Optical system and imaging device

Abstract

To provide an optical system which is compact and light-weight and enables fast autofocusing, and an image capturing device.SOLUTION: The optical system comprises a first positive lens group G1 with positive refractive power disposed on the most object side, a first negative lens group LF1 with negative refractive power configured to move along an optical axis when focusing, and a second negative lens group LF2 with negative refractive power, and is configured such that distances between adjacent lens groups change while focusing. The optical system satisfies the following expression: 0.7<fn1 / fn2<2.0, where fn1 represents a focal length of the first negative lens group and fn2 represents a focal length of the second negative lens group. An image capturing device is also provided, comprising the optical system and an image sensor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device, and more particularly to an optical system and an imaging device suitable for imaging devices using solid-state imaging elements (CCD, CMOS, etc.) such as digital still cameras and digital video cameras. [Background technology]

[0002] Imaging devices using various solid-state imaging elements, such as video cameras, digital still cameras, single-lens reflex cameras, and mirrorless cameras, have become widespread. As these imaging devices become more powerful and compact, their imaging lenses (optical systems) are also required to be even more powerful and compact, and macro lenses are no exception. A macro lens generally refers to an imaging lens with a maximum imaging magnification of 0.5x to 1x. Macro lenses are particularly required to achieve high optical performance across the entire focusing range by suppressing aberration fluctuations during focusing, such as spherical aberration and field curvature fluctuations.

[0003] As such a macro lens, for example, the optical system disclosed in Patent Document 1 is known.

[0004] Patent Document 1 proposes an optical system that employs a refractive power arrangement of positive, negative, positive, negative, positive, in that order from the object side, and focuses by moving the second and fourth lens groups, which have negative refractive power, in the optical axis direction. In this optical system, the negative refractive power of the second lens group is too strong, and it is necessary to arrange positive refractive power in the final lens group, the fifth lens group, for correction of lateral chromatic aberration, etc. This makes it difficult to reduce the diameter of the entire optical system, making it difficult to achieve a compact and lightweight design. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6344965 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system and an imaging device that are small and lightweight and capable of realizing rapid autofocus. [Means for solving the problem]

[0007] In order to solve the above problem, the optical system according to the present invention comprises a first positive lens group arranged closest to the object and having positive refractive power, a first negative lens group having negative refractive power and a second negative lens group having negative refractive power, which move along the optical axis during focusing, and the spacing between adjacent lens groups changes during focusing, and the following formula is satisfied: 0.7 < fn1 / fn2 <2.0 (1) however, fn1: focal length of the first negative lens group fn2: focal length of the second negative lens group

[0008] In order to solve the above problem, the imaging device according to the present invention is characterized by including the above optical system and an imaging element that converts an optical image formed by the optical system into an electrical signal. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical system and an imaging device that are small, lightweight, and capable of achieving rapid autofocusing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a lens cross-sectional view of an optical system according to a first embodiment of the present invention, in which the upper diagram shows an infinity focused state and the lower diagram shows a second close-up object focused state (imaging magnification β) (the same applies to the following lens cross-sectional views). [Figure 2] 3A to 3C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 1 in a state where the optical system is focused on an object at infinity. [Figure 3]3A to 3C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 1 in a state where the optical system is focused on a close object. [Figure 4] FIG. 10 is a cross-sectional view of a lens of an optical system according to a second embodiment of the present invention. [Figure 5] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 2 when focused on an object at infinity. [Figure 6] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 2 in a state where the optical system is focused on a close object. [Figure 7] FIG. 10 is a cross-sectional view of a lens of an optical system according to a third embodiment of the present invention. [Figure 8] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 3 when focused on an object at infinity. [Figure 9] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 3 in a state where the optical system is focused on a close object. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the optical system and the imaging device according to the present invention will be described. However, the optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects.

[0012] 1.Optical system The optical system includes a first positive lens group located closest to the object, a first negative lens group LF1 that moves along the optical axis during focusing, and a second negative lens group LF2, and the spacing between adjacent lens groups changes during focusing. Here, a "lens group" refers to a group consisting of one or more adjacent lenses, and the air spacing between adjacent lens groups changes during focusing. Furthermore, when referring to a "lens group," the air spacing between the lenses in that "lens group" does not change during focusing. Hereinafter, the lens group that moves along the optical axis during focusing will be referred to as the "focus group." In this optical system, the first negative lens group LF1 and the second negative lens group LF2 are the focus groups, and the optical system focuses on objects from infinity to close distances.

[0013] 1-1.Optical configuration (1) First positive lens group The first positive lens group is the lens group arranged closest to the object in the optical system, and there are no particular limitations on the specific lens configuration of the first positive lens group as long as it has positive refractive power.

[0014] (2) First Negative Lens Unit LF1 and Second Negative Lens Unit LF2 The first negative lens group LF1 and the second negative lens group LF2 are lens groups arranged closer to the image than the first positive lens group. The first negative lens group LF1 and the second negative lens group LF2 have negative refractive power. However, the first negative lens group LF1 is arranged closer to the object than the second negative lens group LF2. In this optical system, it is sufficient that the first positive lens group is arranged closest to the object, and the first negative lens group LF1 and the second negative lens group LF2 are arranged on the image side thereof. The optical system may be substantially composed of these three lens groups, or may include other lens groups.

[0015] In this optical system, by satisfying the formula (1) described below, good optical performance can be obtained even when the optical system is substantially composed of three lens groups. At the same time, the amount of movement of the focus group on the optical axis during focusing can be reduced, making it possible to reduce the size and weight of the optical system and achieve rapid autofocusing. Note that "substantially composed of three lens groups" means that of the lens groups constituting the optical system, three lens groups have substantial refractive power. For example, this means that there are no optical elements, such as lens elements, having substantial refractive power on the object side of the first positive lens group, between the lens groups, or on the image side of the second negative lens group LF2.

[0016] It is preferable that at least one of the first negative lens group LF1 and the second negative lens group LF2 be composed of a single lens element. Here, a "lens element" refers to an element composed of only one lens or only one cemented lens formed by cementing together multiple lenses. A "single lens element" refers to one "lens element." By constructing at least one of the first negative lens group LF1 and the second negative lens group LF2, which are focus groups, with a single lens element, it is possible to reduce the size and weight of at least one focus group, making it easier to achieve high-speed autofocus. Furthermore, by reducing the size and weight of at least one focus group, it is possible to reduce the size and weight of the drive mechanism for driving the focus group. To achieve these effects, it is more preferable that both the first negative lens group LF1 and the second negative lens group LF2 be composed of a single lens element.

[0017] (3) Other lens groups (second positive lens group) Here, even when the optical system includes other lens groups in addition to the first positive lens group, the first negative lens group LF1, and the second negative lens group LF2, it is preferable that the second negative lens group LF2 be the substantial final lens group. In other words, it is preferable that there are no lens elements or the like having substantial refractive power on the image side of the second negative lens group LF2. By making the second negative lens group LF2 the substantial final lens group, it is easy to shorten the overall optical length of the optical system, and it is possible to make the optical system smaller and lighter.

[0018] If the optical system includes other lens groups, it is preferable that the other lens group includes a second positive lens group having positive refractive power. By configuring the optical system with two positive lens groups and two negative lens groups, better aberration correction can be achieved. Furthermore, it is preferable that the second positive lens group be disposed between the first negative lens group LF1 and the second negative lens group LF2. By disposing the second positive lens group between the first negative lens group LF1 and the second negative lens group LF2 and configuring the optical system with four or more lens groups, better aberration correction can be achieved, making it easier to obtain better imaging performance.

[0019] In this optical system, the second positive lens group is preferably disposed between the first negative lens group LF1 and the second negative lens group LF2. By disposing the second positive lens group between the first negative lens group LF1 and the second negative lens group LF2, a bundle of rays diverged by the first negative lens group LF1 can be converged by the second positive lens group and made incident on the second negative lens group LF2. This allows the diameter of the second negative lens group LF2 to be reduced, making it easier to reduce the size and weight of the optical system.

[0020] 1-2.Focus operation As described above, in this optical system, the spacing between adjacent lens groups changes during focusing. At that time, at least the first negative lens group LF1 and the second negative lens group LF2 move in the optical axis direction as a focus group to focus on objects at distances from infinity to close range.

[0021] (1) First Negative Lens Unit LF1 and Second Negative Lens Unit LF2 When focusing from infinity to a close-distance object, the first negative lens unit LF1 and the second negative lens unit LF2 may be moved along the same locus in the optical axis direction, or may be moved along different loci. However, if the first negative lens unit LF1 and the second negative lens unit LF2 are moved along different loci during focusing, that is, if a focusing method using a floating system is adopted, it is more preferable because this makes it easier to suppress aberration fluctuations during focusing while maintaining the optical system small and lightweight, and to obtain good imaging performance throughout the entire focusing range.

[0022] On the other hand, when moving the first negative lens group LF1 and the second negative lens group LF2 along the same trajectory during focusing, the first negative lens group LF1 and the second negative lens group LF2 can be moved simultaneously by fixing the first negative lens group LF1 and the second negative lens group LF2 to the same lens frame and driving the lens frame with a single driving mechanism, so there is no need to provide a driving mechanism for each lens group, and the focus driving mechanism can be simplified.

[0023] (2) First positive lens group It is preferable that the first positive lens group be fixed in the optical axis direction during focusing. The first positive lens group, which is located closest to the object in the optical system, has a larger outer diameter and a thicker lens than the first negative lens group LF1 and the second negative lens group LF2, and is therefore likely to be large and heavy. Therefore, if the first positive lens group is made a fixed group, a drive mechanism for moving the first positive lens group in the optical axis direction during focusing is not required, and the entire imaging lens, including the optical system, drive mechanism, lens barrel, etc., can be made smaller and lighter.

[0024] (3) Second positive lens group If the optical system includes a second positive lens group, it is preferable that the second positive lens group be fixed in the optical axis direction during focusing. In this optical system, the first negative lens group LF1 and the second negative lens group LF2 are focus groups. Increasing the number of focus groups is preferable from the viewpoint of suppressing aberration fluctuations during focusing. However, increasing the number of focus groups requires a drive mechanism for moving each focus group in the optical axis direction, making it difficult to reduce the size and weight of the entire imaging lens, including the optical system, drive mechanism, lens barrel, etc. Therefore, if the optical system includes a second positive lens group, it is preferable that the second positive lens group be a fixed group.

[0025] 1-3.Formula It is preferable that the optical system satisfies one or more of the following expressions:

[0026] 1-3-1. Formula (1) 0.7 < fn1 / fn2 <2.0 (1) however, fn1: focal length of the first negative lens unit LF1 fn2: focal length of the second negative lens unit LF2

[0027] Equation (1) defines the ratio between the focal length of the first negative lens unit LF1 and the focal length of the second negative lens unit LF2. By satisfying equation (1), the negative refractive powers distributed to the first negative lens unit LF1 and the second negative lens unit LF2 are well balanced, and an optical system with excellent optical performance and minimal aberration fluctuations during focusing can be obtained, even without disposing any other lens unit on the image side of the second negative lens unit LF2. Furthermore, the amount of movement of the first negative lens unit LF1 and the second negative lens unit LF2 on the optical axis during focusing can be kept within an appropriate range. These factors enable the overall optical length of the optical system to be shortened, thereby enabling the optical system to be made smaller and lighter.

[0028] On the other hand, if the numerical value of formula (1) is below the lower limit, the refractive power of the first negative lens unit LF1 becomes too strong relative to the second negative lens unit LF2, which is favorable in that the backlash magnification (the ratio of the amount of movement of the image plane to the unit amount of movement of the lens unit) increases, but is undesirable because it increases the effects of aberration fluctuations and decentering aberrations during focusing. On the other hand, if the numerical value of formula (1) is above the upper limit, the refractive power of the first negative lens unit LF1 becomes too weak relative to the second negative lens unit LF2, which reduces the backlash magnification. Therefore, the amount of movement of the first negative lens unit LF1 during focusing increases, which is undesirable because it may increase the overall optical length of the optical system.

[0029] To obtain the above effect, the lower limit of formula (1) is preferably 0.8, and more preferably 0.9. The upper limit of formula (1) is preferably 1.8, and more preferably 1.7. However, in formula (1), the inequality sign (<) may be replaced with an inequality sign with an equal sign (≦).

[0030] 1-3-2.Formula (2) |β|≧ 0.5 (2) however, β: Paraxial imaging magnification of the optical system

[0031] The above formula (2) defines the paraxial imaging magnification of the optical system. If formula (2) is satisfied, the optical system is a so-called macro lens, and can obtain an image of the main subject at a paraxial imaging magnification of 0.5 times or more the actual size.

[0032] The lower limit of formula (2) is more preferably 0.8, even more preferably 0.9, and even more preferably 1.0. The upper limit of formula (2) is not particularly limited. However, in the optical system according to the present invention, particularly good optical performance can be obtained when the upper limit of formula (2) is 2.0.

[0033] 2. Imaging device Next, we will explain the imaging device of the present invention. The imaging device of the present invention is characterized by including the imaging lens of the present invention described above and an imaging element that converts an optical image formed by the imaging lens into an electrical signal. The imaging element is preferably provided on the image side of the optical system.

[0034] Here, the imaging element is not particularly limited, and solid-state imaging elements such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor can also be used. The imaging device of the present invention is suitable for imaging devices using such solid-state imaging elements, such as digital cameras and video cameras. The imaging device can also be applied to various imaging devices, such as single-lens reflex cameras, mirrorless single-lens cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone-mounted cameras. These imaging devices may be interchangeable-lens imaging devices or fixed-lens imaging devices in which the lens is fixed to the housing. In particular, the imaging lens has a maximum imaging magnification of 0.5x or more, making it suitable for so-called macro lenses capable of capturing images close to a subject. Therefore, the imaging lens is suitable for applications requiring large-scale imaging of a subject, such as single-lens reflex cameras, mirrorless single-lens cameras, and industrial imaging devices.

[0035] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples. [Example]

[0036] (1) Optical configuration 1 is a lens cross-sectional view of an optical system according to Example 1 of the present invention, with the upper diagram showing a state focused on an object at infinity and the lower diagram showing a state focused on an object at close range (imaging magnification β=-1). The same applies to the lens cross-sectional views shown in each of the following Examples, and therefore further explanation will be omitted below.

[0037] As shown in Figure 1, the optical system includes, in order from the object side, a first lens group G1 (first positive lens group) having positive refractive power, a second lens group G2 (first negative lens group LF1) having negative refractive power, a third lens group G3 (second positive lens group) having positive refractive power, and a fourth lens group G4 (second negative lens group LF2) having negative refractive power. An aperture stop S is located on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0038] In this optical system, the spacing between adjacent lens groups changes during focusing. When focusing from an object at infinity to a close object, the first lens group G1 is fixed in the optical axis direction, the second lens group G2 moves toward the image plane, the third lens group G3 is fixed in the optical axis direction, and the fourth lens group G4 moves toward the image plane. In FIG. 1, "IP" denotes an image plane, specifically the imaging surface of a solid-state imaging device such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. A cover glass CG or the like is provided on the object side of the IP. This is the same for the lens cross-sectional views shown in other embodiments, so further explanation will be omitted.

[0039] (2) Numerical examples Next, a numerical example of the optical system will be described. The lens data, various data, variable distances during focusing, and focal lengths of each lens group of the optical system are shown below. In the "(Lens Data)" section, "No." indicates the order of the lens surface (surface number) counted from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the spacing on the optical axis of the lens surface, "Nd" indicates the refractive index for the d-line (wavelength λ=587.6 nm), and "ABV" indicates the Abbe number for the d-line. In the "No." column, "STOP" displayed next to the surface number indicates the aperture stop, and "*" indicates an aspheric surface. In the "D" column, "D○○" (e.g., D9 in this embodiment) indicates the variable spacing during focusing. In the following numerical examples, all length units are "mm," and all angle of view units are "°."

[0040] In "(Various Data)," "f" is the focal length of the optical system, "β" is the imaging magnification, "Fno" is the F-number, "ω" is the half angle of view, "Y" is the image height, "BF" is the back focus, and "TL" is the total optical length, each showing values ​​when focused on an object at infinity and when focused on an object at close range. Note that the values ​​in the table include values ​​for a 2.5 mm thick cover glass (Nd=1.51633), and the same applies to the back focus shown in other examples.

[0041] "(Variable Distance (in Focus))" shows the variable distance when an object at infinity is in focus and when an object at close range is in focus, along with the focal length (f) and shooting distance at that time. "(Focal length of each lens group)" indicates the lens surfaces included in each lens group and the focal length of each lens group.

[0042] "(Aspherical surface data)" indicates the aspherical coefficients of each aspherical surface. Note that the aspherical surface is defined by the following equation, where x is the amount of displacement from the vertex of the surface in the optical axis direction. x=(h 2 / r) / [1+{1-(1+k)×(h / r) 2} 1 / 2 ] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In the above formula, h is the height from the optical axis, r is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th order aspheric coefficient. Also, "E±XX" represents exponential notation, and is expressed as "×10 ±XX " means.

[0043] Furthermore, the values ​​of formulas (1) and (2) are shown in Table 1 (discussed later). The matters relating to these numerical values ​​are similar to those in other examples, and therefore will not be described below.

[0044] 2 and 3 show longitudinal aberration diagrams of the optical system when focused on an object at infinity and when focused on a close object. In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are shown, from left to right. In the diagrams showing spherical aberration, the vertical axis represents the ratio to the maximum aperture, and the horizontal axis represents defocus. The solid line represents spherical aberration at the d-line (wavelength λ=587.56 nm), the dashed line represents spherical aberration at the C-line (wavelength λ=656.28 nm), and the dash-dotted line represents spherical aberration at the F-line (wavelength λ=486.13 nm). In the diagrams showing astigmatism, the vertical axis represents half angle of view (ω), the horizontal axis represents defocus, the solid line represents the sagittal image plane for the d-line, and the dotted line represents the meridional image plane for the d-line. In the diagrams showing distortion, the vertical axis represents half angle of view (ω), and the horizontal axis represents distortion in percentage. The matters relating to these figures are the same as those for the longitudinal aberration diagrams shown in other embodiments, and therefore, the explanation thereof will be omitted below.

[0045] (lens data) No. RD Nd ABV 1 55.2144 3.7000 1.92286 20.88 2 2831.3180 1.0000 1.65412 39.68 3 29.7297 8.3906 4 63.8574 6.1945 1.59282 68.62 5 -44.5064 1.2885 6 -32.6739 0.8000 1.84666 23.78 7 -836.5892 0.2000 8* 45.5948 7.3667 1.77377 47.17 9* -40.1498 D9 10 -484.6300 0.8000 1.51680 64.20 11 24.8647 D11 12STOP 0.0000 0.8000 13 50.7082 0.8000 1.85478 24.80 14 23.3051 4.1934 15 -96.6402 2.7127 1.90525 35.04 16 -39.0617 5.3601 17 48.5018 6.8067 1.43700 95.10 18 -23.3600 D18 19 -47.6699 1.6000 1.84666 23.78 20 -30.1939 0.7000 1.49700 81.61 21 28.6956 D21 22 0.0000 2.5000 1.51633 64.14 23 0.0000 1.0000

[0046] (Various data) f 92.7000 41.3760 β 0 -1 Fno 2.9100 5.8200 ω 12.6205 9.0852 Y 21.6330 21.6330 BF 55.4000 38.5640 TL 125.0000 125.0000

[0047] (Variable interval (when in focus)) f 92.7000 41.3760 Shooting distance INF 197.4670 D9 1.5000 10.2791 D11 12.7669 3.9878 D18 2.6191 19.4561 D21 51.9008 35.0637

[0048] (focal length of each lens group) Group Surface number Focal length G1 1-9 35.791 G2 10-11 -45.740 G3 12-18 36.766 G4 19-21 -42.307

[0049] (aspheric data) No. K A4 A6 A8 A10 A12 8 0.00000E+00 -5.65839E-06 -3.87057E-09 -2.78239E-11 9.11917E-14 -6.92025E-17 9 -1.00159E+00 1.80536E-06 -1.06473E-08 6.11458E-12 8.58841E-15 3.82931E-18 [Example]

[0050] (1) Optical configuration Fig. 4 is a cross-sectional view of lenses in an optical system according to a second embodiment of the present invention. As shown in Fig. 4, the optical system includes, in order from the object side, a first lens group G1 (first positive lens group) having positive refractive power, a second lens group G2 (first negative lens group LF1) having negative refractive power, a third lens group G3 (second positive lens group) having positive refractive power, a fourth lens group G4 (second negative lens group LF2) having negative refractive power, and a fifth lens group G5 having positive refractive power. An aperture stop S is disposed on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0051] In this optical system, the spacing between adjacent lens groups changes during focusing. When focusing from an object at infinity to an object at a close distance, the first lens group G1 is fixed in the optical axis direction, the second lens group G2 moves toward the image plane, the third lens group G3 is fixed in the optical axis direction, the fourth lens group G4 moves toward the image plane, and the fifth lens group G5 is fixed in the optical axis direction.

[0052] (2) Numerical examples Next, a numerical example of the optical system will be described. The lens data, various data, variable distances during focusing, and focal lengths of each lens group of the optical system are shown below.

[0053] 5 and 6 show longitudinal aberration diagrams of the optical system when focused on an object at infinity and when focused on an object at a close distance.

[0054] (lens data) No. R D Nd ABV 1 118.7112 2.4065 1.85883 30.00 2 305.3128 0.2000 3 43.0253 4.7819 1.92286 20.88 4 521.0830 1.3000 1.59282 68.62 5 22.4336 7.1876 6 -66.2336 1.2000 1.84666 23.78 7 30.2523 6.8376 1.49700 81.61 8 -55.5537 0.2000 9 158.3357 2.7158 1.95375 32.32 10 -239.1887 0.2000 11 32.5764 7.2512 1.49700 81.61 12 -63.8072 D12 13 -169.0552 1.0000 1.67790 55.35 14 43.3892 D14 15STOP 0.0000 1.6518 16 -192.0323 1.0000 2.00100 29.13 17 46.7496 8.8466 1.78590 43.93 18 -19.0973 2.2863 1.85883 30.00 19 -36.1169 0.2000 20 56.0312 3.2157 1.90043 37.37 21 -430.2329 D21 22 -131.2132 2.2000 1.92286 20.88 23 -37.4104 1.0000 1.70154 41.24 24 36.3465 D24 25 -329.6535 6.6164 1.84666 23.78 26 -67.0238 6.0504 27 -31.6155 1.0000 1.80610 40.73 28 92.9052 0.2000 29 40.6762 5.6439 1.48749 70.44 30 -129.1177 19.3285 31 0.0000 2.5000 1.51633 64.14 32 0.0000 1.0000

[0055] (Various data) f 87.7998 38.9769 β 0 -1 Fno 2.9100 5.8200 ω 13.7621 8.2081 Y 21.6330 21.6330 BF 22.8285 22.8285 TL 145.2807 145.2807

[0056] (Variable interval (when in focus)) f 87.7998 38.9769 Shooting distance INF 214.4784 D12 2.0000 17.0000 D14 18.6305 3.6305 D21 2.0000 17.0000 D24 20.3098 5.3098

[0057] (focal length of each lens group) Group Surface number Focal length G1 1-12 47.662 G2 13-14 -50.836 G3 15-21 32.444 G4 22-24 -48.689 G5 25-30 -143.070 [Example]

[0058] (1) Optical configuration Fig. 7 is a cross-sectional view of lenses in an optical system according to a third embodiment of the present invention. As shown in Fig. 7, the optical system includes, in order from the object side, a first lens group G1 (first positive lens group) having positive refractive power, a second lens group G2 (first negative lens group LF1) having negative refractive power, a third lens group G3 (second positive lens group) having positive refractive power, and a fourth lens group G4 (second negative lens group LF2) having negative refractive power. An aperture stop S is disposed on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0059] In this optical system, the spacing between adjacent lens groups changes during focusing. When focusing from an object at infinity to a close object, the first lens group G1 is fixed in the optical axis direction, the second lens group G2 moves toward the image plane, the third lens group G3 is fixed in the optical axis direction, and the fourth lens group G4 moves toward the image plane.

[0060] (2) Numerical examples Next, a numerical example of the optical system will be described. The lens data, various data, variable distances during focusing, and focal lengths of each lens group of the optical system are shown below.

[0061] 8 and 9 show longitudinal aberration diagrams of the optical system when focused on an object at infinity and when focused on an object at a close distance.

[0062] (lens data) No. RD Nd ABV 1 580.7274 3.0524 1.87347 37.87 2 -151.4729 0.2000 3 42.9496 4.7778 1.92286 20.88 4 181.6153 1.0000 1.71855 30.01 5 22.2693 1.3130 6 23.5142 9.6334 1.51355 77.11 7 -65.9430 0.8000 1.84359 23.87 8 100.4505 0.2000 9 43.1015 3.9275 1.77250 49.62 10 437.9983 D10 11 998.3313 0.8000 1.49700 81.61 12 26.8528 D12 13STOP 0.0000 0.8000 14 53.3621 0.8000 1.85478 24.80 15 31.0517 1.5736 16 87.3714 1.0000 1.90525 35.04 17 41.7569 2.7402 18 102.7346 2.7823 1.88535 29.80 19 -102.9791 0.2000 20 34.1015 5.4763 1.43700 95.10 21 -31.9622 D21 22 -2582.8411 3.3000 1.79504 25.44 23 -31.1711 0.7000 1.77191 49.65 24 28.1387 D24 25 0.0000 2.5000 1.51633 64.14 26 0.0000 1.0000

[0063] (Various items) f 135.8005 47.1851 β 0 -1 Fno 3.5181 7.0000 ω 8.6054 5.6374 Y 21.6330 21.6330 BF 62.0716 43.4115 TL 124.0000 124.0000

[0064] (The interval can be changed (when focusing)) f 135.8005 47.1851 Shooting distance INF 250.5545 D10 1.6449 12.4120 D12 14.6853 3.9183 D21 1.5185 20.1806 D24 58.5716 39.9115

[0065] (focal length of each lens group) Group Surface number Focal length G1 1-10 49.027 G2 11-12 -55.539 G3 13-21 41.051 G4 22-24 -37.026

[0066] [Table 1] Example 1 Example 2 Example 3 Equation (1) fn1 / fn2 1.08 1.04 1.50 Formula (2) β2 -1 -1 -1 [Industrial Applicability]

[0067] According to the present invention, it is possible to provide an optical system and an imaging device that are small, lightweight, and capable of achieving rapid autofocusing.

Claims

1. A lens system comprising, in order from the object side, a first positive lens group having positive refractive power, a first negative lens group which moves along the optical axis during focusing and has negative refractive power, a second positive lens group having positive refractive power, and a second negative lens group which moves along the optical axis during focusing and has negative refractive power, wherein the spacing between adjacent lens groups changes during focusing, an aperture stop is disposed adjacent to the second positive lens unit on the object side; at least one of the first negative lens group and the second negative lens group is composed of a single lens element, An optical system characterized in that only the first negative lens unit and the second negative lens unit are moved along the optical axis during focusing, and the following formula is satisfied: 0.9 < fn1 / fn2 < 1.7...(1) however, fn1: focal length of the first negative lens unit fn2: focal length of the second negative lens unit

2. A lens system comprising, in order from the object side, a first positive lens group having positive refractive power, a first negative lens group which moves along the optical axis during focusing and has negative refractive power, a second positive lens group having positive refractive power, and a second negative lens group which moves along the optical axis during focusing and has negative refractive power, wherein the spacing between adjacent lens groups changes during focusing, An optical system characterized in that the second negative lens unit is a lens unit disposed substantially closest to the image side, and the following formula is satisfied: 0.7 < fn1 / fn2 < 2.0 (1) however, fn1: focal length of the first negative lens unit fn2: focal length of the second negative lens unit

3. 3. The optical system according to claim 1, wherein the following formula is satisfied: ｜β｜≧ ０．５ ・・・（２） however, β: Paraxial imaging magnification of the optical system

4. 4. The optical system according to claim 1, wherein the first positive lens group is fixed in the optical axis direction during focusing.

5. 5. The optical system according to claim 1, wherein the second positive lens group is fixed in the optical axis direction during focusing.

6. The optical system according to claim 2 , wherein at least one of the first negative lens group and the second negative lens group is formed of a single lens element.

7. The optical system according to claim 2 , wherein only the first negative lens unit and the second negative lens unit are moved along the optical axis during focusing.

8. 8. An imaging apparatus comprising: the optical system according to claim 1; and an imaging element that converts an optical image formed by the optical system into an electrical signal.

Images