Zoom lens system having a vibration reduction function

A high performance zoom lens system is provided capable of driving a vibration reduction lens group while securing sufficient brightness (small F-number) and sufficient back focal length. The zoom lens system includes a first lens group G1 of positive refractive power, a second lens group G2 of negative refractive power and a last lens group GL of positive refractive power. An interval between the first lens group G1 and the second lens group G2 increases and an interval between the second lens group G2 and the last lens group varies during zooming from a maximum wide-angle state to a maximum telephoto state. The last lens group GL includes a first lens subgroup GL1 of positive refractive power, a second lens subgroup GL2 of positive refractive power and a third lens subgroup GL3 of either positive or negative refractive power. A displacement device prevents vibration by moving the second lens subgroup GL2 in a direction substantially perpendicular to the optical axis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a zoom lens system having a vibration 
reduction function. More particularly, the present invention relates to 
vibration reduction for zoom lenses used in photographing cameras and 
video cameras. 
2. Description of Related Art 
An example of a conventional zoom lens system having a vibration reduction 
function is disclosed in U.S. Pat. No. 5,270,857, the subject matter of 
which is incorporated herein by reference. In this zoom lens system, 
vibration reduction correction is performed by displacing the entire or 
part of the lens group that moves during zooming in a direction 
perpendicular to the optical axis. 
"Vibration reduction" refers to a process of correcting variations of image 
positions caused by shaking of the hand through movement of the lens group 
in a direction substantially perpendicular to the optical axis. "Vibration 
Reduction" causes a result of "image stabilizing." 
However, in the above-described conventional zoom lens system having the 
vibration reduction function, the lens group that moves in the direction 
perpendicular to the optical axis also moves along the optical axis during 
zooming. Hence, problems occur because of the complexity of the mechanism 
for driving the vibration reduction lens group. The F-number becomes large 
to about 3.5-5.6 while the back focal length for a single lens reflex 
camera cannot be achieved. 
SUMMARY OF THE INVENTION 
The present invention provides a high performance zoom lens system capable 
of driving the vibration reduction lens group with a simple mechanism and 
securing sufficient brightness (small F-number) and adequate back focal 
length. 
The present invention provides a zoom lens system having a vibration 
reduction function. The zoom lens system includes a first lens group G1 of 
positive refractive power closest to the object side, a second lens group 
G2 of negative refractive power on the image side of the first lens group 
G1 and a last lens group GL of positive refractive power on the image side 
of the second lens group. The interval between the first lens group G1 and 
the second lens group G2 increases and the interval between the second 
lens group G2 and the last lens group varies during zooming from the 
maximum wide-angle state to the maximum telephoto state. The last lens 
group GL includes, in order from the object side, a first lens subgroup 
GL1 of positive refractive power, a second lens subgroup GL2 of positive 
refractive power and a third lens subgroup GL3 of either positive or 
negative refractive power. The zoom lens system also includes a 
displacement device to prevent vibration by moving the second lens 
subgroup GL2 in a direction substantially perpendicular to the optical 
axis. In one embodiment, a third lens group G3 of positive refractive 
power is located between the second lens group G2 and the last lens group 
GL. 
The present invention preferably satisfy the following Equations: 
EQU 0.2&lt;fL2/fL&lt;8 (1) 
EQU 0.05&lt;fL2/fl1&lt;5.0 (2) 
where fl1 is the focal length of the lens group GL1, fL2 is the focal 
length of the lens group GL2 and fL is the focal length of the last lens 
group GL. 
The present invention includes, in order from the object side, a first lens 
group G1 of positive refractive power, a second lens group G2 of negative 
refractive power and a last lens group GL of positive refractive power 
closest to the image side in order to function well as a zoom lens system 
for use in photographic cameras and video cameras. The present invention 
also has a structure such that the interval between the first lens group 
G1 and the second lens group G2 increases during zooming from the maximum 
wide-angle state to the maximum telephoto state and the interval between 
the second lens group G2 and its image side lens group varies 
non-linearly. 
The characteristics of a zoom lens system having a basic structure as 
described above will now be explained. 
Zoom lens systems are known to include three lens groups, in order from the 
object side, a first lens group G1 of positive refractive power, a second 
lens group G2 of negative refractive power and a last lens group GL of 
positive refractive power placed closest to the image side. 
If a third lens group G3 of positive refractive power is added on the image 
side of the second lens group G2, a bright zoom lens system is obtained 
having a small F-number and large zoom ratio to achieve favorable imaging 
performance for each focal length state. For example, a photograph-use 
zoom lens system having the above structure and an F-number of about 2.8 
is known in the art. 
The above-mentioned zoom lens system is used as a photographic zoom lens 
system and video camera zoom lens system. 
However, in a zoom lens system according to the present invention, the last 
lens group GL includes, in order from the object side, a first lens 
subgroup GL1 of positive refractive power, a second lens subgroup GL2 of 
positive refractive power and a third lens subgroup GL3 of either positive 
or negative refractive power. Moreover, vibration reduction operation is 
performed by moving the second lens subgroup GL2 in a direction 
substantially perpendicular to the optical axis. Hence, a vibration 
reduction lens group is formed to obtain a high performance zoom lens 
system capable of securing sufficient brightness (f-number) and adequate 
back focal length. 
In a zoom lens system where a lens group of positive refractive power 
precedes the other lens groups, the first lens group G1 closest to the 
object side becomes the largest. Thus, a maintenance/driving device for 
moving the first lens group G1 perpendicular to the optical axis for 
vibration reduction is undesirably large. 
Therefore, it is generally desirable to make the first lens group G1 a 
vibration reduction correction optical system. Moreover, if the second 
lens group provides the vibration reduction function, then the 
maintenance/driving mechanism may be undesirably complicated. 
Hence, in the present invention the vibration reduction operation is 
performed by moving the second lens subgroup GL2 in a direction 
substantially perpendicular to the optical axis to secure favorable 
aberration characteristics. 
In order to perform vibration reduction without changing the image quality 
between the center and the perimeter sections, an aperture stop is 
preferably placed close to the vibration reduction second lens subgroup 
GL2. 
Moreover, because the first lens subgroup GL1 of positive refractive power 
is placed on the object side of the vibration reduction second lens 
subgroup GL2, a diameter of the lens positioned on the image side of the 
vibration reduction lens group GL2 can be made smaller. 
Furthermore, the vibration reduction second lens subgroup GL2 and the 
aperture stop are preferably fixed during zooming along the optical axis 
to simplify the maintenance/driving device. Alternatively, the interval 
between the front and rear of the vibration reduction second lens subgroup 
GL2 is constant during zooming. 
Moreover, when the vibration reduction second lens subgroup GL2 moves 
perpendicularly to the optical axis, light rays in the marginal zone away 
from the optical axis may enter the lens group behind the vibration 
reduction second lens subgroup GL2 as undesired light rays. Undesired 
light causes ghost, unnecessary exposure and the like. Hence, in order to 
avoid the incidence of such harmful light, a flare stop (different from 
the aperture stop) may be fixed relative to the optical axis. 
The present invention preferably satisfies the following Equations (1) and 
(2): 
EQU 0.2&lt;fL2/fL &lt;8 (1) 
EQU 0.05&lt;fL2/fl1 &lt;5.0 (2) 
where, 
fl1: focal length of the first lens subgroup GL1, 
fL2: focal length of the vibration reduction second lens subgroup GL2, and 
fL: focal length of the last lens group GL. 
Equation (1) defines an appropriate range for the ratio of the focal length 
fL2 of the second lens subgroup GL2 and the focal length fL of the last 
lens group GL. 
When the upper limit of Equation (1) is exceeded, the focal length of the 
second lens subgroup GL2 becomes large causing a large movement of the 
second lens subgroup GL2 in the direction perpendicular to the optical 
axis to correct the specified movement amount. As a result, in order to 
prevent shielding of light rays during movement of the second lens 
subgroup GL2, the diameter of the second lens subgroup GL2 is made large. 
Also, the total length of the zoom lens system becomes inconveniently 
long. 
On the other hand, when the lower limit of Equation (1) is breached, the 
focal length of the second lens subgroup GL2 becomes too small, causing 
the spherical aberration to become too large during zooming. 
Here, the upper limit and the lower limit of Equation (1) may be preferably 
changed to 2.5 and 0.5, respectively, in order to obtain even better 
imaging quality. 
Equation (2) defines an appropriate range for the ratio of the focal length 
fL2 of the second lens subgroup GL2 to the focal length fl1 of the first 
lens subgroup GL1. This condition achieves favorable imaging performance 
including vibration reduction capability in forming the last lens group 
GL. 
If the upper limit of Equation (2) is exceeded, the spherical aberration 
becomes too large. Moreover, the total length of the zoom lens system 
becomes too long, which is contrary to an object of the present invention 
of miniaturizing the zoom lens system. Moreover, in addition to the 
Petzval sum becoming too large in the positive, the astigmatic difference 
and bending in the image plane become large making it impossible to obtain 
favorable imaging performance. 
On the contrary, if the lower limit of Equation (2) is breached, it is 
difficult to sufficiently secure large back focal length. Thus, such a 
small fL2/fl1 value is undesirable. 
Moreover, the spherical aberration easily becomes too large in the negative 
and undesirable positive coma aberration is easily produced in the light 
rays above the chief ray. 
The upper limit and lower limit of Equation (2) may be preferably changed 
to 1.5 and 0.2, respectively, to obtain better imaging performance. 
The following Equations (3)-(5) are preferably also satisfied. 
EQU .increment.SL/fL2&lt;0.1 (3) 
EQU -15.0&lt;RL/fL2&lt;15.0 (4) 
EQU L/fL&lt;0.6 (5) 
where, 
.increment.SL: magnitude of the maximum displacement of the second lens 
subgroup GL2 in the direction perpendicular to the optical axis during 
vibration reduction operation, 
RL: radius of curvature of the surface closest to the image side in the 
second lens subgroup GL2, and 
L: axial thickness of the second lens subgroup GL2. 
The axial thickness of the second lens subgroup GL2 is a distance between a 
surface closest to the object side and a surface closest to the image 
side. 
Equation (3) defines an appropriate range for the ratio of the focal length 
of the second lens subgroup GL2 to the magnitude of the maximum 
displacement amount of the second lens subgroup GL2 during vibration 
reduction operation. 
If the upper limit of Equation (3) is exceeded, the magnitude of the 
maximum displacement amount of the second lens subgroup GL2 is large 
causing the aberration vibration amount to become too large during 
vibration reduction operation. 
In particular, in a marginal position on the image plane, a difference 
between the best image plane in the meridional direction and the best 
image plane in the sagittal direction becomes inconveniently large. In 
addition, the driving mechanism becomes complicated. Thus, a small value 
of .increment.SL/fL2 is undesirable. 
The upper limit of Equation (3) may be preferably changed to 0.03 to obtain 
even better imaging performance. 
Equation (4) defines an appropriate range for the ratio of the focal length 
fL2 to the radius of curvature of the surface closest to the image plane 
of the second lens subgroup GL2. 
When the upper limit is exceeded or the lower limit is breached in Equation 
(4), variations of the spherical aberration and field curvature become too 
large during zooming. In addition, variations of the spherical aberration 
and coma aberration also become too large during the vibration reduction 
operation making it inconvenient and difficult for aberration correction. 
Thus, the upper limit and the lower limit value of Equation (4) may be 
changed to 5.5 and -6.0, respectively, to obtain even better imaging 
performance. 
Equation (5) defines an appropriate range for the ratio of the focal length 
of the last lens group GL to the axial thickness of the second lens 
subgroup GL2. 
If the upper limit of Equation (5) is exceeded, the axial thickness of the 
second lens subgroup GL2 is too large causing the second lens subgroup GL2 
to be bulky. As a result, the total length of the zoom lens system is too 
large and the vibration reduction mechanism is inconveniently complicated. 
In forming the second lens subgroup GL2, the following Equations (6) and 
(7) are preferably satisfied. 
EQU -4.5&lt;q+&lt;5.0 (6) 
EQU -4.0&lt;q-&lt;5.0 (7) 
where, 
q+: shape factor of the positive lens element in the vibration reduction 
lens group closest to the object side; and 
q-: shape factor of the negative lens element in the vibration reduction 
lens group closest to the image side. 
The shape factor of the lens element is expressed by the following 
Equation. 
EQU q=(R2+R1)/(R2-R1) 
where, 
R1: radius of curvature of the object side surface of the lens element; and 
R2: radius of curvature of the image side surface of the lens element. 
When the upper limit of Equation (6) is exceeded, the spherical aberration 
is extremely large in the negative direction and coma aberration facing 
inward is too large. Thus, a large value of q+ is inconvenient. 
If the lower limit of Equation (6) is breached, the spherical aberration is 
extremely large in the negative direction and astigmatism is too large. 
Thus, a small value of q+ is inconvenient. 
The upper limit and lower limit of Equation (6) may be changed to 2.0 and 
-1.5, respectively, to obtain better imaging performance. 
When the upper limit of Equation (7) is exceeded, the spherical aberration 
is extremely large in the positive direction and the spherical aberration 
and the coma aberration are too large during vibration reduction 
operation. Thus, a large value of q- is undesirable. 
If the lower limit of Equation (7) is breached, the spherical aberration is 
extremely large in the positive direction and the spherical aberration and 
coma aberration are too large during vibration reduction operation. Thus, 
a small value of q- is undesirable. 
The upper limit and lower limit of Equation (7) may be changed to 2.0 and 
0, respectively, to obtain better imaging performance. 
When a third lens group G3 of positive refractive power is placed between 
the second lens group G2 and the last lens group GL, the following 
Equations (8) and (9) are preferably satisfied to obtain even better 
imaging performance. 
EQU 0.15&lt;.vertline.f2.vertline./f1&lt;0.45 (8) 
EQU 0.35&lt;f3/f1&lt;1.3 (9) 
where, 
f1: focal length of the first lens group G1, 
f2: focal length of the second lens group G2, and 
f3: focal length of the third lens group G3. 
When the upper limit of Equation (8) is exceeded, the spherical aberration 
at the maximum telephoto state is extremely large in the negative 
direction and the variation of the coma aberration is too large. Thus, a 
large value of .vertline.f2.vertline./f1 is undesirable. 
If a lower limit of Equation (8) is breached, the astigmatic difference at 
the maximum wide-angle state is too large causing distortion between the 
maximum wide-angle state and the maximum telephoto state to shift 
substantially in the negative direction. In addition, the Petzval sum is 
easily converted to the negative side. Thus, a small value of 
.vertline.f2.vertline./f1 is undesirable. 
If the upper limit of Equation (9) is exceeded, variations of the coma 
aberration are too large and the total length of the zoom lens system is 
too long. Thus, a large value of f3/f1 is undesirable. 
If the lower limit of Equation (9) is breached, the spherical aberration is 
too large in the negative direction and the Petzval sum is easily 
converted to the negative side. Thus, a small value of f3/f1 is 
undesirable. 
If the zoom lens includes the first lens group G1, the second lens group G2 
and the last lens group GL, the first lens group G1 and the last lens 
group GL are preferably moved to perform zooming in accordance with the 
present invention. Thus, a compact optical system is produced, especially 
at the maximum wide-angle state, while obtaining favorable imaging 
performance. 
If the zoom lens system includes the first lens group G1, the second lens 
group G2, the third lens group G3 and the last lens group GL, the first 
lens group G1 and the last lens group GL are preferably fixed so that the 
second lens group G2 and the third lens group G3 are moved to perform 
zooming. In such structure, a driving mechanism for zooming and vibration 
reduction can be simplified while obtaining favorable imaging performance. 
The third lens subgroup GL3 closest to the image side may be of positive or 
negative refractive power. However, if the total length of the zoom lens 
system is desired to be shorter or if the exit pupil is desired to be 
close to the image side, the third lens subgroup GL3 is preferably of 
positive refractive power. On the other hand, if distortion is desired to 
be balanced on the negative side (desired to be corrected on the negative 
side) or if the exit pupil is desired to be away from the image plane, it 
is more effective if the third lens subgroup GL3 is of negative refractive 
power. Moreover, if the third lens subgroup GL3 is of negative refractive 
power, the focal length fL3 of the third lens subgroup GL3 preferably 
satisfies the following Equation (10): 
EQU 0.5&lt;.vertline.fL3.vertline./fL&lt;8 (10) 
The refractive index N+ of the positive lens element closest to the object 
side in the second lens subgroup GL2 relative to d-line (.lambda.=587.6 
nm) and the Abbe's number .nu.+ of the positive lens element closest to 
the second lens subgroup GL2 preferably satisfy the following Equations 
(11) and (12) to obtain favorable imaging performance. 
EQU N+&gt;1.47 (11) 
EQU .nu..sup.+ &gt;45 (12) 
When the first lens subgroup GL1 is one lens (including cemented lens), the 
lens is desirably a positive meniscus lens with the convex surface facing 
the object side. 
Moreover, when the second lens subgroup GL2 is one lens (including cemented 
lens), the lens is desirably a positive lens of glass with an Abbe's 
number no less than 55. 
When the second lens subgroup GL2 includes two lenses (including cemented 
lens), one of the lenses is a positive lens and the other is a negative 
meniscus lens having a convex surface with stronger curvature facing the 
image side. 
When the second lens subgroup GL2 includes three lenses (including cemented 
lens), the three lenses include a biconvex lens, a biconcave lens and a 
positive lens. 
When the second lens subgroup GL2 includes four lenses (including cemented 
lens), the four lenses include a biconvex lens, a biconcave lens, a 
negative meniscus lens and a positive lens. 
The third lens group G3 may be of negative refractive power. Then, the 
third lens group G3 includes at least one positive lens element. 
Moreover, better imaging performance is obtained by introducing a 
non-spherical surface to at least one of the lens surface of the optical 
system. 
Even better imaging performance is obtained using a gradient index lens 
(GRIN lens) for at least one of the lenses within the optical system. 
Internal focusing is possible for focusing on a close-distance object by 
moving a part of the lens group in the second lens group G2 along the 
optical axis. 
Moreover, it is effective to use special low dispersion glass for one of 
the lens groups within the zoom lens system to satisfactorily correct 
chromatic aberration. Preferably, a special low dispersion glass is used 
in the first lens group G1 to result in satisfactory correction of 
chromatic aberration at the maximum telephoto state. 
Other aspects, advantages and salient features of the invention will become 
apparent from the detailed description taken in conjunction with the 
annexed drawings, which disclose preferred embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In the present specification, the term "lens group" designates a portion of 
the total lens system. Each lens group may include one lens or any greater 
number of lenses. Lens groups are also known as lens units. 
In each embodiment of the present invention, the zoom lens system includes 
a vibration reduction function. The system includes a first lens group G1 
of positive refractive power placed closest to the object side, a second 
lens group G2 of negative refractive power placed on the image side of the 
first lens group G1 and a last lens group GL of positive refractive power 
placed closest to the image side. The system includes a mechanism to 
increase the interval between the first lens group G1 and the second lens 
group G2 and vary the interval between the second lens group G2 and the 
lens group placed on the image side of the second lens group G2 during 
zooming from a maximum wide-angle state to a maximum telephoto state. The 
last lens group GL includes, in order from the object side, a first lens 
subgroup GL1 of positive refractive power, a second lens subgroup GL2 of 
positive refractive power and a third lens subgroup GL3 of either positive 
or negative refractive power. A displacement device is provided to prevent 
vibrations caused by moving the second lens subgroup GL2 in a direction 
substantially perpendicular to the optical axis. This type of displacement 
device can include an actuator and controller as disclosed in U.S. Pat. 
Nos. 5,416,558, 5,402,197 and 5,337,098, the subject matters of which are 
incorporated herein by reference and which are assigned to the same 
assignee as the present application. 
FIG. 1 shows a zoom lens system according to a first embodiment. A first 
lens group G1 includes a cemented lens having a negative meniscus lens 
with the convex surface facing the object side, a biconvex lens and a 
positive meniscus lens with the convex surface facing the object side. A 
second lens group G2 includes a negative meniscus lens with the convex 
surface facing the object side, a cemented lens having a positive meniscus 
lens with the convex surface facing the object side and a biconcave lens, 
a cemented lens having a biconcave lens and a positive meniscus lens with 
the concave surface facing the object side, and a biconcave lens. A third 
lens group G3 includes a biconvex lens and a cemented lens having a 
biconvex lens and a negative meniscus lens with a concave surface facing 
the object side. 
A first lens subgroup GL1 includes a positive meniscus lens with the convex 
surface facing the object side. A second lens subgroup GL2 includes a 
biconvex lens, a negative meniscus lens with the concave surface facing 
the object side and a biconvex lens. A third lens subgroup GL3 includes a 
negative meniscus lens with the convex surface facing the object side, a 
biconvex lens and a negative meniscus lens with the concave surface facing 
the object side. 
An aperture stop S is provided between the third lens group G3 and the last 
lens group GL. A flare stop FS is also provided in the last lens group GL. 
FIG. 1 shows the positional relationship of each lens group at the maximum 
wide-angle state. The second lens group G2 and the third lens group G3 
move on the optical axis along the zoom path (described by arrows) when 
zooming to the maximum telephoto state. The first lens group G1 and the 
last lens group GL are fixed along the optical direction during zooming. 
The second lens subgroup GL2 is moved by a vibration reduction mechanism 1 
in a direction substantially perpendicular to the optical axis to correct 
variations of the image position caused by vibrations of the zoom lens 
system. 
The first embodiment is preferably for use with a telephoto zoom lens 
system. 
Table 1 summarizes data values of the first embodiment of the present 
invention. In Table 1, f is the focal length, F.sub.no is the F-number, 
2.omega. is an angle of view and Bf is the back focal length. Numerals in 
the leftmost column represent the order of the lens surfaces from the 
object side, r denotes the radius of curvature of each lens surface, d 
denotes spacing of each lens, n(D) denotes the refractive index relative 
to a d-line (.lambda.=587.6 nm), n(G) denotes the refractive index 
relative to a g-line (.lambda.=435.8 nm) and .nu. denotes the Abbe's 
number with respect to the d-line. 
TABLE 1 
______________________________________ 
f = 81.5-196 
F.sub.no = 2.88-2.90 
2.omega. = 30.64.degree.-12.24.degree. 
r d .nu. N(D) n(G) 
______________________________________ 
1 105.5399 2.8000 25.50 1.804581 
1.846310 
2 73.4058 11.4000 82.52 1.497820 
1.505265 
3 -570.0625 0.1000 
4 118.0775 5.7000 92.52 1.497820 
1.505265 
5 1042.0718 (d5 = variable) 
6 322.9129 2.1000 52.30 1.748099 
1.765893 
7 122.5766 3.8500 
8 -118.7333 3.5000 25.50 1.804581 
1.846310 
9 -61.4330 1.6000 60.69 1.563840 
1.575310 
10 262.6262 (d10 = variable) 
11 -119.9235 1.5000 61.09 1.589130 
1.601033 
12 42.1223 4.5000 25.50 1.804581 
1.846310 
13 118.0410 2.4000 
14 -181.3955 1.8000 45.37 1.796681 
1.818801 
15 139.1660 (d15 = variable) 
16 302.2780 3.3000 46.42 1.582670 
1.598584 
17 -143.1747 0.1000 
18 143.7170 6.9000 69.98 1.518601 
1.527667 
19 -49.9410 1.6000 25.50 1.804581 
1.846310 
20 -113.3388 (d20 = variable) 
21 36.6067 4.8468 82.52 1.497820 
1.505265 
22 46.2861 3.6289 
23 84.1217 4.3123 67.87 1.593189 
1.604034 
24 -491.6227 2.8555 
25 -111.2332 2.0000 28.56 1.795040 
1.831518 
26 -420.6652 20.4975 
27 128.7233 3.2589 49.45 1.772789 
1.792324 
28 -396.1270 2.5000 
29 97.5833 2.0000 25.50 1.804581 
1.846310 
30 80.2047 2.9334 
31 458.0063 3.2960 40.90 1.796310 
1.821068 
32 -88.9133 5.2410 
33 -37.5559 2.0000 49.45 1.772789 
1.792324 
34 -199.2469 (Bf) 
______________________________________ 
______________________________________ 
Variable Interval Upon Zooming 
______________________________________ 
f 81.45000 196.00000 
d5 1.92399 38.13447 
d10 19.63070 19.63070 
d15 27.22503 2.32353 
d20 16.70000 5.39102 
Bf 57.98513 57.98513 
______________________________________ 
PREFERRED VALUES CORRESPONDING TO EQUATIONS 
fL=109.486 
fl1=301.461 
fL2=97.565 
fL3=-146.130 
RL=-396.12698 
L=32.9242 
f1=125.913 
f2=-33.163 
f3=92.138 
(1) fL2/fL=0.891 
(2) fL2/fl1=0.324 
(3) .increment.SL/fL2=0.0103 
(4) RL/fL2=-4.060 
(5) L/fL=0.301 
(6) q+=0.708 
(7) q-=1.719 
(8) .vertline.f2.vertline./f1=0.263 
(9) f3/f1=0.732 
(10) .vertline.fL3.vertline./fL=1.335 
(11) N+=1.593189 
(12) .nu.+=67.87 
VIBRATION REDUCTION DATA 
The maximum displacement amount .increment.SL of the vibration reduction 
second lens subgroup GL2 in the direction perpendicular to the optical 
axis in the maximum wide-angle state . . . 1.0 
Corresponding image movement amount .increment.Y in the maximum wide-angle 
state and the maximum telephoto state . . . +1.0 
The positive sign indicates that the movement of the image stabilizing lens 
is in the same image direction. 
FIGS. 2A-2C respectively show graphs of longitudinal aberrations in the 
maximum wide-angle state, lateral aberrations without vibration reduction 
in the maximum wide-angle state and lateral aberrations in the maximum 
wide-angle state with vibration reduction correction. FIGS. 3A-3C show 
similar graphs for the maximum telephoto state. 
In these graphs, F.sub.no denotes the F-number, Y denotes the image height, 
D denotes the d-line (.lambda.=587.6 nm) and G denotes the g-line 
(.lambda.=435.6 nm). 
Furthermore, in the graphs showing the astigmatism, solid lines indicate 
sagittal image surface while dotted lines indicate meridional image 
surfaces. 
As can be seen from these graphs, various aberrations are satisfactorily 
corrected including those under vibration reduction correction. 
FIG. 4 shows a zoom lens system according to a second embodiment of the 
present invention. A first lens group G1 includes a cemented lens having a 
negative meniscus lens with the convex surface facing the object side and 
a biconvex lens, and a positive meniscus lens with the convex surface 
facing the object side. A second lens group G2 includes a negative 
meniscus lens with the convex surface facing the object side, a cemented 
lens having a positive meniscus lens with the concave surface facing the 
object side and a biconcave lens, a cemented lens having a biconcave lens 
and a positive meniscus lens with the convex surface facing the object 
side, and a biconcave lens. A third lens group G3 includes a biconvex lens 
and a cemented lens having a biconvex lens and a negative meniscus lens 
with a concave surface facing the object side. 
A first lens subgroup GL1 includes a positive meniscus lens with the convex 
surface facing the object side. A second lens subgroup GL2 includes a 
biconvex lens, a biconcave lens and a negative meniscus lens with the 
convex surface facing the object side. A third lens subgroup GL3 includes 
a positive meniscus lens with the concave surface facing the object side 
and a negative meniscus lens with concave surface facing the object side. 
An aperture stop S is provided between the third lens group G3 and the last 
lens group GL. A flare stop FS is also provided in the last lens group GL. 
FIG. 4 shows the positional relationship of each lens group at the maximum 
wide-angle state. The second lens group G2 and the third lens group G3 
move along the optical axis on the zoom path (described by arrows) when 
zooming to the maximum telephoto state. The first lens group G1 and the 
last lens group GL are fixed along the optical direction during zooming. 
The second lens group GL2 is moved by a vibration reduction mechanism 1 in 
a direction substantially perpendicular to the optical axis to correct 
variations of the image position caused by vibrations of the zoom lens 
system. 
The second embodiment is also preferably for use with a telephoto zoom lens 
system. 
Table 2 summarizes data values of the second embodiment. In Table 2, f is 
the focal length, F.sub.no is the F-number, 2.omega. is an angle of view, 
and Bf is the back focal length. Numerals in the leftmost column represent 
the order of the lens surfaces from the object side, r denotes the radius 
of curvature of each lens surface, d denotes spacing of each lens, n(D) 
denotes the refractive index relative to a d-line (.lambda.=587.6 nm), 
n(G) denotes the refractive index relative to a g-line (.lambda.=435.8 nm) 
and .nu. denotes the Abbe's number with respect to the d-line. 
TABLE 2 
______________________________________ 
f = 81.42-196 
F.sub.no = 2.88-2.90 
2.omega. = 30.34.degree.-12.14.degree. 
r d .nu. N(D) n(G) 
______________________________________ 
1 105.5399 2.8000 25.50 1.804581 
1.846310 
2 73.4058 11.4000 82.52 1.497820 
1.505265 
3 -570.0625 0.1000 
4 118.0775 5.7000 82.52 1.497820 
1.505265 
5 1042.072 (d5 = variable) 
6 322.9129 2.1000 52.30 1.748099 
1.765893 
7 122.5766 3.8500 
8 -118.7333 3.5000 25.50 1.804581 
1.846310 
9 -61.4330 1.6000 60.69 1.563840 
1.575310 
10 262.6262 (d10 = variable) 
11 -119.9235 1.5000 61.09 1.589130 
1.601033 
12 42.1223 4.5000 25.50 1.804581 
1.846310 
13 118.0410 2.4000 
14 -181.3955 1.8000 45.37 1.796681 
1.818801 
15 139.1660 (d15 = variable) 
16 302.2780 3.3000 46.42 1.582670 
1.598584 
17 -143.1747 0.1000 
18 143.7170 6.9000 69.98 : 1.518601 
1.527667 
19 -49.9410 1.6000 25.50 1.804581 
1.846310 
20 -113.3388 (d20 = variable) 
21 35.6047 4.5856 82.52 1.497820 
1.505265 
22 40.1635 4.0000 
23 49.5891 6.8043 65.42 1.603001 
1.614372 
24 -183.9129 7.0000 
25 -91.5083 2.0000 32.10 1.672700 
1.699894 
26 216.2384 11.0000 
27 40.7254 2.2000 35.51 1.595071 
1.616844 
28 30.6237 2.3696 
29 71.2512 3.0000 48.04 1.716999 
1.735734 
30 455.0823 5.000 
31 -61.3146 3.2887 25.50 1.804581 
1.846310 
32 -44.3935 3.1258 
33 -29.0066 3.3761 49.45 1.772789 
1.792324 
34 -44.4133 (Bf) 
______________________________________ 
______________________________________ 
Variable Interval Upon Zooming 
______________________________________ 
f 81.42008 196.00000 
d5 1.92399 38.14386 
d10 19.63071 19.63071 
d15 27.22503 2.30801 
d20 18.32023 7.01739 
Bf 56.00000 56.00000 
______________________________________ 
PREFERRED VALUES CORRESPONDING TO EQUATIONS 
fL=109.5 
fl1=472.234 
fL2=105.134 
fL3=-316.255 
RL=455.08230 
L=34.3739 
f1=125.913 
f2=-33.163 
f3=92.138 
(1) fL2/fL=0.960 
(2) fL2/fl1=0.223 
(3) .increment.SL/fL2=0.00951 
(4) RL/fL2=4.329 
(5) L/fL=0.314 
(6) q+=0.575 
(7) q-=0.405 
(8) .vertline.f2.vertline./f1=0.263 
(9) f3/f1=0.732 
(10) .vertline.fL3.vertline./fL=2.888 
(11) N+=1.603001 
(12) .nu.+=65.42 
VIBRATION REDUCTION DATA 
The maximum displacement amount .increment.SL of the vibration reduction 
second lens subgroup GL2 in the direction perpendicular to the optical 
axis in the maximum wide-angle state . . . 1.0 
Corresponding image movement amount .increment.Y in the maximum wide-angle 
state and the maximum telephoto state . . . +1.0 
FIGS. 5A-5C and 6A-6C are graphs similar to FIGS. 2A-2C and 3A-3C showing 
various aberrations at the maximum wide-angle state and at the maximum 
telephoto state. 
In these graphs, F.sub.no denotes the F-number, Y denotes the image height, 
D denotes the d-line (.lambda.=587.6 nm) and G denotes the g-line 
(.lambda.=435.6 nm). 
Furthermore, in the graphs showing the astigmatism, solid lines indicate 
sagittal image surfaces while dotted lines indicate meridional image 
surfaces. 
As can be seen from these graphs, various aberrations are satisfactorily 
corrected including those under vibration reduction correction. 
FIG. 7 shows a zoom lens system according to a third embodiment of the 
present invention. A first lens group G1 includes a cemented lens having a 
negative meniscus lens with the convex surface facing the object side and 
a biconvex lens, a positive meniscus lens with the convex surface facing 
the object side, and a positive meniscus lens with the convex surface 
facing the object side. A second lens group G2 includes a negative 
meniscus lens with the convex surface facing the object side, a cemented 
lens having a positive meniscus lens with the concave surface facing the 
object side and a biconcave lens, a cemented lens having a biconcave lens 
and a biconvex lens, and a biconcave lens. 
A first lens subgroup GL1 includes a biconvex lens, a biconvex lens, a 
concave lens, a biconvex lens and a biconcave lens. A second lens subgroup 
GL2 includes a biconcave lens. A third lens subgroup GL3 includes a 
cemented lens having a biconvex lens and a negative meniscus lens with a 
concave surface facing the object side. 
An aperture stop S is provided between the second lens group G2 and the 
last lens group GL. 
FIG. 7 shows the positional relationship of each lens group at the maximum 
wide-angle state. The second lens group G2 and the third lens group G3 
move on the optical axis along the zoom path (described by arrow) when 
zooming to the maximum telephoto state. The second lens subgroup GL2 is 
moved by the vibration reduction mechanism 1 in a direction substantially 
perpendicular to the optical axis to correct variations of the image 
position caused by vibrations of the zoom lens system. 
The third embodiment is preferably for use on a standard region of a 
photographic lens. 
Table 3 summarizes data values of the third embodiment of the present 
invention. In Table 3, f is the focal length, F.sub.no is the F-number, 
2.omega. is an angle of view, and Bf is the back focal length. Numerals in 
the leftmost column represent the order of the lens surfaces from the 
object side, r denotes the radius of curvature of each lens surface, d 
denotes spacing of each lens, n(D) denotes the refractive index relative 
to a d-line (.lambda.=587.6 nm), n(G) denotes the refractive index 
relative to a g-line (.lambda.=435.8 nm) and .nu. denotes the Abbe's 
number with respect to the d-line. 
TABLE 3 
______________________________________ 
f = 36.0-102.0 
F.sub.no = 3.33-3.73 
2.omega. = 63.8.degree.-23.24.degree. 
r d .nu. N(D) n(G) 
______________________________________ 
1 1288.7810 1.5000 25.35 1.805182 
1.847252 
2 116.4400 8.9000 54.55 1.514540 
1.526319 
3 -160.5000 0.2000 
4 184.1970 4.0000 64.10 1.516800 
1.526703 
5 382.7460 0.2000 
6 54.3630 5.0000 53.93 1.713000 
1.729417 
7 93.0590 (d7 = variable) 
8 71.2770 1.2000 47.47 1.787971 
1.808793 
9 21.0570 5.0000 
10 -451.4520 4.6000 40.90 1.796310 
1.821068 
11 -21.1960 1.0000 60.69 1.563840 
1.575310 
12 65.8510 4.9000 
13 -17.6630 1.0000 42.69 1.567320 
1.584250 
14 40.6510 4.8000 28.56 1.795040 
1.831518 
15 -62.8390 (d15 = variable) 
16 50.1390 3.4000 60.14 1.620409 
1.633173 
17 -190.2720 0.2000 
18 28.7210 6.1000 60.14 1.620409 
1.633173 
19 -530.3020 1.5000 
20 -46.3000 1.2000 47.47 1.787971 
1.808793 
21 155.0060 0.2000 
22 48.2840 4.5000 36.27 1.620040 
1.642085 
23 -44.8120 0.2000 
24 -171.4250 1.3000 25.35 1.805182 
1.847252 
25 24.7610 3.0000 
26 164.0620 4.1000 64.10 1.516800 
1.526703 
27 -45.5000 0.2000 
28 55.5420 8.6000 45.87 1.548139 
1.563282 
29 -19.7140 1.3000 40.90 1.796310 
1.821068 
30 -71.4890 (Bf) 
______________________________________ 
______________________________________ 
Variable Interval Upon Zooming 
______________________________________ 
f 36.00010 102.02572 
d7 1.28 39.22 
d15 19.86 1.72 
Bf 49.25497 67.40116 
______________________________________ 
PREFERRED VALUES CORRESPONDING TO EQUATIONS 
fL=35.483 
fl1=64.398 
fL2=69.389 
fL3=117.439 
RL=-45.5 
L=4.1 
f1=115.5119 
f2=-24.471 
(1) fL2/fL=1.956 
(2) fL2/fl1=1.076 
(3) .increment.SL/fL2=0.00504 
(4) RL/fL2=0.656 
(5) L/fL=0.116 
(6) q+=-0.566 
(8) .vertline.f2.vertline./f1=0.212 
(10) .vertline.fL3.vertline./fL=3.310 
(11) N+=1.516800 
(12) .nu.+=64.10 
VIBRATION REDUCTION DATA 
The maximum displacement amount .increment.SL of the vibration reduction 
second lens subgroup GL2 in the direction perpendicular to the optical 
axis in the maximum wide-angle state . . . 0.35 
Corresponding image movement amount .increment.Y in the maximum wide-angle 
state . . . +0.282 
Corresponding image movement amount .increment.Y in the maximum telephoto 
state . . . +0.373 
FIGS. 8A-8C and 9A-9C are graphs similar to FIGS. 2A-2C and 3A-3C showing 
various aberrations at the maximum wide-angle state and at the maximum 
telephoto state. 
In these graphs, F.sub.no denotes the F-number, Y denotes the image height, 
D denotes the d-line (.lambda.=587.6 nm) and G denotes the g-line 
(.lambda.=435.6 nm). 
Furthermore, in the graphs showing the astigmatism, solid lines indicate 
sagittal image surfaces while dotted lines indicate meridional image 
surfaces. 
As can be seen from these graphs, various aberrations are satisfactorily 
corrected including those under vibration reduction correction. 
As described above, the present invention can create a high performance 
zoom lens system capable of driving the vibration reduction lens group and 
securing sufficient brightness and back focal length suitable for use in a 
photographic camera and a video camera. 
While the invention has been described in relation to preferred 
embodiments, many modifications and variations are apparent from the 
description of the invention. All such modifications and variations are 
intended to be within the scope of the present invention as defined in the 
appended claims.