Imaging lens

Abstract

To further reduce the total optical length to a focal distance and sufficiently obtain the arrangement space of a lens, and achieve the downsizing of the entire imaging lens 1 and the cost reduction of the entire product.SOLUTION: An imaging lens includes: a first lens group G1 constituted of three positive lenses L11, L12 and L13 and two negative lenses L14 and L15 continuous in order from the side of an object OBJ; a second lens group G2 having positive or negative power; and a third lens group G3 constituted of one positive lens L31 and one negative lens L32 in order from the side of the object OBJ and having positive power. When setting a radius having the maximum diameter to Hh in beams imaging on an optical axis Dc from the infinity in the first lens group G1 and setting a radius having the minimum diameter to Hs in the beams imaging on the optical axis Dc from the infinity in the first lens group G1, [Hs / Hh]<0.65 (an optical condition 1) is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an imaging lens that is large-diameter and compact and suitable for use as a medium telephoto interchangeable lens or the like. [Background technology]

[0002] 2. Description of the Related Art Conventionally, an inner focus type lens as described in Patent Document 1 has been known as a medium telephoto imaging lens.

[0003] The imaging lens (inner focus lens) described in Patent Document 1 aims to provide an inner focus lens that is small, lightweight, and has a large aperture while having a moderate focal length when converted into a 35 mm camera. Specifically, the imaging lens is configured to be configured such that, from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power are arranged in that order. The second lens group is made of a negative lens, and this second lens group is configured to move along the optical axis from the object side to the image plane side to perform focusing from an infinity object focused state to a closest object focused state. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-242689 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional imaging lens (inner focus lens) has the following problems.

[0006] That is, although the objective is to provide a small, lightweight, large-diameter lens, the basic configuration employs an inner focus system, and since focusing is performed from an infinity-focused state to a closest-distance-focused state, there is a drawback in that the overall length of the product becomes long when the minimum shooting distance is ensured. In this case, by using a negative lens with strong power in the focus lens group, it is possible to reduce the amount of lens movement and shorten the minimum shooting distance while suppressing the overall length of the product, but on the other hand, the distance variation of aberration becomes large.

[0007] In addition, the maximum lens diameter cannot be made small relative to the aperture ratio, and the back focus is long, making it difficult to secure space for arranging the lenses, which results in the overall lens product tending to become larger.

[0008] An object of the present invention is to provide an imaging lens that solves the problems existing in the background art. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention provides an imaging lens 1 having an entire optical system 100 which is composed of, in order from the object OBJ side to the image IMG side, a first lens group G1, a second lens group G2, and a third lens group G3, the first lens group G1 being composed of three consecutive positive lenses L11, L12, and L13 and two negative lenses L14, L15, the second lens group G2 having positive or negative power, and the third lens group G3 being composed of, in order from the object OBJ side, one positive lens L31 and one negative lens L32 and having positive power, wherein, among the light rays which form an image on the optical axis Dc from infinity in the first lens group G1, a radius which is the maximum diameter is defined as Hh, and, among the light rays which form an image on the optical axis Dc from infinity in the first lens group G1, a radius which is the minimum diameter is defined as Hs, and the imaging lens 1 is characterized in that [Hs / Hh]<0.65 (optical condition 1) is satisfied.

[0010] In this case, according to a preferred embodiment of the invention, the aperture stop STO may be disposed between the first lens group G1 and the second lens group G2, or between the second lens group G2 and the third lens group G3. Meanwhile, in the first lens group G1, the lens surfaces (i=1, 3, 5) of the three positive lenses L11, L12, L13 facing the object OBJ can be set to have successively smaller radii of curvature R in order from the object OBJ side, and the lens surfaces (i=7, 9) of the two negative lenses L14, L15 facing the object OBJ can be set to have successively smaller radii of curvature R in order from the object OBJ side. In addition, the first lens group G1 can set the radius of curvature R of the lens surfaces (i=2, 4) of the two positive lenses L11, L12 located on the object OBJ side to be successively smaller in order from the object OBJ side, and the radius of curvature R of the lens surfaces (i=8, 10) of the two negative lenses L14, L15 to be successively smaller in order from the object OBJ side. Furthermore, it is preferable that the first lens group G1 satisfies νdp>νdn (optical condition 2), where νdp is the Abbe number of the positive lenses L11, L12, L13, and νdn is the Abbe number of the negative lenses L14, L15. The second lens group G2 can be composed of only a cemented lens J21 (J22). On the other hand, when the distance from the lens surface (i=18) closest to the image IMG to the image plane IMG is BF and the total optical length from the lens surface (i=1) closest to the object OBJ to the image plane IMG is TTL, the entire optical system 100 can satisfy [BF / TTL]<0.3 (optical condition 3), and when the focal length of the entire optical system 100 is f and the combined focal length of the second lens group G2 and the third lens group G3 is fr, the entire optical system 100 can satisfy 0.5<[fr / f]<0.75 (optical condition 4). In addition, the entire optical system 100 can set the F-number to F1.4 or less and satisfy [TTL / f]<1.45 (optical condition 5). Effect of the Invention

[0011] The imaging lens 1 according to the present invention having such a configuration provides the following remarkable effects.

[0012] (1) The first lens group G1 is composed of three consecutive positive lenses L11, L12, L13 and two negative lenses L14, L15, in order from the object OBJ side, the second lens group G2 has positive or negative power, and the third lens group G3 is composed of one positive lens L31 and one negative lens L32, in order from the object OBJ side, and has positive power. When the radius of the maximum diameter of the light beam that forms an image on the optical axis Dc from infinity in the first lens group G1 is Hh, and the radius of the minimum diameter of the light beam that forms an image on the optical axis Dc from infinity in the first lens group G1 is Hs, the optical condition 1 satisfies [Hs / Hh]<0.65 (optical condition 1). Therefore, the rear principal point of the entire optical system can be located closer to the object OBJ side. This makes it possible to shorten the total optical length relative to the focal length, and to reduce the diameters of the second lens group G2 and the third lens group G3, thereby making it possible to reduce the size of the entire imaging lens 1 and further reduce the cost of the entire product.

[0013] (2) In a preferred embodiment, the aperture stop STO can be disposed between the first lens group G1 and the second lens group G2. In other words, since the lens group has a so-called shallow angle of view, the aperture stop STO unit mechanism can be disposed between the first lens group G1 and the second lens group G2.

[0014] (3) In a preferred embodiment, the aperture diaphragm STO can be disposed between the second lens group G2 and the third lens group G3. In other words, since the lens has a shallow angle of view, the aperture diaphragm STO unit mechanism can be disposed between the second lens group G2 and the third lens group G3, and the location of the aperture diaphragm STO unit mechanism can be flexibly selected.

[0015] (4) In a preferred embodiment, when configuring the first lens group G1, the radius of curvature R of each lens surface (i=1, 3, 5) of the three positive lenses L11, L12, L13 on the object OBJ side is set to successively smaller values ​​beginning from the object OBJ side, and the radius of curvature R of each lens surface (i=7, 9) of the two negative lenses L14, L15 on the object OBJ side is set to successively smaller values ​​beginning from the object OBJ side. This makes it possible to gently bend light rays using multiple elements, thereby minimizing the occurrence of spherical aberration and appropriately correcting coma aberration.

[0016] (5) In a preferred embodiment, when configuring the first lens group G1, the radius of curvature R of each lens surface (i=2, 4) on the image IMG side of the two positive lenses L11, L12 located on the object OBJ side is set to be successively smaller from the object OBJ side, and the radius of curvature R of each lens surface (i=8, 10) on the image IMG side of the two negative lenses L14, L15 is set to be successively smaller from the object OBJ side, so that the arrangement of the radius of curvature R of each lens surface on the image IMG side in the first lens group G1 can provide a synergistic effect in combination with the arrangement of the radius of curvature R of each lens surface on the object OBJ side. That is, a further suppression effect against the occurrence of spherical aberration can be ensured, and a further correction effect against coma aberration can be ensured.

[0017] (6) In a preferred embodiment, when the second lens group G2 is configured using only the cemented lens J21 (J22), it is possible to suppress variation in performance throughout the second lens group G2 during manufacturing, and to provide favorable correction for chromatic aberration and image aberration.

[0018] (7) According to a preferred aspect, when the Abbe number of the positive lenses L11, L12, and L13 is vdp and the Abbe number of the negative lenses L14 and L15 is vdn, if the first lens group G1 is configured to satisfy vdp>vdn (optical condition 2), chromatic aberration generated in the first lens group G1 can be effectively corrected.

[0019] (8) In a preferred embodiment, when configuring the entire optical system 100, if the distance from the lens surface (i=18) closest to the image IMG to the image plane IMG is BF and the total optical length from the lens surface (i=1) closest to the object OBJ to the image plane IMG is TTL, then by configuring the system to satisfy [BF / TTL]<0.3 (optical condition 3), the back focus can be shortened, and the total optical length can also be shortened, making it possible to secure space for lens arrangement.

[0020] (9) In a preferred embodiment, when the entire optical system 100 is configured such that the focal length of the entire optical system 100 is f and the combined focal length of the second lens group G2 and the third lens group G3 is fr, 0.5<[fr / f]<0.75 (optical condition 4) is satisfied. This makes it possible to shorten the overall optical length and reduce the amount of extension within the range that satisfies optical condition 4.

[0021] (10) In a preferred embodiment, when constructing the entire optical system 100, the F-number is set to F1.4 or less and [TTL / f]<1.45 (optical condition 5) is satisfied, thereby keeping the overall length of the product short. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a configuration diagram of an imaging lens according to a first embodiment of the present invention; [Diagram 2] FIG. 2 is an explanatory diagram of the operation of the imaging lens of the first embodiment; [Diagram 3] FIG. 2 is a longitudinal aberration diagram of the imaging lens of Example 1 at infinity; [Figure 4] A list of optical characteristics (optical conditions) set in each example of the imaging lens according to the preferred embodiment of the present invention; [Diagram 5] FIG. 2 is a diagram showing the configuration of an imaging lens according to a second embodiment of the present invention; [Figure 6] FIG. 13 is a longitudinal aberration diagram of the imaging lens of Example 2 at infinity; [Figure 7] FIG. 3 is a diagram showing the configuration of an imaging lens according to a third embodiment of the present invention; [Figure 8]FIG. 13 is a longitudinal aberration diagram of the imaging lens of Example 3 at infinity; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Next, preferred embodiments of the present invention, that is, Examples 1 to 3, will be described in detail with reference to the drawings. EXAMPLES

[0024] First, an imaging lens 1 of Example 1 according to the present embodiment will be specifically described with reference to FIGS.

[0025] First, the configuration of the entire optical system 100 of the imaging lens 1 according to this embodiment (Example 1) will be described with reference to Fig. 1. In Fig. 1, OBJ indicates the object side (subject side), and IMG indicates the image (imaging element: imaging surface) side. Therefore, the object OBJ side is the front side in the direction of the optical axis Dc, and the image IMG side is the rear side in the direction of the optical axis Dc. STO indicates an aperture stop.

[0026] As shown in FIG. 1, the imaging lens 1 (total optical system 100) according to this embodiment includes a first lens group G1 (front lens group Gf) arranged on the object OBJ side of the aperture stop STO, and a rear lens group Gr arranged on the image IMG side of the aperture stop STO, and this rear lens group Gr is composed of a second lens group G2 arranged on the object OBJ side and a third lens group G3 arranged on the image IMG side.

[0027] In this way, the aperture diaphragm STO can be disposed between the first lens group G1 and the second lens group G2. That is, since a so-called shallow angle of view is provided, the unit mechanism of the aperture diaphragm STO can be disposed between the first lens group G1 and the second lens group G2.

[0028] The first lens group G1, the second lens group G2 and the third lens group G3, i.e., the front lens group Gf and the rear lens group Gr, make up the entire lens system. Note that illustration of a wavelength cut filter, a dustproof glass or other parallel flat plate disposed in front of the image IMG (imaging element) is omitted.

[0029] The first lens group G1 in the entire lens system is composed of five single lenses in total, three consecutive positive lenses L11, L12, L13 and two negative lenses L14, L15, in order from the object OBJ side to the image IMG side, as shown in Fig. 1. Specifically, in order from the object OBJ side, it is composed of a positive lens L11 using a positive meniscus lens whose lens surface (i=1) on the object OBJ side protrudes toward the object OBJ side, a positive lens L12 using a positive meniscus lens whose lens surface (i=3) on the object OBJ side protrudes toward the object OBJ side, a positive lens L13 using a positive meniscus lens whose lens surface (i=5) on the object OBJ side protrudes toward the object OBJ side, a negative lens L14 using a negative meniscus lens whose lens surface (i=7) on the object OBJ side protrudes toward the object OBJ side, and a negative lens L15 using a negative meniscus lens whose lens surface (i=9) on the object OBJ side protrudes toward the object OBJ side.

[0030] In this case, the radius of curvature R of each lens surface (i=1, 3, 5) of the three positive lenses L11, L12, L13 on the object OBJ side is set to be successively smaller starting from the object OBJ side, and the radius of curvature R of each lens surface (i=7, 9) of the two negative lenses L14, L15 on the object OBJ side is set to be successively smaller starting from the object OBJ side. By setting in this way, the light rays can be gently bent by multiple elements, so that the occurrence of spherical aberration can be kept to a minimum and coma aberration can also be appropriately corrected.

[0031] Furthermore, the radius of curvature R of each lens surface (i=2, 4) on the image IMG side of the two positive lenses L11, L12 located on the object OBJ side is set to be successively smaller from the object OBJ side, and the radius of curvature R of each lens surface (i=8, 10) on the image IMG side of the two negative lenses L14, L15 is set to be successively smaller from the object OBJ side. By setting in this way, a synergistic effect can be obtained by combining the arrangement of the radius of curvature R of each lens surface on the image IMG side in the first lens group G1 with the arrangement of the radius of curvature R of each lens surface on the object OBJ side. In other words, since the rear principal point of the entire optical system can be located on the object OBJ side, the total optical length can be made shorter relative to the focal length.

[0032] Furthermore, as shown in FIG. 2, when the radius of the lens surface with the largest diameter (i=1) in the first lens group G1 is Hh and the radius of the lens surface with the smallest diameter (i=10) in the first lens group G1 is Hs, the following optical condition 1 is set to be satisfied. [Hs / Hh]<0.65 … Optical condition 1

[0033] In this case, in the first lens group G1, the lens surface with the maximum diameter of the light beam from infinity forming an image on the optical axis Dc is the lens surface (i=1) on the object OBJ side of the positive lens 11 arranged closest to the object OBJ. That is, the relative pupil position of the light beam from infinity forming an image on the optical axis Dc is the height to the light ray Cf at the position farthest from the optical axis Dc. Also, in the first lens group G1, the lens surface with the minimum diameter of the light beam from infinity forming an image on the optical axis Dc is the lens surface (i=10) on the image IMG side of the negative lens 15 arranged closest to the image IMG. That is, the relative pupil position of the light beam from infinity forming an image on the optical axis Dc is the height to the light ray Cf at the position closest to the optical axis Dc.

[0034] If the optical condition 1 is satisfied, the lens diameters of the second lens group G2 and the third lens group G3 can be reduced relative to the aperture ratio, making it possible to reduce the size of the entire imaging lens 1 and further reduce the cost of the entire product.

[0035] In addition, when the first lens group G1 is configured, the following optical condition 2 is satisfied, where the Abbe number of the positive lenses L11, L12, and L13 is νdp and the Abbe number of the negative lenses L14 and L15 is νdn. νdp>νdn … Optical condition 2

[0036] By setting it in this way, chromatic aberration occurring in the first lens group G1 can be corrected satisfactorily.

[0037] On the other hand, the second lens group G2 is composed of only the cemented lens J21. Specifically, as shown in FIG. 1, the second lens group G2 is composed of a negative lens L21 arranged on the object OBJ side and using a negative meniscus lens having a lens surface (i=11) protruding toward the object OBJ side, and a positive lens L22 arranged on the image IMG side using a biconvex lens, which is cemented together. By configuring the second lens group G2 in this way, it is possible to suppress the variation in performance during manufacturing of the entire second lens group G2, and to perform good correction of chromatic aberration and spherical aberration. In the case of Example 1, this second lens group G2 has a positive power, but in the present invention, it may have a positive power or a negative power.

[0038] On the other hand, the third lens group G3 is composed of one positive lens L31 and one negative lens L32, in that order from the object OBJ side, as shown in Fig. 1. Specifically, it is composed of the positive lens L31 using a biconvex lens arranged on the object OBJ side, and the negative lens L32 using a negative meniscus lens arranged on the image IMG side and protruding toward the image IMG side. In this case, the third lens group G3 has positive power.

[0039] In addition, in the entire optical system 100, when the distance from the lens surface (i=18) closest to the image IMG to the image plane IMG is BF and the total optical length from the lens surface (i=1) closest to the object OBJ to the image plane IMG is TTL, the system is set to satisfy the following optical condition 3. [BF / TTL]<0.3 … Optical conditions 3

[0040] By setting it in this way, the back focus can be shortened, the overall optical length can be shortened, and the space required for lens arrangement can be secured.

[0041] Furthermore, the entire optical system 100 is configured to satisfy the following optical condition 4, where the focal length of the entire optical system 100 is f and the combined focal length of the second lens group G2 and the third lens group G3 is fr. 0.5<[fr / f]<0.75 … Optical condition 4

[0042] As a result, the total optical length can be shortened while maintaining a certain level of performance within the range that satisfies this optical condition. That is, if fr / f exceeds 0.75, performance can be improved, but the total optical length cannot be shortened, and if it falls below 0.5, the power of the second lens group G2 and the third lens group G3 becomes too strong, causing problems in which each aberration appears prominently. In addition, spherical aberration appears prominently, causing resolution degradation, and in particular, changes in resolution due to changes in the distance of the object OBJ appear prominently.

[0043] In addition, when configuring the entire optical system 100, the F-number is set to F1.4 or less, and the following optical condition 5 is satisfied. [TTL / f]<1.45 … Optical condition 5

[0044] By setting it in this way, the overall length of the product can be kept short. However, if it exceeds 1.45, both the resolution and chromatic aberration improve, but the size becomes too large, compromising portability and operability.

[0045] In Table 1, the upper row shows "lens surface data" of the entire lens system in the imaging lens 1 of Example 1, and the lower row shows "focus variable interval" of the same imaging lens 1. In addition, Fig. 4 shows the optical characteristics (optical conditions) of the entire lens system.

[0046] [Table 1]

[0047] In the "Lens Surface Data" in Table 1, the surface number of the lens counted from the object OBJ side is indicated by i, and this surface number i corresponds to the code (number) shown in Figure 1. Correspondingly, the radius of curvature R(i), axial surface spacing D(i), lens refractive index nd(i), and lens Abbe number νd(i) of the lens are indicated. nd(i) and νd(i) are values ​​for the d-line (587.6 [nm]). Axial surface spacing D(i) indicates the lens thickness or air space between opposing surfaces. The units of radius of curvature R(i) and surface spacing D(i) are [mm]. The surface number OBJ indicates the object, STO indicates the aperture stop, and IMG indicates the position of the image (imaging surface). The Infinity of the radius of curvature R(i) is a flat surface. The blanks for the refractive index nd(i) and Abbe number νd(i) indicate air.

[0048] 4, in the front lens group Gf (first lens group G1), the radius Hh of the lens surface (i=1) with the maximum diameter of the light beam that is imaged on the optical axis Dc from infinity is 19.75 [mm], and the radius Hs of the lens surface (i=10) with the minimum diameter is 10.54 [mm], so Hs / Hh is 0.53, which satisfies the optical condition 1 of [Hs / Hh]<0.65. In addition, as shown in Table 1, the Abbe numbers νdp of the positive lenses L11, L12, and L13 of the first lens group G1 are 54.67, and the Abbe numbers νdn of the negative lenses L14 and L15 are 27.74 and 26.58, respectively, which satisfies the optical condition 2 of νdp>νdn. Furthermore, as shown in Figure 4, the distance BF from the lens surface (i = 18) closest to the image IMG to the image plane IMG is 12.57 [mm], and the total optical length TTL from the lens surface (i = 1) closest to the object OBJ to the image plane IMG is 65 [mm], so BF / TTL is 0.19, which satisfies optical condition 3 of [BF / TTL] < 0.3.

[0049] 4, the focal length f of the entire lens system is 48.50 [mm], the focal length fr of the rear lens group Gr (second lens group G2+third lens group G3) is 29.39 [mm], and fr / f is 0.61, which satisfies optical condition 4 of 0.5<[fr / f]<0.75. Furthermore, as shown in Table 1 and FIG. 4, the F-number is F1.23, TTL is 65 [mm], and f is 48.50 [mm], which satisfies optical condition 5 of 0.5<[fr / f]<0.75.

[0050] In this way, Example 1 satisfies all of (Optical Condition 1) to (Optical Condition 5). Fig. 3 shows longitudinal aberration diagrams corresponding to the imaging lens 1 of Example 1 at infinity. From the left, each longitudinal aberration diagram shows spherical aberration (656.3 nm, 587.6 nm, 435.8 nm), astigmatism (587.6 nm), and distortion aberration (587.6 nm). Each scale (1 division) is ±0.25 mm, ±0.25 mm, and ±2.5%.

[0051] The imaging lens 1 of Example 1 has a half angle of view ω of 16.28°, as shown in Table 1. In addition, as is clear from Fig. 3, it can be confirmed that good aberration characteristics, that is, good imaging performance (optical performance) is obtained for all longitudinal aberrations. EXAMPLES

[0052] Next, the imaging lens 1 of Example 2 according to the present embodiment will be described with reference to FIGS.

[0053] The imaging lens 1 of Example 2 differs from Example 1 in the following respects: the lens surface (i=1) of the positive lens L11 in the first lens group G1 on the object OBJ side is formed aspheric, the positive lens L22 in the second lens group G2 is formed by a positive meniscus lens protruding toward the object OBJ side, and the third lens group G3 is composed of only a cemented lens J31, specifically, only a cemented lens J31 obtained by cementing together the positive lens L31 using a biconvex lens arranged on the object OBJ side and the negative lens L32 using a negative meniscus lens protruding toward the image IMG side arranged on the image IMG side.

[0054] Except for these differences and the detailed lens surface data (including focus variable interval and aspheric coefficient) shown in Table 2, the other basic configuration is the same as that of Example 1. That is, the present embodiment is the same as Example 1 in that it includes a first lens group G1 consisting of, in order from the object OBJ side, three consecutive positive lenses L11, L12, L13 and two negative lenses L14, L15, a second lens group G2 having positive or negative power, and a third lens group G3 consisting of, in order from the object OBJ side, one positive lens L31 and one negative lens L32 and having positive power, and in that optical conditions 1-5 are set.

[0055] Table 2 shows the "lens surface data", "focus variable interval" and "aspheric coefficient" of the entire lens system of the imaging lens 1 of Example 2. In the "lens surface data", a surface with A added after the surface number i indicates that the surface shape is aspheric. In addition, the "aspheric coefficient" in Table 2 is expressed by Equation 1 in an orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the direction of the optical axis Dc as Z. In Equation 1, R is the central radius of curvature, A4, A6, and A8 are fourth-order, sixth-order, and eighth-order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis. In Table 2, "E" stands for "×10".

[0056]

number

[0057] [Table 2]

[0058] 4, in the front lens group Gf, the radius Hh of the maximum diameter of the light beam that is imaged on the optical axis Dc from infinity is 19.75 mm, and the radius Hs of the maximum diameter is 10.52 mm, so Hs / Hh is 0.53, which satisfies the optical condition 1 of [Hs / Hh]<0.65. In addition, as shown in Table 2, the Abbe numbers νdp of the positive lenses L11, L12, and L13 of the first lens group G1 are 40.55, 54.67, and 54.67, respectively, and the Abbe numbers νdn of the negative lenses L14 and L15 are 27.74 and 26.58, respectively, which satisfies the optical condition 2 of νdp>νdn. Furthermore, as shown in FIG. 4, BF is 15.96 mm and TTL is 65 mm, so BF / TTL is 0.25, which satisfies optical condition 3 of [BF / TTL]<0.3.

[0059] As shown in Fig. 4, f is 48.52 [mm], the focal length fr of the rear lens group Gr is 32.88 [mm], and fr / f is 0.68, which satisfies optical condition 4 of 0.5<[fr / f]<0.75. Furthermore, as shown in Table 2 and Fig. 4, the F-number is F1.23, TTL is 65 [mm], and f is 48.52 [mm], which means that TTL / f is 1.34, and the F-number is set to F1.4 or less, and optical condition 5 of [TTL / f]<1.45 is satisfied.

[0060] In this way, Example 2 satisfies all of (Optical Condition 1) to (Optical Condition 5). Fig. 6 shows longitudinal aberration diagrams corresponding to the imaging lens 1 of Example 2 at infinity. As shown in Table 2, the imaging lens 1 of Example 2 has a half angle of view ω of 16.198°. As is clear from Fig. 6, it can be confirmed that good aberration characteristics, i.e., good imaging performance (optical performance), are obtained for all longitudinal aberrations. EXAMPLES

[0061] Next, the imaging lens 1 of Example 3 according to the present embodiment will be described with reference to FIG.

[0062] The imaging lens 1 of Example 3 differs from Example 1 in the following respects. That is, when providing the aperture diaphragm STO, it is disposed between the second lens group G2 and the third lens group G3. With this arrangement, the angle of view is shallow, so the arrangement of the unit mechanism of the aperture diaphragm STO can be flexibly selected.

[0063] The second lens group G2 is formed of a cemented lens J22 made of three lenses cemented together. Specifically, the cemented lens J22 is made of three lenses, which are arranged in order from the object OBJ side to the image IMG side, namely, a negative lens L23 made of a negative meniscus lens with its lens surface on the object OBJ side protruding, a positive lens L24 made of a biconvex lens, and a negative lens L25 made of a biconcave lens.

[0064] Except for these differences and the detailed lens surface data (including the focus variable interval) shown in Table 3, the other basic configuration is the same as that of Example 1. That is, the present embodiment is the same as Example 1 in that it includes a first lens group G1 composed of, in order from the object OBJ side, three consecutive positive lenses L11, L12, and L13 and two negative lenses L14 and L15, a second lens group G2 having positive or negative power, and a third lens group G3 composed of, in order from the object OBJ side, one positive lens L31 and one negative lens L32 and having positive power, and in that optical conditions 1-5 are set.

[0065] Table 3 shows the "lens surface data" and "focus variable interval" of the entire lens system in the imaging lens 1 of the third embodiment.

[0066] [Table 3]

[0067] 4, in the front lens group Gf, the maximum radius Hh of the light beam that forms an image on the optical axis Dc from infinity is 29.48 mm, and the minimum radius Hs is 16.12 mm, so Hs / Hh is 0.55, which satisfies the optical condition 1 of [Hs / Hh]<0.65. In addition, as shown in Table 3, the Abbe numbers νdp of the positive lenses L11, L12, and L13 of the first lens group G1 are 68.62, 54.67, and 81.61, respectively, and the Abbe numbers νdn of the negative lenses L14 and L15 are 28.38 and 28.38, respectively, which satisfies the optical condition 2 of νdp>νdn. Furthermore, as shown in FIG. 4, BF is 15.08 [mm] and TTL is 95.49 [mm], so BF / TTL is 0.16, which satisfies optical condition 3 of [BF / TTL]<0.3.

[0068] 4, f is 72.75 [mm], the focal length fr of the rear lens group Gr is 43.74 [mm], and fr / f is 0.60, which satisfies optical condition 4 of 0.5<[fr / f]<0.75. Furthermore, as shown in Table 3 and FIG. 4, the F-number is F1.23, TTL is 95.49 [mm], and f is 72.75 [mm], which means that TTL / f is 1.31, and the F-number is set to F1.4 or less, and optical condition 5 of [TTL / f]<1.45 is satisfied.

[0069] In this way, Example 3 also satisfies all of (Optical Condition 1) to (Optical Condition 5). Fig. 8 shows a longitudinal aberration diagram corresponding to the imaging lens 1 of Example 3 at infinity. As shown in Table 3, the imaging lens 1 of Example 3 has a half angle of view ω of 10.89°. As is clear from Fig. 8, it can be confirmed that good aberration characteristics, i.e., good imaging performance (optical performance), are obtained for all longitudinal aberrations.

[0070] Therefore, the imaging lens 1 according to such an embodiment (Examples 1-3) has a basic configuration including, in order from the object OBJ side, a first lens group G1 composed of three consecutive positive lenses L11, L12, and L13 and two negative lenses L14, L15, a second lens group G2 having positive or negative power, and a third lens group G3 composed of, in order from the object OBJ side, one positive lens L31 and one negative lens L32 and having positive power. When the radius of the maximum diameter of a light ray that forms an image on the optical axis Dc from infinity in the first lens group G1 is Hh and the radius of the minimum diameter of a light ray that forms an image on the optical axis Dc from infinity in the first lens group G1 is Hs, the imaging lens 1 is configured to satisfy [Hs / Hh]<0.65 (optical condition 1), and therefore it is possible to position the rear principal point of the entire optical system closer to the object OBJ side. This allows the overall optical length to be shorter relative to the focal length, and the diameters of the second lens group G2 and the third lens group G3 to be smaller, making it possible to reduce the size of the entire imaging lens 1 and further reduce the cost of the entire product.

[0071] Although the preferred embodiments including Examples 1-3 have been described in detail above, 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 without departing from the gist of the present invention.

[0072] For example, the aperture stop STO is disposed between the first lens group G1 and the second lens group G2, or between the second lens group G2 and the third lens group G3, but the case where the aperture stop STO is disposed at another position is not excluded. In addition, when forming the first lens group G1, it is desirable to set the radii of curvature R of the lens surfaces (i=1, 3, 5) of the three positive lenses L11, L12, L13 on the object OBJ side successively smaller in order from the object OBJ side, and to set the radii of curvature R of the lens surfaces (i=7, 9) of the two negative lenses L14, L15 on the object OBJ side successively smaller in order from the object OBJ side, but this is not a required configuration requirement. Similarly, when constructing the first lens group G1, it is desirable, but not essential, to set the radii of curvature R of the image IMG side lens surfaces (i=2, 4) of the two positive lenses L11, L12 located on the object OBJ side to successively smaller values ​​starting from the object OBJ side, and to set the radii of curvature R of the image IMG side lens surfaces (i=8, 10) of the two negative lenses L14, L15 to successively smaller values ​​starting from the object OBJ side. Furthermore, it is desirable, but not essential, to satisfy optical conditions 2-5. [Industrial Applicability]

[0073] The imaging lens according to the present invention can be used as a dedicated lens or an interchangeable lens in various optical instruments. [Explanation of symbols]

[0074] 1: imaging lens, 100: entire optical system 100, G1: first lens group, G2: second lens group G2, G3: third lens group G3, L11: positive lens L11, L12: positive lens L12, L12: positive lens L13, L14: negative lens L14, L15: negative lens L15, L31: positive lens L31, L32: negative lens L32, J21 (J22): cemented lens, Hh: radius of lens surface (i = 1) that is the maximum of the light beam that forms an image on the optical axis from infinity, Hs: radius of lens surface (i = 10) that is the minimum of the light beam that forms an image on the optical axis from infinity, STO: aperture stop, OBJ: object, IMG: image

Claims

1. The imaging lens has an entire optical system which is composed of, in order from the object side to the image side, a first lens group, a second lens group, and a third lens group, the first lens group being composed of three consecutive positive lenses and two negative lenses, a second lens group having positive or negative power, and a third lens group being composed, in order from the object side, of one positive lens and one negative lens and having positive power, the imaging lens being characterized in that it satisfies the following optical condition 1, where Hh is the radius of the maximum diameter of a light ray which forms an image on the optical axis from infinity in the first lens group, and Hs is the radius of the minimum diameter of a light ray which forms an image on the optical axis from infinity in the first lens group. [Hs / Hh]<0.65...Optical conditions 1

2. 2. The imaging lens according to claim 1, further comprising an aperture stop disposed between the first lens group and the second lens group.

3. 2. The imaging lens according to claim 1, further comprising an aperture stop disposed between the second lens group and the third lens group.

4. 2. The imaging lens according to claim 1, wherein in the first lens group, the radii of curvature of the object-side lens surfaces of the three positive lenses are set to successively decrease from the object side, and the radii of curvature of the object-side lens surfaces of the two negative lenses are set to successively decrease from the object side.

5. 2. The imaging lens according to claim 1, wherein, in the first lens group, the radii of curvature of the image-side lens surfaces of the two positive lenses located on the object side are set to successively smaller values ​​from the object side, and the radii of curvature of the image-side lens surfaces of the two negative lenses are set to successively smaller values ​​from the object side.

6. 2. The imaging lens according to claim 1, wherein the first lens group satisfies the following optical condition 2, where the Abbe number of the positive lens is vdp and the Abbe number of the negative lens is vdn. νdp>νdn … Optical condition 2

7. 2. The imaging lens according to claim 1, wherein the second lens group is composed of only cemented lenses.

8. 2. The imaging lens according to claim 1, wherein the entire optical system satisfies the following optical condition 3, where BF is a distance from the lens surface closest to the image side to the image plane and TTL is a total optical length from the lens surface closest to the object side to the image plane. [BF / TTL]<0.3...Optical conditions 3

9. 2. The imaging lens according to claim 1, wherein the entire optical system satisfies the following optical condition 4, where f is a focal length of the entire optical system and fr is a combined focal length of the second lens group and the third lens group: 0.5<[fr / f]<0.75...Optical condition 4

10. 2. The imaging lens according to claim 1, wherein the F-number of the entire optical system is set to F1.4 or less, and the following optical condition 5 is satisfied: [TTL / f]<1.45...Optical conditions 5

Images