JP7164184B2 - Imaging optical system, imaging optical device and digital equipment - Google Patents

Description

The present invention relates to an imaging optical system, an imaging optical device, and a digital device, and for example, an imaging optical system optimal as a large-aperture, medium-telephoto lens for a lens-interchangeable digital camera, and an image of a subject captured by the imaging optical system. The present invention relates to an imaging optical device for outputting .

In recent years, digital cameras have become popular as interchangeable lens cameras. Since a user of a digital camera can view a photographed image at the same magnification as a monitor, there is an increasing demand for improved imaging performance of the imaging optical system. Among mirrorless interchangeable lens cameras obtained by removing flip-up mirrors from single-lens reflex cameras, there are some that cannot use phase difference AF (autofocus), which has been the mainstream in conventional single-lens reflex cameras. Many of such cameras employ so-called contrast AF, in which focusing is performed by scanning a focus group and searching for a location where contrast is maximized.

In the case of phase-difference AF, information from the AF sensor can be used to calculate the amount of movement of the focus group necessary for focusing, so the focus group can be moved according to that amount. On the other hand, in the case of contrast AF, the information obtained from the AF sensor is only the contrast value at that moment. A focus operation is performed. Therefore, when contrast AF and phase difference AF are compared, the amount of movement of the focus group until focusing is overwhelmingly large in the former case.

For example, in a large aperture (F value: 2 or less) and medium telephoto (full size, focal length: about 70 to 135 mm) imaging optical system as proposed in Patent Documents 1 to 3, an attempt is made to support contrast AF. Then, in order to cover the large amount of movement of the focus group, it is necessary to speed up the AF. However, increasing the speed of the actuator leads to an increase in product size, and increasing the focus sensitivity leads to a decrease in focus accuracy. Therefore, the point is to reduce the weight of the focus group.

Reducing the number of lenses is effective in reducing the weight of the focus group. However, if the number of lenses in the focus group is reduced, it becomes difficult to sufficiently correct aberration fluctuations during focusing. In particular, since the fluctuation of chromatic aberration increases in proportion to the focal length, it is difficult to obtain good imaging performance in a medium-telephoto imaging optical system. Therefore, it is necessary for the imaging optical system to achieve both reduction in the weight of the focus group for speeding up AF and improvement in imaging performance from the infinite end to the closest end.

JP 2017-173409 A JP 2015-96915 A JP 2014-142601 A

In the imaging optical system proposed in Patent Document 1, the number of lenses in the focus group is increased in order to ensure imaging performance during focusing. Therefore, the focus group has not been lightened, and the AF cannot be speeded up. The imaging optical system proposed in Japanese Patent Laid-Open No. 2002-200000 has a configuration in which focusing is performed by a single negative lens that constitutes the second lens group. As a result, aberration fluctuations that occur during focusing are large. Patent document 3 proposes an image pickup optical system in which one negative lens that constitutes the second lens group and one positive lens that constitutes the third lens group are used for focusing. Aberration fluctuations occurring in each lens group during focusing become large.

The present invention has been made in view of this situation, and its object is to achieve both a bright F-number and a lightweight focus group, and to satisfactorily correct aberrations from the infinity end to the closest end. It is an object of the present invention to provide an imaging optical system capable of obtaining uniform image quality over the entire image, an imaging optical apparatus having the same, and a digital apparatus.

To achieve the above object, the imaging optical system of the first invention comprises, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a negative power fourth lens group,
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
It is characterized by satisfying the following conditional expressions (1) , (2) and (5) to (7) .
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
0.8<FL1/FL<1.1 (5)
-1.6<FL2/FL3<-0.9 (6)
-3.6<FL4/FL<-1.8 (7)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
FL1: focal length of the first lens group,
FL2: focal length of the second lens group,
FL3: focal length of the third lens group;
FL4: focal length of the fourth lens group,
FL: focal length of the whole system,
is.

The imaging optical system of the second invention comprises, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power. consists of
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
The fourth lens group has two cemented lenses successively composed of a positive lens and a negative lens in order from the object side, and among the two cemented lenses, the cemented lens on the object side has negative power, and the image the cemented lens on the side has positive power,
It is characterized by satisfying the following conditional expressions (1), (2) and (9) .
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
-2.2<FL(4GrPN1)/FL(4GrPN2)<-1.4 (9)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
FL (4GrPN1): the focal length of the cemented lens on the object side in the fourth lens group;
FL (4GrPN2): the focal length of the cemented lens on the image side in the fourth lens group;
is.

The imaging optical system of the third invention comprises, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power. consists of
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
a position-fixed diaphragm for focusing is arranged between the second lens group and the third lens group;
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
It is characterized by satisfying the following conditional expressions (1) and (2) .
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
is.

A fourth aspect of the present invention is an imaging optical system according to any one of the first to third aspects, wherein the cemented lens has a cemented surface with a concave surface facing the object side, and the following conditional expressions (3) and (4): ) is satisfied.
0.11<nd(2GrP)−nd(2GrN)<0.35 (3)
−20<νd(2GrP)−νd(2GrN)<−5 (4)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(2GrN): refractive index for the d-line of the negative lens in the second lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(2GrN): Abbe number for the d-line of the negative lens in the second lens group,
is.

An imaging optical system according to a fifth aspect of the invention is characterized in that, in any one of the first to fourth aspects of the invention, the following conditional expression (8) is satisfied.
−1.0<D2Gr/D3Gr<−0.45 (8)
however,
D2Gr: movement amount of the second lens group in focusing from infinity to a close object;
D3Gr: movement amount of the third lens group in focusing from infinity to a close object;
, and the amount of movement when the direction of movement is on the image side is positive.

An imaging optical system according to a sixth aspect of the invention is characterized in that, in any one of the first to fifth aspects of the invention, a lens located closest to the image side in the fourth lens group has negative power.

A seventh invention is an imaging optical system according to any one of the first to sixth inventions, wherein the first lens group has at least three continuous positive lenses in order from the object side, one of which The above positive lens is characterized by satisfying the following conditional expression (10).
νd(1GrP)>60 (10)
however,
νd(1GrP): Abbe number for the d-line of the positive lens in the first lens group;
is.

An imaging optical device according to an eighth invention comprises an imaging optical system according to any one of the first to seventh inventions, an imaging device for converting an optical image formed on an imaging surface into an electrical signal, and wherein the imaging optical system is provided so as to form an optical image of a subject on the imaging surface of the imaging device.

A digital device according to a ninth aspect of the present invention is characterized in that at least one of still image shooting and moving image shooting of a subject is added by including the imaging optical device according to the eighth aspect.

According to the present invention, it is possible to obtain a uniform image quality over the entire image by satisfactorily correcting aberrations from the infinity end to the close-up end while achieving both a bright F-number and a lightweight focus group. Optical systems and imaging optics can be implemented. By using the imaging optical system or imaging optical device in a digital device (for example, a digital camera), it becomes possible to compactly add a high-performance image input function to the digital device.

1 is a lens configuration diagram of a first embodiment (Example 1); FIG. FIG. 10 is a lens configuration diagram of a second embodiment (Example 2); The lens block diagram of 3rd Embodiment (Example 3). The lens block diagram of 4th Embodiment (Example 4). FIG. 2 is a longitudinal aberration diagram of Example 1; FIG. 10 is a longitudinal aberration diagram of Example 2; FIG. 10 is a longitudinal aberration diagram of Example 3; FIG. 10 is a longitudinal aberration diagram of Example 4; 4A and 4B are lateral aberration diagrams at the first focus position in Example 1. FIG. 4A and 4B are lateral aberration diagrams at the second focus position in Example 1. FIG. FIG. 11 is a lateral aberration diagram at the first focus position of Example 2; FIG. 11 is a lateral aberration diagram at the second focus position of Example 2; FIG. 11 is a lateral aberration diagram at the first focus position of Example 3; FIG. 11 is a lateral aberration diagram at the second focus position of Example 3; FIG. 11 is a lateral aberration diagram at the first focus position of Example 4; FIG. 11 is a lateral aberration diagram at the second focus position of Example 4; FIG. 1 is a schematic diagram showing an example of a schematic configuration of a digital device equipped with an imaging optical device;

An imaging optical system, an imaging optical device, and a digital device according to embodiments of the present invention will be described below. An imaging optical system according to an embodiment of the present invention includes, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power. lens group (power: amount defined by the reciprocal of the focal length), in focusing from infinity to a close object, the second lens group moves toward the image side, and the third lens group moves toward the object side. It is configured to

The second lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group is composed of a positive lens, and the following conditional expressions (1) and (2) are satisfied. is characterized by
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
is.

In telephoto type lenses with relatively long focal lengths, which can reduce the overall length and lens diameter, it is necessary to condense the on-axis beam diameter with the preceding positive power lens group in order to achieve this effect. There is In addition, it is necessary to place a negative power lens group following the positive power lens group in order to expand the light rays converged with strong positive power and correct the large positive distortion generated by the positive power lens group. There is

In the positive/negative/positive/negative power arrangement that works as described above, if focusing is performed by moving the second lens group with negative power toward the image side and moving the third lens group with positive power toward the object side, focusing is performed. Occasionally occurring aberrations such as spherical aberration and curvature of field can be canceled out by the second lens group and the third lens group. Further, by sharing the focusing action between the second lens group and the third lens group, it is possible to suppress aberration fluctuations during focusing while suppressing an increase in the number of lenses constituting each lens group. Therefore, it is possible to reduce the weight of the focus group with a small number of lenses and obtain good optical performance from infinity to close objects. In particular, in a large-aperture medium-telephoto lens, the effect of reducing the weight of the focus group becomes remarkable, which is advantageous in achieving both improvement in imaging performance and improvement in imaging performance.

By constructing the second lens group with a positive/negative cemented lens, it becomes possible to effectively control various aberrations such as spherical aberration. It is possible to suppress the size in the optical axis direction and the radial direction. If the positive lens in the focus group satisfies the conditional expressions (1) and (2), the positive lens in the second lens group is also made of high-dispersion glass. This is an advantageous configuration for correcting chromatic aberration between Therefore, it is possible to suppress deterioration in performance due to the reduction in the number of focus groups, and obtain good optical performance.

According to the above-mentioned characteristic configuration, it is possible to achieve uniform image quality over the entire image, while achieving both a bright F-number and a lightweight focus group, and excellent correction of aberrations from the infinity end to the close-up end. An imaging optical system and an imaging optical device provided with the same can be realized. By using the imaging optical system or imaging optical device in a digital device (for example, a digital camera), it becomes possible to add a high-performance image input function to the digital device in a lightweight and compact manner. It can contribute to cost reduction, high performance, high functionality, and the like. For example, since the imaging optical system having the above-described characteristic configuration is suitable as a large-aperture, medium-telephoto lens for digital cameras and video cameras, it is possible to realize a lightweight, compact, high-performance interchangeable lens that is convenient to carry. can. Conditions for obtaining these effects in a well-balanced manner and achieving higher optical performance, lighter weight, smaller size, etc. will be described below.

It is desirable that the cemented lens have a cemented surface with a concave surface facing the object side and satisfy the following conditional expressions (3) and (4).
0.11<nd(2GrP)−nd(2GrN)<0.35 (3)
−20<νd(2GrP)−νd(2GrN)<−5 (4)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(2GrN): refractive index for the d-line of the negative lens in the second lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(2GrN): Abbe number for the d-line of the negative lens in the second lens group,
is.

The cemented lens that makes up the second lens group has a cemented surface with a concave surface facing the object side, making it possible to control coma while suppressing the effects on other aberrations. becomes easier. By satisfying conditional expression (3), coma aberration can be effectively corrected in the second lens group. Further, by satisfying conditional expression (4), the occurrence of longitudinal chromatic aberration due to the second lens group is suppressed, so the occurrence of chromatic aberration can be suppressed over the entire focus area.

Regarding the power arrangement of each lens group, it is desirable to satisfy the following conditional expressions (5) to (7).
0.8<FL1/FL<1.1 (5)
-1.6<FL2/FL3<-0.9 (6)
-3.6<FL4/FL<-1.8 (7)
however,
FL1: focal length of the first lens group,
FL2: focal length of the second lens group,
FL3: focal length of the third lens group;
FL4: focal length of the fourth lens group,
FL: focal length of the whole system,
is.

Conditional expression (5) defines the power of the first lens group. By exceeding the lower limit of conditional expression (5), the positive power of the first lens group is prevented from becoming too strong, and the rear focal position of the first lens group can be brought closer to the second lens group. Therefore, it is possible to suppress the amount of driving of the second lens group during focusing, and to suppress variations in spherical aberration that accompany focusing. By falling below the upper limit of conditional expression (5), the positive power of the first lens group is prevented from becoming too weak, the overall length is prevented from increasing, and the light flux incident on the first lens group is gently refracted. Various aberrations such as coma can be suppressed.

Conditional expression (6) defines the power ratio between the second lens group and the third lens group. By exceeding the lower limit of conditional expression (6), it is possible to prevent an increase in the amount of movement of the second lens group and suppress fluctuations in curvature of field that accompany focusing. By falling below the upper limit of conditional expression (6), aberration fluctuations during focusing can be effectively suppressed while suppressing the focus sensitivity of the second lens group.

Conditional expression (7) defines the power of the fourth lens group. By exceeding the lower limit of conditional expression (7), it is possible to prevent the negative power of the fourth lens group from becoming too weak, suppressing the ray passage diameter of the focus group, and preventing an increase in the total length. By falling below the upper limit of conditional expression (7), the negative power of the fourth lens group is prevented from becoming too strong, and the light flux incident on the fourth lens group is gently refracted to reduce various aberrations such as coma. can be suppressed.

Regarding the moving amount ratio of the focus group, it is desirable to satisfy the following conditional expression (8).
−1.0<D2Gr/D3Gr<−0.45 (8)
however,
D2Gr: movement amount of the second lens group in focusing from infinity to a close object;
D3Gr: movement amount of the third lens group in focusing from infinity to a close object;
, and the amount of movement when the direction of movement is on the image side is positive.

Conditional expression (8) defines the ratio of the amount of focus movement between the second lens group and the third lens group. By exceeding the lower limit of conditional expression (8), the amount of movement of the second lens group is regulated so that it does not become too large with respect to the amount of movement of the third lens group. The effect of suppressing aberration fluctuations due to driving (for example, fluctuations in curvature of field, spherical aberration, etc.) is enhanced. By falling below the upper limit of conditional expression (8), it is possible to prevent an increase in the sensitivity of the second lens group and to suppress variations in curvature of field during focusing.

It is desirable that the fourth lens group has two cemented lenses in succession each composed of a positive lens and a negative lens in order from the object side. Since the fourth lens group has two positive and negative cemented lenses in order from the object side, the lens arrangement is in the order of positive, negative, positive, negative, so it is possible to correct the curvature of field while suppressing the occurrence of chromatic aberration. It becomes possible. At least one cemented lens of the two cemented lenses preferably has a cemented surface with a concave surface facing the object side. By having a concave cemented surface on the object side, it becomes possible to control spherical aberration while suppressing the influence on other aberrations, facilitating adjustment of residual spherical aberration. Further, of the two cemented lenses, it is more desirable that the cemented lens on the object side has negative power and the cemented lens on the image side has positive power in order to suppress the occurrence of coma aberration and the like.

The fourth lens group has two cemented lenses successively composed of a positive lens and a negative lens in order from the object side, and among the two cemented lenses, the cemented lens on the object side has negative power, and the image It is desirable that the cemented lens on the side has positive power and satisfies the following conditional expression (9).
-2.2<FL(4GrPN1)/FL(4GrPN2)<-1.4 (9)
however,
FL (4GrPN1): the focal length of the cemented lens on the object side in the fourth lens group;
FL (4GrPN2): the focal length of the cemented lens on the image side in the fourth lens group;
is.

Conditional expression (9) defines the power ratio between the object-side cemented lens and the image-side cemented lens in the fourth lens group. By falling below the upper limit of conditional expression (9), the negative power of the cemented lens on the object side is prevented from becoming too strong, and light rays are gently refracted between the two cemented lenses to prevent coma and other aberrations from occurring. can be suppressed. By exceeding the lower limit of conditional expression (9), the positive power of the cemented lens on the image side is prevented from becoming too strong, and light rays are gently refracted between the cemented lens on the image side and subsequent lenses, Occurrence of coma and the like can be suppressed.

It is desirable that the lens closest to the image side in the fourth lens group has negative power. Since the final lens has a negative power, the diameter of the light beam can be narrowed in the fourth lens group, and the light beam can be greatly bounced and incident on the imaging surface, so the effective diameter in the fourth lens group can be effectively suppressed.

It is preferable that a position-fixed stop in focusing is arranged between the second lens group and the third lens group. Placing an aperture between the second and third lens groups suppresses an increase in the effective diameters of the second and third lens groups, thereby reducing the weight of the second and third lens groups. It becomes possible, leading to an increase in focus speed. In addition, by arranging lens groups having positive and negative power opposite to each other with the diaphragm interposed therebetween, the structure is advantageous in reducing coma aberration.

Preferably, the first lens group has at least three consecutive positive lenses in order from the object side, and one or more positive lenses among them satisfy the following conditional expression (10).
νd(1GrP)>60 (10)
however,
νd(1GrP): Abbe number for the d-line of the positive lens in the first lens group;
is.

If at least three positive lenses are arranged in succession from the object side in the first lens group, and at least one of them satisfies conditional expression (10), chromatic aberration, which tends to be a problem in telephoto lenses, can be effectively eliminated. It is possible to moderately refract the light flux incident on the first lens group while correcting for coma and the like, thereby reducing the occurrence of coma and the like. If a positive lens that satisfies the conditional expression (10) is arranged at the second and subsequent lenses from the object side, it is possible to prevent scratches on lenses that are highly effective in correcting chromatic aberration. If a positive lens that satisfies conditional expression (10) is placed on the third lens from the object side, and a negative lens is cemented to the image side of the positive lens, it is possible to effectively suppress the generation of aberration at the cemented surface. become.

The imaging optical system described above is suitable for use as an imaging optical system for a digital device with an image input function (for example, a digital camera with interchangeable lenses). It is possible to configure an imaging optical device that optically captures and outputs as an electrical signal. An imaging optical device is an optical device that forms the main component of a camera used for capturing still images or moving images of a subject. and an imaging device (image sensor) for converting an optical image formed by the imaging optical system into an electrical signal. By arranging the imaging optical system having the characteristic configuration described above so that an optical image of the subject is formed on the light receiving surface (i.e., the imaging surface) of the imaging element, high performance can be achieved at a small size and low cost. It is possible to realize an image pickup optical device having such a device and a digital device having the same.

Examples of digital equipment with an image input function include cameras such as digital cameras, video cameras, surveillance cameras, security cameras, in-vehicle cameras, and videophone cameras. In addition, personal computers, portable digital devices (e.g., mobile phones, smart phones (high-performance mobile phones), tablet terminals, mobile computers, etc.), these peripheral devices (scanners, printers, mice, etc.), other digital devices (drives recorders, defense equipment, etc.), etc., which have a built-in or external camera function. As can be seen from these examples, it is possible not only to configure a camera by using the imaging optical device, but also to add a camera function by mounting the imaging optical device on various devices. For example, it is possible to configure a digital device with an image input function such as a mobile phone with a camera or a smart phone.

FIG. 17 shows a schematic cross section of 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 installed in the digital equipment DU shown in FIG. , and an imaging element SR for converting an optical image IM formed on a light receiving surface (imaging surface) SS by the imaging optical system LN into an electrical signal. A cover glass of the element SR; which corresponds to an optical filter such as an optical low-pass filter, an infrared cut filter, etc., which is arranged as necessary) is also arranged.

When a digital device DU with an image input function is configured with this imaging optical device LU, the imaging optical device LU is usually arranged inside the body, but when realizing the camera function, a form is adopted according to necessity. It is possible to For example, the unitized imaging optical device LU may be configured to be rotatable with respect to the main body of the digital device DU, and the unitized imaging optical device LU may be used as an interchangeable lens with an image sensor for the digital device DU (that is, a lens It may be configured to be detachable from the main body of an interchangeable camera.

The imaging optical system LN is a single focus lens composed of four groups of positive, negative, positive, and negative, and the positions of the first lens group and the fourth lens group are fixed (that is, the positions are fixed with respect to the image plane IM). Focusing is performed by moving the second lens group with negative power and the third lens group with positive power along the optical axis AX to form an optical image IM on the light receiving surface SS of the image sensor SR. there is As the imaging element SR, a solid-state imaging element such as a CCD (Charge Coupled Device) type image sensor having a plurality of pixels or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor is used. The imaging optical system LN is provided so as to form an optical image IM of the subject on the light receiving surface SS, which is the photoelectric conversion portion of the imaging element SR. Therefore, the optical image IM formed by the imaging optical system LN is It is converted into an electrical signal by the image sensor SR.

The digital device DU includes a signal processing section 1, a control section 2, a memory 3, an operation section 4, a display section 5, etc., in addition to the imaging optical device LU. Signals generated by the image pickup device SR are subjected to predetermined digital image processing, image compression processing, etc. by the signal processing unit 1 as necessary, and are recorded as digital video signals in a memory 3 (semiconductor memory, optical disk, etc.). In some cases, the signal is transmitted to other equipment via a cable or converted into an infrared signal (for example, a communication function of a mobile phone). The control unit 2 consists of a microcomputer, and centralizes control of functions such as photographing functions (still image photographing function, moving image photographing function, etc.), image playback function, etc.; control of lens movement mechanism for focusing, camera shake correction, etc. do it purposefully. 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 section 5 is a section 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, release button) and an operation dial (for example, shooting mode dial), and transmits information input by an operator to the control unit 2 .

Next, first to fourth embodiments of the imaging optical system LN will be given, and their specific optical configurations will be described in more detail. 1 to 4 are lens configuration diagrams corresponding to the imaging optical systems LN constituting the first to fourth embodiments, respectively, and show optical cross sections of the lens arrangement in an infinite object distance state. A plane-parallel plate PT is arranged between the imaging optical system LN and the image plane IM. It is a glass flat plate equivalent to the thickness.

In the first to fourth embodiments, in order from the object side, a first lens group Gr1 with positive power, a second lens group Gr2 with negative power, a third lens group Gr3 with positive power, and a third lens group Gr3 with negative power. It has a positive/negative/positive/negative four-group configuration consisting of four lens groups Gr4, which is suitable as a compact, large-aperture, medium-telephoto, single-focus interchangeable lens. 1 to 4, lens L1# (#=1, 2, 3, 4) is the #-th lens from the object side in first lens group Gr1, and lens L2# (#=1, 2) is the #-th lens. In the second lens group Gr2, it is the #-th lens from the object side, the lens L31 is one lens constituting the third lens group Gr3, and the lens L4# (#=1, 2, . . . , 5) is the fourth lens. It is the #-th lens from the object side in the lens group Gr4.

In the first to fourth embodiments, in focusing from the first focus position POS1 (infinity end: infinite object distance state) to the second focus position POS2 (closest end: close object distance state), the first lens The positions of the group Gr1 and the fourth lens group Gr4 are fixed with respect to the image plane IM, and the second lens group Gr2 and the third lens group Gr3, which are focus groups, move along the optical axis AX. That is, in focusing from infinity to a close object, the second lens group Gr2 moves toward the image side and the third lens group Gr3 moves toward the object side so that the distance between the second lens group Gr2 and the third lens group Gr3 narrows. move to

Arrows m1, m2, ms, m3, and m4 indicate loci of focus movements of the first lens group Gr1, the second lens group Gr2, the diaphragm (aperture stop) ST, the third lens group Gr3, and the fourth lens group Gr4, respectively. ing. However, the first lens group Gr1 and the fourth lens group Gr4, the diaphragm ST arranged between the second lens group Gr2 and the third lens group Gr3, and the aperture ST arranged on the image plane IM side of the imaging optical system LN. The plane-parallel plate PT provided has a fixed focus position.

In the first to fourth embodiments, as described above, in focusing from the infinite end to the closest end, the second lens group Gr2 moves toward the image side, while the third lens group Gr3 moves toward the object side. Move to In this way, by reversing the focus movement directions of the second lens group Gr2 and the third lens group Gr3 to narrow the distance between the second lens group Gr2 and the third lens group Gr3, spherical aberration and image Fluctuations in various aberrations such as surface curvature can be advantageously canceled out by the second lens group Gr2 and the third lens group Gr3. Therefore, it is possible to more effectively correct aberration deterioration during focusing, and to further improve the image quality at the closest end POS2.

The imaging optical system LN (FIG. 1) of the first embodiment has a positive/negative/positive/negative four-group configuration, and each lens group is configured as follows. The first lens group Gr1 is cemented with, in order from the object side, a positive meniscus lens L11 convex to the object side, a positive meniscus lens L12 convex to the object side, a biconvex positive lens L13, and a biconcave negative lens L14. It consists of a lens and The second lens group Gr2 is composed of a cemented lens composed of a biconvex positive lens L21 and a biconcave negative lens L22 in order from the object side. The third lens group Gr3 is composed of a biconvex positive lens L31 (having aspherical surfaces on both sides). The fourth lens group Gr4 includes, in order from the object side, a cemented lens composed of a biconvex positive lens L41 and a biconcave negative lens L42, a cemented lens composed of a biconvex positive lens L43 and a plano-concave negative lens L44, and a biconcave negative lens L45.

The imaging optical system LN (FIG. 2) of the second embodiment has a positive/negative/positive/negative four-group configuration, and each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 convex to the object side, a cemented lens composed of a biconvex positive lens L13 and a biconcave negative lens L14, consists of The second lens group Gr2 is composed of a cemented lens composed of a biconvex positive lens L21 and a biconcave negative lens L22 in order from the object side. The third lens group Gr3 is composed of a biconvex positive lens L31. The fourth lens group Gr4 includes, in order from the object side, a cemented lens composed of a positive meniscus lens L41 convex to the image side and a negative biconcave lens L42, a positive biconvex lens L43 and a negative meniscus lens L44 concave to the object side. and a negative meniscus lens L45 concave on the object side.

The imaging optical system LN (FIG. 3) of the third embodiment has a positive/negative/positive/negative four-group configuration, and each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 convex to the object side, a cemented lens composed of a biconvex positive lens L13 and a biconcave negative lens L14, consists of The second lens group Gr2 is composed of a cemented lens composed of a biconvex positive lens L21 and a biconcave negative lens L22 in order from the object side. The third lens group Gr3 is composed of a biconvex positive lens L31. The fourth lens group Gr4 includes, in order from the object side, a cemented lens composed of a plano-convex positive lens L41 and a plano-concave negative lens L42, a cemented lens composed of a bi-convex positive lens L43 and a bi-concave negative lens L44, and a negative meniscus lens L45 concave on the object side.

The imaging optical system LN (FIG. 4) of the fourth embodiment has a positive/negative/positive/negative four-group configuration, and each lens group is configured as follows. The first lens group Gr1 includes, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 convex to the object side, a cemented lens composed of a biconvex positive lens L13 and a biconcave negative lens L14, consists of The second lens group Gr2 is composed of a cemented lens composed of a biconvex positive lens L21 and a biconcave negative lens L22 in order from the object side. The third lens group Gr3 is composed of a biconvex positive lens L31. The fourth lens group Gr4 includes, in order from the object side, a cemented lens composed of a biconvex positive lens L41 and a biconcave negative lens L42, a cemented lens composed of a biconvex positive lens L43 and a biconcave negative lens L44, and a negative meniscus lens L45 concave on the object side.

Hereinafter, the configuration of the imaging optical system embodying the present invention will be described more specifically with reference to the construction data and the like of Examples. Examples 1 to 4 (EX1 to 4) given here are numerical examples respectively corresponding to the above-described first to fourth embodiments, and are lens configuration diagrams representing the first to fourth embodiments. (FIGS. 1-4) show the optical configurations of the corresponding Examples 1-4, respectively.

In the construction data of each embodiment, as surface data, from the left column, surface number i (OB: object surface, ST: stop, IM: image surface), paraxial curvature radius ri (mm), axial surface distance (Core thickness) di (mm), refractive index nd for d-line (wavelength: 587.56 nm), and Abbe number νd for d-line are shown.

A surface with an asterisk (*) attached to the surface number i is an aspherical surface, and its surface shape is defined by the following equation (AS) using a local orthogonal coordinate system (x, y, z) with the vertex of the surface as the origin. be. Aspheric coefficients and the like are shown as aspheric data. In the aspheric surface data of each example, the coefficients of terms not shown are 0, and En=×10 ⁻ⁿ for all data.
z=(c·h ² )/[1+√{1−(1+K)·c ² ·h ² }]+Σ(Aj·h ^j ) (AS)
however,
h: height in the direction perpendicular to the z-axis (optical axis AX) (h ² =x ² +y ² );
z: amount of sag in the direction of the optical axis AX at the position of height h (based on surface vertex);
c: curvature at surface vertex (reciprocal of curvature radius ri),
K: conic constant,
Aj: j-th order aspheric coefficient,
is.

Various data include the focal length FL (mm) of the entire system, F number (FNO), total angle of view 2ω (°), total lens length TL (the distance from the surface closest to the object side of the imaging optical system LN to the image plane IM ( (without air conversion), mm), and back focus bf (distance from the image side surface of the plane-parallel plate PT to the image plane IM, mm). Furthermore, the variable axis distance di as a variable parameter that changes with focusing is shown for each of the first focus position POS1 (infinity object distance state) and the second focus position POS2 (close object distance state). Here, the object distance is the distance from the object plane OB to the image plane IM, and the closest object distance in each example is 0.8 m (POS2). Table 1 shows the movement amount D2Gr of the second lens group Gr2 and the movement amount D3Gr of the third lens group Gr3 when the focus is moved from the first focus position POS1 to the second focus position POS2. Corresponding values are shown, and Table 2 shows relevant data for the conditional expressions.

5 to 8 are longitudinal aberration diagrams corresponding to Examples 1 to 4 (EX1 to EX4), respectively, where (A) to (C) are the first focus position POS1, (D) to (F) indicate various aberrations at the second focus position POS2. 5 to 8, (A) and (D) are spherical aberration diagrams, (B) and (E) are astigmatism diagrams, and (C) and (F) are distortion diagrams.

The spherical aberration diagram shows the amount of spherical aberration for the C-line (wavelength 656.28 nm) indicated by the dashed line, the amount of spherical aberration for the d-line (wavelength 587.56 nm) indicated by the solid line, and the amount of spherical aberration for the g-line (wavelength 435.84 nm) indicated by the dashed line. The amount of spherical aberration is represented by the amount of deviation (mm) in the direction of the optical axis AX from the paraxial image plane. height). In the astigmatism diagrams, the dashed line T represents the tangential image plane for the d-line, and the solid line S represents the sagittal image plane for the d-line in terms of the amount of deviation (mm) in the direction of the optical axis AX from the paraxial image plane. The vertical axis represents the image height (IMG HT, mm). In the distortion diagrams, the horizontal axis represents distortion (%) with respect to the d-line, and the vertical axis represents image height (IMG HT, mm). Note that the maximum value of the image height IMG HT corresponds to the maximum image height on the image plane IM.

9, 11, 13 and 15 are lateral aberration diagrams corresponding to Examples 1 to 4 (EX1 to EX4) at the first focus position POS1, and FIGS. 16A and 16B are lateral aberration diagrams respectively corresponding to Examples 1 to 4 (EX1 to EX4) at the second focus position POS2. In each of FIGS. 9 to 16, the left column shows the lateral aberration (mm) for the tangential luminous flux, and the right column shows the lateral aberration (mm) for the sagittal luminous flux. In addition, the lateral aberration at the image height ratio (half angle of view ω°) represented by RELATIVE FIELD HEIGHT is shown by the dash-dotted line for the C line (wavelength 656.28 nm) and by the solid line for the d line (wavelength 587.56 nm). , g-line (wavelength 435.84 nm) indicated by a dashed line. Note that the image height ratio is a relative image height obtained by normalizing the image height IMG HT by the maximum image height.

Example 1
Unit: mm
Plane data
i ri di nd vd
0 (OB) ∞
1 57.5871 6.919 1.72916 54.67
2 231.4781 0.571
3 53.3950 4.363 1.49700 81.61
4 122.2631 0.250
5 41.6878 6.971 1.59282 68.62
6 -369.3860 1.881 1.90366 31.32
7 47.1750 d7
8 74.7861 3.900 1.92286 20.88
9 -110.6105 1.200 1.80610 33.27
10 29.0325 d10
11(ST) ∞ d11
12* 42.7555 3.935 1.59349 67.00
13* -180.3484 d13
14 1166.0621 3.475 1.95375 32.32
15 -73.0638 1.500 1.71736 29.50
16 43.0227 8.400
17 70.3789 11.000 1.84850 43.79
18 -30.1875 1.792 1.57135 52.95
19 ∞ 5.548
20 -42.5025 2.500 1.62004 36.30
21 532.2146 10.808
22 ∞ 1.600 1.51680 64.20
23∞bf
24 (IM) ∞

aspherical data
i12 13
K00
A4 -2.58331E-06 -8.91351E-07
A6 -2.74665E-09 -1.91080E-09
A8 -1.09073E-11 -8.22787E-12
A10 0.00000E+00 0.00000E+00
A12 0.00000E+00 0.00000E+00

Various data
FL 83.00
FNO 1.85
2ω 29.53
TL 107.55
bf 2
Variable parameter Object distance d7 d10 d11 d13
∞(POS1) 5.224 14.272 7.442 2.000
0.8m (POS2) 9.898 9.604 1.900 7.540
Group movement amount (POS1→POS2)
D2Gr D3Gr D2Gr/D3Gr
4.673 -5.542 -0.84

Example 2
Unit: mm
Plane data
i ri di nd vd
0 (OB) ∞
1 80.1734 6.282 1.71700 47.98
2 -4807.6515 1.586
3 41.9543 5.640 1.43700 95.10
4 117.0287 0.871
5 58.1172 6.203 1.49700 81.61
6 -241.7619 1.400 1.85026 32.35
7 65.5586 d7
8 138.8823 3.750 1.80809 22.76
9 -114.7710 1.200 1.62004 36.30
10 29.5637 d10
11(ST) ∞ d11
12 41.8535 3.850 1.59349 67.00
13 -418.9839 d13
14 -361.4882 4.412 1.83481 42.72
15 -43.7311 1.200 1.67300 38.15
16 44.7491 4.944
17 56.2446 10.536 1.84850 42.72
18 -42.4152 1.403 1.56732 42.84
19 -224.6045 8.016
20 -36.2911 2.284 1.60342 80.11
21 -619.9962 11.575
22 ∞ 1.600 1.51680 64.20
23∞bf
24 (IM) ∞

Various data
FL 83.00
FNO 1.85
2ω 29.24
TL 111.94
bf 0.92
Variable parameter Object distance d7 d10 d11 d13
∞(POS1) 7.492 12.773 11.211 2.749
0.8m (POS2) 10.879 9.386 3.334 10.626
Group movement amount (POS1→POS2)
D2Gr D3Gr D2Gr/D3Gr
3.387 -7.877 -0.43

Example 3
Unit: mm
Plane data
i ri di nd vd
0 (OB) ∞
1 120.8140 4.940 1.77250 49.62
2 -1000.0000 0.250
3 42.0610 6.120 1.55032 75.50
4 127.2310 0.500
5 62.7420 6.560 1.49700 81.61
6 -165.7530 1.400 1.85025 30.05
7 82.2620 d7
8 438.0320 3.210 1.92286 20.88
9 -84.2650 1.130 1.60342 38.01
10 30.0600 d10
11(ST) ∞ d11
12 54.7570 4.100 1.59349 67.00
13-152.9580 d13
14 ∞ 6.500 1.91082 35.25
15 -43.6900 2.020 1.67270 32.17
16 64.8690 4.900
17 70.5370 8.200 1.84850 43.79
18 -411.6880 4.500 1.60342 38.01
19 130.5830 8.121
20 -35.4045 1.400 1.64769 33.72
21 -69.4719 11.000
22 ∞ 1.600 1.51680 64.20
23∞bf
24 (IM) ∞

Various data
FL 83.00
FNO 1.85
2ω 29.26
TL 111.35
bf 0.92
Variable parameter Object distance d7 d10 d11 d13
∞(POS1) 6.182 13.284 11.915 2.059
0.8m (POS2) 10.020 9.445 5.153 8.821
Group movement amount (POS1→POS2)
D2Gr D3Gr D2Gr/D3Gr
3.838 -6.762 -0.57

Example 4
Unit: mm
Plane data
i ri di nd vd
0 (OB) ∞
1 114.0645 4.566 1.69680 55.46
2 -1003.2810 0.173
3 45.6817 4.904 1.49700 81.61
4 114.9128 0.538
5 50.9360 6.999 1.49700 81.61
6 -188.1267 1.493 1.90366 31.32
7 74.6061 d7
8 87.4333 4.870 1.92286 20.88
9 -95.8114 1.214 1.67270 32.17
10 29.0783 d10
11(ST) ∞ d11
12 46.3133 4.541 1.55032 75.50
13-201.8349 d13
14 630.0245 5.920 1.90366 31.32
15 -37.5067 1.206 1.72825 28.32
16 55.9782 4.459
17 63.6775 6.985 1.84850 42.72
18 -51.1824 1.457 1.62004 36.30
19 147.6730 7.598
20 -33.0806 1.416 1.51633 64.14
21 -255.0489 10.058
22 ∞ 1.600 1.51680 64.20
23∞bf
24 (IM) ∞

Various data
FL 83.00
FNO 1.85
2ω 29.59
TL 111.96
bf 0.92
Variable parameter Object distance d7 d10 d11 d13
∞(POS1) 6.939 10.871 20.176 1.988
0.8m (POS2) 11.581 6.228 12.123 10.040
Group movement amount (POS1→POS2)
D2Gr D3Gr D2Gr/D3Gr
4.643 -8.053 -0.58

DU digital device LU imaging optical device LN imaging optical system Gr1 1st lens group Gr2 2nd lens group Gr3 3rd lens group Gr4 4th lens group L1# In the 1st lens group, #th lens from the object side (#=1, 2,3,4)
L2# #th lens from the object side in the second lens group (#=1, 2)
L31 Lens constituting the third lens group L4# #th lens from the object side in the fourth lens group (#=1, 2, . . . , 5)
ST Aperture 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 (9)

Consists of, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power,
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
An imaging optical system characterized by satisfying the following conditional expressions (1) , (2) and (5) to (7) ;
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
0.8<FL1/FL<1.1 (5)
-1.6<FL2/FL3<-0.9 (6)
-3.6<FL4/FL<-1.8 (7)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
FL1: focal length of the first lens group,
FL2: focal length of the second lens group,
FL3: focal length of the third lens group;
FL4: focal length of the fourth lens group,
FL: focal length of the whole system,
is. Consists of, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power,
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
The fourth lens group has two cemented lenses successively composed of a positive lens and a negative lens in order from the object side, and among the two cemented lenses, the cemented lens on the object side has negative power, and the image the cemented lens on the side has positive power,
An imaging optical system characterized by satisfying the following conditional expressions (1), (2) and (9);
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
-2.2<FL(4GrPN1)/FL(4GrPN2)<-1.4 (9)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
FL (4GrPN1): the focal length of the cemented lens on the object side in the fourth lens group;
FL (4GrPN2): the focal length of the cemented lens on the image side in the fourth lens group;
is. Consists of, in order from the object side, a first lens group with positive power, a second lens group with negative power, a third lens group with positive power, and a fourth lens group with negative power,
In focusing from infinity to a close object, the second lens group moves toward the image side, the third lens group moves toward the object side, and the first lens group and the fourth lens group move toward the image plane. is positionally fixed,
a position-fixed diaphragm for focusing is arranged between the second lens group and the third lens group;
The second lens group consists of a cemented lens of a positive lens and a negative lens in order from the object side, the third lens group consists of a positive lens,
An imaging optical system characterized by satisfying the following conditional expressions (1) and (2);
nd(2GrP)−nd(3GrP)>0.2 (1)
νd(3GrP)−νd(2GrP)>40 (2)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(3GrP): refractive index for the d-line of the positive lens in the third lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(3GrP): Abbe number for the d-line of the positive lens in the third lens group;
is. The imaging optical system according to any one of claims 1 to 3, wherein the cemented lens has a cemented surface with a concave surface facing the object side, and satisfies the following conditional expressions (3) and (4): system;
0.11<nd(2GrP)−nd(2GrN)<0.35 (3)
−20<νd(2GrP)−νd(2GrN)<−5 (4)
however,
nd(2GrP): refractive index for the d-line of the positive lens in the second lens group;
nd(2GrN): refractive index for the d-line of the negative lens in the second lens group;
νd(2GrP): Abbe number for the d-line of the positive lens in the second lens group;
νd(2GrN): Abbe number for the d-line of the negative lens in the second lens group,
is. The imaging optical system according to any one of claims 1 to 4 , wherein the following conditional expression (8) is satisfied;
−1.0<D2Gr/D3Gr<−0.45 (8)
however,
D2Gr: movement amount of the second lens group in focusing from infinity to a close object;
D3Gr: movement amount of the third lens group in focusing from infinity to a close object;
, and the amount of movement when the direction of movement is on the image side is positive. 6. The imaging optical system according to any one of claims 1 to 5, wherein a lens located closest to the image side in the fourth lens group has negative power. Claims 1 to 1, wherein the first lens group has at least three consecutive positive lenses in order from the object side, and at least one of the positive lenses satisfies the following conditional expression (10): 7. The imaging optical system according to any one of 6 ;
νd(1GrP)>60 (10)
however,
νd(1GrP): Abbe number for the d-line of the positive lens in the first lens group;
is. An image pickup optical system according to any one of claims 1 to 7 , and an image pickup device that converts an optical image formed on an image pickup surface into an electrical signal, wherein An imaging optical apparatus, wherein the imaging optical system is provided so as to form an optical image of a subject. 10. A digital device, comprising the imaging optical device according to claim 8 , to which at least one of a still image shooting function and a moving image shooting function of a subject is added.

Images