JP4960714B2 - 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 has a high resolution, a high ability to correct curvature of field, a light weight and a short optical total length when not in use, an imaging device using the zoom lens system, and the The present invention relates to a camera provided with an imaging device.

  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, in the zoom lens disclosed in Patent Document 1, the power per lens is reduced by providing two positive lenses on the image side of the second group, and a plastic lens is used as a lens having a relatively small power. Has been introduced. The plastic lens generally tends to change the image plane position and the like due to environmental fluctuations, but the zoom lens disclosed in Patent Document 1 in which such a plastic lens having a relatively small power is introduced is less susceptible to environmental fluctuations. A wide field of view and a light weight lens system are both achieved.

For example, in the zoom lens disclosed in Patent Document 2, astigmatism is corrected by making the most image side lens of the second lens group aspherical. In addition, the second lens group includes at least positive and negative lens arrangements in order from the object side, and an aspheric plastic lens is arranged on the most image side to correct spherical aberration and coma aberration, or to calculate Petzval sum. The effect is to reduce the curvature of field by reducing it. As described above, in the zoom lens disclosed in Patent Document 2, the aberration generated in the second lens group is suppressed to be small, so that the fluctuation in aberration during zooming is reduced, and the power in one lens group is divided to reduce the lens 1. Attempts have been made to reduce spherical aberration and coma generated in a positive lens by reducing the power per sheet. Furthermore, by introducing a plastic lens, it is easy to form an aspheric surface by injection molding, to reduce manufacturing errors, and to reduce the weight of the entire lens.
JP 2004-144947 A JP 2002-372667 A

  However, in the zoom lens having the three-group configuration disclosed in Patent Document 1, the ratio of the plastic lens power is high in the total power of the second group. Therefore, if the power of the plastic lens is kept small, In order to reduce the power and widen the angle, it is necessary to increase the amount of movement of the second lens unit at the time of zooming, making it difficult to reduce the thickness of the entire zoom lens.

  In addition, in the zoom lens having the three-group structure disclosed in Patent Document 2, the introduction of a plastic lens achieves some reduction in weight and reduction in error during manufacture, but the reduction in weight and error during manufacture are achieved. Reduction and improvement in optical performance and thinning of the entire zoom lens are not fully compatible.

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

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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
The following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
(here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the thickness of the center of the third lens group )
It is characterized by satisfying.

The object is achieved by the following imaging device. That is, the imaging apparatus of the present invention
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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
The following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
(here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the thickness of the center of the third lens group )
It is characterized by satisfying.

Furthermore, the object is achieved by the following camera. That is, the camera of the present invention
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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
The following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
(here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the thickness of the center of the third lens group )
It is characterized by satisfying.

  According to the present invention, it is possible to provide a zoom lens system that is light in weight and has a short optical total length when not in use, and an image pickup apparatus using the zoom lens system, as well as high resolution, as well as excellent curvature of field. 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 has a negative meniscus shape having negative power in order from the object side to the image side and having a convex surface facing the object side. The object side lens element L1 and a positive meniscus image side lens element L2 having positive power and having a convex surface facing the object side. Each of the object side lens element L1 and the image side 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 biconvex third lens element L3, a biconcave fourth lens element L4, It is composed of a biconvex fifth lens element L5. Among these, the third lens element L3 and the fourth lens element L4 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. The fifth lens element L5 which is the most image side lens element of the second lens group G2 is a lens element made of a resin (ZEONEX (registered trademark), manufactured by Nippon Zeon Co., Ltd.) having an aspheric object side surface. .

  In the zoom lens system according to Embodiment 1, the third lens unit G3 comprises solely a bi-convex sixth lens element L6. The sixth lens element L6 has an aspheric image side surface.

  In the zoom lens system according to Embodiment 1, the fifth lens element L5, which is the most image side lens element of the second lens group G2, is a resin lens element having an aspheric surface, and as shown in Table 13 later. In addition, by setting the most image side lens element L5 of the second lens group G2 so that the focal length is long and the power is small, the lens element is thinned and the second lens group G2 as the moving group is lightened. Is. Also, by reducing the power and suppressing the influence of image quality deterioration due to assembly errors, the third lens element L3 and the fourth lens element L4 can be joined, and the thickness of the second lens group G2 can be kept small. Is. Therefore, the zoom lens system according to Embodiment 1 is lightweight and 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 unit G1 has a negative meniscus shape having negative power in order from the object side to the image side and having a convex surface facing the object side. The object side lens element L1 and a positive meniscus image side lens element L2 having positive power and having a convex surface facing the object side. The object side lens element L1 has an aspheric image side surface, and the image side lens element L2 has an aspheric object 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 having a convex surface directed toward the object side, and a biconvex shape. A fourth lens element L4, a biconcave fifth lens element L5, and a biconvex sixth lens element L6 are included. 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. The sixth lens element L6 that is the most image side lens element of the second lens group G2 is a lens element made of resin (ZEONEX (registered trademark), manufactured by Nippon Zeon Co., Ltd.) having 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, the sixth lens element L6 which is the most image side lens element of the second lens group G2 is a resin lens element having an aspherical surface, and as shown in Table 13 later. Further, by setting the most image side lens element L6 of the second lens group G2 so that the focal length is long and the power is small, the lens element is thinned and the second lens group G2 as the moving group is lightened. Is. Also, by reducing the power and suppressing the influence of image quality deterioration due to assembly errors, the fourth lens element L4 and the fifth lens element L5 can be joined, and the thickness of the second lens group G2 can be kept small. Is. Therefore, the zoom lens system according to Embodiment 2 is lightweight and 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 has a negative meniscus shape having negative power in order from the object side to the image side and having a convex surface directed toward the object side. The object side lens element L1 and a positive meniscus image side lens element L2 having positive power and having a convex surface facing the object side. The object side lens element L1 has an aspheric image side surface, and the image side lens element L2 has an aspheric object side surface.

  In the zoom lens system according to Embodiment 3, 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, It is composed of a biconvex fifth lens element L5. Among these, the third lens element L3 and the fourth lens element L4 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. The fifth lens element L5 which is the most image side lens element of the second lens group G2 is a lens element made of a resin (ZEONEX (registered trademark), manufactured by Nippon Zeon Co., Ltd.) having an aspheric object side surface. .

  In the zoom lens system according to Embodiment 3, the third lens unit G3 comprises solely a bi-convex sixth lens element L6. The sixth lens element L6 has two aspheric surfaces.

In the zoom lens system according to Embodiment 3, the fifth lens element L5 which is the most image side lens element of the second lens group G2 is a resin lens element having an aspherical surface, and as shown in Table 13 later. In addition, by setting the most image side lens element L5 of the second lens group G2 so that the focal length is long and the power is small, the lens element is thinned and the second lens group G2 as the moving group is lightened. Is. Also, by reducing the power and suppressing the influence of image quality deterioration due to assembly errors, the third lens element L3 and the fourth lens element L4 can be joined, and the thickness of the second lens group G2 can be kept small. Is. Therefore, the zoom lens system according to Embodiment 3 is lightweight and has a short optical total length when not in use.

  As shown in FIG. 7, in the zoom lens system according to Embodiment 4, the first lens unit G1 has a negative meniscus shape having negative power in order from the object side to the image side and having a convex surface directed toward the object side. The object side lens element L1 and a positive meniscus image side lens element L2 having positive power and having a convex surface facing the object side. The object side lens element L1 has an aspheric image side surface, and the image side lens element L2 has an aspheric object 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 positive meniscus third lens element L3 having a convex surface directed toward the object side, and a biconvex shape. A fourth lens element L4, a biconcave fifth lens element L5, and a biconvex sixth lens element L6 are included. 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. The sixth lens element L6 that is the most image side lens element of the second lens group G2 is a lens element made of resin (ZEONEX (registered trademark), manufactured by Nippon Zeon Co., Ltd.) having 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 two aspheric surfaces.

In the zoom lens system according to Embodiment 4, the sixth lens element L6, which is the most image side lens element of the second lens group G2, is a resin lens element having an aspherical surface, and as shown in Table 13 later. Further, by setting the most image side lens element L6 of the second lens group G2 so that the focal length is long and the power is small, the lens element is thinned and the second lens group G2 as the moving group is lightened. Is. Also, by reducing the power and suppressing the influence of image quality deterioration due to assembly errors, the fourth lens element L4 and the fifth lens element L5 can be joined, and the thickness of the second lens group G2 can be kept small. Is. Therefore, the zoom lens system according to Embodiment 4 is lightweight and has a short optical total length when not in use.

  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 lens element having negative power and one image-side lens element having positive power. The second lens group G2 includes a cemented lens element composed of a positive lens element and a negative lens element, and the third lens group G3 includes 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 particular, the zoom lens system according to Embodiments 1 to 4 includes a resin lens element having at least one aspheric surface as the most image side lens element of the second lens group G2. The entire lens system can be reduced in weight while maintaining performance. Further, such a resin lens element has few errors in manufacturing and can be mass-produced relatively easily. The resin-made lens element used for the most image side lens element is not particularly limited as long as it does not impair the object of the present invention. For example, polymethyl methacrylate, polycarbonate, polystyrene, styrene-acrylonitrile copolymer, etc. A lens element molded from a synthetic resin used as a material of an optical lens so that at least one surface thereof is aspherical can be used.

  Furthermore, in the zoom lens systems according to Embodiments 1 to 4, one biconvex lens element constituting the third lens group G3 has at least one aspheric surface. Therefore, the zoom lens systems according to Embodiments 1 to 4 can further reduce the shift amount of the image forming position of each image height.

  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. A lens group, and the first lens group is composed of one object-side lens element and one image-side lens element having positive power, and constitutes the second lens group. However, a condition that a zoom lens system, which is a resin lens element having at least one aspherical surface, and which forms an optical image of an object so as to be variable in magnification 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 like the zoom lens system according to Embodiments 1 to 4 satisfies the following condition (1).
0.7 <f ₂ / f _2r <1.5 (1)
here,
f ₂ : composite focal length of the second lens group,
f _2r : the focal length of the most image side lens element of the second lens group.

  The condition (1) defines the ratio between the focal length of the entire second lens group and the focal length of the most image side lens element of the second lens group, and the aberration of the most image side lens element in the second lens group. This is a condition that prevents the sensitivity from becoming too high. If the lower limit of the condition (1) is not reached, the power of the second lens group becomes small, and in order to obtain a zoom ratio of 3 times or more, the moving distance of the second lens group must be increased, making it difficult to make it compact. become. If the upper limit of the condition (1) is exceeded, the power of the second lens group increases, and it is difficult to satisfactorily correct the aberration generated in the second lens group in the first lens group and the third lens group. Become.

In addition, the above effect can be further achieved by satisfying at least one of the following conditions (1) ′ and (1) ″.
0.8 <f ₂ / f _2r (1) ′
f ₂ / f _2r <1.1 (1) ''

For example, a zoom lens system like the zoom lens system according to Embodiments 1 to 4 preferably satisfies the following condition (2).
0.2 <f _W / f _2r <0.6 (2)
(However, ω _W > 37)
here,
f _W : focal length of the entire system at the wide-angle end,
f _2r : focal length of the most image side lens element of the second lens group,
ω _W is a half angle of view at the wide angle end.

The condition (2) is a condition that defines an appropriate focal length of the most image side lens element of the second lens group. By satisfying the condition (2), it is possible to prevent the aberration sensitivity of the most image side lens element in all the lens groups from becoming too high.
can do.

In addition, the above effect can be further achieved by further satisfying at least one of the following conditions (2) ′ and (2) ″.
0.35 <f _W / f _2r (2) ′
f _W / f _2r <0.45 (2) ''
(However, ω _W > 37)

In addition, for example, a zoom lens system like the zoom lens systems according to Embodiments 1 to 4 preferably satisfies the following condition (3).
T2 / Y> 0.8 (3)
here,
T2: center thickness of the second lens group,
Y: Maximum image height.

  The condition (3) is a condition that defines the center thickness of the second lens group. By satisfying the condition (3), it is possible to prevent the thickness from becoming too small to perform good aberration correction.

In addition, when the following condition (3) ′ is further satisfied, the above effect can be further achieved. Further, by satisfying the following condition (3) ″, it is possible to eliminate the possibility that the thickness of the second lens group becomes too large and the optical total length when not in use becomes long.
T2 / Y> 0.83 (3) ′
1.10> T2 / Y (3) ''

For example, as in the zoom lens systems according to Embodiments 1 to 4, the zoom lens system in which the second lens group includes at least a cemented lens element of a positive lens element and a negative lens element satisfies the following condition (4 ). rather preferably be satisfied, a zoom lens system like the zoom lens system according to embodiments 1 to 4, characterized by satisfying the following condition (5).
−20 <Rc / Y <−1 (4)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
here,
Rc: radius of curvature of the cemented surface in the cemented lens element of the second lens group,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the center thickness of the third lens group.

The condition (4) is a condition for defining the radius of curvature of the cemented surface in the cemented lens element constituting the second lens group. The condition (5) is a condition that defines the sum of the center thicknesses of the lens groups . By satisfying condition (4), since the power of the lens element located on the most object side in the second lens group that prevents too large, also satisfies the condition (5), the lens groups of total thickness becomes too large, there is no and Turkey lengthen optical total length when not in use.

In addition, the above effect can be further achieved by satisfying at least one of the following conditions (4) ′, (4) ″, (5) ′, and (5) ″.
−12 <Rc / Y (4) ′
Rc / Y <-2 (4) ''
2.3 <(T1 + T2 + T3) / Y (5) ′
(T1 + T2 + T3) / Y <3.1 (5) ''

Further, as in the zoom lens systems according to Embodiments 1 to 4, for example, the zoom lens system in which the third lens group includes one biconvex lens element having at least one aspherical surface has the following conditions. It is preferable to satisfy (6) and (7).
f _3r / f _T <1.5 (6)
T3 / Y <0.8 (7)
(Where ω _T <15)
here,
f _3r : focal length of the biconvex lens element of the third lens group,
f _T : focal length of the entire system at the telephoto end,
T3: Center thickness of the third lens group,
Y: Maximum image height
ω _T : half angle of view at the telephoto end.

  The condition (6) is a condition that defines an appropriate focal length of the biconvex lens elements constituting the third lens group. The condition (7) is a condition for defining the center thickness of the third lens group. By satisfying these conditions (6) and (7), the sensitivity of the aberration of the third lens group with respect to all the lens groups is lowered, and performance deterioration due to the movement of the third lens group at each zoom position is less likely to occur. In addition, it is possible to eliminate the possibility that the thickness of the third lens group becomes too large and the optical total length when not in use becomes long.

In addition, the above effect can be further achieved by satisfying at least one of the following conditions (6) ′ and (7) ′. Further, by satisfying at least one of the following conditions (6) ″ and (7) ″, the moving distance of the third lens unit can be prevented from becoming too large during focusing.
f _3r / f _T <1.3 (6) ′
1.0 <f _3r / f _T (6) ''
T3 / Y <0.5 (7) '
0.2 <T3 / Y (7) ''
(Where ω _T <15)

  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 which is light in weight and has a short optical total length when not in use, while favorably correcting curvature of field.

(Embodiment 5)
FIG. 9 is a schematic perspective view of a digital still camera which is an example of a camera according to the fifth embodiment. In FIG. 9, the digital still camera includes a main body 901, an image pickup apparatus 902 including an image pickup device such as a zoom lens system and a CCD or CMOS, an optical separate finder 903, a strobe 904, and a release button 905. Thus, the zoom lens system according to Embodiment 1 is used as the zoom lens system of the imaging device 902.

  Thus, by using the zoom lens system according to Embodiment 1 for a digital still camera, a thin digital camera with excellent portability and high performance can be provided. 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、Ｅ及びＦはそれぞれ４次、６次、８次、１０次、１２次及び１４次の非球面係数である。 Hereinafter, numerical examples in which the zoom lens systems according to Embodiments 1 to 4 are specifically implemented will be described. In each numerical 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 at the d line, and νd is the Abbe number at the d line. In each numerical example, the surface marked with * is an aspheric surface, and the aspherical sag z 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, E and F are the 4th, 6th, 8th, 10th, 12th and 14th, respectively. The following aspheric coefficient.

Example 1
The zoom lens system of Example 1 corresponds to Embodiment 1 shown in FIG. Table 1 shows lens data of the zoom lens system of Example 1, and Table 2 shows focal length f, F number, field angle 2ω, optical total length L, and variable surface interval data d4, d10, and d12 when the shooting distance is ∞. Table 3 shows the aspheric data.

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

(Example 3)
The zoom lens system of Example 3 corresponds to the third embodiment shown in FIG. Table 7 shows lens data of the zoom lens system of Example 3, and Table 8 shows focal length f, F number, angle of view 2ω, optical total length L, and variable surface interval data d4, d10, and d12 when the shooting distance is ∞. Table 9 shows the aspheric data.

Example 4
The zoom lens system of Example 4 corresponds to Embodiment 4 shown in FIG. Table 10 shows lens data of the zoom lens system of Example 4, and Table 11 shows focal length f, F number, angle of view 2ω, optical total length L, and variable surface interval data d4, d12, and d14 when the shooting distance is ∞. Table 12 shows the aspheric data.

Table 13 below shows corresponding values of the conditions in Examples 1 to 4.

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

  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, distortion, axial chromatic aberration, and lateral chromatic aberration in order from the left side. In the spherical aberration diagram, the vertical axis represents the F-number, and the solid line is the d-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. In the longitudinal chromatic 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 lateral chromatic aberration diagram, the vertical axis represents the half angle of view ω, the short broken line represents the F line characteristic, and the long broken line represents the C line characteristic.

  2, 4, 6, and 8, it can be seen that the zoom lens systems of Examples 1 to 4 have sufficient aberration correction capability to achieve high resolution.

  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 (Example 3) Longitudinal aberration diagram of the zoom lens system of Example 3 Configuration diagram of a zoom lens system according to Embodiment 4 (Example 4) Longitudinal aberration diagram of the zoom lens system of Example 4 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 Object side lens element L2 Image side 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 surface 901 Main body 902 Imaging device 903 Optical separate finder 904 Strobe 905 Release button

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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
A zoom lens system characterized by satisfying the following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the center thickness of the third lens group . The zoom lens system according to claim 1, satisfying the following condition (2):
0.2 <f _W / f _2r <0.6 (2)
(However, ω _W > 37)
here,
f _W : focal length of the entire system at the wide-angle end,
f _2r : focal length of the most image side lens element of the second lens group,
ω _W is a half angle of view at the wide angle end. The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following condition (3):
T2 / Y> 0.8 (3)
here,
T2: center thickness of the second lens group,
Y: Maximum image height. The zoom lens system according to claim 1, wherein the second lens group includes at least a cemented lens element of a positive lens element and a negative lens element, and satisfies the following condition (4 ) :
−20 <Rc / Y <−1 (4 )
In here,
Rc: radius of curvature of the cemented surface in the cemented lens element of the second lens group,
Y: Maximum image height
It is. 2. The zoom lens system according to claim 1, wherein the third lens group includes one biconvex lens element having at least one aspheric surface, and satisfies the following conditions (6) and (7):
f _3r / f _T <1.5 (6)
T3 / Y <0.8 (7)
(Where ω _T <15)
here,
f _3r : focal length of the biconvex lens element of the third lens group,
f _T : focal length of the entire system at the telephoto end,
T3: Center thickness of the third lens group,
Y: Maximum image height
ω _T : half angle of view at the telephoto end. 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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
An imaging apparatus that satisfies the following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the center thickness of the third lens group . The imaging device according to claim 6, wherein the zoom lens system satisfies the following condition (2):
0.2 <f _W / f _2r <0.6 (2)
(However, ω _W > 37)
here,
f _W : focal length of the entire system at the wide-angle end,
f _2r : focal length of the most image side lens element of the second lens group,
ω _W is a half angle of view at the wide angle end. The imaging device according to claim 6, wherein the zoom lens system satisfies the following condition (3):
T2 / Y> 0.8 (3)
here,
T2: center thickness of the second lens group,
Y: Maximum image height. The imaging device according to claim 6, wherein the second lens group of the zoom lens system includes at least a cemented lens element of a positive lens element and a negative lens element, and satisfies the following condition (4 ) :
−20 <Rc / Y <−1 (4 )
In here,
Rc: radius of curvature of the cemented surface in the cemented lens element of the second lens group,
Y: Maximum image height
It is. The imaging according to claim 6, wherein the third lens group of the zoom lens system includes one biconvex lens element having at least one aspheric surface, and satisfies the following conditions (6) and (7). apparatus:
f _3r / f _T <1.5 (6)
T3 / Y <0.8 (7)
(Where ω _T <15)
here,
f _3r : focal length of the biconvex lens element of the third lens group,
f _T : focal length of the entire system at the telephoto end,
T3: Center thickness of the third lens group,
Y: Maximum image height
ω _T : half angle of view at the telephoto end. 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 lens element and one image-side lens element,
The image side lens element of the first lens group has positive power;
The most image side lens element constituting the second lens group is a resin lens element having at least one aspheric surface,
Camera satisfying the following conditions (1) and (5) :
0.7 <f ₂ / f _2r <1.5 (1)
2.0 <(T1 + T2 + T3) / Y <3.5 (5)
here,
f ₂ : composite focal length of the second lens group,
f _2r : focal length of the most image side lens element of the second lens group ,
Y: Maximum image height
T1: Center thickness of the first lens group,
T2: center thickness of the second lens group,
T3: the center thickness of the third lens group .   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