JP2011018009A - Zoom lens and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens having high optical performance applicable to a megapixel imaging element while achieving compactness and wide-angle.SOLUTION: The zoom lens includes in the order from an object, a first lens group G1 having a negative refractive power, a diaphragm, and a second lens group G2 having a positive refractive power. By changing the interval between the first lens group G1 and the second lens group G2 on the optical axis Z, the power is varied while the image surface position following the power variation is corrected by moving the first lens group G1 along the optical axis Z. In addition, a formula (1):-2.4<f1/fw<-2.0 is satisfied. In the formula (1), f1 represents the focal length of the first lens group G1, and fw represents the focal length of the entire system at the wide-angle end, respectively.

Description

  The present invention relates to a zoom lens and an image pickup apparatus, and more particularly to a zoom lens that can be used in a video camera, an electronic still camera, and the like, and can be suitably used particularly as a surveillance camera application, and an image pickup apparatus including the zoom lens. It is.

  Conventionally, surveillance cameras are used for crime prevention and recording purposes. The surveillance camera's photographic lens can be configured compactly when mounted on the surveillance camera, has a wide angle so that a wide range can be monitored, and is large enough to identify the subject even under low illumination conditions. An aperture ratio optical system is required. In recent years, since a zooming function is often required, surveillance cameras using a zoom lens are becoming mainstream.

  As zoom lenses that can be used for surveillance cameras, for example, those described in Patent Documents 1 to 3 below are known. Patent Document 1 describes a seven-lens zoom lens in which a negative first lens group, a stop, and a positive second lens group are arranged in order from the object side. Patent Document 2 describes a 10-lens zoom lens in which a negative first lens group and a positive second lens group are arranged in order from the object side. Patent Document 3 describes a zoom lens having 10 or 11 lenses, in which a negative first lens group, a stop, and a positive second lens group are arranged in order from the object side.

JP 2006-119574 A JP 2007-94371 A JP 2008-216591 A

  Nowadays, with the increasing demand for surveillance cameras, there is an increasing demand for smaller and wider angle zoom lenses. On the other hand, since the image pickup devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) mounted on many cameras in the above fields have advanced, the image pickup device converted into a mega pixel has been developed. There is also a demand for high optical performance that can cope with this.

  However, the zoom lens described in Patent Document 1 is small and wide-angle, but cannot be said to have high performance enough to accommodate a megapixel imaging device. Although the zoom lens described in Patent Document 2 has a wide angle, correction of spherical aberration, astigmatism, and axial chromatic aberration is insufficient, so that it cannot sufficiently cope with a megapixel imaging device. The zoom lens described in Patent Document 3 has high performance, but there is room for improvement in terms of downsizing.

  The present invention has been made in view of the above circumstances. A zoom lens having high optical performance capable of supporting a megapixel imaging element while achieving downsizing and widening of the angle, and imaging including the zoom lens The object is to provide an apparatus.

The zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a diaphragm, and a second lens group having a positive refractive power, and the first lens group and the second lens group. Zooming is performed by changing the distance on the optical axis, and the image plane position is corrected by moving the first lens group along the optical axis. (1) is satisfied.
-2.4 <f1 / fw <-2.0 (1)
However,
f1: focal length of the first lens unit fw: focal length of the entire system at the wide-angle end

  While the zoom lenses described in Patent Documents 1 to 3 do not satisfy the conditional expression (1), the zoom lens according to the present invention is configured to satisfy the conditional expression (1). It is easy to realize high optical performance compatible with megapixel imaging devices while achieving widening and widening of the angle.

  In the zoom lens of the present invention, the first lens group may have a five-lens configuration in which three negative lenses, a positive lens, and a negative lens are arranged in order from the object side. In the zoom lens of the present invention, the second lens group may have a five-lens configuration in which three positive lenses, a negative lens, and a positive lens are arranged in order from the object side. Note that the sign of the refractive power of the lens described here is considered in the paraxial region for an aspheric lens.

In the zoom lens of the present invention, it is preferable that the following conditional expressions (2) to (4) are satisfied. In addition, as a preferable aspect, it may satisfy any one of the following conditional expressions (2) to (4), or may satisfy any combination.
−0.5 <m2w <−0.41 (2)
−0.9 <(r15f−r15r) / (r15f + r15r) <− 0.2 (3)
νd22> 80 (4)
However,
m2w: lateral magnification r15f of the second lens group at the wide angle end: radius of curvature r15r of the object side surface of the lens closest to the image side of the first lens group: image side surface of the lens closest to the image side of the first lens group Curvature radius νd22: Abbe number at the d-line of the second lens from the object side of the second lens group

  The values of the conditional expressions described in this specification are those at the reference wavelength of the zoom lens unless otherwise specified.

  An image pickup apparatus according to the present invention includes the zoom lens according to the present invention described above.

  According to the present invention, in order from the object side, the first lens group having a negative refractive power, a stop, and the second lens group having a positive refractive power, the first lens group and the second lens group are provided. The zooming is performed by changing the interval on the optical axis, and the correction of the image plane position accompanying the zooming is performed by moving the first lens group along the optical axis. The zoom lens having a high optical performance capable of accommodating a megapixel imaging device while achieving downsizing and widening of the angle, and the power of the first lens group is preferably set so as to satisfy An imaging device including a zoom lens can be provided.

Sectional view showing the lens configuration of the zoom lens according to Example 1 of the present invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 2 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 3 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 4 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 5 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 6 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 7 of this invention. 8A to 8H are aberration diagrams of the zoom lens according to Example 1 of the present invention. 9A to 9H are aberration diagrams of the zoom lens according to Example 2 of the present invention. FIGS. 10A to 10H are graphs showing aberrations of the zoom lens according to Example 3 of the present invention. FIGS. 11A to 11H are graphs showing aberrations of the zoom lens according to Example 4 of the present invention. FIGS. 12A to 12H are graphs showing aberrations of the zoom lens according to Example 5 of the present invention. 13A to 13H are aberration diagrams of the zoom lens according to Example 6 of the present invention. FIGS. 14A to 14H are graphs showing aberrations of the zoom lens according to Example 7 of the present invention. 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration example of a zoom lens according to an embodiment of the present invention, and corresponds to a zoom lens of Example 1 described later. 2 to 7 are cross-sectional views showing other configuration examples according to the embodiment of the present invention, and correspond to zoom lenses of Examples 2 to 7 described later, respectively. Since the basic configuration of the example shown in FIGS. 1 to 7 is the same and the method of illustration is also the same, here, a zoom lens according to an embodiment of the present invention will be described mainly with reference to FIG.

  The zoom lens according to the embodiment of the present invention includes a first lens group G1 having a negative refractive power, an aperture stop St, and a second lens having a positive refractive power in order from the object side along the optical axis Z. And a group G2. Such a configuration preceded by negative power is suitable for widening the angle and has a feature that it is relatively easy to ensure back focus.

  Note that the aperture stop St shown in FIG. 1 does not necessarily indicate the size or shape, but indicates the position on the optical axis Z. In FIG. 1, the left side is the object side, the right side is the image side, the upper row shows the lens arrangement at the infinity focus at the wide angle end, and the lower row is the lens at the infinity focus at the telephoto end. This shows the arrangement, and the movement trajectory of each lens unit when zooming from the wide-angle end to the telephoto end is schematically shown by an arrow between the upper and lower stages.

  When applying a zoom lens to an imaging device, various filters such as a cover glass, a prism, an infrared cut filter, and a low-pass filter are provided between the optical system and the image plane Sim depending on the configuration of the camera side on which the lens is mounted. It is preferable to arrange. Therefore, FIG. 1 shows an example in which a parallel plate-shaped optical member PP that assumes these is arranged between the second lens group G2 and the image plane Sim.

  This zoom lens performs zooming by changing the distance between the first lens group G1 and the second lens group G2 on the optical axis Z, and the first lens group G1 is corrected for the image plane position accompanying the zooming. It is configured to perform by moving along the optical axis Z. Note that the aperture stop St is fixed during zooming.

The zoom lens according to the present embodiment is configured to satisfy the following conditional expression (1).
-2.4 <f1 / fw <-2.0 (1)
However,
f1: Focal length of the first lens group G1 fw: focal length of the entire system at the wide angle end

  Conditional expression (1) relates to the ratio of the focal length of the first lens group G1 to the focal length of the entire system, and so to speak, indicates a suitable range of power distribution. If the upper limit of conditional expression (1) is exceeded, high-order astigmatism will occur, and field curvature will be overcorrected. If the lower limit of conditional expression (1) is not reached, the amount of peripheral light at the wide-angle end will be insufficient. In order to cope with a megapixel imaging device, it is required to obtain good image quality up to the periphery of the imaging region. By satisfying conditional expression (1), it is possible to obtain good image quality up to the periphery of the imaging region.

  Increase back focus while capturing light from a large angle of view so that downsizing and widening of the angle can be achieved with a two-group configuration consisting of negative and positive lens groups in order from the object side as in this zoom lens. In order to suppress this, the configuration of the negative first lens group G1 disposed on the object side is important. By setting the power of the first lens group G1 so as to satisfy the conditional expression (1), it is possible to achieve high performance compatible with a megapixel imaging device while achieving a reduction in size and a wide angle. become.

In addition, it is more preferable to satisfy the following conditional expression (1-1). In this case, the effect obtained by satisfying the conditional expression (1) can be further improved.
-2.3 <f1 / fw <-2.1 (1-1)

  As the configuration of the first lens group G1, for example, a five-lens configuration in which three negative lenses, a positive lens, and a negative lens are arranged in order from the object side can be adopted. In the example shown in FIG. 1, the first lens group G1 includes, in order from the object side, a negative meniscus lens L11, a negative meniscus lens L12, a biconcave lens L13, a biconvex lens L14, and a negative meniscus shape. Lens L15.

  Arranging the negative meniscus lens closest to the object side of the lens system is advantageous for widening the angle. By disposing two negative meniscus lenses on the object side in the first lens group G1, distortion aberration that increases as the optical system is widened can be corrected better than when only one negative meniscus lens is used. be able to. In addition, since the first lens group G1 includes the biconcave lens, it becomes easy to secure the negative power required for the first lens group G1, and the first lens group G1 includes the positive lens, thereby the first lens. It becomes easy to balance the chromatic aberration in the group G1. By configuring the first lens group G1 to include four negative lenses and dispersing the negative power, it is easy to correct spherical aberration easily, and a large aperture ratio is easily realized.

  As the configuration of the second lens group G2, a five-lens configuration in which three positive lenses, a negative lens, and a positive lens are arranged in order from the object side can be adopted. In the example shown in FIG. 1, the second lens group G2 includes, in order from the object side, a lens L21 that is a biconvex aspheric lens in the paraxial region, a biconvex lens L22, a positive meniscus lens L23, a negative It comprises a meniscus lens L24 and a biconvex lens L25.

  Since the first lens group G1 has a negative refracting power, the beam height when the light beam diverged from the first lens group G1 is incident on the second lens group is high, which is a high-order spherical aberration or coma aberration. It will cause to generate. In particular, higher-order spherical aberration and coma aberration are likely to occur with a large aperture ratio, but the most object side lens of the second lens group G2 is an aspherical lens as in the example shown in FIG. Thus, it is possible to effectively suppress the occurrence of spherical aberration and coma, and it becomes easy to realize a large aperture ratio. In addition, by configuring the second lens group G2 to include a large number of biconvex lenses, it becomes easy to ensure the positive power required for converging the light beam diverged by the first lens group G1.

  The zoom lens shown in FIG. 1 is composed of a single lens. In this way, by not using as many cemented lenses as possible, the number of air contact surfaces can be increased compared to the case where the same number of lenses are used to include more cemented lenses, and the degree of freedom in design is improved. This is advantageous for realizing a high-performance optical system in which aberrations are satisfactorily corrected up to the periphery of the imaging region.

The zoom lens according to the present embodiment preferably satisfies the following conditional expression (2).
−0.5 <m2w <−0.41 (2)
However,
m2w: lateral magnification of the second lens group G2 at the wide-angle end

  Conditional expression (2) indicates a preferable range of the lateral magnification of the second lens group G2 at the wide-angle end. If the upper limit of conditional expression (2) is exceeded, astigmatism will be insufficiently corrected, and the amount of peripheral light will be insufficient at the wide-angle end. If the lower limit of conditional expression (2) is not reached, the field curvature will be overcorrected and the performance will deteriorate.

Furthermore, it is more preferable to satisfy the following conditional expression (2-1). In this case, the effect obtained by satisfying the conditional expression (2) can be further improved.
−0.48 <m2w <−0.42 (2-1)

The zoom lens according to the present embodiment preferably satisfies the following conditional expression (3).
−0.9 <(r15f−r15r) / (r15f + r15r) <− 0.2 (3)
However,
r15f: radius of curvature of the object side surface of the most image side lens of the first lens group G1 r15r: radius of curvature of the image side surface of the most image side lens of the first lens group G1

  Conditional expression (3) relates to the shape of the lens closest to the aperture stop St among the lenses included in the first lens group G1. If the upper limit of conditional expression (3) is exceeded, spherical aberration will be undercorrected on the telephoto side. If the lower limit of conditional expression (3) is not reached, the amount of peripheral light will be insufficient. If an attempt is made to improve the shortage of the peripheral light amount, the diameter of the front lens (most object side lens) of the first lens group G1 becomes large, which is contrary to miniaturization.

Furthermore, it is more preferable to satisfy the following conditional expression (3-1). In this case, the effect obtained by satisfying the conditional expression (3) can be further improved.
−0.84 <(r15f−r15r) / (r15f + r15r) <− 0.23 (3-1)

In the zoom lens of the present embodiment, when the second lens group G2 has a five-lens configuration in which three positive lenses, a negative lens, and a positive lens are arranged in order from the object side, the following conditional expression ( It is preferable to satisfy 4).
νd22> 80 (4)
However,
νd22: Abbe number at the d-line of the second lens from the object side of the second lens group G2

  Conditional expression (4) means that a low dispersion material is used for the second lens (lens L22) from the object side of the second lens group G2. If the lower limit of conditional expression (4) is not reached, correction of chromatic aberration will be insufficient, and particularly good correction of axial chromatic aberration will be difficult.

In the zoom lens according to the present embodiment, when the lateral magnification β2 of the second lens group G2 is β2 = −1, the length in the optical axis direction from the most object-side surface of the entire system to the image plane Sim is long. It is configured to be minimal. If the focal length of the entire system when β2 = −1 is fm, fm is expressed as follows using the focal length f1 of the first lens group G1 described above.
fm = β2 × f1 = −f1
The zoom magnification Zm of the entire system at this time can be expressed as follows.
Zm = fm / fw = −f1 / fw

  When this zoom lens is used in harsh environments such as outdoors, the lens placed closest to the object is resistant to surface deterioration due to wind and rain, temperature changes due to direct sunlight, and chemicals such as oils and detergents. It is preferable to use a material resistant to chemicals, that is, a material having high water resistance, weather resistance, acid resistance, chemical resistance, etc., and further, a material that is hard and hard to break is preferable. From the above, as the material disposed closest to the object side, specifically, glass is preferably used, or transparent ceramics may be used.

  When the zoom lens is used in a harsh environment, a protective multilayer coating is preferably applied. In addition to the protective coat, an antireflection coating film for reducing ghost light during use may be applied.

  In the example shown in FIG. 1, an example in which the optical member PP is arranged between the lens system and the image plane Sim is shown, but instead of arranging various filters such as a low-pass filter and a specific wavelength band, These various filters may be disposed between the lenses, or a coating having the same action as the various filters may be applied to the lens surface of any lens.

  Next, numerical examples of the zoom lens according to the present invention will be described. The lens sectional views of the zoom lenses of Examples 1 to 7 are those shown in FIGS.

  Table 1 shows lens data of the zoom lens of Example 1, Table 2 shows data relating to zoom, and Table 3 shows aspherical data. Similarly, Tables 4 to 21 show lens data, zoom-related data, and aspherical data of the zoom lenses of Examples 2 to 7, respectively. Hereinafter, the meaning of the symbols in the table will be described by taking the example 1 as an example, but the same applies to the examples 2 to 7.

  In the lens data of Table 1, the column of Si indicates the i-th (i = 1, 2, 3,...) Surface number that sequentially increases toward the image side with the surface of the component closest to the object side as the first. The Ri column shows the radius of curvature of the i-th surface, and the Di column shows the surface spacing on the optical axis Z between the i-th surface and the i + 1-th surface. The sign of the radius of curvature is positive when convex on the object side and negative when convex on the image side.

  In the lens data, in the Ndj column, the d-line (wavelength 587...) Of the j-th lens (j = 1, 2, 3,...) That sequentially increases toward the image side with the most object-side lens as the first lens. 6 nm), and the column νdj indicates the Abbe number of the j-th lens with respect to the d-line. The lens data includes the aperture stop St, and the term “aperture stop” is described in the column of the radius of curvature of the surface corresponding to the aperture stop St.

  In the lens data of Table 1, the variable distance, variable 2, and variable 3 are described in the column of the surface interval in which the interval changes at the time of zooming. Variable 1 is the distance between the first lens group G1 and the aperture stop St, Variable 2 is the distance between the aperture stop St and the second lens group G2, and Variable 3 is the surface closest to the image side of the zoom lens and the optical member. This is the distance from PP.

  The zoom data in Table 2 includes the focal length of the entire system at the wide angle end and the telephoto end, and Fno. (F number), the total angle of view, and the values of the surface spacing corresponding to variable 1, variable 2, and variable 3.

In the lens data in Table 1, the surface number of the aspheric surface is marked with *, and the paraxial radius of curvature is shown as the radius of curvature of the aspheric surface. The aspheric data in Table 3 shows the surface number of the aspheric surface and the aspheric coefficient for each aspheric surface. “E + 00” in the numerical values of the aspherical data in Table 3 means “× 10 ⁺⁰ ”, and “E−n” (n: integer) means “× 10 ⁻ⁿ ”. The aspheric coefficient is a value of each coefficient K, Am (m = 3, 4, 5,... 20) in the following aspheric expression.
Zd = C · h ² / {1+ (1−K · C ² · h ² ) ^1/2 } + ΣAm · h ^m
However,
Zd: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface of height h to a plane perpendicular to the optical axis where the aspherical vertex contacts)
h: Height (distance from the optical axis to the lens surface)
C: Reciprocal number K of paraxial radius of curvature, Am: aspheric coefficient (m = 3, 4, 5,... 20)

  Here, as an example, “mm” is used as the unit of length in each table, “degree” is used as the unit of angle, and “mm” is used as the unit of aspherical type Zd, h. However, since the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can also be used.

  The schematic configuration of the zoom lens of Example 1 is as follows. In the zoom lens of Example 1, in order from the object side, the first lens group G1 includes a meniscus negative lens L11 with a convex surface facing the object side, a meniscus negative lens L12 with a convex surface facing the object side, A biconcave negative lens L13, a biconvex positive lens L14, and a meniscus negative lens L15 having a convex surface facing the image side. The second lens group G2 has a paraxial region. Biconvex positive lens L21, biconvex positive lens L22, meniscus positive lens L23 with a convex surface facing the image side, meniscus negative lens L24 with a convex surface facing the object side, biconvex The positive lens L25 has a five-lens configuration and is a single lens in which all the lenses are not cemented, and an aspheric surface is provided on the object side surface and the image side surface of the lens L21.

  The schematic configuration of the zoom lens of Example 2 is the same as that of the zoom lens of Example 1. The schematic configuration of the zoom lenses of the third and fourth embodiments is the same as that of the zoom lens of the first embodiment except that the lens L13 and the lens L14 are cemented together. The schematic configuration of the zoom lens according to the fifth embodiment is the same as that of the zoom lens according to the first embodiment except that the lens L23 has a biconvex shape. The schematic configuration of the zoom lens of Example 6 is that the lens L13 and the lens L14 are cemented, the lens L21 has a meniscus shape with a convex surface facing the object side in the paraxial region, and the lens L23 has a biconvex shape. This is different from the zoom lens of the first embodiment, and the other points are the same as the zoom lens of the first embodiment. The schematic configuration of the zoom lens of Example 7 is that the lens L21 has a meniscus shape with a convex surface facing the object side in the paraxial region, and the lens L23 has a plano-convex shape with a flat surface facing the object side. Unlike the zoom lens of No. 1, the rest is the same as the zoom lens of Embodiment 1.

  Table 22 shows values corresponding to the conditional expressions (1) to (4) of the zoom lenses of Examples 1 to 7. As can be seen from Table 22, all of Examples 1 to 7 satisfy the conditional expressions (1) to (4).

  8A to 8H show aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and chromatic aberration of magnification (chromatic aberration of magnification) at the wide-angle end and the telephoto end of the zoom lens of Example 1. FIGS. Indicates. The upper-stage WIDE is an aberration diagram at the wide-angle end, and the lower-stage TELE is an aberration diagram at the telephoto end. Each aberration diagram shows the aberration with the d-line (wavelength 587.6 nm) as the reference wavelength, but the spherical aberration diagram and the lateral chromatic aberration diagram show the C-line (wavelength 656.3 nm) and g-line (wavelength 436 nm). Aberrations are also shown. Fno. Of spherical aberration diagram. Means F number, and ω in other aberration diagrams means half angle of view.

  Similarly, FIGS. 9 (A) to 9 (H), 10 (A) to 10 (H), 11 (A) to 11 (H), and 12 (A) to 12 (H). FIGS. 13A to 13H and FIGS. 14A to 14H show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the zoom lenses of Examples 2 to 7, respectively. Each aberration diagram of (distortion aberration) and chromatic aberration of magnification (chromatic aberration of magnification) is shown.

  From the above data, the zoom lenses of Examples 1 to 7 have a zoom ratio of about 2.4 times, a small size, and a large aperture ratio with an F value of 1.25 to 1.26 at the wide angle end. In addition, it has a wide field angle of 138 ° to 151 ° at the wide-angle end, each aberration is corrected well, and both the wide-angle end and the telephoto end have high optical performance. I understand that.

  FIG. 15 shows a schematic configuration diagram of a surveillance camera equipped with a zoom lens according to an embodiment of the present invention, as an embodiment of the imaging apparatus of the present invention. The surveillance camera 10 shown in FIG. 15 is mainly composed of a lens device 6 and a camera body 7. The zoom lens 1 is disposed inside the lens device 6. FIG. 15 schematically shows the zoom lens 1 having the first lens group G1, the aperture stop St, and the second lens group G2.

  Inside the camera body 7, an image pickup device 5 that picks up an image of a subject formed by the zoom lens 1 is disposed. Specific examples of the image sensor 5 include a CCD and a CMOS that convert an optical image formed by a zoom lens into an electric signal. The image sensor 5 is arranged such that its image plane coincides with the image plane of the zoom lens 1.

  Above the lens device 6, a diaphragm mechanism 8 for changing the diaphragm diameter of the aperture diaphragm St is provided. Below the lens device 6, a zoom knob 9 for changing the magnification of the zoom lens 1 and a focus knob 11 for adjusting the focus of the zoom lens 1 are provided.

  Since the zoom lens 1 according to the embodiment of the present invention has the above-described advantages, the imaging device of the present embodiment can be configured in a small size, has a wide angle of view, and can obtain a high-quality image.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, the Abbe number, etc. of each lens component are not limited to the values shown in the above numerical examples, but can take other values.

DESCRIPTION OF SYMBOLS 1 Zoom lens 5 Image pick-up element 6 Lens apparatus 7 Camera main body 8 Aperture mechanism 9 Zoom knob 10 Surveillance camera 11 Focus knob G1 1st lens group G2 2nd lens group Sim Image surface St Aperture stop Z Optical axis

Claims (7)

In order from the object side, a first lens group having a negative refractive power, a diaphragm, and a second lens group having a positive refractive power,
The zooming is performed by changing the distance on the optical axis between the first lens group and the second lens group, and the correction of the image plane position accompanying the zooming is moved along the optical axis. Configured to do
A zoom lens that satisfies the following conditional expression (1):
-2.4 <f1 / fw <-2.0 (1)
However,
f1: Focal length of the first lens group fw: focal length of the entire system at the wide angle end   2. The zoom lens according to claim 1, wherein the first lens group has a five-lens configuration in which three negative lenses, a positive lens, and a negative lens are arranged in order from the object side. .   The second lens group has a five-lens configuration in which three positive lenses, a negative lens, and a positive lens are arranged in order from the object side. Zoom lens. The zoom lens according to any one of claims 1 to 3, wherein the following conditional expression (2) is satisfied.
−0.5 <m2w <−0.41 (2)
However,
m2w: lateral magnification of the second lens group at the wide angle end The zoom lens according to any one of claims 1 to 4, wherein the following conditional expression (3) is satisfied.
−0.9 <(r15f−r15r) / (r15f + r15r) <− 0.2 (3)
However,
r15f: radius of curvature of the object side surface of the lens closest to the image side of the first lens group r15r: radius of curvature of the image side surface of the lens closest to the image side of the first lens group The zoom lens according to claim 3, wherein the following conditional expression (4) is satisfied.
νd22> 80 (4)
However,
νd22: Abbe number at the d-line of the second lens from the object side of the second lens group   An imaging apparatus comprising the zoom lens according to claim 1.

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