Optical system and imaging apparatus including the same

Abstract

To provide a small, lightweight high optical performance optical system.SOLUTION: An optical system L0 comprises a front group La, an aperture diaphragm SP, and a rear group Lb with wholly positive refractive power. The front group includes a first lens L1 with negative refractive power, arranged closest to an object side. The rear group includes a final lens Lp with positive refractive power arranged closest to an image side. The optical system includes four or more lenses arranged between the first lens and the final lens. A lens surface of the final lens close to an optical axis has a meniscus shape with a convex surface facing the object side. Focal distance f of the optical system, half angle of view ω(°) of the optical system, back focus sk of the optical system, lens full length TTL of the optical system, and average value PNdave of refractive index, on d line, of materials of all positive lenses included in the optical system satisfy a predetermined conditional expression.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] With the miniaturization and high pixel density of image sensors, optical systems used in imaging devices are required to be small and have high optical performance. In order to satisfy these requirements, Patent Document 1 proposes an optical system consisting of a first lens with positive refractive power, a second lens with negative refractive power, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in this order from the object side to the image side. The lens surface on the object side of the first lens is convex near the optical axis. The lens surface on the image side of the second lens is concave near the optical axis. The lens surface on the object side of the third lens is convex near the optical axis. The lens surface on the image side of the fourth lens is convex near the optical axis. The lens surface on the object side of the fifth lens is convex near the optical axis. The lens surface on the image side of the sixth lens is concave near the optical axis. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-115174 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to reduce the overall length of the optical system, it is effective to adopt a telephoto type power arrangement and strengthen the positive refractive power on the object side and the negative refractive power on the image side. However, if the power arrangement of the telephoto type is strengthened, pincushion distortion occurs significantly, making it difficult to simultaneously correct distortion and curvature of field with a limited number of lenses. In addition, if the power arrangement of the telephoto type is strengthened, the back focus becomes shorter and the exit angle of the off-axis light beam becomes larger.

[0005] The optical system described in Patent Document 1 employs a telephoto power arrangement to reduce the overall length, and uses multiple aspherical lenses to correct distortion and curvature of field, but the Petzval sum of the entire system is large and the exit angle of the off-axis light beam is also large. Therefore, when attempting to apply the optical system of Patent Document 1 to an imaging device with a large image sensor, the correction of curvature of field and the reduction in peripheral light amount become issues.

[0006] The present invention provides an optical system that is small, lightweight, and has high optical performance. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is an optical system including, in order from the object side to the image side, a front group, an aperture stop, and a rear group having positive refractive power overall, the front group including a first lens having negative refractive power and arranged closest to the object side, the rear group including a final lens having positive refractive power and arranged closest to the image side, the optical system having four or more lenses arranged between the first lens and the final lens, a lens surface of the final lens near the optical axis having a meniscus shape with its convex surface facing the object side, and when the focal length of the optical system is f, the half angle of view of the optical system is ω(°), the back focus of the optical system is sk, the length on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the optical system plus the back focus is TTL, and the average refractive index at the d-line of the material of all the positive lenses included in the optical system is PNdave, 0.1 <TTL / (f×tanω)<4.0 1.50 <PNdave<2.00 0.2 <sk / TTL<1.0 The present invention is characterized in that the following conditional expression is satisfied:

[0008] Other objects and features of the present invention will be described in the following embodiments. Effect of the Invention

[0009] According to the present invention, it is possible to provide an optical system that is small, lightweight, and has high optical performance. [Brief description of the drawings]

[0010] [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 Example 1 when focusing on an object at infinity. [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 Example 2 when focusing on an object at infinity. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 13A to 13C are aberration diagrams of Example 3 when focusing on an object at infinity. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 13A to 13C are aberration diagrams of Example 4 when focusing on an object at infinity. [Figure 9] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment 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. In the drawings, the same members are given the same reference numerals, and duplicated explanations will be omitted.

[0012] 1, 3, 5, and 7 are cross-sectional views of the optical system L0 of Examples 1 to 4. The optical system L0 of each Example is used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide cameras, and surveillance cameras.

[0013] In each lens cross-sectional view, the left side is the object side and the right side is the image side. The optical system L0 of each embodiment is configured with a plurality of lenses, La represents the front group, Lb represents the rear group, L1 represents the negative lens arranged closest to the object side, and Lp represents the positive lens arranged closest to the image side. SP represents an aperture stop. The aperture stop SP determines (limits) the light flux of the open F-number (Fno). IP represents an image plane (paraxial), and when the optical system L0 of each embodiment is used as the photographing optical system of a digital still camera or digital video camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a 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 corresponding to the film surface is disposed on the image plane IP. In this specification, the "front group" and the "rear group" may be configured with a plurality of lenses or may be configured with a single lens.

[0014] 2, 4, 6, and 8 are aberration diagrams of the optical system L0 of Examples 1 to 4 when focused at infinity. In the spherical aberration diagrams, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.56 nm) and the g-line (wavelength 435.84 nm). In the astigmatism diagrams, dS shows the sagittal image plane, and dM shows the meridional image plane. In the distortion aberration diagrams, the amount of distortion aberration for the d-line is shown. In the lateral chromatic aberration diagrams, the amount of lateral chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0015] Next, the characteristic configuration of the optical system L0 in each embodiment will be described.

[0016] The optical system L0 in each embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb having positive refractive power overall, arranged in that order from the object side to the image side. The front group La includes a first lens L1 having negative refractive power and arranged closest to the object side. The rear group Lb includes a final lens Lp having positive refractive power and arranged closest to the image side. Four or more lenses are arranged between the first lens L1 and the final lens Lp. The optical system L0 in each embodiment employs a retrofocus type power arrangement, thereby suppressing the image plane incidence angle of off-axis light beams while maintaining high optical performance.

[0017] Furthermore, in the optical system L0 of each embodiment, the lens surface of the final lens Lp near the optical axis is a meniscus shape with the convex surface facing the object side. This suppresses curvature of field and distortion. Note that the vicinity of the optical axis refers to the paraxial region, and in the case of an aspheric lens, the concave and convex surfaces near 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.

[0018] The focal length of the optical system L0 is f, and the half angle of view of the optical system L0 is ω (°). The back focus of the optical system L0 is sk, and the length (total lens length) obtained by adding the back focus sk to the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the optical system L0 is TTL. In this case, the optical system L0 in each embodiment satisfies the following conditional expression (1).

[0019] 0.1 <TTL / (f×tanω)<4.0 ···(1) Conditional formula (1) specifies the ratio of the total lens length to the image height. If the upper limit of conditional formula (1) is exceeded, the total lens length becomes long, and the optical system L0 becomes large. If the lower limit of conditional formula (1) is not reached and the total lens length becomes short, the refractive power of each lens becomes strong, making it difficult to achieve both curvature of field and distortion.

[0020] The optical system L0 of each embodiment satisfies the following conditional expression (2), where PNdave is the average value of the refractive index at the d-line (wavelength 587.56 nm) of the materials of all the positive lenses included in the optical system L0.

[0021] 1.50 <PNdave<2.00 ···(2) Conditional expression (2) specifies the average refractive index of the positive lenses included in optical system L0. If the average refractive index is higher than the upper limit of conditional expression (2), the color dispersion increases, making it difficult to correct axial chromatic aberration. If the average refractive index is lower than the lower limit of conditional expression (2), the Petzval sum of the entire system increases, making it difficult to correct field curvature.

[0022] The optical system L0 of each embodiment satisfies the following conditional expression (3), where sk is the back focus of the optical system L0.

[0023] 0.2 <sk / TTL<1.0 ···(3) Conditional formula (3) specifies the ratio of the back focal length to the total lens length. If the upper limit of conditional formula (3) is exceeded, the total lens length becomes long. If the back focal length is short enough to fall below the lower limit of conditional formula (3), the effective diameter of the final lens Lp located closest to the image side becomes large, and the optical system L0 becomes large in the radial direction.

[0024] Furthermore, it is preferable that the numerical ranges of the conditional expressions (1) to (3) be the numerical ranges of the following conditional expressions (1a) to (3a).

[0025] 1.0 <TTL / (f×tanω)<3.5 ···(1a) 1.55 <PNdave<1.90 ···(2a) 0.21 <sk / TTL<0.60 ···(3a) It is further preferable that the numerical ranges of the conditional expressions (1) to (3) be the numerical ranges of the following conditional expressions (1b) to (3b).

[0026] 1.5 <TTL / (f×tanω)<3.1 ···(1b) 1.60 <PNdave<1.80 ···(2b) 0.23 <sk / TTL<0.35 ···(3b) Next, the configurations and conditions that the optical system L0 of each embodiment preferably satisfies will be described.

[0027] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (4), where fa is the focal length of the front group La.

[0028] 0.0<|f / fa|<1.0 (4) Conditional expression (4) prescribes the ratio of the focal length of the front group La to the focal length of the optical system L0. If the upper limit of conditional expression (4) is exceeded and the positive refractive power of the front group La becomes stronger, the pincushion distortion becomes large, making it difficult to achieve both curvature of field and distortion, which is undesirable. If the negative refractive power of the front group La becomes stronger and the upper limit of conditional expression (4) is exceeded, the optical system approaches a telecentric optical system on the image side, and the overall lens length becomes long, which is undesirable. Note that the lower limit of conditional expression (4) is not exceeded. If the optical system L0 is a zoom lens, the focal length of the zoom lens at the wide-angle end is taken as f.

[0029] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (5), where fp is the focal length of the final lens Lp.

[0030] 0.6 <fp / f<6.0 ···(5) Conditional formula (5) specifies the ratio of the focal length of the final lens Lp to the focal length of the optical system L0. If the upper limit of conditional formula (5) is exceeded and the refractive power of the final lens Lp becomes weak, it is undesirable because it becomes difficult to correct pincushion distortion and suppress the image plane incidence angle. If the lower limit of conditional formula (5) is exceeded and the refractive power of the final lens Lp becomes strong, it is undesirable because the optical system L0 becomes close to a telecentric optical system on the image side and the overall lens length becomes long.

[0031] It is desirable for the optical system L0 in each embodiment to satisfy the following conditional expression (6).

[0032] 0.1 <sk / f<1.0 ···(6) Conditional formula (6) defines the ratio of the back focus of the optical system L0 to the focal length of the optical system L0. If the back focus is longer than the upper limit of conditional formula (6), the total lens length will be longer, which is not preferable. If the back focus is shorter than the lower limit of conditional formula (6), the effective diameter of the final lens Lp located closest to the image side will be larger, which is not preferable, as the optical system L0 will be larger in the radial direction.

[0033] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (7), where SPIP is the distance on the optical axis from the aperture stop SP to the image plane IP.

[0034] 0.5 <SPIP / TTL<1.0 ···(7) Conditional formula (7) specifies the ratio between the position of the aperture stop SP and the overall lens length. If the position of the aperture stop SP is on the object side and exceeds the upper limit of conditional formula (7), biased vignetting is likely to occur, and the shape of the blur becomes irregular, which is not preferable. If the position of the aperture stop SP is on the image side and falls below the lower limit of conditional formula (7), the exit pupil approaches the image plane IP, which makes it difficult to suppress the angle of incidence of off-axis light beams on the image plane, which is not preferable. Note that when the optical system L0 is a zoom lens, the distance on the optical axis from the aperture stop SP to the image plane IP of the zoom lens at the wide-angle end is defined as SPIP.

[0035] In the optical system L0 of each embodiment, when the paraxial radius of curvature of the object-side lens surface of the final lens Lp is R1 and the paraxial radius of curvature of the image-side lens surface of the final lens Lp is R2, it is preferable that the optical system L0 satisfies the following conditional formula (8).

[0036] 1.0<(R1+R2) / (R2-R1)<50.0 (8) Conditional formula (8) specifies the shape of the final lens Lp. If the upper limit of conditional formula (8) is exceeded and the values ​​of the object side paraxial radius of curvature R1 and the image side paraxial radius of curvature R2 become closer to each other, the refractive power of the final lens Lp becomes weak, making it difficult to suppress the image plane incidence angle of the off-axis light beam, which is undesirable. If the lower limit of conditional formula (8) is exceeded, the image side paraxial radius of curvature R2 of the final lens Lp becomes small, making it difficult to achieve both field curvature and distortion, which is undesirable.

[0037] In the optical system L0 of each embodiment, the final lens Lp is preferably made of plastic. The diameter of the final lens Lp is generally large, and using glass as the material for the final lens Lp is not preferable because the lens weight becomes heavy.

[0038] In the optical system L0 of each embodiment, the final lens Lp is preferably a single lens. If the final lens Lp is a cemented lens, it is not preferable because it lacks refractive power to bend light rays and it becomes difficult to suppress the incident angle of off-axis light beams on the image surface.

[0039] In the optical system L0 of each embodiment, the lens surface on the image side of the final lens Lp is preferably an aspheric surface that has a stronger positive refractive power in the periphery than in the center. If the lens surface on the image side of the final lens Lp is a spherical surface, the refractive power for bending off-axis rays is insufficient, which makes it difficult to suppress the image plane incidence angle and to reduce the field curvature at the same time, which is not preferable.

[0040] In the optical system L0 of each embodiment, it is preferable that the image-side lens surface of the final lens Lp has an inflection point at the periphery. If the image-side lens surface of the final lens Lp does not have an inflection point, the refractive power for bending off-axis rays is insufficient, making it difficult to suppress the image plane incidence angle and reduce the field curvature at the same time, which is not preferable.

[0041] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (9), where the refractive index of the final lens Lp at the d-line is Ndp and the Abbe number of the final lens Lp at the d-line is νdp.

[0042] 1.450 <Ndp<5.000 / νdp+1.550 ···(9) Conditional formula (9) specifies the refractive index of the final lens Lp. If the refractive index of the final lens Lp is higher than the upper limit of conditional formula (9), it becomes impossible to select a material with a low specific gravity, and the weight of the final lens Lp becomes heavy, which is undesirable. If the refractive index of the final lens Lp is lower than the lower limit of conditional formula (9), the Petzval sum of the entire system becomes large, which is undesirable, and it becomes difficult to correct the curvature of field.

[0043] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (10), where the focal length of the front group La is fa and the focal length of the rear group Lb is fb.

[0044] 0.0<|fb / fa|<2.0 ···(10) Conditional formula (10) prescribes the ratio of the focal length of the front group La to the focal length of the rear group Lb. If the upper limit of conditional formula (10) is exceeded and the positive refractive power of the rear group Lb becomes weak, it becomes difficult to correct pincushion distortion and suppress the image plane incidence angle, which is undesirable. If the upper limit of conditional formula (10) is exceeded and the negative refractive power of the front group La becomes strong, it becomes undesirable because the optical system L0 approaches a telecentric optical system on the image side and the overall lens length becomes long. However, the lower limit of conditional formula (10) cannot be exceeded.

[0045] In the optical system L0 of each embodiment, the front group La includes one lens Lap (first positive lens) having positive refractive power, and when the refractive index of the lens Lap at the d-line is Ndap, it is preferable that the following conditional expression (11) is satisfied.

[0046] 1.60 <Ndap<2.00 ···(11) Conditional expression (11) specifies the refractive index of the positive lens Lap. If the refractive index of the positive lens Lap is higher than the upper limit of conditional expression (11), the color dispersion increases, making it difficult to correct axial chromatic aberration, which is not preferable. If the refractive index of the positive lens Lap is lower than the lower limit of conditional expression (11), the Petzval sum of the entire system increases, making it difficult to correct field curvature, which is not preferable.

[0047] In the optical system L0 of each embodiment, the rear group Lb includes a lens Lbp (second positive lens) having a positive refractive power. When the refractive index of the lens Lbp at the d-line is Ndbp, it is preferable that the following conditional expression (12) is satisfied.

[0048] 1.60 <Ndbp<2.00 ···(12) Conditional expression (12) specifies the refractive index of the positive lens Lbp. If the refractive index of the positive lens Lbp is higher than the upper limit of conditional expression (12), the color dispersion increases, making it difficult to correct axial chromatic aberration, which is not preferable. If the refractive index of the positive lens Lbp is lower than the lower limit of conditional expression (12), the Petzval sum of the entire system increases, making it difficult to correct field curvature, which is not preferable.

[0049] In the optical system L0 of each embodiment, the rear group Lb includes a lens Lbn (first negative lens) having negative refractive power, and when the refractive index of the lens Lbn at the d-line is Ndbn, it is preferable that the following conditional expression (13) is satisfied.

[0050] 0.0 <Ndbp-Ndbn<0.4 ···(13) Conditional expression (13) specifies the refractive index difference between the positive lens Lbp and the negative lens Lbn. If a material with a large refractive index difference is selected that exceeds the upper limit of conditional expression (13), achromatization becomes difficult and correction of axial chromatic aberration becomes insufficient, which is not preferable. If a material with a small refractive index difference is selected below the lower limit of conditional expression (13), the Petzval sum of the entire system becomes large, which makes correction of field curvature difficult, which is not preferable.

[0051] In the optical system L0 of each embodiment, it is preferable that the rear group Lb includes a lens Lbp2 (third positive lens) having positive refractive power, and when the refractive index at the d-line of the lens Lbp2 is Ndbp2 and the Abbe number of the lens Lbp2 is νdp2, the following conditional formula (14) is satisfied.

[0052] 1.450 <Ndbp2<5.00 / νdp2+1.550 ···(14) Conditional expression (14) specifies the refractive index of the positive lens Lbp2. If the refractive index of the positive lens Lbp2 is higher than the upper limit of conditional expression (14), the color dispersion increases, making it difficult to correct the axial chromatic aberration and the chromatic aberration of magnification, which is not preferable. If the refractive index of the positive lens Lbp2 is lower than the lower limit of conditional expression (14), the Petzval sum of the entire system increases, making it difficult to correct the curvature of field, which is not preferable.

[0053] It is more preferable that the numerical ranges of the conditional expressions (4) to (14) be the numerical ranges of the following conditional expressions (4a) to (14a).

[0054] 0.1<|f / fa|<0.9 (4a) 1.0 <fp / f<5.0 ···(5a) 0.2 <sk / f<0.7 ···(6a) 0.60 <SPIP / TTL<0.95 ···(7a) 3.0<(R1+R2) / (R2-R1)<40.0 (8a) 1.500 <Ndp<5.000νdp+1.500 ···(9a) 0.13<|fb / fa|<1.50 ···(10a) 1.62 <Ndap<1.97 ···(11a) 1.70 <Ndbp<1.95 ···(12a) 0.02 <Ndbp-Ndbn<0.20 ···(13a) 1.500 <Ndbp2<5.000 / νdp2+1.500···(14a) It is more preferable that the numerical ranges of the conditional expressions (4) to (14) be within the numerical ranges of the following conditional expressions (4b) to (9b).

[0055] 0.15<|f / fa|<0.80 (4b) 2.0 <fp / f<4.5 ···(5b) 0.3 <sk / f<0.5 ···(6b) 0.65 <SPIP / TTL<0.90 ···(7b) 5.0<(R1+R2) / (R2-R1)<35.0 (8b) 1.520 <Ndn<5.000 / νdn+1.470 ···(9b) 0.15<|fb / fa|<1.00 (10b) 1.65 <Ndap<1.96 ···(11b) 1.75 <Ndbp<1.91 ···(12b) 0.030 <Ndbp-Ndbn<0.125 ···(13b) 1.520 <Ndbp2<5.000 / νdp2+1.470···(14b) In the optical system L0 of each embodiment, an optical block such as a cover glass or an IR cut filter may be disposed between the final lens Lp and the image surface IP. The refractive power of a lens refers to the refractive power in the vicinity of the optical axis (paraxial).

[0056] Numerical examples 1 to 4 corresponding to the first to fourth embodiments, respectively, are shown below.

[0057] 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 with respect to the d-line. The Abbe number νd of a certain material is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.56 nm), F-line (486.13 nm), and C-line (656.27 nm).

[0058] If the optical surface is aspheric, a * symbol is added to the right of the surface number. When the aspheric shape is defined as the X axis in the direction of the optical axis, the H axis perpendicular to the optical axis, and the direction of light travelling positive, R is the paraxial radius of curvature, K is the conic constant, and A3 to A14 are the aspheric coefficients,

[0059]

number

[0060] In addition, "e±XX" in each aspheric coefficient is "×10± XX " It means.

[0061] In each numerical example, d, focal length (mm), F-number, and half angle of view (degrees) are all values ​​when the optical system L0 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 length obtained by adding the back focus to the distance on the optical axis from the lens surface closest to the object of the optical system L0 to the final lens surface.

[0062] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -25.177 0.70 1.59270 35.3 13.96 2 20.767 3.17 1.91082 35.2 12.55 3 -43.800 0.99 11.56 4(Aperture) ∞ 2.60 10.15 5 14.261 3.51 1.87070 40.7 9.66 6 -32.837 0.50 1.76182 26.5 8.96 7 12.505 2.07 9.50 8* -235.152 1.68 1.53500 56.0 11.05 9* -10000.000 5.43 13.28 10* -11.334 3.63 1.53500 56.0 22.64 11* -10.218 0.21 24.34 12* 17.642 4.89 1.53500 56.0 32.10 13* 22.064 33.33 Image plane ∞ Aspheric Data Side 8 K = 0.00000e+00 A 4=-1.04566e-03 A 6=-9.37556e-05 A 8=-5.53704e-07 A 3= 9.72583e-04 A 5= 3.63328e-04 A 7= 1.17358e-05 9th page K = 0.00000e+00 A 4=-6.72372e-04 A 6=-5.12270e-05 A 8=-1.85093e-07 A 3= 9.10492e-04 A 5= 2.23735e-04 A 7= 5.42283e-06 Side 10 K =-1.83110e+01 A 4=-6.24412e-04 A 6=-4.26039e-05 A 8=-1.18796e-07 A10= 6.72472e-11 A 3=-5.99283e-04 A 5= 2.67221e-04 A 7= 3.41220e-06 Page 11 K =-4.49148e+00 A 4=-2.32087e-03 A 6=-6.08056e-05 A 8=-1.49652e-07 A10= 7.93407e-11 A 3= 5.15205e-03 A 5= 4.86742e-04 A 7= 4.45108e-06 Side 12 K =-5.38183e+01 A 4=-1.74379e-03 A 6=-2.16819e-05 A 8=-7.33722e-08 A10=-2.80326e-11 A 3= 6.86749e-03 A 5= 2.28224e-04 A 7= 1.52808e-06 A 9= 2.12818e-09 Page 13 K =-2.25124e+01 A 4=-1.07024e-03 A 6=-3.50892e-05 A 8=-1.81411e-07 A10=-7.08372e-11 A 3= 2.06768e-03 A 5= 2.37331e-04 A 7= 3.25539e-06 A 9= 5.54475e-09 Focal length 28.50 F-number: 2.86 Half angle of view (°) 37.20 Image height 21.64 Lens length 42.64 BF 13.25 Single lens data Lens starting surface focal length 1 1 -19.09 2 2 15.84 3 5 11.83 4 6 -11.83 5 8 -450.15 6 10 90.91 7 12 118.74 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -32.094 0.80 1.59270 35.3 14.73 2 13.451 0.22 12.81 3 14.066 3.35 1.91082 35.2 12.77 4 -81.655 0.88 11.75 5(Aperture) ∞ 2.53 11.43 6 15.638 3.46 1.87070 40.7 10.75 7 -22.209 0.50 1.76182 26.5 9.89 8 14.756 1.86 9.39 9* -59.980 1.73 1.53500 56.0 10.55 10* -370.728 5.41 12.83 11* -15.950 4.36 1.53500 56.0 22.66 12* -13.846 0.50 24.95 13* 17.591 4.84 1.53500 56.0 32.60 14* 24.164 34.06 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.08320e-03 A 6=-8.84422e-05 A 8=-4.28559e-07 A 3= 1.36888e-03 A 5= 3.73165e-04 A 7= 1.01971e-05 Page 10 K = 0.00000e+00 A 4=-6.54688e-04 A 6=-5.27521e-05 A 8=-2.13664e-07 A 3= 1.34817e-03 A 5= 2.38290e-04 A 7= 5.74368e-06 Page 11 K =-3.44235e+01 A 4=-6.38343e-04 A 6=-4.26477e-05 A 8=-1.18269e-07 A10 = 7.67530e-11 A 3= 4.85557e-05 A 5= 2.60713e-04 A 7= 3.40467e-06 Page 12 K =-3.08794e+00 A 4=-2.27652e-03 A 6=-6.14607e-05 A 8=-1.47175e-07 A10 = 8.73153e-11 A 3= 6.04115e-03 A 5= 4.80657e-04 A 7= 4.43542e-06 Page 13 K =-4.72297e+01 A 4=-1.76055e-03 A 6=-2.19580e-05 A 8=-7.23737e-08 A10=-3.00758e-11 A 3= 7.41113e-03 A 5= 2.27924e-04 A 7= 1.52563e-06 A 9= 2.15652e-09 Page 14 K =-1.98741e+01 A 4=-1.02271e-03 A 6=-3.50501e-05 A 8=-1.81558e-07 A10=-7.04181e-11 A 3= 2.24813e-03 A 5= 2.31781e-04 A 7= 3.26449e-06 A 9= 5.53025e-09 Focal length 28.50 F-number: 2.55 Half angle of view (°) 37.20 Image height 21.64 Lens length 42.90 BF 12.46 Single lens data Lens starting surface focal length 1 1 -15.89 2 3 13.40 3 6 11.01 4 7 -11.57 5 9 -134.01 6 11 113.90 7 13 96.18 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* -10000.000 1.40 1.58313 59.4 14.29 2* 8.753 1.18 11.59 3 16.891 3.83 1.65160 58.5 11.36 4 -41.966 1.09 9.89 5(Aperture) ∞ 2.29 9.86 6 18.502 3.48 1.75500 52.3 10.45 7 -18.130 0.30 11.14 8 -27.428 4.40 1.61800 63.4 11.24 9 -9.134 1.40 1.72047 34.7 11.97 10 28.012 2.88 13.50 11* -34.743 1.78 1.53500 56.0 14.17 12* -37.819 2.42 16.62 13* -11.863 4.35 1.53500 56.0 21.28 14* -11.484 0.53 23.83 15* 11.840 5.30 1.53500 56.0 33.89 16* 13.127 35.46 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-6.78455e-04 A 6= 1.33354e-05 A 8= 1.35788e-07 A 3=-4.26570e-04 A 5= 6.91920e-05 A 7=-2.74199e-06 2nd side K = 3.64968e-01 A 4=-7.75157e-04 A 6= 7.33843e-06 A 8=-1.12711e-07 A 3=-6.44618e-04 A 5= 5.38136e-05 A 7=-6.10266e-07 Page 11 K = 0.00000e+00 A 4=-3.75054e-04 A 6=-1.13030e-06 A 8= 7.88726e-08 A10=-4.67549e-10 Side 12 K = 0.00000e+00 A 4=-1.45507e-04 A 6=-1.64020e-06 A 8= 7.72645e-08 A10=-3.93531e-10 Page 13 K =-1.27759e+01 A 4= 2.63706e-04 A 6= 5.73607e-06 A 8= 2.93093e-08 A10=-4.45514e-11 A 3=-7.93420e-04 A 5=-3.18814e-05 A 7=-6.11948e-07 Page 14 K =-1.19491e+00 A 4=-2.26442e-06 A 6=-7.81773e-06 A 8=-1.34278e-08 A10=-1.79310e-11 A 3=-1.85363e-04 A 5= 4.90241e-05 A 7= 5.85849e-07 Page 15 K =-1.36904e+00 A 4=-1.04565e-03 A 6=-2.43530e-05 A 8=-1.17262e-07 A10=-4.25806e-11 A 3= 6.74386e-04 A 5= 1.89856e-04 A 7= 2.16124e-06 A 9= 3.46428e-09 Page 16 K =-5.78503e-01 A 4=-8.35374e-04 A 6=-8.61317e-06 A 8=-2.43644e-08 A10=-5.39681e-12 A 3= 6.50288e-04 A 5= 9.88435e-05 A 7= 5.66400e-07 A 9= 5.68901e-10 Focal length 24.50 F-number: 2.88 Half angle of view (°) 41.45 Image height 21.64 Lens length 47.90 BF 11.28 Single lens data Lens starting surface focal length 1 1 -15.00 2 3 18.97 3 6 12.65 4 8 20.29 5 9 -9.41 6 11 -1000.00 7 13 134.24 8 15 92.69 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 14.120 1.50 1.72825 28.5 17.88 2 12.036 4.92 1.80400 46.5 16.78 3 39.963 1.12 15.23 4* 11.035 1.33 1.68040 18.1 13.34 5* 7.194 3.74 11.62 6 (Aperture) ∞ 3.55 10.86 7 -22.824 1.45 1.80400 46.5 9.55 8 -18.868 0.84 10.65 9* -23.270 3.35 1.68040 18.1 11.06 10* -47.108 1.00 15.04 11* -9.509 3.17 1.53110 56.0 16.10 12* -8.011 0.20 17.13 13* 11.951 2.92 1.61550 25.8 21.03 14* 12.696 (variable) 22.14 Image plane ∞ Aspheric Data Side 4 K =-2.68850e+00 A 4=-1.04742e-04 A 6= 5.62415e-07 A 8=-4.65789e-08 A10= 2.52007e-09 A12=-5.22231e-11 A14= 3.79457e-13 5th page K = 0.00000e+00 A 4=-4.81826e-04 A 6=-2.05447e-06 A 8=-4.94086e-08 A10= 1.93962e-09 A12=-6.95594e-11 Page 9 K = 0.00000e+00 A 4=-4.55340e-04 A 6=-4.28696e-06 A 8= 3.05739e-08 A10=-4.04397e-09 A12= 3.30442e-11 Page 10 K = 0.00000e+00 A 4=-4.30569e-04 A 6= 3.47076e-06 A 8=-7.93640e-08 A10= 1.63383e-09 A12=-1.90372e-11 A14= 7.68428e-14 Page 11 K = 0.00000e+00 A 4= 5.25524e-04 A 6=-7.46425e-06 A 8= 3.18527e-07 A10=-4.06261e-09 A12= 1.74226e-11 A14= 2.64968e-14 Page 12 K =-7.76547e-01 A 4= 1.31469e-04 A 6= 1.25454e-06 A 8=-2.88332e-08 A10= 7.18099e-10 A12=-5.93048e-12 A14= 1.52782e-14 Page 13 K = 0.00000e+00 A 4=-5.76433e-04 A 6= 8.17828e-06 A 8=-1.15678e-07 A10= 9.44995e-10 A12=-4.20503e-12 A14= 5.71111e-15 Page 14 K = 0.00000e+00 A 4=-6.44620e-04 A 6= 9.84059e-06 A 8=-1.34057e-07 A10= 1.11603e-09 A12=-5.29814e-12 A14= 9.97952e-15 Focal length 33.08 F-number 1.85 Half angle of view(°) 22.44 Image height 13.66 Lens total length 41.00 BF 11.91 Single lens data Lens starting surface focal length 1 1 -160.68 2 2 19.86 3 4 -35.31 4 7 116.37 5 9 -71.66 6 11 55.21 7 13 132.76 Various values ​​in each numerical example are summarized in Table 1 below.

[0063] [Table 1]

[0064] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 using the optical system L0 of the present invention as an imaging optical system will be described with reference to Fig. 9. In Fig. 9, 13 denotes a camera body, and 11 denotes an imaging optical system constituted by any of the optical systems L0 described in the first to fourth embodiments. 12 denotes 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 may be a so-called mirrorless camera having no quick-turn mirror.

[0065] In this way, by applying the optical system L0 of the present invention to an imaging device such as a digital still camera, it is possible to obtain an imaging device with a small lens.

[0066] The disclosure of each of the above embodiments includes the following configurations.

[0067] (Configuration 1) An optical system comprising, in order from the object side to the image side, a front group, an aperture stop, and a rear group having positive refractive power as a whole, the front group includes a first lens element having negative refractive power and disposed closest to the object side, the rear group includes a final lens having a positive refractive power and disposed closest to the image side, the optical system includes four or more lenses disposed between the first lens and the final lens, a lens surface of the final lens in the vicinity of the optical axis has a meniscus shape with a convex surface facing an object side, Let f be the focal length of the optical system, ω (°) be the half angle of view of the optical system, sk be the back focus of the optical system, TTL be the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the optical system plus the back focus, and PNdave be the average value of the refractive index at the d line of the material of all the positive lenses included in the optical system. 0.1 <TTL / (f×tanω)<4.0 1.50 <PNdave<2.00 0.2 <sk / TTL<1.0 An optical system characterized in that the following condition is satisfied: (Configuration 2) Let fa be the focal length of the front group and f be the focal length of the optical system. 0.0<|f / fa|<1.0 2. The optical system according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the focal length of the final lens is fp, 0.6 <fp / f<6.0 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) 0.1 <sk / f<1.0 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the distance on the optical axis from the aperture stop to the image plane is defined as SPIP, 0.5 <SPIP / TTL<1.0 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the paraxial radius of curvature of the lens surface on the object side of the final lens is R1 and the paraxial radius of curvature of the lens surface on the image side of the final lens is R2, 1.0<(R1+R2) / (R2-R1)<50.0 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) 7. The optical system according to any one of configurations 1 to 6, wherein the final lens is made of plastic. (Configuration 8) The optical system according to any one of configurations 1 to 7, wherein the final lens is a single lens. (Configuration 9) 9. The optical system according to any one of configurations 1 to 8, wherein the lens surface on the image side of the final lens is an aspheric surface having a stronger positive refractive power in the periphery than in the center. (Configuration 10) 10. The optical system according to any one of configurations 1 to 9, wherein the image-side lens surface of the final lens has an inflection point at its periphery. (Configuration 11) When the refractive index of the final lens at the d line is Ndp and the Abbe number of the final lens at the d line is νdp, 1.450 <Ndp<5.000 / νdp+1.550 11. The optical system according to any one of 1 to 10, which satisfies the following conditional expression: (Configuration 12) Let the focal length of the front group be fa and the focal length of the rear group be fb. 0.0<|fb / fa|<2.0 12. The optical system according to any one of configurations 1 to 11, characterized in that the following condition is satisfied: (Configuration 13) the front group includes a first positive lens having positive refractive power, When the refractive index of the first positive lens at the d line is Ndap, 1.60 <Ndap<2.00 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) the rear group includes a second positive lens having a positive refractive power, When the refractive index of the second positive lens at the d line is Ndbp, 1.60 <Ndbp<2.00 14. The optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) the rear group includes a first negative lens having negative refractive power, When the refractive index of the first negative lens at the d line is Ndbn, 0.0 <Ndbp-Ndbn<0.4 15. The optical system according to claim 14, wherein the following condition is satisfied: (Configuration 16) the rear group includes a third positive lens having a positive refractive power, When the refractive index of the third positive lens at the d line is Ndbp2 and the Abbe number of the third positive lens at the d line is νdp2, 1.450 <Ndbp2<5.000 / νdp2+1.550 16. The optical system according to claim 14 or 15, wherein the following condition is satisfied: (Configuration 17) 17. An imaging device comprising the optical system according to any one of configurations 1 to 16, and an imaging element that receives an image formed by the optical system.

[0068] 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]

[0069] L0 optical system La front group SP aperture stop Lb rear group L1 First lens Lp final lens

Claims

1. An optical system comprising, arranged in order from the object side to the image side, a front group, an aperture stop, and a rear group having positive refractive power as a whole, the front group includes a first lens element having negative refractive power and arranged closest to the object, the rear group includes a final lens element having positive refractive power and located closest to the image side, the optical system has four or more lenses disposed between the first lens and the last lens, the lens surface of the final lens in the vicinity of the optical axis has a meniscus shape with the convex surface facing the object side, When the focal length of the optical system is f, the half angle of view of the optical system is ω (°), the back focus of the optical system is sk, the length on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the optical system plus the back focus is TTL, and the average value of the refractive index at the d line of the materials of all the positive lenses included in the optical system is PNdave, 0.1<TTL / (f×tanω)<4.0 1.60<PNdave<2.00 0.2<sk / TTL<1.0 An optical system characterized by satisfying the following conditional expression:

2. When the focal length of the front group is fa and the focal length of the optical system is f, 0.0<|f / fa|<1.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the final lens is fp, 0.6<fp / f<6.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. 0.1<sk / f<1.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the distance on the optical axis from the aperture stop to the image plane is SPIP, 0.5<SPIP / TTL<1.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the paraxial radius of curvature of the object-side lens surface of the final lens is R1 and the paraxial radius of curvature of the image-side lens surface of the final lens is R2, 1.0<(R1+R2) / (R2-R1)<50.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. 2. The optical system of claim 1, wherein the final lens is made of plastic.

8. 2. The optical system of claim 1, wherein the final lens is a single lens.

9. 2. The optical system according to claim 1, wherein the image-side lens surface of the final lens is an aspheric surface having a stronger positive refractive power in the periphery than in the center.

10. 2. The optical system according to claim 1, wherein the image-side lens surface of the final lens has an inflection point at a periphery thereof.

11. When the refractive index of the final lens at the d line is Ndp and the Abbe number of the final lens at the d line is νdp, 1.450<Ndp<5.000 / νdp+1.550 2. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the focal length of the front group is fa and the focal length of the rear group is fb, 0.0<|fb / fa|<2.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

13. the front group includes a first positive lens element having a positive refractive power, When the refractive index of the first positive lens at the d-line is Ndap, 1.60<Ndap<2.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

14. the rear group includes a second positive lens element having a positive refractive power, When the refractive index of the second positive lens at the d-line is Ndbp, 1.60<Ndbp<2.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

15. the rear group includes a first negative lens element having negative refractive power, When the refractive index of the first negative lens at the d-line is Ndbn, 0.0<Ndbp−Ndbn<0.4 15. The optical system according to claim 14, wherein the following condition is satisfied:

16. the rear group includes a third positive lens element having a positive refractive power, When the refractive index of the third positive lens at the d line is Ndbp2 and the Abbe number of the third positive lens at the d line is νdp2, 1.450<Ndbp2<5.000 / νdp2+1.550 15. The optical system according to claim 14, wherein the following condition is satisfied:

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

Images