Optical Lens System

Abstract

To provide an optical lens system which offers a reduced total length and good optical performance.SOLUTION: An optical lens system 100 provided herein comprises a first lens group G1 comprising two positive meniscus lenses (L1, L2) and a first negative lens L3, and a second lens group comprising an aperture stop STO, a first positive lens L5, a cemented lens L6 consisting of a second negative lens L6f and a second positive lens L6r, and a positive final lens L7 arranged in the described order from the object OBJ side to the imaging plane IMG side. The two positive meniscus lenses (L1, L2) of the first lens group G1 and at least one positive lens of the second lens group have refractive indexes nd and Abbe numbers νd for the d-ray that satisfy: nd>1.82 and νd<44. The optical lens system satisfies an optical condition expressed as 0.35<BF / f<0.75, where f represents a focal length of the entire system and BF represents a distance from a final lens surface of the second lens group G2 to the imaging plane IMG.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical lens system in which a first lens group, an aperture stop, and a second lens group are arranged in that order from the object side to the image plane side. [Background technology]

[0002] 2. Description of the Related Art There have been many proposals for the configuration of so-called double Gauss type optical lens systems for interchangeable lenses used in optical equipment for photography and videography. For example, Patent Document 1 (Japanese Patent No. 5217693) specifies the conditions for the lens with the highest refractive index in the first lens group in order to satisfactorily correct various aberrations. Furthermore, in Patent Document 2 (Japanese Patent No. 5966728), the radii of curvature and the like of two lenses in the first lens group are specified in order to reduce the number of lenses and satisfactorily correct various aberrations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5217693 [Patent Document 2] Patent No. 5966728 Summary of the Invention [Problem to be solved by the invention]

[0004] The optical lens systems disclosed in Patent Documents 1 and 2 are said to be capable of satisfactorily correcting various aberrations with a small number of lenses. However, in recent years, there has been a growing demand for miniaturization, and there is a demand for further miniaturization and performance improvement of optical lens systems. [Means for solving the problem]

[0005] Therefore, an object of the present invention is to provide an optical lens system that achieves miniaturization by shortening the overall length and has good optical performance.

[0006] In the present invention, a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in order from the object side to the imaging surface side. The first lens group includes, in order from the object side to the imaging surface side, two positive meniscus lenses with convex surfaces facing the object side and a negative lens with a convex surface facing the object side. The second lens group includes, in order from the object side to the imaging surface side, a positive lens, a cemented lens composed of... and a final positive lens. Negative lens and Positive lens ... and has a final positive lens. A cemented lens is formed by the second positive meniscus lens and the negative lens in the first lens group. When the refractive index of the entire system for the d-line is nd and the Abbe number is νd, two of the positive meniscus lenses in the first lens group and at least one of the positive lenses in the second lens group satisfy the conditional expressions nd > 1.82 and νd < 44. When the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the imaging surface is BF, the optical lens system is characterized by satisfying the conditional expression 0.35 < BF / f < 0.75.

[0007] Thereby, it is possible to provide an optical lens system that shortens the overall length and improves the optical performance with respect to the optical system lens in the prior art.

[0008] Further, at least one positive lens in the second lens group that satisfies the conditional expressions nd > 1.82 and νd < 44 may include the final positive lens.

[0010] Further, the final lens in the second lens group may be formed to have the maximum diameter dimension in the second lens group.

[0011] Also, In the present invention, a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in order from the object side to the image forming surface side. The first lens group has, in order from the object side to the image forming surface side, two positive meniscus lenses with convex surfaces facing the object side and a negative lens with a convex surface facing the object side. The second lens group has, in order from the object side to the image forming surface side, a positive lens, a cemented lens composed of a negative lens with a concave surface facing the object side and a positive lens, and a final positive lens. An aberration correction lens is further arranged in the first lens group on the aperture stop side. When the refractive index of the entire system for the d-line is nd and the Abbe number is νd, two positive meniscus lenses in the first lens group and at least one positive lens in the second lens group satisfy the conditional expressions nd > 1.82 and νd < 44. When the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the image forming surface is BF, the optical lens system is characterized by satisfying the conditional expression 0.35 < BF / f < 0.75. Thereby, the correction of aberration can be further improved in a limited space. Effect of the Invention

[0012] According to the configuration of the optical lens system of the present invention, it is possible to reduce the overall length and improve the optical performance compared to optical lens systems of conventional configurations. [Brief description of the drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

[0014] The optical lens system in this embodiment is used in optical equipment for photography and videography, and is in particular a so-called double Gauss type optical lens system having a first lens group consisting of three lenses, an aperture stop, and a second lens group consisting of four lenses. Each embodiment will be described below with reference to the drawings.

[0015] (First embodiment) An optical lens system 100 in the first embodiment shown in FIG. 1 includes a first lens group G1, an aperture stop STO, and a second lens group G2, which are arranged in this order from an object OBJ side toward an image plane IMG side.

[0016] In this embodiment, the first lens group G1 has, in order from the object OBJ side to the image plane IMG, a first positive meniscus lens L1, a second positive meniscus lens L2, a first negative lens L3, and an aberration correction lens L4. As is clear from Fig. 1, the second positive meniscus lens L2 (the second positive meniscus lens) and the first negative lens L3 are formed as a cemented lens. The first positive meniscus lens L1, the second positive meniscus lens L2, the first negative lens L3, and the aberration correction lens L4 are all formed as convex surfaces (curved surfaces) whose lens center side bulges out toward the object OBJ side from the lens outer peripheral edge side. The lens surfaces (1, 2, 3, 4, 5, 6, 7) are numbered from the object OBJ side. Thus, the first positive meniscus lens L1, the second positive meniscus lens L2, the first negative lens L3, and the aberration correction lens L4 are all arranged with their convex surfaces facing the object OBJ side. The first lens group G1 thus formed has a positive refractive index.

[0017] In this way, all the lenses (L1 to L4) are formed with a convex surface that bulges out toward the lens outer periphery, and are arranged with the convex surface facing the object OBJ, so that the lens center side of all the lenses (L1 to L4) can be offset in one direction. This has the advantage that the arrangement interval of each lens (L1 to L4) in the optical axis direction is minimized, and the optical axis direction length of the first lens group G1 can be shortened. In addition, since the second positive meniscus lens L2 and the first negative lens L3 form a cemented lens, the arrangement interval between the two lenses can be made zero, which offsets part of the increase in the optical axis direction length of the first lens group G1 due to the additional arrangement of the aberration correction lens L4.

[0018] By adopting the above-described configuration of optical lens system 100, it is possible to shorten the overall length of optical lens system 100 in the optical axis direction.

[0019] Next, the second lens group G2 in this embodiment will be described. The second lens group G2 is disposed at a required distance on the image plane IMG side from the aperture stop STO, which is disposed at a required distance on the image plane IMG side of the first lens group G1. In the second lens group G2 in this embodiment, the first positive lens L5, the cemented lens L6, and the final positive lens L7 are arranged in the order listed from the object OBJ side to the image plane IMG side. The surface numbers of the lenses in the second lens group G2 are 9, 10, 11, 12, 13, 14, and 15 in order from the object OBJ side to the image plane IMG side. The first positive lens L5 and the cemented lens L6 are arranged with a required interval between them, and the cemented lens L6 and the final positive lens L7 are arranged with their convex portions butted against each other. The second lens group G2 formed in this way has a positive refractive index.

[0020] The first positive lens L5 has a surface (surface number 9) on the object OBJ side formed with a radius of curvature that is substantially perpendicular to the optical axis, and a surface (surface number 10) on the image plane IMG side formed with a convex surface that bulges slightly toward the lens center toward the lens outer periphery. The cemented lens L6 in the second lens group G2 is formed of a second negative lens L6f formed with a biconcave surface (surface numbers 11, 12), and a second positive lens L6r formed with a biconvex surface (surface numbers 12, 13) that fits into the concave surface (surface number 12) on the image plane IMG side of the second negative lens L6f. The cemented lens L6 thus formed is disposed with its concave surface (surface number 10) facing the object OBJ and its convex surface (surface number 13) facing the image plane IMG. The final positive lens L7, which is the final lens in the second lens group G2, is formed with a biconvex surface (surface numbers 14, 15) and is formed with the largest diameter dimension in the second lens group G2.

[0021] Table 1 shows surface data for each lens constituting the optical lens system 100 in this embodiment.

[0022] [Table 1]

[0023] In Table 1, f, Fno, and ω respectively indicate the focal length, F-number, and half angle of the entire system. The lens surface number counted from the object OBJ side is designated as i, and this surface number i corresponds to the symbol (number) in Figure 1. Table 1 shows the values ​​of the radius of curvature R(i), axial surface spacing D(i), lens refractive index nd(i), lens Abbe number νd(i), and focal length f(i) of each lens corresponding to this surface number (i). nd(i) and νd(i) are values ​​for the d-line (587.56 nm). The axial surface spacing D(i) indicates the lens thickness or air spacing between opposing surfaces. The units of the radius of curvature R(i) and axial surface spacing D(i) are mm. The surface number OBJ indicates the object, and STO and IMG indicate the aperture stop and image plane, respectively.

[0024] As shown in Table 1, in the first positive meniscus lens L1 and the second positive meniscus lens L2 in this embodiment, i.e., in two positive lenses, nd and vd are set to satisfy the optical conditions of nd>1.82 and vd<44. Note that in this embodiment, the nd and vd of the aberration correction lens L4 also satisfy the optical conditions of nd>1.82 and vd<44. For this reason, in this embodiment, a glass material with a high refractive index is used for the first positive meniscus lens L1 and the second positive meniscus lens L2.

[0025] Furthermore, as shown in Table 1, in the respective positive lenses in the second lens group G2 of the optical lens system 100 in this embodiment, the first positive lens L5, the second positive lens L6r, and the final positive lens L7 are all set to satisfy the optical conditional expressions of nd>1.82 and vd<44. That is, in this embodiment, at least one positive lens in the second lens group G2 satisfies the optical conditional expressions of nd>1.82 and vd<44. Therefore, in this embodiment, high-refractive-index optical glasses are used for the first positive lens L5, the second positive lens L6r, and the final positive lens L7.

[0026] Furthermore, for the optical lens system 100 in this embodiment, if the focal length of the optical lens system 100 is f (34.45 mm), and the distance from the surface on the image-forming surface IMG side of the final positive lens L7 in the second lens group G2 (surface number 15: final lens surface) to the image-forming surface IMG (back focus: 15.879 mm here) is BF, then BF / f = 0.461. That is, the optical condition formula of 0.35 < BF / f < 0.75 is satisfied. Note that the optical lens system 100 of this embodiment is used for an optical device equipped with a so-called APS-C size image sensor.

[0027] The longitudinal aberration in such an optical lens system 100 will be described with reference to FIG. 2. The longitudinal aberration diagram in FIG. 2 is, from the left side, (a) spherical aberration diagram (wavelengths 656.27 nm, 587.56 nm, 435.83 nm), (b) astigmatism diagram (wavelength 587.56 nm), and (c) distortion aberration diagram (wavelength 587.56 nm). Note that the horizontal axis scale in each figure is ±0.50 mm, ±0.50 mm, ±3.0%. Also, in the (b) astigmatism diagram, T represents the tangential plane of the focus (yz plane direction), and S represents the sagittal plane (xz plane direction).

[0028] From FIG. 2, it can be confirmed that the optical lens system 100 in this embodiment has good aberration correction in all items (possessing good optical performance). In particular, in this embodiment, the results of spherical aberration correction and field curvature correction are particularly good, with high resolution and contrast, suppressing the occurrence of flare and clarifying the peripheral image.

[0029] (Second Embodiment) In the description of the optical lens system 100 in this embodiment, for the configurations common to the optical lens system 100 in the first embodiment, the same reference numerals as those used in the first embodiment are given, and the detailed description here is omitted.

[0030] The first lens group G1 in this embodiment has a configuration different from that of the first lens group G1 in the first embodiment in that the second positive meniscus lens L2 and the first negative lens L3 are independent and not formed as a cemented lens, and in that the aberration correction lens L4 is omitted. According to such a configuration of the first lens group G1, it is possible to shorten the length of the first lens group G1 in the optical axis direction and to shorten the arrangement distance between the first lens group G1 and the aperture stop STO. Note that, in this embodiment, the first lens group G1 also has a positive refractive index.

[0031] In the second lens group G2 in this embodiment, the outer diameters of the second negative lens L6f and the second positive lens L6r constituting the cemented lens L6 are equal, and the diameter of the final positive lens L7 is the same as the outer diameter of the cemented lens L6 adjacent to the object OBJ side. The cemented lens L6 of the second lens group G2 in this embodiment can be made significantly thinner than the cemented lens L6 in the first embodiment, and the optical axis length of the second lens group G2 can be shortened. Note that, although the BF in the second lens group G2 in this embodiment is slightly longer than the BF in the first embodiment, the optical axis length of the second lens group G2 can be made shorter than the second lens group G2 in the first embodiment.

[0032] By adopting the above-described configuration of optical lens system 100, it is possible to shorten the overall length of optical lens system 100 in the optical axis direction.

[0033] Table 2 shows surface data for each lens constituting the optical lens system 100 in this embodiment.

[0034] [Table 2]

[0035] Table 2 has the same format as Table 1. Also in the optical lens system 100 in the present embodiment, as shown in Table 2, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, that is, the two positive lenses, are set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high-refractive-index optical materials are used for the first positive meniscus lens L1 and the second positive meniscus lens L2.

[0036] The final positive lens L7 in the second lens group G2 is set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the second lens group G2, at least one positive lens satisfies the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high-refractive-index optical materials are used for the final positive lens L7.

[0037] In the present embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the final positive lens L7 satisfies the optical conditional expressions of nd > 1.82 and νd < 44, but at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 only needs to satisfy the above optical conditional expressions.

[0038] Furthermore, for the optical lens system 100 in the present embodiment, if the focal length of the optical lens system 100 is f (38.00 mm) and the distance (19.299 mm) from the surface (surface number 14: final lens surface) on the side of the imaging surface IMG of the final positive lens L7 in the second lens group G2 to the imaging surface IMG is BF, then BF / f = 0.508. That is, the optical conditional expression of 0.35 < BF / f < 0.75 is satisfied. The optical lens system 100 of the present embodiment is used for an optical device equipped with a so-called APS-C size image sensor.

[0039] The longitudinal aberration in such an optical lens system 100 will be described with reference to Fig. 4. The longitudinal aberration diagram in Fig. 4 is expressed in the same way as in Fig. 2. From Fig. 4, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, in this embodiment, the spherical aberration correction is good, the resolution and contrast are high, and the occurrence of flare can be suppressed.

[0040] Third embodiment In describing the optical lens system 100 of this embodiment, detailed descriptions of configurations common to the optical lens system 100 of the first and second embodiments will be omitted by assigning the same symbols as those used in the first and second embodiments.

[0041] The optical lens system 100 in this embodiment has a basic configuration common to that of the first embodiment as shown in FIG. 5, but the specific configuration of the cemented lens L6 in the second lens group G2 is different. That is, the cemented lens L6 in this embodiment is formed by a second negative lens L6f and a second positive lens L6r, both of which have a shape curved toward the image forming surface IMG (surface numbers 11, 12 and surface numbers 12, 13). The outer diameter of the second negative lens L6f is smaller than that of the second positive lens L6r. Furthermore, the final positive lens L7 has both of its two surfaces (surface numbers 14, 15) curved toward the image forming surface IMG. By adopting such a configuration, the optical axis length of the second lens group G2 can be shortened. Note that both of the first lens group G1 and the second lens group G2 in this embodiment have a positive refractive index.

[0042] By adopting the above-described configuration of optical lens system 100, it is possible to shorten the overall length of optical lens system 100 in the optical axis direction.

[0043] Table 3 shows surface data for each lens constituting the optical lens system 100 in this embodiment.

[0044]

Table 3

[0045] Table 3 has the same format as Tables 1 and 2. Also in the optical lens system 100 of the present embodiment, as shown in Table 3, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, that is, the two positive lenses, are set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high refractive index optical materials are used for the first positive meniscus lens L1 and the second positive meniscus lens L2.

[0046] The second positive lens L6r and the final positive lens L7 in the second lens group G2 are set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. That is, in the second lens group G2, at least one positive lens satisfies the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high refractive index optical materials are used for the second positive lens L6r and the final positive lens L7.

[0047] In the present embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the second positive lens L6r and the final positive lens L7 satisfy the optical conditional expressions of nd > 1.82 and νd < 44, but at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 only needs to satisfy the above optical conditional expressions.

[0048] Furthermore, for the optical lens system 100 in the present embodiment, when the focal length of the optical lens system 100 is f (36.50 mm) and the distance from the surface (surface number 15: final lens surface) on the side of the imaging surface IMG of the final positive lens L7 in the second lens group G2 to the imaging surface IMG is BF (20.010 mm), BF / f = 0.548. That is, the optical conditional expression of 0.35 < BF / f < 0.75 is satisfied. The optical lens system 100 of the present embodiment is used for an optical device equipped with a so-called full-size image sensor.

[0049] Longitudinal aberration in such optical lens system 100 will be described with reference to Fig. 6. The longitudinal aberration diagram in Fig. 6 has the same format as the aberration diagrams shown in Figs. 2 and 4. From Fig. 6, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, in this embodiment, distortion correction is good, making it possible to capture images that are faithful to the human visual sense.

[0050] (Fourth embodiment) In describing the optical lens system 100 of this embodiment, detailed descriptions of configurations common to the optical lens systems 100 of the first to third embodiments will be omitted by assigning the same symbols as those used in the first to third embodiments.

[0051] The optical lens system 100 in this embodiment has a basic configuration common to that of the second embodiment as shown in Fig. 7, but the specific shapes of the first positive lens L5 and the final positive lens L7 in the second lens group G2 are different. That is, the first positive lens L5 in this embodiment is formed into a biconvex shape (surface numbers 8 and 9), and the outer diameter of the final positive lens L7 is formed to be larger than the outer diameter of the cemented lens in the second lens group G2. Note that both the first lens group G1 and the second lens group G2 in this embodiment have positive refractive indices.

[0052] Table 4 shows surface data for each lens constituting the optical lens system 100 in this embodiment.

[0053] [Table 4]

[0054] Table 4 has the same format as Tables 1, 2, and 3. Also in the optical lens system 100 of the present embodiment, as shown in Table 4, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, that is, the two positive lenses, are set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high refractive index glass materials are used for the first positive meniscus lens L1 and the second positive meniscus lens L2.

[0055] The second positive lens L6r and the final positive lens L7 in the second lens group G2 are set to satisfy the optical conditional expressions of nd > 1.82 and νd < 44. That is, in the second lens group G2, at least one positive lens satisfies the optical conditional expressions of nd > 1.82 and νd < 44. Therefore, in the present embodiment, high refractive index glass materials are used for the second positive lens L6r and the final positive lens L7.

[0056] In the present embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the second positive lens L6r and the final positive lens L7 satisfy the optical conditional expressions of nd > 1.82 and νd < 44, but at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 only needs to satisfy the above optical conditional expressions.

[0057] Furthermore, for the optical lens system 100 in the present embodiment, when the focal length of the optical lens system 100 is f (42.00 mm) and the distance from the surface (surface number 14: final lens surface) on the image forming surface IMG side of the final positive lens L7 in the second lens group G2 to the image forming surface IMG is BF (22.180 mm), BF / f = 0.528, which satisfies the optical conditional expression of 0.35 < BF / f < 0.75. The optical lens system 100 of the present embodiment is used for an optical device equipped with a so-called full-size image sensor.

[0058] By adopting the configuration of the optical lens system 100 as described above, it is possible to shorten the overall length of the optical lens system 100 in the optical axis direction.

[0059] Longitudinal aberration in such optical lens system 100 will be described with reference to Fig. 8. The longitudinal aberration diagram in Fig. 8 has the same format as Figs. 2, 4, and 6. From Fig. 8, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, in this embodiment, both spherical aberration correction and distortion correction are extremely good, and it is possible to achieve high resolution and contrast, suppress the occurrence of flare, and capture images that are faithful to the human visual sense.

[0060] As in the optical lens systems of the first to fourth embodiments described above, the first lens group G1 includes a first positive meniscus lens L1 and a second positive meniscus lens L2 as two positive meniscus lenses with a high refractive index, and the second lens group G2 includes a final positive lens L7 as one positive lens with a high refractive index. This means that the lenses at both ends of the object side and the image plane side of a so-called double Gauss type optical lens system are constructed with lenses with a high refractive index, making it possible to shorten the length in the optical axial direction of the first lens group G1 and the second lens group G2 and to correct spherical aberration and astigmatism.

[0061] (Reference embodiment) Next, an optical lens system 100 in a reference embodiment will be described. In the reference embodiment, components common to the optical lens system 100 in the first to fourth embodiments will be denoted by the same reference symbols as those in the first to fourth embodiments, and detailed descriptions thereof will be omitted here.

[0062] The configuration of the optical lens system 100 in the reference embodiment is the same as that of the first embodiment in terms of the basic configuration as shown in FIG. 9, but the specific shapes are different. That is, the configuration is different from that of the first embodiment in that the convex surfaces are formed on the image plane IMG side on both surfaces (surface numbers 11 and 12) of the second negative lens L6f and both surfaces (surface numbers 12 and 13) of the second positive lens L6r in the cemented lens L6. Note that both the first lens group G1 and the second lens group G2 in the reference embodiment have positive refractive indices.

[0063] Table 5 shows the surface data of each lens constituting the optical lens system 100 in the present embodiment.

[0064]

Table 5

[0065] Table 5 has the same format as Tables 1, 2, 3, and 4. The optical lens system 100 in the reference embodiment satisfies the optical conditional expressions of nd > 1.82 and νd < 44 only in the aberration correction lens in the first lens group G1, and none of the positive lenses satisfy the optical conditional expressions of nd > 1.82 and νd < 44. Also, the optical conditional expressions of nd > 1.82 and νd < 44 are satisfied only in the first positive lens L5, which is a part of the positive lenses in the second lens group G2.

[0066] Incidentally, when the distance from the surface (surface number 15: the final lens surface) on the image plane IMG side of the final positive lens L7 in the second lens group G2 of the optical lens system 100 in the reference embodiment to the image plane IMG is BF (15.880 mm), BF / f = 0.432, and the optical conditional expression of 0.35 < BF / f < 0.75 is satisfied. Note that the optical lens system 100 of the reference embodiment is used for an optical device equipped with a so-called APS-C size image sensor.

[0067] The results of the experiment on longitudinal aberration for the optical lens system 100 in the reference embodiment were the same as those in the first to fourth embodiments, as follows. (a) Regarding the spherical aberration diagram (wavelengths 656.27 nm, 587.56 nm, 435.83 nm), the spherical aberration bends greatly, the resolution decreases, flare occurs, and the contrast decreases. (b) Regarding the astigmatism diagram (wavelength 587.56 nm), the field curvature increases, and the peripheral image does not form on the sensor plane. (c) Regarding the distortion aberration diagram (wavelength 587.56 nm), the distortion increases, and a photograph as seen cannot be taken.

[0068] Furthermore, in the reference embodiment, it became clear that the following problems occurred. It is impossible to secure the amount of light covering the sensor size and it cannot be used with APS-C or full-size image sensors. A large amount of coma aberration occurs and the MTF performance deteriorates. The longitudinal chromatic aberration increases, and the image becomes colored towards the periphery of the screen. Aberration correction is insufficient, and the above performance deterioration is particularly prominent on the close-distance side. The front lens diameter increases, and the maximum diameter of the product becomes thick. The radius of curvature of the lens becomes small, which is accompanied by difficulties in processing. Or it costs a large amount for production. The allowable tolerance for manufacturing errors becomes extremely small, and there is no productivity.

[0069] Therefore, just by using one positive lens that satisfies nd > 1.82 and νd < 44 in each of the first lens group G1 and the second lens group G2 like the optical lens system 100 in the reference embodiment and satisfying the optical condition of 0.35 < BF / f < 0.75, there are the above-mentioned problems compared to the optical lens system 100 in Embodiments 1 to 4, and it cannot be a solution to the problems that the present invention aims to solve.

[0070] As described above, according to the configuration of the optical lens system 100 in the first to fourth embodiments, it is possible to make the overall length in the optical axis direction more compact compared to the optical lens system 100 in the prior art and the reference embodiments, and it is also possible to improve the aberration performance.

[0071] Although the configuration of the optical lens system 100 according to the present invention has been described in detail based on a number of embodiments, the technical scope of the present invention is not limited to the above embodiments. It is also possible to adopt forms that appropriately combine modified examples described in the specification and other known configurations. [Explanation of symbols]

[0072] 100 Optical lens system G1 First lens group STO aperture stop G2 2nd lens group L1 1st positive meniscus lens L2 Second positive meniscus lens L3 1st negative lens L4 aberration correction lens L5 1st positive lens L6 cemented lens L6f 2nd negative lens L6r 2nd positive lens L7 Final positive lens nd Refractive index of the entire system at d line νd Abbe number f focal length of the entire system BF: Distance from the final lens surface in the second lens group to the image plane (back focus)

Claims

1. a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in this order from the object side to the image forming surface side; the first lens group includes, in order from the object side to the image plane side, two positive meniscus lenses each having a convex surface facing the object side and a negative lens each having a convex surface facing the object side, the second lens group includes, in order from the object side to the image forming surface side, a positive lens, a cemented lens including a negative lens and a positive lens, the cemented lens having a concave surface facing the object side, and a final positive lens, a cemented lens is formed by the second positive meniscus lens and the negative lens in the first lens group, When the refractive index at the d line of the entire system is nd and the Abbe number is vd, The two positive meniscus lenses in the first lens group and the at least one positive lens in the second lens group are nd>1.82 and νd<44 is satisfied, and if the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the image-forming surface is BF, then 0.35<BF / f<0.75 An optical lens system characterized in that the following condition is satisfied:

2. 2. The optical lens system according to claim 1, wherein the at least one positive lens in the second lens group that satisfies the conditions nd>1.82 and νd<44 includes the final positive lens.

3. 3. The optical lens system according to claim 1, wherein the final positive lens in the second lens group is formed to have the largest diameter in the second lens group.

4. a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in this order from the object side to the image forming surface side; the first lens group includes, in order from the object side to the image plane side, two positive meniscus lenses each having a convex surface facing the object side and a negative lens each having a convex surface facing the object side, the second lens group includes, in order from the object side to the image forming surface side, a positive lens, a cemented lens including a negative lens and a positive lens, the cemented lens having a concave surface facing the object side, and a final positive lens, the first lens group further includes an aberration correction lens disposed on the aperture stop side; When the refractive index at the d line of the entire system is nd and the Abbe number is vd, The two positive meniscus lenses in the first lens group and the at least one positive lens in the second lens group are nd>1.82 and νd<44 is satisfied, and if the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the image-forming surface is BF, then 0.35<BF / f<0.75 An optical lens system characterized in that the following condition is satisfied:

5. 5. The optical lens system according to claim 4, wherein the at least one positive lens in the second lens group that satisfies the conditions nd>1.82 and νd<44 includes the final positive lens.

6. 6. The optical lens system according to claim 4, wherein the final positive lens in the second lens group is formed to have the largest diameter in the second lens group.

Images