Optical system and imaging device having the same

Abstract

To provide an optical system which suppresses oblique incidence to the periphery of an image sensor, has a short total lens length, and offers superior optical performance.SOLUTION: An optical system L0 provided herein consists of a first lens L1 with positive refractive power, an aperture stop SP, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4, a fifth lens L5, and a sixth lens L6 arranged in order from the object side to the image side, and satisfies the following conditional expressions: 0.5<SPIP / TTL<1.0, 1.65<PNdave<2.00, where SPIP represents an optical axial distance from the aperture stop to the image plane using a back focus as an air-equivalent length, TTL represents an optical axial distance from an object-side lens surface of the first lens to the image plane using the back focus as an air-equivalent length, and PNdave represents an average refractive index of materials of all positive lenses included in the optical system for the d-line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, surveillance cameras, and the like. [Background technology]

[0002] In recent years, imaging devices have become smaller, and optical systems (imaging optical systems) used in imaging devices are required to have short overall lens lengths and high optical performance.

[0003] As an optical system that meets these demands, Patent Document 1 discloses an optical system made up of six lenses. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-24337 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, when the total lens length of an optical system is shortened, various aberrations such as spherical aberration and curvature of field increase, and optical performance is likely to deteriorate. In addition, when the position of the aperture diaphragm approaches the imaging surface due to the shortening of the total lens length, shading is likely to occur due to the oblique incidence of light beams (oblique incidence) at the periphery of the imaging element in an imaging device using an imaging element such as a digital still camera. The occurrence of shading can be suppressed by arranging the aperture diaphragm closer to the object side than the center of the optical system, but since the lens configuration (refractive power arrangement) of the optical system becomes asymmetric with respect to the aperture diaphragm, it is difficult to satisfactorily correct various aberrations, and the number of lenses tends to increase. In the optical system described in Patent Document 1, it was insufficient to achieve both a shortened total lens length and high optical performance.

[0006] In order to achieve both a shorter overall lens length and higher performance while suppressing oblique incidence on the periphery of the image sensor, it is important to appropriately set the lens configuration of the optical system (material, number, shape, etc.) in addition to the number of lenses and the sign of the refractive power of each lens.

[0007] An object of the present invention is to provide an optical system that suppresses oblique incidence on the periphery of an image sensor, has a short overall lens length, and has excellent optical performance. [Means for solving the problem]

[0008] An optical system according to one aspect of the present invention is an optical system including, arranged in order from an object side to an image side, a first lens having a positive refractive power, an aperture stop, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens, a fifth lens, and a sixth lens, a lens surface on an object side of the sixth lens includes a region that is a convex surface near the optical axis, and a lens surface on an image side of the sixth lens includes a region that is a concave surface near the optical axis, Let SPIP be the distance on the optical axis from the aperture stop to the image plane, with the back focus being the air-equivalent length, TTL be the distance on the optical axis from the lens surface on the object side of the first lens to the image plane, with the back focus being the air-equivalent length, and PNdave be the average refractive index at the d-line of the materials of all the positive lenses included in the optical system. 0.5 <SPIP / TTL<1.0 1.65 <PNdave<2.00 The present invention is characterized in that the following condition is satisfied:

[0009] Other objects and features of the present invention will be described in the following embodiments. Effect of the Invention

[0010] According to the present invention, it is possible to realize an optical system that has a short overall lens length and excellent optical performance while suppressing oblique incidence on the periphery of the image sensor. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the optical system of Example 1. [Diagram 3]FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 11A to 11C are aberration diagrams of the optical system of Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 11A to 11C are aberration diagrams of the optical system of Example 3. [Figure 7] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical system and an image pickup apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0013] 1, 3 and 5 are lens sectional views of the optical systems of Examples 1 to 3 when focused on an object at infinity, respectively.

[0014] The optical system L0 in each embodiment is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, and surveillance cameras.

[0015] In each lens cross-sectional view, the left side is the object side (magnification side) and the right side is the image side (reduction side). The optical system L0 in each embodiment is configured to include a plurality of lenses.

[0016] The optical system L0 in each embodiment consists of a first lens L1 with positive refractive power, an aperture stop SP, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in that order from the object side to the image side.

[0017] In each lens cross-sectional view, "Li" (i is a natural number) represents the "i-th lens" when counting the lenses that make up optical system L0 from the object side to the image side. SP is an aperture stop that determines (limits) the light flux at the maximum F-number (Fno). IP is an image plane, and when the optical system L0 of each embodiment is used as the photographing optical system of a digital video camera or digital still camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system L0 of each embodiment is used as the photographing optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP.

[0018] Moreover, focusing from an object point at infinity to an object point at a close distance is performed by moving the entire optical system L0 along the optical axis.

[0019] In the optical system L0 of each embodiment, one or more lenses may be decentered so as to include a component perpendicular to the optical axis during image blur correction, thereby providing a function as an anti-vibration optical system. In addition, a parallel plate having substantially no refractive power, such as a low-pass filter or an infrared cut filter, may be disposed between the lens disposed closest to the image side and the imaging surface.

[0020] 2, 4, and 6 are aberration diagrams of the optical systems L0 of Examples 1 to 3 when focused on an object at infinity, respectively.

[0021] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, dS shows the amount of astigmatism on the sagittal image plane, and dM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (°), which is the angle of view calculated by paraxial calculation.

[0022] Next, the characteristic configuration of the optical system L0 in each embodiment will be described.

[0023] The optical system L0 in each embodiment is composed of a first lens L1 with positive refractive power, an aperture stop SP, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in that order from the object side to the image side.

[0024] Furthermore, the optical system L0 of each embodiment satisfies the following conditional expressions (1) and (2).

[0025] 0.5 <SPIP / TTL<1.0 ···(1) 1.65 <PNdave<2.00 ···(2) Here, SPIP is the distance on the optical axis from the aperture stop SP to the image plane IP, with the back focus being the air-equivalent length. TTL is the total lens length (the distance on the optical axis from the lens surface on the object side of the first lens L1 to the image plane IP, with the back focus being the air-equivalent length). PNdave is the average refractive index at the d-line of the materials of all the positive lenses included in the optical system L0.

[0026] Conditional formula (1) relates to the ratio of the distance on the optical axis from the aperture stop SP to the image plane IP, with the back focus being the air-equivalent length, to the total lens length. If the lower limit of conditional formula (1) is not met, the position of the aperture stop SP approaches the image plane IP, and the angle of incidence of off-axis light rays on the image plane IP increases. This is undesirable because shading occurs in the periphery of the image sensor. If the upper limit of conditional formula (1) is exceeded, it means that the position of the aperture stop SP is closer to the object side than the first lens L1. In this case, the lens configuration of the optical system with respect to the aperture stop SP becomes asymmetric, making it difficult to satisfactorily correct various aberrations. In addition, the diameter of the lens close to the image plane IP tends to increase, making it difficult to miniaturize the lens.

[0027] Conditional formula (2) relates to the average refractive index at the d-line of the materials of all the positive lenses included in the optical system L0. If the average refractive index of the materials of the positive lenses is smaller than the lower limit of conditional formula (2), the Petzval sum is likely to be large, which is undesirable because it makes it difficult to correct field curvature and the like. If the average refractive index of the materials of the positive lenses is larger, it becomes easier to correct field curvature and the like, but generally the dispersion of materials with high refractive indexes tends to be larger than the dispersion of materials with low refractive indexes. Therefore, if the average refractive index of the materials of the positive lenses is larger than the upper limit of conditional formula (2), it is undesirable because it makes it difficult to correct axial chromatic aberration.

[0028] The optical system L0 of each embodiment has the above-mentioned configuration, thereby suppressing oblique incidence on the periphery of the image sensor, while achieving a short overall lens length and excellent optical performance.

[0029] Furthermore, it is more preferable that the numerical ranges of the conditional expressions (1) and (2) be within the ranges of the following conditional expressions (1a) and (2a).

[0030] 0.6 <SPIP / TTL<0.9 ···(1a) 1.65 <PNdave<1.90 ···(2a) It is further preferable that the numerical ranges of the conditional expressions (1) and (2) be within the ranges of the following conditional expressions (1b) and (2b).

[0031] 0.7 <SPIP / TTL<0.9 ···(1b) 1.70 <PNdave<1.80 ···(2b) Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described.

[0032] It is preferable that the optical system L0 in each embodiment satisfies one or more of the following conditional expressions (3) to (10).

[0033] 0.80 <f1 / f<2.00 ···(3) 0.30 <f2 / f<0.80 ···(4) -0.70 <f3 / f<-0.25 ···(5) 0.20 <BF / TTL<0.40 ···(6) 1.5<(L1R2+L1R1) / (L1R2-L1R1)<4.0 (7) 15 <Nνdave<30 ···(8) 0.90 <TTL / f<1.40 ···(9) Here, f1 is the focal length of the first lens L1. f is the focal length of the optical system L0. f2 is the focal length of the second lens L2. f3 is the focal length of the third lens L3. BF is the back focus of the optical system L0, which is the air-equivalent length of the distance on the optical axis from the image-side lens surface of the sixth lens L6 to the image surface IP. L1R2 is the radius of curvature of the image-side lens surface of the first lens L1. L1R1 is the radius of curvature of the object-side lens surface of the first lens L1. Nνdave is the average Abbe number at the d-line of the materials of all the negative lenses included in the optical system L0.

[0034] Conditional expression (3) relates to the ratio of the focal length of the first lens L1 to the focal length of the optical system L0. If the lower limit of conditional expression (3) is not satisfied, the refractive power of the first lens L1 becomes too strong, making it difficult to sufficiently correct various aberrations including spherical aberration. On the other hand, if the upper limit of conditional expression (3) is exceeded, the refractive power of the first lens L1 becomes too weak, making it difficult to sufficiently shorten the overall lens length.

[0035] Conditional expression (4) relates to the ratio of the focal length of the second lens L2 to the focal length of the optical system L0. If the lower limit of conditional expression (4) is not satisfied, the refractive power of the second lens L2 becomes too strong, making it difficult to sufficiently correct various aberrations including spherical aberration. On the other hand, if the upper limit of conditional expression (4) is exceeded, the refractive power of the second lens L2 becomes too weak, making it difficult to sufficiently shorten the overall lens length.

[0036] Conditional expression (5) relates to the ratio of the focal length of the third lens L3 to the focal length of the optical system L0. If the lower limit of conditional expression (5) is exceeded, the refractive power of the third lens L3 becomes weak, making it difficult to sufficiently shorten the overall lens length. On the other hand, if the upper limit of conditional expression (5) is exceeded, the refractive power of the third lens L3 becomes strong, making it difficult to sufficiently correct various aberrations including spherical aberration.

[0037] Conditional expression (6) relates to the ratio of the back focus to the total lens length of the optical system L0. If the lower limit of conditional expression (6) is exceeded, the back focus becomes too short, the angle of incidence of off-axis light rays on the image plane IP becomes large, and shading occurs, which is undesirable. Alternatively, the lens diameter becomes large in order to suppress the occurrence of shading, making it difficult to miniaturize the lens. On the other hand, if the upper limit of conditional expression (6) is exceeded, the back focus becomes too long, and the total lens length increases, which is undesirable.

[0038] Condition (7) relates to the shape of the first lens L1. Satisfying condition (7) means that the first lens L1 has a positive refractive power and therefore has a meniscus shape convex toward the object side. By satisfying condition (7), various aberrations including spherical aberration can be effectively corrected.

[0039] Conditional expression (8) relates to the average Abbe number at the d-line of the materials of all the negative lenses included in the optical system L0. If the lower limit of conditional expression (8) is exceeded, the dispersion increases, making it difficult to correct the axial chromatic aberration and the lateral chromatic aberration, which is not preferable. Furthermore, the refractive index of a material with a large dispersion generally tends to be higher than that of a material with a small dispersion. Therefore, the average refractive index of the negative lens increases, the Petzval sum tends to increase, and it becomes difficult to correct the curvature of field, which is not preferable. On the other hand, if the upper limit of conditional expression (8) is exceeded, the dispersion becomes too small, making it difficult to correct the axial chromatic aberration and the lateral chromatic aberration, which is not preferable.

[0040] Condition (9) relates to the ratio of the focal length to the total lens length of the optical system L0. If the lower limit of condition (9) is exceeded, the total lens length becomes too short, making it difficult to sufficiently correct spherical aberration and other aberrations. On the other hand, if the upper limit of condition (9) is exceeded, the total lens length becomes too long.

[0041] It is more preferable that the numerical ranges of the conditional expressions (3) to (9) be within the ranges of the following conditional expressions (3a) to (9a).

[0042] 0.80 <f1 / f<1.80 ···(3a) 0.30 <f2 / f<0.70 ···(4a) -0.60 <f3 / f<-0.25 ···(5a) 0.25 <BF / TTL<0.38 ···(6a) 2.0<(L1R2+L1R1) / (L1R2-L1R1)<3.5 (7a) 15 <Nνdave<25 ···(8a) 1.00 <TTL / f<1.30 ···(9a) It is more preferable that the numerical ranges of the conditional expressions (3) to (9) be within the ranges of the following conditional expressions (3b) to (9b).

[0043] 0.80 <f1 / f<1.60 ···(3b) 0.30 <f2 / f<0.65 ···(4b) -0.55 <f3 / f<-0.30 ···(5b) 0.28 <BF / TTL<0.35 ···(6b) 2.5<(L1R2+L1R1) / (L1R2-L1R1)<3.5 (7b) 18 <Nνdave<25 ···(8b) 1.10 <TTL / f<1.30 ···(9b) Next, a description will be given of configurations that are preferably satisfied in the optical system L0 of each embodiment.

[0044] It is preferable that the optical system L0 has two or more negative lenses, which makes it easier to correct the curvature of field, as well as the axial chromatic aberration and lateral chromatic aberration.

[0045] In addition, the fourth lens L4 preferably has an area having negative refractive power near the optical axis. In addition, the fourth lens L4 preferably has aspheric surfaces on both sides, and includes an area in the vicinity of the optical axis where the lens surface on the object side is a concave surface, and includes an area in the vicinity of the optical axis where the lens surface on the image side is a convex surface. This makes it easier to correct the curvature of field.

[0046] In addition, the fifth lens L5 preferably has an area having a positive refractive power near the optical axis. In addition, the fifth lens L5 preferably has aspheric surfaces on both sides, and includes an area in the vicinity of the optical axis where the lens surface on the object side is a concave surface, and includes an area in the vicinity of the optical axis where the lens surface on the image side is a convex surface. This makes it easier to correct the curvature of field.

[0047] In addition, the sixth lens L6 preferably has an area with positive refractive power near the optical axis. In addition, the sixth lens L6 preferably has aspheric surfaces on both sides, and includes an area where the lens surface on the object side is a convex surface near the optical axis, and includes an area where the lens surface on the image side is a concave surface near the optical axis. This makes it easier to correct the curvature of field.

[0048] In addition, the vicinity of the optical axis means the paraxial region, and in the case of an aspheric lens, the concave and convex surfaces in the vicinity of the optical axis are defined by the sign of the paraxial radius of curvature. Similarly, the positive and negative refractive powers are calculated from the paraxial radius of curvature.

[0049] Next, the optical system L0 of each embodiment will be described in detail.

[0050] The optical system L0 of each embodiment is composed of a first lens L1, an aperture stop SP, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in order from the object side to the image side. The first lens L1 has positive refractive power. The second lens L2 has positive refractive power. The third lens L3 has negative refractive power. The fourth lens L4 has negative refractive power near the optical axis. The fifth lens L5 has positive refractive power near the optical axis. The sixth lens has positive refractive power near the optical axis. The fourth lens L4 has aspheric surfaces on both sides, the object side surface faces the object side concave surface near the optical axis, and the image side surface faces the image side convex surface near the optical axis. The fifth lens L5 has aspheric surfaces on both sides, the object side surface faces the object side concave surface near the optical axis, and the image side surface faces the image side convex surface near the optical axis. The sixth lens L6 has aspheric surfaces formed on both sides, with the object-side surface facing the object side and convex near the optical axis, and the image-side surface facing the image side and concave near the optical axis.

[0051] Numerical Examples 1 to 3 corresponding to Examples 1 to 3, respectively, are shown below.

[0052] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. In addition, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0053] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus (BF)" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image surface expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the lens surface closest to the object to the final surface plus the back focus.

[0054] The entrance pupil position is the distance from the lens surface closest to the object (first surface) to the entrance pupil. The exit pupil position is the distance from the lens surface closest to the image (last lens surface) to the exit pupil. The front principal point position is the distance from the first lens surface to the front principal point. The rear principal point position is the distance from the last lens surface to the rear principal point. Each of these numerical values ​​is a paraxial quantity, and the signs are positive in the direction from the object side to the image side.

[0055] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, A12, and A14 are the aspheric coefficients of each order: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 +A14×h 14 In addition, "e±XX" in each aspheric coefficient is "×10± XX " It means.

[0056] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1 6.172 0.75 1.78800 47.4 2 12.606 0.86 3(Aperture) ∞ 0.42 4 6.266 0.90 1.88300 40.8 5 -115.141 0.40 1.72825 28.5 6 4.413 1.89 7* -11.615 0.80 1.67070 19.3 8* -68.826 0.46 9* -6.873 1.25 1.61550 25.8 10* -4.882 0.61 11* 7.239 1.90 1.53500 56.0 12* 8.458 BF Image plane ∞ Aspheric Data Side 7 K = 0.00000e+000 A 4=-1.17343e-002 A 6= 6.62086e-004 A 8= 7.11821e-005 A10=-1.57795e-005 A12= 1.24628e-007 Side 8 K = 0.00000e+000 A 4=-9.33591e-003 A 6= 9.10480e-004 A 8=-5.56359e-005 A10=1.86493e-006 A12=-2.51762e-008 9th page K = 0.00000e+000 A 4= 8.82669e-003 A 6=-7.18264e-004 A 8= 3.71234e-005 A10=-8.01992e-007 A12= 8.77474e-010 Side 10 K = 0.00000e+000 A 4= 3.92160e-003 A 6= 9.31874e-005 A 8=-8.10394e-006 A10=2.91020e-007 A12=-2.38551e-009 Page 11 K = 0.00000e+000 A 4=-7.49451e-003 A 6= 3.07261e-004 A 8=-5.64465e-006 A10= 9.78774e-010 A12= 1.44863e-009 A14=-1.61988e-011 Side 12 K = 0.00000e+000 A 4=-6.85204e-003 A 6= 2.82220e-004 A 8=-1.01045e-005 A10= 2.47381e-007 A12=-3.28540e-009 A14= 1.78261e-011 Focal length 13.00 F-number: 2.88 Half angle of view (°) 31.25 Image height 7.89 Lens length 15.35 BF 5.11 Entrance pupil position 1.47 Exit pupil position -7.51 Front principal point position 1.07 Back principal point position -7.89 Single lens data Lens starting surface focal length 1 1 14.60 2 4 6.75 3 5 -5.83 4 7 -20.95 5 9 22.10 6 11 60.82 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1 8.823 1.15 1.88300 40.8 2 16.892 2.16 3(Aperture) ∞ 0.52 4 6.147 0.91 2.00100 29.1 5 -25.011 0.10 6 -14.102 0.40 1.92286 20.9 7 5.154 1.50 8* -45.358 0.80 1.67070 19.3 9* -357.393 0.57 10* -255.281 1.25 1.63910 23.5 11* -11.726 0.15 12* 6.200 1.90 1.54390 56.0 13* 6.564 BF Image plane ∞ Aspheric Data Side 8 K = 0.00000e+000 A 4=-4.26820e-003 A 6= 1.77770e-003 A 8=-2.26805e-004 A10= 1.42590e-005 A12=-3.72229e-007 9th page K = 0.00000e+000 A 4=-1.10581e-002 A 6= 2.37005e-003 A 8=-2.13564e-004 A10=9.92956e-006 A12=-1.98013e-007 Side 10 K = 0.00000e+000 A 4=-2.65169e-003 A 6= 3.87732e-004 A 8=-3.29307e-005 A10= 1.51180e-006 A12=-2.70444e-008 Page 11 K = 0.00000e+000 A 4= 1.51347e-003 A 6=-3.58082e-004 A 8= 3.04816e-005 A10=-1.03923e-006 A12= 1.28063e-008 Side 12 K = 0.00000e+000 A 4=-7.34033e-003 A 6= 2.53991e-005 A 8= 1.97107e-005 A10=-1.02262e-006 A12= 2.13649e-008 A14=-1.76667e-010 Page 13 K = 0.00000e+000 A 4=-6.88663e-003 A 6= 1.95188e-004 A 8=-4.24138e-006 A10= 3.40242e-008 A12= 7.17160e-010 A14=-1.74573e-011 Focal length 12.61 F-number: 2.88 Half angle of view (°) 32.03 Image height 7.89 Lens length 16.23 BF 4.82 Entrance pupil position 3.43 Exit pupil position -6.16 Front principal point position 1.55 Back principal point position -7.79 Single lens data Lens starting surface focal length 1 1 19.61 2 4 5.00 3 6 -4.05 4 8 -77.54 5 10 19.19 6 12 72.36 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1 4.861 1.00 1.72916 54.7 2 8.926 1.09 3(Aperture) ∞ 0.55 4 7.814 0.81 2.00100 29.1 5 -255.281 0.10 6 -61.921 0.40 1.92286 20.9 7 6.728 1.52 8* -10.405 0.80 1.68040 18.1 9* -18.578 0.69 10* -7.505 1.28 1.63560 23.9 11* -5.889 0.12 12* 7.492 1.90 1.54390 56.0 13* 7.255 BF Image plane ∞ Aspheric Data Side 8 K = 0.00000e+000 A 4=-1.16579e-002 A 6= 9.23400e-004 A 8=-1.96407e-004 A10=3.26667e-005 A12=-5.02605e-006 9th page K = 0.00000e+000 A 4=-1.19318e-002 A 6= 7.01526e-004 A 8= 7.06491e-005 A10=-1.24604e-005 A12= 5.15017e-007 Side 10 K = 0.00000e+000 A 4=-2.01834e-004 A 6=-1.54371e-004 A 8= 3.25581e-005 A10=-1.09711e-006 A12=-2.61832e-009 Page 11 K = 0.00000e+000 A 4= 1.50168e-003 A 6=-3.40868e-005 A 8=-1.74033e-005 A10= 1.74869e-006 A12=-4.27577e-008 Side 12 K = 0.00000e+000 A 4=-6.28654e-003 A 6= 7.04829e-005 A 8= 1.06047e-005 A10=-5.31978e-007 A12= 9.95925e-009 A14=-6.85704e-011 Page 13 K = 0.00000e+000 A 4=-6.57786e-003 A 6= 2.21104e-004 A 8=-7.14307e-006 A10= 1.69631e-007 A12=-2.34045e-009 A14= 1.30153e-011 Focal length 12.61 F-number: 2.88 Half angle of view (°) 32.03 Image height 7.89 Lens length 14.45 BF 4.19 Entrance pupil position 2.07 Exit pupil position -6.28 Front principal point position -0.50 Back principal point position -8.42 Single lens data Lens starting surface focal length 1 1 13.26 2 4 7.59 3 6 -6.56 4 8 -36.20 5 10 32.91 6 12 231.34 Various values ​​in each numerical example are summarized in Table 1 below.

[0057] [Table 1]

[0058] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 using the optical system L0 of each embodiment as an imaging optical system will be described with reference to Fig. 7. In Fig. 7, 13 is a camera body, and 11 is an imaging optical system constituted by any of the optical systems L0 described in the first to third embodiments. 12 is a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body 13 and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 13 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror.

[0059] In this way, by applying the optical system of the present invention to an imaging device such as a digital still camera, it is possible to obtain an imaging device that has a short overall lens length and excellent optical performance while suppressing oblique incidence on the periphery of the image sensor.

[0060] The optical systems of the above-described embodiments can be applied not only to imaging devices such as digital still cameras, but also to various optical instruments such as telescopes.

[0061] Although the 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 the gist of the present invention. [Explanation of symbols]

[0062] L0 optical system L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 5th lens L6 6th lens SP aperture stop

Claims

1. An optical system including a first lens having a positive refractive power, an aperture stop, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens, a fifth lens, and a sixth lens, which are arranged in this order from an object side to an image side, the object-side lens surface of the sixth lens includes a convex area in the vicinity of the optical axis, the image-side lens surface of the sixth lens includes a concave area in the vicinity of the optical axis, Let SPIP be the distance on the optical axis from the aperture stop to the image plane, with the back focus being the air-equivalent length, TTL be the distance on the optical axis from the lens surface on the object side of the first lens to the image plane, with the back focus being the air-equivalent length, and PNdave be the average refractive index at the d-line of the materials of all the positive lenses included in the optical system. 0.5<SPIP / TTL<1.0 1.65<PNdave<2.00 An optical system characterized in that the following condition is satisfied:

2. When the focal length of the first lens is f1 and the focal length of the optical system is f, 0.80<f1 / f<2.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the second lens is f2 and the focal length of the optical system is f, 0.30<f2 / f<0.80 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the third lens is f3 and the focal length of the optical system is f, -0.70<f3 / f<-0.25 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the air-equivalent length of the distance on the optical axis from the image-side lens surface of the sixth lens to the image plane is BF, 0.20<BF / TTL<0.40 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the radius of curvature of the lens surface on the object side of the first lens is L1R1 and the radius of curvature of the lens surface on the image side of the first lens is L1R2, 1.5<(L1R2+L1R1) / (L1R2-L1R1)<4.0 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. The optical system has two or more negative lenses, and when the average Abbe number at the d line of the materials of all the negative lenses included in the optical system is Nνdave, 15<Nvdave<30 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the focal length of the optical system is f, 0.90<TTL / f<1.40 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. An optical system comprising a first lens having a positive refractive power, an aperture stop, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens, a fifth lens, and a sixth lens, arranged in this order from an object side to an image side, the fourth lens includes a region having negative refractive power in the vicinity of an optical axis, The fourth lens has aspheric surfaces on both sides thereof, the object-side lens surface of the fourth lens includes a concave area in the vicinity of the optical axis, the image-side lens surface of the fourth lens includes a convex area in the vicinity of the optical axis, Let SPIP be the distance on the optical axis from the aperture stop to the image plane, with the back focus being the air-equivalent length, TTL be the distance on the optical axis from the lens surface on the object side of the first lens to the image plane, with the back focus being the air-equivalent length, and PNdave be the average refractive index at the d-line of the materials of all the positive lenses included in the optical system. 0.5<SPIP / TTL<1.0 1.65<PNdave<2.00 An optical system characterized in that the following condition is satisfied:

10. An optical system comprising a first lens having a positive refractive power, an aperture stop, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens, a fifth lens, and a sixth lens, arranged in this order from an object side to an image side, the fifth lens includes a region having a positive refractive power in the vicinity of an optical axis, The fifth lens has aspheric surfaces on both sides thereof, the object-side lens surface of the fifth lens includes a concave area in the vicinity of the optical axis, the image-side lens surface of the fifth lens includes a convex area in the vicinity of the optical axis, Let SPIP be the distance on the optical axis from the aperture stop to the image plane, with the back focus being the air-equivalent length, TTL be the distance on the optical axis from the lens surface on the object side of the first lens to the image plane, with the back focus being the air-equivalent length, and PNdave be the average refractive index at the d-line of the materials of all the positive lenses included in the optical system. 0.5<SPIP / TTL<1.0 1.65<PNdave<2.00 An optical system characterized in that the following condition is satisfied:

11. An optical system comprising a first lens having a positive refractive power, an aperture stop, a second lens having a positive refractive power, a third lens having a negative refractive power, a fourth lens, a fifth lens, and a sixth lens, arranged in this order from an object side to an image side, the sixth lens includes a region having a positive refractive power in the vicinity of an optical axis, The sixth lens has aspheric surfaces on both sides thereof, the sixth lens has an object-side lens surface including a convex region in the vicinity of the optical axis, the sixth lens has an image-side lens surface including a concave area in the vicinity of the optical axis; Let SPIP be the distance on the optical axis from the aperture stop to the image plane, with the back focus being the air-equivalent length, TTL be the distance on the optical axis from the lens surface on the object side of the first lens to the image plane, with the back focus being the air-equivalent length, and PNdave be the average refractive index at the d-line of the materials of all the positive lenses included in the optical system. 0.5<SPIP / TTL<1.0 1.65<PNdave<2.00 An optical system characterized in that the following condition is satisfied:

12. 12. An imaging apparatus comprising: the optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

Images