Optical system and imaging device

Abstract

Despite having a large aperture ratio, the overall lens system is compact, and it provides an optical system that effectively corrects various aberrations, including chromatic aberration, resulting in high optical performance. [Solution] The system consists of a positive first lens group, an aperture diaphragm, and a positive second lens group, arranged in order from the object side to the image side. The first lens group has a positive first lens and a negative second lens, arranged in order from the object side to the image side, and a negative fourth lens and a positive third lens, arranged in order from the image side to the object side. The second lens group has a negative fifth lens, a positive sixth lens, and two or more lenses, arranged in order from the object side to the image side. In the infinity focus state, the air distance on the optical axis between the first lens group and the second lens group is greater than the sum of the air distances between each lens included in the second lens group. The total focal length, the Petzval sum for the second lens, and the average value of the Abbe numbers of the fourth and fifth lenses are appropriately set.

Description

[Technical Field]

[0001] This invention relates to an optical system and an imaging device. [Background technology]

[0002] In recent years, there has been a strong demand for optical systems used in imaging devices that offer a large aperture ratio while maintaining a compact overall lens system and high optical performance.

[0003] For standard angle-of-view lenses with a maximum half-angle of view of about 20° to 30°, an imaging optical system called a double Gauss type is known. Patent Document 1 discloses a compact imaging optical system with a large aperture ratio, consisting of a front group with positive refractive power, an aperture diaphragm, and a rear group with positive refractive power, arranged in order from the object side to the image side. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 39-10178 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0005] In a double Gauss-type imaging optical system, achieving good correction of field curvature requires increasing the refractive index of the entire positive lens and decreasing the Petzval sum of the entire optical system. However, in this case, chromatic aberration correction becomes difficult because high refractive index lens materials generally have high dispersion properties. The present invention aims to provide an optical system that achieves high optical performance by having a large aperture ratio, while maintaining a compact overall lens system and effectively correcting various aberrations, including chromatic aberration. [Means for solving the problem]

[0006] An optical system as one aspect of the present invention comprises a first lens group with positive refractive power, an aperture diaphragm, and a second lens group with positive refractive power, arranged sequentially from the object side to the image side, wherein the first lens group consists of a first subgroup and a second subgroup, arranged sequentially from the object side to the image side, the first subgroup has a positive first lens and a negative second lens, arranged sequentially from the object side to the image side, the second subgroup consists of a positive third lens and a negative fourth lens, arranged sequentially from the object side to the image side, the second lens group has a negative fifth lens, a positive sixth lens, and two or more lenses, arranged sequentially from the object side to the image side, the total number of lenses arranged in the optical system is 10 or less, and in the infinity focus state, the air distance on the optical axis between the first lens group and the second lens group is greater than the sum of the air distances of each lens included in the second lens group, and when the focal length of the optical system is f, the Petzval sum for the second lens is PL2, and the average value of the Abbe numbers of the fourth lens and the fifth lens is vdL45, -1.00 ≤ f × ​​PL2 ≤ -0.15 15.00 ≤ vdL45 ≤ 32.00 It is characterized by satisfying the following conditions.

[0007] Another aspect of the present invention is an optical system comprising a first lens group with positive refractive power, an aperture diaphragm, and a second lens group with positive refractive power, arranged sequentially from the object side to the image side, wherein the first lens group consists of a first subgroup and a second subgroup, arranged sequentially from the object side to the image side, the first subgroup has a positive first lens and a negative second lens, arranged sequentially from the object side to the image side, the second subgroup consists of a positive third lens and a negative fourth lens, arranged sequentially from the object side to the image side, the second lens group has a negative fifth lens, a positive sixth lens, and two or more lenses, arranged sequentially from the object side to the image side, the total number of lenses arranged in the optical system is 10 or less, and when the focal length of the optical system is f, the Petzval sum with respect to the second lens is PL2, and the average value of the Abbe numbers of the fourth lens and the fifth lens is vdL45, -0.61 ≤ f × ​​PL² ≤ 0.15 15.00 ≤ vdL45 ≤ 27.50 It is characterized by satisfying the following conditions.

[0008] Another aspect of the present invention is an optical system comprising a first lens group with positive refractive power, an aperture diaphragm, and a second lens group with positive refractive power, arranged in order from the object side to the image side, characterized in that, in the infinity focus state, the air distance between the first lens group and the second lens group on the optical axis is greater than the sum of the air distances of each lens included in the second lens group. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical system that has a large aperture ratio, yet the entire lens system is compact, and that can effectively correct various aberrations, including chromatic aberration, and obtain high optical performance. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of the optical system of Example 1 when it is in focus at infinity. [Figure 2] This is an aberration diagram of the optical system of Example 1 when it is focused at infinity. [Figure 3] This is a cross-sectional view of the optical system of Example 2 when it is in focus at infinity. [Figure 4] This is an aberration diagram of the optical system of Example 2 when it is focused at infinity. [Figure 5] This is a cross-sectional view of the optical system of Example 3 when it is in focus at infinity. [Figure 6] This is an aberration diagram of the optical system of Example 3 when it is focused at infinity. [Figure 7] This is a cross-sectional view of the optical system of Example 4 when it is in focus at infinity. [Figure 8] This is an aberration diagram of the optical system of Example 4 when it is focused at infinity. [Figure 9] This is a cross-sectional view of the optical system of Example 5 when it is in focus at infinity. [Figure 10] This is an aberration diagram of the optical system of Example 5 when it is focused at infinity. [Figure 11] This is a cross-sectional view of the optical system of Example 6 when it is in focus at infinity. [Figure 12]It is an aberration diagram of the optical system in Example 6 when focused at infinity. [Figure 13] It is a cross-sectional view of the optical system in Example 7 when focused at infinity. [Figure 14] It is an aberration diagram of the optical system in Example 7 when focused at infinity. [Figure 15] It is a cross-sectional view of the optical system in Example 8 when focused at infinity. [Figure 16] It is an aberration diagram of the optical system in Example 8 when focused at infinity. [Figure 17] It is a cross-sectional view of the optical system in Example 9 when focused at infinity. [Figure 18] It is an aberration diagram of the optical system in Example 9 when focused at infinity. [Figure 19] It is a diagram schematically showing an imaging device. [Figure 20] It is a diagram schematically showing a lens device.

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to the description of specific Examples 1 to 9, matters common to each example will be described. FIGS. 1, 3, 5, 7, 9, 11, 13, 15, and 17 each show a cross-sectional view of the optical systems of Examples 1 to 9 in a state of being focused on an object at infinity. In each cross-sectional view, SP is an aperture stop, FL is an optical block corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, etc., and IP indicates an image plane. On the image plane IP, an imaging surface (light-receiving surface) of an imaging device or a film surface (photosensitive surface) of a silver halide film is arranged.

[0012] FIG. 19 schematically shows an imaging device including an optical system of any one of Examples 1 to 9. FIG. 20 schematically shows a lens device including an optical system of any one of Examples 1 to 9. The optical system of each embodiment consists of a first lens group B1 with positive refractive power, an aperture diaphragm SP, and a second lens group B2 with positive refractive power, arranged sequentially from the object side to the image side. By adopting this configuration, the optical system of the present invention enables a double Gauss-type symmetrical lens arrangement, resulting in a good aberration correction effect, making it suitable for imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, and surveillance cameras.

[0013] Furthermore, the first lens group B1 consists of a first subgroup and a second subgroup, arranged sequentially from the object side to the image side. The first subgroup has a positive first lens L1 and a negative second lens L2, arranged sequentially from the object side to the image side. With this configuration, the object side of the first lens L1 and the image side of the second lens L2 have a concentric shape with respect to the aperture diaphragm SP, thereby suppressing the occurrence of off-axis aberrations. The second subgroup consists of a positive third lens and a negative fourth lens L4, arranged sequentially from the object side to the image side. The second lens group B2 has a negative fifth lens L5 and a positive sixth lens L6, arranged sequentially from the object side to the image side. By using this double Gauss-type lens arrangement, a strong spherical aberration correction effect is provided to the air lens located at the aperture diaphragm SP, and by symmetrical lens arrangement around the aperture diaphragm SP, good correction effects for coma aberration, distortion aberration, and lateral chromatic aberration are obtained.

[0014] Furthermore, the second lens group B2 has two or more positive lenses on the image side of the sixth lens L6. By arranging the two positive lenses closest to the image side in this double Gauss type configuration, a concave air lens is provided within the second lens group B2, and a good correction effect for higher-order coma aberration is obtained due to the strong positive power effect against off-axis light.

[0015] Furthermore, the second lens group B2 consists of a second a lens group B2a that moves along the optical axis together with the first lens group B1 and the aperture diaphragm SP when in focus, and a second b lens group B2b that remains stationary relative to the image plane IP when in focus. By positioning the group that is fixed to the image plane IP on the image side in this way, spherical aberration fluctuations and field curvature fluctuations when in focus can be suppressed.

[0016] Furthermore, in the optical system of each embodiment, the total number of lenses is 10 or less, and the sum of the air gaps on the optical axis between each lens in the second lens group B2 when focused at infinity is smaller than the air gaps on the optical axis between the first lens group B1 and the second lens group B2. With this configuration, a large aperture can be achieved despite the compact size, thanks to the excellent spherical aberration correction effect of the strong negative power of the air lens located at the aperture diaphragm SP, and the advantages of a double Gauss type lens can be fully utilized.

[0017] Furthermore, the first lens L1 and the second lens L2 form a cemented lens by joining them together. This cemented lens has a convex shape on the object-side surface and possesses a meniscus shape with positive refractive power. With this configuration, the object-side and image-side surfaces of the cemented lens become concentric with respect to the aperture diaphragm SP, which allows each lens to have strong power while suppressing the occurrence of off-axis aberrations, resulting in a good correction effect for chromatic aberration. Furthermore, the fifth lens L5 and the sixth lens L6 are joined together to form a cemented lens. This configuration provides excellent correction of axial chromatic aberration.

[0018] Furthermore, the maximum half-angle of view for each optical system is approximately 20-30°. This standard angle of view lens specification is known to be a range in which, in a double Gauss-type lens configuration, it is possible to maintain a concentric lens shape centered on the aperture diaphragm SP while providing strong negative power to the air lens located at the aperture diaphragm SP. This enables good correction of spherical aberration and suppression of off-axis aberration, allowing each optical system to achieve both a large aperture ratio of around F-number 1.2 and good aberration correction.

[0019] Furthermore, in each optical system, negative sign distortion remains due to the reduction in lens diameter. Therefore, in an imaging device including the optical system of the present invention, this remaining distortion can be corrected in software through electronic correction processing, thereby achieving both miniaturization of the optical system and correction of distortion. When focusing from an infinity focus state to a nearby object, the subgroup consisting of the first lens group B1, the aperture diaphragm SP, and the seconda lens group B2a moves together along the optical axis toward the object, while the secondb lens group B2b remains stationary relative to the image plane IP. In each figure, the solid arrows indicate the direction of movement of the subgroup when focusing from an infinity focus state to a nearby object.

[0020] Furthermore, in each embodiment, when the total focal length of the optical system is f, the Petzval sum with respect to the second lens L2 is PL2, and the average value of the Abbe numbers with respect to the d line of the fourth lens L4 and the fifth lens L5 is vdL45, -1.00 ≤ f × ​​PL² ≤ -0.15 ···(1) 15.00 ≤ vdL45 ≤ 32.00 ···(2) The following conditions (1) and (2) are satisfied. Here, the Petzval sum PL2 is given by, where NdL2 is the refractive index of the second lens L2 and fL2 is the focal length of the second lens L2, PL2 = 1 / (NdL2 × fL2) It is derived using the following formula.

[0021] Conditional equation (1) indicates an appropriate range for the product of the total focal length of the optical system and the Petzval sum with respect to the second lens L2. If PL2 becomes large enough that f × PL2 exceeds the upper limit of conditional equation (1), the power of the second lens L2 becomes strong, disrupting the symmetrical power distribution of the double Gauss type, and making it difficult to correct coma aberration and distortion aberration, which is undesirable. If PL2 becomes small enough that f × PL2 falls below the lower limit of conditional equation (1), the Petzval sum for the entire optical system becomes large, making it difficult to correct field curvature aberration, which is also undesirable.

[0022] Conditional equation (2) indicates an appropriate range for the average value vdL45 of the Abbe numbers of the fourth lens L4 and the fifth lens L5. If the Abbe numbers of the fourth lens L4 and the fifth lens L5 increase so that vdL45 exceeds the upper limit of conditional equation (2), it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration, which is undesirable. If the Abbe numbers of the fourth lens L4 and the fifth lens L5 decrease so that vd45 falls below the lower limit of conditional equation (2), the refractive index of the fourth lens L4 and the fifth lens L5 increases because high-dispersion glass materials generally have high refractive indices, the Petzval sum for the entire optical system increases, and it becomes difficult to correct field curvature aberration, which is also undesirable.

[0023] Furthermore, it is even preferable to set the numerical ranges of equations (1) and (2) as follows. -0.87≦f×PL2≦-0.17 (1a) 16.47≦vdL45≦31.47 (2a) Furthermore, it is even preferable to set the numerical ranges of equations (1) and (2) as follows. -0.74≦f×PL2≦-0.19 (2b) 17.94≦vdL45≦30.93 (2b) Furthermore, it is even preferable to set the numerical ranges of equations (1) and (2) as follows. -0.61≦f×PL2≦-0.21 (2c) 19.41≦vdL45≦27.50 (2c)

[0024] By having the above configuration and satisfying the conditions (1) to (2), it is possible to provide an optical system and an imaging device having the same, which have a large aperture ratio, yet the entire lens system is compact, and which can correct various aberrations including chromatic aberration well and obtain high optical performance.

[0025] In each embodiment, when the optical system is focused at infinity, the focal length of the air lens at the aperture diaphragm SP between the first lens group B1 and the second lens group B2 is denoted as fSP. -0.28 ≤ fSP / f ≤ -0.12 ···(3) It is preferable that the following conditions be satisfied. Furthermore, fSP is calculated when the refractive indices of the fourth lens L4 and fifth lens L5 at the d line are NdL4 and NdL5, respectively, the radius of curvature of the image-side surface of the fourth lens L4 is R2L4, the radius of curvature of the object-side surface of the fifth lens L5 is R1L5, and the air distance on the optical axis between the first lens group B1 and the second lens group B2 is TSP. fSP=1 / [(1-NdL4) / R2L4-(1-NdL5) / R1L5 +(1-NdL4)×(1-NdL5)×TSP / (R2L4×R1L5)] ...(a) This is derived from the following.

[0026] Conditional equation (3) indicates an appropriate range for the ratio of the focal length fSP of the air lens located at the aperture diaphragm SP to the total focal length of the optical system. If fSP / f exceeds the upper limit of conditional equation (3), it is undesirable because a good spherical aberration correction effect by the air lens cannot be obtained, making it difficult to achieve a large aperture ratio. If fSP / f falls below the lower limit of conditional equation (3), it is undesirable because the radius of curvature of each surface of the air lens becomes small, making it difficult to suppress sagittal coma flare generated by the air lens.

[0027] In each embodiment, when the distance along the optical axis between the object-side surface and the image-side surface of the optical system (total lens length) is denoted as TD, 0.18 ≤ TSP / TD ≤ 0.33 ···(4) It is preferable that the following conditions be satisfied.

[0028] Conditional equation (4) indicates an appropriate range for the ratio of the air gap on the optical axes of the first lens group B1 and the second lens group B2 to the total length of the lenses in the optical system. If TSP becomes large enough that TSP / TD exceeds the upper limit of conditional equation (4), the entire optical system becomes larger, which is undesirable. If TSP becomes small enough that TSP / TD falls below the lower limit of conditional equation (4), the lens surfaces before and after the aperture diaphragm SP take on a concentric shape around the aperture diaphragm SP in order to suppress the occurrence of off-axis aberrations. This reduces the radius of curvature of these surfaces, making it difficult to suppress sagittal coma flare, which is also undesirable.

[0029] In each embodiment, when the distance along the optical axis between the object-side surface and the image-side surface of the first lens group B1 is TB1, and the distance along the optical axis between the object-side surface and the image-side surface of the second lens group B2 is TB2, 0.72≦(TB1+TB2) / f≦1.12 (5) It is preferable that the following conditions be satisfied.

[0030] Conditional equation (5) indicates an appropriate range for the ratio of the sum of the thickness of the first lens group B1 and the thickness of the second lens group B2 on the optical axis to the total focal length of the optical system. If (TB1+TB2) becomes large enough that (TB1+TB2) / f exceeds the upper limit of conditional equation (5), the overall length of the optical system increases, making the entire optical system larger, which is undesirable. If (TB1+TB2) becomes small enough that (TB1+TB2) / f falls below the lower limit of conditional equation (5), the radius of curvature of each lens becomes smaller due to the need for strong divergence and convergence of light rays, making it difficult to suppress higher-order aberrations, which is also undesirable.

[0031] In each embodiment, the optical system has a back focus of Sk, 0.42 ≤ Sk / f ≤ 0.60 ···(6) It is preferable that the following conditions be satisfied.

[0032] Conditional equation (6) indicates an appropriate range for the ratio of the back focus of the optical system to the total focal length of the optical system. If Sk becomes large enough so that Sk / f exceeds the upper limit of conditional equation (6), the overall length of the optical system increases, making the entire optical system larger, which is undesirable. If Sk becomes small enough so that Sk / f falls below the lower limit of conditional equation (6), the power of the first lens group B1 becomes strong, disrupting the symmetrical power distribution of the double Gauss type, making it difficult to correct coma aberration and distortion aberration, which is also undesirable.

[0033] In each embodiment, when NdLp is the average value of the refractive index of all positive lenses included in the optical system at the d line, 1.77 ≤ NdLp ≤ 1.97 ···(7) It is preferable that the following conditions be satisfied.

[0034] Conditional equation (7) indicates an appropriate range for the average value of the refractive indices of all positive lenses included in the optical system. If NdLp becomes large enough to exceed the upper limit of conditional equation (7), it is undesirable because the Abbe number of the positive lenses decreases due to the high dispersion of high refractive index lens materials, making it difficult to correct axial chromatic aberration and lateral chromatic aberration. If NdLp becomes small enough to fall below the lower limit of conditional equation (7), it is undesirable because the Petzval sum for the entire optical system becomes large, making it difficult to correct field curvature aberration.

[0035] In each embodiment, when the Petzval sum for the second lens L2, the fourth lens L4, and the fifth lens L5 is PL245, -3.10 ≤ f × ​​PL245 ≤ -2.21 ···(8) It is preferable that the following conditions be satisfied. Furthermore, when the refractive indices of the second lens L2, fourth lens L4, and fifth lens L5 at the d line are NdL2, NdL4, and NdL5, respectively, and the focal lengths of the second lens L2, fourth lens L4, and fifth lens L5 are fL2, fL4, and fL5, respectively, PL245=1 / (NdL2×fL2)+1 / (NdL4×fL4) +1 / (NdL5×fL5) ···(b) This is derived from the following.

[0036] Conditional equation (8) indicates an appropriate range for the product of the total focal length of the optical system and the Petzval sum for the second lens L2, the fourth lens L4, and the fifth lens L5. If f × PL245 becomes large enough to exceed the upper limit of conditional equation (8), the Petzval sum of the entire optical system becomes large, making it difficult to correct field curvature aberration, which is undesirable. If f × PL245 becomes small enough to fall below the lower limit of conditional equation (8), the Abbe numbers of the second lens L2, the fourth lens L4, and the fifth lens L5 become large because low refractive index lens materials generally have low dispersion, making it difficult to correct chromatic aberration occurring in the positive lens, which is also undesirable.

[0037] In each embodiment, when the combined focal length of the first lens group B1 and the second a lens group B2a is fB1B2a, and the focal length of the second b lens group B2b is fB2b, 0.23 ≤ fB1B2a / fB2b ≤ 0.56 ···(9) It is preferable that the following conditions be satisfied.

[0038] Conditional equation (9) indicates an appropriate range for the ratio of the combined focal length of the first lens group B1 and the second a lens group B2a, which move during focusing, to the focal length of the lens group B2b, which remains stationary relative to the image plane IP during focusing. If fB1B2a / fB2b becomes large enough to exceed the upper limit of conditional equation (9), the travel distance of the movable group during focusing increases, making it difficult to achieve quick and quiet focusing, which is undesirable. If fB1B2a / fB2b becomes small enough to fall below the lower limit of conditional equation (9), it becomes difficult to suppress spherical aberration fluctuations during focusing, which is also undesirable.

[0039] In each embodiment, when the shape factor of the second lens L2 is set to SFL2, -2.80 ≤ SFL2 ≤ 0.62 ···(10) It is preferable that the following conditions be satisfied. Furthermore, when the radii of curvature of the object side and image side of the second lens L2 are R1L2 and R2L2, respectively, SFL2 is defined as follows: SFL2=(R2L2+R1L2) / (R2L2-R1L2) ···(c) This is derived from the following.

[0040] Conditional equation (10) indicates an appropriate range for the shape factor of the second lens L2. If SFL2 becomes large enough to exceed the upper limit of conditional equation (10), the angle of light rays incident on the object-side surface of the second lens L2 becomes large, making it difficult to suppress off-axis aberrations, which is undesirable. If SFL2 becomes small enough to fall below the lower limit of conditional equation (10), it becomes difficult to avoid strong total internal reflection ghosting, which is prone to occur in double Gauss-type optical systems, which is also undesirable.

[0041] In each embodiment, when the shape factor of the final lens Lr, which is positioned closest to the image in the optical system, is denoted as SFLr, -0.08 ≤ SFLr ≤ 4.55 ···(11) It is preferable that the following conditions be satisfied. Furthermore, SFLr is calculated when the radii of curvature of the object side and image side of the final lens Lr are R1Lr and R2Lr, respectively. SFLr=(R2Lr+R1Lr) / (R2Lr-R1Lr) ···(d) This is derived from the following.

[0042] Conditional equation (11) indicates an appropriate range for the shape factor value of the final lens Lr. If SFLr becomes large enough to exceed the upper limit of conditional equation (11), multiple reflections occur between the image plane IP and the final lens Lr, making it difficult to avoid highly image-forming ghosts, which is undesirable. If SFLr becomes small enough to fall below the lower limit of conditional equation (11), it becomes difficult to suppress coma aberration and field curvature fluctuations during focusing, which is also undesirable.

[0043] In each embodiment, when the distance (total optical length) between the lens surface on the object side of the optical system and the image plane IP is denoted as TL, 1.50 ≤ TL / f ≤ 2.02 ···(12) It is preferable that the following conditions be satisfied.

[0044] Conditional equation (12) indicates an appropriate range for the ratio of the total optical length of the optical system to the total focal length of the optical system. If TL becomes large enough that TL / f exceeds the upper limit of conditional equation (12), the total length of the optical system increases, making the entire optical system larger, which is undesirable. If TL becomes small enough that TL / f falls below the lower limit of conditional equation (12), the radius of curvature of each lens becomes smaller due to the need for strong divergence and convergence of light rays, making it difficult to suppress higher-order aberrations, which is also undesirable.

[0045] In each embodiment, when the focal length of the first lens group B1 is fB1 and the focal length of the second lens group B2 is fB2, 2.07 ≤ fB1 / fB2 ≤ 4.93 ···(13) It is preferable that the following conditions be satisfied.

[0046] Conditional equation (13) indicates an appropriate range for the ratio of the focal length of the first lens group B1 to the focal length of the second lens group B2. If fB1 becomes large enough that fB1 / fB2 exceeds the upper limit of conditional equation (13), the back focus of the optical system expands, and the entire optical system becomes larger, which is undesirable. If fB1 becomes small enough that fB1 / fB2 falls below the lower limit of conditional equation (13), the symmetrical power distribution of the double Gauss type is disrupted, making it difficult to correct coma aberration and distortion aberration, which is also undesirable.

[0047] In each embodiment, when the combined focal length of the first lens L1 and the second lens L2 is fL1L2, 0.31 ≤ fL1L2 / fB1 ≤ 1.98 ···(14) It is preferable that the following conditions be satisfied.

[0048] Conditional equation (14) indicates an appropriate range for the ratio of the combined focal length of the first lens L1 and the second lens L2 to the focal length of the first lens group B1. If fL1L2 becomes large enough that fL1L2 / fB1 exceeds the upper limit of conditional equation (14), the angle of light rays incident on the lens adjacent to the image side of the second lens L2 becomes large, making it difficult to correct higher-order coma aberrations, which is undesirable. If fL1L2 becomes small enough that fL1L2 / fB1 falls below the lower limit of conditional equation (14), the convergence effect of the light rays weakens, and the entire optical system becomes larger, which is also undesirable.

[0049] In each embodiment, when the focal length of the fifth lens L5 is fL5 and the focal length of the sixth lens L6 is fL6, -1.20 ≤ fL5 / fL6 ≤ -0.64 ···(15) It is preferable that the following conditions be satisfied.

[0050] Conditional equation (15) indicates an appropriate range for the ratio of the focal length of the fifth lens L5 to the focal length of the sixth lens L6. If fL5 becomes large enough that fL5 / fL6 exceeds the upper limit of conditional equation (15), the first-order axial chromatic aberration will be undercorrected, which is undesirable. If fL5 becomes small enough that fL5 / fL6 falls below the lower limit of conditional equation (15), the first-order axial chromatic aberration will be overcorrected, which is also undesirable.

[0051] The optical system of each embodiment, when the maximum half-angle of view is ω(°), 18.00≦ω≦32.00 ···(16) It is preferable that the following conditions be satisfied.

[0052] Conditional equation (16) indicates an appropriate range for the maximum half-angle of view of the optical system. If ω becomes large enough to exceed the upper limit of conditional equation (16), the symmetrical power distribution of the double Gauss type is disrupted due to the widening of the optical system, making it difficult to correct coma aberration and distortion, which is undesirable. If ω becomes small enough to fall below the lower limit of conditional equation (16), if a concentric lens shape is adopted around the aperture diaphragm SP to suppress the occurrence of off-axis aberrations, the curvature of the lens surfaces before and after the aperture diaphragm SP becomes gentler, making it difficult to properly correct spherical aberration in the air lens located at the aperture diaphragm SP, which is also undesirable.

[0053] In each embodiment, when the F-number of the optical system is denoted as Fno, Fno ≤ 2.07 ···(17) It is preferable that the following conditions be satisfied.

[0054] Conditional equation (17) indicates an appropriate range for the F-number value of the optical system. By satisfying the range of conditional equation (17), an optical system with a large aperture ratio is realized.

[0055] In each embodiment, when the maximum value of the distortion aberration in the central projection method is Di, -8.47 ≤ Di ≤ -3.27 ···(18) It is preferable that the following conditions be satisfied.

[0056] Conditional equation (18) indicates an appropriate range for the amount of distortion relative to the maximum half-angle of view. If Di becomes large enough to exceed the upper limit of conditional equation (18), the symmetrical power distribution of the double Gauss type is disrupted, making it difficult to correct coma aberration and chromatic aberration, which is undesirable. If Di becomes small enough to fall below the lower limit of conditional equation (18), it becomes difficult to reduce the lens diameter by utilizing electronic correction of distortion, which is also undesirable.

[0057] Furthermore, it is preferable to set the numerical ranges for conditional expressions (3) to (18) as follows. -0.27≦fSP / f≦-0.13 (3a) 0.19≦TSP / TD≦0.32 (4a) 0.74≦(TB1+TB2) / f≦1.10 (5a) 0.43 ≤ Sk / f ≤ 0.59 ···(6a) 1.78 ≤ NdLp ≤ 1.96 ···(7a) -3.05≦f×PL245≦-2.26 (8a) 0.25≦fB1B2a / fB2b≦0.54 (9a) -2.61≦SFL2≦0.43 (10a) 0.18≦SFLr≦4.29 (11a) 1.53≦TL / f≦1.99 (12a) 2.23≦fB1 / fB2≦4.77 (13a) 0.40≦fL1L2 / fB1≦1.89 (14a) -1.17≦fL5 / fL6≦-0.67 (15a) 19.12≦ω≦30.13 (16a) Fno ≤ 1.86 ···(17a) -8.18≦Di≦-3.56 (18a) Furthermore, it is even more preferable to set the numerical ranges of conditional expressions (3a) to (18a) as follows. -0.26≦fSP / f≦-0.14 (3b) 0.20≦TSP / TD≦0.31 (4b) 0.76≦(TB1+TB2) / f≦1.08 (5b) 0.44 ≤ Sk / f ≤ 0.58 ···(6b) 1.79 ≤ NdLp ≤ 1.95 ···(7b) -3.00≦f×PL245≦-2.31 (8b) 0.27≦fB1B2a / fB2b≦0.52 (9b) -2.42≦SFL2≦0.24 (10b) 0.44≦SFLr≦4.03 (11b) 1.56≦TL / f≦1.96 (12b) 2.39≦fB1 / fB2≦4.61 (13b) 0.49≦fL1L2 / fB1≦1.80 (14b) -1.14≦fL5 / fL6≦-0.70 (15b) 20.24≦ω≦28.27 (16b) Fno ≤ 1.46 ···(17b) -7.89≦Di≦-3.85 (18b)

[0058] Furthermore, it is even preferable to set the numerical ranges of conditional expressions (3b) to (18b) as follows. -0.25≦fSP / f≦-0.15 (3c) 0.21≦TSP / TD≦0.30 (4c) 0.78≦(TB1+TB2) / f≦1.06 (5c) 0.45 ≤ Sk / f ≤ 0.57 ···(6c) 1.80 ≤ NdLp ≤ 1.94 ···(7c) -2.95≦f×PL245≦-2.36 (8c) 0.29≦fB1B2a / fB2b≦0.50 (9c) -2.23≦SFL2≦0.05 (10c) 0.70≦SFLr≦3.77 (11c) 1.59≦TL / f≦1.93 (12c) 2.55≦fB1 / fB2≦4.45 (13c) 0.58≦fL1L2 / fB1≦1.71 (14c) -1.11≦fL5 / fL6≦-0.73 (15c) 21.36≦ω≦26.40 (16c) Fno ≤ 1.24 ···(17c) -7.60≦Di≦-4.14 (18c) [Examples]

[0059] The configurations of the optical systems in Examples 1 to 9 will be described in detail below. First, the configuration of the first lens group B1 will be described. In Examples 1 to 5 and 7 to 9, the first lens group B1 consists of a positive lens (first lens) L1, a negative lens (second lens) L2, a positive lens (third lens) L3, and a negative lens (fourth lens) L4, arranged in order from the object side to the image side. In Example 6, the first lens group B1 consists of a positive lens (first lens) L1, a negative lens (second lens) L2, a positive lens, a positive lens (third lens) L3, and a negative lens (fourth lens) L4, arranged in order from the object side to the image side.

[0060] Next, the configuration of the second lens group B2 will be described. In all embodiments, the second lens group B2 consists of the second a lens group B2a and the second b lens group B2b, which are arranged in order from the object side to the image side. In embodiments 1-3, 5-6, and 8, the second a lens group B2a consists of a negative lens (fifth lens) L5, a positive lens (sixth lens) L6, a negative lens, and a positive lens, which are arranged in order from the object side to the image side. In embodiment 4, the second a lens group B2a consists of a negative lens (fifth lens) L5, a positive lens (sixth lens) L6, and a positive lens, which are arranged in order from the object side to the image side. In embodiment 7, the second a lens group B2a consists of a negative lens (fifth lens) L5, a positive lens (sixth lens) L6, a negative lens, and a positive lens, which are arranged in order from the object side to the image side. In Example 9, the second a lens group B2a consists of a negative lens (fifth lens) L5, a positive lens (sixth lens) L6, a negative lens, a positive lens, and a positive lens, arranged in order from the object side to the image side. In Examples 1-6, 8, and 9, the second b lens group B2b consists of one positive lens (final lens Lr), while in Example 7, the second b lens group B2b consists of a negative lens and a positive lens (final lens Lr).

[0061] The numerical Examples 1 to 9 corresponding to Examples 1 to 9 are shown below. In each numerical example, the surface number i indicates the order of the surfaces from the object side. r is the radius of curvature (mm) of the i-th surface, d is the lens thickness or air gap (mm) on the optical axis between the i-th surface and the (i + 1)-th surface. nd is the refractive index at the d-line of the optical material between the i-th surface and the (i + 1)-th surface, νd is the Abbe number based on the d-line of the optical material, and the effective diameter is the effective ray diameter of the i-th surface.

[0062] The Abbe number νd based on the d-line is defined as follows. When the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are nd, nF, and nC, νd = (nd - 1) / (nF - nC) ···(e) and is expressed by the following formula. BF represents the back focus (mm). The back focus is defined as the distance on the optical axis from the final surface (the lens surface closest to the image side) of the lens to the paraxial image plane, expressed in terms of the air-equivalent length. The overall length of the lens (mm) is the distance on the optical axis from the lens surface farthest from the object side to the lens surface closest to the image side, and the optical overall length (mm) is the length obtained by adding the back focus to the overall length of the lens.

[0063] The "*" attached to the right of the surface number means that the surface is a lens surface having an aspherical shape. The aspherical shape is expressed by the following formula when x is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients. The "e-M" of the conic constant and the aspherical coefficients means "×10 -M ". 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 ··(f)

[0064] Furthermore, Table 1 summarizes the values ​​corresponding to conditional equations (1) to (18) in numerical examples 1 to 9. The optical systems of each numerical example satisfy all the conditions of conditional equations (1) to (18). Furthermore, Figures 2, 4, 6, 8, 10, 12, 14, 16, and 18 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of numerical examples 1 to 9 at infinity focus, respectively. In the spherical aberration diagram, Fno indicates the F number, the solid line shows the spherical aberration with respect to the d line (wavelength 587.6 nm), and the dashed line shows the spherical aberration with respect to the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS shows the sagittal image plane, and the dashed line ΔM shows the meridional image plane. Distortion is shown with respect to the d line. The chromatic aberration diagram shows the lateral chromatic aberration at the g line. ω is the half-angle of view (°) obtained from paraxial calculations.

[0065] [Numerical Example 1] Unit: mm Surface data Face number rd nd vd Effective diameter 1 58.809 5.82 1.91082 35.3 37.87 2 -199.152 1.45 1.68893 31.1 37.29 3 111.296 0.20 35.82 4 22.473 6.90 1.95375 32.3 33.18 5 37.446 0.35 30.00 6 40.746 1.25 1.84666 23.9 29.91 7 15.729 8.95 24.80 8 (aperture) ∞ 5.60 24.03 9 -22.093 1.00 1.84666 23.9 23.42 10 30.212 8.36 1.95375 32.3 26.52 11 -36.844 0.60 27.40 12* -55.440 3.00 1.53504 55.7 27.25 13* -64.575 0.60 28.85 14 185.451 5.35 1.83481 42.7 33.03 15 -51.445 2.00 34.00 16 53.806 4.02 1.69680 55.5 37.73 17 119.308 23.16 37.61 18 ∞ 2.00 1.51633 64.1 50.00 19 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4=-4.13127e-06 A 6= 3.26661e-08 A 8=-3.30309e-10 A10= 1.45131e-12 A12=-2.20726e-15 Page 13 K = 0.00000e+00 A 4=-1.05724e-06 A 6= 2.61774e-08 A 8=-2.11056e-10 A10= 8.70223e-13 A12=-1.17242e-15 Various data Focal length 46.35 F-number 1.22 Half-angle (°): 23.62 Image height 20.27 Lens length 55.45 Optical total length 80.73 BF 25.28 Single lens data Lens starting plane, focal length 1 1 50.39 2 2 -103.44 3 4 48.11 4 6 -30.97 5 9 -14.94 6 10 18.53 7 12 -827.16 8 14 48.74 9 16 137.20

[0066] [Numerical Example 2] Unit: mm Surface data Face number rd nd vd Effective diameter 1 63.146 6.04 1.91082 35.3 38.74 2 -144.139 1.45 1.68893 31.1 37.28 3 98.192 0.20 34.10 4 22.941 7.13 1.91082 35.3 32.21 5 36.161 0.44 28.61 6 40.224 1.25 1.71338 26.0 28.49 7 15.612 8.59 24.12 8 (aperture) ∞ 5.93 23.43 9 -20.715 1.00 1.75575 24.7 22.84 10 29.090 8.10 1.91082 35.3 26.00 11 -38.091 0.60 26.76 12* -59.962 3.00 1.53504 55.7 26.59 13* -64.440 0.60 29.11 14 278.856 5.49 1.83481 42.7 32.90 15 -47.240 2.00 34.00 16 53.158 4.38 1.69680 55.5 37.94 17 122.609 22.14 37.79 18 ∞ 2.00 1.51633 64.1 50.00 19 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4=-4.08513e-06 A 6= 9.87225e-09 A 8=-2.91010e-10 A10= 1.81417e-12 A12=-3.34519e-15 Page 13 K = 0.00000e+00 A 4= 1.68915e-06 A 6=-1.66585e-09 A 8=-1.15871e-10 A10= 9.95219e-13 A12=-1.82759e-15 Various data Focal length 44.29 F-number 1.22 Half-angle (°): 24.54 Image height 20.22 Lens length 56.19 Optical total length 80.46 BF 24.26 Single lens data Lens starting plane, focal length 1 1 48.89 2 2 -84.57 3 4 54.81 4 6 -36.54 5 9 -15.87 6 10 19.21 7 12 -2104.06 8 14 48.76 9 16 131.28

[0067] [Numerical Example 3] Unit: mm Surface data Face number rd nd vd Effective diameter 1 57.628 5.62 1.91082 35.3 37.87 2 -239.077 1.45 1.68893 31.1 37.32 3 107.380 0.20 35.86 4 22.691 6.98 1.95375 32.3 33.29 5 32.201 0.40 29.49 6 34.885 1.25 1.79631 22.6 29.39 7 15.706 8.98 24.81 8 (aperture) ∞ 5.57 24.00 9 -22.443 1.00 1.84666 23.9 23.37 10 29.910 8.50 1.95375 32.3 26.29 11 -37.452 0.60 27.21 12* -53.948 3.00 1.53504 55.7 27.05 13* -64.454 0.60 28.62 14 168.233 5.25 1.83481 42.7 32.88 15 -52.953 2.00 33.81 16 53.536 4.03 1.69680 55.5 37.51 17 119.921 22.93 37.39 18 ∞ 2.00 1.51633 64.1 50.00 19 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4=-4.53352e-06 A 6= 5.92268e-08 A 8=-6.00072e-10 A10= 2.55427e-12 A12=-3.91981e-15 Page 13 K = 0.00000e+00 A 4=-7.43691e-07 A 6= 3.86827e-08 A 8=-3.52492e-10 A10= 1.37587e-12 A12=-1.80871e-15 Various data Focal length 46.35 F-number 1.22 Half-angle (°): 23.54 Image height 20.19 Lens length: 55.43 Optical total length 80.48 BF 25.05 Single lens data Lens starting plane, focal length 1 1 51.45 2 2 -107.37 3 4 59.32 4 6 -36.94 5 9 -15.01 6 10 18.58 7 12 -686.97 8 14 48.77 9 16 135.41

[0068] [Numerical Example 4] Unit: mm Surface data Face number rd nd vd Effective diameter 1 56.901 5.60 1.91082 35.3 38.71 2 -330.330 1.45 1.69895 30.1 38.15 3 102.117 0.20 36.69 4 22.155 6.90 1.95375 32.3 33.96 5 39.483 0.23 31.24 6 41.742 1.25 1.84666 23.9 31.19 7 15.600 9.62 25.38 8 (aperture) ∞ 5.59 24.47 9 -22.712 1.00 1.84666 23.9 23.82 10 34.944 7.30 1.95375 32.3 26.62 11 -42.615 2.35 27.40 12* 241.579 6.50 1.85400 40.4 28.86 13* -45.367 2.00 31.11 14 53.028 3.13 1.67790 55.3 35.40 15 127.097 23.51 35.42 16 ∞ 2.00 1.51633 64.1 50.00 17 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4=-2.00913e-06 A 6= 7.10693e-09 A 8=-4.73193e-11 A10= 5.42810e-15 Page 13 K = 0.00000e+00 A 4= 8.96474e-07 A 6=-6.93112e-09 A 8= 2.68096e-11 A10=-1.15923e-13 Various data Focal length 47.38 F-number 1.22 Half-angle (°): 23.22 Image height 20.33 Lens length: 53.13 Optical total length 78.76 BF 25.63 Single lens data Lens starting plane, focal length 1 1 53.66 2 2 -111.45 3 4 44.31 4 6 -30.08 5 9 -16.13 6 10 21.10 7 12 45.20 8 14 131.97

[0069] [Numerical Example 5] Unit: mm Surface data Face number rd nd vd Effective diameter 1 58.148 6.61 1.91082 35.3 37.87 2 -110.059 1.45 1.71736 29.5 37.27 3 82.486 0.20 35.27 4 22.853 7.40 1.85150 40.8 33.20 5 28.437 1.25 1.62200 30.7 28.76 6 15.412 9.30 24.89 7 (aperture) ∞ 5.59 23.99 8 -22.365 1.00 1.69895 30.1 23.30 9 30.359 10.37 1.78800 47.4 25.59 10 -28.352 0.69 26.67 11 -25.595 2.00 1.84666 23.8 26.77 12 -47.819 0.60 30.45 13* 172.444 7.34 1.89190 37.1 36.48 14* -40.805 2.00 37.82 15 60.400 4.05 1.69680 55.5 40.95 16 127.598 23.46 40.70 17 ∞ 2.00 1.51633 64.1 50.00 18 ∞ 0.80 50.00 Image plane ∞ Aspherical data Page 13 K = 0.00000e+00 A 4=-1.63300e-06 A 6=-1.61694e-09 A 8= 4.20250e-12 A10=-1.58345e-14 Page 14 K = 0.00000e+00 A 4= 1.67366e-06 A 6=-6.33745e-09 A 8= 2.24169e-11 A10=-3.92604e-14 Various data Focal length 46.35 F-number 1.22 Half-angle (°): 23.97 Image height 20.61 Lens length: 59.85 Optical total length 85.43 BF 25.58 Single lens data Lens starting plane, focal length 1 1 42.57 2 2 -65.52 3 4 84.92 4 5 -56.17 5 8 -18.28 6 9 20.18 7 11 -67.85 8 13 37.61 9 15 160.62

[0070] [Numerical Example 6] Unit: mm Surface data Face number rd nd vd Effective diameter 1 37.853 5.58 1.95375 32.3 39.62 2 108.395 1.45 1.76182 26.5 38.64 3 36.973 2.31 36.01 4 64.290 2.65 1.95375 32.3 35.96 5 141.129 0.25 35.48 6 21.998 4.97 1.95375 32.3 32.12 7 34.938 0.61 30.32 8 40.558 1.25 1.84666 23.9 30.22 9 15.887 9.03 25.08 10 (aperture) ∞ 5.92 24.28 11 -22.320 1.00 1.84666 23.9 23.58 12 32.253 7.87 1.95375 32.3 26.56 13 -39.332 0.86 27.40 14* -51.734 3.00 1.53504 55.7 27.33 15* -53.909 1.14 27.95 16 145.068 5.78 1.83481 42.7 33.64 17 -50.367 2.00 34.57 18 51.662 2.93 1.69680 55.5 37.83 19 92.767 23.90 37.69 20 ∞ 2.00 1.51633 64.1 50.00 21 ∞ 0.80 50.00 Image plane ∞ Aspherical data Page 14 K = 0.00000e+00 A 4=-2.83051e-06 A 6= 8.02748e-09 A 8=-2.06031e-10 A10= 1.26748e-12 A12=-2.35419e-15 Page 15 K = 0.00000e+00 A 4= 1.61914e-06 A 6=-1.45666e-08 A 8= 6.68526e-11 A10=-6.09716e-14 A12= 4.71218e-17 Various data Focal length 48.50 F-number 1.22 Half-angle (°): 22.47 Image height 20.06 Lens length 58.61 Optical total length 84.63 BF 26.02 Single lens data Lens starting plane, focal length 1 1 58.72 2 2 -74.31 3 4 121.75 4 6 52.44 5 8 -31.58 6 11 -15.45 7 12 19.63 8 14 -4616.58 9 16 45.40 10 18 162.57

[0071] [Numerical Example 7] Unit: mm Surface data Face number rd nd vd Effective diameter 1 59.415 5.61 1.91082 35.3 37.87 2 -235.281 1.45 1.68893 31.1 37.31 3 129.550 0.20 35.99 4 22.960 7.07 1.95375 32.3 33.25 5 34.041 0.35 29.45 6 36.705 1.25 1.84666 23.9 29.36 7 16.000 8.73 24.80 8 (aperture) ∞ 5.65 24.00 9 -22.636 1.00 1.84666 23.9 23.32 10 29.783 9.39 1.95375 32.3 26.17 11 -36.629 0.60 27.31 12* -53.913 3.00 1.53504 55.7 27.08 13* -55.548 0.60 29.11 14 255.198 4.84 1.83481 42.7 33.09 15 -55.184 2.00 34.00 16 -314.211 1.50 1.96300 24.1 36.02 17 150.629 0.50 36.96 18 53.202 5.78 1.91082 35.3 39.97 19 -2603.192 21.91 39.99 20 ∞ 2.00 1.51633 64.1 50.00 21 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4= 7.84525e-07 A 6= 1.49776e-10 A 8=-2.82568e-10 A10= 1.72724e-12 A12=-3.04733e-15 Page 13 K = 0.00000e+00 A 4= 2.89958e-06 A 6= 4.68979e-09 A 8=-1.95912e-10 A10= 1.04036e-12 A12=-1.52350e-15 Various data Focal length 46.35 F-number 1.22 Half-angle (°): 23.48 Image height 20.14 Lens length: 59.53 Optical total length 83.56 BF 24.03 Single lens data Lens starting plane, focal length 1 1 52.56 2 2 -121.07 3 4 56.38 4 6 -34.46 5 9 -15.06 6 10 18.50 7 12 -9494.40 8 14 54.74 9 16 -105.56 10 18 57.30

[0072] [Numerical Example 8] Unit: mm Surface data Face number rd nd vd Effective diameter 1 47.732 7.00 1.91082 35.3 40.44 2 -1801.946 1.55 1.67270 32.1 39.40 3 93.743 0.20 37.61 4 23.371 6.97 2.00100 29.1 34.31 5 44.286 0.18 31.37 6 46.338 1.25 1.92286 20.9 31.31 7 15.992 9.26 25.34 8 (aperture) ∞ 5.21 24.21 9 -25.289 1.00 1.92286 20.9 23.33 10 33.884 6.92 2.00069 25.5 25.27 11 -41.471 1.51 25.90 12* -58.916 3.00 1.53504 55.7 25.63 13* -68.394 0.85 27.36 14 112.733 7.00 1.83481 42.7 32.75 15 -52.131 2.00 34.31 16 64.710 3.67 1.65160 58.5 37.44 17 133.784 20.74 37.43 18 ∞ 2.00 1.51633 64.1 50.00 19 ∞ 0.80 50.00 Image plane ∞ Aspherical data Side 12 K = 0.00000e+00 A 4=-7.27810e-06 A 6= 1.02478e-07 A 8=-1.13696e-09 A10= 5.89581e-12 A12=-1.12642e-14 Page 13 K = 0.00000e+00 A 4=-1.05724e-06 A 6= 2.61774e-08 A 8=-2.11056e-10 A10= 8.70223e-13 A12=-1.17242e-15 Various data Focal length 49.50 F-number 1.22 Half-angle (°): 22.67 Image height 20.68 Lens length 57.57 Optical total length 80.43 BF 22.86 Single lens data Lens starting plane, focal length 1 1 51.15 2 2 -132.42 3 4 42.37 4 6 -26.99 5 9 -15.57 6 10 19.53 7 12 -893.11 8 14 43.54 9 16 188.39

[0073] [Numerical Example 9] Unit: mm Surface data Face number rd nd vd Effective diameter 1 53.036 7.17 1.95375 32.3 38.71 2 -114.083 1.45 1.72825 28.5 37.99 3 67.150 0.20 35.40 4 25.418 6.50 1.95375 32.3 33.62 5 48.048 0.50 30.88 6 56.446 1.25 1.78470 26.3 30.76 7 17.349 8.55 25.90 8 (aperture) ∞ 5.59 25.28 9 -26.285 1.00 1.68893 31.1 24.72 10 25.406 10.60 1.85150 40.8 27.11 11 -28.163 0.83 27.57 12 -24.955 2.00 1.72825 28.5 27.26 13 -81.883 0.76 28.05 14* -6479.785 3.00 1.53504 55.7 28.07 15* -554.987 0.71 31.30 16 239.455 7.70 1.77250 49.6 35.26 17 -36.092 2.00 36.63 18 95.816 3.61 1.77250 49.6 39.41 19 304.263 24.59 39.38 20 ∞ 2.00 1.51633 64.1 50.00 21 ∞ 0.80 50.00 Image plane ∞ Aspherical data Page 14 K = 0.00000e+00 A 4=-2.85186e-05 A 6= 4.80836e-09 A 8=-1.14332e-10 A10= 4.01236e-13 Page 15 K = 0.00000e+00 A 4=-1.58615e-05 A 6=-8.00676e-09 A 8= 3.11911e-11 A10= 8.90237e-14 Various data Focal length 47.38 F-number 1.22 Half angle of view (°) 23.55 Image height 20.65 Overall lens length 63.43 Overall optical length 90.13 BF 26.71 Single lens data Lens starting surface focal length 1 1 38.77 2 2 -57.85 3 4 49.62 4 6 -32.38 5 9 -18.61 6 10 17.26 7 12 -50.03 8 14 1134.25 9 16 41.10 10 18 179.69

[0074] [Table 1]

[0075] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 using the optical system of the present invention as an imaging optical system will be described with reference to FIG. 19. In FIG. 19, 13 is a camera body, and 11 is an imaging optical system composed of any of the optical systems described in Examples 1 to 9. 12 is a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body 13 and receives the optical image formed by the imaging optical system 11 and performs photoelectric conversion. The camera body 13 may be a so-called single-lens reflex camera having a quick return mirror, or a so-called mirrorless camera not having a quick return mirror.

[0076] In addition, it is preferable that the imaging device 10 has a function of correcting distortion aberration generated in the imaging optical system 11 by software. With this function, it is possible to achieve both miniaturization of the optical system and correction of the distortion aberration remaining in the captured image. By applying the optical system of the present invention to an imaging device such as a digital still camera in this way, an imaging device with a small lens can be obtained.

[0077] [Lens Device] FIG. 20 is a schematic view of the lens device 20 of the present invention. The lens device 20 is a so-called interchangeable lens that is detachably attached to a camera body (not shown). The lens device 20 has a photographing optical system 21 that is the same as any of the optical systems of Examples 1 to 9. The lens device 20 also has focus operation means 22 and operation means 23 for changing the photographing mode.

[0078] When the user operates the focus operation means 22, the arrangement of the lens group of the photographing optical system 21 changes mechanically or electrically, and the focal position changes. Further, when the user operates the operation means 23, the arrangement of the lens group of the photographing optical system 21 may be changed for purposes other than focusing. For example, the arrangement of the lens group of the photographing optical system 21 may be changed mechanically or electrically in accordance with the operation of the operation means 23, and the aberration of the photographing optical system 21 may be changed. At this time, it is preferable that the focus position does not substantially change.

[0079] The disclosure of this embodiment includes the following configurations. (Configuration 1) An optical system including a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power, arranged in order from the object side to the image side, The first lens group is composed of a first subgroup and a second subgroup arranged in order from the object side to the image side, The first subgroup has a positive first lens and a negative second lens arranged in order from the object side to the image side, The aforementioned second subgroup consists of a positive third lens and a negative fourth lens, arranged in order from the object side to the image side. The second lens group comprises a negative fifth lens, a positive sixth lens, and two or more lenses arranged in order from the object side to the image side. The total number of lenses arranged in the optical system is 10 or less. In the infinity focus state, the air distance between the first lens group and the second lens group along the optical axis is greater than the sum of the air distances between each lens included in the second lens group. When the total focal length of the optical system is f, the Petzval sum with respect to the second lens is PL2, and the average value of the Abbe numbers of the fourth and fifth lenses is vdL45, -1.00 ≤ f × ​​PL2 ≤ -0.15 15.00 ≤ vdL45 ≤ 32.00 An optical system characterized by satisfying the following conditions. (Configuration 2) An optical system comprising a first lens group having positive refractive power, an aperture diaphragm, and a second lens group having positive refractive power, arranged in order from the object side to the image side, The aforementioned first lens group consists of a first subgroup and a second subgroup, arranged in order from the object side to the image side. The first subgroup comprises a positive first lens and a negative second lens, arranged in order from the object side to the image side. The aforementioned second subgroup consists of a positive third lens and a negative fourth lens, arranged in order from the object side to the image side. The second lens group comprises a negative fifth lens, a positive sixth lens, and two or more lenses arranged in order from the object side to the image side. The total number of lenses arranged in the optical system is 10 or less. When the total focal length of the optical system is f, the Petzval sum with respect to the second lens is PL2, and the average value of the Abbe numbers of the fourth and fifth lenses is vdL45, -0.61 ≤ f × ​​PL² ≤ -0.15 15.00 ≤ vdL45 ≤ 27.50 An optical system characterized by satisfying the following conditions. (Composition 3) When the refractive index of the fourth lens is NdL4, the refractive index of the fifth lens is NdL5, the radius of curvature of the image-side lens surface of the fourth lens is R2L4, the radius of curvature of the object-side lens surface of the fifth lens is R1L5, and the focal length of the air lens located between the first lens group and the second lens group is fSP, -0.28≦fSP / f≦-0.12 however, fSP=1 / [(1-NdL4) / R2L4-(1-NdL5) / R1L5 +(1-NdL4)×(1-NdL5)×TSP / (R2L4×R1L5)] The optical system according to configuration 1 or 2, characterized by satisfying the following conditions. (Composition 4) In the state of infinity focus, when the distance along the optical axis between the image-side lens surface of the first lens group and the object-side lens surface of the second lens group is TSP, and the distance along the optical axis between the object-side lens surface of the optical system and the image-side lens surface is TD, 0.18 ≤ TSP / TD ≤ 0.33 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditions. (Composition 5) In the state of infinity focus, when TB1 is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image of the first lens group, and TB2 is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image of the second lens group, 0.72 ≤ (TB1 + TB2) / f ≤ 1.12 An optical system according to any one of configurations 1 to 4, characterized by satisfying the following conditions. (Composition 6) When the back focus of the optical system is Sk, 0.42 ≤ Sk / f ≤ 0.60 An optical system according to any one of configurations 1 to 5, characterized by satisfying the following conditions. (Composition 7) When NdLp is the average refractive index of all positive lenses, 1.77 ≤ NdLp ≤ 1.97 The optical system according to any one of Configurations 1 to 6, characterized by satisfying the following conditions. (Configuration 8) When the Petzval sum for the second lens, the fourth lens, and the fifth lens is PL245, the refractive index of the second lens is NdL2, the refractive index of the fourth lens is NdL4, the refractive index of the fifth lens is NdL5, the focal length of the second lens is fL2, the focal length of the fourth lens is fL4, and the focal length of the fifth lens is fL5, -3.10 ≤ f × PL245 ≤ -2.21 However, PL245 = 1 / (NdL2 × fL2) + 1 / (NdL4 × fL4) + 1 / (NdL5 × fL5) The optical system according to any one of Configurations 1 to 7, characterized by satisfying the following conditions. (Configuration 9) The second lens group consists of a second a lens group and a second b lens group, arranged in order from the object side to the image side. When focusing from an infinite object to a close object, the first lens group, the aperture stop, and the second a lens group move together on the optical axis, and the second b lens group remains stationary with respect to the image plane for focusing. The optical system according to any one of Configurations 1 to 8, characterized by this. (Configuration 10) When the combined focal length of the first lens group and the second a lens group is fB1B2a and the focal length of the second b lens group is fB2b, 0.23 ≤ fB1B2a / fB2b ≤ 0.56 The optical system according to Configuration 9, characterized by satisfying the following conditions. (Configuration 11) When the value of the shape factor of the second lens is SFL2, the radius of curvature of the object side surface of the second lens is R1L2, and the radius of curvature of the image side surface of the second lens is R2L2, -2.80 ≤ SFL2 ≤ 0.62 However, SFL2 = (R2L2 + R1L2) / (R2L2 - R1L2) The optical system according to any one of Configurations 1 to 10, characterized by satisfying the following conditions. (Configuration 12) When the shape factor of the final lens positioned closest to the image is SFLr, the radius of curvature of the object-side lens surface of the final lens is R1Lr, and the radius of curvature of the image-side lens surface of the final lens is R2Lr, -0.08 ≤ SFLr ≤ 4.55 However, SFLr = (R2Lr + R1Lr) / (R2Lr - R1Lr) An optical system according to any one of configurations 1 to 11, characterized by satisfying the following conditions. (Composition 13) When TL is the distance along the optical axis from the lens surface closest to the object in the aforementioned optical system to the image plane, 1.50 ≤ TL / f ≤ 2.02 An optical system according to any one of configurations 1 to 12, characterized by satisfying the following conditions. (Composition 14) When the focal length of the first lens group is fB1 and the focal length of the second lens group is fB2, 2.07 ≤ fB1 / fB2 ≤ 4.93 An optical system according to any one of configurations 1 to 13, characterized by satisfying the following conditions. (Composition 15) The optical system according to any one of configurations 1 to 14, characterized in that the first lens and the second lens are joined together to form a cemented lens. (Composition 16) The optical system according to configuration 15, characterized in that the cemented lens has a convex shape on the object-side surface and a meniscus shape having positive refractive power. (Composition 17) When the combined focal length of the first lens and the second lens is fL1L2, 0.31 ≤ fL1L2 / fB1 ≤ 1.98 An optical system according to any one of configurations 1 to 16, characterized by satisfying the following conditions. (Composition 18) The optical system according to any one of configurations 1 to 17, characterized in that the fifth lens and the sixth lens are joined together to form a cemented lens. (Composition 19) When the focal length of the fifth lens is fL5 and the focal length of the sixth lens is fL6, -1.20 ≤ fL5 / fL6 ≤ -0.64 An optical system according to any one of configurations 1 to 18, characterized by satisfying the following conditions. (Composition 20) The optical system according to any one of configurations 1 to 19, characterized in that the second lens group has two or more positive lenses on the image side of the sixth lens. (Composition 21) When the optical system is in focus at infinity, and the maximum half-angle of view (°) obtained from the paraxial calculation of the optical system is denoted as ω, 18.00≦ω≦32.00 An optical system according to any one of configurations 1 to 20, characterized by satisfying the following conditions. (Composition 22) When the F-number of the optical system is denoted as Fno, Fno ≤ 2.06 An optical system according to any one of configurations 1 to 21, characterized by satisfying the following conditions. (Composition 23) When the maximum value of the distortion aberration in the central projection method of the optical system is Di, -8.47 ≤ Di ≤ -3.27 An optical system according to any one of configurations 1 to 22, characterized by satisfying the following conditions. (Composition 24) An optical system comprising a first lens group having positive refractive power, an aperture diaphragm, and a second lens group having positive refractive power, arranged in order from the object side to the image side, An optical system characterized in that, in the state of infinity focus, the air distance on the optical axis between the first lens group and the second lens group is greater than the sum of the air distances between each lens included in the second lens group. (Composition 25) An imaging device characterized by having an optical system described in any of configurations 1 to 24, and an image sensor that captures an image formed by the optical system.

[0080] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various combinations, modifications, and changes are possible within the scope of its essence. [Explanation of Symbols]

[0081] B1 First lens group B2 Second lens group L1 First Lens L2 Second Lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens SP aperture diaphragm

Claims

1. An optical system comprising a first lens group having positive refractive power, an aperture diaphragm, and a second lens group having positive refractive power, arranged in order from the object side to the image side, The aforementioned first lens group consists of a first subgroup and a second subgroup arranged in order from the object side to the image side. The first subgroup comprises a positive first lens and a negative second lens, arranged in order from the object side to the image side. The aforementioned second subgroup consists of a positive third lens and a negative fourth lens, arranged in order from the object side to the image side. The second lens group comprises a negative fifth lens, a positive sixth lens, and two or more lenses arranged in order from the object side to the image side. The total number of lenses arranged in the optical system is 10 or less. In the infinity focus state, the air distance between the first lens group and the second lens group along the optical axis is greater than the sum of the air distances between each lens included in the second lens group. When the total focal length of the optical system is f, the Petzval sum with respect to the second lens is PL2, and the average value of the Abbe numbers of the fourth and fifth lenses is vdL45, -1.00 ≤ f × ​​PL² ≤ -0.15 15.00 ≤ vdL45 ≤ 32.00 An optical system characterized by satisfying the following conditions.

2. An optical system comprising a first lens group having positive refractive power, an aperture diaphragm, and a second lens group having positive refractive power, arranged in order from the object side to the image side, The aforementioned first lens group consists of a first subgroup and a second subgroup arranged in order from the object side to the image side. The first subgroup comprises a positive first lens and a negative second lens, arranged in order from the object side to the image side. The aforementioned second subgroup consists of a positive third lens and a negative fourth lens, arranged in order from the object side to the image side. The second lens group comprises a negative fifth lens, a positive sixth lens, and two or more lenses arranged in order from the object side to the image side. The total number of lenses arranged in the optical system is 10 or less. When the total focal length of the optical system is f, the Petzval sum with respect to the second lens is PL2, and the average value of the Abbe numbers of the fourth and fifth lenses is vdL45, -0.61 ≤ f × ​​PL² ≤ -0.15 15.00 ≤ vdL45 ≤ 27.50 An optical system characterized by satisfying the following conditions.

3. When the refractive index of the fourth lens is NdL4, the refractive index of the fifth lens is NdL5, the radius of curvature of the image-side lens surface of the fourth lens is R2L4, the radius of curvature of the object-side lens surface of the fifth lens is R1L5, and the focal length of the air lens located between the first lens group and the second lens group is fSP, -0.28 ≤ fSP / f ≤ -0.12 however, fSP=1 / [(1-NdL4) / R2L4-(1-NdL5) / R1L5 +(1-NdL4)×(1-NdL5)×TSP / (R2L4×R1L5)] The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. In the state of infinity focus, when the distance along the optical axis between the image-side lens surface of the first lens group and the object-side lens surface of the second lens group is TSP, and the distance along the optical axis between the object-side lens surface of the optical system and the image-side lens surface is TD, 0.18 ≤ TSP / TD ≤ 0.33 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. In the state of infinity focus, when TB1 is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image of the first lens group, and TB2 is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image of the second lens group, 0.72≦(TB1+TB2) / f≦1.12 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. When the back focus of the optical system is Sk, then 0.42 ≤ Sk / f ≤ 0.60 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When NdLp is the average value of the refractive index of all positive lenses, 1.77 ≤ NdLp ≤ 1.97 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When the Petzval sum for the second lens, the fourth lens, and the fifth lens is PL245, the refractive index of the second lens is NdL2, the refractive index of the fourth lens is NdL4, the refractive index of the fifth lens is NdL5, the focal length of the second lens is fL2, the focal length of the fourth lens is fL4, and the focal length of the fifth lens is fL5, -3.10 ≤ f × ​​PL245 ≤ -2.21 however, PL245=1 / (NdL2×fL2)+1 / (NdL4×fL4) +1 / (NdL5 × fL5) The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. The second lens group consists of a second a lens group and a second b lens group, arranged in order from the object side to the image side. The optical system according to claim 1, characterized in that when focusing from an object at infinity to an object at a close distance, the first lens group, the aperture diaphragm, and the second a lens group move together along the optical axis, and the second b lens group remains stationary with respect to the image plane for focusing.

10. When the combined focal length of the first lens group and the second a lens group is fB1B2a, and the focal length of the second b lens group is fB2b, 0.23 ≤ fB1B2a / fB2b ≤ 0.56 The optical system according to claim 9, characterized in that it satisfies the following conditions.

11. When the shape factor of the second lens is SFL2, the radius of curvature of the object side of the second lens is R1L2, and the radius of curvature of the image side of the second lens is R2L2, -2.80 ≤ SFL2 ≤ 0.62 However, SFL2 = (R2L2 + R1L2) / (R2L2 - R1L2) The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. When the shape factor of the final lens positioned closest to the image is SFLr, the radius of curvature of the object-side lens surface of the final lens is R1Lr, and the radius of curvature of the image-side lens surface of the final lens is R2Lr, -0.08 ≤ SFLr ≤ 4.55 However, SFLr = (R2Lr + R1Lr) / (R2Lr - R1Lr) The optical system according to claim 1, characterized in that it satisfies the following conditions.

13. When TL is the distance along the optical axis from the lens surface closest to the object in the aforementioned optical system to the image plane, 1.50 ≤ TL / f ≤ 2.02 The optical system according to claim 1, characterized in that it satisfies the following conditions.

14. When the focal length of the first lens group is fB1 and the focal length of the second lens group is fB2, 2.07 ≤ fB1 / fB2 ≤ 4.93 The optical system according to claim 1, characterized in that it satisfies the following conditions.

15. The optical system according to claim 1, characterized in that the first lens and the second lens are joined together to form a cemented lens.

16. The optical system according to claim 15, characterized in that the bonded lens has a convex shape on the object-side surface and a meniscus shape having positive refractive power.

17. When the combined focal length of the first lens and the second lens is fL1L2, 0.31 ≤ fL1L2 / fB1 ≤ 1.98 The optical system according to claim 1, characterized in that it satisfies the following conditions.

18. The optical system according to claim 1, characterized in that the fifth lens and the sixth lens are joined together to form a cemented lens.

19. When the focal length of the fifth lens is fL5 and the focal length of the sixth lens is fL6, -1.20 ≤ fL5 / fL6 ≤ -0.64 The optical system according to claim 1, characterized in that it satisfies the following conditions.

20. The optical system according to claim 1, characterized in that the second lens group has two or more positive lenses on the image side of the sixth lens.

21. When the optical system is in focus at infinity, and the maximum half-angle of view (°) obtained from the paraxial calculation of the optical system is denoted as ω, 18.00 ≤ ω ≤ 32.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

22. When the F-number of the optical system is denoted as Fno, Fno ≤ 2.06 The optical system according to claim 1, characterized in that it satisfies the following conditions.

23. When Di is the maximum value of the distortion aberration in the central projection method of the optical system, -8.47 ≤ Di ≤ -3.27 The optical system according to claim 1, characterized in that it satisfies the following conditions.

24. An optical system comprising a first lens group having positive refractive power, an aperture diaphragm, and a second lens group having positive refractive power, arranged in order from the object side to the image side, An optical system characterized in that, in the state of infinity focus, the air distance on the optical axes of the first lens group and the second lens group is greater than the sum of the air distances between each lens included in the second lens group.

25. An imaging device characterized by having an optical system according to any one of claims 1 to 24 and an image sensor for capturing an image formed by the optical system.

Images