JP4870527B2 - Zoom lens system, imaging device and camera - Google Patents

Description

  The present invention relates to a zoom lens system, an imaging device, and a camera. In particular, the present invention provides a zoom lens system having a high ability to correct curvature of field and a short optical total length when not in use, an imaging device using the zoom lens system, and the imaging device, as well as high resolution. It relates to the camera provided.

  2. Description of the Related Art Conventionally, many optical devices that form an image of a subject on an image sensor via a lens and capture the image as an image have been developed. Recently, products such as digital still cameras and digital video cameras have become widespread, and as the number of users increases, the demand for these products has also increased. Among various product forms, an optical device having a zoom ratio of about 3 times is relatively small and has an optical zoom function, and is particularly popular as a digital camera classified into a compact type and a stylish type.

  The compact digital camera is required to be further miniaturized in order to facilitate carrying. In order to achieve further miniaturization of digital cameras, the overall optical length when not in use (distance from the apex of the lens surface closest to the object side to the image plane in the entire lens system) is shortened, and the main body is used with a multistage barrel when in use. It is necessary to have a lens arrangement that can store the lens element that protrudes before the main body.

  By the way, as a zoom lens system suitable for a compact digital still camera, for example, in order from the object side to the image side, a negative power first lens group, a positive power second lens group, and a positive power third lens are used. Many zoom lens systems having a three-group configuration in which a lens group is arranged have been proposed.

  In the zoom lens system having the three-group structure as described above, the air space between the first lens group and the second lens group monotonously decreases during zooming from the wide-angle end to the telephoto end. And the third lens group is configured to be fixed or moved.

  Focus adjustment in a zoom lens system having a three-group configuration is performed by moving the first lens group or the third lens group in the optical axis direction. In particular, in order to reduce the size of the entire optical apparatus, focus adjustment is often performed with a lightweight third lens group, and the focus is adjusted on a subject at an infinite distance to a short distance. On the other hand, when focus adjustment is performed using the first lens group, the first lens group is larger than the third lens group, so a large motor is required, and the entire optical apparatus tends to be large.

  The third lens group having positive power normally corrects the curvature of field and makes the incident light on the imaging surface telecentric. The third lens group is often composed of one or two lens elements having a small outer diameter, and can be driven at high speed using a small motor. Therefore, when the third lens group is a lens group for focus adjustment, it is possible to provide an optical device that is small and capable of focusing in a short time.

  Both the first lens group and the second lens group move in parallel along the optical axis along a cam groove cut in the cylindrical cam. The cam groove is connected to the zooming groove and the non-use groove, and the non-use groove has a configuration in which the distance between the lens groups is reduced and all three lens groups are moved toward the image sensor. By taking it, it becomes possible to shorten the optical total length when not in use. In this case, if the thickness of each lens group is small, the optical total length when not in use can be further shortened.

  As described above, conventionally, the zoom lens system is configured as described above, and a device for engaging in the focus adjustment and the entire lens system when not in use are designed to be small, and the total optical length of the digital still camera is shortened.

  For example, Patent Document 1 discloses, in order from the object side to the image side, a negative power first lens group composed of a negative power lens and a positive power lens having an aspherical surface, a positive power second lens group, and a positive power lens. A three-group zoom lens comprising a power third lens group is disclosed. In such a three-group zoom lens, by increasing the refractive index of the negative power lens closest to the object side in the first lens group, while correcting the curvature of field at the wide-angle end, the lens thickness at the peripheral portion is suppressed to be small. The entire lens group is thinned to reduce the size of the optical system.

Further, for example, Patent Document 2 includes, in order from the object side to the image side, a negative power first lens group, a positive power second lens group having a stop, and a positive power third lens group. When zooming, the first lens group moves so as to be relatively close to the second lens group, the second lens group monotonously moves to the object side, and the third lens group moves to the object side and then reverses. When the object distance is infinity, a three-unit zoom lens is disclosed in which the position at the wide angle end is closer to the object side than the position at the telephoto end. In such a three-group zoom lens, the focal length condition of the first lens group is defined so that correction of curvature of field and downsizing of the optical system are compatible.
JP 2005-134746 A Japanese Patent Laid-Open No. 2005-084597

  However, in the configuration of the three-group zoom lens disclosed in Patent Document 1, since the positive power lens on the image side of the first lens group has a low refractive index and is a spherical lens, correction of field curvature is insufficient. There is a problem that.

  In the configuration of the three-group zoom lens disclosed in Patent Document 2, the focal length of the first lens group is set to be short in order to reduce the size. However, in this case, although the radial direction of the lens can be made relatively small, if the first lens group is composed of two lenses, the power of the object side lens is increased, and the thickness of the image side lens is also increased in order to correct chromatic aberration. It gets bigger. As a result, there is a problem that the total optical length when not in use is increased.

  The present invention has been made to solve the above-described problems in the background art, and has a high resolution, a high ability to correct curvature of field, and a short optical total length when not in use. An object of the present invention is to provide an imaging apparatus using the zoom lens system and a camera including the imaging apparatus.

The object is achieved by the following zoom lens system. That is, the zoom lens system of the present invention is a zoom lens system for forming an optical image of an object so as to be variable,
In order from the object side to the image side consists of a first lens unit having a negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
The following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
(here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: maximum image height )
It is characterized by satisfying.

The object is achieved by the following imaging device. That is, the imaging device of the present invention is an imaging device capable of converting an optical image of a subject into an electrical image signal and outputting it,
A zoom lens system for forming an optical image of the subject so as to be variable, and
An image sensor that converts an optical image of a subject formed by the zoom lens system into an electrical image signal;
Wherein the zoom lens system consists of from the object side is the object side to the image side in this order, a first lens group having negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
The following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
(here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: maximum image height )
It is characterized by satisfying.

Furthermore, the object is achieved by the following camera. That is, the camera of the present invention is a camera that can shoot a subject and output it as an electrical image signal,
An imaging apparatus comprising: a zoom lens system that forms an optical image of the subject so as to be variable in magnification; and an imaging device that converts an optical image of the subject formed by the zoom lens system into an electrical image signal. Prepared,
Wherein the zoom lens system consists of from the object side is the object side to the image side in this order, a first lens group having negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
The following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
(here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: maximum image height )
It is characterized by satisfying.

  According to the present invention, the zoom lens system and the zoom lens system have a high resolution as well as a good correction of curvature of field, a small thickness of the first lens unit, and a short optical total length when not in use. An imaging apparatus using the can be provided. Furthermore, according to the present invention, it is possible to provide a small and high-performance camera equipped with such an imaging device.

(Embodiments 1 to 4)
FIG. 1 is a configuration diagram of a zoom lens system according to the first embodiment. FIG. 3 is a configuration diagram of a zoom lens system according to the second embodiment. FIG. 5 is a configuration diagram of a zoom lens system according to Embodiment 3. FIG. 7 is a configuration diagram of a zoom lens system according to Embodiment 4. Each figure shows a zoom lens system in an infinite focus state. In each figure, (a) is a lens configuration at the wide-angle end (shortest focal length state: focal length f _W ), and (b) is a substantially intermediate position (intermediate focal length state: focal length f _M = √ (f _W * f). _T )) and (c) represent the telephoto end (longest focal length state: focal length f _T ), respectively.

  In each of the zoom lens systems according to Embodiments 1 to 4, in order from the object side to the image side, the negative lens first lens group G1, the aperture A, the positive power second lens group G2, and the positive power The third lens group G3. In the zoom lens systems according to Embodiments 1 to 4, during zooming from the wide-angle end to the telephoto end, the first lens group G1 moves along a locus convex toward the image side, and the second lens group G2 and the aperture stop A The first lens unit G3 is moved monotonously, and the third lens group G3 is moved by changing the distance from the second lens group G2. In other words, in the zoom lens systems according to Embodiments 1 to 4, the distance between the first lens group G1 and the second lens group G2 is reduced during zooming from the wide-angle end to the telephoto end, and the second lens group G2 and the second lens group G2. Each lens group is moved along the optical axis so that the distance from the three lens groups G3 changes. In each figure, the straight line described on the rightmost side in the figure represents the position of the image plane S, and a parallel plate P equivalent to an optical low-pass filter, a face plate of an image sensor, or the like is provided on the object side. Yes.

  As shown in FIG. 1, in the zoom lens system according to Embodiment 1, the first lens group G1 includes a negative meniscus object-side negative lens element having a convex surface directed toward the object side in order from the object side to the image side. L1 and a positive meniscus image side positive lens element L2 having a convex surface facing the object side. Each of the object-side negative lens element L1 and the image-side positive lens element L2 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 1, the second lens group G2 includes, in order from the object side to the image side, a positive meniscus third lens element L3 with a convex surface facing the object side, and a convex surface facing the object side. Negative meniscus fourth lens element L4, negative meniscus fifth lens element L5 having a convex surface facing the object side, and biconvex sixth lens element L6. Among these, the third lens element L3 and the fourth lens element L4 are positively cemented lens elements joined together, and the fifth lens element L5 and the sixth lens element L6 are positively joined lens elements joined together. is there. The third lens element L3 that is the most object side lens element of the second lens group G2 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 1, the third lens unit G3 comprises solely a positive meniscus seventh lens element L7 with the convex surface facing the image side. The seventh lens element L7 has an aspheric image side surface.

  As shown in Table 13 later, the zoom lens system according to Embodiment 1 has a particularly high refractive index of the image-side positive lens element L2 constituting the first lens group G1, and a light ray height at the object-side negative lens element L1. The thickness of the high portion can be easily secured and the lens thickness can be reduced. Therefore, the zoom lens system according to Embodiment 1 has a short optical total length when not in use.

  As shown in FIG. 3, in the zoom lens system according to Embodiment 2, the first lens group G1 includes a negative meniscus object-side negative lens element having a convex surface directed toward the object side in order from the object side to the image side. L1 and a positive meniscus image side positive lens element L2 having a convex surface facing the object side. Each of the object-side negative lens element L1 and the image-side positive lens element L2 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 2, the second lens group G2 includes, in order from the object side to the image side, a positive meniscus third lens element L3 with a convex surface facing the object side, and a convex surface facing the object side. Is formed of a positive meniscus fourth lens element L4 with a convex surface, a negative meniscus fifth lens element L5 with a convex surface facing the object side, and a biconvex sixth lens element L6. Among these, the fourth lens element L4 and the fifth lens element L5 are cemented lens elements that are cemented with each other. The third lens element L3 that is the most object side lens element of the second lens group G2 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 2, the third lens unit G3 comprises solely a bi-convex seventh lens element L7. The seventh lens element L7 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 2, as shown later in Table 13, the refractive index of the image-side positive lens element L2 constituting the first lens group G1 is relatively high, and even if the lens center thickness is reduced, the zoom lens system is not covered. It is relatively easy to ensure the thickness, and the lens thickness can be reduced. Therefore, the zoom lens system according to Embodiment 2 has a short optical total length when not in use.

  As shown in FIG. 5, in the zoom lens system according to Embodiment 3, the first lens unit G1 includes, in order from the object side to the image side, a biconcave object-side negative lens element L1, and a convex surface on the object side. And a positive meniscus image-side positive lens element L2 facing the lens. Each of the object-side negative lens element L1 and the image-side positive lens element L2 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 3, the second lens unit G2 includes, in order from the object side to the image side, a positive meniscus third lens element L3 with a convex surface facing the object side, and a convex surface facing the object side. Negative meniscus fourth lens element L4, negative meniscus fifth lens element L5 having a convex surface facing the object side, and biconvex sixth lens element L6. Among these, the third lens element L3 and the fourth lens element L4 are positively cemented lens elements joined together, and the fifth lens element L5 and the sixth lens element L6 are positively joined lens elements joined together. is there. The third lens element L3 that is the most object side lens element of the second lens group G2 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 3, the third lens unit G3 comprises solely a positive meniscus seventh lens element L7 with the convex surface facing the image side. The seventh lens element L7 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 3, as shown later in Table 13, the refractive index of the object-side negative lens element L1 constituting the first lens group G1 is low, and the thickness of the portion where the light beam height is high is reduced. Yes. However, since the refractive index of the image side positive lens element L2 of the first lens group G1 is relatively high and the image side has an aspherical surface, the light ray height of the object side negative lens element L1 is high. Even if the thickness is small and correction of distortion and curvature of field on the wide-angle end side is insufficient, the correction effect of the image side positive lens element L2 causes the entire zoom lens system according to Embodiment 3 to perform the image side positive lens element L2. Thus, it is possible to sufficiently correct distortion and curvature of field on the wide-angle end side.

  As shown in FIG. 7, in the zoom lens system according to Embodiment 4, the first lens group G1 includes a negative meniscus object-side negative lens element having a convex surface directed toward the object side in order from the object side to the image side. L1 and a positive meniscus image side positive lens element L2 having a convex surface facing the object side. Each of the object-side negative lens element L1 and the image-side positive lens element L2 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 4, the second lens group G2 includes, in order from the object side to the image side, a biconvex third lens element L3, a biconcave fourth lens element L4, A negative meniscus fifth lens element L5 having a convex surface facing the object side and a biconvex sixth lens element L6. Among these, the third lens element L3 and the fourth lens element L4 are positively cemented lens elements joined together, and the fifth lens element L5 and the sixth lens element L6 are positively joined lens elements joined together. is there. The third lens element L3 that is the most object side lens element of the second lens group G2 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 4, the third lens unit G3 comprises solely a bi-convex seventh lens element L7. The seventh lens element L7 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 4, the two lens elements L1 and L2 constituting the first lens group G1 are brought into contact with each other in the vicinity where the light beam from the object passes, so that the entire thickness of the first lens group G1 is reached. Can be reduced. Even if the object-side negative lens element L1 and the image-side positive lens element L2 of the first lens group G1 approach each other and the ability to correct distortion is reduced, the image-side positive lens element L2 is later shown in Table 13. In addition, since the lens element has a relatively high refractive index and an aspheric surface on the image side, the entire zoom lens system according to Embodiment 4 can satisfactorily correct distortion at the wide-angle end.

  As described above, the zoom lens systems according to Embodiments 1 to 4 can reduce the size of the entire lens system while maintaining excellent optical performance by arranging each lens group G1 to G3 in a desired power arrangement. ing.

  In particular, in the zoom lens systems according to Embodiments 1 to 4, the first lens group G1 is composed of one object-side negative lens element and one image-side positive lens element with a convex surface facing the object side. The second lens group G2 is composed of two positive cemented lens elements each composed of two lens elements cemented, or one pair of cemented lens elements is sandwiched between one positive lens element from the object side and the image side. The third lens group G3 is composed of a single lens element. Thus, the zoom lens systems according to Embodiments 1 to 4 are lens systems in which the number of lens elements constituting each lens group is small, and the optical total length when not in use is short.

  In the zoom lens systems according to Embodiments 1 to 4, as described above, the second lens group G2 is composed of two pairs of positive cemented lens elements, or one pair of cemented lens elements is arranged on the object side and the image side. However, in addition to this, for example, it may be composed of a pair of positive cemented lens elements and one positive lens element in order from the object side to the image side. After all, a lens system having a short optical total length when not in use can be obtained.

  Further, in the zoom lens systems according to Embodiments 1 to 4, each of the two object-side negative lens elements and image-side positive lens elements constituting the first lens group G1 has an aspheric surface, and is on the image side. The positive lens element has a specific refractive index and Abbe number. Therefore, the zoom lens systems according to Embodiments 1 to 4 are particularly excellent in optical performance such as a field curvature correction capability.

  Hereinafter, as in the zoom lens systems according to Embodiments 1 to 4, for example, in order from the object side to the image side, the first lens group having the negative power, the second lens group having the positive power, and the third lens having the positive power. The first lens group is composed of one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side, and constitutes the first lens group. The conditions that should be satisfied by a zoom lens system in which these two lens elements each have an aspherical surface will be described. In the zoom lens system according to each embodiment, a plurality of conditions to be satisfied are defined, but the configuration of the zoom lens system that satisfies all the conditions is most desirable. However, by satisfying individual conditions, it is possible to obtain a zoom lens system that exhibits corresponding effects.

For example, a zoom lens system such as the zoom lens systems according to Embodiments 1 to 4 satisfies the following conditions (1) and (2).
n12> 1.95 (1)
ν12 < 24 (2)
here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens unit.

  The conditions (1) and (2) are conditions that define the refractive index and Abbe number of the image-side positive lens element constituting the first lens group. Satisfying these conditions (1) and (2) reduces the center thickness of the image-side positive lens element, and further suppresses curvature of field at the wide-angle end without increasing the curvature, particularly the curvature of the image side surface. In addition, since it is easy to secure the edge thickness, the thickness of the first lens group can be reduced. Therefore, the thickness of the entire zoom lens system is also reduced, and the total optical length when not in use can be shortened.

In particular, when the following condition (1) is satisfied, the Z value (difference between the curvature of the object side surface and the curvature of the image side surface) of the image side positive lens element of the first lens group can be increased, and the lens The centering becomes even easier. Further, when the following condition (2) is satisfied, chromatic aberration generated in the first lens group can be corrected more satisfactorily .

For example, a zoom lens system like the zoom lens systems according to Embodiments 1 to 4 preferably satisfies the following conditions (3), (4), (5), and (6).
n11> 1.50 (3)
ν11> 35 (4)
n12-n11> 0.10 (5)
ν11−ν12> 15.0 (6)
here,
n11: Refractive index of the object side negative lens element of the first lens group,
ν11: Abbe number of the object side negative lens element of the first lens unit,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens unit.

  The conditions (3) and (4) are conditions that define the refractive index and Abbe number of the object-side negative lens element constituting the first lens group. Conditions (5) and (6) are a zoom lens system in which the first lens group is a negative lead having negative power, and the first lens group includes an object-side negative lens element and an image-side positive lens element. This is a condition for satisfactorily correcting the chromatic aberration. By satisfying these conditions (3), (4), (5) and (6), the thickness in the optical axis direction of the lens element increases as the light beam height increases, and the center thickness is increased in order to further improve the manufacturability. Increasing the value eliminates the risk of further increasing the thickness of the entire first lens group and corrects chromatic aberration satisfactorily.

In addition, the above effect can be further achieved by satisfying at least one of the following conditions (3) ′, (4) ′, (5) ′, and (6) ′. Further, by satisfying at least one of the following conditions (4) ″ and (6) ″, chromatic aberration generated in the first lens group can be corrected more satisfactorily.
n11> 1.75 (3) ′
ν11> 38 (4) ′
65> ν11 (4) ''
n12-n11> 0.12 (5) ′
ν11−ν12> 17.5 (6) ′
45.0> ν11−ν12 (6) ″

For example, in a zoom lens system like the zoom lens system according to Embodiments 1 to 4, it is preferable that the following condition (7) is satisfied.
T1 / Y <1.5 (7)
here,
T1: Center thickness of the first lens group,
Y: Maximum image height.

  The condition (7) is a condition that defines the center thickness of the first lens group in a zoom lens system that tends to be large because the first lens group is a negative lead having negative power. By satisfying the condition (7), it is possible to eliminate the possibility that the thickness of the first lens group becomes too large and the optical total length when not in use is increased.

Further, by satisfying the following condition (7) ′, it is possible to give power to the air lens in the first lens group, so that it becomes easier to correct curvature of field especially on the wide angle side.
0.8 <T1 / Y (7) '

Further, for example, the zoom lens system like the zoom lens system according to Embodiments 1 to 4, characterized by satisfying the following condition (8).
(T1 + T2 + T3) / Y < 3.2 (8)
here,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: Maximum image height.

  The condition (8) is a condition that defines the sum of the center thicknesses of the lens groups. By satisfying the condition (8), it is possible to eliminate the possibility that the total thickness of the lens units becomes too large and the optical total length when not in use is increased.

Further, by satisfying the following condition (8) ′ , it is possible to secure the thickness of each lens group, particularly the thickness of the first lens group and the thickness of the second lens group, and further excellent correction of field curvature. Is possible.
2.5 <(T1 + T2 + T3) / Y (8) ′

  Each of the lens groups constituting the zoom lens system according to Embodiments 1 to 4 has a refractive lens element that deflects incident light by refraction (that is, deflection is performed at the interface between media having different refractive indexes). However, the present invention is not limited to this. For example, a diffractive lens element that deflects incident light by diffraction, a refractive / diffractive hybrid lens element that deflects incident light by a combination of diffractive action and refractive action, and a refractive index that deflects incident light according to the refractive index distribution in the medium Each lens group may be composed of a distributed lens element or the like.

  In the zoom lens systems according to Embodiments 1 to 4, the optical path may be bent before, after, or during the zoom lens system by disposing the reflecting surface in the optical path. The folding position may be set as necessary, and the apparent thinning of the camera can be achieved by appropriately bending the optical path.

  Further, in the zoom lens systems according to Embodiments 1 to 4, the configuration in which the parallel plate P including the optical low-pass filter is disposed between the outermost image side surface of the third lens group G3 and the image surface S is shown. Examples of the low-pass filter include a birefringence low-pass filter made of quartz crystal whose direction of a predetermined crystal axis is adjusted, and a phase-type low-pass filter that achieves a required optical cutoff frequency characteristic by a diffraction effect. Applicable. Moreover, what is necessary is just to arrange | position this parallel flat plate P as needed.

  As described above, according to the present invention, it is possible to obtain a zoom lens system in which the curvature of the field is satisfactorily corrected, the first lens group is thin, and the optical total length when not in use is short.

(Embodiment 5)
FIG. 9 is a schematic configuration diagram of a digital still camera according to the fifth embodiment. In FIG. 9, the digital still camera includes an image pickup apparatus including a zoom lens system 1 and an image pickup device 2 that is a CCD, a liquid crystal monitor 3, and a housing 4. As the zoom lens system 1, the zoom lens system according to Embodiment 1 is used. In FIG. 9, the zoom lens system 1 includes a first lens group G1, a diaphragm A, a second lens group G2, and a third lens group G3. In the housing 4, the zoom lens system 1 is disposed on the front side, and the imaging element 2 is disposed on the rear side of the zoom lens system 1. A liquid crystal monitor 3 is disposed on the rear side of the housing 4, and an optical image of the subject by the zoom lens system 1 is formed on the image plane S.

  The lens barrel includes a main lens barrel 5, a movable lens barrel 6, and a cylindrical cam 7. When the cylindrical cam 7 is rotated, the first lens group G1, the second lens group G2, and the third lens group G3 are moved to predetermined positions with reference to the image sensor 2, and the magnification is changed from the wide-angle end to the telephoto end. It can be performed. The third lens group G3 is movable in the optical axis direction by a focus adjustment motor.

  Thus, by using the zoom lens system according to Embodiment 1 for a digital still camera, it is possible to provide a small digital still camera that has a high ability to correct resolution and curvature of field and has a short optical total length when not in use. it can. Note that the digital still camera shown in FIG. 9 may use any of the zoom lens systems according to Embodiments 2 to 4 instead of the zoom lens system according to Embodiment 1. Further, the optical system of the digital still camera shown in FIG. 9 can be used for a digital video camera for moving images. In this case, not only a still image but also a moving image with high resolution can be taken.

  In addition, an imaging apparatus including the zoom lens system according to Embodiments 1 to 4 described above and an imaging element such as a CCD or a CMOS is used as a monitoring camera in a mobile phone device, a PDA (Personal Digital Assistance), or a monitoring system. It can also be applied to Web cameras, in-vehicle cameras, and the like.

ここで、ｈは光軸からの高さ、ｃは曲率、ｋはコーニック定数、Ａ、Ｂ、Ｃ、Ｄ及びＥはそれぞれ４次、６次、８次、１０次及び１２次の非球面係数である。 Hereinafter, numerical examples and reference examples in which the zoom lens systems according to Embodiments 1 to 4 are specifically implemented will be described. In each numerical example and reference example , the units of length in the table are all mm, r is the radius of curvature, d is the surface spacing, nd is the refractive index in the d line, and νd is the Abbe number in the d line. Show. In each numerical example and reference example, the surface marked with * is an aspheric surface, and the sag z of the aspheric surface is defined by the following equation.

Here, h is the height from the optical axis, c is the curvature, k is the conic constant, A, B, C, D and E are the 4th, 6th, 8th, 10th and 12th aspherical coefficients, respectively. It is.

Example 1
The zoom lens system of Example 1 corresponds to Embodiment 1 shown in FIG. The lens data of the zoom lens system of Example 1 is shown in Table 1, the aspherical data is shown in Table 2, and the focal length f, F number, angle of view 2ω, optical total length L, and variable surface distance data when the shooting distance is ∞. Table 4 shows d4, d11, and d13.

(Example 2)
The zoom lens system of Example 2 corresponds to Embodiment 2 shown in FIG. The lens data of the zoom lens system of Example 2 is shown in Table 4, the aspherical data is shown in Table 5, and the focal length f, F number, angle of view 2ω, optical total length L, and variable surface distance data when the shooting distance is ∞. Table 6 shows d4, d12, and d14.

( Reference Example 1 )
The zoom lens system of Reference Example 1 corresponds to Embodiment 3 shown in FIG. The lens data of the zoom lens system of Reference Example 1 is shown in Table 7, the aspherical data is shown in Table 8, and the focal length f, F number, angle of view 2ω, optical total length L, and variable surface distance data when the shooting distance is ∞. Table 9 shows d4, d11, and d13.

(Example 3 )
The zoom lens system of Example 3 corresponds to the fourth embodiment shown in FIG. The lens data of the zoom lens system of Example 3 is shown in Table 10, the aspherical data is shown in Table 11, and the focal length f, F number, angle of view 2ω, optical total length L, and variable surface interval data when the shooting distance is ∞. Table 12 shows d4, d11, and d13.

Table 13 below shows corresponding values of the conditions in Examples 1 to 3 and Reference Example 1 .

2 is a longitudinal aberration diagram of the zoom lens system of Example 1. FIG. FIG. 4 is a longitudinal aberration diagram of the zoom lens system of Example 2. 6 is a longitudinal aberration diagram of the zoom lens system of Reference Example 1. FIG. FIG. 8 is a longitudinal aberration diagram of the zoom lens system of Example 3 .

  In each longitudinal aberration diagram, (a) shows the respective aberrations at the wide-angle end, (b) at the substantially intermediate position, and (c) at the telephoto end. Each longitudinal aberration diagram shows spherical aberration, astigmatism, and distortion aberration in order from the left side. In the spherical aberration diagram, the vertical axis represents the F number, the solid line is the d line, the short broken line is the F line, and the long broken line is the C line characteristic. In the astigmatism diagram, the vertical axis represents the half angle of view ω, the solid line is the sagittal plane (indicated by s), and the broken line is the meridional plane (indicated by m in the figure). In the distortion diagram, the vertical axis represents the half angle of view ω.

  The zoom lens system according to the present invention is applicable to cameras such as a digital still camera, a digital video camera, a mobile phone device, a PDA (Personal Digital Assistance), a surveillance camera in a surveillance system, a web camera, and an in-vehicle camera. It is suitable for cameras that require high image quality, such as still cameras and digital video cameras.

Configuration diagram of a zoom lens system according to Embodiment 1 (Example 1) Longitudinal aberration diagram of the zoom lens system of Example 1 Configuration diagram of a zoom lens system according to Embodiment 2 (Example 2) Longitudinal aberration diagram of the zoom lens system of Example 2 Configuration diagram of a zoom lens system according to Embodiment 3 ( Reference Example 1 ) Longitudinal aberration diagram of zoom lens system of Reference Example 1 Configuration diagram of a zoom lens system according to Embodiment 4 (Example 3 ) Longitudinal aberration diagram of the zoom lens system of Example 3 Schematic configuration diagram of a digital still camera according to Embodiment 5

Explanation of symbols

G1 1st lens group G2 2nd lens group G3 3rd lens group L1 1st lens element L2 2nd lens element L3 3rd lens element L4 4th lens element L5 5th lens element L6 6th lens element L7 7th lens element A Aperture P Parallel plate S Image plane 1 Zoom lens system 2 Image sensor 3 Liquid crystal monitor 4 Case 5 Main barrel 6 Moving barrel 7 Cylindrical cam

Claims (13)

A zoom lens system for forming an optical image of an object so as to be variable,
In order from the object side to the image side consists of a first lens unit having a negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
A zoom lens system characterized by satisfying the following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: Maximum image height . The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following conditions (3), (4), (5), and (6):
n11> 1.50 (3)
ν11> 35 (4)
n12-n11> 0.10 (5)
ν11−ν12> 15.0 (6)
here,
n11: Refractive index of the object side negative lens element of the first lens group,
ν11: Abbe number of the object side negative lens element of the first lens unit,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens unit. The zoom lens system according to claim 1, satisfying the following condition (7):
T1 / Y <1.5 (7)
here,
T1: Center thickness of the first lens group,
Y: Maximum image height.   The zoom lens system according to claim 1, wherein the third lens group includes one lens element.   The object side surface of the most object side lens element constituting the second lens group is an aspherical surface, and the second lens group is arranged in order from the object side to the image side, with one set of positive cemented lens elements and one positive lens element. The lens element according to claim 1, comprising one positive lens element and one set of cemented lens elements and one positive lens element, or comprising two sets of positive cemented lens elements. Zoom lens system. An imaging device capable of converting an optical image of a subject into an electrical image signal and outputting the electrical image signal,
A zoom lens system for forming an optical image of the subject so as to be variable, and
An image sensor that converts an optical image of a subject formed by the zoom lens system into an electrical image signal;
Wherein the zoom lens system consists of from the object side is the object side to the image side in this order, a first lens group having negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
An imaging apparatus characterized by satisfying the following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: Maximum image height . The imaging device according to claim 6 , wherein the zoom lens system satisfies the following conditions (3), (4), (5), and (6):
n11> 1.50 (3)
ν11> 35 (4)
n12-n11> 0.10 (5)
ν11−ν12> 15.0 (6)
here,
n11: Refractive index of the object side negative lens element of the first lens group,
ν11: Abbe number of the object side negative lens element of the first lens unit,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens unit. The imaging device according to claim 6 , wherein the zoom lens system satisfies the following condition (7):
T1 / Y <1.5 (7)
here,
T1: Center thickness of the first lens group,
Y: Maximum image height. The imaging device according to claim 6 , wherein the third lens group of the zoom lens system includes one lens element. The object side surface of the most object side lens element constituting the second lens group of the zoom lens system is an aspheric surface, and the second lens group includes a pair of positive junction lens elements in order from the object side to the image side. A single positive lens element, or a single positive lens element and a pair of cemented lens elements and a single positive lens element, or two pairs of positive lens elements. 6. The imaging device according to 6 . A camera that can shoot a subject and output it as an electrical image signal,
An imaging apparatus comprising: a zoom lens system that forms an optical image of the subject so as to be variable in magnification; and an imaging device that converts an optical image of the subject formed by the zoom lens system into an electrical image signal. Prepared,
Wherein the zoom lens system consists of from the object side is the object side to the image side in this order, a first lens group having negative power, a second lens group having positive power, a third lens group of positive power,
During zooming from the wide-angle end to the telephoto end, each lens group is irradiated with light so that the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group changes. Move along each axis to change magnification,
The first lens group includes one object-side negative lens element and one image-side positive lens element having a convex surface facing the object side,
Each of the two lens elements constituting the first lens group has an aspheric surface,
A camera characterized by satisfying the following conditions (1) , (2) and (8) :
n12> 1.95 (1)
ν12 < 24 (2)
(T1 + T2 + T3) / Y <3.2 (8)
here,
n12: refractive index of the image-side positive lens element of the first lens group,
ν12: Abbe number of the image-side positive lens element of the first lens group ,
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: Center thickness of the third lens group,
Y: Maximum image height . The camera according to claim 11 , wherein the camera is a digital still camera capable of acquiring a still image of a subject. The camera according to claim 11 , which is a digital video camera capable of acquiring a moving image of a subject.

Images