JP2016145928A - Zoom lens and image capturing device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which comprises a compact lens system, has a wide view angle, and easily provides superior optical performance over an entire zoom range.SOLUTION: A zoom lens comprises first, second, and third lens groups having negative, positive, and negative refractive power, respectively, and is configured to move each of the lens groups while zooming such that a distance between each pair of adjacent lens groups changes. The first lens group has one or more each of negative lenses and positive lenses, and the second lens group has one or more positive lenses. A refractive index nF of a material at a wavelength of 486.13 nm, a refractive index nd of the material at a wavelength of 587.6 nm, a refractive index nC of the material at a wavelength of 656.27 nm, a refractive index nt of the material at a wavelength of 1013.98 nm, an Abbe number νd, a partial dispersion ratio θCt, an Abbe number νdA of a material of a positive lens A, a partial dispersion ratio θCtA, a focal length f1 of the first lens group, and a focal length fw of the entire system at the wide-angle end are each set appropriately.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a zoom lens, and is particularly suitable as an imaging optical system used in an imaging apparatus such as a surveillance camera, a digital camera, a video camera, and a broadcast camera.

  The imaging optical system used in an imaging device using a solid-state image sensor is a wide-angle zoom lens that has high optical performance that can cope with high-definition of the solid-state image sensor and can easily shoot a wide area. There is a desire to be.

  In particular, from the viewpoint of high image quality, it has high optical performance that can sufficiently handle SD (Standard Definition) image quality, megapixels, full HD (High Definition) image quality, and image sensors with more pixels. Is desired. In recent years, with the rapid expansion of the surveillance camera market, a zoom lens used in a surveillance camera is required to have a wide angle of view and a small Fno. A general surveillance camera uses visible light for daytime photography and near infrared light for nighttime photography.

  For example, in many cases, surveillance cameras use a near-infrared light having a wavelength of 800 nm to 1000 nm to facilitate shooting under low illuminance in night shooting. For this reason, zoom lenses used in surveillance cameras are required to have good correction of chromatic aberration in a wide wavelength range from visible light (wavelength 400 nm to wavelength 700 nm) to the near infrared region, and to reduce focus deviation. ing.

  Furthermore, in order to facilitate installation indoors and outdoors, regardless of location, it is also desired that the entire system be particularly small. As a zoom lens satisfying these demands, a negative lead type zoom lens in which a lens group having a negative refractive power is disposed closest to the object side is known. As a negative lead type zoom lens, it is composed of first to third lens groups having negative, positive, and negative refractive powers in order from the object side to the image side, and a three-group zoom in which all the lens groups move during zooming. Lenses are known (Patent Documents 1 and 2).

JP 2013-061388 A JP 2006-343552 A

  In the negative lead type three-group zoom lens described above, it is important to properly set the lens configuration of each lens group in order to obtain high optical performance over the entire zoom range while the entire system is small and has a wide angle of view. It becomes. In particular, in a zoom lens used for a surveillance camera, it is important to set the lens configuration so that chromatic aberration is corrected well and focus deviation is reduced over a wide wavelength range from the visible range to the near infrared range.

  For example, in order to satisfactorily correct chromatic aberration in a wide wavelength range and reduce the focus shift, the lens configuration of the first lens group and the second lens group and the material of the lens used for these lens groups are appropriately selected. Setting is important. If these configurations are inappropriate, it becomes very difficult to obtain a zoom lens having a wide angle of view and high optical performance over a wide wavelength range while reducing the size of the entire system.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens in which the entire lens system is small, has a wide angle of view, and can easily obtain high optical performance in the entire zoom range, and an imaging apparatus having the zoom lens.

The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. In a zoom lens in which each lens group moves so that the interval between the matching lens groups changes, the first lens group has a negative lens and a positive lens, and the refractive index of the material for light with a wavelength of 486.13 nm is nF, the wavelength The refractive index of the material for light of 587.6 nm is nd, the refractive index of the material for light of wavelength 656.27 nm is nC, the refractive index of the material for light of wavelength 1013.98 nm is nt, the Abbe number νd of the material and the partial dispersion ratio θCt is represented by νd = (nd−1) / (nF−nC), respectively.
θCt = (nC−nt) / (nF−nC)
And when
The second lens group includes:
85 <νd
−0.25 <θCt− (0.0047 × νd + 0.546) <− 0.10
When the positive lens satisfying the following conditional expression is satisfied, the focal length of the first lens unit is f1, and the focal length of the entire system at the wide angle end is fw.
−3.5 <f1 / fw <−1.8
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens in which the entire lens system is small, has a wide angle of view, and can easily obtain high optical performance in the entire zoom range.

Lens cross-sectional view and movement trajectory at the wide-angle end of Example 1 (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 1. Lens cross-sectional view and movement locus diagram at the wide-angle end of Example 2 (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 2. Lens cross-sectional view and movement locus diagram at the wide-angle end of Example 3 (A), (B), (C) Aberration diagrams of Example 3 at the wide-angle end, the intermediate zoom position, and the telephoto end Optical path diagram at the wide-angle end, the intermediate zoom position, and the telephoto end in Embodiment 1 Schematic diagram of the main part of the surveillance camera (imaging device) of the present invention

  Hereinafter, a zoom lens of the present invention and an image pickup apparatus having the same will be described with reference to the drawings. The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. Each lens unit moves so that the interval between adjacent lens units changes during zooming.

  FIG. 1 is a lens cross-sectional view at the wide-angle end (short focal length end) of the zoom lens according to Embodiment 1 of the present invention. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end (long focal length end) of the zoom lens according to the first exemplary embodiment of the present invention. Example 1 is a zoom lens having a zoom ratio of 3.9 and an F number of 1.47 to 3.23. FIG. 3 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 2 of the present invention. FIGS. 4A, 4B, and 4C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the second embodiment of the present invention. The second embodiment is a zoom lens having a zoom ratio of 3.4 and an F number of 1.44 to 2.66.

  FIG. 5 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 3 of the present invention. FIGS. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the third exemplary embodiment of the present invention. The third exemplary embodiment is a zoom lens having a zoom ratio of 4.9 and an F number of 1.44 to 3.85. FIGS. 7A, 7B, and 7C are optical path diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the first exemplary embodiment. FIG. 8 is a schematic view of a main part of a surveillance camera (imaging device) having the zoom lens of the present invention.

  The zoom lens of each embodiment is an image pickup optical system used in the image pickup apparatus. In the lens cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). The zoom lens of each embodiment may be used in an optical device such as a projector. In this case, the left side is a screen and the right side is a projected image. In the lens cross-sectional view, L1 is a first lens group having negative refractive power (optical power = reciprocal of focal length), L2 is a second lens group having positive refractive power, and L3 is a third lens group having negative refractive power. It is. SP is an F number determining member (hereinafter also referred to as “aperture stop”) that functions as an aperture stop that determines (limits) an open F number (Fno) light beam.

  G is an optical block corresponding to an optical filter, a face plate, a quartz low-pass filter, an infrared cut filter, or the like. IP is an image plane, and when used as a photographing optical system of a video camera or a digital still camera, an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed.

  The arrows indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end. An arrow 3a related to the third lens unit L3 indicates a movement locus during zooming from the wide-angle end to the telephoto end when focusing at infinity. An arrow 3b indicates a movement locus during zooming from the wide-angle end to the telephoto end when focusing on a short distance. An arrow 3c relating to the third lens unit L3 indicates a moving direction during focusing from infinity to a short distance.

  In spherical aberration, d-line (wavelength 587.6 nm), C-line (wavelength 656.3 nm), F-line (wavelength 486.13 nm), wavelength 850 nm, and t-line (wavelength 1013.98 nm) are displayed. In astigmatism, ΔM represents a meridional image plane, and ΔS represents a sagittal image plane. In the distortion aberration, the d line is displayed. In the lateral chromatic aberration, aberrations of C line, F line, wavelength 850 nm, and t line with respect to the d line are displayed. Fno is an F number, and ω is a half angle of view (degrees).

  The present invention is a compact zoom lens having a wide field angle and a bright brightness with a high optical performance over the entire zoom range while the entire system is small, and with little focus shift in a wide wavelength range from visible light to near infrared light. It is. The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a negative refractive power. This is a three-group zoom lens. When zooming from the wide-angle end to the telephoto end, the lens units move in different directions in the direction of the arrows.

  The zoom type of the zoom lens of the present invention has a three-group configuration of negative lead (negative lens group preceding). While the first lens unit L1 has negative refracting power, zooming is performed by changing the interval between the lens units, which is suitable for widening the angle of view. The second lens unit L2 and the third lens unit L3 move along different trajectories to perform zooming, and the image plane variation associated therewith is moved and corrected by the first lens unit L1 closest to the object side. Focusing is performed by the third lens unit L3.

In each embodiment, the first lens unit L1 includes a negative lens and a positive lens. The second lens unit L2 has one or more positive lenses. Here, the refractive index of the material for light with a wavelength of 486.13 nm is nF, the refractive index of the material for light with a wavelength of 587.6 nm is nd, the refractive index of the material for light with a wavelength of 656.27 nm is nC, and the light with a wavelength of 1013.98 nm. Let nt be the refractive index of the material. Then, the Abbe number νd and the partial dispersion ratio θCt of the material are represented by νd = (nd−1) / (nF−nC), respectively.
θCt = (nC−nt) / (nF−nC)
And

The Abbe number of the material of at least one positive lens A of the positive lenses included in the second lens unit L2 is νdA, and the partial dispersion ratio is θCtA. The focal length of the first lens unit L1 is f1, and the focal length of the entire system at the wide angle end is fw. At this time,
85 <νdA (1)
−0.25 <θCtA− (0.0047 · νdA + 0.546) <− 0.10 ·· (2)
−3.5 <f1 / fw <−1.8 (3)
The following conditional expression is satisfied. In addition, the value of each parameter is a value in d line (wavelength 587.6 nm) unless otherwise specified.

  Next, the technical meaning of each conditional expression described above will be described. Conditional expressions (1) and (2) are for reducing defocusing in a wide wavelength range from visible light to near-infrared light over the entire zoom range and obtaining high optical performance. In order to correct the focus shift in a wide wavelength range, it is preferable to reduce the axial chromatic aberration by using a material having a large Abbe number, that is, a small dispersion, as the material of the positive lens having a high marginal ray of the axial light beam.

  In the zoom lens having the three-group structure of each embodiment, as shown in FIGS. 7A, 7B, and 7C, the marginal ray of the axial beam is incident on the second lens unit L2 in the entire zoom range. (Hw) becomes high. Conditional expressions (1) and (2) define the optical characteristics of the material of at least one positive lens included in the second lens unit L2.

  The Abbe number νd is defined as described above using the refractive indices nd, nF, and nC of the d-line, F-line, and C-line in the visible light region. Therefore, by selecting the lens material based on the Abbe number νd, it becomes easy to correct chromatic aberration in the visible light range. However, since the Abbe number νd does not prescribe the characteristics in the near infrared region, even if the lens material is selected only by the value of the Abbe number νd, chromatic aberration is not necessarily produced in the near infrared region having a wavelength of 900 nm or more. It cannot be corrected well.

  Therefore, by selecting the material of the lens by paying attention to the partial dispersion ratio θCt in the t-line in addition to the Abbe number νd, axial chromatic aberration is controlled in both the visible light range and the near-infrared wavelength range. Defocus is reduced in the wavelength range. In addition, by selecting such a material, the correction of lateral chromatic aberration in the near-infrared region is performed well.

  Conditional expression (1) and conditional expression (2) define the material characteristics of at least one positive lens included in the second lens unit L2. When a material having a small Abbe number (that is, a large dispersion) is applied beyond the lower limit of conditional expression (1), it is difficult to satisfactorily correct axial chromatic aberration in the visible light region.

  A material having a relationship between the partial dispersion ratio θCt and the Abbe number νd exceeding the lower limit of the conditional expression (2) can easily suppress the axial chromatic aberration in the near infrared region, but at present, such a characteristic is obtained. It is difficult to manufacture an optical material that realizes the above. Conversely, if the partial dispersion ratio θCtA exceeds the upper limit of the conditional expression (2) and becomes too large, the difference in refractive index depending on the wavelength in the near infrared region becomes too large, making it difficult to correct axial chromatic aberration.

  Conditional expression (3) is for obtaining a high angle of view while the entire system is small. When the focal length of the entire system at the wide-angle end is shortened, the power of the first lens unit L1 is appropriately set accordingly. It is stipulated in. When the upper limit value of conditional expression (3) is exceeded, the negative power of the first lens unit L1 becomes too strong (the absolute value of the negative refractive power becomes too large). This makes it difficult to balance the various aberrations, and it is difficult to satisfactorily correct various aberrations such as field curvature and chromatic aberration over the entire zoom range.

  When the lower limit of conditional expression (3) is exceeded, the negative power of the first lens unit L1 is too weak (the absolute value of the negative refractive power is too small). This not only makes it difficult to widen the angle of view, but also increases the amount of movement associated with zooming from the wide-angle end to the telephoto end of the first lens unit L1, increases the overall lens length, and increases the effective diameter of the front lens. And the entire system becomes larger.

In each embodiment, the zoom lens having the high optical performance with a wide angle of view and a wide angle of view with little focus shift from visible light to near-infrared light over the entire zoom range while having a small size of the entire system by configuring as described above. Have gained. Preferably, the numerical ranges of conditional expressions (1) to (3) are set as follows.
90 <νdA (1a)
−0.22 <θCtA− (0.0047 · νdA + 0.546) <− 0.12
... (2a)
-3.2 <f1 / fw <-1.9 (3a)

  The zoom lens that is the object of the present invention is realized by satisfying the above-described configuration. Furthermore, in each embodiment, it is preferable to satisfy one or more of the following conditions.

  The focal length of the second lens unit L2 is f2, and the focal length of the third lens unit L3 is f3. The refractive index and the Abbe number of the material of at least one positive lens 1p among the positive lenses included in the first lens unit L1 are Nd1p and νd1p, respectively. The first lens group L1 has two or more negative lenses, and the second lens group L2 has three or more positive lenses and one or more negative lenses.

  The amount of movement of the third lens unit L3 during zooming from the wide-angle end to the telephoto end is M3. Here, the amount of movement of the lens unit accompanying zooming from the wide-angle end to the telephoto end refers to the difference between the position on the optical axis at the wide-angle end of the lens unit and the position on the optical axis at the telephoto end. The sign of the amount of movement is positive when the lens group is located on the image side at the telephoto end compared to the wide-angle end, and negative when it is located on the object side. The total lens length at the wide angle end is OALw.

  The lateral magnification at the wide-angle end of the second lens unit L2 is β2w, the lateral magnification at the telephoto end of the second lens unit L2 is β2t, the lateral magnification at the wide-angle end of the third lens unit L3 is β3w, and the telephoto end of the third lens unit L3 Let β3t be the lateral magnification at. At this time, it is preferable to satisfy one or more of the following conditional expressions.

−0.50 <f2 / f3 <−0.15 (4)
1.80 <Nd1p (5)
νd1p <26.0 (6)
−1.2 <f1 / f2 <−0.4 (7)
-20.0 <f3 / fw <-5.0 (8)
0.12 <-M3 / OALw <0.50 (9)
0.28 <(β3t / β3w) / (β2t / β2w) <0.70 (10)

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (4) defines the power relationship between the second lens unit L2 and the third lens unit L3. The second lens group L2 and the third lens group L3 are both lens groups that bear the multiplication effect.

  Conditional expression (4) defines the power conditions of the second lens unit L2 and the third lens unit L3, and achieves a high zoom ratio while maintaining good optical performance. If the upper limit of conditional expression (4) is exceeded and the positive power of the second lens unit L2 becomes too strong, various aberrations such as spherical aberration and coma increase, which is not preferable. Exceeding the lower limit of conditional expression (4), if the negative power of the third lens unit L3 is too strong (the absolute value of the negative refractive power is too large), various aberrations such as coma increase, which is not preferable. .

The numerical value range of conditional expression (4) is more preferably limited as follows.
−0.45 <f2 / f3 <−0.17 (4a)
Conditional expressions (5) and (6) define the material of at least one positive lens 1p included in the first lens unit L1. Exceeding the lower limit of conditional expression (5) is not preferable because spherical aberration tends to increase in the over direction at the telephoto end. Furthermore, it is necessary to reduce the radius of curvature or increase the lens thickness in order to obtain the power of the positive lens, which is not preferable from the viewpoint of miniaturization.

  Conditional expression (6) is mainly for favorably correcting chromatic aberration. Conditional expression (6) is for correcting chromatic aberration generated from the negative lens of the first lens unit L1. If the upper limit of conditional expression (6) is exceeded, correction of lateral chromatic aberration will be insufficient. For example, aberrations on the short wavelength side such as g-line and F-line with respect to d-line increase in the under direction in the aberration diagram, which is not preferable.

The numerical ranges of conditional expression (5) and conditional expression (6) are more preferably set as follows.
1.90 <Nd1p (5a)
νd1p <20.0 (6a)
Conditional expression (7) indicates that the focal length of the second lens unit L2, which is one of the lens units for zooming, and the focal point of the first lens unit L1 that requires negative power for widening the angle of view. It defines the relationship of distance.

  The first lens unit L1 is configured to include at least two or more negative lenses in order to facilitate a wide angle of view, and the second lens unit L2 is likely to have a zooming function as a lens unit having a positive refractive power. In order to achieve this, it is preferable to have a configuration having at least three positive lenses. Further, the first lens unit L1 and the second lens unit L2 are preferably configured to have at least one positive lens and one negative lens from the viewpoint of aberration correction.

  If the upper limit of conditional expression (7) is exceeded and the negative power of the first lens unit L1 becomes too strong, it will be difficult to correct field curvature and chromatic aberration in a well-balanced manner. In addition, if the upper limit of conditional expression (7) is exceeded and the positive power of the second lens unit L2 becomes too weak, the amount of movement of the second lens unit L2 during zooming increases and the entire system can be downsized. It becomes difficult.

If the lower limit of conditional expression (7) is exceeded and the negative power of the first lens unit L1 becomes too weak, the amount of movement increases as a correction for image plane variation during zooming, and the total lens length increases. Effective diameter increases. In addition, if the positive power of the second lens unit L2 becomes too strong beyond the lower limit of conditional expression (7), various aberrations such as spherical aberration increase. The numerical range of conditional expression (7) is more preferably set as follows.
−1.0 <f1 / f2 <−0.5 (7a)

  Conditional expression (8) appropriately defines the power of the third lens unit L3 to be driven during focusing while providing a zooming effect. If the upper limit of conditional expression (8) is exceeded and the negative power of the third lens unit L3 becomes too strong, off-axis aberrations such as astigmatism and field curvature increase, which is not preferable. Furthermore, the sensitivity in focusing becomes too high, making it difficult to manufacture with high accuracy.

If the lower limit of conditional expression (8) is exceeded and the negative power of the third lens unit L3 becomes too weak, the amount of movement of the third lens unit L3 during focusing and zooming increases, and the entire system becomes smaller. Becomes difficult. The numerical value range of conditional expression (8) is more preferably limited as follows.
−16.0 <f3 / fw <−6.0 (8a)

  Conditional expression (9) relates to the amount of movement of the third lens unit L3 during zooming. The total lens length OALw is a value obtained by adding an air-converted back focus to the distance from the surface vertex of the lens closest to the object side to the final lens surface. If the amount of movement of the third lens unit L3 occupying the entire length of the lens exceeds the upper limit of conditional expression (9), the amount of movement of the first lens unit L1 and the second lens unit L2 during zooming is a predetermined amount. It becomes difficult to secure. As a result, it is necessary to increase the power of the other lens units, and as a result, the fluctuations in various aberrations become large.

If the lower limit of conditional expression (9) is exceeded and the amount of movement of the third lens unit L3 decreases, it becomes difficult to obtain a predetermined zoom ratio, and the negative power of the third lens unit L3 needs to be increased. As a result, aberration fluctuations during focusing increase. In addition, it is preferable to introduce an aspherical surface to the third lens unit L3. According to this, it becomes easy to reduce the thickness of the third lens group L3 by reducing the number of lenses constituting the third lens group L3, and it becomes easy to reduce the size of the drive mechanism as the focus lens group. The numerical range of conditional expression (9) is more preferably limited as follows.
0.16 <-M3 / OALw <0.40 (9a)

  Conditional expression (10) defines the relationship between the lateral magnification ratio of the third lens unit L3 at the wide-angle end and the telephoto end with respect to the lateral magnification at the wide-angle end and the telephoto end of the second lens unit L2. That is, the ratio of variable magnification sharing between the second lens unit L2 and the third lens unit L3 is defined. If the upper limit of the conditional expression (10) is exceeded, the variable magnification share of the third lens unit L3 becomes too large, and it is necessary to increase the amount of movement of the third lens unit L3 during zooming, which reduces the size of the entire system. It becomes difficult.

When the lower limit of the conditional expression (10) is exceeded, the variable magnification sharing of the second lens unit L2 becomes too large, and it is necessary to increase the amount of movement of the second lens unit L2 during zooming, which reduces the size of the entire system. It becomes difficult. The numerical range of conditional expression (10) is more preferably limited as follows.
0.34 <(β3t / β3w) / (β2t / β2w) <0.60 (10a)

  Further, when the zoom lens of the present invention is applied to an image pickup apparatus having an image pickup element that receives an image formed by the zoom lens, it is preferable that at least one of the following conditional expressions is satisfied. The open F number at the wide-angle end of the zoom lens is Fnow, and the open F number at the telephoto end of the zoom lens is Fnot.

  The focal length of the entire system at the telephoto end is ft, the focal length of the entire system at the wide-angle end with respect to light with a wavelength of 850 nm is fw_850, and the focal length of the entire system at the telephoto end with respect to light with a wavelength of 850 nm is ft_850. Let p be the pixel pitch of the image sensor.

At this time, one or more of the following conditional expressions should be satisfied.
2.0 <Fnow · ((fw_850−fw) / p) <30.0 (11)
10.0 <Fnot · ((ft — 850−ft) / p) <120.0 (12)
Next, the technical meaning of each conditional expression will be described.

  Conditional expressions (11) and (12) are for reducing the focus shift in the wavelength range from visible light to near infrared light. Conditional expression (11) appropriately defines the focal length of the entire system at the wide-angle end at near-infrared light (850 nm) and the focal length of the entire system at the wide-angle end at d-line. Conditional expression (12) appropriately defines the focal length of the entire system at the telephoto end at near-infrared light (850 nm) and the focal length of the entire system at the telephoto end at d-line. Conditional expressions (11) and (12) appropriately define the F number that causes the focus shift level and the sensor pitch of the image sensor.

  Conditional expression (11) is for obtaining a high resolving power in the wavelength range from visible light to near-infrared light at the telephoto end, and conditional expression (12) is for the same technical meaning. If the upper limit of conditional expression (11) and conditional expression (12) is exceeded, the difference between the focal length of the wavelength 850 nm and the d-line with respect to the sensor pitch tends to increase, so the wavelength from visible light to near infrared light The focus shift in the range increases. For this reason, it is difficult to obtain a high resolving power from the visible light region to the near infrared region.

  If the lower limit of conditional expressions (11) and (12) is exceeded, it will be necessary to use a very low dispersion material to correct axial chromatic aberration, making it difficult to reduce the size of the entire system, and as a lens. It becomes difficult to manufacture with good accuracy.

More preferably, the numerical ranges of conditional expressions (11) and (12) are set as follows.
3.0 <Fnow · ((fw — 850−fw) / p) <30 (11a)
20.0 <Fnot · ((ft — 850−ft) / p) <120 (12a)

  As described above, according to each of the embodiments, a zoom lens and a bright lens having a wide angle of view with a high optical performance over the entire zoom range, a small focus shift in visible to near-infrared light, and a wide angle of view. An imaging device having the same is obtained. In particular, it is possible to obtain a zoom lens that covers a photographing field angle at the wide-angle end of 90 ° or more and an F-number at the wide-angle end of about 1.4. In addition, a zoom lens can be obtained that can sufficiently cope with an image pickup apparatus having an image pickup element with full HD or more pixels.

  In the zoom lens according to the present invention, the first lens unit L1 has, in order from the object side to the image side, a negative lens having a concave surface on the image side, a negative lens having a concave surface on the image side, and a convex lens on the object side. Consists of a positive lens. The second lens unit L2 includes, in order from the object side to the image side, a biconvex positive lens, a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented, and a biconvex positive lens. The

  Alternatively, the second lens unit L2 includes, in order from the object side to the image side, a biconvex positive lens, a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented, a biconvex positive lens, Consists of a convex positive lens. The third lens unit L3 includes a negative lens having a concave surface on the object side.

Next, a specific lens configuration of each embodiment will be described.
Example 1
In the following description, it is assumed that each lens group is arranged in order from the object side to the image side. The first lens unit L1 includes a negative meniscus lens G11 convex on the object side, a biconcave negative lens G12, and a positive meniscus lens G13 (positive lens 1p) convex on the object side. The positive lens G13 corrects chromatic aberration satisfactorily by using a high dispersion material.

  The second lens unit L2 includes a biconvex positive lens G21, a biconvex positive lens G22, a biconcave negative lens G23, and a biconvex positive lens G24. The positive lens G22 and the negative lens G23 are bonded to each other, and the chromatic aberration is favorably corrected by taking a large difference in Abbe number between the materials of both lenses. Moreover, both surfaces of the positive lens G21 are aspherical.

  This is because an aspherical surface is appropriately arranged on the object side of the second lens unit L2 in which the optical axis height of the axial light beam that determines the F-number is large, and the spherical aberration that tends to increase due to the large aperture ratio is corrected well. ing. In addition, an ultra-low dispersion material (Abbe number exceeding 90) is used as the material of any positive lens in the second lens unit L2, thereby correcting axial chromatic aberration satisfactorily. The third lens unit L3 includes a meniscus negative lens G31 having a convex image side. The negative lens G31 corrects off-axis aberrations such as astigmatism favorably by making both surfaces aspherical.

(Example 2)
The first lens unit L1 includes a meniscus negative lens G11 having a convex object side surface, a biconcave negative lens G12, and a biconvex positive lens G13 (positive lens 1p). The second lens unit L2 includes a biconvex positive lens G21, a biconvex positive lens G22, a biconcave negative lens G23, and a biconvex positive lens G24. The positive lens G22 and the negative lens G23 are bonded together. Moreover, both surfaces of the positive lens 21 are aspherical. The third lens unit L3 includes a meniscus negative lens G31 having a convex image side. At this time, both surfaces of G31 are aspherical.

(Example 3)
The first lens unit L1 includes a meniscus negative lens G11 having a convex object side surface, a biconcave negative lens G12, and a biconvex positive lens G13 (positive lens 1p). The negative lens G12 and the positive lens G13 are bonded together. The second lens unit L2 includes a biconvex positive lens G21, a biconvex positive lens G22, a biconcave negative lens G23, a biconvex positive lens G24, and a biconvex positive lens G25. . The positive lens G22 and the positive lens G23 are bonded together. Further, both surfaces of the positive lens G21 and the positive lens G24 are aspherical. The third lens unit L3 includes a meniscus negative lens G31 having a convex image side. At this time, both surfaces of G31 are aspherical.

  Next, an embodiment of a monitoring camera (imaging device) using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 8, reference numeral 30 denotes a surveillance camera body, and 31 denotes an imaging optical system constituted by any of the zoom lenses described in the first to third embodiments. Reference numeral 32 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the imaging optical system 31 and is built in the camera body. In order to obtain high resolution, a high-definition image sensor such as full HD (1920 × 1080) is configured. In the embodiment, the pixel pitch is 1.4 μm (Examples 1 and 2) and 2.75 μm (Example 3).

  Reference numeral 33 denotes a memory that records information corresponding to the subject image photoelectrically converted by the solid-state imaging device 32. Reference numeral 34 denotes a network cable for transferring a subject image photoelectrically converted by the photographed 32.

  As described above, each embodiment has a small zoom lens and high optical performance over the entire zoom range, suppresses focus shift from visible light to near-infrared light, and has a wide zoom lens and a wide zoom lens. An imaging device can be obtained. These embodiments are a small zoom lens that covers a maximum field angle 2ω of 90 ° or more and Fno of about 1.4 and is compatible with a high-pixel image sensor of full HD or more, and an image pickup apparatus having the same.

In each embodiment, the following means may be taken.
-It is not limited to the shape and number of glasses shown in the examples, but should be changed as appropriate.
At the time of zooming, the aperture stop SP is moved independently of the other lens groups during fixing or zooming.
-The material of the aspherical lens is not limited to glass, but a hybrid type aspherical lens in which an aspherical surface is formed with a resin material on the spherical lens surface (with an aspherical component on it) or an aspherical lens made of a plastic material is used. about.

-Move some lenses and lens groups so that they have a component in a direction perpendicular to the optical axis, thereby correcting image blur due to vibration such as camera shake.
-Correct distortion or chromatic aberration of the zoom lens by means of electrical correction when used in an imaging device.
-Focusing is performed by moving a lens group other than the third lens group.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments and optical specifications (view angle and Fno), and various modifications and changes can be made within the scope of the gist.

  Next, the numerical data of the Example corresponding to each Example are shown. In the numerical data of each embodiment, the surface number i indicates the order of the optical surfaces counted from the object side. ri is the radius of curvature of the i-th optical surface. di is the i-th and i + 1-th surface spacing. ndi and νdi respectively indicate the refractive index and Abbe number of the material of the optical member with respect to the d line. The partial dispersion ratio θCt is a numerical value calculated by (nC−nt) / (nF−nC). The reason why the distance d7 in Example 1 and the distance d6 in Example 3 have negative values is that the aperture stop SP and the second lens unit L2 are counted in order from the object side to the image side. * Means an aspherical surface.

  The back focus (BF) is an air conversion distance from the last lens surface to the paraxial image plane. The total lens length is defined as a value obtained by adding back focus (BF) to the distance from the front lens surface to the final lens surface. Also, when K is the eccentricity, A4, A6, A8, A10, and A12 are aspherical coefficients, and the displacement in the optical axis direction at the position of the height H from the optical axis is x with respect to the surface apex, the aspherical surface The shape is

Is displayed. Where R is the radius of curvature. For example, the display of “e-Z” means “10-Z”. Table 1 shows the correspondence with the above-described conditional expressions in each example. f is a focal length (d line), Fno is an F number, and a half angle of view (ω) is a numerical value relating to a shootable angle of view in consideration of the amount of distortion. The focal length (850 nm) is a focal length with a wavelength of 850 nm.

[Example 1]
Unit mm
Surface data
Surface number rd nd νd θCt
1 37.276 0.5 1.51633 64.1 0.8687
2 3.708 2.67
3 -9.176 0.45 1.6968 55.5 0.8330
4 22.101 0.15
5 11.283 0.86 1.95906 17.5 0.6264
6 31.995 (variable)
7 (Aperture) ∞ -0.14
8 * 4.918 2.38 1.4971 81.6 0.8349
9 * -6.85 0.1
10 7.81 1.64 1.437 95.1 0.8427
11 -10.779 0.65 1.90366 31.3 0.6968
12 5.063 0.54
13 7.948 2.6 1.72 50.2 0.7931
14 -5.627 (variable)
15 * -12.409 0.5 1.75501 51.2 0.8042
16 * -283.257 (variable)
17 ∞ 0.6 1.51633 64.1-
Image plane ∞

Aspheric data
8th page
K = 1.71905e-001 A 4 = -1.72272e-003 A 6 = -3.28988e-005 A 8 = 4.96438e-007
A10 = -1.55833e-007
9th page
K = 0.00000e + 000 A 4 = 1.61742e-003 A 6 = -1.29861e-005 A 8 = 2.23105e-007
A10 = -1.68559e-008
15th page
K = 8.08018e-001 A 4 = -7.90203e-003
16th page
K = 0.00000e + 000 A 4 = -7.31578e-003 A 6 = 7.57632e-005

Various data
Zoom ratio 3.9
Wide angle Medium telephoto
Focal length 2.1000 5.3781 8.1970
Focal length (850nm) 2.1104 5.3970 8.2212
Fno 1.47 2.41 3.23
Half angle of view (ω) (degrees) 46.7 16.9 11.0
Image height 1.58 1.58 1.58
Total lens length 28.50 23.14 24.12
BF 2.31 5.96 8.71

Distance Wide angle Medium telephoto
d 6 11.81 2.69 0.59
d14 1.5 1.61 1.94
d16 1.49 5.14 7.89

Each group focal length
1 group -5.19
2 groups 5.97
3 groups -17.2

Pixel pitch of solid-state image sensor: 0.0014 [mm]

[Example 2]
Unit mm
Surface data
Surface number rd nd νd θCt
1 81.883 0.5 1.60311 60.6 0.8321
2 4.785 2.78
3 -5.342 0.45 1.6968 55.5 0.8330
4 40.015 0.17
5 32.621 0.89 1.95906 17.5 0.6264
6 -27.041 (variable)
7 (Aperture) ∞ 0.55
8 * 5.523 2.23 1.4971 81.6 0.8349
9 * -11.967 0.1
10 12.555 1.7 1.437 95.1 0.8427
11 -9.016 0.3 1.90366 31.3 0.6968
12 14.94 0.57
13 6.623 2.24 1.59282 68.6 0.7960
14 -6.838 (variable)
15 * -4.602 0.75 1.75501 51.2 0.8042
16 * -6.385 (variable)
17 ∞ 0.6 1.51633 64.1-
Image plane ∞

Aspheric data
8th page
K = 1.71905e-001 A 4 = -9.76188e-004 A 6 = -5.45335e-005 A 8 = 5.46064e-007
A10 = -1.79190e-007
9th page
K = 0.00000e + 000 A 4 = 6.16798e-004 A 6 = -2.83657e-005 A 8 = -1.98708e-006
A10 = 1.55926e-007
15th page
K = 1.57008e + 000 A 4 = -4.45778e-003 A 6 = 2.83105e-004 A 8 = 1.23099e-005
A10 = 8.32708e-006
16th page
K = 0.00000e + 000 A 4 = -3.92074e-003 A 6 = 1.11257e-004 A 8 = 2.44653e-005

Various data
Zoom ratio 3.4
Wide angle Medium telephoto
Focal length 2.1002 4.6100 7.1397
Focal length (850nm) 2.1086 4.6269 7.1650
Fno 1.44 2.04 2.66
Half angle of view (ω) (degrees) 51.3 19.9 12.7
Image height 1.58 1.58 1.58
Total lens length 28.50 24.38 25.59
BF 3.51 7.02 10.46

Distance Wide angle Medium telephoto
d 6 10.27 2.67 0.4
d14 1.5 1.47 1.5
d16 2.76 6.27 9.71

Each group focal length
1 group -4.61
2 groups 5.83
3 groups -26.65

Pixel pitch of solid-state image sensor: 0.0014 [mm]

[Example 3]
Unit mm
Surface data
Surface number rd nd νd θCt
1 27.876 0.5 1.59522 67.7 0.7953
2 5.385 3.79
3 -6.479 0.45 1.6968 55.5 0.8330
4 20.356 1 1.95906 17.5 0.6264
5 -73.186 (variable)
6 (Aperture) ∞ -0.34
7 * 5.977 2.44 1.4971 81.6 0.8349
8 * -23.466 0.17
9 14.447 2.2 1.437 95.1 0.8427
10 -8.129 0.36 1.801 35.0 0.7255
11 11.965 0.52
12 * 6.226 2.2 1.4971 81.6 0.8349
13 * -31.597 0.2
14 34.176 1.37 1.883 40.8 0.7397
15 -12.849 (variable)
16 * -8.346 0.75 1.68893 31.2 0.6972
17 * -24.69 (variable)
18 ∞ 0.6 1.51633 64.1
Image plane ∞

Aspheric data
7th page
K = 1.71905e-001 A 4 = -3.33036e-004 A 6 = -9.87827e-006 A 8 = 1.23665e-006
A10 = -1.01218e-007 A12 = 1.16810e-009
8th page
K = 0.00000e + 000 A 4 = 4.19740e-004 A 6 = 4.07730e-006 A 8 = 6.63670e-007
A10 = -9.46456e-008 A12 = 1.48221e-009
12th page
K = 0.00000e + 000 A 4 = -6.52538e-004 A 6 = -4.78683e-006 A 8 = -1.31423e-006
Side 13
K = 0.00000e + 000 A 4 = 1.70578e-004 A 6 = 4.10856e-006 A 8 = 1.58203e-008
A10 = -8.55304e-009
16th page
K = 1.57008e + 000 A 4 = -2.72570e-003 A 6 = 2.84051e-004 A 8 = -3.66403e-006
A10 = -1.88077e-007
17th page
K = 0.00000e + 000 A 4 = -2.19739e-003 A 6 = 3.02610e-004 A 8 = -9.57983e-006

Various data
Zoom ratio 4.9
Wide angle Medium telephoto
Focal length 2.1503 5.2024 10.5489
Focal length (850nm) 2.1615 5.2205 10.5756
Fno 1.44 2.3 3.85
Half angle of view (ω) (degrees) 48.5 17.6 8.57
Image height 1.58 1.58 1.58
Total lens length 35.50 29.60 33.24
BF 3.50 7.90 15.10

Distance Wide angle Medium telephoto
d 5 14.89 4.64 0.89
d15 1.5 1.45 1.64
d17 0.66 5.06 12.26

Each group focal length
1 group -5.16
2 groups 6.88
3 groups -18.65

Pixel pitch of solid-state image sensor: 0.00275 [mm]

L1 First lens group L2 Second lens group L3 Third lens group

Claims (13)

In order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, and the distance between adjacent lens groups changes during zooming. In the zoom lens in which each lens group moves,
The first lens group includes a negative lens and a positive lens;
The refractive index of the material for light with a wavelength of 486.13 nm is nF,
The refractive index of the material for light having a wavelength of 587.6 nm is nd
The refractive index of the material for light with a wavelength of 656.27 nm is nC,
The refractive index of the material for light with a wavelength of 101.98 nm is nt,
The Abbe number νd and the partial dispersion ratio θCt of the material are represented by νd = (nd-1) / (nF-nC), respectively.
θCt = (nC−nt) / (nF−nC)
And when
The second lens group includes:
85 <νd
−0.25 <θCt− (0.0047 × νd + 0.546) <− 0.10
A positive lens that satisfies the conditional expression
When the focal length of the first lens group is f1, and the focal length of the entire system at the wide angle end is fw,
−3.5 <f1 / fw <−1.8
A zoom lens satisfying the following conditional expression: When the focal length of the second lens group is f2, and the focal length of the third lens group is f3,
−0.50 <f2 / f3 <−0.15
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the refractive index and Abbe number of the material of the positive lens included in the first lens group are Nd1p and νd1p, respectively, the first lens group is
1.80 <Nd1p
νd1p <26.0
The zoom lens according to claim 1, further comprising a positive lens that satisfies the following conditional expression: The first lens group has two or more negative lenses,
The second lens group has three or more positive lenses and one or more negative lenses,
When the focal length of the second lens group is f2,
−1.2 <f1 / f2 <−0.4
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the third lens group is f3,
-20.0 <f3 / fw <-5.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the amount of movement of the third lens unit in zooming from the wide-angle end to the telephoto end is M3, and the total lens length at the wide-angle end is OALw,
0.12 <-M3 / OALw <0.50
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. The lateral magnification at the wide-angle end of the second lens group is β2w, the lateral magnification at the telephoto end of the second lens group is β2t, the lateral magnification at the wide-angle end of the third lens group is β3w, and the telephoto end of the third lens group When the lateral magnification at is β3t,
0.28 <(β3t / β3w) / (β2t / β2w) <0.70
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   In order from the object side to the image side, the first lens group includes a negative lens having a concave surface on the image side, a negative lens having a concave surface on the image side, and a positive lens having a convex surface on the object side. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.   The second lens group includes, in order from the object side to the image side, a biconvex positive lens, a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented, and a biconvex positive lens. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.   The second lens group includes, in order from the object side to the image side, a biconvex positive lens, a cemented lens in which a biconvex positive lens and a biconcave negative lens are cemented, a biconvex positive lens, and a biconvex lens. The zoom lens according to claim 1, wherein the zoom lens is configured by a positive lens having a shape.   The zoom lens according to claim 1, wherein the third lens group includes a negative lens having a concave surface on the object side.   An image pickup apparatus comprising: the zoom lens according to claim 1; and an image pickup element that receives an image formed by the zoom lens. The open F number at the wide-angle end of the zoom lens is Fnow, the open F-number at the telephoto end of the zoom lens is Fnot, the focal length of the entire system at the telephoto end is ft, and the focal length of the entire system at the wide-angle end with respect to light having a wavelength of 850 nm. Fw_850, the focal length of the entire system at the telephoto end with respect to light having a wavelength of 850 nm is ft_850, and the pixel pitch of the image sensor is p,
2.0 <Fnow. ((Fw_850-fw) / p) <30.0
10.0 <Fnot · ((ft — 850−ft) / p) <120.0
The imaging apparatus according to claim 12, wherein the following conditional expression is satisfied.