# Patent

## Title
Zoom lens

## Abstract

A zoom lens includes, sequentially from an object side, a positive first lens group; a negative second lens group; a positive third lens group; and a positive fourth lens group, where 2.0≦D23W/FW≦3.0 is satisfied. D23W is an interval, at a wide angle edge, between a lens that among lenses of the second lens group, is farthest on an imaging plane side and a lens that among lenses of the third lens group, is farthest on the object side. FW is a focal length of an optical system of the zoom lens at infinity focus, at the wide angle edge.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present document incorporates by reference the entire contents of Japanese priority document, 2009-189203, 2009-189204 and 2009-189205 filed in Japan on Aug. 18, 2009.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens.
2. Description of the Related Art
In recent years, further reductions in size and increased power are demanded of digital cameras and the like. To address these demands, a compact, high power zoom lens is proposed in Japanese Patent Application Laid-Open Publication Nos. 2008-176230 and 2008-185782, for example.
The zoom lenses recited in Japanese Patent Application Laid-Open Publication Nos. 2008-176230 and 2008-185782 are high power zoom lenses that include at least 4 lenses, a positive lens, a negative lens, and two positive lenses, sequentially from an object side. In particular, the zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2008-176230 realizes an angle of view that exceeds 77° at the wide angle edge and a zoom ratio of approximately 9.4. Further, the zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2008-185782 realizes an angle of view that exceeds 61° at the wide angle edge and a zoom ratio of approximately 9.5.
Although the zoom lenses recited in Japanese Patent Application Laid-Open Publication Nos. 2008-176230 and 2008-185782 achieve zoom ratios of 9 or greater, the zoom lenses have a relatively large lens diameter and thus, are not applicable to imaging apparatuses for which greater compactness is demanded. Furthermore, the angle of view is less than 80°, which is narrow and insufficient.
Moreover, the size of the zoom lenses when retracted is too large for application to imaging apparatuses for which reductions in size are demanded. In addition, it cannot be said that the optical performance of these lenses is sufficient.
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 positive first lens group; a negative second lens group; a positive third lens group; and a positive fourth lens group, where 2.0≦D23W/FW≦3.0 is satisfied. D23W is an interval, at a wide angle edge, between a lens that among lenses of the second lens group, is farthest on an imaging plane side and a lens that among lenses of the third lens group, is farthest on the object side. FW is a focal length of an optical system of the zoom lens at infinity focus, at the wide angle edge.
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 is a cross sectional view (along an optical axis) of a zoom lens according to a first example;
FIG. 2 is a diagram of various types of aberration of the zoom lens according to the first example;
FIG. 3 is a cross sectional view (along the optical axis) of a zoom lens according to a second example;
FIG. 4 is a diagram of various types of aberration of the zoom lens according to the second example;
FIG. 5 is a cross sectional view (along the optical axis) of a zoom lens according to a third example;
FIG. 6 is a diagram of various types of aberration of the zoom lens according to the third example;
FIG. 7 is a cross sectional view (along the optical axis) of a zoom lens according to a fourth example;
FIG. 8 is a diagram of various types of aberration of the zoom lens according to the fourth example;
FIG. 9 is a cross sectional view (along the optical axis) of a zoom lens according to a fifth example;
FIG. 10 is a diagram of various types of aberration of the zoom lens according to the fifth example;
FIG. 11 is a cross sectional view (along the optical axis) of a zoom lens according to a sixth example;
FIG. 12 is a diagram of various types of aberration of the zoom lens according to the sixth example;
FIG. 13 is a cross sectional view (along the optical axis) of a zoom lens according to a seventh example;
FIG. 14 is a diagram of various types of aberration of the zoom lens according to the seventh example;
FIG. 15 is a cross sectional view (along the optical axis) of a zoom lens according to an eighth example;
FIG. 16 is a diagram of various types of aberration of the zoom lens according to the eighth example;
FIG. 17 is a cross sectional view (along the optical axis) of a zoom lens according to a ninth example; and
FIG. 18 is a diagram of various types of aberration of the zoom lens according to the ninth example.



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 an embodiment 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. The zoom lens zooms from a wide angle edge to a telephoto edge by moving the first to the third lens groups along the optical axis. Further, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image by moving the fourth lens group along the optical axis.
One object of the present invention is to provide a compact zoom lens that has a wide angle of view and high optical performance and that is capable of high zoom ratios.
Another object of the present invention is to provide a high power zoom lens that has a wide angle of view and with respect to a retracted state, has a thinner size than a conventional zoom lens. To achieve such objects, various conditions are set below.
The zoom lens according to the embodiment preferably satisfies the following conditional expression, where in the zoom lens, at the wide angle edge, an interval between the lens that among the lenses of the second lens group, is farthest on the imaging plane side and the lens that among the lenses of the third lens group, is farthest on the object side is D23W and the focal length (infinity focus) of the entire optical system at the wide angle edge is FW.

2.0≦D23W/FW≦3.0  (1)

Conditional expression (1) prescribes a condition to reduce the effective diameter of the first lens group while ensuring a wide angle of view of 80° or greater at the wide angle edge. Satisfaction of conditional expression (1) enables a wide angle of 80° or greater to be achieved together with a reduced aperture of the first lens group. Below the lower limit of conditional expression (1), although the effective diameter of the first lens group becomes smaller, achieving a smaller aperture of the first lens group, the maintenance of a wide angle of view of 80° or greater becomes difficult. On the other hand, beyond the upper limit of conditional expression (1), the effective diameter of the first lens group becomes large at the wide angle edge, making reduction of the aperture of the first lens group difficult.
The zoom lens according to the embodiment preferably satisfies the following conditional expression, where the focal length of the first lens group is F1and the focal length of the second lens group is F2.

5.7≦|F1/F2|≦10  (2)

Conditional expression (2) prescribes a condition to reduce the effective diameter of the first lens group, increase the angle of view at the wide angle edge, and maintain high optical performance over the entire zoom range. Below the lower limit of conditional expression (2), although high optical performance can be maintained, the effective diameter of the lens group becomes difficult to decrease and the wide angle becomes difficult to increase. On the other hand, beyond the upper limit of conditional expression (2), although the power of the second lens group becomes strong, facilitating reduction of the aperture of the first lens group and increase of the angle of view, the correction of various types of aberration becomes difficult.
The zoom lens according to the embodiment preferably satisfies the following conditional expression, where the total length (distance from the surface farthest on the object side to the imaging plane) of the optical system, at the wide angle edge is TaW, the total length (distance from the surface farthest on the object side to the imaging plane) of the optical system, at the telephoto edge is Tat, the half angle of view of the optical system, at the wide angle edge is ωW, and the maximum paraxial image height at the wide angle edge is Ymax.

15≦(TaW+TaT)/(tan(ωW)×Ymax)≦33  (3)

Conditional expression (3) prescribes a condition to reduce the aperture of the first lens group and maintain an angle of view of 80° or greater at the wide angle edge while realizing a zoom ratio of 8 or greater. Below the lower limit of conditional expression (3), although the aperture of the first lens group can be reduced and the angle of view at the wide angle edge can be increased, a zoom ratio of 8 or greater becomes difficult to realize. On the other hand, beyond the upper limit of conditional expression (3), although a zoom ratio of 8 or greater can be achieved, reduction of the aperture of the first lens group and increase of the angle of view at the wide angle edge become difficult to realize.
As described, by satisfying conditional expression (1), the zoom lens according to the embodiment has a small aperture while being able to maintain a wide angle of view of 80° or greater. Further, by satisfying conditional expression (2), the zoom lens is compact and has a wide angle of view while being able to maintain high optical performance over the entire zoom range. Additionally, by satisfying conditional expression (3), the zoom lens is able to be compact, have a wide angle of view and a high zoom ratio.
Favorable results can be expected by satisfying any one of the conditional expressions above, as described. Nonetheless, satisfaction of more than one of the conditional expressions above, as compared to satisfaction of only one condition expression, further improves results.
Furthermore, the zoom lens according to the embodiment preferably satisfies the following conditional expression, where a total thickness along the optical axis of the lens groups is ΣD, the half angle of view of the optical system, at the wide angle edge is ωW, and the maximum paraxial image height at the wide angle edge is Ymax.

3.5≦ΣD/(tan(ωW)×Ymax)≦5.5  (4)

Conditional expression (4) prescribes a condition for a suitable total thickness along the optical axis of the lens groups to achieve a thinner retracted-state size, while providing for a wide angle of view of 80° or greater. Satisfaction of conditional expression (4) enables both an angle of view of 80° or greater and a thinner retracted-state size. Below the lower limit of conditional expression (4), such a thin lens thickness is called for the lens groups that lens processing becomes difficult. Further, such a wide angle of view is called for that aberration correction for the angle of view becomes difficult. On the other hand, beyond the upper limit of conditional expression (4), the total thickness of the lens groups becomes too large, making a thinner retracted-state size difficult to achieve.
The zoom lens according to the embodiment preferably satisfies the following conditional expression, where the focal length of the second lens group is F2, the focal length of the third lens group is F3, and the focal length (infinity focus) of the entire optical system at the wide angle edge is FW.

8.0≦|F2×F3|/FW≦15  (5)

Conditional expression (5) prescribes a condition to maintain an angle of view of 80° or greater at the wide angle edge, while achieving a thinner retracted-state size and a high zoom ratio. Below the lower limit of conditional expression (5), although an angle of view of 80° or greater at the wide angle edge can be maintained and a thinner retracted-state size can be achieved, the refractive power of the second lens group and of the third lens group becomes too strong, making the correction of various types of aberration difficult. On the other hand, beyond the upper limit of conditional expression (5), the refractive power of the second lens group and of the third lens group becomes too weak. If the realization of a high zoom ratio is attempted under such conditions, displacement of the second lens group and of the third lens group has to be increased, which means that the cam barrel for moving the lens groups has to be lengthened, whereby a thinner retracted-state size becomes difficult to realize. Furthermore, if the refractive power of the second lens and of the third lens is weak, an angle of view of 80° or greater at the wide angle edge becomes difficult to achieve.
The zoom lens according to the embodiment preferably satisfies the following conditional expression, where the focal length of the second lens group is F2, a thickness along the direction of the optical axis of the second lens group is D2, and the maximum paraxial image height at the wide angle edge is Ymax.

5.0≦F2×D2|/Ymax≦10  (6)

Conditional expression (6) prescribes a condition for reducing the thickness of the second lens group and for a suitable refractive power of the second lens group to realize a greater angle of view and a thinner retracted-state size. Below the lower limit of conditional expression (6), the refractive power of the second lens group becomes too strong, making the correction of various types of aberration difficult, which is undesirable. On the other hand, beyond the upper limit of conditional expression (6), the refractive power of the second lens group becomes too weak, making an angle of view of 80° or greater difficult to achieve. Further, the thickness of the second lens group becomes thick, making a thinner retracted-state size difficult to realize.
As described, the zoom lens according to the embodiment, in addition to maintaining a wide angle of view, is able to realize a thinner retracted-state size and a high zoom ratio. For example, satisfaction of conditional expression (4) obtains a suitable total thickness along the optical axis of the lens groups constituting the zoom lens and enables a wide angle of view (80° or greater) and a thinner retracted-state size to be realized. Furthermore, satisfaction of conditional expression (5) obtains a suitable refractive power for the second lens group and of the third lens group and enables a wide angle of view of 80° or greater while further enabling a thinner retracted-state size and a high zoom ratio to be achieved. In addition, satisfaction of conditional expression (6) enables a reduction in the thickness of the second lens group, obtains a suitable refractive power for the second lens group, and enables an increase of the angle of view and a thinner retracted-state size.
Favorable results can be expected by satisfying any one of the conditional expressions above, as described. Nonetheless, satisfaction of more than one of the conditional expressions above, as compared to satisfaction of only one condition expression, further improves results.
In the zoom lens according to the embodiment, the first lens group includes plural positive lenses. The zoom lens preferably satisfies the following conditional expression, where with respect to the d-line of the positive lenses of the first lens group, the average Abbe number is λdP1 and the average refractive index is NdP1.

25≦λdP1/NdP1≦35  (7)

Condition expression (7) prescribes a condition to maintain an angle of view of 80° or greater at the wide angle edge, reduce the thickness of the first lens group and achieve satisfactory correction of chromatic aberration of magnification at the telephoto edge of the zoom lens. Below the lower limit of conditional expression (7), although a reduction of the thickness of the first lens group is easily achieved, the correction of chromatic aberration of magnification with respect to long wavelengths (C-line) at the telephoto edge becomes difficult achieve. On the other hand, beyond the upper limit of conditional expression (7), the refractive index with respect to the d-line of the positive lenses in the first lens group has to be lowered and the Abbe number has to be increased. If maintenance of a suitable refractive power of the first lens group is attempted under such conditions, the thickness of the first lens group increases, making reductions in thickness difficult. Further, the correction of chromatic aberration of magnification with respect to short wavelengths (g-line) at the telephoto edge becomes difficult achieve.
In the zoom lens according to the embodiment, the second lens group includes plural negative lenses including sequentially from the object side, a first negative lens and a second negative lens. The zoom lens preferably satisfies the following conditional expression, where with respect to the d-line of the second negative lens, the Abbe number is λdM2and the refractive index is NdM2.

20≦λdM2/NdM2≦31  (8)

Conditional expression (8) prescribes a condition to reduce the thickness of the second lens group and achieve satisfactory correction of chromatic aberration of magnification at the wide angle edge of the zoom lens. Below the lower limit of conditional expression (8), although a reduction in the thickness of the second lens group is easily achieved, the correction of longitudinal chromatic aberration at the telephoto edge becomes difficult. On the other hand, beyond the upper limit of conditional expression (8), in order to maintain an appropriate refractive power of the second lens group, the curvature of radius of the second negative lens has to be significantly increased, making a reduction in the thickness of the second lens group difficult. In addition, satisfactory correction of spherical aberration and astigmatism in the zoom lens, as well as chromatic aberration of magnification with respect to short wavelengths (g-line) at the wide angle edge become difficult.
In the zoom lens according to the embodiment, the third lens group includes plural positive lenses. The zoom lens preferably satisfies the following conditional expression, where with respect to the d-line of the positive lens that, among the lenses of the third lens group, is farthest on the object side, the Abbe number is λdP3, and the refractive index is NdP3.

2≦(λdM2/NdM2)−(λdP3/NdP3)≦12  (9)

Conditional expression (9) prescribes a condition to realize a high zoom ratio (8 or greater) while achieving satisfactory correction of chromatic aberration at the wide angle edge and at the telephoto edge. Below the lower limit of conditional expression (9), although the correction of chromatic aberration of magnification at the wide angle edge is easily achieved, the correction of longitudinal chromatic aberration at the telephoto edge becomes difficult. On the other hand, beyond the upper limit of conditional expression (9), although the correction of longitudinal chromatic aberration for short wavelengths at the telephoto edge is easily achieved, the correction of chromatic aberration of magnification at the wide angle edge becomes difficult.
Additionally, in the zoom lens according to the embodiment, the second lens group, in addition to the negative lenses, includes at least 1 positive lens having an aspheric surface on the imaging plane side. The zoom lens preferably satisfies the following conditional expression, where deviation of the paraxial curvature radius at a height that is 10% of the effective diameter of the aspheric surface and the aspheric shape is S10, and the height of 10% of the effective diameter is H10.

−0.1<S10/H10<−0.005  (10)

Conditional expression (10) prescribes the aspheric shape of a positive lens in the second lens group. By adopting in the second lens group, a lens having an aspheric shape satisfying conditional expression (10), various types of aberration such as spherical aberration, astigmatism, and distortion can be corrected satisfactorily over the entire zoom range. Below the lower limit of conditional expression (10), the inflection point of the aspheric shape becomes prominent, making lens processing difficult and causing problems with lens manufacture. On the other hand, beyond the upper limit of conditional expression (10), a reduction in the size of the first lens group becomes difficult and sufficient correction of the various types of aberration cannot be achieved.
As described, satisfaction of conditional expression (7) maintains a wide angle of view of 80° or greater, reduces the thickness of the first lens group, and enables satisfactory correction of chromatic aberration of magnification at the telephoto edge of the zoom lens. Satisfaction of conditional expression (8) reduces the thickness of the second lens group and enables satisfactory correction of chromatic aberration of magnification at the wide angle edge of the zoom lens. Satisfaction of conditional expression (9) realizes a high zoom ratio (8 or greater), while achieving satisfactory correction of chromatic aberration at the wide angle edge and at the telephoto edge. In addition, satisfaction of conditional expression (10) enables further improvement of aberration correction. Satisfaction of each of the conditional expressions above enables the zoom lens according to the embodiment to maintain a wide angle of view and high optical performance and have a thinner retracted-state size and a high zoom ratio.
Favorable results can be expected by satisfying any one of the conditional expressions above, as described. Nonetheless, satisfaction of more than one of the conditional expressions above, as compared to satisfaction of only one conditional expression, further improves results.
FIG. 1 is a cross sectional view (along the optical axis) of a zoom lens according to a first example. The zoom lens includes, sequentially from a non-depicted object side, a positive first lens group G11, a negative second lens group G12, a positive third lens group G13 and a positive fourth lens group G14. Further, a diaphragm STP is disposed between the second lens group G12 and the third lens group G13. A cover glass CG (or filter) is disposed between the fourth lens group G14 and an imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, an optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G11 includes sequentially from the object side, a negative lens L111, a positive lens L112, and a positive lens L113. The negative lens L111 and the positive lens L112 are cemented together.
The second lens group G12 includes sequentially from the object side, a negative lens L121, a negative lens L122, and a positive lens L123. Both surfaces of the negative lens L121 and a surface on the imaging plane IMG side of the positive lens L123 are aspheric. Further, the negative lens L122 and the positive lens L123 are cemented together.
The third lens group G13 includes sequentially from the object side, a positive lens L131, a negative lens L132, and a positive lens L133. A surface on the object side of the positive lens L131 is aspheric. Further, the positive lens L131 and the negative lens L132 are cemented together.
The fourth lens group G14 includes a positive lens L141. Both surfaces of the positive lens L141 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G11, the second lens group G12, and the third lens group G13 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G14 along the optical axis.
Various values related to the zoom lens according to the first example are indicated below.

    Focal length of zoom lens system=4.365 (wide angle edge) to 13.109 (intermediate zoom position) to 41.178 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.84 (intermediate zoom position) to 5.75 (telephoto edge)
    Angle of view (2ω)=87.6° (wide angle edge) to 33.6° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (1))

    At wide angle edge, interval between lens farthest on imaging plane side among lenses of the second lens group G12 and lens farthest on object side among lenses of the third lens group G13 (D23W)=11.532
    D23W/FW=2.64

(Values Related to Conditional Expression (2))

    Focal length of the first lens group G11 (F1)=35.5194
    Focal length of the second lens group G12 (F2)=−5.8942
    |F1/F2|=6.03

(Values Related to Conditional Expression (3))

    Total length of optical system, at wide angle edge (TaW)=38.5991
    Total length of optical system, at telephoto edge (TaT)=55.5311
    Half angle of view of optical system, at wide angle edge (ωW)=43.80
    Maximum paraxial image height at wide angle edge (Ymax)=4.1858
    (TaW+TaT)/(tan(ωW)×Ymax)=23.45
    r1=42.4567
    
        d1=0.7000 nd1=1.92286 νd1=20.88
    
    
    r2=23.7410
    
        d2=2.8893 nd2=1.61800 νd2=63.39
    
    
    r3=123.2525
    
        d3=0.1500
    
    
    r4=24.3075
    
        d4=2.2214 nd3=1.88300 νd3=40.80
    
    
    r5=72.0512
    
        d5=0.5000 (wide angle edge) to 8.4947 (intermediate zoom position) to 19.7731 (telephoto edge)
    
    
    r6=18.2902 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1413 (aspheric surface)
    
        d7=2.6217
    
    
    r8=−104.4554
    
        d8=0.4500 nd5=1.74330 νd5=49.22
    
    
    r9=8.5587
    
        d9=1.6559 nd6=2.00170 νd6=19.32
    
    
    r10=31.8881 (aspheric surface)
    
        d10=11.1821 (wide angle edge) to 3.0587 (intermediate zoom position) to 0.1871 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.4041 (aspheric surface)
    
        d12=1.1356 nd7=1.80611 νd7=40.73
    
    
    r13=8.7508
    
        d13=1.4251 nd8=1.94595 νd8=17.98
    
    
    r14=4.0934
    
        d14=0.3433
    
    
    r15=10.1848
    
        d15=1.1959 nd9=1.61800 νd9=63.39
    
    
    r16=−10.1848
    
        d16=3.5000 (wide angle edge) to 5.7939 (intermediate zoom position) to 13.5388 (telephoto edge)
    
    
    r17=15.7815 (aspheric surface)
    
        d17=1.5000 nd10=1.55332 νd10=71.67
    
    
    r18=−1000.0000 (aspheric surface)
    
        d18=4.4707 (wide angle edge) to 7.8402 (intermediate zoom position) to 3.0627 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.0081 (wide angle edge) to 1.0126 (intermediate zoom position) to 1.0311 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k) and Aspheric coefficients (A, B, C, D

(Sixth Plane)

    K=0,
    A=1.16028×10−4, B=−4.00446×10−5,
    C=9.99964×10−7, D=−7.76320×10−9 

(Seventh Plane)

    K=−0.1858,
    A=6.53494×10−4, B=2.25949×10−5,
    C=−7.88249×10−6, D=7.04313×10−9 

(Tenth Plane)

    K=0,
    A=−5.92227×10−4, B=4.38745×10−6,
    C=1.94199×10−7, D=−1.48702×10−9 

(Twelfth Plane)

    K=−0.5353,
    A=9.52249×10−6, B=4.17341×10−5,
    C=−8.84871×10−6, D=1.17972×10−6 

(Seventeenth Plane)

    K=−1.6970,
    A=−6.34973×10−4, B=3.53883×10−5,
    C=−2.81373×10−6, D=3.86441×10−8 

(Eighteenth Plane)

    K=0,
    A=−6.44317×10−1, B=1.51939×10−5,
    C=−1.68208×10−6, D=1.60171×10−8 


FIG. 2 is a diagram of various types of aberration of the zoom lens according to the first example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 2 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 3 is a cross sectional view (along the optical axis) of a zoom lens according to a second example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G21, a negative second lens group G22, a positive third lens group G23, and a positive fourth lens group G24. Further, a diaphragm STP is disposed between the second lens group G22 and the third lens group G23. A cover glass CG (or filter) is disposed between the fourth lens group G24 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G21 includes sequentially from the object side, a negative lens L211, a positive lens L212, and a positive lens L213. The negative lens L211 and the positive lens L212 are cemented together.
The second lens group G22 includes sequentially from the object side, a negative lens L221, a negative lens L222, and a positive lens L223. Both surfaces of the negative lens L221 and a surface on the imaging plane IMG side of the positive lens L223 are aspheric. Further, the negative lens L222 and the positive lens L223 are cemented together.
The third lens group G23 includes sequentially from the object side, a positive lens L231, a negative lens L232, and a positive lens L233. A surface on the object side of the positive lens L231 is aspheric. Further, the positive lens L231 and the negative lens L232 are cemented together.
The fourth lens group G24 includes a positive lens L241. Both surfaces of the positive lens L241 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G21, the second lens group G22, and the third lens group G23 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G24 along the optical axis.
Various values related to the zoom lens according to the second example are indicated below.

    Focal length of zoom lens system=4.378 (wide angle edge) to 13.059 (intermediate zoom position) to 40.991 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.88 (intermediate zoom position) to 5.66 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (1))

    At wide angle edge, interval between lens farthest on imaging plane side among lenses of the second lens group G22 and lens farthest on object side among lenses of the third lens group G23 (D23W)=11.363
    D23W/FW=2.60

(Values Related to Conditional Expression (2))

    Focal length of the first lens group G21 (F1)=35.3573
    Focal length of the second lens group G22 (F2)=−5.7182
    |F1/F2|=6.18

(Values Related to Conditional Expression (3))

    Total length of optical system, at wide angle edge (TaW)=38.7179
    Total length of optical system, at telephoto edge (TaT)=55.4904
    Half angle of view of optical system, at wide angle edge (ωW)=43.70
    Maximum paraxial image height at wide angle edge (Ymax)=4.1839
    (TaW+TaT)/(tan(ωW)×Ymax)=23.56
    r1=35.3665
    
        d1=0.7000 nd2=1.92286 νd2=20.88
    
    
    r2=22.7365
    
        d2=2.8303 nd2=1.61800 νd2=63.39
    
    
    r3=94.1318
    
        d3=0.1500
    
    
    r4=22.1345
    
        d4=2.1521 nd3=1.78800 νd3=47.49
    
    
    r5=57.3854
    
        d5=0.5000 (wide angle edge) to 8.0817 (intermediate zoom position) to 19.4548 (telephoto edge)
    
    
    r6=19.8247 (aspheric surface)
    
        d6=0.8000 nd4=1.85639 νd4=40.10
    
    
    r7=4.0732 (aspheric surface)
    
        d7=2.6721
    
    
    r8=701.8212
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.1000
    
        d9=1.6506 nd6=2.01390 νd6=19.32
    
    
    r10=27.7772 (aspheric surface)
    
        d10=11.0131 (wide angle edge) to 3.0593 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6428 (aspheric surface)
    
        d12=1.3959 nd7=1.80610 νd7=40.74
    
    
    r13=9.1218
    
        d13=1.2040 nd8=1.94595 νd8=17.98
    
    
    r14=4.3311
    
        d14=0.3125
    
    
    r15=9.9065
    
        d15=1.2138 nd9=1.61800 νd9=63.39
    
    
    r16=−9.9065
    
        d16=4.2017 (wide angle edge) to 7.1778 (intermediate zoom position) to 13.6497 (telephoto edge)
    
    
    r17=16.9814 (aspheric surface)
    
        d17=1.5000 nd10=1.55516 νd10=71.67
    
    
    r18=−224.2761 (aspheric surface)
    
        d18=4.1129 (wide angle edge) to 7.3262 (intermediate zoom position) to 3.4643 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d26=1.0090 (wide angle edge) to 0.9591 (intermediate zoom position) to 0.8904 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k) and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.09571×10−4, B=−2.97768×10−5,
    C=6.21695×10−7, D=−3.72502×10−9 

(Seventh Plane)

    K=−0.1858,
    A=7.30061×10−4, B=3.77662×10−6,
    C=−3.03192×10−6, D=−1.86011×10−7 

(Tenth Plane)

    K=0,
    A=−6.01399×10−4, B=3.30880×10−6,
    C=1.07 326×10−7, D=−4.56889×10−10 

(Twelfth Plane)

    K=−0.5322,
    A=2.34771×10−5, B=1.08796×10−5,
    C=−1.60048×10−6, D=5.07288×10−7 

(Seventeenth Plane)

    K=−4.3209,
    A=−6.78620×10−4, B=3.28433×10−5,
    C=−1.41788×10−6, D=−9.87708×10−9 

(Eighteenth Plane)

    K=0,
    A=−8.87070×10−4, B=3.42 669×10−5,
    C=−1.76375×10−6, D=3.39007×10−9 


FIG. 4 is a diagram of various types of aberration of the zoom lens according to the second example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 4 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 5 is a cross sectional view (along the optical axis) of a zoom lens according to a third example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G31, a negative second lens group G32, a positive third lens group G33, and a positive fourth lens group G34. Further, a diaphragm STP is disposed between the second lens group G32 and the third lens group G33. A cover glass CG (or filter) is disposed between the fourth lens group G34 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G31 includes sequentially from the object side, a negative lens L311, a positive lens L312, and a positive lens L313. The negative lens L311 and the positive lens L312 are cemented together.
The second lens group G32 includes sequentially from the object side, a negative lens L321, a negative lens L322, and a positive lens L323. Both surfaces of the negative lens L322 and a surface on the imaging plane IMG side of the positive lens L323 are aspheric. Further, the negative lens L322 and the positive lens L323 are cemented together.
The third lens group G33 includes sequentially from the object side, a positive lens L331, a negative lens L332, and a positive lens L333. A surface on the object side of the positive lens L331 is aspheric. Further, the positive lens L331 and the negative lens L332 are cemented together.
The fourth lens group G34 includes a positive lens L341. Both surfaces of the positive lens L341 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G31, the second lens group G32, and the third lens group G33 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G34 along the optical axis.
Various values related to the zoom lens according to the third example are indicated below.

    Focal length of zoom lens system=4.381 (wide angle edge) to 13.307 (intermediate zoom position) to 41.113 (telephoto edge)
    F number=3.60 (wide angle edge) to 4.82 (intermediate zoom position) to 5.71 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (1))

    At wide angle edge, interval between lens farthest on imaging plane side among lenses of the second lens group G32 and lens farthest on object side among lenses of the third lens group G33 (D23W)=10.771
    D23W/FW=2.50

(Values Related to Conditional Expression (2))

    Focal length of the first lens group G31 (F1)=35.4149
    Focal length of the second lens group G32 (F2)=−5.6003
    |F1/F2|=6.32

(Values Related to Conditional Expression (3))

    Total length of optical system, at wide angle edge (TaW)=38.1391
    Total length of optical system, at telephoto edge (TaT)=55.6475
    Half angle of view of optical system, at wide angle edge (ωW)=43.70
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1861
    (TaW+TaT)/(tan(ωW)×Ymax)=23.45
    r1=33.2686
    
        d1=0.8000 nd1=1.84666 νd1=23.78
    
    
    r2=19.8000
    
        d2=3.0214 nd2=1.61800 νd2=63.39
    
    
    r3=80.0497
    
        d3=0.1500
    
    
    r4=24.5713
    
        d4=2.2786 nd3=1.78800 νd3=47.49
    
    
    r5=78.2687
    
        d5=0.5000 (wide angle edge) to 9.5000 (intermediate zoom position) to 19.6766 (telephoto edge)
    
    
    r6=25.2886 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1057 (aspheric surface)
    
        d7=2.4507
    
    
    r8=562.3556
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.5000
    
        d9=1.5324 nd6=2.00170 νd6=19.32
    
    
    r10=31.7164 (aspheric surface)
    
        d10=10.4212 (wide angle edge) to 3.2143 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6699 (aspheric surface)
    
        d12=1.1969 nd7=1.80610 νd7=40.74
    
    
    r13=9.2400
    
        d13=1.3621 nd8=1.94595 νd8=17.98
    
    
    r14=4.4271
    
        d14=0.3144
    
    
    r15=10.8758
    
        d15=1.2266 nd9=1.61800 νd9=63.39
    
    
    r16=−9.1157
    
        d16=4.0000 (wide angle edge) to 7.1658 (intermediate zoom position) to 13.6403 (telephoto edge)
    
    
    r17=17.2904 (aspheric surface)
    
        d17=1.5000 nd10=1.59201 νd10=67.02
    
    
    r18=−500.0000 (aspheric surface)
    
        d18=3.6718 (wide angle edge) to 6.6915 (intermediate zoom position) to 3.2000 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.6130 (wide angle edge) to 1.0391 (intermediate zoom position) to 1.0475 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k), and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.70699×10−4, B=−3.32288×10−5,
    C=7.95002×10−7, D=−6.27099×10−9 

(Seventh Plane)

    K=−0.1858,
    A=8.43675×10−4, B=6.56293×10−6,
    C=−2.00670×10−6, D=−2.29541×10−7 

(Tenth Plane)

    K=0,
    A=−5.64411×10−4, B=−1.75974×10−5,
    C=1.70798×10−6, D=−3.89949×10−8 

(Twelfth Plane)

    K=−0.5973,
    A=−1.92725×10−5, B=8.22671×10−5,
    C=−2.28281×10−5, D=2.78115×10−6 

(Seventeenth Plane)

    K=1.6141,
    A=−5.92164×10−4, B=1.68205×10−5,
    C=−7.73392×10−7, D=−2.40077×10−8 

(Eighteenth Plane)

    K=0,
    A=−6.47064×10−4, B=2.16671×10−5,
    C=−1.42681×10−6, D=−6.03161×10−10 


FIG. 6 is a diagram of various types of aberration of the zoom lens according to the third example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 6 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
Among the values for the examples 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); 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 the equation hereinafter, where Z=the depth of the aspheric surface, y=the height from the optical axis, and the direction of travel of light is positive.




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




Where, R is paraxial radii of curvature; K is constant of the cone; and A, B, C, D are the fourth, sixth, eighth, and tenth aspheric coefficients, respectively.
As described above, the zoom lens according to each of the examples above has a small aperture, has a wide angle of view (80° or greater), is able to maintain high optical performance over the entire zoom range, and has a high zoom ratio (8 or greater), by satisfying the conditional expressions above.
FIG. 7 is a cross sectional view (along the optical axis) of a zoom lens according to a fourth example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G11, a negative second lens group G12, a positive third lens group G13, and a positive fourth lens group G14. Further, a diaphragm STP is disposed between the second lens group G12 and the third lens group G13. A cover glass CG (or filter) is disposed between the fourth lens group G14 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G11 includes sequentially from the object side, a negative lens L111, a positive lens L112, and a positive lens L113. The negative lens L111 and the positive lens L112 are cemented together.
The second lens group G12 includes sequentially from the object side, a negative lens L121, a negative lens L122, and a positive lens L123. Both surfaces of the negative lens L121 and a surface on the imaging plane IMG side of the positive lens L123 are aspheric. Further, the negative lens L122 and the positive lens L123 are cemented together.
The third lens group G13 includes sequentially from the object side, a positive lens L131, a negative lens L132, and a positive lens L133. A surface on the object side of the positive lens L131 is aspheric. Further, the positive lens L131 and the negative lens L132 are cemented together.
The fourth lens group G14 includes a positive lens L114. Both surfaces of the positive lens L141 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G11, the second lens group G12, and the third lens group G13 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G14 along the optical axis.
Various values related to the zoom lens according to the fourth example are indicated below.

    Focal length of zoom lens system=4.365 (wide angle edge) to 13.109 (intermediate zoom position) to 41.178 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.84 (intermediate zoom position) to 5.75 (telephoto edge)
    Angle of view (2ω)=87.6° (wide angle edge) to 33.6° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (4))

    Total thickness along optical axis of lens groups (ΣD)=17.0882
    Half angle of view of optical system, at wide angle edge (ωW)=43.80
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1858
    ΣD/(tan(ωW)×Ymax)=4.26

(Values Related to Conditional Expression (5))

    Focal length of the second lens group G12 (F2)=−5.8942
    Focal length of the third lens group G13 (F3)=8.9547

Focal length (infinity focus) of the entire optical system at wide angle edge (FW)=4.3649

    |F2×F3|/FW=12.09

(Values Related to Conditional Expression (6))

    Focal length of the second lens group G12 (F2)=−5.8942
    Thickness along direction of optical axis of the second lens group G12 (D2)=5.5275
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1858
    |F2×D2|/Ymax=7.78
    r1=42.4567
    
        d1=0.7000 nd1=1.92286 νd1=20.88
    
    
    r2=23.7410
    
        d2=2.8893 nd2=1.61800 νd2=63.39
    
    
    r3=123.2525
    
        d3=0.1500
    
    
    r4=24.3075
    
        d4=2.2214 nd3=1.88300 νd3=40.80
    
    
    r5=72.0512
    
        d5=0.5000 (wide angle edge) to 8.4947 (intermediate zoom position) to 19.7731 (telephoto edge)
    
    
    r6=18.2902 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1413 (aspheric surface)
    
        d7=2.6217
    
    
    r8=−104.4554
    
        d8=0.4500 nd5=1.74330 νd5=49.22
    
    
    r9=8.5587
    
        d9=1.6559 nd6=2.00170 νd6=19.32
    
    
    r10=31.8881 (aspheric surface)
    
        d10=11.1821 (wide angle edge) to 3.0587 (intermediate zoom position) to 0.1871 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.4041 (aspheric surface)
    
        d12=1.1356 nd7=1.80611 νd7=40.73
    
    
    r13=8.7508
    
        d13=1.4251 nd8=1.94595 νd8=17.98
    
    
    r14=4.0934
    
        d14=0.3433
    
    
    r15=10.1848
    
        d15=1.1959 nd9=1.61800 νd9=63.39
    
    
    r16=−10.1848
    
        d16=3.5000 (wide angle edge) to 5.7939 (intermediate zoom position) to 13.5388 (telephoto edge)
    
    
    r17=15.7815 (aspheric surface)
    
        d17=1.5000 nd10=1.55332 νd10=71.67
    
    
    r18=−1000.0000 (aspheric surface)
    
        d18=4.4707 (wide angle edge) to 7.8402 (intermediate zoom position) to 3.0627 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.0081 (wide angle edge) to 1.0126 (intermediate zoom position) to 1.0311 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k) and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.16028×10−4, B=−4.00446×10−5,
    C=9.99964×10−7, D=−7.76320×10−9 

(Seventh Plane)

    K=−0.1858,
    A=6.53494×10−4, B=2.25949×10−5,
    C=−7.88249×10−6, D=7.04313×10−5 

(Tenth Plane)

    K=0,
    A=−5.92227×10−4, B=4.38745×10−6,
    C=1.94199×10−7, D=−1.48702×10−5 

(Twelfth Plane)

    K=−0.5353,
    A=9.52249×10−6, B=4.17341×10−5,
    C=−8.84871×10−6, D=1.17972×10−6 

(Seventeenth Plane)

    K=−1.6970,
    A=−6.34973×10−4, B=3.53883×10−5,
    C=−2.81373×10−6, D=3.86441×10−6 

(Eighteenth Plane)

    K=0,
    A=−6.44317×10−4, B=1.51939×10−5,
    C=−1.68208×10−6, D=1.60171×10−5 


FIG. 8 is a diagram of various types of aberration of the zoom lens according to the fourth example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 8 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 9 is a cross sectional view (along the optical axis) of a zoom lens according to a fifth example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G21, a negative second lens group G22, a positive third lens group G23, and a positive fourth lens group G24. Further, a diaphragm STP is disposed between the second lens group G22 and the third lens group G23. A cover glass CG (or filter) is disposed between the fourth lens group G24 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G21 includes sequentially from the object side, a negative lens L211, a positive lens L212, and a positive lens L213. The negative lens L211 and the positive lens L212 are cemented together.
The second lens group G22 includes sequentially from the object side, a negative lens L221, a negative lens L222, and a positive lens L223. Both surfaces of the negative lens L221 and a surface on the imaging plane IMG side of the positive lens L223 are aspheric. Further, the negative lens L222 and the positive lens L223 are cemented together.
The third lens group G23 includes sequentially from the object side, a positive lens L231, a negative lens L232, and a positive lens L233. A surface on the object side of the positive lens L231 is aspheric. Further, the positive lens L231 and the negative lens L232 are cemented together.
The fourth lens group G24 includes a positive lens L241. Both surfaces of the positive lens L241 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G21, the second lens group G22, and the third lens group G23 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G24 along the optical axis.
Various values related to the zoom lens according to the fifth example are indicated below.

    Focal length of zoom lens system=4.378 (wide angle edge) to 13.059 (intermediate zoom position) to 40.991 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.88 (intermediate zoom position) to 5.66 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (4))

    Total thickness along optical axis of lens groups (ΣD)=17.0313
    Half angle of view of optical system, at wide angle edge (ωW)=43.70
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1839
    ΣD/(tan(ωW)×Ymax)=4.26

(Values Related to Conditional Expression (5))

    Focal length of the second lens group G22 (F2)=−5.7182
    Focal length of the third lens group G23 (F3)=8.8889
    Focal length (infinity focus) of the entire optical system at wide angle edge (FW)=4.3782
    |F2×F3|/FW=11.61

(Values Related to Conditional Expression (6))

Focal length of the second lens group G22 (F2)=−5.7182

    Thickness along direction of optical axis of the second lens group G22 (D2)=5.5727
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1839
    |F2×D2|/Ymax=7.62
    r1=35.3665
    
        d1=0.7000 nd1=1.92286 νd1=20.88
    
    
    r2=22.7365
    
        d2=2.8303 nd2=1.61800 νd2=63.39
    
    
    r3=94.1318
    
        d3=0.1500
    
    
    r4=22.1345
    
        d4=2.1521 nd3=1.78800 νd3=47.49
    
    
    r5=57.3854
    
        d5=0.5000 (wide angle edge) to 8.0817 (intermediate zoom position) to 19.4548 (telephoto edge)
    
    
    r6=19.8247 (aspheric surface)
    
        d6=0.8000 nd4=1.85639 νd4=40.10
    
    
    r7=4.0732 (aspheric surface)
    
        d7=2.6721
    
    
    r8=701.8212
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.1000
    
        d9=1.6506 nd6=2.01390 νd6=19.32
    
    
    r10=27.7772 (aspheric surface)
    
        d10=11.0131 (wide angle edge) to 3.0593 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6428 (aspheric surface)
    
        d12=1.3959 nd7=1.80610 νd7=40.74
    
    
    r13=9.1218
    
        d13=1.2040 nd8=1.94595 νd8=17.98
    
    
    r14=4.3311
    
        d14=0.3125
    
    
    r15=9.9065
    
        d15=1.2138 nd9=1.61800 νd9=63.39
    
    
    r16=−9.9065
    
        d16=4.2017 (wide angle edge) to 7.1778 (intermediate zoom position) to 13.6497 (telephoto edge)
    
    
    r17=16.9814 (aspheric surface)
    
        d17=1.5000 nd10=1.55516 νd10=71.67
    
    
    r18=−224.2761 (aspheric surface)
    
        d18=4.1129 (wide angle edge) to 7.3262 (intermediate zoom position) to 3.4643 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.0090 (wide angle edge) to 0.9591 (intermediate zoom position) to 0.8904 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k) and Aspheric coefficients (A, B, C, D

(Sixth Plane)

    K=0,
    A=1.09571×10−4, B=−2.97768×10−5,
    C=6.21695×10−7, D=−3.72502×10−9 

(Seventh Plane)

    K=−0.1858,
    A=7.30061×10−4, B=3.77662×10−6,
    C=−3.03192×10−6, D=−1.86011×10−7 

(Tenth Plane)

    K=0,
    A=−6.01399×10−4, B=3.30880×10−6,
    C=1.07326×10−7, D=−4.56889×10−10 

(Twelfth Plane)

    K=−0.5322,
    A=2.34771×10−5, B=1.08796×10−5,
    C=−1.60048×10−6, D=5.07288×10−7 

(Seventeenth Plane)

    K=−4.3209,
    A=−6.78620×10−4, B=3.28433×10−5,
    C=−1.41788×10−6, D=−9.87708×10−9 

(Eighteenth Plane)

    K=0,
    A=−8.87070×10−4, B=3.42669×10−5,
    C=−1.76375×10−6, D=3.39007×10−9 


FIG. 10 is a diagram of various types of aberration of the zoom lens according to the fifth example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 10 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 11 is a cross sectional view (along the optical axis) of a zoom lens according to a sixth example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G31, a negative second lens group G32, a positive third lens group G33, and a positive fourth lens group G34. Further, a diaphragm STP is disposed between the second lens group G32 and the third lens group G33. A cover glass CG (or filter) is disposed between the fourth lens group G34 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, an optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G31 includes sequentially from the object side, a negative lens L311, a positive lens L312, and a positive lens L313. The negative lens L311 and the positive lens L312 are cemented together.
The second lens group G32 includes sequentially from the object side, a negative lens L321, a negative lens L322, and a positive lens L323. Both surfaces of the negative lens L321 and a surface on the imaging plane IMG side of the positive lens L323 are aspheric. Further, the negative lens L322 and the positive lens L323 are cemented together.
The third lens group G33 includes sequentially from the object side, a positive lens L331, a negative lens L332, and a positive lens L333. A surface on the object side of the positive lens L331 is aspheric. Further, the positive lens L331 and the negative lens L332 are cemented together.
The fourth lens group G34 includes a positive lens L341. Both surfaces of the positive lens L341 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G31, the second lens group G32, and the third lens group G33 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G34 along the optical axis.
Various values related to the zoom lens according to the sixth example are indicated below.

    Focal length of zoom lens system=4.381 (wide angle edge) to 13.307 (intermediate zoom position) to 41.113 (telephoto edge)
    F number=3.60 (wide angle edge) to 4.82 (intermediate zoom position) to 5.71 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (4))

    Total thickness along optical axis of lens groups (ΣD)=17.0831
    Half angle of view of optical system, at wide angle edge (ωW)=43.70
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1861
    ΣD/(tan(ωW)×Ymax)=4.27

(Values Related to Conditional Expression (5))

    Focal length of the second lens group G32 (F2)=−5.6003
    Focal length of the third lens group G33 (F3)=8.7461
    Focal length (infinity focus) of entire optical system at wide angle edge (FW)=4.3805
    |F2×F3|/FW=11.18

(Values Related to Conditional Expression (6))

    Focal length of the second lens group G32 (F2)=−5.6003
    Thickness along direction of optical axis of the second lens group G32 (D2)=5.2331
    Maximum paraxial image height at the wide angle edge (Ymax)=4.1861
    |F2×D2|/Ymax=7.00
    r1=33.2686
    
        d1=0.8000 nd1=1.84666 νd1=23.78
    
    
    r2=19.8000
    
        d2=3.0214 nd2=1.61800 νd2=63.39
    
    
    r3=80.0497
    
        d3=0.1500
    
    
    r4=24.5713
    
        d4=2.2786 nd3=1.78800 νd3=47.49
    
    
    r5=78.2687
    
        d5=0.5000 (wide angle edge) to 9.5000 (intermediate zoom position) to 19.6766 (telephoto edge)
    
    
    r6=25.2886 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1057 (aspheric surface)
    
        d7=2.4507
    
    
    r8=562.3556
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.5000
    
        d9=1.5324 nd6=2.00170 νd6=19.32
    
    
    r10=31.7164 (aspheric surface)
    
        d10=10.4212 (wide angle edge) to 3.2143 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6699 (aspheric surface)
    
        d12=1.1969 nd7=1.80610 νd7=40.74
    
    
    r13=9.2400
    
        d13=1.3621 nd6=1.94595 νd8=17.98
    
    
    r14=4.4271
    
        d14=0.3144
    
    
    r15=10.8758
    
        d15=1.2266 nd9=1.61800 νd9=63.39
    
    
    r16=−9.1157
    
        d16=4.0000 (wide angle edge) to 7.1658 (intermediate zoom position) to 13.6403 (telephoto edge)
    
    
    r17=17.2904 (aspheric surface)
    
        d17=1.5000 nd10=1.59201 νd10=67.02
    
    
    r18=−500.0000 (aspheric surface)
    
        d18=3.6718 (wide angle edge) to 6.6915 (intermediate zoom position) to 3.2000 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.6130 (wide angle edge) to 1.0391 (intermediate zoom position) to 1.0475 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k), and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.70699×10−4, B=−3.32288×10−5,
    C=7.95002×10−7, D=−6.27099×10−9 

(Seventh Plane)

    K=−0.1858,
    A=8.43675×10−4, B=6.56293×10−6,
    C=−2.00670×10−6, D=−2.29541×10−7 

(Tenth Plane)

    K=0,
    A=−5.64411×10−4, B=−1.75974×10−5,
    C=1.70798×10−6, D=−3.89949×10−9 

(Twelfth Plane)

    K=−0.5973,
    A=−1.92725×10−5, B=8.22671×10−5,
    C=−2.28281×10−5, D=2.78115×10−6 

(Seventeenth Plane)

    K=1.6141,
    A=−5.92164×10−4, B=1.68205×10−5,
    C=−7.73392×10−7, D=−2.40077×10−8 

(Eighteenth Plane)

    K=0,
    A=−6.47064×10−4, B=2.16671×10−5,
    C=−1.42681×10−6, D=−6.03161×10−10 


FIG. 12 is a diagram of various types of aberration of the zoom lens according to the sixth example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 12 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
Among the values for the examples 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); 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 the equation hereinafter, where Z=the depth of the aspheric surface, y=the height from the optical axis, and the direction of travel of light is positive.




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




Where, R is paraxial radii of curvature; K is constant of the cone; and A, B, C, D are the fourth, sixth, eighth, and tenth aspheric coefficients, respectively.
As described above, the zoom lens according to each of the examples above realizes a thinner retracted-state size and an increased angle of view (80° or greater) while having a high zoom ratio (8 or greater) by satisfying the conditional expressions above. Since a lens having a suitable aspheric surface is employed, satisfactory optical performance can be maintained with fewer lenses.
FIG. 13 is a cross sectional view (along the optical axis) of a zoom lens according to a seventh example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G11, a negative second lens group G12, a positive third lens group G13, and a positive fourth lens group G14. Further, a diaphragm STP is disposed between the second lens group G12 and the third lens group G13. A cover glass CG (or filter) is disposed between the fourth lens group G14 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G11 includes sequentially from the object side, a negative lens L111, a positive lens L112, and a positive lens L113. The negative lens L111 and the positive lens L112 are cemented together.
The second lens group G12 includes sequentially from the object side, a negative lens L121 (first negative lens), a negative lens L122 (second negative lens), and a positive lens L123. Both surfaces of the negative lens L121 and a surface on the imaging plane IMG side of the positive lens L123 are aspheric. Further, the negative lens L122 and the positive lens L123 are cemented together.
The third lens group G13 includes sequentially from the object side, a positive lens L131, a negative lens L132, and a positive lens L133. A surface on the object side of the positive lens L131 is aspheric. Further, the positive lens L131 and the negative lens L132 are cemented together.
The fourth lens group G14 includes a positive lens L141. Both surfaces of the positive lens L141 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G11, the second lens group G12, and the third lens group G13 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G14 along the optical axis.
Various values related to the zoom lens according to the seventh example are indicated below.

    Focal length of zoom lens system=4.365 (wide angle edge) to 13.109 (intermediate zoom position) to 41.178 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.82 (intermediate zoom position) to 5.75 (telephoto edge)
    Angle of view (2ω)=87.6° (wide angle edge) to 33.6° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (7))

    Average Abbe number with respect to d-line of positive lenses (positive lens L112, positive lens L113) of the first lens group G11 (λdP1)=52.0500
    Average refractive index with respect to d-line of positive lens (positive lens L112, positive lens L113) of the first lens group G1 (NdP1)=1.7505
    λdP1/NdP1=29.73

(Values Related to Conditional Expression (8))

    Abbe number with respect to d-line of second negative lens (negative lens L122) (λdM2)=49.2000
    Refractive index with respect to d-line of second negative lens (negative lens L122) (NdM2)=1.7433
    λdM2/NdM2=28.22

(Values Related to Conditional Expression (9))

    Abbe number with respect to d-line of positive lens (positive lens L131) that among lenses of the third lens group G13 is farthest on object side (λdP3)=40.7000
    Refractive index with respect to d-line of positive lens (positive lens L131) that among lenses of the third lens group G13 is farthest on object side (NdP3)=1.8061
    (λdM2NdM2)−(λdP3/NdP3)=5.69

(Values Related to Conditional Expression (10))

    Deviation of paraxial curvature radius at height that is 10% of the effective diameter of aspheric surface on the imaging plane IMG side of the positive lens L123 in the second lens group G12 and the aspheric shape (S10)=−0.1000
    Height of 10% of effective diameter of the aspheric surface on the imaging plane IMG side of the positive lens L123 in the second lens group G12 (H10)=3.7
    S10/H10=−0.0270
    r1=42.4567
    
        d1=0.7000 nd1=1.92286 νd1=20.88
    
    
    r2=23.7410
    
        d2=2.8893 nd2=1.61800 νd2=63.39
    
    
    r3=123.2525
    
        d3=0.1500
    
    
    r4=24.3075
    
        d4=2.2214 nd3=1.88300 νd3=40.80
    
    
    r5=72.0512
    
        d5=0.5000 (wide angle edge) to 8.4947 (intermediate zoom position) to 19.7731 (telephoto edge)
    
    
    r6=18.2902 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1413 (aspheric surface)
    
        d7=2.6217
    
    
    r9=−104.4554
    
        d8=0.4500 nd5=1.74330 νd5=49.22
    
    
    r9=8.5587
    
        d9=1.6559 nd6=2.00170 νd6=19.32
    
    
    r10=31.8881 (aspheric surface)
    
        d10=11.1821 (wide angle edge) to 3.0587 (intermediate zoom position) to 0.1871 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.4041 (aspheric surface)
    
        d12=1.1356 nd7=1.80611 νd7=40.73
    
    
    r13=8.7508
    
        d13=1.4251 ndB=1.94595 νd8=17.98
    
    
    r14=4.0934
    
        d14=0.3433
    
    
    r15=10.1848
    
        d15=1.1959 nd9=1.61800 νd9=63.39
    
    
    r16=−10.1848
    
        d16=3.5000 (wide angle edge) to 5.7939 (intermediate zoom position) to 13.5388 (telephoto edge)
    
    
    r17=15.7815 (aspheric surface)
    
        d17=1.5000 nd10=1.55332 νd10=71.67
    
    
    r16=−1000.0000 (aspheric surface)
    
        d18=4.4707 (wide angle edge) to 7.8402 (intermediate zoom position) to 3.0627 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.0081 (wide angle edge) to 1.0126 (intermediate zoom position) to 1.0311 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k), and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.16028×10−4, B=−4.00446×10−5,
    C=9.99964×10−7, D=−7.76320×10−9 

(Seventh Plane)

    K=−0.1858,
    A=6.53494×10−4, B=2.25949×10−5,
    C=−7.88249×10−6, D=7.04313×10−9 

(Tenth Plane)

    K=0,
    A=−5.92227×10−4, B=4.38745×10−6,
    C=1.94199×10−7, D=−1.48702×10−9 

(Twelfth Plane)

    K=−0.5353,
    A=9.52249×10−6, B=4.17341×10−5,
    C=−8.84871×10−6, D=1.17972×10−6 

(Seventeenth Plane)

    K=−1.6970,
    A=−6.34973×10−4, B=3.53883×10−5,
    C=−2.81373×10−6, D=3.86441×10−8 

(Eighteenth Plane)

    K=0,
    A=−6.44317×10−4, B=1.51939×10−5,
    C=−1.68208×10−6, D=1.60171×10−8 


FIG. 14 is a diagram of various types of aberration of the zoom lens according to the seventh example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 14 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 15 is a cross sectional view (along the optical axis) of a zoom lens according to an eighth example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G21, a negative second lens group G22, a positive third lens group G23, and a positive fourth lens group G24. Further, a diaphragm STP is disposed between the second lens group G22 and the third lens group G23. A cover glass CG (or filter) is disposed between the fourth lens group G24 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G21 includes sequentially from the object side, a negative lens L211, a positive lens L212, and a positive lens L213. The negative lens L211 and the positive lens L212 are cemented together.
The second lens group G22 includes sequentially from the object side, a negative lens L221 (first negative lens), a negative lens L222 (second negative lens), and a positive lens L223. Both surfaces of the negative lens L221 and a surface on the imaging plane IMG side of the positive lens L223 are aspheric. Further, the negative lens L222 and the positive lens L223 are cemented together.
The third lens group G23 includes sequentially from the object side, a positive lens L231, a negative lens L232, and a positive lens L233. A surface on the object side of the positive lens L231 is aspheric. Further, the positive lens L231 and the negative lens L232 are cemented together.
The fourth lens group G24 includes a positive lens L241. Both surfaces of the positive lens L241 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G21, the second lens group G22, and the third lens group G23 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G24 along the optical axis.
Various values related to the zoom lens according to the eighth example are indicated below.

    Focal length of zoom lens system=4.378 (wide angle edge) to 13.059 (intermediate zoom position) to 40.991 (telephoto edge)
    F number=3.58 (wide angle edge) to 4.82 (intermediate zoom position) to 5.66 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (7))

    Average Abbe number with respect to d-line of positive lenses (positive lens L212, positive lens L213) in the first lens group G21 (λdP1)=55.3500
    Average refraction index with respect to d-line of positive lenses (positive lens L212, positive lens L213) in the first lens group G21 (NdP1)=1.7030
    λdP1/NdP1=32.50

(Values Related to Conditional Expression (8))

    Abbe number with respect to d-line of second negative lens (negative lens L222) (λdM2)=49.6000
    Refractive index with respect to d-line of second negative lens (negative lens L222) (NdM2)=1.7725
    λdM2/ NdM2=27.98

(Values Related to Conditional Expression (9))

    Abbe number with respect to d-line of positive lens (positive lens L231) that among lenses of the third lens group G23, is farthest on object side (λdP3)=40.7000
    Refractive index with respect to d-line of positive lens (positive lens L231) that among lenses of the third lens group G23, is farthest on object side (NdP3)=1.8061
    (λdM2/NdM2)−(λdP3/NdP3)=5.45

(Values Related to Conditional Expression (10))

    Deviation of paraxial curvature radius at height that is 10% of effective diameter of aspheric surface on the imaging plane IMG side of positive lens L223 in the second lens group G22 and the aspheric shape (S10)=−0.0909
    Height of 10% of effective diameter of the aspheric surface on the imaging plane IMG side of the positive lens L223 in the second lens group G22 (H10)=3.6
    S10/H10=−0.0253
    r1=35.3665
    
        d1=0.7000 nd1=1.92286 νd1=20.88
    
    
    r2=22.7365
    
        d2=2.8303 nd2=1.61800 νd2=63.39
    
    
    r3=94.1318
    
        d3=0.1500
    
    
    r4=22.1345
    
        d4=2.1521 nd3=1.78800 νd3=47.49
    
    
    r5=57.3854
    
        d5=0.5000 (wide angle edge) to 8.0817 (intermediate zoom position) to 19.4548 (telephoto edge)
    
    
    r6=19.8247 (aspheric surface)
    
        d6=0.8000 nd4=1.85639 νd4=40.10
    
    
    r7=4.0732 (aspheric surface)
    
        d7=2.6721
    
    
    r8=701.8212
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.1000
    
        d9=1.6506 nd6=2.01390 νd6=19.32
    
    
    r10=27.7772 (aspheric surface)
    
        d10=11.0131 (wide angle edge) to 3.0593 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6428 (aspheric surface)
    
        d12=1.3959 nd7=1.80610 νd7=40.74
    
    
    r13=9.1218
    
        d13=1.2040 nd8=1.94595 νd8=17.98
    
    
    r14=4.3311
    
        d14=0.3125
    
    
    r15=9.9065
    
        d15=1.2138 nd9=1.61800 νd9=63.39
    
    
    r16=−9.9065
    
        d16=4.2017 (wide angle edge) to 7.1778 (intermediate zoom position) to 13.6497 (telephoto edge)
    
    
    r17=16.9814 (aspheric surface)
    
        d17=1.5000 nd10=1.55516 νd10=71.67
    
    
    r18=−224.2761 (aspheric surface)
    
        d18=4.1129 (wide angle edge) to 7.3262 (intermediate zoom position) to 3.4643 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.0090 (wide angle edge) to 0.9591 (intermediate zoom position) to 0.8904 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k), and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.09571×10−4, B=−2.97768×10−5,
    C=6.21695×10−7, D=−3.72502×10−9 

(Seventh Plane)

    K=−0.1858,
    A=7.30061×10−4, B=3.77662×10−6,
    C=−3.03192×10−6, D=−1.86011×10−7 

(Tenth Plane)

    K=0,
    A=−6.01399×10−4, B=3.30880×10−6,
    C=1.07326×10−7, D=−4.56889×10−10 

(Twelfth Plane)

    K=−0.5322,
    A=2.34771×10−5, B=1.08796×10−5,
    C=−1.60048×10−6, D=5.07288×10−7 

(Seventeenth Plane)

    K=−4.3209,
    A=−6.78620×10−4, B=3.28433×10−5,
    C=−1.41788×10−6, D=−9.87708×10−9 

(Eighteenth Plane)

    K=0,
    A=−8.87070×10−4, B=3.42669×10−5,
    C=−1.76375×10−6, D=3.39007×10−9 


FIG. 16 is a diagram of various types of aberration of the zoom lens according to the eighth example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 16 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
FIG. 17 is a cross sectional view (along the optical axis) of a zoom lens according to a ninth example. The zoom lens includes, sequentially from the non-depicted object side, a positive first lens group G31, a negative second lens group G32, a positive third lens group G33, and a positive fourth lens group G34. Further, a diaphragm STP is disposed between the second lens group G32 and the third lens group G33. A cover glass CG (or filter) is disposed between the fourth lens group G34 and the imaging plane IMG. The cover glass CG (or filter) is disposed as needed and may be omitted when not necessary. Further, at the imaging plane IMG, the optical receiving surface of an imaging element such as a CCD, a CMOS, etc. is disposed.
The first lens group G31 includes sequentially from the object side, a negative lens L311, a positive lens L312, and a positive lens L313. The negative lens L311 and the positive lens L312 are cemented together.
The second lens group G32 includes sequentially from the object side, a negative lens L321 (first negative lens), a negative lens L322 (second negative lens), and a positive lens L323. Both surfaces of the negative lens L321 and a surface on the imaging plane IMG side of the positive lens L323 are aspheric. Further, the negative lens L322 and the positive lens L323 are cemented together.
The third lens group G33 includes sequentially from the object side, a positive lens L331, a negative lens L332, and a positive lens L333. A surface on the object side of the positive lens L331 is aspheric. Further, the positive lens L331 and the negative lens L332 are cemented together.
The fourth lens group G34 includes a positive lens L341. Both surfaces of the positive lens L341 are aspheric.
The zoom lens zooms from the wide angle edge to the telephoto edge by moving the first lens group G31, the second lens group G32, and the third lens group G33 along the optical axis. Furthermore, the zoom lens corrects imaging plane (image location) variation accompanying zoom and focuses the image, by moving the fourth lens group G34 along the optical axis.
Various values related to the zoom lens according to the ninth example are indicated below.

    Focal length of zoom lens system=4.381 (wide angle edge) to 13.307 (intermediate zoom position) to 41.113 (telephoto edge)
    F number=3.60 (wide angle edge) to 4.82 (intermediate zoom position) to 5.71 (telephoto edge)
    Angle of view (2ω)=87.4° (wide angle edge) to 33.12° (intermediate zoom position) to 10.56° (telephoto edge)

(Values Related to Conditional Expression (7))

    Average Abbe number with respect to d-line of positive lenses (positive lens L312, positive lens L313) in the first lens group G31 (λdP1)=55.3500
    Average refraction index with respect to d-line of positive lenses (positive lens L312, positive lens L313) in the first lens group G31 (NdP1)=1.7030
    λdP1/NdP1=32.50

(Values Related to Conditional Expression (8))

    Abbe number with respect to d-line of second negative lens (negative lens L322) (λdM2)=49.6000
    Refractive index with respect to d-line of second negative lens (negative lens L322) (NdM2)=1.7725
    λdM2/NdM2=27.98

(Values Related to Conditional Expression (9))

    Abbe number with respect to d-line of positive lens (positive lens L331) that among lenses of the third lens group G33, is farthest on object side (λdP3)=40.7000
    Refractive index with respect to d-line of positive lens (positive lens L331) that among lenses of the third lens group G33, is farthest on object side (NdP3)=1.8061
    (λdM2/NdM2)−(λdP3/NdP3)=5.45

(Values Related to Conditional Expression (10))

    Deviation of paraxial curvature radius at height that is 10% of the effective diameter of aspheric surface on the imaging plane IMG side of the positive lens L323 in the second lens group G32 and the aspheric shape (S10)=−0.0893
    Height of 10% of effective diameter of the aspheric surface on the imaging plane IMG side of the positive lens L323 in the second lens group G32 (H10)=3.5
    S10/H10=−0.0255
    r1=33.2686
    
        d1=0.8000 nd1=1.84666 νd1=23.78
    
    
    r2=19.8000
    
        d2=3.0214 nd2=1.61800 νd2=63.39
    
    
    r3=80.0497
    
        d3=0.1500
    
    
    r4=24.5713
    
        d4=2.2786 nd3=1.78800 νd3=47.49
    
    
    r5=78.2687
    
        d5=0.5000 (wide angle edge) to 9.5000 (intermediate zoom position) to 19.6766 (telephoto edge)
    
    
    r6=25.2886 (aspheric surface)
    
        d6=0.8000 nd4=1.85135 νd4=40.10
    
    
    r7=4.1057 (aspheric surface)
    
        d7=2.4507
    
    
    r8=562.3556
    
        d8=0.4500 nd5=1.77250 νd5=49.62
    
    
    r9=8.5000
    
        d9=1.5324 nd6=2.00170 νd6=19.32
    
    
    r10=31.7164 (aspheric surface)
    
        d10=10.4212 (wide angle edge) to 3.2143 (intermediate zoom position) to 0.1500 (telephoto edge)
    
    
    r11=∞ (diaphragm)
    
        d11=0.3500
    
    
    r12=4.6699 (aspheric surface)
    
        d12=1.1969 nd7=1.80610 νd7=40.74
    
    
    r13=9.2400
    
        d13=1.3621 nd8=1.94595 νd8=17.98
    
    
    r14=4.4271
    
        d14=0.3144
    
    
    r15=10.8758
    
        d15=1.2266 nd9=1.61800 νd9=63.39
    
    
    r16=−9.1157
    
        d16=4.0000 (wide angle edge) to 7.1658 (intermediate zoom position) to 13.6403 (telephoto edge)
    
    
    r17=17.2904 (aspheric surface)
    
        d17=1.5000 nd10=1.59201 νd10=67.02
    
    
    r18=−500.0000 (aspheric surface)
    
        d18=3.6718 (wide angle edge) to 6.6915 (intermediate zoom position) to 3.2000 (telephoto edge)
    
    
    r19=∞
    
        d19=0.5000 nd11=1.51680 νd11=64.20
    
    
    r20=∞
    
        d20=1.6130 (wide angle edge) to 1.0391 (intermediate zoom position) to 1.0475 (telephoto edge)
    
    
    r21=∞ (image plane)

Constant of cone (k), and Aspheric coefficients (A, B, C, D)

(Sixth Plane)

    K=0,
    A=1.70699×10−4, B=−3.32288×10−5,
    C=7.95002×10−7, D=−6.27099×10−9 

(Seventh Plane)

    K=−0.1858,
    A=8.43675×10−4, B=6.56293×10−6,
    C=−2.00670×10−6, D=−2.29541×10−7 

(Tenth Plane)

    K=0,
    A=−5.64411×10−4, B=−1.75974×10−5,
    C=1.70798×10−6, D=−3.89949×10−8 

(Twelfth Plane)

    K=−0.5973,
    A=−1.92725×10−5, B=8.22671×10−5,
    C=−2.28281×10−5, D=2.78115×10−6 

(Seventeenth Plane)

    K=1.6141,
    A=−5.92164×10−4, B=1.68205×10−5,
    C=−7.73392×10−7, D=−2.40077×10−8 

(Eighteenth Plane)

    K=0,
    A=−6.47064×10−4, B=2.16671×10−5,
    C=−1.42681×10−6, D=−6.03161×10−10 


FIG. 18 is a diagram of various types of aberration of the zoom lens according to the ninth example. In the diagram “g”, “d”, and “c” respectively represent aberrations for wavelengths corresponding to g-line (λ=435.83 nm), d-line (λ=587.56 nm), and c-line (λ=656.27 nm). In a portion of FIG. 18 indicating astigmatism, ΔS and ΔM represent aberration with respect to a sagittal image plane and a meridional image plane, respectively.
Among the values for the examples 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); ν1, 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 the equation hereinafter, where Z=the depth of the aspheric surface, y=the height from the optical axis, and the direction of travel of light is positive.




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




Where, R is paraxial radii of curvature; K is constant of the cone; and A, B, C, D are the fourth, sixth, eighth, and tenth aspheric coefficients, respectively.
As described above, the zoom lens according to each of the examples above is able to have a wide angle of view of 80° or greater, high optical performance, a thinner retracted-state size, and a zoom ratio of 8 or greater by satisfying the conditional expressions above. Further, since a lens having a suitable aspheric surface is employed, the zoom lens according to each of the examples can maintain satisfactory optical performance with fewer lenses.
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.

## Claims

1. A zoom lens comprising, sequentially from an object side:
a positive first lens group;
a negative second lens group;
a positive third lens group; and
a positive fourth lens group,
wherein 2.0≦D23W/FW≦3.0 is satisfied, D23W being an interval, at a wide angle edge, between a lens that among lenses of the second lens group, is farthest on an imaging plane side and a lens that among lenses of the third lens group, is farthest on the object side, FW being a focal length of an optical system of the zoom lens at infinity focus, at the wide angle edge, and
wherein 15≦(TaW+TaT)/(tan(ωW)×Ymax)≦33 is satisfied, TaW being a total length of the optical system, at the wide angle, from a surface farthest on the object side to an imaging plane edge, TaT being a total length of the optical system, at a telephoto edge, from the surface farthest on the object side to an imaging plane, ωW being a half angle of view of the optical system, at the wide angle edge, and Ymax being a maximum paraxial image height at the wide angle edge.

2. The zoom lens according to claim 1, wherein 5.7≦|F1/F2|≦10 is satisfied, F1being a focal length of the first lens group and F2being a focal length of the second lens group.

3. A zoom lens comprising, sequentially from an object side:
a positive first lens group;
a negative second lens group;
a positive third lens group; and
a positive fourth lens group, wherein 3.5≦ΣD/(tan(ωW)×Ymax)≦5.5 is satisfied, ΣD being a total thickness along an optical axis of the first, the second, the third, and the fourth lens groups, ωW being a half angle of view of an optical system of the zoom lens, at a wide angle edge, and Ymax being a maximum paraxial image height at the wide angle edge.

4. The zoom lens according to claim 3, wherein 8.0≦|F2×F3|/FW≦15 is satisfied, F2being a focal length of the second lens group, F3being a focal length of the third lens group, and FW being a focal length of the optical system at infinity focus, at the wide angle edge.

5. The zoom lens according to claim 3, wherein 5.0≦|F2×D2|/Ymax≦10 is satisfied, F2being the focal length of the second lens group, D2being a thickness along an optical axis of the second lens group, and Ymax being the maximum paraxial image height at the wide angle edge.

6. The zoom lens according to claim 4, wherein 5.0≦|F2×D2|/Ymax≦10 is satisfied, F2being the focal length of the second lens group, D2being the thickness along an optical axis of the second lens group, and Ymax being the maximum paraxial image height at the wide angle edge.

7. A zoom lens comprising, sequentially from an object side:
a positive first lens group;
a negative second lens group;
a positive third lens group; and
a positive fourth lens group,
wherein the first lens group includes plural positive lenses, and 25 ≦λdP1/NdP1≦35 is satisfied, λdP1being an average Abbe number with respect to a d-line of the positive lenses of the first lens group and NdP1 being an average refractive index with respect to the d-line of the positive lenses of the first lens group, and
wherein the second lens group includes a first negative lens and a second negative lens, and 20≦λdM2/NdM2≦31 is satisfied, λdM2 being an Abbe number with respect to a d-line of the second negative lens and NdM2being a refractive index with respect to the d-line of the second negative lens.

8. The zoom lens according to claim 7, wherein the second lens group includes sequentially from the object side, the first negative lens and the second negative lens,
the third lens group includes plural positive lenses, and
2≦(λdM2/NdM2)−(λdP3/NdP3)≦12 is satisfied, λdM2being the Abbe number with respect to the d-line of the second negative lens, NdM2being the refractive index with respect to the d-line of the second negative lens, λdP3being an Abbe number with respect to a d-line of a positive lens that is farthest on the object side among the positive lenses of the third lens group, and NdP3is a refractive index with respect to the d-line of the positive lens that is farthest on the object side among the lenses of the third lens group.

9. A zoom lens comprising, sequentially from an object side:
a positive first lens group;
a negative second lens group;
a positive third lens group; and
a positive fourth lens group,
wherein 2.0≦D23W/FW≦2.64 is satisfied, D23W being an interval, at a wide angle edge, between a lens that among lenses of the second lens group, is farthest on an imaging plane side and a lens that among lenses of the third lens group, is farthest on the object side, FW being a focal length of an optical system of the zoom lens at infinity focus, at the wide angle edge.

10. A zoom lens comprising, sequentially from an object side:
a positive first lens group;
a negative second lens group;
a positive third lens group; and
a positive fourth lens group,
wherein the first lens group includes plural positive lenses, and 29.73≦λdP1/ NdP1≦35 is satisfied, λdP1 being an average Abbe number with respect to a d-line of the positive lenses of the first lens group and NdP1 being an average refractive index with respect to the d-line of the positive lenses of the first lens group.