)<40  (5)
 
   
       where R is a radius of curvature of an objective surface of the foremost lens piece in the second lens group, f(wide) is a focal length of the comprehensive lens optics at the wide-angle end, and ω(wide) is a half field angle of the comprehensive lens optics at the wide-angle end. 
     
     
         3 . The zoom lens according to  claim 2 , comprising the first lens group or the leading lens group of positive refractivity, the second lens group of negative refractivity, and the remaining trailing groups of positive refractivity, as a whole, at least one group of positive refractivity among the trailing groups including two or more negative lens pieces, at least one of which is connected on its surface to another lens piece to form a duplicated composite lens so that the junction between two of them functions to diverge incident beams; assuming now that a sum of the refractivities of all the junctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities that substances before and after the junction of the composite lenses respectively have, R is a radius of curvature of the junction, f(tele) is a focal length of the comprehensive lens optics of the zoom lens at the telephoto end, and φ(tele)=1/f(tele) is the refractivity of the comprehensive lens optics at the telephoto end, the requirement as defined in the following formula are satisfied:
   2<Σφ/φ(tele)<10  (6)
 
 
     
     
         4 . The zoom lens according to  claim 2 , wherein at least one group of positive refractivity among the third lens group and all the succeeding lens groups includes a triplicated composite lens of negative-positive-negative power configuration of three of the lens pieces.