Optical system and imaging device having the same

Abstract

To provide a compact optical system which is of a large diameter and yet has a good optical performance from a center of a field angle through a periphery.SOLUTION: An optical system comprises a lens group L that includes a plurality of lenses arranged in order from an object side to an image side, and a final lens Gn having negative refractive power. An image-side lens surface of the final lens includes a concave region in the vicinity of the optical axis and an aspherical shape provided with an inflection point. When it is assumed that Nd represents an average value of refractive indices of all lenses included in the lens group L, a conditional expression 1.780<Nd<2.500 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Imaging devices such as digital cameras, surveillance cameras, and in-vehicle cameras using solid-state image sensors require a compact optical system with good optical performance from the center to the periphery of the field of view and a small overall length. In particular, surveillance cameras and in-vehicle cameras require an optical system with a small F-number (Fno) (bright) to enable shooting in dark places. However, bright optical systems tend to require a large aperture.

[0003] Furthermore, correcting aberrations is difficult in large-aperture optical systems, particularly field curvature and spherical aberration. To correct these, optical systems tend to become larger.

[0004] Patent Document 1 discloses a bright optical system consisting of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6546656 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, while the optical system in Patent Document 1 has a relatively small Fno and good optical performance at the edges of the field of view, it is insufficient in terms of miniaturization.

[0007] This invention provides a compact optical system that, despite having a large aperture, exhibits excellent optical performance from the center to the periphery of the field of view. [Means for solving the problem]

[0008] One aspect of the present invention is an optical system consisting of seven lenses arranged in order from the object side to the image side. Consists of Lens group and final lens with negative refractive power and, An optical system comprising the following, wherein the image-side lens surface of the final lens includes a concave region near the optical axis and has an aspherical shape with an inflection point, and the lens group All lenses included Materials The average refractive index is Nd, and the distance along the optical axis from the image-side lens surface to the image plane of the final lens when the optical system is focused at infinity is... Separation skd, the maximum image height in the image plane is Hmax The paraxial radius of curvature of the image-side lens surface of the final lens is R2Gn, and the focal length of the optical system is f In that case, 1.780 <Nd<2.500 0.10 <skd / Hmax<0.30 0.725 ≤ R²Gn / f ≤ 2.0 It is characterized by satisfying the following conditional expression.

[0009] Other objects and features of the present invention are described in the following embodiments. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a compact optical system that has a large aperture while exhibiting good optical performance from the center to the periphery of the field of view. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of the lens in Example 1 when it is focused at infinity. [Figure 2] This is an aberration diagram of Example 1 when focused at infinity. [Figure 3] This is a cross-sectional view of the lens in Example 2 when it is focused at infinity. [Figure 4]It is an aberration diagram in a state of focusing at infinity in Example 2. [Figure 5] It is a lens cross-sectional view in a state of focusing at infinity in Example 3. [Figure 6] It is an aberration diagram in a state of focusing at infinity in Example 3. [Figure 7] It is a lens cross-sectional view in a state of focusing at infinity in Example 4. [Figure 8] It is an aberration diagram in a state of focusing at infinity in Example 4. [Figure 9] It is a lens cross-sectional view in a state of focusing at infinity in Example 5. [Figure 10] It is an aberration diagram in a state of focusing at infinity in Example 5. [Figure 11] It is a schematic diagram of the main part of an imaging device including the optical systems of Examples 1 to 5. [Figure 12] It is an explanatory diagram regarding the opening angle.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the optical system of the present invention and an imaging device having the same will be described based on the accompanying drawings.

[0013] FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 are lens cross-sectional views in a state where the optical systems of Examples 1 to 5 are focused at infinity, respectively.

[0014] The optical systems of each embodiment are optical systems used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, TV cameras, surveillance cameras, night vision cameras, in-vehicle cameras, etc. Note that the optical systems of each embodiment can also be used as projection optical systems for projectors.

[0015] In each lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). In each lens cross-sectional view, OL is an imaging optical system (optical system).

[0016] In each embodiment, the lens group is composed of multiple lenses. The lens group may also include an aperture diaphragm.

[0017] The optical system OL in each embodiment consists of a lens group L containing multiple lenses arranged sequentially from the object side to the image side, and a final lens Gn with negative refractive power (optical power = reciprocal of focal length).

[0018] In each embodiment, focusing may be performed by moving all or part of the lenses of the optical system OL in the optical axis direction according to the object distance. In each embodiment, the optical system OL can be a pan-focus lens, so a focusing mechanism is not required.

[0019] Furthermore, in each lens cross-sectional view, SP is the aperture diaphragm that determines (limits) the light beam at the open F-number (Fno). IP is the image plane, and when the optical system OL of each embodiment is used as the shooting optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed there. When the optical system OL of each embodiment is used as the shooting optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP. FL is an optical block corresponding to an optical filter, faceplate, low-pass filter, infrared cut filter, sensor protective glass, etc.

[0020] Figures 2, 4, 6, 8, and 10 are aberration diagrams of the optical systems OL of Examples 1 to 5 when focused at infinity.

[0021] In the spherical aberration diagram, Fno is the F-number and indicates the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS indicates the amount of astigmatism at the sagittal image plane, and ΔM indicates the amount of astigmatism at the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration at the g-line is shown. ω is the half-angle of view (°) and is the angle of view determined by ray tracing.

[0022] Next, we will describe the characteristic configurations of the optical systems in each embodiment.

[0023] The optical system OL in each embodiment consists of a lens group L including multiple lenses arranged sequentially from the object side to the image side, and a final lens Gn with negative refractive power. The image-side lens surface of the final lens Gn has an aspherical shape that includes a concave region near the optical axis and has an inflection point.

[0024] Furthermore, the optical system OL of each embodiment satisfies the following condition (1), where Nd is the average refractive index of all lenses included in the lens group L.

[0025] 1.780 <Nd<2.500 ···(1) The optical system OL in each embodiment consists of a lens group L and a final lens Gn with negative refractive power, arranged sequentially from the object side to the image side. This allows the final lens Gn to correct aberrations generated in the lens group L in the optical system OL of each embodiment. To miniaturize the optical system OL, especially to shorten the overall length, it is effective to use high refractive index glass material for the lenses constituting the lens group L. By using high refractive index glass material for each lens, the curvature of each lens can be made gentler, making it possible to shorten the overall length. If high refractive index glass material is used for the negative refractive power lenses constituting the lens group L for miniaturization, the positive Petzval sum will increase (large field curvature will occur and underexpose will occur). By making the image-side lens surface of the final lens Gn concave towards the image side near the optical axis, the negative refractive power will be increased, making it possible to correct the positive Petzval sum generated in the lens group L.

[0026] Furthermore, the image-side lens surface of the final lens Gn has an inflection point. An inflection point is defined as the point where, when x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the direction perpendicular to the optical axis (radial direction), and x(h) is the aspherical shape, the second derivative of x(h) obtained by differentiating x(h) twice with respect to h is zero, and the sign of the second derivative changes before and after that point. In other words, an inflection point is the point where the surface shape switches from a concave shape to a convex shape, or from a convex shape to a concave shape. Because the image-side lens surface of the final lens Gn has an inflection point, the peripheral refractive power can be determined independently of the paraxial refractive power, making it easier to correct image field curvature. In addition, it is possible to suppress the increase in the angle of incidence of light rays passing through the optical system OL onto the imaging plane (image sensor). The inflection point can be placed at any position radially outward from the optical axis, as long as it is within the effective diameter of the image-side lens surface of the final lens Gn. Preferably, the inflection point is located in the peripheral part of the image-side lens surface of the final lens Gn.

[0027] Condition (1) specifies the average refractive index of all lenses included in lens group L. If it exceeds the upper limit of condition (1), lens molding becomes difficult. If it falls below the lower limit of condition (1), the average refractive index of the lenses constituting lens group L becomes smaller, and the curvature required to ensure refractive power becomes tighter. As a result, the overall length of lens group L increases in order to ensure edge thickness and lens spacing, and consequently, lens group L becomes larger.

[0028] Furthermore, it is preferable that the numerical range of conditional expression (1) be within the range of conditional expression (1a) below.

[0029] 1.782 <Nd<2.000 ···(1a) Furthermore, it is even more preferable that the numerical range of conditional expression (1) be within the range of conditional expression (1b) below.

[0030] 1.783 <Nd<1.850 ···(1b) This makes it possible to create a compact optical system that, despite having a large aperture, exhibits excellent optical performance from the center to the periphery of the field of view.

[0031] Next, we will describe the configurations that are preferable to satisfy in the optical system OL of each embodiment.

[0032] The lens group L preferably includes an aperture diaphragm SP. This facilitates miniaturization of the lens group L.

[0033] The image-side lens surface of the final lens Gn preferably has an aspherical shape that includes a concave region near the optical axis and provides an extreme point. An extreme point is defined as the point where the first derivative of x(h) obtained by differentiating x(h) with respect to h is zero, where x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the direction perpendicular to the optical axis (radial direction), and the aspherical shape is x(h). In other words, an extreme point is a point on the aspherical surface such that the tangent plane to the point is a plane perpendicular to the optical axis. A saddle point can also be used instead of an extreme point. This makes it possible to suppress the occurrence of distortion aberration, correct image field curvature well, and obtain high resolution performance from the center to the periphery of the field of view. The extreme point can be placed at any position radially outward from the optical axis, as long as it is within the effective diameter of the image-side lens surface of the final lens Gn.

[0034] It is preferable that the lens group L has a lens G1 with negative refractive power closest to the object. This makes it possible to miniaturize the front element of the optical system OL. As shown in Example 5, a lens with positive refractive power may be further arranged closer to the object than lens G1.

[0035] The lens group L preferably includes at least six lenses. By reducing the power of each lens, it becomes easier to suppress various aberrations such as spherical aberration that occur in the lens group L.

[0036] Next, we will describe the conditions that the optical system OL of each embodiment preferably satisfies. The optical system OL of each embodiment preferably satisfies one or more of the following conditional equations (2) to (13).

[0037] 0.05 <skd / TL<0.15 ···(2) 0.10 <skd / Hmax<0.30 ···(3) 1.0 <TL / D<2.0 ···(4) 0.3 <R2Gn / f<3.0 ···(5) 1.0 < |fGn / f| < 1.8 ... (6) 7.0 <EA / skd<13.0 ···(7) 0.50 <TL / DL<0.95 ···(8) 1.45 <NdGn<1.65 ···(9) 1.75 <Ndn<2.50 ···(10) 0.60 <fL / f<0.95 ···(11) 5°<|Θf|<65° ···(12) 5°<|Θr|<65° ···(13) Here, skd is the distance along the optical axis from the image-side lens surface (final lens surface) of the final lens Gn to the image plane IP when the optical system OL is focused at infinity. Away( (Back focus) TL is the distance along the optical axis from the aperture diaphragm SP to the image plane IP when the optical system OL is focused at infinity. Separate Yes. Hmax is the maximum image height at the image plane IP. D is the aperture diameter of the aperture diaphragm SP. R2Gn is the paraxial radius of curvature of the image-side lens surface of the final lens Gn. f is the focal length of the optical system OL. fGn is the focal length of the final lens Gn. EA is the effective diameter of the final lens Gn. DL is the total optical length of the optical system OL when it is focused at infinity (the distance along the optical axis from the lens surface closest to the object to the image plane IP). NdGn is the refractive index of the final lens Gn. Ndn is the refractive index of the lens with the strongest negative refractive power (the largest absolute value of refractive power) among the negative refractive power lenses included in the lens group L. fL is the focal length of the lens group L. Θf is the opening angle (°) of the object-side lens surface of the final lens Gn. Θr is the opening angle (°) of the image-side lens surface of the final lens Gn.

[0039] Condition (2) is the optical axis from the aperture diaphragm SP to the image plane IP when the optical system OL is focused at infinity. distance On the optical axis from the image-side lens surface to the image plane IP of the final lens Gn relative to TL distanceskd is defined. By positioning the final lens Gn away from the aperture diaphragm SP, the light beam converges sufficiently and the diameter of the on-axis light beam becomes smaller, making it possible to correct field curvature and distortion without affecting spherical aberration. If the upper limit of condition (2) is exceeded, the height (absolute value) of the off-axis light rays incident on the final lens Gn becomes too small. The on-axis light beam and off-axis light beam passing through the final lens Gn are not sufficiently separated in the direction perpendicular to the optical axis, making field curvature correction difficult and undesirable. If the lower limit of condition (2) is exceeded, the above-mentioned correction effect increases, but the arrangement of the optical block FL becomes difficult and undesirable.

[0040] Condition (3) is the maximum image height Hmax at the image plane IP, and the optical axis from the image-side lens surface of the final lens Gn to the image plane IP when the optical system OL is focused at infinity. distance This defines skd. If it exceeds the upper limit of condition (3), the height (absolute value) of the off-axis rays incident on the final lens Gn becomes too small. This is undesirable because the on-axis and off-axis light beams passing through the final lens Gn are not sufficiently separated in the direction perpendicular to the optical axis, making field curvature correction difficult. If it falls below the lower limit of condition (3), the above-mentioned correction effect increases, but it is undesirable because the arrangement of the optical block FL becomes difficult.

[0041] Condition (4) is the optical axis from the aperture diaphragm SP to the image plane IP when the optical system OL is focused at infinity, relative to the aperture diaphragm diameter D. distance This defines TL. If it exceeds the upper limit of condition (4), the negative refractive power of lens group L becomes too strong, resulting in an undesirable increase in the optical length. If it falls below the lower limit of condition (4), the radial length increases due to the larger aperture, which is also undesirable.

[0042] Conditional equation (5) specifies the paraxial curvature radius R2Gn of the image-side lens surface of the final lens Gn for the focal length f of the optical system OL. If it exceeds the upper limit of conditional equation (5), the correction of field curvature will be insufficient, which is undesirable. If it falls below the lower limit of conditional equation (5), the correction of field curvature will be excessive, and a large amount of astigmatism will occur, which is also undesirable.

[0043] Conditional equation (6) specifies the focal length fGn of the final lens Gn for a given focal length f of the optical system OL. Exceeding the upper limit of conditional equation (6) is undesirable because it results in excessive correction of field curvature. Exceeding the lower limit of conditional equation (6) is undesirable because it results in insufficient correction of field curvature.

[0044] Condition (7) is the optical axis from the image-side lens surface to the image plane IP of the final lens Gn when the optical system OL is focused at infinity. distance This defines the effective diameter EA of the final lens Gn relative to skd. Here, the effective diameter EA refers to the diameter on the lens surface of the light beam that passes through the position furthest from the optical axis in the radial direction (perpendicular to the optical axis) among the light beams passing through the lens surface. The effective diameter EA of the final lens Gn is defined as the surface with the largest effective diameter on either the object-side or image-side lens surface of the final lens Gn. The effective diameter EA may also be the diameter of the portion where an aspherical shape is formed, or it may be the outer diameter of the lens. If it exceeds the upper limit of condition (7), the lens diameter of the final lens Gn becomes large, and the optical system OL becomes larger in the radial direction, which is undesirable. If it falls below the lower limit of condition (7), the on-axis light beam and off-axis light beam passing through the final lens Gn are not sufficiently separated in the direction perpendicular to the optical axis, making it difficult to correct field curvature and distortion simultaneously, which is undesirable.

[0045] Condition (8) is the optical axis from the aperture diaphragm SP to the image plane IP when the optical system OL is focused at infinity, relative to the total optical length DL when the optical system OL is focused at infinity. distance The TL (Light Limit) is defined. By positioning the aperture diaphragm SP closer to the object than the center of the optical system OL (optical lens), the incident angle of light rays passing through the optical system OL onto the imaging plane (image sensor) is suppressed, while miniaturizing the optical system OL. If the upper limit of condition (8) is exceeded, the height of the on-axial light beam passing through the aperture diaphragm SP becomes too high, causing the aperture diaphragm SP to become larger. As a result, the radial size of the optical system OL becomes larger, which is undesirable. If the lower limit of condition (8) is exceeded, the entrance pupil position moves away from the first lens surface of the optical system OL, causing the effective diameter of the front element to increase, and thus the optical system OL becomes larger, which is undesirable.

[0046] Conditional equation (9) specifies the refractive index NdGn of the final lens Gn under normal temperature conditions of 25 degrees Celsius. Exceeding the upper limit of conditional equation (9) is undesirable because it makes lens molding difficult. Exceeding the lower limit of conditional equation (9) is also undesirable because it causes the opening angle of the lens surface of the final lens Gn to become too large.

[0047] Conditional equation (10) specifies the refractive index Ndn of the lens with the strongest negative refractive power among the negative refractive power lenses included in lens group L. By using high refractive index glass material for lenses with large negative refractive power, the curvature can be reduced, making it easier to shorten the overall length of the optical system OL. Exceeding the upper limit of conditional equation (10) is undesirable because it makes lens molding difficult. Exceeding the lower limit of conditional equation (10) is undesirable because the average refractive index of the lenses constituting lens group L becomes too small, requiring a steeper curvature to maintain refractive power. This increases the overall length of lens group L to maintain the lens spacing, resulting in a larger lens group L, which is undesirable.

[0048] Conditional equation (11) specifies the focal length fL of the lens group L for a given focal length f of the optical system OL. If the value exceeds the upper limit of conditional equation (11), the refractive power of the lens group L becomes too small, making it difficult to miniaturize the optical system OL, which is undesirable. If the value falls below the lower limit of conditional equation (11), the refractive power of the lens group L becomes too large, making it difficult to correct spherical aberration, which is also undesirable.

[0049] Conditional equation (12) specifies the absolute value of the opening angle Θf of the object-side lens surface of the final lens Gn. In order to suppress astigmatism in the final lens Gn, it is preferable that off-axis rays incident on the object-side lens surface of the final lens Gn at an angle that is nearly perpendicular to the lens surface. Exceeding the upper limit of conditional equation (12) is undesirable because it makes lens molding difficult. Exceeding the lower limit of conditional equation (12) is undesirable because it makes it difficult to suppress astigmatism.

[0050] The definition of the opening angle Θ is explained using Figure 12. The opening angle Θ is calculated by the following formula, where the origin O is the intersection of a line passing through the vertex A of the surface of the lens with effective diameter EA and parallel to the optical axis, and the normal to the tangent line passing through position B on the lens surface with effective diameter EA, and the length of the line OB is the radius of curvature of the reference sphere, and R is the length of the line OB.

[0051] Θ = ∠BOA = sin⁻¹{(EA / 2) / R} Here, the radius of curvature R of the reference sphere refers to the radius of curvature of the sphere passing through the vertex of the surface and position B on the lens surface.

[0052] Conditional equation (13) specifies the absolute value of the opening angle Θr of the image-side lens surface of the final lens Gn. Exceeding the upper limit of conditional equation (13) is undesirable because it makes lens molding difficult. Exceeding the lower limit of conditional equation (13) is also undesirable because it makes it difficult to suppress the large incident angle of light rays passing through the optical system OL onto the image-forming surface (image sensor).

[0053] Furthermore, it is more preferable that the numerical ranges of conditional expressions (2) to (13) be within the ranges of conditional expressions (2a) to (13a) below.

[0054] 0.06 <skd / TL<0.14 ···(2a) 0.14 <skd / Hmax<0.25 ···(3a) 1.2 <TL / D<1.9 ···(4a) 0.4 <R2Gn / f<2.3 ···(5a) 1.1 < |fGn / f| < 1.7 ···(6a) 7.2 <EA / skd<12.5 ···(7a) 0.55 <TL / DL<0.90 ···(8a) 1.50 <NdGn<1.60 ···(9a) 1.79 <Ndn<2.00 ···(10a) 0.70 <fL / f<0.94 ···(11a) 20°<|Θf|<63° ···(12a) 6°<|Θr|<60° ···(13a) Furthermore, it is even more preferable that the numerical ranges of conditional expressions (2) to (13) be within the ranges of the following conditional expressions (2b) to (13b).

[0055] 0.07 <skd / TL<0.13 ···(2b) 0.15 <skd / Hmax<0.24 ···(3b) 1.4 <TL / D<1.8 ···(4b) 0.5 <R2Gn / f<2.0 ···(5b) 1.2 < |fGn / f| < 1.6 ···(6b) 7.4 <EA / skd<12.0 ···(7b) 0.64 <TL / DL<0.88 ···(8b) 1.51 <NdGn<1.58 ···(9b) 1.80 <Ndn<1.98 ···(10b) 0.80 <fL / f<0.93 ···(11b) 40°<|Θf|<61° ···(12b) 7°<|Θr|<35° ···(13b) Next, the optical system OL of each embodiment will be described in detail.

[0056] The optical systems OL of embodiments 1, 2, 3, and 4 shown in Figures 1, 3, 5, and 7 consist of a lens group L1 and a final lens Gn with negative refractive power, arranged in order from the object side to the image side. The lens group L1 consists of a negative lens, a positive lens, an aperture diaphragm SP, a positive lens, a cemented lens of a positive and a negative lens, and a cemented lens of a negative and a positive lens, arranged in order from the object side to the image side.

[0057] The optical system OL of Embodiment 5 shown in Figure 9 consists of a lens group L1 and a final lens Gn with negative refractive power, arranged in order from the object side to the image side. The lens group L1 consists of a positive lens, a negative lens, an aperture diaphragm SP, a positive lens, a cemented lens of a positive and a negative lens, and a cemented lens of a negative and a positive lens, arranged in order from the object side to the image side.

[0058] The numerical values ​​corresponding to Examples 1 to 5 are shown below.

[0059] 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 m-th surface and the (m + 1)-th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index with respect to the d-line of each optical member, and νd represents the Abbe number of the optical member. Note that the Abbe number νd of a certain material is expressed as νd = (Nd - 1) / (NF - NC) when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively.

[0060] In each numerical example, d, focal length (mm), F-number, and half angle (°) are all the values when the optical system of each example is focused on an infinitely distant object. The half angle indicates the angular field calculated by paraxial approximation. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image side) to the paraxial image plane. Separate There is. "Overall lens length" is the length obtained by adding the back focus to the distance on the optical axis from the frontmost surface (the lens surface closest to the object side) to the final surface of the optical system. "Lens group" includes not only the case where it is composed of a plurality of lenses but also the case where it is composed of a single lens.

[0061] When the optical surface is an aspherical surface, an asterisk (*) is attached to the right side of the surface number. The aspherical shape is expressed as x=(h / R) / [1+{1-(1+k)(h / R) 2}^ 2 +A4×h 1 / 2 ^ 4 + A6×h 6 ^ 8 +A8×h 10 ^ 12 XX}]], where X is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspherical coefficients of each order. Note that "e±XX" in each aspherical coefficient means "×10±

[0062] [Numerical Example 1] Unit: mm Surface data Face number rd nd νd Effective diameter 1 -13.230 0.65 1.56732 42.8 2 -556.432 0.10 3 12.115 1.63 2.00100 29.1 4 23.466 1.60 5 (aperture) ∞ -0.50 6* 14.904 2.40 1.76802 49.2 7* -23.793 0.10 8 91.141 3.69 1.83481 42.7 9 -9.345 0.46 1.95906 17.5 10 26.563 0.86 11 -51.000 0.49 1.51742 52.4 12 11.704 3.89 2.00100 29.1 13 -30.167 3.37 14* -19.774 1.20 1.53110 55.9 11.63 15* 15.005 0.88 14.46 16 ∞ 0.50 1.51633 64.1 17 ∞ 0.43 Image plane ∞ Aspherical data Page 6 K = 0.00000e+000 A 4=-1.13433e-004 A 6=-1.86886e-007 A 8=-1.33697e-008 Side 7 K = 0.00000e+000 A 4= 1.63863e-004 A 6=-1.05546e-006 A 8=-2.97841e-009 Side 14 K = 0.00000e+000 A 4=-3.79721e-003 A 6= 8.71603e-005 A 8=-7.64087e-007 A10=-1.93734e-008 A12= 4.17224e-010 Page 15 K = 0.00000e+000 A 4=-2.85274e-003 A 6= 7.79552e-005 A 8=-1.39826e-006 A10= 1.42733e-008 A12=-6.07417e-011 Focal length 12.39 F-number 1.30 Half-angle (°): 32.84 Image height 8.00 Lens length: 21.75 [Numerical Example 2] Unit: mm Surface data Face number rd nd νd Effective diameter 1 -12.600 1.00 1.65412 39.7 2 41.811 0.39 3* 13.558 3.34 1.85135 40.1 4* -17.486 2.58 5 (aperture) ∞ -0.16 6 16.386 2.64 1.77250 49.6 7 -16.237 0.46 1.95906 17.5 8 18.692 1.20 9 364.889 0.49 1.51742 52.4 10 11.336 3.91 1.95375 32.3 11 -33.666 4.46 12* -13.170 1.20 1.53110 55.9 11.81 13* 23.204 0.79 14.62 14 ∞ 0.50 1.51633 64.1 15 ∞ 0.11 Image plane ∞ Aspherical data 3rd page K = 0.00000e+000 A 4=-1.35241e-004 A 6=-8.30587e-007 A 8= 1.45600e-008 Side 4 K = 0.00000e+000 A 4= 7.04830e-005 A 6=-1.17794e-006 A 8= 1.90580e-008 Side 12 K = 0.00000e+000 A 4=-3.51146e-003 A 6= 1.08913e-004 A 8=-2.33209e-006 A10=2.61924e-008 A12=-7.96411e-011 Page 13 K = 0.00000e+000 A 4=-2.55539e-003 A 6= 6.82893e-005 A 8=-1.03255e-006 A10=8.08461e-009 A12=-2.43705e-011 Focal length 12.40 F-number 1.30 Half-angle (°): 32.83 Image height 8.00 Lens length: 22.91 [Numerical Example 3] Unit: mm Surface data Face number rd nd νd Effective diameter 1 -34.982 1.72 1.56732 42.8 2 -1471.329 0.26 3 32.035 4.31 2.00100 29.1 4 62.050 4.23 5 (aperture) ∞ -1.32 6* 39.410 6.35 1.76802 49.2 7* -62.914 0.26 8 240.996 9.76 1.83481 42.7 9 -24.711 1.22 1.95906 17.5 10 70.238 2.27 11 -134.854 1.30 1.51742 52.4 12 30.947 10.29 2.00100 29.1 13 -79.769 8.91 14* -52.288 3.17 1.53110 55.9 30.75 15* 39.677 2.33 38.24 16 ∞ 1.32 1.51633 64.1 17 ∞ 1.15 Image plane ∞ Aspherical data Page 6 K = 0.00000e+000 A 4=-6.13545e-006 A 6=-1.44574e-009 A 8=-1.47924e-011 Side 7 K = 0.00000e+000 A 4= 8.86317e-006 A 6=-8.16501e-009 A 8=-3.29535e-012 Side 14 K = 0.00000e+000 A 4=-2.05387e-004 A 6= 6.74266e-007 A 8=-8.45397e-010 A10=-3.06569e-012 A12= 9.44273e-015 Page 15 K = 0.00000e+000 A 4=-1.54301e-004 A 6= 6.03056e-007 A 8=-1.54705e-009 A10=2.25864e-012 A12=-1.37472e-015 Focal length 32.77 F-number 1.30 Half-angle (°): 33.43 Image height 21.63 Lens length: 57.52 [Numerical Example 4] Unit: mm Surface data Face number rd nd νd Effective diameter 1 -18.944 0.60 1.56732 42.8 2 64.073 0.10 3 10.234 1.24 2.00100 29.1 4 15.665 2.72 5 (aperture) ∞ -0.91 6* 13.321 2.38 1.85135 40.1 7* -38.300 0.10 8 33.773 2.53 1.72916 54.7 9 -10.143 0.36 1.89286 20.4 10 14.000 1.36 11 -68.406 0.43 1.51742 52.4 12 12.849 3.35 1.95375 32.3 13 -20.435 4.12 14* 72.982 1.20 1.53110 55.9 12.07 15* 9.258 1.12 14.83 16 ∞ 0.50 1.51633 64.1 17 ∞ 0.43 Image plane ∞ Aspherical data Page 6 K = 0.00000e+000 A 4=-1.62447e-004 A 6=-5.91901e-007 A 8= 4.11336e-008 Side 7 K = 0.00000e+000 A 4= 1.05526e-004 A 6= 1.20470e-007 A 8= 3.93658e-008 Side 14 K = 0.00000e+000 A 4=-3.92508e-003 A 6= 8.56282e-005 A 8=-6.61534e-007 A10 = -4.48628e-009 Page 15 K = 0.00000e+000 A 4=-3.19957e-003 A 6= 7.24731e-005 A 8=-1.35769e-006 A10=1.87146e-008 A12=-1.30390e-010 Focal length 12.77 F-number 1.30 Half-angle (°): 32.06 Image height 8.00 Lens length: 21.62 [Numerical Example 5] Unit: mm Surface data Face number rd nd νd Effective diameter 1 16.592 1.00 2.00100 29.1 2 35.757 2.22 3 -12.450 0.49 1.64769 33.8 4 18.208 1.00 5 (aperture) ∞ -0.87 6* 12.197 2.94 1.85135 40.1 7* -16.387 0.10 8 118.520 2.02 1.72916 54.7 9 -11.807 0.49 1.80810 22.8 10 14.190 0.47 11 16.029 0.50 1.78472 25.7 12 8.467 4.23 2.00100 29.1 13 -71.075 4.53 14* 25.229 1.10 1.53110 55.9 11.06 15* 7.268 1.06 13.81 16 ∞ 0.50 1.51633 64.1 17 ∞ 0.45 Image plane ∞ Aspherical data Page 6 K = 0.00000e+000 A 4=-1.14931e-004 A 6= 4.45417e-007 A 8=-2.36743e-008 Side 7 K = 0.00000e+000 A 4= 5.95842e-005 A 6= 2.16407e-007 A 8=-1.41825e-008 Side 14 K = 0.00000e+000 A 4=-6.87777e-003 A 6= 2.46251e-004 A 8=-7.49558e-006 A10 = 9.35756e-008 Page 15 K = 0.00000e+000 A 4=-6.38748e-003 A 6= 2.48242e-004 A 8=-7.63309e-006 A10= 1.27959e-007 A12=-9.02853e-010 Focal length 12.80 F-number 1.30 Half-angle (°): 32.00 Image height 8.00 Lens length: 22.23 The 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) using the optical system OL of the present invention as an imaging optical system will be described with reference to Figure 11. Figure 11 is a schematic diagram of the main parts of a camera 10 (imaging device) equipped with the optical system of the present invention. In Figure 11, 13 is the camera body, and 11 is the imaging optical system composed of any of the optical systems described in Embodiments 1 to 5. 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor, CMOS sensor, or SPAD sensor, which is built into the camera body and receives the subject image formed by the imaging optical system 11. The camera body 13 may be a so-called single-lens reflex camera with a quick-turn mirror, or a so-called mirrorless camera without a quick-turn mirror.

[0065] By applying the optical system OL of the present invention to an imaging device such as a digital still camera, an imaging device with a compact lens can be obtained.

[0066] Although preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of its gist. [Explanation of Symbols]

[0067] Lens group L Final lens Gn

Claims

1. An optical system comprising a lens group consisting of seven lenses arranged sequentially from the object side to the image side, and a final lens with negative refractive power, The image-side lens surface of the final lens has an aspherical shape that includes a concave region near the optical axis and has an inflection point. When Nd is the average refractive index of all the lens materials included in the lens group, skd is the distance along the optical axis from the image-side lens surface to the image plane of the final lens when the optical system is focused at infinity, Hmax is the maximum image height at the image plane, R2Gn is the paraxial radius of curvature of the image-side lens surface of the final lens, and f is the focal length of the optical system, 1.780<Nd<2.500 0.10<skd / Hmax<0.30 0.725 ≤ R²Gn / f ≤ 2.0 An optical system characterized by satisfying the following conditional equation.

2. The optical system according to claim 1, characterized in that the lens group includes an aperture diaphragm.

3. When the optical system is in focus at infinity, the distance along the optical axis from the aperture diaphragm to the image plane is denoted as TL. 0.05<skd / TL<0.15 The optical system according to claim 2, characterized in that it satisfies the following conditional expression.

4. When the optical system is in focus at infinity, let TL be the distance along the optical axis from the aperture diaphragm to the image plane, and let D be the diameter of the aperture diaphragm. 1.0<TL / D<2.0 The optical system according to claim 2 or 3, characterized in that it satisfies the following conditional expression.

5. When the focal length of the optical system is f and the focal length of the final lens is fGn, 1.0<|fGn / f|<1.8 The optical system according to any one of claims 1 to 4, characterized in that it satisfies the following conditional expression.

6. The optical system according to any one of claims 1 to 5, characterized in that the lens group includes a lens with negative refractive power closest to the object.

7. When the effective diameter of the final lens is EA, 7.0<EA / skd<13.0 The optical system according to any one of claims 1 to 6, characterized in that it satisfies the following conditional expression.

8. When the optical system is focused at infinity, let TL be the distance along the optical axis from the aperture diaphragm to the image plane, and let DL be the total optical length of the optical system when it is focused at infinity. 0.50<TL / DL<0.95 The optical system according to any one of claims 2 to 4, characterized in that it satisfies the following conditional expression.

9. When the refractive index of the final lens is NdGn, 1.45<NdGn<1.65 The optical system according to any one of claims 1 to 8, characterized in that it satisfies the following conditional expression.

10. When Ndn is the refractive index of the lens with the largest absolute value of refractive power among the negative refractive power lenses included in the aforementioned lens group, 1.75<Ndn<2.50 The optical system according to any one of claims 1 to 9, characterized in that it satisfies the following conditional expression.

11. The optical system according to any one of claims 1 to 10, characterized in that the image-side lens surface of the final lens has an aspherical shape with an extreme point.

12. When the focal length of the optical system is f and the focal length of the lens group is fL, 0.60<fL / f<0.95 The optical system according to any one of claims 1 to 11, characterized in that it satisfies the following conditional expression.

13. When the opening angle of the object-side lens surface of the final lens is Θf, 5°<|Θf|<65° The optical system according to any one of claims 1 to 12, characterized in that it satisfies the following conditional expression.

14. When the opening angle of the image-side lens surface of the final lens is Θr, 5°<|Θr|<65° The optical system according to any one of claims 1 to 13, characterized in that it satisfies the following conditional expression.

15. The optical system according to any one of claims 1 to 14, characterized in that the inflection point is located in the peripheral part of the image-side lens surface of the final lens.

16. An imaging device characterized by having an optical system according to any one of claims 1 to 15 and an image sensor that receives an image formed by the optical system.

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