# Patent

## Title
Zoom lens

## Abstract

A zoom lens includes sequentially from an object side, a first lens section G11 having a negative refractive power and a second lens section G12 having a positive refractive power. The first lens section G11 includes sequentially from the object side, a negative lens L111, a negative lens L112, and a positive lens L113. Both surface of the negative lens L112 are aspheric. The second lens section G12 includes sequentially from the object side, a front group G12F having a positive refractive power and a rear group G12R having a positive refractive power. Both surfaces of a negative lens L126 included in the rear group G12R are aspheric. The zoom lens can maintain high imaging performance while achieving size reductions and wide angle views by satisfying given conditions.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact wide angle zoom lens.
2. Description of the Related Art
As a wide angle zoom lens widely used on single-lens reflex cameras, a 4-group zoom lens includes sequentially from an object side, lens groups having negative, positive, negative, and positive refractive powers, respectively (see, for example, Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883).
The zoom lenses recited in Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883 respectively include sequentially from the object side, lens groups having negative, positive, negative, and positive refractive powers, respectively and are capable of 1.5× or greater zoom. The zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-276452, secures an angle of view on the order of 80 degrees at the wide angle edge, and is capable of 2.8× zoom. The zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-39531, secures an angle of view on the order of 105.8 degrees at the wide angle edge, and is capable of 1.95× to 2.36× zoom. The zoom lens recited in Japanese Patent No. 3391883 secures an angle of view on the order of 99 degrees at the wide angle edge, and is capable 1.85× zooming.
As with the zoom lenses recited in Japanese Patent Laid-Open Publication Nos. 2006-276452 and 2006-39531, and Japanese Patent No. 3391883, conventional wide angle zoom lenses, in general, have aspheric surfaces formed on multiple surfaces of the lenses configuring a first lens group, to achieve both correction of prominent aberration consequent to increasing the angle of view at the wide angle edge and a reduction of the size of the first lens group. In particular, a large-diameter, aspheric glass lens is employed for the lens disposed farthest on the object side of the zoom lens.
In the zoom lens recited in Japanese Patent Laid-Open Publication No. 2006-276452, an aspheric lens having a strong negative refractive power is disposed farthest on the object side of the zoom lens, and the zoom lens suppresses the effective diameter of the front frame and secures high imaging performance at wide angles. However, this zoom lens has a narrow angle of view on the order of 80 degrees at the wide angle edge and meeting demands for a wider angle of view is difficult. In addition, since the glass lens disposed farthest on the object side is aspheric, a problem of extremely high manufacturing cost arises.
The zoom lenses recited in Japanese Patent Laid-Open Publication No. 2006-39531 and Japanese Patent No. 3391883, both have an aspheric lens of a strong negative refractive power disposed farthest on the object side and are designed to achieve both an ultra wide angle and reduction of the front frame. Although these zoom lenses both have angles of view on the order of 100 degrees at the wide angle edge and are designed to achieve sufficiently wide angles, the first lens group is large and thus, are not suitable for imaging apparatuses of which compactness is strongly demanded of late. In addition, since the glass lens disposed farthest on the object side of the zoom lens is aspheric, a problem of extremely high manufacturing cost further arises.
SUMMARY OF THE INVENTION
It is an object of the present invention to at least solve the above problems in the conventional technologies.
A zoom lens according to one aspect of the present invention includes sequentially from an object side, a first lens section having a negative refractive power, and a second lens section formed by multiple lens groups and having an overall refractive power that is positive. The first lens section is configured by multiple lenses including sequentially from the object side, a first lens that is a spherical lens having a negative refractive power and a second lens that is an aspheric lens having a negative refractive power. The second lens section is configured to include at least 1 aspheric lens having a negative refractive power. Zooming from a wide angle edge to a telephoto edge is performed by varying an interval between the first lens section and the second lens section, or an interval between the first lens section and the second lens section and intervals between the lens groups configuring the second lens section. Focusing from infinity to a minimum object distance is performed by moving any 1 of the lens groups configuring the second lens section. A conditional expression (1) −8.0≦F12/D23≦−1.0 is satisfied, where, F12 is a focal length of the second lens, and with respect to the first lens section, D23 is a distance between an image-side surface of the second lens and an object-side surface of a lens disposed nearest an image plane, among the lenses configuring the first lens section.
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 diagram depicting one example of the shape of a second lens included in a first lens section;
FIG. 2 is a diagram depicting one example of the shape of an aspheric lens included in a second lens section and having a negative refractive power;
FIG. 3 is a cross sectional view (along the optical axis) of a zoom lens according to a first embodiment;
FIG. 4 is a diagram of various types of aberration occurring in the zoom lens according to the first embodiment;
FIG. 5 is a cross sectional view (along the optical axis) of the zoom lens according to a second embodiment;
FIG. 6 is a diagram of various types of aberration occurring in the zoom lens according to the second embodiment;
FIG. 7 is a cross sectional view (along the optical axis) of the zoom lens according to a third embodiment;
FIG. 8 is a diagram of various types of aberration occurring in the zoom lens according to the third embodiment;
FIG. 9 is a cross sectional view (along the optical axis) of the zoom lens according to a fourth embodiment;
FIG. 10 is a diagram of various types of aberration occurring in the zoom lens according to the fourth embodiment
FIG. 11 is a cross sectional view (along the optical axis) of the zoom lens according to a fifth embodiment;
FIG. 12 is a diagram of various types of aberration occurring in the zoom lens according to the fifth embodiment;
FIG. 13 is a cross sectional view (along the optical axis) of the zoom lens according to a sixth embodiment; and
FIG. 14 is a diagram of various types of aberration occurring in the zoom lens according to the sixth embodiment.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the accompanying drawings, preferred embodiments of a zoom lens according to the present invention are explained in detail below.
The zoom lens according to the present invention includes sequentially from the object side, a first lens section having a negative refractive power and a second lens section formed by multiple lens groups and having an overall refractive power that is positive. The first lens section is configured by multiple lenses, including sequentially from the object side, a first lens that is a spherical lens having a negative refractive power and a second lens that is an aspheric lens having a negative refractive power. The second lens section is configured to include at least 1 aspheric lens having a negative refractive power.
Thus, a low cost spherical lens is disposed farthest on the object side of the zoom lens, and by forming lenses of small diameters (not the large diameter lens disposed farthest on the object side) to be aspheric, lens processing becomes relatively simple, enabling the manufacturing cost of the optical system to be reduced.
The zoom lens according to the present invention zooms from a wide angle edge to a telephoto edge by varying the interval between the first lens section and the second lens section, or the interval between the first lens section and the second lens section and the intervals between the lens groups configuring the second lens section. Further, by moving any 1 of the lens groups configuring the second lens section, focusing from infinity to the minimum object distance is performed.
By zooming and focusing via such lens movements, aberration fluctuations occurring during zooming and focusing can be suppressed.
An object of the present invention is to provide an angle of view that exceeds 100 degrees, while realizing size reductions with respect to a diameter dimension of the optical system. Another object of the present invention is to reduce the manufacturing cost of the optical system. To achieve objects of the present invention, various conditions such as the following are set.
The zoom lens according to the present invention preferably satisfies the following conditional expression where, F12 is the focal length of the second lens included in the first lens section; and with respect to the first lens section, D33 is the distance between an image-side surface of the second lens (the surface facing toward the image plane) and an object-side surface of the lens disposed nearest the image plane, among the lenses of the first lens section (the surface facing toward the object).

−8.0≦F12/D23≦−1.0  (1)

Conditional expression (1) represents a condition for maintaining good imaging performance on top of achieving both size reductions of the optical system and wide angles. Satisfaction of conditional expression (1) enables an ultra wide angle exceeding 100 degrees to be achieved as well as size reductions with respect to a diameter dimension of the first lens section and maintenance of good imaging performance. Below the lower limit of conditional expression (1), the negative power of the second lens becomes too weak, and to achieve both the breadth of the angle of view at the wide angle edge and size reductions of the first lens section, the negative power of the first lens has to be increased. If the negative power of the first lens is increased, various types of aberration occurring at the first lens become prominent and therefore, an aspheric surface has to be formed on the first lens. As described, since the first lens has the largest diameter in the optical system, formation of an aspheric surface on the first lens bounces back to the issue of manufacturing cost and thus, has to be avoided. Meanwhile, above the upper limit of conditional expression (1), the negative power of the second lens becomes too strong and even if an aspheric surface is formed on the second lens, various types of aberration occurring at the second lens cannot be corrected; or within the first lens section, the interval between the second lens and the lens disposed opposing the image-side surface of the second lens becomes too short, the balance of power within the first lens section is lost and maintenance of good imaging performance may be jeopardized. Neither case is desirable.
If conditional expression (1) is within the following range, more favorable results can be expected.

−6.5≦F12/D23≦−1.4  (1)′

Satisfaction of conditional expression (1)′ enables further improvement in size reductions of the optical system, wide angle views, and imaging performance.

If conditional expression (1)′ is within the following range, yet more favorable results can be expected.

−5.0≦F12/D23≦−1.8  (1)′′

Satisfaction of conditional expression (1)′′ enables yet further improvement in size reductions of the optical system, wide angle views, and imaging performance.

The zoom lens according to the present invention preferably satisfies the following conditional expression, where Fw is the focal length of the optical system overall at the wide angle edge.

−20.0≦(Fw×F12)/(D23)2≦−1.0  (2)

Conditional expression (2) also represents a condition for maintaining good imaging performance on top of achieving both size reductions of the optical system and wide angle views. In addition to conditional expression (1), satisfaction of conditional expression (2), enables more favorable results to be expected. Below the lower limit of conditional expression (2), the negative power of the second lens becomes too weak, and to achieve both the breadth of the angle of view at the wide angle edge and size reductions of the first lens section, the negative power of the first lens has to be increased. If the negative power of the first lens is increased, various types of aberration occurring at the first lens become prominent and therefore, an aspheric surface has to be formed on the first lens. As described, since the first lens has the largest diameter in the optical system, formation of an aspheric surface on the first lens bounces back to the issue of manufacturing cost and thus, has to be avoided. Meanwhile, above the upper limit of conditional expression (2), the negative power of the second lens become too strong and even if an aspheric surface is formed on the second lens, various types of aberration occurring at the second lens cannot be corrected; or within the first lens section, the interval between the second lens and the lens disposed opposing the image-side surface of the second lens becomes too short, the balance of power within the first lens section is lost and maintenance of good imaging performance may become jeopardized. Neither case is desirable.
If conditional expression (2) is within the following range, more favorable results can be expected.

−18.0≦(Fw×F12)/(D23)2≦−1.5  (2)′

Satisfaction of conditional expression (2)′ enables further improvement in size reductions of the optical system, wide angle views, and imaging performance.

If conditional expression (2)′ is within the following range, yet more favorable results can be expected.

−15.0≦(Fw×F12)/(D23)2≦−2.5  (2)′′

Satisfaction of conditional expression (2)′′ enables yet further improvement in size reductions of the optical system, wide angle views, and imaging performance.

The zoom lens according to the present invention preferably satisfies the following conditional expression where, as depicted in FIG. 1, φ1 is the maximum effective diameter of the image-side surface of the second lens, and Δ1(Δ1=C1A−C1B) is the difference of the perimeter edge of aspheric surface C1A and a perimeter edge of paraxial spherical surface C1B, on a perimeter of an area demarcated by the maximum effective diameter φ of the image-side surface of the second lens.

2.5≦|100×Δ1/φ1|≦10.0  (3)

Conditional expression (3) represents a condition for realizing an optical system of low cost and having good imaging performance. Below the lower limit of conditional expression (3), favorable aberration correction becomes impossible and an aspheric surface has to be formed on the first lens, even if an aspheric surface is formed on the second lens included in the first lens section. As described, since the first lens has the largest diameter in the optical system, if an aspheric surface is formed on the first lens, processing becomes more difficult and manufacturing cost increases. Meanwhile, above the upper limit of conditional expression (3), peripheral image height aberration is over corrected by the aspheric surface formed on the second lens, inviting deterioration of imaging performance.
If conditional expression (3) is within the following range, more favorable results can be expected.

2.9≦|100×Δ1/φ1|≦9.0  (3)′

Satisfaction of conditional expression (3)′ enables realization of an optical system that is low cost and has good imaging performance.

If conditional expression (3)′ is within the following range, yet more favorable results can be expected.

3.3≦|100×Δ1/φ1|≦8.0  (3)′′

Satisfaction of conditional expression (3)′′ enables an optical system that is low cost and has yet better imaging performance to be realized.

The zoom lens according to the present invention preferably satisfies the conditional expression below, where, as depicted in FIG. 2, φ2 is the maximum effective diameter of the image-side surface of the negative aspheric lens included in the second lens section, and Δ2 (Δ2=C2A−C2B) is the difference of the perimeter edge of aspheric surface C2A and the perimeter edge of paraxial spherical surface C2B, on the perimeter of an area demarcated by the maximum effective diameter φ2 of the image-side surface of the negative aspheric lens included in the second lens section.

3.0≦100×|(Δ1/φ1)−(Δ2/φ2)|≦12.0  (4)

Conditional expression (4) represents a condition for realizing an optical system having excellent imaging performance. Below the lower limit of conditional expression (4), the aberration correction effect of the second lens of the first lens section and the aspheric lens included in the second lens section becomes too weak, inviting deterioration of imaging performance. Meanwhile, above the upper limit of conditional expression (4), aberration correction of the second lens of the first lens section and the aspheric lens included in the second lens section becomes excessive, causing imaging performance to deteriorate.
If conditional expression (4) is within the following range, more favorable results can be expected.

3.8≦100×|(Δ1/φ1)−(Δ2/φ2)|≦11.0  (4)′

Satisfaction of conditional expression (4)′ enables further improvement of the imaging performance of the optical system.

If conditional expression (4)′ is within the following range, yet more favorable results can be expected.

4.5≦100×|(Δ1/φ1)−(Δ2/φ2)≦10.0  (4)′′

Satisfaction of conditional expression (4)′′ enables yet further improvement of the imaging performance of the optical system.

In the zoom lens according to the present invention, the second lens section includes sequentially from the object side, a front group having a positive refractive power and a rear group having a positive refractive power, where the front group is moved in a direction along the optical axis to perform focusing from infinity to the minimum object distance. By such a configuration, aberration fluctuations consequent to focusing can be suppressed and a zoom lens having excellent imaging performance can be realized.
Further in the zoom lens according to the present invention, the second lens section may include sequentially from the object side, a front group having a positive refractive power, an intermediate group having a positive refractive power, and a rear group having a positive or a negative refractive power, where the intermediate group is moved in a direction along the optical axis to perform focusing from infinity to the minimum object distance. By this configuration as well, aberration fluctuations consequent to focusing can be suppressed and a zoom lens having excellent imaging performance can be realized.
Additionally in the zoom lens according to the present invention, the second lens section may include sequentially from the object side, a front group having a positive refractive power, an intermediate group having a positive refractive power, and a rear group having a positive or a negative refractive power, where the intermediate group is moved in a direction along the optical axis to perform focusing from infinity to the minimum object distance, and a lens included in the front group can be moved in a direction substantially orthogonal to the optical axis to correct camera-shake (image point vibration). By such a configuration, aberration fluctuations consequent to focusing can be suppressed and a zoom lens having excellent imaging performance can be realized. In addition, the zoom lens can be realized having a camera-shake correction function.
In the zoom lens according to the present invention, in particular, the first lens section includes sequentially from the object side, a spherical lens having a negative refractive power and a meniscal-shape where the concave surface faces toward the image plane, an aspheric lens having a negative refractive power and a concave surface facing toward the image plane, and a lens having a positive refractive power. By disposing farthest on the object side of the optical system, a low cost spherical lens having the largest diameter in the optical system, the manufacturing cost of the optical system can be reduced. In addition, both wide angle views and reductions in the size of the optical system can be achieved easily.
In the zoom lens according to the present invention, the negative aspheric lens included in the second lens section is disposed farthest on the image side of the second lens section, whereby various types of aberration that cannot be corrected by the first lens section can be easily corrected. In other words, prominent aberration consequent to wide angle views can be corrected well by the second lens section and a zoom lens having yet better imaging performance can be realized.
As described, the zoom lens according to the present invention enables the manufacturing cost of the optical system to be reduced by disposing a low cost spherical lens farthest on the object side and by forming lenses of small diameters (not the large diameter lens disposed farthest on the object side) to be aspheric. Furthermore, by additionally satisfying the conditional expressions above, a compact zoom lens can be realized that has excellent imaging performance and an angle of view that exceeds 100 degrees. In addition, as described, by suitably moving a lens to perform zooming, focusing, and camera-shake correction, a yet better zoom lens can be realized.
Hereinafter, embodiments of the zoom lens according to the present invention will be described in detail with reference to the accompanying drawings. Nonetheless, the invention is not limited to the following embodiments.
FIG. 3 is a cross sectional view (along the optical axis) of the zoom lens according to a first embodiment. The zoom lens includes sequentially from a side nearest a non-depicted object (object side), a first lens section G11 having a negative refractive power and a second lens section G12 having a positive refractive power.
The first lens section G11 includes sequentially from the object side, a negative lens L111 (first lens), a negative lens L112 (second lens), and a positive lens L113. The negative lens L111 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L112 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L112 are aspheric.
The second lens section G12 includes sequentially from the object side, a front group G12F having a positive refractive power and a rear group G12R having a positive refractive power. The front group G12F includes sequentially from the object side, an aperture stop ST prescribing a given aperture, a negative lens L121, and a positive lens L122. The negative lens L121 and the positive lens L122 are cemented. The rear group G12R includes sequentially from the object side, a positive lens L123, a negative lens L124, a positive lens L125, and a negative lens L126 (aspheric lens). Both surfaces of the positive lens L123 are aspheric. The negative lens L124 and the positive lens L125 are cemented. Both surfaces of the negative lens L126 are aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G11 along the optical axis, from the object side toward the image side, and by respectively moving the front group G12F and the rear group G12R along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the front group G12F along the optical axis, from the object side toward the image side.
Here, various values related to the zoom lens according to the first embodiment are given. Focal length of zoom lens overall=10.2992(Fw: wide angle edge) to 12.5000(intermediate position) to 17.4999(telephoto edge)

    F number=4.1(wide angle edge) to 4.1(intermediate position) to 4.1 (telephoto edge)
    Half-angle(ω)=54.98(wide angle edge) to 49.85(intermediate position) to 38.62(telephoto edge)
    Zoom ratio: 1.699














(Lens data)











r1 = 31.7816





d1 = 1.3000
nd1 = 1.77250
νd1 = 49.62



r2 = 12.8710



d2 = 5.9116










r3 = 39.9393 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 12.1565 (aspheric)












d4 = 8.5689





r5 = 28.4099



d5 = 3.5000
nd3 = 1.84666
νd3 = 23.78



r6 = 66.0507










d6 = D(6) (variable)




r7 = ∞(aperture stop)











d7 = 1.0000





r8 = 23.1071



d8 = 0.8000
nd4 = 1.90366
νd4 = 31.31



r9 = 12.4927



d9 = 3.5000
nd5 = 1.59551
νd5 = 39.22










r10 = −80.0040




d10 = D(10) (variable)



r11 = 15.4056 (aspheric)











d11 = 2.0000
nd6 = 1.61881
νd6 = 63.85










r12 = 42.9654 (aspheric)












d12 = 3.0989





r13 = 14.1040



d13 = 0.8000
nd7 = 1.80610
νd7 = 33.27



r14 = 8.6774



d14 = 6.3000
nd8 = 1.49700
νd8 = 81.61



r15 = −11.7706



d15 = 0.2000










r16 = −13.0933 (aspheric)












d16 = 1.2000
nd9 = 1.85135
νd9 = 40.10










r17 = 183.3464 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = 4.95634 × 10−5, B = −7.90310 × 10−7,



C = 4.63906 × 10−9, D = −1.24036 × 10−11,



E = 0



(Fourth plane)



K = 0,



A = −4.13305 × 10−6, B = −9.52818 × 10−7,



C = −5.62899 × 10−9, D = 8.48925 × 10−11,



E = −4.86537 × 10−13



(Eleventh plane)



K = 0,



A = 1.28687 × 10−5, B = 8.97529 × 10−7,



C = −3.30614 × 10−8, D = 9.08219 × 10−10,



E = 0



(Twelfth plane)



K = 0,



A = 9.65316 × 10−6, B = 1.86173 × 10−6,



C = −5.11469 × 10−8, D = 1.35414 × 10−9,



E = 0



(Sixteenth plane)



K = 0,



A = 9.58940 × 10−4, B = −2.78957 × 10−5,



C = 3.88208 × 10−7, D = −2.26870 × 10−9,



E = 0



(Seventeenth plane)



K = 0,



A = 1.11782 × 10−3, B = −2.38818 × 10−5,



C = 3.36860 × 10−7, D = −2.11204 × 10−9,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
15.0603
9.3234
2.0065


D(10)
7.4341
5.2857
3.6802









(Values related to conditional expression (1))

    F12(focal length of negative lens L112)=−20.943
    D23(interval between image-side surface of negative lens L112 and object-side surface of positive lens L113)=8.569

F12/D23=−2.444

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−2.9388

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L112)=19.40
    Δ1(difference of perimeter edge of aspheric surface C1A and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L112)=−1.036

|100×Δ1/φ1|=5.338

(Values related to conditional expression (4))

    φ2(maximum effective diameter of image-side surface of negative lens L126)=12.00
    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L126)=0.316

100×|(Δ1/φ1)−(Δ2/φ2)|=1=7.975



FIG. 4 is a diagram of various types of aberration occurring in the zoom lens according to the first embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
FIG. 5 is a cross sectional view (along the optical axis) of the zoom lens according to a second embodiment. The zoom lens includes sequentially from the object side, a first lens section G21 having a negative refractive power and a second lens section G22 having a positive refractive power.
The first lens section G21 includes sequentially from the object side, a negative lens L211 (first lens), a negative lens L212 (second lens), and a positive lens L213. The negative lens L211 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L212 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L212 are aspheric.
The second lens section G22 includes sequentially from the object side, a front group G22F having a positive refractive power, an intermediate group G22M having a positive refractive power, and a rear group G22R having a positive refractive power. The front group G22F includes sequentially from the object side, a negative lens L221, a positive lens L222, and the aperture stop ST prescribing a given aperture. The negative lens L221 and the positive lens L222 are cemented. The intermediate group G22M is configured by a positive lens L223. Both surfaces of the positive lens L223 are aspheric. The rear group G22R includes sequentially from the object side, a negative lens L224, a positive lens L225, and a negative lens L226 (aspheric lens). The negative lens L224 and the positive lens L225 are cemented. Both surfaces of the negative lens L226 are aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G21 along the optical axis, from the object side toward the image side, and by moving the second lens section G22 along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the intermediate group G22M along the optical axis, from the image side toward the object side.
Here, various values related to the zoom lens according to the second embodiment are given.

    Focal length of zoom lens overall=10.2993(Fw: wide angle edge) to 12.4992(intermediate position) to 17.4990(telephoto edge)
    F number=3.6(wide angle edge) to 3.8(intermediate position) to 4.0(telephoto edge)
    Half-angle(ω)=55.02(wide angle edge) to 49.05(intermediate position) to 38.88(telephoto edge)
    Zoom ratio: 1.699














(Lens data)











r1 = 28.0536





d1 = 1.5000
nd1 = 1.83481
νd1 = 42.72



r2 = 13.0579



d2 = 7.2984










r3 = 82.6038 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 12.9284 (aspheric)












d4 = 6.8839





r5 = 33.0842



d5 = 3.5000
nd3 = 1.84666
νd3 = 23.78



r6 = −34473.0453










d6 = D(6) (variable)












r7 = 16.4693





d7 = 0.8000
nd4 = 1.90366
νd4 = 31.31



r8 = 8.5000



d8 = 3.3000
nd5 = 1.59551
νd5 = 39.22



r9 = −125.4304



d9 = 1.2000










r10 = ∞ (aperture stop)












d10 = 5.9501












r11 = 41.9266 (aspheric)












d11 = 2.5000
nd6 = 1.59201
νd6 = 67.02










r12 = −65.9904 (aspheric)












d12 = 1.7000





r13 = 33.2313



d13 = 1.0000
nd7 = 1.69895
νd7 = 30.05



r14 = 11.8016



d14 = 5.3000
nd8 = 1.49700
νd8 = 81.61



r15 = −19.2021



d15 = 2.5709










r16 = −42.4918 (aspheric)












d16 = 1.0000
nd9 = 1.85135
νd9 = 40.10










r17 = 86.8262 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = 3.77248 × 10−5, B = −4.82207 × 10−7,



C = 2.52327 × 10−9, D = −5.53606 × 10−12,



E = 0



(Fourth plane)



K = 0,



A = −3.19307 × 10−5, B = −4.94567 × 10−7,



C = −5.29875 × 10−9, D = 6.20691 × 10−11,



E = −2.83735 × 10−13



(Eleventh plane)



K = 0,



A = −1.11816 × 10−5, B = −7.65302 × 10−7,



C = 2.32430 × 10−8, D = 8.59980 × 10−11,



E = 0



(Twelfth plane)



K = 0,



A = −4.64567 × 10−5, B = −5.92188 × 10−7,



C = 3.93860 × 10−9, D = 3.58575 × 10−10,



E = 0



(Sixteenth plane)



K = 0,



A = 1.89154 × 10−4, B = −4.46191 × 10−6,



C = 8.91938 × 10−9, D = 2.53860 × 10−10,



E = 0



(Seventeenth plane)



K = 0,



A = 3.16118 × 10−4, B = −4.72371 × 10−6,



C = 3.10546 × 10−8, D = 1.75862 × 10−11,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
18.2967
11.2482
1.8196









(Values related to conditional expression (1))

    F12(focal length of negative lens L212)=−18.147
    D23(interval between image-side surface of negative lens L212 and object-side surface of positive lens L213)=6.884

F12/D23=−2.636

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−3.944

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L212)=21.20
    Δ1(difference of perimeter edge of aspheric surface C1A and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L212)=−1.504

100×Δ1/φ1|=7.095

(Values related to conditional expression (4))

    φ2(maximum effective diameter of image-side surface of negative lens L226)=13.70
    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L226)=0.306

100×|(Δ1/φ1)−(Δ2/φ2)|=9.329



FIG. 6 is a diagram of various types of aberration occurring in the zoom lens according to the second embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
FIG. 7 is a cross sectional view (along the optical axis) of the zoom lens according to a third embodiment. The zoom lens includes sequentially from the object side, a first lens section G31 having a negative refractive power and a second lens section G32 having a positive refractive power.
The first lens section G31 includes sequentially from the object side, a negative lens L311 (first lens), a negative lens L312 (second lens), and a positive lens L313. The negative lens L311 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L312 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L312 are aspheric.
The second lens section G32 includes sequentially from the object side, a front group G32F having a positive refractive power, an intermediate group G32M having a positive refractive power, and a rear group G32R having a positive refractive power. The front group G32F includes sequentially from the object side, a negative lens L321, a positive lens L322, and the aperture stop ST prescribing a given aperture. The negative lens L321 and the positive lens L322 are cemented. The intermediate group G32M is configured by a positive lens L323. Both surfaces of the positive lens L323 are aspheric. The rear group G32R includes sequentially from the object side, a negative lens L324, a positive lens L325, and a negative lens L326 (aspheric lens). The negative lens L324 and the positive lens L325 are cemented. Both surfaces of the negative lens L326 are aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G31 along the optical axis, from the object side toward the image side, and by respectively moving the front group G32F, the intermediate group G32M and the rear group G32R, along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the intermediate group G32M along the optical axis, from the image side toward the object side.
Here, various values related to the zoom lens according to the third embodiment are given. Focal length of zoom lens overall=10.3039(Fw: wide angle edge) to 12.5049(intermediate position) to 17.5071(telephoto edge)

    F number=3.6(wide angle edge) to 3.8(intermediate position) to 4.0(telephoto edge)
    Half-angle(ω)=54.98(wide angle edge) to 49.02(intermediate position) to 38.94(telephoto edge)
    Zoom ratio: 1.699














(Lens data)











r1 = 29.1198





d1 = 1.5000
nd1 = 1.83481
νd1 = 42.72



r2 = 13.1003



d2 = 7.2001










r3 = 69.8822 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 12.9172 (aspheric)












d4 = 6.9761





r5 = 32.7186



d5 = 3.5000
nd3 = 1.84666
νd3 = 23.78










r6 = 1528.6256




d6 = D(6) (variable)











r7 = 16.1189





d7 = 0.8000
nd4 = 1.90366
νd4 = 31.31



r8 = 8.5000



d8 = 3.2000
nd5 = 1.59551
νd5 = 39.22










r9 = −212.0872












d9 = 1.2000












r10 = ∞ (aperture stop)




d10 = D(10) (variable)



r11 = 41.7024 (aspheric)











d11 = 2.5000
nd6 = 1.59201
νd6 = 67.02










r12 = −78.6776 (aspheric)




d12 = D(12) (variable)











r13 = 30.6698





d13 = 1.0000
nd7 = 1.72825
νd7 = 28.32



r14 = 12.3584



d14 = 4.6371
nd8 = 1.49700
νd8 = 81.61



r15 = −20.0455



d15 = 2.7972










r16 = −47.1564 (aspheric)












d16 = 1.0000
nd9 = 1.85135
νd9 = 40.10










r17 = 86.8262 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = 3.91172 × 10−5, B = −5.15238 × 10−7,



C = 2.73775 × 10−9, D = −5.93388 × 10−12,



E = 0



(Fourth plane)



K = 0,



A = −3.04683 × 10−5, B = −5.21452 × 10−7,



C = −5.43653 × 10−9, D = 6.59653 × 10−11,



E = −3.00854 × 10−13



(Eleventh plane)



K = 0,



A = −7.90160 × 10−6, B = −8.02610 × 10−7,



C = 1.34383 × 10−8, D = 2.16272 × 10−10,



E = 0



(Twelfth plane)



K = 0,



A = −3.41004 × 10−5, B = −8.24775 × 10−7,



C = −7.77380 × 10−10, D = 4.15702 × 10−10,



E = 0



(Sixteenth plane)



K = 0,



A = 2.86476 × 10−4, B = −7.25801 × 10−6,



C = 4.09409 × 10−8, D = 1.08437 × 10−10,



E = 0



(Seventeenth plane)



K = 0,



A = 4.08742 × 10−4, B = −7.44810 × 10−6,



C = 5.99352 × 10−8, D = −8.87625 × 10−11,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
18.6418
11.4735
1.8291


D(10)
5.5582
5.8068
6.1367


D(12)
2.2785
2.0299
1.7000









(Values related to conditional expression (1))

    F12(focal length of negative lens L312)=−18.795
    D23(interval between image-side surface of negative lens L312 and object-side surface of positive lens L313)=6.976

F12/D23=−2.694

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−3.980

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L312)=21.30
    Δ1(difference of perimeter edge of aspheric surface CIA and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L312)=−1.548

|100×Δ1/φ1|=7.268

(Values related to conditional expression (4))φ2(maximum effective diameter of image-side surface of negative lens L326)=13.70

    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L326)=0.297

100×|(Δ1/φ1)−(Δ2/φ2)|=9.434



FIG. 8 is a diagram of various types of aberration occurring in the zoom lens according to the third embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
FIG. 9 is a cross sectional view (along the optical axis) of the zoom lens according to a fourth embodiment. The zoom lens includes sequentially from the object side, a first lens section G41 having a negative refractive power and a second lens section G42 having a positive refractive power.
The first lens section G41 includes sequentially from the object side, a negative lens L411 (first lens), a negative lens L412 (second lens), and a positive lens L413. The negative lens L411 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L412 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L412 are aspheric.
The second lens section G42 includes sequentially from the object side, a front group G42F having a positive refractive power, an intermediate group G42M having a positive refractive power, and a rear group G42R having a negative refractive power. The front group G42F includes sequentially from the object side, a negative lens L421, a positive lens L422, and the aperture stop ST prescribing a given aperture. The negative lens L421 and the positive lens L422 are cemented. The intermediate group G42M is configured by a positive lens L423. Both surfaces of the positive lens L423 are aspheric. The rear group G42R includes sequentially from the object side, a negative lens L424, a positive lens L425, and a negative lens L426 (aspheric lens). The negative lens L424 and the positive lens L425 are cemented. Both surfaces of the negative lens L426 are aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G41 along the optical axis, from the object side toward the image side, and by respectively moving the front group G42F, the intermediate group G42M and the rear group G42R along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the intermediate group G42M along the optical axis, from the image side toward the object side.
Here, various values related to the zoom lens according to the fourth embodiment are given.

    Focal length of zoom lens overall=10.30(Fw: wide angle edge) to 12.50(intermediate position) to 17.50(telephoto edge)
    F number=4.10(wide angle edge) to 4.10(intermediate position) to 4.10(telephoto edge)
    Half-angle(ω)=55.05(wide angle edge) to 49.06(intermediate position) to 38.97(telephoto edge)
    Zoom ratio: 1.699














(Lens data)











r1 = 24.5641





d1 = 1.3000
nd1 = 1.83481
νd1 = 42.72



r2 = 12.4205



d2 = 6.9634










r3 = 80.9157 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 12.3254 (aspheric)












d4 = 8.3197





r5 = 35.9449



d5 = 3.0000
nd3 = 1.84666
νd3 = 23.78



r6 = 1537.5016










d6 = D(6) (variable)












r7 = 16.1541





d7 = 0.8000
nd4 = 1.90366
νd4 = 31.31



r8 = 8.5000



d8 = 3.3000
nd5 = 1.59551
νd5 = 39.22










r9 = −521.4563












d9 = 1.2000












r10 = ∞ (aperture stop)




d10 = D(10) (variable)



r11 = 39.7672 (aspheric)











d11 = 2.0000
nd6 = 1.59201
νd6 = 67.02










r12 = −45.3773 (aspheric)




d12 = D(12) (variable)











r13 = 22.5000





d13 = 1.0000
nd7 = 1.90366
νd7 = 31.31



r14 = 10.1715



d14 = 5.0000
nd8 = 1.49700
νd8 = 81.61



r15 = −19.3392



d15 = 1.9857










r16 = −45.3966 (aspheric)












d16 = 1.0000
nd9 = 1.85135
νd9 = 40.10










r17 = 69.5133 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = 3.28812 × 10−5, B = −4.35799 × 10−7,



C = 2.22432 × 10−9, D = −5.14760 × 10−12,



E = 0



(Fourth plane)



K = 0,



A = −4.86859 × 10−5, B = −4.29034 × 10−7,



C = −7.97657 × 10−9, D = 8.39364 × 10−11,



E = −4.07696 × 10−13



(Eleventh plane)



K = 0,



A = −5.92137 × 10−5, B = −1.33847 × 10−6,



C = 1.67253 × 10−8, D = 3.49851 × 10−12,



E = 0



(Twelfth plane)



K = 0,



A = −8.86050 × 10−5, B = −1.21824 × 10−6,



C = 6.52842 × 10−9, D = 9.67347 × 10−11,



E = 0



(Sixteenth plane)



K = 0,



A = 7.35180 × 10−5, B = −8.13193 × 10−7,



C = −3.62480 × 10−8, D = 5.12502 × 10−10,



E = 0



(Seventeenth plane)



K = 0,



A = 1.80453 × 10−4, B = −1.69902 × 10−6,



C = −6.00872 × 10−9, D = 1.79871 × 10−10,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
17.4071
10.7566
1.8290


D(10)
5.0135
5.1135
5.2135


D(12)
4.3324
4.2324
4.1324









(Values related to conditional expression (1))

    F12(focal length of negative lens L412)=−17.218
    D23(interval between image-side surface of negative lens L412 and object-side surface of positive lens L413)=8.320

F12/D23=−2.070

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−2.562

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L412)=19.80
    Δ1(difference of perimeter edge of aspheric surface C1A and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L412)=−1.274

|100×Δ1/φ1|=6.435

(Values related to conditional expression (4))

    φ2(maximum effective diameter of image-side surface of negative lens L426)=13.40
    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L426)=0.198

100×|(Δ1/φ1)−(Δ2/φ2)|=7.909



FIG. 10 is a diagram of various types of aberration occurring in the zoom lens according to the fourth embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
FIG. 11 is a cross sectional view (along the optical axis) of the zoom lens according to a fifth embodiment. The zoom lens includes sequentially from the object side, a first lens section G51 having a negative refractive power and a second lens section G52 having a positive refractive power.
The first lens section G51 includes sequentially from the object side, a negative lens L511 (first lens), a negative lens L512 (second lens), and a positive lens L513. The negative lens L511 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L512 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L512 are aspheric.
The second lens section G52 includes sequentially from the object side, a front group G52F having a positive refractive power, an intermediate group G52M having a positive refractive power, and a rear group G52R having a negative refractive power. The front group G52F includes sequentially from the object side, a positive lens L521, the aperture stop ST prescribing a given aperture, a negative lens L522, and a positive lens L523. The negative lens L522 and the positive lens L523 are cemented. The intermediate group G52M is configured by a positive lens L524. Both surfaces of the positive lens L524 as aspheric. The rear group G52R includes sequentially from the object side, a negative lens L525, a positive lens L526, and a negative lens L527 (aspheric lens). The negative lens L525 and the positive lens L526 are cemented. Both surfaces of the negative lens L527 are aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G51 along the optical axis, from the object side toward the image side, and by respectively moving the front group G52F, the intermediate group G52M and the rear group G52R along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the intermediate group G52M along the optical axis, from the image side toward the object side. Camera-shake correction is performed by moving the negative lens L521 included in the front group G52F, in a direction substantially orthogonal to the optical axis.
Here, various values related to the zoom lens according to the fifth embodiment are given.

    Focal length of zoom lens overall=10.30(Fw: wide angle edge) to 12.50(intermediate position) to 17.50(telephoto edge)
    F number=3.6(wide angle edge) to 3.8(intermediate position) to 4.0(telephoto edge)
    Half-angle(ω)=54.98(wide angle edge) to 49.02(intermediate position) to 38.82(telephoto edge)
    Zoom ratio: 1.699














(Lens data)











r1 = 27.3115





d1 = 1.5000
nd1 = 1.83481
νd1 = 42.72



r2 = 12.9354



d2 = 7.3177










r3 = 143.7387 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 12.2925 (aspheric)












d4 = 4.9164





r5 = 26.5844



d5 = 3.5000
nd3 = 1.84666
νd3 = 23.78



r6 = −871.0441










d6 = D(6) (variable)












r7 = −18.2092





d7 = 0.8000
nd4 = 1.84666
νd4 = 23.78



r8 = −26.1747



d8 = 1.5000










r9 = ∞ (aperture stop)












d9 = 1.0000





r10 = 20.6662



d10 = 0.8000
nd5 = 1.90366
νd5 = 31.31



r11 = 10.1275



d11 = 3.4000
nd6 = 1.58144
νd6 = 40.89



r12 = −29.0999










d12 = D(12) (variable)




r13 = 30.7643 (aspheric)











d11 = 2.4000
nd7 = 1.58313
νd7 = 59.46










r14 = −79.7492 (aspheric)




d14 = D(14) (variable)











r15 = 18.9650





d15 = 1.0000
nd8 = 1.91082
νd8 = 35.25



r16 = 9.6254



d16 = 6.5000
nd9 = 1.49700
νd9 = 81.61



r17 = −18.2359



d17 = 0.7205










r18 = −43.0714 (aspheric)












d18 = 1.0000
nd10 = 1.85135
νd10 = 40.10










r19 = 45.0000 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = 7.96481 × 10−5, B = −9.84278 × 10−7,



C = 5.69053 × 10−9, D = −1.36247 × 10−11,



E = 0



(Fourth plane)



K = 0,



A = 4.87539 × 10−6, B = −8.75480 × 10−7,



C = −9.15535 × 10−9, D = 1.33681 × 10−10,



E = −6.46855 × 10−13



(Thirteenth plane)



K = 0,



A = −2.74416 × 10−5, B = −2.98083 × 10−7,



C = 2.49494 × 10−8, D = −6.63205 × 10−11,



E = 0



(Fourteenth plane)



K = 0,



A = −4.48753 × 10−5, B = −3.02221 × 10−7,



C = 1.76339 × 10−8, D = 2.79950 × 10−11,



E = 0



(Eighteenth plane)



K = 0,



A = 2.24011 × 10−4, B = − 5.27123 × 10−6,



C = 6.49618 × 10−8, D = −3.99383 × 10−10,



E = 0



(Nineteenth plane)



K = 0,



A = 3.22992 × 10−4, B = −5.30917 × 10−6,



C = 6.69786 × 10−8, D = −4.62773 × 10−10,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
18.4950
11.5917
2.3290


D(12)
4.8027
4.8502
4.6046


D(14)
6.1478
6.1003
6.3459









(Values related to conditional expression (1))

    F12(focal length of negative lens L512)=−15.856
    D23(interval between image-side surface of negative lens L512 and object-side surface of positive lens L513)=4.916

F12/D23=−3.225

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−6.757

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L512)=20.65
    Δ1(difference of perimeter edge of aspheric surface C1A and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L512)=−1.557

|100×Δ1/φ1|=7.538

(Values related to conditional expression (4))

    φ2(maximum effective diameter of image-side surface of negative lens L527)=14.20
    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L527)=0.239

|100×|(Δ1/φ1)−(Δ2/φ2)|==9.222



FIG. 12 is a diagram of various types of aberration occurring in the zoom lens according to the fifth embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
FIG. 13 is a cross sectional view (along the optical axis) of the zoom lens according to a sixth embodiment. The zoom lens includes sequentially from the object side, a first lens section G61 having a negative refractive power and a second lens section G62 having a positive refractive power.
The first lens section G61 includes sequentially from the object side, a negative lens L611 (first lens), a negative lens L612 (second lens), and a positive lens L613. The negative lens L611 is configured by a spherical lens having a meniscal-shape where the concave surface faces toward the image plane. The negative lens L612 is configured by an aspheric lens having a concave surface facing toward the image plane. Both surfaces of the negative lens L612 are aspheric.
The second lens section G62 includes sequentially from the object side, a front group G62F having a positive refractive power, an intermediate group G62M having a positive refractive power, and a rear group G62R having a negative refractive power. The front group G62F includes sequentially from the object side, a positive lens L621, the aperture stop ST prescribing a given aperture, a negative lens L622, and a positive lens L623. The negative lens L622 and the positive lens L623 are cemented. The intermediate group G62M is configured by a positive lens L624. Both surfaces of the positive lens 624 are aspheric. The rear group G62R includes sequentially from the object side, a negative lens L625, a positive lens L626, and a negative lens L627 (aspheric lens). The negative lens L625 and the positive lens L626 are cemented. The surface of the negative lens L627, facing toward the image plane is aspheric.
In the zoom lens, zooming from the wide angle edge to the telephoto edge is performed by moving the first lens section G61 along the optical axis, from the object side toward the image side, and by respectively moving the front group G62F, the intermediate group G62M and the rear group G62R along the optical axis, from the image side toward the object side. Focusing from infinity to the minimum object distance is performed by moving the intermediate group G62M along the optical axis, from the image side toward the object side.
Here, various values related to the zoom lens according to the sixth embodiment are given.

    Focal length of zoom lens overall=11.30(Fw: wide angle edge) to 12.50(intermediate position) to 17.50(telephoto edge)
    F number-4.1(wide angle edge) to 4.1(intermediate position) to 4.1(telephoto edge)
    Half-angle(ω)=52.42(wide angle edge) to 49.17(intermediate position) to 38.65(telephoto edge)
    Zoom ratio: 1.549














(Lens data)











r1 = 20.4987





d1 = 1.3000
nd1 = 1.83481
νd1 = 42.72



r2 = 9.4632



d2 = 5.4014










r3 = 78.1683 (aspheric)












d3 = 1.2000
nd2 = 1.85135
νd2 = 40.10










r4 = 11.5955 (aspheric)












d4 = 3.7376





r5 = 23.4921



d6 = 3.0000
nd3 = 1.84666
νd3 = 23.78



r6 = −6053.3755










d6 = D(6) (variable)












r7 = −24.2364





d7 = 0.8000
nd4 = 1.84666
νd4 = 23.78










r8 = −40.8523












d8 = 1.5000












r9 = ∞ (aperture stop)












d9 = 1.0000





r10 = 17.4651



d10 = 0.8000
nd5 = 1.90366
νd5 = 31.31



r11 = 8.8500



d11 = 3.4000
nd6 = 1.58144
νd6 = 40.89



r12 = −26.9518










d12 = D(12) (variable)




r13 = 26.6015 (aspheric)











d11 = 2.4000
nd7 = 1.58313
νd7 = 59.46










r14 = −59.6858 (aspheric)




d14 = D(14) (variable)











r15 = 25.9484





d15 = 1.0000
nd8 = 1.91082
νd8 = 35.25



r16 = 10.1953



d16 = 6.5000
nd9 = 1.49700
νd9 = 81.61



r17 = −17.9337



d17 = 1.3655



r18 = −52.7390



d18 = 1.0000
nd10 = 1.85135
νd10 = 40.10










r19 = 47.3932 (aspheric)













Constants of the cone (K) and aspheric coefficients (A, B, C, D, E)



(Third plane)



K = 0,



A = −1.11149 × 10−5, B = 2.59248 × 10−7,



C = −l,44219 × 10−9, D = −1.48549 × 10−11,



E = 0



(Fourth plane)



K = 0,



A = −1.21186 × 10−4, B = −2.83516 × 10−7,



C = 3.15813 × 10−9, D = −2.13216 × 10−10,



E = 8.18843 × 10−13



(Thirteenth plane)



K = 0,



A = −6.64662 × 10−5, B = −1.18357 × 10−6,



C = 3.81781 × 10−8, D = 1.73852 × 10−10,



E = 0



(Fourteenth plane)



K = 0,



A = −9.95515 × 10−5, B = −7.43846 × 10−7,



C = 1.21368 × 10−8, D = 4.63810 × 10−10,



E = 0



(Nineteenth plane)



K = 0,



A = 1.15065 × 10−4, B = −2.14857 × 10−7,



C = 1.10024 × 10−8, D = −1.21146 × 10−10,



E = 0











(Zoom data)











Wide angle edge
Intermediate position
Telephoto edge





D(6)
11.8911
9.2879
2.1599


D(12)
4.2004
4.2579
3.9230


D(14)
4.5762
4.5187
4.8536









(Values related to conditional expression (1))

    F12(focal length of negative lens L612)=−16.126
    D23(interval between image-side surface of negative lens L612 and object-side surface of positive lens L613)=3.738

F12/D23=−4.315

(Values related to conditional expression (2))

(Fw×F12)/(D23)2=−13.044

(Values related to conditional expression (3))

    φ1(maximum effective diameter of image-side surface of negative lens L612)=15.40
    Δ1(difference of perimeter edge of aspheric surface C1A and perimeter edge of paraxial spherical surface C1B (Δ1=C1A−C1B), on perimeter of area demarcated by maximum effective diameter φ of image-side surface of negative lens L612)=−0.553

|100×Δ1/φ1|=3.591

(Values related to conditional expression (4))

    φ2(maximum effective diameter of image-side surface of negative lens L627)=13.90
    Δ2(difference of perimeter edge of aspheric surface C2A and perimeter edge of paraxial spherical surface C2B (Δ2=C2A−C2B), on perimeter of area demarcated by maximum effective diameter φ2 of image-side surface of negative lens L627)=0.272

|100×|(Δ1/φ1)−(Δ2/φ2)|=5.550



FIG. 14 is a diagram of various types of aberration occurring in the zoom lens according to the sixth embodiment. In the diagram, g indicates the wavelength aberration corresponding to g-line (λ=435.83 nm), d indicates the wavelength aberration corresponding to d-line (λ=587.56 nm), and C indicates the wavelength aberration corresponding to C-line (λ=656.28 nm). S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.
Among the values for each of the embodiments, r1, r2, . . . indicate radii of curvature for each lens, diaphragm surface, etc.; d1, d2, . . . indicate the thickness of the lenses, diaphragm, etc. or the distance between surfaces thereof; nd1, nd2, . . . indicate the refraction index of each lens with respect to the d-line (λ=587.56 nm); and νd1, νd2, . . . indicate the Abbe number with respect to the d-line (λ=587.56 nm) of each lens. Lengths are indicated in units of [mm] and angles are indicated in [degrees].
Each aspheric surface shape above is expressed by equation [1], where z is the depth of the aspheric surface; y is a height in a direction orthogonal to the optical axis; and the travel direction of light is positive.




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




Where, R is paraxial radius of curvature; K is the constant of the cone; A, B, C, D, and E are the fourth, sixth, eighth, tenth, and twelfth order aspheric coefficients, respectively.
As described, the zoom lens according to each of the embodiments above enables the manufacturing cost of the optical system to be reduced by disposing a low cost spherical lens farthest on the object side and by forming lenses of small diameters (not the large diameter lens disposed farthest on the object side) to be aspheric. Furthermore, by additionally satisfying the conditional expressions above, a compact zoom lens can be realized that has excellent imaging performance and an angle of view that exceeds 100 degrees.
As described, the zoom lens according to the present invention is suitable for compact imaging devices and in particular, is ideal for single-lens reflex cameras of which wide angles of view are demanded.
The present invention enables the manufacturing cost of the optical system to be reduced by disposing a low cost spherical lens farthest on the object side and by forming lenses of small diameters (not the large diameter lens disposed farthest on the object side) to be aspheric. In addition, although an ultra wide angle exceeding 100 degrees is achieved, both maintenance of imaging performance and size reductions with respect to a diameter dimension of the first lens section can also be achieved.
Further, the present invention enables reductions in the weight of the focusing group since focusing can be performed by moving the front group alone.
The present invention also enables reductions in the weight of the focusing group since focusing can be performed by moving the intermediate group alone.
The present invention enables the zoom lens to be realized further having a camera-shake correction function.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.
The present document incorporates by reference the entire contents of Japanese priority document, 2011-183026 filed in Japan on Aug. 24, 2011.

## Claims

1. A zoom lens comprising sequentially from an object side, a first lens section having a negative refractive power, and a second lens section formed by multiple lens groups and having an overall refractive power that is positive, wherein
the first lens section comprises multiple lenses including sequentially from the object side, a first lens that is a spherical lens having a negative refractive power and a second lens that is an aspheric lens having a negative refractive power,
the second lens section is configured to include at least one aspheric lens having a negative refractive power,
zooming from a wide angle edge to a telephoto edge is performed by varying an interval between the first lens section and the second lens section, or an interval between the first lens section and the second lens section and intervals between the lens groups comprising the second lens section,
focusing from infinity to a minimum object distance is performed by moving any one of the lens groups comprising the second lens section,
a conditional expression (1) −8.0≦F12/D23≦−1.0 is satisfied, where, F12 is a focal length of the second lens, and with respect to the first lens section, D23 is a distance between an image-side surface of the second lens and an object-side surface of a lens disposed nearest an image plane, among the lenses comprising the first lens section, and
a conditional expression (2) 2.5≦|100×Δ1/φ1 |≦10.0 is satisfied, where, φ1 is a maximum effective diameter of an image-side surface of the second lens, and Δ1 is a difference of a perimeter edge thickness of an aspheric surface and a perimeter edge thickness of a paraxial spherical surface, on a perimeter of an area demarcated by the maximum effective diameter φ1 of the image-side surface of the second lens.

2. The zoom lens according to claim 1, wherein
a conditional expression (3) −20.0≦(Fw×F12)/(D23)2≦−1.0 is satisfied, where, Fw is focal length of the optical system overall at the wide angle edge.

3. The zoom lens according to claim 1, wherein a conditional expression (4) 3.0≦100×|(Δ1/φ1)−(Δ2/φ2)|≦12.0 is satisfied, where, φ2 is a maximum effective diameter of an image-side surface of the aspheric lens included in the second lens section and having a negative refractive power, and Δ2 is a difference of a perimeter edge thickness of an aspheric surface and a perimeter edge thickness of a paraxial spherical surface, on a perimeter of an area demarcated by the maximum effective diameter φ2 of the image-side surface of the aspheric lens included in the second lens section and having a negative refractive power.

4. The zoom lens according to claim 1, wherein
the second lens section includes sequentially from the object side, a front group having a positive refractive power and a rear group having a positive refractive power, and
the focusing from infinity to the minimum object distance is performed by moving the front group in a direction along an optical axis.

5. The zoom lens according to claim 1, wherein
the second lens section includes sequentially from the object side, a front group having a positive refractive power, an intermediate group having a positive refractive power, and a rear group having a positive or a negative refractive power, and
the focusing from infinity to the minimum object distance is performed by moving the intermediate group in a direction along an optical axis.

6. The zoom lens according to claim 1, wherein
the second lens section includes sequentially from the object side, a front group having a positive refractive power, an intermediate group having a positive refractive power, and a rear group having a positive or a negative refractive power,
the focusing from infinity to the minimum object distance is performed by moving the intermediate group in a direction along an optical axis, and
camera-shake correction is performed by moving a lens included in the front group, in a direction substantially orthogonal to the optical axis.

7. The zoom lens according to claim 1, wherein
the first lens section includes sequentially from the object side, a spherical lens having a negative refractive power and a meniscal-shape where a concave surface faces toward an image plane, an aspheric lens having a negative refractive power and a concave surface facing toward the image plane, and a lens having a positive refractive power.

8. The zoom lens according to claim 1, wherein
the aspheric lens included in the second lens section and having a negative refractive power is disposed nearest the image plane among the lenses of the second lens section.