Optical lens system

Abstract

To provide a large-diameter lens with improved aberrations.SOLUTION: An optical lens system 100 is configured so that a front group G1 and a back group G2 are sequentially arranged from an object OBJ side to an image IMG side and the distance between the front group G1 and the back group G2 is changed at focusing. The front group G1 has a positive bending force, and the back group G2 has a positive bending force and is divided into a first back group G2A and a second back group G2B before and after a diaphragm STOP. The respective lens surfaces which are the closest to the object OBJ of the front group G1, the first back group G2A, and the second back group G2B are recessed to the direction of the object OBJ side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical lens system that is a large-diameter lens and is composed of a front group on the object side and a rear group on the image-forming surface side, in which the distance between adjacent groups changes during focusing. [Background technology]

[0002] In recent years, there has been an increasing demand for large aperture lenses in photo cameras and video cameras to accommodate expressions that utilize a shallow depth of field (so-called bokeh expressions).

[0003] For example, Patent Document 1 (JP 2022-71325 A) discloses a single focal length lens with a large aperture, F-number of about 1.4, in which various aberrations are well corrected. Patent Document 1 discloses the following configuration. That is, the lens of Patent Document 1 consists, from the object side to the image side, of a first lens group having positive power and a second lens group having positive power. The first lens group consists, from the object side to the image side, of a 1A lens group having negative power and a 1B lens group having positive power, the 1A lens group and the 1B lens group being separated by the maximum air space within the first lens group. The second lens group consists, from the object side to the image side, of a 2A lens group, an aperture stop and a 2B lens group, the object side surface of the lens adjacent to the image side of the aperture stop is convex facing the object side, and when focusing from an object at infinity to an object at a close distance, the first lens group is fixed with respect to the image plane and the second lens group moves toward the object side to satisfy -2.0<focal length of 1A lens group / focal length of 1B lens group<-1.0. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-71325 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the configuration disclosed in Patent Document 1 makes it easy to increase the aperture, there is a problem in that various aberrations must be further improved. [Means for solving the problem]

[0006] SUMMARY OF THE PRESENT INVETION The present invention has been made in consideration of the above circumstances, and has an object to provide a large-diameter lens in which various aberrations are improved.

[0007] The present invention solves the above problems by the solution means described below as one embodiment. That is, it is an optical lens system in which a front group and a rear group are arranged in that order from the object side to the image side, and the distance between the front group and the rear group changes during focusing, wherein the front group has positive refractive power, the rear group has positive refractive power, and is divided into a first rear group and a second rear group before and after a stop, and the lens surfaces closest to the object of each of the front group, the first rear group, and the second rear group have a concave shape toward the object side. By adopting this configuration, it is possible to improve coma aberration and Petzval sum.

[0008] The second rear group has two sets of cemented lenses and an aspherical lens closest to the image side, and the shape of the air space on the object side of the aspherical lens is biconvex. According to this configuration, by making the final surface an aspherical lens, the light path at each image height can be controlled by the aspherical surface, and the sagittal and meridional field curvatures can be corrected. In addition, by making the spatial interval in front of the aspherical surface into a biconvex shape, a strong negative power can be formed in combination with the negative lenses before and after, and the back focus can be shortened while maintaining the image circle. As a result, the entire optical system can be made compact.

[0009] The present invention is also characterized in that the difference between the number of lenses in the second rear group excluding the aspherical lens and the number of lenses in the first rear group is one or less, and when the focal length of the first rear group is fa and the focal length of the second rear group is fb, the relationship 0.7≦fa / fb≦1.5 is satisfied. According to this configuration, by setting the number of lens elements and the power that make up each group under the same conditions, there is an effect of canceling out the aberrations generated in the first rear group and the second rear group.

[0010] Further, the second rear group has a plurality of positive lens components, and negative lenses are arranged on both sides of the plurality of positive lens components. According to this configuration, good aberration characteristics can be obtained for the angle of view from wide angle to standard range.

[0011] Further, when the Abbe number of the positive lens of the front group is νdp and the Abbe number of the negative lens of the front group is νdn, νdp > νdn is satisfied, and at least one of the negative lenses satisfies θgF < A. Here, θgF refers to the partial dispersion ratio, and A refers to the following formula for anomalous dispersibility. A = -1.62×10 -3 ×νd + 0.64

[0012] Further, the first rear group has at least two positive lenses and negative lenses, and a biconcave lens and a positive lens are arranged in order from the object side. According to this configuration, it is possible to reduce the coma aberration variation during close focusing.

[0013] Further, a cemented lens is arranged in the first rear group, and the difference in refractive index of the cemented lens is 0.15 or more and the difference in νd is 10 or less. According to this configuration, the Petzval sum can be reduced and the field curvature can be corrected well.

[0014] Further, a cemented lens is arranged in the second rear group, and the difference in refractive index of the cemented lens is 0.15 or more. According to this configuration, the Petzval sum can be reduced and the field curvature can be corrected well.

[0015] Further, when the focal length of the front group is ff and the focal length of the rear group is fr, 1.7 < ff / fr < 3 is satisfied. According to this configuration, the amount of movement of the rear group can be reduced without impairing the overall aberration balance, leading to a reduction in the size of the entire optical system.

[0016] When the focal length of the entire system is f, the distance on the optical axis from the lens surface closest to the object to the image-forming position is TTL, and the distance on the optical axis from the lens surface closest to the image to the image-forming position is BF, the lens is characterized by satisfying BF / TTL<0.25 and BF / f<0.45. According to this configuration, it is possible to shorten the BF relative to the total optical length, and it is possible to ensure a space for arranging the lenses. Effect of the Invention

[0017] It is possible to realize a large-aperture lens with improved aberrations. [Brief description of the drawings]

[0018] [Figure 1] 1 is a configuration diagram of an optical lens system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a longitudinal aberration diagram of the optical lens system according to the first embodiment of the present invention at infinity. [Diagram 3] FIG. 11 is a diagram illustrating the configuration of an optical lens system according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a longitudinal aberration diagram of the optical lens system according to the second embodiment of the present invention at infinity. [Diagram 5] FIG. 11 is a diagram illustrating the configuration of an optical lens system according to a third embodiment of the present invention. [Figure 6] FIG. 11 is a longitudinal aberration diagram of the optical lens system according to the third embodiment of the present invention at infinity. [Figure 7] FIG. 11 is a diagram illustrating the configuration of an optical lens system according to a fourth embodiment of the present invention. [Figure 8] FIG. 13 is a longitudinal aberration diagram of the optical lens system according to the fourth embodiment of the present invention at infinity. [Figure 9] FIG. 13 is a diagram illustrating the configuration of an optical lens system according to a fifth embodiment of the present invention. [Figure 10]FIG. 13 is a longitudinal aberration diagram of the optical lens system according to the fifth embodiment of the present invention at infinity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0020] 2, 4, 6, 8, and 10, the legends for C-line (wavelength 656.27 nm), d-line (wavelength 587.56 nm), and g-line (wavelength 435.83 nm) are shown in the upper right corner. In all the drawings for explaining each embodiment, the same reference numerals are used for members having the same functions, and repeated explanations thereof may be omitted.

[0021] The optical lens systems 100, 200, 300, 400, and 500 in the respective embodiments are, by way of example, imaging lenses used in photo cameras or video cameras. As shown in Figures 1, 3, 5, 7 and 9, a front group G1 and a rear group G2 are disposed on the optical axis from an object OBJ to an image plane IMG, and focusing is performed by changing the distance between the front group G1 and the rear group G2. In addition, the rear group G2 includes, from the object OBJ toward the image plane IMG, a first rear group G2A, a diaphragm portion STOP, and a second rear group G2B.

[0022] For convenience, the surfaces of the lenses are numbered in Figures 1, 3, 5, 7, and 9, but the surface numbers do not necessarily correspond between the embodiments. Also, the cemented surfaces of cemented lenses are given the same number. Furthermore, because the aperture stop STOP is counted as a virtual surface, the consecutive surface numbers are omitted.

[0023] (First embodiment) In the first embodiment, a large-aperture imaging lens 100 having a total focal length f=48.5 mm, an F-number of 1.43, and a half angle of view ω=23.7° will be illustrated and described in FIG.

[0024] The imaging lens 100 in this embodiment has a front group G1 and a rear group G2, and is a rear focus type in which the rear group G2 moves relative to the front group G1 and focuses by adjusting the distance between the front group G1 and the rear group G2. The rear group G2 is divided into a first rear group G2A and a second rear group G2B with an aperture section STOP in between. Moreover, both the front group G1 and the rear group G2 of the imaging lens 100 have a positive refractive index.

[0025] The lens surfaces of the front group G1, the first rear group G2A, and the second rear group G2B facing the object OJT are each concave toward the object OJT side. According to Figure 1, these are lens surfaces 1, 6, and 14. By facing the concave shape toward the object OJT side in this way, coma aberration from infinity to close distances can be improved.

[0026] The front group G1 has a concave meniscus lens L1 with its concave shape facing the object OJT side, and a cemented lens L2. The cemented lens L2 consists of a concave meniscus lens L2f with its convex shape facing the object OJT side, and a biconvex lens L2r cemented to the image surface IMG side of the concave meniscus lens L2f.

[0027] The first rear group G2A has a biconcave lens L3 with its concave shape facing the object OJT side, a biconvex lens L4, and a cemented lens L5. The cemented lens L5 is made up of a biconcave lens L5f disposed on the object OBJ side, and a biconvex lens L5r cemented to the image plane IMG side of the biconcave lens L5f. In this way, the first rear group G2A is composed of at least two positive lenses and two negative lenses, which can reduce coma aberration fluctuations during close-range focusing.

[0028] The diaphragm unit STOP is disposed on the image plane IMG side of the first rear group G2A, and the second rear group G2B is disposed on the image plane IMG side of the diaphragm unit STOP. The second rear group G2B is composed of two cemented lenses L6, a cemented lens L7, and an aspheric lens L8 arranged in this order from the object OBJ side to the image plane IMG side. Also, the aspherical lens L8 has a concave shape toward the object OBJ side. Therefore, the air gap between the image forming surface IMG side of the cemented lens L7 and the object OBJ side of the aspherical lens L8 has a biconvex shape. With this configuration, the biconcave lens L7r, the air gap, and the aspherical lens L8 can have a strong negative power, and the back focus can be shortened while ensuring the image circle. This allows the entire optical system to be made compact. Also, by making the aspherical lens L8 closest to the image forming surface IMG, the light path at each image height can be controlled by the aspherical surface, which is effective in correcting the sagittal and meridional field curvature.

[0029] Of the two cemented lenses in the second rear group G2B, the cemented lens L6 is made up of a biconcave lens L6f arranged on the object OBJ side, and a biconvex lens L6r cemented to the image plane IMG side of the biconcave lens L6f. The cemented lens L7 is made up of a biconvex lens L7f arranged on the object OBJ side, and a biconcave lens L7r cemented to the image plane IMG side of the biconvex lens L7f. Therefore, the second rear group G2B has at least a plurality of positive lens components, and negative lenses are arranged on both sides thereof. That is, by having a power arrangement of convex-concave-convex, good aberration characteristics can be obtained within the angle of view from wide angle to standard range.

[0030] The number of lenses in the first rear group G2A is 4, and the number of lenses in the second rear group G2B excluding the aspherical lens L8 is 4. Therefore, the difference in the number of lenses between the first rear group G2A and the second rear group G2B is 0 (1 or less). And as shown in Table 1 described later, when fa is the focal length of the first rear group G2A and fb is the focal length of the second rear group G2B, fa / fb = 1.32, satisfying 0.7 ≦ fa / fb ≦ 1.5. That is, by setting the number of lenses and the power of the first rear group G2A and the second rear group G2B under similar conditions, the aberrations generated in the first rear group G2A and the second rear group G2B can be canceled out.

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

Table 1

[0032] According to Table 1, ff / fr = 2.26, satisfying 1.7 < ff / fr < 3. Thereby, while maintaining good aberration characteristics, the extension amount of the rear group G2 can be reduced, and the entire optical system can be shortened.

[0033] Also according to Table 1, BF / TTL = 0.19, satisfying BF / TTL < 0.25. Also, BF / f = 0.38, satisfying BF / f < 0.45. Thereby, BF can be shortened with respect to the overall optical length, and a space for arranging lenses can be secured.

[0034] Next, Tables 2 to 4 show lens data for the optical lens system 100 according to the first embodiment shown in FIG.

[0035] [Table 2]

[0036] Table 2 shows the radius of curvature R (mm) corresponding to the virtual surface and lens surface counted from the object OBJ side, the surface spacing D (mm) on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens. If the lens has an aspheric shape, it is indicated with an * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. In addition, nd and νd are values ​​for the d line (587.56 nm). Also, D is the distance from the first surface to the next surface. Furthermore, the blanks in nd and νd indicate air.

[0037] [Table 3]

[0038] Table 3 shows the variable spacing between the lenses.

[0039] [Table 4]

[0040] The surface shape (aspheric coefficients) of an aspheric lens are shown in Table 4. In this case, in an orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the following formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, and A12 are the 4th, 6th, 8th, 10th, and 12th order aspheric coefficients, respectively, and H is the distance from the origin on the optical axis.

[0041] [Number]

[0042] Also, according to Table 2, if the Abbe number of the positive lens of the front group G1 is νdp and the Abbe number of the negative lens is νdn, then νdp > νdn is satisfied. And, among the negative lenses in the front group G1, one satisfies θgF < A. Here, θgF refers to the partial dispersion ratio, and A is an expression for anomalous dispersion, as follows. A = -1.62×10-3×νd + 0.64 By setting the conditions of the front group G1 in this way, the occurrence of chromatic aberration within the front group G1 can be prevented.

[0043] Also, according to Table 2, the difference in refractive index of the cemented lens L5 in the first rear group G2A is 0.18069, which is 0.15 or more. The difference in Abbe number of the cemented lens L5 in the first rear group G2A is 3.04, which is 10 or less. By setting the conditions of the cemented lens L5 of the first rear group G2A in this way, the Petzval sum can be reduced and the field curvature can be corrected well.

[0044] Furthermore, according to Table 2, the difference in refractive index of the cemented lens L6 in the second rear group G2B is 0.2115, and the difference in refractive index of the cemented lens L7 is 0.20078, and each is 0.15 or more. By setting the conditions of the cemented lenses L6 and L7 of the second rear group G2B in this way, the Petzval sum can be reduced and the field curvature can be corrected well.

[0045] Fig. 2 shows spherical aberration, astigmatism, and distortion in the optical lens system 100. Note that each scale is ±0.50 mm, ±0.50 mm, and ±5.00%. As shown in Fig. 2, it can be confirmed that good aberrations are obtained in all cases.

[0046] (Second Embodiment) Next, the second embodiment will be described by taking as an example a large-aperture imaging lens 200 in FIG. 3, with a total system focal length F=49.3 mm, an F-number of 1.50, and a half angle of view ω=23.3°.

[0047] The imaging lens 200 in this embodiment has a front group G1 and a rear group G2, and is a rear focus type in which the rear group G2 moves relative to the front group G1 and focuses by adjusting the distance between the front group G1 and the rear group G2. The rear group G2 is divided into a first rear group G2A and a second rear group G2B with a diaphragm section STOP in between. Moreover, both the front group G1 and the rear group G2 of the imaging lens 200 have a positive refractive index.

[0048] The lens surfaces of the front group G1, the first rear group G2A, and the second rear group G2B facing the object OJT are each concave toward the object OJT side. According to Figure 3, these include lens surfaces 1, 6, and 14. By facing the concave shape toward the object OJT side in this way, coma aberration can be improved.

[0049] The front group G1 has a concave meniscus lens L9 with its concave shape facing the object OJT side, and a cemented lens L10. The cemented lens L10 is composed of a concave meniscus lens L10f with its convex shape facing the object OJT side, and a biconvex lens L10r cemented to the image surface IMG side of the concave meniscus lens L10f.

[0050] The first rear group G2A has a biconcave lens L11 with its concave shape facing the object OJT side, a biconvex lens L12, and a cemented lens L13. The cemented lens L13 is made up of a convex meniscus lens L13f disposed on the object OBJ side, and a concave meniscus lens L13r cemented to the image plane IMG side of the convex meniscus lens L13f. In this way, the first rear group G2A is composed of at least two positive lenses and two negative lenses, which can reduce coma aberration fluctuations during close-range focusing.

[0051] The diaphragm unit STOP is disposed on the image plane IMG side of the first rear group G2A, and the second rear group G2B is disposed on the image plane IMG side of the diaphragm unit STOP. The second rear group G2B is composed of two cemented lenses L14, a cemented lens L15, and an aspheric lens L16 arranged in this order from the object OBJ side to the image plane IMG side. Also, the aspherical lens L16 has a concave shape toward the object OBJ side. Therefore, the air gap between the image forming surface IMG side of the cemented lens L15 and the object OBJ side of the aspherical lens L16 has a biconvex shape. With this configuration, the biconcave lens L15r, the air gap, and the aspherical lens L16 can have a strong negative power, and the back focus can be shortened while ensuring the image circle. This allows the entire optical system to be made compact. Also, by making the aspherical lens L16 the lens closest to the image forming surface IMG, the light path at each image height can be controlled by the aspherical surface, and the sagittal and meridional field curvatures can be corrected.

[0052] Of the two cemented lenses in the second rear group G2B, the cemented lens L14 is made up of a biconcave lens L14f arranged on the object OBJ side, and a biconvex lens L14r cemented to the image plane IMG side of the biconcave lens L14f. The cemented lens L15 is made up of a biconvex lens L15f arranged on the object OBJ side, and a biconcave lens L15r cemented to the image plane IMG side of the biconvex lens L15f. Therefore, the second rear group G2B has at least a plurality of positive lens components, with negative lenses arranged on both sides of them. In other words, the second rear group G2B has a concave-convex-concave power arrangement, which makes it possible to obtain good aberration characteristics from wide angles to standard angles of view.

[0053] The first rear group G2A has four lenses, and the second rear group G2B has four lenses, excluding the aspheric lens L16. Therefore, the difference in the number of lenses between the first rear group G2A and the second rear group G2B is 0 (one or less). And as shown in Table 5 described later, when fa is the focal length of the first rear group G2A and fb is the focal length of the second rear group G2B, fa / fb = 1.22, and 0.7 ≦ fa / fb ≦ 1.5 is satisfied. That is, by setting the number of lenses and the power of the first rear group G2A and the second rear group G2B under the same conditions, the aberrations generated in the first rear group G2A and the second rear group G2B can be canceled out.

[0054] Table 5 shows a table summarizing various data of the second embodiment.

Table 5

[0055] According to Table 5, ff / fr = 2.10, and 1.7 < ff / fr < 3 is satisfied. Thereby, while maintaining good aberration characteristics, the extension amount of the rear group G2 can be reduced, and the entire optical system can be shortened.

[0056] Also according to Table 5, BF / TTL = 0.18, and BF / TTL < 0.25 is satisfied. Also, BF / f = 0.35, and BF / f < 0.45 is satisfied. Thereby, BF can be shortened with respect to the overall optical length, and a space for arranging the lenses can be secured.

[0057] Subsequently, the lens data of the optical lens system 200 of the second embodiment shown in FIG. 3 are shown in Tables 6 to 8.

[0058]

Table 6

[0059] In Table 6, the radius of curvature R (mm) corresponding to the virtual surface and the lens surface counted from the object OBJ side, the surface interval D (mm) on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens are shown respectively. When it has an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are the values for the d-line (587.56 nm). Also, D is the distance from one surface to the surface with the next number. Furthermore, the blank columns for nd and νd indicate that it is air.

[0060]

Table 7

[0061] Table 7 is a table showing the variable interval between the lenses.

[0062]

Table 8

[0063] Table 8 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the above formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, A12 are the aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders respectively, and H is the distance from the origin on the optical axis. Here, formula 1 is omitted.

[0064] Also, according to Table 6, if the Abbe number of the positive lens of the front group G1 is νdp and the Abbe number of the negative lens is νdn, then νdp > νdn is satisfied. And, among the negative lenses in the front group G1, one satisfies θgF < A. However, θgF refers to the partial dispersion ratio, and A is an expression for anomalous dispersion, as follows. A = -1.62×10-3×νd + 0.64 By setting the conditions of the front group G1 in this way, it is possible to prevent chromatic aberration from occurring within the front group G1.

[0065] According to Table 6, the refractive index difference in the cemented lens L13 of the first rear group G2A is 0.18069, which is 0.15 or more, and the Abbe ratio difference in the cemented lens L13 of the first rear group G2A is 3.04, which is 10 or less. By setting the conditions of the cemented lens L13 of the first rear group G2A as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0066] Furthermore, according to Table 6, the difference in refractive index in the cemented lens L14 of the second rear group G2B is 0.2115, and the difference in refractive index in the cemented lens L15 is 0.22302, both of which are 0.15 or more. By setting the conditions of the cemented lenses L14 and L15 of the second rear group G2B as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0067] Fig. 4 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 4, it can be confirmed that good aberration is obtained for all of them.

[0068] Third embodiment Next, in the third embodiment, a large-aperture imaging lens 300 having a total focal length F=49.1 mm, an F-number of 1.44, and a half angle of view ω=23.4° will be described by way of example in FIG.

[0069] The imaging lens 300 in this embodiment has a front group G1 and a rear group G2, and is a rear focus type in which the rear group G2 moves relative to the front group G1 and focuses by adjusting the distance between the front group G1 and the rear group G2. The rear group G2 is divided into a first rear group G2A and a second rear group G2B with an aperture section STOP in between. Moreover, both the front group G1 and the rear group G2 of the imaging lens 300 have a positive refractive index.

[0070] The lens surfaces of the front group G1, the first rear group G2A, and the second rear group G2B facing the object OJT are each concave toward the object OJT side. According to Figure 5, these include lens surfaces 1, 6, and 15. By facing the concave shape toward the object OJT side in this way, coma aberration can be improved.

[0071] The front group G1 has a concave meniscus lens L17 with its concave shape facing the object OJT side, and a cemented lens L18. The cemented lens L18 is composed of a concave meniscus lens L18f with its convex shape facing the object OJT side, and a biconvex lens L18r cemented to the image surface IMG side of the concave meniscus lens L10f.

[0072] The first rear group G2A has a biconcave lens L19 with its concave shape facing the object OJT side, a convex meniscus lens L20, a biconvex lens L21, and a biconcave lens L22. In this way, the first rear group G2A is composed of at least two positive lenses and two negative lenses, which can reduce coma aberration fluctuations during close-range focusing.

[0073] The diaphragm unit STOP is disposed on the image plane IMG side of the first rear group G2A, and the second rear group G2B is disposed on the image plane IMG side of the diaphragm unit STOP. The second rear group G2B is composed of two cemented lenses L23, a cemented lens L24, and an aspheric lens L25 arranged in this order from the object OBJ side to the image plane IMG side. Also, the aspherical lens L25 has a concave shape toward the object OBJ side. Therefore, the air gap between the image forming surface IMG side of the cemented lens L24 and the object OBJ side of the aspherical lens L25 has a biconvex shape. With this configuration, the biconcave lens L24r, the air gap, and the aspherical lens L25 can have a strong negative power, and the back focus can be shortened while ensuring the image circle. This allows the entire optical system to be made compact. Also, by making the aspherical lens L16 the lens closest to the image forming surface IMG, the ray path at each image height can be controlled by the aspherical surface, and the sagittal and meridional field curvatures can be corrected.

[0074] Of the two cemented lenses in the second rear group G2B, the cemented lens L23 is made up of a biconcave lens L23f arranged on the object OBJ side, and a biconvex lens L23r cemented to the image plane IMG side of the biconcave lens L23f. The cemented lens L24 is made up of a biconvex lens L24f arranged on the object OBJ side, and a biconcave lens L24r cemented to the image plane IMG side of the biconvex lens L24f. Therefore, the second rear group G2B has at least a plurality of positive lens components, with negative lenses arranged on both sides of them. In other words, the second rear group G2B has a concave-convex-concave power arrangement, which makes it possible to obtain good aberration characteristics from wide angles to standard angles of view.

[0075] The first rear group G2A has four lenses, and the second rear group G2B has four lenses, excluding the aspheric lens L25. Therefore, the difference in the number of lenses between the first rear group G2A and the second rear group G2B is 0 (one or less). Furthermore, as shown in Table 9 below, when fa is the focal length of the first rear group G2A and fb is the focal length of the second rear group G2B, fa / fb=1.22, which satisfies 0.7≦fa / fb≦1.5. In other words, by setting the numbers of lenses constituting the first rear group G2A and the second rear group G2B to similar conditions in terms of power, it is possible to cancel out aberrations occurring in the first rear group G2A and the second rear group G2B.

[0076] Table 9 shows a summary of various data for the third embodiment. [Table 9] In Table 9, ff is the focal length of the front group G1, fr is the focal length of the rear group G2, fa is the focal length of the first rear group G2A, fb is the focal length of the second rear group G2B, BF is the distance from the lens surface closest to the image-forming surface to the image-forming surface IMG, TTL is the distance from the lens surface closest to the object to the image-forming surface IMG, and f is the focal length of the entire system.

[0077] According to Table 9, ff / fr = 1.92, which satisfies 1.7 < ff / fr < 3. As a result, while maintaining good aberration characteristics, the extension amount of the rear group G2 can be reduced, and the overall optical system can be shortened.

[0078] Also according to Table 9, BF / TTL = 0.17, which satisfies BF / TTL < 0.25. Also, BF / f = 0.34, which satisfies BF / f < 0.45. As a result, BF can be shortened with respect to the overall optical length, and a space for arranging the lenses can be secured.

[0079] Subsequently, the lens data of the optical lens system 300 of the third embodiment shown in FIG. 5 are shown in Tables 10 to 12.

[0080]

Table 10

[0081] In Table 10, the radius of curvature R (mm) corresponding to the virtual surface and the lens surface counted from the object OBJ side, the distance D (mm) between the surfaces on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens are shown respectively. When having an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are values for the d-line (587.56 nm). Also, D is the distance from one surface to the surface with the next number. Furthermore, the blank spaces for nd and νd indicate that it is air.

[0082]

Table 11

[0083] Table 11 is a table showing the variable interval between the lenses.

[0084]

Table 12

[0085] Table 12 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the above formula (1). In formula (1), R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, and A12 are the aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders respectively, and H is the distance from the origin on the optical axis. Here, formula (1) is omitted.

[0086] Also, according to Table 10, when the Abbe number of the positive lens in the front group G1 is νdp and the Abbe number of the negative lens is νdn, νdp > νdn is satisfied. And, one of the negative lenses in the front group G1 satisfies θgF < A. However, θgF refers to the partial dispersion ratio, and A is an expression of anomalous dispersion, as follows. A = -1.62×10 - 3×νd + 0.64 By setting the conditions of the front group G1 in this way, the occurrence of chromatic aberration within the front group G1 can be prevented.

[0087] Also, according to Table 10, the difference in refractive index in the cemented lens L23 of the second rear group G2B is 0.2115, and the difference in refractive index in the cemented lens L24 is 0.22302, each being 0.15 or more. By setting the conditions of the cemented lenses L23 and L24 of the second rear group G2B in this way, the Petzval sum can be reduced and the field curvature can be corrected well.

[0088] Figure 6 shows the spherical aberration, coma aberration, and distortion aberration in the optical lens system 200. Each scale is ±0.50 mm, ±0.50 mm, ±5.00%. As shown in Figure 6, it can be confirmed that good aberrations are obtained in all cases.

[0089] (Fourth Embodiment) Subsequently, in the fourth embodiment, a large-aperture imaging lens 400 with a focal length F = 48.5 mm, an F-number of 1.44, and a semi-field angle ω = 23.8° in the entire system will be illustrated and described with reference to FIG. 7.

[0090] The imaging lens 400 in this embodiment has a front group G1 and a rear group G2, and is a rear focus type in which the rear group G2 moves relative to the front group G1 and focuses by adjusting the distance between the front group G1 and the rear group G2. The rear group G2 is divided into a first rear group G2A and a second rear group G2B with a diaphragm section STOP in between. Moreover, both the front group G1 and the rear group G2 of the imaging lens 400 have a positive refractive index.

[0091] The lens surfaces of the front group G1, the first rear group G2A, and the second rear group G2B facing the object OJT have a concave shape toward the object OJT side. According to Figure 7, these are lens surfaces 1, 6, and 14. By facing the concave shape toward the object OJT side in this way, coma aberration can be improved.

[0092] The front group G1 has a concave meniscus lens L26 with its concave shape facing the object OJT side, and a cemented lens L27. The cemented lens L27 consists of a concave meniscus lens L27f with its convex shape facing the object OJT side, and a biconvex lens L27r cemented to the image surface IMG side of the concave meniscus lens L27f.

[0093] The first rear group G2A has a biconcave lens L28 with its concave shape facing the object OJT side, a biconvex lens L29, and a cemented lens L30. The cemented lens L30 is made up of a biconcave lens L30f disposed on the object OBJ side and a biconvex lens L30r cemented to the coupling surface IMG side of the biconcave lens L30f. In this way, the first rear group G2A is composed of at least two positive lenses and two negative lenses, which can reduce coma aberration fluctuations during close-range focusing.

[0094] The diaphragm unit STOP is disposed on the image plane IMG side of the first rear group G2A, and the second rear group G2B is disposed on the image plane IMG side of the diaphragm unit STOP. The second rear group G2B is arranged in this order from the object OBJ side to the image plane IMG side: a cemented lens L31, a biconvex lens L32, a cemented lens L33, and an aspheric lens L34. Also, the aspherical lens L34 has a concave shape toward the object OBJ side. Therefore, the air gap between the image forming surface IMG side of the cemented lens L33 and the object OBJ side of the aspherical lens L34 has a biconvex shape. With this configuration, the biconcave lens L33, the air gap, and the aspherical lens L34 can have a strong negative power, and the back focus can be shortened while ensuring the image circle. This allows the entire optical system to be made compact. Also, by making the aspherical lens L34 the lens closest to the image forming surface IMG, the light path at each image height can be controlled by the aspherical surface, and the sagittal and meridional field curvatures can be corrected.

[0095] Of the two cemented lenses in the second rear group G2B, the cemented lens L31 is made up of a biconcave lens L31f arranged on the object OBJ side, and a biconvex lens L31r cemented to the image plane IMG side of the biconcave lens L31f. The cemented lens L33 is made up of a biconvex lens L33f arranged on the object OBJ side and a biconcave lens L33r cemented to the image plane IMG side of the biconvex lens L33f. In addition, a biconvex lens L32 is disposed between the cemented lens L31 and the cemented lens L33. Therefore, the second rear group G2B has at least a plurality of positive lens components, with negative lenses arranged on both sides of them. In other words, the second rear group G2B has a concave-convex-concave power arrangement, which makes it possible to obtain good aberration characteristics from wide angles to standard angles of view.

[0096] The first rear group G2A has four lenses, and the second rear group G2B has five lenses, excluding the aspheric lens L34. Therefore, the difference in the number of lenses between the first rear group G2A and the second rear group G2B is one lens. Furthermore, as shown in Table 13 below, when fa is the focal length of the first rear group G2A and fb is the focal length of the second rear group G2B, fa / fb=1.05, which satisfies 0.7≦fa / fb≦1.5. In other words, by setting the numbers of lenses constituting the first rear group G2A and the second rear group G2B to similar conditions in terms of power, it is possible to cancel out aberrations occurring in the first rear group G2A and the second rear group G2B.

[0097] Table 13 shows a table summarizing various data of the fourth embodiment.

Table 13

[0098] According to Table 13, ff / fr = 2.05, which satisfies 1.7 < ff / fr < 3. Thereby, while maintaining good aberration characteristics, the extension amount of the rear group G2 can be reduced, and the entire optical system can be shortened.

[0099] Also according to Table 13, BF / TTL = 0.16, which satisfies BF / TTL < 0.25. Also, BF / f = 0.33, which satisfies BF / f < 0.45. Thereby, BF can be shortened with respect to the overall optical length, and a space for arranging the lens can be secured.

[0100] Subsequently, the lens data of the optical lens system 400 of the fourth embodiment shown in FIG. 7 are shown in Tables 14 to 16.

[0101]

Table 14

[0102] In Table 14, the radius of curvature R (mm), the distance D (mm) between surfaces on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens corresponding to the virtual surface and the lens surface counted from the object OBJ side are shown respectively. When having an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are values for the d-line (587.56 nm). Also, D is defined as the distance from one surface to the surface with the next number. Furthermore, the blanks for nd and νd indicate that they are air.

[0103]

Table 15

[0104] Table 15 is a table showing the variable interval between the lenses.

[0105]

Table 16

[0106] Table 16 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the above formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, A12 are the aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders respectively, and H is the distance from the origin on the optical axis. Here, formula 1 is omitted.

[0107] Also, according to Table 14, if the Abbe number of the positive lens in the front group G1 is νdp and the Abbe number of the negative lens is νdn, then νdp > νdn is satisfied. And, among the negative lenses in the front group G1, one satisfies θgF < A. However, θgF refers to the partial dispersion ratio, and A is an expression for anomalous dispersivity, as follows. A = -1.62×10 - 3×νd + 0.64 By setting the conditions of the front group G1 in this way, the occurrence of chromatic aberration within the front group G1 can be prevented.

[0108] According to Table 14, the difference in refractive index in the cemented lens L30 of the first rear group G2A is 0.18069, which is 0.15 or more, and the difference in Abbe ratio in the cemented lens L30 of the first rear group G2A is 3.04, which is 10 or less. By setting the conditions of the cemented lens L30 of the first rear group G2A as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0109] Furthermore, according to Table 14, the difference in refractive index in the cemented lens L31 of the second rear group G2B is 0.2115, and the difference in refractive index in the cemented lens L33 is 0.2214, both of which are 0.15 or more. By setting the conditions of the cemented lenses L31 and L33 of the second rear group G2B as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0110] Fig. 8 shows the spherical aberration, astigmatism, and distortion in the optical lens system 200. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 8, it can be confirmed that good aberration is obtained for all of them.

[0111] Fifth embodiment Next, in the fifth embodiment, a large-aperture imaging lens 500 having a total system focal length F=48.5 mm, an F-number of 1.43, and a half angle of view ω=23.7° will be described by way of example in FIG.

[0112] The imaging lens 500 in this embodiment has a front group G1 and a rear group G2, and is a floating focus type in which the front group G1 and the rear group G2 move and adjust the distance between the front group G1 and the rear group G2 to achieve focusing. The rear group G2 is divided into a first rear group G2A and a second rear group G2B with an aperture section STOP in between. Moreover, both the front group G1 and the rear group G2 of the imaging lens 500 have a positive refractive index.

[0113] The lens surfaces of the front group G1, the first rear group G2A, and the second rear group G2B facing the object OJT have a concave shape toward the object OJT side. According to Figure 9, these are lens surfaces 1, 6, and 14. By facing the concave shape toward the object OJT side in this way, coma aberration can be improved.

[0114] The front group G1 has a concave meniscus lens L35 with its concave shape facing the object OJT side, and a cemented lens L36. The cemented lens L36 is composed of a concave meniscus lens L36f with its convex shape facing the object OJT side, and a biconvex lens L36r cemented to the image surface IMG side of the concave meniscus lens L36f.

[0115] The first rear group G2A has a biconcave lens L37 with its concave shape facing the object OJT side, a biconvex lens L38, and a cemented lens L39. The cemented lens L39 is made up of a biconcave lens L39f disposed on the object OBJ side and a biconvex lens L39r cemented to the coupling surface IMG side of the biconcave lens L39f. In this way, the first rear group G2A is composed of at least two positive lenses and two negative lenses, which can reduce coma aberration fluctuations during close-range focusing.

[0116] The diaphragm unit STOP is disposed on the image plane IMG side of the first rear group G2A, and the second rear group G2B is disposed on the image plane IMG side of the diaphragm unit STOP. The second rear group G2B is composed of two cemented lenses L40, a cemented lens L41, and an aspheric lens L42 arranged in this order from the object OBJ side to the image plane IMG side. Also, the aspherical lens L42 has a concave shape toward the object OBJ side. Therefore, the air gap between the image forming surface IMG side of the cemented lens L41 and the object OBJ side of the aspherical lens L42 has a biconvex shape. With this configuration, the biconcave lens L41r, the air gap, and the aspherical lens L42 can have a strong negative power, and the back focus can be shortened while ensuring the image circle. This allows the entire optical system to be made compact. Also, by making the aspherical lens L42 the lens closest to the image forming surface IMG, the ray path at each image height can be controlled by the aspherical surface, and the sagittal and meridional field curvatures can be corrected.

[0117] Of the two cemented lenses in the second rear group G2B, the cemented lens L40 is made up of a biconcave lens L40f arranged on the object OBJ side, and a biconvex lens L40r cemented to the image plane IMG side of the biconcave lens L40f. The cemented lens L41 is made up of a biconvex lens L41f arranged on the object OBJ side and a biconcave lens L41r cemented to the image plane IMG side of the biconvex lens L41f. Therefore, the second rear group G2B has at least a plurality of positive lens components, with negative lenses arranged on both sides of them. In other words, the second rear group G2B has a concave-convex-concave power arrangement, which makes it possible to obtain good aberration characteristics from wide angles to standard angles of view.

[0118] The first rear group G2A has four lenses, and the second rear group G2B has four lenses, excluding the aspheric lens L34. Therefore, the difference in the number of lenses between the first rear group G2A and the second rear group G2B is 0 (one or less). Furthermore, as shown in Table 17 below, when fa is the focal length of the first rear group G2A and fb is the focal length of the second rear group G2B, fa / fb=1.44, which satisfies 0.7≦fa / fb≦1.5. In other words, by setting the numbers of lenses constituting the first rear group G2A and the second rear group G2B to similar conditions in terms of power, it is possible to cancel out aberrations occurring in the first rear group G2A and the second rear group G2B.

[0119] Table 17 shows a table summarizing various data of the fifth embodiment.

Table 17

[0120] According to Table 17, ff / fr = 2.66, which satisfies 1.7 < ff / fr < 3. As a result, while maintaining good aberration characteristics, the extension amount of the rear group can be reduced, and the entire optical system can be shortened.

[0121] Also according to Table 17, BF / TTL = 0.19, which satisfies BF / TTL < 0.25. Also, BF / f = 0.37, which satisfies BF / f < 0.45. As a result, BF can be shortened with respect to the overall optical length, and a space for arranging the lenses can be secured.

[0122] Subsequently, the lens data of the optical lens system 500 of the fifth embodiment shown in FIG. 9 are shown in Tables 18 to 20.

[0123]

Table 18

[0124] In Table 18, the radius of curvature R (mm), the distance D (mm) between surfaces on the optical axis, the refractive index nd of the lens, and the Abbe number νd of the lens corresponding to the virtual surface and the lens surface counted from the object OBJ side are shown respectively. When having an aspherical shape, it is represented by * in the ASP column. When the lens surface is convex with respect to the object OBJ, the radius of curvature R is positive, and when the lens surface is concave with respect to the object OBJ, the radius of curvature R is negative. Also, nd and νd are values for the d-line (587.56 nm). Also, D is defined as the distance from one surface to the next numbered surface. Furthermore, the blanks for nd and νd indicate that they are air.

[0125]

Table 19

[0126] Table 19 is a table showing the variable interval between the lenses.

[0127]

Table 20

[0128] Table 20 shows the surface shape (aspherical coefficient) of the aspherical lens. In this case, in the orthogonal coordinate system (X, Y, Z) with the center of the surface as the origin and the optical axis direction as Z, Z is defined by the above formula 1. In formula 1, R is the radius of curvature, K is the conic constant, A4, A6, A8, A10, A12 are the aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders respectively, and H is the distance from the origin on the optical axis. Here, formula 1 is omitted.

[0129] Also, according to Table 18, if the Abbe number of the positive lens in the front group G1 is νdp and the Abbe number of the negative lens is νdn, then νdp > νdn is satisfied. And, among the negative lenses in the front group G1, one satisfies θgF < A. However, θgF refers to the partial dispersion ratio, and A is an expression for anomalous dispersion, as follows. A = -1.62×10-3×νd + 0.64 By setting the conditions of the front group G1 in this way, it is possible to prevent the occurrence of chromatic aberration within the front group G1.

[0130] Also, according to Table 18, the difference in refractive index in the cemented lens L39 of the first rear group G2A is 0.18069, which is 0.15 or more. The difference in Abbe number in the cemented lens L39 of the first rear group G2A is 3.04, which is 10 or less. By setting the conditions of the cemented lens L39 of the first rear group G2A as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0131] Furthermore, according to Table 18, the difference in refractive index in the cemented lens L40 of the second rear group G2B is 0.2108, and the difference in refractive index in the cemented lens L41 is 0.2230, both of which are 0.15 or more. By setting the conditions of the cemented lenses L40 and L41 of the second rear group G2B as described above, the Petzval sum can be made small and the curvature of field can be corrected satisfactorily.

[0132] Fig. 10 shows spherical aberration, astigmatism, and distortion in the optical lens system 500. The scales are ±0.50 mm, ±0.50 mm, and ±5.00%, respectively. As shown in Fig. 10, it can be confirmed that good aberration is obtained for all of them.

[0133] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the scope of the present invention. [Explanation of symbols]

[0134] 100 Optical lens system 200 Optical Lens System 300 Optical Lens System 400 Optical Lens System 500 Optical Lens System G1 front group G2 rear group G2A 1st rear group G2B 2nd rear group L1 concave meniscus lens L2 cemented lens L2f concave meniscus lens L2r Biconvex Lens L3 Biconcave Lens L4 biconvex lens L5 cemented lens L5f biconcave lens L5r biconvex lens L6 cemented lens L6f biconcave lens L6r Biconvex Lens L7 cemented lens L7f biconvex lens L7r Biconcave Lens L8 Aspheric Lens L9 concave meniscus lens L10 cemented lens L10f concave meniscus lens L10r Biconvex Lens L11 Biconcave Lens L12 biconvex lens L13 cemented lens L13f Convex meniscus lens L13r concave meniscus lens L14 cemented lens L14f biconcave lens L14r Biconvex Lens L15 cemented lens L15f biconvex lens L15r Biconcave Lens L16 Aspheric Lens L17 concave meniscus lens L18 cemented lens L18f concave meniscus lens L18r biconvex lens L19 Biconcave Lens L20 Convex meniscus lens L21 Biconvex lens L22 biconcave lens L23 cemented lens L23f Biconcave Lens L23r Biconvex Lens L24 cemented lens L24f biconvex lens L24r Biconcave Lens L25 aspheric lens L26 concave meniscus lens L27 cemented lens L27f concave meniscus lens L27r Biconvex Lens L28 Biconcave Lens L29 Biconvex Lens L30 cemented lens L30f biconcave lens L30r Biconvex Lens L31 cemented lens L31f biconcave lens L31r Biconvex Lens L32 biconvex lens L33 cemented lens L33f biconvex lens L33r Biconcave Lens L34 Aspheric Lens L35 concave meniscus lens L36 cemented lens L36f concave meniscus lens L36r Biconvex Lens L37 Biconcave Lens L38 biconvex lens L39 cemented lens L39f biconcave lens L39r Biconvex Lens L40 cemented lens L40f biconcave lens L40r biconvex lens L41 cemented lens L41f biconvex lens L41r Biconcave Lens L42 Aspheric Lens STOP Squeezing section OBJ object IMG Image plane

Claims

1. An optical lens system in which a front group and a rear group are disposed in this order from an object side to an image side, and a distance between the front group and the rear group is changed during focusing, the front group has positive refractive power, the rear group has positive refractive power and is divided into a first rear group and a second rear group before and after the aperture stop; an optical lens system, wherein the lens surfaces of said front group, said first rear group and said second rear group closest to the object side are each concave toward the object side.

2. 2. The optical lens system according to claim 1, wherein the second rear group comprises two pairs of cemented lenses and an aspherical lens closest to the image side, and the shape of the air space on the object side of the aspherical lens is biconvex.

3. the difference between the number of lenses in the second rear group excluding the aspherical lens and the number of lenses in the first rear group is one or less, When the focal length of the first rear lens unit is fa and the focal length of the second rear lens unit is fb, 0.7≦fa / fb≦1.5 3. The optical lens system according to claim 2, wherein the following is satisfied:

4. the second rear group has a plurality of positive lens components, 3. The optical lens system according to claim 1, further comprising a negative lens disposed on both sides of said plurality of positive lens components.

5. If the Abbe number of the positive lens in the front group is νdp and the Abbe number of the negative lens in the front group is νdn, then 2. The optical lens system according to claim 1, wherein vdp>vdn is satisfied, and at least one of the negative lenses satisfies θgF<A. where θgF refers to the partial dispersion ratio, A refers to the anomalous dispersion formula: A=-1.62×10 －３ ×νd+0.64

6. the first rear group includes at least two positive lenses and one negative lens, 2. The optical lens system according to claim 1, further comprising a biconcave lens and a positive lens arranged in this order from the most object side.

7. 2. The optical lens system according to claim 1, wherein a cemented lens is disposed in the first rear group, the difference in refractive index of the cemented lens being 0.15 or more and the difference in vd being 10 or less.

8. 2. The optical lens system according to claim 1, wherein a cemented lens is disposed in the second rear group, and a difference in refractive index of the cemented lens is 0.15 or more.

9. When the focal length of the front group is ff and the focal length of the rear group is fr, 1.7<ff / fr<3 2. The optical lens system according to claim 1, wherein the following is satisfied:

10. When the focal length of the entire system is f, the distance on the optical axis from the lens surface closest to the object side to the image forming position is TTL, and the distance on the optical axis from the lens surface closest to the image side to the image forming position is BF, BF / TTL<0.25 BF / f<0.45 2. The optical lens system according to claim 1, wherein the following is satisfied:

Images