Optical lens system

Abstract

To provide an optical lens system that is miniaturized and improves an optical performance by improving various aberrations.SOLUTION: An optical lens system 100 is composed of a first lens group G1 having a positive refractive index, and a second lens group G2 having a positive refractive index and being disposed in a side of an image IMG relative to the first lens group G1, where only the second lens group G2 travels to an object side in focusing. The first lens group G1 is configured so as to include at least two positive meniscus lenses L1, L2 with convex faces toward the object side, and a negative meniscus lens L4 with concave faces toward the side of the image IMG in the furthest side of the image IMG in sequence from the side of an object OBJ, and so as not to include a cemented lens, the second lens group G2 is configured so as to include a 2-1 lens group G21 having a positive refractive index, an aperture diaphragm STO, and a 2-2 lens group G22 having a positive refractive index in sequence from the side of the object OBJ, and the 2-1 lens group G21 is composed of only one positive lens L5, and a cemented lens in which a positive lens L6 and a negative lens L7 are cemented.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Generally, when attempting to promote large aperture and miniaturization of lenses for interchangeable-lens cameras used in equipment such as cameras for photography and video shooting, various aberrations and chromatic aberrations may increase, leading to a performance decline.

[0003] Therefore, as a large-aperture optical lens system, Patent Document 1 (Japanese Patent No. 7020674) discloses that, in order from the object side, a first lens group having a positive refractive power and a second lens group G2 having a positive refractive power are arranged. The first lens group consists of one or more convex lenses and one concave lens or one cemented concave lens component from the object side, and includes a first a lens group having a positive refractive power as a whole, a first b lens group consisting of a cemented concave lens component having a negative refractive power, and a first c lens group having a positive refractive power. The second lens group G2 is composed of a second a lens group consisting of one or more convex lenses and a cemented concave lens component having a negative refractive power, an aperture stop, and a second b lens group. When focusing from infinity to a close object, the first lens group is fixed with respect to the image plane, and the second lens group is moved from the image plane side to the object side along the optical axis, and it is described that the refractive power, Abbe number, and anomalous dispersion are 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 first lens group that is fixed during focusing includes a cemented lens. However, when the cemented lens is included in the first lens group, it is difficult to increase the lens power, so the lens diameter of the first lens group becomes large, and there is a problem that it is difficult to achieve miniaturization.

Means for Solving the Problem

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

[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 includes, in order from the object side, two or more positive meniscus lenses with convex surfaces facing the object side and, on the most image side, a negative meniscus lens with a concave surface facing the image side, and does not include a cemented lens. The second lens group includes, 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 and a cemented lens in which a positive lens and a negative lens are cemented together.

[0008] By adopting this configuration, since the first lens group does not include a cemented lens, it is possible to realize high performance and miniaturization while suppressing the increase in size. Further, since the first lens group has a plurality of positive meniscus lenses and negative meniscus lenses, various aberrations can be effectively corrected while achieving miniaturization. Further, since all of the first lens group, the second lens group, the second-1 lens group, and the second-2 lens group have positive refractive powers, it contributes to miniaturization. Further, by configuring the second-1 lens group from only one positive lens and a cemented lens in which a positive lens and a negative lens are cemented together, miniaturization can be effectively achieved. Further, when focusing, only the second lens group moves, and since the second lens group has a strong positive lens component, the focusing amount can be reduced, which contributes to the miniaturization of the entire product.

[0009] Any one of the positive lenses of the first lens group is characterized by satisfying the following conditional expression. Gr1P - ΔPgF > 0.019 However, Gr1P - ΔPgF is the value of the largest ΔPgF, and 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). According to this configuration, chromatic aberration can be corrected by using a positive lens having a positive abnormal partial dispersibility in the first lens group.

[0010] The negative meniscus lens closest to the image side of the first lens group is characterized by satisfying the following two conditional expressions. 56.00 > Gr1N - vd > 34.00 1.750 > Gr1N - nd > 1.550 However, Gr1N - vd is the Abbe number of the d line (wavelength λ = 587.56 nm), and Gr1N - nd is the refractive index of the d line (wavelength λ = 587.56 nm). According to this configuration, high performance can be achieved and chromatic aberration can be corrected.

[0011] When the focal length of the entire optical lens system is f and the focal length of the second - 1 lens group is f21, it is characterized by satisfying f21 / f > 5.8. According to this configuration, by setting the focal length of the second - 1 lens group to a certain distance with respect to the focal length of the entire optical lens system, it is possible to contribute to miniaturization.

[0012] When the focal length of the entire optical lens system is f and the focal length of the second - 2 lens group is f22, it is characterized by satisfying f22 / f > 0.8. According to this configuration, by setting the focal length of the second - 2 lens group to a certain distance with respect to the focal length of the entire optical lens system, the amount of focus movement can be suppressed, and it is possible to contribute to miniaturization.

[0013] The second - 2 lens group includes, in order from the object side, a negative lens with a concave surface facing the object side, a positive lens joined to this negative lens, a positive lens, and a negative lens joined to this positive lens, and includes two sets of joined lenses. According to this configuration, by using many joined lenses in the lens group on the image side, various aberrations can be corrected, and it contributes to miniaturization. Also, by arranging the joined lens immediately after the aperture stop, chromatic aberration and field curvature can be effectively corrected.

[0014] Any one of the positive lenses in the second - 2 lens group is characterized by satisfying the following two conditional expressions. Gr22P - vd < 38.00 Gr22P - nd > 1.900 However, Gr22P - vd is the Abbe number of the d - line (wavelength λ = 587.56nm), and Gr22P - nd is the refractive index of the d - line (wavelength λ = 587.56nm). According to this configuration, by using a high - refractive - index and high - dispersion lens for the positive lens of the second - 2 lens group, chromatic aberration can be corrected, and it contributes to miniaturization.

[0015] Any one of the positive lenses in the 22nd lens group satisfies the following conditional expression. Gr22P - ΔPgF > 0.019 However, Gr22P - ΔPgF is the value of the largest ΔPgF, where 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). 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 can be corrected by using a positive lens with a positive abnormal partial dispersibility in the 2-2nd lens group.

[0016] The lens closest to the image side in the 2-2nd lens group is an aspherical lens. According to this configuration, it contributes to high performance and miniaturization.

[0017] When the focal length of the entire optical lens system is f and the overall optical length is L - H, it is characterized by satisfying L - H / f < 1.55. According to this configuration, the ratio of the overall optical length to the focal length of the entire system can be reduced, contributing to miniaturization.

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

Embodiments 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 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.

[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 drawings 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] In addition, in each embodiment, the optical lens systems 100, 200, and 300 move only the second lens group G2 when focusing on a near-distance object. Therefore, the focusing amount can be reduced, contributing to the miniaturization of the product.

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

[0025] (First Embodiment) In the first embodiment, a small-sized large-aperture imaging lens 100 with a focal length f = 72.502 mm, an F-number 1.449, and a semi-field angle ω = 16.885° of the entire system 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 positive refractive powers for all lens groups in this way, it contributes to miniaturization.

[0027] The first lens group G1 includes, in order from the object OBJ, a positive meniscus lens L1 with a convex surface facing the object OBJ side, a positive meniscus lens L2 with a convex surface facing the object OBJ side, a positive lens L3, and a negative meniscus lens L4 with a concave surface facing the imaging surface IMG side. In this way, by not using a cemented lens in the first lens group G1, it is possible to achieve high performance and miniaturization while suppressing an increase in size. In addition, since the first lens group G1 has a plurality of meniscus lenses such as two positive meniscus lenses and one negative meniscus lens, it is possible to effectively perform miniaturization and correction of various aberrations, which were difficult to achieve with a biconvex lens.

[0028] The second - 1 lens group G21 that constitutes the second lens group G2 includes, in order from the object OBJ, a positive meniscus lens L5 with a convex surface facing the object OBJ side, a positive meniscus lens L6 with a convex surface facing the object OBJ side, and only a negative meniscus lens L7 that is cemented to this positive meniscus lens L6 and has a concave surface facing the imaging surface IMG side. By configuring the second - 1 lens group G21 in such a lens arrangement, effective miniaturization can be achieved.

[0029] The second - 2 lens group G22 arranged on the imaging surface IMG side rather than the second - 1 lens group G21 includes, in order from the object OBJ, a biconcave lens L8, a positive lens L9 cemented to this biconcave lens L8, a biconvex lens L10, a biconcave lens L11, a biconvex lens L12 cemented to this biconcave lens L11, and a negative meniscus lens L13 which is an aspherical lens with a convex surface facing the imaging surface IMG side. In this way, since the second - 2 lens group G22 arranges a cemented lens immediately after the aperture stop STO (on the imaging surface IMG side), it is possible to effectively correct chromatic aberration and field curvature. Also, by using a plurality of cemented lenses in the second - 2 lens group G22, which is the group closest to the imaging surface IMG side, it is possible to correct various aberrations while achieving miniaturization. Furthermore, by making the lens closest to the imaging surface IMG side in the second - 2 lens group G22 an aspherical lens, it contributes to high performance and miniaturization.

[0030] Table 1 shows a table summarizing various data of the first embodiment. [Table 1]

[0031] Note that in Table 1, Gr1P-ΔPgF is the positive abnormal partial dispersibility of the first lens group G1, Gr1N-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of the negative lens L4 on the image forming surface IMG side of the first lens group G1, and Gr1N-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of the negative lens L4 on the image forming surface IMG side of the first lens group G1. Also, in Table 1, Gr22P-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of any positive lens of the second - 2 lens group G22, Gr22P-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of any positive lens of the second - 2 lens group G22, and Gr22P-ΔPgF is the positive abnormal partial dispersibility of the second - 2 lens group G22.

[0032] According to Table 1, at least one of the positive lenses of the first lens group G1 has Gr1P-ΔPgF = 0.0374 and satisfies Gr1P-ΔPgF>0.019. By using a positive lens with positive abnormal partial dispersibility, chromatic aberration can be corrected.

[0033] Also, according to Table 1, the negative meniscus lens L4 on the image forming surface IMG side of the first lens group G1 has Gr1N-vd = 39.70 and Gr1N-nd = 1.654, and satisfies the two equations of 56.00>Gr1N-vd>34.00 and 1.750>Gr1N-nd>1.550. Therefore, high performance can be achieved and chromatic aberration can be corrected.

[0034] According to Table 1, at least one of the positive lenses of the second - second lens group G22 satisfies Gr22P - vd = 29.13, Gr22P - nd = 2.001, and the two equations Gr22P - vd < 38.00 and Gr22P - nd > 1.900. In this way, by using a high - refractive - index and high - dispersion lens for the positive lens of the second - second lens group, chromatic aberration can be corrected and it contributes to miniaturization.

[0035] According to Table 1, at least one of the positive lenses of the second - second lens group G22 satisfies Gr22P - ΔPgF = 0.0192 and Gr22P - ΔPgF > 0.019. By using a positive lens with positive anomalous partial dispersion, chromatic aberration can be corrected.

[0036] According to Table 1, f21 / f = 7.78 and f21 / f > 5.8. Therefore, taking the focal length f21 of the second - first lens group as a certain distance with respect to the focal length f of the entire optical lens system 100, it can contribute to miniaturization.

[0037] According to Table 1, f22 / f = 0.81 and f22 / f > 0.8. Therefore, taking the focal length f22 of the second - second lens group as a certain distance with respect to the focal length f of the entire optical lens system 100, the amount of focus movement can be suppressed and it can contribute to miniaturization.

[0038] According to Table 1, L - H / f = 1.51 and L - H / f < 1.55. Therefore, the ratio of the overall optical length to the focal length of the entire system can be reduced to contribute to miniaturization.

[0039] 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.

[0040]

Table 2

[0041] In Table 2, 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 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 the numerical 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 columns for nd and νd indicate that it is air.

[0042]

Table 3

[0043] Table 3 is a table showing the variable interval between the lenses.

[0044]

Table 4

[0045] 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.

[0046]

Equation

[0047] Fig. 2 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 100. Note that each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Fig. 2, it can be confirmed that good aberrations are obtained in all cases.

[0048] (Second Embodiment) Subsequently, in the second embodiment, a small and large-aperture imaging lens 200 with an overall focal length f = 87.550 mm, an F-number 1.431, and a semi-field angle ω = 13.618° will be exemplified and described with reference to FIG. 3.

[0049] 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 a second-1 lens group G21 and a 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 positive refractive powers for all lens groups in this way, it contributes to miniaturization.

[0050] The first lens group G1 includes, in order from the object OBJ, a positive meniscus lens L14 with a convex surface facing the object OBJ side, a positive meniscus lens L15 with a convex surface facing the object OBJ side, a negative meniscus lens L16 with a concave surface facing the image formation surface IMG side, and a negative meniscus lens L17 with a concave surface facing the image formation surface IMG side. In this way, by not using cemented lenses for the first lens group G1, high performance and miniaturization can be achieved while suppressing an increase in size. In addition, since the first lens group G1 has a plurality of meniscus lenses such as two positive meniscus lenses and two negative meniscus lenses, miniaturization and correction of various aberrations, which were difficult to achieve with biconvex lenses, can be effectively performed.

[0051] The second-1 lens group G21 that constitutes the second lens group G2 includes, in order from the object OBJ, a positive meniscus lens L18 with a convex surface facing the object OBJ side, a positive meniscus lens L19 with a convex surface facing the object OBJ side, and only a negative meniscus lens L20 that is cemented to the positive meniscus lens L19 and has a concave surface facing the image formation surface IMG side. By configuring the second-1 lens group G21 with such a lens arrangement, miniaturization can be effectively achieved.

[0052] The 2-2 lens group G22 disposed closer to the imaging surface IMG than the 2-1 lens group G21 includes, in order from the object OBJ, a biconcave lens L21, a biconvex lens L22 joined to the biconcave lens L21, a positive meniscus lens L23 with its convex surface facing the imaging surface IMG side, a biconcave lens L24 joined to the positive meniscus lens L23, a negative meniscus lens L25 with its concave surface facing the object OBJ side, and an aspherical biconvex lens L26. Thus, since the 2-2 lens group G22 has a cemented lens disposed immediately behind the aperture stop STO (on the imaging surface IMG side), it can effectively correct chromatic aberration and field curvature. In addition, by using a plurality of cemented lenses in the 2-2 lens group G22, which is the group closest to the imaging surface IMG side, it is possible to correct various aberrations while reducing the size. Furthermore, by using an aspherical lens as the lens closest to the imaging surface IMG side in the 2-2 lens group G22, it contributes to high performance and size reduction.

[0053] Table 5 shows a table summarizing various data of the second embodiment.

Table 5

[0054] Note that in Table 5, Gr1P-ΔPgF is the positive anomalous partial dispersibility of the first lens group G1, Gr1N-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of the negative lens L17 closest to the imaging surface IMG side in the first lens group G1, and Gr1N-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of the negative lens L17 closest to the imaging surface IMG side in the first lens group G1. Also, in Table 5, Gr22P-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of any positive lens in the 2-2 lens group G22, Gr22P-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of any positive lens in the 2-2 lens group G22, and Gr22P-ΔPgF is the positive anomalous partial dispersibility of the 2-2 lens group G22.

[0055] According to Table 5, at least one of the positive lenses in the first lens group G1 has Gr1P - ΔPgF = 0.0192, satisfying Gr1P - ΔPgF > 0.019. By using a positive lens with positive abnormal partial dispersibility, chromatic aberration can be corrected.

[0056] Also according to Table 5, the negative meniscus lens L17 on the imaging surface IMG side of the first lens group G1 has Gr1N - vd = 39.70 and Gr1N - nd = 1.654, satisfying the two equations 56.00 > Gr1N - vd > 34.00 and 1.750 > Gr1N - nd > 1.550. Therefore, high performance can be achieved and chromatic aberration can be corrected.

[0057] Also according to Table 5, at least one of the positive lenses in the second - 2 lens group G22 has Gr22P - vd = 29.13 and Gr22P - nd = 2.001, satisfying the two equations Gr22P - vd < 38.00 and Gr22P - nd > 1.900. In this way, by using a high - refractive - index and high - dispersion lens for the positive lens of the second - 2 lens group, chromatic aberration can be corrected and it contributes to miniaturization.

[0058] Also according to Table 5, at least one of the positive lenses in the second - 2 lens group G22 has Gr22P - ΔPgF = 0.0374, satisfying Gr22P - ΔPgF > 0.019. By using a positive lens with positive abnormal partial dispersibility, chromatic aberration can be corrected.

[0059] Also according to Table 5, f21 / f = 8.89, satisfying f21 / f > 5.8. Therefore, with the focal length f21 of the second - 1 lens group being a certain distance with respect to the focal length f of the entire optical lens system 200, it can contribute to miniaturization.

[0060] Also, according to Table 5, f22 / f = 0.81, satisfying f22 / f > 0.8. Therefore, with the focal length f22 of the second lens group as a constant distance with respect to the overall focal length f of the optical lens system 200, the amount of focus movement can be suppressed, contributing to miniaturization.

[0061] Also, according to Table 5, L-H / f = 1.33, satisfying L-H / f < 1.55. Therefore, the ratio of the overall optical length to the focal length of the entire system can be reduced, contributing to miniaturization.

[0062] 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.

[0063]

Table 6

[0064] In Table 6, the radius of curvature R (mm) corresponding to the virtual surface and the lens surface counted from the object OBJ side, the 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 indicated 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 numerical 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 columns for nd and νd indicate that it is air.

[0065]

Table 7

[0066] Table 7 is a table showing the variable intervals between the lenses.

[0067]

Table 8

[0068] 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 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. Note that Equation 1 is as described above and is omitted here.

[0069] Figure 4 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 200. Note that each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Figure 4, it can be confirmed that good aberrations are obtained in all cases.

[0070] (Third Embodiment) Subsequently, in the third embodiment, a small wide-angle imaging lens 300 with a focal length f = 97.184 mm, an F-number of 1.451, and a semi-field angle ω = 12.702° in the entire system will be exemplified and described with reference to FIG. 5.

[0071] 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 positive refractive powers for all lens groups in this way, it contributes to miniaturization.

[0072] The first lens group G1 includes, in order from the object OBJ, a positive meniscus lens L27 with a convex surface facing the object OBJ side, a positive meniscus lens L28 with a convex surface facing the object OBJ side, a positive meniscus lens L29 with a convex surface facing the object OBJ side, a negative meniscus lens L30 with a concave surface facing the image formation surface IMG side, and a negative meniscus lens L31 with a concave surface facing the image formation surface IMG side. In this way, by not using a cemented lens for the first lens group G1, it is possible to achieve high performance and miniaturization while suppressing an increase in size. In addition, since the first lens group G1 includes a plurality of meniscus lenses such as three positive meniscus lenses and two negative meniscus lenses, it is possible to effectively perform miniaturization and correction of various aberrations, which were difficult to achieve with a biconvex lens.

[0073] The second - 1 lens group G21 that constitutes the second lens group G2 includes, in order from the object OBJ, a positive meniscus lens L32 with a convex surface facing the object OBJ side, a positive meniscus lens L33 with a convex surface facing the object OBJ side, and only a negative meniscus lens L34 that is joined to the positive meniscus lens L33 and has a concave surface facing the image forming surface IMG side. By configuring the second - 1 lens group G21 in such a lens arrangement, miniaturization can be effectively achieved.

[0074] The second - 2 lens group G22 arranged on the image forming surface IMG side with respect to the second - 1 lens group G21 includes, in order from the object OBJ, a biconcave lens L35, a biconvex lens L36 joined to the biconcave lens L35, a positive meniscus lens L37 with a convex surface facing the image forming surface IMG side, a biconcave lens L38 joined to the positive meniscus lens L37, a negative meniscus lens L39 with a concave surface facing the object OBJ side, and an aspherical biconvex lens L40. In this way, since the second - 2 lens group G22 arranges a cemented lens immediately behind the aperture stop STO (on the image forming surface IMG side), chromatic aberration and field curvature can be effectively corrected. Also, by using a plurality of cemented lenses for the second - 2 lens group G22, which is the group closest to the image forming surface IMG side, it is possible to correct various aberrations while achieving miniaturization. Furthermore, by using an aspherical lens for the lens closest to the image forming surface IMG side in the second - 2 lens group G22, it contributes to high performance and miniaturization.

[0075] Table 9 shows a table summarizing various data of the third embodiment.

[0076]

Table 9

[0077] Note that in Table 9, Gr1P-ΔPgF is the positive abnormal partial dispersibility of the first lens group G1, Gr1N-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of the negative lens L31 on the image-forming surface IMG side of the first lens group G1, and Gr1N-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of the negative lens L31 on the image-forming surface IMG side of the first lens group G1. Also, in Table 9, Gr22P-vd is the Abbe number of the d-line (wavelength λ = 587.56 nm) of any positive lens in the second - 2 lens group G22, Gr22P-nd is the refractive index of the d-line (wavelength λ = 587.56 nm) of any positive lens in the second - 2 lens group G22, and Gr22P-ΔPgF is the positive abnormal partial dispersibility of the second - 2 lens group G22.

[0078] According to Table 9, at least one of the positive lenses in the first lens group G1 has Gr1P-ΔPgF = 0.0374 and satisfies Gr1P-ΔPgF>0.019. By using a positive lens with positive abnormal partial dispersibility, chromatic aberration can be corrected.

[0079] Also, according to Table 9, the negative meniscus lens L31 on the image-forming surface IMG side of the first lens group G1 has Gr1N-vd = 39.70 and Gr1N-nd = 1.654, satisfying the two equations 6.00>Gr1N-vd>34.00 and 1.750>Gr1N-nd>1.550. Therefore, high performance can be achieved and chromatic aberration can be corrected.

[0080] Also, according to Table 9, at least one of the positive lenses in the second - 2 lens group G22 has Gr22P-vd = 29.13 and Gr22P-nd = 2.001, satisfying the two equations Gr22P-vd<38.00 and Gr22P-nd>1.900. In this way, by using a high-refractive-index and high-dispersion lens for the positive lens of the second two-lens group, chromatic aberration can be corrected, which contributes to miniaturization.

[0081] Also, according to Table 9, at least one of the positive lenses of the second two-lens group G22 satisfies Gr22P - ΔPgF = 0.0374 and Gr22P - ΔPgF > 0.019. By using a positive lens with positive abnormal partial dispersibility, chromatic aberration can be corrected.

[0082] Also, according to Table 9, f21 / f = 5.89 and f21 / f > 5.8. Therefore, by setting the focal length f21 of the second one-lens group to a certain distance with respect to the overall focal length f of the optical lens system 300, miniaturization can be achieved.

[0083] Also, according to Table 9, f22 / f = 0.90 and f22 / f > 0.8. Therefore, by setting the focal length f22 of the second two-lens group to a certain distance with respect to the overall focal length f of the optical lens system 300, the amount of focus movement can be suppressed, contributing to miniaturization.

[0084] Also, according to Table 9, L - H / f = 1.31 and L - H / f < 1.55. Therefore, the ratio of the overall optical length to the overall focal length of the system can be reduced, contributing to miniaturization.

[0085] 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.

[0086]

Table 10

[0087] 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 having an aspherical shape, it is indicated 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 defined as the distance from one surface to the surface with the next number. Furthermore, the blanks for nd and νd indicate that it is air.

[0088]

Table 11

[0089] Table 11 is a table showing the variable interval between the lenses.

[0090]

Table 12

[0091] 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 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. Note that Equation 1 is as described above and is omitted here.

[0092] Figure 6 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 300. Each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Figure 6, it can be confirmed that good aberrations are obtained in all cases.

[0093] 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 Signs

[0094] 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 Biconcave lens L34 Biconvex lens L35 Biconvex lens L36 Biconvex 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, only the second lens group moves toward the object side, and it is an optical lens system in which the distance between the first lens group and the second lens group changes, The first lens group includes, in order from the object side, two or more positive meniscus lenses with convex surfaces facing the object side and, on the most image side, a negative meniscus lens with a concave surface facing the image side, and does not include a cemented lens, The second lens group includes, 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 composed of only one positive lens and a cemented lens in which a positive lens and a negative lens are cemented, and it is an optical lens system.

2. The optical lens system according to claim 1 or claim 2, wherein any one of the positive lenses of the first lens group satisfies the following conditional expression. Gr1P - ΔPgF > 0.019 However, Gr1P - ΔPgF is the value of the largest ΔPgF, 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 = 656.27nm), 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).

3. The optical lens system according to claim 1 or claim 2, wherein the negative meniscus lens on the most image side of the first lens group satisfies the following two conditional expressions. 56.00 > Gr1N - vd > 34.00 1.750 > Gr1N - nd > 1.550 However, Gr1N - vd is the Abbe number of the d line (wavelength λ = 587.56nm), and Gr1N - nd is the refractive index of the d line (wavelength λ = 587.56nm).

4. The optical lens system according to claim 1 or claim 2, when the focal length of the entire optical lens system is f and the focal length of the second - 1 lens group is f21, satisfies f21 / f > 5.

8.

5. The optical lens system according to claim 1 or claim 2, when the focal length of the entire optical lens system is f and the focal length of the second - 2 lens group is f22, satisfies f22 / f > 0.

8.

6. The second 2-2 lens group includes two sets of cemented lenses, which are, in order from the object side, a negative lens with a concave surface facing the object side, a positive lens cemented to this negative lens, a positive lens, and a negative lens cemented to this positive lens, according to the optical lens system described in claim 1 or claim 2.

7. Any one of the positive lenses of the second 2-2 lens group satisfies the following two conditional expressions, according to the optical lens system described in claim 1 or claim 2. Gr22P - vd < 38.00 Gr22P - nd > 1.900 However, Gr22P - vd is the Abbe number of the d-line (wavelength λ = 587.56 nm), and Gr22P - nd is the refractive index of the d-line (wavelength λ = 587.56 nm).

8. Any one of the positive lenses of the 22nd lens group satisfies the following conditional expression, according to the optical lens system described in claim 1 or claim 2. Gr22P - ΔPgF > 0.019 However, Gr22P - ΔPgF is the value of the largest ΔPgF, and 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). 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).

9. The lens closest to the image side of the second 2-2 lens group is an aspherical lens, according to the optical lens system described in claim 1 or claim 2.

10. When the focal length of the entire optical lens system is f and the overall optical length is L - H, L - H / f < 1.55 is satisfied, according to the optical lens system described in claim 1 or claim 2.

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