Optical lens system

Abstract

To provide an optical lens system which can be made smaller and lighter, specifically, an optical lens system which offers a reduced total length by reducing the number of lenses and inter-lens spaces and a large aperture diameter and yet maintains good optical performance.SOLUTION: An optical lens system U provided herein comprises a first lens group G1, optical aperture stop STO, and a second lens group G2 arranged in the described order from the object OBJ side to the imaging plane IMG side. The second lens group G2 consists of a cemented lens L4, a positive lens L5, a cemented lens L6, and a single lens L7 closely arranged in the described order, where the single lens L7 located on the most imaging plane IMG side has at least one aspherical surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical lens system in which a first lens group, an optical diaphragm unit, and a second lens group are arranged in this order from the object side to the image plane side, for example, as provided in a large-diameter standard lens. [Background technology]

[0002] Generally, interchangeable lenses used in photographic and videography equipment, particularly large-aperture standard lenses, have the property of having a certain degree of angle of view even in the focal length range where chromatic aberration begins to become noticeable, and shortening the overall length of the lens not only increases chromatic aberration but also has an effect on other aberrations. For this reason, with this type of large-aperture lens, when improving optical performance, the overall length of the lens tends to increase, and there is a limit to how compact the lens can be while maintaining sufficient optical performance.

[0003] A conventional optical lens system that addresses this problem is the optical lens system disclosed in Patent Document 1. Along the optical axis, the optical lens system has, in order from the object side, a front lens group GF having positive refractive power and a rear lens group GR having positive refractive power. The front lens group GF has, in order from the object side, a first lens component G1 having positive refractive power and a second lens component G2 having positive refractive power. The rear lens group GR has, in order from the object side, a cemented lens G89 formed by cementing a positive lens G8 and a negative lens G9 together. This corrects various aberrations, particularly chromatic aberration, across the entire image plane, achieving high optical performance across the entire image plane (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5151635 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the optical lens system shown in Patent Document 1 is a modified Gaussian type, and the lenses before and after the aperture have approximately symmetrical shapes. This symmetry makes it easy to correct distortion aberration, but when attempting to further increase the aperture diameter, there is a problem in that coma aberration and the like cannot be sufficiently corrected. [Means for solving the problem]

[0006] An object of the present invention is to solve the problems present in the background art, and to provide an optical lens system that can be made compact and lightweight by reducing the number of lenses and the spaces between lenses to shorten the overall lens length, and that can maintain optical performance even when the overall lens length is shortened and the aperture is increased.

[0007] In order to achieve the above object, the present invention has the following configuration. An optical lens system in which a first lens group, an optical diaphragm, and a second lens group are arranged in this order from the object side to the image forming surface side, the first lens group comprising, in order from the object side to the image forming surface side, a first positive lens, a second positive lens, and a third negative lens closest to the image forming surface, the third negative lens having a concave surface facing the image forming surface side, the first positive lens closest to the object side having at least one aspherical surface, the second lens group comprising, in order from the object side to the image forming surface side, a fourth cemented lens, a fifth positive lens, a sixth cemented lens, and a seventh single lens, the seventh single lens being arranged in this order from the object side to the image forming surface side, Both sides It is characterized by an aspherical surface with the center of curvature facing the imaging surface side. As a result, by closely arranging the first positive lens and the second positive lens in that order from the object side toward the image plane side, it is possible to minimize the distance between each lens in the optical axis direction, and by making at least one surface of the first positive lens closest to the object side aspherical, it is possible to correct aberrations such as coma and distortion within a limited space, which can contribute to the correction of aberrations that accompany larger lens diameters. In addition, since the second lens group arranged on the image forming surface side from the optical aperture part is configured by arranging six lenses including a fourth cemented lens, a fifth positive lens, a sixth cemented lens, and a seventh single lens in close proximity, it is possible to reduce the number of components, shorten the overall length of the lens, and achieve miniaturization and weight reduction. In particular, by arranging the seventh single lens including an aspherical surface closest to the image forming surface side, even when the aperture is increased, optical aberrations can be corrected and optical characteristics can be maintained.

[0011] Assuming that the focal length of the entire optical lens system is f and the distance (total track) from the first surface of the first convex lens closest to the object side to the image forming surface IMG is TT, TT / f < 1.72. When the focal length f becomes longer due to an increase in the aperture of the optical lens system, the total track TT tends to increase, but in the present invention, it could be suppressed relatively small.

[0012] Assuming that the focal length of the entire optical lens system is f and the focal length of the single lens closest to the image forming surface is fle, -0.33 < f / fle < 0.53. Thus, the power of the single lens arranged closest to the image forming surface side with respect to the focal length f of the entire optical lens system is suppressed small.

Advantages of the Invention

[0013] It is possible to provide an optical lens system capable of shortening the overall length of the lens by reducing the number of lenses and the space between lenses, and achieving miniaturization and weight reduction while maintaining optical performance even when the overall length of the lens is shortened.

Brief Description of the Drawings

[0014] [Figure 1] It is a cross-sectional view showing the configuration of the optical lens system according to the first embodiment. [Figure 2] It is a longitudinal aberration diagram of the optical lens system of FIG. 1, where (a) is a spherical aberration diagram, (b) is an astigmatism diagram, and (c) is a distortion aberration diagram. [Figure 3] It is a cross-sectional view showing the configuration of the optical lens system according to the second embodiment. [Figure 4]4A, 4B, and 4C are longitudinal aberration diagrams of the optical lens system of FIG. 3, in which (a) is a spherical aberration diagram, (b) is an astigmatism diagram, and (c) is a distortion diagram. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the optical lens system will now be described with reference to the drawings. The optical lens system shown in this embodiment is used in optical equipment for photography and videography, and will be described using as an example an optical lens system U used in a large-aperture standard lens with a focal length of the entire system F=50 mm and an Fno (F number) of 1.0.

[0016] [First Example] As shown in FIG. 1, the optical lens system U includes a first lens group G1, an optical diaphragm unit STO, and a second lens group G2 arranged in this order from the object OBJ side to the image plane IMG side.

[0017] The first lens group G1 has, in order from the object OBJ side, at least two positive lenses and, closest to the image plane, a negative lens with its concave surface facing the image plane side, and at least one surface of the first lens closest to the object side is aspherical. 1, a first positive lens (positive meniscus lens) L1, a second positive lens (positive meniscus lens) L2, and a third negative lens (negative meniscus lens) L3 are arranged in close proximity in this order from the object OBJ side to the image plane IMG side. The surface numbers of the lens surfaces of the lenses L1 to L3 (first and second surfaces, third and fourth surfaces, fifth and sixth surfaces) are designated 1, 2, 3, 4, 5, and 6 from the object OBJ side to the image plane IMG side.

[0018] Of these, the lens surface (first surface: surface number 1) corresponding to the position closest to the object OBJ side of the first positive lens L1 is formed as an aspheric surface with the center of curvature facing the image plane IMG side. Aspheric surface data will be described later. In this way, including a positive meniscus lens in at least the first positive lens L1 of the first lens group G1 can contribute to aberration correction associated with larger apertures.

[0019] Furthermore, if the focal length of the entire optical lens system U is f and the distance from the first surface of the first positive lens L1 to the image plane IMG (total track) is TT, then TT / f<1.72. Although the total track TT tends to increase as the diameter of the optical lens system increases, this embodiment was able to keep it relatively small. In this way, by closely arranging the lenses L1 to L3 that make up the first lens group G1, namely the first positive lens L1, the second positive lens L2, and the third negative lens L3, which are convex toward the object OBJ, it is possible to minimize the distance between each lens in the optical axis direction, and by making the first surface of the first positive lens L1, which is closest to the object OBJ, an aspherical surface, it is possible to correct aberrations such as coma and distortion in a limited space. Note that although the first surface of the first positive lens L1 is aspherical, the second surface may also be aspherical, and furthermore both surfaces (the first surface and the second surface) may also be aspherical.

[0020] The second lens group G2 includes, in order from the object OBJ side to the image plane IMG side, a fourth cemented lens L4 (a cemented lens of a fourth negative lens L4f and a fourth positive lens L4r), a fifth positive lens L5, a sixth cemented lens L6 (a cemented lens of a sixth positive lens L6f and a sixth negative lens L6r), and a seventh single lens (a negative meniscus lens) L7. The surface numbers of the lens surfaces of each of the lenses L4 to L7 (surfaces 8, 9, and 10, surfaces 11 and 12, surfaces 13, surfaces 14 and 15, and surfaces 16 and 17) are numbered 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17, from the object OBJ side to the image plane IMG side. Surface number 7 is the optical diaphragm STO.

[0021] It is preferable that at least one surface (surface 16 or 17) of the seventh single lens (negative meniscus lens) L7, which is located closest to the image plane IMG, is aspherical, because this makes it possible to correct optical aberrations and maintain optical characteristics even when the aperture is increased. In this embodiment, both surfaces (the 16th and 17th surfaces: surface numbers 16 and 17) of the seventh single lens (negative meniscus lens) L7 are aspheric surfaces with the center of curvature facing the image plane IMG side. Aspheric surface data will be described later. Also, when the focal length of the entire optical lens system U is f and the focal length of the seventh single lens L7 is fle, -0.33 < f / fle < 0.53. The negative power of the seventh single lens L7, which is arranged closest to the imaging surface IMG side with respect to the focal length f of the entire optical lens system U, is suppressed to be small. Thus, since the second lens group G2 arranged on the imaging surface side from the optical aperture part STO is composed of six lenses arranged in proximity, the number of components can be reduced, the overall length of the lens can be shortened, and miniaturization and weight reduction can be achieved. In particular, by making both surfaces of the seventh single lens L7, which is closest to the imaging surface side, aspherical surfaces, off-axis aberrations that cannot be fully corrected by the fourth cemented lens L4, the fifth positive lens L5, and the sixth cemented lens L6 can be corrected. Therefore, even when the aperture is increased, optical aberrations can be corrected and optical characteristics can be maintained. Note that although both surfaces of the seventh single lens L7 are aspherical surfaces, either one of the surfaces (the 16th surface or the 17th surface) may be an aspherical surface.

[0022] Here, the lens data of the optical lens system U with a focal length f = 50 mm and an Fno (f-number) of 1.0 shown in FIG. 1 are shown in Table 1 and Table 2. In Table 1, the surface number of the lens surface counted from the object OBJ side is i, and this surface number corresponds to the reference numeral (number) shown in FIG. 1. Correspondingly, the radius of curvature of the lens surface is R, the interval between surfaces on the optical axis is D, the refractive index nd of the lens, and the absolute value of the Abbe number νd of the lens are shown respectively. nd and νd are values for the d-line (587.56 [nm]). The interval D between surfaces on the optical axis indicates the lens thickness or air space between opposite surfaces. Note that the units of the radius of curvature R and the interval D between surfaces are [mm]. OBJ of the surface number indicates the object, STO indicates the optical aperture part, and IMG indicates the position of the imaging surface. INF of the radius of curvature R is a plane, and a surface with an A attached after the surface number indicates that the surface shape is an aspherical surface. Also, a blank in the refractive index nd and the Abbe number νd indicates that it is air.

[0023]

Table 1

[0024] Table 2 shows the surface shape (aspherical coefficients) of the aspherical surface in Example 1. In this case, in a Cartesian coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, when ASP is the aspherical surface number, Z is defined by the following equation 1. In equation 1, R is the central radius of curvature, K is the conic constant, A4, A6, A8, A10, A12, and A14 are the 4th-, 6th-, 8th-, 10th-, 12th-, and 14th-order aspherical coefficients, respectively, and H is the distance from the origin on the optical axis. In Table 2, "E" means "×10."

[0025] [Table 2]

[0026]

number

[0027] Furthermore, Figure 2 shows longitudinal aberration diagrams for the optical lens system U according to Example 1. From the left, these longitudinal aberration diagrams show (a) spherical aberration diagram (656.27 nm, 587.56 nm, 435.83 nm), (b) astigmatism diagram (587.6 nm), and (c) distortion diagram (587.6 nm). The scales are ±0.50 mm, ±0.50 mm, and ±3.00%, respectively. It can be seen that good aberrations are obtained in all cases.

[0028] [Second Example] Next, another example of the optical lens system U shown in Fig. 1 will be described with reference to Fig. 3. The same members as those in the first embodiment are given the same numbers and the description will be incorporated herein. As shown in FIG. 3, the optical lens system U is similarly configured with a first lens group G1, an optical diaphragm section STO, and a second lens group G2 arranged in this order from the object OBJ side to the image plane IMG side.

[0029] The first lens group G1 has, in order from the object OBJ side, at least two positive lenses and, closest to the image plane, a negative lens with its concave surface facing the image plane side, and at least one surface of the first lens closest to the object side is aspherical. Specifically, as shown in FIG. 3, the first lens group G1 includes a first positive lens (positive meniscus lens) L1, a second positive lens (positive meniscus lens) L2, and a third negative lens (negative meniscus lens) L3, arranged in this order from the object OBJ side toward the image plane IMG side. Of these, the lens surface (first surface: surface number 1) corresponding to the position closest to the object OBJ side of the first positive lens L1 is formed as an aspheric surface with its center of curvature facing the image plane side. The aspheric surface data will be described later. In this way, including a positive meniscus lens in at least the first positive lens L1 of the first lens group G1 can contribute to aberration correction associated with larger lens diameters. Furthermore, if the focal length of the entire optical lens system U is f and the distance from the first surface of the first positive lens L1 to the image plane IMG (total track) is TT, the configuration where TT / f<1.72 is the same as in the first embodiment.

[0030] In this way, by closely arranging the lenses L1 to L3 that make up the first lens group G1, namely the first positive lens L1, the second positive lens L2, and the third negative lens L3, which are convex toward the object OBJ, it is possible to minimize the distance between each lens in the optical axis direction, and by making the first surface of the first positive lens L1, which is closest to the object OBJ, an aspherical surface, it is possible to correct aberrations such as coma and distortion in a limited space. Note that although the first surface of the first positive lens L1 is aspherical, the second surface may also be aspherical, and furthermore both surfaces (the first surface and the second surface) may also be aspherical.

[0031] The second lens group G2 includes, in order from the object OBJ side to the imaging surface IMG side, a fourth cemented lens L4 (a cemented lens of a fourth negative lens L4f and a fourth positive lens L4r), a fifth positive lens (a positive meniscus lens) L5', a sixth cemented lens L6 (a cemented lens of a sixth positive lens L6f and a sixth negative lens L6r), and a seventh single lens (a positive meniscus lens) L7'. The surface numbers of the lens surfaces of each of the lenses L4 to L7' (the eighth surface, the ninth surface and the tenth surface, the eleventh surface and the twelfth surface, the thirteenth surface, the fourteenth surface and the fifteenth surface, the sixteenth surface and the seventeenth surface) are 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 in the direction from the object OBJ side to the imaging surface IMG side. Note that the surface number 7 is the aperture stop STO.

[0032] It is preferable that at least one surface (the sixteenth surface or the seventeenth surface) of the seventh single lens (a positive meniscus lens) L7' disposed at the position closest to the imaging surface IMG side is an aspherical surface. This is because optical aberrations can be corrected and optical characteristics can be maintained even when the aperture is increased. In this embodiment, both surfaces (the sixteenth surface and the seventeenth surface: surface numbers 16, 17) of the seventh single lens (a positive meniscus lens) L7' are aspherical surfaces. The aspherical data will be described later. Also, when the focal length of the entire optical lens system is f and the focal length of the seventh single lens L7' is fle, -0.33 < f / fle < 0.53, which is the same as in the first embodiment. The positive power of the seventh single lens L7' disposed closest to the imaging surface with respect to the focal length f of the entire optical lens system U is relatively small. As described above, since the second lens group G2 disposed on the imaging surface side of the aperture stop STO is configured by arranging six lenses in close proximity, the number of components can be reduced, the overall length of the lens can be shortened, and miniaturization and weight reduction can be achieved. In particular, since both surfaces (the sixteenth surface and the seventeenth surface) of the seventh single lens L7' closest to the imaging surface side are aspherical surfaces with the center of curvature facing the imaging surface IMG side, off-axis aberrations that cannot be completely corrected by the fourth cemented lens L4, the fifth positive lens L5', and the sixth cemented lens L6 can be corrected, so that optical aberrations can be corrected and optical characteristics can be maintained even when the aperture is increased. [[ID=X]]

[0033] [[ID=Y]] Tables 3 and 4 show lens data for the optical lens system U shown in FIG. 3, which has a focal length f=50 mm and an Fno (F number) of 1.0. In Table 3, the surface number of the lens surface counted from the object (OBJ) side is designated i, and this surface number corresponds to the symbol (number) shown in Figure 1. Correspondingly, the radius of curvature of the lens surface is R, the surface spacing on the optical axis is D, the refractive index of the lens is nd, and the absolute value of the lens Abbe number νd are shown. nd and νd are values ​​relative to the d-line (587.56 nm). The surface spacing D on the optical axis indicates the lens thickness or air space between opposing surfaces. The radius of curvature R and surface spacing D are in mm. In the surface number, OBJ indicates the object, STO indicates the optical aperture, and IMG indicates the position of the image plane. In the radius of curvature R, INF indicates a flat surface, and surfaces with an A after the surface number indicate an aspherical surface. Furthermore, blanks in the refractive index nd and Abbe number νd indicate air.

[0034] [Table 3]

[0035] Table 4 shows the aspherical surface shape (aspherical coefficients) of the second embodiment. In this case, in a Cartesian coordinate system (X, Y, Z) with the origin at the center of the surface and Z in the optical axis direction, when ASP is the aspherical surface number, Z is defined by Equation 1 from the first embodiment. In Equation 1, R is the central radius of curvature, K is the conic constant, A4, A6, A8, A10, A12, and A14 are the 4th-, 6th-, 8th-, 10th-, 12th-, and 14th-order aspherical coefficients, respectively, and H is the distance from the origin on the optical axis. In Table 2, "E" means "×10."

[0036] [Table 4]

[0037] Furthermore, Figure 4 shows longitudinal aberration diagrams for the optical lens system U according to the second example. From the left, these longitudinal aberration diagrams show (a) spherical aberration diagram (656.27 nm, 587.56 nm, 435.83 nm), (b) astigmatism diagram (587.56 nm), and (c) distortion diagram (587.56 nm). The scales are ±0.50 mm, ±0.50 mm, and ±3.00%, respectively. It can be seen that good aberrations are obtained in all cases.

[0038] The optical lens system described above can be used as a large-diameter standard lens, a dedicated lens for various optical devices such as digital cameras and video cameras, or an interchangeable lens. [Explanation of symbols]

[0039] U Optical lens system G1 First lens group G2 Second lens group OBJ Object STO Optical aperture IMG Image plane L1 First positive lens L2 Second positive lens L3 Third negative lens L4 Fourth cemented lens L4r Fourth negative lens L4r Fourth positive lens L5, L5´ Fifth positive lens L6 Sixth cemented lens L6f Sixth positive lens L6r Sixth negative lens L7, L7´ Seventh single lens 1 Surface number of first lens surface 2 Surface number of second lens surface 3 Surface number of third lens surface 4 Surface number of fourth lens surface 5 Surface number of fifth lens surface 6 Surface number of sixth lens surface 7 Surface number of seventh lens surface 8 Surface number of eighth lens surface 9 Surface number of ninth lens surface 10 Surface number of tenth lens surface 11 Surface number of eleventh lens surface 12 Surface number of twelfth lens surface 13 Surface number of thirteenth lens surface 14 Surface number of lens surface 14 15 Surface number of lens surface 15 16 Surface number of lens surface 16 17 Surface number of lens surface 17

Claims

1. An optical lens system in which a first lens group, an optical diaphragm unit, and a second lens group are arranged in this order from an object side to an image plane side, the first lens group includes, in order from the object side to the image forming surface side, a first positive lens, a second positive lens, and a third negative lens closest to the image forming surface, the third negative lens having a concave surface facing the image forming surface side, the first positive lens closest to the object side having at least one aspherical surface; the second lens group comprises a fourth cemented lens, a fifth positive lens, a sixth cemented lens, and a seventh single lens arranged in this order from the object side to the image plane side, and both surfaces of the seventh single lens, which is located closest to the image plane side, are aspheric surfaces with a center of curvature facing the image plane side.

2. 2. The optical lens system of claim 1, wherein said seventh singlet lens is a negative meniscus lens.

3. 2. The optical lens system of claim 1, wherein said seventh singlet lens is a positive meniscus lens.

Images