Optical system and imaging device having the same

Abstract

There is a need to provide an optical system that is small, lightweight, and has good correction for various aberrations. [Solution] The optical system is an optical system consisting of a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, and satisfies predetermined conditions.

Description

[Technical Field]

[0001] The present invention relates to an optical system and is suitable for imaging devices such as digital video cameras, digital still cameras, broadcast cameras, and silver halide film cameras. [Background technology]

[0002] Optical systems suitable for digital video cameras and digital still cameras have been proposed for some time. For example, see Patent Document 1. In such optical systems, there is a need for a system that is small, lightweight, and has good correction of various aberrations. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-157964 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] There is a need to provide an optical system that is small, lightweight, and has good correction for various aberrations. [Means for solving the problem]

[0005] An optical system as one aspect of the present invention is an optical system consisting of a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, wherein the front group has a positive lens Gp1 positioned closest to the object, and the rear group has a negative lens Gn, and when the focal length of the entire system is f, the back focus is sk, the refractive index and Abbe number of the material of the negative lens Gn with respect to the d line are Ndn and νdn respectively, the distance on the optical axis from the lens surface closest to the object to the image plane of the optical system is TL, and the distance on the optical axis from the lens surface of the negative lens Gn to the image plane is Ln, 0.01 <sk / f<0.40 2.160 <Ndn+0.02174×νdn<2.320 1.600 <Ndn<1.850 0.10 <Ln / TL<0.40 It is characterized by satisfying the following conditional expression.

[0006] Another aspect of the present invention is an optical system comprising a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, wherein the front group has two or more positive lenses, and the rear group has two or more negative lenses, and when the focal length of the entire system is f and the back focus is sk, 0.10 <sk / f<0.40 It is characterized by satisfying the following conditional expression. [Effects of the Invention]

[0007] According to the above-described method, it is possible to provide an optical system that is small, lightweight, and has good correction of various aberrations. [Brief explanation of the drawing]

[0008] [Figure 1] Cross-sectional view of the lens when the optical system of Example 1 is focused to infinity. [Figure 2] Aberration diagram when the optical system of Example 1 is focused to infinity. [Figure 3] Cross-sectional view of the lens when focused to infinity in the optical system of Example 2. [Figure 4] Aberration diagram when the optical system of Example 2 is focused to infinity. [Figure 5] Cross-sectional view of the lens when focused to infinity in the optical system of Example 3. [Figure 6] Aberration diagram when the optical system of Example 3 is focused to infinity. [Figure 7] Cross-sectional view of the lens when focused to infinity in the optical system of Example 4. [Figure 8] Aberration diagram when the optical system of Example 4 is focused to infinity. [Figure 9] Schematic diagram showing the imaging device

Embodiment for Carrying Out the Invention

[0009] Hereinafter, examples of the optical system according to the embodiment of the present invention and an imaging device having the same will be described based on the accompanying drawings.

[0010] FIGS. 1, 3, 5, and 7 are lens cross-sectional views when focusing at infinity in the optical systems L0 of Examples 1 to 4, respectively. The optical system L0 of each example is an optical system used in an imaging device such as a digital video camera, a digital still camera, a broadcast camera, a silver halide film camera, a surveillance camera, an in-vehicle camera, or the like.

[0011] In each lens cross-sectional view, the left side is the object side and the right side is the image side. Note that the optical system L0 of each example may be used as a projection lens for a projector or the like. In this case, the left side is the screen side and the right side is the side of the projected image.

[0012] In each lens cross-sectional view, SP is the aperture stop. IP is the image plane. When the optical system L0 of each example is used in a digital still camera or a digital video camera, the imaging surface of a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is arranged at the image plane. When the optical system L0 of each example is used as the imaging optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed at the image plane IP.

[0013] The optical system L0 of each example includes a front group La, an aperture stop SP, and a rear group Lb, which are arranged in order from the object side to the image side. The front group La and the rear group Lb may be composed of one lens or a plurality of lenses.

[0014] The solid arrow shown downward in each lens cross-sectional view represents the movement locus of one or more lenses during focusing from infinity to the closest distance.

[0015] FIGS. 2, 4, 6, and 8 are aberration diagrams when focusing at infinity in the optical systems L0 of Examples 1 to 4, respectively.

[0016] In the spherical aberration diagram, Fno is the F-number and indicates the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, Sagi indicates the aberration ΔS at the sagittal image plane, and Meri indicates the aberration ΔM at the meridional image plane. The distortion diagram shows the amount of distortion for the d-line. The chromatic aberration diagram shows the amount of lateral chromatic aberration for the g-line. ω is the half-angle of view (°).

[0017] Here, the Abbe number νd is known as a parameter related to the correction of chromatic aberration in optical systems. When the refractive indices of the material for the F line (486.1 nm), C line (656.3 nm), and d line (587.6 nm) are NF, NC, and Nd, respectively, the Abbe number νd is expressed by the following formula. νd = (Nd-1) / (NF-NC)

[0018] Next, we will describe the optical system L0 according to the first embodiment.

[0019] The optical system L0 according to the first embodiment consists of a front group La, an aperture diaphragm SP, and a rear group Lb, arranged in order from the object side to the image side. The front group La has a positive lens Gp1 positioned closest to the object, and the rear group Lb has a negative lens Gn. This configuration makes it easy to position the principal point of the optical system L0 on the object side, and makes it easy to shorten the overall lens length. Here, the overall lens length is the sum of the distance along the optical axis from the lens surface closest to the object to the surface closest to the image in the optical system L0, and the back focus. Here, the back focus is the distance along the optical axis between the lens surface closest to the image and the image plane in the optical system L0, converted to an air distance.

[0020] The optical system L0 according to the first embodiment is configured to satisfy the following condition. 0.01 <sk / f<0.40···(1) 2.160 <Ndn+0.02174×νdn<2.320···(2) 1.600 <Ndn<1.850···(3) 0.10 <Ln / TL<0.40···(4)

[0021] Here, f is the focal length of the entire system, and sk is the back focus. Ndn and νdn are the refractive index and Abbe number of the negative lens Gn material with respect to the d line, respectively. TL is the distance along the optical axis from the lens surface closest to the object to the image plane of the optical system L0. Ln is the distance along the optical axis from the lens surface closest to the object to the image plane of the negative lens Gn.

[0022] If the back focus exceeds the upper limit of condition (1), the overall length of the lens increases, which is undesirable. If it falls below the lower limit of condition (1), the back focus becomes too short. As a result, when an image sensor is positioned, the intensity of ghost light generated by reflection between the image sensor and the lens positioned closest to the image in the optical system L0 becomes strong, which is undesirable.

[0023] If the Abbe number of the negative lens Gn material increases beyond the upper limit of condition (2), then low-dispersion glass must be selected as the negative lens Gn material. As a result, the partial dispersion ratio between the g-line and the F-line becomes small, and the refractive index for the g-line becomes too small. Consequently, chromatic aberration between the g-line and the F-line becomes too large, which is undesirable.

[0024] Here, the partial dispersion ratio θgf of the g-line and the F-line is expressed by the following formula, where the g-line wavelength is 435.8 nm and the F-line wavelength is 486.1 nm. θgf = (Ng - NF) / (NF - NC)

[0025] If the Abbe number of the negative lens Gn material falls below the lower limit of condition (2), it is undesirable because the chromatic aberration between the F and C lines becomes too large.

[0026] If the refractive index of the negative lens Gn with respect to the d line exceeds the upper limit of condition (3), the reflectivity of the lens surface of the negative lens Gn increases, which is undesirable as it tends to increase the intensity of ghost light.

[0027] If the refractive index of the negative lens Gn with respect to the d line falls below the lower limit of condition (3), the absolute value of the curvature of at least one of the object-side lens surface and the image-side lens surface of the negative lens Gn becomes too large. As a result, the edge thickness of the negative lens Gn becomes thicker, and the overall length of the lens tends to increase, which is undesirable.

[0028] If the negative lens Gn is positioned on the object side beyond the upper limit of condition (4), the height of the off-axis rays passing through the negative lens Gn from the optical axis becomes too low, making it difficult to correct chromatic aberration.

[0029] If the negative lens Gn is positioned on the image side below the lower limit of condition (4), it is undesirable because, when an image sensor is positioned, ghost light generated by reflection between the image sensor and the negative lens Gn is more likely to be concentrated on the image sensor.

[0030] By satisfying the above configuration, the optical system L0 according to the first embodiment becomes compact and easily corrects various aberrations well.

[0031] Furthermore, it is preferable that the conditions (1), (2), (3), and (4) are set to the following conditions, respectively. 0.05 <sk / f<0.35···(1a) 2.180 <Ndn+0.02174×νdn<2.310···(2a) 1.610 <Ndn<1.820···(3a) 0.150 <Ln / TL<0.380···(4a)

[0032] Furthermore, it is preferable that the conditional expressions (1), (2), (3), and (4) are set to the following conditions, respectively. 0.10 <sk / f<0.28···(1b) 2.250 <Ndn+0.02174×νdn<2.300···(2b) 1.620 <Ndn<1.800···(3b) 0.180 <Ln / TL<0.350···(4b)

[0033] Next, we will describe the optical system L0 according to the second embodiment.

[0034] The optical system L0 according to the second embodiment consists of a front group La, an aperture diaphragm SP, and a rear group Lb, arranged in order from the object side to the image side. The front group La has two or more positive lenses, and the rear group Lb has two or more negative lenses. This configuration makes it easy to strengthen the positive refractive power of the front group La and the negative refractive power of the rear group Lb, so that the principal point of the optical system L0 is located on the object side, and it is easy to shorten the overall length of the lenses.

[0035] The optical system L0 according to the second embodiment is configured to satisfy the following condition. 0.01 <sk / f<0.40···(1)

[0036] Here, f is the focal length of the entire system, and sk is the back focus.

[0037] If the back focus exceeds the upper limit of condition (1), the overall length of the lens becomes longer, which is undesirable. If it falls below the lower limit of condition (1), the back focus becomes too short. As a result, when an image sensor is positioned, the intensity of ghost light generated by reflection between the image sensor and the lens positioned closest to the image in the optical system L0 becomes stronger, which is undesirable.

[0038] By satisfying the above configuration, the optical system L0 according to the second embodiment becomes compact and easily corrects various aberrations well.

[0039] By satisfying the above configuration, the optical system L0 according to the second embodiment becomes compact and easily corrects various aberrations well.

[0040] Furthermore, it is preferable that condition (1) be set to the following conditions. 0.05 <sk / f<0.35···(1a)

[0041] Furthermore, it is preferable that condition (1) be set to the following conditions. 0.10 <sk / f<0.28···(1b)

[0042] Furthermore, in the optical system L0 according to the second embodiment, it is preferable that at least one of the negative lenses arranged in the rear group Lb is a negative lens Gn, and that at least one of the following conditional expressions is satisfied. 2.160 <Ndn+0.02174×νdn<2.320···(2) 1.600 <Ndn<1.850···(3) 0.10 <Ln / TL<0.40···(4)

[0043] Here, Ndn and νdn are the refractive index and Abbe number of the negative lens Gn material with respect to the d line, respectively. TL is the distance along the optical axis from the lens surface closest to the object to the image plane in the optical system L0. Ln is the distance along the optical axis from the lens surface on the object side of the negative lens Gn to the image plane.

[0044] If the Abbe number of the negative lens Gn material increases beyond the upper limit of condition (2), then low-dispersion glass must be selected as the negative lens Gn material. As a result, the partial dispersion ratio between the g-line and the F-line becomes small, and the refractive index for the g-line becomes too small. Consequently, chromatic aberration between the g-line and the F-line becomes too large, which is undesirable.

[0045] Here, the partial dispersion ratio θgf of the g-line and the F-line is expressed by the following formula, where the g-line wavelength is 435.8 nm and the F-line wavelength is 486.1 nm. θgf = (Ng - NF) / (NF - NC)

[0046] If the Abbe number of the negative lens Gn material falls below the lower limit of condition (2), it is undesirable because the chromatic aberration between the F and C lines becomes too large.

[0047] If the refractive index of the negative lens Gn with respect to the d line exceeds the upper limit of condition (3), the reflectivity of the lens surface of the negative lens Gn increases, which is undesirable as it tends to increase the intensity of ghost light.

[0048] If the refractive index of the negative lens Gn with respect to the d line falls below the lower limit of condition (3), the absolute value of the curvature of at least one of the object-side lens surface and the image-side lens surface of the negative lens Gn becomes too large. As a result, the edge thickness of the negative lens Gn becomes thicker, and the overall length of the lens tends to increase, which is undesirable.

[0049] If the negative lens Gn is positioned on the object side beyond the upper limit of condition (4), the height of the off-axis rays passing through the negative lens Gn from the optical axis becomes too low, making it difficult to correct chromatic aberration.

[0050] If the negative lens Gn is positioned on the image side below the lower limit of condition (4), it is undesirable because, when an image sensor is positioned, ghost light generated by reflection between the image sensor and the negative lens Gn is more likely to be concentrated on the image sensor.

[0051] Furthermore, it is preferable that conditional expressions (2), (3), and (4) be set to the following conditions, respectively. 2.180 <Ndn+0.02174×νdn<2.310···(2a) 1.610 <Ndn<1.820···(3a) 0.150 <Ln / TL<0.380···(4a)

[0052] Furthermore, it is preferable that conditional expressions (2), (3), and (4) are set to the following conditions, respectively. 2.250 <Ndn+0.02174×νdn<2.300···(2b) 1.620 <Ndn<1.800···(3b) 0.180 <Ln / TL<0.350···(4b)

[0053] Furthermore, in the optical system L0 according to the first or second embodiment, multiple negative lenses Gn satisfying conditions (2) and (3) may be arranged in the rear group Lb. Arranging multiple lenses makes it easier to suppress chromatic aberration and the like.

[0054] Next, preferred configurations of the optical system L0 according to each embodiment will be described.

[0055] The front group La preferably consists of a first subgroup B1p having positive refractive power and a second subgroup B1n having negative refractive power, arranged in order from the object side to the image side. This makes it easier to position the principal point of the optical system L0 on the object side and to shorten the overall length of the lens.

[0056] When focusing from infinity to near, it is preferable that the first subgroup B1p remains stationary and the second subgroup B1n moves integrally toward the image. As the on-axial light beam passes through the first subgroup B1p, which has positive refractive power, the on-axial light beam converges. Therefore, the second subgroup B1n is positioned at the position where the on-axial light beam converges, and thus the diameter of the lens positioned in the second subgroup B1n becomes relatively small.

[0057] In other words, by designating the group that moves together during focusing from infinity to near as the second subgroup B1n, it becomes easier to miniaturize the group that moves during focusing.

[0058] In the front group La, it is preferable that the lens positioned closest to the object and the second-to-last lens from the object have positive refractive power. These two lenses converge the axial light beam, making it easier to reduce the diameter of each lens positioned closer to the image than the second-to-last lens from the object.

[0059] The rear group Lb preferably has a third subgroup B3 that moves integrally during focusing. Since the diameter of the lenses arranged in the rear group Lb is relatively small, the movement of the third subgroup B3 during focusing makes it easy to miniaturize the group that moves during focusing.

[0060] In each embodiment, the optical system L0 preferably satisfies one or more of the following conditional expressions. -1.50 <fGn / f<-0.05···(5) -1.0 × 10-5 / ℃ <dGn<-1.0×10 -7 / ℃···(6) 0.85 <Ndn / Ndp3<1.10···(7) 0.30 < νdn / νdp3 < 0.90 ... (8) 0.85 < |fGn / fGp3| < 4.50 ···(9) 1.700 <Ndp2<2.200···(10) 15.0 < νdp2 < 23.0 ... (11) 0.30 <fB1p / f<1.80···(12) 0.20 <Ln / Ls<0.80···(13) 2.0 < 2ωSL < 40.0 ···(14)

[0061] Here, fGn is the focal length of the negative lens Gn, and dGn is the temperature coefficient of the negative lens Gn at 20°C. The temperature coefficient of the refractive index is expressed as dn / dT, where n is the refractive index and T is the temperature.

[0062] In the rear group Lb, when the negative lens Gn is joined with the positive lens Gp3, Ndp3 and νdp3 are the refractive index and Abbe number of the material of the positive lens Gp3 in the rear group Lb, respectively, at the d line. fGp3 is the focal length of the positive lens Gp3.

[0063] In the second subgroup B1n, when the lens Gp2 positioned closest to the object has a positive refractive power, Ndp2 and νdp2 are the refractive index and Abbe number of the lens Gp2 material at the d line, respectively. fB1p is the focal length of the first subgroup B1p, Ls is the distance along the optical axis from the aperture diaphragm SP to the image plane, and 2ωSL is the total angle of view when the optical system L0 is focused at infinity.

[0064] Next, we will explain the technical meaning of the aforementioned conditional equations (5) to (15).

[0065] If the refractive power of the negative lens Gn becomes too strong, exceeding the upper limit of condition (5), it is undesirable because the distortion aberrations generated by the negative lens Gn become too large. If the refractive power of the negative lens Gn becomes too weak, falling below the lower limit of condition (5), it is undesirable because the principal point of the optical system L0 tends to be positioned on the image side, and the overall length of the lens increases.

[0066] Conditional equation (6) specifies the change in refractive index of the negative lens Gn with respect to temperature. If the change in refractive index of the negative lens Gn with respect to temperature is small, exceeding the upper limit of conditional equation (6), it becomes difficult to reduce the change in focus position and aberrations due to the change in refractive index of the positive lens placed in the optical system L0 with respect to temperature, which is undesirable.

[0067] If the change in refractive index of the negative lens Gn with respect to temperature is large, below the lower limit of condition (6), it is undesirable because the change in focal position and aberration caused by temperature changes in the negative lens Gn will become too large.

[0068] If the refractive index of the material of the positive lens Gp3 is small, exceeding the upper limit of condition (7), the Petzval sum of the entire system will increase. As a result, it becomes difficult to correct the field curvature, which is undesirable.

[0069] If the refractive index of the negative lens Gn material is small, below the lower limit of condition (7), the absolute value of the curvature on at least one side of the negative lens Gn—either the object side or the image plane side—becomes too strong, making it difficult to correct distortion and other aberrations.

[0070] If the Abbe number of the material of the positive lens Gp3 is small, exceeding the upper limit of condition (8), the chromatic aberration generated in the positive lens Gp3 becomes too large, which is undesirable.

[0071] If the Abbe number of the material of the positive lens Gp3 is large, below the lower limit of condition (8), the material of the positive lens Gp3 will have a low refractive index. As a result, the absolute value of the curvature of the object side or image side of the positive lens Gp3 becomes too large, which is undesirable because it increases spherical aberration and other distortions.

[0072] If the refractive power of the positive lens Gp3 exceeds the upper limit of condition (9), the spherical aberration and other distortions generated by the positive lens Gp3 become too large, which is undesirable.

[0073] If the refractive power of the positive lens Gp3 weakens below the lower limit of condition (9), the width of the on-axial light beam perpendicular to the optical axis of the lens positioned on the image side of the positive lens Gp3 becomes too large. As a result, the diameter of the lens positioned on the image side of the positive lens Gp3 becomes too large, which is undesirable.

[0074] If the refractive index of the material of the positive lens Gp2 exceeds the upper limit of condition (10), the reflectivity of the lens surface of the positive lens Gp2 increases, which is undesirable as it tends to increase the intensity of ghost light.

[0075] If the refractive index of the material of the positive lens Gp2 falls below the lower limit of condition (10), the absolute value of the curvature on at least one side of the positive lens Gp2 (either the object side or the image plane side) becomes too strong, which is undesirable because it causes spherical aberration and other distortions to become too large in the positive lens Gp2.

[0076] If the Abbe number of the material of the positive lens Gp2 is small, exceeding the upper limit of condition (11), the chromatic aberration generated in the positive lens Gp2 becomes too large, which is undesirable.

[0077] If the Abbe number of the material of the positive lens Gp2 is large, below the lower limit of condition (11), the material of the positive lens Gp2 will have a low refractive index. As a result, the absolute value of the curvature of the object side or image side of the positive lens Gp2 becomes too large, which is undesirable because it increases spherical aberration.

[0078] If the refractive power of the first subgroup B1p weakens beyond the upper limit of condition (12), the principal point of the optical system L0 will be positioned on the image side, and the overall length of the lens will increase, which is undesirable.

[0079] If the refractive power of the first subgroup B1p becomes too strong, below the lower limit of condition (12), the spherical aberration and other distortions occurring in the first subgroup B1p become too large, which is undesirable.

[0080] If the distance along the optical axis from the aperture diaphragm SP to the image plane becomes shorter than the upper limit of condition (13), the position of the exit pupil of the optical system L0 becomes too close to the image plane. As a result, the angle of incidence of off-axis light rays to the image plane becomes too large, which is undesirable because it tends to increase color shading when an image sensor is placed on the image plane.

[0081] If the negative lens Gn is closer to the image side, below the lower limit of condition (13), the distance along the optical axis from the aperture diaphragm SP to the image plane becomes longer. As a result, the overall length of the lens in the optical system L0 becomes too long, which is undesirable.

[0082] If the total field of view when the optical system L0 is focused at infinity exceeds the upper limit of condition (14), the height of the off-axis rays incident on the first subgroup B1p from the optical axis becomes too high. As a result, distortion and other aberrations occurring in the first subgroup B1p become too large, which is undesirable.

[0083] When the total angle of view at which the optical system L0 is focused at infinity falls below the lower limit of condition (14), the focal length of the optical system L0 increases. As a result, the overall length of the lens of the optical system L0 tends to increase, which is undesirable.

[0084] Furthermore, it is more preferable that conditions (5) through (14) be set as follows. -1.20 <fGn / f<-0.06···(5a) -7.0 × 10 -6 / ℃ <dGn<-5.0×10 -7 / ℃···(6a) 0.860 <Ndn / Ndp3<1.080···(7a) 0.40<νdn / νdp3<0.87 (8a) 1.00<|fGn / fGp3|<4.00 (9a) 1.750 <Ndp2<2.000···(10a) 17.0 < νdp2 < 22.9 ···(11a) 0.35 <fB1p / f<1.40···(12a) 0.25 <Ln / Ls<0.78···(13a) 4.0 < 2ωSL < 35.0 ···(14a)

[0085] More preferably, conditional expressions (4) to (16) are set as follows. -1.00 <fGn / f<-0.07···(5b) -6.0 × 10 -6 / ℃ <dGn<-7.0×10 -7 / ℃···(6b) 0.870 <Ndn / Ndp3<1.060···(7b) 0.42<νdn / νdp3<0.85 (8b) 1.10<|fGn / fGp3|<3.50···(9b) 1.800 <Ndp2<1.900···(10b) 19.0 < νdp2 < 22.8 ···(11b) 0.40 <fB1p / f<1.10···(12b) 0.30 <Ln / Ls<0.77···(13b) 5.0 < 2ωSL < 32.0 ···(14b)

[0086] Next, we will describe the details of the configuration of the optical system L0 in each embodiment. From Embodiment 2 onward, we will mainly describe the differences from Embodiment 1.

[0087] [Example 1] The optical system L0 of Example 1 consists of a front group La with positive refractive power, an aperture diaphragm SP, and a rear group Lb, arranged in order from the object side to the image side. The front group La consists of a first subgroup B1p with positive refractive power and a second subgroup B1n with negative refractive power, and the rear group Lb has a third subgroup B3.

[0088] The second subgroup B1n and the third subgroup B3 each contain a positive and a negative lens. When focusing from infinity to near, the second subgroup B1n moves together toward the image, and the third subgroup B3 moves together toward the object. The first subgroup B1p remains stationary when focusing from infinity to near.

[0089] This design allows for a lightweight lens while effectively suppressing aberration fluctuations that occur during focusing.

[0090] Furthermore, the presence of a fixed negative lens positioned between the second subgroup B1n and the third subgroup B3, which remains stationary during focusing, makes it easier to reduce the angle of incidence of the on-axis marginal rays incident on the second subgroup B1n. As a result, it becomes easier to suppress aberration fluctuations that occur in the second subgroup B1n during focusing.

[0091] Furthermore, the positive lens Gp1, which is positioned closest to the object, is a biconvex lens. This configuration makes it easier to strengthen the positive refractive power, and the principal point of the optical system L0 is more likely to be positioned closer to the object. As a result, it becomes easier to shorten the overall length of the lens.

[0092] The rear group Lb has a negative lens Gn. This configuration makes it easier for the principal point of the optical system L0 to be located on the object side, thus making it easier to shorten the overall length of the lens.

[0093] [Example 2] In the optical system L0 of Example 2, the lens group that moves during focusing is the second subgroup B1n located in the front group La. This configuration makes it easier to reduce the weight of the lens group that moves during focusing.

[0094] Furthermore, the lens positioned closest to the image in the optical system L0 is a negative meniscus lens with its convex surface facing the image. This configuration makes it easier to suppress field curvature.

[0095] [Example 3] In the optical system L0 of Example 3, the lens positioned closest to the image is a cemented lens in which a positive lens and a negative lens are joined together. This configuration makes it easier to suppress chromatic aberration.

[0096] Furthermore, the lens positioned adjacent to the image side of the aperture diaphragm SP is a cemented lens, where a positive lens and a negative lens are joined together. This configuration makes it easier to suppress axial chromatic aberration.

[0097] [Example 4] In the optical system L0 of Example 4, the positive lens Gp1, which is positioned closest to the object, is a positive meniscus lens with its convex surface facing the object. This configuration makes it easier to suppress spherical aberration.

[0098] Furthermore, the lens positioned closest to the image sensor in the optical system L0 has a biconvex shape. This configuration makes it easier to suppress pincushion distortion.

[0099] [Differentiation] In Example 1, the number of positive lenses arranged in the first subgroup B1p may be two or fewer. This results in a configuration that is easier to reduce in weight.

[0100] In the case of Example 1, at least one of the second subgroup B1n and the third subgroup B3, which move during focusing from infinity to near, may be composed of a single lens. This makes it easier to reduce the weight of the lens group that moves during focusing.

[0101] In the optical system L0 of each embodiment, it is preferable to deposit a fluorine coating on the object-side lens surface of the lens positioned closest to the object and the image-side lens surface of the lens positioned closest to the image. Since the object-side lens surface of the lens positioned closest to the object and the image-side lens surface of the lens positioned closest to the image are more susceptible to external exposure, depositing a fluorine coating enhances water and oil repellency, suppresses flare, and allows for high optical performance. In particular, since the object-side lens surface of the lens positioned closest to the object has a large diameter, it is preferable to deposit a fluorine coating there.

[0102] In the cemented lens arranged in the optical system L0 of each embodiment, it is preferable that the positive and negative lenses constituting at least one cemented lens are bonded together with an adhesive having a thickness of 0.005 mm or more and 0.05 mm or less along the optical axis. If it is less than 0.005 mm, it is prone to peeling, and if it is greater than 0.03 mm, the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image becomes longer, thus increasing the overall length of the lens. It is more preferable to satisfy the condition of 0.008 mm or more and 0.02 mm or less.

[0103] In each embodiment, at least one lens arranged in the optical system L0 is coated with an anti-reflective coating to prevent reflection, and the anti-reflective coating is composed of multiple films. Here, it is preferable that the anti-reflective coating PC has a refractive index of 1.32 or less when Nd is the refractive index of the film closest to the air interface with respect to the d line. By setting Nd to 1.32 or less, the refractive index difference with air can be reduced, making it possible to further reduce light reflection and reduce ghosting.

[0104] Specific examples of the configuration of the anti-reflective coating PC include, but are not limited to, the multilayer film using the wet method described in Japanese Patent Publication No. 2012-230211 and Japanese Patent Publication No. 2014-95877. More preferably, ghosting can be further reduced by setting Nd to 1.30 or less.

[0105] Here, it is preferable to apply an anti-reflective coating PC to the image-side lens surface of the negative lens with its concave surface facing the image side, among the negative lenses arranged in the optical system L0. Light reflected by a negative lens with its concave surface facing the image side tends to be reflected at a large angle with respect to the normal direction of the lens surface of the negative lens with its concave surface facing the image side, so the reflectivity tends to be high. Also, light reflected by a negative lens with its concave surface facing the image side tends to be focused at the image plane, so ghosting is likely to be noticeable. Therefore, by applying an anti-reflective coating PC to the image-side lens surface of a negative lens with its concave surface facing the image side, ghosting can be reduced.

[0106] The numerical examples 1 to 4 corresponding to Examples 1 to 4 are shown below.

[0107] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the on-axis distance (distance on the optical axis) between the m-th surface and the (m + 1)-th surface. Here, m is the surface number counted from the light incident side.

[0108] Also, nd represents the refractive index with respect to the d-line of each optical member, νd, and θgf represents the Abbe number and the partial dispersion ratio between the g-line and the F-line of the optical member, respectively. The Abbe number νd and the partial dispersion ratio θgf of a certain material are expressed as follows. That is, the g-line (wavelength 435.8 nm) of the Fraunhofer line is used. Further, when the refractive indices at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm) are Ng, Nd, NF, and NC, νd = (Nd - 1) / (NF - NC) θgf = (Ng - NF) / (NF - NC) are represented by.

[0109] BF is the back focus. The back focus is the value obtained by converting the distance from the lens surface arranged closest to the object side in the optical system L0 to the image plane into air. The overall length of the lens is the value obtained by adding the on-axis distance from the lens surface on the object side to the lens surface on the image side of the optical system L0 and the back focus.

[0110] Also, when the optical surface is an aspherical surface, an asterisk (*) is attached to the right side of the surface number. The aspherical shape is given by, when X is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients of each order, x = (h 2 / R) / [1 + {1 - (1 + k)(h / R) 2}^(1 / 2)] + A4×h 1 / 2 ^2 + A6×h 4 ^4 + A8×h 6 ^6 + A10×h 8 ^8 + A12×h 10+A12×h 12 This is expressed as follows. Note that "e±XX" in each aspherical coefficient is "×10± XX It means "...".

[0111] The effective aperture is the diameter of the lens at which light rays passing through each lens pass through the outermost edge before reaching the image plane.

[0112] [Numerical Example 1] Unit: mm Face number rd nd νd Effective diameter θgf 1 56.267 10.09 1.48749 70.2 56.58 2 -2731.034 0.48 55.72 3 64.986 3.91 1.48749 70.2 52.24 4 112.976 0.47 51.32 5 44.597 11.60 1.49700 81.5 47.86 6 -127.027 1.09 1.90110 27.1 45.46 7 85.944 (variable) 42.01 8 166.552 5.46 1.89286 20.4 41.16 9 -92.344 1.07 1.58144 40.8 40.23 10 31.256 (variable) 34.42 11 (aperture diaphragm) ∞ 2.92 31.86 12 -71.350 1.12 1.59551 39.2 31.44 13 -164.793 (variable) 31.33 14 40.681 5.40 1.52841 76.5 29.12 15 -125.508 3.80 28.39 16* 234.562 3.99 1.80400 46.5 29.34 17* -100.539 1.00 30.38 18 121.740 0.95 1.56732 42.8 30.48 19 33.187 (variable) 30.20 20 15070.701 5.71 2.00100 29.1 30.35 21 -33.061 1.05 1.75575 24.7 30.81 0.6291 22 -468.360 6.12 31.44 23 -39.154 1.07 1.59270 35.3 32.01 24 -1428.333 (BF) 33.97 Image plane ∞ Aspherical data Page 16 K = 0.00000e+00 A 4=-1.60594e-05 A 6=-2.01881e-08 A 8=-6.03873e-11 Page 17 K = 0.00000e+00 A 4=-1.23954e-05 A 6=-1.87162e-08 A 8=-3.60371e-11 Focal length 81.47 F-number 1.44 Half-angle 14.87 Image height 21.64 Lens length: 106.92 BF 12.87 Surface number When focusing at infinity When focusing at close range (object distance -850mm) 7 2.56 6.88 10 12.28 7.96 13 8.00 1.20 19 3.91 10.71 Group data Group starting plane focal length 1 1 82.02 2 8 -104.99 3 12 -212.25 4 14 58.98 5 20 -210.77

[0113] [Numerical Example 2] Unit: mm Face number rd nd νd Effective diameter θgf 1 92.543 10.38 1.59522 67.7 71.11 2 -535.647 0.50 70.47 3 77.930 7.00 1.49700 81.5 65.30 4 270.733 0.50 64.10 5 197.614 6.61 1.49700 81.5 63.03 6 -213.509 1.10 1.89190 37.1 61.69 7 218.167 (Variable) 59.08 8 560.624 6.98 1.89286 20.4 58.22 9 -99.049 1.10 1.85478 24.8 57.43 10 181.097 (Variable) 54.28 11 (aperture diaphragm) ∞ 4.80 34.67 12 53.797 1.91 1.61293 37.0 30.91 13 27.513 6.61 28.83 14 37.879 5.95 1.69680 55.5 27.88 15 -79.589 2.54 1.75575 24.7 26.97 0.6291 16 -480.107 0.25 25.57 17 159.282 4.75 1.57099 50.8 25.77 18 31.171 8.99 26.31 19 93.291 8.50 1.63636 35.4 31.96 20 -35.433 1.92 1.49700 81.5 32.86 21* -88.648 5.54 33.51 22 -23.784 1.10 1.51823 58.9 33.01 23 -62.899 (BF) 35.40 Image plane ∞ Aspherical data Page 22 K = 0.00000e+00 A 4=-1.32101e-05 A 6=-1.17629e-08 A 8=-1.34021e-11 A10 = -2.48742e-14 Focal length 128.00 F-number 1.80 Half-angle 9.59 Image height 21.64 Lens length: 145.81 BF 17.45 Surface number When focusing at infinity When focusing at close range (object distance -2000mm) 10 2.50 21.24 13 39.83 20.10 Group data Group starting plane focal length 1 1 107.29 2 8 -368.74 3 11 -1735.71

[0114] [Numerical Example 3] Unit: mm Face number rd nd νd Effective diameter θgf 1 280.184 12.10 1.48749 70.2 100.87 2 -278.802 8.00 100.52 3 106.382 18.00 1.43387 95.1 92.06 4 -257.501 0.53 90.14 5 -242.171 3.38 1.65412 39.7 89.82 6 231.213 8.01 85.23 7 59.513 13.65 1.43387 95.1 77.62 8 197.275 2.26 75.41 9 50.186 2.80 1.51633 64.1 65.30 10 38.307 (variable) 59.51 11 4049.491 5.54 1.80810 22.8 50.44 12 -106.278 2.67 1.83481 42.7 49.50 13 85.710 (Variable) 46.34 14 (aperture diaphragm) ∞ 2.86 39.37 15 139.571 7.46 1.59282 68.6 38.55 16 -51.190 0.80 1.78472 25.7 37.99 17 -98.686 3.43 37.69 18 72.497 4.90 1.77047 29.7 33.82 19 -111.325 3.55 1.63854 55.4 33.20 20 33.049 6.84 30.66 21 -81.254 1.10 1.81600 46.6 30.94 22 111.413 9.00 31.94 23 100.414 5.45 1.56732 42.8 39.74 24 -124.497 1.45 40.31 25 64.187 3.67 1.75575 24.7 42.37 0.6291 26 38.218 9.36 1.66672 48.3 41.55 27 187.182 (BF) 41.24 Image plane ∞ Focal length 292.53 F-number 2.90 Half-angle 4.23 Image height 21.64 Lens length: 273.24 BF 70.38 Surface number When focusing at infinity When focusing at close range (object distance -2000mm) 10 27.22 43.46 13 38.84 22.60 Group data Group starting plane focal length 1 1 151.02 2 11 -102.18 3 14 -243.13

[0115] [Numerical Example 4] Unit: mm Face number rd nd νd Effective diameter θgf 1 166.022 6.54 1.49700 81.5 82.68 2 405.253 10.00 82.10 3 93.236 13.75 1.43700 95.1 79.53 4 -1660.811 1.59 77.85 5 87.201 5.50 1.65160 58.5 72.07 6 53.991 14.10 1.43700 95.1 65.76 7 -462.595 0.80 64.68 8 -363.045 4.50 1.73400 51.5 64.17 9 149.722 10.00 60.17 10 169.228 6.00 1.74100 52.6 55.80 11 155.475 60.00 53.32 12 85.566 1.00 1.77250 49.6 28.29 13 29.061 5.87 1.54814 45.8 27.08 14 134.666 (variable) 26.17 15 109.805 2.46 1.80810 22.8 23.10 16 176.357 1.00 1.77250 49.6 22.41 17 51.367 (Variable) 21.84 18 (aperture diaphragm) ∞ 15.72 16.99 19 -60.903 2.14 1.85451 25.2 13.92 20 -24.069 1.00 1.81600 46.6 14.33 21 111.256 4.99 14.99 22 89.180 6.86 1.64769 33.8 18.35 23 -23.789 3.00 1.71338 26.0 19.60 0.6297 24 -191.528 16.66 21.11 25 58.085 5.98 1.58144 40.8 29.87 26 -84.964 3.93 30.09 27 -93.367 3.00 1.85026 32.3 29.77 28 48.811 1.00 30.46 29 53.813 8.38 1.65412 39.7 31.24 30 -121.541 (BF) 32.34 Image plane ∞ Focal length 482.00 F-number 5.83 Half-angle 2.57 Image height 21.64 Lens length: 296.64 BF 56.06 Surface number When focusing at infinity When focusing at close range (object distance -4500mm) 14 2.156 20.363 17 22.669 4.461 Group data Group starting plane focal length 1 1 213.61 2 15 -130.41 3 18 775.17

[0116] The various values ​​in each numerical example are summarized in Table 1 below. Note that the value of conditional expression (14) is twice the half-angle value described in each numerical example.

[0117] [Table 1]

[0118] [Imaging device] Next, an example of a digital still camera (imaging device) using the optical system of the embodiment of the present invention as an imaging optical system will be described with reference to Figure 9. In Figure 9, 11 is an imaging optical system composed of any of the optical systems described in Examples 1 to 4. 12 is an image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which is built into the camera body 10 and receives the optical image formed by the imaging optical system 11 and converts it into photoelectric light. The camera body 10 may be a so-called single-lens reflex camera with a quick-return mirror, or a so-called mirrorless camera without a quick-return mirror.

[0119] Thus, by applying the optical system of the embodiment of the present invention to an imaging device such as a digital still camera, it is possible to obtain lightweight images with good correction of various aberrations, even with a long focal length.

[0120] Each embodiment disclosed includes the following configuration:

[0121] (Composition 1) An optical system consisting of a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, The aforementioned front group has a positive lens Gp1 positioned closest to the object, The aforementioned rear group has a negative lens Gn, When the focal length of the entire system is f, the back focus is sk, the distance along the optical axis from the lens surface closest to the object to the image plane of the optical system is TL, the refractive index and Abbe number of the material of the negative lens Gn with respect to the d line are Ndn and νdn, respectively, and the distance along the optical axis from the lens surface of the negative lens Gn closest to the object to the image plane is Ln, 0.01 <sk / f<0.40 2.160 <Ndn+0.02174×νdn<2.320 1.600 <Ndn<1.850 0.10 <Ln / TL<0.40 An optical system characterized by satisfying the following conditional equation.

[0122] (Configuration 2) When the focal length of the negative lens Gn is fGn, -1.50 <fGn / f<-0.05 The optical system according to configuration 1, characterized by satisfying the following conditional equation.

[0123] (Composition 3) When the temperature coefficient of the negative lens Gn is denoted as dGn, -1.0 × 10 -5 / ℃ <dGn<-1.0×10 -7 / ℃ The optical system according to configuration 1 or 2, characterized by satisfying the following conditional expression.

[0124] (Composition 4) The aforementioned rear group has a positive lens Gp3, and the positive lens Gp3 and the negative lens Gn are joined together, and when the refractive index of the material of the positive lens Gp3 in the d line is Ndp3 and the Abbe number is νdp3, 0.85 <Ndn / Ndp3<1.10 0.30 < νdn / νdp3 < 0.90 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditional expression.

[0125] (Composition 5) The rear group has a positive lens Gp3, and the positive lens Gp3 and the negative lens Gn are joined together, and when the focal length of the positive lens Gp3 is fGp3, 0.85 < |fGn / fGp3| < 4.50 An optical system according to any one of configurations 1 to 4, characterized in that it satisfies the following conditional expression.

[0126] (Composition 6) The aforementioned group consists of a first subgroup having positive refractive power and a second subgroup having negative refractive power, arranged in order from the object side to the image side. The optical system according to any one of configurations 1 to 5, characterized in that, when focusing from infinity to near, the first subgroup remains stationary and the second subgroup moves toward the image.

[0127] (Composition 7) In the second subgroup, the lens Gp2 positioned closest to the object has a positive refractive power, and when the refractive index of the material of lens Gp2 at the d line is Ndp2 and the Abbe number is νdp2, 1.700 <Ndp2<2.200 15.0 < νdp2 < 23.0 The optical system according to configuration 6, characterized in that it satisfies the following conditional equation.

[0128] (Composition 8) When the focal length of the first subgroup is fB1p, 0.30 <fB1p / f<1.80 The optical system according to configuration 6 or 7, characterized by satisfying the following conditional expression.

[0129] (Composition 9) When Ls is the distance along the optical axis from the aperture diaphragm to the image plane, 0.20 <Ln / Ls<0.80 An optical system according to any one of configurations 1 to 8, characterized by satisfying the following conditional expression.

[0130] (Composition 10) When the total field of view of the optical system is 2ωSL, 2.0 < 2ωSL < 40.0 An optical system according to any one of configurations 1 to 9, characterized by satisfying the following conditional expression.

[0131] (Composition 11) The optical system according to any one of configurations 1 to 10, characterized in that the front group has a positive lens arranged adjacent to the image side of the positive lens Gp1.

[0132] (Composition 12) The optical system according to any one of configurations 1 to 11, characterized in that the aforementioned rear group has a third subgroup that moves during focusing.

[0133] (Composition 13) An optical system consisting of a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, The aforementioned front group has two or more positive lenses, The aforementioned rear group has two or more negative lenses, When the focal length of the entire system is f and the back focus is sk, 0.01 <sk / f<0.40 An optical system characterized by satisfying the following conditional equation.

[0134] (Composition 14) An imaging device characterized by having an optical system according to any one of configurations 1 to 13 and an image sensor that receives an image formed by the optical system.

[0135] Although preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of its gist. [Explanation of Symbols]

[0136] La front group SP aperture diaphragm Lb rear group In the Gp1 front group La, the positive lens is positioned closest to the object. Gn rear group Lb has a negative lens

Claims

1. An optical system comprising a front group, an aperture diaphragm, and a rear group, arranged in order from the object side to the image side, The aforementioned front group includes a positive lens Gp1 positioned closest to the object, and a positive lens positioned adjacent to the image side of the positive lens Gp1. The aforementioned rear group has two or more negative lenses, including a negative lens Gn. When the total focal length of the optical system is f, the back focus is sk, the refractive index of the negative lens Gn material with respect to the d line is Ndn, the focal length of the negative lens Gn is fGn, and the total angle of view of the optical system is 2ωSL, 0.10<sk / f≦0.263 1.620 < Ndn ≤ 1.756 -0.989 ≤ fGn / f ≤ -0.080 5.0<2ωSL<32.0 An optical system characterized by satisfying the following conditional equation.

2. When the temperature coefficient of the negative lens Gn is denoted as dGn, -1.0×10 －５ / ℃<dGn<-1.0×10 －７ / ℃ The optical system according to claim 1, characterized in that it satisfies the following condition.

3. The aforementioned rear group has a positive lens Gp3, and the positive lens Gp3 and the negative lens Gn are joined together, and when the refractive index of the material of the positive lens Gp3 in the d line is Ndp3 and the Abbe number is νdp3, 0.85<Ndn / Ndp3<1.10 0.30<νdn / νdp3<0.90 The optical system according to claim 1, characterized in that it satisfies the following condition.

4. The rear group has a positive lens Gp3, and the positive lens Gp3 and the negative lens Gn are joined together, and when the focal length of the positive lens Gp3 is fGp3, 0.85<|fGn / fGp3|<4.50 The optical system according to claim 1, characterized in that it satisfies the following condition.

5. The aforementioned group consists of a first subgroup having positive refractive power and a second subgroup having negative refractive power, arranged in order from the object side to the image side. The optical system according to claim 1, characterized in that, when focusing from infinity to near, the first subgroup remains stationary and the second subgroup moves toward the image.

6. In the second subgroup, the lens Gp2 positioned closest to the object has a positive refractive power, and when the refractive index of the material of lens Gp2 at the d line is Ndp2 and the Abbe number is νdp2, 1.700<Ndp2<2.200 15.0<νdp2<23.0 The optical system according to claim 5, characterized in that it satisfies the following conditional expression.

7. When the focal length of the first subgroup is fB1p, 0.30<fB1p / f<1.80 The optical system according to claim 5, characterized in that it satisfies the following conditional expression.

8. When Ls is the distance along the optical axis from the aperture diaphragm to the image plane, 0.20<Ln / Ls<0.80 The optical system according to claim 1, characterized in that it satisfies the following condition.

9. The optical system according to claim 1, characterized in that the aforementioned rear group has a third subgroup that moves during focusing.

10. An imaging device characterized by having an optical system according to any one of claims 1 to 9 and an image sensor that receives an image formed by the optical system.

Images