JP2010107652A - Zoom lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact wide-angle zoom lens suitable for a video camera etc., and having good optical performance. <P>SOLUTION: The zoom lens includes in order from an object side: a first negative lens group G1; a second negative lens group G2; a diaphragm; a third positive lens group G3; and a fourth positive lens group G4. The first lens group G1 includes, closest to the object side, a negative meniscus lens with a convex surface facing the object side. Upon zooming from a wide-angle end to a telephoto end, the first lens group G1 is fixed, and at least the second lens group G2 and the third lens group G3 are moved in the optical axis direction. The zoom lens satisfies a conditional inequality (1). (1): 1.30&lt;¾f1/f2¾&lt;3.0, wherein f1 denotes focal length of the first lens group G1, f2 denotes focal length of the second lens group G2. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a zoom lens and an imaging apparatus, and more particularly to a zoom lens that can be suitably used for a video camera, an electronic still camera, a surveillance camera, and the like, and an imaging apparatus including the zoom lens.

  Conventionally, as a zoom lens used for a consumer video camera or the like, a zoom lens having a high zoom ratio of 10 times or more and an F number of about 1.8 is often used. As a lens type, many 4-group type zoom lenses have been proposed in which a first lens group that is fixed at the time of zooming and has a positive refractive power is disposed closest to the object side.

Examples of other lens types known in the art include those described in Patent Documents 1 and 2, for example. Patent Document 1 describes a three-group type zoom lens in which a first lens group having negative refractive power is disposed closest to the object side. Patent Document 2 describes a four-group type zoom lens in which a first lens group having negative refractive power is disposed closest to the object side.
JP 2006-078581 A JP 2007-156239 A

  However, in recent years, the demands of users have diversified, and apart from the trend of demanding high zoom ratios, there has been an increasing demand for more compactness and wider angle of view than high zoom ratios.

  The four-group type having the positive first lens group described above is easy to ensure a large aperture ratio and can reduce the variation in aperture ratio accompanying zooming, but is not suitable for downsizing or widening the angle. When attempting to widen the angle with this four-group type, the effective diameter of the lens of the first lens group becomes very large, so this type is originally designed with the focal length as close to the telephoto side as possible. There were many. For this reason, in order to photograph a wide angle of view with this type of zoom lens, it is often the case that another lens such as a wide converter must be additionally mounted.

  In the case where the zoom ratio may be small, for example, it is conceivable to employ a three-group type zoom lens having a negative first lens group as described in Patent Document 1 above. This lens type is advantageous for downsizing and widening the angle. However, since the zoom lens described in Patent Document 1 is for a digital still camera, the retractable method is adopted, and the first lens group is moved. In the video camera application, it is not necessary to retract the lens. Rather, the configuration in which the first lens unit moves is unsuitable, and it is preferable to arrange a fixed lens unit or a fixed flat plate on the most object side.

  Patent Document 2 describes a zoom lens having a first lens group that is fixed at the time of zooming. However, the angle of view is as small as about 60 degrees, which does not satisfy the demand for wide angle. Patent Document 2 also describes a zoom lens with a wide angle of view of 77 degrees, but is not suitable for video camera applications because the first lens group is configured to move.

  The present invention has been made in view of the above circumstances, and provides a zoom lens suitable for video cameras and the like and an image pickup apparatus including the zoom lens, which is configured with a small size and a wide angle while maintaining good optical performance. It is intended.

The zoom lens of the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a stop, and a third lens group having a positive refractive power. And a fourth lens group having a positive refractive power. The first lens group has a negative meniscus lens having a convex surface facing the object side closest to the object side, and zooming from the wide-angle end to the telephoto end. In this case, the first lens group is fixed, and at least the second lens group and the third lens group are moved in the optical axis direction to satisfy the following conditional expression (1).
1.30 <| f1 / f2 | <3.0 (1)

  In the present invention, each “lens group” includes not only a plurality of lenses but also a lens group.

  The zoom lens according to the present invention includes, in order from the object side, a lens group having negative, negative, positive, and positive powers. In other words, the object of the three-group type preceding the negative lens group that is advantageous for downsizing and widening the angle. In addition, one negative fixed group is arranged on the side, and a negative meniscus lens having a shape that is advantageous for widening the angle is arranged on the most object side of the first lens group, thereby further widening the angle as well as downsizing. It becomes easy to realize. Further, the zoom lens according to the present invention is configured to satisfy the conditional expression (1), so that it is easy to obtain a wide optical angle by suppressing distortion and to obtain a good optical performance with a small size. .

  In the zoom lens of the present invention, the first lens group may be composed of one negative meniscus lens.

In the zoom lens according to the present invention, it is preferable that the following conditional expression (2) is satisfied.
1.05 <fw / IH <1.65 (2)
However,
fw: focal length of entire system at wide angle end IH: maximum image height

  In the zoom lens of the present invention, the second lens group may be composed of two lenses, a negative lens and a positive lens, in order from the object side.

  In the zoom lens of the present invention, the third lens group may be composed of two positive lenses and one negative lens.

  In the zoom lens of the present invention, the fourth lens group may be composed of one positive lens.

In the zoom lens according to the present invention, it is preferable that the following conditional expression (3) is satisfied.
0.2 <D12min / D2G <1.0 (3)
However,
D12min: minimum distance on the optical axis between the first lens group and the second lens group in zooming from the wide-angle end to the telephoto end D2G: light from the most object-side surface to the most image-side surface of the second lens group Axis distance

In the zoom lens of the present invention, the second lens group may be configured to include one positive lens. In that case, it is preferable that the following conditional expression (4) is satisfied.
ν2p <23.0 (4)
However,
ν2p: Abbe number at the d-line of the positive lens in the second lens group

In the zoom lens of the present invention, it is preferable that the following conditional expression (5) is satisfied when the second lens group includes one positive lens.
N2p> 1.85 (5)
However,
N2p: Refractive index at the d-line of the positive lens in the second lens group

  In the zoom lens of the present invention, the third lens group may be composed of three lenses in order from the object side: a positive lens, a negative lens, and a positive lens. At this time, it is preferable that the most image-side positive lens in the third lens group has at least one aspheric surface.

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

  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 negative first lens group, the negative second lens group, the positive third lens group, and the positive fourth lens group, the first lens group is a fixed group, A zoom lens suitable for a video camera or the like that is configured to satisfy the conditional expression (1) by suitably setting the configuration of the first lens group and is configured to be small and wide-angle while maintaining good optical performance. And an imaging device provided with the zoom lens can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a zoom lens according to an embodiment of the present invention, and corresponds to a zoom lens of Example 1 described later. FIGS. 2 to 6 are cross-sectional views each showing a configuration of a zoom lens of Examples 2 to 6 described later. Since the basic configuration of the zoom lens shown in FIGS. 1 to 6 is the same and the method of illustration is also the same, the following description will be mainly made with reference to FIG. 1 as an example.

  The zoom lens according to the embodiment of the present invention includes a first lens group G1 having a negative refractive power, a second lens group G2 having a negative refractive power, and an aperture in order from the object side along the optical axis Z. A stop St, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power are provided.

  In this zoom lens, when zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed, and at least the second lens group G2 and the third lens group G3 move in the optical axis Z direction. It is comprised so that it may carry out by doing.

  In FIG. 1, the left side is the object side, the right side is the image side, the upper stage shows the lens arrangement at infinity focusing at the wide angle end, the lower stage shows the lens arrangement at infinity focusing at the telephoto end, and the wide angle end. Schematic movement trajectories of the lens groups when zooming from the telephoto end to the telephoto end are indicated by arrows. 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 image plane is shown as Sim. For example, when this zoom lens is applied to an image pickup apparatus, the zoom lens is arranged so that the image pickup surface of the image pickup element is positioned on the image plane Sim.

  When applying a zoom lens to an imaging device, depending on the configuration of the camera side on which the lens is mounted, a cover glass, prism, infrared cut filter, low-pass filter, etc. are provided between the lens closest to the image side and the imaging surface. Various filters and the like are preferably arranged, and FIG. 1 shows an example in which a parallel plate-shaped optical member PP assuming these is arranged between the lens group closest to the image side and the image plane Sim.

  The zoom lens according to the present embodiment includes first, second, third, and fourth lens groups G1, G2, G3, and G4 having negative, negative, positive, and positive powers in order from the object side. When only the second, third, and fourth lens groups G2, G3, and G4 of the present embodiment are viewed, the power arrangement is the same as that of the three-group type zoom lens described in Patent Document 1.

  Originally, the zoom lens of the three-group type preceding the negative lens group as described in Patent Document 1 has an advantage that it can be configured very compactly and can be easily widened, but the lens group closest to the object moves. However, it was not preferable for a video camera. Therefore, in the present embodiment, a configuration in which the first lens group G1 fixed at the time of zooming is additionally provided to the three-group type zoom lens is employed.

  By disposing the first lens group G1, which is a fixed group, on the most object side, the size of the lens system is slightly increased, but a video camera suitable for photographing a person in a room can be realized. Further, by adding the first lens group G1 to the three-group type, the aberration correction effect at the wide-angle end is improved and it is advantageous for widening the angle and increasing the zoom ratio compared to the three-group type.

  For example, the zoom lens described in Patent Document 1 has an angle of view of about 60 degrees and a magnification of about 3 times, but the first lens group G1 of the present embodiment has about 70 to 85 as shown in Examples described later. A magnification of about 5 times can be realized at a field angle of degrees. As described above, the first lens group G1 can realize a wide angle of view that has been difficult to realize with the above-described four-group type that precedes the positive lens group that has been proposed in the past.

  The first lens group G1 of the zoom lens according to the present embodiment is configured to have a negative meniscus lens having a convex surface facing the object side closest to the object side. Arranging the negative meniscus lens having such a shape closest to the object side is advantageous for widening the angle.

  Specifically, for example, the zoom lens of the present embodiment can take a configuration as shown in FIG. That is, the first lens group G1 can have a single lens configuration of a negative lens L11 of a meniscus lens having a convex surface facing the object side. The first lens group G1 having a single lens structure is advantageous for downsizing.

  For example, the second lens group G2 may have a two-lens configuration including a negative lens L21 and a positive lens L22 in order from the object side.

  The third lens group G3 can be configured to include, for example, two positive lenses and one negative lens. More specifically, the third lens group G3 may be configured to include three lenses of a positive lens L31, a negative lens L32, and a positive lens L33 in order from the object side. In this case, it is preferable that the most image-side positive lens L33 has at least one aspheric surface. Since the third lens group G3 has an aspheric lens, spherical aberration can be favorably corrected in the entire zoom range.

  The fourth lens group G4 can be configured to include, for example, one positive lens L41.

The zoom lens according to the present embodiment is configured to satisfy the following conditional expression (1).
1.30 <| f1 / f2 | <3.0 (1)
However,
f1: Focal length of the first lens group G1 f2: Focal length of the second lens group G2

  Conditional expression (1) defines the ratio of the focal length of the first lens group G1 and the focal length of the second lens group G2, and is a condition for realizing a wide angle while preventing an increase in distortion. . If the lower limit of conditional expression (1) is not reached, the power of the first lens group G1 becomes strong, and it becomes difficult to correct distortion. Alternatively, the power of the second lens group G2 becomes weak and it is difficult to widen the angle. If the upper limit of conditional expression (1) is exceeded, the power of the first lens group G1 becomes weak, and the front lens diameter (the diameter of the lens closest to the object side) increases. If the power of the first lens group G1 is too weak, the aberration correction effect is reduced, and compared with the conventional three-group type zoom lens that does not have the first lens group G1 of the present embodiment, The role of promoting widening is reduced. Alternatively, since the power of the second lens group G2 is increased, the allowable amount of manufacturing error and assembly error is reduced, which is not preferable.

In addition to the above-described configuration, the zoom lens according to the present embodiment is preferably configured to satisfy the following conditional expression, whereby even better characteristics can be obtained. In addition, as a preferable aspect, any one of the following conditional expressions may be satisfied, or any combination may be satisfied.
1.05 <fw / IH <1.65 (2)
0.2 <D12min / D2G <1.0 (3)
ν2p <23.0 (4)
N2p> 1.85 (5)
However,
fw: focal length of the entire system at the wide angle end IH: maximum image height D12 min: minimum distance D2G on the optical axis Z between the first lens group G1 and the second lens group G2 in zooming from the wide angle end to the telephoto end: Distance ν2p on the optical axis Z from the most object side surface to the most image side surface of the two lens group G2: When the second lens group G2 includes one positive lens, the Abbe number of the positive lens at the d-line N2p: When the second lens group G2 includes one positive lens, the refractive index of the positive lens at the d-line

  Conditional expression (2) defines the ratio between the focal length of the entire system at the wide-angle end and the maximum image height. If the lower limit of conditional expression (2) is not reached, the front lens diameter will increase. In addition, it becomes difficult to correct lateral chromatic aberration at the wide-angle end. If the upper limit of conditional expression (2) is exceeded, the total length of the lens system becomes long and the lens system becomes large. At this time, the second lens group G2 is more likely to approach the image side at the wide-angle end, and the second lens group G2 is more likely to be closer to the object side at the telephoto end, resulting in an increase in the front lens diameter.

  Conditional expression (3) indicates that the minimum distance on the optical axis Z between the first lens group G1 and the second lens group G2 and the optical axis Z from the most object side surface to the most image side surface of the second lens group G2. The ratio of the distance is specified. If the lower limit of conditional expression (3) is not reached, the holding members of the first lens group G1 and the second lens group G2 may interfere with each other, which is not preferable. When the upper limit of conditional expression (3) is exceeded, the total length of the lens system becomes long and the front lens diameter increases.

  Conditional expression (4) defines a preferable range of the Abbe number of the positive lens when the second lens group G2 includes a positive lens. By satisfying this conditional expression, it becomes easy to satisfactorily correct chromatic aberration even when the second lens group G2 includes only one positive lens. Selecting a material with a larger Abbe number that exceeds the upper limit of conditional expression (4) reduces the effect of correcting chromatic aberration in the second lens group G2, and achieves the magnification and high performance required for video cameras and the like. It becomes difficult to do.

  Conditional expression (5) defines a preferable range of the refractive index of the positive lens when the second lens group G2 includes a positive lens. If the lower limit of conditional expression (5) is not reached, it will be difficult to suppress fluctuations in coma during zooming. In general, since an optical material with a high refractive index has a small Abbe number, satisfying conditional expression (5) can provide the effect of correcting chromatic aberration as in the case of satisfying conditional expression (4).

It is more preferable that the zoom lens of the present embodiment further satisfies the following conditional expressions (1-1), (2-1), (3-1), (4-1), and (5-1). Conditional expressions (1-1), (2-1), (2-1), (3-1), (4-1), (5-1) are satisfied to satisfy conditional expressions (1), (2), (3). , (4) and (5), the effects obtained by satisfying each can be further enhanced.
1.30 <| f1 / f2 | <2.8 (1-1)
1.10 <fw / IH <1.6 (2-1)
0.3 <D12min / D2G <0.9 (3-1)
ν2p <21.0 (4-1)
N2p> 1.90 (5-1)

  In addition, 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 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, and the like, and further, a material that is hard and difficult to break. From the above, as the material arranged closest to the object side, specifically, glass is preferably used, or transparent ceramics may be used.

  It is preferable to use plastic as the material of the lens on which the aspherical shape is formed. In this case, the aspherical shape can be manufactured with high accuracy, and the weight and cost can be reduced. Become.

  When the zoom lens is required to be usable in a wide temperature range, it is preferable to use a material having a small linear expansion coefficient as the material of each lens. In addition, 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 a low-pass filter, various filters that cut a specific wavelength range, or the like, 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.

  As described above, according to the zoom lens of the present embodiment, according to the required specifications and the like, by appropriately adopting the preferred configuration described above, it can be configured compactly without significantly increasing the number of lenses, It is possible to achieve both good aberration correction and cost reduction.

  Next, numerical examples of the zoom lens according to the present invention will be described. The lens cross-sectional views of the zoom lenses of Examples 1 to 6 are those shown in FIGS.

  Table 1 shows basic lens data of the zoom lens according to Example 1, Table 2 shows data relating to zooming (magnification), and Table 3 shows aspherical data. Similarly, basic data, zoom-related data, and aspherical data of the zoom lenses according to Examples 2 to 6 are shown in Tables 4 to 18. In the following, the meaning of the symbols in the table will be described mainly using Example 1 as an example, but the same applies to Examples 2 to 6.

  In the basic lens data of Table 1, Si indicates the i-th (i = 1, 2, 3,...) Surface number that increases sequentially toward the image side with the most object-side component surface being first. Indicates the radius of curvature of the i-th surface, and Di indicates the surface interval on the optical axis Z between the i-th surface and the i + 1-th surface. The bottom column of the surface interval indicates the surface interval between the final surface in the table and the image surface Sim. In the basic lens data, Ndj is the d-line (wavelength: 587.6 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases toward the image side with the most object-side lens as the first lens. ), And νdj represents the Abbe number of the j-th optical element with respect to the d-line. The basic lens data includes the aperture stop St and the optical member PP. In the column of the radius of curvature of the surface corresponding to the aperture stop St, (aperture stop) is described. The sign of the radius of curvature of the basic lens data is positive when convex on the object side and negative when convex on the image side.

  In the zoom lens of Example 1, the second lens group G2, the third lens group G3, and the fourth lens group G4 move during zooming.

  In the basic lens data in Table 1, the interval changes at the time of zooming, the interval between the first lens group G1 and the second lens group G2, the interval between the second lens group G2 and the aperture stop St, the third lens group G3 and the fourth lens group. In the column of the distance between the lens groups G4 and the surface distance corresponding to the distance between the fourth lens group G4 and the optical member PP, D2 (variable), D6 (variable), D12 (variable), and D14 (variable) are described. ing.

  In the zoom lenses of Examples 2 and 4-6, as in Example 1, the second lens group G2, the third lens group G3, and the fourth lens group G4 move during zooming. In the zoom lens No. 3, the second lens group G2 and the third lens group G3 move during zooming. Therefore, in the table of Example 3, the surface intervals at which the interval changes upon zooming are D2 (variable), D6 (variable), and D12 (variable).

  The zoom-related data in Table 2 includes the focal length f of the entire system at the wide-angle end and the telephoto end, the F number Fno. , The total field angle 2ω, and the values of the surface spacings D2, D6, D12, and D14 that change with zooming. The unit of the total angle of view 2ω is degrees.

  As the unit of Ri and Di in Table 1 and the units of f, D2, D6, D12, and D14 in Table 2, “mm” can be used. Since the performance can be obtained, the unit is not limited to “mm”, and other appropriate units can be used.

In the basic 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 aspherical data in Table 3 shows the sign of a lens that is an aspherical lens, the surface number of the aspherical surface, and the aspherical coefficients related to these aspherical surfaces. The aspheric coefficient is a value of each coefficient KA, RA _m (m = 3, 4, 5,... 10) in the aspheric expression expressed by the following expression (A).

Zd = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣRA _m · h ^m (A)
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 of paraxial radius of curvature KA, RA _m : aspheric coefficient (m = 3, 4, 5,... 10)
In addition, when mm is used as the unit of Ri and Di in Table 1, the unit of Zd and h is also mm.

  Table 19 shows values corresponding to the conditional expressions (1) to (5) in Examples 1 to 6. As can be seen from Table 19, all of Examples 1 to 6 satisfy the conditional expressions (1) to (5).

  7A to 7H show respective aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide-angle end and the telephoto end of the zoom lens of Example 1. FIG. Each aberration diagram shows the aberration with the d-line (wavelength 587.6 nm) as the reference wavelength, while the spherical aberration diagram and the magnification chromatic aberration diagram also show the aberrations for the wavelength 460.0 nm and the wavelength 615.0 nm. Fno. Of spherical aberration diagram. Means F number, and ω in other aberration diagrams means half angle of view.

  Similarly, FIG. 8 (A) to FIG. 8 (H), FIG. 9 (A) to FIG. 9 (H), FIG. 10 (A) to FIG. 10 (H), FIG. 11 (A) to FIG. FIGS. 12A to 12H are graphs showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide-angle end and the telephoto end of the zoom lenses of Examples 2 to 6, respectively. Show.

  From the above data, the zoom lenses of Examples 1 to 6 have a magnification of about 5 times, and the entire angle of view at the wide-angle end is 70 to 85 degrees and a wide angle while achieving a reduction in size. It can be seen that the F-number is as small as about 2.5, each aberration is corrected well, and both the wide-angle end and the telephoto end have high optical performance in the visible range. These zoom lenses can be suitably used for imaging devices such as surveillance cameras, video cameras, and electronic still cameras.

  FIG. 11 is a configuration diagram of a video camera 10 configured using the zoom lens 1 according to the embodiment of the present invention as an example of the imaging device of the embodiment of the present invention. In FIG. 11, the negative first lens group G1, the negative second lens group G2, the aperture stop St, the positive third lens group G3, and the positive fourth lens group G4 included in the zoom lens 1 are schematically illustrated. Show.

  The video camera 10 includes a zoom lens 1, a filter 2 having functions such as a low-pass filter and an infrared cut filter disposed on the image side of the zoom lens 1, an image pickup device 4 disposed on the image side of the filter 2, and a signal. And a processing circuit 5. The image sensor 4 converts an optical image formed by the zoom lens 1 into an electrical signal, and for example, a CCD (Charge Coupled Device) can be used. The image sensor 4 is arranged such that its image plane coincides with the image plane of the zoom lens 1. After the output signal from the image sensor 4 is processed by the signal processing circuit 5, an image is displayed on the display device 6.

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

  When a conventional three-group zoom lens is used as a retractable digital still camera, the lens group is moved by a cam so that it can be stored compactly when not in use. If this mechanism is used as it is, the noise during zooming will increase. In an apparatus for a video camera, the lens group is preferably moved electronically along the guide bar, which can reduce noise.

  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.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Zoom lens 2 Filter 4 Image pick-up element 5 Signal processing circuit 6 Display apparatus 10 Video camera G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group PP Optical member St Aperture stop Sim Image plane Z Optical axis

Claims (12)

In order from the object side, the first lens group having a negative refractive power, the second lens group having a negative refractive power, a stop, a third lens group having a positive refractive power, and a positive refractive power A fourth lens group,
The first lens group includes a negative meniscus lens having a convex surface facing the object side closest to the object side,
During zooming from the wide-angle end to the telephoto end, the first lens group is fixed and at least the second lens group and the third lens group are moved in the optical axis direction.
A zoom lens that satisfies the following conditional expression (1):
1.30 <| f1 / f2 | <3.0 (1)
However,
f1: Focal length of the first lens group f2: Focal length of the second lens group   2. The zoom lens according to claim 1, wherein the first lens group includes one of the negative meniscus lenses. The zoom lens according to claim 1, wherein the following conditional expression (2) is satisfied.
1.05 <fw / IH <1.65 (2)
However,
fw: focal length of entire system at wide angle end IH: maximum image height   4. The zoom lens according to claim 1, wherein the second lens group includes a negative lens and a positive lens in order from the object side. 5.   5. The zoom lens according to claim 1, wherein the third lens group includes two positive lenses and one negative lens. 6.   The zoom lens according to any one of claims 1 to 5, wherein the fourth lens group includes a single positive lens. The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied.
0.2 <D12min / D2G <1.0 (3)
However,
D12min: minimum distance on the optical axis between the first lens group and the second lens group in zooming from the wide-angle end to the telephoto end D2G: surface closest to the image side from the most object side surface of the second lens group Distance on the optical axis to The zoom lens according to claim 1, wherein the second lens group includes one positive lens and satisfies the following conditional expression (4).
ν2p <23.0 (4)
However,
ν2p: Abbe number at the d-line of the positive lens of the second lens group 9. The zoom lens according to claim 1, wherein the second lens group includes one positive lens and satisfies the following conditional expression (5).
N2p> 1.85 (5)
However,
N2p: Refractive index at the d-line of the positive lens of the second lens group   10. The zoom lens according to claim 1, wherein the third lens group includes a positive lens, a negative lens, and a positive lens in order from the object side.   The zoom lens according to claim 10, wherein the positive lens closest to the image side of the third lens group has at least one aspheric surface.   An imaging apparatus comprising the zoom lens according to claim 1.

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