Variable magnification optical system, optical apparatus, and method for producing variable magnification optical system

Abstract

A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

What is claimed is: 
     
         1 . A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group;
 upon varying a magnification from a wide angle end state to a telephoto end state, the first lens group being moved along an optical axis, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied;   the variable magnification optical system including at least one focusing lens group which is moved upon carrying out focusing from an infinite distance object to a close distance object;   the focusing lens group being composed of one or two lenses; and   the following conditional expressions being satisfied:           0.40       <               -fl         /     ftM1       <       2   .00                       0.80       <               fF         /     ftM1       <       4   .00                       0.70       <               fF         /     ft           <       3.30                   38.00   °       <       ω   w       <       85   .00   °           where f1 denotes a focal length of the first lens group, ftM1 denotes a focal length of the first intermediate lens group in a telephoto end state, fF denotes a focal length of a focusing lens group having a strongest refractive power in the focusing lens groups, ft denotes a focal length of the variable magnification optical system in the telephoto end state, and ωw denotes a half angle of view of the variable magnification optical system in the wide angle end state.   
     
     
         2 . A variable magnification optical system according to  claim 1 , wherein
 the following conditional expression is satisfied:           0.60       <           f1N     /     f1           <       2.00           where f1N denotes a focal length of a lens having a strongest negative refractive power in the first lens group.   
     
     
         3 . A variable magnification optical system according to  claim 1 , wherein
 the following conditional expression is satisfied:           2.00       <           D1Mw     /     fw           <       4.00           where D1Mw denotes a distance along the optical axis between the first lens group and the first intermediate lens group in the wide angle end state, and fw denotes a focal length of the variable magnification optical system in the wide angle end state.   
     
     
         4 . A variable magnification optical system according to  claim 1 , wherein
 the following conditional expression is satisfied:           2.00       <           υ   M1P     /     υ   M1N       <       3   .00               where νM1P denotes an Abbe’s number of a lens having a strongest positive refractive power in the first intermediate lens group, and νM1N denotes an Abbe’s number of a lens having a strongest negative refractive power in the first intermediate lens group.   
     
     
         5 . A variable magnification optical system according to  claim 1 , wherein the following conditional expression is satisfied:
         0.20       <           fM1P     /     fM1N       <       0   .80               where fM1P denotes a focal length of a lens having a strongest positive refractive power in the first intermediate lens group, and fM1N denotes a focal length of a lens having a strongest negative refractive power in the first intermediate lens group.   
     
     
         6 . A variable magnification optical system according to  claim 1 , wherein the first intermediate lens group comprises at least two lenses having negative refractive power. 
     
     
         7 . A variable magnification optical system according to  claim 1 , wherein the first intermediate lens group comprises, in order from the object side, a second lens group having positive refractive power and a third lens group having positive refractive power. 
     
     
         8 . A variable magnification optical system according to  claim 1 , wherein
 the following conditional expression is satisfied:           0.10       <           BFw     /     fw           <       1.00           where BFw denotes a back focus of the variable magnification optical system in the wide angle end state, and fw denotes a focal length of the variable magnification optical system in the wide angle end state.   
     
     
         9 . An optical apparatus comprising a variable magnification optical system according to  claim 1 . 
     
     
         10 . A method for manufacturing a variable magnification optical system which comprises, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group, comprising the steps of:
 constructing such that, upon varying a magnification from a wide angle end state to a telephoto end state, the first lens group is moved along an optical axis, a distance between the first lens group and the first intermediate lens group is varied, a distance between the first intermediate lens group and the second intermediate lens group is varied, and a distance between the second intermediate lens group and the rear lens group is varied;   constructing such that the variable magnification optical system includes at least one focusing lens group which is moved upon carrying out focusing from an infinite distance object to a close distance object;   constructing such that the focusing lens group is composed of one or two lenses, and   constructing such that the following conditional expressions are satisfied:           0.40       <               -fl         /     ftM1           <       2.00                   0.80       <               fF         /     ftM1           <   4.00                   0.70       <               fF         /     ft           <       3.30                   38.00   °       <       ω   w       <       85   .00   °           where f1 denotes a focal length of the first lens group, ftM1 denotes a focal length of the first intermediate lens group in the telephoto end state, fF denotes a focal length of a focusing lens group having a strongest refractive power in the focusing lens groups, ft denotes a focal length of the variable magnification optical system in the telephoto end state, and ωw denotes a half angle of view of the variable magnification optical system in the wide angle end state.