Optical system and image pickup apparatus including the same

Abstract

To provide a wide-angle and small-sized optical system having high optical performance.SOLUTION: An optical system includes a front group, an aperture stop, and a rear group arranged in order from an object side to an image side, and the front group includes a negative lens LN and satisfies a predetermined condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for use in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, and cameras for silver halide film. [Background technology]

[0002] In recent years, there has been a demand for optical systems used in imaging devices that have high optical performance, a wide angle, and a small size.

[0003] In order to obtain a wide-angle optical system, Patent Document 1 discloses a configuration in which the lens arranged closest to the object side has negative refractive power. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-35865 Summary of the Invention [Problem to be solved by the invention]

[0005] In the optical system of Patent Document 1, the partial dispersion ratio of the material of the negative lens arranged on the image side of the aperture stop is small, making it difficult to correct chromatic aberration of magnification between the g-line and the F-line, etc. Alternatively, since there is only one positive lens arranged on the image side of the aperture stop, it is difficult to suppress various aberrations that occur in lenses arranged on the object side of the aperture stop.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a wide-angle, compact optical system having high optical performance. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is a single focal length optical system comprising a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, wherein the front group has a negative lens LN, and when the refractive index of the material of the negative lens LN at the d-line is ndN, the Abbe number of the material of the negative lens LN is νdN, the back focus of the entire system is BF, and the focal length of the entire system is f, then: 2.160 <ndN+(0.02174×νdN)<2.370 1.600 <ndN<1.870 0.05 <BF / f<0.75 The present invention is characterized in that the following conditional expression is satisfied:

[0008] An optical system according to another aspect of the present invention is an optical system including a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, wherein the front group has a negative lens LN, the rear group has two or more positive lenses, and when the refractive index of the material of the negative lens LN at the d-line is ndN, 1.600 <ndN<1.870 The present invention is characterized in that the following conditional expression is satisfied: [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a wide-angle, compact optical system having high optical performance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of the optical system of Example 1 when focusing to infinity. [Figure 2] In the optical system of Example 1, (a) is a diagram showing aberrations when focusing at infinity, and (b) is a diagram showing aberrations when focusing at close range. [Figure 3] 1 is a cross-sectional view of the optical system of Example 2 when focusing to infinity. [Figure 4] In the optical system of Example 2, (a) is a diagram showing aberrations when focusing at infinity, and (b) is a diagram showing aberrations when focusing at close range. [Figure 5]10 is a cross-sectional view of the optical system of Example 3 when focusing to infinity. [Figure 6] In the optical system of Example 3, (a) is a diagram showing aberrations when focusing at infinity, and (b) is a diagram showing aberrations when focusing at close range. [Figure 7] 10 is a cross-sectional view of the optical system of Example 4 when focusing to infinity. [Figure 8] In the optical system of Example 4, (a) is a diagram showing aberrations when focusing at infinity, and (b) is a diagram showing aberrations when focusing at close range. [Figure 9] 10 is a cross-sectional view of the optical system of Example 5 when focusing to infinity. [Figure 10] In the optical system of Example 5, (a) is a diagram showing aberrations when focusing at infinity, and (b) is a diagram showing aberrations when focusing at close range. [Figure 11] Schematic diagram showing an imaging device DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, examples of an optical system according to an embodiment of the present invention and an imaging device having the same will be described with reference to the accompanying drawings.

[0012] 1, 3, 5, 7, and 9 are cross-sectional views of the optical system L0 of Examples 1 to 5, respectively, when focused at infinity. The optical system L0 of each Example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and vehicle-mounted cameras.

[0013] In each lens cross-sectional view, the left side is the object side and the right side is the image side. Note that the optical system L0 of each embodiment may be used as a projection lens for a projector, etc. In this case, the left side is the screen side and the right side is the projected image side.

[0014] In each lens cross-sectional view, SP denotes an aperture stop. IP denotes an image plane, and when the optical system L0 of each embodiment is used in a digital still camera or digital video camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system L0 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.

[0015] The optical system L0 in each embodiment is composed of, arranged in order from the object side to the image side, a front lens unit L1, an aperture stop SP, and a rear lens unit LR. Each lens unit may be composed of a single lens or multiple lenses.

[0016] The solid arrows shown above each lens cross-sectional diagram represent the movement locus of one or more lenses that move during focusing from infinity to close range.

[0017] 2, 4, 6, 8, and 10 are aberration diagrams (a) when focusing at infinity and (b) when focusing at close range in the optical system L0 of Examples 1 to 5, respectively.

[0018] In the spherical aberration diagram, Fno is the F-number, the solid line shows the amount of spherical aberration for the d-line (wavelength 587.6 nm), and the dashed line shows the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line shows the amount of aberration ΔS on the sagittal image plane, and the dashed line shows the amount of aberration ΔM on the meridional image plane. The distortion diagram shows the amount of distortion for the d-line. The chromatic aberration diagram shows the amount of lateral chromatic aberration for the g-line. ω is the half angle of view (°).

[0019] Here, the Abbe number vd and the partial dispersion ratio θgf for the g-line and F-line are known as parameters related to the correction of chromatic aberration in an optical system. When the refractive indices of materials for the g-line (wavelength 435.8 nm), F-line (486.1 nm), C-line (656.3 nm), and d-line (587.6 nm) are Ng, NF, NC, and Nd, respectively, the Abbe number vd and the partial dispersion ratio θgf for the g-line and F-line are respectively expressed by the following equations. νd=(Nd-1) / (NF-NC) θgf=(Ng-NF) / (NF-NC)

[0020] Next, the optical system L0 according to the first embodiment will be described.

[0021] The optical system L0 according to the first embodiment is a single-focal-length optical system consisting of, in order from the object side to the image side, a front group L1, an aperture stop SP, and a rear group LR. By arranging the front group L1 on the object side and the rear group LR on the image side of the aperture stop SP, it is easy to achieve a symmetrical arrangement, and it is a configuration that makes it easy to correct various aberrations.

[0022] The front unit L1 has a negative lens LN and is configured to satisfy the following conditional expression. 2.160 <ndN+(0.02174×νdN)<2.370···(1) 1.600 <ndN<1.870···(2) 0.05 <BF / f<0.75···(3)

[0023] Here, ndN and νdN are the refractive index at the d-line of the material of the negative lens LN, and the Abbe number of the material of the negative lens LN, respectively. BF is the back focus of the entire system. Here, the back focus is the air-equivalent value of the distance on the optical axis between the surface of the optical system L0 closest to the image and the image plane. f is the focal length of the entire system.

[0024] If the Abbe number of the material of the negative lens LN becomes large, exceeding the upper limit of conditional expression (1), low-dispersion glass must be selected as the material of the negative lens LN. This reduces the partial dispersion ratio between the g-line and the F-line, and the refractive index for the g-line becomes too small. This makes it difficult to correct chromatic aberration of magnification between the g-line and the F-line, which is undesirable.

[0025] If the Abbe number of the material of the negative lens LN falls below the lower limit of conditional expression (1) and becomes small, chromatic aberration of magnification between the F-line and C-line becomes too large, which is not preferable.

[0026] If the upper limit of conditional expression (2) is exceeded and the refractive index of the material of the negative lens LN for the d-line becomes large, the reflectance of the lens surface of the negative lens LN becomes high, which tends to increase the intensity of ghost light, which is undesirable.

[0027] If the refractive index of the material of the negative lens LN at the d-line becomes small by falling below the lower limit of conditional expression (2), the absolute value of the curvature of at least one of the object-side lens surface and image-side lens surface of the negative lens LN becomes too large. As a result, the sag amount of the negative lens LN increases, which undesirably increases the overall lens length. Here, the overall lens length is the sum of the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the optical system L0, and the back focus.

[0028] If the upper limit of conditional expression (3) is exceeded, the back focal length becomes too long, which is undesirable as the overall lens length becomes long. If the lower limit of conditional expression (3) is not exceeded, the back focal length becomes too short. As a result, the intensity of ghost light that is generated by reflection between the image sensor and the lens located closest to the image side in optical system L0 becomes strong, which is undesirable.

[0029] The optical system L0 according to the first embodiment satisfies the above configuration, and thus it is possible to provide an optical system L0 that has high optical performance, is wide-angle, and is compact.

[0030] Here, wide angle refers to the optical system L0 in which the maximum value of the imaging half angle of view is 21.0 degrees or more.

[0031] It is preferable that the conditional expressions (1), (2), and (3) are set to the following conditions, respectively. 2.180 <ndN+(0.02174×νdN)<2.350···(1a) 1.605 <ndN<1.850···(2a) 0.150 <BF / f<0.747···(3a)

[0032] Furthermore, it is preferable that the conditional expressions (1), (2), and (3) are set to the following conditions, respectively. 2.200 <ndN+(0.02174×νdN)<2.330···(1b) 1.610 <ndN<1.830···(2b) 0.250 <BF / f<0.745···(3b)

[0033] Furthermore, it is preferable that the conditional expressions (1), (2), and (3) are set to the following conditions, respectively. 2.250 <ndN+(0.02174×νdN)<2.300···(1c) 1.615 <ndN<1.800···(2c) 0.300 <BF / f<0.743···(3c)

[0034] Next, the optical system L0 according to the second embodiment will be described.

[0035] The optical system L0 according to the second embodiment is an optical system that is composed of, in order from the object side to the image side, a front group L1, an aperture stop SP, and a rear group LR. By arranging the front group L1 on the object side and the rear group LR on the image side of the aperture stop SP, it is easy to achieve a symmetrical arrangement and a configuration that makes it easy to correct various aberrations.

[0036] By including two or more positive lenses in the rear group LR, it becomes easier to suppress various aberrations that occur in lenses that are positioned closer to the object side than the aperture stop SP.

[0037] The front unit L1 has a negative lens LN and is configured to satisfy the following conditional expression. 1.600 <ndN<1.870···(2)

[0038] Here, ndN is the refractive index of the material of the negative lens LN for the d-line.

[0039] If the upper limit of conditional expression (2) is exceeded and the refractive index of the material of the negative lens LN for the d-line increases, the reflectance of the lens surface of the positive lens Gp increases, which is undesirable as it tends to increase the intensity of ghost light.

[0040] If the refractive index of the material of the negative lens LN at the d-line becomes small, falling below the lower limit of conditional expression (2), the absolute value of the curvature of at least one of the object-side lens surface and image-side lens surface of the negative lens LN becomes too large, which undesirably increases the sag amount of the negative lens LN and the overall lens length.

[0041] The optical system L0 according to the second embodiment satisfies the above-mentioned requirements, and thus can provide a wide-angle, compact optical system L0 with high optical performance. The optical system L0 according to the second embodiment may be a zoom lens.

[0042] Moreover, the wide angle refers to the optical system L0 in which the maximum value of the imaging half angle of view is 21.0 degrees or more.

[0043] It is preferable that conditional expression (2) be set to the following condition. 1.605 <ndN<1.850···(2a)

[0044] Furthermore, it is preferable that conditional expression (2) be set to the following condition. 1.610 <ndN<1.830···(2b)

[0045] Furthermore, it is preferable that conditional expression (2) be set to the following condition. 1.615 <ndN<1.800···(2c)

[0046] Next, a preferred configuration of the optical system L0 according to each embodiment will be described.

[0047] The rear group LR has a first focus lens group L2, and it is preferable that the front group L1 remains stationary and the first focus lens group L2 moves during focusing. Because the front group L1 is relatively heavy and large, keeping the front group L1 stationary and moving the first focus lens group L2 makes it easier to reduce the size of the lens group that moves during focusing.

[0048] The rear group further includes a second focus lens group L3 disposed adjacent to the image side of the first focus lens group L2. Preferably, the second focus lens group moves during focusing so that the distance between the first and second focus lens groups changes. By having multiple lens groups move along different trajectories during focusing, fluctuations in various aberrations that occur during focusing can be easily suppressed.

[0049] It is preferable that the rear group LR has four or more lenses, which makes it easier to suppress various aberrations that occur in the front group L1.

[0050] It is preferable that the lens element closest to the object in the front unit L1 has a negative meniscus shape with its convex surface facing the object, which allows off-axial rays to bend gently by the lens element closest to the object in the front unit L1, making it easier to suppress astigmatism and other aberrations.

[0051] It is preferable that the optical system L0 according to each embodiment satisfies one or more of the following conditional expressions. 0.50<|fN / f|<6.00 (4) 1.85 <ndP<2.40···(5) 10.0<νdP<35.0 (6) 0.75 <fP / f<4.00···(7) 1.00<|fF / f|<5.00 (8) 0.25 <d2 / d1<0.80···(9) 0.020<θgFN-(0.6418-0.00162×νdN)<0.045 (10) 20.0<ω<60.0 (11) 1.0 <Fno<3.0···(12)

[0052] Here, fN is the focal length of the negative lens LN. The front group L1 has a positive lens LP, ndP is the refractive index of the material of the positive lens LP at the d-line, and νdN is the Abbe number of the material of the positive lens LP. fP is the focal length of the positive lens LP. fF is the focal length of the front group L1.

[0053] d1 is the distance on the optical axis from the object side surface of the lens located closest to the object in the front group L1 to the aperture stop SP, and d2 is the distance on the optical axis from the object side surface of the negative lens LN to the aperture stop SP.

[0054] θgFN is the partial dispersion ratio of the material of the negative lens LN. ω is the maximum half angle of view when the optical system L0 is focused on an object at infinity. The unit is degrees. Fno is the F-number when the optical system L0 is focused on an object at infinity.

[0055] Next, the technical meaning of the above-mentioned conditional expressions (4) to (12) will be explained.

[0056] If the upper limit of conditional expression (4) is exceeded and the refractive power of the negative lens LN becomes weak, it becomes difficult to correct axial chromatic aberration and the like that occurs in the positive lens arranged in the optical system L0. If the lower limit of conditional expression (4) is not reached and the refractive power of the negative lens LN becomes strong, the axial light beam will diverge due to the negative lens LN, and the effective diameter of the lens arranged on the image side of the negative lens LN will become too large, which is undesirable.

[0057] If the upper limit of conditional expression (5) is exceeded and the refractive index of the material of the positive lens LP for the d-line becomes large, the reflectance of the lens surface of the positive lens LP becomes high, which tends to increase the intensity of ghost light, which is undesirable.

[0058] If the refractive index of the material of the positive lens element LP at the d-line becomes small, falling below the lower limit of conditional expression (5), the absolute value of the curvature of at least one of the object-side lens surface and image-side lens surface of the positive lens element LP becomes too large, which results in an increase in the amount of sag of the positive lens element LP and an increase in the overall lens length, which is undesirable.

[0059] If the Abbe number of the material of the positive lens LP becomes large, exceeding the upper limit of conditional expression (6), it becomes difficult to correct longitudinal chromatic aberration and the like that occurs in the negative lens disposed in the optical system L0. If the Abbe number of the material of the positive lens LP becomes small, falling below the lower limit of conditional expression (6), it is undesirable because chromatic aberration of magnification and the like that occurs in the positive lens LP becomes too large.

[0060] If the upper limit of conditional expression (7) is exceeded and the refractive power of the positive lens LP becomes weak, the principal point of the optical system L0 is likely to be located on the image side, which is undesirable as the overall lens length becomes long.If the lower limit of conditional expression (7) is exceeded and the refractive power of the positive lens LP becomes strong, the Petzval sum is likely to become large, which is undesirable.

[0061] If the refractive power of the front unit L1 becomes weaker beyond the upper limit of conditional expression (8), and if the refractive power of the front unit L1 is positive, the principal point of the optical system L0 is likely to be located on the image side, undesirably increasing the overall lens length. Also, if the refractive power of the front unit L1 is negative, the refractive power of the negative lens disposed in the front unit L1 becomes too weak, undesirably increasing the lens diameter of the negative lens.

[0062] If the refractive power of the front unit L1 becomes too strong, going below the lower limit of condition (8), the various aberrations produced by the front unit L1 become too large, making it difficult to correct them with the rear unit LR.

[0063] If the upper limit of conditional expression (9) is exceeded and the negative lens LN is positioned closer to the object, the off-axial rays will be positioned at a higher height from the optical axis. As a result, chromatic aberration of magnification between the g-line and the F-line will be over-corrected, which is undesirable. If the lower limit of conditional expression (9) is exceeded and the negative lens LN is positioned closer to the image, the off-axial rays will be positioned at a lower height from the optical axis. As a result, chromatic aberration of magnification between the g-line and the F-line will be under-corrected, which is undesirable.

[0064] If the upper limit of conditional expression (10) is exceeded and the partial dispersion ratio of the negative lens LN becomes too large, lateral chromatic aberration between the g-line and the F-line is undesirably over-corrected, whereas if the lower limit of conditional expression (10) is exceeded and the partial dispersion ratio of the negative lens LN becomes too small, lateral chromatic aberration between the g-line and the F-line is undesirably under-corrected.

[0065] If the upper limit of conditional expression (11) is exceeded and the maximum half angle of view becomes large, the height from the optical axis of off-axial rays incident on the front unit L1 becomes too high. As a result, the radial size of the lenses arranged in the front unit L1 becomes large, which is undesirable. If the lower limit of conditional expression (11) is exceeded, the maximum half angle of view becomes too small, which narrows the angle of view, which is undesirable.

[0066] If the F-number exceeds the upper limit of conditional expression (12) and becomes large, noise tends to increase when an image is captured by an imaging element, which is not preferable. If the F-number falls below the lower limit of conditional expression (12) and becomes small, the optical system L0 becomes large, which is not preferable.

[0067] It is more preferable that conditional expressions (4) to (12) be set as follows: 0.60<|fN / f|<5.50 (4a) 1.86 <ndP<2.30···(5a) 14.0<νdP<31.0 (6a) 1.00 <fP / f<3.50···(7a) 1.26<|fF / f|<4.50 (8a) 0.30 <d2 / d1<0.77···(9a) 0.022<θgFN-(0.6418-0.00162×νdN)<0.041 (10a) 27.0<ω<50.0 (11a) 1.10 <Fno<2.50···(12a)

[0068] Furthermore, it is preferable that conditional expressions (4) to (12) be set as follows. 0.63<|fN / f|<5.30 (4b) 1.87 <ndP<2.20···(5b) 16.0<νdP<30.0 (6b) 1.20 <fP / f<3.20···(7b) 1.35<|fF / f|<4.25 (8b) 0.33 <d2 / d1<0.73···(9b) 0.023<θgFN-(0.6418-0.00162×νdN)<0.039 (10b) 29.0<ω<46.0 (11b) 1.13 <Fno<2.10···(12b)

[0069] Furthermore, it is more preferable that conditional expressions (4) to (12) be set as follows: 0.67<|fN / f|<5.04 (4c) 1.89 <ndP<2.11···(5c) 17.0<νdP<27.0 (6c) 1.33 <fP / f<3.09···(7c) 1.52<|fF / f|<4.00 (8c) 0.36 <d2 / d1<0.70···(9c) 0.024<θgFN-(0.6418-0.00162×νdN)<0.037...(10c) 31.0<ω<43.0···(11c) 1.15 <Fno<2.00···(12c)

[0070] Next, the configuration of the optical system L0 in each embodiment will be described in detail. From embodiment 2 onwards, differences from embodiment 1 will be mainly described.

[0071] [Example 1] The optical system L0 of Example 1 is composed of, arranged in order from the object side to the image side, a front group L1, an aperture stop SP, and a rear group LR. The rear group LR is composed of a first focus lens group L2, a second focus lens group L3, and a fourth lens group L4. During focusing, the front group L1, the aperture stop SP, and the fourth lens group L4 remain stationary, and move along different loci from the first focus lens group L2 and the second focus lens group L3. By having the first focus lens group L2 and the second focus lens group L3 move along different loci, it becomes easier to suppress fluctuations in various aberrations that occur during focusing.

[0072] The negative lens element LN is the fifth lens element counting from the object side, and the positive lens element LP is the seventh lens element counting from the object side, which facilitates good correction of lateral chromatic aberration and the like.

[0073] Furthermore, the lens located closest to the object side in the front group L1 has positive refractive power, which makes it easier to correct distortion.

[0074] [Example 2] In the optical system L0 of Example 2, the lens in the front group L1 located closest to the object has a negative meniscus shape with its convex surface facing the object side, which causes off-axial rays to bend gently by the lens in the front group L1 located closest to the object, making it easier to suppress astigmatism and the like.

[0075] Furthermore, the lens element in the rear group LR that is positioned closest to the image side has a negative meniscus shape with its convex surface facing the image side, which allows for excellent correction of field curvature.

[0076] Furthermore, by adding one negative lens to the second focus lens unit L3 compared to Example 1, it becomes easier to suppress fluctuations in various aberrations that occur during focusing.

[0077] [Example 3] The optical system L0 of the third embodiment has a configuration in which the fourth lens unit L4 is made up of a cemented lens, which makes it easy to reduce the intensity of ghost light.

[0078] [Example 4] The optical system L0 of Example 4 is composed of, arranged in order from the object side to the image side, a front group L1, an aperture stop SP, and a rear group LR. The rear group LR is composed of a first focus lens group L2 and a third lens group L3, and during focusing, the front group L1, aperture stop SP, and third lens group L3 remain stationary, while the first focus lens group L2 moves. By limiting the number of lens groups that move during focusing to one, it becomes easier to suppress relative decentering of the lens groups that occurs during focusing.

[0079] [Example 5] The optical system L0 of Example 5 is composed of, arranged in order from the object side to the image side, a front group L1, an aperture stop SP, and a rear group LR. The rear group LR is composed of a first focus lens group L2, and during focusing, the front group L1 and the aperture stop SP are stationary, while the first focus lens group L2 moves. By having one lens group that moves during focusing and one lens group that is stationary during focusing, it becomes easier to suppress changes in performance due to relative decentering of each lens group.

[0080] In the optical system L0 of each embodiment, it is preferable to deposit a fluorine coating on the object-side lens surface of the lens positioned closest to the object and the image-side lens surface of the lens positioned closest to the image. Because the object-side lens surface of the lens positioned closest to the object and the image-side lens surface of the lens positioned closest to the image are easily exposed to the outside world, depositing a fluorine coating on them can improve water and oil repellency, suppress flare, and achieve high optical performance. In particular, because the object-side lens surface of the lens positioned closest to the object has a large diameter, it is preferable to deposit a fluorine coating on them.

[0081] In the cemented lenses arranged in the optical system L0 of each embodiment, it is preferable that the positive lens and negative lens constituting at least one cemented lens are bonded with an adhesive having an axial thickness of 0.005 mm or more and 0.05 mm or less. If it is less than 0.005 mm, the adhesive is prone to peeling, and if it is more than 0.03 mm, the axial distance from the lens surface closest to the object to the lens surface closest to the image becomes long, resulting in a long overall lens length. It is more preferable that the adhesive thickness be 0.008 mm or more and 0.02 mm or less.

[0082] At least one lens in the optical system L0 in each embodiment is provided with an anti-reflection coating to prevent reflection, and the anti-reflection coating is composed of multiple films. Here, when the refractive index of the film closest to the air interface with respect to the d-line is Nd, the anti-reflection coating PC is preferably an Nd of 1.32 or less. By setting Nd to 1.32 or less, the difference in refractive index with air can be reduced, thereby further reducing light reflection and reducing ghosting.

[0083] Specific examples of the antireflection film PC include, but are not limited to, multilayer films formed using a wet method, as described in JP-A Nos. 2012-230211 and 2014-95877. More preferably, ghosts can be further reduced by setting Nd to 1.30 or less.

[0084] Here, it is preferable to apply an anti-reflection coating PC to the image-side lens surface of the negative lens arranged in the optical system L0, which has a concave surface facing the image side. Light reflected by a negative lens with a concave surface facing the image side is likely to be reflected at a large angle relative to the normal to the lens surface of the negative lens with a concave surface facing the image side, and therefore tends to have a high reflectance. Furthermore, light reflected by a negative lens with a concave surface facing the image side is likely to be focused on the image plane, making ghost images noticeable. Therefore, ghost images can be reduced by applying an anti-reflection coating PC to the image-side lens surface of a negative lens with a concave surface facing the image side.

[0085] Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively, are shown below.

[0086] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth surface and the (m+1)th surface, where m is the surface number counted from the light incident side.

[0087] Furthermore, nd is the refractive index of each optical element at the d-line, νd and θgf are the Abbe number of the optical element and the partial dispersion ratio between the g-line and the F-line, respectively. The Abbe number νd and the partial dispersion ratio θgf between the g-line and the F-line of a certain material are expressed as follows. That is, let us assume that the Fraunhofer line is the g-line (wavelength 435.8 nm). Furthermore, if the refractive indices at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm) and C-line (wavelength 656.3 nm) are Ng, Nd, NF and NC, respectively, then νd=(Nd-1) / (NF-NC) θgf=(Ng-NF) / (NF-NC) It is expressed as:

[0088] BF is the back focus.

[0089] 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 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. 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.

[0090] (Numerical Example 1) Surface number rd nd νd θgf 1 100.883 4.39 1.85033 42.7 2 256.406 0.30 3 147.675 1.50 1.49700 81.5 4* 23.377 9.55 5 57.813 3.10 2.05090 26.9 6 140.424 5.93 7 -113.659 1.00 1.51823 58.9 8 60.658 7.22 9 -33.425 1.00 1.79631 22.6 0.641 10 42.698 10.23 1.80400 46.5 11 -64.116 0.30 12 106.182 6.93 2.10420 17.0 13 -106.198 0.30 14 30.530 5.48 1.43875 94.7 15 44.549 1.94 16 65.394 1.00 1.85478 24.8 17 24.053 11.77 1.49700 81.5 18 -304.647 (variable) 19 (Aperture) ∞ 14.25 20 -46.043 1.00 1.75520 27.5 21 1067.248 0.30 22 35.197 6.81 1.49700 81.5 23 -133.625 (variable) 24 36.240 4.35 1.91082 35.2 25 99.871 7.96 26* -296.212 2.90 1.85400 40.4 27* -499.007 (variable) 28 236.589 3.93 1.77250 49.6 29 -76.666 1.96 30 -40.755 1.00 1.56732 42.8 31 105.252 11.00 Image plane ∞ Aspheric data Side 4 K = 0.00000e+00 A 4=-2.27494e-06 A 6=-2.16232e-09 A 8=-1.51867e-11 A10= 3.88418e-14 A12=-7.49051e-17 Page 26 K = 0.00000e+00 A 4=-2.70433e-06 A 6= 6.45897e-08 A 8=-9.59358e-11 A10=-3.53427e-13 A12= 6.13959e-16 Page 27 K = 0.00000e+00 A 4= 1.47114e-05 A 6= 6.16222e-08 A 8= 4.17474e-11 A10=-7.04497e-13 A12= 9.21963e-16 Focal length 34.80 F-number 1.24 Half angle of view: 31.87 Image height 21.64 Lens total length 135.00 d18 0.43 d23 4.01 d27 3.15 d31 11:00 Group starting plane focal length L1 1 72.27 L2 19 971.85 L3 24 64.33 L4 28 -185.18

[0091] (Numerical Example 2) Surface number rd nd νd θgf 1 52.072 2.00 1.48749 70.2 2 24.933 7.83 3* 53.818 2.50 1.59201 67.0 4* 24.046 6.18 5 60.328 4.99 2.00100 29.1 6 -241.280 1.01 7 -100.437 1.00 1.43875 94.7 8 32.641 8.76 9 -32.381 1.00 1.79631 22.6 0.641 10 34.853 8.39 1.85150 40.8 11 -89.361 0.91 12 76.331 5.70 2.10420 17.0 13 -110.704 0.03 14 61.292 7.68 1.59349 67.0 15 -65.995 1.20 1.77047 29.7 16 21.466 12.43 1.65160 58.5 17 -104.253 (variable) 18 (Aperture) ∞ 9.08 19 -44.008 1.00 1.77047 29.7 20 84.508 0.05 21 29.338 8.78 1.49700 81.6 22 -61.516 (variable) 23 34.437 5.07 1.95375 32.3 24 -2066.470 1.61 25 -70.843 1.00 1.77047 29.7 26 -915.785 7.47 27* 770.331 2.50 1.85400 40.4 28* 273.083 (variable) 29 901.258 4.91 1.60311 60.6 30 -35.582 1.31 31 -27.540 1.00 1.90043 37.4 32 -77.617 11.00 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4= 4.91796e-06 A 6= 1.29767e-09 A 8=-5.98577e-12 A10= 2.31063e-14 A12=-2.36814e-17 Side 4 K = 0.00000e+00 A 4= 2.08292e-06 A 6=-2.77792e-09 A 8= 7.56474e-12 A10=-1.99571e-14 A12= 2.68960e-17 Page 27 K = 0.00000e+00 A 4=-4.17918e-05 A 6=-2.32909e-09 A 8= 7.38895e-10 A10=-2.73684e-12 A12= 2.83579e-16 Page 28 K = 0.00000e+00 A 4=-1.81573e-05 A 6= 2.49986e-09 A 8= 9.97096e-10 A10=-4.10114e-12 A12= 4.09465e-15 Focal length 24.72 F-number 1.24 Half angle of view 41.19 Image height 21.64 Lens total length 130.00 d17 1.00 d22 1.00 d28 1.62 d32 11.00 Group starting plane focal length L1 1 54.80 L2 18 -1041.49 L3 23 55.97 L4 29 -345.65

[0092] (Numerical Example 3) Surface number rd nd νd θgf 1 71.600 1.50 1.49700 81.5 2* 21.803 20.70 3 -26.764 1.48 1.66382 27.4 0.632 4 65.484 10.68 1.72916 54.1 5 -36.179 0.30 6 45.301 7.66 1.94594 18.0 7 -904.012 6.42 8 -344.750 1.00 1.76182 26.5 9 19.029 13.19 1.72916 54.7 10 -7138.458 (variable) 11 (Aperture) ∞ 12.55 12 -44.527 1.00 1.73037 32.2 13 79.265 0.31 14 26.851 6.71 1.43875 94.7 15 -131.974 (variable) 16 28.325 5.51 1.88300 40.8 17 81.740 5.39 18* 213.570 2.38 1.76450 49.1 19* 1894.551 (variable) 20 -85.114 6.91 1.43875 94.7 21 -23.342 1.00 1.61340 44.3 22 -500.000 11.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-3.16564e-06 A 6=-4.34848e-09 A 8=-2.11253e-11 A10= 4.85169e-14 A12=-1.47324e-16 Page 18 K = 0.00000e+00 A 4=-2.20467e-05 A 6= 1.98460e-09 A 8= 4.15875e-10 A10=-1.75720e-12 A12= 6.21735e-16 Page 19 K = 0.00000e+00 A 4= 6.61607e-06 A 6= 1.92786e-09 A 8= 7.20728e-10 A10=-2.99889e-12 A12= 2.44720e-15 Focal length 33.95 F-number 1.44 Half angle of view 32.51 Image height 21.64 Lens total length 125.00 d10 1.98 d15 3.11 d19 4.23 d22 11.00 Group starting plane focal length L1 1 58.78 L2 11 -179.99 L3 16 41.86 L4 20 -86.54

[0093] (Numerical Example 4) Surface number rd nd νd θgf 1 206.289 1.50 1.58313 59.4 2* 21.953 11.45 3 -19.368 1.00 1.62200 30.7 0.625 4 -66.179 4.37 1.80400 46.5 5 -25.676 0.30 6 37.526 4.61 1.89286 20.4 7 219.726 6.97 8 565.434 1.00 1.76182 26.5 9 19.623 10.01 1.65160 58.5 10 -51.141 (variable) 11 (Aperture) ∞ 11.92 12 -50.772 1.00 1.63980 34.5 13 84.115 0.30 14 23.911 6.73 1.43875 94.7 15 -199.844 3.71 16 28.618 3.55 1.95375 32.3 17 44.247 8.66 18* 258.303 2.50 1.80400 46.5 19* 194.652 (variable) 20 -27.419 1.84 1.62004 36.3 21 -41.841 11.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4= 1.25372e-06 A 6= 3.23895e-09 A 8= 5.16213e-11 A10=-4.23814e-13 A12= 1.70661e-15 Page 18 K = 0.00000e+00 A 4=-5.15875e-05 A 6=-3.96579e-08 A 8=-2.20805e-10 A10= 5.41068e-12 A12=-1.96075e-14 Page 19 K = 0.00000e+00 A 4=-2.28444e-05 A 6=-6.64256e-08 A 8= 8.49287e-10 A10=-1.09836e-12 A12=-3.01685e-15 Focal length 34.24 F-number 1.85 Half angle of view 32.29 Image height 21.64 Lens total length 100.00 d10 1.50 d19 6.08 d21 11:00 Group starting plane focal length L1 1 52.34 L2 11 75.89 L3 20 -134.87

[0094] (Numerical Example 5) Surface number rd nd νd θgf 1 71.491 1.50 1.49700 81.5 2 19.105 10.02 3* 63.859 2.00 1.58313 59.4 4* 19.739 4.15 5 61.004 3.25 2.05090 26.9 6 6042.554 9.25 7 -68.913 2.00 1.68430 26.8 0.623 8 -364.282 0.50 9 66.231 5.67 1.58913 61.1 10 -29.198 2.33 11 -58.746 1.50 1.67270 32.1 12 149.701 5.48 13 (Aperture) ∞ (Variable) 14 21.952 7.78 1.43875 94.7 15 -67.020 0.05 16 33.902 3.86 1.53775 74.7 17 -64885.303 1.88 18 -43.805 2.00 1.67270 32.1 19 -402.973 12.16 20* -74.903 3.00 1.58313 59.4 21* -520.882 18.33 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4= 4.50715e-06 A 6=-3.61106e-08 A 8= 5.90954e-11 A10=-1.65860e-13 Side 4 K = 0.00000e+00 A 4=-1.87107e-06 A 6=-4.87870e-08 A 8=-2.37273e-11 A10=-2.21384e-13 Page 20 K = 0.00000e+00 A 4=-1.11378e-04 A 6= 1.92343e-07 A 8=-1.66299e-09 A10= 1.37455e-11 A12=-6.06091e-14 Page 21 K = 0.00000e+00 A 4=-5.44556e-05 A 6= 2.29778e-07 A 8= 1.12484e-10 A10=-7.20558e-13 A12=-2.66382e-15 Focal length 24.72 F-number 1.85 Half angle of view 41.19 Image height 21.64 Lens total length 110.00 d13 13.29 d21 18.33 Group starting plane focal length L1 1 -98.72 L2 14 35.77

[0095] The table below shows the various values ​​for each example.

[0096] [Table 1]

[0097] [Imaging device] Next, an example of a digital still camera (imaging device) that uses the optical system L0 of this embodiment as an imaging optical system will be described with reference to Fig. 11. In Fig. 11, 11 denotes an imaging optical system configured using any of the optical systems described in Examples 1 to 5. 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into a camera body 10 and receives and photoelectrically converts an optical image formed by the imaging optical system 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.

[0098] In this way, by applying the optical system L0 of this embodiment to an imaging device such as a digital still camera, it is possible to obtain a high-resolution image with a wide angle of view.

[0099] The disclosure of each embodiment includes the following configuration.

[0100] (Configuration 1) A single-focus optical system consisting of a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, the front group has a negative lens LN, When the refractive index of the material of the negative lens LN for the d-line is ndN, the Abbe number of the material of the negative lens LN is νdN, the back focus of the entire system is BF, and the focal length of the entire system is f, 2.160 <ndN+(0.02174×νdN)<2.370 1.600 <ndN<1.870 0.05 <BF / f<0.75 An optical system characterized by satisfying the following conditional expression:

[0101] (Configuration 2) An optical system consisting of a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, the front group has a negative lens LN, the rear group has two or more positive lenses, When the refractive index of the material of the negative lens LN for the d-line is ndN, 1.600 <ndN<1.870 An optical system characterized by satisfying the following conditional expression:

[0102] (Configuration 3) When the focal length of the negative lens LN is fN, 0.50<|fN / f|<6.00 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied:

[0103] (Configuration 4) the front group has a positive lens LP, When the refractive index of the material of the positive lens LP with respect to the d line is ndP and the Abbe number of the material of the positive lens LP is νdN, 1.85 <ndP<2.40 10.0<νdP<35.0 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied:

[0104] (Configuration 5) When the focal length of the positive lens LP is fP, 0.75 <fP / f<4.00 5. The optical system according to configuration 4, wherein the following condition is satisfied:

[0105] (Configuration 6) the rear group includes a first focus lens group, 6. The optical system according to any one of configurations 1 to 5, wherein the front group is stationary and the first focus lens group is movable during focusing.

[0106] (Configuration 7) the rear group includes a second focus lens group disposed adjacent to the image side of the first focus lens group, The optical system described in any one of configurations 1 to 6, wherein the second focus lens group moves during focusing so that the distance between the first focus lens group and the second focus lens group changes.

[0107] (Configuration 8) The optical system according to any one of configurations 1 to 7, wherein the rear group has four or more lenses.

[0108] (Configuration 9) When the focal length of the front group is fF, 1.00<|fF / f|<5.00 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied:

[0109] (Configuration 10) Let d1 be the distance on the optical axis from the object side surface of the lens located closest to the object in the front group to the aperture stop, and d2 be the distance on the optical axis from the object side surface of the negative lens LN to the aperture stop, 0.25 <d2 / d1<0.80 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied:

[0110] (Configuration 11) When the partial dispersion ratio of the material of the negative lens LN is θgFN, 0.020<θgFN-(0.6418-0.00162×νdN)<0.045 11. The optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied:

[0111] (Configuration 12) When the maximum half angle of view when focused on an object at infinity is ω [degrees], 20.0<ω<60.0 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied:

[0112] (Configuration 13) When the F-number when focused on an object at infinity is Fno, 1.0 <Fno<3.0 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied:

[0113] (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the lens arranged closest to the object side in the front group has a negative meniscus shape with a convex surface facing the object side.

[0114] (Configuration 15) the rear group includes the first focus lens group and a third lens group arranged adjacent to the first focus lens group on the image side, 7. The optical system according to configuration 6, wherein the third lens group is stationary during focusing.

[0115] (Configuration 16) 8. The optical system according to configuration 7, wherein the rear group is made up of the first focus lens group and the second focus lens group.

[0116] (Configuration 17) the rear group includes the first focus lens group, the second focus lens group, and a fourth lens group arranged adjacent to the image side of the second focus lens group, 8. The optical system according to configuration 7, wherein the fourth lens group is stationary during focusing.

[0117] (Configuration 18) an optical system according to any one of configurations 1 to 17; an imaging device having an imaging element that receives an image formed by the optical system;

[0118] 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]

[0119] L1 front group SP aperture stop LR rear group LN: A predetermined negative lens element in the front group

Claims

1. A single-focus optical system consisting of a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, the front group has a negative lens LN, When the refractive index of the material of the negative lens LN for the d-line is ndN, the Abbe number of the material of the negative lens LN is νdN, the back focus of the entire system is BF, and the focal length of the entire system is f, 2.160<ndN+(0.02174×νdN)<2.370 1.600<ndN<1.870 0.05<BF / f<0.75 An optical system characterized by satisfying the following conditional expression:

2. When the focal length of the negative lens LN is fN, 0.50<|fN / f|<6.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. The front group has a positive lens LP, When the refractive index of the material of the positive lens LP for the d line is ndP and the Abbe number of the material of the positive lens LP is νdP, 1.85<ndP<2.40 10.0<νdP<35.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the positive lens LP is fP, 0.75<fP / f<4.00 4. The optical system according to claim 3, wherein the following condition is satisfied:

5. the rear group includes a first focus lens group, 2. The optical system according to claim 1, wherein the front lens group is stationary and the first focus lens group is movable during focusing.

6. the rear group includes a second focus lens group disposed adjacent to the image side of the first focus lens group, 6. The optical system according to claim 5, wherein the second focus lens group moves during focusing so that the distance between the first focus lens group and the second focus lens group changes.

7. 2. The optical system according to claim 1, wherein the rear group includes four or more lenses.

8. When the focal length of the front group is fF, 1.00<|fF / f|<5.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

9. Let d1 be the distance on the optical axis from the object side surface of the lens located closest to the object side in the front group to the aperture stop, and d2 be the distance on the optical axis from the object side surface of the negative lens LN to the aperture stop. 0.25<d2 / d1<0.80 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the partial dispersion ratio of the material of the negative lens LN is θgFN, 0.020<θgFN-(0.6418-0.00162×νdN)<0.045 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the maximum half angle of view when focused on an object at infinity is ω [degrees], 20.0<ω<60.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the F-number when focused on an object at infinity is Fno, 1.0<Fno<3.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

13. 2. The optical system according to claim 1, wherein the lens element arranged closest to the object side in said front group has a negative meniscus shape with a convex surface facing the object side.

14. the rear group includes the first focus lens group and a third lens group arranged adjacent to the first focus lens group on the image side, 6. The optical system according to claim 5, wherein the third lens group remains stationary during focusing.

15. 7. The optical system according to claim 6, wherein the rear group comprises the first focus lens group and the second focus lens group.

16. the rear group includes the first focus lens group, the second focus lens group, and a fourth lens group arranged adjacent to the second focus lens group on the image side, 7. The optical system according to claim 6, wherein the fourth lens group remains stationary during focusing.

17. An optical system consisting of a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, the front group has a negative lens LN, the rear group has two or more positive lenses, When the refractive index of the material of the negative lens LN for the d line is ndN, 1.600<ndN<1.870 An optical system characterized by satisfying the following conditional expression:

18. An optical system according to any one of claims 1 to 17; an imaging device having an imaging element that receives an image formed by the optical system;

Images