JP6631412B2 - Imaging lens, imaging optical device and digital equipment - Google Patents

Description

  The present invention relates to an imaging lens, an imaging optical device, and a digital device. For example, an imaging device (for example, a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal-Oxide Semiconductor) image sensor, etc.) A large-diameter imaging lens suitable for an interchangeable-lens digital camera captured by a solid-state imaging device, an imaging optical device that outputs an image of a subject captured by the imaging lens and the imaging device as an electric signal, A digital device with an image input function, such as a digital camera equipped with an imaging optical device.

  In recent years, in a digital single-lens reflex camera, in addition to the progress of the increase in the number of pixels, a user can easily confirm an image at the same magnification. For this reason, the required optical performance level of a large-aperture lens is becoming higher. Further, in a mirrorless type digital camera with interchangeable lenses without a flip-up mirror, it is required to reduce the weight of the focus group in order to further increase the speed of contrast AF (autofocus) focusing. In order to meet such demands, Patent Documents 1 to 3 propose imaging lenses of a type suitable for reducing the weight of a focus group while maintaining high optical performance.

JP 2010-271458 A JP 2012-48084 A JP 2013-83783 A

  However, in the imaging lenses described in Patent Literatures 1 and 2, since the power of the third lens group is large, aberration fluctuation of astigmatism and spherical aberration due to focusing is large. In addition, each of the imaging lenses includes three or more focus groups, and the weight of the focus group has not been reduced.

  In the imaging lens described in Patent Literature 3, focusing can be performed at high speed by reducing the number of lenses in a focus group and reducing the weight. However, since the positive lens is disposed closest to the object side of the first lens group, the power of the negative lens before the stop becomes very large, so that coma and astigmatism generated in the first lens group are generated. However, the correction has not been properly performed on the entire imaging lens. Further, since the power of the second lens group is large, the fluctuation of spherical aberration due to focusing is large.

  The present invention has been made in view of such a situation, and an object of the present invention is to reduce the weight of a focus group and perform focusing on a wide shooting area while maintaining high optical performance at all shooting distances. An object of the present invention is to provide an imaging lens, an imaging optical device including the same, and a digital device.

In order to achieve the above object, an imaging lens according to a first aspect includes, in order from an object side, a first lens group having a positive power, a second lens group having a negative power, and a second lens group having a positive power. It comprises three lens groups and a fourth lens group having negative power,
At the time of focusing, the first lens group and the fourth lens group are fixed in position with respect to the image plane, and the second lens group and the third lens group move in the optical axis direction such that the distance between the lens groups changes. And
The first lens group has a negative meniscus lens convex to the object side closest to the object side;
The second lens group and the third lens group each include two or less lenses,
It is characterized by satisfying the following conditional expression (1).
−7.6 <f2 / f <−3.0 (1)
However,
f2: focal length of the second lens group,
f: focal length of the whole system,
It is.

An imaging lens according to a second aspect is characterized in that, in the first aspect, the following conditional expression (2) is satisfied.
−5.1 <f4 / f <−1.4 (2)
However,
f4: focal length of the fourth lens group,
f: focal length of the whole system,
It is.

An imaging lens according to a third aspect is characterized in that, in the first or second aspect, the following conditional expression (3) is satisfied.
1.0 <f2 / f4 <2.2 (3)
However,
f2: focal length of the second lens group,
f4: focal length of the fourth lens group,
It is.

An imaging lens according to a fourth aspect is characterized in that, in any one of the first to third aspects, the following conditional expression (4) is satisfied.
0.8 <f1 / f3 <1.8 (4)
However,
f1: focal length of the first lens group,
f3: focal length of the third lens group,
It is.

  According to a fifth aspect of the present invention, in the imaging lens according to any one of the first to fourth aspects, the second lens group includes a cemented lens including a negative lens and a positive lens in order from the object side. And

  A sixth aspect of the present invention is the imaging lens according to any one of the first to fifth aspects, wherein at least one of the second and third lens groups includes only one lens.

  An imaging lens according to a seventh aspect of the present invention is the imaging lens according to any one of the first to sixth aspects, wherein the aperture is located closer to the object side than the second lens group.

  An imaging lens according to an eighth aspect is characterized in that, in any one of the first to seventh aspects, the third lens group includes at least one aspheric surface.

An imaging lens according to a ninth aspect is characterized in that, in any one of the first to eighth aspects, the following conditional expression (1a) is satisfied.
-7.6 <f2 / f <-3.7 (1a)
However,
f2: focal length of the second lens group,
f: focal length of the whole system,
It is.

An imaging lens according to a tenth aspect is characterized in that, in any one of the first to ninth aspects, the following conditional expression (2a) is satisfied.
−5.1 <f4 / f <−3.5 (2a)
However,
f4: focal length of the fourth lens group,
f: focal length of the whole system,
It is.

  An imaging lens according to an eleventh aspect is the imaging lens according to any one of the first to tenth aspects, wherein an aperture is provided in the first lens group.

  A twelfth aspect of the present invention is the imaging lens according to any one of the first to eleventh aspects, wherein in focusing to a near object distance, the second lens group moves to the image side, and the third lens group moves to the object side. Moving to the side.

  An imaging lens according to a thirteenth aspect is the imaging lens according to any one of the first to eleventh aspects, wherein the second lens group and the third lens group move to the object side during focusing to a near object distance. Features.

  An imaging optical device according to a fourteenth aspect includes the imaging lens according to any one of the first to thirteenth aspects, and an imaging element that converts an optical image formed on an imaging surface into an electric signal. Wherein the imaging lens is provided so that an optical image of a subject is formed on an imaging surface of the imaging device.

  According to a fifteenth aspect of the present invention, there is provided a digital apparatus including the imaging optical device according to the fourteenth aspect, wherein at least one of a function of photographing a still image and a moving image of a subject is added.

  According to the present invention, it is possible to realize an imaging lens and an imaging optical device in which a focus group is reduced in weight and which can focus on a wide imaging area while maintaining high optical performance at all imaging distances. By using the imaging lens or the imaging optical device in a digital device (for example, a digital camera), a high-performance image input function can be added to the digital device in a lightweight and compact manner.

FIG. 2 is a lens configuration diagram of the first embodiment (Example 1). FIG. 9 is a lens configuration diagram of a second embodiment (Example 2). FIG. 13 is a lens configuration diagram of a third embodiment (Example 3). FIG. 14 is a lens configuration diagram of a fourth embodiment (Example 4). FIG. 14 is a lens configuration diagram of a fifth embodiment (Example 5). FIG. 4 is a longitudinal aberration diagram of the first embodiment. FIG. 10 is a longitudinal aberration diagram of the second embodiment. FIG. 13 is a longitudinal aberration diagram of the third embodiment. FIG. 14 is a longitudinal aberration diagram of the fourth embodiment. FIG. 16 is a longitudinal aberration diagram of the fifth embodiment. FIG. 5 is a lateral aberration diagram at a first focus position according to the first embodiment. FIG. 5 is a lateral aberration diagram at a second focus position according to the first embodiment. FIG. 10 is a lateral aberration diagram at a first focus position according to the second embodiment. FIG. 14 is a lateral aberration diagram at a second focus position according to the second embodiment. FIG. 14 is a lateral aberration diagram at a first focus position according to the third embodiment. FIG. 14 is a lateral aberration diagram at a second focus position according to the third embodiment. FIG. 14 is a lateral aberration diagram at the first focus position according to the fourth embodiment. FIG. 14 is a lateral aberration diagram at a second focus position according to the fourth embodiment. FIG. 14 is a lateral aberration diagram at the first focus position in the fifth embodiment. FIG. 18 is a lateral aberration diagram at the second focus position in the fifth embodiment. FIG. 1 is a schematic diagram illustrating a schematic configuration example of a digital device equipped with an imaging optical device.

Hereinafter, an imaging lens, an imaging optical device, and a digital device according to an embodiment of the present invention will be described. The imaging lens according to the embodiment of the present invention includes, in order from the object side, a first lens group having positive power, a second lens group having negative power, a third lens group having positive power, A fourth lens group having a negative power (power: an amount defined by the reciprocal of the focal length), and the first lens group and the fourth lens group are fixed in position with respect to an image plane during focusing; The second lens group and the third lens group move in the direction of the optical axis so that the distance between the lens groups changes. The first lens group has a negative meniscus lens convex to the object side closest to the object side, and the second lens group and the third lens group each include two or less lenses, and the following conditional expression (1) ).
−7.6 <f2 / f <−3.0 (1)
However,
f2: focal length of the second lens group,
f: focal length of the whole system,
It is.

  In focusing from an object at infinity to an object at a close distance, a floating method in which the first lens unit and the fourth lens unit are fixed, and the second lens unit and the third lens unit are moved as a focus unit, is used. While expanding the area, high optical performance can be achieved without deteriorating performance from infinity to close range (higher performance during focusing). Further, when this configuration is adopted, the weight of the focus group can be reduced by reducing the number of lenses in the focus group, and the focus speed can be increased (higher focusing speed). In other words, if the weight of the focus group is reduced, it is possible to increase the speed of autofocus and reduce the focus movement time, which has the advantage of obtaining excellent usability and reducing the load on the motor. Etc.

  When the negative meniscus lens convex to the object side is arranged closest to the object side, the power of the first lens group does not become too large, and various aberrations including spherical aberration generated in front of the diaphragm are corrected well, The generation of chromatic coma after the stop can be suppressed, and high optical performance can be achieved from the center to the periphery of the screen.

  Further, in the floating system in which the second group and the third group are focus groups in a four-group configuration having positive, negative, positive, and negative power arrangements, the power ratio of the second lens group to the entire system shortens the focal length of the entire system, In addition, this is important in favorably performing aberration correction, and must be within the range of conditional expression (1). The conditional expression (1) defines a preferable condition range regarding the power of the second lens group from this viewpoint.

  By exceeding the lower limit of conditional expression (1), the power of the second lens unit does not become too small, and it is possible to satisfactorily correct field curvature, astigmatism, and the like generated in the lens unit after the stop. A homogeneous and high-performance solution can be provided from the center to the periphery of the screen. On the other hand, when the value goes below the upper limit of the conditional expression (1), the power of the second lens unit does not become too large, and the fluctuation of spherical aberration due to focusing is suppressed while suppressing coma and the like generated in the lens unit after the stop. Thus, high optical performance can be achieved while expanding the photographing area. Also, if the power of the second lens group becomes too large, the power of the first lens group becomes relatively small and it becomes difficult to correct chromatic aberration in the entire optical system. Thus, a power arrangement for better correcting aberrations is provided. Therefore, by satisfying the conditional expression (1), it is possible to achieve a good balance between high performance at the time of focusing and high speed of focusing in a compact and large-diameter imaging lens.

  According to the above-described characteristic configuration, it is possible to realize an imaging lens in which a focus group is reduced in weight and capable of focusing on a wide imaging area while maintaining high optical performance at all imaging distances, and an imaging optical apparatus including the imaging lens. Can be. For example, it is a large-diameter wide-angle lens in which performance variation at the time of focusing is suppressed while expanding a focusable shooting area, and it is possible to effectively cope with contrast AF by reducing the weight of the focus group. An imaging lens and an imaging optical device can be realized. By using the imaging lens or the imaging optical device in a digital device (for example, a digital camera), a high-performance image input function can be added to the digital device in a lightweight and compact manner. It can contribute to cost reduction, higher performance, higher functionality, and the like. For example, an imaging lens having the above-described characteristic configuration is suitable as an interchangeable lens for digital cameras and video cameras, so that a lightweight and small-sized interchangeable lens that is convenient to carry can be realized. The conditions for achieving these effects in a well-balanced manner and achieving higher optical performance, lighter weight, smaller size, and the like will be described below.

It is desirable to satisfy the following conditional expressions (1a).
-7.6 <f2 / f <-3.7 (1a)
The conditional expression (1a) defines a more preferable condition range based on the viewpoints and the like, among the conditional ranges defined by the conditional expression (1). Therefore, preferably, by satisfying conditional expression (1a), the above effect can be further enhanced.

It is desirable to satisfy the following conditional expressions (2).
−5.1 <f4 / f <−1.4 (2)
However,
f4: focal length of the fourth lens group,
f: focal length of the whole system,
It is.

  Conditional expression (2) defines a preferable condition range regarding the power of the fourth lens unit. When the lower limit of conditional expression (2) is exceeded, the power of the fourth lens unit does not become too small, and coma aberration generated in the lens unit after the stop can be suppressed. In addition, since the power of the first lens group can be relatively prevented from becoming too small, the occurrence of field curvature in the first lens group can also be suppressed. On the other hand, when the value goes below the upper limit of the conditional expression (2), the power of the fourth lens unit does not become too large, and the generation of sagittal coma in the lens unit after the stop can be suppressed. In addition, since the power of the first lens unit can be relatively prevented from becoming excessively large, the occurrence of coma in the first lens unit can also be suppressed. Therefore, when the value is within the range of the conditional expression (2), the power of the fourth lens group is kept optimal, and various aberrations including coma are favorably corrected, and the optical performance around the screen is improved. be able to.

It is desirable to satisfy the following conditional expressions (2a).
−5.1 <f4 / f <−3.5 (2a)
The conditional expression (2a) defines a more preferable conditional range based on the viewpoints and the like, among the conditional ranges defined by the conditional expression (2). Therefore, preferably, by satisfying conditional expression (2a), the above effect can be further enhanced.

It is desirable to satisfy the following conditional expressions (3).
1.0 <f2 / f4 <2.2 (3)
However,
f2: focal length of the second lens group,
f4: focal length of the fourth lens group,
It is.

  Conditional expression (3) defines a preferable condition range regarding the power ratio between the second lens unit and the fourth lens unit. When the lower limit of conditional expression (3) is exceeded, the power of the second lens unit with respect to the fourth lens unit does not become too large, so that the occurrence of chromatic aberration can be suppressed, and the fluctuation of spherical aberration due to focusing can be suppressed. On the other hand, when the value is below the upper limit of the conditional expression (3), the power of the fourth lens unit with respect to the second lens unit does not become too large, and the occurrence of field curvature and astigmatism can be suppressed. Therefore, by being within the range of the conditional expression (3), the power ratio between the second lens unit and the fourth lens unit is kept optimal, and the occurrence of various aberrations in the entire optical system is favorably corrected. High optical performance can be achieved at the center of the screen.

It is desirable to satisfy the following conditional expressions (4).
0.8 <f1 / f3 <1.8 (4)
However,
f1: focal length of the first lens group,
f3: focal length of the third lens group,
It is.

  Conditional expression (4) defines a preferable condition range regarding the power ratio between the first lens unit and the third lens unit. When the lower limit of conditional expression (4) is exceeded, the power of the first lens group with respect to the third lens group does not become too large, and chromatic aberration generated in the first lens group can be corrected well. Further, the power of the lens group relatively after the stop becomes small, and the occurrence of field curvature can be suppressed. On the other hand, when the value goes below the upper limit of the conditional expression (4), the power of the third lens unit with respect to the first lens unit does not become too large, and chromatic aberration occurring after the stop is corrected well, and astigmatism due to focusing. Variations in spherical aberration can be suppressed. Further, the power of the first lens group is relatively optimized, and the occurrence of chromatic aberration in the first lens group can be suppressed. Therefore, by being within the range of the conditional expression (4), the power ratio between the first lens unit and the third lens unit is kept optimal, and the occurrence of various aberrations in the entire optical system is corrected favorably. High optical performance can be achieved from the center to the periphery.

  It is preferable that the second lens group includes a cemented lens composed of a negative lens and a positive lens in order from the object side. Since the second lens group is a negative / positive cemented lens, variation in chromatic aberration due to focusing can be suppressed, and high optical performance can be achieved in all photographing regions. Further, since the number of lenses can be reduced, the weight of the focus group can be reduced. It is more desirable that the second lens group is composed of a cemented lens composed of a biconcave lens and a biconvex lens in order from the object side, and it is possible to more effectively suppress the chromatic aberration fluctuation due to focusing.

  It is preferable that at least one of the second and third lens groups includes only one lens. When the second lens group is composed of only one negative lens, the weight of the focus group can be reduced by reducing the number of lenses, and chromatic aberration fluctuation due to focus can be corrected well. As the negative lens, a negative meniscus lens is preferable. By forming the second lens group with one negative meniscus lens, it is possible to more effectively achieve the reduction in the weight of the focus group and the suppression of chromatic aberration fluctuation during focusing. . Further, when the third lens group is composed of only one positive lens, the weight of the focus group can be reduced by reducing the number of lenses, and the fluctuation of coma due to focus can be corrected well. As the positive lens, a biconvex lens is more preferable. Therefore, when the second lens group and the third lens group each include one lens, it is possible to further reduce the weight of the focus group and to more effectively suppress the chromatic aberration variation and the coma aberration variation due to focusing. It becomes.

  It is desirable that the stop be located closer to the object side than the second lens group. By disposing the second and third lens groups, which are focus groups, after the stop, it is possible to satisfactorily correct the chromatic aberration fluctuation due to focus.

  It is desirable to have an aperture in the first lens group. When a stop is arranged in the first lens group, the diameter of the entire imaging lens can be reduced, and the diameters of the second and third lens groups, which are focus groups, can be reduced at the same time.

  It is desirable that the lens adjacent to the image side of the stop be a positive meniscus lens having a convex surface facing the image side. By arranging the positive meniscus lens having the convex surface facing the image side adjacent to the image side of the stop, it is possible to satisfactorily correct spherical aberration occurring before and after the stop.

  It is preferable that the third lens group includes at least one aspheric surface. By including one or more aspherical surfaces in the third lens group, it is possible to satisfactorily correct sagittal coma while correcting various aberrations caused by focusing. Note that the arrangement of the aspheric surface in the third lens group is effective on either the object side or the image side, but the arrangement on the image side is more effective.

  In focusing on a near object distance, it is preferable that the second lens group moves to the image side and the third lens group moves to the object side. According to this focus movement type, the power of the second lens group does not become too small, and it is possible to satisfactorily correct the field curvature, astigmatism, and the like, which occur in the lens group after the stop, from the center of the screen to the periphery of the screen. A homogeneous and high-performance solution can be provided. In addition, the power of the fourth lens group does not become too small, and coma generated in the lens group after the stop can be suppressed. Further, since the power of the first lens group can be relatively suppressed from becoming too small, the occurrence of field curvature in the first lens group can also be suppressed. In this focus movement type, it is more desirable to move the second lens group and the third lens group so that the distance between the second lens group and the third lens group becomes narrower when focusing on a near object distance.

  At the time of focusing to a near object distance, it is preferable that each of the second lens group and the third lens group moves to the object side. According to this focus movement type, the power of the second lens group does not become too large, and while suppressing coma occurring in the lens group after the diaphragm, it is possible to suppress spherical aberration fluctuation due to focus, thereby expanding the shooting area. However, high optical performance can be achieved. In addition, the power of the fourth lens unit does not become too large, and the occurrence of sagittal coma in the lens unit after the stop can be suppressed. Further, since the power of the first lens group can be relatively prevented from becoming too large, the occurrence of coma in the first lens group can also be suppressed. In this focus movement type, it is more desirable to move the second lens group and the third lens group so as to increase the distance when focusing on a near object distance.

  The imaging lens described above is suitable for use as an imaging lens for digital equipment with an image input function (for example, a digital camera with interchangeable lenses). By combining this with an imaging device or the like, an image of an object can be optically captured. An imaging optical device that takes in the data and outputs it as an electrical signal can be configured. The imaging optical device is an optical device that is a main component of a camera used for still image shooting and moving image shooting of a subject, and includes, for example, an imaging lens that forms an optical image of the object in order from the object (ie, the subject) side, An image sensor that converts an optical image formed by the imaging lens into an electric signal. The imaging lens having the above-described characteristic configuration is arranged such that an optical image of the subject is formed on the light receiving surface (that is, the imaging surface) of the imaging device, thereby achieving high performance at a small size and at low cost. An imaging optical device and a digital device including the same can be realized.

  Examples of digital devices with an image input function include digital cameras, video cameras, surveillance cameras, security cameras, in-vehicle cameras, cameras for videophones, and the like. In addition, personal computers, portable digital devices (for example, mobile phones, smartphones (high-performance mobile phones), tablet terminals, mobile computers, etc.), peripheral devices (scanners, printers, mice, etc.), and other digital devices (drives, etc.) Recorders, defense equipment, etc.) or the like, having a built-in or external camera function. As can be seen from these examples, not only can a camera be configured by using an imaging optical device, but also a camera function can be added by mounting an imaging optical device on various devices. For example, a digital device with an image input function such as a mobile phone with a camera can be configured.

  FIG. 21 is a schematic cross-sectional view showing a schematic configuration example of a digital device DU as an example of a digital device with an image input function. The imaging optical device LU mounted on the digital device DU shown in FIG. 21 includes, in order from the object (ie, subject) side, an imaging lens LN (AX: optical axis) that forms an optical image (image plane) IM of the object; An image sensor SR that converts the optical image IM formed on the light receiving surface (imaging surface) SS by the imaging lens LN into an electrical signal, and a parallel plane plate (for example, the image sensor SR) (Corresponding to an optical filter such as an optical low-pass filter and an infrared cut filter that are arranged as necessary). When a digital device DU with an image input function is constituted by the imaging optical device LU, the imaging optical device LU is usually arranged inside the body, but when realizing the camera function, a form suitable for the necessity is adopted. It is possible to do. For example, the unitized imaging optical device LU can be configured to be detachable or rotatable with respect to the main body of the digital device DU.

  The imaging lens LN is a four-group imaging lens. During focusing, the first lens group having positive power and the fourth lens group having negative power are fixed in position with respect to the image plane, and the distance between the lens groups changes. As described above, the inner focus method in which the second lens group having negative power and the third lens group having positive power move in the direction of the optical axis AX is adopted, and an optical image IM is formed on the light receiving surface SS of the image sensor SR. It has a configuration. As the imaging device SR, for example, a solid-state imaging device such as a CCD image sensor or a CMOS image sensor having a plurality of pixels is used. Since the imaging lens LN is provided so that the optical image IM of the subject is formed on the light receiving surface SS, which is a photoelectric conversion unit of the imaging device SR, the optical image IM formed by the imaging lens LN is It is converted into an electrical signal by the SR.

  The digital device DU includes a signal processing unit 1, a control unit 2, a memory 3, an operation unit 4, a display unit 5, and the like, in addition to the imaging optical device LU. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, and the like as necessary in the signal processing unit 1, and is recorded as a digital video signal in the memory 3 (semiconductor memory, optical disk, or the like). In some cases, the data is transmitted to another device via a cable or converted into an infrared signal or the like (for example, a communication function of a mobile phone). The control unit 2 is composed of a microcomputer, and centralizes control of functions such as a photographing function (still image photographing function, moving image photographing function, etc.) and an image reproducing function; control of a lens moving mechanism for focusing, camera shake correction, and the like. Do it. For example, the control unit 2 controls the imaging optical device LU so as to perform at least one of still image shooting and moving image shooting of the subject. The display unit 5 is a part including a display such as a liquid crystal monitor, and displays an image using an image signal converted by the image sensor SR or image information recorded in the memory 3. The operation unit 4 includes operation members such as an operation button (for example, a release button) and an operation dial (for example, a shooting mode dial), and transmits information input by the operator to the control unit 2.

  Next, the specific optical configuration of the imaging lens LN will be described in further detail with reference to first to fifth embodiments. 1 to 5 are lens configuration diagrams respectively corresponding to the imaging lenses LN constituting the first to fifth embodiments. The first focus position POS1 (object distance state at infinity) and the second focus position POS2. The lens arrangement in (the shortest object distance state) is shown in an optical section. Arrows mF2 and mF3 indicate movement of the second lens unit Gr2 and the third lens unit Gr3 during focusing from the first focus position POS1 to the second focus position POS2.

  In any of the embodiments, the imaging lens LN has a positive, negative, positive, and negative four-group configuration. For focusing, the first lens group Gr1 and the fourth lens group Gr4 are fixed groups, and the second lens group Gr2 and the third lens group Gr4. The lens group Gr3 is a movable group (focus group). The lens L11 closest to the object side is a negative meniscus lens convex to the object side, has a stop (aperture stop) ST in the first lens group Gr1, and has the number of lenses in the second lens group Gr2 and the third lens group Gr3. Is two or less in each case. Note that a parallel flat plate PT is disposed between the imaging lens LN and the image plane IM, and the parallel flat plate PT is a glass flat plate equivalent to the total optical thickness of a cover glass or the like of the image sensor SR. .

  In the imaging lens LN (FIG. 1) of the first embodiment, each lens group is configured as follows in order from the object side. The first lens group Gr1 includes a negative meniscus lens L11 having a convex surface facing the object side, a cemented lens including a biconvex positive lens L12 and a biconcave negative lens L13, a biconcave negative lens L14, and a biconvex negative lens. It comprises a cemented lens composed of a positive lens L15, a biconcave negative lens L16 and a biconvex positive lens L17, a biconvex positive aspherical lens L18, and a stop ST. The second lens group Gr2 is constituted solely by a negative meniscus lens L21 having a double-sided aspheric surface with the convex surface facing the object. The third lens group Gr3 is composed of only a biconvex positive aspherical double-sided positive lens L31. The fourth lens group Gr4 includes only a biconcave negative lens L41. At the time of focusing to a near object distance, the second lens group Gr2 moves toward the image side (arrow mF2) so that the distance between the second lens group Gr2 and the third lens group Gr3 is reduced (arrow mF2), and the third lens group Gr3 is moved. Move to the object side (arrow mF3).

  In the imaging lens LN (FIG. 2) of the second embodiment, each lens group is configured as follows in order from the object side. The first lens group Gr1 includes a negative meniscus lens L11 having a convex surface facing the object side, a biconcave negative lens L12, a biconvex positive lens L13, a biconvex positive lens L14, and a biconvex positive lens L15. And a cemented lens composed of a biconcave negative lens L16, a stop ST, and a positive meniscus lens L17 having a convex surface facing the image side. The second lens group Gr2 is composed of only a cemented lens composed of a biconcave negative lens L21 and a biconvex positive lens L22, and the most image-side lens surface of this cemented lens is an aspheric surface. The third lens group Gr3 is composed of only a biconvex positive aspherical double-sided positive lens L31. The fourth lens group Gr4 includes only a cemented lens including a biconcave negative lens L41 and a positive meniscus lens L42 having a convex surface facing the object. At the time of focusing to a near object distance, the second lens unit Gr2 and the third lens unit Gr3 move toward the object side, respectively, such that the distance between the second lens unit Gr2 and the third lens unit Gr3 increases (arrow mF2, mF3).

  In the imaging lens LN (FIG. 3) of the third embodiment, each lens group is configured as follows in order from the object side. The first lens group Gr1 includes a negative meniscus lens L11 having a convex surface facing the object side, a biconcave negative lens L12, a positive meniscus lens L13 having a convex surface facing the image side, and a biconvex positive lens L14. It is composed of a cemented lens composed of a convex positive lens L15 and a biconcave negative lens L16, a stop ST, and a positive meniscus lens L17 having a convex surface facing the image side. The second lens group Gr2 is composed of only a cemented lens composed of a biconcave negative lens L21 and a biconvex positive lens L22, and the most image-side lens surface of this cemented lens is an aspheric surface. The third lens group Gr3 is composed of only a biconvex positive aspherical double-sided positive lens L31. The fourth lens group Gr4 includes only a cemented lens including a biconcave negative lens L41 and a positive meniscus lens L42 having a convex surface facing the object. At the time of focusing to a near object distance, the second lens unit Gr2 and the third lens unit Gr3 move toward the object side, respectively, such that the distance between the second lens unit Gr2 and the third lens unit Gr3 increases (arrow mF2, mF3).

  In the imaging lens LN (FIG. 4) of the fourth embodiment, each lens group is configured as follows from the object side. The first lens group Gr1 includes a negative meniscus lens L11 having a convex surface facing the object side, a biconcave negative lens L12, a positive meniscus lens L13 having a convex surface facing the image side, and a biconvex positive lens L14. It is composed of a cemented lens composed of a convex positive lens L15 and a biconcave negative lens L16, a stop ST, and a positive meniscus lens L17 having a convex surface facing the image side. The second lens group Gr2 is composed of only a cemented lens composed of a biconcave negative lens L21 and a biconvex positive lens L22, and the most image-side lens surface of this cemented lens is an aspheric surface. The third lens group Gr3 is composed of only a biconvex positive aspherical double-sided positive lens L31. The fourth lens group Gr4 includes only a cemented lens including a biconcave negative lens L41 and a positive meniscus lens L42 having a convex surface facing the object. At the time of focusing to a near object distance, the second lens unit Gr2 and the third lens unit Gr3 move toward the object side, respectively, such that the distance between the second lens unit Gr2 and the third lens unit Gr3 increases (arrow mF2, mF3).

  In the imaging lens LN (FIG. 5) of the fifth embodiment, each lens group is configured as follows from the object side. The first lens group Gr1 includes a negative meniscus lens L11 having a convex surface facing the object side, a biconcave negative lens L12, a biconvex positive lens L13, a biconvex positive lens L14, and a biconvex positive lens L15. And a cemented lens composed of a biconcave negative lens L16, a stop ST, and a positive meniscus lens L17 having a convex surface facing the image side. The second lens group Gr2 is composed of only a cemented lens composed of a biconcave negative lens L21 and a biconvex positive lens L22, and the most image-side lens surface of this cemented lens is an aspheric surface. The third lens group Gr3 is composed of only a biconvex positive aspherical double-sided positive lens L31. The fourth lens group Gr4 includes only a cemented lens including a biconcave negative lens L41 and a biconvex positive lens L42. At the time of focusing to a near object distance, the second lens group Gr2 and the third lens group Gr3 move toward the object side, respectively, such that the distance between the second lens group Gr2 and the third lens group Gr3 becomes narrower (arrow mF2). mF3).

  Hereinafter, the configuration and the like of the imaging lens embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 to 5 (EX1 to 5) cited here are numerical examples corresponding to the above-described first to fifth embodiments, respectively, and are lens configuration diagrams showing the first to fifth embodiments. (FIGS. 1 to 5) show the corresponding optical configurations of Examples 1 to 5, respectively.

  In the construction data of each embodiment, as surface data, surface number i (OB: object surface, ST: aperture surface, IM: image surface), paraxial radius of curvature Ri (mm), upper surface of the axis in order from the left column The distance Di (mm), the refractive index Nd for the d-line (wavelength: 587.56 nm), and the Abbe number νd for the d-line are shown.

A surface with * added to the surface number i is an aspheric surface, and its surface shape is defined by the following equation (AS) using a local rectangular coordinate system (x, y, z) whose origin is the surface vertex. You. As the aspherical surface data, an aspherical surface coefficient and the like are shown. In the aspherical surface data of each embodiment, the coefficient of a term that is not described is 0, and E−n = × 10 ⁻ⁿ for all data.
z = (ch · h ² ) / [1+ {1− (1 + K) · c ² · h ² }] + Σ (Aj · h ^j ) (AS)
However,
h: height (h ² = x ² + y ² ) in the direction perpendicular to the z-axis (optical axis AX),
z: sag amount in the optical axis AX direction at the position of height h (based on surface vertex);
c: curvature at the surface vertex (reciprocal of the radius of curvature r),
K: conical constant,
Aj: j-th order aspherical coefficient,
It is.

  As various data, the focal length (f, mm) of the entire system, the F number (FNO.), The total angle of view (2ω, °), the maximum image height (y′max, mm), the total lens length (TL, mm), Indicates the back focus (BF, mm). However, the back focus BF used here is the distance from the image side surface of the plane parallel plate PT to the image plane IM, and the total lens length TL is the distance from the frontmost lens to the image plane IM.

  Further, a variable axial upper surface distance Di (mm) is shown for each of the first focus position POS1 and the second focus position POS2 as a variable parameter that changes by focusing, and the focal length of the first lens group Gr1 as lens group data. (F1, mm), the focal length of the second lens group Gr2 (f2, mm), the focal length of the third lens group Gr3 (f3, mm), and the focal length of the fourth lens group Gr4 (f4, mm). . Table 1 shows the values corresponding to the conditional expressions in each embodiment.

  6 to 10 are longitudinal aberration diagrams respectively corresponding to Examples 1 to 5 (EX1 to EX5), wherein (A) to (C) are first focus positions POS1, (D) to (F). Indicates various aberrations at the second focus position POS2. 6 to 10, (A) and (D) are spherical aberration diagrams, (B) and (E) are astigmatism diagrams, and (C) and (F) are distortion aberration diagrams.

  The spherical aberration diagram shows the amount of spherical aberration with respect to the C line (wavelength 656.28 nm) indicated by the dashed line, the amount of spherical aberration with respect to the d line (wavelength 587.56 nm) indicated by the solid line, and the g line (wavelength 435.84 nm) indicated by the broken line. The spherical aberration amount is represented by a deviation amount (mm) in the optical axis AX direction from the paraxial image plane, and the vertical axis represents the F value. In the astigmatism diagram, a dashed line M represents a meridional image plane with respect to the d-line, and a solid line S represents a sagittal image plane with respect to the d-line, each of which is represented by a shift amount (mm) from the paraxial image plane in the optical axis AX direction. The axis represents the image height Y ′ (mm). In the distortion diagram, the horizontal axis represents distortion (%) with respect to the d-line, and the vertical axis represents image height Y '(mm). The image height Y 'corresponds to the maximum image height y'max on the image plane IM (half the diagonal length of the light receiving surface SS of the image sensor SR).

  FIGS. 11, 13, 15, 17, and 19 are lateral aberration diagrams corresponding to Examples 1 to 5 (EX1 to EX5) at the first focus position POS1, respectively, and FIGS. 16, FIG. 18, FIG. 18, and FIG. 20 are transverse aberration diagrams corresponding to the first to fifth embodiments (EX1 to EX5) at the second focus position POS2, respectively. In each of FIGS. 11 to 20, (A) to (C) denote meridional coma (mm), (D) to (F) denote sagittal coma (mm), and for each image height Y ′ (mm). Is shown. 6 to 10, the dashed line is the C line (wavelength 656.28 nm), the solid line is the d line (wavelength 587.56 nm), and the broken line is the g line (wavelength 435.84 nm).

Example 1
Unit: mm
Surface data
i Ri (mm) Di (mm) Nd νd
0 (OB) ∞ ∞
1 107.684 2.20 1.5168 64.2
2 26.867 12.62
3 42.333 9.55 1.9212 24.0
4 -111.501 2.00 1.5688 56.0
5 24.982 11.31
6 -39.056 2.00 1.6727 32.2
7 301.060 0.40
8 59.363 8.41 1.8348 42.7
9 -47.408 0.81
10 -69.545 1.80 1.8052 25.5
11 24.613 10.86 1.5928 68.6
12 -214.044 0.40
13 * 48.233 8.29 1.7432 49.3
14 * -78.841 2.50
15 (ST) ∞ 3.52
16 * 102.809 1.80 1.5831 59.4
17 * 39.230 20.74
18 * 46.667 8.34 1.8086 40.4
19 * -45.905 2.50
20 -566.682 1.50 1.6477 33.8
21 34.836 25.43
22 ∞ 2.00 1.5168 64.2
23 ∞ 1.00
24 (IM) ∞ 0.00

Aspheric surface 13th surface
K = 0.00000E + 00
A4 = -0.17067E-05
A6 = -0.20919E-08
A8 = 0.68691E-11
A10 = -0.34731E-14

Aspherical data surface 14
K = 0.00000E + 00
A4 = 1.71541E-06
A6 = -4.18702E-09
A8 = 1.06397E-11
A10 = -1.07892E-14

Aspherical data surface 16
K = 0.00000E + 00
A4 = 0.59648E-05
A6 = -0.57361E-08
A8 = 0.00000E + 00
A10 = 0.00000E + 00

Aspherical surface 17th surface
K = 0.00000E + 00
A4 = 5.59203E-06
A6 = 2.40969E-10
A8 = -2.04447E-11
A10 = 2.11460E-14

Aspheric surface 18th surface
K = 0.00000E + 00
A4 = -0.18309E-05
A6 = -0.59764E-08
A8 = 0.30810E-10
A10 = -0.49169E-13

Aspherical surface data page 19
K = 0.00000E + 00
A4 = 7.35080E-06
A6 = -1.16284E-08
A8 = 3.85069E-11
A10 = -5.50894E-14

Various data
f = 34.20
FNO. = 1.44
2ω = 64.55
y'max = 21.60
TL = 140.00
BF = 1.00

Variable parameters (interval)
D0 D15 D17 D19
POS1 ∞ 3.52 20.74 2.50
POS2 160.00 11.01 11.79 3.97

Lens group data
f1 = 47.836
f2 = -109.496
f3 = 29.650
f4 = -50.270

Example 2
Unit: mm
Surface data
i Ri (mm) Di (mm) Nd νd
0 (OB) ∞ ∞
1 139.851 2.10 1.4970 81.6
2 33.329 17.44
3 -68.350 1.30 1.8467 23.8
4 99.847 7.18
5 129.921 10.89 1.7292 54.7
6 -64.491 4.35
7 64.745 6.58 1.9229 20.9
8 -869.001 5.24
9 33.335 9.93 1.6968 55.5
10 -65.301 1.30 1.7552 27.5
11 26.859 6.40
12 (ST) ∞ 3.90
13 -39.131 2.36 1.8340 37.3
14 -35.376 9.73
15 -26.577 1.91 1.6477 33.8
16 35.322 6.30 1.8042 46.5
17 * -63.555 2.19
18 * 93.622 9.00 1.5928 68.6
19 * -28.104 2.32
20 -222.695 1.80 1.6727 32.2
21 71.073 3.74 1.8348 42.7
22 158.931 21.79
23 ∞ 1.41 1.5168 64.2
24 ∞ 0.80
25 (IM) ∞ 0.00

Aspherical surface 17th surface
K = -8.33024E + 00
A4 = 4.09750E-07
A6 = 3.57499E-08
A8 = -1.06617E-10
A10 = 3.61125E-13

Aspheric surface 18th surface
K = -8.30491E + 01
A4 = 2.46604E-06
A6 = -2.62684E-08
A8 = 2.09763E-11
A10 = 0.00000E + 00

Aspherical surface data page 19
K = 7.95219E-01
A4 = 5.82103E-06
A6 = 0.00000E + 00
A8 = 0.00000E + 00
A10 = 0.00000E + 00

Various data
f = 34.13
FNO. = 1.44
2ω = 64.66
y'max = 21.60
TL = 140.00
BF = 0.80

Variable parameters (interval)
D0 D14 D17 D19
POS1 ∞ 9.73 2.19 2.32
POS2 160.00 4.22 2.39 7.63

Lens group data
f1 = 62.662
f2 = -165.896
f3 = 37.366
f4 = -164.850

Example 3
Unit: mm
Surface data
i Ri (mm) Di (mm) Nd νd
0 (OB) ∞ ∞
1 170.800 2.30 1.4970 81.6
2 32.766 17.57
3 -41.320 1.70 1.9212 24.0
4 1000.000 2.08
5 -814.174 9.53 1.7292 54.7
6 -44.196 3.17
7 77.662 7.01 1.9229 20.9
8 -152.330 4.57
9 38.906 9.79 1.6968 55.5
10 -56.096 4.21 1.7552 27.5
11 32.955 5.92
12 (ST) ∞ 4.42
13 -35.349 2.46 1.8340 37.3
14 -32.201 10.64
15 -26.254 1.90 1.6477 33.8
16 42.298 6.30 1.8042 46.5
17 * -51.922 3.05
18 * 180.516 9.00 1.5928 68.6
19 * -27.509 2.25
20 -11019.982 1.80 1.6727 32.2
21 66.256 6.30 1.8348 42.7
22 98.672 21.79
23 ∞ 1.41 1.5168 64.2
24 ∞ 0.80
25 (IM) ∞ 0.00

Aspherical surface 17th surface
K = -1.51263E + 01
A4 = -5.93338E-06
A6 = 4.46039E-08
A8 = -1.08164E-10
A10 = 3.26021E-13

Aspheric surface 18th surface
K = -3.33030E + 02
A4 = 1.22251E-06
A6 = -2.42964E-08
A8 = 2.25081E-11
A10 = 0.00000E + 00

Aspherical surface data page 19
K = 6.22224E-01
A4 = 5.02896E-06
A6 = 0.00000E + 00
A8 = 0.00000E + 00
A10 = 0.00000E + 00

Various data
f = 35.53
FNO. = 1.44
2ω = 62.64
y'max = 21.60
TL = 140.00
BF = 0.80

Variable parameters (interval)
D0 D14 D17 D19
POS1 ∞ 10.64 3.05 2.25
POS2 160.00 4.48 3.40 8.06

Lens group data
f1 = 69.049
f2 = -257.167
f3 = 40.786
f4 = -165.073

Example 4
Unit: mm
Surface data
i Ri (mm) Di (mm) Nd νd
0 (OB) ∞ ∞
1 131.492 2.30 1.4970 81.6
2 32.076 20.51
3 -40.171 1.70 1.9212 24.0
4 1000.000 2.03
5 -848.667 9.33 1.7292 54.7
6 -43.256 3.00
7 74.030 7.05 1.9229 20.9
8 -151.422 2.80
9 39.546 9.86 1.6968 55.5
10 -55.476 4.37 1.7552 27.5
11 33.297 5.97
12 (ST) ∞ 4.29
13 -39.098 3.58 1.8340 37.3
14 -34.880 10.02
15 -26.096 1.90 1.6477 33.8
16 38.047 6.30 1.8042 46.5
17 * -66.282 2.36
18 * 90.697 9.00 1.5928 68.6
19 * -27.712 2.28
20 -270.761 1.80 1.6727 32.2
21 97.453 5.51 1.8348 42.7
22 122.103 21.79
23 ∞ 1.41 1.5168 64.2
24 ∞ 0.80
25 (IM) ∞ 0.00

Aspherical surface 17th surface
K = -1.50231E + 01
A4 = -5.84653E-06
A6 = 4.74667E-08
A8 = -1.11917E-10
A10 = 3.12540E-13

Aspheric surface 18th surface
K = -8.67177E + 01
A4 = -4.59806E-07
A6 = -1.81578E-08
A8 = 1.63557E-11
A10 = 0.00000E + 00

Aspherical surface data page 19
K = 6.67878E-01
A4 = 5.84582E-06
A6 = 0.00000E + 00
A8 = 0.00000E + 00
A10 = 0.00000E + 00

Various data
f = 35.83
FNO. = 1.52
2ω = 62.17
y'max = 21.60
TL = 140.00
BF = 0.80

Variable parameters (interval)
D0 D14 D17 D19
POS1 ∞ 10.02 2.36 2.28
POS2 160.00 4.26 2.56 7.83

Lens group data
f1 = 61.096
f2 = -136.230
f3 = 36.723
f4 = -129.055

Example 5
Unit: mm
Surface data
i Ri (mm) Di (mm) Nd νd
0 (OB) ∞ ∞
1 80.976 2.34 1.4970 81.6
2 26.843 24.10
3 -38.099 1.85 1.9183 24.0
4 1000.000 2.20
5 1099.622 10.39 1.7292 54.7
6 -42.472 2.35
7 75.702 6.92 1.9229 20.9
8 -169.790 3.75
9 44.667 9.41 1.6968 55.5
10 -49.147 2.95 1.7552 27.5
11 42.833 5.69
12 (ST) ∞ 3.81
13 -56.673 2.78 1.8340 37.3
14 -42.143 10.18
15 -27.235 2.00 1.6477 33.8
16 43.642 6.30 1.8042 46.5
17 * -53.989 3.19
18 * 1364.266 6.51 1.5928 68.6
19 * -30.573 2.46
20 -56.799 1.80 1.6727 32.2
21 136.135 4.59 1.8348 42.7
22 -173.569 22.19
23 ∞ 1.41 1.5168 64.2
24 ∞ 0.80
25 (IM) ∞ 0.00

Aspherical surface 17th surface
K = -2.16710E + 01
A4 = -1.00149E-05
A6 = 3.76307E-08
A8 = -9.24834E-11
A10 = 1.24226E-13

Aspheric surface 18th surface
K = -3.45124E + 17
A4 = 4.52556E-07
A6 = -1.75130E-08
A8 = -5.92798E-12
A10 = 0.00000E + 00

Aspherical surface data page 19
K = 8.86388E-01
A4 = 7.27378E-06
A6 = 0.00000E + 00
A8 = 0.00000E + 00
A10 = 0.00000E + 00

Various data
f = 35.05
FNO. = 1.58
2ω = 63.29
y'max = 21.60
TL = 140.00
BF = 0.80

Variable parameters (interval)
D0 D14 D17 D19
POS1 ∞ 10.18 3.19 2.46
POS2 160.00 4.29 2.25 9.29

Lens group data
f1 = 45.314
f2 = -263.165
f3 = 50.355
f4 = -175.486

DU Digital equipment LU Imaging optical device LN Imaging lens Gr1 First lens group Gr2 Second lens group Gr3 Third lens group Gr4 Fourth lens group ST Stop SR Image sensor SS Light receiving surface (Imaging surface)
IM image plane (optical image)
AX optical axis 1 signal processing unit 2 control unit 3 memory 4 operation unit 5 display unit

Claims (15)

In order from the object side, it comprises a first lens group having positive power, a second lens group having negative power, a third lens group having positive power, and a fourth lens group having negative power. ,
At the time of focusing, the first lens group and the fourth lens group are fixed in position with respect to the image plane, and the second lens group and the third lens group move in the optical axis direction such that the distance between the lens groups changes. And
The first lens group has a negative meniscus lens convex to the object side closest to the object side;
The second lens group and the third lens group each include two or less lenses,
An imaging lens characterized by satisfying the following conditional expression (1);
−7.6 <f2 / f <−3.0 (1)
However,
f2: focal length of the second lens group,
f: focal length of the whole system,
It is. 2. The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied;
−5.1 <f4 / f <−1.4 (2)
However,
f4: focal length of the fourth lens group,
f: focal length of the whole system,
It is. The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied;
1.0 <f2 / f4 <2.2 (3)
However,
f2: focal length of the second lens group,
f4: focal length of the fourth lens group,
It is. The imaging lens according to any one of claims 1 to 3, wherein the following conditional expression (4) is satisfied;
0.8 <f1 / f3 <1.8 (4)
However,
f1: focal length of the first lens group,
f3: focal length of the third lens group,
It is.   The imaging lens according to claim 1, wherein the second lens group includes a cemented lens including a negative lens and a positive lens in order from the object side.   The imaging lens according to claim 1, wherein at least one of the second and third lens groups includes only one lens.   The imaging lens according to any one of claims 1 to 6, wherein the stop is located closer to the object side than the second lens group.   The imaging lens according to claim 1, wherein the third lens group includes one or more aspheric surfaces. The imaging lens according to any one of claims 1 to 8, wherein the following conditional expression (1a) is satisfied;
-7.6 <f2 / f <-3.7 (1a)
However,
f2: focal length of the second lens group,
f: focal length of the whole system,
It is. The imaging lens according to any one of claims 1 to 9, wherein the following conditional expression (2a) is satisfied;
−5.1 <f4 / f <−3.5 (2a)
However,
f4: focal length of the fourth lens group,
f: focal length of the whole system,
It is.   The imaging lens according to claim 1, further comprising a stop in the first lens group.   The imaging apparatus according to any one of claims 1 to 11, wherein, at the time of focusing to a near object distance, the second lens group moves to the image side, and the third lens group moves to the object side. lens.   The imaging lens according to any one of claims 1 to 11, wherein upon focusing to a near object distance, the second lens group and the third lens group move to the object side, respectively.   An image pickup lens according to claim 1, and an image pickup device for converting an optical image formed on the image pickup surface into an electric signal, wherein a subject is provided on the image pickup surface of the image pickup device. An image pickup optical device, wherein the image pickup lens is provided so that an optical image is formed.   A digital device comprising the imaging optical device according to claim 14, wherein at least one of a function of photographing a still image of a subject and a function of photographing a moving image is added.

Images