Optical system and image capturing apparatus including optical system

Abstract

A compact optical system having high optical performance is provided. The optical system comprises, in order from the object side to the upper side, a first lens having a positive refractive power, a second lens having a negative refractive power, a bending optical element, and a rear lens having a negative refractive power, wherein the second lens is positioned adjacent to the upper side of the first lens and satisfies a predetermined conditional equation, wherein NdG1 is the refractive index of the material of the first lens and νdG1 is the Abbe number for the d-line of the material of the first lens.

Description

Technology Field

[0001] The disclosure of this specification relates to an optical system and an imaging device having the optical system, and in particular to an imaging optical system suitable for cameras for portable terminals such as smartphones, digital still cameras and video cameras, and an imaging device having the imaging optical system. Background Technology

[0002] Recently, imaging optical systems used in cameras for portable terminals such as smartphones, digital still cameras, and video cameras are required to be small while having high optical performance.

[0003] In the specification of U.S. Patent Application Publication No. 2021 / 0165192, a telephoto lens is disclosed comprising two lenses arranged in order from the object side, a bending optical element, and a rear lens group having a plurality of lenses. means of solving the problem

[0004] According to one aspect of the present disclosure, an optical system comprises, in order from the object side to the upper side, a first lens having a positive refractive power, a second lens having a negative refractive power, a bending optical element, and a rear lens having a negative refractive power, wherein the second lens is positioned adjacent to (positioned next to) the upper side of the first lens and satisfies the following condition:

[0005] 1.30 <NdG1<1.60

[0006] 73.0<νdG1<120.0

[0007] At this time, NdG1 is the refractive index of the material of the first lens, and νdG1 is the Abbe number for the d-line of the material of the first lens.

[0008] Another feature of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings. The following description of embodiments is given by way of example. Brief explanation of the drawing

[0009] FIG. 1 is a cross-sectional view of an optical system according to Example 1. FIG. 2 is an aberration diagram of an optical system according to Example 1. FIG. 3 is a cross-sectional view of an optical system according to Example 2. FIG. 4 is an aberration diagram of an optical system according to Example 2. FIG. 5 is a cross-sectional view of an optical system according to Example 3. FIG. 6 is an aberration diagram of the optical system according to Example 3. FIG. 7 is a cross-sectional view of an optical system according to Example 4. FIG. 8 is an aberration diagram of the optical system according to Example 4. FIG. 9 is a cross-sectional view of an optical system according to Example 5. FIG. 10 is an aberration diagram of the optical system according to Example 5. FIG. 11 is a cross-sectional view of an optical system according to Example 6. FIG. 12 is an aberration diagram of an optical system according to Example 6. FIG. 13 is a cross-sectional view of an optical system according to Example 7. FIG. 14 is an aberration diagram of the optical system according to Example 7. FIG. 15 is a cross-sectional view of an optical system according to Example 8. FIG. 16 is an aberration diagram of the optical system according to Example 8. FIG. 17 is a cross-sectional view of an optical system according to Example 9. FIG. 18 is an aberration diagram of the optical system according to Example 9. FIG. 19 is a cross-sectional view of an optical system according to Example 10. FIG. 20 is an aberration diagram of an optical system according to Example 10. FIG. 21 is a cross-sectional view of an optical system according to Example 11. FIG. 22 is an aberration diagram of the optical system according to Example 11. FIG. 23 is a cross-sectional view of an optical system according to Example 12. FIG. 24 is an aberration diagram of an optical system according to Example 12. FIGS. 25a to 25c are drawings for explaining embodiments of a folded optical element. FIG. 26 is a schematic diagram of the main parts of an imaging device to which the optical system of each embodiment is applied. Specific details for implementing the invention

[0010] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the drawings. In each drawing, the same reference numeral is used for identical components, and redundant descriptions are omitted.

[0011] FIGS. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 are cross-sectional views of optical systems L0 according to Examples 1 to 12, respectively. The optical system L0 of each example is used in imaging devices such as digital still cameras, digital video cameras, surveillance cameras, vehicle-mounted cameras, and smartphones.

[0012] In each cross-sectional view, the left side is the object side (front side) and the right side is the upper side (rear side). The aperture diaphragm SP determines (limits) the luminous flux of the maximum aperture F number (Fno). The optical system L0 of each embodiment has a plurality of lenses or optical elements. The optical system L0 of each embodiment may further include an aspherical lens, a Fresnel lens, a metric lens, a diffractive optical element, and an optical element that has substantially no refractive power, such as a cover glass.

[0013] When the optical system of each embodiment is used in an imaging device such as a camera for a portable terminal, a video camera, or a digital camera, the upper surface IP corresponds to a solid-state imaging device (photoelectric conversion device) such as a charge-coupled device (CCD) sensor or a complementary metal-oxide-semiconductor (CMOS) sensor. When the optical system of each embodiment is used in an imaging device of a silver halide film camera, the upper surface IP corresponds to a film surface.

[0014] FIGS. 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 are aberration diagrams of optical systems L0 of Examples 1 to 12 at infinity focus, respectively.

[0015] In the spherical aberration diagram, Fno represents the F number, the solid line represents spherical aberration for the d-line (wavelength 587.6 nm), and the dotted line represents spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S represents the sagittal plane, and the dotted line M represents the meridional plane. The distortion aberration diagram represents the distortion aberration for the d-line. The chromatic aberration diagram represents the chromatic aberration for the g-line. Also, ω is the angle of half-angle (degrees, °).

[0016] Next, the characteristic configuration of the optical system L0 of each embodiment is described.

[0017] The optical system L0 of each embodiment has a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR for bending the optical path, and a rear lens GR having negative refractive power, arranged in order from the object side to the upper side.

[0018] By arranging the positive and negative lenses as the first lens G1 and the second lens G2, respectively, the lenses are arranged in a so-called telephoto type optical power arrangement, and the light rays are strongly converged by the first lens G1. Because of this, the optical system L0 can be miniaturized.

[0019] A bending optical element PR has the function of bending the incident light beam. Optical elements such as prisms or mirrors having a reflective surface correspond to the bending optical element PR. Details regarding the bending optical element PR will be described later. The space between the bending optical element PR and the image plane is characterized by a lower height for axial rays and a higher height for off-axis rays. For this reason, by placing a negative rear lens GR above the bending optical element PR, it becomes possible to effectively correct off-axis aberrations such as astigmatism and coma.

[0020] Next, the desirable conditions that the optical system L0 of each embodiment satisfies are described.

[0021] It is preferable that the optical system L0 of each embodiment satisfies at least one of the following condition equations (1) to (14).

[0022] 1.30 <NdG1<1.60 (1)

[0023] 65.0<νdG1<120.0 (2)

[0024] 0.20<|fG2 / f|<4.00 (3)

[0025] 0.10<|fGR / f|<2.00 (4)

[0026] 0.20 <fG1 / f<1.00 (5)

[0027] 0.20<|fGR / fG1|<3.00 (6)

[0028] -2.00<(G1R1+G1R2) / (G1R1-G1R2)<0.50 (7)

[0029] -3.00 <G2R1+G2R2) / (G2R1-G2R2)<7.00 (8)

[0030] -8.00 <GRR1+GRR2) / (GRR1-GRR2)<1.00 (9)

[0031] 0.005<θgFG1-0.6438+0.001682×νdG1<0.100 (10)

[0032] 0.01 <LD / f<0.60 (11)

[0033] 0.40 <TTL / f<4.00 (12)

[0034] 1<ω<20 (13)

[0035] 0.20 <EA_IMG / EA_OBJ<1.00 (14)

[0036] At this time, for each conditional expression, the values ​​are expressed as follows.

[0037] NdG1 is the refractive index of the material of the first lens G1 for the d-line, νdG1 is the Abbe number of the material of the first lens G1 for the d-line, and νdG2 is the Abbe number of the material of the second lens G2 for the d-line.

[0038] f is the focal length of the entire optical system L0, and TTL is the total optical length of the optical system L0.

[0039] fG1 is the focal length of the first lens G1, fG2 is the focal length of the second lens G2, and fGR is the focal length of the rear lens GR.

[0040] LD is the distance on the optical axis from the object-side lens surface of the first lens G1 to the object-side lens surface of the folded optical element.

[0041] ω is the half-angle of view (degrees, °) for the maximum image height of the optical system L0.

[0042] G1R1 is the radius of curvature of the object-side lens surface of the first lens G1, and G1R2 is the radius of curvature of the upper-side lens surface of the first lens G1.

[0043] G2R1 is the radius of curvature of the object-side lens surface of the second lens G2, and G2R2 is the radius of curvature of the upper-side lens surface of the second lens G2.

[0044] GRR1 is the radius of curvature of the object-side lens surface of the rear lens GR, and GRR2 is the radius of curvature of the upper-side lens surface of the rear lens GR.

[0045] θgFG1 is the partial dispersion ratio of the material of the first lens G1.

[0046] EA_OBJ is the effective diameter of the object-side lens surface of the lens closest to the object side of optical system L0, and EA_IMG is the effective diameter of the upper-side lens surface of the lens closest to the upper side of optical system LO.

[0047] The conditional formula (1) specifies the refractive index of the first lens G1 for the d-line. A value greater than the upper limit specified by the conditional formula (1) is undesirable because it increases the dispersion of the material of the first lens G1 and causes the correction of chromatic aberration to become excessive. A value smaller than the lower limit specified by the conditional formula (1) is undesirable because it decreases the refractive index of the first lens G1, increases the radius of curvature of the first lens G1, and causes the optical system L0 to become larger in the direction of the optical axis.

[0048] In addition, it is preferable that the upper limit defined by condition (1) is any one of 1.595, 1.590, 1.585, 1.580, 1.575, 1.570, 1.565, 1.560, 1.555, 1.550, 1.545, 1.540, 1.535, and 1.530.

[0049] In addition, the lower limit specified by condition (1) is preferably one of 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.42, and 1.43.

[0050] The conditional equation (2) specifies the Abbe number for the d-line of the first lens G1. A value greater than the upper limit specified by the conditional equation (2) is undesirable because it results in excessive correction of chromatic aberration. A value smaller than the lower limit specified by the conditional equation (2) is undesirable because it results in excessive axial chromatic aberration and magnification chromatic aberration occurring in the first lens G1, making it difficult to properly correct chromatic aberration throughout the entire optical system.

[0051] In addition, the upper limit defined by condition (2) is preferably one of 118.0, 116.0, 114.0, 112.0, 110.0, 108.0, 106.0, 104.0, 102.0, 100.0, 99.0, 98.0, 97.0, 96.0 and 95.0.

[0052] In addition, the lower limit defined by condition (2) is preferably one of 81.0 among 66.0, 67.0, 68.0, 69.0, 70.0, 71.0, 72.0, 73.0, 74.0, 75.0, 76.0, 77.0, 78.0, 79.0, and 80.0.

[0053] The conditional equation (3) specifies the refractive power of the second lens G2. A value greater than the upper limit specified by the conditional equation (3) is undesirable because the refractive power of the second lens G2 becomes excessively weak, making it difficult to correct the spherical aberration and axial chromatic aberration occurring in the first lens G1 using the second lens G2. A value smaller than the lower limit specified by condition (3) is undesirable because the refractive power of the second lens G2 becomes excessively strong, which leads to an overcorrection of spherical aberration and astigmatism occurring in the first lens G1.

[0054] The conditional equation (4) specifies the refractive power of the rear lens GR. A value greater than the upper limit specified by the conditional equation (4) is undesirable because the refractive power of the rear lens GR becomes excessively weak, making it difficult to correct spherical aberration and axial chromatic aberration occurring on the object side of the rear lens GR by the rear lens GR. A value smaller than the lower limit specified by the conditional equation (4) is undesirable because the refractive power of the rear lens GR becomes excessively strong, resulting in excessive correction of coma aberration and astigmatism.

[0055] The conditional formula (5) specifies the refractive power of the first lens G1. A value greater than the upper limit specified by the conditional formula (5) is undesirable because the refractive power of the first lens G1 becomes excessively weak, causing the height of the light rays incident on the lens placed above the first lens G1 to increase and the diameter of the lens placed above the first lens G1 to increase. A value smaller than the lower limit specified by the conditional formula (5) is undesirable because the refractive power of the first lens G1 becomes excessively strong, causing strong spherical aberration and coma aberration.

[0056] The conditional equation (6) specifies the ratio of the refractive power of the first lens G1 and the rear lens GR. A value greater than the upper limit specified by the conditional equation (6) is undesirable because the refractive power of the rear lens GR becomes excessively weak relative to the refractive power of the first lens G1, making it difficult to correct the astigmatism and magnification chromatic aberration occurring in the first lens G1 by the rear lens GR. A value smaller than the lower limit specified by the conditional equation (6) is undesirable because the refractive power of the rear lens GR becomes excessively strong, causing strong astigmatism and distortion aberrations.

[0057] The conditional equation (7) defines the shape of the lens surface of the first lens G1. A value greater than the upper limit defined by the conditional equation (7) is undesirable because the upper lens surface of the first lens G1 becomes a concave surface with a strong concave shape facing the object side, causing strong coma aberration in the first lens G1. A value smaller than the lower limit defined by the conditional equation (7) is undesirable because the first lens G1 becomes a meniscus lens with a strong convex surface facing the object side, causing strong spherical aberration in the first lens G1.

[0058] The conditional equation (8) defines the shape of the lens surface of the second lens G2. A value greater than the upper limit defined by the conditional equation (8) results in the second lens G2 becoming a meniscus lens with a strong convex surface facing the object side, which is undesirable as it leads to excessive correction of spherical aberration. A value smaller than the lower limit defined by the conditional equation (8) results in the second lens G2 becoming a meniscus lens with a strong concave surface facing the object side, which is undesirable as it prevents the second lens G2 from converging light rays, making it difficult to reduce the diameter of the optical element after the second lens G2.

[0059] The conditional formula (9) defines the shape of the lens surface of the rear lens GR. A value greater than the upper limit defined by the conditional formula (9) is undesirable because the rear lens GR becomes a meniscus lens with a strong concave surface facing the object, resulting in excessive correction of spherical aberration. A value smaller than the lower limit defined by the conditional formula (9) is undesirable because the second lens G2 becomes a meniscus lens with a strong convex surface facing the object, resulting in excessive correction of magnification chromatic aberration and coma aberration.

[0060] The conditional formula (10) specifies the partial dispersion ratio for the g-line and F-line of the material of the first lens G1. A value greater than the upper limit specified by the conditional formula (10) is undesirable because it results in excessive correction of axial chromatic aberration and magnification chromatic aberration. A value smaller than the lower limit specified by the conditional formula (10) is undesirable because it results in insufficient correction of axial chromatic aberration and magnification chromatic aberration.

[0061] The conditional formula (11) defines the distance along the optical axis from the object-side lens surface of the first lens G1 to the object-side of the bending optical element. A value greater than the upper limit defined by the conditional formula (11) is undesirable because the distance along the optical axis from the first lens G1 to the bending optical element PR increases, causing the optical system L0 to expand in the direction of the optical axis. A value smaller than the lower limit defined by the conditional formula (11) is undesirable because the thickness of the first lens G1 and the second lens G2 placed on the object-side of the bending optical element decreases, causing the refractive power of the first lens G1 and the second lens G2 to become excessively weak.

[0062] The conditional formula (12) defines the ratio of the total optical length of the optical system L0 to the focal length of the entire optical system L0. At this time, the total optical length represents the distance along the optical axis from the lens surface closest to the object side to the image plane. If optical elements that do not substantially possess refractive power, such as cover glass and folded optical elements, are placed further to the object side than the lens surface closest to the object side, these optical elements are not considered in the calculation of the total optical length. A value greater than the upper limit defined by the conditional formula (12) is undesirable because the total optical length of the optical system L0 becomes too large, causing the optical system L0 to become enlarged in the direction of the optical axis. A value smaller than the lower limit defined by the conditional formula (12) is undesirable because the refractive power of the first lens G1 and the second lens G2 becomes excessively strong, making it difficult to correct various aberrations.

[0063] The conditional formula (13) specifies the desirable range of the angle of view for the maximum image height of the optical system L0. The maximum image height of the optical system L0 refers to the distance from the position on the optical axis where the peripheral light intensity is 10% when the light intensity at the position on the optical axis is 100% in the image plane IP. A value greater than the upper limit specified by the conditional formula (13) is undesirable because Fno becomes excessively small, causing the lens diameter of the lens constituting the optical system L0 to increase, and thus the optical system L0 becomes enlarged in the radial direction. A value smaller than the lower limit specified by the conditional formula (13) is undesirable because the height of the light ray incident on the first lens G1 becomes excessively small, causing the optical path length TTL to increase, and thus the optical system L0 becomes enlarged in the optical axis direction.

[0064] Conditional formula (14) defines the ratio of the effective diameter of the light beam on the object-side lens surface of the lens closest to the object in the optical system L0 to the effective diameter of the light beam on the upper-side lens surface of the lens closest to the upper-side. In this case, the lens refers to a lens having refractive power. Therefore, the effective diameter of optical elements such as cover glass, mirrors, and prisms that do not substantially have refractive power is not included in this conditional formula.

[0065] A value greater than the upper limit specified by the conditional formula (14) is undesirable because the lens diameter of the lens placed closest to the upper side of the optical system L0 becomes too large, causing the optical system L0 to become enlarged in the diameter direction. A value smaller than the lower limit specified by the conditional formula (14) is undesirable because the refractive power of the lens placed closest to the upper side of the optical system L0 becomes excessively strong, making it difficult to correct various aberrations.

[0066] In addition, it is more preferable to set the numerical range of conditional expressions (1) to (14) to the numerical range defined by the following conditional expressions (1a) to (14a).

[0067] 1.40 <NdG1<1.57 (1a)

[0068] 73.0<νdG1<110.0 (2a)

[0069] 0.30<|fG2 / f|<3.00 (3a)

[0070] 0.15<|fGR / f|<1.50 (4a)

[0071] 0.25 <fG1 / f<0.80 (5a)

[0072] 0.50<|fGR / fG1|<2.70 (6a)

[0073] -1.80<(G1R1+G1R2) / (G1R1-G1R2)<0.30 (7a)

[0074] -2.00 <G2R1+G2R2) / (G2R1-G2R2)<6.00 (8a)

[0075] -7.00 <GRR1+GRR2) / (GRR1-GRR2)<0.60 (9a)

[0076] 0.010<θgFG1-0.6438+0.001682×νdG1<0.080 (10a)

[0077] 0.05 <LD / f<0.50 (11a)

[0078] 0.60 <TTL / f<3.00 (12a)

[0079] 2<ω<15 (13a)

[0080] 0.35 <EA_IMG / EA_OBJ<0.95 (14a)

[0081] In addition, it is more preferable to set the numerical range of conditional expressions (1) to (14) to the numerical range defined by the following conditional expressions (1b) to (14b).

[0082] 1.42 <NdG1<1.55 (lb)

[0083] 85.0<νdG1<100.0 (2b)

[0084] 0.40<|fG2 / f|<2.50 (3b)

[0085] 0.30<|fGR / f|<1.20 (4b)

[0086] 0.30 <fG1 / f<0.70 (5b)

[0087] 0.70<|fGR / fG1|<2.40 (6b)

[0088] -1.50<(G1R1+G1R2) / (G1R1-G1R2)<0.10 (7b)

[0089] -0.50 <G2R1+G2R2) / (G2R1-G2R2)<5.00 (8b)

[0090] -6.00 <GRR1+GRR2) / (GRR1-GRR2)<2.00 (9b)

[0091] 0.020<θgFG1-0.6438+0.001682×νdG1<0.050 (10b)

[0092] 0.07 <LD / f<0.40 (1lb)

[0093] 0.80 <TTL / f<2.00 (12b)

[0094] 3<ω<12 (13b)

[0095] 0.50 <EA_IMG / EA_OBJ<0.90 (14b)

[0096] Next, the configuration preferred to be satisfied in the optical system L0 of each embodiment is described.

[0097] In the optical system L0 of each embodiment, it is preferable that the bending optical element PR be positioned adjacent to the upper side of the second lens G2. Accordingly, since the height of the axial light rays passing through the second lens G2 can be increased, spherical aberration and axial chromatic aberration can be corrected effectively.

[0098] In the optical system L0 of each embodiment, it is preferable that at least one of the object-side lens surface and the image-side lens surface of the first lens G1 has an aspherical shape. By arranging an aspherical lens as the first lens G1, spherical aberration and coma aberration occurring in the first lens G1 can be reduced. Furthermore, to further enhance the aforementioned effect, it is preferable that the aspherical shape of at least one of the object-side lens surface and the image-side lens surface of the first lens G1 is a shape that weakens positive refractive power from the center of the optical axis toward the periphery.

[0099] Here, a shape that weakens the refractive power from the center of the optical axis toward the periphery is described. The aforementioned shape refers to a shape in which, when comparing the refractive power at the center of the optical axis, the point where the image height is 50%, and the periphery, the refractive power at the center of the optical axis is the strongest, the refractive power at the point where the image height is 50% is weaker than the refractive power at the center of the optical axis, and the refractive power at the periphery becomes even weaker. The same applies to a shape that weakens the refractive power from the center of the optical axis toward the periphery.

[0100] In the optical system L0 of each embodiment, it is preferable that at least one of the object-side lens surface and the image-side lens surface of the second lens G2 has an aspherical shape. By arranging an aspherical lens as the second lens G2, spherical aberration, coma aberration, and astigmatism generated in the first lens G1 can be effectively corrected. Furthermore, to further enhance the aforementioned effect, it is preferable that the aspherical shape of at least one of the object-side lens surface and the image-side lens surface of the second lens G2 has a shape that strengthens negative refractive power from the center of the optical axis toward the periphery.

[0101] In the optical system L0 of each embodiment, it is preferable that at least one of the object-side lens surface and the upper lens surface of the upper lens GR has an aspherical shape. By placing an aspherical lens as the rear lens GR, coma aberration and astigmatism generated in the first lens G1 can be effectively corrected.

[0102] In each embodiment, the optical system L0 is preferably a second lens G2 made of a resin material. Accordingly, the second lens G2 can be made lighter, thereby enabling the miniaturization of the optical system L0.

[0103] In each embodiment, the optical system L0 is preferably a rear lens GR made of a resin material. Accordingly, the rear lens GR can be made lighter, thereby enabling the miniaturization of the optical system L0.

[0104] In the optical system L0 of each embodiment, it is preferable that the bending optical element PR reflects the light rays multiple times. By bending the light rays multiple times, the overall length of the optical system L0 can be shortened, thereby enabling the miniaturization of the optical system L0.

[0105] In the optical system L0 of each embodiment, it is preferable that the number of lenses having refractive power among the optical elements included in the optical system L0 is 4 or fewer. By reducing the number of lenses constituting the optical system L0, the optical system L0 can be miniaturized.

[0106] Next, the optical systems L0 of Examples 1 to 12 will be described in detail. In the optical system L0 of each example, descriptions of configurations similar to the optical system L0 according to other examples will be omitted, and the differences from Example 1 will be described mainly.

[0107] [Example 1]

[0108] FIG. 1 is a cross-sectional view of the optical system L0 of Example 1. The optical system L0 of Example 1 consists of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR, and a rear lens GR, arranged in order from the object side. The second lens G2 is a meniscus lens having a convex surface facing the object side.

[0109] In the optical system L0 of Example 1, the bending optical element PR is positioned adjacent to the upper side of the second lens G2. Accordingly, the height of the axial light rays passing through the second lens G2 can be increased, so spherical aberration and axial chromatic aberration can be corrected well.

[0110] In the optical system L0 of Example 1, the upper lens surface of the first lens G1 has an aspherical shape that weakens the positive refractive power from the center of the optical axis toward the periphery. Additionally, the object-side lens surface of the second lens G2 has an aspherical shape that strengthens the negative refractive power from the center of the optical axis toward the periphery.

[0111] In the optical system L0 of Example 1, the second lens G2 and the rear lens GR are made of resin material.

[0112] [Example 2]

[0113] FIG. 3 is a cross-sectional view of the optical system L0 of Example 2. The optical system L0 of Example 2 consists of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR, and a rear lens GR, arranged in order from the object side. The second lens G2 is a meniscus lens having a convex surface facing upward.

[0114] [Examples 3 to 7]

[0115] FIGS. 5, 7, 9, 11, and 13 are cross-sectional views of optical systems L0 of Examples 3 to 7, respectively. Optical systems L0 of Examples 3 to 7 consist of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a folded optical element PR, and a rear lens GR, arranged in order from the object side. The second lens G2 is a meniscus lens having a convex surface facing the object side.

[0116] [Example 8]

[0117] FIG. 15 is a cross-sectional view of the optical system L0 of Example 8. The optical system L0 of Example 8 consists of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR, and rear lenses GR1 and GR2 having negative refractive power, arranged in order from the object side. The second lens G2 is a meniscus lens having a convex surface facing the object side. The rear lens GR2 is a meniscus lens having a convex surface facing upward.

[0118] In the optical system L0 of Example 8, two rear lenses GR1 and GR23 having negative refractive power are arranged above the folded optical element PR. In order to effectively correct out-of-axis aberrations such as astigmatism and coma aberration, it is desirable to have negative refractive power above the folded optical element PR. By sharing this negative refractive power between the two rear lenses, the refractive power of a single negative lens can be weakened. As a result, the occurrence of spool-shaped distortion aberrations and field curvature can be suppressed.

[0119] [Examples 9 and 10]

[0120] FIGS. 17 and 19 are cross-sectional views of the optical system L0 of Examples 9 and 10, respectively. The optical system L0 of Examples 9 and 10 consists of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR, and a rear lens GR, arranged in order from the object side. The second lens G2 is a meniscus lens having a convex surface facing the object side.

[0121] [Example 11]

[0122] FIG. 21 is a cross-sectional view of the optical system L0 of Example 11. The optical system L0 of Example 11 is composed, in order from the object side, of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a third lens G3 having positive refractive power, a bending optical element PR, and a rear lens GR having negative refractive power. The second lens G2 is a meniscus lens having a convex surface facing the object side. The rear lens GR is a meniscus lens having a convex surface facing upward.

[0123] [Example 12]

[0124] FIG. 23 is a cross-sectional view of the optical system L0 of Example 12. The optical system L0 of Example 12 consists of an aperture diaphragm SP, a first lens G1 having positive refractive power, a second lens G2 having negative refractive power, a bending optical element PR, and a rear lens GR having negative refractive power, arranged in order from the object side. The first lens G1 and the second lens G2 are joined together. The second lens G2 is a meniscus lens having a convex surface facing upward. The rear lens GR is a meniscus lens having a convex surface facing upward.

[0125] In the optical system L0 of Example 12, the first lens G1 and the second lens G2 are joined together. Accordingly, the eccentric error occurring in the first lens G1 and the second lens G2 can be suppressed, thereby improving the optical performance of the optical system L0.

[0126] Hereinafter, numerical examples 1 to 12 for Examples 1 to 12 are presented. In each numerical example, the face number i indicates the order of the faces when counted from the object side. r is the radius of curvature (mm) of the i-th face from the object side, d is the lens thickness (mm) or air gap (mm) on the optical axis between the i-th face and the (i+1)-th face, and nd is the refractive index of the optical material with respect to the d-line between the i-th face and the (i+1)-th face. Additionally, the sign of d is positive for the direction from the object side toward the upward side on the optical axis. νd is the Abbe number based on the d-line of the optical material between the i-th face and the (i+1)-th face. θgF is the partial dispersion ratio of the optical material between the i-th face and the (i+1)-th face.

[0127] BF represents the aforementioned back focus length (mm). The total optical length is the distance along the optical axis from the lens plane (foremost plane) positioned closest to the object side of the optical system L0 to the image plane. If the optical plane is aspherical, an "*" symbol is placed to the right of the plane number. The aspherical shape is expressed by the following equation, where X is the displacement from the plane vertex in the direction of the optical axis, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the radius of paraxial curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspherical coefficients for each order.

[0128] X=(h 2 / R) / [1+(1-(1+k)(h / R) 2 )) 1 / 2 +A4xh 4 +A6xh 6 +A8xh 8 +A10xh 10 +A12xh 12

[0129] "e±XX" for each aspherical coefficient is "×10± XX It means "

[0130] [Numerical Example 1]

[0131]

[0132] [Numerical Example 2]

[0133]

[0134] [Numerical Example 3]

[0135]

[0136] [Numerical Example 4]

[0137]

[0138] [Numerical Example 5]

[0139]

[0140] [Numerical Example 6]

[0141]

[0142] [Numerical Example 7]

[0143]

[0144] [Numerical Example 8]

[0145]

[0146] [Numerical Example 9]

[0147]

[0148] [Numerical Example 10]

[0149]

[0150] [Numerical Example 11]

[0151]

[0152] [Numerical Example 12]

[0153]

[0154] The values ​​of the aforementioned physical quantities in each embodiment are shown in Table 1, and the values ​​of the conditional expressions in each embodiment are shown in Table 2.

[0155]

[0156]

[0157] [Folded Optical Element]

[0158] Next, the bending optical element PR of each embodiment will be described in detail with reference to FIGS. 25 to 25c. FIGS. 25a to 25c show an example of the configuration of the bending optical element PR included in the optical system L0 of Example 1.

[0159] In FIG. 25a, a light ray is bent at the REF1 surface inside the bending optical element PR.

[0160] The bending angle is 45°. The numerical value of the distance L1 from the surface on the object side to the surface of REF1 and the numerical value of the distance L2 from the surface of REF1 to the surface on the upper side of the bending optical element PR are shown in FIG. 25a.

[0161] In FIG. 25b, a light ray is bent at two surfaces, REF1 and REF2, inside the bending optical element. The bending angle is 45°. The numerical values ​​of the distance L1 from the surface on the object side to the REF1 surface, the numerical value of the distance L2 from the REF1 surface to the REF2 surface, and the numerical value of the distance L3 from the REF2 surface to the upper surface of the bending optical element PR are shown in FIG. 25b.

[0162] In FIG. 25c, within the folded optical element PR, light rays are folded at three surfaces: REF1, REF2, and REF3. The folding angle is 45°. The numerical values ​​of L1, the distance from the object-side surface to the REF1 surface, L2, the distance from the REF1 surface to the REF2 surface, L3, the distance from the REF2 surface to the REF3 surface, and L4, the distance from the REF3 surface to the upper surface of the folded optical element OR, are shown in FIG. 25c.

[0163] As shown in FIGS. 25a to 25c, even if a light ray is bent at any angle and a certain number of times within a bendable optical element, if the total optical axis distance within the bendable optical element is the same, the resulting aberration is the same. For this reason, the optical system can be considered as the same imaging optical system.

[0164] In this embodiment, a prism is used as an example of a folded optical element PR. However, a mirror may be used instead of a prism. In addition, the reflection angle of the prism or mirror may be 30°, 60°, or other angles instead of 45°. In addition, the reflective surface of the prism or mirror may be a curved surface or an aspherical surface.

[0165] [Imaging device]

[0166] Next, an example of an imaging device using the optical system L0 of each embodiment as an imaging optical system will be described with reference to FIG. 26. In FIG. 26, the camera body (20) has an imaging optical system (21) similar to any one of the optical systems L0 described in Examples 1 to 12, and a solid-state imaging element (photoelectric conversion element) (22) embedded in the camera body (20) and receiving light from the image of a subject formed by the imaging optical system (21). The solid-state imaging element (22) is a sensor such as a CCD sensor or a CMOS sensor. The memory (23) is a recording unit that records the image of a subject received by the solid-state imaging element (22). The viewfinder (24) is formed on the solid-state imaging element (22) and is used to observe the image of a subject displayed on a display element (not shown).

[0167] The camera body (20) may be a single-lens reflex camera having a quick-return mirror, a mirrorless camera not having a quick-return mirror, or a camera built into a portable terminal such as a smartphone.

[0168] The aforementioned solid imaging element (22) may be perpendicular to the incident light or inclined toward the incident light. In this case, it is preferable that the angle of inclination of the solid imaging element (22) toward the incident light and the angle of inclination of the reflective surface of the folded optical element PR are each appropriately set according to the configuration of the optical system L0 and the imaging device.

[0169] In this way, by applying the optical system L0 of each embodiment to an imaging device such as a digital still camera, an imaging optical system that is small / lightweight and has high optical performance, and an imaging device having the imaging optical system can be obtained.

[0170] Although preferred embodiments and examples of the disclosure have been described above, the disclosure is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist thereof.

[0171] In the optical system L0 of each embodiment, all or some of the lenses included in the optical system L0 may be used as image stabilization lens parts, or image stabilization function may be provided by moving the imaging plane in a direction parallel to the optical axis.

[0172] In the optical system L0 of each embodiment, all or some of the lenses included in the optical system L0 may be used for focusing.

[0173] Although the present invention has been described with reference to exemplary embodiments, it is obvious that the invention is not limited to these embodiments. The scope of protection of the following claims shall be interpreted as broadly as possible to encompass all variations, equivalent structures, and functions.

Claims

Claim 1 An optical system comprising, in order from the object side to the upper side, a first lens having a positive refractive power, a second lens having a negative refractive power, a bending optical element, and a rear lens having a negative refractive power, wherein the second lens is positioned adjacent to the upper side of the first lens and satisfies the following condition: 1.30 <NdG1<1.6073.0<νdG1<120.0이때 NdG1은 상기 제1렌즈의 재료의 굴절률이고, νdG1은 상기 제1렌즈의 재료의 d선에 대한 아베수이다. Claim 2 In claim 1, an optical system satisfying the following condition: 0.20 < |fG2 / f| < 4.00, where fG2 is the focal length of the second lens and f is the focal length of the entire optical system. Claim 3 In the first paragraph, an optical system satisfying the following condition: 0.10 < |fGR / f| < 2.00, where fGR is the focal length of the rear lens and f is the focal length of the entire optical system. Claim 4 In claim 1, the bending optical element is an optical system positioned adjacent to the upper side of the second lens. Claim 5 In Clause 1, an optical system satisfying the following condition: 0.20 <fG1 / f<1.00이때 fG1은 상기 제1렌즈의 초점거리이고, f는 전체 광학계의 초점거리이다. Claim 6 In claim 1, an optical system satisfying the following condition: 0.20 < |fGR / fG1| < 3.00, where fG1 is the focal length of the first lens and fGR is the focal length of the rear lens. Claim 7 In claim 1, an optical system satisfying the following condition: -2.00 < (G1R1 + G1R2) / (G1R1 - G1R2) < 0.50, where G1R1 is the radius of curvature of the object-side lens surface of the first lens, and G1R2 is the radius of curvature of the upper-side lens surface of the first lens. Claim 8 In claim 1, an optical system satisfying the following condition: -3.00 < (G2R1 + G2R2) / (G2R1 - G2R2) < 7.00, where G2R1 is the radius of curvature of the object-side lens surface of the second lens, and G2R2 is the radius of curvature of the upper-side lens surface of the second lens. Claim 9 In claim 1, an optical system satisfying the following condition: -8.00 < (GRR1 + GRR2) / (GRR1 - GRR2) < 1.00, where GRR1 is the radius of curvature of the object-side lens surface of the rear lens, and GRR2 is the radius of curvature of the upper-side lens surface of the rear lens. Claim 10 In claim 1, an optical system satisfying the following condition: 0.005 < θgFG1 - 0.6438 + 0.001682 × νdG1 < 0.100, where θgFG1 is the partial dispersion ratio of the material of the first lens. Claim 11 In Clause 1, an optical system satisfying the following condition: 0.01 <LD / f<0.60이때 LD은 상기 제1렌즈의 물체측 렌즈면으로부터 상기 절곡 광학 소자의 물체측면까지의 광축 상의 거리이고, f는 전체 광학계의 초점거리이다. Claim 12 In Clause 1, an optical system satisfying the following condition: 0.40 <TTL / f<4.00이때 TTL는 상기 광학계의 전체 광학 길이이고, f는 전체 광학계의 초점거리이다. Claim 13 In claim 1, an optical system satisfying the following condition: 1 < ω < 20, where ω is the half-angle of the image of the optical system [°]. Claim 14 In Clause 1, an optical system satisfying the following condition: 0.20 <EA_IMG / EA_OBJ<1.00이때 EA_OBJ는 상기 광학계의 물체측에 가장 가깝게 배치된 렌즈의 물체측 렌즈면의 광선 유효 직경이고, EA_IMG는 상기 광학계의 상측에 가장 가깝게 배치된 렌즈의 상측 렌즈면의 광선 유효 직경이다. Claim 15 In claim 1, the second lens is an optical system having an aspherical shape. Claim 16 In claim 15, the aspherical shape of the second lens is an optical system in which the negative refractive power is strengthened from the center of the optical axis toward the periphery. Claim 17 In claim 1, the rear lens is an optical system having an aspherical shape. Claim 18 In claim 17, the aspherical shape of the rear lens is an optical system in which the negative refractive power is strengthened from the center of the optical axis toward the periphery. Claim 19 In claim 1, the bending optical element is an optical system that reflects an incident light ray multiple times within the bending optical element. Claim 20 An optical system according to claim 1, wherein the number of lenses included in the optical system is 4 or fewer. Claim 21 An optical system having the first lens, the second lens, the bending optical element, and the rear lens arranged in order from the object side to the upper side in the first paragraph. Claim 22 An optical system according to claim 1, comprising the first lens, the second lens, the bending optical element, the third lens having a negative refractive power, and the fourth lens having a negative refractive power, wherein at least one of the third lens and the fourth lens is the rear lens. Claim 23 An optical system according to claim 1, comprising the first lens, the second lens, the bending optical element, the third lens having a positive refractive power, and the rear lens, arranged in order from the object side to the upper side. Claim 24 An optical system comprising a first lens having positive refractive power, a second lens having negative refractive power, a bending optical element, and a rear lens having negative refractive power, arranged in order from the object side to the upper side, wherein the object-side lens surface of the first lens is a convex surface facing the object side. Claim 25 An imaging device having an optical system described in any one of claims 1 to 24 and an imaging element that receives an image formed by the optical system.

Images