Optical lens system

Abstract

In wide-angle lenses, it is possible to achieve miniaturization while correcting aberrations. [Solution] The optical system consists of a first lens group G1 having positive refractive power, an open aperture STO, and a second lens group G2 having positive refractive power, in order from the object side. The first lens group G1 and the second lens group G2 move independently toward the object OBJ. The first lens group G1 consists of at least one negative lens L1 from the object side, at least one cemented lens L2 consisting of at least one positive lens L2f and a negative lens L2r from the object side, and at least one positive lens L3 and one cemented lens L4 having positive refractive power, in order from the object side. The second lens group G2 includes one cemented lens L5 with negative refractive power, a positive lens L6, and at least one cemented lens L7 with negative refractive power, in order from the object side. When the amount of movement of the first lens group and the second lens group, respectively, is X1 and X2, the distance of the optical system is TL, and the focal length of the entire optical system is f, then X2-X1>0 and 2

Description

Technical Field

[0001] The present invention relates to an optical lens system as a lens for an interchangeable-lens camera.

Background Art

[0002] In an optical lens system as a lens for an interchangeable-lens camera, miniaturization and further improvement in performance of a wide-angle lens are desired. For example, according to the optical lens system disclosed in Patent Document 1 (Japanese Patent No. 7546909), in an imaging lens including a front lens group arranged on the object side with respect to an aperture stop and a rear lens group arranged on the image side with respect to the aperture stop, the front lens group is composed of two positive lenses and at least two negative lenses, and the rear lens group is configured, in order from the object side, by a cemented lens of a biconcave lens and a biconvex lens, a positive lens, a negative lens, and a negative singlet lens.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, by adopting the above-described configuration, higher performance and miniaturization than in the prior art have been achieved. However, due to higher pixel counts of camera bodies and demands from users, further improvement in performance is required, and in particular, there is a problem that a configuration capable of more sufficiently correcting chromatic aberration is required.

Means for Solving the Problems

[0005] In view of the above circumstances, the present invention is made, and an object thereof is to provide a high-performance optical lens system that can achieve miniaturization and particularly sufficiently correct chromatic aberration in a wide-angle lens.

[0006] In one embodiment, the present invention solves the above problems by means described below. That is, it consists of a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power in order from the object side. The first lens group and the second lens group each move independently toward the object side during close focusing. The first lens group has, in order from the object side, a first a lens group, a first b lens group, and a first c lens group. The first a lens group has a negative refractive power and consists of at least one negative lens with a convex surface facing the object side. The first b lens group has a negative refractive power and consists of at least one positive lens and one negative lens, or at least one cemented lens consisting of at least one positive lens and a negative lens cemented to this positive lens, from the most object side. The first c lens group has a positive refractive power and consists of at least one positive lens and one cemented lens having a positive refractive power from the object side. The second lens group has, in order from the object side, a second a lens group, a second b lens group, and a second c lens group. The second a lens group has a negative refractive power and consists of at least one cemented lens. The second b lens group has a positive refractive power. The second c lens group has a negative refractive power and includes at least one cemented lens. When the movement amounts from infinity focus to closest focus of the first lens group and the second lens group are X1 and X2, respectively, and the distance on the optical axis from the most object-side surface of the optical system to the image plane is TL and the focal length of the entire optical system is f, then X2 - X1 > 0 ··· (1), 2 < TL / f < 2.5 ··· (2). It is characterized by satisfying the above formula (1) and the above formula (2). According to this configuration, by appropriately arranging these predetermined lenses, an optical lens system capable of achieving miniaturization and correcting chromatic aberration can be realized.

[0007] Further, it is characterized in that the most object-side negative lens of the first a lens group is an aspherical lens. According to this configuration, by arranging an aspherical lens on the most object side, it contributes to miniaturization and high performance.

[0008] Also, when the focal length of the first lens group is f1 and the focal length of the second lens group is f2, 1 < f1 / f2 < 1.14 ··· (3), and it is characterized by satisfying the above formula (3). According to this configuration, by making the ratio of the focal lengths of the first lens group and the second lens group approach 1, the power arrangement before and after the aperture stop becomes symmetric, and the change in performance when the object distance changes can be suppressed.

[0009] Also, when the focal length of the first lens group is f1, the combined focal length of the first a lens group and the first b lens group is f1ab, the distance on the optical axis from the most object-side surface of the optical system to the image plane is TL, and the distance on the optical axis from the most object-side surface of the optical system to the most image-side of the first b lens group is TLab, then f1 / f1ab < -1.95 ··· (4), TLab / TL ≤ 0.15 ··· (5), and it is characterized by satisfying the above formula (4) and formula (5). According to this configuration, by arranging a lens group with a strong negative refractive power on the object side of the first lens group, the peripheral light rays can be bent rapidly, contributing to miniaturization.

[0010] Also, the most object-side positive lens and negative lens of the first b lens group satisfy nd1bp > 1.76 ··· (6), 1.86 > nd1bm > 1.76 ··· (7), νd1bp > 29 ··· (8), 30 ≥ νd1bm > 28.4 ··· (9), and it is characterized by satisfying the above formula (6), formula (7), formula (8) and formula (9). Here, nd1bp is the refractive index of the d line (wavelength λ = 587.56 nm) of the most object-side positive lens of the first b lens group. nd1bm is the refractive index of the d line (wavelength λ = 587.56 nm) of the most object-side negative lens of the first b lens group. νd1bp is the Abbe number of the d line (wavelength λ = 587.56 nm) of the most object-side positive lens of the first b lens group. νd1bm is the Abbe number of the d line (wavelength λ = 587.56 nm) of the most object-side negative lens of the first b lens group. With this configuration, by using a glass material that satisfies the above equation for the positive lens closest to the object in the first b lens group, even if the light rays are sharply bent, the occurrence of aberrations is suppressed, and it works favorably for the Petzval sum, contributing to the correction of field curvature. Furthermore, by using a glass material that satisfies the above equation for the negative lens closest to the object in the first b lens group, high performance and correction of chromatic aberration (second-order spectrum) can be achieved.

[0011] Furthermore, when the refractive index of the positive lens in the second lens group is nd2p and the anomalous partial dispersion is ΔPgF2p, at least two or more positive lenses satisfy the following equation (10), and at least one of the lenses satisfying equation (10) satisfies the following equation (11). ΔPgF2p>0.013··(10), nd2p>1.62··(11), where ΔPgF=PgF-0.64833+0.00180νd :g, anomalous partial dispersion between F lines. PgF=(ng-nF) / (nF-nC):g, partial dispersion ratio between F lines. nC: refractive index of the C line (wavelength λ=656.27nm). nF: refractive index of the F line (wavelength λ=486.13nm). ng: refractive index of the g line (wavelength λ=435.83nm). This configuration allows for the correction of chromatic aberration (second-order spectrum) by using multiple positive lenses with positive anomalous partial dispersion, and simultaneously corrects various aberrations and chromatic aberration by using positive lenses with a refractive index greater than 1.62.

[0012] Furthermore, when the refractive index of the negative lens in the second lens group is nd2m and the anomalous partial dispersion is ΔPgF2m, at least two or more negative lenses are characterized by satisfying the following equations (12) and (13): nd2m < 1.73 (12), ΔPgF2m < -0.002 (13), where ΔPgF = PgF - 0.64833 + 0.00180νd :g, anomalous partial dispersion between F lines. PgF = (ng - nF) / (nF - nC) :g, partial dispersion ratio between F lines. nC: refractive index of the C line (wavelength λ = 656.27 nm). nF: refractive index of the F line (wavelength λ = 486.13 nm). ng: refractive index of the g line (wavelength λ = 435.83 nm). In this configuration, chromatic aberration (second-order spectrum) is corrected by using multiple negative lenses with negative anomalous partial dispersion in the second lens group, and the Petzval sum is improved by using negative lenses with a refractive index of less than 1.73, contributing to the correction of field curvature.

[0013] Furthermore, when the focal length of the cemented lens closest to the object in the second a lens group is f2abal, the focal length of the negative lens of this cemented lens is f2abalm, and the anomalous partial dispersions of the positive and negative lenses of this cemented lens are ΔPgF2abalp and ΔPgF2abalm respectively, the cemented lens closest to the object in the second a lens group is characterized in that it satisfies the following equations (14), (15), (16), and (17). -55 <f2abal<0··(14)、f2abal / f2abalm> 3.75··(15), ΔPgF2abalp>0.013··(16), ΔPgF2abalm<―0.002··(17), where ΔPgF=PgF-0.64833+0.00180νd :g, anomalous partial dispersion between F lines. PgF=(ng-nF) / (nF-nC):g, partial dispersion ratio between F lines. nC: refractive index of the C line (wavelength λ=656.27nm). nF: refractive index of the F line (wavelength λ=486.13nm). ng: refractive index of the g line (wavelength λ=435.83nm). With this configuration, by employing a cemented lens with negative refractive power in the 2a lens group, which is formed by bonding a lens with strong positive refractive power and a lens with strong negative refractive power using glass materials that satisfy the above conditions, various aberrations and chromatic aberration can be corrected.

[0014] Also, when the focal length of the second lens group is f2, the focal length of the second b lens group is f2b, and the abnormal partial dispersibility of the lens with the strongest positive refractive power in the second b lens group is ΔPgF2bp, it is characterized by satisfying the following formula (18) and the following formula (19). f2 / f2b>2.5··(18), ΔPgF2bp> -0.001··(19), where ΔPgF = PgF - 0.64833 + 0.00180νd: abnormal partial dispersibility between g and F lines. PgF = (ng - nF) / (nF - nC): partial dispersion ratio between g and F lines. nC: refractive index of C line (wavelength λ = 656.27nm). nF: refractive index of F line (wavelength λ = 486.13nm). ng: refractive index of g line (wavelength λ = 435.83nm). By arranging a positive component with a significantly strong refractive power in the second b lens group and using a glass material that satisfies the above conditions, various aberrations and chromatic aberration can be corrected.

Effects of the Invention

[0015] In a wide-angle lens, it is possible to provide a high-performance optical lens system that can achieve miniaturization and particularly sufficiently correct chromatic aberration.

Brief Description of the Drawings

[0016] [Figure 1] It is a configuration diagram of the optical lens system in the first embodiment of the present invention. [Figure 2] It is a longitudinal aberration diagram at infinity of the optical lens system in the first embodiment of the present invention. [Figure 3] It is a configuration diagram of the optical lens system in the second embodiment of the present invention. [Figure 4] It is a longitudinal aberration diagram at infinity of the optical lens system in the second embodiment of the present invention. [Figure 5] It is a configuration diagram of the optical lens system in the third embodiment of the present invention. [Figure 6] It is a longitudinal aberration diagram at infinity of the optical lens system in the third embodiment of the present invention.

Modes for Carrying Out the Invention

[0017] Hereinafter, each embodiment will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of an optical lens system 100 according to the first embodiment of the present invention. FIG. 2 is a longitudinal aberration diagram of the optical lens system 100 at infinity according to the first embodiment of the present invention. FIG. 3 is a configuration diagram of an optical lens system 200 according to the second embodiment of the present invention. FIG. 4 is a longitudinal aberration diagram of the optical lens system 200 at infinity according to the second embodiment of the present invention. FIG. 5 is a configuration diagram of an optical lens system 300 according to the third embodiment of the present invention. FIG. 6 is a longitudinal aberration diagram of the optical lens system 300 at infinity according to the third embodiment of the present invention.

[0018] In the upper right of FIGS. 2, 4, and 6, legends of C line (wavelength 656.27 nm), d line (wavelength 587.56 nm), and g line (wavelength 435.83 nm) are described. In all the drawings for explaining each embodiment, members having the same function are denoted by the same reference numerals, and repeated explanations thereof may be omitted.

[0019] The optical lens systems 100, 200, and 300 in each embodiment are, as an example, interchangeable imaging lenses used in a photographic camera or a video camera. As shown in FIGS. 1, 3, and 5, the optical lens systems 100, 200, and 300 include a first lens group G1, an aperture stop STO, and a second lens group G2 on the optical axis from an object OBJ toward an imaging surface IMG.

[0020] Also, the first lens group G1 and the second lens group G2 each independently move toward the object OBJ side during close focusing.

[0021] For convenience, in FIGS. 1, 3, and 5, numbers are assigned to the surfaces of each lens, but the surface numbers do not necessarily correspond between embodiments. Also, a single number is assigned to the joint surface in a cemented lens. Further, since the aperture stop STO is counted as a virtual surface, the continuous surface numbers are skipped.

[0022] (First Embodiment) In the first embodiment, Figure 1 illustrates and explains an imaging lens 100 with an overall focal length f = 28.84 mm, an F-number of 2.06, and a half-angle of view ω = 37.00°.

[0023] In this embodiment, the imaging lens 100 comprises, in order along the optical axis from the object OBJ to the image plane IMG, a first lens group G1 having positive refractive power, an aperture diaphragm STO, and a second lens group G2 having positive refractive power. Since both the first lens group G1 and the second lens group G2 have positive refractive power, this contributes to miniaturizing the entire imaging lens 100.

[0024] The first lens group G1 comprises, in order from the object OBJ, the firsta lens group G1a, the firstb lens group G1b, and the firstc lens group G1c. The first lens group G1a consists of a single negative meniscus lens L1 with a negative refractive power and a convex surface facing the object OBJ. The negative meniscus lens L1 is an aspherical lens. The first lens group G1b consists of a single cemented lens L2 with negative refractive power, with its concave surface facing the object OBJ side. The cemented lens L2 consists of a positive meniscus lens L2f with its convex surface facing the image plane IMG side and a negative meniscus lens L2r bonded to the positive meniscus lens L2f with its concave surface facing it. The first lens group G1c has a positive refractive power as a whole and includes a biconvex lens L3 with its convex surface facing the object OBJ, and a cemented lens L4 consisting of a biconvex lens L4f and a biconcave lens L4r bonded to the biconvex lens L4f.

[0025] As mentioned above, the negative meniscus lens L1, which is the negative lens of the first lens group G1a, employs an aspherical lens. By using an aspherical lens closest to the object OBJ, high performance and miniaturization can be achieved.

[0026] The second lens group G2 is positioned on the image plane IMG side of the aperture diaphragm STO, and consists of the seconda lens group G2a, the secondb lens group G2b, and the secondc lens group G2c, in that order from the object OBJ. The 2a lens group G2a consists of a single cemented lens L5 having a negative refractive power, and the cemented lens L5 consists of a biconcave lens L5f and a biconvex lens L5r cemented to the biconcave lens L5f. The 2b lens group G2b consists of a single biconvex lens L6. The 2c lens group G2c has a negative refractive power as a whole, and consists of a cemented lens L7 including a biconvex lens L7f and a biconcave lens L7r cemented to the biconvex lens L7f, and an aspherical lens L8 which is a biconcave lens.

[0027] Table 1 shows a table summarizing various data of the first embodiment.

Table 1

[0028] In Table 1, TL is the overall optical length, TLab is the distance on the optical axis from the most object-side surface of the optical system to the most image-side surface of the 1b lens group, f1 is the focal length of the first lens group G1, f1ab is the combined focal length of the first a lens group G1a and the first b lens group G1b, f2 is the focal length of the second lens group G2, f2abal is the focal length of the cemented lens L5 of the 2a lens group G2a, f2abalm is the focal length of the biconcave lens L5f which is the negative lens of the cemented lens L5 of the 2a lens group G2a, f2b is the focal length of the 2b lens group G2b, X1 is the movement amount from infinity focus to closest focus of the first lens group G1, and X2 is the movement amount from infinity focus to closest focus of the second lens group G2.

[0029] As shown in Table 1, in the first embodiment, X2 - X1 = 1.04, satisfying X2 - X1 > 0. Further, TL / f = 2.47, satisfying 2 < TL / f < 2.5. Thus, in the first embodiment, with the lens arrangement described above and satisfying the above two equations, miniaturization can be achieved in a wide-angle lens while correcting chromatic aberration.

[0030] Also, in the first embodiment, f1 / f2 = 1.074, satisfying 1 < f1 / f2 < 1.14. In this way, the ratio of the focal lengths of the first lens group G1 and the second lens group G2 can be brought closer to 1, resulting in a symmetrical power distribution before and after the aperture diaphragm STO, which suppresses performance changes when the object distance changes.

[0031] Furthermore, in the first embodiment, f1 / f1ab = -1.961 and f1 / f1ab < -1.95. Furthermore, TLab / TL = 0.148, and TLab / TL ≤ 0.15. In the first embodiment, by satisfying the two equations above, a lens group with a strong negative refractive power is placed on the object OBJ side of the first lens group G1, which allows for sharp bending of peripheral light rays and contributes to miniaturization.

[0032] Next, Table 2 shows the lens data for the optical lens system 100 of the first embodiment shown in Figure 1.

[0033] [Table 2]

[0034] Table 2 shows the radius of curvature R (mm) corresponding to the virtual plane and lens surface counted from the object OBJ side, the interplanar spacing D (mm) on the optical axis, the refractive index nd of the lens, the Abbe number νd of the lens, and the anomalous partial dispersion ΔPgF between the g·F lines, respectively. The radius of curvature R is considered positive when the lens surface is convex relative to the object OBJ, and negative when the lens surface is concave relative to the object OBJ. Furthermore, nd and νd are values ​​for the d-line (wavelength λ = 587.56 nm). Furthermore, D represents the distance from one face to the next numbered face. Additionally, the blanks for nd and νd indicate air. If the shape is aspherical, it is indicated with an asterisk (*) in the ASP column.

[0035] The anomalous partial dispersion ΔPgF between the g and F lines is calculated as PgF - 0.64833 + 0.00180νd, where PgF = (ng - nF) / (nF - nC): partial dispersion ratio between g and F lines, nC: refractive index of the C line (wavelength λ = 656.27 nm), nF: refractive index of the F line (wavelength λ = 486.13 nm), and ng: refractive index of the g line (wavelength λ = 435.83 nm).

[0036] From the results in Table 2, in the first embodiment, the refractive index of the positive meniscus lens L2f on the object OBJ side of the first lens group G1b is 1.76385, satisfying nd1bp > 1.76. The refractive index of the negative meniscus lens L2r closest to the object OBJ in the first lens group G1b is 1.77047, satisfying 1.86 > nd1bm > 1.76. The Abbe number of the positive meniscus lens L2f, which is closest to the object OBJ in the first lens group G1b, is 48.49, satisfying νd1bp > 29. The Abbe number of the negative meniscus lens L2r closest to the object OBJ in the first lens group G1b is 29.74, satisfying 30≧νd1bm>28.4. By using a glass material that satisfies the above two equations for the positive meniscus lens L2f, the closest positive meniscus lens on the object side of the first lens group G1b, even if the light rays are sharply bent, the occurrence of aberrations is suppressed, and it works favorably for the Petzval sum, contributing to the correction of field curvature. Furthermore, by using a glass material that satisfies the above two equations for the negative meniscus lens L2r, the closest negative meniscus lens on the object side of the first lens group G1b, high performance and correction of chromatic aberration (second-order spectrum) can be achieved.

[0037] In the second lens group G2 of the first embodiment, three positive lenses are arranged: biconvex lens L5r, biconvex lens L6, and biconvex lens L7f. Their respective anomalous partial dispersion values ​​ΔPgF are 0.0139, -0.0005, and 0.0277. Therefore, the biconvex lenses L5r and L7f satisfy the anomalous partial dispersion property ΔPgF > 0.013. Furthermore, among the biconvex lenses L5r and L7f that satisfy the above equation, the refractive index of biconvex lens L5r is nd = 1.62846 and nd > 1.62. Thus, by using a plurality of positive lenses having a positive abnormal partial dispersibility in the second lens group G2, chromatic aberration (secondary spectrum) can be corrected, and by using a positive lens having a refractive index greater than 1.62, various aberrations and chromatic aberration can be corrected simultaneously.

[0038] Among the negative lenses in the second lens group G2 of the first embodiment, three negative lenses, i.e., a biconcave lens L5f, a biconcave lens L7r, and an aspherical lens L8 which is a biconcave lens, are arranged, and their refractive indices nd are 1.72047, 1.72047, and 1.80610, respectively. Therefore, the biconcave lens L5f and the biconcave lens L7r satisfy nd < 1.73. Furthermore, the partial dispersibilities ΔPgF of the biconcave lens L5f and the biconcave lens L7r that satisfy the above formula are -0.0025 and -0.0025, respectively, and satisfy ΔPgF < -0.002. Thus, in the second lens group G2, by using a plurality of negative lenses having a negative abnormal partial dispersibility, chromatic aberration (secondary spectrum) can be corrected, and by using a negative lens having a refractive index less than 1.73, the Petzval sum can be made a good value and contribute to the correction of field curvature.

[0039] Also, from Table 1, the focal length f2abal of the cemented lens L5 of the second a lens group G2a is -49.26, and satisfies -55 < f2abal < 0. And since the focal length f2abalm of the biconcave lens L5f of this cemented lens L5 is -12.70, f2abal / f2abalm = 3.88, and satisfies f2abal / f2abalm > 3.75. Furthermore, from Table 2, the partial dispersibilities ΔPgF of the biconcave lens L5f and the biconvex lens L5r that constitute this cemented lens L5 are -0.0025 and 0.0139, respectively, and satisfy ΔPgF2abalm < -0.002 and ΔPgF2abalp > 0.013. Thus, by using glass materials that satisfy the four equations above, the cemented lens L5 of the second lens group G2a can be adopted in the second lens group G2a as a cemented lens L5 with negative refractive power, which is formed by bonding a lens with strong positive refractive power and a lens with strong negative refractive power, thereby correcting various aberrations and chromatic aberration.

[0040] Furthermore, from Table 1, in the second lens group G2b, f2 / f2b = 2.57, and f2 / f2b > 2.5. According to Table 2, the lens with the strongest positive refractive power in the second lens group G2 is the biconvex lens L6, with an anomalous dispersion ΔPgF = -0.0005, satisfying ΔPgF > -0.001. Thus, by placing a biconvex lens L6 with significantly stronger refractive power in the second lens group G2b, and by using glass material that satisfies the two equations above, various aberrations and chromatic aberration can be corrected.

[0041] [Table 3]

[0042] Table 3 shows the variable spacing between lenses.

[0043] [Table 4]

[0044] Table 4 shows the surface shape (aspheric coefficient) of an aspherical lens. In this case, in a Cartesian coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the following equation 1. In equation 1, R is the radius of curvature, K is the cone constant, A4, A6, A8, A10, and A12 are the 4th, 6th, 8th, 10th, and 12th order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis.

[0045]

number

[0046] Next, Figure 2 shows the spherical aberration, astigmatism, and distortion in the optical lens system 100. The scales for each measurement are ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Figure 2, it can be confirmed that good aberration correction is achieved in all cases.

[0047] (Second Embodiment) Next, as a second embodiment, Figure 3 illustrates and explains an imaging lens 200 with an overall focal length f=28.84mm, an F-number of 2.06, and a half-angle of view ω=37.02°.

[0048] In this embodiment, the imaging lens 200 comprises, in order along the optical axis from the object OBJ to the image plane IMG, a first lens group G1 having positive refractive power, an aperture diaphragm STO, and a second lens group G2 having positive refractive power. Thus, since both the first lens group G1 and the second lens group G2 have positive refractive power, this contributes to the overall miniaturization of the imaging lens 100.

[0049] The first lens group G1 comprises, in order from the object OBJ, the firsta lens group G1a, the firstb lens group G1b, and the firstc lens group G1c. The first lens group G1a consists of a single negative meniscus lens L9 with a negative refractive power and a convex surface facing the object OBJ. The negative meniscus lens L9 is an aspherical lens. The first lens group G1b consists of a single cemented lens L10 with negative refractive power and a concave surface facing the object OBJ side. The cemented lens L10 consists of a positive meniscus lens L10f with a convex surface facing the image plane IMG side and a negative meniscus lens L10r bonded to the positive meniscus lens L10f with its concave surface facing it. The first lens group G1c has a positive refractive power as a whole and includes a biconvex lens L11 with its convex surface facing the object OBJ, and a cemented lens L12 consisting of a biconvex lens L12f and a biconcave lens L12r bonded to the biconvex lens L12f.

[0050] As mentioned above, the negative meniscus lens L9, which is the negative lens of the first lens group G1a, employs an aspherical lens. By using an aspherical lens closest to the object OBJ, high performance and miniaturization can be achieved.

[0051] The second lens group G2 is positioned on the image plane IMG side of the aperture diaphragm STO, and consists of the seconda lens group G2a, the secondb lens group G2b, and the secondc lens group G2c, in that order from the object OBJ. The second lens group G2a consists of a single cemented lens L13 having negative refractive power, and the cemented lens L13 consists of a biconcave lens L13f and a biconvex lens L13r cemented to this biconcave lens L13f. The second lens group G2b consists of a single biconvex lens L14. The second lens group G2c has a negative refractive power as a whole and consists of a bonded lens L15, which is made up of a biconvex lens L15f and a biconcave lens L15r bonded to the biconvex lens L15f, and an aspherical lens L16, which is a biconcave lens.

[0052] Table 5 shows a table summarizing the various data for the second embodiment.

[0053] [Table 5]

[0054] In Table 5, TL represents the total optical length, TLab is the distance along the optical axis from the object-side surface of the optical system to the image-plane-side surface of the first lens group Gb, f1 is the focal length of the first lens group G1, f1ab is the combined focal length of the first lens group G1a and the first lens group G1b, f2 is the focal length of the second lens group G2, f2abal is the focal length of the cemented lens L5 of the second lens group G2a, f2abalm is the focal length of the biconcave lens L5f, which is the negative lens of the cemented lens L5 of the second lens group G2a, f2b is the focal length of the second lens group G2b, X1 is the amount of movement of the first lens group G1 from infinity focus to closest focus, and X2 is the amount of movement of the second lens group G2 from infinity focus to closest focus.

[0055] As shown in Table 5, in the second embodiment, X2 - X1 = 0.47, which satisfies X2 - X1 > 0. Further, TL / f = 2.47, which satisfies 2 < TL / f < 2.5. Thus, in the second embodiment, with the lens arrangement described above and by satisfying the above two equations, miniaturization can be achieved in the wide-angle lens while correcting chromatic aberration.

[0056] Also, in the second embodiment, f1 / f2 = 1.085, which satisfies 1 < f1 / f2 < 1.14. In this way, the ratio of the focal lengths of the first lens group G1 and the second lens group G2 can be made closer to 1, the power arrangement before and after the aperture stop STO becomes symmetric, and the change in performance when the object distance changes can be suppressed.

[0057] Also, in the second embodiment, f1 / f1ab = -1.955, which satisfies f1 / f1ab < -1.95. Furthermore, TLab / TL = 0.147, which satisfies TLab / TL ≤ 0.15. In the second embodiment, by satisfying the above two equations, a lens group with a strong negative refractive power is arranged on the object OBJ side of the first lens group G1, and peripheral light rays can be bent sharply, contributing to miniaturization.

[0058] Subsequently, the lens data of the optical lens system 200 of the second embodiment shown in FIG. 3 is shown in Table 6.

[0059]

Table 6

[0060] In Table 6, the radius of curvature R (mm) corresponding to the virtual surface and the lens surface counted from the object OBJ side, the surface interval D (mm) on the optical axis, the refractive index nd of the lens, the Abbe number νd of the lens, and the abnormal partial dispersion ΔPgF between the g·F lines are shown respectively. The radius of curvature R is considered positive when the lens surface is convex relative to the object OBJ, and negative when the lens surface is concave relative to the object OBJ. Furthermore, nd and νd are values ​​for the d-line (wavelength λ = 587.56 nm). Furthermore, D represents the distance from one face to the next numbered face. Additionally, the blanks for nd and νd indicate air. If the shape is aspherical, it is indicated with an asterisk (*) in the ASP column.

[0061] The anomalous partial dispersion ΔPgF between the g and F lines is calculated as PgF - 0.64833 + 0.00180νd, where PgF = (ng - nF) / (nF - nC): partial dispersion ratio between g and F lines, nC: refractive index of the C line (wavelength λ = 656.27 nm), nF: refractive index of the F line (wavelength λ = 486.13 nm), and ng: refractive index of the g line (wavelength λ = 435.83 nm).

[0062] From the results in Table 6, in the second embodiment, the refractive index of the positive meniscus lens L10f on the object OBJ side of the first lens group G1b is 1.85150, satisfying nd1bp > 1.76. The refractive index of the negative meniscus lens L10r, which is closest to the object OBJ in the first lens group G1b, is 1.78880, satisfying 1.86 > nd1bm > 1.76. The Abbe number of the positive meniscus lens L10f, which is closest to the object OBJ in the first lens group G1b, is 40.78, and satisfies νd1bp > 29. The Abbe number of the negative meniscus lens L10r, which is closest to the object OBJ in the first lens group G1b, is 28.43, satisfying 30 ≥ νd1bm > 28.4. By using a glass material that satisfies the above two equations for the positive meniscus lens L10f, the closest positive meniscus lens on the object side of the first lens group G1b, even if the light rays are sharply bent, the occurrence of aberrations is suppressed, and it works favorably for the Petzval sum, contributing to the correction of field curvature. Furthermore, by using a glass material that satisfies the above two equations for the negative meniscus lens L10r, the closest negative meniscus lens on the object side of the first lens group G1b, high performance and correction of chromatic aberration (second-order spectrum) can be achieved.

[0063] Among the second lens group G2 of the second embodiment, the positive lenses include three biconvex lenses L13r, L14, and L15f, and their abnormal partial dispersions ΔPgF are 0.0139, -0.0005, and 0.0277 respectively. Therefore, the biconvex lenses L13r and L15f satisfy the condition that the abnormal partial dispersion ΔPgF > 0.013. Furthermore, among the biconvex lenses L13r and L15f that satisfy the above formula, the refractive index nd of the biconvex lens L13r is 1.62846, which satisfies nd > 1.62. Thus, by using a plurality of positive lenses with positive abnormal partial dispersions in the second lens group G2, chromatic aberration (secondary spectrum) can be corrected, and by using positive lenses with a refractive index greater than 1.62, various aberrations and chromatic aberration can be corrected simultaneously.

[0064] Among the negative lenses in the second lens group G2 of the second embodiment, there are three negative lenses, namely, the biconcave lens L13f, the biconcave lens L15r, and the aspherical lens L16 which is also a biconcave lens, and their respective refractive indices nd are 1.72047, 1.72047, and 1.80610. Therefore, the biconcave lenses L13f and L15r satisfy the condition that nd < 1.73. Furthermore, the partial dispersions ΔPgF of the biconcave lenses L13f and L15r that satisfy the above formula are -0.0025 and -0.0025 respectively, which satisfy the condition that ΔPgF < -0.002. Thus, in the second lens group G2, by using a plurality of negative lenses with negative abnormal partial dispersions, chromatic aberration (secondary spectrum) can be corrected, and by using negative lenses with a refractive index less than 1.73, the Petzval sum can be set to a good value to contribute to the correction of field curvature.

[0065] Also, from Table 5, the focal length f2abal of the cemented lens L13 of the second lens group G2a is -47.89, which satisfies the condition that -55 < f2abal < 0. Furthermore, since the focal length of the biconcave lens L13f of this cemented lens L13 is f2abalm = -12.67, f2abal / f2abalm = 3.78, and thus f2abal / f2abalm > 3.75. Furthermore, from Table 6, the partial dispersion ΔPgF of the biconcave lens L13f and biconvex lens L13r constituting this cemented lens L13 is -0.0025 and 0.0139, satisfying ΔPgF2abalm < -0.002 and ΔPgF2abalp > 0.013. Thus, by using glass materials that satisfy the four equations above, the cemented lens L13 of the second lens group G2a is adopted in the second lens group G2a as a cemented lens L13 with negative refractive power, which is formed by bonding a lens with strong positive refractive power and a lens with strong negative refractive power, thereby correcting various aberrations and chromatic aberration.

[0066] Furthermore, from Table 5, in the second lens group G2b, f2 / f2b = 2.61, and f2 / f2b > 2.5. According to Table 6, the lens with the strongest positive refractive power in the second lens group G2 is the biconvex lens L14, with an anomalous dispersion ΔPgF = -0.0005, satisfying ΔPgF > -0.001. Thus, by placing a biconvex lens L14 with significantly stronger refractive power in the second lens group G2b, and by using glass material that satisfies the two equations above, various aberrations and chromatic aberration can be corrected.

[0067] [Table 7]

[0068] Table 7 shows the variable spacing between lenses.

[0069] [Table 8]

[0070] Table 8 shows the surface shape (aspheric coefficient) of an aspherical lens. In this case, in a Cartesian coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the following equation 1. In equation 1, R is the radius of curvature, K is the cone constant, A4, A6, A8, A10, and A12 are the 4th, 6th, 8th, 10th, and 12th order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. Equation 1 is as described above and is therefore omitted here.

[0071] Next, Figure 4 shows the spherical aberration, astigmatism, and distortion of the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Figure 4, it can be confirmed that good aberration control is achieved in all cases.

[0072] (Third embodiment) Next, as a third embodiment, Figure 5 illustrates and explains an imaging lens 300 with an overall focal length f=28.84mm, an F-number of 2.06, and a half-angle of view ω=36.87°.

[0073] In this embodiment, the imaging lens 300 comprises, in order along the optical axis from the object OBJ to the image plane IMG, a first lens group G1 having positive refractive power, an aperture diaphragm STO, and a second lens group G2 having positive refractive power. Thus, since both the first lens group G1 and the second lens group G2 have positive refractive power, this contributes to the overall miniaturization of the imaging lens 100.

[0074] The first lens group G1 comprises, in order from the object OBJ, the firsta lens group G1a, the firstb lens group G1b, and the firstc lens group G1c. The first lens group G1a consists of a single negative meniscus lens L17 with a negative refractive power and a convex surface facing the object OBJ. The negative meniscus lens L17 is an aspherical lens. The first lens group G1b has a negative refractive power as a whole and consists of a positive meniscus lens L18 with its concave surface facing the object OBJ side and a negative meniscus lens L19 with its concave surface facing the object OBJ side. The first lens group G1c has a positive refractive power as a whole and includes a biconvex lens L20 and a cemented lens L21 consisting of a biconvex lens L21f and a biconcave lens L21r bonded to the biconvex lens L21f.

[0075] As mentioned above, the negative meniscus lens L17, which is the negative lens of the first lens group G1a, employs an aspherical lens. By using an aspherical lens closest to the object OBJ, high performance and miniaturization can be achieved.

[0076] The second lens group G2 is positioned on the image plane IMG side of the aperture diaphragm STO, and consists of the seconda lens group G2a, the secondb lens group G2b, and the secondc lens group G2c, in that order from the object OBJ. The second lens group G2a consists of a single cemented lens L22 having negative refractive power, and the cemented lens L22 consists of a biconcave lens L22f and a biconvex lens L22r cemented to this biconcave lens L22f. The second lens group G2b consists of a single biconvex lens L23. The second lens group G2c has a negative refractive power as a whole and consists of a bonded lens L24 which is made up of a biconvex lens L24f and a biconcave lens L24r bonded to the biconvex lens L24f, and an aspherical lens L25 which is a biconcave lens.

[0077] Table 9 shows a table summarizing the various data for the third embodiment.

[0078] [Table 9]

[0079] Note that in Table 9, TL is the overall optical length, TLab is the distance on the optical axis from the most object-side surface of the optical system to the most image-side surface of the first lens group, f1 is the focal length of the first lens group G1, f1ab is the combined focal length of the first lens group G1a and the first lens group G1b, f2 is the focal length of the second lens group G2, f2abal is the focal length of the cemented lens L22 of the second lens group G2a, f2abalm is the focal length of the biconcave lens L22f which is the negative lens of the cemented lens L22 of the second lens group G2a, f2b is the focal length of the second lens group G2b, X1 is the movement amount from infinity focus to closest focus of the first lens group G1, and X2 is the movement amount from infinity focus to closest focus of the second lens group G2.

[0080] As shown in Table 9, in the third embodiment, X2 - X1 = 0.45, satisfying X2 - X1 > 0. Further, TL / f = 2.47, satisfying 2 < TL / f < 2.5. Thus, in the third embodiment, with the lens arrangement described above and by satisfying the above two equations, miniaturization can be achieved in a wide-angle lens while correcting chromatic aberration.

[0081] Also, in the third embodiment, f1 / f2 = 1.138, satisfying 1 < f1 / f2 < 1.14. In this way, the ratio of the focal lengths of the first lens group G1 and the second lens group G2 can be made close to 1, the power arrangement before and after the aperture stop STO becomes symmetric, and the performance change when the object distance changes can be suppressed.

[0082] Also, in the third embodiment, f1 / f1ab = -2.482, satisfying f1 / f1ab < -1.95. Furthermore, TLab / TL = 0.150, satisfying TLab / TL ≤ 0.15. In the third embodiment, by satisfying the above two equations, a lens group with a strong negative refractive power is arranged on the object OBJ side of the first lens group G1, and peripheral rays can be bent sharply, contributing to miniaturization.

[0083] Next, Table 10 shows the lens data for the optical lens system 300 of the third embodiment shown in Figure 5.

[0084] [Table 10]

[0085] Table 10 shows the radius of curvature R (mm) corresponding to the virtual plane and lens surface counted from the object OBJ side, the interplanar spacing D (mm) on the optical axis, the refractive index nd of the lens, the Abbe number νd of the lens, and the anomalous partial dispersion ΔPgF between the g·F lines, respectively. The radius of curvature R is considered positive when the lens surface is convex relative to the object OBJ, and negative when the lens surface is concave relative to the object OBJ. Furthermore, nd and νd are values ​​for the d-line (wavelength λ = 587.56 nm). Furthermore, D represents the distance from one face to the next numbered face. Additionally, the blanks for nd and νd indicate air. If the shape is aspherical, it is indicated with an asterisk (*) in the ASP column.

[0086] The anomalous partial dispersion ΔPgF between the g and F lines is calculated as PgF - 0.64833 + 0.00180νd, where PgF = (ng - nF) / (nF - nC): partial dispersion ratio between g and F lines, nC: refractive index of the C line (wavelength λ = 656.27 nm), nF: refractive index of the F line (wavelength λ = 486.13 nm), and ng: refractive index of the g line (wavelength λ = 435.83 nm).

[0087] From the results in Table 10, in the third embodiment, the refractive index of the positive meniscus lens L18 on the object OBJ side of the first lens group G1b is 2.00100, satisfying nd1bp > 1.76. The refractive index of the negative meniscus lens L19, which is closest to the object OBJ in the first lens group G1b, is 1.85883, satisfying 1.86 > nd1bm > 1.76. The Abbe number of the positive meniscus lens L18, which is closest to the object OBJ in the first lens group G1b, is 29.13, satisfying νd1bp > 29. The Abbe number of the negative meniscus lens L19, which is closest to the object OBJ in the first lens group G1b, is 30.00, satisfying 30 ≥ νd1bm > 28.4. By using a glass material that satisfies the above two equations for the positive meniscus lens L18, the closest positive meniscus lens on the object side of the first lens group G1b, even if the light rays are sharply bent, the occurrence of aberrations is suppressed, and it works favorably for the Petzval sum, contributing to the correction of field curvature. Furthermore, by using a glass material that satisfies the above two equations for the negative meniscus lens L19, the closest negative meniscus lens on the object side of the first lens group G1b, high performance and correction of chromatic aberration (second-order spectrum) can be achieved.

[0088] In the third embodiment, the second lens group G2 consists of three positive lenses: biconvex lens L22r, biconvex lens L23, and biconvex lens L24f. Their respective anomalous partial dispersion values ​​ΔPgF are 0.0139, -0.0001, and 0.0277. Therefore, the biconvex lenses L22r and L24f satisfy the anomalous partial dispersion property ΔPgF > 0.013. Furthermore, among the biconvex lenses L22r and L24f that satisfy the above equation, the refractive index of the biconvex lens L22r is nd = 1.62846 and satisfies nd > 1.62. Thus, by using multiple positive lenses with positive anomalous partial dispersion in the second lens group G2, chromatic aberration (second-order spectrum) can be corrected, and by using positive lenses with a refractive index greater than 1.62, various aberrations and chromatic aberration can be corrected simultaneously.

[0089] In the third embodiment, the second lens group G2 consists of three negative lenses: a biconcave lens L22f, a biconcave lens L24r, and a biconcave aspherical lens L25. Their respective refractive indices nd are 1.72047, 1.72047, and 1.80610. Therefore, the biconcave lenses L22f and L24r satisfy nd < 1.73. Furthermore, the partial dispersion ΔPgF values ​​of the biconcave lenses L22f and L24r that satisfy the above equation are -0.0025 and -0.0025, respectively, and satisfy ΔPgF < -0.002. Thus, in the second lens group G2, by using a plurality of negative lenses having a negative abnormal partial dispersion, chromatic aberration (secondary spectrum) is corrected, and by using a negative lens having a refractive index of less than 1.73, the Petzval sum is made a good value to contribute to the correction of field curvature.

[0090] Also, from Table 9, the focal length f2abal of the cemented lens L22 of the second a lens group G2a is -52.06, satisfying -55 < f2abal < 0. And since the focal length f2abalm of the biconcave lens L22f of this cemented lens L22 is -12.74, f2abal / f2abalm = 4.09, satisfying f2abal / f2abalm > 3.75. Furthermore, from Table 10, the partial dispersions ΔPgF of the biconcave lens L22f and the biconvex lens L22r constituting this cemented lens L22 are -0.0025 and 0.0139, satisfying ΔPgF2abalm < -0.002 and ΔPgF2abalp > 0.013. Thus, by using a lens material that satisfies the above four equations for the cemented lens L22 of the second a lens group G2a, and adopting it as the cemented lens L22 having a negative refractive power formed by bonding a lens with a strong positive refractive power and a lens with a strong negative refractive power in the second a lens group G2a, various aberrations and chromatic aberration can be corrected.

[0091] Also, from Table 9, in the second b lens group G2b, f2 / f2b = 2.56, satisfying f2 / f2b > 2.5. And according to Table 10, the lens having the strongest positive refractive power in the second lens group G2 is the biconvex lens L23, and its abnormal dispersion ΔPgF = -0.0001, satisfying ΔPgF > -0.001. Thus, by arranging the biconvex lens L23 having a significantly strong refractive power in the second b lens group G2b and using a lens material that satisfies the above two equations, various aberrations and chromatic aberration can be corrected.

[0092]

Table 11

[0093] Table 11 shows the variable spacing between lenses.

[0094] [Table 12]

[0095] Table 12 shows the surface shape (aspheric coefficient) of an aspherical lens. In this case, in a Cartesian coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the following equation 1. In equation 1, R is the radius of curvature, K is the cone constant, A4, A6, A8, A10, and A12 are the 4th, 6th, 8th, 10th, and 12th order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. Equation 1 is as described above and is therefore omitted here.

[0096] Next, Figure 6 shows the spherical aberration, astigmatism, and distortion of the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Figure 6, it can be confirmed that good aberrations are obtained in all cases.

[0097] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the scope of the present invention. [Explanation of symbols]

[0098] 100 Optical Lens Systems 200 Optical Lens System 300 Optical Lens System G1 First Lens Group G1a 1a lens group G1b 1st lens group G1c 1st lens group G2 Second Lens Group G2a 2a lens group G2b 2b lens group G2c 2nd lens group L1 Negative Meniscus Lens L2 cemented lens L2f positive meniscus lens L2r Negative Meniscus Lens L3 Biconvex Lens L4 cemented lens L4f biconvex lens L4r biconcave lens L5 Bonded Lens L5f biconcave lens L5r biconvex lens L6 Biconvex Lens L7 cemented lens L7f biconvex lens L7r Biconcave Lens L8 Aspherical Lens L9 Negative Meniscus Lens L10 Bonded Lens L10f positive meniscus lens L10r Negative Meniscus Lens L11 Biconvex Lens L12 Bonded Lens L12f biconvex lens L12r biconcave lens L13 Bonded Lens L13f biconcave lens L13r biconvex lens L14 Biconvex Lens L15 Bonded Lens L15f biconvex lens L15r biconcave lens L16 Aspherical Lens L17 Negative Meniscus Lens L18 Meniscus Lens L19 Negative Meniscus Lens L20 Biconvex Lens L21 Bonded Lens L21f Biconvex Lens L21r Biconcave Lens L22 Bonded Lens L22f biconcave lens L22r biconvex lens L23 Biconvex Lens L24 Bonded Lens L24f biconvex lens L24r biconcave lens L25 Aspherical Lens STO aperture diaphragm

Claims

1. It consists of, in order from the object side, a first lens group with positive refractive power, a wide-open aperture, and a second lens group with positive refractive power. The first lens group and the second lens group move independently toward the object when focusing at close range. The first lens group comprises, in order from the object side, the first a lens group, the first b lens group, and the first c lens group. The first lens group a has negative refractive power and consists of at least one negative lens with its convex surface facing the object. The first b lens group has a negative refractive power and consists of at least one positive lens and one negative lens from the object side, or at least one cemented lens consisting of at least one positive lens and a negative lens cemented to this positive lens from the object side. The first c lens group has a positive refractive power and consists of at least one positive lens and one cemented lens having a positive refractive power, from the object side. The second lens group comprises, in order from the object side, a second a lens group, a second b lens group, and a second c lens group. The second lens group a has negative refractive power and consists of at least one cemented lens. The second b lens group has a positive refractive power, The second lens group c has a negative refractive power and includes at least one cemented lens. Let X1 and X2 be the amounts of movement of the first and second lens groups from infinity focus to closest focus, respectively, and let TL be the distance along the optical axis from the object-side surface of the optical system to the image plane, and let f be the focal length of the entire optical system. X2-X1>0...(1) 2<TL / f<2.5...(2) An optical lens system characterized by satisfying the above formulas (1) and (2).

2. The optical lens system according to claim 1, characterized in that the negative lens closest to the object in the 1a lens group is aspherical.

3. If the focal length of the first lens group is f1 and the focal length of the second lens group is f2, 1<f1 / f2<1.14...(3) The optical lens system according to claim 1, characterized in that it satisfies the above formula (3).

4. Let the focal length of the first lens group be f1, and the combined focal length of the first a lens group and the first b lens group be f1ab. Let TL be the distance along the optical axis from the object-side surface of the optical system to the image plane, and let TLab be the distance along the optical axis from the object-side surface of the optical system to the image-side of the first b lens group. f1 / f1ab<-1.95...(4) TLab / TL≦0.15...(5) The optical lens system according to claim 1, characterized in that it satisfies formulas (4) and (5) above.

5. The positive and negative lenses closest to the object in the first b lens group are nd1bp>1.76...(6) 1.86>nd1bm>1.76...(7) νd1bp>29...(8) 30 ≥ νd1bm > 28.4 ... (9) The optical lens system according to claim 1, characterized in that it satisfies formulas (6), (7), (8), and (9) above. However, nd1bp is the refractive index of the d-line (wavelength λ = 587.56 nm) of the positive lens closest to the object in the first b lens group. nd1bm is the refractive index of the d-line (wavelength λ = 587.56 nm) of the negative lens closest to the object in the first b lens group. νd1bp is the Abbe number of the d-line (wavelength λ = 587.56 nm) of the positive lens closest to the object in the first b lens group. νd1bm is the Abbe number of the d-line (wavelength λ = 587.56 nm) of the negative lens closest to the object in the first b lens group.

6. When the refractive index of the positive lens in the second lens group is nd2p and the anomalous partial dispersion is ΔPgF2p, at least two or more positive lenses satisfy the following equation (10), The optical lens according to claim 1, characterized in that at least one positive lens among the lenses that satisfy the following formula (10) satisfies the following formula (11). ΔPgF2p>0.013...(10) nd2p>1.62...(11) However, ΔPgF = PgF - 0.64833 + 0.00180νd: anomalous partial dispersion between g and F lines. PgF = (ng - nF) / (nF - nC): Partial variance ratio between the g and F lines. nC: Refractive index of the C line (wavelength λ = 656.27 nm). nF: Refractive index of the F line (wavelength λ = 486.13 nm). ng: Refractive index of the g-line (wavelength λ = 435.83 nm).

7. The optical lens system according to claim 1, characterized in that, when the refractive index of the negative lens of the second lens group is nd2m and the anomalous partial dispersion is ΔPgF2m, at least two or more negative lenses satisfy the following formula (12) and the following formula (13). nd2m<1.73...(12) ΔPgF2m<-0.002...(13) However, ΔPgF = PgF - 0.64833 + 0.00180νd: anomalous partial dispersion between g and F lines. PgF = (ng - nF) / (nF - nC): Partial variance ratio between the g and F lines. nC: Refractive index of the C line (wavelength λ = 656.27 nm). nF: Refractive index of the F line (wavelength λ = 486.13 nm). ng: Refractive index of the g-line (wavelength λ = 435.83 nm).

8. Let f2abal be the focal length of the cemented lens closest to the object in the second lens group a, and f2abalm be the focal length of the negative lens of this cemented lens. When the anomalous partial dispersions of the positive and negative lenses of this cemented lens are ΔPgF2abalp and ΔPgF2abalm, respectively, The optical lens system according to claim 1, characterized in that the cemented lens on the object side of the second a lens group satisfies the following formulas (14), (15), (16), and (17). -55<f2abal<0...(14) f2abal / f2abalm>3.75...(15) ΔPgF2abalp>0.013...(16) ΔPgF2abalm<-0.002...(17) However, ΔPgF = PgF - 0.64833 + 0.00180νd: anomalous partial dispersion between g and F lines. PgF = (ng - nF) / (nF - nC): Partial variance ratio between the g and F lines. nC: Refractive index of the C line (wavelength λ = 656.27 nm). nF: Refractive index of the F line (wavelength λ = 486.13 nm). ng: Refractive index of the g-line (wavelength λ = 435.83 nm).

9. The optical lens system according to claim 1, characterized in that, when the focal length of the second lens group is f2, the focal length of the second b lens group is f2b, and the anomalous partial dispersion of the lens with the strongest positive refractive power among the second b lens group is ΔPgF2bp, the following formulas (18) and (19) are satisfied. f2 / f2b>2.5...(18) ΔPgF2bp>-0.001...(19) However, ΔPgF = PgF - 0.64833 + 0.00180νd: anomalous partial dispersion between g and F lines. PgF = (ng - nF) / (nF - nC): Partial variance ratio between the g and F lines. nC: Refractive index of the C line (wavelength λ = 656.27 nm). nF: Refractive index of the F line (wavelength λ = 486.13 nm). ng: Refractive index of the g-line (wavelength λ = 435.83 nm).

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