JP5854978B2 - Zoom lens - Google Patents

Description

  The present invention relates to a zoom lens suitable for a small image pickup apparatus equipped with a high pixel image sensor, such as a video camera, a digital still camera, a video conference system camera, and a surveillance camera.

  As a conventional imaging lens used in a camera equipped with an image sensor, a zoom lens having four lens groups having positive, negative, positive, and positive refractive power in order from the object side is well known. (For example, refer to Patent Documents 1 to 3.)

Japanese Patent Laid-Open No. 2002-244045 JP 2004-252204 A JP 2011-145565 A

  In recent years, as the number of pixels of image sensors has increased, imaging cameras such as video cameras and digital still cameras can also record bright zoom lenses with high zoom ratio and high resolution so that clear images can be recorded. Needs are growing. A wide-angle zoom lens is also required from the viewpoint of moving image shooting. In addition, since there is a strong demand for downsizing of the imaging apparatus, it is preferable that the zoom lens be simple and small.

  Conventionally, in order to realize a zoom lens with a high zoom ratio, for example, measures such as increasing the amount of movement of the zoom lens group or increasing the number of zoom lens groups have been taken. However, when these methods are employed, there are disadvantages such as an increase in the total length of the optical system and an increase in manufacturing costs.

  For example, although the zoom lens described in Patent Document 1 has a zoom ratio of about 10 times, the total length of the optical system is long and cannot be said to be small. The zoom lens described in Patent Document 2 is a dark lens having a short optical system total length but a small zoom ratio of 3 times or less and a large F value. In addition, the zoom lenses described in Patent Documents 1 and 2 have a small angle of view at the wide-angle end, and are not satisfactory for moving image shooting. Furthermore, although the zoom lens described in Patent Document 3 has a zoom ratio of about 10 to 20 times, it is a long lens with a long overall optical system and a dark F value of 1.85.

  The present invention provides a high-power zoom lens having a resolution that can be applied to a high-pixel image sensor while achieving downsizing, wide-angle, and large aperture ratio in order to solve the above-described problems caused by the conventional technology. For the purpose.

In order to solve the above-described problems and achieve the object, a zoom lens according to the present invention includes a first lens group having a positive refractive power and a second lens having a negative refractive power, which are sequentially arranged from the object side. A group, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power , wherein the third lens group is arranged in order from the object side. A front group consisting of a positive lens and a rear group consisting of one or more negative lenses, and in zooming from the wide-angle end to the telephoto end, the second lens group, the rear group of the third lens group , The fourth lens group moves along the optical axis and satisfies the following conditional expression.
(1) 70 ≦ 2ω _w ≦ 80
_{(2) 5.6 ≦ L 0 /} (f t / f w) ≦ 6.8
(3) 1.50 ≦ F _w ≦ 1.65
(4) 0.09 ≦ D ₃ / f ₃ ≦ 0.20
Where ω _w is the half angle of view of the optical system at the wide angle end, L ₀ is the total length of the optical system, _ft is the focal length of the entire optical system at the telephoto end, and f _w is the focal length of the entire optical system at the wide angle end. F _w is the F value of the optical system at the wide angle end, D ₃ is the moving distance during zooming rear group of the third lens group, f ₃ denotes a focal length of the third lens group.

According to the present invention, it is possible to provide a high-power zoom lens having a resolving power that can be reduced in size, widened in angle, and large in aperture ratio and compatible with a high pixel image sensor.

Furthermore, the zoom lens according to the present invention is the zoom lens according to the present invention, wherein the second lens group is a front group composed of two or more negative lenses arranged in order from the object side, and a rear group composed of one or more positive lenses. It is composed of a group, a positive lens located closest to the image side of the second lens group satisfies the conditional expressions shown below.
(5) 1.9 ≦ N ₁ ≦ 2.1
N ₁ represents the refractive index with respect to d-line of the material of the positive lens located closest to the image plane of the second lens group.

  ADVANTAGE OF THE INVENTION According to this invention, the zoom lens provided with the more outstanding resolving power can be provided.

  According to the present invention, there is an effect that it is possible to provide a zoom lens with a high magnification having a resolving power that can be applied to a high pixel image sensor while achieving a reduction in size, a wide angle, and a large aperture ratio. Specifically, it is possible to provide a small zoom lens having a short overall optical system length while enabling high zooming of about 10 to 12 times. In addition, it is possible to provide a bright zoom lens having a resolving power capable of corresponding to a high pixel image sensor by sufficiently correcting various aberrations from the wide-angle end to the telephoto end while being wide-angle.

FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the zoom lens according to Example 1; FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to Example 1 with respect to the d line. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a zoom lens according to Example 2; FIG. 9 is a diagram illustrating various aberrations of the zoom lens according to Example 2 with respect to the d line.

  Hereinafter, preferred embodiments of the zoom lens according to the present invention will be described in detail.

The zoom lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are arranged in order from the object side. When, a fourth lens group having positive refractive power and a. The third lens group includes a front group composed of one or more positive lenses and a rear group composed of one or more negative lenses arranged in order from the object side. Then, zooming from the wide-angle end to the telephoto end is performed by moving the second lens group along the optical axis. Further, by moving the rear group of the third lens group and the fourth lens group along the optical axis, the fluctuation of the image plane position due to zooming is corrected. The rear group of the first lens group and the third lens group is always fixed. In zooming from the wide-angle end to the telephoto end, by moving the rear group of the third lens group along the optical axis, various aberrations, particularly spherical aberration, in the entire zooming range can be corrected well.

  An object of the present invention is to provide a high-power zoom lens having a high resolution and a small size, wide angle, and large aperture ratio, which is most suitable for a small-sized imaging device equipped with a high-pixel image sensor. Therefore, in order to achieve this purpose, various conditions as shown below are set.

First, in the zoom lens according to the present invention, in the above configuration, the half angle of view of the optical system at the wide angle end is ω _w , the total length of the optical system is L ₀ , the focal length of the entire optical system at the telephoto end is f _t , and the wide angle end Is the focal length of the entire optical system at f _w , the F value of the optical system at the wide-angle end is F _w , the moving distance of the rear group of the third lens unit during zooming is D ₃ , and the focal length of the third lens unit is When f ₃ is satisfied, it is preferable that the following conditional expression is satisfied.
(1) 70 ≦ 2ω _w ≦ 80
_{(2) 5.6 ≦ L 0 /} (f t / f w) ≦ 6.8
(3) 1.50 ≦ F _w ≦ 1.65
(4) 0.09 ≦ D ₃ / f ₃ ≦ 0.20

  Conditional expression (1) is an expression indicating a condition for securing a field angle suitable for an imaging apparatus capable of moving image shooting. If the lower limit value of conditional expression (1) is not reached, the angle of view at the time of moving image shooting will be insufficient. On the other hand, if the upper limit value is exceeded in conditional expression (1), it becomes difficult to correct distortion.

  Conditional expression (2) is an expression showing conditions for achieving both high resolution and miniaturization of the optical system. If the lower limit value of conditional expression (2) is not reached, correction of various aberrations will be insufficient. In particular, a reduction in resolving power is caused by an increase in spherical aberration at the telephoto end. On the other hand, if the upper limit value is exceeded in conditional expression (2), the optical total length is extended, and it becomes difficult to achieve a sufficient size reduction of the optical system.

  Conditional expression (3) is an expression for achieving both good manufacturability of the optical system and ensuring image brightness. If the lower limit value of conditional expression (3) is not reached, high precision is required for the optical components constituting the optical system and the mechanism for holding it, making it difficult to manufacture the optical system. As a result, the manufacturing cost of the optical system and its holding mechanism increases. On the other hand, if the upper limit value in conditional expression (3) is exceeded, the image obtained by the optical system becomes dark and high resolution cannot be obtained.

  Conditional expression (4) is an expression showing conditions for ensuring a high zoom ratio while maintaining the miniaturization and high resolution of the optical system. If the lower limit value of conditional expression (4) is not reached, correction of various aberrations becomes difficult. In particular, correction of spherical aberration is insufficient. On the other hand, if the upper limit value in conditional expression (4) is exceeded, the total optical length is extended, and the optical system cannot be downsized.

Further, in the zoom lens according to the present invention, the second lens group, disposed in order from the object side, a front group formed of 2 or more negative lenses, and a rear group composed of one or more positive lenses, from Good. Then, the refractive index at the d-line of the positive lens of the material closest to the image plane side of the second lens group when the N _1, it is preferable to satisfy the following condition.
(5) 1.9 ≦ N ₁ ≦ 2.1

  Conditional expression (5) is an expression showing conditions for obtaining a higher resolving power in a high-magnification zoom lens in which miniaturization, wide angle, and large aperture ratio are achieved. If the lower limit of conditional expression (5) is not reached, it will be difficult to correct spherical aberration at the wide angle end. In addition, it becomes difficult to correct curvature of field and longitudinal chromatic aberration at the telephoto end. On the other hand, if the upper limit value in conditional expression (5) is exceeded, it will be difficult to correct spherical aberration at the telephoto end.

  As described above, the zoom lens according to the present invention has the above-described configuration, thereby achieving a reduction in size, a wide angle, a large aperture ratio, and a high magnification, and a resolving power compatible with a high pixel image sensor. Can be provided. In particular, by satisfying the above conditional expressions, it is possible to achieve both a reduction in size, a wide angle, a large aperture ratio, and a high magnification while maintaining a high resolving power.

  Embodiments of the zoom lens according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by the following examples.

FIG. 1 is a cross-sectional view along the optical axis showing the configuration of the zoom lens according to the first embodiment. The zoom lens includes a first lens group G ₁₁ having a positive refractive power, a second lens group G ₁₂ having a negative refractive power, and a third lens group having a positive refractive power in order from an object side (not shown). G ₁₃ and a fourth lens group G ₁₄ having a positive refractive power are arranged.

A second lens group G ₁₂ between the third lens group G _13, an aperture stop S is disposed to define a predetermined diameter. Further, an infrared cut filter G is disposed between the fourth lens group G ₁₄ and the image plane I. In addition, on the image plane I, the light receiving surface of the image sensor is arranged.

The first lens group G ₁₁ includes, in order from the object side, a negative meniscus lens L ₁₁₁ with a concave surface facing the image side, a positive bilens lens L _112, and a positive meniscus lens L with a convex surface facing the object side. ₁₁₃ are arranged. The negative meniscus lens L ₁₁₁ and the positive lens L ₁₁₂ are cemented.

The second lens group G ₁₂ includes, formed in order from the object side, a front group G _12F having negative refractive power, and the group G _12R after having positive refractive power, is the arrangement. The front group G _12F includes, in order from the object side, a negative meniscus lens L ₁₂₁ having a concave surface directed toward the image side and a biconcave negative lens L ₁₂₂ . The rear group G _12R includes a positive meniscus lens L ₁₂₃ having a convex surface directed toward the object side.

The third lens group G ₁₃ includes, in order from the object side, a front group G _13F having a positive refractive power and a rear group G _13R having a negative refractive power. The front group G _13F is configured by a biconvex positive lens L ₁₃₁ . Aspherical surfaces are formed on both surfaces of the positive lens _L131 . The rear group G _13R includes a negative meniscus lens L ₁₃₂ having a concave surface facing the image side.

The fourth lens group G ₁₄ is constituted, in order from the object side, a negative meniscus lens L ₁₄₁ with a concave surface facing the image side, a positive meniscus lens L ₁₄₂ with a convex surface facing the object side, is the arrangement . The negative meniscus lens L ₁₄₁ and the positive meniscus lens L ₁₄₂ are cemented. An aspheric surface is formed on the image side surface of the positive meniscus lens L ₁₄₂ .

In this zoom lens, the first lens group G ₁₁ , the aperture stop S, and the front group G _{13F of} the third lens group G ₁₃ are always fixed. Then, from the wide-angle end (WIDE) during zooming to the telephoto end (TELE), the second lens group G ₁₂ is the image side from the object side along the optical axis so as to widen the distance between the first lens group G ₁₁ Moving. At this time, the rear group G _{13R of} the third lens group G ₁₃ moves on the optical axis so as to increase the distance from the front group G _13F, and the fourth lens group G ₁₄ moves to the rear group of the third lens group G ₁₃ . By moving on the optical axis so as to change the distance from G _13R , the movement of the image plane I accompanying zooming is corrected and the position is held constant.

  Various numerical data related to the zoom lens according to Example 1 will be described below.

Focal length of the zoom lens system = 4.600 (f _w: the wide-angle end) ～15.800 (intermediate region) ~54.290 (f _t: telephoto end)
F value = 1.615 (F _w : wide angle end)-1.875 (middle range)-1.885 (telephoto end)
Half angle of view (ω) = 37.0385 (ω _w : wide angle end) to 11.0915 (middle range) to 3.228 (telephoto end)

(Lens data)
r ₁ = 54.851
d ₁ = 1.000 nd ₁ = 1.92286 νd ₁ = 18.9
r ₂ = 34.544
d ₂ = 5.669 nd ₂ = 1.592824 νd ₂ = 68.63
r ₃ = -218.342
d ₃ = 0.200
r ₄ = 27.149
d ₄ = 3.269 nd ₃ = 1.72916 νd ₃ = 53.94
r ₅ = 65.792
d ₅ = D (5) (variable)
r ₆ = 67.001
d ₆ = 0.600 nd ₄ = 1.883 νd ₄ = 40.8
r ₇ = 9.291
d ₇ = 2.889
r ₈ = -15.041
d ₈ = 0.600 nd ₅ = 1.72916 νd ₅ = 53.94
r ₉ = 11.680
d ₉ = 0.231
r ₁₀ = 13.095
d ₁₀ = 1.830 nd ₆ = 2.00272 νd ₆ = 19.32
r ₁₁ = 62.030
d ₁₁ = D (11) (variable)
r ₁₂ = ∞ (aperture stop)
d ₁₂ = 0.830
r ₁₃ = 10.249 (aspherical surface)
d ₁₃ = 2.786 nd ₇ = 1.618806 νd ₇ = 63.85
r ₁₄ = -35.378 (aspherical surface)
d ₁₄ = D (14) (variable)
r ₁₅ = 63.400
d ₁₅ = 0.600 nd ₈ = 1.805181 νd ₈ = 25.46
r ₁₆ = 19.523
d ₁₆ = D (16) (variable)
r ₁₇ = 8.357
d ₁₇ = 2.260 nd ₉ = 1.805181 νd ₉ = 25.46
r ₁₈ = 4.568
d ₁₈ = 5.064 nd ₁₀ = 1.58313 νd ₁₀ = 59.46
r ₁₉ = 218.593 (aspherical surface)
d ₁₉ = D (19) (variable)
r ₂₀ = ∞
d ₂₀ = 2.000 nd ₁₁ = 1.516798 νd ₁₁ = 64.2
r ₂₁ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D)
(13th page)
k = -0.29226371,
A = -0.000119404, B = 2.1180 × 10 ^-6 ,
C = -4.6046 × 10 ⁻⁸ , D = −8.4322 × 10 ⁻¹⁰
(14th page)
k = 0,
A = -9.0645 × 10 ^-6 , B = 3.7152 × 10 ^-6 ,
C = -1.2262 × 10 ^-7 , D = 3.3282 × 10 ^-10
(19th page)
k = 0,
A = 0.000528218, B = -1.1829 × 10 ⁻⁵ ,
C = 1.2696 × 10 ⁻⁶ , D = −6.1934 × 10 ⁻⁸

(Scaled data)
Wide angle end Intermediate range Telephoto end
D (5) 0.792 14.304 23.201
D (11) 23.816 10.304 1.407
D (14) 0.100 2.074 3.904
D (16) 7.794 3.097 3.670
D (19) 1.761 4.484 2.081

(Numerical values related to conditional expression (1))
2ω _w (angle of view of the optical system at the wide-angle end) = 74.077

(Numerical value related to conditional expression (2))
L ₀ (total length of optical system) = 67.00
_{L 0 / (f t / f} w) = 5.68

(Numerical values related to conditional expression (3))
F _w (F value of the optical system at the wide angle end) = 1.615

(Numerical values related to conditional expression (4))
D ₃ (movement distance at the time of zooming of the rear group G _13R of the third lens group G ₁₃ ) = 3.68
f ₃ (focal length of the third lens group G ₁₃ ) = 18.80
D ₃ / f ₃ = 0.196

(Numerical values related to conditional expression (5))
N ₁ (refractive index of the material of the positive meniscus lens L ₁₂₃ with respect to the d-line) = 2.00272

  FIG. 2 is a diagram illustrating various aberrations of the zoom lens according to Example 1 with respect to the d-line (λ = 587.56 nm). In the figure, IMG HT indicates the image height. Further, S and M in the astigmatism diagram represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the zoom lens according to the second embodiment. In this zoom lens, in order from the object side (not shown), a first lens group G ₂₁ having a positive refractive power, a second lens group G ₂₂ having a negative refractive power, and a third lens group having a positive refractive power. G ₂₃ and a fourth lens group G ₂₄ having a positive refractive power are arranged.

An aperture stop S that defines a predetermined aperture is disposed between the second lens group G ₂₂ and the third lens group G ₂₃ . Further, an infrared cut filter G is disposed between the fourth lens group G ₂₄ and the image plane I. In addition, on the image plane I, the light receiving surface of the image sensor is arranged.

The first lens group G ₂₁ includes, in order from the object side, a negative meniscus lens L ₂₁₁ having a concave surface facing the image side, a positive bilens lens L _212, and a positive meniscus lens L having a convex surface facing the object side. ₂₁₃ are arranged. The negative meniscus lens L ₂₁₁ and the positive lens L ₂₁₂ are cemented.

The second lens group G ₂₂ includes, in order from the object side, a front group G _22F having a negative refractive power and a rear group G _22R having a positive refractive power. The front group G _22F includes, in order from the object side, a negative meniscus lens L ₂₂₁ having a concave surface directed toward the image side, and a biconcave negative lens L ₂₂₂ . The rear group G _22R includes a positive meniscus lens L ₂₂₃ having a convex surface directed toward the object side.

The third lens group G ₂₃ includes, in order from the object side, a front group G _23F having a positive refractive power, constructed and the group G _23R, are disposed after having a negative refractive power. The front group G _23F includes a biconvex positive lens L ₂₃₁ . Aspherical surfaces are formed on both surfaces of the positive lens _L231 . The rear group G _23R includes a negative meniscus lens L ₂₃₂ having a concave surface facing the image side.

The fourth lens group G ₂₄ includes, in order from the object side, a negative meniscus lens L ₂₄₁ having a concave surface facing the image side and a positive meniscus lens L ₂₄₂ having a convex surface facing the object side. . The negative meniscus lens L ₂₄₁ and the positive meniscus lens L ₂₄₂ are cemented. An aspheric surface is formed on the image side surface of the positive meniscus lens _L242 .

In this zoom lens, the first lens group G ₂₁ , the aperture stop S, and the front group G _{23F of} the third lens group G ₂₃ are always fixed. When zooming from the wide-angle end (WIDE) to the telephoto end (TELE), the second lens group G ₂₂ extends from the object side to the image side along the optical axis so as to widen the distance from the first lens group G ₂₁ . Moving. At this time, the rear group G _{23R of} the third lens group G ₂₃ moves on the optical axis so as to increase the distance from the front group G _23F, and the fourth lens group G ₂₄ moves to the rear group of the third lens group G ₂₃ . By moving on the optical axis so as to change the distance from G _23R , the movement of the image plane I accompanying zooming is corrected, and the position is held constant.

  Various numerical data related to the zoom lens according to Example 2 will be described below.

Focal length of the zoom lens system = 4.600 (f _w: the wide-angle end) ～14.550 (intermediate region) ~46.000 (f _t: telephoto end)
F value = 1.568 (F _w: the wide-angle end) ～1.858 (intermediate region) ～1.659 (telephoto end)
Half angle of view (ω) = 37.047 (ω _w : wide angle end)-11.929 (middle range)-3.7925 (telephoto end)

(Lens data)
r ₁ = 59.565
d ₁ = 1.000 nd ₁ = 1.92286 νd ₁ = 18.9
r ₂ = 36.995
d ₂ = 5.634 nd ₂ = 1.592824 νd ₂ = 68.63
r ₃ = -202.406
d ₃ = 0.200
r ₄ = 28.095
d ₄ = 3.336 nd ₃ = 1.72916 νd ₃ = 53.94
r ₅ = 69.356
d ₅ = D (5) (variable)
r ₆ = 145.751
d ₆ = 0.600 nd ₄ = 1.883 νd ₄ = 40.8
r ₇ = 9.838
d ₇ = 2.989
r ₈ = -18.369
d ₈ = 0.600 nd ₅ = 1.72916 νd ₅ = 53.94
r ₉ = 10.943
d ₉ = 0.231
r ₁₀ = 11.977
d ₁₀ = 2.187 nd ₆ = 1.92286 νd ₆ = 20.88
r ₁₁ = 95.893
d ₁₁ = D (11) (variable)
r ₁₂ = ∞ (aperture stop)
d ₁₂ = 0.830
r ₁₃ = 9.673 (aspherical surface)
d ₁₃ = 2.739 nd ₇ = 1.618806 νd ₇ = 63.85
r ₁₄ = -52.598 (aspherical surface)
d ₁₄ = D (14) (variable)
r ₁₅ = 43.032
d ₁₅ = 0.600 nd ₈ = 1.805181 νd ₈ = 25.46
r ₁₆ = 16.007
d ₁₆ = D (16) (variable)
r ₁₇ = 7.867
d ₁₇ = 2.454 nd ₉ = 1.805181 νd ₉ = 25.46
r ₁₈ = 4.339
d ₁₈ = 5.121 nd ₁₀ = 1.58313 νd ₁₀ = 59.46
r ₁₉ = 100.065 (aspherical surface)
d ₁₉ = D (19) (variable)
r ₂₀ = ∞
d ₂₀ = 2.000 nd ₁₁ = 1.516798 νd ₁₁ = 64.2
r ₂₁ = ∞

Cone coefficient (k) and aspheric coefficient (A, B, C, D)
(13th page)
k = -0.223041282,
A = -0.000101524, B = 1.5627 × 10 ^-6 ,
C = -6.3257 × 10 ^-8 , D = -9.8365 × 10 ^-10
(14th page)
k = 0,
A = 1.53 × 10 ⁻⁵ , B = 2.7828 × 10 ⁻⁶ ,
C = -1.4504 × 10 ⁻⁷ , D = 5.4257 × 10 ⁻¹⁰
(19th page)
k = 0,
A = 0.000664189, B = -3.7398 × 10 ^-6 ,
C = 8.0668 × 10 ⁻⁷ , D = −5.4383 × 10 ⁻⁸

(Scaled data)
Wide angle end Intermediate range Telephoto end
D (5) 1.002 14.417 23.522
D (11) 24.662 11.247 2.143
D (14) 0.100 1.145 2.108
D (16) 6.111 2.844 3.386
D (19) 1.688 3.911 2.407

(Numerical values related to conditional expression (1))
2ω _w (angle of view of the optical system at the wide angle end) = 74.094

(Numerical value related to conditional expression (2))
L ₀ (total length of optical system) = 67.50
_{L 0 / (f t / f} w) = 6.75

(Numerical values related to conditional expression (3))
F _w (F value of the optical system at the wide angle end) = 1.568

(Numerical values related to conditional expression (4))
D ₃ (movement distance at the time of zooming of the rear group G _23R of the third lens group G ₂₃ ) = 2.01
f ₃ (focal length of the third lens group G ₂₃ ) = 20.81
D ₃ / f ₃ = 0.097

(Numerical values related to conditional expression (5))
N ₁ (refractive index of the material of the positive meniscus lens L ₂₂₃ with respect to d-line) = 1.92286

  FIG. 4 is a diagram illustrating various aberrations of the zoom lens according to Example 2 with respect to the d-line (λ = 587.56 nm). In the figure, IMG HT indicates the image height. Further, S and M in the astigmatism diagram represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

In the numerical data in each of the above embodiments, r ₁ , r ₂ ,... Are the curvature radii of the lenses and the diaphragm surface, and d ₁ , d ₂ ,. Thickness or spacing between them, nd ₁ , nd ₂ ,... Is the refractive index with respect to d-line (λ = 587.56 nm) of each lens, νd ₁ , νd ₂ ,. The Abbe number with respect to the d-line (λ = 587.56 nm) is shown. The unit of length is all “mm”, and the unit of angle is “°”.

  In addition, each of the above aspherical shapes has an optical axis direction of X, a height from the optical axis of h, a paraxial radius of curvature of r, a conical coefficient of k, fourth-order, sixth-order, eighth-order, and tenth-order aspherical surfaces. When the coefficients are A, B, C, and D, respectively, and the light traveling direction is positive, it is expressed by the following formula.

  As described above, in the zoom lens of each of the above embodiments, an F-number of 1.5 to 1.6 is obtained by arranging a lens or a cemented lens appropriately formed with an aspheric surface and satisfying the above conditional expressions. A small, wide-angle, high-magnification (about 10 to 12 times) photographic lens with high resolution that is optimal for a small-sized imaging device equipped with a high-pixel image sensor. be able to.

  As described above, the zoom lens according to the present invention is useful for a small-sized imaging device equipped with a high pixel image sensor, and is particularly suitable for an imaging device capable of shooting a moving image.

G _11, G ₂₁ first lens group G _12, G ₂₂ second lens group G _13, G ₂₃ third lens group G _14, G ₂₄ fourth lens group _{G 12F, G 13F, G 22F} , G 23F front group G _{12R, G 13R, G 22R,} G 23R rear group _{L 111, L 121, L 132} , L 141, L 211, L 221, L 232, L 241 negative meniscus lens _{L 113, L 123, L 142} , L 213 , L ₂₂₃ , L ₂₄₂ positive meniscus lens L ₁₂₂ , L ₂₂₂ negative lens L ₁₁₂ , L ₁₃₁ , L ₂₁₂ , L ₂₃₁ positive lens S aperture stop I image plane

Claims (2)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power, which are arranged in order from the object side. and the fourth lens group is composed of,
The third lens group is composed of a front group composed of one or more positive lenses and a rear group composed of one or more negative lenses arranged in order from the object side,
Upon zooming from the wide-angle end to the telephoto end, the second lens group, the rear group of the third lens group , and the fourth lens group move along the optical axis,
A zoom lens that satisfies the following conditional expression:
(1) 70 ≦ 2ω _w ≦ 80
_{(2) 5.6 ≦ L 0 /} (f t / f w) ≦ 6.8
(3) 1.50 ≦ F _w ≦ 1.65
(4) 0.09 ≦ D ₃ / f ₃ ≦ 0.20
Where ω _w is the half angle of view of the optical system at the wide angle end, L ₀ is the total length of the optical system, _ft is the focal length of the entire optical system at the telephoto end, and f _w is the focal length of the entire optical system at the wide angle end. F _w is the F value of the optical system at the wide angle end, D ₃ is the moving distance during zooming rear group of the third lens group, f ₃ denotes a focal length of the third lens group. The second lens group, disposed in order from the object side, a front group formed of 2 or more negative lenses, is composed of a rear group composed of one or more positive lenses,
2. The zoom lens according to claim 1, wherein the positive lens located closest to the image plane in the second lens group satisfies the following conditional expression.
(5) 1.9 ≦ N ₁ ≦ 2.1
N ₁ represents the refractive index with respect to d-line of the material of the positive lens located closest to the image plane of the second lens group.

Images