Zoom optical system, optical device, and method for manufacturing zoom optical system
A zoom optical system comprises a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a succeeding lens group, which are arranged in order from an object side. During zooming, distances between adjacent said lens groups change. The succeeding lens group comprises a first focusing lens group having a negative refractive power which is moved during focusing, and a second focusing lens group having a positive refractive power which is moved during focusing, which are arranged in order from an object side. Further, the following conditional expression is satisfied: 0.80<(− fF 1)/ fF 2<5.00, where fF1 represents a focal length of the first focusing lens group, and fF2 represents a focal length of the second focusing lens group.
1 . A zoom optical system comprising a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a succeeding lens group, which are arranged in order from an object side,
wherein
the succeeding lens group comprises:
a fourth lens group disposed closest to an object in the succeeding lens group,
a first focusing lens group having a negative refractive power which is disposed closer to an image than the fourth lens group and is moved during focusing, and
a second focusing lens group having a positive refractive power which is disposed on an image side of the first focusing lens group and is disposed next to the first focusing lens group and is moved during focusing,
during zooming, distances between all adjacent lens groups change,
the first focusing lens group and the second focusing lens group are moved axially during zooming, and
the following conditional expressions are satisfied:
0.80<(− fF 1)/ fF 2<5.00
2.70< f 1/(− f 2)<4.50
1.20< f 1/ f 4<4.00
0.42<BF w/fw< 0.85,
where f1 represents a focal length of the first lens group,
f2 represents a focal length of the second lens group,
f4 represents a focal length of the fourth lens group,
BFw represents a back focus of the zoom optical system in a wide angle end state,
fw represents a focal length of the zoom optical system in the wide angle end state,
fF1 represents a focal length of the first focusing lens group, and
fF2 represents a focal length of the second focusing lens group.
2 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
−2.00< mTF 1/ mTF 2<−0.10,
where mTF1 represents an amount of movement of the first focusing lens group during focusing from an infinite distant object to a short-distance object in a telephoto end state (in which the sign of the amount of movement to the object side is +, and the sign of the amount of movement to an image side is represented by −), and
mTF2 represents an amount of movement of the second focusing lens group during focusing from the infinite distant object to the short-distance object in the telephoto end state (in which the sign of the amount of movement to the object side is represented by +, and the sign of the amount of movement to the image side is represented by −).
3 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.10<β TF 1/β TF 2<1.00,
where βTF1 represents a lateral magnification of the first focusing lens group during focusing on an infinite distant object in the telephoto end state, and
βTF2 represents a lateral magnification of the second focusing lens group during focusing on the infinite distant object in the telephoto end state.
4 . The zoom optical system according to claim 1 , wherein the first focusing lens group moves toward an image surface during focusing from an infinite distant object to a short-distance object.
5 . The zoom optical system according to claim 1 , wherein the second focusing lens group moves toward the object during focusing from an infinite distant object to a short-distance object.
6 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
−10.00<(β TF 1/β WF 1)×(β TF 2/β WF 2)<10.00,
where βTF1 represents a lateral magnification of the first focusing lens group during focusing on an infinite distant object in a telephoto end state,
βWF1 represents a lateral magnification of the first focusing lens group during focusing on the infinite distant object in a wide angle end state,
βTF2 represents a lateral magnification of the second focusing lens group during focusing on the infinite distant object in the telephoto end state, and
βWF2 represents a lateral magnification of the second focusing lens group during focusing on the infinite distant object in the wide angle end state.
7 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.80< f 1/ f 3<2.50,
where
f3 represents a focal length of the third lens group.
8 . The zoom optical system according to claim 1 , wherein the third lens group moves toward an image surface during zooming from a wide angle end state to a telephoto end state.
9 . The zoom optical system according to claim 1 , wherein the second lens group comprises a positive lens satisfying the following conditional expression:
18.0<ν dP< 35.0
1.83< ndP +(0.01425×ν dp )<2.12
0.702<θ gFP +(0.00316×ν dP ),
where νdP represents Abbe number based on d-line of the positive lens,
ndP represents a refractive index of the positive lens for the d-line, and
θgFP represents a partial dispersion ratio of the positive lens, and is defined by the following expression:
θ gFP =( ngP−nFP )/( nFP−nCP ),
where a refractive index of the positive lens for g-line is represented by ngP, a refractive index of the positive lens for F-line is represented by nFP, and a refractive index of the positive lens for C-line is represented by nCP.
10 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
25.00°<2ω w< 50.00°,
where 2ωw represents a full angle of view of the zoom optical system in a wide angle end state.
11 . The zoom optical system according to claim 1 , wherein the following conditional expression is satisfied:
5.00°<2ω t< 20.00°
where 2ωt represents a full angle of view of the zoom optical system in a telephoto end state.
12 . An optical device comprising the zoom optical system according to claim 1 and a lens barrel in which the zoom optical system is installed.
13 . The zoom optical system according to claim 1 , wherein
the succeeding lens group comprises, in order from the object side, the fourth lens group having a positive refractive power, a fifth lens group having a negative refractive power, a sixth lens group having a positive refractive power, and a seventh lens group having a negative refractive power, and
the fifth lens group is the first focusing lens group, and the sixth lens group is the second focusing lens group.
14 . A method for manufacturing a zoom optical system comprising:
arranging, in a lens barrel and in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a succeeding lens group,
the arranging being such that
the succeeding lens group comprises:
a fourth lens group disposed closest to an object in the succeeding lens group,
a first focusing lens group having a negative refractive power which is disposed closer to an image than the fourth lens group and is moving during focusing, and
a second focusing lens group having a positive refractive power which is disposed on an image side of the first focusing lens group and is disposed next to the first focusing lens group and is moving during focusing,
during zooming, distances between all adjacent lens groups change,
the first focusing lens group and the second focusing lens group are moved axially during zooming, and
the following conditional expressions are satisfied:
0.80<(− fF 1)/ fF 2<5.00
2.70< f 1/(− f 2)<4.50
1.20< f 1/ f 4<4.00
0.42<BF w/fw< 0.85,
where f1 represents a focal length of the first lens group,
f2 represents a focal length of the second lens group,
f4 represents a focal length of the fourth lens group,
BFw represents a back focus of the zoom optical system in a wide angle end state,
fw represents a focal length of the zoom optical system in the wide angle end state,
fF1 represents a focal length of the first focusing lens group, and
fF2 represents a focal length of the second focusing lens group.