JP4662428B2 - Zoom lens system, imaging device including zoom lens system, and device including imaging device - Google Patents

Description

  The present invention relates to a zoom lens system mainly mounted on a digital still camera, a video camera, a mobile phone terminal, and the like, and an image pickup apparatus including the zoom lens system. Specifically, a lens group having a negative power precedes 3. The present invention relates to a group zoom lens system and an imaging apparatus including the lens system. The present invention also relates to a device such as a digital still camera, a video camera, and a mobile phone terminal provided with the imaging device.

  In recent years, at the same time as the need for miniaturization and high definition of digital still cameras and video cameras has increased, there has been an increasing demand for higher functions such as zooming from a fixed focus in an imaging device mounted on a mobile phone terminal. On the other hand, solid-state image sensors such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxcic Semiconductor) have been developed to be small and high-pixel, and a smaller image pickup apparatus using a small solid-state image sensor can be configured. It has been demanded.

  The zoom lens system used in such an image pickup apparatus is not only small, but also requires good telecentricity in order to avoid the influence of shading caused by the angle formed by the light rays incident on the solid-state image sensor. Also, in order to withstand the impact when dropped, such a zoom lens system is suitable for a lens barrel having a constant optical system length, and an optical system with little change in the total length is required.

  Conventionally, as a miniaturized zoom lens system, it consists of two lens groups, a first lens group having a negative power and a second lens group having a positive power, and the magnification is changed by changing the distance between the lens groups. A two-group zoom lens system has been proposed. However, the two-group zoom lens system has a problem that the total optical length changes greatly due to zooming.

As another compact zoom lens system, a three-group zoom lens system including a first lens group having negative power, a second lens group having positive power, and a third lens group having positive power is proposed. (See Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 2004-4765 Japanese Patent Laid-Open No. 2003-140043

  However, the zoom lens systems described in Patent Document 1 and Patent Document 2 have a long total lens length and a large change in the total optical length during zooming, and thus the above-described problems have not been sufficiently solved. Further, the zoom lens systems described in Patent Document 1 and Patent Document 2 have a problem of high manufacturing cost because a large number of expensive optical materials are required.

  An object of the present invention is a zoom lens system that is suitable for an imaging apparatus using a solid-state imaging device, does not require an expensive optical material, has a short total lens length, and has a small change in the total optical length during zooming, and the zoom lens system It is providing an imaging device provided with. Moreover, the objective of this invention is providing the apparatus provided with the imaging device.

The above object is achieved by the following zoom lens system. A zoom lens system that forms an optical image of an object so as to be variable, and in order from the object side, has a first lens group having a negative power, a second lens group having a positive power, and a positive power a third lens group consists of a stop which moves integrally with the second lens group, the first lens group is composed of a negative-positive two lenses, upon zooming from the wide-angle end to the telephoto end, The first lens unit moves to the object side after moving on the optical axis while drawing a convex locus on the image surface side, and then moves to the object side, and the second lens unit moves monotonously on the optical axis to the object side. At the same time, the third lens unit moves on the optical axis during the focus adjustment, and the following conditional expression (1) is satisfied.
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system.

It is preferable that the following conditional expression (2) is satisfied.
(2) 0.7 <L2 / Y <1.5
Where L2 is the axial distance from the most object-side surface of the second lens group closest to the object side to the image-side surface of the second lens group closest to the image plane side, and Y is the maximum image height. is there.

It is preferable that the following conditional expression (3) is satisfied.
(3) 0.5 <L12 / √ (fW · fT) <0.7 (fT / fW> 1.6)
Where L12 is the maximum amount of change in the distance between the first lens group and the second lens group, the difference between the wide-angle end and the telephoto end of the distance between the first lens group and the second lens group, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system.

Preferably, it is desirable to satisfy the following conditional expression (4).
(4) 0.6 <f2 / √ (fW · fT) <1.2 (fT / fW> 1.6)
Here, fW is the focal length at the wide-angle end of the zoom lens system, fT is the focal length at the telephoto end of the zoom lens system, and f2 is the focal length of the second lens group.

It is preferable that the following conditional expression (5) is satisfied.
(5) 1.5 <| f1 | / f2 <2.0
Here, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

It is preferable that the following conditional expression (6) is satisfied.
(6) 1.0 <f3 / f2 <1.5
Here, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

Preferably, among the negative-positive two lenses constituting the first lens group, one of them belongs to the range of the conditional expression (7), remains one of the lenses belong to the range of the conditional expression (8) Is desirable.
(7) 1.75 <nd <1.90 and 35 <νd <48
(8) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

Preferably, the second lens group includes three lens elements, that is, a positive single lens element and a positive / negative cemented lens element, and the positive power lens of the cemented lens element falls within the range of the conditional expression (9). It is desirable that the negative lens belongs to the range of conditional expression (10).
(9) 1.75 <nd <1.90 and 35 <νd <48
(10) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

Preferably, the third lens group is composed of a positive single lens element, and belongs to the range of conditional expression (11).
(11) 1.75 <nd <1.90 and 35 <νd <48
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

Preferably, the third lens group includes a positive single lens element, and the single lens element preferably satisfies one or both of the following conditional expressions (12) and (13).
(12) 6.5 <| R31 | / | R32 | (R32> 0)
(13) 0 <| R32 | / Y <3.0 (R32> 0)
However, R31 is the radius of curvature of the object side surface of the single lens constituting the third lens group, R32 is the radius of curvature of the image side surface of the single lens constituting the third lens group, and Y is the maximum image height.

It is preferable that the following conditional expression (14) is satisfied.
(14) 0.8 <LfW / LfT <1.2 (fT / fW> 1.6)
Where LfW is the axial distance from the most object side to the image plane of the first lens group at the wide angle end, LfT is the axial distance from the most object side to the image plane of the first lens group at the telephoto end, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system.

The above object is achieved by the following imaging device. An imaging apparatus used for acquiring an electrical image signal of a subject, which is formed by a zoom lens system that forms an optical image of a subject, a lens barrel that holds the zoom lens system, and a zoom lens system The zoom lens system includes, in order from the object side, a first lens group having a negative power and a second lens group having a positive power. The solid-state imaging device converts an optical image into an electrical image signal. When, a third lens group having a positive power, consists of a stop which moves integrally with the second lens group, the first lens group is composed of a negative-positive two lenses, telephoto from the wide-angle end At the time of zooming to the end, the first lens group moves once on the optical axis while drawing a locus convex to the image plane side, then moves to the object side, and then moves to the object side, and the second lens group moves on the optical axis. Is moved to the object side monotonously and at the time of focus adjustment, Third lens unit moves on the optical axis, satisfies the following conditional expression (1).
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system.

The above object is achieved by the following equipment. An apparatus including an imaging device that acquires an electrical image signal of a subject, the imaging device including a zoom lens system that forms an optical image of the subject, a lens barrel that holds the zoom lens system, and a zoom lens system The zoom lens system includes, in order from the object side, a first lens group having a negative power and a first lens having a positive power. and second lens group, a third lens group having a positive power, consists of a stop which moves integrally with the second lens group, the first lens group is composed of a negative-positive two lenses, wide angle At the time of zooming from the end to the telephoto end, the first lens group moves once on the optical axis while drawing a convex locus on the image side, then moves to the object side, and then moves to the object side. Moves to the object side monotonously on the optical axis and adjusts the focus And, the third lens group is moved along the optical axis, satisfies the following conditional expression (1).
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system.

  Preferably, the device is an electronic still camera. Preferably, the device is a mobile phone terminal.

  According to the present invention, a zoom lens system suitable for an imaging apparatus using a solid-state imaging device, which does not require an expensive optical material, has a short overall lens length, and a small change in the overall optical length during zooming, and the zoom lens system thereof An imaging apparatus including the above can be provided. Further, according to the present invention, it is possible to provide a device including the imaging device.

(Embodiment 1)
FIG. 1 is a configuration diagram of a zoom lens system according to Embodiment 1 of the present invention. FIG. 5 is a configuration diagram of a zoom lens system according to Embodiment 2 of the present invention. FIG. 9 is a configuration diagram of a zoom lens system according to Embodiment 3 of the present invention. FIG. 13 is a configuration diagram of a zoom lens system according to Embodiment 4 of the present invention. FIG. 17 is a configuration diagram of a zoom lens system according to Embodiment 5 of the present invention. FIG. 21 is a configuration diagram of a zoom lens system according to Embodiment 6 of the present invention. FIG. 25 is a configuration diagram of a zoom lens system according to Embodiment 7 of the present invention.

  The zoom lens systems according to Embodiments 1 to 7 are each composed of six lenses, and in order from the object side, a first lens group G1 having negative power, a second lens group G2 having positive power, The third lens group G3 has a positive power. In the zoom lens systems according to Embodiments 1 to 7, in the case where the shooting distance is ∞, the first lens unit G1 moves once on the optical axis to the image plane side upon zooming from the wide-angle end to the telephoto end. The second lens group G2 moves monotonously on the optical axis to the object side. In the zoom lens systems according to Embodiments 1 to 7, the third lens group G3 moves on the optical axis for focus adjustment. The aperture and the shutter are integrated with the second lens group G2, and move on the optical axis along with the movement of the second lens group G2.

  In the zoom lens systems according to Embodiments 1 to 7, the first lens unit G1 includes, in order from the object side, a lens having negative power and a positive positive surface convex toward the object side with a strong curvature surface facing the object side. It is composed of a meniscus lens having power. The second lens group G2, in order from the object side, has a convex surface with a strong curvature toward the object side, and is joined to a positive lens having a flat image surface side, a biconvex positive lens, and an image side surface of the positive lens. It consists of a biconcave negative lens. The third lens group G3 includes only positive power lenses. A diaphragm and a shutter are attached to the object side of the second lens group G2. The positions of the aperture and the shutter are indicated by straight lines.

  In the zoom lens systems according to Embodiments 1 to 7, at least one aspheric surface is formed on the first lens that is the most object side lens in the first lens group. In the zoom lens systems according to Embodiments 1 to 7, at least one aspheric surface is also formed on the lenses constituting the second lens group G2. Further, in the zoom lens systems according to Embodiments 1 to 7, the image surface side surface of the lens of the third lens group G3 is aspheric.

  An infrared cut filter, an optical low-pass filter, and a solid-state image sensor are disposed on the image plane side of the third lens group G3. In each figure, one equivalent parallel plate is arranged for the infrared cut filter, the optical low-pass filter, and the cover glass of the solid-state imaging device. The light beam that has exited the subject and passed through the zoom lens system and the parallel plate forms an image on the imaging surface of the solid-state imaging device corresponding to the image surface.

  Next, a basic configuration common to the embodiments will be described. The zoom lens system according to each embodiment performs zooming by changing the interval between the first lens group G1 and the second lens group G2. The zoom lens system according to each embodiment performs focus adjustment by moving the third lens group G3 in the optical axis direction.

  In the zoom lens system of each embodiment, the optical total length at the wide-angle end and the optical total length at the telephoto end are substantially equal to each other, so that the maximum optical total length in use is reduced. In addition, in the zoom lens system according to each embodiment, the focal length between the second lens group G2 and the third lens group G3 is particularly appropriately set in order to maintain good optical performance while being compact. .

  The zoom lens system of each embodiment is devised as follows in order to shorten the optical total length and obtain good imaging performance. First, in the first lens group G1, distortion and astigmatism are favorably corrected by making both surfaces of the most object side lens aspherical.

  The second lens group G2 has a positive, positive, and negative three-element configuration from the object side, and a lens having the strongest positive power is disposed on the most object side. With this configuration, the principal point position on the object side of the second lens group G2 is more shifted to the object side. As a result, the distance from the image plane side principal point position of the first lens group G1 to the object side principal point position of the second lens group G2 at the telephoto end where the first lens group G1 and the second lens group G2 come close again. Can be shortened. Since the principal point interval is shortened, the focal length of the second lens group G2 can be shortened, and the overall length can be shortened. Furthermore, a shorter lens group is realized by configuring the second lens group G2 with three lenses.

  The third lens group G3 is the lightest lens group among the lens groups constituting the zoom lens system according to each embodiment, and is therefore suitable for a focus adjustment lens that requires high-speed autofocus. Further, the third lens group G3 has an effect of improving the telecentricity with respect to a light beam having a large principal ray angle emitted from a negative power lens having a strong convex surface on the object side closest to the object side of the second lens group G2. Have As a result, the third lens group G3 is optically applied to a solid-state image sensor that improves the light collection efficiency and improves sensitivity on the light receiving surface, specifically, a solid-state image sensor in which a microlens is formed for each pixel. It is suitable for an imaging optical system that forms a typical image.

  Hereinafter, conditions to be satisfied by the zoom lens system according to each embodiment will be described. In the zoom lens system according to each embodiment, a plurality of conditions to be satisfied are defined, but a zoom lens system configuration that satisfies all the conditions is most desirable. However, by satisfying individual conditions, it is possible to obtain a zoom lens system that exhibits the corresponding effects.

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (1).
(1) 2.5 <(L / Y) / √ (fT / fW) <5.0 (fT / fW> 1.6)
Where L is the axial distance from the object-side surface of the lens element closest to the object side of the first lens group to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW is the zoom lens The focal length at the wide angle end of the system, fT is the focal length at the telephoto end of the zoom lens system.

  Conditional expression (1) is a condition for shortening the total lens length and at the same time having good imaging performance. If the zoom ratio is increased while maintaining good imaging performance, the focal length of each lens group becomes relatively long. Therefore, in order to perform sufficient aberration correction for each group, it is necessary to increase the total lens length. . On the other hand, if the imaging performance is divisible even when the zoom ratio is large, the power of each lens group can be increased to shorten the optical total length.

  Conditional expression (1) is a condition obtained in consideration of these. Exceeding the upper limit of conditional expression (1) is not preferable because the total lens length becomes too large. If the lower limit is not reached, sufficient imaging performance cannot be obtained.

In addition, the said conditional expression (1) can further improve the said effect by prescribing | regulating the following ranges further.
(1) '3.4 <(L / Y) / √ (fT / fW)
(1) '' (L / Y) / √ (fT / fW) <4.5

Furthermore, the conditional expression (1) can achieve the above effect most remarkably by defining the following range.
(1) '''3.8<(L / Y) / √ (fT / fW)
(1) '''' (L / Y) / √ (fT / fW) <4.0

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (2).
(2) 0.7 <L2 / Y <1.5
Where L2 is the axial distance from the most object-side surface of the second lens group closest to the object side to the image-side surface of the second lens group closest to the image plane side, and Y is the maximum image height. is there.

  Conditional expression (2) is a condition for shortening the overall lens length and at the same time obtaining good imaging performance. If the thickness of the second lens group G2 is reduced, the curvature of each surface increases, and large spherical aberration and astigmatism occur. On the other hand, by increasing the thickness of the second lens group G2, the curvature of each surface constituting the second lens group G2 is reduced, but the overall length of the lens is increased and it is difficult to make the lens compact.

  Conditional expression (2) is a condition obtained in consideration of these. If the upper limit of conditional expression (2) is exceeded, the imaging performance is good, but the total length of the lens is increased because the thickness of the second lens group G2 is increased. On the other hand, if the lower limit of conditional expression (2) is exceeded, the radius of curvature of each lens composing the second lens group G2 increases, so that spherical aberration and astigmatism that occur on the lens surface increase, resulting in good results. Image performance cannot be obtained.

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (3).
(3) 0.5 <L12 / √ (fW · fT) <0.7 (fT / fW> 1.6)
Where L12 is the maximum amount of change in the distance between the first lens group and the second lens group, the difference between the wide-angle end and the telephoto end of the distance between the first lens group and the second lens group, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system.

  Conditional expression (3) is a condition for shortening the overall lens length and at the same time obtaining good imaging performance. In order to shorten the entire lens length, it is expected that the moving range of the second lens group G2 due to zooming is narrow, but in order to narrow the moving range, the power of the second lens group G2 is increased. Become. When the power of the lens group becomes strong, various aberrations occur in the second lens group G2, and good optical performance cannot be obtained. On the other hand, by reducing the power of the second lens group G2, various aberrations generated in the second lens group G2 can be reduced. However, since the moving distance is increased, the lens cannot be configured compactly.

  Conditional expression (3) is a condition obtained in consideration of these. If the upper limit of conditional expression (3) is exceeded, various aberrations occurring in the second lens group will be small, but the total lens length will be long, and it will not be possible to make it compact. On the other hand, if the lower limit of conditional expression (3) is not reached, the power required for the second lens group G2 becomes strong, so that various aberrations cannot be sufficiently suppressed and a compact lens can be obtained, but sufficient optical performance is obtained. I can't.

In addition, the said conditional expression (3) can raise the said effect further by prescribing | regulating the following ranges further.
(3) ′ 0.56 <2 / √ (fW · fT)
(3) '' 2 / √ (fW · fT) <0.61

Furthermore, the conditional expression (3) can achieve the above effect most remarkably by defining the following range.
(3) '''0.59<2 / √ (fW · fT)
(3) ″ ″ 2 / √ (fW · fT) <0.6

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (4).
(4) 0.6 <f2 / √ (fW · fT) <1.2 (fT / fW> 1.6)
Here, fW is the focal length at the wide-angle end of the zoom lens system, fT is the focal length at the telephoto end of the zoom lens system, and f2 is the focal length of the second lens group.

  Conditional expression (4) is a condition for shortening the overall lens length and at the same time obtaining good imaging performance. In order to shorten the total lens length, it is necessary to increase the power of the second lens group G2 to narrow the movement range of the second lens group G2 accompanying zooming. However, when the power of the second lens group is increased, various aberrations occur greatly, and good imaging performance cannot be obtained. Although the occurrence of various aberrations can be suppressed if the power of the lens group is weakened, the moving range of the second lens group G2 becomes large and the entire lens length becomes long, so that a compact zoom lens system cannot be realized.

  Conditional expression (4) is a condition obtained in consideration of these. If the upper limit of conditional expression (4) is exceeded, the focal length of the second lens group G2 becomes long and various aberrations can be suppressed. However, since the moving distance of the lens group accompanying zooming becomes long, the total lens length becomes long. It will be long. On the other hand, if the value is below the lower limit, the focal length of the second lens group G2 is shortened and the moving range of the second lens group G2 due to zooming is narrowed, but the suppression of various aberrations is insufficient and good imaging performance is obtained. Can't get.

In addition, the said conditional expression (4) can further improve the said effect by prescribing | regulating the following ranges further.
(4) ′ 0.8 <f2 / √ (fW · fT)
(4) '' f2 / √ (fW · fT) <1.0

Furthermore, the conditional expression (4) can achieve the above effect most remarkably by defining the following range.
(4) '''0.9<f2 / √ (fW · fT)
(4) ″ ″ f2 / √ (fW · fT) <0.96

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (5).
(5) 1.5 <| f1 | / f2 <2.0
Here, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

  Conditional expression (5) is a condition for correcting various aberrations generated in the first lens group G1 and the second lens group G2 in a well-balanced manner and shortening the total lens length. If the focal length f2 of the second lens group G2 is too short compared to the absolute value | f1 | of the focal length of the first lens group G1, various aberrations such as distortion aberration generated in G1 can be suppressed, but the front lens diameter Since the focal length on the telephoto side is insufficient even when G1 and G2 are closest to each other, a large zoom ratio cannot be obtained with respect to the moving distance of G2. On the other hand, if f2 is too long compared to | f1 |, the front lens diameter can be reduced. However, since the distance between G1 and G2 is increased, a compact zoom lens system cannot be configured.

  Conditional expression (5) is a condition obtained in consideration of these. If the upper limit of conditional expression (5) is exceeded, various aberrations can be suppressed, but even when the first lens group G1 and the second lens group G2 are closest, the image point position of the first lens group G1 and the second lens group. The distance of the group G2 becomes long, and as a result, the second lens group G2 cannot obtain a sufficient focal length with respect to the telephoto side, so that a large zoom ratio cannot be obtained. On the other hand, if the lower limit is not reached, the occurrence of various aberrations in the first lens group increases, and the movement range of the second lens group G2 increases, so that good optical performance cannot be obtained, and a compact zoom lens system is provided. Can't get.

In addition, the said conditional expression (5) can raise the said effect further by prescribing | regulating the following ranges further.
(5) '1.6 <| f1 | / f2
(5) '' | f1 | / f2 <1.8

Furthermore, the conditional expression (5) can achieve the above effect most remarkably by defining the following range.
(5) '''1.65<| f1 | / f2
(5) '''' | f1 | / f2 <1.75

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (6).
(6) 1.0 <f3 / f2 <1.5
Here, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

  Conditional expression (6) is a condition for correcting various aberrations generated in the second lens group G2 and the third lens group G3 in a well-balanced manner and obtaining good telecentricity. If the focal length of the second lens group G2 is too short compared to the focal length of the third lens group G3, a sufficient zoom ratio can be obtained, but the exit angle from the second lens group G2 becomes large, which is favorable. Can't get telecentricity. Further, if the focal length of the third lens group is too short with respect to the focal length of the second lens group G2, good telecentricity can be obtained, but the magnification at the time of zooming generated by the third lens group G3. The change in chromatic aberration becomes large, and good imaging performance cannot be obtained.

  Conditional expression (6) is a condition obtained in consideration of these. If the upper limit of conditional expression (6) is exceeded, good telecentricity cannot be obtained, and it is not suitable for an imaging system using a solid-state imaging device. On the other hand, if the lower limit of conditional expression (6) is not reached, a large change in chromatic aberration of magnification will occur during zooming, making it impossible to obtain good imaging performance.

In addition, the said conditional expression (6) can further improve the said effect by prescribing | regulating the following ranges further.
(6) '1.1 <f3 / f2
(6) '' f3 / f2 <1.35

Furthermore, the conditional expression (6) can achieve the above effect most remarkably by defining the following range.
(6) '''1.25<f3 / f2
(6) '''' f3 / f2 <1.32.

In the zoom lens system according to each embodiment, the first lens group G1 includes two negative and positive lenses, one of which belongs to the range of the conditional expression (7), and the other lens is a condition. It is preferable to belong to the range of the formula (8).
(7) 1.75 <nd <1.90 and 35 <νd <48
(8) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

  In the first lens group G1, as the lens group, a combination of achromaticity is necessary to suppress the occurrence of large magnification color and axial chromatic aberration due to zooming, and relatively small in order to reduce the curvature of the lens surface. It is necessary to use an optical material having a high refractive index. Considering a combination that has a sufficiently high refractive index and can be achromatic, it is preferable to combine glass materials in the range of conditional expression (7) and conditional expression (8).

In the zoom lens system according to each embodiment, the second lens group G2 includes three lens elements, that is, a positive single lens element and a positive / negative cemented lens element, and a positive power lens of the cemented lens element. Belongs to the range of conditional expression (9), and the negative lens preferably belongs to the range of conditional expression (10).
(9) 1.75 <nd <1.90 and 35 <νd <48
(10) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

  In the second lens group G2, the lens group largely moves at the time of zooming, so that aberration fluctuations when entering the second lens group G2 with a high light ray height become large. Therefore, each lens constituting the second lens group G2 It is desirable that the curvature of is small. For this purpose, it is necessary to use a glass material having a relatively high refractive index. In addition, since the second lens group G2 has two axial positive lenses from the object side, the axial chromatic aberration becomes under, so the lens with the most negative power on the image plane side also corrects the axial chromatic aberration. It is desirable to belong to the range of conditional expression (10). By belonging to the range of conditional expression (10), the curvature of the image side surface of the second lens group G2 closest to the image side is reduced, and astigmatism and coma are suppressed. it can.

In the zoom lens system according to each embodiment, it is preferable that the third lens group G3 includes a positive single lens element and belongs to the range of the conditional expression (11).
(11) 1.75 <nd <1.90 and 35 <νd <48
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number.

  In the third lens group G3, the weight is reduced in order to increase the speed of autofocus, and the third lens group G3 is configured by a single lens. However, the change in magnification chromatic aberration is relatively large due to the movement due to the focus adjustment accompanying the zooming. Further, in order to reduce the weight, it is necessary to reduce the lens thickness. For this purpose, it is necessary to reduce the curvature and to obtain sufficient power even if the lens is thin. The single lens constituting G3 preferably belongs to the range of conditional expression (11).

In the zoom lens system according to each embodiment, the third lens group G3 includes a positive single lens element. This single lens element is one of the following conditional expressions (12) and (13) or It is desirable to satisfy both.
(12) 6.5 <| R31 | / | R32 | (R32> 0)
(13) 0 <| R32 | / Y <3.0 (R32> 0)
However, R31 is the radius of curvature of the object side surface of the single lens constituting the third lens group, R32 is the radius of curvature of the image side surface of the single lens constituting the third lens group, and Y is the maximum image height.

  As described above, the single lens constituting the third lens group G3 has the function of adjusting the focus of the entire zoom lens system and the function of improving the telecentricity of the light beam incident on the solid-state imaging device. Outside the range of the conditional expression (12), the telecentricity of the light beam incident on the solid-state imaging device is deteriorated, and the aberration fluctuation at the time of focus adjustment becomes large, which is not desirable. Outside the range of conditional expression (13), the telecentricity of the light beam incident on the solid-state imaging device is deteriorated, and the amount of peripheral light is significantly reduced, which is not desirable.

In addition, the said conditional expression (12) can raise the said effect further by prescribing | regulating the following ranges further.
(12) ′ 7.0 <| R31 | / | R32 | and 0 <| R32 | / | R31 |

The conditional expression (13) can further enhance the above effect by further defining the following range.
(13) '0 <| R32 | / Y <2.5
(13) '' 0 <| R32 | / Y <2.48

It is desirable that the zoom lens system according to each embodiment satisfies the following conditional expression (14).
(14) 0.8 <LfW / LfT <1.2 (fT / fW> 1.6)
Where LfW is the axial distance from the most object side to the image plane of the first lens group at the wide angle end, LfT is the axial distance from the most object side to the image plane of the first lens group at the telephoto end, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system.

  Conditional expression (14) is a conditional expression related to a change in the overall length of the zoom lens system. If the range of the conditional expression (14) is exceeded, the total length largely changes between the lens configuration at the wide-angle end and the lens configuration at the telephoto end, so that it becomes difficult to achieve a compact zoom lens system.

  Each lens group constituting the zoom lens system of each embodiment includes a refractive lens that deflects incident light by refraction (that is, a lens that is deflected at an interface between media having different refractive indexes). ) Only, but is not limited thereto. For example, a diffractive lens that deflects incident light by diffraction, a refractive / diffractive hybrid lens that deflects incident light by a combination of diffractive action and refracting action, and refractive index distribution that deflects incident light according to the refractive index distribution in the medium Each lens group may be composed of a mold lens or the like.

  In the zoom lens system of each embodiment, the optical path may be bent before, after, or in the middle of 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.

  Furthermore, the zoom lens system according to each embodiment has a configuration in which a flat plate including an optical low-pass filter disposed between the final surface and the image sensor S is shown. A birefringent low-pass filter made of quartz or the like whose crystal axis direction is adjusted, a phase-type low-pass filter that achieves a required optical cutoff frequency characteristic by a diffraction effect, and the like are applicable. In the zoom lens system according to each embodiment, the low-pass filter may be omitted.

Next, a device to which any of the zoom lens systems according to Embodiments 1 to 7 is applied will be described.
(Embodiment 8)
FIG. 29 is a schematic exploded view showing a schematic configuration of a lens barrel according to Embodiment 8 of the present invention. In FIG. 29, a lens barrel 2900 is roughly composed of a zoom lens system holding portion and a cam barrel 2911. The holding unit of the zoom lens system includes a zoom lens system (first lens group 2901, second lens group 2903, and third lens group 2904), an aperture shutter unit 2902, two guide poles 2907, and an optical low-pass filter. And a parallel flat plate 2905 corresponding to an infrared cut filter and the like, and a solid-state imaging device 2906. In addition, the lens system in any one of Embodiment 1-7 mentioned above is used for a zoom lens system.

Each lens group of the zoom lens system is held by two guide poles 2907 so as to be movable in a direction parallel to the optical axis. Further, the parallel plate 2905 and the solid-state imaging device 2906 are fixed to the end portion of the guide pole 2907. Aperture shutter unit 2902 is integrally fixed to the second lens group 290 3, it is movably held with the second lens group 290 3 in a direction parallel to the optical axis.

Cam tube 2911 includes a cam groove 2915 corresponding to the moving locus of the first lens group 2901 at the time of zooming, and a cam groove 2916 corresponding to the moving locus of the second lens group 290 3 during zooming. The first lens group 2901 is engaged with the cam cylinder 2911 by a connecting portion 2910 formed integrally with the first lens group 2901, and in response to rotation along an axis parallel to the optical axis of the cam cylinder 11. The connecting portion 2910 is guided by the cam groove 2915 and moves in the optical axis direction. Similarly, the second lens group 2903 is engaged with the cam cylinder 2911 by a connecting portion 2909 formed integrally with the second lens group 2903, and rotates along an axis parallel to the optical axis of the cam cylinder 11. Accordingly, the connecting portion 2909 is guided by the cam groove 2916 and moves in the optical axis direction.

  The cam cylinder 2911 has a gear portion formed outside. This gear part and the screw fixed to the rotating shaft of the zooming stepping motor 2912 are engaged with each other. With this configuration, when the stepping motor 2912 rotates, the cam cylinder 11 rotates, and the first lens group 2901 and the second lens group 2903 move in a direction parallel to the optical axis.

On the other hand, the third lens group 290 4, the third lens group 290 4 are integrally formed with connecting portions 2908 and the screw 2913, and is connected to the stepping motor 2914. With this configuration, when the stepping motor 2912 rotates, the screw 2913 rotates and the third lens group 2904 is driven in a direction parallel to the optical axis.

(Embodiment 9)
FIG. 30 is a control block diagram of the imaging apparatus according to Embodiment 9 of the present invention. The imaging apparatus according to the ninth embodiment is mainly configured by a lens barrel 2900, a digital signal processing unit 3009, and a microcomputer 3003 according to the eighth embodiment.

  In FIG. 30, the microcomputer 3003 can input a signal from the zoom position switching input unit 3001 via the A / D conversion unit 3002. The microcomputer 3003 can output a signal to the zoom mechanism driving unit 3005 and the focus adjustment lens system driving control unit 3006 via the D / A conversion unit 3004.

  A zoom position switching input unit 3001 is a zoom position switching switch operated by an operator of the imaging apparatus. The zoom mechanism driving unit 3005 is a driver circuit for a stepping motor that rotates a cam cylinder to move the first lens group and the second lens group in the optical axis direction based on a control signal from the microcomputer 3003. A focus adjustment lens system drive control unit 3006 is a driver circuit of a stepping motor for moving the third lens group in the optical axis direction based on a control signal from the microcomputer 3003.

Further, the image signal output from the solid-state imaging device, an analog signal processing unit 3007, via the A / D converter 3008, are inputted to the digital signal processing section 30 09. The analog signal processing unit 3007 performs white balance processing and shading processing on the captured analog image signal. The analog image signal is subjected to predetermined processing by the analog signal processing unit 3007, converted to a digital signal by the A / D conversion unit 3008, and input to the digital signal processing unit 3009.

  The digital signal processing unit 3009 can further output a digital image signal to the image feature extraction unit 3012, the image storage unit 3010, and the image display unit 3011. The image storage unit 3010 is a semiconductor memory that stores digital image signals. The image display unit 3011 is a liquid crystal monitor that visually displays a digital image signal to an operator. The image feature extraction unit 3012 generates image data for detecting the in-focus state, for example, by extracting the contour of the image or separating frequency components, and transmits the image data to the microcomputer.

  In the above configuration, when the operator turns on the power of the imaging apparatus, the zoom lens system is disposed at the initial position, and an optical image formed by the zoom lens system is formed on the solid-state imaging device. An optical image is converted into an analog image signal by a solid-state imaging device. The analog image signal is subjected to predetermined image processing by the analog signal processing unit 3007 and the digital signal processing unit 3009 and then visually displayed on the image display unit 3011 according to an instruction from the microcomputer 3003. The digital signal is subjected to processing such as feature extraction by the image feature extraction unit 3012, and then the microcomputer 3003 calculates information about the deviation from the focused state.

  The microcomputer 3003 outputs information regarding the deviation from the in-focus state to the focus adjustment lens system drive control unit via the D / A conversion unit 3004. The focus adjustment lens system drive control unit drives the third lens group based on this information. After the third lens group has moved, the analog image signal output from the solid-state imaging device is again subjected to the same processing and input to the digital signal processing unit. By such control, auto-focusing of the image pickup apparatus is performed.

On the other hand, when the operator operates the zoom position switching switch, a control signal from the zoom position switching input unit 3001 is input to the microcomputer 3003 via the A / D conversion unit 3002. The microcomputer 3003 outputs this control signal to the zoom mechanism driving unit 3005 via the D / A conversion unit 3004. The zoom mechanism driving unit 3005 calculates the amount of rotation of the cam cylinder based on the current cam cylinder position and a signal from the zoom position switching input unit 3001, and performs zooming by rotating the cam cylinder.

  After the focus adjustment or zoom is performed, when the operator gives a command to capture a still image by operating a shutter or the like, the digital image processed by the digital signal processing unit 3009 is stored in the image storage unit 3010. Stored. Similarly, in the case of a moving image, the digital image processed by the digital signal processing unit 3009 is stored in the image storage unit 3010.

  As described above, the imaging apparatus according to Embodiment 8 is controlled. Since the imaging apparatus according to Embodiment 8 has the zoom lens system according to any one of Embodiments 1 to 7 as a zoom lens system, the imaging apparatus is a compact imaging apparatus.

(Embodiment 10)
FIG. 31 is a schematic configuration diagram of an electronic still camera according to Embodiment 10 of the present invention. An electronic still camera according to Embodiment 10 includes a lens barrel 3101 according to Embodiment 8, a housing 3102, an optical viewfinder 3103, a strobe unit 3104, a shutter button 3105, a battery 3106, and a semiconductor memory. 3107, a liquid crystal monitor 3108, and a zoom position changeover switch 3109.

  The optical viewfinder 3103 has an optical system that is configured separately from the zoom lens system held in the lens barrel 3101, and can change the magnification in conjunction with the zoom lens system, and transmits the subject light to the operator. Is optically transmitted into the pupil. The strobe unit 3104 and the shutter button 3105 have known configurations, and are operated for flash emission and imaging instruction by the operation of the operator. The battery 3106 is a dry battery or a secondary battery for starting the electronic still camera. The semiconductor memory 3107 corresponds to the image storage unit described above. The liquid crystal monitor corresponds to the image display unit described above. The zoom position switching switch 3109 corresponds to the zoom position switching input unit described above.

  As described above, the electronic still camera according to Embodiment 10 is configured. Since the electronic still camera according to Embodiment 9 includes a lens barrel including any of the zoom lens systems according to Embodiments 1 to 7 as a zoom lens system, the electronic still camera is a compact electronic still camera.

In this embodiment, the optical viewfinder is used to check the shooting range and focal length of the subject. However, a liquid crystal viewfinder may be used, and there is no finder. Means may be used. Further, the liquid crystal monitor 3108 is taken as an example of the monitor , but an image display means such as an organic EL may be used, for example. The image storage unit has shown image recording means such as the semiconductor memory 3107. However, the recording means may or may not be removable from the main body of the electronic still camera. A communication function with an external control device may be provided.

(Embodiment 11)
FIG. 32 is a block diagram of the mobile phone terminal according to Embodiment 11 of the present invention. The cellular phone terminal includes a housing 3201, an imaging device 3202 according to Embodiment 9, and a liquid crystal monitor 3203. Since the mobile phone terminal according to the eleventh embodiment includes a lens barrel including any one of the zoom lens systems according to the first to seventh embodiments as a zoom lens system, the mobile phone terminal is a compact mobile phone terminal.

  The devices shown in the tenth and eleventh embodiments are examples of application of the imaging apparatus according to the ninth embodiment, and needless to say, the devices can be applied to other devices. The imaging device according to the ninth embodiment may be applied to, for example, a monitoring camera device installed in a building or a highway, an in-vehicle camera device installed in an automobile, or the like. In addition, the imaging apparatus according to the ninth embodiment may be applied to a personal computer, a PDA (Personal Digital Assistance), or a Web camera connected to a video conference system or a video phone system.

ここで、κは円錐定数、ＡＤ，ＡＥ，ＡＦ，ＡＧはそれぞれ４次、６次、８次、１０次の非球面係数、ｈは光軸からの高さ、Ｚは光軸と面頂点の交点を原点とした場合の高さｈにおけるサグ量である。 Hereinafter, numerical examples in which the zoom lens systems according to Embodiments 1 to 5 are specifically implemented will be described. The units of length in the tables of the numerical examples are all mm. In the table, f is the focal length, Fno. Is the F number, 2ω is the angle of view, r is the radius of curvature, d is the surface spacing, nd and νd are the refractive index and Abbe number at the d-line, respectively. The aspheric shape is defined by the following equation (AS).

Where κ is a conic constant, AD, AE, AF, and AG are fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, h is the height from the optical axis, and Z is the optical axis and the vertex of the surface. This is the sag amount at the height h when the intersection is the origin.

Example 1
The zoom lens system of Numerical Example 1 corresponds to Embodiment 1 shown in FIG. Table 1 shows lens data of the zoom lens system of Example 1, Table 2 shows aspherical data, and Table 3 shows focal length, F number, angle of view, optical total length, and variable surface distance data when the shooting distance is ∞. Shown in

  FIG. 10, FIG. 11, and FIG. 12 show aberration diagrams (spherical aberration, astigmatism, distortion aberration) when the photographing distance of the zoom lens system shown in FIG. 10 shows the case at the wide-angle end, FIG. 11 shows the case at a substantially intermediate position, and FIG. 12 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the characteristic of the sagittal plane, and the broken line is the characteristic of the meridional plane.

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

  Aberration diagrams (spherical aberration, astigmatism, distortion aberration) when the photographing distance of the zoom lens system shown in FIG. 5 is ∞ and the aperture is opened are shown in FIGS. 6 shows the case at the wide-angle end, FIG. 7 shows the case at a substantially intermediate position, and FIG. 8 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the characteristic of the sagittal plane, and the broken line is the characteristic of the meridional plane.

(Example 3)
The zoom lens system of Numerical Example 3 corresponds to Embodiment 3 shown in FIG. The lens data of the zoom lens system of Example 3 is shown in Table 7, the aspherical data is shown in Table 8, and the focal length, F number, angle of view, optical total length, and variable surface interval data when the shooting distance is ∞ are shown in Table 9. Shown in

  FIG. 10, FIG. 11, and FIG. 12 show aberration diagrams (spherical aberration, astigmatism, distortion aberration) when the photographing distance of the zoom lens system shown in FIG. 10 shows the case at the wide-angle end, FIG. 11 shows the case at a substantially intermediate position, and FIG. 12 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the sagittal plane, and the broken line is the meridional plane.

Example 4
The zoom lens system of Numerical Example 4 corresponds to Embodiment 4 shown in FIG. Table 10 shows lens data of the zoom lens system of Example 4, Table 11 shows aspherical data, and Table 12 shows focal length, F number, angle of view, optical total length, and variable surface interval data when the shooting distance is ∞. Shown in

  FIG. 14, FIG. 15, and FIG. 16 show aberration diagrams (spherical aberration, astigmatism, distortion) when the zoom lens system shown in FIG. 14 shows the case at the wide-angle end, FIG. 15 shows the case at an almost intermediate position, and FIG. 16 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the sagittal plane and the dashed line is the meridional plane

(Example 5)
The zoom lens system of Numerical Example 5 corresponds to Embodiment 5 shown in FIG. Table 13 shows lens data of the zoom lens system of Example 5, Table 14 shows aspherical data, and Table 15 shows focal length, F number, angle of view, optical total length, and variable surface distance data when the shooting distance is ∞. Shown in

  FIG. 18, FIG. 19, and FIG. 20 show aberration diagrams (spherical aberration, astigmatism, distortion) when the photographing distance of the zoom lens system shown in FIG. 18 shows the case at the wide-angle end, FIG. 19 shows the case at an almost intermediate position, and FIG. 20 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the sagittal plane, and the broken line is the meridional plane.

(Example 6)
The zoom lens system of Numerical Example 6 corresponds to Embodiment 6 shown in FIG. Table 16 shows the lens data of the zoom lens system of Example 6, Table 17 shows the aspheric data, Table 18 shows the focal length, F number, angle of view, optical total length, and variable surface interval data when the shooting distance is ∞. Shown in

  FIG. 22, FIG. 23, and FIG. 24 show aberration diagrams (spherical aberration, astigmatism, distortion aberration) when the photographing distance of the zoom lens system shown in FIG. FIG. 22 shows the case at the wide-angle end, FIG. 23 shows the case at a substantially intermediate position, and FIG. 24 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the sagittal plane, and the broken line is the meridional plane.

(Example 7)
The zoom lens system of Numerical Example 7 corresponds to Embodiment 7 shown in FIG. Table 19 shows lens data of the zoom lens system of Example 7, Table 21 shows aspheric data, Table 22 shows focal length, F number, field angle, optical total length, and variable surface distance data when the shooting distance is ∞. Shown in

  FIG. 26, FIG. 27, and FIG. 28 show aberration diagrams (spherical aberration, astigmatism, distortion) when the photographing distance of the zoom lens system shown in FIG. FIG. 26 shows the case at the wide-angle end, FIG. 27 shows the case at a substantially intermediate position, and FIG. 28 shows the case at the telephoto end. In the spherical aberration diagram, the solid line is the d-line characteristic, the short broken line is the F-line characteristic, and the long broken line is the C-line characteristic. In the astigmatism diagram, the solid line is the characteristic of the sagittal plane, and the broken line is the characteristic of the meridional plane.

Table 22 below shows corresponding values of main parameters in Examples 1 to 7. Table 23 below shows corresponding values of the conditional expressions in Examples 1 to 7.

  The zoom lens system according to the present invention is compact and can provide good imaging performance, and thus is useful for a compact electronic still camera or a mobile imaging device such as a mobile phone.

Configuration diagram of a zoom lens system according to Embodiment 1 (Example 1) of the present invention Aberration diagram at the wide-angle end of the zoom lens system according to Embodiment 1 (Example 1) of the present invention. Aberration diagram of intermediate position of zoom lens system of Embodiment 1 (Example 1) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 1 (Example 1) of the present invention. Configuration diagram of a zoom lens system according to Embodiment 2 (Example 2) of the present invention Aberration diagram at the wide-angle end of the zoom lens system according to Embodiment 2 (Example 2) of the present invention. Aberration diagram of intermediate position of zoom lens system of Embodiment 2 (Example 2) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 2 (Example 2) of the present invention. Configuration diagram of a zoom lens system according to Embodiment 3 (Example 3) of the present invention Aberration diagram at the wide-angle end of the zoom lens system according to Embodiment 3 (Example 3) of the present invention Aberration diagram of intermediate position of zoom lens system of Embodiment 3 (Example 3) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 3 (Example 3) of the present invention. Configuration diagram of a zoom lens system according to Embodiment 4 (Example 4) of the present invention Aberration diagram at the wide-angle end of the zoom lens system according to Embodiment 4 (Example 4) of the present invention. Aberration diagram of intermediate position of zoom lens system of Embodiment 4 (Example 4) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 4 (Example 4) of the present invention. Configuration diagram of a zoom lens system according to Embodiment 5 (Example 5) of the present invention Aberration diagram at wide-angle end of zoom lens system according to Embodiment 5 (Example 5) of the present invention Aberration diagram of intermediate position of zoom lens system of Embodiment 5 (Example 5) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 5 (Example 5) of the present invention Configuration diagram of a zoom lens system according to Embodiment 6 (Example 6) of the present invention Aberration diagram at wide-angle end of zoom lens system according to Embodiment 6 (Example 6) of the present invention Aberration diagram at intermediate position of zoom lens system of Embodiment 6 (Example 6) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 6 (Example 6) of the present invention. Configuration diagram of a zoom lens system according to Embodiment 7 (Example 7) of the present invention Aberration diagram at wide-angle end of zoom lens system according to Embodiment 7 (Example 7) of the present invention Aberration diagram of intermediate position of zoom lens system according to Embodiment 7 (Example 7) of the present invention Aberration diagram at the telephoto end of the zoom lens system according to Embodiment 7 (Example 7) of the present invention. Configuration diagram of lens barrel in the eighth embodiment of the present invention Configuration diagram of imaging apparatus according to Embodiment 9 of the present invention Configuration diagram of an electronic still camera according to Embodiment 10 of the present invention Configuration diagram of mobile phone in Embodiment 11 of the present invention

Explanation of symbols

G1, 2901 1st lens group G2, 2903 2nd lens group G3, 2904 3rd lens group 2900 Lens barrel 2902 Aperture shutter unit 2905 Parallel plate 2906 Solid-state imaging device 2907 Guide pole 2908 Connection portion 2909 Connection portion 2910 Connection portion 2911 Cam tube 2912 Stepping motor 2913 Screw 2914 Stepping motor 2915 Cam groove 2916 Cam groove 3001 Zoom one switching input unit 3002 A / D conversion unit 3003 Microcomputer 3004 D / A conversion unit 3005 Zoom mechanism drive unit 3006 Focus adjustment lens system drive control unit 3007 Analog Signal processing unit 3008 A / D conversion unit 3009 Digital signal processing unit 3010 Image storage unit 3011 Image display unit 3012 Image feature extraction unit 3101 Lens barrel 3102 Case 310 3 Optical Viewfinder 3104 Strobe Unit 3105 Shutter Button 3106 Battery 3107 Semiconductor Memory 3108 Liquid Crystal Monitor 3106 Zoom Position Change Switch 3201 Housing 3202 Imaging Device 3203 Liquid Crystal Monitor

Claims (15)

A zoom lens system capable of zooming an optical image of an object, in order from the object side,
A first lens group having negative power;
A second lens group having positive power;
A third lens group having positive power;
Consists of a stop which moves integrally with the second lens group,
The first lens group is composed of two negative and positive lenses,
Upon zooming from the wide-angle end to the telephoto end, the first lens group moves once on the optical axis to the image plane side while drawing a convex locus on the image plane side, then moves to the object side, and then moves to the second lens group. However, while moving monotonously on the optical axis,
During focus adjustment, the third lens group moves on the optical axis,
A zoom lens system that satisfies the following conditional expression (1):
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system. The zoom lens system according to claim 1, wherein the following conditional expression (2) is satisfied:
(2) 0.7 <L2 / Y <1.5
Where L2 is the axial distance from the most object-side surface of the second lens group closest to the object side to the image-side surface of the second lens group closest to the image plane side, and Y is the maximum image height. is there. The zoom lens system according to claim 1, wherein the following conditional expression (3) is satisfied:
(3) 0.5 <L12 / √ (fW · fT) <0.7 (fT / fW> 1.6)
Where L12 is the maximum amount of change in the distance between the first lens group and the second lens group, the difference between the wide-angle end and the telephoto end of the distance between the first lens group and the second lens group, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system. The zoom lens system according to claim 1, wherein the following conditional expression (4) is satisfied:
(4) 0.6 <f2 / √ (fW · fT) <1.2 (fT / fW> 1.6)
Here, fW is the focal length at the wide-angle end of the zoom lens system, fT is the focal length at the telephoto end of the zoom lens system, and f2 is the focal length of the second lens group. The zoom lens system according to claim 1, wherein the following conditional expression (5) is satisfied:
(5) 1.5 <| f1 | / f2 <2.0
Here, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group. The zoom lens system according to claim 1, wherein the following conditional expression (6) is satisfied:
(6) 1.0 <f3 / f2 <1.5
Here, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group. The negative lens and the positive lens constituting the first lens group, one of them belongs to the range of the conditional expression (7), and the other lens belongs to the range of the conditional expression (8). Zoom lens system according to 1:
(7) 1.75 <nd <1.90 and 35 <νd <48
(8) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number. The second lens group includes three lens elements, a positive single lens element and a positive / negative cemented lens element, and the positive power lens of the cemented lens element belongs to the range of conditional expression (9). The zoom lens system according to claim 1, wherein the negative lens belongs to the range of the conditional expression (10):
(9) 1.75 <nd <1.90 and 35 <νd <48
(10) nd> 1.82 and νd <24
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number. 2. The zoom lens system according to claim 1, wherein the third lens group includes a positive single lens element and belongs to the range of the conditional expression (11).
(11) 1.75 <nd <1.90 and 35 <νd <48
Here, nd is the refractive index with respect to the d-line, and νd is the Abbe number. The zoom lens system according to claim 1, wherein the third lens group includes a positive single lens element, and the single lens element satisfies one or both of the following conditional expressions (12) and (13). :
(12) 6.5 <| R31 | / | R32 | (R32> 0)
(13) 0 <| R32 | / Y <3.0 (R32> 0)
However, R31 is the radius of curvature of the object side surface of the single lens constituting the third lens group, R32 is the radius of curvature of the image side surface of the single lens constituting the third lens group, and Y is the maximum image height. The zoom lens system according to claim 1, wherein the zoom lens system satisfies the following conditional expression (14):
(14) 0.8 <LfW / LfT <1.2 (fT / fW> 1.6)
Where LfW is the axial distance from the most object side to the image plane of the first lens group at the wide angle end, LfT is the axial distance from the most object side to the image plane of the first lens group at the telephoto end, and fW is the zoom lens. The focal length at the wide-angle end of the system, fT, is the focal length at the telephoto end of the zoom lens system. An imaging device used to acquire an electrical image signal of a subject,
A zoom lens system that forms an optical image of the subject;
A lens barrel holding the zoom lens system;
A solid-state imaging device that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system, in order from the object side,
A first lens group having negative power;
A second lens group having positive power;
A third lens group having positive power;
Consists of a stop which moves integrally with the second lens group,
The first lens group is composed of two negative and positive lenses,
Upon zooming from the wide-angle end to the telephoto end, the first lens group moves once on the optical axis to the image plane side while drawing a convex locus on the image plane side, then moves to the object side, and then moves to the second lens group. However, while moving monotonously on the optical axis,
During focus adjustment, the third lens group moves on the optical axis,
An imaging device that satisfies the following conditional expression (1):
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system. An apparatus including an imaging device that acquires an electrical image signal of a subject, the imaging device includes:
A zoom lens system that forms an optical image of the subject;
A lens barrel holding the zoom lens system;
A solid-state imaging device that converts an optical image formed by the zoom lens system into an electrical image signal;
The zoom lens system, in order from the object side,
A first lens group having negative power;
A second lens group having positive power;
A third lens group having positive power;
Consists of a stop which moves integrally with the second lens group,
The first lens group is composed of two negative and positive lenses,
Upon zooming from the wide-angle end to the telephoto end, the first lens group moves once on the optical axis to the image plane side while drawing a convex locus on the image plane side, then moves to the object side, and then moves to the second lens group. However, while moving monotonously on the optical axis,
During focus adjustment, the third lens group moves on the optical axis,
Equipment that satisfies the following conditional expression (1):
(1) 2.5 <(L / Y) / √ (fT / fW) ≦ 4.03 (fT / fW> 1.6)
Where L is the axial distance from the object side surface of the lens element closest to the object side of the first lens group at the wide angle end to the surface closest to the image plane of the lens of the third lens group, Y is the maximum image height, and fW Is the focal length at the wide-angle end of the zoom lens system, and fT is the focal length at the telephoto end of the zoom lens system.   The device according to claim 13, wherein the device is an electronic still camera. The device according to claim 13, wherein the device is a mobile phone terminal.

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