Optical lens system

Abstract

To reduce distortion, prevent occurrence of a curvature of field, and correct Petzval sum and chromatic aberration.SOLUTION: An optical lens system comprises: an aperture stop STO; a partially symmetrical group G1 with a positive refractive force as a whole, in which a cemented lens and one positive lens are each arranged symmetrically across the aperture stop STO; one object-side negative lens L1 arranged closer to an object OBJ than the partially symmetrical group G1; and one image-side negative lens L8 arranged closer to an image IMG than the partially symmetrical group G1. Each cemented lens has a concave surface facing the aperture stop STO side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical lens system as a lens for an interchangeable-lens camera.

Background Art

[0002] There is an optical lens system disclosed in Patent Document 1 (Japanese Patent No. 6548590) that is used in conventional photographic and video shooting equipment. The optical lens system disclosed in Patent Document 1 is of a double-Gauss type in which the lens arrangement is symmetric with respect to the aperture stop. The double-Gauss type optical lens system is said to have high symmetry in the entire optical system and be strong against aberration fluctuations due to changes in the shooting distance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An optical lens system including a symmetric lens arrangement part such as the double-Gauss type has high symmetry in the entire optical system and is strong against aberration fluctuations due to changes in the shooting distance as described above. However, on the other hand, there is also a problem that the back focus is long, resulting in a long overall product length.

[0005] Therefore, in the configuration described in Patent Document 1, a negative lens is arranged closer to the image side than the Gauss type to shorten the back focus and shorten the overall product length. However, by arranging a negative lens closer to the image side than the Gauss type, the symmetry of the lens is sacrificed, resulting in a large distortion, and there are also problems such as the occurrence of field curvature and the deterioration of the Petzval sum and chromatic aberration.

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 can reduce distortion in a lens including a symmetric portion in lens arrangement such as a double Gaussian type, prevent the occurrence of field curvature, and correct Petzval sum and chromatic aberration.

[0007] In one embodiment of the present invention, the above problems are solved by the following solution means. That is, a stop, a cemented lens, and a single positive lens are symmetrically arranged with respect to the stop in lens configuration, respectively, and a partially symmetric group having a positive refractive power as a whole, and one most object-side negative lens arranged on the object side of the partially symmetric group, and one most image-side negative lens arranged on the image side of the partially symmetric group, and each of the cemented lenses is characterized in that the concave surface faces the stop side. By adopting this configuration, by making the power arrangement completely symmetric with the stop in between, it is possible to reduce distortion and performance degradation due to distance variation. In addition, since two negative lenses are added compared to the conventional double Gaussian type, the occurrence of field curvature can be prevented, and Petzval sum and chromatic aberration can be corrected.

[0008] The most object-side negative lens is a negative meniscus lens with the convex surface facing the object side, and the most image-side negative lens is a negative meniscus lens with the convex surface facing the image side. If the most object-side negative lens and the most image-side negative lens are both biconcave lenses, the symmetry is broken, image plane variation due to distance variation occurs, the magnification chromatic aberration increases, and the peripheral light quantity cannot be maintained when wide-angle conversion is attempted. However, according to this configuration, symmetry can be maintained, image plane variation due to distance variation can be prevented from occurring, the magnification chromatic aberration can be reduced, and the peripheral light quantity can be maintained when wide-angle conversion is attempted.

[0009] Among the positive lenses arranged on the image side of the stop in the partially symmetric group, at least one satisfies νd>70. According to this configuration, chromatic aberration can be improved.

[0010] Among the positive lenses arranged on the object side of the aperture stop in the partial symmetry group, at least one satisfies nd > 1.72. If nd ≤ 1.72, the radius of curvature of each positive lens becomes small, and the meridional and sagittal coma aberrations increase. However, according to this configuration, the radius of curvature of each positive lens becomes large, the meridional and sagittal coma aberrations can be reduced, and the overall length of the product can be shortened, contributing to miniaturization.

[0011] Among the light beams imaging on the optical axis from infinity, when the distance from the optical axis at the point farthest from the optical axis among the lens groups arranged on the object side of the aperture stop in the partial symmetry group is defined as Hf, and the distance from the optical axis at the point farthest from the optical axis among the lens groups arranged on the image side of the aperture stop in the partial symmetry group is defined as Hr, it is characterized by satisfying 1.25 < Hf / Hr < 1.45. According to this configuration, the powers of the lens group on the object side and the lens group on the image side separated by the aperture stop can be made equal, and the deterioration of aberrations due to distance variation can be prevented.

[0012] When the focal length of the partial symmetry group is defined as fsy and the focal length of the entire system is defined as f, it is characterized by satisfying 0.48 < fsy / f < 0.72. According to this configuration, by setting fsy / f < 0.72, the whole can be miniaturized, and by setting 0.48 < fsy / f, the occurrence of spherical aberration and coma aberration can be particularly prevented, and the resolution at the time of aperture stop opening can be improved.

[0013] When the focal length of the partial symmetry group is defined as fsy and the distance from the image-side lens surface of the most image-side negative lens to the imaging surface is defined as BF, it is characterized by satisfying 0.73 < fsy / BF < 1.15. According to this configuration, the paraxial balance of the lens group on the object side and the lens group on the image side separated by the aperture stop can be maintained, and good aberration characteristics can be maintained.

[0014] When the distance from the object-side lens surface of the frontmost object-side negative lens to the image-side lens surface of the rearmost image-side negative lens is defined as OAL, and the distance from the image-side lens surface of the rearmost image-side negative lens to the imaging surface is defined as BF, it is characterized by satisfying 0.9 < OAL / BF < 1.55. According to this configuration, the overall length of the lens can be shortened, and the distance from the lens surface of the rearmost image-side negative lens to the imaging surface can be lengthened. Further, for example, it can be adopted in a retractable camera.

[0015] It is characterized in that all lenses are composed only of spherical lenses. According to this configuration, it is possible to increase the aperture while avoiding an increase in cost.

[0016] When focusing from infinity to a short distance, focusing is performed by moving the entire optical system toward the object side.

Advantages of the Invention

[0017] It is possible to realize an optical lens system capable of reducing distortion, preventing the occurrence of field curvature, and correcting Petzval sum and chromatic aberration.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0019] Hereinafter, each embodiment will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of an optical lens system 100 in the first embodiment of the present invention. FIG. 2 is a longitudinal aberration diagram at infinity of the optical lens system 100 in the first embodiment of the present invention. FIG. 3 is a configuration diagram of an optical lens system 200 in the second embodiment of the present invention. FIG. 4 is a longitudinal aberration diagram at infinity of the optical lens system 200 in the second embodiment of the present invention. FIG. 5 is a configuration diagram of an optical lens system 300 in the third embodiment of the present invention. FIG. 6 is a longitudinal aberration diagram at infinity of the optical lens system 300 in the third embodiment of the present invention. FIG. 7 is a configuration diagram of an optical lens system 400 in the fourth embodiment of the present invention. FIG. 8 is a longitudinal aberration diagram at infinity of the optical lens system 400 in the fourth embodiment of the present invention. FIG. 9 is a configuration diagram of an optical lens system 500 in the fifth embodiment of the present invention. FIG. 10 is a longitudinal aberration diagram at infinity of the optical lens system 500 in the fifth embodiment of the present invention.

[0020] In the upper right of each of FIGS. 2, 4, 6, 8, and 10, legends for C line (wavelength 656.27 nm), d line (wavelength 587.56 nm), and g line (wavelength 435.83 nm) are described. In all the drawings for explaining each embodiment, members having the same function are denoted by the same reference numerals, and repeated explanations may be omitted.

[0021] The optical lens systems 100, 200, 300, 400, and 500 in each embodiment are, as an example, imaging lenses used in a photographic camera or a video camera. As shown in FIGS. 1, 3, 5, 7, and 9, an aperture stop STO, a partial symmetry group G1 in which a plurality of lenses are arranged symmetrically with respect to the aperture stop STO with a space therebetween, a most object-side negative lens arranged on the object OBJ side of the partial symmetry group G1, and a most image-side negative lens arranged on the image plane IMG side of the partial symmetry group G1 are provided on the optical axis from the object OBJ toward the image plane IMG.

[0022] In each embodiment, the partial symmetry group G1 of the optical lens systems 100, 200, 300, 400, and 500 will be described below with the part of the partial symmetry front group G1F on the object OBJ side of the aperture stop STO and the part of the partial symmetry rear group G1B on the image plane IMG side of the aperture stop STO. As described above, the lens configurations of the partial symmetry front group G1F and the partial symmetry rear group G1B are configured to be symmetric with respect to the aperture stop STO. In addition, the optical lens systems 100, 200, 300, 400, and 500 in each embodiment are configured to perform focusing by moving the entire optical system toward the object side when focusing from infinity to a short distance.

[0023] For convenience, in FIGS. 1, 3, 5, 7, and 9, 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 of the cemented lens. Further, since the aperture stop STO is counted as a virtual surface, the consecutive surface numbers are skipped.

[0024] (First Embodiment) In the first embodiment, an imaging lens 100 with a focal length f = 49.10 mm, an F-number 3.56, and a semi-field angle ω = 23.94° of the entire system will be described by taking FIG. 1 as an example.

[0025] The imaging lens 100 in the present embodiment has a partial symmetry group G1 including a partial symmetry front group G1F and a partial symmetry rear group G1B in which the lens configurations are symmetrically arranged with the aperture stop STO interposed therebetween. The partial symmetry group G1 has a positive refractive power.

[0026] The front partial symmetry group G1F includes, in order from the object OBJ, a positive meniscus lens L2, a biconvex lens L3, and a biconcave lens L4 joined to the biconvex lens L3. That is, the lens surfaces of the joined lenses L3 and L4 on the aperture stop STO side face the aperture stop STO with concave surfaces. The rear partial symmetry group G1B includes, in order from the object OBJ, a biconcave lens L5, a biconvex lens L6 joined to the biconcave lens L5, and a biconvex lens L7. That is, the lens surfaces of the joined lenses L5 and L6 on the aperture stop STO side face the aperture stop STO with concave surfaces. In this way, the partial symmetry group G1 composed of the front partial symmetry group G1F and the rear partial symmetry group G1B consists of six lenses.

[0027] On the object OBJ side of the partial symmetry group G1, a negative meniscus lens L1 with a convex surface facing the object OBJ is arranged. On the image plane IMG side of the partial symmetry group G1, a negative meniscus lens L8 with a convex surface facing the image plane IMG side is arranged. In this way, by arranging negative lenses before and after the partial symmetry group G1 respectively, the Petzval sum and chromatic aberration correction can be achieved. Also, by using negative meniscus lenses before and after the partial symmetry group G1, symmetry is maintained, image plane fluctuation due to distance variation is suppressed, magnification chromatic aberration can be reduced, and peripheral light quantity can be maintained when wide-angle conversion is achieved.

[0028] When considering the lens configuration of this embodiment, in order from the object OBJ side, taking the negative meniscus lens L1 as the first group, the partial symmetry group G1 as the second group, and the negative meniscus lens L8 as the third group, it can be considered as a combination of three groups: negative, positive, and negative. In this case, although the F-number cannot be made smaller than in the case of the positive, negative, positive combination, there is an advantage that the back focus can be shortened and the product can be miniaturized. Also, since the partial symmetry group G1 as the second group is configured to be a positive, negative, positive combination, it is possible to make the F-number as small as possible even when considering the combination of three groups: negative, positive, and negative as a whole.

[0029] And, as described above, since the overall configuration of the optical lens system 100 of the present embodiment is completely symmetric with respect to the aperture stop STO across the aperture stop STO, it is possible to reduce performance degradation due to distortion and distance variation.

[0030] In addition, the entire lens constituting the optical lens system 100 of the present embodiment is composed of eight lenses, all of which are spherical lenses. Therefore, it is possible to increase the aperture diameter without increasing the cost.

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

Table 1

[0032] Note that in Table 1, Hf is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the partially symmetric front group G1F in the light beam that forms an image on the optical axis from infinity. Hr is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the partially symmetric rear group G1B in the light beam that forms an image on the optical axis from infinity. According to the first embodiment, Hf / Hr = 1.36, satisfying 1.25 < Hf / Hr < 1.45. Therefore, it is possible to equalize the powers of the partially symmetric front group G1F and the partially symmetric rear group G1B separated by the aperture stop STO, and prevent deterioration of aberration due to distance variation.

[0033] In addition, according to the first embodiment, fsy / f = 0.67, satisfying 0.48 < fsy / f < 0.72. Therefore, since fsy / f < 0.72, the overall size can be reduced, and since 0.48 < fsy / f, in particular, the occurrence of spherical aberration and coma aberration can be prevented, and the resolution at the time of aperture stop open can be improved.

[0034] Also, according to the first embodiment, fsy / BF = 0.99, and 0.73 < fsy / BF < 1.15 is satisfied. Therefore, the paraxial balance between the lens group on the object OBJ side separated by the aperture stop STO and the lens group on the imaging plane IMG side can be maintained, and good aberration characteristics can be ensured.

[0035] Also, according to the first embodiment, OAL / BF = 1.10, and 0.9 < OAL / BF < 1.55 is satisfied. Therefore, the overall length of the lens can be shortened, and the distance from the lens surface of the most image-side negative lens L8 to the imaging plane IMG can be lengthened.

[0036] Subsequently, Table 2 shows the lens data of the optical lens system 100 of the first embodiment shown in FIG. 1.

[0037]

Table 2

[0038] In Table 2, the radius of curvature R (mm), 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 corresponding to the virtual surface and the lens surface counted from the object OBJ side are shown respectively. 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 blanks for nd and νd indicate that it is air.

[0039] In the first embodiment, among the positive lenses of the partially symmetric rear group G1B, the biconvex lens L6 has νd = 81.86, and νd > 70 is satisfied. Therefore, according to this configuration, chromatic aberration can be improved.

[0040] In the first embodiment, among the positive lenses of the partially symmetrical front group G1F, the positive meniscus lens L2 has nd = 1.88300, and at least one positive lens satisfies the condition that nd > 1.72. Therefore, the radius of curvature of the positive lens becomes large, which can reduce the meridional and sagittal coma aberrations, and also contribute to miniaturization by shortening the overall length of the product.

[0041] Fig. 2 shows the spherical aberration, astigmatism, and distortion of the optical lens system 100. Each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Fig. 2, it can be confirmed that good aberrations are obtained in all cases.

[0042] (Second Embodiment) Subsequently, as the second embodiment, an imaging lens 200 with a focal length f = 51.00 mm, an F-number of 3.52, and a semi-field angle ω = 23.02° in the entire system will be exemplified and described with reference to Fig. 3.

[0043] The imaging lens 200 in this embodiment has a partially symmetrical group G1 composed of a partially symmetrical front group G1F and a partially symmetrical rear group G1B, with the lens configurations arranged symmetrically across the aperture stop STO. The partially symmetrical group G1 has a positive refractive power.

[0044] The partially symmetrical front group G1F includes, in order from the object OBJ, a positive meniscus lens L10, a biconvex lens L11, and a biconcave lens L12 joined to the biconvex lens L11. That is, the lens surfaces of the joined lenses L11 and L12 on the aperture stop STO side face the aperture stop STO with concave surfaces. The partially symmetrical rear group G1B includes, in order from the object OBJ, a biconcave lens L13, a biconvex lens L14 joined to the biconcave lens L13, and a biconvex lens L15. That is, the lens surfaces of the joined lenses L13 and L14 on the aperture stop STO side face the aperture stop STO with concave surfaces. In this way, the partially symmetrical group G1 composed of the partially symmetrical front group G1F and the partially symmetrical rear group G1B consists of six lenses.

[0045] On the object OBJ side of the partial symmetry group G1, a negative meniscus lens L9 with a convex surface facing the object OBJ side is arranged. On the imaging surface IMG side of the partial symmetry group G1, a negative meniscus lens L16 with a convex surface facing the imaging surface IMG side is arranged. The negative meniscus lens L16 is joined to the biconvex lens L15 of the partial symmetry group G1 and configured as a joined lens. In this way, by arranging negative lenses before and after the partial symmetry group G1 respectively, Petzval sum and chromatic aberration correction can be performed. Also, by using negative lenses before and after the partial symmetry group G1 as meniscus lenses, symmetry is maintained, image plane fluctuation due to distance variation can be suppressed, magnification chromatic aberration can be reduced, and peripheral light quantity can be maintained when wide-angleization is achieved.

[0046] When considering the lens configuration of this embodiment in order from the object OBJ side, taking the negative meniscus lens L9 as the first group, the partial symmetry group G1 as the second group, and the negative meniscus lens L16 as the third group, it can be considered as a combination of three groups of negative, positive, and negative. In this case, although the F-number cannot be made smaller than in the case of the positive, negative, positive combination, there is an advantage that the back focus can be shortened and the product can be miniaturized. Also, since the partial symmetry group G1 as the second group is configured to be a positive, negative, positive combination, it is possible to make the F-number as small as possible as a combination of three groups of negative, positive, and negative as a whole.

[0047] And, as described above, since the overall configuration of the optical lens system 200 of this embodiment is completely symmetric with respect to the aperture stop STO with the aperture stop STO in between, performance degradation due to distortion and distance variation can be reduced.

[0048] Also, the total number of lenses constituting the optical lens system 200 of this embodiment is eight, and all are spherical lenses. Therefore, it is possible to increase the aperture diameter without increasing the cost.

[0049] Table 3 shows a table summarizing various data of the second embodiment.

Table 3

[0050] Note that in Table 3, Hf is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the front partial symmetry group G1F in the light beam that forms an image on the optical axis from infinity. Hr is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the rear partial symmetry group G1B in the light beam that forms an image on the optical axis from infinity. According to the second embodiment, Hf / Hr = 1.42, satisfying 1.25 < Hf / Hr < 1.45. Therefore, the powers of the front partial symmetry group G1F and the rear partial symmetry group G1B separated by the aperture stop STO can be made equal, and deterioration of aberration due to distance variation can be prevented.

[0051] Also, according to the second embodiment, fsy / f = 0.51, satisfying 0.48 < fsy / f < 0.72. Therefore, since fsy / f < 0.72, the whole can be miniaturized, and since 0.48 < fsy / f, generation of spherical aberration and coma aberration can be particularly prevented, and the resolution at the time of aperture stop opening can be improved.

[0052] Also, according to the second embodiment, fsy / BF = 0.77, satisfying 0.73 < fsy / BF < 1.15. Therefore, the paraxial balance between the lens group on the object OBJ side and the lens group on the image plane IMG side separated by the aperture stop STO can be maintained, and good aberration characteristics can be maintained.

[0053] Also, according to the second embodiment, OAL / BF = 1.16, satisfying 0.9 < OAL / BF < 1.55. Therefore, the overall length of the lens can be shortened, and the distance from the lens surface of the most image-side negative lens L8 to the image plane IMG can be lengthened.

[0054] Subsequently, the lens data of the optical lens system 200 of the second embodiment shown in FIG. 3 is shown in Table 4.

[0055]

Table 4

[0056] In Table 4, 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 the lens surface is convex with respect to the object OBJ, the radius of curvature R is set to be positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is set to be 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 spaces for nd and νd indicate that it is air.

[0057] In the second embodiment, among the positive lenses of the partially symmetric rear group G1B, the biconvex lens L14 has νd = 81.61, satisfying νd > 70. Therefore, according to this configuration, chromatic aberration can be improved.

[0058] Also, in the second embodiment, among the positive lenses of the partially symmetric front group G1F, the positive meniscus lens L10 has nd = 1.88300, and the biconvex lens L11 has nd = 1.74400, satisfying the condition that at least one positive lens has nd > 1.72. Therefore, the radius of curvature of the positive lens becomes large, the meridional and sagittal coma aberrations can be reduced, and the overall length of the product can be shortened, contributing to miniaturization.

[0059] Fig. 4 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. Note that each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Fig. 4, it can be confirmed that good aberrations are obtained in all cases.

[0060] (Third Embodiment) Subsequently, in the third embodiment, an imaging lens 300 with a focal length f = 41.00 mm, an F-number 2.87, and a semi-field angle ω = 28.00° in the entire system will be illustrated and described with reference to Fig. 5.

[0061] The imaging lens 300 in this embodiment has a partially symmetric group G1 composed of a partially symmetric front group G1F and a partially symmetric rear group G1B, with the aperture stop STO sandwiched between them. The partially symmetric group G1 has a positive refractive power.

[0062] The partially symmetric front group G1F includes, in order from the object OBJ, a positive meniscus lens L18, a biconvex lens L19, and a biconcave lens L20 joined to the biconvex lens L19. That is, the lens surfaces of the joined lenses L19 and L20 on the aperture stop STO side face the aperture stop STO with concave surfaces. The partially symmetric rear group G1B includes, in order from the object OBJ, a biconcave lens L21, a biconvex lens L22 joined to the biconcave lens L21, and a positive meniscus lens L23. That is, the lens surfaces of the joined lenses L20 and L21 on the aperture stop STO side face the aperture stop STO with concave surfaces. Thus, the partially symmetric group G1 composed of the partially symmetric front group G1F and the partially symmetric rear group G1B consists of six lenses.

[0063] On the object OBJ side of the partially symmetric group G1, a negative meniscus lens L17 with a convex surface facing the object OBJ is arranged. On the image plane IMG side of the partially symmetric group G1, a negative meniscus lens L24 with a convex surface facing the image plane IMG side is arranged. Thus, by arranging negative lenses before and after the partially symmetric group G1 respectively, the Petzval sum and chromatic aberration correction can be achieved. Also, by using meniscus lenses as the negative lenses before and after the partially symmetric group G1, symmetry can be maintained, image plane fluctuation due to distance variation can be suppressed, magnification chromatic aberration can be reduced, and peripheral light quantity can be maintained when wide-angle conversion is achieved.

[0064] When the lens configuration of this embodiment is considered with the negative meniscus lens L17 as the first group, the partially symmetric group G1 as the second group, and the negative meniscus lens L24 as the third group in order from the object OBJ side, it can be considered as a combination of three groups of negative, positive, and negative. In this case, although the F-number cannot be made smaller than in the case of the positive, negative, positive combination, there is an advantage that the back focus can be shortened and the product can be miniaturized. In addition, since the partially symmetric group G1 as the second group is configured to have a positive, negative, positive combination, it is possible to make the F-number as small as possible even when considered as a combination of three groups of negative, positive, and negative as a whole.

[0065] And, as described above, since the overall configuration of the optical lens system 300 of this embodiment is completely symmetric with respect to the aperture stop STO with the aperture stop STO in between, deterioration of performance due to distortion and distance variation can be reduced.

[0066] In addition, all the lenses constituting the optical lens system 300 of this embodiment are composed of 8 lenses, and all are spherical lenses. Therefore, it is possible to increase the aperture diameter without increasing the cost.

[0067] Table 5 shows a table summarizing various data of the third embodiment.

Table 5

[0068] Note that in Table 5, Hf is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the partially symmetric front group G1F in the light beam that forms an image on the optical axis from infinity. Hr is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the partially symmetric rear group G1B in the light beam that forms an image on the optical axis from infinity. According to the third embodiment, Hf / Hr = 1.37, which satisfies 1.25 < Hf / Hr < 1.45. Therefore, the powers of the partially symmetric front group G1F and the partially symmetric rear group G1B separated by the aperture stop STO can be made equal, and deterioration of aberration due to distance variation can be prevented.

[0069] Also, according to the third embodiment, fsy / f = 0.66, satisfying 0.48 < fsy / f < 0.72. Therefore, since fsy / f < 0.72, the overall size can be reduced, and since 0.48 < fsy / f, it is possible to particularly prevent the occurrence of spherical aberration and coma aberration and improve the resolution when the aperture stop is open.

[0070] Also, according to the third embodiment, fsy / BF = 1.06, satisfying 0.73 < fsy / BF < 1.15. Therefore, it is possible to maintain the paraxial balance between the lens group on the object OBJ side separated by the aperture stop STO and the lens group on the imaging surface IMG side and maintain good aberration characteristics.

[0071] Also, according to the third embodiment, OAL / BF = 1.48, satisfying 0.9 < OAL / BF < 1.55. Therefore, the overall length of the lens can be shortened, and the distance from the lens surface of the most image-side negative lens L8 to the imaging surface IMG can be increased.

[0072] Subsequently, the lens data of the optical lens system 300 of the third embodiment shown in FIG. 5 are shown in Table 6.

[0073]

Table 6

[0074] 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 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. Further, the blanks for nd and νd indicate that it is air.

[0075] In the third embodiment, among the positive lenses of the partially symmetric rear group G1B, the biconvex lens L22 has νd = 75.50, satisfying νd > 70. Therefore, according to this configuration, chromatic aberration can be improved.

[0076] Also, in the third embodiment, among the positive lenses of the partially symmetric front group G1F, the positive meniscus lens L18 has nd = 1.88300, and the biconvex lens L19 has nd = 1.72916, satisfying the condition that at least one positive lens has nd > 1.72. Therefore, the curvature radius of the positive lens becomes large, the meridional and sagittal coma aberrations can be reduced, and the overall product length can be shortened, contributing to miniaturization.

[0077] Fig. 6 shows the spherical aberration, astigmatism, and distortion of the optical lens system 300. Each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Fig. 6, it can be confirmed that good aberrations are obtained in all cases.

[0078] (Fourth Embodiment) Subsequently, in the fourth embodiment, an imaging lens 400 with a focal length f = 48.50 mm, an F-number of 3.50, and a semi-field angle ω = 24.02° in the entire system will be exemplified and described with reference to Fig. 7.

[0079] The imaging lens 400 in this embodiment has a partially symmetric group G1 composed of a partially symmetric front group G1F and a partially symmetric rear group G1B, with the lens configurations arranged symmetrically across the aperture stop STO. The partially symmetric group G1 has a positive refractive power.

[0080] The partially symmetric front group G1F includes, in order from the object OBJ, a biconvex lens L26, a biconcave lens L27 joined to the biconvex lens L26, and a positive meniscus lens L28. That is, the lens surfaces of the joined lenses L26 and L27 on the aperture stop STO side face the aperture stop STO with concave surfaces. The partially symmetric rear group G1B includes, in order from the object OBJ, a positive meniscus lens L29, a biconcave lens L30, and a biconvex lens L31 joined to the biconcave lens L30. That is, the lens surfaces of the joined lenses L30 and L31 on the aperture stop STO side face the aperture stop STO with concave surfaces. In this way, the partially symmetric group G1 composed of the partially symmetric front group G1F and the partially symmetric rear group G1B consists of six lenses.

[0081] On the object OBJ side of the partially symmetric group G1, a negative meniscus lens L25 with a convex surface facing the object OBJ is arranged. On the image plane IMG side of the partially symmetric group G1, a negative meniscus lens L32 with a convex surface facing the image plane IMG side is arranged. In this way, by arranging negative lenses before and after the partially symmetric group G1 respectively, Petzval sum and chromatic aberration correction can be achieved. Also, by using negative meniscus lenses before and after the partially symmetric group G1, symmetry is maintained, image plane fluctuation due to distance variation is suppressed, magnification chromatic aberration can be reduced, and peripheral light quantity can be maintained when wide-angleization is achieved.

[0082] When considering the lens configuration of this embodiment in order from the object OBJ side, taking the negative meniscus lens L25 as the first group, the partially symmetric group G1 as the second group, and the negative meniscus lens L32 as the third group, it can be considered as a combination of three groups: negative, positive, and negative. In this case, although the F-number cannot be made smaller than in the case of a positive, negative, positive combination, there is an advantage that the back focus can be shortened and the product can be miniaturized. Also, since the partially symmetric group G1 as the second group is configured to have a positive, negative, positive combination, it is possible to make the F-number as small as possible as a combination of three groups: negative, positive, and negative as a whole.

[0083] And, as described above, since the overall configuration of the optical lens system 400 of this embodiment is completely symmetric with respect to the aperture stop STO with the aperture stop STO in between, performance degradation due to distortion and distance variation can be reduced.

[0084] In addition, the entire lens that constitutes the optical lens system 400 of the present embodiment is composed of eight lenses, all of which are spherical lenses. Therefore, it is possible to increase the aperture diameter without increasing the cost.

[0085] Table 7 shows a table summarizing various data of the fourth embodiment.

Table 7

[0086] Note that in Table 7, Hf is the distance from the optical axis at the point where the distance from the optical axis is the farthest among the lens groups of the partial symmetric front group G1F in the light beam that forms an image on the optical axis from infinity. Hr is the distance from the optical axis at the point where the distance from the optical axis is the farthest among the lens groups of the partial symmetric rear group G1B in the light beam that forms an image on the optical axis from infinity. According to the fourth embodiment, Hf / Hr = 1.38, which satisfies 1.25 < Hf / Hr < 1.45. Therefore, it is possible to equalize the powers of the partial symmetric front group G1F and the partial symmetric rear group G1B separated by the aperture stop STO, and prevent the deterioration of aberration due to distance variation.

[0087] In addition, according to the fourth embodiment, fsy / f = 0.55, which satisfies 0.48 < fsy / f < 0.72. Therefore, since fsy / f < 0.72, the whole can be miniaturized, and since 0.48 < fsy / f, in particular, the occurrence of spherical aberration and coma aberration can be prevented, and the resolution at the time of aperture stop opening can be improved.

[0088] In addition, according to the fourth embodiment, fsy / BF = 0.94, which satisfies 0.73 < fsy / BF < 1.15. Therefore, it is possible to maintain the paraxial balance between the lens group on the object OBJ side and the lens group on the image plane IMG side separated by the aperture stop STO, and maintain good aberration characteristics.

[0089] Also, according to the fourth embodiment, OAL / BF = 1.43, satisfying 0.9 < OAL / BF < 1.55. Therefore, the overall length of the lens can be shortened, and the distance from the lens surface of the most image-side negative lens L8 to the imaging surface IMG can be lengthened.

[0090] Subsequently, Table 8 shows the lens data of the optical lens system 400 of the fourth embodiment shown in FIG. 7.

[0091]

Table 8

[0092] In Table 8, 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 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.

[0093] In the fourth embodiment, among the positive lenses of the partially symmetric rear group G1B, the positive meniscus lens L29 has νd = 81.61, satisfying νd > 70. Therefore, according to this configuration, chromatic aberration can be improved.

[0094] Also, in the fourth embodiment, among the positive lenses of the partially symmetric front group G1F, the biconvex lens L26 has nd = 1.85150, satisfying the condition that at least one positive lens has nd > 1.72. Therefore, the radius of curvature of the positive lens becomes large, the meridional and sagittal coma aberrations can be reduced, and the overall length of the product can be shortened, contributing to miniaturization.

[0095] Fig. 8 shows the spherical aberration, astigmatism, and distortion in the optical lens system 400. Each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Fig. 8, it can be confirmed that good aberrations are obtained in all cases.

[0096] (Fifth Embodiment) Subsequently, in the fifth embodiment, an imaging lens 500 with a focal length f = 48.50 mm, an F-number of 3.51, and a semi-field angle ω = 24.02° of the entire system will be exemplified and described with reference to Fig. 9.

[0097] The imaging lens 500 in this embodiment has a partially symmetric group G1 composed of a partially symmetric front group G1F and a partially symmetric rear group G1B, with the lens configurations arranged symmetrically with the aperture stop STO in between. The partially symmetric group G1 has a positive refractive power.

[0098] The partially symmetric front group G1F includes, in order from the object OBJ, a positive meniscus lens L34, a negative meniscus lens L35, and a positive meniscus lens L36 joined to the negative meniscus lens L35 and having the lens surface on the aperture stop STO side facing the aperture stop STO with a concave surface. The partially symmetric rear group G1B includes, in order from the object OBJ, a positive meniscus lens L37 having the lens surface on the aperture stop STO side facing the aperture stop STO with a concave surface, a negative meniscus lens L38 joined to this positive meniscus lens L37, and a positive meniscus lens L39. In this way, the partially symmetric group G1 composed of the partially symmetric front group G1F and the partially symmetric rear group G1B consists of six lenses.

[0099] On the object OBJ side of the partially symmetric group G1, a negative meniscus lens L33 with a convex surface facing the object OBJ is arranged. On the image plane IMG side of the partially symmetric group G1, a negative meniscus lens L40 with a convex surface facing the image plane IMG is arranged. In this way, by arranging negative lenses before and after the partial symmetry group G1 respectively, Petzval sum and chromatic aberration correction can be achieved. Further, by using the negative lenses before and after the partial symmetry group G1 as meniscus lenses, symmetry can be maintained, image plane fluctuation due to distance variation can be suppressed, magnification chromatic aberration can be reduced, and peripheral light quantity can be maintained when wide-angle conversion is achieved.

[0100] When the lens configuration of this embodiment is regarded as having a negative meniscus lens L33 as the first group, a partial symmetry group G1 as the second group, and a negative meniscus lens L40 as the third group in order from the object OBJ side, it can be considered as a combination of three groups of negative, positive, and negative. In this case, although the F-number cannot be made smaller than in the case of a positive, negative, positive combination, there is an advantage that the back focus can be shortened and the product can be miniaturized. Further, since the partial symmetry group G1 as the second group is configured to be a positive, negative, positive combination, it is possible to make the F-number as small as possible even as a combination of three groups of negative, positive, and negative as a whole.

[0101] And as described above, since the overall configuration of the optical lens system 500 of this embodiment is completely symmetric with respect to the aperture stop STO with the aperture stop STO interposed therebetween, deterioration of performance due to distortion and distance variation can be reduced.

[0102] Further, all the lenses constituting the optical lens system 500 of this embodiment are composed of 8 lenses and are all spherical lenses. Therefore, it is possible to increase the aperture diameter without increasing the cost.

[0103] Table 9 shows a table summarizing various data of the fifth embodiment.

Table 9

[0104] Note that in Table 9, Hf is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the front partial-symmetry group G1F in the light beam that forms an image on the optical axis from infinity. Hr is the distance from the optical axis at the point farthest from the optical axis among the lens groups of the rear partial-symmetry group G1B in the light beam that forms an image on the optical axis from infinity. According to the fifth embodiment, Hf / Hr = 1.37, satisfying 1.25 < Hf / Hr < 1.45. Therefore, the powers of the front partial-symmetry group G1F and the rear partial-symmetry group G1B separated by the aperture stop STO can be made equal, and deterioration of aberrations due to distance variation can be prevented.

[0105] Also, according to the fifth embodiment, fsy / f = 0.59, satisfying 0.48 < fsy / f < 0.72. Therefore, since fsy / f < 0.72, the overall size can be reduced, and since 0.48 < fsy / f, generation of spherical aberration and coma aberration can be particularly prevented, and the resolution at the time of aperture stop opening can be improved.

[0106] Also, according to the fifth embodiment, fsy / BF = 0.90, satisfying 0.73 < fsy / BF < 1.15. Therefore, the paraxial balance between the lens group on the object OBJ side and the lens group on the image plane IMG side separated by the aperture stop STO can be maintained, and good aberration characteristics can be maintained.

[0107] Also, according to the fifth embodiment, OAL / BF = 1.16, satisfying 0.9 < OAL / BF < 1.55. Therefore, the overall length of the lens can be shortened, and the distance from the lens surface of the most image-side negative lens L8 to the image plane IMG can be lengthened.

[0108] Subsequently, the lens data of the optical lens system 500 of the fifth embodiment shown in FIG. 9 is shown in Table 10.

[0109]

Table 10

[0110] 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 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. Further, the blanks for nd and νd indicate that it is air.

[0111] In the fifth embodiment, among the positive lenses of the partially symmetric rear group G1B, the positive meniscus lens L37 has νd = 81.61, satisfying νd > 70. Therefore, according to this configuration, chromatic aberration can be improved.

[0112] Also, in the fifth embodiment, among the positive lenses of the partially symmetric front group G1F, the positive meniscus lens L34 has nd = 1.77250, and the positive meniscus lens L36 has nd = 1.84666, satisfying the condition that at least one positive lens has nd > 1.72. Therefore, the radius of curvature of the positive lens becomes large, the meridional and sagittal coma aberrations can be reduced, and the overall length of the product can be shortened, contributing to miniaturization.

[0113] Fig. 10 shows the spherical aberration, astigmatism, and distortion of the optical lens system 400. Each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Fig. 10, it can be confirmed that good aberrations are obtained in all cases.

[0114] 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

[0115] 100 Optical lens system 200 Optical lens system 300 Optical lens system 400 Optical lens system 500 optical lens system G1 partial symmetry group G1F front partial symmetry group G1B rear partial symmetry group L1 negative meniscus lens L2 positive meniscus lens L3 biconvex lens L4 biconcave lens L5 biconcave lens L6 biconvex lens L7 biconvex lens L8 negative meniscus lens L9 negative meniscus lens L10 positive meniscus lens L11 biconvex lens L12 biconcave lens L13 biconcave lens L14 biconvex lens L15 biconvex lens L16 negative meniscus lens L17 negative meniscus lens L18 positive meniscus lens L19 biconvex lens L20 biconcave lens L21 biconcave lens L22 biconvex lens L23 positive meniscus lens L24 negative meniscus lens L25 negative meniscus lens L26 biconvex lens L27 biconcave lens L28 positive meniscus lens L29 positive meniscus lens L30 biconcave lens L31 biconvex lens L32 negative meniscus lens L33 negative meniscus lens L34 positive meniscus lens L35 negative meniscus lens L36 positive meniscus lens L37 positive meniscus lens L38 negative meniscus lens L39 Positive meniscus lens L40 Negative meniscus lens STO Aperture stop

Claims

1. An aperture stop, a cemented lens and a single positive lens are symmetrically arranged with respect to the lens configuration with the aperture stop therebetween, forming a partially symmetric group having a positive refractive power as a whole, a single most object-side negative lens arranged on the object side of the partially symmetric group, a single most image-side negative lens arranged on the image side of the partially symmetric group, and each of the cemented lenses faces a concave surface toward the aperture stop side, characterized in that it is an optical lens system.

2. The most object-side negative lens is a negative meniscus lens with a convex surface facing the object side, The optical lens system according to claim 1, characterized in that the most image-side negative lens is a negative meniscus lens with a convex surface facing the image side.

3. Among the positive lenses arranged on the image side of the aperture stop in the partially symmetric group, at least one satisfies νd > 70, characterized in that it is an optical lens system according to claim 1 or claim 2.

4. Among the positive lenses arranged on the object side of the aperture stop in the partially symmetric group, at least one satisfies nd > 1.72, characterized in that it is an optical lens system according to claim 1 or claim 2.

5. Among the light beams imaging on the optical axis from infinity, let the distance from the optical axis at the point farthest from the optical axis among the lens groups arranged on the object side of the aperture stop in the partially symmetric group be Hf, when the distance from the optical axis at the point farthest from the optical axis among the lens groups arranged on the image side of the aperture stop in the partially symmetric group is Hr, 1.25 < Hf / Hr < 1.45, characterized in that it is an optical lens system according to claim 1 or claim 2.

6. When the focal length of the partially symmetric group is fsy and the focal length of the entire system is f, 0.48 < fsy / f < 0.72, characterized in that it is an optical lens system according to claim 1 or claim 2.

7. When the focal length of the partially symmetric group is fsy and the distance from the image-side lens surface of the most image-side negative lens to the imaging surface is BF, 0.73 < fsy / BF < 1.15, characterized in that it is an optical lens system according to claim 1 or claim 2.

8. When the distance from the object-side lens surface of the most object-side negative lens to the image-side lens surface of the most image-side negative lens is OAL and the distance from the image-side lens surface of the most image-side negative lens to the imaging surface is BF, 0.9 < OAL / BF < 1.55, characterized in that it is an optical lens system according to claim 1 or claim 2.

9. The optical lens system according to claim 1 or claim 2, characterized in that all lenses are composed only of spherical lenses.

10. The optical lens system according to claim 1 or claim 2, characterized in that focusing is performed by moving the entire optical system toward the object side when focusing from infinity to a short distance.

Images