JP2011175161A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which simultaneously achieves a higher aperture ratio, a higher magnification, a smaller size, and satisfactory correction of various aberration arising in light from visible light region to a near-infrared light region. <P>SOLUTION: This zoom lens includes, in order from an object side, a first lens group G<SB>11</SB>having negative refractive power and a second lens group G<SB>12</SB>having positive refractive power. A cemented lens composed of a positive lens L<SB>121</SB>and a negative lens L<SB>122</SB>and having positive refractive power as a whole is disposed in the side closest to the object in the second lens group G<SB>12</SB>. This cemented lens makes it possible to obtain a high color aberration correcting effect (the correction of a color aberration arising in light from the visible light region to the near-infrared light region and the suppression of a frame aberration on the shortwave upper light beam side), compared to a single lens that obtains only a color aberration correcting effect dependent on the dispersion characteristics of glass itself. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zoom lens optimal for a surveillance camera.

  A surveillance camera such as CCTV (Closed Circuit TeleVision) is preferably equipped with a lens system that can be used day and night. A surveillance camera used outdoors usually shoots with visible light during the day and shoots with near-infrared light at night. In general, in a lens system designed for the visible light region, chromatic aberration occurs particularly in the near-infrared light region, causing a focus shift when photographing with near-infrared light at night. Therefore, as a lens system mounted on a surveillance camera, a lens system that satisfactorily corrects wide-band chromatic aberration so that the focus position is constant with respect to light in a wide wavelength range from the visible light range to the near infrared light range. (For example, refer to Patent Documents 1 to 3.)

  Each of the zoom lenses described in Patent Documents 1 to 3 includes a front group having a negative refractive power and a rear group having a positive refractive power, which are arranged in order from the object side. This is a two-group type zoom lens with good correction.

JP 2008-52214 A Japanese Patent No. 3548525 Japanese Patent No. 4280538

  In recent years, as a lens system for surveillance cameras, in addition to being able to handle a wide range of wavelengths from the visible light range to the near infrared light range, in addition to a large aperture ratio and shooting to support shooting at low illuminance There are also increasing demands for higher magnification for enhancing the selectivity of scenes and for miniaturization for enhancing the versatility of installation locations.

  However, in the related art including the lens system disclosed in the above-mentioned patent document, it is difficult to maintain optical performance while satisfying a large aperture ratio, high magnification, and miniaturization. In other words, when a large aperture ratio, a high magnification, and a miniaturization are achieved, it becomes difficult to correct chromatic aberration generated for light in the visible light region to the near infrared light region. The problem of increasing occurs.

  In order to eliminate the above-mentioned problems caused by the prior art, the present invention has a large aperture ratio, a high magnification, a miniaturization, and favorable aberrations generated for light in the visible to near-infrared range. An object of the present invention is to provide a zoom lens that can realize correction simultaneously.

  In order to solve the above-described problems and achieve the object, a zoom lens according to a first aspect of the present invention has a first lens group having a negative refractive power, arranged in order from the object side, and a positive refractive power. A second lens group, and performing zooming from the wide-angle end to the telephoto end by moving the second lens group toward the object side along the optical axis, and moving the first lens group along the optical axis. The zoom lens is configured to correct an image plane variation due to zooming by moving the zoom lens toward the image side, and a positive refracting power as a whole is provided closest to the object side of the second lens group. A cemented lens is disposed.

  According to the first aspect of the present invention, it is possible to effectively correct chromatic aberration generated by realizing a large aperture ratio, high magnification, and miniaturization of the optical system (from visible light region to near infrared light region). Correction of chromatic aberration generated with respect to light and suppression of short-wavelength upper ray side coma can be achieved.

A zoom lens according to a second aspect of the present invention is the zoom lens according to the first aspect, wherein the combined focal length of the cemented lens is fB, and the focal lengths of the entire optical system at the wide-angle end and the telephoto end are fW and fT, respectively. The following conditional expressions are satisfied.
(1) 5.6 ≦ fB / fW ≦ 7.9
(2) 2.5 ≦ fB / fT ≦ 5.0

  According to the second aspect of the present invention, various aberrations generated with respect to light in the visible light region to the near infrared light region can be corrected in a balanced manner.

A zoom lens according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the following conditional expression is satisfied when the combined image forming magnification of the second lens group is β2. And
(3) −1.1 ≦ β2 ≦ −0.3

  According to the third aspect of the invention, it is possible to reduce the size of the optical system while maintaining good optical performance.

A zoom lens according to a fourth aspect of the present invention is the zoom lens according to any one of the first to third aspects, wherein the first lens group includes a single lens having a positive refractive power. When the Abbe number with respect to the e-line of a single lens having the positive refractive power disposed on the most image side in one lens group is νe1p, the following conditional expression is satisfied.
(4) νe1p ≦ 18.0

  According to the fourth aspect of the present invention, it is possible to achieve both miniaturization and high magnification of the optical system and good correction of chromatic aberration of magnification.

  A zoom lens according to a fifth aspect of the present invention is the zoom lens according to any one of the first to fourth aspects, wherein an aspherical surface is formed on at least one surface of the cemented lens in contact with air. Features.

  According to the fifth aspect of the present invention, spherical aberration can be corrected satisfactorily.

  A zoom lens according to a sixth aspect of the present invention is the zoom lens according to any one of the first to fifth aspects, wherein an aspheric surface is formed on at least one surface of the lens other than the cemented lens. And

  According to the sixth aspect of the present invention, spherical aberration can be corrected more satisfactorily.

  According to the present invention, there is provided a zoom lens capable of simultaneously realizing a large aperture ratio, a high magnification, a miniaturization, and good correction of various aberrations generated for light in the visible light region to the near infrared light region. There is an effect that can be done.

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 all aberrations at the wide-angle end of the zoom lens according to Example 1; FIG. 6 is a diagram illustrating various aberrations at an intermediate end of the zoom lens according to the first example. FIG. 7 is a diagram illustrating all aberrations at the telephoto end of the zoom lens according to Example 1; FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a zoom lens according to Example 2; FIG. 10 is a diagram illustrating all aberrations at the wide-angle end of the zoom lens according to Example 2; FIG. 6 is a diagram illustrating various aberrations at an intermediate end of the zoom lens according to the second example. FIG. 10 is a diagram illustrating all aberrations at the telephoto end of the zoom lens according to Example 2;

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

  The zoom lens according to this embodiment includes a first lens group having a negative refractive power and a second lens group having a positive refractive power, which are arranged in order from the object side. This zoom lens performs zooming from the wide-angle end to the telephoto end by moving the second lens group toward the object side along the optical axis. Further, the first lens group is moved to the image side along the optical axis, thereby correcting the imaging plane variation (imaging position) accompanying zooming.

  The present invention provides a zoom lens capable of simultaneously realizing a large aperture ratio, a high magnification, a miniaturization, and good correction of various aberrations generated for light in the visible light region to the near infrared light region. It is an object. Therefore, in order to achieve this purpose, various conditions as shown below are set.

  First, a cemented lens having a positive refractive power as a whole is disposed on the most object side of the second lens group. In a zoom lens having a two-group configuration, the light beam spreads most by the lens disposed closest to the object side of the second lens group, and thus the lens mainly corrects spherical aberration and coma aberration. Therefore, by using a cemented lens for the lens, a chromatic aberration correction effect higher than that of a single lens that can only obtain a chromatic aberration correction effect that depends on the dispersion characteristics of the glass itself (for light in the visible to near-infrared light range). Correction of chromatic aberration generated in this manner, and suppression of short-wavelength upper side coma). In particular, it is possible to effectively correct chromatic aberration generated by realizing a large aperture ratio, high magnification, and miniaturization of the optical system.

Furthermore, in the zoom lens according to this embodiment, when the combined focal length of the cemented lens is fB and the focal lengths of the entire optical system at the wide angle end and the telephoto end are fW and fT, respectively, the following conditional expressions are satisfied. It is preferable to do.
(1) 5.6 ≦ fB / fW ≦ 7.9
(2) 2.5 ≦ fB / fT ≦ 5.0

  Conditional expression (1) defines the ratio of the combined focal length of the cemented lens to the focal length at the wide angle end of the entire zoom lens system. Conditional expression (2) defines the ratio of the combined focal length of the cemented lens to the focal length at the telephoto end of the entire zoom lens system. Each of the conditional expressions defines conditions for correcting various aberrations generated with respect to light from the visible light region to the near infrared light region in a well-balanced manner. If the lower limit of Conditional Expression (1) and Conditional Expression (2) is less than that, it is not preferable because the spherical aberration at the telephoto end increases and the contrast decreases. On the other hand, exceeding the upper limit in conditional expression (1) and conditional expression (2) is not preferable because astigmatism from the wide-angle end to the intermediate end increases.

Furthermore, in the zoom lens according to this embodiment, it is preferable that the following conditional expression is satisfied when the combined imaging magnification of the second lens group is β2.
(3) −1.1 ≦ β2 ≦ −0.3

  Conditional expression (3) is an expression that defines the conditions necessary to reduce the size of the optical system while maintaining good optical performance. If the lower limit of conditional expression (3) is not reached, spherical aberration that occurs in the entire zoom range increases, which is not preferable. On the other hand, if the upper limit of conditional expression (3) is exceeded, the focal point movement accompanying the movement of the second lens group becomes large, and it is necessary to move the first lens group greatly in order to correct this. . As a result, there arises a problem of inhibiting the miniaturization of the optical system, which is not preferable.

Furthermore, in the zoom lens according to this embodiment, the first lens group includes a single lens having a positive refractive power. It is preferable that the following conditional expression is satisfied when the Abbe number with respect to the e-line of a single lens having a positive refractive power disposed on the most image side in the first lens group is νe1p.
(4) νe1p ≦ 18.0

  Conditional expression (4) is an expression for prescribing a condition necessary for correcting chromatic aberration of magnification that occurs as the optical system is downsized or increased in magnification. By satisfying conditional expression (4), it is possible to achieve both reduction in size and increase in magnification of the optical system and good correction of chromatic aberration of magnification.

  Furthermore, in the zoom lens according to this embodiment, it is preferable that an aspheric surface is formed on at least one of the surfaces in contact with air in the cemented lens. By doing so, spherical aberration can be corrected satisfactorily.

  Furthermore, in the zoom lens according to this embodiment, it is preferable that an aspherical surface is formed on at least one surface of the lens other than the cemented lens. By doing so, spherical aberration can be corrected more satisfactorily.

  As described above, the zoom lens according to the present embodiment satisfies the above-described conditions, thereby increasing the aperture ratio, increasing the magnification, and reducing the size of light from the visible light region to the near infrared light region. On the other hand, good correction of various aberrations occurring can be realized at the same time. Moreover, by satisfying a plurality of the above conditions at the same time, more excellent optical performance can be obtained.

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 negative refractive power and a second lens group G ₁₂ having a positive refractive power arranged in order from the object side (not shown). Further, the first lens group G ₁₁ is provided between the second lens group G _12, an aperture stop STO is disposed to define a predetermined diameter. Between the second lens group G ₁₂ and the image plane IMG, a filter FL consisting of low-pass filter, a cover glass CG of the image pickup element is disposed. The filter FL and the cover glass CG are arranged as necessary, and can be omitted if unnecessary. In addition, a light receiving surface of an image sensor such as a CCD or a CMOS is disposed on the imaging plane IMG.

The first lens group G ₁₁ includes a negative lens L ₁₁₁ , a negative lens L ₁₁₂ , and a positive lens L ₁₁₃ arranged in order from the object side.

The second lens group G ₁₂ is composed of a positive lens L ₁₂₁ and a negative lens L _{122 in} order from the object side, and has a positive refractive power as a whole, a positive lens L ₁₂₃ , a negative lens L ₁₂₄ , and a positive lens L ₁₂₅ is arranged and configured. In this embodiment, an example in which an aspheric surface is formed on the object side surface of the positive lens L ₁₂₁ constituting the cemented lens is shown. The cemented lens is necessary depending on the angle of view and the zoom ratio of the optical system. It is only necessary to form an aspherical surface, and the aspherical surface is not essential. Further, in this embodiment, an example in which aspheric surface is formed on both surfaces of the negative lens L _124, similar optical performance to form aspherical surfaces on both sides of the positive lens L ₁₂₅ rather than the negative lens L ₁₂₄ Is obtained.

Forming the zoom lens performs zooming to the telephoto end from the wide-angle end by moving the second lens group G ₁₂ the object side along the optical axis, along a first lens group G ₁₁ to the optical axis By moving to the image plane IMG side, image plane variation (image position) associated with zooming is corrected. Further, the zoom lens adopts a so-called front focus system, it is possible to perform focusing by moving along the first lens group G ₁₁ to the optical axis.

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

Focal length of the entire zoom lens = 2.99 mm (fW: wide-angle end) to 4.93 mm (intermediate end) to 8.15 mm (fT: telephoto end)
F number = 1.03 (wide-angle end) to 1.34 (intermediate end) to 1.88 (telephoto end)
Half angle of view (ω) = 65.9 ° (wide-angle end) to 36.2 ° (intermediate end) to 21.4 ° (telephoto end)
Composite focal length of the cemented lens (fB) = 21.24

(Numerical values related to conditional expression (1))
fB / fW = 7.10533

(Numerical value for conditional expression (2))
fB / fT = 2.60532

(Numerical value for conditional expression (3))
Synthesis imaging magnification of the second lens group _{G 12 (β2) = - 0.389262} ( wide angle end) - - 1.06161 (telephoto end)

(Numerical values related to conditional expression (4))
Abbe number (νe1p) with respect to the e-line of a single lens having a positive refractive power (positive lens L ₁₁₃ ) disposed closest to the image side in the first lens group G ₁₁ = 17.8

r ₁ = 41.602
d ₁ = 0.600 ne ₁ = 1.83944 νe ₁ = 42.5
r ₂ = 6.842
d ₂ = 5.047
r ₃ = -16.776
d ₃ = 0.500 ne ₂ = 1.73234 ν e ₂ = 54.4
r ₄ = 39.645
d ₄ = 0.150
r ₅ = 20.185
d ₅ = 1.471 ne ₃ = 1.95825 νe ₃ = 17.8
r ₆ = 172.187
d ₆ = 12.170 (wide-angle end) to 4.014 (intermediate end) to 1.939 (telephoto end)
r ₇ = ∞ (aperture stop)
d ₇ = 8.664 (wide-angle end) to 5.984 (intermediate end) to 1.500 (telephoto end)
r ₈ = 12.350 (aspherical surface)
d ₈ = 0.200 ne ₄ = 1.53920 νe ₄ = 40.9
r ₉ = 15.620
d ₉ = 4.772 ne ₅ = 1.49845 ν e ₅ = 81.2
r ₁₀ = -17.436
d ₁₀ = 0.500 ne ₆ = 1.73432 νe ₆ = 28.1
r ₁₁ = -35.415
d ₁₁ = 0.150
r ₁₂ = 10.929
d ₁₂ = 4.847 ne ₇ = 1.49845 νe ₇ = 81.2
r ₁₃ = -23.977
d ₁₃ = 0.150
r ₁₄ = 19.240 (aspherical surface)
d ₁₄ = 0.601 ne ₈ = 1.69415 νe ₈ = 30.9
r ₁₅ = 6.046 (aspherical surface)
d ₁₅ = 1.067
r ₁₆ = 7.748
d ₁₆ = 2.411 ne ₉ = 1.59489 νe ₉ = 68.3
r ₁₇ = -1000.000
d ₁₇ = 3.200 (wide-angle end) to 5.881 (intermediate end) to 10.365 (telephoto end)
r ₁₈ = ∞
d ₁₈ = 3.000 ne ₁₀ = 1.51872 νe ₁₀ = 64.0
r ₁₉ = ∞
d ₁₉ = 1.000
r ₂₀ = ∞
d ₂₀ = 0.500 ne ₁₁ = 1.51872 νe ₁₁ = 64.0
r ₂₁ = ∞
d ₂₁ = 1.000
r ₂₂ = ∞ (imaging plane)

Conic coefficient (K) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(8th page)
K = -1.51093,
A ₄ = -5.93025 × 10 ^-5 , A ₆ = -1.30343 × 10 ^-6 ,
A ₈ = 1.54222 × 10 ^-8 , A ₁₀ = -1.81481 × 10 ^-10
(14th page)
K = 0,
A ₄ = -1.10480 × 10 ⁻⁴ , A ₆ = 1.16911 × 10 ⁻⁶ ,
A ₈ = -3.60392 × 10 ^-8 , A ₁₀ = -9.96303 × 10 ^-10
(15th page)
K = -9.45779 × 10 ^-2 ,
A ₄ = 1.03467 × 10 ^-4 , A ₆ = -4.30363 × 10 ^-6 ,
A ₈ = 4.54350 × 10 ^-7 , A ₁₀ = -1.49735 × 10 ^-8

  FIG. 2 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to the first example. FIG. 3 is a diagram illustrating various aberrations at the intermediate end of the zoom lens according to the first example. FIG. 4 is a diagram illustrating various aberrations at the telephoto end of the zoom lens according to the first example. In the figure, e-line, F-line, and g-line represent aberrations with wavelengths corresponding to 546.1 nm, 486.1 nm, and 435.8 nm, respectively. In the astigmatism diagrams, ΔS and ΔM represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the zoom lens according to the second embodiment. The zoom lens includes a first lens group G ₂₁ having a negative refractive power and a second lens group G ₂₂ having a positive refractive power arranged in order from the object side (not shown). In addition, an aperture stop STO that defines a predetermined aperture is disposed between the first lens group G ₂₁ and the second lens group G ₂₂ . Between the second lens group G ₂₂ and the image plane IMG, a filter FL consisting of low-pass filter, a cover glass CG of the image pickup element is disposed. The filter FL and the cover glass CG are arranged as necessary, and can be omitted if unnecessary. In addition, a light receiving surface of an image sensor such as a CCD or a CMOS is disposed on the imaging plane IMG.

The first lens group G ₂₁ includes a negative lens L ₂₁₁ , a negative lens L ₂₁₂ , and a positive lens L ₂₁₃ arranged in order from the object side.

The second lens group G ₂₂ is composed of a positive lens L ₂₂₁ and a negative lens L _{222 in} order from the object side, and has a positive refractive power as a whole, a positive lens L ₂₂₃ , a negative lens L ₂₂₄ , and a positive lens L ₂₂₅ is arranged and configured. In this embodiment, an example in which aspheric surfaces are formed on both surfaces of the positive lens L ₂₂₃ is shown, but the same optical performance can be obtained even if aspheric surfaces are formed on lens surfaces other than the positive lens L ₂₂₃ .

Forming the zoom lens performs zooming to the telephoto end from the wide-angle end by moving the second lens group G ₂₂ to the object side along the optical axis, along a first lens group G ₂₁ to the optical axis By moving to the image plane IMG side, image plane variation (image position) associated with zooming is corrected. Further, the zoom lens adopts a so-called front focus system, it is possible to perform focusing by moving along the first lens group G ₂₁ to the optical axis.

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

Focal length of the entire zoom lens = 3.09 mm (fW: wide-angle end) to 4.90 mm (intermediate end) to 7.76 mm (fT: telephoto end)
F number = 1.03 (wide-angle end) to 1.26 (intermediate end) to 1.64 (telephoto end)
Half angle of view (ω) = 60.5 ° (wide-angle end) to 35.9 ° (intermediate end) to 22.2 ° (telephoto end)
Composite focal length (fB) of the cemented lens = 23.64

(Numerical values related to conditional expression (1))
fB / fW = 7.65015

(Numerical value for conditional expression (2))
fB / fT = 3.0464

(Numerical value for conditional expression (3))
Synthesis imaging magnification of the second lens group _{G 22 (β2) = - 0.351856} ( wide angle end) - - 0.883586 (telephoto end)

(Numerical values related to conditional expression (4))
Abbe number (νe1p) with respect to the e-line of a single lens (positive lens L ₂₁₃ ) having a positive refractive power arranged on the most image side in the first lens group G ₂₁ = 17.8

r ₁ = 29.868
d ₁ = 0.800 ne ₁ = 1.83944 νe ₁ = 42.5
r ₂ = 7.266
d ₂ = 5.893
r ₃ = -23.382
d ₃ = 0.500 ne ₂ = 1.69980 ν e ₂ = 55.3
r ₄ = 30.477
d ₄ = 0.150
r ₅ = 18.103
d ₅ = 1.859 ne ₃ = 1.95825 νe ₃ = 17.8
r ₆ = 51.642
d ₆ = 14.636 (wide-angle end) to 5.688 (intermediate end) to 2.164 (telephoto end)
r ₇ = ∞ (aperture stop)
d ₇ = 7.130 (wide-angle end) to 4.978 (intermediate end) to 1.500 (telephoto end)
r ₈ = 10.716
d ₈ = 4.615 ne ₄ = 1.62032 νe ₄ = 63.1
r ₉ = -26.634
d ₉ = 0.500 ne ₅ = 1.65222 νe ₅ = 33.6
r ₁₀ = 36.573
d ₁₀ = 0.150
r ₁₁ = 9.733 (aspherical surface)
d ₁₁ = 2.859 ne ₆ = 1.59412 νe ₆ = 66.7
r ₁₂ = -22.259 (aspherical surface)
d ₁₂ = 0.343
r ₁₃ = -47.133
d ₁₃ = 1.520 ne ₇ = 1.73432 ν e ₇ = 28.1
r ₁₄ = 9.581
d ₁₄ = 1.083
r ₁₅ = 18.385
d ₁₅ = 2.262 ne ₈ = 1.73234 νe ₈ = 54.4
r ₁₆ = -15.650
d ₁₆ = 3.200 (wide-angle end) to 5.352 (intermediate end) to 8.830 (telephoto end)
r ₁₇ = ∞
d ₁₇ = 3.000 ne ₉ = 1.51872 νe ₉ = 64.0
r ₁₈ = ∞
d ₁₈ = 1.000
r ₁₉ = ∞
d ₁₉ = 0.500 ne ₁₀ = 1.51872 νe ₁₀ = 64.0
r ₂₀ = ∞
d ₂₀ = 1.000
r ₂₁ = ∞ (imaging plane)

Conic coefficient (K) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(11th page)
K = -5.95052 × 10 ^-1 ,
A ₄ = -1.26226 × 10 ^-4 , A ₆ = 9.64742 × 10 ^-7 ,
A ₈ = -5.05232 × 10 ^-8 , A ₁₀ = -9.86542 × 10 ^-10
(Twelfth surface)
K = 0,
A ₄ = 3.83807 × 10 ^-4 , A ₆ = -1.84046 × 10 ^-6 ,
A ₈ = -7.50547 × 10 ^-8 , A ₁₀ = 4.18185 × 10 ^-10

  FIG. 6 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to the second example. FIG. 7 is a diagram of various aberrations at the intermediate end of the zoom lens according to the second example. FIG. 8 is a diagram illustrating all aberrations at the telephoto end of the zoom lens according to the second example. In the figure, e-line, F-line, and g-line represent aberrations with wavelengths corresponding to 546.1 nm, 486.1 nm, and 435.8 nm, respectively. In the astigmatism diagrams, ΔS and ΔM 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 respective lenses and diaphragm surfaces, and d ₁ , d ₂ ,. Thickness or spacing between them, ne ₁ , ne ₂ ,... Is the refractive index with respect to e-line (λ = 546.1 nm) of each lens, νe ₁ , νe ₂ ,. The Abbe number with respect to the e-line (λ = 546.1 nm) is shown.

  Each of the aspheric shapes is expressed by the following equation when the distance from the apex of the lens surface in the optical axis direction is Z, the height in the direction perpendicular to the optical axis is h, and the light traveling direction is positive. Is done.

Here, c is a paraxial curvature at the lens apex, K is a conic coefficient, and A ₄ , A ₆ , A ₈ , and A ₁₀ are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.

  As described above, the zoom lens according to each of the above embodiments satisfies the above-described conditions, thereby increasing the aperture ratio, increasing the magnification, and reducing the size, and with respect to light from the visible light region to the near infrared light region. Thus, it is possible to achieve good correction of various aberrations generated at the same time. In addition, since the zoom lens of each of the above embodiments uses a lens with an aspheric surface as appropriate, it is possible to maintain good optical performance with a small number of lenses.

  As described above, the zoom lens of the present invention is useful for surveillance cameras, and is particularly suitable when high aperture ratio, high magnification, and miniaturization and high optical performance are required.

G ₁₁ , G ₂₁ first lens group G ₁₂ , G ₂₂ second lens group L ₁₁₁ , L ₁₁₂ , L ₁₂₂ , L ₁₂₄ , L ₂₁₁ , L ₂₁₂ , L ₂₂₂ , L ₂₂₄ negative lenses L ₁₁₃ , L ₁₂₁ , L ₁₂₃ , L ₁₂₅ , L ₂₁₃ , L ₂₂₁ , L ₂₂₃ , L ₂₂₅ Positive lens STO Aperture stop CG Cover glass FL filter IMG Imaging surface

Claims (6)

A first lens group having a negative refractive power and a second lens group having a positive refractive power, arranged in order from the object side,
The second lens group is zoomed from the wide-angle end to the telephoto end by moving the second lens group to the object side along the optical axis, and the zooming is performed by moving the first lens group toward the image side along the optical axis. A zoom lens configured to correct image plane fluctuations associated with
A zoom lens, wherein a cemented lens having a positive refractive power as a whole is disposed closest to the object side of the second lens group. The following conditional expression is satisfied, where fB is a combined focal length of the cemented lens and fW and fT are focal lengths of the entire optical system at the wide-angle end and the telephoto end, respectively. Zoom lens.
(1) 5.6 ≦ fB / fW ≦ 7.9
(2) 2.5 ≦ fB / fT ≦ 5.0 3. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when a combined imaging magnification of the second lens group is β <b> 2.
(3) −1.1 ≦ β2 ≦ −0.3 The first lens group includes a single lens having a positive refractive power, and has an Abbe number with respect to the e-line of a single lens having a positive refractive power disposed on the most image side in the first lens group. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when νe1p is satisfied.
(4) νe1p ≦ 18.0   5. The zoom lens according to claim 1, wherein an aspheric surface is formed on at least one of the surfaces in contact with air in the cemented lens.   The zoom lens according to claim 1, wherein an aspheric surface is formed on at least one surface of the lens other than the cemented lens.

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