Optical system and imaging device

Abstract

To provide an optical system that has high optical performance and furthermore is small-sized, and an imaging apparatus.SOLUTION: An optical system is comprised of, in order from an object side to an image side, a first lens group (G1) having positive refractive power, a second lens group (G2) having positive refractive power, and a third lens group (G3) having negative refractive power, wherein at a time of zooming, the first lens group (G1) and the third lens group (G3) are fixed in an optical axis direction with respect to an image surface, and the second lens group (G2) is moved along the optical axis. The first lens group (G1) is comprised of, in order from the object side to the image side, a 1a group (G1a) having negative refractive power, an aperture stop, and a 1b group (G1b) having positive refractive power, and satisfies a prescribed expression.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, imaging devices using solid-state imaging elements such as digital still cameras have become widespread. Along with this, the optical system has been improved in performance and miniaturized, and small imaging device systems have been rapidly spreading. In conventional lenses, particularly in surveillance lenses, video camera lenses, digital still camera lenses, single-lens reflex camera lenses, mirrorless single-lens camera lenses, etc., where an optical system with a short overall length and small size is desired, it is an issue to miniaturize the optical system while maintaining high optical performance.

[0003] Patent Document 1 discloses an invention of an optical system including, in order from the object side, a first lens group with a positive refractive power, a second lens group with a positive refractive power, and a third lens group with a negative refractive power, and moving the second lens group in the optical axis direction during focusing. However, in the lenses described in Examples 2 to 5, since the refractive power of the lens group arranged on the object side of the aperture stop is weaker than the refractive power of the first lens group, the lens diameter becomes large, which hinders miniaturization of the lens barrel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a small optical system while having high optical performance.

Means for Solving the Problems

[0006] To solve the above problems, the optical system according to the present invention is composed of, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power. When in focus, the first lens group and the third lens group are fixed in the direction of the optical axis with respect to the image plane, the second lens group moves along the optical axis, and the first lens group is composed of, in order from the object side to the image side, a firsta group having negative refractive power, an aperture diaphragm, and a firstb group having positive refractive power, satisfying the following equation. -2.50 ≦ f1a / f ≦ -0.05 (1) -3.45 ≦ f3 / f ≦ -1.35 (2) however, f1a: Focal length of the aforementioned group 1a f3: Focal length of the third lens group f: Focal length when the optical system is focused at infinity

[0007] Furthermore, in order to solve the above-mentioned problems, the imaging device according to the present invention is characterized by comprising the optical system and an image sensor that converts the optical image formed by the optical system into an electrical signal. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a compact optical system while having high optical performance. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the optical system of Example 1. [Figure 2] This is a longitudinal aberration diagram of the optical system of Example 1 in the state of infinity focus. [Figure 3] This is a cross-sectional view of the optical system of Example 2. [Figure 4] This is a longitudinal aberration diagram of the optical system of Example 2 in the state of infinity focus. [Figure 5] This is a cross-sectional view of the optical system of Example 3. [Figure 6] This is a longitudinal aberration diagram of the optical system of Example 3 in the state of infinity focus. [Figure 7] It is a cross-sectional view of the optical system of Example 4. [Figure 8] It is a longitudinal aberration diagram of the optical system of Example 4 in an infinitely focused state. [Figure 9] It is a cross-sectional view of the optical system of Example 5. [Figure 10] It is an aberration diagram of the optical system of Example 5 in an infinitely focused state. [Figure 11] It is a diagram schematically showing an example of the configuration of an imaging device according to an embodiment of the present invention.

Embodiments for Carrying out the Invention

[0010] 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.

[0011] 1. Optical System 1-1. Optical Configuration The optical system according to the present invention is composed of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. With this configuration, miniaturization becomes easy.

[0012] (1) First Lens Group The first lens group has a positive refractive power, and as long as it is a lens group that is fixed with respect to the image plane during focusing, its specific configuration is not particularly limited. The first lens group is composed of, in order from the object side to the image side, a first a group having a negative refractive power, an aperture stop, and a first b group having a positive refractive power. By having this configuration, particularly the configuration in which the first a group (that is, all the lenses arranged in front of the aperture stop among the lenses included in the first lens group) has a negative refractive power, various aberrations are suppressed and miniaturization becomes easy.

[0013] Here, the "lens group" is composed of one or a plurality of adjacent lenses, and the distance between adjacent lens groups along the optical axis changes during focusing. When one lens group is composed of a plurality of lenses, the distance on the optical axis between each lens included in that one lens group shall not change during focusing.

[0014] The first sub-group of the first lens group is not particularly limited as long as it has a negative refractive power, but the lens component arranged on the most object side of the first sub-group (hereinafter also referred to as the "most object-side lens component") preferably has a negative refractive power. Here, the "lens component" refers to a single lens, a cemented lens in which a plurality of single lenses are integrated without an air gap, or a composite lens in which a single lens and resin are integrated without an air gap, etc. When the most object-side lens component is a cemented lens or a composite lens, it only needs to have a negative refractive power as a whole for the cemented lens or composite lens, and the configuration is not particularly limited.

[0015] (2) The second lens group The second lens group has a positive refractive power, and its specific configuration is not particularly limited as long as it is a lens group that moves along the optical axis during focusing. The second lens group preferably consists of one lens component for moving rapidly on the optical axis during focusing. Also, the second lens group preferably has a biconvex lens on the most image side. With this configuration, while correcting aberrations, miniaturization becomes easy.

[0016] (3) The third lens group The third lens group negative has the refractive power of, and its specific configuration is not particularly limited as long as it is a lens group fixed with respect to the image plane during focusing. The third lens group preferably arranges a biconcave lens on the most image side. With this configuration, it becomes easy to suppress the overall length while correcting distortion aberration. Also, the third lens group preferably consists of only one lens component for miniaturization.

[0017] (4) Aperture stop In this optical system, the specific configuration of the aperture diaphragm is not particularly limited, as long as it is located within the first lens group. By arranging the aperture diaphragm within the first lens group, aberrations can be efficiently canceled out before and after the aperture diaphragm, which is preferable for obtaining an optical system with high optical performance.

[0018] 1-2.Operation (1) Focus The specific operation of the optical system is not particularly limited, as long as the second lens group moves along the optical axis when focusing from infinity to a close distance. Furthermore, it is preferable that the second lens group moves along the optical axis toward the object when focusing from infinity to a close distance.

[0019] 1-3. Formula The optical system should employ the configuration described above and, moreover, satisfy at least one of the following equations.

[0020] 1-3-1.Formula (1) -2.50 ≦ f1a / f ≦ -0.05 (1) however, f1a: Focal length of group 1a f: Focal length when the optical system is focused at infinity

[0021] Equation (1) is a formula for defining the ratio of the focal length of the first lens group to the focal length of the first a group, which is positioned on the object side of the aperture diaphragm. By satisfying equation (1), various aberrations can be corrected well while miniaturization becomes easier.

[0022] If the refractive power falls below the lower limit of equation (1), the refractive power of the 1a group becomes weak, resulting in insufficient reduction in the diameter of the lens group positioned on the object side of the aperture diaphragm. This also hinders miniaturization of the lens barrel. On the other hand, if the refractive power exceeds the upper limit of equation (1), the refractive power of the 1a group becomes strong, making it difficult to correct various aberrations such as coma and distortion.

[0023] To obtain the above effect, the lower limit of equation (1) is preferably -2.40, and more preferably -2.30. Furthermore, the upper limit of equation (1) is preferably -0.10, and more preferably -0.20. When adopting these preferred lower or upper limits, the equality sign (≦) in equation (1) may be replaced with an inequality sign (<). The same principle applies to the other equations.

[0024] 1-3-2.Formula (2) -3.45 ≦ f3 / f ≦ -1.35 (2) however, f3: Focal length of the third lens group f: Focal length when the optical system is focused at infinity

[0025] Equation (2) is used to define the ratio of the focal length of the third lens group to the focal length of the optical system when it is focused at infinity. By satisfying equation (2), it becomes easier to miniaturize the third lens group while effectively correcting various aberrations.

[0026] If the refractive power falls below the lower limit of equation (2), the refractive power of the third lens group weakens, resulting in insufficient reduction of the rear element diameter of the third lens group. On the other hand, if the refractive power exceeds the upper limit of equation (2), the refractive power of the third lens group becomes too strong, making it difficult to correct astigmatism and chromatic aberration.

[0027] To obtain the above effect, the lower limit of equation (2) is preferably -3.40, and more preferably -3.30. Furthermore, the upper limit of equation (2) is preferably -1.40, and more preferably -1.50.

[0028] 1-3-3.Formula (3) 0.05 ≦ f1 / f ≦ 4.30 (3) however, f: Focal length when the optical system is focused at infinity

[0029] Equation (3) is used to define the ratio of the focal length of the first lens group to the focal length of the optical system when it is focused at infinity. By satisfying equation (3), it becomes easier to miniaturize the first lens group while effectively correcting various aberrations.

[0030] If the refractive power falls below the lower limit of equation (3), the refractive power of the first lens group becomes too strong, making it difficult to correct various aberrations such as spherical aberration and coma aberration. On the other hand, if the refractive power exceeds the upper limit of equation (3), the refractive power of the first lens group becomes too weak, resulting in insufficient reduction in the diameter of the second lens group. This also leads to an increase in the size of the drive unit, making it difficult to miniaturize the lens barrel.

[0031] To obtain the above effect, the lower limit of equation (3) is preferably 0.10, more preferably 0.20, and more preferably 1.00. Furthermore, the upper limit of equation (3) is preferably 4.00, and more preferably 3.70.

[0032] 1-3-4.Formula (4) 1.10 ≤ (1-β2 2 )×β3 2 ≤ 5.00·····(4) however, β2: Lateral magnification of the second lens group when focused at infinity. β3: Horizontal magnification of the third lens group when focused at infinity.

[0033] Equation (4) is used to define the absolute value of the focusing sensitivity of the second lens group, which moves along the optical axis when focusing occurs, that is, the amount of image plane movement when the second lens group moves by a unit amount. By satisfying equation (4), the amount of movement during focusing can be suppressed, making it easier to miniaturize the lens barrel.

[0034] Conversely, if the value of equation (4) falls below the lower limit, the amount of movement of the second lens group, which moves along the optical axis during focusing, becomes large, making it difficult to reduce the overall optical length. On the other hand, if it exceeds the upper limit of equation (4), the amount of movement of the second lens group to correct the misalignment of the focus position becomes too small, requiring high-precision control, which is undesirable.

[0035] To obtain the above effect, the lower limit of formula (4) is preferably 1.20, and more preferably 1.30. Furthermore, the upper limit of formula (4) is preferably 4.50, and more preferably 4.00.

[0036] 1-3-5.Formula (5) 1.60 ≦ Nd11 ≦ 2.15 (5) however, Nd11: Refractive index at the d line of the lens component located closest to the object in the first lens group.

[0037] Equation (5) defines the refractive index at the d-line of the lens component positioned closest to the object. By satisfying equation (5), various aberrations can be corrected well while miniaturization becomes easier.

[0038] If the refractive index of the first lens component falls below the lower limit of equation (5), the refractive index of the first lens component is small, which increases the diameter of the front element and makes it difficult to reduce the diameter of the lens barrel. On the other hand, if the refractive index of the first lens component exceeds the upper limit of equation (5), it becomes difficult to correct field curvature aberration, making it difficult to achieve high optical performance. Note that when the lens component is a cemented lens, it may be a single lens or a cemented lens of two or more lenses. Also, when the first lens component is a cemented lens, it is preferable that the lens closest to the object satisfies equation (5).

[0039] To obtain the above effect, the lower limit of equation (5) is preferably 1.65, and more preferably 1.70. Furthermore, the upper limit of equation (5) is preferably 2.10, and more preferably 2.05.

[0040] 1-3-6.Formula (6) 0.50 ≦ f11 / f1a ≦ 1.70 (6) however, f11: Focal length of the lens component located closest to the object in the first lens group.

[0041] Equation (6) is used to define the ratio of the focal length of the first lens component, which is positioned closest to the object in the first lens group, to the focal length of the first a group. By satisfying equation (6), various aberrations can be corrected well while miniaturization becomes easier.

[0042] If the value falls below the lower limit of equation (6), the refractive power of the first lens component becomes strong, making it difficult to correct various aberrations such as astigmatism and chromatic aberration. On the other hand, if the value exceeds the upper limit of equation (6), the refractive power of the first lens component becomes weak, resulting in insufficient reduction of the front element diameter. Furthermore, it becomes difficult to miniaturize the lens barrel.

[0043] To obtain the above effect, the lower limit of equation (6) is preferably 0.55, more preferably 0.60, and even more preferably 0.80. Furthermore, the upper limit of equation (6) is preferably 1.65, and more preferably 1.60.

[0044] 1-3-7.Formula (7) -1.25 ≦ f11 / f1 ≦ -0.35 (7)

[0045] Equation (7) is used to define the ratio of the first lens component located closest to the object in the first lens group to the focal length of the first lens group. By satisfying equation (7), various aberrations can be corrected well while miniaturization becomes easier.

[0046] If the value falls below the lower limit of equation (7), the refractive power of the first lens component weakens, resulting in insufficient reduction of the front lens diameter. Furthermore, miniaturization of the lens barrel becomes difficult. On the other hand, if the value exceeds the upper limit of equation (7), the refractive power of the first lens component strengthens, making it difficult to correct various aberrations such as astigmatism and chromatic aberration.

[0047] To obtain the above effect, the lower limit of equation (7) is preferably -1.20, and more preferably -1.15. Furthermore, the upper limit of equation (7) is preferably -0.40, and more preferably -0.45.

[0048] 1-3-8. Formula (8) -1.10 ≦ f1a / f1 ≦ -0.05 (8)

[0049] Equation (8) is used to define the ratio of the focal length of the first lens group to the focal length of the first a group, which is positioned on the object side of the aperture diaphragm. By satisfying equation (8), various aberrations can be corrected well while miniaturization becomes easier.

[0050] If the refractive power falls below the lower limit of equation (8), the refractive power of the 1a group becomes weak, resulting in insufficient reduction in the diameter of the lens group positioned on the object side of the aperture diaphragm. This also hinders miniaturization of the lens barrel. On the other hand, if the refractive power exceeds the upper limit of equation (8), the refractive power of the 1a group becomes strong, making it difficult to correct various aberrations such as coma and distortion.

[0051] To obtain the above effect, the lower limit of equation (8) is preferably -1.00, and more preferably -0.90. Furthermore, the upper limit of equation (8) is preferably -0.10, and more preferably -0.20.

[0052] 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 comprising the optical system according to the present invention and an image sensor that converts the optical image formed by the optical system into an electrical signal. Preferably, the image sensor is provided on the image side of the optical system.

[0053] There are no particular limitations on the image sensor, and solid-state image sensors 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 such solid-state image sensors, such as digital cameras and video cameras. Furthermore, the imaging device can be applied to various imaging devices such as single-lens reflex cameras, mirrorless cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone 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 optical system according to the present invention is suitable for the optical system of imaging devices equipped with large image sensors such as full-frame sensors. Because the optical system is generally small, lightweight, and has high optical performance, high-quality images can be obtained even when used as an optical system for such imaging devices.

[0054] Figure 11 is a schematic diagram showing an example of the configuration of an imaging device according to this embodiment. As shown in Figure 11, the imaging device 1 has a camera 2 and a lens 3 that can be attached to or removed from the camera 2. The imaging device 1 is one embodiment of an imaging device.

[0055] Camera 2 has a CCD sensor 21 as an image sensor and a cover glass 22. The CCD sensor 21 is positioned in camera 2 at a location where the optical axis of the optical system in the lens 3 mounted on camera 2 is the central axis. Camera 2 may have an IR cut filter or the like instead of the cover glass 22.

[0056] Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples. [Examples]

[0057] (1) Optical configuration Figure 1 is a cross-sectional view of the optical system of Embodiment 1 of the present invention when it is in focus at infinity. The optical system is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

[0058] When focusing from an object at infinity to a nearby object, the second lens group G2 moves along the optical axis from the image side to the object side.

[0059] The first lens group G1 consists of, in order from the object side, the first a group G1a, the aperture diaphragm S, and the first b group G1b. The first a group G1a consists of, in order from the object side, a negative meniscus lens (the lens component closest to the object), a negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens. The first b group G1b consists of, in order from the object side, a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a positive meniscus lens, a biconvex lens, and a biconcave lens.

[0060] The second lens group G2 consists only of biconvex lenses.

[0061] The third lens group G3 consists solely of biconcave composite aspherical lenses, each having an aspherical surface on the object side.

[0062] In Figure 1, "IP" refers to the image plane, specifically the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. A cover glass CG is provided on the object side of the image plane IP. This is the same in the cross-sectional lens diagrams shown in other embodiments, so further explanation is omitted.

[0063] (2) Numerical Examples Next, we will describe numerical examples in which specific numerical values ​​of the optical system are applied. Below, we show the "Lens Data," "Specifications Table," "Variable Interval," "Aspherical Coefficient," and "Focal Length of Each Lens Group." The values ​​for each formula (Table 1) are shown together after Example 5. In the following numerical examples, the unit of length is "mm" and the unit of angle is "°."

[0064] In the (lens data), "Surface No." indicates the order of the lens surfaces counted from the object side, "r" indicates the radius of curvature of the lens surface, "D" indicates the lens thickness or air gap on the optical axis, "Nd" indicates the refractive index at the d line (wavelength λ=587.56nm), and "vd" indicates the Abbe number at the d line. In the "Surface No." column, an asterisk (*) after the number indicates that the lens surface is aspherical, and "S" indicates that the surface is an aperture diaphragm S. In the "D" column, "D(7)", "D(10)", etc., indicate that the spacing of the lens surfaces on the optical axis is a variable spacing that changes when in focus. In the radius of curvature column, "∞" indicates that the lens surface is flat.

[0065] In the specifications table, "f" is the focal length of the optical system, "Fno." is the F-number, and "ω" is the half-angle of view. The values ​​shown are for when the lens is in focus at infinity and when it is in focus at close range, respectively.

[0066] The values ​​for (variable interval) when the object is in focus at infinity and when it is in focus at close range are shown, respectively.

[0067] The (aspheric coefficient) represents the aspheric coefficient when the aspheric shape is defined as follows: where x is the displacement from the reference plane in the direction of the optical axis, r is the radius of paraxial curvature, H is the height from the optical axis in the direction perpendicular to the optical axis, K is the conicity coefficient, and An is the nth-order aspheric coefficient. Also, in the "Aspheric Coefficient" table, "E±XX" represents exponential notation, and "×10" represents exponential notation. ±XX It means "...".

[0068]

number

[0069] Since the details in each of these numerical examples are the same in other examples, further explanation will be omitted.

[0070] Figure 2 also shows the longitudinal aberration diagrams of the optical system when an object at infinity is in focus. The longitudinal aberration diagrams shown in each figure, from left to right, represent spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the spherical aberration diagram, the solid line represents the spherical aberration at the d line (wavelength 587.56 nm), the long dashed line represents the spherical aberration at the F line (wavelength 486.13 nm), and the short dashed line represents the spherical aberration at the C line (wavelength 656.28 nm). In the astigmatism diagram, the vertical axis is the half-angle of view (ω) and the horizontal axis is defocus, with the solid line representing the sagittal image plane (S) at the d line and the dashed line representing the meridional image plane (T) at the d line. In the distortion diagram, the vertical axis is the half-angle of view (ω) and the horizontal axis is distortion. These matters are the same in the aberration diagrams shown in other embodiments, so further explanation is omitted.

[0071] (Lens data) Surface No. r D Nd vd 1 23.0814 1.3000 1.69680 55.46 2 9.5000 3.8122 3* 23.4834 0.9000 1.59201 67.02 4* 10.4049 3.3950 5 -77.3884 0.8100 1.49700 81.61 6 22.7686 2.8852 1.91268 31.83 7 -112.9005 2.5831 8S ∞ 2.0049 9 27.2055 0.8000 1.76729 25.24 10 9.2640 3.5569 1.51641 77.12 11 -47.6755 3.2862 12 -249.3209 2.7156 1.92042 21.15 13 -19.8093 0.5217 14* 51.7169 4.5570 1.49710 81.56 15* -12.1735 0.1000 16 -21.1008 0.8000 1.71309 27.86 17 20.1206 D(17) 18 33.4718 5.7074 1.49700 81.61 19 -22.6116 D(19) 20* -138.8796 0.2000 1.53610 41.21 21 -66.7308 1.0000 1.90043 37.37 22 70.0000 15.0744 23 ∞ 2.5000 1.51680 64.20 24 ∞ 1.0000

[0072] (Specifications table) f 16.4814 15.8322 Fno. 2.8843 2.8961 ω 54.9227 54.8843

[0073] (Variable interval) Magnification ∞ -0.1154 D(17) 3.7929 2.7838 D(19) 2.4975 3.5066

[0074] (Aspherical coefficient) Surface No. K A4 A6 A8 A10 3 0.00000E+00 6.82780E-05 -9.99113E-07 5.12613E-09 0.00000E+00 4 0.00000E+00 7.14175E-05 -1.14562E-06 -5.34864E-09 0.00000E+00 14 0.00000E+00 -2.92014E-05 -2.49463E-07 -6.03768E-11 0.00000E+00 15 0.00000E+00 9.17837E-05 -3.87076E-07 2.46877E-09 0.00000E+00 20 0.00000E+00 -3.02348E-05 -1.12435E-07 1.17164E-10 0.00000E+00

[0075] (Focal length of each lens group) G1 30.706 G2 28.103 G3 -44.933 [Examples]

[0076] (1) Optical configuration Figure 3 is a cross-sectional view of the optical system of Embodiment 2 of the present invention when it is in focus at infinity. The optical system is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

[0077] When focusing from an object at infinity to a nearby object, the second lens group G2 moves along the optical axis from the image side to the object side.

[0078] The first lens group G1 consists of, in order from the object side, the first a group G1a, the aperture diaphragm S, and the first b group G1b. The first a group G1a consists of, in order from the object side, a negative meniscus lens (the lens component closest to the object), a negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens. The first b group G1b consists of, in order from the object side, a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a biconvex lens, a biconvex lens, a biconvex lens, and a biconcave lens.

[0079] The second lens group G2 consists only of biconvex lenses.

[0080] The third lens group G3 consists solely of biconcave composite aspherical lenses, each having an aspherical surface on the object side.

[0081] (2) Numerical Examples Next, we will show an example of applying specific numerical values ​​to the optical system. Furthermore, Figure 4 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0082] (Lens data) Surface No. r D Nd vd 1 22.7424 1.3000 1.69680 55.46 2 8.8352 4.6915 3* 32.5332 0.9000 1.59201 67.02 4* 11.2658 2.8359 5 -406.9572 0.8100 1.49700 81.61 6 20.6064 3.2305 1.91082 35.25 7 -94.4209 3.5321 8S ∞ 2.0000 9 41.7689 0.8000 1.75211 25.05 10 10.3064 3.6808 1.49700 81.61 11 -27.2522 2.3793 12 110.4840 2.7446 1.86966 20.02 13 -22.5696 0.6460 14* 74.7953 3.8332 1.49710 81.56 15* -13.1969 0.2000 16 -23.4567 0.8000 1.78472 25.72 17 21.8059 D(17) 18 48.2189 5.1869 1.49700 81.61 19 -19.6894 D(19) 20* -176.9605 0.2000 1.53610 41.21 21 -70.9987 1.0000 1.90043 37.37 22 73.9218 15.0000 23 ∞ 2.5000 1.51680 64.20 24 ∞ 1.0000

[0083] (Specifications table) f 15.8110 15.2446 Fno. 2.8840 2.8995 ω 56.0468 56.1871

[0084] (Variable interval) Magnification ∞ -0.1107 D(17) 4.0290 3.0446 D(19) 2.5004 3.4848

[0085] (Aspherical coefficient) Surface No. K A4 A6 A8 A10 3 0.00000E+00 7.26547E-05 -1.02670E-06 4.33587E-09 0.00000E+00 4 0.00000E+00 6.23251E-05 -1.15432E-06 -1.27734E-08 0.00000E+00 14 0.00000E+00 -2.26052E-05 -1.58588E-07 -8.32590E-10 0.00000E+00 15 0.00000E+00 8.36388E-05 -4.47202E-07 1.13438E-09 0.00000E+00 20 0.00000E+00 -3.87171E-05 -9.81562E-08 -3.87217E-10 0.00000E+00

[0086] (Focal length of each lens group) G1 28.312 G2 28.862 G3 -49.017 [Examples]

[0087] (1) Optical configuration Figure 5 is a cross-sectional view of the optical system of Embodiment 3 of the present invention when it is in focus at infinity. The optical system is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

[0088] When focusing from an object at infinity to a nearby object, the second lens group G2 moves along the optical axis from the image side to the object side.

[0089] The first lens group G1 consists of, in order from the object side, the first a group G1a, the aperture diaphragm S, and the first b group G1b. The first a group G1a consists of, in order from the object side, a negative meniscus lens (the lens component closest to the object), a negative meniscus lens, and a cemented lens formed by joining a negative meniscus lens and a positive meniscus lens. The first b group G1b consists of, in order from the object side, a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a biconvex lens, a biconvex lens, and a biconcave lens.

[0090] The second lens group G2 consists only of biconvex lenses.

[0091] The third lens group G3 consists solely of biconcave composite aspherical lenses, each having an aspherical surface on the object side.

[0092] (2) Numerical Examples Next, we will show a numerical example in which specific values ​​of the optical system are applied. Furthermore, Figure 6 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0093] (Lens data) Surface No. r D Nd vd 1 22.4358 1.3000 1.77250 49.62 2 8.2652 4.1325 3* 20.7394 0.9000 1.61881 63.86 4* 11.4094 2.5630 5 140.2929 0.8100 1.49700 81.61 6 17.3243 4.3457 1.90366 31.32 7 44.2243 2.5000 8S ∞ 2.4758 9 18.9894 0.8000 1.84666 23.78 10 10.9150 4.0175 1.49700 81.61 11 -26.7127 2.3720 12 49.2918 2.8745 1.86966 20.02 13 -26.5307 0.2000 14* 47.0076 2.9932 1.49710 81.56 15* -18.5096 0.2000 16 -26.0067 0.8000 1.84666 23.78 17 18.5284 D(17) 18 34.4262 5.4142 1.49700 81.61 19 -18.5986 D(19) 20* -1251.3915 0.2000 1.53610 41.21 21 -88.7095 1.0000 1.90043 37.37 22 49.2248 16.8333 23 ∞ 2.5000 1.51680 64.20 24 ∞ 1.0000

[0094] (Specifications table) f 16.1597 15.6244 Fno. 2.8840 2.9208 ω 55.2222 55.2293

[0095] (Variable interval) Magnification ∞ -0.1154 D(17) 3.6817 2.8587 D(19) 3.0869 3.9100

[0096] (Aspherical coefficient) Surface No. K A4 A6 A8 A10 3 0.00000E+00 1.27560E-04 -8.33243E-07 -9.28556E-09 0.00000E+00 4 0.00000E+00 9.45114E-05 -5.25690E-07 -4.74923E-08 0.00000E+00 14 0.00000E+00 -4.15675E-05 -3.56142E-07 -9.80924E-10 0.00000E+00 15 0.00000E+00 2.82561E-05 -4.19613E-07 1.24271E-12 0.00000E+00 20 0.00000E+00 -6.36104E-05 -1.38232E-07 2.14449E-10 0.00000E+00

[0097] (Focal length of each lens group) G1 42.008 G2 25.149 G3 -43.721 [Examples]

[0098] (1) Optical configuration Figure 7 is a cross-sectional view of the optical system of Embodiment 4 of the present invention when it is in focus at infinity. The optical system is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

[0099] When focusing from an object at infinity to a nearby object, the second lens group G2 moves along the optical axis from the image side to the object side.

[0100] The first lens group G1 consists of, in order from the object side, the first a group G1a, the aperture diaphragm S, and the first b group G1b. The first a group G1a consists of, in order from the object side, a negative meniscus lens (the lens component closest to the object), a negative meniscus lens, and a biconvex composite aspherical lens having an aspherical surface on the object side. The first b group G1b consists of, in order from the object side, a biconvex lens and a cemented lens formed by joining a positive meniscus lens and a negative meniscus lens.

[0101] The second lens group G2 consists of a biconcave aspherical lens and a biconvex aspherical lens, in that order from the object side.

[0102] The third lens group G3 consists solely of biconcave composite aspherical lenses, each having an aspherical surface on the object side.

[0103] (2) Numerical Examples Next, we will show a numerical example in which specific values ​​of the optical system are applied. Furthermore, Figure 8 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0104] (Lens data) Surface No. r D Nd vd 1 19.8611 1.2000 1.88300 40.81 2 9.4923 5.8751 3 156.9035 1.0000 1.49700 81.61 4 10.4878 2.6977 5* 55.2977 0.2000 1.53610 41.21 6 29.4087 2.3472 1.91082 35.25 7 -84.5403 6.0300 8S ∞ 1.5000 9 25.4275 3.7629 1.49700 81.61 10 -14.7214 0.6836 11 -32.6671 4.0004 1.78590 43.93 12 -8.2866 0.7000 1.88100 40.13 13 -30.6235 D(13) 14* -64.1141 0.8000 1.80139 45.45 15* 81.9216 0.7144 16* 29.8488 6.7390 1.49700 81.61 17* -10.1153 D(17) 18* -53.8636 0.2000 1.53610 41.21 19 -40.2005 1.0000 1.64769 33.84 20 23.5243 20.2092 21 ∞ 2.5000 1.51680 64.20 22 ∞ 1.0000

[0105] (Specifications table) f 16.4811 15.8986 Fno. 2.8878 2.9113 ω 54.3806 54.6280

[0106] (Variable interval) Magnification ∞ -0.0905 D(13) 2.6917 2.2614 D(17) 1.9992 2.4296

[0107] (Aspherical coefficient) Surface No. K A4 A6 A8 A10 5 0.00000E+00 4.45639E-05 8.12432E-07 -1.14394E-08 1.96460E-10 14 0.00000E+00 1.44370E-04 -2.84799E-06 -5.84227E-08 5.20571E-10 15 0.00000E+00 1.85613E-04 1.88726E-06 -1.35773E-07 1.20959E-09 16 0.00000E+00 -1.27270E-04 5.40504E-06 -9.21760E-08 4.95535E-10 17 0.00000E+00 9.44297E-05 -4.03657E-07 7.01258E-09 0.00000E+00 18 0.00000E+00 5.77689E-06 -4.71936E-07 0.00000E+00 0.00000E+00

[0108] (Focal length of each lens group) G1 22.363 G2 21.72 G3 -24.683 [Examples]

[0109] (1) Optical configuration Figure 9 is a cross-sectional view of the optical system of Embodiment 5 of the present invention when it is in focus at infinity. The optical system is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

[0110] When focusing from an object at infinity to a nearby object, the second lens group G2 moves along the optical axis from the image side to the object side.

[0111] The first lens group G1 consists of, in order from the object side, the first a group G1a, the aperture diaphragm S, and the first b group G1b. The first a group G1a consists of, in order from the object side, a negative meniscus lens (the lens component closest to the object), a negative meniscus lens, and a biconvex composite aspherical lens having an aspherical surface on the object side. The first b group G1b consists of, in order from the object side, a biconvex lens and a cemented lens formed by joining a biconvex lens and a biconcave lens.

[0112] The second lens group G2 consists of a biconcave aspherical lens and a biconvex aspherical lens, in that order from the object side.

[0113] The third lens group G3 consists solely of biconcave composite aspherical lenses, each having an aspherical surface on the object side.

[0114] (2) Numerical Examples Next, we will show a numerical example in which specific values ​​of the optical system are applied. Furthermore, Figure 10 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0115] (Lens data) Surface No. r D Nd vd 1 19.1175 1.2000 1.88300 40.81 2 9.1370 6.0287 3 215.1384 1.0000 1.49700 81.61 4 10.9693 2.5426 5* 59.9342 0.2000 1.53610 41.21 6 34.0236 2.3466 1.91082 35.25 7 -59.3684 6.0321 8S ∞ 1.5000 9 35.1168 3.5416 1.49700 81.61 10 -14.9146 0.6046 11 309.6062 4.9668 1.80611 40.73 12 -8.5126 0.7000 1.88202 37.22 13 108.2794 D(13) 14* -125.0396 0.8000 1.76802 49.24 15* 115.7335 0.5563 16* 29.9394 6.8106 1.49700 81.61 17* -10.0903 D(17) 18* -57.3545 0.2000 1.53610 41.21 19 -41.4948 1.0000 1.64769 33.84 20 26.2967 19.6246 21 ∞ 2.5000 1.51680 64.20 22 ∞ 1.0000

[0116] (Specifications table) f 16.4815 15.9592 Fno. 2.8840 2.8956 ω 54.3231 54.4370

[0117] (Variable interval) Magnification ∞ -0.0909 D(13) 2.6973 2.2663 D(17) 1.9988 2.4298

[0118] (Aspherical coefficient) Surface No. K A4 A6 A8 A10 5 0.00000E+00 3.92816E-05 9.14059E-07 -1.33687E-08 2.27928E-10 14 0.00000E+00 1.60363E-04 -2.38349E-06 -6.96530E-08 5.26355E-10 15 0.00000E+00 1.94354E-04 2.08207E-06 -1.47505E-07 1.27820E-09 16 0.00000E+00 -1.09702E-04 4.61856E-06 -8.14767E-08 4.40973E-10 17 0.00000E+00 1.07871E-04 -5.40057E-07 7.25856E-09 0.00000E+00 18 0.00000E+00 1.16402E-05 -5.68300E-07 0.00000E+00 0.00000E+00

[0119] (Focal length of each lens group) G1 42.848 G2 18.932 G3 -27.115

[0120] (Table 1) Example 1 Example 2 Example 3 Example 4 Example 5 Formula (1) f1a / f -1.268 -1.433 -0.780 -1.221 -1.300 Equation (2) f3 / f -2.726 -3.100 -2.706 -1.498 -1.645 Equation (3) f1 / f 1.863 1.791 2.600 1.357 2.600 Equation (4)(1-β2 2 )×β3 2 1.669 1.549 1.948 3.201 3.201 Formula (5) Nd11 1.697 1.697 1.773 1.883 1.883 Equation (6) f11 / f1a 1.154 0.952 1.400 1.082 0.980 Equation (7) f11 / f1 -0.785 -0.762 -0.420 -0.974 -0.490 Equation (8) f1a / f1 -0.681 -0.800 -0.300 -0.900 -0.500 f 16.482 15.811 16.160 16.481 16.482 f1 30.706 28.312 42.008 22.363 42.848 f1a -20.899 -22.652 -12.604 -20.127 -21.424 f11 -24.118 -21.563 -17.645 -21.773 -21.005 f3 -44.933 -49.017 -43.721 -24.683 -27.115 β2 0.384 0.409 0.266 0.381 0.210 β3 1.399 1.364 1.448 1.935 1.830 [Industrial applicability]

[0121] The optical system according to the present invention can be suitably applied as the optical system of imaging devices such as film cameras, digital still cameras, and digital video cameras. [Explanation of symbols]

[0122] S ···Opening diaphragm CG ···Cover glass IP...Image plane G1 ···First lens group G2 ···Second lens group G3 ···Third lens group G1a...Group 1a G1b...Group 1b 1. Imaging device 2 ···Camera 3...lens 21. CCD sensor or CMOS sensor 22... Cover glass or IR cut filter

Claims

1. It consists of, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power. When focusing, the first lens group and the third lens group are fixed in the direction of the optical axis with respect to the image plane, and the second lens group moves along the optical axis. The first lens group consists of, in order from the object side to the image side, a first a group having negative refractive power, an aperture diaphragm, and a first b group having positive refractive power. An optical system that satisfies the following equation. -1.433 ≦ f1a / f ≦ -0.05 (1) -3.45 ≦ f3 / f ≦ -1.35 (2) 1.357 ≦ f1 / f ≦ 4.30 (3) １．６６９ ≦ （１－β２ ２ ）×β３ ２ ≦ ５．００・・・・・（４） however, f1a: Focal length of the 1a group f3: Focal length of the third lens group f: Focal length of the optical system when focused at infinity f1: Focal length of the first lens group β2: Lateral magnification of the second lens group when focused at infinity. β3: Lateral magnification of the third lens group when focused at infinity.

2. The optical system according to claim 1, wherein the lens component of the first lens group that is positioned closest to the object satisfies the following formula. 1.60 ≦ Nd11 ≦ 2.15 (5) however, Nd11: Refractive index at the d line of the lens component closest to the object in the first lens group.

3. The optical system according to claim 1 or claim 2, wherein the lens component of the first lens group positioned closest to the object satisfies the following formula. 0.50 ≦ f11 / f1a ≦ 1.70 (6) however, f11: Focal length of the lens component located closest to the object in the first lens group.

4. The optical system according to any one of claims 1 to 3, wherein the lens component of the first lens group positioned closest to the object satisfies the following formula. -1.25 ≦ f11 / f1 ≦ -0.35 (7) however, f11: Focal length of the lens component located closest to the object in the first lens group. f1: Focal length of the first lens group

5. The optical system according to any one of claims 1 to 4, characterized in that it satisfies the following formula. -1.10 ≦ f1a / f1 ≦ -0.05 (8) however, f1: Focal length of the first lens group

6. An imaging device comprising an optical system according to any one of claims 1 to 5, and an image sensor on the image side of the optical system that converts an optical image formed by the optical system into an electrical signal.

Images