Optical lens system

Abstract

To provide an optical lens system which improves various aberrations while achieving reduction in the size and the weight, and has improved optical performances.SOLUTION: An optical lens system 100 is composed of a first lens group G1 having positive refractive power, an aperture diaphragm STO, and a second lens group G2 having positive refractive power. The first lens group G1 is composed of two lenses of a negative meniscus lens L1 with a convex surface facing an object OBJ side and a lens L2 of a positive lens component in order from the object OBJ side. The second lens group is composed of a 2-1st lens group G2A, a 2-2nd lens group G2B, and a 2-3rd lens group G2C in order from the object OBJ side. The 2-1st lens group G2A is composed of a negative lens L3 with a concave surface facing the object OBJ side and a positive lens L4 joined to the negative lens in order from the object OBJ side. The 2-2nd lens group G2B is composed of three or less lenses including a positive lens L5 and a negative lens L6. The 2-3rd lens group G2C is composed of one aspherical lens L7 of the positive lens component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a small, wide-angle optical lens system that can achieve small size and high performance as a lens for an interchangeable lens camera. [Background technology]

[0002] Generally, when lenses for interchangeable lens cameras used in photographic and videography equipment are made smaller, problems arise in that component processing errors become larger, optical performance deteriorates, and manufacturing becomes more difficult.

[0003] Patent Document 1 (Japanese Patent No. 7171017) discloses an optical lens system that is composed of, in order from the object side, a first lens group having positive refractive power, an aperture stop, a second lens group having positive refractive power, and a third lens group having negative refractive power, and that when focusing from an object at infinity to an object at a close distance, the distance between the first lens group and the second lens group decreases and the distance between the second lens group and the third lens group G3 increases, and the second lens group moves towards the object side.

[0004] Furthermore, Patent Document 2 (Japanese Patent No. 7026605) discloses an optical lens system having only three lens groups consisting of, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, in which an aperture stop is disposed between the lens surface of the first lens group closest to the image side and the lens surface of the third lens group closest to the object side, in which, when focusing from an object at infinity to a closest object, the first lens group and the third lens group are fixed with respect to the image plane and the second lens group moves along the optical axis, in which the first lens group consists, in order from the object side to the image side, of a negative lens and a positive lens, and in which the third lens group includes, in order from the object side to the image side, a negative lens and a positive lens. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7171017 [Patent Document 2] Patent No. 7026605 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the configurations disclosed in Patent Documents 1 and 2 employ an inner focus system in which the second lens group is movable along the optical axis, which results in a complex structure and the need for a large number of lens holding frames inside the housing, resulting in an increase in size and weight. Moreover, in the configuration disclosed in Patent Document 2, the lens located closest to the image is a positive lens constituted by a spherical surface. This means that the back focus tends to become long in order to improve peripheral performance, making it difficult to shorten the length of the lens system in the optical axis direction. [Means for solving the problem]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical lens system which is compact and lightweight, has improved optical performance by improving various aberrations.

[0008] The present invention solves the above problems by the solution means described below as one embodiment. That is, it is an optical lens system composed of a first lens group having positive refractive power, an aperture stop, and a second lens group having positive refractive power, wherein the first lens group is composed of two lenses, a negative meniscus lens with a convex surface facing the object side, and a lens of a positive lens component, in that order from the object side, the second lens group is composed of a 2-1 lens group, a 2-2 lens group, and a 2-3 lens group, in that order from the object side, the 2-1 lens group is composed of a negative lens with a concave surface facing the object side and a positive lens cemented to this negative lens, the 2-2 lens group is composed of three or less lenses including a positive lens and a negative lens, and the 2-3 lens group is composed of one aspherical lens of a positive lens component.

[0009] By configuring the first lens group from two lenses as described above, it is possible to reduce the size of the lens system in front of the aperture diaphragm, which has a significant effect on the size of the product, and this contributes to miniaturization. Furthermore, by configuring the 2-1st lens group, which is located on the image side of the aperture stop, from the object side, with a negative lens whose concave surface faces the object side and a positive lens cemented to this negative lens, it is possible to effectively correct chromatic aberration and curvature of field, thereby improving optical performance. Furthermore, by using an aspherical lens for the lens in the second lens group closest to the image side, it is possible to contribute to size reduction while maintaining peripheral performance.

[0010] The lens having the highest refractive index among the positive lenses in the first lens group has a reference refractive index (nd) that satisfies nd > 1.9.

[0011] With the above configuration, the higher the refractive index of the positive lens, the better the correction of spherical aberration and coma aberration, which contributes to miniaturization. In addition, the radius of curvature of the lens can be reduced, making it easier to polish and reducing the sensitivity of the entire optical system to decentering.

[0012] When the refractive index of the negative lens constituting the 2-1st lens group is nd_n1 and the refractive index of the positive lens is nd_p1, the relationship nd_p1>nd_n1 is satisfied.

[0013] The refractive index of the negative lens in the 2-1 group needs to be lower than that of the positive lens in the 2nd lens group, but the above-described configuration prevents the occurrence of astigmatism without worsening the Petzval sum, and also prevents the 2-2nd lens group and the 2-3rd lens group from becoming bulky, contributing to size reduction.

[0014] The aspherical lens in the 2-3rd lens group is an aspherical lens of a positive lens component with a convex surface facing the image side.

[0015] Generally, when the incident angle to the imaging device is large, it will cause a decrease in the peripheral light quantity. However, with the above configuration, the incident angle to the imaging device, that is, the light ray emission angle from the imaging optical system, can be suppressed, and a decrease in sensitivity can be suppressed. In addition, by using an aspherical lens, an optical lens system with improved peripheral optical performance can be realized.

[0016] It is characterized in that the reference refractive index (nd) of the lens with the highest refractive index among the positive lenses of the second - 2 lens group satisfies nd > 1.9.

[0017] With the above configuration, the higher the refractive index of the positive lens, the better the spherical aberration and coma aberration can be corrected, which contributes to miniaturization. Also, the radius of curvature of the lens can be suppressed, reducing the polishing difficulty and the decentration sensitivity of the entire optical system.

[0018] It is characterized in that when the focal length of the second - 3 lens group is f23 and the focal length of the entire system is f, 1.0 < f23 / f < 3.0 is satisfied.

[0019] With the above configuration, a constant focal length can be set with respect to the focal length of the entire system, which contributes to miniaturization.

[0020] When focusing on a near - distance object, it is characterized by moving the entire lens.

Advantages of the Invention

[0021] An optical lens system with improved optical performance by improving various aberrations while achieving miniaturization and weight reduction can be realized.

Brief Description of the Drawings

[0022] [Figure 1] It is a configuration diagram of the optical lens system in the first embodiment of the present invention. [Diagram 2] It is a longitudinal aberration diagram of the optical lens system in the first embodiment of the present invention at infinity. [Diagram 3]FIG. 11 is a diagram illustrating the configuration of an optical lens system according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a longitudinal aberration diagram of the optical lens system according to the second embodiment of the present invention at infinity. [Diagram 5] FIG. 11 is a diagram illustrating the configuration of an optical lens system according to a third embodiment of the present invention. [Figure 6] FIG. 11 is a longitudinal aberration diagram of the optical lens system according to the third embodiment of the present invention at infinity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Each embodiment will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an optical lens system 100 according to a first embodiment of the present invention. FIG. 2 is a diagram showing longitudinal aberration of the optical lens system 100 according to the first embodiment of the present invention at infinity. FIG. 3 is a diagram showing the configuration of an optical lens system 200 according to a second embodiment of the present invention. FIG. 4 is a diagram showing longitudinal aberration of the optical lens system 200 according to the second embodiment of the present invention at infinity. FIG. 5 is a diagram showing the configuration of an optical lens system 300 according to a third embodiment of the present invention. FIG. 6 is a diagram showing longitudinal aberration of the optical lens system 300 according to the third embodiment of the present invention at infinity.

[0024] 2, 4, and 6, the legends for C-line (wavelength 656.27 nm), d-line (wavelength 587.56 nm), and g-line (wavelength 435.83 nm) are shown in the upper right corner. Note that in all the drawings for explaining each embodiment, members having the same functions are given the same reference numerals, and repeated explanations thereof may be omitted.

[0025] The optical lens systems 100, 200, and 300 in each embodiment are, by way of example, imaging lenses used in photo cameras or video cameras. As shown in Figures 1, 3, and 5, a first lens group G1 and a second lens group G2 are arranged on the optical axis from an object OBJ to an image plane IMG, and an aperture stop STO is arranged between the first lens group G1 and the second lens group G2. The second lens group G2 is made up of, from the object OBJ to the image plane IMG, a 2-1 lens group G2A, a 2-2 lens group G2B, and a 2-3 lens group G2C.

[0026] In addition, the optical lens systems 100, 200, and 300 in each embodiment move all of the lenses when focusing on a close-up object, and do not employ an inner focus system, which makes it possible to reduce the size and weight of the system without complicating the structure.

[0027] For convenience, the surfaces of the lenses are numbered in Figures 1, 3, and 5, but the surface numbers do not necessarily correspond between the embodiments. Also, the cemented surfaces of cemented lenses are given the same number. Furthermore, because the diaphragm portion STO is counted as a virtual surface, the consecutive surface numbers are omitted.

[0028] (First embodiment) In the first embodiment, a small wide-angle imaging lens 100 having a total focal length f=18.54 mm, an F-number of 2.82, and a half angle of view ω=37.95° will be illustrated and described in FIG.

[0029] The imaging lens 100 in this embodiment has a first lens group G1 and a second lens group G2, and has an aperture stop STO between the first lens group G1 and the second lens group G2. Both the first lens group G1 and the second lens group G2 have positive refractive power.

[0030] The first lens group G1 is composed of, in order from the object OBJ, a negative meniscus lens L1 with a convex surface facing the object OBJ side, and a biconvex lens L2 with a convex surface facing the object OBJ side. In this way, by constructing the first lens group G1 using two lenses, L1 and L2, a negative lens and a positive lens, it is possible to reduce the size of the lens system in front of the aperture stop STO, which has a significant effect on the size of the product, and this can contribute to miniaturization.

[0031] The second lens group G2 is composed of a second-1 lens group G2A, a second-2 lens group G2B, and a second-3 lens group G2C.

[0032] The second-1 lens group G2A is composed of, in order from the object OBJ, a negative lens L3 with a concave surface facing the object OBJ side and a positive lens L4 joined to this negative lens L3. Specifically, the second-1 lens group G2A is composed of a cemented lens in which a biconcave lens L3 and a biconvex lens L4 are cemented together. By configuring the second-1 lens group G2A in this way, chromatic aberration and field curvature can be effectively corrected, and the optical performance can be improved.

[0033] The second-2 lens group G2B is composed of, in order from the object OBJ, a positive meniscus lens L5 with a concave surface facing the object side OBJ and a negative meniscus lens L6 joined to this positive meniscus lens L5 and having a concave surface facing the object side OBJ. That is, the second-2 lens group G2B is composed of three or fewer lenses including a positive lens and a negative lens.

[0034] The second-3 lens group is composed of only an aspherical lens L7 having a positive lens component. In this way, by using the aspherical lens L7 for the lens closest to the image IMG side of the second lens group G2, it is possible to contribute to miniaturization while maintaining the peripheral performance.

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

Table 1

[0036] According to Table 1, when the focal length of the second-3 lens group is f23 and the focal length of the entire system is f, f23 / f = 1.98, which satisfies 1.0 < f23 / f < 3.0. For this reason, a constant focal length can be set with respect to the focal length of the entire system, contributing to miniaturization.

[0037] Next, Tables 2 to 4 show lens data for the optical lens system 100 according to the first embodiment shown in FIG.

[0038] [Table 2]

[0039] Table 2 shows the radius of curvature R (mm) corresponding to the virtual surface and lens surface counted from the object OBJ side, the surface spacing D (mm) on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens. If the lens has an aspheric shape, it is indicated with an * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. In addition, nd and νd are values ​​for the d line (587.56 nm). Also, D is the distance from the first surface to the next surface. Furthermore, the blanks in nd and νd indicate air.

[0040] [Table 3]

[0041] Table 3 shows the variable spacing between the lenses.

[0042] [Table 4]

[0043] The surface shape (aspheric coefficients) of an aspheric lens are shown in Table 4. In this case, in an orthogonal 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 formula 1. In formula 1, R is the radius of curvature, K is the conic 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.

[0044]

number

[0045] Furthermore, according to Table 2, the lens L2 has the highest refractive index among the positive lenses in the first lens group G1, and its refractive index nd = 2.00100. In other words, the lens L2 has the highest refractive index among the positive lenses in the first lens group G1, and satisfies the condition that the refractive index nd > 1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0046] Also, according to Table 2, the refractive index nd_n1 of the negative lens L3 constituting the 2-1st lens group G2A is 1.71736, and the refractive index nd_p1 of the positive lens L4 is 1.90043, which satisfies nd_p1>nd_n1. This configuration prevents the occurrence of astigmatism without deteriorating the Petzval sum, and also prevents the 2-2nd lens group G2B and the 2-3rd lens group G2C from becoming bulky, contributing to size reduction.

[0047] Furthermore, according to Table 2, the lens L5 has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, and its refractive index nd=1.90043. In other words, the refractive index nd of the lens L5, which has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, satisfies nd>1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0048] Fig. 2 shows the spherical aberration, astigmatism, and distortion in the optical lens system 100. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 2, it can be confirmed that good aberration is obtained for all of them.

[0049] Second embodiment Next, in the second embodiment, a small wide-angle imaging lens 200 with a total system focal length f=18.54 mm, an F-number of 2.81, and a half angle of view ω=37.95° will be described by way of example in FIG.

[0050] The imaging lens 200 in this embodiment has a first lens group 2G1 and a second lens group G2, and has an aperture stop STO between the first lens group G1 and the second lens group G2. Both the first lens group G1 and the second lens group G2 have positive refractive power.

[0051] The first lens group G1 is composed of, in order from the object OBJ, a negative meniscus lens L8 with a convex surface facing the object OBJ side, and a biconvex lens L9 with a convex surface facing the object OBJ side. In this way, by constructing the first lens group G1 using two lenses, L8 and L9, a negative lens and a positive lens, it is possible to reduce the size of the lens system in front of the aperture stop STO, which has a significant effect on the size of the product, and this can contribute to miniaturization.

[0052] The second lens group G2 is made up of a 2-1 lens group G2A, a 2-2 lens group G2B, and a 2-3 lens group G2C.

[0053] The 2-1st lens group G2A is composed of, in order from the object OBJ, a negative lens L10 with its concave surface facing the object side OBJ, and a positive lens L11 cemented to this negative lens L10. Specifically, the 2-1st lens group G2A is composed of a cemented lens in which the biconcave lens L10 and the biconvex lens L11 are cemented together. By configuring the 2-1st lens group G2A in this way, chromatic aberration and curvature of field can be effectively corrected, and optical performance can be improved.

[0054] The 2-2nd lens group G2B is composed of, in order from the object OBJ, a positive meniscus lens L12 with its concave surface facing the object side OBJ, a negative meniscus lens L13 cemented to this positive meniscus lens L12 with its concave surface facing the object side OBJ, and a negative meniscus lens L14 with its concave surface facing the object side OBJ. That is, the second second lens group G2B is composed of three or fewer lenses including a positive lens and a negative lens.

[0055] The second third lens group is composed of only the aspherical lens L15 of the positive lens component. Thus, by using the aspherical lens L15 for the lens closest to the image IMG side of the second lens group G2, it is possible to contribute to miniaturization while maintaining peripheral performance.

[0056] Table 5 shows a table summarizing various data of the second embodiment.

Table 5

[0057] According to Table 5, when the focal length of the second third lens group is f23 and the focal length of the entire system is f, f23 / f = 1.80, which satisfies 1.0 < f23 / f < 3.0. Therefore, it is possible to set a constant focal length with respect to the focal length of the entire system, contributing to miniaturization.

[0058] Subsequently, the lens data of the optical lens system 200 of the second embodiment shown in FIG. 3 are shown in Tables 6 to 8.

[0059]

Table 6

[0060] In Table 6, the radius of curvature R (mm), the distance D (mm) between surfaces on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens corresponding to the virtual surface and the lens surface counted from the object OBJ side are shown respectively. When having an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are values for the d line (587.56 nm). Also, D is the distance from the first surface to the next surface. Furthermore, the blanks in nd and νd indicate air.

[0061] [Table 7]

[0062] Table 7 shows the variable spacing between lenses.

[0063] [Table 8]

[0064] Table 8 shows the surface shape (aspheric coefficients) of the aspheric lens. In this case, in an orthogonal 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 above-mentioned formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, and A12 are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. Formula 1 is as described above and will be omitted here.

[0065] Furthermore, according to Table 6, the lens L9 has the highest refractive index among the positive lenses in the first lens group G1, and its refractive index nd = 2.00100. In other words, the lens L9 has the highest refractive index among the positive lenses in the first lens group G1, and satisfies the condition that the refractive index nd > 1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0066] Also, according to Table 6, the refractive index nd_n1 of the negative lens L10 constituting the 2-1st lens group G2A is 1.71736, and the refractive index nd_p1 of the positive lens L11 is 1.90043, which satisfies nd_p1>nd_n1. This configuration prevents the occurrence of astigmatism without deteriorating the Petzval sum, and also prevents the 2-2nd lens group G2B and the 2-3rd lens group G2C from becoming bulky, contributing to size reduction.

[0067] Furthermore, according to Table 6, the lens L12 has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, and its refractive index nd = 1.90043. In other words, the refractive index nd of the lens L12, which has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, satisfies nd > 1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0068] Fig. 4 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 4, it can be confirmed that good aberration is obtained for all of them.

[0069] Next, in the third embodiment, a small wide-angle imaging lens 300 having a total system focal length f=18.54 mm, an F-number of 2.82, and a half angle of view ω=37.95° will be described by way of example in FIG.

[0070] The imaging lens 300 in this embodiment has a first lens group 2G1 and a second lens group G2, and has an aperture stop STO between the first lens group G1 and the second lens group G2. Both the first lens group G1 and the second lens group G2 have positive refractive power.

[0071] The first lens group G1 is composed of, in order from the object OBJ, a negative meniscus lens L16 with a convex surface facing the object OBJ, and a biconvex lens L17 with a convex surface facing the object OBJ. In this way, by constructing the first lens group G1 using two lenses, L16 and L17, a negative lens and a positive lens, it is possible to reduce the size of the lens system in front of the aperture stop STO, which has a significant effect on the size of the product, and this can contribute to miniaturization.

[0072] The second lens group G2 is made up of a 2-1 lens group G2A, a 2-2 lens group G2B, and a 2-3 lens group G2C.

[0073] The 2-1st lens group G2A is composed of, in order from the object OBJ, a negative lens L18 with its concave surface facing the object side OBJ, and a positive lens L19 cemented to this negative lens L18. Specifically, the 2-1st lens group G2A is composed of a cemented lens in which the biconcave lens L18 and the biconvex lens L19 are cemented together. By configuring the 2-1st lens group G2A in this way, chromatic aberration and curvature of field can be effectively corrected, and optical performance can be improved.

[0074] The 2-2nd lens group G2B is composed of, in order from the object OBJ, a positive meniscus lens L20 with its concave surface facing the object side OBJ, and a negative meniscus lens L21 cemented to this positive meniscus lens L20 with its concave surface facing the object side OBJ. That is, the 2-2nd lens group G2B is composed of three or less lenses including a positive lens and a negative lens.

[0075] The 2-3rd lens group is composed solely of an aspheric lens L22 which is a positive lens component. In this way, by using the aspherical lens L22 as the lens in the second lens group G2 closest to the image IMG side, it is possible to contribute to size reduction while maintaining peripheral performance.

[0076] Table 9 shows a summary of various data for the third embodiment. [Table 9]

[0077] According to Table 9, when the focal length of the second-third lens group is f23 and the focal length of the entire system is f, f23 / f = 1.78, satisfying 1.0 < f23 / f < 3.0. Therefore, it is possible to set a constant focal length with respect to the focal length of the entire system, contributing to miniaturization.

[0078] Subsequently, the lens data of the optical lens system 300 of the third embodiment shown in FIG. 5 are shown in Tables 10 to 12.

[0079]

Table 10

[0080] In Table 10, the radius of curvature R (mm) corresponding to the virtual surface and the lens surface counted from the object OBJ side, the distance D (mm) between the surfaces on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens are shown respectively. When having an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are values for the d-line (587.56 nm). Also, D is the distance from one surface to the surface with the next number. Furthermore, the blank spaces for nd and νd indicate that it is air.

[0081]

Table 11

[0082] Table 11 is a table showing the variable intervals between the lenses.

[0083]

Table 12

[0084] Table 12 shows the surface shape (aspheric coefficients) of the aspheric lens. In this case, in an orthogonal 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 above-mentioned formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, and A12 are the fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. Formula 1 is as described above and will be omitted here.

[0085] Also, according to Table 9, the lens L17 has the highest refractive index among the positive lenses in the first lens group G1, and its refractive index nd = 2.00100. In other words, the lens L17 has the highest refractive index among the positive lenses in the first lens group G1, and satisfies the condition that the refractive index nd > 1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0086] Also, according to Table 9, the refractive index nd_n1 of the negative lens L18 constituting the 2-1st lens group G2A is 1.71736, and the refractive index nd_p1 of the positive lens L19 is 1.90043, which satisfies nd_p1>nd_n1. This configuration prevents the occurrence of astigmatism without deteriorating the Petzval sum, and also prevents the 2-2nd lens group G2B and the 2-3rd lens group G2C from becoming bulky, contributing to size reduction.

[0087] Also, according to Table 9, the lens L20 has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, and its refractive index nd=1.90043. In other words, the refractive index nd of the lens L20, which has the highest refractive index among the positive lenses in the 2-2nd lens group G2B, satisfies nd>1.9. This configuration allows for good correction of spherical aberration and coma aberration, contributing to miniaturization. It also allows for a smaller radius of curvature of the lens, making polishing less difficult and reducing the sensitivity of the entire optical system to decentering.

[0088] Fig. 6 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 6, it can be confirmed that good aberration is obtained for all of them.

[0089] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the present invention. [Explanation of symbols]

[0090] 100 Optical lens system 200 Optical Lens System 300 Optical Lens System G1 First lens group G2 2nd lens group G2A 2nd-1st lens group G2B 2nd-2nd lens group G2C 2nd-3rd lens group L1 negative meniscus lens L2 biconvex lens L3 Biconcave Lens L4 biconvex lens L5 positive meniscus lens L6 negative meniscus lens L7 Aspheric Lens L8 negative meniscus lens L9 Biconvex Lens L10 Biconcave Lens L11 Biconvex lens L12 positive meniscus lens L13 negative meniscus lens L14 negative meniscus lens L15 aspheric lens L16 negative meniscus lens L17 Biconvex lens L18 Biconcave Lens L19 Biconvex Lens L20 positive meniscus lens L21 negative meniscus lens L22 Aspheric Lens OBJ object STO aperture stop IMG Image

Claims

1. An optical lens system comprising a first lens group having a positive refractive power, an aperture stop, and a second lens group having a positive refractive power, The first lens group is composed of two lenses, in that order from the object side, a negative meniscus lens having a convex surface facing the object side and a lens having a positive lens component, the second lens group is composed of, in order from the object side, a 2-1 lens group, a 2-2 lens group, and a 2-3 lens group, The 2-1st lens group is composed of, in order from the object side, a negative lens having a concave surface facing the object side and a positive lens cemented to the negative lens, The 2-2 lens group is composed of three or less lenses including a positive lens and a negative lens, The optical lens system is characterized in that the 2-3 lens group is composed of one aspherical lens that is a positive lens component.

2. The reference refractive index (nd) of the lens having the highest refractive index among the positive lenses in the first lens group is n d > 1.9 2. The optical lens system according to claim 1, wherein the following is satisfied:

3. When the refractive index of the negative lens constituting the 2-1st lens group is nd_n1 and the refractive index of the positive lens is nd_p1, nd_p1 > nd_n1 2. The optical lens system according to claim 1, wherein the following is satisfied:

4. 2. The optical lens system according to claim 1, wherein the aspherical lens in the second-third lens group is an aspherical lens of a positive lens component with a convex surface facing the image side.

5. The reference refractive index (nd) of the lens having the highest refractive index among the positive lenses in the 2-2 lens group is n d > 1.9 2. The optical lens system according to claim 1, wherein the following is satisfied:

6. When the focal length of the 2-3 lens group is f23 and the focal length of the entire system is f, 1.0<f23 / f<3.0 2. The optical lens system according to claim 1, wherein the following is satisfied:

7. 2. The optical lens system according to claim 1, wherein all of the lenses are moved when focusing on a close-distance object.

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