Optical system and imaging device

Abstract

To provide an optical system which is bright with a small F-number, has a large aperture, and yet offers suppressed image plane variation and chromatic aberration while shifting focus, and to provide an image capturing device.SOLUTION: An optical system is provided, comprising, in order from the object side, a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, a third lens group (G3) having positive refractive power, and a fourth lens group (G4) having negative refractive power, the second lens group having at least one positive lens and at least one negative lens. When shifting focus from infinity to a shortest distance, the first and fourth lens groups are stationary relative to the image plane while the second and third lens groups move along an optical axis. The optical system satisfies given conditional expressions. An image capturing device comprising such optical system is also provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system and an imaging device.

Background Art

[0002] In recent years, as the demand for full-size mirrorless cameras has been expanding, there has been a growing need for lenses that can handle high resolution with the increase in sensor pixel count and resolution of monitors and the like.

[0003] Generally, bright large-aperture lenses with an F-number of about 1.4 have a shallower depth of field, and when focusing from infinity to the closest object distance, it is necessary to further suppress image plane fluctuations. Also, correction of axial chromatic aberration and lateral chromatic aberration, such as color fringing of the image on the sensor imaging plane and color fringing of the blurred image in the out-of-focus area, has become more important.

[0004] Conventionally, optical systems for bright large-aperture lenses with an F-number of about 1.4 are known. For example, the optical systems disclosed in Patent Documents 1 and 2 are composed of a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power in order from the object side to the image side, and an inner focus type focusing method is adopted in which the second lens group is moved along the optical axis direction for focusing. The optical system disclosed in Patent Document 3 is composed of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power in order from the object side to the image side, and a floating focus type focusing method is adopted in which the second lens group and the third lens group are moved along the optical axis direction for focusing.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the optical system described in Patent Document 1, since the power arrangement of the first lens group and the second lens group is not appropriate, the diameter of the lenses constituting the first lens group becomes relatively large. As a result, the entire product becomes large-sized. In addition, the image plane fluctuation and chromatic aberration correction during focusing are insufficient, and an improvement in optical performance is required.

[0007] In the optical system described in Patent Document 2, since focusing is performed by a single lens group, the image plane fluctuation becomes large during focusing from infinity to the closest distance. Therefore, suppression of image plane fluctuation over the entire focusing range is required.

[0008] The optical system described in Patent Document 3 performs focusing by a floating focus method. The lenses used in the lens group that moves during focusing use glass with low anomalous dispersibility. Therefore, the correction of axial chromatic aberration and lateral chromatic aberration over the entire focusing range is insufficient, and color bleeding at the imaging plane becomes prominent.

[0009] An object of the present invention is to provide an optical system and an imaging device that have a bright large-aperture lens with a small F-number and suppress image plane fluctuation and chromatic aberration over the entire focusing range.

Means for Solving the Problems

[0010] In order to solve the above problems, the optical system according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power. The second lens group has at least one positive lens and at least one negative lens. When focusing from infinity to the closest distance, the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group move along the optical axis direction, respectively, and satisfy the following formula. -0.55 ≦ f1 / f2 ≦ -0.01 ·····(1) ν2 ≦ 25.0 ·····(2) However, f1: Focal length of the first lens group f2: Focal length of the second lens group ν2: Abbe number of any one of the positive lenses included in the second lens group at the d-line

[0011] In addition, in order to solve the above problems, the imaging device according to the present invention is characterized by comprising the above optical system and an imaging element that converts an optical image formed by the optical system into an electrical signal on the image side of the optical system.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments 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.

[0014] 1. Optical System 1-1. Optical Configuration The optical system of the present embodiment is composed of a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, in order from the object side.

[0015] By adopting the above refractive power arrangement, the optical system can easily correct the aberrations of a bright large-aperture optical system with an F value of about 1.4 and a small F value.

[0016] (1) First Lens Group The specific configuration of the first lens group is not particularly limited, except that it is a lens group having a positive refractive power. The fact that the first lens group is a lens group having a positive refractive power can suppress various aberrations and facilitate miniaturization. Also, for example, if the first lens group has a configuration having a negative lens, it is preferable because it is easy to suppress chromatic aberration and obtain good optical performance. Further, in the first lens group, if it has a configuration having a cemented lens of a positive lens and a negative lens, it is preferable because it is easy to suppress chromatic aberration and the sensitivity of each lens. If the largest air interval among the air intervals arranged between the most object-side lens surface of the first lens group and the most image-side lens surface of the fourth lens group is arranged in the first lens group, it is preferable because it is easy to correct coma aberration.

[0017] Here, the "lens group" refers to a group consisting of one or a plurality of lenses adjacent to each other. Also, the lens group changes the adjacent interval with respect to other lenses along the optical axis direction during focusing. When one lens group is composed of a plurality of lenses, the distance on the optical axis between each lens included in the one lens group shall not change during focusing.

[0018] (2) The second lens group The second lens group is a lens group having a negative refractive power, and its specific configuration is not particularly limited as long as it has one or more lenses having a negative refractive power. In the second lens group, it may have one or more lenses having a positive refractive power and one or more lenses having a negative refractive power, respectively. Also, in the second lens group, if it is composed of a negative lens and a positive lens from the object side, chromatic aberration can be suppressed well, which is preferable.

[0019] (3) The third lens group The third lens group is a lens group having a positive refractive power. As long as it has one or more lenses with positive refractive power, its specific configuration is not particularly limited. For example, in the third lens group, it may have one or more lenses with positive refractive power and one or more lenses with negative refractive power respectively. Also, in the third lens group, if it has a configuration with a cemented lens of a positive lens and a negative lens, it is preferable because it is easy to suppress chromatic aberration and suppress the sensitivity of each lens. In suppressing various aberrations, the shape of the lens arranged closest to the object side is preferably convex on the object side surface. Also, the shape of the lens arranged closest to the image side is preferably convex on the image side surface.

[0020] (3) The fourth lens group The fourth lens group is a lens group having a negative refractive power. As long as it has one or more lenses with negative refractive power, its specific configuration is not particularly limited. Also, by having at least one negative lens, it is easy to suppress chromatic aberration and obtain good optical performance, which is preferable. Also, for example, if the fourth lens group has a configuration with a positive lens, it is easy to suppress chromatic aberration and obtain good optical performance, which is preferable. Also, in the fourth lens group, if it has a configuration with a cemented lens of a positive lens and a negative lens, it is preferable because it is easy to suppress chromatic aberration and suppress the sensitivity of each lens. Also, in the fourth lens group, if it has a positive lens, a negative lens, and a negative lens in order from the object side, it is preferable because it is easy to correct various aberrations.

[0021] (4) Aperture stop In this optical system, the arrangement of the aperture stop is not particularly limited. However, the aperture stop mentioned here refers to the aperture stop that defines the light beam diameter of the optical system, that is, the aperture stop that defines the F-number of the optical system. However, it is preferable to arrange the aperture stop within the first lens group in order to miniaturize the aperture unit.

[0022] 1-2. Focusing When the optical system focuses from infinity to the closest distance, the first lens group and the fourth lens group are fixed with respect to the image plane, and as long as the second lens group and the third lens group move along the optical axis direction respectively, their specific operations are not particularly limited. Further, when focusing from infinity to a short distance, a configuration in which the second lens group moves toward the image side on the optical axis and the third lens group moves toward the object side on the optical axis is preferable because it can suppress image plane fluctuations. Further, when focusing from infinity to a short distance, it is more preferable that the second lens group and the third lens group move on the optical axis with different moving amounts. With this configuration, it is possible to have high optical performance when focusing from infinity to the closest distance. Furthermore, when focusing from infinity to the closest distance, it is more preferable that the second lens group has a larger moving amount on the optical axis with respect to the image plane than the third lens group. With this configuration, it is possible to have even higher optical performance when focusing from infinity to the closest distance.

[0023] 1-3. Equation In the optical system, it is preferable to adopt the above-described configuration and satisfy one or more of the following equations.

[0024] 1-3-1. Equation (1) -0.55 ≦ f1 / f2 ≦ -0.01 ·····(1) However, f1: Focal length of the first lens group f2: Focal length of the second lens group

[0025] Equation (1) is an equation that defines the ratio of the focal lengths of the first lens group and the second lens group. By satisfying Equation (1), various aberrations can be corrected well while shortening the overall optical length, and it becomes easy to miniaturize the second lens group.

[0026] On the other hand, when the value of Equation (1) is below the lower limit value, the power of the first lens group becomes weak, and it becomes difficult to miniaturize the optical system. On the other hand, when the numerical value of Equation (1) exceeds the upper limit value, the power of the first lens group becomes strong, and the fluctuations of coma aberration and distortion aberration generated within the first lens group become large, making it difficult to correct various aberrations.

[0027] In order to obtain the above effects, the lower limit value of formula (1) is preferably -0.53, more preferably -0.50. Also, the upper limit value of formula (1) is preferably -0.02, more preferably -0.03.

[0028] 1-3-2. Formula (2) ν2 ≦ 25.0 ·····(2) However, ν2: Abbe number at the d-line of any one of the positive lenses included in the second lens group

[0029] Formula (2) is a formula that defines the Abbe number at the d-line of any one of the positive lenses included in the second lens group. By satisfying formula (2), it becomes possible to correct the axial chromatic aberration and the magnification chromatic aberration from an infinite object to a closest object at the time of focusing. When the second lens group has a plurality of positive lenses, the effect can be obtained as long as only any one of the lenses satisfies formula (2). Also, if a plurality of lenses satisfy formula (2), it is more preferable in obtaining the above effect.

[0030] On the other hand, when the numerical value of formula (2) exceeds the upper limit value, the correction of the axial chromatic aberration and the magnification chromatic aberration becomes insufficient, the color bleeding of the image on the imaging surface becomes noticeable, and the color bleeding of the blurred image in the out-of-focus part becomes prominent, which is not preferable.

[0031] In order to obtain the above effects, the lower limit value of formula (2) is preferably 10.0, more preferably 15.0. Also, the upper limit value of formula (2) is preferably 24.0, more preferably 22.0.

[0032] 1-3-3. Formula (3) -0.50 ≦ f / f2 ≦ -0.01 ·····(3) However, f: Focal length when the optical system is focused at infinity

[0033] Equation (3) is an equation that defines the ratio between the focal length of the optical system at infinity focus and the focal length of the second lens group. By satisfying Equation (3), various aberrations can be corrected well while shortening the overall optical length, and it becomes easier to miniaturize the second lens group.

[0034] On the other hand, when the value of Equation (3) is below the lower limit value, the power of the second lens group becomes weak and the movement amount increases, making it difficult to miniaturize while correcting various aberrations. On the other hand, when the numerical value of Equation (3) exceeds the upper limit value, the power of the second lens group becomes strong and it is more likely to be affected by the second lens group of lens manufacturing errors, so the decentering sensitivity becomes strong. Also, the image plane fluctuation becomes significant. Further, when focusing from infinity to the closest distance, it becomes difficult to suppress aberration fluctuations.

[0035] In order to obtain the above effects, the lower limit value of Equation (3) is preferably -0.45, and more preferably -0.40. Also, the upper limit value of Equation (3) is preferably -0.05, and more preferably -0.10.

[0036] 1-3-4. Equation (4) ν1 ≦ 25.0 ·····(4) However, ν1: Abbe number of the negative lens included in the first lens group in the d-line

[0037] Equation (4) is an equation that defines the Abbe number of the negative lens included in the first lens group in the d-line. By having at least one negative lens that satisfies Equation (4) in the first lens group, it becomes possible to correct axial chromatic aberration and lateral chromatic aberration when focusing from infinity to the closest distance.

[0038] On the other hand, when the numerical value of Equation (4) exceeds the upper limit value, the sagittal coma flare expands, and further, the correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient, the color bleeding of the image on the imaging plane becomes noticeable, and the color bleeding of the blurred image in the out-of-focus part becomes prominent, which is not preferable.

[0039] In order to obtain the above effects, the lower limit value of the formula (4) is preferably 10.0, and more preferably 15.0. Further, the upper limit value of the formula (4) is preferably 24.0, and more preferably 22.0.

[0040] 1-3-5. Formula (5) 39.0 ≦ f1R ≦ 85.0 ·····(5) However, f1R: Composite focal length (mm) of the lenses on the image side of the aperture in the first lens group

[0041] Formula (5) is a formula that defines the composite focal length of the lenses on the image side of the aperture in the first lens group. By satisfying formula (5), the light rays incident on the second lens group can be regulated, and the aberration variation at the time of focusing of the second lens group can be suppressed, so that good correction becomes possible.

[0042] On the other hand, when the numerical value of formula (5) is below the lower limit value, the light ray incident angle with respect to the second lens group becomes large. In addition, the aberration sensitivity of the second lens group increases, the decentration sensitivity of the lens group due to lens manufacturing errors increases, and it becomes difficult to obtain an optical system with high optical performance. On the other hand, when the numerical value of formula (5) exceeds the upper limit value, the light ray incident angle with respect to the second lens group becomes small. Although it is possible to reduce the aberration sensitivity of the lens group, it causes the second lens group to become larger and heavier, and further expands the outer diameter of the product, which is not preferable.

[0043] In order to obtain the above effects, the lower limit value of the formula (5) is preferably 40.0, and more preferably 41.0. Further, the upper limit value of the formula (5) is preferably 83.0, more preferably 80.0, and even more preferably 75.0.

[0044] 1-3-6. Formula (6) -10.0≦(R1f+R1r) / (R1f-R1r)≦1.2·····(6) However, R1f: Curvature radius of the image side surface of the lens arranged on the object side with the largest air interval in the first lens group R1r: The radius of curvature of the object-side surface of the lens arranged on the image side across the largest air interval within the first lens group

[0045] Equation (6) is an equation that defines the radii of curvature of the lens surfaces on the object side and the image side across the largest air interval in the first lens group. By satisfying Equation (6), the sagittal coma aberration and the chromatic aberration of magnification generated in the first lens group can be corrected well.

[0046] On the other hand, when the numerical value of Equation (6) is below the lower limit value, the incident angle of off-axis rays changes. In particular, the change in the g-line becomes large, and the chromatic aberration of magnification becomes large. Also, the sagittal coma aberration, which is a problem in large-aperture lenses, expands, making it difficult to correct the aberration. On the other hand, when the numerical value of Equation (6) exceeds the upper limit value, the fluctuations in the sagittal coma aberration and the distortion aberration become large, making it difficult to correct the aberration.

[0047] In order to obtain the above effects, the lower limit value of Equation (6) is preferably -9.5, and more preferably -9.3. Also, the upper limit value of Equation (6) is preferably 1.0, and more preferably 0.8.

[0048] 1-3-7. Equation (7) 0.5 ≦ BF / Y ≦ 1.3 ·····(7) However, BF: The distance on the optical axis from the vertex of the most image-side surface of the fourth lens group to the image plane Y: The maximum image height of the optical system

[0049] Equation (7) is an equation that defines the distance from the vertex of the most image-side surface of the fourth lens group to the image plane and the maximum image height of the image plane in the optical system. By satisfying Equation (7), the influence of the peripheral light quantity becomes minor. Also, the optical system can shorten the overall length, making it easy to miniaturize.

[0050] On the other hand, when the numerical value of Expression (7) is below the lower limit value, the principal ray incident angle (the incident angle of the principal ray that the pixels on the sensor light-receiving surface can tolerate) at which the principal ray incident on the image plane from the most image-side surface of the optical system becomes tight, and the peripheral light quantity becomes insufficient (shading) and is affected by color bleeding. On the other hand, when the numerical value of Expression (7) exceeds the upper limit value, the back focus becomes long and the overall length of the optical system becomes long. Further, it is disadvantageous for miniaturization of the optical system and is unsuitable for a mirrorless camera.

[0051] In order to obtain the above effects, the lower limit value of Expression (7) is preferably 0.52, and more preferably 0.55. Further, the upper limit value of Expression (7) is preferably 1.2, and more preferably 1.1.

[0052] 1-3-8. Expression (8) 0.80 ≦ FD / f ≦ 1.50 ·····(8) However, FD: The distance on the optical axis from the most object-side lens surface of the second lens group to the most image-side lens surface of the fourth lens group when focused at infinity f: The focal length of the optical system when focused at infinity

[0053] Expression (8) is an expression that defines the ratio of the distance on the optical axis from the most object-side lens surface of the second lens group to the most image-side lens surface of the fourth lens group to the focal length of the optical system when focused at infinity. By satisfying Expression (8), it is possible to optimize the size of the second lens group while suppressing the aberration variation during focusing. Further, the influence of the peripheral light quantity becomes minor. In addition, the overall length of the optical system can be shortened and miniaturization becomes easy.

[0054] On the other hand, when the numerical value of Expression (8) is below the lower limit value, the overall length cannot be suppressed and miniaturization becomes difficult. On the other hand, when the numerical value of Expression (8) exceeds the upper limit value, the aberration variation during focusing becomes large and correction of various aberrations becomes difficult.

[0055] In order to obtain the above effects, the lower limit value of the formula (8) is preferably 0.85, more preferably 0.90. Further, the upper limit value of the formula (8) is preferably 1.45, more preferably 1.40.

[0060] 1-3-10. Formula (10) 0.95 ≦ βb ≦ 1.50 ·····(10) However, βb: Lateral magnification of the fourth lens group at infinite focus

[0061] Formula (10) is a formula that defines the lateral magnification of the fourth lens group. By satisfying formula (10), miniaturization of the optical system and correction of various aberrations are made possible.

[0062] On the other hand, when the numerical value of formula (10) is below the lower limit value, the overall length cannot be suppressed and miniaturization becomes difficult. On the other hand, when the numerical value of formula (10) exceeds the upper limit value, the aberration variation at the time of focusing becomes large and correction of various aberrations becomes difficult.

[0063] In order to obtain the above effects, the lower limit value of the formula (10) is preferably 0.98, more preferably 1.00. Further, the upper limit value of the formula (10) is preferably 1.48, more preferably 1.46.

[0064] 2. Imaging device Next, the imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by including the optical system according to the present invention and an imaging element provided on the image side of the optical system for converting the optical image formed by the optical system into an electrical signal.

[0065] Here, there is no particular limitation on the imaging device or the like, and solid-state imaging devices such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device according to the present invention is suitable for imaging devices using these solid-state imaging devices such as digital cameras and video cameras. Further, the imaging device may be a lens-fixed imaging device in which the lens is fixed to the housing, or of course, may be an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

[0066] FIG. 41 is a diagram schematically showing an example of the configuration of the imaging device 1. The camera 2 has a detachable optical system 3, an imaging device 21 (CCD sensor or CMOS sensor) disposed on the image plane IP of the optical system 3, and a cover glass 22 disposed on the object side of the imaging device 21. The optical system 3 has an aperture stop 31.

[0067] Next, the present invention will be specifically described by showing examples. However, the present invention is not limited to the following examples.

Example

[0068] (1) Optical configuration of the optical system FIG. 1 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system of Example 1 according to the present invention.

[0069] The optical system is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a close object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0070] The configurations of the respective lens groups will be described below. The first lens group G1 is composed of, in order from the object side, a positive meniscus lens L1 with a concave surface facing the object side and a negative meniscus lens L2 with a concave surface facing the object side joined together to form a positive refractive power joined lens, a negative meniscus lens L3 with a convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with a convex surface facing the object side, a negative refractive power joined lens formed by joining a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0071] The second lens group G2 is composed of a plano-concave lens L9 with a flat surface on the object side and a biconvex lens L10.

[0072] The third lens group G3 is composed of a positive meniscus lens L11 with a concave surface facing the object side.

[0073] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with a convex surface facing the object side.

[0074] "IP" shown in FIG. 1 is an imaging surface, specifically, the imaging surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor, or the film surface of a silver halide film, etc. Also, on the object side of the imaging surface IP, a parallel flat plate having substantially no refractive power such as a cover glass CG is provided. Since these points are the same in each lens cross-sectional view shown in other embodiments, the description will be omitted below.

[0075] (2) Numerical Examples Next, numerical examples applying the specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focusing)", "focal lengths of the respective lens groups", and "aspherical data" of the optical system are shown below. Also, the values (conditional expression corresponding values) of each formula are summarized after Example 8.

[0076] In the "surface data", "surface number" represents the order of the lens surfaces counted from the object side, "R" represents the radius of curvature of the lens surface, "D" represents the distance on the optical axis between the lens surfaces, "Nd" represents the refractive index for the d-line (wavelength λ = 587.6 nm), and "νd" represents the Abbe number for the d-line. Also, "ASPH" displayed next to the surface number indicates that the corresponding lens surface is an aspherical surface, and "STOP" represents the aperture stop. Furthermore, in the column for the distance on the optical axis between the lens surfaces, notations such as "D(15)", "D(19)", etc. mean that the distance on the optical axis of the corresponding lens surface is a variable distance that changes when focusing at the shooting distance. Note that the unit of length in each table is all "mm", and the unit of the angle of view is all "°". Also, "0.0000" in the column for the radius of curvature means a plane surface. Note that the 29th and 30th surfaces in Table 1 are the surface data of the cover glass CG.

[0077] "Various data" indicates the "F" focal length, "Fno" F-number, "W" semi-angle of view, "Y" image height, and "BF" back focus of the optical system at infinity focus and closest focus. Note that the value of "BF" of the optical system is a value including a cover glass (Nd = 1.5168) with a thickness of 2.5 mm, and the back focus shown in other embodiments is the same.

[0078] "Variable interval (at focus)" indicates each variable interval at focus for a predetermined shooting distance.

[0079] "Focal length of each lens group" indicates the focal length of each lens group constituting the optical system.

[0080] "Aspherical data" indicates the aspherical coefficients of each aspherical surface. However, the aspherical surface is defined by the following formula with x being the displacement amount 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 represents the height from the optical axis, r represents the paraxial curvature radius, k represents the conic coefficient, and An represents the aspherical coefficient of the nth order. Also, "E±XX" represents exponential notation and means "×10 ±XX ". Since the matters regarding these tables are the same in each table shown in other embodiments, the description will be omitted below.

[0081] Also, FIGS. 2, 3, 4, and 5 show the longitudinal aberration diagrams and lateral aberration diagrams of the optical system at infinity focus and closest focus. The longitudinal aberration diagrams shown in each figure are, in order from the left side toward the drawing, spherical aberration (mm), coma aberration (mm), and distortion (%) respectively. In the spherical aberration diagram, the solid line indicates the spherical aberration at the d line (wavelength 587.6 nm), and the dashed line indicates the spherical aberration at the g line (wavelength 435.8 nm). In the coma aberration diagram, the vertical axis is the semi-field angle (ω), the horizontal axis is the defocus, the solid line indicates the sagittal image plane (ds) of the d line, and the dashed line indicates the meridional image plane (dm) of the d line respectively. In the distortion diagram, the vertical axis is the semi-field angle (ω), and the horizontal axis is the distortion. The lateral aberration diagrams shown in each figure are, in order from the left side toward the drawing, meridional coma aberration (mm) and sagittal coma aberration (mm) respectively. From the top to the bottom of the drawing, they are the coma aberrations at the semi-field angle (ω) with a ratio of 1.0 to 0.0. The solid line indicates the coma aberration at the d line, and the dashed line indicates the coma aberration at the g line. Since these matters are the same in each aberration diagram shown in other embodiments, the description will be omitted below.

[0082] [Surface Data] Surface Number R D Nd νd 1 -1112.3474 5.8449 1.83481 42.72 2 -76.9745 1.3000 1.92286 20.88 3 -210.0000 0.2000 4 912.7674 1.5500 1.72947 51.78 5 29.2979 12.6247 6 37.4056 8.0335 1.77012 24.46 7 -184.3239 9.3213 8ASPH 73.0859 1.3200 1.58313 59.42 9ASPH 26.8077 5.9985 10 -44.5673 1.2500 1.84666 23.78 11 26.5193 10.3945 1.74126 51.15 12 -39.7111 2.0000 13STOP 0.0000 2.0000 14 78.5899 7.1050 1.77250 49.62 15 -55.6186 D(15) 16 0.0000 1.2000 1.74167 32.84 17 37.9326 4.3916 18 81.4598 3.7061 1.92286 20.88 19 -538.5562 D(19) 20 -1603.1667 4.9642 1.70802 53.04 21 -49.8250 D(21) 22 32.7713 9.4981 1.49700 81.61 23 -69.7355 0.2000 24 -241.3847 1.0000 1.65620 29.82 25 28.7255 4.6346 26ASPH 107.2719 1.8500 1.85108 40.12 27ASPH 42.7204 3.0998 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0083] [Various data] Shooting distance INF to closest F 33.3896 32.2974 Fno 1.4500 1.4500 W 32.8185 31.2228 Y 21.633 21.633 BF 17.500 17.500

[0084] [Variable interval (when in focus)] Shooting distance INF to closest D(0) ∞ 320.0288 D(15) 2.1937 8.9177 D(19) 9.5193 2.2299 D(21) 0.4000 0.9654 D(30) 1.0000 1.0000

[0085] [Focal length of each lens group] Group Surface number Focal length G1 1 - 15 37.8392 G2 16 - 19 - 186.367 G3 20 - 21 72.5337 G4 22 - 27 - 85.4053

[0086] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 - 1.64135E - 05 - 2.94174E - 08 8.96861E - 11 8.35605E - 14 9 - 8.23823E - 01 1.20196E - 06 - 2.58683E - 08 3.11021E - 11 3.67239E - 13 26 0.00000E+00 - 1.75503E - 05 - 8.41385E - 09 - 3.09446E - 11 6.41687E - 14 27 0.00000E+00 - 5.70161E - 06 7.86503E - 10 4.91575E - 13 4.95011E - 14 Surface number A12 8 - 5.23312E - 16 9 - 1.28157E - 15 26 0.00000E+00 27 0.00000E+00

Example

[0087] (1) Optical configuration of the optical system FIG. 6 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system of Example 2 according to the present invention.

[0088] The optical system includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a close object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0089] Hereinafter, the configuration of each lens group will be described. The first lens group G1 includes, in order from the object side, a positive meniscus lens L1 with a concave surface facing the object side and a negative refractive power cemented lens formed by cementing a biconcave lens L2, a biconvex lens L3, a negative meniscus lens L4 with a convex surface facing the object side, a positive refractive power cemented lens formed by cementing a biconcave lens L5 and a biconvex lens L6, the aperture stop S, and a biconvex lens L7.

[0090] The second lens group G2 includes, in order from the object side, a negative refractive power cemented lens formed by cementing a biconvex lens L8 and a biconcave lens L9, and a biconvex lens L10.

[0091] The third lens group G3 is composed of a biconvex lens L11.

[0092] The fourth lens group G4 includes, in order from the object side, a biconvex lens L12, biconcave lenses L13 and L14.

[0093] (2) Numerical examples Next, a numerical example applying specific numerical values of the optical system will be described. The following shows the "surface data", "various data", "variable interval (at focus)", "focal length of each lens group", and "aspherical data" of the optical system.

[0094] [Surface Data] Surface Number R D Nd νd 1 -3861.4979 8.0746 1.61692 56.07 2 -45.3488 1.6500 1.59867 38.84 3 31.5068 6.7310 4 38.0602 6.9105 1.92119 23.96 5 -324.9412 7.5142 6 ASPH 114.7520 1.3200 1.58313 59.42 7 ASPH 25.8590 7.0110 8 -57.4174 1.2500 1.82140 22.97 9 26.6490 0.0010 1.56732 42.84 10 26.6490 11.7877 1.74320 49.34 11 -48.3089 2.0000 12 STOP 0.0000 2.0000 13 74.6318 8.5601 1.77250 49.62 14 -57.8627 D(14) 15 552.0331 3.0000 1.72916 54.67 16 -179.6380 1.0000 1.94728 29.07 17 40.8417 4.1464 18 123.9079 4.0082 1.94595 17.98 19 -163.8626 D(19) 20 75.5778 7.9360 1.77250 49.62 21 -64.1003 D(21) 22 53.6737 6.6944 1.49700 81.61 23 -103.7803 0.2000 24 -295.5789 1.0000 1.68893 31.16 25 30.1757 5.7954 26ASPH 997.7596 1.8500 1.85108 40.12 27ASPH 81.6478 3.0987 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0095] [Various data] Shooting distance INF to closest F 40.3989 38.4571 Fno 1.4100 1.4726 W 27.8608 26.1523 Y 21.633 21.633 BF 17.4987 17.4987

[0096] [Variable interval (when in focus)] Shooting distance INF to closest D( 0) ∞ 320.0781 D(14) 1.9972 8.4486 D(19) 9.0634 2.0835 D(21) 1.0000 1.5285 D(30) 1.0000 1.0000

[0097] [Focal lengths of each lens group] Group Plane number Focal length G1 1-14 42.3197 G2 15-19 -121.959 G3 20-21 46.0380 G4 22-27 -50.5631

[0098] [Aspherical Data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -1.15559E-05 -1.81351E-08 4.30716E-11 8.09943E-14 7 -6.15033E-01 3.84438E-06 -1.43478E-08 -1.90530E-11 3.35123E-13 26 0.00000E+00 -1.51181E-05 -1.31262E-08 4.54774E-11 -2.16222E-14 27 0.00000E+00 -5.12939E-06 -7.00821E-09 7.14763E-11 -4.60828E-14 Surface number A12 6 -2.64140E-16 7 -7.75048E-16 26 0.00000E+00 27 0.00000E+00

Example

[0099] (1) Optical configuration of the optical system FIG. 11 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system according to Example 3 of the present invention.

[0100] The optical system is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power, in order from the object side. When focusing from an infinite object to a close object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0101] The configurations of the respective lens groups will be described below. The first lens group G1 is composed of a negative refractive power cemented lens formed by cementing a positive meniscus lens L1 with its concave surface facing the object side and a negative meniscus lens L2 with its concave surface facing the object side, a biconvex lens L3, a negative meniscus lens L4 with its convex surface facing the object side, a positive refractive power cemented lens formed by cementing a biconcave lens L5 and a biconvex lens L6, an aperture stop S, and a biconvex lens L7.

[0102] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L8 with its concave surface facing the image side and a biconvex lens L9.

[0103] The third lens group G3 is composed of a biconvex lens L10.

[0104] The fourth lens group G4 is composed of, in order from the object side, a negative refractive power cemented lens formed by cementing a biconvex lens L11 and a biconcave lens L12, and a biconcave lens L13.

[0105] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focusing)", "focal lengths of the respective lens groups", and "aspherical data" of the optical system are shown below.

[0106] [Surface Data] Surface No. R D Nd νd 1 -85.0429 8.0000 1.90366 31.31 2 -29.9056 1.6500 1.93211 23.42 3 -153.0497 0.2000 4 67.2583 6.9594 1.92119 23.96 5 -144.6815 1.2881 6 ASPH 78.8292 1.3200 1.58313 59.42 7 ASPH 26.5688 16.2436 8 -35.0794 1.2500 1.70287 27.15 9 41.0964 10.8441 1.77250 49.62 10 -43.8325 2.0000 11 STOP 0.0000 2.0000 12 79.2385 5.2508 1.77250 49.62 13 -159.3262 D(13) 14 17575.3702 1.2000 1.74317 47.32 15 42.0250 3.5969 16 206.9434 3.0697 1.92286 20.88 17 -225.6701 D(17) 18 69.3808 8.5634 1.77250 49.62 19 -68.0892 D(19) 20 64.9150 8.1710 1.77250 49.62 21 -56.1403 1.0000 1.71823 26.74 22 32.8244 6.4330 23 ASPH -535.2130 1.8500 1.85135 40.10 24 ASPH 99.5002 3.7462 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0107] [Various data] Shooting distance INF to closest F 48.5017 45.4920 Fno 1.4399 1.5474 W 23.7670 21.4597 Y 21.633 21.633 BF 18.1462 18.1462

[0108] [Variable interval (when focusing)] Shooting distance INF closest D(0) ∞ 324.8170 D(13) 1.9888 12.4470 D(17) 13.4766 2.1062 D(19) 0.7500 1.6622 D(27) 1.0000 1.0000

[0109] [Focal length of each lens group] Group Surface number Focal length G1 1 - 13 55.2474 G2 14 - 17 - 118.122 G3 18 - 19 45.7261 G4 20 - 24 - 56.1795

[0110] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 - 3.08885E - 06 - 6.33741E - 09 4.04863E - 14 8.15307E - 15 7 - 3.99165E - 01 4.84256E - 06 1.26947E - 09 5.26078E - 12 - 4.27315E - 15 23 0.00000E+00 - 2.43881E - 05 2.84540E - 08 - 2.26609E - 11 6.28328E - 14 24 0.00000E+00 - 1.62108E - 05 3.28709E - 08 - 6.10781E - 12 2.73903E - 14 Surface number A12 6 - 7.30680E - 18 7 3.48953E - 17 23 0.00000E+00 24 0.00000E+00

Example

[0111] (1) Optical configuration of the optical system FIG. 16 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system according to Embodiment 4 of the present invention.

[0112] The optical system includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side while the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction. The aperture stop S is disposed inside the first lens group G1.

[0113] Hereinafter, the configuration of each lens group will be described. The first lens group G1 includes a negative meniscus lens L1 with a concave surface facing the object side and a biconcave lens L2 joined to the object side, a positive refractive power joined lens, a biconvex lens L3, a negative meniscus lens L4 with a convex surface facing the object side, a positive refractive power joined lens formed by joining a biconcave lens L5 and a biconvex lens L6, an aperture stop S, and a biconvex lens L7.

[0114] The second lens group G2 includes, in order from the object side, a plano-concave lens L8 with a flat object side and a biconvex lens L9.

[0115] The third lens group G3 is composed of a biconvex lens L10.

[0116] The fourth lens group G4 includes, in order from the object side, a negative refractive power joined lens formed by joining a biconvex lens L11 and a biconcave lens L12, and a biconcave lens L13.

[0117] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. Hereinafter, the "surface data", "various data", "variable interval (at focus)", "focal length of each lens group", and "aspherical data" of the optical system are shown.

[0118] [Surface Data] Surface No. R D Nd νd 1 -228.0707 9.2744 1.61207 56.13 2 -33.4559 1.6500 1.62434 32.26 3 52.8155 2.1424 4 49.1826 6.8951 1.92119 23.96 5 -138.7195 5.0245 6ASPH 76.0775 1.3200 1.82115 24.06 7ASPH 32.4415 10.4748 8 -26.6038 1.2500 1.64863 30.34 9 79.7838 8.9693 1.83559 40.92 10 -33.6165 2.0000 11STOP 0.0000 2.0000 12 52.7128 6.4330 1.49700 81.61 13 -115.2491 D(13) 14 0.0000 1.2000 1.86485 38.15 15 44.1417 2.5752 16 128.7199 3.3271 1.92286 20.88 17 -235.1172 D(17) 18 77.2245 8.0235 1.77250 49.62 19 -61.2723 D(19) 20 68.9607 8.6126 1.77250 49.62 21 -43.5976 1.1129 1.73256 25.83 22 35.5320 5.8861 23ASPH -846.2459 1.8500 1.85108 40.12 24ASPH 81.3907 3.1015 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0119] [Various data] Shooting distance INF to closest F 45.5424 42.9123 Fno 1.4500 1.5435 W 25.1291 22.9702 Y 21.633 21.633 BF 17.5015 17.5015

[0120] [Variable interval (when in focus)] Shooting distance INF to closest D( 0) ∞ 326.9244 D(13) 1.9931 12.2469 D(17) 13.0915 2.0952 D(19) 0.5500 1.2926 D(27) 1.0000 1.0000

[0121] [Focal length of each lens group] Group Surface number Focal length G1 1-13 53.0404 G2 14-17 -127.289 G3 18-19 45.3719 G4 20-24 -53.7838

[0122] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -4.62733E-06 -1.30739E-08 -5.66238E-12 -1.65355E-14 7 -5.18276E-01 4.17552E-06 -3.40382E-09 -1.61178E-11 1.30079E-15 23 0.00000E+00 -3.32507E-05 5.31909E-08 -2.74049E-11 -5.47803E-15 24 0.00000E+00 -2.46297E-05 6.19703E-08 -2.71967E-11 -2.86687E-15 Surface number A12 6 4.04711E-17 7 -2.40030E-17 23 0.00000E+00 24 0.00000E+00

Example

[0123] (1) Optical configuration of the optical system Figure 21 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system of Example 5 according to the present invention.

[0124] The optical system is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a close object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0125] Hereinafter, the configuration of each lens group will be described. The first lens group G1 is composed of a positive refractive power cemented lens formed by cementing a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object side, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a negative refractive power cemented lens formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0126] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L9 with a flat object side and a biconvex lens L10.

[0127] The third lens group G3 is composed of a biconvex lens L11.

[0128] The fourth lens group G4 is composed of a biconvex lens L12, a biconcave lens L13, and a biconcave lens L14 in order from the object side.

[0129] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focusing)", "focal length of each lens group", and "aspherical data" of the optical system are shown below.

[0130] [Surface Data] Surface Number R D Nd νd 1 771.1109 7.4367 1.83481 42.72 2 -55.3704 1.3000 1.92119 23.96 3 -212.2186 0.2000 4 -7833.9757 1.5500 1.48749 70.44 5 21.9033 15.3480 6 30.4735 6.6151 1.82898 23.95 7 -141.9773 1.2819 8 ASPH 71.4042 1.3200 1.83441 37.28 9 ASPH 23.2956 6.8381 10 -36.8428 1.2500 1.84666 23.78 11 26.3609 9.7232 1.75746 50.33 12 -37.4388 2.0000 13 STOP 0.0000 2.0000 14 96.1773 6.5028 1.77250 49.62 15 -48.8457 D(15) 16 0.0000 1.2000 1.74218 36.71 17 39.5754 2.5352 18 91.1801 3.3773 1.92286 20.88 19 -413.4901 D(19) 20 318.6990 4.5321 1.75198 50.60 21 -55.4532 D(21) 22 31.2848 8.6005 1.49700 81.61 23 -64.8295 0.2000 24 -172.0204 1.0000 1.73842 25.60 25 29.9718 4.4796 26ASPH -271.4701 1.8500 1.85108 40.12 27ASPH 115.4858 3.1000 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0131] [Various data] Shooting distance INF to closest F 31.4732 30.5281 Fno 1.4601 1.4852 W 34.5150 32.9635 Y 21.633 21.633 BF 17.5000 17.5000

[0132] [Variable interval (when in focus)] Shooting distance INF to closest D( 0) ∞ 330.0319 D(15) 1.9878 8.2936 D(19) 8.8217 2.0595 D(21) 0.5500 1.0064 D(30) 1.0000 1.0000

[0133] [Focal length of each lens group] Group Plane number Focal length G1 1-15 37.3918 G2 16 - 19 - 172.976 G3 20 - 21 63.1415 G4 22 - 27 - 79.3352

[0134] [Aspherical Data] Surface number k A4 A6 A8 A10 8 0.00000E + 00 - 1.36185E - 05 - 2.39755E - 08 8.40427E - 11 - 2.51782E - 15 9 - 5.83033E - 01 3.26236E - 06 - 2.06282E - 08 3.20478E - 11 1.59786E - 13 26 0.00000E + 00 1.12564E - 05 - 6.68072E - 08 - 1.23570E - 11 1.55764E - 13 27 0.00000E + 00 2.47794E - 05 - 5.75350E - 08 1.93230E - 11 1.39863E - 13 Surface number A12 8 - 2.32666E - 16 9 - 6.55543E - 16 26 0.00000E + 00 27 0.00000E + 00

Example

[0135] (1) Optical configuration of the optical system FIG. 26 is a lens cross - sectional view showing the lens configuration at infinity focus of the optical system of Example 6 according to the present invention.

[0136] The optical system is composed of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a near - distance object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is arranged inside the first lens group G1.

[0137] The configurations of the respective lens groups will be described below. The first lens group G1 is composed of, in order from the object side, a positive refractive power cemented lens formed by cementing a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object side, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a negative refractive power cemented lens formed by cementing a biconcave lens L6 and a biconvex lens L7, a diaphragm S, and a biconvex lens L8.

[0138] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L9 with a flat object side and a biconvex lens L10.

[0139] The third lens group G3 is composed of a biconvex lens L11.

[0140] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with its convex surface facing the object side.

[0141] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focus)", "focal lengths of the respective lens groups", and "aspherical data" of the optical system are shown below.

[0142] [Surface Data] Surface Number R D Nd νd 1 173.7978 8.9679 1.83481 42.72 2 -63.9488 1.3000 1.92119 23.96 3 -240.3604 1.5000 4 -220.5721 1.5500 1.48749 70.44 5 20.4720 16.0381 6 30.4538 5.9926 1.83284 23.72 7 -116.2805 0.2000 8ASPH 82.5260 1.3200 1.83441 37.28 9ASPH 23.7204 6.4492 10 -35.5547 1.2500 1.84666 23.78 11 26.7926 0.0010 1.56732 42.84 12 26.7926 9.2332 1.77250 49.62 13 -37.0378 2.0000 14STOP 0.0000 2.0000 15 91.7715 6.2826 1.77250 49.62 16 -51.1134 D(16) 17 0.0000 1.2000 1.74265 41.05 18 40.4868 2.4271 19 108.4402 3.2198 1.92119 23.96 20 -295.8316 D(20) 21 492.4813 4.2604 1.77250 49.62 22 -55.8168 D(22) 23 31.0567 8.5715 1.49700 81.61 24 -66.4032 0.2000 25 -193.7372 1.0000 1.71466 26.60 26 28.4787 4.7194 27ASPH 1926.3038 1.8500 1.85108 40.12 28ASPH 106.5676 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0143] [Various data] Shooting distance INF to closest F 31.0124 30.1903 Fno 1.4400 1.4856 W 34.9133 33.3701 Y 21.633 21.633 BF 17.500 17.500

[0144] [Variable interval (when focusing)] Shooting distance INF closest D(0) ∞ 330.0363 D(16) 1.9737 7.6918 D(20) 8.4445 2.0906 D(22) 0.5500 1.1858 D(31) 1.0000 1.0000

[0145] [Focal length of each lens group] Group surface number Focal length G1 1-16 37.6960 G2 17-20 -162.130 G3 21-22 65.1197 G4 23-28 -102.190

[0146] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.01087E-05 -3.35865E-08 9.33889E-11 2.32372E-13 9 -4.61533E-01 5.22094E-06 -2.94241E-08 -9.54051E-12 8.66882E-13 27 0.00000E+00 -7.90613E-06 -1.41361E-09 -8.38477E-11 1.35651E-13 28 0.00000E+00 4.50209E-06 5.24274E-09 -4.18014E-11 1.14135E-13 Surface number A12 8 -9.34433E-16 9 -2.41711E-15 27 0.00000E+00 28 0.00000E+00

Embodiment

[0147] (1) Optical configuration of the optical system FIG. 31 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system of Embodiment 7 according to the present invention.

[0148] The optical system includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a close object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0149] Hereinafter, the configuration of each lens group will be described. The first lens group G1 includes, in order from the object side, a positive refractive power cemented lens formed by cementing a negative meniscus lens L1 having a convex surface facing the object side and a biconvex lens L2, a negative meniscus lens L3 having a convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 having a convex surface facing the object side, a negative refractive power cemented lens formed by cementing a biconcave lens L6 and a biconvex lens L7, the aperture stop S, and a biconvex lens L8.

[0150] The second lens group G2 includes, in order from the object side, a plano-concave lens L9 having a flat surface on the object side and a biconvex lens L10.

[0151] The third lens group G3 is composed of a biconvex lens L11.

[0152] The fourth lens group G4 includes, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 having a convex surface facing the object side, and a negative meniscus lens L14 having a convex surface facing the object side.

[0153] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focusing)", "focal length of each lens group", and "aspherical data" of the optical system are shown below.

[0154] [Surface Data] Surface Number R D Nd νd 1 250.0000 1.5000 1.92286 20.88 2 91.3371 5.4833 1.66386 56.12 3 -284.4015 0.5000 4 864.4431 1.6500 1.49700 81.61 5 21.6476 20.8072 6 28.5497 6.1373 1.93107 23.11 7 -660.6291 0.2000 8 ASPH 90.6064 1.3200 1.83441 37.28 9 ASPH 23.9800 6.4664 10 -42.6079 1.2500 1.84666 23.78 11 24.0973 9.8154 1.77250 49.62 12 -40.4448 2.0000 13 STOP 0.0000 2.0000 14 59.6619 5.2243 1.77250 49.62 15 -118.9867 D(15) 16 0.0000 1.2000 1.74077 27.76 17 42.1415 2.9042 18 212.5356 3.8056 1.92286 20.88 19 -83.7584 D(19) 20 52.7404 4.3972 1.77250 49.62 21 -1579.0980 D(21) 22 39.8190 7.1079 1.49700 81.61 23 -70.5632 0.2000 24 152.5886 1.0000 1.78322 24.04 25 23.2826 5.9758 26ASPH 378.8394 1.8500 1.85108 40.12 27ASPH 135.9702 3.1003 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0155] [Various data] Shooting distance INF to closest F 29.0222 28.0795 Fno 1.4432 1.4628 W 36.7181 35.8784 Y 21.633 21.633 BF 17.5003 17.5003

[0156] [Variable interval (when in focus)] Shooting distance INF to closest D( 0) ∞ 330.0427 D(15) 1.9754 4.8815 D(19) 7.1799 2.3193 D(21) 0.5500 2.5044 D(30) 1.0000 1.0000

[0157] [Focal length of each lens group] Group Plane number Focal length G1 1-15 41.5286 G2 16-19 -869.596 G3 20-21 66.1435 G4 22-27 -90.4289

[0158] [Aspherical Data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -4.28786E-06 -2.52717E-08 9.50604E-11 -1.29592E-14 9 -3.35657E-01 6.46108E-06 -1.37717E-08 -5.13782E-11 9.09925E-13 26 0.00000E+00 -4.23342E-05 7.45101E-08 -2.48716E-10 7.05368E-13 27 0.00000E+00 -3.10941E-05 8.91765E-08 -1.49046E-10 6.40234E-13 Surface number A12 8 -2.99395E-16 9 -2.08971E-15 26 0.00000E+00 27 0.00000E+00

Example

[0159] (1) Optical configuration of the optical system FIG. 36 is a lens cross-sectional view showing the lens configuration at infinity focus of the optical system of Example 8 according to the present invention.

[0160] The optical system includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing from an infinite object to a near object, the first lens group G1 and the fourth lens group G4 are fixed in the optical axis direction, the second lens group G2 moves toward the image side, and the third lens group G3 moves toward the object side. The aperture stop S is disposed inside the first lens group G1.

[0161] The configurations of the respective lens groups will be described below. The first lens group G1 is composed of, in order from the object side, a positive refractive power cemented lens formed by cementing a biconcave lens L1 and a biconvex lens L2, a negative meniscus lens L3 with its convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a negative refractive power cemented lens formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0162] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L9 with its convex surface facing the object side and a biconvex lens L10.

[0163] The third lens group G3 is composed of a biconvex lens L11.

[0164] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, and a negative meniscus lens L14 with its convex surface facing the object side.

[0165] (2) Numerical Examples Next, numerical examples applying specific numerical values of the optical system will be described. The "surface data", "various data", "variable interval (at focus)", "focal lengths of the respective lens groups", and "aspherical data" of the optical system are shown below.

[0166] [Surface Data] Surface Number R D Nd νd 1 -383.2756 1.5000 1.92286 20.88 2 159.6775 4.6368 1.89930 35.51 3 -206.6054 0.5000 4 192.7697 1.6500 1.49700 81.61 5 21.7668 17.9391 6 0.0000 2.8000 7 29.9836 6.1586 1.92439 23.96 8 -332.8322 0.2000 9ASPH 89.8504 1.3200 1.85135 40.10 10ASPH 24.7941 6.4858 11 -39.1059 1.2500 1.84666 23.78 12 25.8283 9.5478 1.77250 49.62 13 -39.9770 2.0000 14STOP 0.0000 2.0000 15 63.5839 5.5981 1.77250 49.62 16 -96.0612 D(16) 17 390.3404 1.2000 1.74077 27.76 18 40.4417 3.3313 19 237.4962 3.7739 1.92286 20.88 20 -89.6564 D(20) 21 56.9933 4.2450 1.77250 49.62 22 -1377.1300 D(22) 23 41.5995 7.1973 1.49700 81.61 24 -71.5673 0.2000 25 125.8501 1.5449 1.78667 23.94 26 24.2525 5.6791 27ASPH 424.4833 1.8500 1.85108 40.12 28ASPH 115.8130 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0167] [Various data] Shooting distance INF to closest F 29.0933 28.1356 Fno 1.4500 1.4733 W 36.9290 36.0637 Y 21.633 21.633 BF 17.5000 17.5000

[0168] [Variable interval (when focusing)] Shooting distance INF to closest D(0) ∞ 330.0429 D(16) 1.9719 4.9204 D(20) 7.3703 2.3161 D(22) 0.5500 2.6557 D(31) 1.0000 1.0000

[0169] [Focal length of each lens group] Group Surface number Focal length G1 1 - 16 40.9541 G2 17 - 20 - 825.245 G3 21 - 22 70.9373 G4 23 - 28 - 95.2085

[0170] [Aspherical data] Surface number k A4 A6 A8 A10 9 0.00000E+00 - 4.12277E - 06 - 2.81947E - 08 8.70743E - 11 3.56984E - 14 10 - 3.50599E - 01 6.46480E - 06 - 1.84803E - 08 - 4.39047E - 11 7.82031E - 13 27 0.00000E+00 - 3.82861E - 05 8.62244E - 08 - 1.91624E - 10 3.68250E - 13 28 0.00000E+00 - 2.72470E - 05 1.02161E - 07 - 1.33095E - 10 3.82708E - 13 Surface number A12 9 - 3.35643E - 16 10 - 1.67421E - 15 27 0.00000E+00 28 0.00000E+00

[0171] [Conditional corresponding value] Example 1 Example 2 Example 3 Example 4 Conditional formula (1) f1 / f2 -0.20 -0.35 -0.47 -0.42 Conditional formula (2) ν2 20.88 17.98 20.88 20.88 Conditional formula (3) f / f2 -0.18 -0.33 -0.41 -0.36 Conditional formula (4) ν1 20.88 22.97 23.42 24.06 Conditional formula (5) f1R 43.16 43.41 69.17 73.71 Conditional formula (6) (R1f + R1r) / (R1f -R1r) -8.23 0.48 -0.14 0.10 Conditional formula (7) BF / Y 0.81 0.81 0.84 0.81 Conditional formula (8) FD / f 1.24 1.13 0.99 1.0 2 Article Conditional formula (10) βb 1.08 1.35 1.30 1.30 Example 5 Example 6 Example 7 Example 8 Conditional formula (1) f1 / f2 -0.22 -0.23 -0.05 -0.05 Conditional formula (2) ν2 20.88 23.96 20.88 20.88 Conditional formula (3) f / f2 -0.18 -0.19 -0.03 -0.04 Conditional formula (4) ν1 23.78 23.78 20.88 20.88 Conditional formula (5) f1R 42.77 43.33 52.10 50.30 Conditional formula (6) (R1f + R1r) / (R1f -R1r) -6.11 -5.10 -7.27 -6.30 Conditional formula (7) BF / Y 0.81 0.81 0.81 0.81 Conditional formula (8) FD / f 1.18 1.18 1.25 1.27 Article Unit (10) βb 1.12 1.07 1.16 1.13

Industrial Applicability

[0172] According to the present invention, it is possible to provide an optical system and an imaging device that have a bright large-diameter lens with a small F value and suppress image plane fluctuations and chromatic aberration over the entire focusing range.

Explanation of Reference Numerals

[0173] G1 ··· First lens group G2 ··· Second lens group G3 ··· Third lens group G4 ··· Fourth lens group S ··· Aperture stop CG ··· Cover glass IP ··· Image formation plane

Claims

1. Composed of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, the second lens group has at least one positive lens and at least one negative lens, when focusing from infinity to the closest distance, the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group move along the optical axis direction respectively, and satisfy the following formulas (1) and (2), the first lens group has at least one negative lens that satisfies the following formula (4), an optical system. -0.47 ≤ f1 / f2 ≤ -0.01 ······ (1) ν2 ≤ 25.0 ······ (2) ν1 ≤ 25.0 ······ (4) However, f1: The focal length of the first lens group f2: The focal length of the second lens group ν2: The Abbe number at the d-line of any one of the positive lenses included in the second lens group ν1: The Abbe number at the d-line of the negative lenses included in the first lens group

2. The optical system according to Claim 1, which satisfies the following formula. -0.50 ≤ f / f2 ≤ -0.01 ······ (3) However, f: The focal length when the optical system is focused at infinity

3. The first lens group has a diaphragm, and the optical system according to Claim 1 or 2, which satisfies the following formula. 39.0 ≤ f1R ≤ 85.0 ······ (5) However, f1R: The combined focal length (mm) of the lenses on the image side of the diaphragm in the first lens group

4. In the first lens group, among the air intervals arranged between the most object-side lens surface of the first lens group and the most image-side lens surface of the fourth lens group, the optical system according to any one of Claims 1 to 3, in which the largest air interval is arranged.

5. The first lens group, the optical system according to any one of Claims 1 to 4, which satisfies the following formula. -10.0 ≤ (R1f + R1r) / (R1f - R1r) ≤ 1.2 ······ (6) However, R1f: The radius of curvature of the image-side surface of the lens arranged on the object side across the largest air interval within the first lens group R1r: The radius of curvature of the object-side surface of the lens arranged on the image side across the largest air interval within the first lens group

6. The optical system according to any one of Claims 1 to 5, which satisfies the following formula. 0.5 ≤ BF / Y ≤ 1.3 ······ (7) However, BF: The distance on the optical axis from the vertex of the most image-side surface of the fourth lens group to the image plane Y: The maximum image height of the optical system

7. The optical system according to any one of claims 1 to 6, wherein the first lens group has at least one cemented lens.

8. The optical system according to any one of claims 1 to 7, satisfying the following formula. 0.80 ≦ FD / f ≦ 1.50 ・・・・・(8) However, FD: The distance on the optical axis from the most object-side lens surface of the second lens group to the most image-side lens surface of the fourth lens group when focused at infinity f: The focal length of the optical system when focused at infinity

9. The optical system according to any one of claims 1 to 8, satisfying the following formula. 0.95 ≦ βb ≦ 1.50 ・・・・・(10) However, βb: The lateral magnification of the fourth lens group when focused at infinity

10. An imaging device comprising the optical system according to any one of claims 1 to 9, and an image sensor that converts the optical image formed by the optical system into an electrical signal on the image side of the optical system.

Images