Optical lens system

Abstract

To provide a high-performance optical lens system while keeping the size down. [Solution] The lens group consists of a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power and moving when focusing at close range, with the lens closest to the object in the first lens group being a negative lens L1 with a concave surface facing the object, and the lens closest to the image being a negative lens L5 with a concave surface facing the image, and the lens closest to the object in the second lens group being a positive lens L6 with a convex surface facing the object, and the lens closest to the image being a negative lens L11 with a convex surface facing the image, with the lens closest to the object being a positive lens L6, and the lens closest to the image being a negative lens L11 with a convex surface facing the image, with the second lens group consisting of a 21st lens group G21 having positive refractive power, an aperture diaphragm STO, and a 22nd lens group G22 having positive refractive power, with the 22nd lens group consisting of a 221st lens group G221 having a negative lens L8f with a concave surface facing the object, and a negative lens L10r with a concave surface facing the image, and a 222nd lens group G222 consisting of a negative lens L11 on the image side.

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 high performance of a standard-angle-of-view lens are desired. For example, according to the optical lens system disclosed in Patent Document 1 (Japanese Patent No. 7048521), it includes a first lens group having a positive refractive power, a second lens group that moves during focusing, an aperture stop, and a third lens group that moves during focusing. All the lenses in the second lens group move integrally during focusing. The third lens group consists of all the lenses that move integrally with the second lens group during focusing. The combined focal length of the second lens group and the third lens group is positive. The first lens group includes at least four positive lenses and at least three negative lenses. The first lens group includes at least two cemented lenses in which at least one positive lens and at least one negative lens are cemented together. The most image-side cemented lens of the first lens group has a cemented surface facing the object side with a concave surface. The second cemented lens from the image side of the first lens group has a cemented surface facing the image side with a concave surface. The second lens group is disclosed to have a configuration consisting of two or three positive lenses and one negative lens.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-mentioned Patent Document 1, the first lens group, which is fixed when focusing, includes at least three negative lenses and a cemented lens. However, with this configuration of the first lens group, it is difficult to increase the lens power of the cemented lens, and the three negative lenses cause the lens on the image sensor side to become larger than these lenses, resulting in a problem where the diameter of the first lens group becomes large. [Means for solving the problem]

[0005] This invention has been made in view of the above circumstances, and aims to provide a high-performance optical lens system while suppressing an increase in size.

[0006] The present invention solves the above problem by a solution described below as one embodiment. In other words, the first lens group has positive refractive power, followed by a second lens group with positive refractive power, in order from the object side. When focusing at close range, only the second lens group moves towards the object. The first lens group has at least one lens on the object side that is a negative lens with a concave surface facing the object, and the lens on the image side that is a negative lens with a concave surface facing the image. The second lens group has at least one lens on the object side that is a positive lens with a convex surface facing the object, and the lens on the image side that is a negative lens with a convex surface facing the image. The second lens group consists of, in order from the object side, a 21st lens group with positive refractive power, an aperture diaphragm, and a 22nd lens with positive refractive power. The 22nd lens group consists of a 221st lens group having at least one negative lens on the object side that is a concave surface facing the object, and a 222nd lens group consisting only of the negative lens on the image side. This configuration allows for a high-performance optical lens system while keeping the overall size down.

[0007] Furthermore, the first lens group is characterized by not including a cemented lens. The presence of a cemented lens would cause the lens on the object side to become larger, but by not including a cemented lens in the first lens group, as in this configuration, the increase in size can be suppressed.

[0008] Furthermore, all lenses in the first lens group except for the lens closest to the object and the lens closest to the image are positive lenses. This configuration allows for minimizing the number of negative lenses, thereby shortening the overall lens length and preventing an increase in lens diameter.

[0009] Furthermore, one of the positive lenses in the first lens group satisfies the following condition (1): Gr1p-ΔPgF>0.020···(1), where Gr1p-ΔPgF is the largest value of ΔPgF, and 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, chromatic aberration can be corrected by using a positive lens with positive anomalous partial dispersion in the first lens group.

[0010] Furthermore, one of the positive lenses in the first lens group is characterized by satisfying the following conditions (2) and (3): Gr1p-νd < 23.00···(2), Gr1p-nd > 1.800···(3), where Gr1p-νd is the smallest Abbe number value, and Gr1p-nd is the refractive index of the d line (wavelength λ = 587.56 nm). With this configuration, the positive lens in the first lens group has high refractive index and high dispersion, which allows for good correction of spherical aberration, coma aberration, and chromatic aberration, contributing to a compact design while improving performance.

[0011] Furthermore, one of the negative lenses in the first lens group is characterized by satisfying the following conditions (4) and (5): 56.00>Gr1N-νd>34.00···(4), 1.730>Gr1N-nd>1.550···(5), where Gr1N-νd: Abbe number of the d line (wavelength λ=587.56nm). Gr1N-nd: refractive index of the d line (wavelength λ=587.56nm). With this configuration, chromatic aberration can be corrected and performance improved by using a negative lens with negative anomalous partial dispersion in the first lens group.

[0012] Furthermore, the 21st lens group is characterized by comprising one positive lens and a cemented lens composed of the positive lens and a negative lens bonded to the positive lens. This configuration allows for the inclusion of a telephoto type lens in the 21st lens group, effectively achieving miniaturization.

[0013] Furthermore, the positive lens closest to the object in the 21st lens group is characterized by being an aspherical lens. This configuration contributes to correcting coma aberration and improves performance.

[0014] Furthermore, the positive lens closest to the object in the 21st lens group is characterized by satisfying the following condition (6): Gr21p1-nd > 1.850···(6), where Gr21p1-nd is the refractive index of the d line (wavelength λ = 587.56 nm). This configuration allows for correction of image field curvature (Petzval sum), contributing to improved performance.

[0015] Furthermore, the 221 lens group is characterized in that, starting from the object side, it consists of a cemented lens comprising at least a negative lens with a concave surface facing the object side and a positive lens bonded to this negative lens, one or more positive lenses, and a cemented lens comprising a positive lens and at least a negative lens bonded to this positive lens with a concave surface facing the image side. This configuration allows for effective correction of chromatic aberration and field curvature by placing a cemented lens immediately after the aperture diaphragm.

[0016] Furthermore, the negative lens of the 222 lens group is characterized by being an aspherical lens with a convex surface facing the image side. This configuration can correct image field curvature and contribute to improved performance. [Effects of the Invention]

[0017] It is possible to provide a high-performance optical lens system while suppressing enlargement.

Brief Description of the Drawings

[0018] [Figure 1] It is a configuration diagram of an 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 an 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 an 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

[0019] 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 in the first embodiment of the present invention. FIG. 2 is a longitudinal aberration diagram at infinity of the optical lens system 100 in the first embodiment of the present invention. FIG. 3 is a configuration diagram of an optical lens system 200 in the second embodiment of the present invention. FIG. 4 is a longitudinal aberration diagram at infinity of the optical lens system 200 in the second embodiment of the present invention. FIG. 5 is a configuration diagram of an optical lens system 300 in the third embodiment of the present invention. FIG. 6 is a longitudinal aberration diagram at infinity of the optical lens system 300 in the third embodiment of the present invention.

[0020] 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 may be omitted.

[0021] In each embodiment, the optical lens systems 100, 200, and 300 are, for example, interchangeable imaging lenses used in a photographic camera or a video camera. As shown in Figures 1, 3, and 5, the optical lens systems 100, 200, and 300 are equipped with a first lens group G1 and a second lens group G2 on the optical axis, extending from the object OBJ to the image plane IMG.

[0022] Furthermore, the second lens group G2 consists of a 21st lens group G21 with positive refractive power, an aperture diaphragm STO, and a 22nd lens G22 with positive refractive power, in that order from the object OBJ side. When focusing at close range, only the second lens group (21st lens group G21, aperture diaphragm STO, and 22nd lens G22) moves towards the object.

[0023] For convenience, numbers are assigned to the surfaces of each lens in Figures 1, 3, and 5, but these surface numbers do not necessarily correspond between the different embodiments. Furthermore, the bonding surface in cemented lenses is assigned the number 1. Additionally, since the aperture diaphragm STO is treated as a virtual surface, consecutive surface numbers are omitted.

[0024] (First Embodiment) In the first embodiment, Figure 1 illustrates and explains an imaging lens 100 with an overall focal length f = 50.15 mm, an F-number of 1.435, and a half-angle of view ω = 23.12°.

[0025] In this embodiment, the imaging lens 100 comprises a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, arranged sequentially along the optical axis from the object OBJ to the image plane IMG. 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.

[0026] The first lens group G1 consists of, in order from the object OBJ, a biconcave lens L1, a biconvex lens L2, a biconvex lens L3, a biconvex lens L4, and a negative meniscus lens L5 with its convex surface facing the object OBJ. Thus, in the first lens group G1, the lens L1 closest to the object (OBJ) is a negative lens with its concave surface facing the object, and the lens L5 closest to the image sensor (IMG) is a negative lens with its concave surface facing the image.

[0027] Thus, the first lens group G1 does not include a cemented lens. By omitting a cemented lens from the first lens group G1 in this configuration, it is possible to suppress an increase in size.

[0028] Furthermore, all lenses in the first lens group G1 except for the biconcave lens L1 closest to the object (OBJ) and the negative meniscus lens L5 closest to the image plane (IMG) (L2-L4) are positive lenses. In this way, by minimizing the number of negative lenses, it is possible to shorten the overall length of the lens and prevent an increase in the lens diameter.

[0029] The second lens group G2 consists of, in order from the object OBJ side, the 21st lens group G21 having positive refractive power, the aperture diaphragm STO, and the 22nd lens G22 having positive refractive power.

[0030] The 21st lens group G21 consists of, in order from the object OBJ side, a positive meniscus lens L6 with its convex surface facing the object OBJ side, a cemented lens L7 which is made up of a positive meniscus lens L7f with its convex surface facing the object OBJ side and a negative meniscus lens L7r which is cemented to the positive meniscus lens L7f with its convex surface facing it. In this way, the 21st lens group G21 is configured as a telephoto type, which allows for effective miniaturization.

[0031] The positive meniscus lens L6, which is the lens closest to the object's obj (obj) in lens group G21, is an aspherical lens. Therefore, it contributes to correcting coma aberration and can improve performance.

[0032] The aperture diaphragm STO is positioned on the image sensor side (IMG) of the 21st lens group G21, and the 22nd lens group G22 is positioned on the image sensor side (IMG) of the aperture diaphragm STO.

[0033] The 22nd lens group G22 consists of the 221st lens group G221 and the 222nd lens group G222, in order from the object OBJ side. The 221st lens group G221 consists of, in order from the object OBJ side, a bonded lens L8 consisting of a biconcave lens L8f and a biconvex lens L8r bonded to the biconcave lens L8f, a biconvex lens L9, and a bonded lens L10 consisting of a positive meniscus lens L10f with its convex surface facing the image plane IMG side and a biconcave lens L10r bonded to the positive meniscus lens L10f. The 222nd lens group G222 consists of a negative meniscus lens L11 with a convex surface facing the image plane IMG.

[0034] Thus, in the 221st lens group G221, chromatic aberration and field curvature can be effectively corrected by placing the cemented lens L8 immediately after the aperture diaphragm STO. Furthermore, the negative meniscus lens L11, which constitutes the 222nd lens group G222, is an aspherical lens, and therefore can correct field curvature and contribute to improved performance.

[0035] Table 1 shows a table summarizing various data from the first embodiment. [Table 1]

[0036] In Table 1, Gr1_L is the total length of the first lens group G1, Gr2_L is the total length of the second lens group G2, Gr1 is the focal length of the first lens group G1, Gr2 is the focal length of the second lens group G2, Gr21 is the focal length of the 21st lens group G21, Gr22 is the focal length of the 22nd lens group G22, G221 is the focal length of the 221st lens group G221, and G222 is the focal length of the 222nd lens group G222.

[0037] Furthermore, Gr1P-ΔPgF is the largest positive anomalous partial dispersion value among the lenses of the first lens group G1, ΔPgF=PgF-0.64833+0.00180νd is the anomalous partial dispersion between the g and F lines, PgF=(ng-nF) / (nF-nC) is the partial dispersion ratio between the g and F lines, nC is the refractive index of the C line (wavelength λ=656.27nm), nF is the refractive index of the F line (wavelength λ=486.13nm), and ng is the refractive index of the g line (wavelength λ=435.83nm). Gr1P-νd is the smallest Abbe number value among the lenses in the first lens group G1, Gr1P-nd is the refractive index value of the d line of Gr1P-νd, Gr1N-νd is the Abbe number value of the negative lens among the lenses in the first lens group G1, Gr1N-nd is the refractive index value of the d line of Gr1N-νd, and Gr21P1-nd is the refractive index value of the d line of the positive lens in the 21st lens group G21 that is closest to the object OBJ.

[0038] As shown in Table 1, in the first embodiment, Gr1P-ΔPgF=0.023 and Gr1P-ΔPgF>0.020 is satisfied. Therefore, chromatic aberration can be corrected by having the positive lens of the first lens group G1 possess positive anomalous partial dispersion.

[0039] Furthermore, as shown in Table 1, in the first embodiment, Gr1P-νd = 22.76, Gr1P-nd = 1.8081, and Gr1P-νd < 23.00, Gr1P-nd > 1.800. Therefore, the positive lens of the first lens group G1 has high refractive index and high dispersion, which allows for good correction of spherical aberration, coma aberration, and chromatic aberration, contributing to a more compact design while improving performance.

[0040] Furthermore, as shown in Table 1, in the first embodiment, Gr1N-νd = 55.07 and Gr1N-nd = 1.553, satisfying 56.00 > Gr1N-νd > 34.00 and 1.730 > Gr1N-nd > 1.550. Therefore, the negative lens in the first lens group G1 has negative anomalous partial dispersion, which corrects chromatic aberration and improves performance.

[0041] Furthermore, as shown in Table 1, in the first embodiment, Gr21P1-nd = 1.851 and Gr21P1-nd > 1.850 is satisfied. Therefore, it is possible to correct image field curvature (Petzval sum) and contribute to improved performance.

[0042] Next, Table 2 shows the lens data for the optical lens system 100 of the first embodiment shown in Figure 1.

[0043] [Table 2]

[0044] Table 2 shows the radius of curvature R (mm), interplanar spacing D (mm), refractive index nd, and Abbe number νd of the lens, corresponding to the virtual plane and lens surface counted from the object OBJ side. 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.

[0045] [Table 3]

[0046] Table 3 shows the variable spacing between lenses.

[0047] [Table 4]

[0048] 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.

[0049]

number

[0050] 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.

[0051] (Second Embodiment) Next, as a second embodiment, Figure 3 illustrates and explains an imaging lens 200 with an overall focal length f=50.82mm, an F-number of 1.442, and a half-angle of view ω=22.92°.

[0052] In this embodiment, the imaging lens 200 comprises a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, arranged sequentially along the optical axis from the object OBJ to the image plane IMG. 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 200.

[0053] The first lens group G1 consists of, in order from the object OBJ, a biconcave lens L12, a biconvex lens L13, a biconvex lens L14, a biconvex lens L15, a biconvex lens L16, and a negative meniscus lens L17 with its convex surface facing the object OBJ. Thus, in the first lens group G1, the lens L12 closest to the object (OBJ) is a negative lens with its concave surface facing the object, and the lens L16 closest to the image sensor (IMG) is a negative lens with its concave surface facing the image.

[0054] Thus, the first lens group G1 does not include a cemented lens. By omitting a cemented lens from the first lens group G1 in this configuration, it is possible to suppress an increase in size.

[0055] Furthermore, all lenses in the first lens group G1 except for the biconcave lens L12 closest to the object (OBJ) and the negative meniscus lens L17 closest to the image plane (IMG) (L13-L16) are positive lenses. In this way, by minimizing the number of negative lenses, it is possible to shorten the overall length of the lens and prevent an increase in the lens diameter.

[0056] The second lens group G2 consists of, in order from the object OBJ side, the 21st lens group G21 having positive refractive power, the aperture diaphragm STO, and the 22nd lens G22 having positive refractive power.

[0057] The 21st lens group G21 consists of, in order from the object OBJ side, a positive meniscus lens L18 with its convex surface facing the object OBJ side, a biconvex lens L19f, and a bonded lens L19 which is made up of a biconcave lens L19r joined to the biconvex lens L19f. In this way, the 21st lens group G21 is configured as a telephoto type, which allows for effective miniaturization.

[0058] The positive meniscus lens L18, which is the lens closest to the object's obj (obj) in lens group G21, is an aspherical lens. Therefore, it contributes to correcting coma aberration and can improve performance.

[0059] The aperture diaphragm STO is positioned on the image sensor side (IMG) of the 21st lens group G21, and the 22nd lens group G22 is positioned on the image sensor side (IMG) of the aperture diaphragm STO.

[0060] The 22nd lens group G22 consists of the 221st lens group G221 and the 222nd lens group G222, in order from the object OBJ side. The 221st lens group G221 consists of, in order from the object OBJ side, a bonded lens L20 consisting of a biconcave lens L20f and a biconvex lens L20r bonded to the biconcave lens L20f, a biconvex lens L21, and a bonded lens L22 consisting of a positive meniscus lens L220f with its convex surface facing the image plane IMG side and a biconcave lens L22r bonded to the positive meniscus lens L22f. The 222nd lens group G222 consists of a negative meniscus lens L23 with a convex surface facing the image plane IMG.

[0061] Thus, in the 221st lens group G221, chromatic aberration and field curvature can be effectively corrected by placing the cemented lens L20 immediately after the aperture diaphragm STO. Furthermore, the negative meniscus lens L23, which constitutes the 222nd lens group G222, is an aspherical lens, and therefore can correct field curvature and contribute to improved performance.

[0062] Table 5 shows a table summarizing the various data for the second embodiment. [Table 5]

[0063] In Table 5, Gr1_L is the total length of the first lens group G1, Gr2_L is the total length of the second lens group G2, Gr1 is the focal length of the first lens group G1, Gr2 is the focal length of the second lens group G2, Gr21 is the focal length of the 21st lens group G21, Gr22 is the focal length of the 22nd lens group G22, G221 is the focal length of the 221st lens group G221, and G222 is the focal length of the 222nd lens group G222.

[0064] Furthermore, Gr1P-ΔPgF is the largest positive anomalous partial dispersion value among the lenses of the first lens group G1, ΔPgF=PgF-0.64833+0.00180νd is the anomalous partial dispersion between the g and F lines, PgF=(ng-nF) / (nF-nC) is the partial dispersion ratio between the g and F lines, nC is the refractive index of the C line (wavelength λ=656.27nm), nF is the refractive index of the F line (wavelength λ=486.13nm), and ng is the refractive index of the g line (wavelength λ=435.83nm). Gr1P-νd is the smallest Abbe number value among the lenses in the first lens group G1, Gr1P-nd is the refractive index value of the d line of Gr1P-νd, Gr1N-νd is the Abbe number value of the negative lens among the lenses in the first lens group G1, Gr1N-nd is the refractive index value of the d line of Gr1N-νd, and Gr21P1-nd is the refractive index value of the d line of the positive lens in the 21st lens group G21 that is closest to the object OBJ.

[0065] As shown in Table 5, in the second embodiment, Gr1P-ΔPgF=0.023 and Gr1P-ΔPgF>0.020 is satisfied. Therefore, chromatic aberration can be corrected by having the positive lens of the first lens group G1 possess positive anomalous partial dispersion.

[0066] Furthermore, as shown in Table 5, in the second embodiment, Gr1P-νd=22.76, Gr1P-nd=1.8081, and Gr1P-νd<23.00, Gr1P-nd>1.800 are satisfied. Therefore, the positive lens of the first lens group G1 has high refractive index and high dispersion, which allows for good correction of spherical aberration, coma aberration, and chromatic aberration, contributing to a more compact design while improving performance.

[0067] Furthermore, as shown in Table 5, in the second embodiment, Gr1N-νd = 55.07 and Gr1N-nd = 1.553, satisfying 56.00 > Gr1N-νd > 34.00 and 1.730 > Gr1N-nd > 1.550. Therefore, the negative lens in the first lens group G1 has negative anomalous partial dispersion, which corrects chromatic aberration and improves performance.

[0068] Furthermore, as shown in Table 5, in the second embodiment, Gr21P1-nd = 1.851 and Gr21P1-nd > 1.850 is satisfied. Therefore, it is possible to correct image field curvature (Petzval sum) and contribute to improved performance.

[0069] Next, Table 6 shows the lens data for the optical lens system 200 of the second embodiment shown in Figure 3.

[0070] [Table 6]

[0071] Table 6 shows the radius of curvature R (mm), interplanar spacing D (mm), refractive index nd, and Abbe number νd of the lens, corresponding to the virtual plane and lens surface counted from the object OBJ side. 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.

[0072] [Table 7]

[0073] Table 7 shows the variable spacing between lenses.

[0074] [Table 8]

[0075] 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.

[0076] 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.

[0077] (Third embodiment) Next, as a third embodiment, Figure 5 illustrates and explains an imaging lens 300 with an overall focal length f=50.87mm, an F-number of 1.456, and a half-angle of view ω=22.85°.

[0078] In this embodiment, the imaging lens 300 comprises a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, arranged sequentially along the optical axis from the object OBJ to the image plane IMG. Since both the first lens group G1 and the second lens group G2 have positive refractive power, this contributes to miniaturization of the entire imaging lens 300.

[0079] The first lens group G1 consists of, in order from the object OBJ, a biconcave lens L24, a biconvex lens L25, a biconvex lens L26, a biconvex lens L27, and a negative meniscus lens L28 with its convex surface facing the object OBJ. The biconvex lens L26 is also an aspherical lens. Thus, in the first lens group G1, the lens L24 closest to the object (OBJ) is a negative lens with its concave surface facing the object, and the lens L28 closest to the image sensor (IMG) is a negative lens with its concave surface facing the image.

[0080] Thus, the first lens group G1 does not include a cemented lens. By omitting a cemented lens from the first lens group G1 in this configuration, it is possible to suppress an increase in size.

[0081] Furthermore, all lenses in the first lens group G1 except for the biconcave lens L24 closest to the object (OBJ) and the negative meniscus lens L26 closest to the image plane (IMG) (L24-L27) are positive lenses. In this way, by minimizing the number of negative lenses, it is possible to shorten the overall length of the lens and prevent an increase in the lens diameter.

[0082] The second lens group G2 consists of, in order from the object OBJ side, the 21st lens group G21 having positive refractive power, the aperture diaphragm STO, and the 22nd lens G22 having positive refractive power.

[0083] The 21st lens group G21 consists of, in order from the object OBJ side, a positive meniscus lens L29 with its convex surface facing the object OBJ side, a biconvex lens L30f, and a bonded lens L30 which is made up of a biconcave lens L30r joined to the biconvex lens L30f. In this way, the 21st lens group G21 is configured as a telephoto type, which allows for effective miniaturization.

[0084] The positive meniscus lens L29, which is the lens closest to the object's obj (obj.) in the 21st lens group G21, is an aspherical lens. Therefore, it contributes to correcting coma aberration and can improve performance.

[0085] The aperture diaphragm STO is positioned on the image sensor side (IMG) of the 21st lens group G21, and the 22nd lens group G22 is positioned on the image sensor side (IMG) of the aperture diaphragm STO.

[0086] The 22nd lens group G22 consists of the 221st lens group G221 and the 222nd lens group G222, in order from the object OBJ side. The 221st lens group G221 consists of, in order from the object OBJ side, a bonded lens L31 consisting of a biconcave lens L31f and a biconvex lens L31r bonded to the biconcave lens L31f, a biconvex lens L32, and a bonded lens L33 consisting of a positive meniscus lens L33f with its convex surface facing the image plane IMG side and a biconcave lens L33r bonded to the positive meniscus lens L33f. The 222nd lens group G222 consists of a negative meniscus lens L34 with a convex surface facing the image plane IMG.

[0087] Thus, in the 221st lens group G221, chromatic aberration and field curvature can be effectively corrected by placing the cemented lens L31 immediately after the aperture diaphragm STO. Furthermore, the negative meniscus lens L34, which constitutes the 222nd lens group G222, is an aspherical lens, and therefore can correct field curvature and contribute to improved performance.

[0088] Table 9 shows a table summarizing the various data for the third embodiment.

[0089] [Table 9]

[0090] In Table 9, Gr1_L is the total length of the first lens group G1, Gr2_L is the total length of the second lens group G2, Gr1 is the focal length of the first lens group G1, Gr2 is the focal length of the second lens group G2, Gr21 is the focal length of the 21st lens group G21, Gr22 is the focal length of the 22nd lens group G22, G221 is the focal length of the 221st lens group G221, and G222 is the focal length of the 222nd lens group G222.

[0091] Furthermore, Gr1P-ΔPgF is the largest positive anomalous partial dispersion value among the lenses of the first lens group G1, ΔPgF=PgF-0.64833+0.00180νd is the anomalous partial dispersion between the g and F lines, PgF=(ng-nF) / (nF-nC) is the partial dispersion ratio between the g and F lines, nC is the refractive index of the C line (wavelength λ=656.27nm), nF is the refractive index of the F line (wavelength λ=486.13nm), and ng is the refractive index of the g line (wavelength λ=435.83nm). Gr1P-νd is the smallest Abbe number value among the lenses in the first lens group G1, Gr1P-nd is the refractive index value of the d line of Gr1P-νd, Gr1N-νd is the Abbe number value of the negative lens among the lenses in the first lens group G1, Gr1N-nd is the refractive index value of the d line of Gr1N-νd, and Gr21P1-nd is the refractive index value of the d line of the positive lens in the 21st lens group G21 that is closest to the object OBJ.

[0092] As shown in Table 9, in the third embodiment, Gr1P-ΔPgF=0.023 and Gr1P-ΔPgF>0.020 is satisfied. Therefore, chromatic aberration can be corrected by having the positive lens of the first lens group G1 possess positive anomalous partial dispersion.

[0093] Furthermore, as shown in Table 9, in the third embodiment, Gr1P-νd=22.76, Gr1P-nd=1.8081, and Gr1P-νd<23.00, Gr1P-nd>1.800 are satisfied. Therefore, the positive lens of the first lens group G1 has high refractive index and high dispersion, which allows for good correction of spherical aberration, coma aberration, and chromatic aberration, contributing to a more compact design while improving performance.

[0094] Furthermore, as shown in Table 9, in the third embodiment, Gr1N-νd = 55.07 and Gr1N-nd = 1.553, satisfying 56.00 > Gr1N-νd > 34.00 and 1.730 > Gr1N-nd > 1.550. Therefore, the negative lens in the first lens group G1 has negative anomalous partial dispersion, which corrects chromatic aberration and improves performance.

[0095] Furthermore, as shown in Table 9, in the third embodiment, Gr21P1-nd = 1.851 and Gr21P1-nd > 1.850 is satisfied. Therefore, it is possible to correct image field curvature (Petzval sum) and contribute to improved performance.

[0096] Next, Table 10 shows the lens data for the optical lens system 300 of the third embodiment shown in Figure 5.

[0097] [Table 10]

[0098] Table 10 shows the radius of curvature R (mm), interplanar spacing D (mm), refractive index nd, and Abbe number νd of the lens, corresponding to the virtual plane and lens surface counted from the object OBJ side. 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.

[0099] [Table 11]

[0100] Table 11 shows the variable spacing between lenses.

[0101] [Table 12]

[0102] 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.

[0103] 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.

[0104] 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]

[0105] 100 Optical Lens Systems 200 Optical Lens System 300 Optical Lens System G1 First Lens Group G2 Second Lens Group G21 21st lens group G22 22nd lens group G221 Lens group 221 G222 Lens group 222 L1 Biconcave Lens L2 Biconvex Lens L3 Biconvex Lens L4 Biconvex Lens L5 Negative Meniscus Lens L6 positive meniscus lens L7f positive meniscus lens L7r Negative Meniscus Lens L7 cemented lens L8f biconcave lens L8r biconvex lens L8 cemented lens L9 Biconvex Lens L10f positive meniscus lens L10r Biconcave Lens L10 Bonded Lens L11 Negative Meniscus Lens L12 Biconcave Lens L13 Biconvex Lens L14 Biconvex Lens L15 Biconvex Lens L16 Biconvex Lens L17 Negative Meniscus Lens L18 Meniscus Lens L19f biconvex lens L19r biconcave lens L19 Bonded Lens L20f Biconcave Lens L20r biconvex lens L20 Bonded Lens L21 Biconvex Lens L22f positive meniscus lens L22r Biconcave Lens L22 Bonded Lens L23 Negative Meniscus Lens L24 Biconcave Lens L25 Biconvex Lens L26 Biconvex Lens L27 Biconvex Lens L28 Negative Meniscus Lens L29 positive meniscus lens L30f Biconvex Lens L30r Biconcave Lens L30 Bonded Lens L31f Biconcave Lens L31r biconvex lens L31 Bonded Lens L32 Biconvex Lens L33f positive meniscus lens L33r Biconcave Lens L33 Bonded Lens L34 Negative Meniscus Lens STO aperture diaphragm

Claims

1. It consists of a first lens group having positive refractive power and a second lens group having positive refractive power, in that order from the object side. When focusing at close range, only the second lens group moves toward the object. The lens closest to the object in the first lens group is a negative lens with at least one concave surface facing the object, and the lens closest to the image is a negative lens with one concave surface facing the image. The lens closest to the object in the second lens group is a positive lens with its convex surface facing the object, and the lens closest to the image is a negative lens with its convex surface facing the image. The second lens group consists of, in order from the object side, a 21st lens group having positive refractive power, an aperture diaphragm, and a 22nd lens having positive refractive power. The 22nd lens group is an optical lens system comprising a 221st lens group having a negative lens in which the lens closest to the object has at least one concave surface facing the object, and a 222nd lens group consisting only of the negative lens closest to the image.

2. The optical lens system according to claim 1, wherein the first lens group does not include a cemented lens.

3. The optical lens system according to the claim that all lenses in the first lens group except the lens closest to the object and the lens closest to the image are positive lenses.

4. The optical lens system according to claim 1, wherein any of the positive lenses of the first lens group satisfy the following condition (1). Gr1p-ΔPgF>0.020...(1) However, Gr1p - ΔPgF is the largest value of ΔPgF, ΔPgF = PgF - 0.64833 + 0.00180νd: Anomalous partial dispersion between the 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).

5. The optical lens system according to claim 1, wherein at least one of the positive lenses in the first lens group satisfies the following conditions (2) and (3). Gr1p−νd<23.00...(2) Gr1p-nd>1.800...(3) However, Gr1p-νd: the smallest Abbe number value. Gr1p-nd: Refractive index of the d line (wavelength λ = 587.56 nm).

6. The optical lens system according to claim 1, wherein at least one of the negative lenses in the first lens group satisfies the following conditions (4) and (5). 56.00>Gr1N-νd>34.00...(4) 1.730>Gr1N-nd>1.550...(5) However, Gr1N-νd: the Abbe number of the d-line (wavelength λ = 587.56 nm). Gr1N-nd: Refractive index of the d line (wavelength λ = 587.56 nm).

7. The optical lens system according to claim 1, wherein the 21st lens group comprises a positive lens and a cemented lens composed of a positive lens and a negative lens bonded to the positive lens.

8. The optical lens system according to claim 1, wherein the positive lens closest to the object in the 21st lens group is an aspherical lens.

9. The positive lens closest to the object in the 21st lens group is the optical lens system according to claim 1, which satisfies the following condition (6). Gr21p1-nd>1.850...(6) However, this refers to the refractive index of the Gr21p1-nd line (wavelength λ = 587.56 nm).

10. The aforementioned 221 lens group is arranged in order from the object side: A cemented lens consisting of at least a negative lens with its concave side facing the object and a positive lens bonded to this negative lens, One or more positive lenses, A cemented lens consisting of a positive lens and a negative lens bonded to this positive lens, with at least one concave surface facing the image side. The optical lens system according to claim 1, comprising the above.

11. The optical lens system according to claim 1, wherein the negative lens of the 222 lens group is an aspherical lens with a convex surface facing the image side.

Images