Optical system and imaging device having the same

Abstract

To provide an optical system which constitutes a large-aperture and a compact lens, and yet reduces ghost images in particular in a desired wavelength range.SOLUTION: An optical system OL provided herein consists of a front lens group L and a negative lens Gn disposed on the image side of the front lens group L, and is configured such that the focal length of the optical system OL, the focal length of the negative lens Gn, the effective diameter D of an object-side lens surface of the negative lens Gn, the diameter ST of an aperture stop that determines an axial ray, and the optical axial distance from a point located closest to an edge of a ray effective area of the object-side lens surface of the negative lens Gn to a point on the optical axis of the negative lens Gn satisfy given conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, there has been a demand for high-performance, compact optical systems. Furthermore, there is a demand for optical systems with small F-numbers (brightness) so that photography can be performed in dark places.

[0003] However, bright optical systems tend to have large apertures, which makes it difficult to reduce their weight. Patent Document 1 discloses a compact optical system with an eight-lens configuration and an F-number of 2.0. The optical system in Patent Document 1 uses glass materials to make the optical system compact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-106159 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the optical system of Patent Document 1, the refractive power and shape of the negative lens closest to the image side are not appropriate, and therefore, if the F-number is increased further, it becomes difficult to correct aberrations and achieve size reduction.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system that is bright, compact, lightweight, and has good optical performance. [Means for solving the problem]

[0007] The optical system of the present invention is an optical system consisting of a front lens group and a negative lens Gn arranged on the image side of the front lens group, wherein the focal length of the optical system is f, the focal length of the negative lens Gn is fn, the effective diameter of the object-side lens surface of the negative lens Gn is D, the diameter of the aperture stop which determines the axial light beam is ST, the distance on the optical axis from a point located at the most edge of the effective light beam area of ​​the object-side lens surface of the negative lens Gn to a point on the optical axis of the negative lens Gn is SAG1, the refractive index of the material of the negative lens Gn is NdGn, and the average of the refractive indexes of the materials of all the positive lenses included in the optical system is NdGp, -10.0 <fn / f<-0.7 0.9 <D / ST<1.4 -0.50 <SAG1 / f<-0.16 1.45 <NdGn<1.70 1.78 <NdGp<2.2 The present invention is characterized in that the following conditional expression is satisfied: [Effects of the Invention]

[0008] According to the present invention, it is possible to realize an optical system that can reduce ghosts particularly in a desired wavelength range, while using a large-diameter, compact lens. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a lens of an optical system according to a first embodiment. [Figure 2] 3A to 3C are aberration diagrams of the optical system of Example 1. [Figure 3] FIG. 10 is a cross-sectional view of a lens of an optical system according to a second embodiment. [Figure 4] 10A to 10C are aberration diagrams of the optical system of Example 2. [Figure 5] FIG. 10 is a cross-sectional view of a lens of an optical system according to a third embodiment. [Figure 6] 10A to 10C are aberration diagrams of the optical system of Example 3. [Figure 7] FIG. 10 is a cross-sectional view of a lens of an optical system according to a fourth embodiment. [Figure 8] 10A to 10C are aberration diagrams of the optical system of Example 4. [Figure 9]FIG. 10 is a cross-sectional view of a lens of an optical system according to a fifth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the optical system of Example 5. [Figure 11] FIG. 1 is a schematic diagram showing an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of an optical system and an imaging apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0011] 1, 3, 5, 7, and 9 are cross-sectional views of the optical system OL of Examples 1 to 5. The optical system OL of each Example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, surveillance cameras, in-vehicle cameras, cameras for wearable devices, and cameras for mobile devices.

[0012] In each lens cross-sectional view, the left side is the object side and the right side is the image side.

[0013] The optical system OL in each embodiment is composed of a front lens unit L and a negative lens Gn arranged on the image side of the front lens unit L. The front lens unit L is provided with an aperture stop SP.

[0014] In each lens cross-sectional view, IP is an image plane, and when the optical system OL of each embodiment is used in a digital camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system OL of each embodiment is used as a photographic optical system for a silver halide film camera, a photosensitive surface corresponding to the film surface is disposed at the image plane IP. FL is an optical block corresponding to an optical filter, faceplate, low-pass filter, infrared cut filter, sensor protection glass, etc. In addition, the front lens group L may include a flare cut diaphragm that cuts out unwanted light (flare light).

[0015] In the optical system OL of each embodiment, focusing may be performed by moving the entire optical system OL or a part of the lenses of the optical system OL in the optical axis direction.

[0016] 2, 4, 6, 8, and 10 are aberration diagrams of the optical systems OL of Examples 1 to 5, respectively, showing the cases where the object distance is infinity and the case where the object distance is close.

[0017] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS shows the amount of aberration on the sagittal image plane, and ΔM shows the amount of aberration on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration of magnification for the g-line is shown. ω is the half angle of view (°).

[0018] Next, the characteristic configuration of the optical system of each embodiment will be described.

[0019] In the optical system OL of each embodiment, the negative lens Gn is positioned closest to the image side, thereby moving the principal point of the entire optical system OL forward (toward the object), shortening the overall length of the optical system OL while allowing the negative lens Gn to correct aberrations occurring in the front lens group L.

[0020] Furthermore, in order to provide a wide-angle, bright optical system (for example, an F-number brighter than 1.8), the optical system OL is designed to satisfy the following conditions (1), (2), and (3): By arranging the negative lens Gn in this way, the optical system OL is made compact while effectively correcting the axial spherical aberration, peripheral coma, and field curvature that are specific to bright optical systems. -10.0 <fn / f<-0.7 (1) 0.9 <D / ST<1.4 (2) -0.50 <SAG1 / f<-0.16 (3)

[0021] Here, the focal length of the optical system OL is f, the focal length of the negative lens Gn is fn, and the effective diameter of the object-side lens surface of the negative lens Gn is D. The diameter of the aperture stop that determines the axial light beam is ST, and the distance on the optical axis from the point located at the extreme edge (peripheralmost part) of the effective light beam area on the object-side lens surface of the negative lens Gn to a point on the optical axis on the object-side lens surface of the negative lens Gn is SAG1. Here, the effective diameter of the lens is the diameter of a circle whose radius is the height from the optical axis of the ray that passes through the lens surface at the position farthest from the optical axis. Furthermore, the image side of SAG1 is negative.

[0022] Conditional expression (1) indicates a condition regarding the focal length fn of the negative lens Gn. If fn exceeds the upper limit of conditional expression (1), it becomes difficult to correct on-axis spherical aberration using the negative lens Gn, which is undesirable. If fn falls below the lower limit of conditional expression (1), it becomes difficult to correct field curvature using the negative lens Gn, which is undesirable. Furthermore, the diameter of the negative lens Gn becomes large, which hinders miniaturization.

[0023] Conditional formula (2) defines the ratio of the maximum effective diameter D of the object-side surface of the negative lens Gn to the aperture stop diameter ST, which determines the axial light beam of the optical system OL. If D exceeds the upper limit of conditional formula (2), the maximum effective diameter of the negative lens Gn becomes large relative to the aperture stop diameter ST, making it difficult to achieve a large aperture while reducing the size, which is undesirable. If D falls below the lower limit of conditional formula (2), it becomes difficult to achieve a wide angle, which is undesirable. In addition, the peripheral light beam becomes smaller than the axial light beam, making it impossible to ensure a sufficient light intensity ratio, which is undesirable.

[0024] Conditional formula (3) appropriately defines the ratio between SAG1 and the focal length f of the optical system OL. If SAG1 exceeds the upper limit of conditional formula (3), it becomes difficult to achieve a wide angle, which is undesirable. Furthermore, the angle of the peripheral chief ray incident on the object-side surface of the negative lens Gn relative to the axial direction becomes small, which lengthens the exit pupil and increases the overall length, hindering compactness. Furthermore, the peripheral light beam becomes smaller than the axial light beam, which makes it impossible to ensure a sufficient light intensity ratio, which is undesirable. If SAG1 falls below the lower limit of conditional formula (3), the open angle of the object-side surface of the negative lens Gn becomes large, making it difficult to process or mold the lens.

[0025] With the above configuration, it is possible to realize an optical system that can reduce ghosts in particular in a desired wavelength range, while using a large-diameter, compact lens.

[0026] Preferably, at least one of the upper and lower limits of the numerical ranges of the conditional expressions (1), (2), and (3) should be set to one of the following values. -8.0 <fn / f<-1.0 (1a) 0.9 <D / ST<1.3 (2a) -0.45 <SAG1 / f<-0.16 (3a)

[0027] It is even more preferable to set at least one of the upper and lower limits of the numerical ranges of the conditional expressions (1), (2), and (3) to one of the following values. -5.0 <fn / f<-1.1 (1b) 0.92 <D / ST<1.2 (2b) -0.35 <SAG1 / f<-0.16 (3b)

[0028] Next, the configurations and conditions that the optical systems of the respective examples preferably satisfy will be described.

[0029] The front lens group L preferably includes an aperture stop SP, which makes it easier to make the lens group L compact.

[0030] Furthermore, it is preferable that the image-side lens surface of the negative lens Gn has a concave surface facing the image side near the optical axis and is an aspheric surface having at least one extremum point. The extremum point refers to a point on the aspheric surface where the value of the first derivative of x(h) differentiated once with respect to h is zero, where x is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis (radial direction), and x(h) is a function indicating the aspheric shape. In other words, it refers to a point on the aspheric surface where the tangent plane to that point is a plane perpendicular to the optical axis. A saddle point may be used instead of an extremum point. Having such an aspheric surface on the image-side lens surface of the negative lens Gn suppresses distortion while effectively correcting field curvature, thereby achieving high resolution performance from the center to the periphery of the angle of view. The position of the extremum point can be set at any position within the effective diameter of the image-side lens surface of the negative lens Gn.

[0031] Furthermore, it is preferable that the front lens group L be composed of at least six lenses. By constituting the front lens group L with a plurality of lenses in this way and reducing the power (the reciprocal of the focal length) of each lens, it becomes easy to suppress various aberrations such as spherical aberration that occur in the front lens group L.

[0032] Furthermore, to achieve a wider angle of view for the optical system OL, it is preferable that the lens closest to the object side be a negative lens having a concave surface facing the object side, which enables distortion correction together with the negative lens while achieving a wider angle of view.

[0033] It is also preferable that the image-side lens surface of the negative lens Gn have at least one inflection point. The inflection point refers to a point where, when x is the displacement from the surface vertex in the optical axis direction, h is the height from the direction perpendicular to the optical axis (radial direction), and the aspheric shape is x(h), the value of the second derivative obtained by differentiating x(h) twice with respect to h becomes zero, and the sign of the second derivative changes around that point. In other words, it refers to a point where the surface shape switches from concave to convex, or from convex to concave. Having an inflection point allows the peripheral refractive power to be determined independently of the paraxial refractive power, making it easier to correct field curvature. Furthermore, it is possible to prevent the angle of incidence of light passing through the optical system OL onto the imaging plane (image sensor) from becoming too large. The inflection point may be located anywhere on the image-side surface of the lens Gn, but it is more preferable to locate it in the peripheral portion.

[0034] Furthermore, in order to provide the optical system OL with a wide angle of view and a large aperture ratio, it is preferable that the optical system OL have a lens configuration including, from the object side, a negative lens, a positive lens, and a positive lens, which allows for good correction of spherical aberration.

[0035] Next, the conditional expressions that should preferably be satisfied in the optical system OL of each embodiment will be described. It is preferable that the optical system OL of each embodiment satisfy one or more of the following conditional expressions.

[0036] Furthermore, it is preferable that the optical system OL in each embodiment satisfies at least one of the conditions of the following expressions (4) to (13). -0.35<-SAG2 / f<0 (4) 0.5 <GnR2 / f<10 (5) 0.1 <Td / f<2.5 (6) 0 <STd / f<0.15 (7) 0.05 <skd / SL<0.15 (8) 1.45 <NdGn<1.70 (9) 0.6 <gGn<1.7 (10) 0.08 <SF1<12.0 (11) 0.6<|f1 / f2|<5.0 (12) 1.78 <NdGp<2.2 (13)

[0037] Here, SAG2 is the distance on the optical axis from the extreme edge (peripheralmost part) of the effective light beam area of ​​the image-side lens surface of the negative lens Gn to a point on the optical axis of the image-side lens surface of the negative lens Gn. Note that SAG2 and GnR2 are positive on the image side. GnR2 is the radius of curvature of the image-side lens surface of the negative lens Gn. Td is the air-equivalent distance (total length) on the optical axis from the surface vertex of the lens surface closest to the object in the optical system OL to the image plane IP. STd is the distance between the surface vertices of the lenses located before and after the aperture stop SP. skd is the air-equivalent distance (back focus) on the optical axis from the image-side lens surface of the negative lens Gn to the image plane IP when the optical system OL is focused at infinity. SL is the air-equivalent distance on the optical axis from the aperture stop SP to the image plane IP. Note that, for skd and SL, if an optical block FL is located between the negative lens Gn and the image plane IP, the air-equivalent thickness of the optical block FL is used. The refractive index of the negative lens Gn is NdGn. The specific gravity (g / mm 3 ) is defined as gGn. Also, the shape factor of the lens G1 located closest to the object in the optical system OL is defined as SF1. Here, SF1 is given by SF1 = (R2 + R1) / (R2 - R1), where R1 is the lens surface of lens G1 closest to the object and R2 is the lens surface closest to the image.

[0038] The focal length of lens G1 is f1, the focal length of lens G2, the second lens from the object side in optical system OL, is f2, and the average refractive index of the positive lenses included in optical system OL is NdGp.

[0039] Conditional expression (4) specifies the condition for effectively correcting primarily field curvature when the optical system OL is made compact while increasing the aperture ratio. If SAG2 exceeds the upper limit of conditional expression (4), the ratio of the axial to peripheral thicknesses of the negative lens Gn becomes large, making manufacturing (molding) difficult. Furthermore, this is undesirable because it increases the angle of incidence on the image sensor, making it more likely that vignetting of the light amount will occur due to microlenses located on the object side of the image sensor.

[0040] If SAG2 is below the lower limit of conditional expression (4), the effect of correcting curvature of field by the negative lens Gn will be reduced, making it difficult to correct curvature of field, which is undesirable.

[0041] Conditional formula (5) defines the condition for effectively correcting curvature of field and distortion when the optical system OL is made large-diameter and compact. If GnR2 exceeds the upper limit of conditional formula (5), it becomes difficult to correct curvature of field. In addition, the ratio of the axial thickness of the negative lens Gn to its peripheral thickness becomes large, making manufacturing (molding) difficult.

[0042] If GnR2 falls below the lower limit of conditional expression (5), negative distortion will occur, which is undesirable. Also, the distance between the negative lens element Gn and the image sensor will become shorter, particularly at the periphery of the negative lens element Gn, requiring more space, which will hinder efforts to make the optical system OL more compact.

[0043] Conditional formula (6) defines the condition for achieving a wide angle and a large aperture while miniaturizing the optical system OL. If Td exceeds the upper limit of conditional formula (6), the total length Td becomes long, making it difficult to achieve a compact size. If Td is below the lower limit of conditional formula (6), it becomes difficult to achieve a wide angle and a large aperture.

[0044] Condition (7) defines the condition for making the entire system compact while maintaining a large aperture.

[0045] If STd / f exceeds the upper limit of conditional expression (7), it becomes difficult to correct spherical aberration when the aperture is increased. In addition, the overall length of the lens increases, hindering compactness.

[0046] If STd / f is below the lower limit of conditional expression (7), the distance between the lenses arranged adjacent to the aperture stop SP becomes too close, which increases the occurrence of unwanted light such as ghosts, which is undesirable.

[0047] Conditional expression (8) appropriately defines the ratio between the distance skd from the image-side lens surface of the negative lens Gn to the image plane IP when focused at infinity, and the distance SL from the aperture stop SP to the image plane IP. By positioning the negative lens Gn at a position that is an appropriate distance away from the aperture stop SP, the light beam converges sufficiently and the diameter of the on-axis light beam becomes small, making it possible to correct field curvature and distortion without significantly affecting spherical aberration.

[0048] If skd / SL exceeds the upper limit of conditional expression (8), the height (absolute value) of the off-axial ray incident on the negative lens Gn becomes small, and the on-axis light beam and the off-axis light beam passing through the negative lens Gn are not sufficiently separated in the direction perpendicular to the optical axis, making it difficult to correct the field curvature.

[0049] If skd / SL is below the lower limit of conditional expression (8), the above-mentioned correction effect increases, but it becomes difficult to arrange the optical block FL, which is not preferable.

[0050] Conditional expression (9) defines the condition for correcting field curvature while reducing the size of the optical system OL. If NdGn exceeds the upper limit of conditional expression (9), as the optical system OL is reduced in size, the Petzval sum of the entire optical system OL becomes too positive, which undesirably causes the image surface to curve toward the object side. If NdGn falls below the lower limit of conditional expression (9), the Petzval sum of the entire optical system OL becomes too negative, which undesirably causes the image surface to curve toward the image side.

[0051] Conditional formula (10) appropriately defines the specific gravity gGn of the material of the negative lens element Gn to reduce the size and weight of the optical system OL. Specifically, a transparent resin material is assumed. If the specific gravity gGn exceeds the upper limit of conditional formula (10), the lens weight increases when the aperture ratio is increased, hindering weight reduction. Furthermore, when focusing by moving the entire lens element, the actuator used to move it becomes larger, which undesirably increases the size of the entire lens barrel. If the specific gravity gGn falls below the lower limit of conditional formula (10), the negative lens element Gn becomes lighter, but the strength of the material generally weakens, which is undesirable.

[0052] Condition (11) appropriately defines the shape factor SF1 of the lens G1 for effectively correcting aberrations while widening the angle and increasing the aperture of the optical system OL.

[0053] If SF1 exceeds the upper limit of equation (11), it becomes difficult to widen the angle, which is not preferable.If SF1 falls below the lower limit of equation (11), it becomes difficult to correct distortion when the angle is widened, which is also not preferable.

[0054] Conditional expression (12) appropriately defines the ratio between the focal length f1 of lens G1 and the focal length f2 of lens G2 in order to effectively correct primarily spherical aberration and distortion when the optical system OL is made wider-angle and larger-aperture.

[0055] If f1 / f2 exceeds the upper limit of formula (12), it becomes difficult to achieve a wider angle, which is undesirable. If f1 / f2 falls below the lower limit of formula (12), it becomes difficult to correct distortion and spherical aberration, which is undesirable. In addition, the sensitivity of aberrations to the relative decentering of lens G2 and subsequent lenses increases, making manufacturing difficult and potentially causing degradation of optical performance.

[0056] Conditional expression (13) appropriately defines the average refractive index NdGp of the positive lens elements in order to achieve a large aperture ratio while miniaturizing the optical system OL. If NdGp exceeds the upper limit of conditional expression (13), the curvature of field will be over-corrected, which is undesirable. In addition, this is likely to result in a glass material with low transmittance in the visible range, which is undesirable as it reduces transmittance. If NdGp falls below the lower limit of conditional expression (13), it becomes difficult to correct the curvature of field with the negative lens element Gn, which is undesirable. Furthermore, the thickness of the positive lens element must be increased in order to ensure the lens edge, which hinders miniaturization.

[0057] It is also preferable that at least one of the upper limit and lower limit of the numerical range of conditional expressions (4) to (13) be within the range of the following conditional expressions (4a) to (13a). -0.25<-SAG2 / f<0 (4a) 0.5 <GnR2 / f<5.0 (5a) 0.5 <Td / f<2.4 (6a) 0 <STd / f<0.12 (7a) 0.06 <skd / SL<0.13 (8a) 1.45 <NdGn<1.68 (9a) 0.7 <gGn<1.4 (10a) 0.08 <SF1<5.0 (11a) 0.6<|f1 / f2|<4.0 (12a) 1.78 <NdGp<2.0 (13a)

[0058] It is even more preferable that at least one of the upper limit or lower limit of the numerical range of conditional expressions (4) to (13) is set to the range of the following conditional expressions (4b) to (13b). -0.15<-SAG2 / f<0 (4b) 0.5 <GnR2 / f<3.0 (5b) 1.0 <Td / f<2.3 (6b) 0 <STd / f<0.10 (7b) 0.08 <skd / SL<0.13 (8b) 1.50 <NdGn<1.65 (9b) 0.7 <gGn<1.3 (10b) 0.09 <SF1<3.0 (11b) 0.65<|f1 / f2|<3.0 (12b) 1.79 <NdGp<1.95 (13b)

[0059] Next, the specific configuration of the optical system OL in Examples 1 to 5 will be described.

[0060] The optical system OL of Example 1 shown in Figure 1 has a front lens group L and a negative lens Gn. The front lens group L includes, arranged in order from the object side to the image side, a negative lens, a positive lens, an aperture stop SP, a positive lens, a cemented lens of a positive lens and a negative lens, and a cemented lens of a negative lens and a positive lens. A flare-cutting stop FP may be provided between the two cemented lenses in the front lens group L.

[0061] The front lens group L of the optical system OL of Example 2 shown in FIG. 3 includes, arranged in order from the object side to the image side, a negative lens, a positive lens, an aperture stop SP, a cemented lens of a positive lens and a negative lens, and a cemented lens of a negative lens and a positive lens.

[0062] The front lens group L of the optical system OL of Example 3 shown in FIG. 5 includes, arranged in order from the object side to the image side, a negative lens, a cemented lens of a negative lens and a positive lens, an aperture stop SP, a positive lens, a cemented lens of a positive lens and a negative lens, and a positive lens.

[0063] The front lens unit L of the optical system OL of Example 4 shown in FIG. 7 includes, arranged in order from the object side to the image side, a negative lens, a positive lens, an aperture stop SP, a positive lens, a cemented lens of a positive lens and a negative lens, and a positive lens.

[0064] The front lens group L of the optical system OL of Example 5 shown in FIG. 9 includes, arranged in order from the object side to the image side, a positive lens, a negative lens, an aperture stop SP, a positive lens, a cemented lens of a positive lens and a negative lens, and a cemented lens of a negative lens and a positive lens.

[0065] Numerical examples 1 to 5 corresponding to the first to fifth embodiments, respectively, are shown below.

[0066] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (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. Furthermore, nd represents the refractive index of each optical element at the d-line, and vd represents the Abbe number of the optical element. The Abbe number vd of a certain material is given by Nd, NF, NC, and Ng, respectively, when the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm) are Nd, NF, NC, and Ng, respectively. νd=(Nd-1) / (NF-NC) It is expressed as:

[0067] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, A12, ... are the aspherical coefficients of each order. x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In addition, "e±XX" in each aspherical coefficient is "×10± XX " means.

[0068] [Numerical Example 1] Unit: mm Surface Data Surface 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 11.30 15* 15.005 0.88 13.98 16 ∞ 0.50 1.51633 64.1 17 ∞ 0.43 Image plane ∞ Aspheric data Side 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 Page 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 of view (°) 32.84 Image height 8.00 Lens length 21.75

[0069] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -13.635 1.00 1.63930 44.9 2 99.154 0.39 3* 13.334 3.34 1.85135 40.1 4* -28.879 1.16 5 (Aperture) ∞ -0.16 6 18.082 2.64 1.83400 37.2 7 -19.812 0.46 1.95906 17.5 8 16.122 1.20 9 22.990 0.49 1.51742 52.4 10 12.198 3.91 1.95375 32.3 11 -69.042 4.46 12* 58.200 1.20 1.63560 23.9 10.93 13* 10.051 0.79 13.74 14 ∞ 1.00 1.51633 64.1 15 ∞ 0.50 Image plane ∞ Aspheric data 3rd page K = 0.00000e+000 A 4=-9.49960e-005 A 6= 8.85709e-008 A 8= 8.38781e-009 Side 4 K = 0.00000e+000 A 4= 5.89387e-005 A 6= 2.33112e-008 A 8= 1.02643e-008 Side 12 K = 0.00000e+000 A 4=-4.66496e-003 A 6= 1.73987e-004 A 8=-7.91841e-006 A10= 2.13902e-007 A12=-2.31797e-009 Page 13 K = 0.00000e+000 A 4=-3.43721e-003 A 6= 1.12362e-004 A 8=-2.98646e-006 A10= 4.53813e-008 A12=-2.87945e-010 Focal length 12.40 F-number 1.30 Half angle of view (°) 32.83 Image height 8.00 Lens length 22.05 BF 1.95

[0070] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* -50.102 1.10 1.85135 40.1 2* 60.435 2.82 3 -43.713 0.44 1.69895 30.1 4 9.812 4.20 1.83400 37.2 5 -26.101 1.24 6 (Aperture) ∞ -0.46 7* 34.752 3.25 1.85135 40.1 8* -15.201 0.10 9 11.387 2.80 1.83400 37.2 10 69.014 0.46 1.95906 17.5 11 7.552 3.60 12 -23.007 2.15 1.69895 30.1 13 -12.236 2.19 14* 20.283 1.10 1.53110 55.9 12.29 15* 8.129 1.08 14.23 16 ∞ 1.00 1.51633 64.1 17 ∞ 0.50 Image plane ∞ Aspheric data Front page K = 0.00000e+000 A 4= 7.62920e-004 A 6=-1.51293e-005 A 8= 1.15810e-007 A10=-8.03081e-010 2nd side K = 0.00000e+000 A 4= 1.08116e-003 A 6=-9.48912e-006 A 8= 6.59401e-008 Side 7 K = 0.00000e+000 A 4=-4.96708e-005 A 6=-5.81139e-007 A 8= 8.30871e-009 A10=-1.26619e-010 Side 8 K = 0.00000e+000 A 4= 5.56396e-006 A 6=-2.06162e-008 A 8= 4.56601e-010 Page 14 K = 0.00000e+000 A 4=-3.77565e-003 A 6= 7.45432e-005 A 8=-1.07369e-006 A10= 5.61779e-009 Page 15 K = 0.00000e+000 A 4=-3.98006e-003 A 6= 9.25568e-005 A 8=-2.12771e-006 A10= 2.98794e-008 A12=-2.01103e-010 Various data Focal length 12.20 F-number 1.37 Half angle of view (°) 33.25 Image height 8.00 Lens length 27.23 BF 2.24

[0071] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -13.868 1.00 1.56732 42.8 2 50.002 0.36 3 12.482 1.50 2.00100 29.1 4 22.261 1.76 5 (Aperture) ∞ -0.81 6* 13.699 2.63 1.76802 49.2 7* -38.118 0.10 8 17.204 3.11 1.49700 81.5 9 -16.333 0.46 1.89286 20.4 10 14.000 0.49 11 18.318 3.80 2.00100 29.1 12 -22.325 4.22 13* -19.695 1.20 1.53110 55.9 11.53 14* 16.255 0.97 14.38 15 ∞ 1.00 1.51633 64.1 16 ∞ 0.45 Image plane ∞ Aspheric data Side 6 K = 0.00000e+00 A 4=-1.54601e-04 A 6= 7.86515e-07 A 8=-4.25057e-08 Side 7 K = 0.00000e+00 A 4= 9.17321e-05 A 6= 4.92069e-08 A 8=-2.57543e-08 Page 13 K = 0.00000e+00 A 4=-3.60228e-03 A 6= 1.48933e-04 A 8=-5.68173e-06 A10= 1.33854e-07 A12=-1.40815e-09 Page 14 K = 0.00000e+00 A 4=-2.44186e-03 A 6= 9.07676e-05 A 8=-2.27946e-06 A10= 3.20157e-08 A12=-1.96449e-10 Focal length 12.40 F-number 1.20 Half angle of view (°) 32.83 Image height 8.00 Lens length 21.89 BF 2.08

[0072] [Numerical Example 5] Unit: mm Surface Data Surface 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 10.83 15* 7.268 1.06 13.45 16 ∞ 0.50 1.51633 64.1 17 ∞ 0.45 Image plane ∞ Aspheric data Side 6 K = 0.00000e+00 A 4=-1.14931e-04 A 6= 4.45417e-07 A 8=-2.36743e-08 Side 7 K = 0.00000e+00 A 4= 5.95842e-05 A 6= 2.16407e-07 A 8=-1.41825e-08 Page 14 K = 0.00000e+00 A 4=-6.87777e-03 A 6= 2.46251e-04 A 8=-7.49558e-06 A10= 9.35756e-08 Page 15 K = 0.00000e+00 A 4=-6.38748e-03 A 6= 2.48242e-04 A 8=-7.63309e-06 A10= 1.27959e-07 A12=-9.02853e-10 Various data Focal length 12.80 F-number 1.30 Half angle of view (°) 32.00 Image height 8.00 Lens length 22.06 BF 1.84

[0073] The following table summarizes various values ​​for the optical system OL of each example.

[0074] [Table 1]

[0075] [Imaging device] Next, an embodiment of a digital still camera (image capture device) using the optical system of the present invention will be described with reference to Fig. 11. In Fig. 11, 10 is a camera body, and 11 is a lens device including any of the optical systems OL described in Examples 1 to 5.

[0076] Reference numeral 12 denotes a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body and receives and photoelectrically converts the optical image formed by the lens device 11. The camera body 10 may be a so-called single-lens reflex camera that has a quick-turn mirror, or a so-called mirrorless camera that does not have a quick-turn mirror.

[0077] In this way, by applying the optical system OL of the present invention to an imaging device such as a digital camera, it is possible to obtain an imaging device that is small and lightweight, can obtain high-quality images while ensuring a sufficient amount of light.

[0078] 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]

[0079] OL optical system L Front lens group Gn negative lens

Claims

1. An optical system comprising a front lens group and a negative lens Gn arranged on the image side of the front lens group, When the focal length of the optical system is f, the focal length of the negative lens Gn is fn, the effective diameter of the object-side lens surface of the negative lens Gn is D, the diameter of the aperture stop that determines the axial light beam is ST, the distance on the optical axis from a point located at the most end of the effective light beam area of ​​the object-side lens surface of the negative lens Gn to a point on the optical axis of the negative lens Gn is SAG1, the refractive index of the material of the negative lens Gn is NdGn, and the average of the refractive indexes of the materials of all the positive lenses included in the optical system is NdGp, -10.0<fn / f<-0.7 0.9<D / ST<1.4 -0.50<SAG1 / f<-0.16 1.45<NdGn<1.70 1.78<NdGp<2.2 An optical system characterized by satisfying the following conditional expression:

2. When the distance on the optical axis from a point located at the end of the effective light beam area on the image side lens surface of the negative lens Gn to a point on the optical axis on the image side lens surface of the negative lens Gn is SAG2, -0.35<-SAG2 / f<0 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the radius of curvature of the image-side lens surface of the negative lens Gn is GnR2, 0.5<GnR2 / f<10 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the air-equivalent distance on the optical axis from the vertex of the lens surface closest to the object side of the optical system to the image plane is Td, 0.1<Td / f<2.5 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the distance between the vertices of the lenses disposed before and after the aperture stop is STd, 0<STd / f<0.15 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the air-equivalent distance on the optical axis from the image-side lens surface of the negative lens Gn to the image plane is skd and the air-equivalent distance on the optical axis from the aperture stop to the image plane is SL, 0.05<skd / SL<0.15 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. The specific gravity (g / mm ３ ) is gGn, 0.6<gGn<1.7 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the shape factor of the lens G1 arranged closest to the object side in the optical system is SF1, 0.08<SF1<12.0 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the focal length of the lens G1 arranged closest to the object side in the optical system is f1, and the focal length of the second lens G2 counting from the object side in the optical system is f2, 0.6<|f1 / f2|<5.0 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. 10. The optical system according to claim 1, wherein the image-side lens surface of the negative lens Gn is an aspheric surface having at least one extreme point.

11. 11. The optical system according to claim 1, wherein the front lens group is made up of at least six lenses.

12. 12. The optical system according to claim 1, wherein a lens G1 arranged closest to the object side of the optical system is a negative lens having a concave surface on the object side.

13. 13. The optical system according to claim 1, wherein the front lens group comprises a negative lens arranged closest to the object, a positive lens arranged adjacent to the image side of the negative lens, and a positive lens arranged adjacent to the image side of the positive lens.

14. 14. 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