# Patent

## Title
Zoom lens

## Abstract

A zoom lens includes, sequentially 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 fourth lens group having a positive refractive power. Zoom is performed by moving the second and the third lens groups in a direction along an optical axis. The fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group configured by a cemented lens formed by a positive lens and a negative lens and having an overall refractive power that is negative, and a rear group having a positive refractive power. Blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens ideal for digital still and motion cameras (DSMC), single-lens reflex cameras, and the like.
2. Description of the Related Art
Recently, in DSMCs and single-lens reflex cameras, zoom lenses are used in which a portion of the lenses in the first group are moved along the optical axis during focusing (see, for example, Japanese Patent Application Laid-Open Publication Nos. 2002-162564 and 2003-344766). Zoom lenses are also used in which a third or a fourth group configured by plural intermediate diameter lenses is moved along the optical axis during focusing (see, for example, Japanese Patent Application Laid-Open Publication No. 2010-44372).
For example, the zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2002-162564 has, sequentially from an object side, a front lens component that includes plural lenses for performing zoom and focusing; and a rear lens component that includes a relay lens group having an imaging function. The rear lens component has, sequentially from the object side, a lens group A having a positive refractive power, a lens group B having a negative refractive power and movable so as to have a component in a direction orthogonal to the optical axis, and a lens group C having a positive refractive power, where the movement of the lens group B so as to have a component in a direction orthogonal to the optical axis causes displacement of the image.
The zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2003-344766 includes, sequentially from the object side, a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, where the second lens group and the third lens group are moved in a direction along the optical axis to perform zooming. The first lens group is configured sequentially by a positive front group and a rear group having a stronger refractive power than the front group, where the rear group is moved in a direction along the optical axis to perform near focus and the front group is configured sequentially by a negative meniscus lens having a convex surface facing toward the object side, a positive lens whose object-side surface is convex, and a positive lens whose object-side surface is convex. The rear group is configured sequentially by a negative meniscus lens having a convex surface facing toward the object side, and a positive lens component.
The zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2010-44372 has a first lens group having a positive refractive power and disposed farthest on the object side, a second lens group disposed on the image plane side of the first lens group, a Gn lens group disposed farthest on the image plane side, a Gn-1 lens group disposed on the object side of the Gn lens group, and at least 1 lens group disposed between the second lens group and the Gn-1 lens group. When zoom is performed, the first lens group and the Gn lens group are fixed. When focusing is performed, at least 1 lens group disposed between the second lens group and the Gn-1 lens group is moved and at least a portion of the Gn lens group is moved so as to have a component in a direction substantially orthogonal to the optical axis.
Nonetheless, although the anti-blur coefficient (in blur correction, the ratio of the shift amount of the image point and the shift amount of the anti-blur group) is large for the zoom lenses disclosed in Japanese Patent Application Laid-Open Publication Nos. 2002-162564 and 2003-344766, the anti-blur group is configured by 2 negative lenses and 1 positive lens and therefore, is heavy. To move the heavy anti-blur group, a strong driving power is demanded of the actuator that drives the anti-blur group. As a result, a problem arises in that the power consumption of the actuator becomes large.
Further, the zoom lens disclosed in Japanese Patent Application Laid-Open Publication No. 2010-44372 has an anti-blur group that is configured by 2 lenses and although this zoom lens having an anti-blur group configured by 2 lenses is thus, excellent on the point of the anti-blur group being light weight, since the anti-blur coefficient of the anti-blur group is small, even when a minimal image point shift is to be corrected, the anti-blur group must be shifted a lot. Consequently, the driving amount of the actuator that drives the anti-blur group becomes large and as a result, a problem arises in that the power consumption of the actuator becomes large.
SUMMARY OF THE INVENTION
It is an object of the present invention to at least solve the above problems in the conventional technologies.
A zoom lens according to one aspect of the present invention includes, sequentially 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 fourth lens group having a positive refractive power. Zoom is performed by moving the second lens group and the third lens group in a direction along an optical axis. The fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group configured by a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group having a positive refractive power. Blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis, and a conditional expression (1) 1.85<|Ft×F4M/(F4F×F4R)|<4 is satisfied, where Ft represents overall optical system focal length, at a telephoto edge, in an infinity focus state, F4F represents the focal length of the front group of the fourth lens group, F4M represents the focal length of the intermediate group of the fourth lens group, and F4R represents the focal length of the rear group of the fourth lens group.
The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a cross-sectional view (along the optical axis) of a zoom lens according to a first embodiment;
FIG. 2 is a diagram of various types of aberration at a wide angle edge of the zoom lens of the first embodiment according to the invention;
FIG. 3 is a diagram of various types of aberration at an intermediate position of the zoom lens of the first embodiment according to the invention;
FIG. 4 is a diagram of various types of aberration at a telephoto edge of the zoom lens of the first embodiment according to the invention;
FIG. 5 depicts a cross-sectional view (along the optical axis) of the zoom lens according to a second embodiment;
FIG. 6 is a diagram of various types of aberration at the wide angle edge of the zoom lens of the second embodiment according to the invention;
FIG. 7 is a diagram of various types of aberration at the intermediate position of the zoom lens of the second embodiment according to the invention;
FIG. 8 is a diagram of various types of aberration at the telephoto edge of the zoom lens of the second embodiment according to the invention;
FIG. 9 depicts a cross-sectional view (along the optical axis) of the zoom lens according to a third embodiment;
FIG. 10 is a diagram of various types of aberration at the wide angle edge of the zoom lens of the third embodiment according to the invention;
FIG. 11 is a diagram of various types of aberration at the intermediate position of the zoom lens of the third embodiment according to the invention; and
FIG. 12 is a diagram of various types of aberration at the telephoto edge of the zoom lens of the third embodiment according to the invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the accompanying drawings, exemplary embodiments according to the present invention are explained in detail below.
A zoom lens according to the present invention includes, sequentially 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 fourth lens group having a positive refractive power. Further, the second lens group and third lens group are moved in a direction along the optical axis, whereby zoom is performed from a wide angle edge to a telephoto edge.
An object of the present invention is to provide a zoom lens that maintains high optical performance and facilitates reductions in the size, weight and anti-blur shift amount of the anti-blur group, and that has an excellent blur correction function. To achieve this object, various conditions are set as indicated below.
In the zoom lens according to the present invention, the fourth lens group consists of, sequentially from an object side, a front group having a positive refractive power; an intermediate group configured by a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens, and having an overall refractive power that is negative; and a rear group having a positive refractive power. Blur (image point shift) correction is performed by moving the intermediate group in a direction orthogonal to the optical axis. The zoom lens preferably satisfies the following conditional expression, where Ft represents overall optical system focal length, at the telephoto edge, in an infinity focus state; F4F represents the focal length of the front group of the fourth lens group; F4M represents the focal length of the intermediate group of the fourth lens group; and F4R represents the focal length of the rear group of the fourth lens group.

1.85<|Ft×F4M/(F4F×F4R)|<4  (1)

Conditional expression (1) represents a condition for maintaining high optical performance and facilitating reductions in the size and weight of the intermediate group of the fourth lens group. Below the lower limit of conditional expression (1), the refractive power (reciprocal of focal length) of the front group and that of the rear group of the fourth lens group become too weak, whereby the effective diameter of the intermediate group, which is the anti-blur group, has to be increased, making reductions in the size and weight of the anti-blur group difficult. On the other hand, above the upper limit of conditional expression (1), although the effective diameter of the intermediate group can be made smaller, the correction of various types of aberration becomes difficult.
More favorable results can be expected if conditional expression (1) is satisfied within the following range.

1.85<|Ft×F4M/(F4F×F4R)|<2.5  (1)′

By satisfying the range prescribed by conditional expression (1)′, on top of realizing reductions in the size and weight of the anti-blur group, the optical performance of the anti-blur group can be improved further.
The zoom lens according to the present invention preferably satisfies the following conditional expression, where AT is the anti-blur coefficient for the intermediate group of the fourth lens group.

−2.0<AT<−1.3  (2)

Furthermore, AT=(1−βM)×βR, where βM represents lateral magnification of the intermediate group of the fourth lens group, at the telephoto edge and βR represents lateral magnification of the rear group of the fourth lens group, at the telephoto edge.
Conditional expression (2) represents a condition for maintaining high optical performance and reducing the anti-blur shift amount of the anti-blur group. Below the lower limit of conditional expression (2), although the shift amount of the anti-blur group during blur correction can be reduced, the refractive power of the anti-blur group becomes strong, making the correction of various types of aberration difficult. On the other hand, above the upper limit of conditional expression (2), although advantageous in correcting various types of aberration, the shift amount of the anti-blur group increases, increasing the driving amount of the actuator that drives the anti-blur group and hence, increasing the power consumption of the actuator.
More favorable results can be expected if conditional expression (2) is satisfied within the following range.

−1.6<AT<−1.3  (2)′

By satisfying the range prescribed by conditional expression (2)′, the optical performance of the anti-blur group can be further improved, on top of reducing the shift amount of the anti-blur group during blur corrections.
In the zoom lens according to the present invention, the intermediate group of the fourth lens group includes at least 1 aspheric surface and compared to a spherical surface having a paraxial radius of curvature, the aspheric surface has a shape where the positive refractive power toward the lens periphery from the optical axis becomes stronger or the negative refractive power becomes weaker. Further, the zoom lens preferably satisfies the following conditional expression, where ΔS represents the deviation of the paraxial radius of curvature at the height of the effective diameter of the aspheric surface of the intermediate group and aspheric surface shape and φS represents the effective diameter of the aspheric surface of the intermediate group.

0.1<|100×ΔS/φS|<1.0  (3)

Conditional expression (3) represents a condition for improving the optical performance of the intermediate group (anti-blur group) of the fourth lens group. Below the lower limit of conditional expression (3), an aspheric surface cannot be formed among the intermediate group, whereby the correction of various types of aberration at the intermediate group cannot be performed. On the other hand, above the upper limit of conditional expression (3), coma aberration correction becomes difficult.
More favorable results can be expected if conditional expression (3) is satisfied within the following range.

0.2<|100×ΔS/φS|<0.5  (3)′

By satisfying the range prescribed by conditional expression (3)′, coma aberration can be favorably corrected and high optical performance can be maintained.
As described, the zoom lens according to the present invention, the intermediate group (anti-blur group) of the fourth lens group is configured by 2 lenses, whereby a reduction in the weight of the anti-blur group is facilitated. By satisfying conditional expression (1), the focal lengths of the lens groups preceding and subsequent to the anti-blur group become appropriate, high optical performance is maintained, and the effective diameter of the anti-blur group is reduced, enabling reductions in the size of the anti-blur group to be facilitated. By satisfying conditional expression (2), the lateral magnification of the anti-blur group and that of the lens groups subsequent thereto become appropriate, enabling the anti-blur coefficient to be sufficiently large. As a result, optical performance can be maintained and the anti-blur shift amount of the anti-blur group during blur correction can be reduced. By satisfying conditional expression (3) (or conditional expression (3)′), the optical performance of the anti-blur group can be further improved. Thus, according to the zoom lens of the present invention, reductions in the size, weight and anti-blur shift amount of the anti-blur group can be facilitated, whereby even with a small actuator, blur correction can be performed quickly, promoting actuator power savings without deterioration in optical performance.
FIG. 1 depicts a cross-sectional view (along the optical axis) of the zoom lens according to a first embodiment. The zoom lens includes sequentially from an object side (object not depicted), a first lens group G11 having a positive refractive power, a second lens group G12 having a negative refractive power, a third lens group G13 having a positive refractive power, and a fourth lens group G14 having a positive refractive power. Further, at an imaging plane IMG, the light receiving surface of an imaging element, such as a CCD and CMOS, is disposed.
The fourth lens group G14 consists of, sequentially from the object side, a front group G14(F) having a positive refractive power, an intermediate group G14(M) configured by a cemented lens formed by a positive lens and a negative lens and having an overall refractive power that is negative, and a rear group G14(R) having a positive refractive power. In the front group G14(F), an aperture stop ST prescribing a given aperture is disposed. Further, in the intermediate group G14(M), the surface farthest on the imaging plane IMG side is formed to be aspheric.
The zoom lens, by uniformly moving the second lens group G12 and the third lens group G13 along the optical axis, from the object side to the imaging plane IMG side, zooms from a wide angle edge to a telephoto edge. Further, by moving a portion of the third lens group G13 in a direction along the optical axis, the zoom lens performs focusing and by moving the intermediate group G14(M) in a direction substantially orthogonal to the optical axis, corrects blur (performs anti-blur).
Various values related to the zoom lens according to the first embodiment are indicated below.

    Focal length (mm) of entire zoom lens=71.5336 (wide angle edge) to 111.5353 (intermediate position) to 194.092 8 (telephoto edge)
    Focal length (mm) of first lens group G11=144.469
    Focal length (mm) of second lens group G12=−33.664
    Focal length (mm) of third lens group G13=90.870
    Focal length (mm) of fourth lens group G14=82.798
    F number=2.9 (wide angle edge) to 2.9 (intermediate state) to 2.9 (telephoto edge)
    Angle of view (2ω)=34.66° (wide angle edge) to 20.71° (intermediate state) to 12.48° (telephoto edge)
    Zoom ratio=2.713

(Values Related to Conditional Expression (1))

    Overall optical system focal length (Ft) (mm) at telephoto edge, in infinity focus state=194.0928
    Focal length (F4F) (mm) of front group G14(F)=62.032
    Focal length (F4M) (mm) of intermediate group G14(M)=−43.400
    Focal length (F4R) (mm) of rear group G14(R)=57.268

|Ft×F4M/(F4F×F4R)|=2.3712

(Values Related to Conditional Expression (2))

    Lateral magnification (βM) of intermediate group G14(M) at telephoto edge=−5.133
    Lateral magnification (βR) of rear group G14(R) at telephoto edge=−0.255
    AT=−1.5639
    (Where, AT=(1−βM)×βR)

(Values Related to Conditional Expression (3))

    Deviation (ΔS) of paraxial radius of curvature at height of effective diameter of aspheric surface of intermediate group G14(M) and aspheric surface shape=−0.1151
    Effective diameter (φS) of aspheric surface of intermediate group G14(M)=26.0

|100×ΔS/φS|=0.4427

r1=222.8728

d1=2.0000 nd1=1.91082 νd1=35.25

r2=103.7846

d2=10.5000 nd2=1.45860 νd2=90.19

r3=−300.7820

d3=0.2000

r4=88.4625

d4=9.0000 nd3=1.49700 νd3=81.61

r5=−9494.4089

d5=1.3857 (wide angle edge) to 31.7756 (intermediate position) to 54.1401 (telephoto edge)

r6=1908.7598

d6=5.2000 nd4=1.90366 νd4=31.31

r7=−69.4016

d7=1.3500 nd5=1.61800 νd5=63.39

r8=69.4016

d8=3.8890

r9=−141.8243

d9=1.2000 nd6=1.49700 νd6=81.61

r10=52.9228

d10=3.3000 nd7=1.84666 νd7=23.78

r11=111.5902

d11=4.4169

r12=−60.5428

d12=1.2000 nd8=1.88300 νd8=40.80

r13=174.6335

d13=15.4455 (wide angle edge) to 11.6391 (intermediate position) to 1.6000 (telephoto edge)

r14=113.7835 (aspheric surface)

d14=6.3000 nd9=1.58313 νd9=59.46

r15=−65.7348 (aspheric surface)

d15=13.7091

r16=−163.7249

d16=1.4000 nd10=1.92286 νd10=20.88

r17=−439.7863

d17=40.4088 (wide angle edge) to 13.8254 (intermediate position) to 1.5000 (telephoto edge)

r18=125.0060

d18=5.1184 nd11=1.61800 νd11=63.39

r19=−95.7349

d19=1.7000

r20=∞ (aperture stop)

d20=1.7000

r21=37.0745

d21=9.5000 nd12=1.49700 νd12=81.61

r22=−65.1203

d22=2.5000 nd13=1.71736 νd13=29.50

r23=105.7968

d23=14.2949

r24=−88.9484

d24=2.3000 nd14=1.80809 νd14=22.76

r25=−39.7920

d25=1.4000 nd15=1.69350 νd15=53.20

r26=41.7941 (aspheric surface) (effective diameter φ26.0)

d26=10.5167

r27=80.4222

d27=7.5000 nd16=1.61800 νd16=63.39

r28=−44.5394

d28=11.5916

r29=−28.1673

d29=1.5000 nd17=1.71300 νd17=53.94

r30=−64.7347

d30=2.5887

r31=140.8610

d31=5.5000 nd18=1.56883 νd18=56.04

r32=−92.8595

d32=51.37

r33=∞ (imaging plane)

    Constant of Cone (K) and Aspheric Coefficients (A, B, C, D, E, F)

(Fourteenth Plane)

K=−11.9954,

A=0, B=2.66677×10−7,

C=1.55243×10−9, D=−2.91159×10−12,

E=2.12840×10−16, F=3.53783×10−18 

(Fifteenth Plane)

K=−0.5492,

A=0, B=1.02602×10−8,

C=1.30471×10−9, D=−6.07503×10−13,

E=−3.7893×10−15, F=5.96719×10−18 

(Twenty-Sixth Plane)

K=−1.4774,

A=0, B=−1.17887×10−6,

C=−1.07533×10−9, D=−3.90498×10−12,

E=8.54852×10−15, F=0



FIG. 2 is a diagram of various types of aberration at the wide angle edge of the zoom lens of the first embodiment according to the invention; FIG. 3 is a diagram of various types of aberration at the intermediate position of the zoom lens of the first embodiment according to the invention; and FIG. 4 is a diagram of various types of aberration at the telephoto edge of the zoom lens of the first embodiment according to the invention. In the diagrams, g, d, and C represent wavelength aberration corresponding to the g-line (λ=435.83 nm), the d-line (λ=587.56 nm), and the C-line (λ=656.27 nm), respectively; and ΔS and ΔM in a portion depicting astigmatism, indicate aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 5 depicts a cross-sectional view (along the optical axis) of the zoom lens according to a second embodiment. The zoom lens includes sequentially from an object side (object not depicted), a first lens group G21 having a positive refractive power, a second lens group G22 having a negative refractive power, a third lens group G23 having a positive refractive power, and a fourth lens group G24 having a positive refractive power. Further, at the imaging plane IMG, the light receiving surface of an imaging element, such as a CCD and CMOS, is disposed.
The fourth lens group G24 consists of, sequentially from the object side, a front group G24(F) having a positive refractive power, an intermediate group G24(M) configured by a cemented lens formed by a positive lens and a negative lens and having an overall refractive power that is negative, and a rear group G24(R) having a positive refractive power. In the front group G24(F), the aperture stop ST prescribing a given aperture is disposed. Further, in the intermediate group G24(M), the surface farthest on the imaging plane IMG side is formed to be aspheric.
The zoom lens, by uniformly moving the second lens group G22 and the third lens group G23 along the optical axis, from the object side to the imaging plane IMG side, zooms from the wide angle edge to the telephoto edge. Further, by moving a portion of the third lens group G23 in a direction along the optical axis, the zoom lens performs focusing and by moving the intermediate group G24(M) in a direction substantially orthogonal to the optical axis, corrects blur (performs anti-blur).
Various values related to the zoom lens according to the second embodiment are indicated below.

    Focal length (mm) of entire zoom lens=71.5209 (wide angle edge) to 117.5105 (intermediate position) to 194.068 1 (telephoto edge)
    Focal length (mm) of first lens group G21=144.087
    Focal length (mm) of second lens group G22=−33.304
    Focal length (mm) of third lens group G23=90.526
    Focal length (mm) of fourth lens group G24=82.744
    F number=2.9 (wide angle edge) to 2.9 (intermediate state) to 2.9 (telephoto edge)
    Angle of view (2ω)=34.66° (wide angle edge) to 20.71° (intermediate state) to 12.48° (telephoto edge)
    Zoom ratio=2.713

(Values Related to Conditional Expression (1))

    Overall optical system focal length (Ft) (mm), at telephoto edge, in infinity focus state=194.0681
    Focal length (F4F) (mm) of front group G24(F)=61.080
    Focal length (F4M) (mm) of intermediate group G24(M)=−43.295
    Focal length (F4R) (mm) of rear group G24(R)=58.453

|Ft×F4M/(F4F×F4R)|=2.3534

(Values Related to Conditional Expression (2))

    Lateral magnification (βM) of intermediate group G24(M), at telephoto edge=−6.244
    Lateral magnification (βR) of rear group G24(R), at telephoto edge=−0.216

AT=−1.5647

    (Where, AT=(1−βM)×βR)

(Values Related to Conditional Expression (3))

    Deviation (ΔS) of paraxial radius of curvature at height of effective diameter of aspheric surface of intermediate group G24(M) and aspheric surface shape=−0.1081
    Effective diameter (φS) of aspheric surface of intermediate group G24(M)=25.6

|100×ΔS/φS|=0.4223

r1=222.2214

d1=2.0000 nd1=1.91082 νd1=35.25

r2=103.4753

d2=10.5000 nd2=1.45860 νd2=90.19

r3=−298.5174

d3=0.2000

r4=88.2603

d4=8.8000 nd3=1.49700 ν3=81.61

r5=−10563.5431

d5=1.2000 (wide angle edge) to 31.5776 (intermediate position) to 53.9008 (telephoto edge)

r6=1009.5052

d6=5.2000 nd4=1.90366 νd4=31.31

r7=−70.2509

d7=1.3500 nd5=1.61800 νd5=63.39

r8=70.2509

d8=3.7528

r9=−156.3665

d9=1.2000 nd6=1.49700 νd6=81.61

r10=49.6801

d10=3.3000 nd7=1.84666 νd7=23.78

r11=95.2516

d11=4.6178

r12=−58.7772

d12=1.2000 nd8=1.88300 νd8=40.80

r13=177.1970

d13=15.1042 (wide angle edge) to 11.3976 (intermediate position) to 1.6000 (telephoto edge)

r14=102.9577 (aspheric surface)

d14=6.7500 nd9=1.51633 νd9=64.06

r15=−59.5060 (aspheric surface)

d15=13.4571

r16=−137.5555

d16=1.4000 nd10=1.92286 νd10=20.88

r17=−252.3951

d17=40.6970 (wide angle edge) to 14.0261 (intermediate position) to 1.5000 (telephoto edge)

r18=113.0406

d18=5.2838 nd11=1.61800 νd11=63.39

r19=−98.7983

d19=1.7000

r20=∞(aperture stop)

d20=1.7000

r21=36.3568

d21=9.5000 nd12=1.49700 νd12=81.61

r22=−67.3140

d22=3.0000 nd13=1.71736 νd13=29.50

r23=96.8404

d23=13.5679

r24=−91.3000

d24=2.3000 nd14=1.80809 νd14=22.76

r25=−39.7728

d25=1.4300 nd15=1.69350 νd15=53.20

r26=41.0718 (aspheric surface) (effective diameter φ25.6)

d26=10.0244

r27=75.9182

d27=8.0000 nd16=1.61800 νd16=63.39

r28=−45.6371

d28=12.1798

r29=−27.5459

d29=1.5000 nd17=1.71300 νd17=53.94

r30=−65.7082

d30=3.8260

r31=127.8003

d31=5.5000 nd18=1.56883 νd18=56.04

r32=−96.1226

d32=48.305

r33=∞ (imaging plane)

Constant of Cone (K) and Aspheric Coefficients (A, B, C, D, E, F)

(Fourteenth Plane)

K=−5.6100,

A=0, B=−6.34506×10−9,

C=−2.39141×10−9, D=1.90231×10−11,

E=−4.99934×10−14, F=4.49558×10−17 

(Fifteenth Plane)

K=−0.6649,

A=0, B=2.19580×10−7,

C=−3.02130×10−9, D=2.14493×10−11,

E=−5.34576×10−14, F=4.66441×10−17 

(Twenty-Sixth Plane)

K=−1.3886,

A=0, B=−1.07914×10−6,

C=−2.70333×10−9, D=4.27338×10−12,

E=−7.70848×10−15, F=0



FIG. 6 is a diagram of various types of aberration at the wide angle edge of the zoom lens of the second embodiment according to the invention; FIG. 7 is a diagram of various types of aberration at the intermediate position of the zoom lens of the second embodiment according to the invention; and FIG. 8 is a diagram of various types of aberration at the telephoto edge of the zoom lens of the second embodiment according to the invention. In the diagrams, g, d, and C represent wavelength aberration corresponding to the g-line (λ=435.83 nm), the d-line (λ=587.56 nm), and the C-line (λ=656.27 nm), respectively; and ΔS and ΔM in a portion depicting astigmatism, indicate aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 9 depicts a cross-sectional view (along the optical axis) of the zoom lens according to a third embodiment. The zoom lens includes sequentially from an object side (object not depicted), a first lens group G31 having a positive refractive power, a second lens group G32 having a negative refractive power, a third lens group G33 having a positive refractive power, and a fourth lens group G34 having a positive refractive power. Further, at the imaging plane IMG, the light receiving surface of an imaging element, such as a CCD and CMOS, is disposed.
The fourth lens group G34 consists of, sequentially from the object side, a front group G34(F) having a positive refractive power, an intermediate group G34(M) configured by a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group G34(R) having a positive refractive power. In the front group G34(F), the aperture stop ST prescribing a given aperture is disposed. Further, in the intermediate group G34(M), the surface farthest on the imaging plane IMG side is formed to be aspheric.
The zoom lens, by uniformly moving the second lens group G32 and the third lens group G33 in a direction along the optical axis, zooms from the wide angle edge to the telephoto edge. Further, by moving a portion of the third lens group G33 in a direction along the optical axis, the zoom lens performs focusing and by moving the intermediate group G34(M) in a direction substantially orthogonal to the optical axis, corrects blur (performs anti-blur).
Various values related to the zoom lens according to the third embodiment are indicated below.

    Focal length (mm) of entire zoom lens=71.50 (wide angle edge) to 117.50 (intermediate position) to 194.0 (telephoto edge)
    Focal length (mm) of first lens group G31=116.472
    Focal length (mm) of second lens group G32=−33.989
    Focal length (mm) of third lens group G33=95.458
    Focal length (mm) of fourth lens group G34=101.417
    F number=2.9 (wide angle edge) to 2.9 (intermediate state) to 2.9 (telephoto edge)
    Angle of view (2ω)=34.66° (wide angle edge) to 20.71° (intermediate state) to 12.48° (telephoto edge)
    Zoom ratio=2.713

(Values Related to Conditional Expression (1))

    Overall optical system focal length (Ft) (mm), at telephoto edge, in infinity focus state=194.0
    Focal length (F4F) (mm) of front group G34(F)=80.447
    Focal length (F4M) (mm) of intermediate group G34(M)=−53.233
    Focal length (F4R) (mm) of rear group G34(R)=67.250

|Ft×F4M/(F4F×F4R)|=1.9082

(Values Related to Conditional Expression (2))

    Lateral magnification (βM) of intermediate group G34(M), at telephoto edge=−13.442
    Lateral magnification (βR) of rear group G34(R), at telephoto edge=−0.092

AT=−1.3287

(Where, AT=(1−βM)×βR)

(Values Related to Conditional Expression (3))

    Deviation (ΔS) of paraxial radius of curvature at height of effective diameter of aspheric surface of intermediate group G34(M) and aspheric surface shape=−0.0554
    Effective diameter (φS) of aspheric surface of intermediate group G34(M)=26.6

|100×ΔS/φS|=0.2083

r1=260.8335

d1=2.0000 nd1=1.90366 νd1=31.31

r2=96.5008

d2=10.0000 nd2=1.49700 νd2=81.61

r3=−536.8467

d3=13.9737

r4=101.3178

d4=7.6000 nd3=1.48749 νd3=70.44

r5=−2665.6863

d5=0.2000

r6=138.3704

d6=5.8000 nd4=1.48749 νd4=70.44

r7=32778.0796

d7=1.7344 (wide angle edge) to 26.1822 (intermediate position) to 41.4529 (telephoto edge)

r8=−535.6803

d8=4.4879 nd5=1.84666 νd5=23.78

r9=−73.5688

d9=1.2000 nd6=1.49700 νd6=81.61

r10=58.3764

d10=3.3638

r11=−335.6856

d11=1.2000 nd7=1.61800 νd7=63.39

r12=54.7363

d12=3.1182 nd8=1.92286 νd8=20.88

r13=131.0940

d13=3.9834

r14=−60.4808

d14=1.2000 nd9=1.90366 νd9=31.31

r15=201.8372

d15=32.3700 (wide angle edge) to 20.7934 (intermediate position) to 1.2000 (telephoto edge)

r16=140.2250

d16=5.0000 nd10=1.49700 νd10=81.61

r17=−80.4431

d17=0.2000

r18=−364.7242

d18=6.5000 nd11=1.61800 νd11=63.39

r19=−40.5605

d19=1.2000 nd12=1.83481 νd12=42.72

r20=−104.6322

d20=14.2588 (wide angle edge) to 1.3876 (intermediate position) to 5.7103 (telephoto edge)

r21=79.9122

d21=4.8884 nd13=1.83481 νd13=42.72

r22=−305.5741

d22=1.1000

r23=∞ (aperture stop)

d23=0.9000

r24=30.3564

d24=8.0000 nd14=1.49700 νd14=81.61

r25=−900.4981

d25=1.2000 nd15=1.80518 νd15=25.46

r26=39.2300

d26=6.8611

r27=−123.2542

d27=1.2000 nd16=1.80610 νd16=40.73

r28=28.0015

d28=3.5000 nd17=1.82115 νd17=24.06

r29=65.2493 (aspheric surface) (effective diameter φ26.6)

d29=14.3219

r30=173.5739

d30=4.5000 nd18=1.88300 νd18=40.80

r31=−88.7106

d31=21.2945

r32=−29.1676

d32=1.2000 nd19=1.80518 νd19=25.46

r33=−40.5665

d33=8.0346

r34=81.7278

d34=6.0000 nd20=1.61800 νd20=63.39

r35=−549.0507

d35=42.610

r36=∞ (imaging plane)

    Constant of Cone (K) and Aspheric Coefficients (A, B, C, D, E, F)

(Twenty-Ninth Plane)

K=−0.8792,

A=0, B=−1.16677×10−6,

C=−6.37406×10−10, D=−4.56666×10−12,

E=1.02081×10−14, F=0



FIG. 10 is a diagram of various types of aberration at the wide angle edge of the zoom lens of the third embodiment according to the invention; FIG. 11 is a diagram of various types of aberration at the intermediate position of the zoom lens of the third embodiment according to the invention; and FIG. 12 is a diagram of various types of aberration at the telephoto edge of the zoom lens of the third embodiment according to the invention. In the diagrams, g, d, and C represent wavelength aberration corresponding to the g-line (λ=435.83 nm), the d-line (λ=587.56 nm), and the C-line (λ=656.27 nm), respectively; and ΔS and ΔM in a portion depicting astigmatism, indicate aberration with respect to a sagittal image plane and a meridional image plane, respectively.
Among the values for each of the embodiments above, r1, r2, . . . indicate radii of curvature for each lens, diaphragm surface, etc.; d1, d2, . . . indicate the thickness of the lenses, diaphragm, etc. or the distance between surfaces thereof; nd1, nd2, . . . indicate the refraction index of each lens with respect to the d-line (λ=587.56 nm); and νd1, νd2, . . . indicate the Abbe number with respect to the d-line (λ=587.56 nm) of each lens.
Each of the aspheric surfaces above can be expressed by equation [1], where Z is aspheric surface depth, y is the height from the optical axis, and the travel direction of light is positive.




  
    
      
        Z
        =
        
          
            
              y
              2
            
            
              
                R
                ⁡
                
                  (
                  
                    1
                    +
                    
                      
                        1
                        -
                        
                          
                            (
                            
                              1
                              +
                              K
                            
                            )
                          
                          ⁢
                          
                            y
                            /
                            
                              R
                              2
                            
                          
                        
                      
                    
                  
                  )
                
              
              2
            
          
          +
          
            Ay
            2
          
          +
          
            By
            4
          
          +
          
            Cy
            6
          
          +
          
            Dy
            8
          
          +
          
            Ey
            10
          
          +
          
            Fy
            12
          
        
      
    
    
      
        [
        1
        ]
      
    
  




Where, R is the paraxial radius of curvature; K is the constant of the cone; and A, B, C, D, E, F are the second, fourth, sixth, eighth, tenth, and twelfth aspheric coefficients, respectively.
In the embodiments, the invention is applied and examples configuring a large diameter, internal focusing telephoto zoom lens having at the wide angle edge, a focal length of 72 mm or less, a zoom ratio of 2.7× or more and an F number of 3 or less. As shown in these embodiments, by satisfying the conditions above, reductions in the size, weight and the anti-blur shift amount of the anti-blur group are facilitated, whereby even with a small actuator, blur correction can be performed quickly. Actuator power savings can also be promoted, without deterioration of optical performance. Further, the zoom lens of each of the embodiments employs a lens having a suitable aspheric surface, whereby favorable optical performance can be maintained with fewer lenses.
Additionally, according to the present invention, the optical performance of the anti-blur group can be improved.
According to the present invention, a zoom lens is effected that maintains high optical performance; facilitates reductions in the size, weight, and the anti-blur shift amount of the anti-blur group; and has an excellent blur correction function.
As described, the zoom lens of the present invention is useful in imaging apparatuses such as DSMCs and single-lens reflex cameras, and is particularly ideal when quick blur correction is demanded.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.
The present document incorporates by reference the entire contents of Japanese priority document, 2010-203703 filed in Japan on Sep. 10, 2010.

## Claims

1. A zoom lens comprises sequentially 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 fourth lens group having a positive refractive power, wherein
zoom is performed by moving the second lens group and the third lens group along an optical axis,
the fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group consisting of only a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group having a positive refractive power,
blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis, and
a conditional expression (1)1.85<|Ft×F4M/(F4F×F4R)|<4 is satisfied, where Ft represents overall optical system focal length, at a telephoto edge, in an infinity focus state, F4F represents the focal length of the front group of the fourth lens group, F4M represents the focal length of the intermediate group of the fourth lens group, and F4R represents the focal length of the rear group of the fourth lens group.

2. The zoom lens according to claim 1, wherein |Ft×F4M/(F4F×F4R)| is greater than or equal to 1.9082 and less than or equal to 2.3712.

3. A zoom lens comprises sequentially 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 fourth lens group having a positive refractive power, wherein
zoom is performed by moving the second lens group and the third lens group along an optical axis,
the fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group configured by a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group having a positive refractive power,
blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis,
a conditional expression (1)1.85<|Ft×F4M/(F4F×F4R)|<4 is satisfied, where Ft represents overall optical system focal length, at a telephoto edge, in an infinity focus state, F4F represents the focal length of the front group of the fourth lens group, F4M represents the focal length of the intermediate group of the fourth lens group, and F4R represents the focal length of the rear group of the fourth lens group, and
a conditional expression (2)−2.0<AT<−1.3 is satisfied, where AT is an anti-blur coefficient of the intermediate group of the fourth lens group at the telephoto edge, AT=(1−βM)×βR, βM represents lateral magnification of the intermediate group of the fourth lens group, at the telephoto edge, and βR represents lateral magnification of the rear group of the fourth lens group at the telephoto edge.

4. The zoom lens according to claim 3, wherein
at least one surface of the intermediate group of the fourth lens group is aspheric,
the aspheric surface, compared to a spherical surface having a paraxial radius of curvature, has a shape where a positive refractive power toward the lens periphery increases or a negative refractive power decreases, and
a conditional expression (3)0.1<|100×ΔS/φS|<1.0 is satisfied, where ΔS represents a deviation of the paraxial radius of curvature at a height of the effective diameter of the aspheric surface of the intermediate group and aspheric surface shape and φS represents an effective diameter of the aspheric surface of the intermediate group.