Imaging lens

Abstract

To provide an image capturing lens which is used as an interchangeable lens or the like for digital still cameras and offers reduced total cost, size, and weight while ensuring sufficient optical performance.SOLUTION: A front lens group 101 comprises three convex lenses L1, L2, L3 and two concave lenses L4, L5 in order from the object (OBJ) side to the image (IMG) side. At least two convex lenses L2, L3 satisfy the following conditional expressions: nd<1.54 ...(1), and νd>76 ...(2), where nd represents a refractive index for the d-ray and νd represents an Abbe number. The front lens group 101 is configured to have positive refractive power as a whole. A rear lens group 102 comprises a convex lens L6 and a concave lens L7 in order from the object (OBJ) side to the image (IMG) side. The following conditional expression is satisfied: 1.5<(f1 / f)<3.5 ...(3), where f1 represents a focal length of the front lens group 101 and f represents a focal length of an entire system 100.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging lens suitable for use in an interchangeable lens or the like, which has, in order from the object side to the image side, a front lens group, an aperture stop, and a rear lens group. [Background technology]

[0002] Generally, interchangeable lenses used in digital still cameras and the like, particularly imaging lenses with a half angle of view of about 13.5° and an F-number of about F2.8, have a focal length range in which chromatic aberration begins to become noticeable, and shortening the overall length of the lens not only increases the chromatic aberration but also affects other aberrations, resulting in a decrease in optical performance. For this reason, with this type of imaging lens, improving optical performance tends to increase the overall length of the lens, and there has been a limit to how compact the lens can be while maintaining sufficient optical performance.

[0003] Known examples of lenses that address this issue include the large-aperture lens disclosed in Patent Document 1 and the optical system disclosed in Patent Document 2. The large-aperture lens in Patent Document 1 aims to provide a large-aperture medium telephoto lens that improves the optical performance of large-aperture lenses by comprehensively improving various aberrations, and that shortens the overall length to make it more compact, lightweight, and inexpensive. Specifically, the front lens group is made up of three positive lenses, of which at least two positive lenses have an Abbe number vd that satisfies the optical condition vd>75 and a refractive index nd1 that satisfies the optical condition nd1<1.57, and is also designed to satisfy the optical condition (TT / f)<1.3, where TT is the distance from the object-side surface of the lens closest to the object to the image and f is the focal length of the entire system.

[0004] The optical system in Document 2 aims to provide an optical system that can effectively correct various aberrations including chromatic aberration, and specifically, is composed of, in order from the object side to the image side, a front group having positive refractive power, an aperture stop, and a rear group, the front group consisting of a first lens group having positive refractive power, and the rear group having a second lens group adjacent to the aperture stop that moves during focusing, the first lens group having n positive lenses and one or more negative lenses, wherein, when the anomalous partial dispersion of a material is ΔθgF, the material of at least two of the positive lenses in the first lens group satisfies the condition 0.0100<ΔθgF, and the material of at least one of the positive lenses satisfies the condition 0.0272<ΔθgF, the refracting surface closest to the image side of the first lens group has a concave shape and its radius of curvature, the refracting surface closest to the object side of the second lens group has a concave shape and its radius of curvature, and the focal length of the entire system are all set appropriately. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-122918 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-114133 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the imaging lenses disclosed in the above-mentioned Patent Documents 1 and 2 have the following problems to be solved.

[0007] First, because low-order aberrations are corrected by arranging lenses (lens groups) symmetrically with respect to the aperture stop, the exit pupil position and back focus tend to be long, and the overall lens length relative to the focal length tends to be long. In addition, because high-order coma aberrations cannot be sufficiently corrected, there is a problem of reduced resolution when the aperture stop is fully opened. Ultimately, there is room for further improvement in this type of imaging lens from the perspective of making the entire lens more compact and lightweight while maintaining sufficient optical performance.

[0008] Secondly, since various aberrations were improved (corrected) by combining aspherical lenses with spherical lenses in the entire lens system, at least one or more aspherical lenses were required, which not only increased the cost of the lens itself but also posed the difficulty of making it difficult to achieve a large aperture.

[0009] An object of the present invention is to provide an imaging lens that solves the problems present in the background art. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the present invention provides an imaging lens 1 including an entire system 100 that is configured with six or seven single lenses or cemented lenses in total, and that is set to have at least positive refractive power, and that is configured such that, in order from the object OBJ side to the image IMG side, the front lens group 101 is configured with a sub-group consisting of only three positive lenses L1, L2, and L3, and a sub-group having two negative lenses L4 and L5 including a cemented lens J5, and that the at least two positive lenses L2 and L3 satisfy "nd<1.54: [Conditional formula 1]" and "νd>76: [Conditional formula 2]" (where n The front lens group 101 is configured to have a positive refractive power as a whole, and the rear lens group 102 is composed of a positive lens L6 and a negative lens L7, in that order from the object OBJ side to the image IMG side, and is configured to satisfy "1.5<[f1 / f]<3.5 (conditional formula 3)" where f1 is the focal length of the front lens group 101 and f is the focal length of the entire system 100, and is configured to satisfy "1.5<[f1 / f]<3.5 (conditional formula 3)" and also satisfy "[TTL / f]<1.2 (conditional formula 4)" where TTL is the distance from the object OBJ side surface (i=1) of the convex lens L1 that is located closest to the object OBJ in the entire system 100 to the image, and f is the focal length of the entire system 100.

[0011] In this case, according to a preferred embodiment of the invention, when configuring the front lens group 101, the negative lens L5 closest to the image IMG side may be configured as a single lens, or may be configured as a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 together. Furthermore, when configuring the rear lens group 102, it may be configured as a convex lens L6 on the object OBJ side using a single lens and a concave lens L7 on the image IMG side using a single lens, or may be configured as a cemented lens J6 formed by cementing a convex lens Lp6 on the object OBJ side and a concave lens Ln7 on the image IMG side. [Effects of the Invention]

[0012] The imaging lens 1 according to the present invention having such a configuration provides the following significant effects.

[0013] (1) The front lens group 101 is composed of, in order from the object OBJ side to the image IMG side, a subgroup consisting of only three positive lenses L1, L2, and L3, and a subgroup having two negative lenses L4 and L5 including a cemented lens J5, and at least the two positive lenses L2 and L3 satisfy "nd<1.54: [Conditional Formula 1]" and "νd>76: [Conditional Formula 2]" (where nd: refractive index at the d line, νd: Abbe number), and the entire front lens group 101 is set to positive refractive power. The rear lens group 102 is composed of, in order from the object OBJ side to the image IMG side, a positive lens L6 and a negative lens L7, and is configured to satisfy "1.5<[f1 / f]<3.5: [Conditional Formula 3]", where f1 is the focal length of the front lens group 101 and f is the focal length of the entire system 100. The imaging lens 1 can be constructed using a relatively small number of lenses, around 7-8, while ensuring favorable characteristics for various aberrations without using aspherical lenses. This allows the imaging lens 1 to be used as an interchangeable lens for a digital still camera, etc., to achieve overall cost reduction, compactness, and weight reduction while ensuring sufficient optical performance.

[0014] (2) When the distance from the surface (i=1) of the positive lens L1 located closest to the object OBJ in the entire system 100 to the image on the object OBJ side is TTL and the focal length of the entire system 100 is f, the system is configured to satisfy "(TTL / f)<1.2: [Conditional formula 4]." This makes it possible to shorten the overall lens length while ensuring the necessary and sufficient optical performance (various aberrations) of the imaging lens 1, and further ensure the required imaging angle of view and brightness.

[0015] (3) In a preferred embodiment, when constructing the front lens group 101, if the negative lens L5 closest to the image IMG is constructed from a single lens, it is sufficient to prepare one single lens, thereby achieving cost benefits in terms of components.

[0016] (4) In a preferred embodiment, when configuring the front lens group 101, if the negative lens L5 closest to the image IMG is configured as a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 together, chromatic aberration can be corrected effectively, thereby increasing design freedom and contributing to improved optical characteristics.

[0017] (5) In a preferred embodiment, when constructing the rear lens group 102, if it is constructed using a convex lens L6 on the object OBJ side that uses a single lens and a concave lens L7 on the image IMG side that uses a single lens, the rear lens group 102 can be constructed using a combination of two single lenses, which can provide cost benefits in terms of components.

[0018] (6) In a preferred embodiment, when configuring the rear lens group 102, if it is configured using a cemented lens J6 formed by cementing together a convex lens Lp6 on the object OBJ side and a concave lens Ln7 on the image IMG side, the rear lens group 102 can be constructed using a single cemented lens J6, which reduces the overall length in the optical axis direction and contributes to making the entire imaging lens 1 even smaller and more compact. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view of the entire imaging lens system according to Example 1 of a preferred embodiment of the present invention; [Figure 2] A list of numerical values ​​corresponding to the conditional expressions of Examples 1 to 3; [Figure 3] FIG. 2 is a longitudinal aberration diagram of the entire imaging lens system according to Example 1 at infinity; [Figure 4] FIG. 10 is a cross-sectional view showing the entire system of the imaging lens according to Example 2; [Figure 5] FIG. 10 is a longitudinal aberration diagram of the entire imaging lens system according to Example 2 at infinity; [Figure 6] FIG. 10 is a cross-sectional view showing the entire system of the imaging lens according to the third embodiment; [Figure 7] FIG. 10 is a longitudinal aberration diagram of the entire imaging lens system according to Example 3 at infinity; DETAILED DESCRIPTION OF THE INVENTION

[0020] Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[0021] First, the configuration of an imaging lens 1 according to this embodiment will be described with reference to FIG. 1 (and FIGS. 4 and 6).

[0022] As shown in Figures 1, 4, and 6, the imaging lens 1 according to this embodiment is intended to achieve optical performance with a photographing angle of view of ±13-16° and an F-number of 2.8-2.9. Figure 1 shows an entire system 100 of the imaging lens 1, and the basic main configuration will be described with reference to Figure 1. The imaging lens 1 of Figure 1 also serves as Example 1. The entire system 100 roughly comprises a front lens group 101, an aperture stop STO, and a rear lens group 102, arranged in this order from the object (subject) OBJ side to the image (image sensor) IMG side.

[0023] The front lens group 101 is basically configured with three positive lenses L1, L2, and L3 on the object OBJ side and negative lenses L4 and L5 on the image IMG side, and the entire front lens group 101 is set to have positive refractive power. The rear lens group 102 is basically configured with a convex lens L6 on the object OBJ side and a concave lens L7 on the image IMG side.

[0024] In this case, when configuring the front lens group 101, at least two positive lenses are configured by three positive lenses L1, L2, and L3, for example, the refractive index nd of the positive lenses L2 and L3 is nd<1.54 … [Condition 1] The condition is satisfied, and the Abbe number νd is νd>76 … [Conditional expression 2] The lens characteristics are set to satisfy the above condition.

[0025] By satisfying these [Conditional Formula 1] and [Conditional Formula 2], it is possible to correct axial chromatic aberration and shorten the back focus while maintaining the length in the optical axis direction of the front lens group 101. In this way, the three positive lenses L1, L2, and L3, each of which can have a large radius of curvature, can shorten the length in the optical axis direction and the back focus, and therefore, by correcting spherical aberration and astigmatism in conjunction with this lens configuration, it is possible to easily improve (correct) all aberrations.

[0026] Furthermore, the concave lens L5 in the front lens group 101 closest to the image IMG side may be formed of a single lens as in the first embodiment shown in Fig. 1, or it may be formed of a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 as in the second and third embodiments shown in Figs. 4 and 6, which will be described later. If the concave lens L5 in the front lens group 101 closest to the image IMG side is formed of a single lens, it is sufficient to prepare one single lens, thereby providing cost benefits in terms of components. Furthermore, if the concave lens L5 is formed of a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5, chromatic aberration can be effectively corrected, thereby increasing design freedom and contributing to improved optical characteristics.

[0027] On the other hand, the rear lens group 102 may be configured using a convex lens L6 on the object OBJ side using a single lens and a concave lens L7 on the image IMG side using a single lens, as in the first embodiment shown in Fig. 1 and the second embodiment shown in Fig. 4, or it may be configured using a cemented lens J6 formed by cementing a convex lens Lp6 on the object OBJ side with a concave lens Ln7 on the image IMG side, as in the third embodiment shown in Fig. 6, which will be described later. In this way, if the rear lens group 102 is configured using a convex lens L6 and a concave lens L7 using single lenses, the rear lens group 102 can be constructed by combining two single lenses, which offers cost benefits in terms of components, and if the rear lens group 102 is configured using a cemented lens J6 formed by cementing a convex lens Lp6 and a concave lens Ln7, the rear lens group 102 can be constructed using a single cemented lens J6, which shortens the overall length in the optical axis direction, which has the advantage of contributing to further miniaturization and compactness of the entire imaging lens 1.

[0028] On the other hand, when configuring the front lens group 101 and the entire system 100, if f1 is the focal length of the front lens group 101 and f is the focal length of the entire system 100, then: 1.5<[f1 / f]<3.5 … [Conditional expression 3] This allows the ratio between the focal length of the front lens group 101 and the focal length of the entire system 100, particularly the back focal length, to be appropriately controlled.

[0029] Furthermore, when the distance from the surface (i=1) of the positive lens L1 located closest to the object OBJ in the entire system 100 on the object OBJ side to the image is TTL (see FIG. 1), and the focal length of the entire system 100 is f, then: [TTL / f]<1.2 … [Conditional expression 4] With this configuration, it is possible to ensure the necessary and sufficient optical performance (various aberrations) of the imaging lens 1, while shortening the overall lens length and further ensuring the required imaging angle of view and brightness.

[0030] The above configuration is the basic configuration of the imaging lens 1 according to this embodiment. As such, as the basic configuration of the imaging lens 1, the front lens group 101 is configured by arranging, in order from the object OBJ side to the image IMG side, three convex lenses L1, L2, L3 and two concave lenses L4, L5, at least the two convex lenses L2, L3 satisfy "nd<1.54: [Conditional formula 1]" and "νd>76: [Conditional formula 2]" (where nd: refractive index at the d line, νd: Abbe number), and the entire front lens group 101 is set to have a positive refractive power, The rear lens group 102 is composed of a convex lens L6 and a concave lens L7 arranged in this order from the object OBJ side to the image IMG side, and is configured to satisfy "1.5<[f1 / f]<3.5 (conditional formula 3)," where f1 is the focal length of the front lens group 101 and f is the focal length of the entire system 100. This makes it possible to construct an imaging lens 1 with a relatively small number of lenses, around 7 or 8, while ensuring good characteristics regarding various aberrations and without using aspherical lenses. This makes it possible to achieve overall cost reduction, compactness, and weight reduction in an imaging lens 1 used as an interchangeable lens for a digital still camera, etc., while ensuring sufficient optical performance.

[0031] Next, specific examples (Examples 1 to 3) of the imaging lens 1 according to this embodiment will be described with reference to FIGS. [Example]

[0032] First, an imaging lens 1 according to Example 1 will be described in detail with reference to Figures 1 to 3. As shown in Figure 1, the imaging lens 1 according to Example 1 has a front lens group 101 that is composed of, in order from the object OBJ side to the image IMG side, a positive meniscus lens L1, a positive meniscus lens L2, a positive meniscus lens L3, and a negative meniscus lens L4 and a negative meniscus lens L5 disposed on the image IMG side, and the entire front lens group 101 is set to have a positive refractive power.

[0033] In the front lens group 101, the surfaces of all lenses L1, L2, L3, L4, and L5 (i=1, 2, 3, 4, 5, 6, 7, 8, 9, and 10) are formed as curved surfaces that bulge outward toward the object OBJ from the lens periphery, where i indicates the surface number counted from the object OBJ.

[0034] In this way, when configuring the front lens group 101, if the surfaces of all the lenses L1... (i=1, 2, 3... 10) are formed as curved surfaces whose central sides bulge out toward the object OBJ relative to the peripheral sides, the central sides of all the lenses L1... will have shapes that are offset in one direction, making it possible to minimize the intervals (gap spaces) between the lenses L1... in the optical axis direction. This has the advantage of shortening the length of the front lens group 101, and further the imaging lens 1, in the optical axis direction.

[0035] In particular, when the radii of curvature of the surfaces (i=1, 3, 5) facing the object OBJ are L1Ri, L2Ri, L3Ri in order from the object OBJ side, the three positive lenses L1, L2, L3 in the front lens group 101 are set to satisfy the condition L1Ri>L2Ri>L3Ri. By setting them in this way, the distances (clear spaces) between the lenses L1... in the optical axis direction can basically be made close to zero at a distance where they do not contact, thereby further shortening the lengths of the front lens group 101 and, further, the imaging lens 1 in the optical axis direction.

[0036] Furthermore, as mentioned above, the concave lens L5 in the front lens group 101, which is closest to the image IMG, is formed from a single lens as shown in Fig. 1. By forming the concave lens L5 from a single lens in this way, it is sufficient to prepare one single lens, thereby achieving cost benefits in terms of components.

[0037] On the other hand, the rear lens group 102 is composed of a convex lens L6 made of a single lens and arranged on the object OBJ side, and a concave meniscus lens L7 made of a single lens and arranged on the image IMG side, formed with a curved surface bulging toward the image IMG side. In this way, when configuring the rear lens group 102, by configuring the convex lens L6 made of a single lens and arranged on the object OBJ side, and the concave lens L7 made of a single lens and arranged on the image IMG side, the rear lens group 102 can be constructed by combining two single lenses, which provides cost benefits in terms of components.

[0038] Table 1 shows lens data for the entire system of the imaging lens 100 according to Example 1 shown in FIG.

[0039] [Table 1]

[0040] In Table 1, f denotes the focal length of the entire system, Fno denotes the F-number, and ω denotes the half angle of view. Furthermore, 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 R(i), the on-axis surface spacing D(i), the lens refractive index nd(i), the lens Abbe number νd(i), and the focal length fp(i) of each lens are shown. nd(i) and νd(i) are values ​​relative to the d-line (587.6 nm). The on-axis surface spacing D(i) indicates the lens thickness or air space between opposing surfaces. The units for the radius of curvature R(i) and surface spacing D(i) are in mm. The surface number OBJ indicates the object, STO indicates the aperture stop, and IMG indicates the image position. The "Infinity" in the radius of curvature R(i) indicates a flat surface. Moreover, the blanks for the refractive index nd(i) and Abbe number νd(i) indicate air.

[0041] In addition, parallel plane plates such as a filter plate (protective glass), a color selection filter (infrared filter), and a low-pass filter (high-frequency cut filter) may be arranged between the rear surface of the rearmost lens and the image IMG, but these do not affect the configuration of the imaging lens 1 according to this embodiment.

[0042] 2 shows longitudinal aberration diagrams for the entire system 100 of the imaging lens 1 according to Example 1. From the left, the longitudinal aberration diagrams show (a) spherical aberration diagram (656.3 nm, 587.6 nm, 435.8 nm), (b) astigmatism diagram (587.6 nm), and (c) distortion aberration diagram (587.6 nm). The scales are ±0.15 mm, ±0.15 mm, and ±1.5%, respectively. As can be seen, it can be confirmed that good aberrations are obtained in all cases.

[0043] Furthermore, Fig. 3 shows a list of numerical values ​​corresponding to each of conditional expressions 1 to 4. As shown in Fig. 3, in Example 1, the refractive index nd of the convex lens L2 is "1.437", the refractive index nd of the convex lens L3 is also "1.437", so the two convex lenses L2 and L3 satisfy the condition of "nd<1.54" of [Conditional Expression 1], and the Abbe number vd of the convex lens L2 is "95.10", the Abbe number vd of the convex lens L3 is also "95.10", so the two convex lenses L2 and L3 satisfy the condition of "vd>76" of [Conditional Expression 2]. Furthermore, the focal length f1 [mm] of the front lens group 101 is "228.25", the focal length f [mm] of the entire system 100 is "87.30", and [f1 / f] is "2.61", which satisfies the condition of "1.5<[f1 / f]<3.5", which is [Conditional Formula 3], and the distance TTL [mm] is "85.83", which is [TTL / f] is "0.98", which satisfies the condition of "[TTL / f]<1.2", which is [Conditional Formula 4].

[0044] In this way, the imaging lens 1 of Example 1 satisfies all of the conditions of Conditional Expressions 1 to 4, and while ensuring sufficient optical performance (various aberrations) in the imaging lens 1, it is possible to achieve overall cost reduction, compactness, and weight reduction, as well as shortening the overall lens length and achieving the objective of ensuring the required imaging angle of view and brightness. [Example]

[0045] Next, the imaging lens 1 according to Example 2 will be specifically described with reference to FIGS. 4, 5 and 3. FIG.

[0046] The imaging lens 1 according to Example 2 differs from the imaging lens 1 according to Example 1 in that, when forming the concave lens L5 in the front lens group 101 closest to the image IMG, Example 1 shows a case in which a negative meniscus lens made of a single lens is used, whereas Example 2 shows a case in which the concave lens L5 is formed by cementing a convex lens Lp5 and a concave lens Ln5 together.

[0047] In this way, if the concave lens L5 in the front lens group 101, which is closest to the image IMG, is configured as a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 together, the optical characteristics of the lens can be easily set, thereby increasing the degree of freedom in design and contributing to improving the optical characteristics.

[0048] The basic differences between Example 2 and Example 1 are the above points only, except for the detailed lens elements in Table 2 shown below and Table 1 described above, and the other basic lens configurations of the entire system 100 in Example 2 and Example 1 are the same.

[0049] Table 2 shows lens data for the entire system of the imaging lens 1 according to Example 2 shown in FIG.

[0050] [Table 2]

[0051] 5A to 5C show longitudinal aberration diagrams for the entire system 100 of the imaging lens 1 according to Example 2. As shown in Fig. 5A to 5C, it can be confirmed that good aberrations are obtained in all cases.

[0052] Furthermore, as shown in FIG. 3 , in Example 2, the refractive index nd of the convex lens L2 is "1.497", and the refractive index nd of the convex lens L3 is also "1.437", so that the two convex lenses L2 and L3 satisfy the condition of "nd<1.54" of [Conditional Formula 1], and the Abbe number vd of the convex lens L2 is "81.61", and the Abbe number vd of the convex lens L3 is also "95.10", so that the two convex lenses L2 and L3 satisfy the condition of "vd>76" of [Conditional Formula 2]. Furthermore, the focal length f1 [mm] of the front lens group 101 is "186.14", the focal length f [mm] of the entire system 100 is "88.50", and [f1 / f] is "2.10", which satisfies the condition of "1.5<[f1 / f]<3.5", which is [Conditional Formula 3], and the distance TTL [mm] is "85.83", which is [TTL / f] is "0.97", which satisfies the condition of "[TTL / f]<1.2", which is [Conditional Formula 4].

[0053] In this way, the imaging lens 1 of Example 2 also satisfies all of the conditions of Conditional Expressions 1 to 4, and Example 2 also ensures sufficient optical performance (various aberrations) in the imaging lens 1, while achieving overall cost reduction, compactness, and weight reduction, shortening the overall lens length, and further achieving the objective of ensuring the required imaging angle of view and brightness. [Example]

[0054] Next, the imaging lens 1 according to Example 3 will be specifically described with reference to FIGS. 6, 7 and 3. FIG.

[0055] The imaging lens 1 according to Example 3 differs from the imaging lens 1 according to Example 1 in that, when forming the concave lens L5 in the front lens group 101 closest to the image IMG side, Example 1 showed a case where a negative meniscus lens made of a single lens was used, but Example 3 shows a case where the concave lens L5 is formed by a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 together, and, when forming the rear lens group 102, Example 1 showed a case where the rear lens group 102 is formed by a convex lens L6 on the object OBJ side made of a single lens and a concave meniscus lens L7 on the image IMG side made of a single lens and formed with a curved surface bulging towards the image IMG side, but Example 3 shows a case where the rear lens group 102 is formed by a cemented lens J6 formed by cementing a convex lens Lp6 on the object OBJ side and a concave lens Ln7 on the image IMG side.

[0056] In this way, by configuring the rear lens group 102 using the cemented lens J6 formed by cementing together the convex lens Lp6 and the concave lens Ln7, it is possible to construct the rear lens group 102 using a single cemented lens J6, which has the advantage of shortening the overall length in the optical axis direction and contributing to making the entire imaging lens 1 even smaller and more compact.

[0057] The fundamental differences between Example 3 and Example 1 are the above points only, except for the detailed lens elements in Table 3 shown below and Table 1 described above, and the other basic lens configurations of the entire system 100 in Example 2 and Example 1 are the same.

[0058] Table 3 shows lens data for the entire system of the imaging lens 1 according to Example 3 shown in FIG.

[0059] [Table 3]

[0060] 7 shows longitudinal aberration diagrams for the entire system 100 of the imaging lens 1 according to Example 3. As shown in Figures 7(a) to (c), it can be confirmed that good aberrations are obtained in all cases.

[0061] Furthermore, as shown in FIG. 3 , in Example 3, the refractive index nd of the convex lens L2 is "1.437", and the refractive index nd of the convex lens L3 is also "1.437", so that the two convex lenses L2 and L3 satisfy the condition of "nd<1.54" of [Conditional Formula 1], and the Abbe number vd of the convex lens L2 is "95.10", and the Abbe number vd of the convex lens L3 is also "95.10", so that the two convex lenses L2 and L3 satisfy the condition of "vd>76" of [Conditional Formula 2]. Furthermore, the focal length f1 [mm] of the front lens group 101 is "135.71", the focal length f [mm] of the entire system 100 is "75.00", and [f1 / f] is "1.81", which satisfies the condition of "1.5<[f1 / f]<3.5", which is [Conditional Formula 3], and the distance TTL [mm] is "74.73", which is [TTL / f] is "1.00", which satisfies the condition of "[TTL / f]<1.2", which is [Conditional Formula 4].

[0062] In this way, the imaging lens 1 of Example 3 also satisfies all of the conditions of Conditional Expressions 1 to 4, and Example 3 also ensures sufficient optical performance (various aberrations) in the imaging lens 1, while achieving overall cost reduction, compactness, and weight reduction, as well as shortening the overall lens length and ensuring the required imaging angle of view and brightness.

[0063] The above describes in detail preferred embodiments including Examples 1, 2, and 3, but the present invention is not limited to such embodiments, and the detailed configuration, shape, material, quantity, numerical values, etc. can be changed, added, or deleted as desired within the scope of the gist of the present invention.

[0064] For example, in configuring the front lens group 101, the concave lens L5 closest to the image IMG side has been illustrated as being a single lens, or as being a cemented lens J5 formed by cementing a convex lens Lp5 and a concave lens Ln5 together, but this can be replaced with various other lenses as long as they function as negative lenses. Similarly, in configuring the rear lens group 102, the following has been illustrated: a convex lens L6 on the object OBJ side using a single lens and a concave lens L7 on the image IMG side using a single lens, or a cemented lens J6 formed by cementing a convex lens Lp6 on the object OBJ side and a concave lens Ln7 on the image IMG side, but this can be replaced with other similar lens configurations, such as a convex lens L6 using a cemented lens and a concave lens L7 using a cemented lens, as long as the convex lens L6 and concave lens L7 are arranged in order from the object OBJ side to the image IMG side. [Industrial Applicability]

[0065] The imaging lens according to the present invention can be used as a dedicated lens or an interchangeable lens in various optical devices such as digital still cameras and video cameras. [Explanation of symbols]

[0066] 1: Imaging lens, 100: Whole system, 101: Front lens group, 102: Rear lens group, OBJ: Object, IMG: Image, STO: Aperture stop, L1: Convex lens (positive lens), L2: Convex lens (positive lens), L3: Convex lens (positive lens), L4: Concave lens (negative lens), L5: Concave lens (negative lens), Lp5: Biconvex lens, Ln5: Biconcave lens, L6: Convex lens, Lp6: Biconvex lens, L7: Concave lens, Ln7: Concave lens, J5: Cemented lens, J6: Cemented lens

Claims

1. an imaging lens having an entire system consisting of, in order from the object side to the image side, a front lens group, an aperture stop, and a rear lens group, consisting of six or seven single lenses or cemented lenses in total, and set to have at least positive refractive power; wherein the front lens group is composed of, in order from the object side to the image side, a sub-group consisting of only three positive lenses, and a sub-group having two negative lenses including a cemented lens, at least two of the positive lenses satisfy [Conditional Formula 1] and [Conditional Formula 2], and the entire front lens group is set to have positive refractive power; the rear lens group is composed of, in order from the object side to the image side, a positive lens and a negative lens; the entire system and the front lens group are configured to satisfy [Conditional Formula 3], and when the distance from the object-side surface of the positive lens that is located closest to the object in the entire system to the image is defined as TTL, the imaging lens is configured to satisfy [Conditional Formula 4]. [Conditional formula 1] nd<1.54 [Conditional expression 2] νd>76 [Conditional Expression 3] 1.5<[f1 / f]<3.5 [Conditional expression 4] [TTL / f]<1.2 where nd is the refractive index at the d line, νd is the Abbe number, f1 is the focal length of the front lens group, and f is the focal length of the entire system.

2. 2. The imaging lens according to claim 1, wherein the front lens group includes a negative lens element closest to the image side, the negative lens element being a single lens element.

3. 2. The imaging lens according to claim 1, wherein the front lens group comprises a cemented lens in which a negative lens closest to the image side is cemented together with a convex lens and a concave lens.

4. 2. The imaging lens according to claim 1, wherein the rear lens group comprises a single lens element and a convex lens element on the object side, and a single lens element and a concave lens element on the image side.

5. 2. The imaging lens according to claim 1, wherein the rear lens group is constructed by a cemented lens in which a convex lens on the object side and a concave lens on the image side are cemented together.

Images