Optical lens system

Abstract

To provide an optical lens system which is miniaturized, furthermore is improved in various aberrations thereby having improved optical performance.SOLUTION: An optical lens system is provided which is comprised of a first lens group G1 with positive refractive power, and a second lens group G2 with positive refractive power, and in which only the second lens group G2 moves to an object side, so that an interval between the first lens group G1 and the second lens group G2 changes. The first lens group G1 is comprised of four or more lenses including, in order from an object side: two negative lenses L1, L2 directing their protruding surfaces to the object side; one positive lens L3; and a negative lens L4 directing its recessed surface to the object side. The second lens group G2 comprises, in order from the object side, a second-1 lens group G21 with positive refractive power, an aperture stop STO, and a second-2 lens group G22 with positive refractive power. The second-1 lens group G21 is comprised of only one positive lens, or a positive lens L6 and a negative lens L7 bonded to the positive lens L6.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Generally, in a lens for an interchangeable-lens camera used in equipment for photographing and video shooting, etc., when promoting miniaturization, the component processing error becomes large, so the optical performance deteriorates, the accuracy required for component processing becomes high, and the manufacturing difficulty increases.

[0003] As a large-aperture optical lens system, Patent Document 1 (Japanese Patent No. 7140571) discloses that, in order from the object side, there is a first lens group having a positive refractive power, and a second lens group disposed on the image side of the first lens group and having a positive refractive power. The interval between adjacent lens groups changes during focusing, and when focusing from infinity to a close object, the second lens group moves toward the object side. The second lens group has, in order from the object side to the image side, a first positive lens, an aperture stop, and a second positive lens, and it is described that the abnormal partial dispersibility ΔθgF of the material is specified.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the configuration described in Patent Document 1, the lens on the object side of the aperture stop employs a lens having a high refractive index and abnormal partial dispersibility. However, since a lens with a high refractive index has a large dispersion, it is difficult to correct chromatic aberration, and a large number of lenses are required for chromatic aberration correction, so there is a problem that miniaturization is difficult.

Means for Solving the Problems

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical lens system that improves optical performance by improving various aberrations while achieving miniaturization.

[0007] The present invention solves the above problems by means of the solution described below as one embodiment. That is, it is composed of a first lens group having a positive refractive power and a second lens group disposed on the image side of the first lens group and having a positive refractive power. When focusing on a near object, only the second lens group moves toward the object side, and the distance between the first lens group and the second lens group changes. The first lens group is composed of four or more lenses including, in order from the object side, two negative lenses with convex surfaces facing the object side, one positive lens, and a negative lens with a concave surface facing the object side. The second lens group is composed of, in order from the object side, a second-1 lens group having a positive refractive power, an aperture stop, and a second-2 lens group having a positive refractive power. The second-1 lens group is characterized by being composed of only one positive lens or a positive lens and a negative lens joined to the positive lens.

[0008] By moving only the second lens group for focusing as described above, the weight of the moving lens group can be reduced, and the strength of the mechanical components supporting it can be decreased, thus contributing to the miniaturization of the entire product. In addition, by making all of the first lens group, the second lens group, the second-1 lens group, and the second-2 lens group have positive refractive power components, it contributes to miniaturization. In addition, by configuring the first lens group as described above, a decrease in component accuracy can be prevented, and various aberrations can be effectively corrected. By making the third lens from the object side of the first lens group a convex lens, the front and rear lenses can be reduced in diameter. In addition, by making the second-1 lens group a single lens, difficulties during manufacturing can be prevented, and it greatly contributes to miniaturization.

[0009] The two negative lenses on the object side of the first lens group are concave meniscus lenses, and one of the two concave meniscus lenses is an aspherical lens. According to this configuration, it contributes to high performance and miniaturization.

[0010] The positive lens on the object side of the first lens group is a lens with convex shapes on both sides. According to this configuration, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product.

[0011] Any one of the positive lenses in the first lens group satisfies the following two conditional expressions. Gr1p-vd < 24.00 Gr1p-nd > 1.77000 However, Gr1p-vd is the Abbe number of the d line (wavelength λ = 587.56 nm), and Gr1p-nd is the refractive power of the d line (wavelength λ = 587.56 nm). According to this configuration, by using a high-refractive-index and high-dispersion lens as the positive lens of the first lens group, it contributes to the correction of chromatic aberration and miniaturization.

[0012] Any one of the positive lenses in the first lens group satisfies the following conditional expression. Gr1p-ΔPgF > 0.02 However, ΔPgF is PgF - 0.64833 + 0.00180vd, which represents the abnormal partial dispersion between the g and F lines. PgF is (ng - nF) / (nF - nC), which represents the partial dispersion ratio between the g and F lines. nC is the refractive index of the C line (wavelength λ = 656.27 nm), nF is the refractive index of the F line (wavelength λ = 486.13 nm), and ng is the refractive index of the g line (wavelength λ = 435.83 nm). According to this configuration, chromatic aberration can be corrected by using a positive lens with positive abnormal partial dispersion in the first lens group.

[0013] When the focal length of the second lens group is f2 and the focal length of the second - 1 lens group is f21, it is characterized by satisfying 1.0 < f21 / f2 < 2.0. According to this configuration, by setting the focal length of the second - 1 lens group relative to the focal length of the second lens group within a predetermined range, it contributes to miniaturization.

[0014] The second - 2 lens group is composed of, in order from the object side, a negative lens with a concave surface facing the object side, a positive lens joined to the negative lens, and two or more lenses including a positive lens and a negative lens. According to this configuration, by using a cemented lens immediately after the aperture stop, chromatic aberration and field curvature can be effectively corrected.

[0015] Any one of the negative lenses of the second - 2 lens group is characterized by satisfying the following two conditional expressions. 56.00 > Gr22N - vd > 34.00 1.75000 > Gr22N - nd > 1.55000 However, Gr22N - vd is the Abbe number of the d - line (wavelength λ = 587.56 nm), and Gr22N - nd is the refractive power of the d - line (wavelength λ = 587.56 nm). According to this configuration, high performance can be achieved and chromatic aberration can be corrected.

[0016] The lens closest to the imaging side of the second - 2 lens group is an aspherical lens with a negative lens component having a convex surface facing the imaging side. According to this configuration, it can contribute to high performance and miniaturization.

[0017] Any one of the positive lenses of the second - 2 lens group is characterized by satisfying the following conditional expression. Gr22p - ΔPgF > 0.03 However, ΔPgF = PgF - 0.64833 + 0.00180vd, which represents the abnormal partial dispersibility between the g and F lines. PgF = (ng - nF) / (nF - nC), which represents the partial dispersion ratio between the g and F lines. nC is the refractive index of the C line (wavelength λ = 656.27 nm), nF is the refractive index of the F line (wavelength λ = 486.13 nm), and ng is the refractive index of the g line (wavelength λ = 435.83 nm). According to this configuration, chromatic aberration is corrected by using a positive lens having positive abnormal partial dispersibility for the second - 2 lens.

Advantages of the Invention

[0018] It is possible to realize an optical lens system with improved optical performance by improving various aberrations while achieving miniaturization.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0020] 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 a 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 a 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 a 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.

[0021] 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 figures for explaining each embodiment, members having the same function are denoted by the same reference numerals, and repeated explanations may be omitted.

[0022] The optical lens systems 100, 200, and 300 in each embodiment are, as an example, imaging lenses used in a photographic camera or a video camera. As shown in FIGS. 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 toward an imaging surface IMG. The second lens group G2 is composed of a second-1 lens group G21 on the object OBJ side and a second-2 lens group G22 on the imaging surface IMG side, and an aperture stop STO is arranged between the second-1 lens group G21 and the second-2 lens group G22.

[0023] Also, in focusing on a close-distance object, the optical lens systems 100, 200, and 300 in each embodiment are configured to move only the second lens group G2. Therefore, the weight of the moving lens group can be reduced, and the strength of the mechanical components supporting it can be lowered, contributing to the miniaturization of the entire product.

[0024] Incidentally, for convenience, in FIGS. 1, 3, and 5, the surfaces of each lens are numbered, but the surface numbers do not necessarily correspond between the embodiments. Also, a single number is assigned to the joint surface of the cemented lens. Further, since the aperture stop STO is counted as a virtual surface, the consecutive surface numbers are skipped.

[0025] (First Embodiment) In the first embodiment, a small wide-angle imaging lens 100 with an overall focal length f = 24.08 mm, an F-number 1.43, and a semi-field angle ω = 41.59° will be exemplified and described with reference to FIG. 1.

[0026] 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 second - 1 lens group G21 and the second - 2 lens group that constitute the second lens group G2. The first lens group G1, the second lens group G2, the second - 1 lens group G21, and the second - 2 lens group G22 all have positive refractive powers. By having all the lens groups have positive refractive powers in this way, it contributes to miniaturization.

[0027] The first lens group G1 includes, in order from the object OBJ, a negative meniscus lens L1 with a convex surface facing the object OBJ side, a negative meniscus lens L2 with a convex surface facing the object OBJ side, a biconvex lens L3, a negative meniscus lens L4 with a concave surface facing the object OBJ side, and a biconvex lens L5. In this way, the first lens group G1 can prevent a decrease in component accuracy and effectively correct various aberrations by arranging the lenses in the above order from the object OBJ side.

[0028] Making at least one of the two negative meniscus lenses L1 and L2 on the object OBJ side of the first lens group G1 an aspherical lens contributes to high performance and miniaturization. Also, by making the third lens from the object OBJ side of the first lens group G1 a biconvex lens L3, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product. In addition, by using a biconvex lens L5 as the lens on the imaging surface IMG side of the first lens group G1, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product.

[0029] The second - 1 lens group G21 that constitutes the second lens group G2 is composed of, in order from the object OBJ, only a biconvex lens L6 and a biconcave lens L7 joined to this biconvex lens L6. With such a configuration, the second - 1 lens group G21 prevents difficulties during manufacturing and greatly contributes to miniaturization.

[0030] The second - 2 lens group G22 disposed on the imaging surface IMG side of the second - 1 lens group G21 is composed of, in order from the object OBJ, a biconcave lens L8, a biconvex lens L9 joined to this biconcave lens L8, a biconvex lens L10, a biconvex lens L11, a negative meniscus lens L12 with its convex surface facing the object OBJ side, and a negative meniscus lens L13 with its concave surface facing the object OBJ side. In this way, since the second - 2 lens group G22 uses a cemented lens immediately after the aperture stop STO, it can effectively correct chromatic aberration and field curvature. In addition, by making the surface 25 on the imaging surface IMG side of the negative meniscus lens L13 on the most imaging surface IMG side an aspherical shape, it contributes to high - performance and miniaturization.

[0031] Table 1 shows a table summarizing various data of the first embodiment.

Table 1

[0032] Note that in Table 1, Gr1p-vd is the smallest Abbe number among the positive lenses of the first lens group G1, Gr1p-nd is the refractive power of the d-line (wavelength λ = 587.56 nm) of Gr1p-vd, Gr1p-ΔPgF is the positive anomalous partial dispersibility of the first lens group G1, Gr22N-vd is the Abbe number of the d-line of the concave lens of the second - 2 lens group G22, Gr22N-nd is the refractive power of the d-line (wavelength λ = 587.56 nm) of Gr22N-vd, and Gr22p-ΔPgF is the positive anomalous partial dispersibility of the second - 2 lens group G22.

[0033] According to Table 1, at least one of the positive lenses of the first lens group G1 satisfies the two formulas of Gr1p-vd < 24.00 and Gr1p-nd > 1.77000, which contributes to the correction of chromatic aberration and miniaturization. Also, at least one of the negative lenses of the second - 2 lens group G22 satisfies the two formulas of 56.00 > Gr22N-vd > 34.00 and 1.75000 > Gr22N-nd > 1.55000, which can improve the performance and correct the chromatic aberration.

[0034] Moreover, since f21 / f2 is 1.95 and satisfies 1.0 < f21 / f2 < 2.0, by setting the focal length f21 of the second - 1 lens group G21 within a predetermined range with respect to the focal length f2 of the second lens group G2, it can contribute to miniaturization.

[0035] Also, Gr1p-ΔPgF is actually 0.0213 and satisfies Gr1p-ΔPgF > 0.02. Since a positive lens with positive anomalous partial dispersibility is used for the first lens group G1, chromatic aberration can be corrected. Note that ΔPgF is PgF - 0.64833 + 0.00180vd, which represents the anomalous partial dispersibility between the g and F lines. PgF is the partial dispersion ratio between the g and F lines, which is represented by (ng - nF) / (nF - nC). Here, nC is the refractive index of the C-line (wavelength λ = 656.27 nm), nF is the refractive index of the F-line (wavelength λ = 486.13 nm), and ng is the refractive index of the g-line (wavelength λ = 435.83 nm). The description of ΔPgF is the same below and will be omitted.

[0036] Also, Gr22p - ΔPgF is 0.04, which satisfies Gr22p - ΔPgF > 0.03, and since a positive lens with positive abnormal partial dispersion is used for the second - second lens group G22, chromatic aberration can be corrected.

[0037] Subsequently, the lens data of the optical lens system 100 of the first embodiment shown in FIG. 1 are shown in Tables 2 to 4.

[0038] [Table 2]

[0039] In Table 2, the radius of curvature R (mm), the axial distance D (mm) between surfaces, 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 one surface to the surface with the next number. Furthermore, the blank spaces for nd and νd indicate that it is air.

[0040] [Table 3]

[0041] Table 3 is a table showing the variable intervals between the lenses.

[0042] [Table 4]

[0043] Table 4 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the 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 Equation 1. In Equation 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th orders respectively, and H is the distance from the origin on the optical axis.

[0044]

Number

[0045] Figure 2 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 100. Each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Figure 2, it can be confirmed that good aberrations are obtained in all cases.

[0046] (Second Embodiment) Subsequently, in the second embodiment, a small wide-angle lens 200 with a focal length f = 24.51 mm, an F-number of 1.45, and a semi-field angle ω = 41.54° for the entire system will be illustrated and described with reference to Figure 3.

[0047] The imaging lens 200 in this embodiment has a first lens group G1 and a second lens group G2, and has an aperture stop STO between the second - 1 lens group G21 and the second - 2 lens group that constitute the second lens group G2. The first lens group G1, the second lens group G2, the second - 1 lens group G21, and the second - 2 lens group G22 all have positive refractive powers. Having all lens groups with positive refractive powers in this way contributes to miniaturization.

[0048] The first lens group G1 includes, in order from the object OBJ, a negative meniscus lens L15 with a convex surface facing the object OBJ side, a negative meniscus lens L16 with a convex surface facing the object OBJ side, a biconvex lens L17, a negative meniscus lens L18 with a concave surface facing the object OBJ side, and a biconvex lens L19. In this way, by arranging the lenses in the above order from the object OBJ side, the first lens group G1 can prevent a decrease in component accuracy and effectively correct various aberrations.

[0049] By using at least one of the two negative meniscus lenses L15 and L16 on the object OBJ side of the first lens group G1 as an aspherical lens, it contributes to high performance and miniaturization. Also, by using the third lens from the object OBJ side of the first lens group G1 as a biconvex lens L17, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product. Also, by using the lens on the most image-forming surface IMG side of the first lens group G1 as a biconvex lens L19, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product.

[0050] The second - 1 lens group G21 that constitutes the second lens group G2 is composed of only a biconvex lens L20. With such a configuration, the second - 1 lens group G21 prevents difficulties during manufacturing and greatly contributes to miniaturization.

[0051] The second - 2 lens group G22 arranged on the image - forming surface IMG side of the second - 1 lens group G21 includes, in order from the object OBJ, a biconcave lens L21, a biconvex lens L22 joined to this biconcave lens L21, a biconvex lens L23, a biconvex lens L24, a negative meniscus lens L25 with its convex surface facing the object OBJ side, and a negative meniscus lens L26 with its concave surface facing the object OBJ side. In this way, since the second - 2 lens group G22 uses a cemented lens immediately after the aperture stop STO, it can effectively correct chromatic aberration and field curvature. Also, by making the surface 24 on the image - forming surface IMG side of the negative meniscus lens L26 on the most image - forming surface IMG side an aspherical shape, it contributes to high performance and miniaturization.

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

Table 5

[0053] Note that in Table 5, Gr1p-vd is the smallest Abbe number among the positive lenses of the first lens group G1, Gr1p-nd is the refractive power of the d-line (wavelength λ = 587.56 nm) of Gr1p-vd, Gr1p-ΔPgF is the positive anomalous partial dispersibility of the first lens group G1, Gr22N-vd is the Abbe number of the d-line of the concave lens of the second - 2 lens group G22, Gr22N-nd is the refractive power of the d-line (wavelength λ = 587.56 nm) of Gr22N-vd, and Gr22p-ΔPgF is the positive anomalous partial dispersibility of the second - 2 lens group G22.

[0054] According to Table 1, at least one of the positive lenses of the first lens group G1 satisfies the two formulas of Gr1p-vd < 24.00 and Gr1p-nd > 1.77000, which contributes to the correction of chromatic aberration and miniaturization. Also, at least one of the negative lenses of the second - 2 lens group G22 satisfies the two formulas of 56.00 > Gr22N-vd > 34.00 and 1.75000 > Gr22N-nd > 1.55000, which can improve the performance and correct the chromatic aberration.

[0055] Also, since f21 / f2 is 1.05 and satisfies 1.0 < f21 / f2 < 2.0, by setting the focal length f21 of the second - 1 lens group G21 within a predetermined range with respect to the focal length f2 of the second lens group G2, it can contribute to miniaturization.

[0056] Also, Gr1p-ΔPgF is 0.04 and satisfies Gr1p-ΔPgF > 0.02. Since a positive lens with positive anomalous partial dispersibility is used for the first lens group G1, chromatic aberration can be corrected. Note that the explanation of ΔPgF is as described in the first embodiment, and the explanation is omitted.

[0057] Also, Gr22p-ΔPgF is 0.04 and satisfies Gr22p-ΔPgF > 0.03. Since a positive lens with positive anomalous partial dispersibility is used for the second - 2 lens group G22, chromatic aberration can be corrected.

[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 one surface to the surface with the next number. Furthermore, the blank spaces for nd and νd indicate that it is air.

[0061]

Table 7

[0062] Table 7 is a table showing the variable interval between lenses.

[0063]

Table 8

[0064] Table 8 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the 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 mathematical formula 1. In mathematical formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, A12, A14 are the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th orders, respectively, and H is the distance from the origin on the optical axis. Note that the mathematical formula 1 is as described above and is omitted here.

[0065] Figure 4 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. Each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Figure 4, it can be confirmed that good aberrations are obtained in all cases.

[0066] (Third Embodiment) Subsequently, in the third embodiment, a small wide-angle imaging lens 300 with a focal length f = 24.51 mm, an F-number of 1.44, and a semi-field angle ω = 42.47° for the entire system will be exemplified and described with reference to Figure 5.

[0067] The imaging lens 300 in this embodiment has a first lens group G1 and a second lens group G2, and has an aperture stop STO between the second - 1 lens group G21 and the second - 2 lens group that constitute the second lens group G2. The first lens group G1, the second lens group G2, the second - 1 lens group G21, and the second - 2 lens group G22 all have positive refractive powers. By having all the lens groups have positive refractive powers in this way, it contributes to miniaturization.

[0068] The first lens group G1 includes, in order from the object OBJ, a negative meniscus lens L27 with a convex surface facing the object OBJ side, a negative meniscus lens L28 with a convex surface facing the object OBJ side, a biconvex lens L29, a biconcave lens L30, and a biconvex lens L31 joined to this biconcave lens. In this way, by arranging the lenses in the above order from the object OBJ side, the first lens group G1 can prevent a decrease in component accuracy and can effectively correct various aberrations.

[0069] By making at least one of the two negative meniscus lenses L27 and L28 on the object OBJ side of the first lens group G1 an aspherical lens, it contributes to high performance and miniaturization. Also, by making the third lens from the object OBJ side of the first lens group G1 a biconvex lens L29, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product. In addition, by using a biconvex lens L31 as the lens on the imaging surface IMG side of the first lens group G1, the front and rear lenses can be miniaturized, contributing to the miniaturization of the entire product.

[0070] The second - 1 lens group G21 that constitutes the second lens group G2 is composed of only a biconvex lens L32. With such a configuration, the second - 1 lens group G21 prevents difficulties during manufacturing and greatly contributes to miniaturization.

[0071] The second - 2 lens group G22 arranged on the imaging surface IMG side of the second - 1 lens group G21 includes, in order from the object OBJ, a biconcave lens L33, a biconvex lens L34 joined to this biconcave lens L33, a biconvex lens L35, a biconvex lens L36, a negative meniscus lens L37 with its convex surface facing the object OBJ side, and a negative meniscus lens L38 with its concave surface facing the object OBJ side. In this way, since the second - 2 lens group G22 uses a cemented lens immediately after the aperture stop STO, it can effectively correct chromatic aberration and field curvature. In addition, by making the surface 23 on the imaging surface IMG side of the negative meniscus lens L38 on the most imaging surface IMG side an aspherical shape, it contributes to high - performance and miniaturization.

[0072] Table 9 shows a table summarizing various data of the third embodiment.

Table 9

[0073] Note that in Table 9, Gr1p - vd is the smallest Abbe number among the positive lenses of the first lens group G1, Gr1p - nd is the refractive power of the d - line (wavelength λ = 587.56nm) of Gr1p - vd, Gr1p - ΔPgF is the positive anomalous partial dispersive power of the first lens group G1, Gr22N - vd is the Abbe number of the d - line of the concave lens of the second - 2 lens group G22, Gr22N - nd is the refractive power of the d - line (wavelength λ = 587.56nm) of Gr22N - vd, and Gr22p - ΔPgF is the positive anomalous partial dispersive power of the second - 2 lens group G22.

[0074] According to Table 9, at least one of the positive lenses of the first lens group G1 satisfies the two formulas of Gr1p-vd < 24.00 and Gr1p-nd > 1.77000, contributing to the correction of chromatic aberration and miniaturization. Also, at least one of the negative lenses of the second - 2 lens group G22 satisfies the two formulas of 56.00 > Gr22N-vd > 34.00 and 1.75000 > Gr22N-nd > 1.55000, achieving high performance and being able to correct chromatic aberration.

[0075] Also, f21 / f2 is 1.06 and satisfies 1.0 < f21 / f2 < 2.0. Therefore, by setting the focal length f21 of the second - 1 lens group G21 within a predetermined range with respect to the focal length f2 of the second lens group G2, it can contribute to miniaturization.

[0076] Also, Gr1p-ΔPgF is 0.022 and satisfies Gr1p-ΔPgF > 0.02. Since a positive lens with positive abnormal partial dispersibility is used in the first lens group G1, chromatic aberration can be corrected. Note that the explanation of ΔPgF is as described in the first embodiment, and the explanation is omitted.

[0077] Also, Gr22p-ΔPgF is 0.04 and satisfies Gr22p-ΔPgF > 0.03. Since a positive lens with positive abnormal partial dispersibility is used in the second - 2 lens group G22, chromatic aberration can be corrected.

[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 surface interval D (mm) on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens are shown respectively. When it has 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 the 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 interval between the lenses.

[0083]

Table 12

[0084] Table 12 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the 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, A12, A14 are the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th orders respectively, and H is the distance from the origin on the optical axis. Note that formula 1 is as described above and is omitted here.

[0085] Fig. 6 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 300. Note that each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Fig. 6, it can be confirmed that good aberrations are obtained in all cases.

[0086] Note that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the present invention.

Explanation of Reference Numerals

[0087] 100 Optical lens system 200 Optical lens system 300 Optical lens system G1 First lens group G2 Second lens group G21 Second-1 lens group G22 Second-2 lens group L1 Negative meniscus lens L2 Negative meniscus lens L3 Biconvex lens L4 Negative meniscus lens L5 Biconvex lens L6 Biconvex lens L7 Biconcave lens L8 Biconcave lens L9 Biconvex lens L10 Biconvex lens L11 Biconvex lens L12 Negative meniscus lens L13 Negative meniscus lens L15 Negative meniscus lens L16 Negative meniscus lens L17 Biconvex lens L18 Negative meniscus lens L19 Biconvex lens L20 Biconvex lens L21 Biconcave lens L22 Biconvex lens L23 Biconvex lens L24 Biconvex lens L25 Negative meniscus lens L26 Negative meniscus lens L27 Negative meniscus lens L28 Negative meniscus lens L29 Biconvex lens L30 Biconcave lens L31 Biconvex lens L32 Biconvex lens L33 Bi-concave lens L34 Bi-convex lens L35 Bi-convex lens L36 Bi-convex lens L37 Negative meniscus lens L38 Negative meniscus lens STO Aperture stop

Claims

1. It is composed of a first lens group having a positive refractive power and a second lens group disposed on the image side of the first lens group and having a positive refractive power. When focusing on a near object, it is an optical lens system in which only the second lens group moves toward the object side and the distance between the first lens group and the second lens group changes. The first lens group is composed of four or more lenses including, in order from the object side, two negative lenses with convex surfaces facing the object side, one positive lens, and a negative lens with a concave surface facing the object side. The second lens group is composed of, in order from the object side, a second - 1 lens group having a positive refractive power, an aperture stop, and a second - 2 lens group having a positive refractive power. The second - 1 lens group is characterized by being composed of only one positive lens or a positive lens and a negative lens joined to the positive lens.

2. The two negative lenses on the most object - side of the first lens group are concave meniscus lenses, and among the two concave meniscus lenses, one of them is an aspherical lens. The optical lens system according to Claim 1.

3. The positive lens on the most object - side of the first lens group is a lens with both surfaces convex. The optical lens system according to Claim 1.

4. Any one of the positive lenses in the first lens group satisfies the following two conditional expressions. The optical lens system according to Claim 1. Gr1p - vd < 24.00 Gr1p - nd > 1.77000 However, Gr1p - vd is the Abbe number of the d - line (wavelength λ = 587.56 nm), and Gr1p - nd is the refractive power of the d - line (wavelength λ = 587.56 nm).

5. Any one of the positive lenses in the first lens group satisfies the following conditional expression. The optical lens system according to Claim 1. Gr1p - ΔPgF > 0.02 However, ΔPgF is PgF - 0.64833 + 0.00180vd, which represents the abnormal partial dispersibility between the g and F lines. PgF is (ng - nF) / (nF - nC), which represents the partial dispersion ratio between the g and F lines. nC is the refractive index of the C line (wavelength λ = 656.27 nm), nF is the refractive index of the F line (wavelength λ = 486.13 nm), and ng is the refractive index of the g line (wavelength λ = 435.83 nm).

6. When the focal length of the second lens group is f2 and the focal length of the second - 1 lens group is f21, 1.0 < f21 / f2 < 2.0 The optical lens system according to claim 1, which satisfies the above condition.

7. The second - 2 lens group is composed of, in order from the object side, a negative lens with a concave surface facing the object side, a positive lens joined to the negative lens, and two or more lenses including a positive lens and a negative lens. The optical lens system according to claim 1.

8. Any one of the negative lenses in the second - 2 lens group satisfies the following two conditional expressions. The optical lens system according to claim 1. 56.00 > Gr22N - vd > 34.00 1.75000 > Gr22N - nd > 1.55000 However, Gr22N - vd is the Abbe number of the d line (wavelength λ = 587.56 nm), and Gr22N - nd is the refractive power of the d line (wavelength λ = 587.56 nm).

9. The lens closest to the image - forming side in the second - 2 lens group is an aspherical lens with a negative lens component having a convex surface facing the image - forming side. The optical lens system according to claim 1.

10. Any one of the positive lenses in the second - 2 lens group satisfies the following conditional expression. The optical lens system according to claim 1. Gr22p - ΔPgF > 0.03 However, ΔPgF is PgF - 0.64833 + 0.00180vd, which represents the abnormal partial dispersibility between the g and F lines. PgF is (ng - nF) / (nF - nC), which represents the partial dispersion ratio between the g and F lines. nC is the refractive index of the C line (wavelength λ = 656.27 nm), nF is the refractive index of the F line (wavelength λ = 486.13 nm), and ng is the refractive index of the g line (wavelength λ = 435.83 nm).

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