Variable magnification optical system, optical apparatus, and method for producing variable magnification optical system
A variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having positive refractive power; upon varying a magnification, a distance between the first lens group and the second lens group being varied, a distance between the second lens group and the third lens group being varied, and a distance between the third lens group and the rear lens group being varied; the rear lens group comprising a focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expression(s) being satisfied, thereby various aberrations being corrected superbly.
1. A variable magnification optical system comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group having positive refractive power;
upon varying a magnification, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied;
said rear lens group comprising a focusing lens group which is moved upon carrying out focusing; and
the following conditional expressions being satisfied:
−1.00< f 3 f/f 3 r<− 0.0500
0.100< BFw/fw< 1.00
where f3f denotes a focal length of a most image plane side negative lens component in said third lens group; f3r denotes a composite focal length of lens components disposed on a side which is closer to the object than said most image side negative lens component, in said third lens group; BFw denotes a back focus of said variable magnification optical system in a wide angle end state; and fw denotes a focal length of said 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:
2.00< f 1/ fw< 8.000
where f1 denotes a focal length of the first lens group, and fw denotes a focal length of the variable magnification optical system in the wide angle end state.
3. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
0.040<β Fw< 0.800
where βFw denotes transverse magnification of the focusing lens group in the wide angle end state.
4. A variable magnification optical system according to claim 1 , wherein
the rear lens group comprises a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power, and
the following conditional expression is satisfied:
−3.000 <f 5 /f 3<−0.500
where f3 denotes a focal length of the third lens group, and f5 denotes a focal length of the fifth lens group.
5. A variable magnification optical system according to claim 4 , wherein
said fourth lens group comprises said focusing group.
6. A variable magnification optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
4.000 <f 1 /f 1 Rw< 9.000
where f1 denotes a focal length of the first lens group, and f1Rw denotes a composite focal length of lens groups in the wide angle end state disposed on the side which is closer to the image plane than the first lens group.
7. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
nd 3 fp< 1.800
where nd3fp denotes refractive index of a lens having the largest refractive index in the third lens group.
8. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
50.000<ν d 3 p
where νd3p denotes Abbe's number of a lens having the smallest Abbe's number in the third lens group.
9. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
0.500<1/β Rw< 1.000
where βRw denotes a transverse magnification of lens group disposed at the most image plane side in the wide angle end state.
10. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
0.500< f 2 fn/f 2<1.100
where f2fn denotes a focal length of a most object side lens component in the second lens group, and f2 denotes a focal length of the second lens group.
11. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
0.300< fF/ft< 1.400
where fF denotes a focal length of the focusing lens group, and ft denotes a focal length of the variable magnification optical system in the telephoto end state.
12. A variable magnification optical system according to claim 1 , wherein
the following conditional expression is satisfied:
40.00 °<ωw< 85.00°
where ωw denotes a half angle of view of the variable magnification optical system in the telephoto end state.
13. An optical apparatus comprising a variable magnification optical system according to claim 1 .
14. A method for manufacturing a variable magnification optical system which comprises, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power and a rear lens group having positive refractive power; the method comprising the following steps:
constructing such that, upon varying a magnification, a distance between the first lens group and the second lens group is varied, a distance between the second lens group and the third lens group is varied, and a distance between the third lens group and the rear lens group is varied;
constructing such that the rear lens group comprises a focusing lens group which is moved upon carrying out focusing; and
constructing such that the following conditional expressions are satisfied:
−1.00< f 3 f/f 3 r<− 0.0500
0.100 <BFw/fw< 1.00
where f3f denotes a focal length of a most image plane side negative lens component in said third lens group; f3r denotes a composite focal length of lens components disposed on a side which is closer to the object than the most image plane side negative lens component, in the third lens group; BFw denotes a back focus of the variable magnification optical system in a wide angle end state; and fw denotes a focal length of the variable magnification optical system in the wide angle end state.