Optical system and imaging device having the same

Abstract

To provide a compact, light-weight optical system for a wide-angle lens, which offers high optical performance.SOLUTION: An optical system comprises a front group having positive refractive power and a rear group having positive refractive power arranged in order from the object side to the image side, and is configured such that the distance between the front group and the rear group changes for focusing. Curvature radii of object-side and image-side surfaces of a lens with positive refractive power located on the most image side are set appropriately.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system and an imaging device having the same.

Background Art

[0002] As a photographing optical system with a wide photographing angle, a so-called retrofocus type photographing optical system in which an optical system having a negative refractive power is arranged on the object side and an optical system having a positive refractive power is arranged on the image side is known, and it is used for, for example, a single-focus wide-angle lens.

[0003] Furthermore, in digital cameras and video cameras, the number of pixels of solid-state imaging devices such as CCDs and CMOS sensors has been increasing, and high optical performance including chromatic aberration is required for photographing lenses, and miniaturization has been progressing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, in wide-angle lens systems used in imaging devices, there has been a demand for lenses that are small as a whole while having high optical performance. In general, wide-angle lenses are designed to reduce overall lens length by placing the lens with the most negative refractive power closest to the image sensor. However, this shortens the exit pupil and increases the angle at which off-axis rays enter the image sensor, leading to shading and other issues due to the image sensor's oblique incident light characteristics. Furthermore, wide-angle lenses have a higher off-axis ray angle, resulting in greater fluctuations in field curvature and distortion during focusing. To address these issues, it is necessary to optimize the lens shape and focusing group that make up the rear group.

[0006] Patent Document 1 discloses a lens consisting of a front group with positive refractive power and a rear group composed of a single lens with positive refractive power, in order from the object side, wherein the front group moves in the direction of the optical axis during focusing. The lens closest to the image has a smaller radius of curvature on the object side than on the image side, and has a stronger positive refractive power relative to the entire system, which is undesirable as it leads to a deterioration of image field curvature mainly caused by off-axis rays.

[0007] Patent Document 2 discloses a lens consisting of a front group with positive refractive power and a rear group composed of a single lens with negative refractive power, arranged sequentially from the object side, wherein the front group moves in the direction of the optical axis during focusing. In a wide-angle lens, placing the lens with negative refractive power closest to the image side makes it possible to reduce the overall length of the lens. However, this is undesirable because the exit pupil becomes shorter, increasing the angle at which off-axis rays enter the image sensor, and causing shading and other issues due to the influence of the oblique incident light characteristics of the image sensor.

[0008] The present invention aims to provide a wide-angle lens with a compact and lightweight optical system that exhibits high optical performance while suppressing aberration fluctuations due to focusing, as well as an imaging device having the same. [Means for solving the problem]

[0009] To achieve the above objective, the optical system of the present invention consists of a front group and a rear group of positive refractive powers arranged sequentially from the object side to the image side, wherein the lens positioned closest to the object in the front group has negative refractive power, and for focusing, the front group moves in the optical axis direction, while the rear group remains stationary, and the final lens positioned closest to the image in the rear group has positive refractive power. The front group has an aperture, Let GLR1 be the radius of curvature of the object side of the final lens, and GLR2 be the radius of curvature of the image side. L12 is the distance between the lens closest to the object and the second lens from the object in the front group, L23 is the distance between the second lens from the object and the third lens from the object in the front group, PD is the distance along the optical axis from the object-side surface of the lens closest to the object to the aperture when in focus at infinity, and LD is the distance along the optical axis from the object-side surface of the lens closest to the object to the image-side surface of the last lens when in focus at infinity. In that case, 0.1<(GLR1+GLR2) / (GLR1-GLR2)<10.0 0.1 <L12 / L23<5.0 PD / LD < 0.45 It is characterized by satisfying the following conditional expression. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an optical system for wide-angle lenses that is compact, lightweight, and has high optical performance with suppressed aberration fluctuations due to focusing, as well as an imaging device having the same. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of the lens in Example 1 when the object distance is infinite. [Figure 2] This is an aberration diagram for Example 1 when the object distance is infinite. [Figure 3] This is a cross-sectional view of the lens in Example 2 when the object distance is infinite. [Figure 4] This is an aberration diagram for Example 2 when the object distance is infinite. [Figure 5] This is a cross-sectional view of the lens in Example 3 when the object distance is infinite. [Figure 6] This is an aberration diagram for Example 3 when the object distance is infinite. [Figure 7] This is a cross-sectional view of the lens in Example 4 when the object distance is infinite. [Figure 8] This is an aberration diagram for Example 4 when the object distance is infinite. [Figure 9] It is a cross-sectional view of the lens when the object distance is infinite in Example 5. [Figure 10] It is an aberration diagram when the object distance is infinite in Example 5. [Figure 11] It is a schematic diagram of the main part of the imaging device of the present invention.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings. Figs. 1, 3, 5, 7, and 9 are cross-sectional views of the optical systems of Examples 1 to 5 of the present invention when the object distance is infinite. Figs. 2, 4, 6, 8, and 10 are aberration diagrams of the optical systems of Examples 1 to 5 of the present invention when the object distance is infinite.

[0013] The optical systems of each embodiment are used in imaging devices such as digital still cameras, video cameras, surveillance cameras, and in-vehicle cameras. In the cross-sectional view of the lens, the left side is the object side (front), and the right side is the image side (rear).

[0014] SP is an aperture. IP is an image plane. When used as a photographing optical system of a digital still camera or a video camera, the imaging surface of a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is placed. Also, when used as a photographing optical system of a camera for silver halide film, the photosensitive surface of the film surface is placed.

[0015] In the aberration diagram, Fno is the F-number, and ω is the semi-aperture angle (degrees). In the spherical aberration diagram, d is the d-line (wavelength 587.56 nm), and g is the g-line (wavelength 435.835 nm).

[0016] In the astigmatism diagram, ΔS is the sagittal image plane at the d-line, and ΔM is the meridional image plane at the d-line. The distortion aberration is shown for the d-line. The chromatic aberration diagram is the longitudinal chromatic aberration and is shown for the g-line. The present invention has a front group of lenses having positive refractive power, arranged sequentially from the object side to the image side, and a rear group having at least one lens with positive refractive power, wherein the distance between the front group and the rear group changes during focusing, and when infinity focus is achieved, the radius of curvature of the object side of the positive refractive power lens closest to the image is GLR1, and the radius of curvature of the image side is GLR2. 0.1<(GLR1+GLR2) / (GLR1-GLR2)<10.0 ···(1) It is characterized by satisfying the following conditional expression.

[0017] In wide-angle lenses, by appropriately setting the lens shape located closest to the image sensor, the exit pupil can be lengthened, reducing the angle at which off-axis rays enter the image sensor. This makes the image sensor less susceptible to the effects of obliquely incident light characteristics, thus reducing shading and other distortions. It also allows for proper correction of distortion and chromatic aberration, which are mainly caused by off-axis rays. Furthermore, by moving the front group along the optical axis during focusing, it is possible to suppress variations in various aberrations during focusing while simultaneously reducing the weight of the focusing group compared to when the entire system is a single focusing group.

[0018] Condition (1) specifies the shape factor of the lens positioned closest to the image. Optimizing the shape allows for both reduction of shading by ensuring sufficient exit pupil length and suppression of various aberration fluctuations during focusing. Exceeding the upper limit of condition (1) increases the positive refractive power of the lens positioned closest to the image, resulting in a longer exit pupil and reduced shading. However, this increases the refractive power of the rear group, which is advantageous for miniaturizing the overall lens length, but leads to a deterioration of field curvature aberration, mainly caused by off-axis rays. Exceeding the lower limit of condition (1) decreases the positive refractive power of the lens positioned closest to the image, resulting in a shorter exit pupil, which is undesirable.

[0019] Preferably, the numerical range of conditional expression (1) should be set as follows. 0.2<(GLR1+GLR2) / (GLR1-GLR2)<7.0 ···(1a) More preferably, the numerical range of the conditional expression (1a) should be set as follows. 0.3<(GLR1+GLR2) / (GLR1-GLR2)<5.0 (1b) As described above, by satisfying condition (1), it is possible to provide a wide-angle lens with a compact, lightweight optical system and high optical performance, as well as an imaging device having the same.

[0020] In each embodiment, it is even more preferable that one or more of the following conditions are satisfied. Let sk be the distance from the image-side lens surface of the lens closest to the image (back focus in air equivalent), and LD be the distance along the optical axis from the object-side surface of the lens closest to the object to the image-side surface of the lens closest to the image. Let f11 be the focal length of the lens system positioned closer to the object than the aperture in the front group, and f12 be the focal length of the lens system positioned closer to the image than the aperture in the front group. Let LB be the distance along the optical axis between the front and rear groups. Let f be the focal length of the entire system, f1 be the focal length of the front group, and f2 be the focal length of the rear group. Let ESinf be the focus sensitivity of the front group when focused at infinity. The focus sensitivity ESinf is calculated when the lateral magnification of the front and rear groups are β1 and β2, respectively, when focused at infinity. ESinf=(1- β1 2 )×β2 2 This is expressed as follows: When the lens is in focus at infinity, the distance on the optical axis from the object-side surface of the lens closest to the object to the aperture is denoted as PD. The distance between the lens closest to the object and the second lens from the object-side is denoted as L12, and the distance between the second lens from the object-side and the third lens from the object-side is denoted as L23. The radius of curvature of the image side of the second lens from the object-side is denoted as G2R2, and the radius of curvature of the object side of the third lens from the object-side is denoted as G3R1. Within the front group, the focal length of the lens closest to the object that has negative refractive power is denoted as fGn1. In the lens system located closer to the object than the aperture within the front group, the average Abbe number of the lenses with negative refractive power is denoted as νdn, and the average Abbe number of the lenses with positive refractive power is denoted as νdp. 0.1 <sk / LD<0.5 ··(2) -5.0 <f11 / f12<5.0 ··(3) 0.05 <LB / LD<0.60 ··(4) 1.0 <f2 / f<7.0 ··(5) 0.2 <ESinf<2.0 ··(6) PD / LD < 0.45 ··(7) -3.0 <f11 / f<12.0 ··(8) 0.1 <L12 / L23<5.0 ··(9) -8.0<(G2R2+G3R1) / (G2R2-G3R1)<-0.1···(10) 0.1 <fGn1 / f11<7.0 ··(11) 0.3 < νdn / νdp < 4.5 ··(12) The Abbe number νd is given by the Fraunhofer lines d, F, and C, where Nd, NF, and NC are the refractive indices of the d, F, and C lines, respectively. νd = (Nd-1) / (NF-NC) It is defined as follows.

[0021] Conditional equation (2) defines the ratio of the LD between the back focus sk and the optical axis distance from the object side of the lens closest to the object to the image side of the lens closest to the image. If the upper limit of conditional equation (2) is exceeded, the distance of the back focus sk increases, making it impossible to place the lens closer to the image sensor. This makes it difficult to improve field curvature and chromatic aberration, resulting in lower image quality, which is undesirable. If the lower limit of conditional equation (2) is exceeded, the distance of the back focus sk decreases, allowing the lens to be placed closer to the image sensor. This is advantageous for improving field curvature and chromatic aberration, but it makes it difficult to arrange shutter components and other elements.

[0022] Conditional equation (3) defines the ratio of the focal length f11 of the lens system located on the object side of the aperture within the front group (first sub-lens group) to the focal length f12 of the lens system located on the object side of the aperture within the front group (second sub-lens group). Exceeding the upper limit of conditional equation (3) increases the refractive power of the lens system located on the object side of the aperture within the front group, which is advantageous for miniaturizing the lens system, but is undesirable because it worsens distortion and chromatic aberration caused by off-axis rays. Exceeding the lower limit of conditional equation (3) decreases the refractive power of the lens system located on the object side of the aperture within the front group, which is advantageous for suppressing various aberrations, but is undesirable because it increases the lens diameter.

[0023] Conditional equation (4) defines the ratio of the distance LD (Landing Distance) between the front and rear lens groups, which is the distance along the optical axis between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image. Exceeding the upper limit of conditional equation (4) is advantageous because it allows for a smaller diameter of the image-side lens in the front group, but it is undesirable because it increases the overall length of the lens. Exceeding the lower limit of conditional equation (4) is also advantageous because it allows for a smaller overall length of the lens, but it is undesirable because it becomes difficult to arrange the mechanical components necessary to change the distance between the front and rear lens groups.

[0024] Conditional equation (5) specifies the ratio of the focal length f2 of the rear group to the focal length f of the entire system. By optimizing the focal length of the rear group, it is possible to achieve both a smaller overall lens length and suppression of various aberration fluctuations during focusing. Exceeding the upper limit of conditional equation (5) weakens the positive refractive power of the rear group, which is advantageous for suppressing various aberrations, but leads to a larger overall lens length. Exceeding the lower limit of conditional equation (5) strengthens the positive refractive power of the rear group, which leads to a smaller overall lens length, but is undesirable because it worsens field curvature and spherical aberration.

[0025] Conditional equation (6) defines the focus sensitivity ESinf of the front group when focused at infinity. Exceeding the upper limit of conditional equation (6) is undesirable because it increases the change in angle of view with respect to the amount of movement of the focusing lens group during focusing. It is also undesirable because it becomes difficult to suppress fluctuations in spherical aberration and field curvature during focusing. Exceeding the lower limit of conditional equation (6) makes it easier to suppress changes in spherical aberration and field curvature during focusing, but it increases the amount of movement of the focusing lens group during focusing, leading to an increase in the overall length of the lens.

[0026] Conditional equation (7) specifies the aperture position for the entire system. By optimizing the aperture position, it is possible to reduce the diameter of the lens on the object side. Exceeding the upper limit of conditional equation (7) is undesirable because it becomes difficult to reduce the diameter of the lens on the object side.

[0027] Conditional equation (8) specifies the ratio of the focal length f1 of the front group to the focal length f of the entire system. Primarily, optimizing the refractive power of the front group allows for both miniaturization of the lens system and good optical performance. Exceeding the upper limit of conditional equation (8) increases the refractive power of the front group, which is advantageous for miniaturizing the overall lens length, but leads to a deterioration of field curvature aberration. Exceeding the lower limit of conditional equation (8) decreases the refractive power of the front group, which is advantageous for suppressing the occurrence of various aberrations, but is undesirable because it makes it difficult to miniaturize the overall lens length.

[0028] Condition (9) defines the ratio of the distance L12 between the lens closest to the object and the second lens from the object, and the distance L23 between the second lens from the object and the third lens from the object. If the upper limit of condition (9) is exceeded, the distance L12 between the lens closest to the object and the second lens from the object becomes longer, and the off-axis marginal rays passing through the lens closest to the object become higher, which is undesirable because it increases the lens diameter. If the lower limit of condition (9) is exceeded, the distance L23 between the second lens from the object and the third lens from the object becomes longer, and the on-axis marginal rays passing through the third lens from the object become higher, which is advantageous for correcting spherical aberration, but is undesirable because it increases the lens diameter.

[0029] Conditional equation (10) defines the shape (shape factor) of the air lens between the image-side surface of the second lens from the object side and the object-side surface of the third lens from the object side. By optimizing the shape, good optical performance can be achieved, mainly within the front group. If the upper limit of conditional equation (10) is exceeded, the refractive power of the air lens weakens, which is advantageous in suppressing the occurrence of various aberrations, but is undesirable. If the lower limit of conditional equation (10) is exceeded, the refractive power of the air lens strengthens, which is advantageous in reducing the overall length of the lens, but off-axis rays diverge greatly, leading to a deterioration of chromatic aberration.

[0030] Conditional equation (11) specifies the ratio of the focal length fGn1 of the lens closest to the object with negative refractive power in the front group to the total focal length f of the entire system. By optimizing the focal length of the lens closest to the object with negative refractive power in the front group, it is possible to achieve both a smaller lens diameter and good optical performance. If the upper limit of conditional equation (11) is exceeded, the refractive power of the lens closest to the object with negative refractive power in the front group becomes weaker, which is advantageous in suppressing the occurrence of various aberrations, but it is undesirable because the lens diameter becomes larger. If the lower limit of conditional equation (11) is exceeded, the refractive power of the lens closest to the object with negative refractive power in the front group becomes stronger, which is advantageous in reducing the lens diameter, but it is undesirable because chromatic aberration worsens.

[0031] Conditional equation (12) defines the ratio of the average Abbe number νdn of lenses with negative refractive power in the front group to the average Abbe number νdp of lenses with positive refractive power. By optimizing the Abbe number of lenses in the front group, it is possible to achieve both a smaller lens diameter and suppression of lateral chromatic aberration occurring in the front group. If the upper limit of conditional equation (12) is exceeded, the correction effect of lateral chromatic aberration increases, but it leads to a deterioration of axial chromatic aberration and makes it difficult to optimize the refractive power of lenses with negative refractive power, resulting in a larger lens diameter. If the lower limit of condition (12) is exceeded, the refractive power of the lens with negative refractive power can be optimized, and the lens diameter can be reduced. However, this is undesirable because it becomes difficult to properly correct chromatic aberration. Preferably, the numerical ranges of conditional expressions (2) to (12) should be set as follows. 0.15 <sk / LD<0.40 ··(2a) -3.0 <f11 / f12<4.5 ··(3a) 0.08 <LB / LD<0.30 ··(4a) 2.2 <f2 / f<6.2 ··(5a) 0.4 <ESinf<1.0 ··(6a) PD / LD < 0.4 ··(7a) -2.6 <f11 / f<10.0 ··(8a) 0.3 <L12 / L23<4.0 ··(9a) -4.0<(G2R2+G3R1) / (G2R2-G3R1)<-0.3·(10a) 0.3 <fGn1 / f1<4.0 ··(11a) 0.8 < νdn / νdp < 3.2 ··(12a) More preferably, the numerical ranges of conditional expressions (2a) to (12a) should be set as follows. 0.2 <sk / LD<0.36 ··(2b) -1.5 <f11 / f12<4.0 ··(3b) 0.10 <LB / LD<0.20 ··(4b) 3.4 <f2 / f<5.5 ··(5b) 0.5 <ESinf<0.82 ··(6b) PD / LD < 0.35 ··(7b) -2.2 <f11 / f<9.0 ··(8b) 0.9 <L12 / L23<3.0 ··(9b) -2.7<(G2R2+G3R1) / (G2R2-G3R1)<-1.1·(10b) 0.5 <fGn1 / f1<2.1 ··(11b) 1.1 < νdn / νdp < 2.6 ··(12b)

[0032] When the focus group moves from infinity focus to closest focus, it is desirable that the rear group be fixed. Furthermore, it is desirable to have only one focus group. This reduces the number of parts such as motors required to move the focus group, thus enabling weight reduction.

[0033] Within the front group, it is desirable that there be only one lens with positive refractive power in the lens system located on the object side of the aperture within the front group. This makes it possible to correct chromatic aberration occurring in the front group while simultaneously reducing the overall size of the lens.

[0034] Within the front lens group, it is desirable that at least one positive refractive lens in the lens system positioned closer to the object than the aperture has a convex surface on its image side relative to the image side. This makes it possible to correct spherical aberration and reduce the overall size of the lens.

[0035] The front group preferably has at least one cemented lens consisting of a lens with positive refractive power and a lens with negative refractive power. Preferably, it has two cemented lenses consisting of a lens with positive refractive power and a lens with negative refractive power. This makes it possible to correct axial chromatic aberration and lateral chromatic aberration.

[0036] The front group should preferably have at least one aspherical lens. This makes it possible to appropriately correct the focusing-induced variation in image field curvature, which is mainly caused by off-axis rays.

[0037] The rear group is preferably composed of a single lens with positive refractive power. This makes it possible to achieve both sufficient exit pupil size and reduced lens weight.

[0038] When image shake correction is performed by moving the image shake correction group perpendicular to the optical axis, some of the lenses in the entire system may have a movement mechanism (vibration stabilization mechanism). [Examples]

[0039] Hereinafter, numerical examples 1 to 5 will be referred to as these embodiments. In each numerical example, ri is the radius of curvature of the i-th surface, starting from the object side; di is the lens thickness and air gap between the i-th and (i+1)-th surfaces, starting from the object side; and ndi and νdi are the refractive index and Abbe number of the optical medium between the i-th and (i+1)-th surfaces, starting from the object side, respectively.

[0040] The aspherical shape is defined as having the X-axis in the direction of the optical axis, the H-axis perpendicular to the optical axis, with the direction of light propagation being positive, R being the radius of paraxial curvature, K being the cone constant, and A4, A6, A8, A10, A12, and A14 being the aspherical coefficients, respectively.

number

[0041] The asterisk (*) to the right of the face number indicates that the face has an aspherical shape. "ex" means "×10 -x This means "back focus". BF indicates back focus. Next, an embodiment of a digital still camera using the optical system of the present invention as a photographic optical system will be described with reference to Figure 11. In Figure 11, 10 is the camera body, and 11 is the imaging optical system composed of one of the zoom lenses described in Examples 1 to 5. 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which is built into the camera body and receives the subject image formed by the imaging optical system 11.

[0042] [Numerical Example 1] Unit: mm Surface data Face number rd nd vd 1 41.307 1.20 1.60311 60.6 2 9.978 4.26 3 30.342 1.00 1.48749 70.2 4 12.124 3.17 5 28.492 2.01 1.83481 42.7 6 -662.034 5.01 7 (aperture) ∞ 1.80 8 47.613 5.77 1.81600 46.6 9 -8.980 0.91 1.90366 31.3 10 -16.902 5.69 11 -18.534 0.92 1.69895 30.1 12 29.517 4.40 1.59282 68.6 13 -35.692 1.10 14* -54.759 2.10 1.53110 55.9 15* -34.782 6.57 16 -161.374 4.59 1.60311 60.6 17 -34.257 12.94 Image plane ∞ Aspherical data Page 14 K = 0.00000e+000 A 4= 4.57136e-005 A 6=-1.97209e-006 A 8= 3.74538e-008 A10=-4.12263e-010 A12= 1.59769e-012 Page 15 K = 0.00000e+000 A 4= 1.03365e-004 A 6=-1.10800e-006 A 8= 1.95771e-008 A10=-1.88559e-010 A12= 6.52817e-013 Various data Focal length 18.20 F-number 2.90 Half-angle 45.00 Image height 18.20 Lens length: 63.45 BF 12.94 Lens group data Group starting plane focal length 1 1 21.96 2 16 71.14

[0043] [Numerical Example 2] Unit: mm Surface data Face number rd nd vd 1 25.173 1.20 1.59522 67.7 2 9.960 4.83 3 22.509 1.00 1.49700 81.5 4 7.529 1.81 5 57.731 1.65 1.91650 31.6 6 -98.374 3.25 7 (aperture) ∞ 1.80 8 64.342 6.53 1.88300 40.8 9 -7.326 0.91 2.00069 25.5 10 -12.387 3.52 11 -19.745 0.92 1.69895 30.1 12 23.747 5.10 1.49700 81.5 13 -27.013 1.44 14* -29.866 2.10 1.53110 55.9 15* -17.802 6.34 16 -62.773 4.14 1.64000 60.1 17 -26.587 10.97 Image plane ∞ Aspherical data Page 14 K = 0.00000e+000 A 4=-2.73841e-005 A 6=-3.88135e-007 A 8= 2.67267e-008 A10=-4.37155e-010 A12= 2.30061e-012 A14=-5.75662e-015 Page 15 K = 0.00000e+000 A 4= 7.95764e-005 A 6=-3.58079e-007 A 8= 2.89945e-008 A10=-3.41257e-010 A12= 1.23584e-012 A14=-2.30241e-016 Focal length 14.28 F-number 2.91 Half-angle 51.88 Image height 18.20 Lens length 57.50 BF 10.97 Lens group data Group starting plane focal length 1 1 16.48 2 16 68.99

[0044] [Numerical Example 3] Unit: mm Surface data Face number rd nd vd 1 27.125 1.10 1.60311 60.6 2 9.735 3.67 3 30.493 1.00 1.48749 70.2 4 10.586 3.21 5 40.191 1.71 1.83400 37.2 6 -392.360 5.43 7 (aperture) ∞ 1.80 8 38.857 6.25 1.83481 42.7 9 -8.128 0.90 1.90366 31.3 10 -16.045 4.69 11 -16.526 0.92 1.68893 31.1 12 19.781 5.80 1.59282 68.6 13 -26.412 0.91 14* -50.009 2.10 1.53110 55.9 15* -32.615 6.74 16 -109.118 4.42 1.62299 58.2 17 -31.658 12.54 Image plane ∞ Aspherical data Page 14 K = 0.00000e+000 A 4= 5.22756e-005 A 6=-1.92650e-006 A 8= 3.51677e-008 A10=-3.71946e-010 A12= 1.36387e-012 Page 15 K = 0.00000e+000 A 4= 1.10438e-004 A 6=-1.14287e-006 A 8= 2.01498e-008 A10=-1.88642e-010 A12= 6.28660e-013 Focal length 16.48 F-number 2.90 Half-angle 47.84 Image height 18.20 Lens length: 63.19 BF 12.54 Lens group data Group starting plane focal length 1 1 19.70 2 16 70.05

[0045] [Numerical Example 4] Unit: mm Surface data Face number rd nd vd 1 23.402 1.20 1.65160 58.5 2 9.036 4.12 3 42.789 0.90 1.49700 81.5 4 13.075 1.50 5 53.278 1.58 1.91082 35.3 6 -3366.466 6.15 7 (aperture) ∞ 1.66 8 30.996 6.92 1.83481 42.7 9 -8.459 0.87 1.90366 31.3 10 -16.835 4.39 11 -17.793 0.93 1.68893 31.1 12 17.113 7.09 1.61800 63.4 13 -24.767 0.50 14* -88.687 2.10 1.53110 55.9 15* -49.891 6.99 16 -37.109 3.65 1.60311 60.6 17 -22.451 13.47 Image plane ∞ Aspherical data Page 14 K = 0.00000e+000 A 4= 3.20994e-005 A 6=-1.17847e-006 A 8= 5.68853e-009 A10=-3.19562e-011 A12= 1.12210e-014 Page 15 K = 0.00000e+000 A 4= 1.04857e-004 A 6=-6.86726e-007 A 8= 1.82918e-009 Focal length 16.48 F-number 2.91 Half-angle 48.31 Image height 18.50 Lens length: 64.04 BF 13.47 Lens group data Group starting plane focal length 1 1 18.71 2 16 86.17

[0046] [Numerical Example 5] Unit: mm Surface data Face number rd nd vd 1 370.091 1.20 1.65160 58.5 2 10.962 11.82 3 23.532 2.35 1.81600 46.6 4 -261.263 1.97 5 (aperture) ∞ 1.80 6 55.000 6.46 1.81600 46.6 7 -9.617 0.91 1.90366 31.3 8 -22.024 4.64 9 -15.178 0.92 1.69895 30.1 10 37.405 3.54 1.59282 68.6 11 -45.470 2.59 12* -18.407 2.10 1.53110 55.9 13* -15.903 6.80 14 111.462 5.73 1.51633 64.1 15 -53.364 11.16 Image plane ∞ Aspherical data Side 12 K = 0.00000e+000 A 4=-4.23116e-005 A 6=-3.29069e-007 A 8= 3.49757e-008 A10=-2.97301e-010 A12= 7.14062e-013 A14=-9.39720e-016 Page 13 K = 0.00000e+000 A 4= 5.00081e-005 A 6=-5.09273e-007 A 8= 3.35843e-008 A10=-2.22271e-010 A12= 2.03270e-013 A14= 1.10164e-015 Focal length 20.10 F-number 2.90 Half-angle 42.16 Image height 18.20 Lens length 63.99 BF 11.16 Lens group data Group starting plane focal length 1 1 24.37 2 14 70.73

[0047] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist. [Table 1]

Claims

1. It consists of a front group and a back group of positive refractive powers, arranged sequentially from the object side to the image side. In the aforementioned front group, the lens positioned closest to the object has a negative refractive power. For focusing, the front group moves in the optical axis direction, while the rear group remains stationary. In the aforementioned rear group, the final lens positioned closest to the image has a positive refractive power. The front group has an aperture, When the radius of curvature of the object side of the final lens is GLR1, the radius of curvature of the image side is GLR2, the distance between the lens closest to the object and the second lens from the object side in the front group is L12, the distance between the second lens from the object side and the third lens from the object side in the front group is L23, the distance along the optical axis from the object-side surface of the lens closest to the object to the aperture when in focus at infinity is PD, and the distance along the optical axis from the object-side surface of the lens closest to the object to the image-side surface of the final lens when in focus at infinity is LD, 0.1<(GLR1+GLR2) / (GLR1-GLR2)<10.0 0.1<L12 / L23<5.0 PD / LD<0.45 An optical system characterized by satisfying the following conditional equation.

2. When the distance from the image-side lens surface to the image plane of the final lens (back focus in air equivalent) is denoted as sk, 0.1<sk / LD<0.5 The optical system according to claim 1, characterized in that it satisfies the following condition.

3. When the focal length of the first sub-lens group located on the object side of the aperture within the front group is f11, and the focal length of the second sub-lens group located on the image side of the aperture within the front group is f12, -5.0<f11 / f12<5.0 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

4. When the distance between the front group and the rear group on the optical axis at infinity focus is denoted as LB, 0.05<LB / LD<0.60 The optical system according to any one of claims 1 to 3, characterized in that it satisfies the following conditional expression.

5. When the focus sensitivity of the front group at infinity is denoted as ESinf, 0.2<ESinf<2.0 The optical system according to any one of claims 1 to 4, characterized in that it satisfies the following conditional expression.

6. When the focal length of the first sub-lens group located on the object side of the aperture within the front group is f11, and the focal length of the entire system is f, -3.0<f11 / f<12.0 The optical system according to any one of claims 1 to 5, characterized in that it satisfies the following conditional expression.

7. The optical system according to any one of claims 1 to 6, characterized in that the first sub-lens group located on the object side of the aperture within the front group includes three lenses.

8. The optical system according to claim 7, characterized in that the first sub-lens group includes a lens having positive refractive power.

9. When the radius of curvature of the image-side surface of the second lens from the object side is G2R2, and the radius of curvature of the object-side surface of the third lens from the object side is G3R1, -8.0<(G2R2+G3R1) / (G2R2-G3R1)<-0.1 The optical system according to any one of claims 1 to 8, characterized in that it satisfies the following conditional expression.

10. When the focal length of the lens closest to the object and having negative refractive power within the front group is fGn1, and the focal length of the first sub-lens group located closer to the object than the aperture within the front group is f11, 0.1<fGn1 / f11<7.0 The optical system according to any one of claims 1 to 9, characterized in that it satisfies the following conditional expression.

11. When νdn is the average Abbe number of the materials of the negative refractive power lenses located on the object side of the aperture within the front group, and νdp is the average Abbe number of the materials of the positive refractive power lenses located on the object side of the aperture within the front group, 0.3<νdn / νdp<4.5 The optical system according to any one of claims 1 to 10, characterized in that it satisfies the following conditional expression.

12. The optical system according to any one of claims 1 to 11, characterized in that the lens positioned closest to the object in the front group is a negative meniscus lens with its convex surface facing the object.

13. Consists of a front group and a rear group of positive refractive powers arranged in order from the object side to the image side, In the aforementioned front group, the lens positioned closest to the object has a negative refractive power. For focusing, the front group moves in the optical axis direction, while the rear group remains stationary. In the aforementioned rear group, the final lens positioned closest to the image has a positive refractive power. The front group has an aperture, When the radius of curvature of the final lens on the object side is GLR1, the radius of curvature of the image side is GLR2, the distance between the lens closest to the object and the second lens from the object side in the front group is L12, the distance between the second lens from the object side and the third lens from the object side in the front group is L23, the focal length of the first sub-lens group located on the object side of the aperture in the front group is f11, the focal length of the second sub-lens group located on the image side of the aperture in the front group is f12, the focal length of the lens closest to the object with negative refractive power in the front group is fGn1, and the focal length of the first sub-lens group located on the object side of the aperture in the front group is f11, 0.1<(GLR1+GLR2) / (GLR1-GLR2)<10.0 0.1<L12 / L23<5.0 -5.0<f11 / f12<5.0 0.1<fGn1 / f11<7.0 An optical system characterized by satisfying the following conditional equation.

14. An imaging device characterized by having an optical system according to any one of claims 1 to 13, and an image sensor that receives an image formed by the optical system.

Images