Variable magnification optical system, optical equipment, imaging equipment and method for manufacturing variable magnification optical system
A variable magnification optical system comprises, in order from an object side, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, a third lens group G 3 having positive refractive power and a fourth lens group G 4 having negative refractive power; upon varying a magnification, a distance between the first lens group G 1 and the second lens group G 2 being varied, a distance between the second lens group G 2 and the third lens group G 3 being varied, and a distance between the third lens group G 3 and the fourth lens group G 4 being varied; upon focusing, the fourth lens group G 4 being moved; and a predetermined conditional expression being satisfied. With such a configuration, there is provided a variable magnification optical system whose focusing lens group is compact in size and reduced in weight, so high speed and quiet focusing can be effected without lens barrel being made large in size, and further by which variations in aberrations upon varying magnification from the wide angle end state to the telephoto end state as well as variations in aberrations upon focusing from the infinite distance object to the close distance object can be superbly suppressed.
1 . 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 fourth lens group;
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 fourth lens group being varied; and
the following conditional expressions being satisfied:
1.40< f 1/ fw ≤2.115
2.30< f 1/(− f 2)<4.00
where f1 denotes a focal length of the first lens group, f2 denotes a focal length of the second lens group and fw denotes a focal length of the variable magnification optical system in the wide angle end state.
2 . The variable magnification optical system according to claim 1 , comprises a vibration reduction lens group that is movable to have a displacement component in a direction perpendicular to the optical axis,
wherein the following conditional expression is satisfied:
0.70<| fvr|/f 3≤1.111
where f3 denotes a focal length of the third lens group and fvr denotes a focal length of the vibration reduction lens group.
3 . The variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.82<(− f 2)/ f 3<1.25
where f3 denotes a focal length of the third lens group.
4 . The variable magnification optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.55< f 2/ f 4<1.40
where f4 denotes a focal length of the fourth lens group.
5 . The variable magnification optical system according to claim 1 , wherein, upon varying a magnification, the first lens group is fixed in position, with respect to the image plane.
6 . The variable magnification optical system according to claim 1 , wherein, upon varying a magnification, a lens group at the most image side is fixed in position, with respect to the image plane.
7 . The variable magnification optical system according to claim 1 , wherein the first lens group consists of two lens components.
8 . The variable magnification optical system according to claim 1 , wherein the fourth lens group comprises, in order from the object side, a positive lens and a negative lens.
9 . The variable magnification optical system according to claim 8 , wherein the following conditional expression is satisfied:
2.20< fP /(− fN )≤3.056
where fP denotes a focal length of the positive lens in the fourth lens group and fN denotes a focal length of the negative lens in the fourth lens group.
10 . An optical equipment comprising a variable magnification optical system according to claim 1 .
11 . A method for manufacturing 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 fourth lens group, comprising the steps of:
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 fourth lens group is varied; and
constructing such that the following conditional expressions are satisfied:
1.40< f 1/ fw≤ 2.115
2.30<£1/(− f 2)<4.00
where f1 denotes a focal length of the first lens group, f2 denotes a focal length of the second lens group and fw denotes a focal length of the variable magnification optical system in the wide angle end state.