Optical Department

Abstract

To provide an optical system that reduces variations in image magnification while correcting various aberrations during image formation by appropriately distributing refractive powers.SOLUTION: An optical system includes, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power. When adjusting focus from a long distance to a short distance, at least the second lens group G2 moves to the object side. The second lens group G2 includes, in order from the object side, a front subgroup G2A and a rear subgroup G2B of the second lens group G2. The front subgroup G2A and the rear subgroup G2B of the second lens group G2 each include at least one lens with positive refractive power and at least one lens with negative refractive power, satisfying predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 The present invention relates to an optical system suitable for a lens used in an imaging device such as a still camera, a video camera, or a projection device, and relates to an optical system capable of effectively correcting image magnification fluctuations. 【Background Art】 【0002】 In recent years, with the improvement of the video function of digital cameras and the reduction in price of video devices such as video cameras, it has become necessary to suppress fluctuations in the angle of view accompanying changes in the focus position for optical systems used in imaging devices and the like. 【0003】 In conventionally proposed optical systems, there has been a proposal to correct fluctuations in aberrations by moving a group composed of a plurality of lenses at the time of focusing. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 International Publication No. 2019 / 73744 【Patent Document 2】 International Publication No. 2021 / 199923 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, the above-described conventional technologies have had the following problems. For example, in Patent Document 1, an optical system that corrects fluctuations in aberrations by moving a group composed of a plurality of lenses at the time of focusing has been proposed. However, the optical system described in Patent Document 1 has a large image magnification fluctuation and is not suitable for shooting videos. Patent Document 2 also has the same problem. 【0006】 This invention has been made in view of these circumstances, and aims to provide an optical system that corrects various aberrations during imaging and suppresses fluctuations in image magnification by appropriately arranging refractive power. [Means for solving the problem] 【0007】 To achieve the above objective, the optical system according to the present invention has, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, and when focusing from a long distance to a close distance, at least the second lens group G2 moves toward the object side. The spacing between the lenses in front of and behind the second lens group G2 changes, while the lens groups other than the second lens group G2 are fixed in position relative to the image plane. The second lens group G2 is composed of the front lens group G2A and the rear lens group G2B in order from the object side, and the front lens group G2A and the rear lens group G2B each have one or more lenses with positive refractive power and one or more lenses with negative refractive power, and the following condition (1) , (2) and (3-1) It is characterized by satisfying the following conditions. (1)(1 / F1-1 / F3)×F2 > 0.60 (2) DAB / D2 > 0.050 (3-1)nd2Bp > 1.85 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces located between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: Distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: Distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. nd2Bp: The average refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. Furthermore, the optical system according to the present invention has, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, and when focusing from a long distance to a short distance, at least the second lens group G2 moves toward the object, the distance between the front and rear of the second lens group G2 changes, the positions of the groups other than the second lens group G2 are fixed with respect to the image plane, the second lens group G2 is composed of a front lens group G2A and a rear lens group G2B in order from the object side, the front lens group G2A and the rear lens group G2B each have one or more lenses with positive refractive power and one or more lenses with negative refractive power, and is characterized in that it satisfies the following conditional equations (1), (2) and (5). (1)(1 / F1-1 / F3)×F2 > 0.60 (2) DAB / D2 > 0.050 (5)vd2Ap > 60.00 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces located between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: Distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: Distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. vd2Ap: The average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group. Furthermore, the optical system according to the present invention has, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, and when focusing from a long distance to a short distance, at least the second lens group G2 moves toward the object, the distance between the front and rear of the second lens group G2 changes, the positions of the groups other than the second lens group G2 are fixed with respect to the image plane, the second lens group G2 is composed of a front lens group G2A and a rear lens group G2B in order from the object side, the front lens group G2A and the rear lens group G2B each have one or more lenses with positive refractive power and one or more lenses with negative refractive power, and is characterized in that it satisfies the following conditional equations (1), (2), (3) and (6-1). (1)(1 / F1-1 / F3)×F2 > 0.60 (2) DAB / D2 > 0.050 (3)nd2Bp > 1.80 (6-1)vd2An ≤ 29.74 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces located between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: Distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: Distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. nd2Bp: The average refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. 【0008】 <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ nd2Bp: The average refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. nd2Bn: The average refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. Furthermore, the optical system according to the present invention is preferably characterized by satisfying the following conditional equations (4) and (5). (4)nd2Bn < 1.75 (5)vd2Ap > 60.00 however, nd2Bn: The average refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2Ap: The average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group. 【0009】 Furthermore, the optical system according to the present invention is preferably characterized in that the rear group G2B of the second lens group has an aspherical surface such that the positive refractive power weakens, the negative refractive power strengthens, or the refractive power changes from positive to negative in the vicinity of the effective ray diameter with respect to the optical axis center. 【0010】 Furthermore, the optical system according to the present invention is preferably characterized in that the aperture diaphragm is arranged within the first lens group G1 or adjacent to it on the image plane side. [Effects of the Invention] 【0011】 According to the optical system of the present invention, by appropriately arranging the refractive power, it is possible to provide an optical system that corrects various aberrations during imaging and suppresses fluctuations in image magnification. [Brief explanation of the drawing] 【0012】 [Figure 1] This is a diagram of the lens configuration of the optical system of Example 1 at infinity. [Figure 2] This is a longitudinal aberration diagram of the optical system of Example 1 at infinity. [Figure 3] This is a longitudinal aberration diagram of the optical system of Example 1 at a shooting distance of 275 mm. [Figure 4] This is a diagram of the lateral aberration of the optical system of Example 1 at infinity. [Figure 5] This is a lateral aberration diagram of the optical system of Example 1 at a shooting distance of 275 mm. [Figure 6]This is a diagram of the lens configuration of the optical system in Example 2 at infinity. [Figure 7] This is a longitudinal aberration diagram of the optical system of Example 2 at infinity. [Figure 8] This is a longitudinal aberration diagram of the optical system of Example 2 at a shooting distance of 395 mm. [Figure 9] This is a diagram of the lateral aberration of the optical system of Example 2 at infinity. [Figure 10] This is a lateral aberration diagram of the optical system of Example 2 at a shooting distance of 395 mm. [Figure 11] This is a diagram of the lens configuration of the optical system of Example 3 at infinity. [Figure 12] This is a longitudinal aberration diagram of the optical system of Example 3 at infinity. [Figure 13] This is a longitudinal aberration diagram of the optical system of Example 3 at a shooting distance of 276.15 mm. [Figure 14] This is a diagram of the lateral aberration of the optical system of Example 3 at infinity. [Figure 15] This is a lateral aberration diagram of the optical system of Example 3 at a shooting distance of 276.15 mm. [Figure 16] This is a diagram of the lens configuration of the optical system of Example 4 at infinity. [Figure 17] This is a longitudinal aberration diagram of the optical system of Example 4 at infinity. [Figure 18] This is a longitudinal aberration diagram of the optical system of Example 4 at a shooting distance of 275 mm. [Figure 19] This is a diagram of the lateral aberration of the optical system of Example 4 at infinity. [Figure 20] This is a lateral aberration diagram of the optical system of Example 4 at a shooting distance of 275 mm. [Figure 21] This is a diagram of the lens configuration of the optical system of Example 5 at infinity. [Figure 22] This is a longitudinal aberration diagram of the optical system of Example 5 at infinity. [Figure 23] This is a longitudinal aberration diagram of the optical system of Example 5 at a shooting distance of 276.15 mm. [Figure 24] This is a diagram showing the transverse aberration of the optical system of Example 5 at infinity. [Figure 25] This is a lateral aberration diagram of the optical system of Example 5 at a shooting distance of 276.15 mm. [Figure 26] This is a diagram of the lens configuration of the optical system of Example 6 at infinity. [Figure 27] This is a longitudinal aberration diagram of the optical system of Example 6 at infinity. [Figure 28] This is a longitudinal aberration diagram of the optical system of Example 6 at a shooting distance of 275 mm. [Figure 29] This is a diagram showing the transverse aberration of the optical system of Example 6 at infinity. [Figure 30] This is a lateral aberration diagram of the optical system of Example 6 at a shooting distance of 275 mm. [Modes for carrying out the invention] 【0013】 The following describes in detail an embodiment of the optical system according to the present invention. Note that the following description of the embodiment illustrates an example of the optical system of the present invention, and the present invention is not limited to this embodiment without departing from its spirit. 【0014】 As can be seen from the lens configuration diagrams shown in Figures 1, 6, 11, 16, 21, and 26, the optical system of the present invention has, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, and is characterized in that at least the second lens group G2 moves toward the object when focusing from a long distance to a close distance. 【0015】 The present invention aims to provide an optical system that suppresses both image magnification fluctuations and aberration fluctuations during focusing, and it is important to appropriately select the arrangement of the groups that move during focusing. 【0016】 In particular, in inner-focus optical systems, a method of focusing is known to vary the position of the principal point of the entire optical system. However, when such a method is used, the distance from the optical axis to the point through which the off-axis principal rays pass varies greatly during focusing, causing a large variation in off-axis aberrations, especially distortion. When distortion changes, the image magnification changes, making it impossible to fix the angle of view at a constant level. 【0017】 Therefore, by arranging a first lens group G1 with positive refractive power and a second lens group G2 with positive refractive power in order from the object side, and moving at least the second lens group G2 toward the object side when focusing from a long distance to a short distance, and by adjusting the refractive power of each group to an appropriate range, it becomes possible to focus by changing the focal length of the optical system, thereby suppressing changes in the principal point position and suppressing changes in image magnification. 【0018】 Furthermore, the optical system of the present invention is characterized by satisfying the following conditions (1) and (2). (1)(1 / F1-1 / F3)×F2 > 0.60 (2) DAB / D2 > 0.050 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces located between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: Distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: Distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. 【0019】 Conditional equation (1) defines a preferred range for the change in the focal length of the optical system when focusing is achieved. 【0020】 By setting these conditions, the positive refractive power of the entire optical system increases as the second lens group G2 moves toward the object, resulting in a smaller change in the principal point position at focus. Consequently, the change in the distance from the optical axis to the position through which the off-axis principal rays pass is also reduced, making it possible to suppress fluctuations in image magnification. 【0021】 When the lower limit of condition (1) is exceeded, and the sum of the positive refractive power of the first lens group G1 and the negative refractive power of the lens group on the image side of the second lens group G2 becomes small, the change in the focal length of the optical system at focusing is insufficient, and the movement of the focus becomes dependent on the movement of the principal point, making it difficult to suppress fluctuations in image magnification. 【0022】 Furthermore, by setting the lower limit of condition (1) to 0.80, the effects of the present invention can be achieved more reliably. 【0023】 Conditional equation (2) defines a preferred range for the distance between the front group G2A and the rear group G2B of the second lens group and the surface closest to the object. 【0024】 By setting these conditions, it becomes possible to control the correction of different aberrations in each lens group, such that axial aberration is corrected in the front lens group G2A, where the distance between the marginal ray and the optical axis is relatively higher than that of the rear lens group G2B, and field curvature is mainly corrected in the rear lens group G2B, where the distance between the off-axis principal ray and the optical axis is relatively higher than that of the front lens group G2A. 【0025】 When the lower limit of condition (2) is exceeded, and the distance on the optical axis between the image-side surface of the front lens group G2A and the object-side surface of the rear lens group G2B becomes small, the distance of the off-axis principal rays from the optical axis increases in the front lens group G2A, or the distance of the marginal rays from the optical axis increases in the rear lens group G2B. As a result, it becomes difficult to correct axial chromatic aberration in the front lens group G2A while simultaneously correcting field curvature in the rear lens group G2B. 【0026】 Furthermore, by setting the lower limit of condition (2) to 0.100, the effects of the present invention can be achieved more reliably. 【0027】 Furthermore, it is desirable that the lens LA of the optical system of the present invention satisfies the following conditions (3), (4), (5), and (6). (3)nd2Bp > 1.80 (4)nd2Bn < 1.75 (5)vd2Ap > 60.00 (6) vd2An < 35.00 however, nd2Bp: The average refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. nd2Bn: Average refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2Ap: Average Abbe number of positive refractive power lenses included in the front group G2A of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. 【0028】 Conditional equation (3) specifies a preferred range for the average value of the refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. 【0029】 When the lower limit of condition (3) is exceeded and the average refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group becomes small, it becomes difficult to correct the field curvature. 【0030】 Also, set the lower limit of condition (3) to 1.85. The following condition (3-1) is satisfied. By doing so, the effects of the present invention can be achieved more reliably. 【0031】 Conditional equation (4) specifies a preferred range for the average value of the refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. 【0032】 When the upper limit of condition (4) is exceeded and the average refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group becomes large, it becomes difficult to correct the field curvature. 【0033】 Furthermore, by setting the upper limit of condition (4) to 1.70, the effects of the present invention can be achieved more reliably. 【0034】 Conditional equation (5) specifies a preferred range for the average value of the Abbe numbers of the positive refractive power lenses included in the front group G2A of the second lens group. 【0035】 When the lower limit of condition (5) is exceeded and the average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group becomes small, it becomes difficult to correct axial chromatic aberration. 【0036】 Furthermore, by setting the lower limit of condition (5) to 63.00, the effects of the present invention can be achieved more reliably. 【0037】 Conditional equation (6) specifies a preferred range for the average value of the Abbe numbers of lenses with negative refractive power included in the front group G2A of the second lens group. 【0038】 When the upper limit of condition (6) is exceeded and the average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group becomes large, it becomes difficult to correct axial chromatic aberration. 【0039】 Furthermore, by setting the upper limit of condition (6) to 33.00, the effects of the present invention can be achieved more reliably. Furthermore, by satisfying condition (6-1), where the upper limit of condition (6) is set to the corresponding value of 29.74 in Example 6, the effects of the present invention can be achieved more reliably. 【0040】 Furthermore, in the optical system of the present invention, it is desirable that the rear group G2B of the second lens group has an aspherical surface such that the positive refractive power weakens, the negative refractive power strengthens, or the refractive power changes from positive to negative in the peripheral area of ​​the effective ray diameter with respect to the optical axis center. 【0041】 By configuring the optical system of the present invention in this way, it becomes possible to effectively correct distortion aberration. 【0042】 Furthermore, in the optical system of the present invention, it is desirable that the aperture diaphragm is arranged within the first lens group G1, or adjacent to it on the image plane side. 【0043】 By configuring the optical system of the present invention in this way, it becomes possible to reduce the weight of the second lens group G2, which is the group that moves during focusing, while suppressing vignetting. 【0044】 The lens configurations, numerical examples, and corresponding values ​​for conditional expressions of each embodiment of the optical system of the present invention are described below. In the following description, the lens configurations are described in order from the object side to the image plane side. 【0045】 In the [surface data], the surface number is the number of the lens surface or aperture diaphragm counted from the object side, r is the radius of curvature of each lens surface, d is the spacing between each lens surface, nd is the refractive index for the d line (wavelength 587.56 nm), and vd is the Abbe number for the d line. 【0046】 The asterisk (*) next to the surface number indicates that the lens surface shape is aspherical. BF indicates the back focus, and the object surface distance indicates the distance from the subject to the first lens surface. 【0047】 The (diaphragm) next to the face number indicates that an aperture diaphragm is located at that position. The radius of curvature relative to the plane or aperture diaphragm is indicated with ∞ (infinity). 【0048】 The [Aspherical Data] section shows the values ​​of the coefficients that give the aspherical shape of the lens surface marked with an asterisk (*) in the [Surface Data] section. The shape of the aspherical surface is expressed by the following formula. In the following formula, y represents the displacement from the optical axis in the direction perpendicular to the optical axis, z represents the displacement (sag) in the direction of the optical axis from the intersection of the aspherical surface and the optical axis, r represents the radius of curvature of the reference sphere, and K represents the conic coefficient. The 4th, 6th, 8th, 10th, and 12th order aspherical coefficients are represented by A4, A6, A8, A10, and A12, respectively. 【0049】 TIFF0007873849000001.tif19147 【0050】 The [Various Data] section shows the values ​​for focal length, etc., for each focal length state or each shooting distance focus state. 【0051】 The [Variable Interval Data] section shows the variable interval and BF values ​​for each focal length state or each shooting distance focus state. 【0052】 The [Lens Group Data] shows the object-side face number for each lens group and the combined focal length of the entire group. 【0053】 Furthermore, in the aberration diagrams corresponding to each embodiment, d, g, and C represent the d line, g line, and C line, respectively, and △S and △M represent the sagittal image plane and meridional image plane, respectively. 【0054】 In addition, for all the specifications listed below, the units of focal length f, radius of curvature r, lens plane spacing d, and other lengths are millimeters (mm) unless otherwise specified. However, since equivalent optical performance can be obtained in both proportional magnification and proportional reduction in the optical system, this is not the only unit of measurement. [Examples] 【0055】 Figure 1 is a diagram of the lens configuration of the optical system of Example 1 at infinity. 【0056】 Example 1 consists 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. 【0057】 The first lens group G1 consists of, in order from the object side, a negative meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane, and a negative meniscus lens L9 with its convex surface facing the object. The lens surfaces on both sides of the negative meniscus lens L1 with its convex surface facing the object have a predetermined aspherical shape. An aperture diaphragm is positioned between the negative meniscus lens L8 with its convex surface facing the image plane and the negative meniscus lens L9 with its convex surface facing the object. 【0058】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, a biconcave lens L14, and a positive meniscus lens L15 with its convex surface facing the image plane side. The lens surfaces on both sides of the positive meniscus lens L15 with its convex surface facing the image plane side have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L10 and the biconcave lens L11 corresponds to the front group G2A of the second lens group in claim 1, and the positive meniscus lens L15 with its convex surface facing the image plane side corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object side when focusing from an object distance of infinity to a close distance. 【0059】 The third lens group G3 consists solely of a negative meniscus lens L16 with its convex surface facing the image plane. 【0060】 The specifications of the optical system according to Example 1 are shown below. Numerical Example 1 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1* 104.4625 2.9172 1.51633 64.06 2* 79.3939 0.5000 3 48.5008 1.4000 1.43700 95.10 4 21.6406 11.6812 5 -63.9370 1.2000 1.59270 35.45 6 133.3628 0.2684 7 78.6364 4.2917 2.00100 29.13 8 -134.2859 6.5845 9 -34.1778 1.2000 1.65412 39.68 10 31.0506 10.0000 1.59282 68.62 11 -46.0527 0.1500 12 58.0532 9.4131 2.00100 29.13 13 -38.4363 1.2000 1.85451 25.15 14 -146.3292 1.0000 15 (aperture) ∞ 1.0000 16 75.2553 1.2000 1.85451 25.15 17 39.1284 (d17) 18 29.5172 9.7714 1.55032 75.50 19 -27.4980 1.0000 1.85451 25.15 20 51.5833 4.8476 21 48.4938 5.5110 2.00100 29.13 22 -54.9615 0.1794 23 1419.4634 0.9000 1.61340 44.27 24 70.2041 1.7992 25 -370.3402 0.9000 1.56732 42.84 26 64.5030 3.2849 27* -400.0000 2.3554 1.80610 40.73 28* -79.5075 (d28) 29 -65.5518 1.0000 1.51680 64.20 30 -1000.0000 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 27, Page 28 K 0.00000 -1.75000 0.00000 0.00000 A4 1.04188E-05 1.30115E-05 -2.03589E-05 -1.95833E-06 A6 -1.27178E-08 -1.32789E-08 -3.29116E-08 -1.40472E-08 A8 4.78718E-12 -4.04021E-12 4.49014E-10 3.51441E-10 A10 -1.13623E-14 -5.71250E-15 -1.69529E-12 -8.37574E-13 A12 1.10745E-17 1.53201E-17 2.21191E-15 4.41164E-16 [Various Data] INF 275mm Focal length 34.10 31.45 F-number 1.46 1.65 Full angle of view 2ω 65.36 62.88 Image height Y 21.63 21.63 Lens length 112.00 112.00 [Variable interval data] INF 275mm d0 ∞ 163.0000 d17 7.3813 1.7352 d28 3.0637 8.7098 BF 16.0000 16.0000 [Lens group data] Group starting plane focal length G1 1 78.48 G2 18 51.21 G3 29 -135.79 G2A 18 -176.76 G2B 21 36.36 [Examples] 【0061】 Figure 6 is a diagram of the lens configuration of the optical system of Example 2 at infinity. 【0062】 Example 2 consists 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. 【0063】 The first lens group G1 consists of, in order from the object side, a positive meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, and a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane. The aperture diaphragm is positioned adjacent to the image plane side of the negative meniscus lens L8 with its convex surface facing the image plane. 【0064】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L9 and a biconcave lens L10, a biconvex lens L11, a biconcave lens L12, a biconcave lens L13, and a positive meniscus lens L14 with its convex surface facing the image plane. The lens surfaces on both sides of the positive meniscus lens L14 with its convex surface facing the image plane have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L9 and the biconcave lens L10 corresponds to the front group G2A of the second lens group in claim 1, and the positive meniscus lens L14 with its convex surface facing the image plane corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object when focusing from an object distance of infinity to a close distance. 【0065】 The third lens group G3 consists solely of a negative meniscus lens L15 with its convex surface facing the image plane. 【0066】 The specifications of the optical system according to Example 2 are shown below. Numerical Example 2 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1 39.2000 5.3326 2.00100 29.13 2 49.5607 0.5000 3 35.7440 1.4000 1.61340 44.27 4 23.5835 13.0763 5 -59.8411 1.2000 1.59270 35.45 6 68.0015 1.2453 7 46.4503 6.1425 1.90043 37.37 8 -124.6896 2.7780 9 -47.7105 1.2000 1.77047 29.74 10 35.4786 7.1638 1.59282 68.62 11 -230.1804 0.1500 12 70.8127 8.1108 2.00100 29.13 13 -45.3802 1.2000 1.77047 29.74 14 -120.0068 1.0000 15 (aperture) ∞ (d15) 16 43.6538 8.5717 1.55032 75.50 17 -28.4759 1.0000 1.85451 25.15 18 54.6583 3.2304 19 48.6986 4.9542 2.05090 26.94 20 -54.2103 0.5381 21 -80.3993 0.9000 1.67300 38.26 22 87.2327 2.8459 23 -46.7859 0.9000 1.59270 35.45 24 123.7184 2.4551 25* -400.0000 4.4774 1.80610 40.73 26* -31.9225 (d26) 27 -38.7131 1.1605 1.51742 52.15 28 -510.7165 (BF) Image plane ∞ [Aspherical data] Pages 25 and 26 K 0.00000 0.00000 A4 -1.31534E-05 6.97039E-07 A6 1.06364E-08 1.28555E-08 A8 -3.30780E-10 -3.17342E-10 A10 1.46262E-12 1.36692E-12 A12 -1.93907E-15 -1.74801E-15 [Various Data] INF 395mm Focal length 48.50 42.13 F-number 1.46 1.67 Full angle of view 2ω 47.84 47.77 Image height Y 21.63 21.63 Lens length 109.00 109.00 [Variable interval data] INF 395mm d0 ∞ 286.0000 d15 9.1405 2.1066 d26 2.3270 9.3609 BF 16.0000 16.0000 [Lens group data] Group starting plane focal length G1 1 65.70 G2 16 55.48 G3 27 -81.02 G2A 16 -84.37 G2B 19 34.84 [Examples] 【0067】 Figure 11 is a diagram of the lens configuration of the optical system of Example 3 at infinity. 【0068】 Example 3 consists 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. 【0069】 The first lens group G1 consists of, in order from the object side, a negative meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane, and a negative meniscus lens L9 with its convex surface facing the object. The lens surfaces on both sides of the negative meniscus lens L1 with its convex surface facing the object have a predetermined aspherical shape. An aperture diaphragm is positioned between the negative meniscus lens L8 with its convex surface facing the image plane and the negative meniscus lens L9 with its convex surface facing the object. 【0070】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, and a negative meniscus lens L14 with its convex surface facing the image plane side. The lens surfaces on both sides of the negative meniscus lens L14 with its convex surface facing the image plane side have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L10 and the biconcave lens L11 corresponds to the front group G2A of the second lens group in claim 1, and the negative meniscus lens L14 with its convex surface facing the image plane side from the biconvex lens L12 corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object side when focusing from an object distance of infinity to a close distance. 【0071】 The third lens group G3 consists solely of a negative meniscus lens L15 with its convex surface facing the image plane. 【0072】 The specifications of the optical system according to Example 3 are shown below. Numerical Example 3 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1* 62.5541 3.1145 1.51633 64.06 2* 37.8870 1.5313 3 34.1296 1.5016 1.43700 95.10 4 21.5414 11.6845 5 -47.7462 1.2000 1.56732 42.84 6 85.3151 0.6328 7 69.2292 5.3048 1.95375 32.32 8 -68.1035 4.6283 9 -32.6436 1.2000 1.67300 38.26 10 29.6857 9.8169 1.59282 68.62 11 -48.9467 0.1500 12 56.1579 9.6064 2.00100 29.13 13 -37.6230 1.2000 1.85451 25.15 14 -136.7174 1.0000 15 (aperture) ∞ 1.0000 16 81.3378 1.2000 1.85451 25.15 17 35.9063 (d17) 1.55032 75.50 18 27.5581 10.1547 19 -28.0156 1.0000 1.85451 25.15 20 53.4357 5.6054 21 47.2431 5.5395 2.05090 26.94 22 -60.5571 0.1500 23 473.6353 1.0000 1.59270 35.45 24 42.9419 4.8289 25* -160.5611 1.4000 1.80610 40.73 26* -191.2720 (d26) 27 -107.4155 1.0000 1.77047 29.74 28 -1000.0000 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 25, Page 26 K 0.00000 -1.75000 0.00000 0.00000 A4 9.78852E-06 1.62987E-05 -2.14257E-05 -1.08081E-06 A6 -2.12770E-08 -1.97232E-08 1.55800E-09 2.38669E-08 A8 2.02901E-11 -9.06362E-12 2.90601E-10 2.17706E-10 A10 -3.69931E-15 7.08563E-14 -1.59875E-12 -8.32751E-13 A12 -7.46380E-19 -4.99681E-17 2.51104E-15 7.77782E-16 [Various Data] INF 276.15mm Focal length 34.10 31.74 F-number 1.46 1.65 Full angle of view 2ω 64.80 61.71 Image height Y 21.63 21.63 Lens length 112.15 112.15 [Variable interval data] INF 276.15mm d0 ∞ 164.0000 d17 7.2918 1.6699 d26 3.2585 8.8804 BF 16.1500 16.1500 [Lens group data] Group starting plane focal length G1 1 92.83 G2 18 49.83 G3 27 -156.27 G2A 18 -305.20 G2B 21 37.78 [Examples] 【0073】 Figure 16 is a diagram of the lens configuration of the optical system of Example 4 at infinity. 【0074】 Example 4 consists of a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, in that order from the object side. 【0075】 The first lens group G1 consists of, in order from the object side, a negative meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane, and a negative meniscus lens L9 with its convex surface facing the object. The lens surfaces on both sides of the negative meniscus lens L1 with its convex surface facing the object have a predetermined aspherical shape. An aperture diaphragm is positioned between the negative meniscus lens L8 with its convex surface facing the image plane and the negative meniscus lens L9 with its convex surface facing the object. 【0076】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, a biconcave lens L14, and a positive meniscus lens L15 with its convex surface facing the image plane side. The lens surfaces on both sides of the positive meniscus lens L15 with its convex surface facing the image plane side have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L10 and the biconcave lens L11 corresponds to the front group G2A of the second lens group in claim 1, and the positive meniscus lens L15 with its convex surface facing the image plane side corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object side when focusing from an object distance of infinity to a close distance. 【0077】 The specifications of the optical system according to Example 4 are shown below. Numerical Example 4 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1* 46.0616 2.4822 1.59201 67.02 2* 30.1713 3.2924 3 33.3919 1.4000 1.43700 95.10 4 19.5832 12.0775 5 -47.8182 1.2921 1.59270 35.45 6 2191.1564 0.3155 7 135.8450 6.4258 2.05090 26.94 8 -91.5312 3.1836 9 -27.7308 2.2874 1.67300 38.26 10 34.6221 9.2737 1.59282 68.62 11 -37.5955 0.2690 12 59.5784 8.2254 2.00100 29.13 13 -39.9666 1.2000 1.85451 25.15 14 -123.8691 1.0000 15 (aperture) ∞ 1.0000 16 67.1022 1.2000 1.85451 25.15 17 39.0467 (d17) 18 31.7015 9.2323 1.55032 75.50 19 -25.6281 1.0000 1.85451 25.15 20 52.8218 4.0422 21 52.1204 5.1592 2.00100 29.13 22 -49.3134 1.0197 23 307.8218 0.9000 1.67300 38.26 24 68.1202 1.9862 25 -165.2656 0.9000 1.59270 35.45 26 70.7854 3.2794 27* -208.3256 2.1515 1.80610 40.73 28* -77.6588 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 27, Page 28 K 0.00000 -1.75000 0.00000 0.00000 A4 1.47331E-05 2.46851E-05 -2.26748E-05 -2.16368E-06 A6 -2.30911E-08 -1.90995E-08 -2.84978E-08 -5.94597E-09 A8 1.30723E-11 -2.37613E-11 4.38346E-10 3.17811E-10 A10 -3.42639E-15 5.87180E-14 -1.74335E-12 -7.31441E-13 A12 6.72928E-18 -4.19933E-17 2.38628E-15 2.62883E-16 [Various Data] INF 275mm Focal length 28.50 27.52 F-number 1.46 1.62 Full angle of view 2ω 75.19 72.92 Image height Y 21.63 21.63 Lens length 112.00 112.00 [Variable interval data] INF 275mm d0 ∞ 163.0000 d17 7.2082 2.0636 BF 20.1967 25.3412 [Lens group data] Group starting plane focal length G1 1 70.15 G2 18 58.96 G3 - ∞ G2A 18 -129.39 G2B 21 37.70 [Examples] 【0078】 Figure 21 is a diagram of the lens configuration of the optical system of Example 5 at infinity. 【0079】 Example 5 consists 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. 【0080】 The first lens group G1 consists of, in order from the object side, a negative meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane, and a negative meniscus lens L9 with its convex surface facing the object. The lens surfaces on both sides of the negative meniscus lens L1 with its convex surface facing the object have a predetermined aspherical shape. An aperture diaphragm is positioned between the negative meniscus lens L8 with its convex surface facing the image plane and the negative meniscus lens L9 with its convex surface facing the object. 【0081】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, a biconcave lens L14, and a positive meniscus lens L15 with its convex surface facing the image plane side. The lens surfaces on both sides of the positive meniscus lens L15 with its convex surface facing the image plane side have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L10 and the biconcave lens L11 corresponds to the front group G2A of the second lens group in claim 1, and the positive meniscus lens L15 with its convex surface facing the image plane side corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object side when focusing from an object distance of infinity to a close distance. 【0082】 The third lens group G3 consists solely of a negative meniscus lens L16 with its convex surface facing the image plane. 【0083】 The specifications of the optical system according to Example 5 are shown below. Numerical Example 5 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1* 46.9970 2.3500 1.59201 67.02 2* 29.9400 3.2253 3 32.7215 1.4000 1.43700 95.10 4 19.7763 12.2103 5 -48.2733 1.5018 1.59270 35.45 6 1172.1753 0.2690 7 123.5376 6.1498 2.05090 26.94 8 -97.8792 3.4111 9 -28.4141 2.0806 1.67300 38.26 10 33.9467 9.4407 1.59282 68.62 11 -38.5779 0.2928 12 57.5448 8.2484 2.00100 29.13 13 -40.8638 1.2000 1.85451 25.15 14 -135.2407 1.0000 15 (aperture) ∞ 1.0000 16 61.6129 1.2000 1.85451 25.15 17 37.2120 (d17) 18 31.4929 9.1318 1.55032 75.50 19 -25.6765 1.0000 1.85451 25.15 20 53.3034 3.9670 21 51.5127 5.1184 2.00100 29.13 22 -50.1696 1.1445 23 375.5144 0.9000 1.65412 39.68 24 72.8303 1.9169 25 -157.7400 0.9000 1.59270 35.45 26 66.7131 3.2175 27* -289.0911 2.0489 1.80610 40.73 28* -77.1450 (d28) 29 -90.8519 1.3658 1.72825 28.32 30 -106.1452 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 27, Page 28 K 0.00000 -1.75000 0.00000 0.00000 A4 1.49523E-05 2.49686E-05 -2.28124E-05 -2.14906E-06 A6 -2.26395E-08 -1.81963E-08 -2.85124E-08 -5.16897E-09 A8 9.32834E-12 -2.06870E-11 4.45702E-10 3.23486E-10 A10 7.10925E-16 2.79386E-14 -1.78035E-12 -7.45472E-13 A12 4.41672E-18 -3.69087E-18 2.45516E-15 2.44555E-16 [Various Data] INF 276.15mm Focal length 28.50 27.44 F-number 1.46 1.61 Full angle of view 2ω 75.19 72.96 Image height Y 21.63 21.63 Lens length 112.15 112.15 [Variable interval data] INF 276.15mm d0 ∞ 164.0000 d17 7.1492 2.3284 d28 3.1602 7.9810 BF 16.1500 16.1500 [Lens group data] Group starting plane focal length G1 1 70.61 G2 18 56.11 G3 29 -899.73 G2A 18 -133.79 G2B 21 36.80 [Examples] 【0084】 Figure 26 is a diagram of the lens configuration of the optical system of Example 6 at infinity. 【0085】 Example 6 consists 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. 【0086】 The first lens group G1 consists of, in order from the object side, a negative meniscus lens L1 with its convex surface facing the object, a negative meniscus lens L2 with its convex surface facing the object, a biconcave lens L3, a biconvex lens L4, a cemented lens consisting of a biconcave lens L5 and a biconvex lens L6, a cemented lens consisting of a biconvex lens L7 and a negative meniscus lens L8 with its convex surface facing the image plane, and a negative meniscus lens L9 with its convex surface facing the object. The lens surfaces on both sides of the negative meniscus lens L1 with its convex surface facing the object have a predetermined aspherical shape. An aperture diaphragm is positioned between the negative meniscus lens L8 with its convex surface facing the image plane and the negative meniscus lens L9 with its convex surface facing the object. 【0087】 The second lens group G2 consists of, in order from the object side, a cemented lens consisting of a biconvex lens L10 and a biconcave lens L11, a biconvex lens L12, a biconcave lens L13, a biconcave lens L14, and a positive meniscus lens L15 with its convex surface facing the image plane. The lens surfaces on both sides of the positive meniscus lens L15 with its convex surface facing the image plane have a predetermined aspherical shape. The cemented lens consisting of the biconvex lens L10 and the biconcave lens L11 corresponds to the front group G2A of the second lens group in claim 1, and the positive meniscus lens L15 with its convex surface facing the image plane from the biconvex lens L12 corresponds to the rear group G2B of the second lens group in claim 1. The second lens group G2 as a whole moves towards the object when focusing from an object distance of infinity to a close distance. 【0088】 The third lens group G3 consists solely of a negative meniscus lens L15 with its convex surface facing the image plane. 【0089】 The specifications of the optical system according to Example 6 are shown below. Numerical Example 6 Unit: mm [Surface data] Face number rd nd vd Object surface ∞ (d0) 1* 86.7467 4.0000 1.80610 40.73 2* 73.9218 0.5178 3 47.6287 1.4000 1.43700 95.10 4 21.1938 13.7101 5 -42.8821 1.2126 1.59270 35.45 6 129.9459 0.1500 7 70.8920 5.4042 2.00100 29.13 8 -64.6985 3.6871 9 -33.2964 1.2219 1.73037 32.23 10 33.6844 9.4494 1.59282 68.62 11 -47.9808 0.1500 12 72.3170 9.5425 2.00100 29.13 13 -34.1157 1.2000 1.85451 25.15 14 -94.8668 1.0000 15 (aperture) ∞ 1.0000 16 62.2115 1.2000 1.85451 25.15 17 37.2348 (d17) 18 27.0524 10.3581 1.49700 81.61 19 -27.5035 1.0000 1.77047 29.74 20 42.7483 3.6187 21 47.4157 5.4203 2.00100 29.13 22 -52.2098 0.1970 23 -747.2985 1.4772 1.77047 29.74 24 92.0326 1.9127 25 -150.8873 0.9000 1.59270 35.45 26 65.1863 3.1844 27* -400.0000 2.0557 1.80610 40.73 28* -81.8928 (d28) 29 -131.5251 1.0000 1.80518 25.46 30 -1000.0000 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 27, Page 28 K 0.00000 -1.75000 0.00000 0.00000 A4 7.37773E-06 1.05485E-05 -2.04766E-05 -9.93470E-07 A6 -6.81281E-09 -6.77109E-09 -8.33963E-08 -6.20947E-08 A8 2.55136E-12 -5.15614E-12 8.22128E-10 6.78931E-10 A10 -1.63601E-14 -2.20159E-14 -2.75985E-12 -1.60119E-12 A12 1.52472E-17 3.04610E-17 3.34514E-15 9.69770E-16 [Various Data] INF 275mm Focal length 34.10 31.65 F-number 1.46 1.68 Full angle of view 2ω 65.37 62.16 Image height Y 21.63 21.63 Overall lens length 112.00 112.00 [Variable interval data] INF 275mm d0 ∞ 163.0000 d17 7.8040 1.5000 d28 2.2263 8.5303 BF 16.0000 16.0000 [Lens group data] Group Starting surface Focal length G1 1 72.79 G2 18 58.92 G3 29 -188.18 G2A 18 -168.32 G2B 21 39.07 【0090】 The conditional formula corresponding values of each embodiment are shown below. [Conditional formula corresponding values] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 (1) (1 / F1 - 1 / F3)×F2 > 0.6 1.03 1.53 0.86 0.84 0.86 1.12 (2) DAB / D2 > 0.050 0.159 0.108 0.189 0.136 0.135 0.120 (3) nd2Bp > 1.80 1.90 1.93 2.05 1.90 1.90 1.90 (4) nd2Bn < 1.75 1.59 1.63 1.70 1.63 1.62 1.68 (5) vd2Ap > 60.00 75.50 75.50 75.50 75.50 75.50 81.61 (6) vd2An < 35.00 25.15 25.15 25.15 25.15 25.15 29.74 【Explanation of symbols】 【0091】 S: Aperture diaphragm I: image plane G1: First lens group G2: Second lens group G3: Third lens group G2A: Front group of the second lens element G2B: Second lens group, rear group C: C line (wavelength λ=656.3nm) d:d line (wavelength λ=587.6nm) g:g line (wavelength λ=435.8nm) Y: Image height ΔS: Sagittal image plane ΔM: Median image plane

Claims

[Claim 1] Starting from the object side, it has a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. When focusing from a long distance to a close distance, the second lens group G2 moves toward the object, the distance between the front and rear of the second lens group G2 changes, and the lens groups other than the second lens group G2 remain fixed in position relative to the image plane. The second lens group G2 is composed of the front lens group G2A and the rear lens group G2B in order from the object side. The front group G2A and the rear group G2B of the second lens group each have one or more lenses with positive refractive power and one or more lenses with negative refractive power. An optical system characterized by satisfying the following conditions (1), (2), and (3-1). (1) (1 / F1-1 / F3) x F2 > 0.60 (2) DAB / D2 > 0.050 (3-1) nd2Bp > 1.85 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces arranged between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: The distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: The distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. nd2Bp: The average value of the refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. [Claim 2] The lens comprises, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, When focusing from a long distance to a close distance, the second lens group G2 moves toward the object, the distance between the front and rear of the second lens group G2 changes, and the lens groups other than the second lens group G2 remain fixed in position relative to the image plane. The second lens group G2 is composed of the front lens group G2A and the rear lens group G2B in order from the object side. The front group G2A and the rear group G2B of the second lens group each have one or more lenses with positive refractive power and one or more lenses with negative refractive power. An optical system characterized by satisfying the following conditions (1), (2), and (5). (1) (1 / F1-1 / F3) x F2 > 0.60 (2) DAB / D2 > 0.050 (5) vd2Ap > 60.00 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces arranged between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: The distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: The distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. vd2Ap: The average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group. [Claim 3] The lens comprises, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, When focusing from a long distance to a close distance, the second lens group G2 moves toward the object, the distance between the front and rear of the second lens group G2 changes, and the lens groups other than the second lens group G2 remain fixed in position relative to the image plane. The second lens group G2 is composed of the front lens group G2A and the rear lens group G2B in order from the object side. The front group G2A and the rear group G2B of the second lens group each have one or more lenses with positive refractive power and one or more lenses with negative refractive power. An optical system characterized by satisfying the following conditions (1), (2), (3), and (6-1). (1) (1 / F1-1 / F3) x F2 > 0.60 (2) DAB / D2 > 0.050 (3) nd2Bp > 1.80 (6-1) vd2An ≦ 29.74 however, F1: Focal length of the first lens group G1 F2: Focal length of the second lens group G2 F3: The total focal length of all optical surfaces arranged between the second lens group G2 and the image plane. However, if there are no optical surfaces between the second lens group G2 and the image plane, F3 is calculated as F3 = ∞. DAB: The distance along the optical axis between the image-plane-side surface of the front lens group G2A and the object-side-side surface of the rear lens group G2B. D2: The distance along the optical axis between the object-side surface and the image-side surface of the second lens group G2. nd2Bp: The average value of the refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. [Claim 4] The optical system according to claim 1, characterized in that it satisfies the following conditional equations (4), (5), and (6). (4) nd2Bn < 1.75 (5) vd2Ap > 60.00 (6) vd2An < 35.00 however, nd2Bn: The average value of the refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2Ap: The average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. [Claim 5] The optical system according to Claim 2, characterized in that it satisfies the following conditional equations (3), (4), and (6). (3) nd2Bp > 1.80 (4) nd2Bn < 1.75 (6) vd2An < 35.00 however, nd2Bp: The average value of the refractive index of the positive refractive power lenses included in the rear group G2B of the second lens group. nd2Bn: The average value of the refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2An: The average Abbe number of the negative refractive power lenses included in the front group G2A of the second lens group. [Claim 6] The optical system according to Claim 3, characterized in that it satisfies the following conditional equations (4) and (5). (4) nd2Bn < 1.75 (5) vd2Ap > 60.00 however, nd2Bn: The average value of the refractive index of the negative refractive power lenses included in the rear group G2B of the second lens group. vd2Ap: The average Abbe number of the positive refractive power lenses included in the front group G2A of the second lens group. [Claim 7] An optical system according to any one of claims 1 to 6, characterized in that the rear group G2B of the second lens group has an aspherical surface such that the positive refractive power weakens, the negative refractive power strengthens, or the refractive power changes from positive to negative in the vicinity of the effective ray diameter with respect to the optical axis center. [Claim 8] An optical system according to any one of claims 1 to 6, characterized in that an aperture diaphragm is arranged within the first lens group G1 or adjacent to it on the image plane side.

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