Optical system and imaging apparatus

Abstract

To prevent bleeding and a variation in optical performance in focusing.SOLUTION: An optical system L0 comprises a first lens group L1, a second lens group L2 having a negative refractive power, a third lens group L3 having a positive refractive power, and a fourth lens group L4. The third lens group includes a plurality of lenses. In focusing, the second lens group and the third lens group move. When the focal length of the second lens group is defined as f2, the focal length of the third lens group as f3, an air gap on an optical axis from a lens surface on the most image side of the second lens group to a lens surface on the most object side of the third lens group while being focused on an infinite object as LB2B3, and the distance on the optical axis from a lens surface on the object side of a lens on the most object side of the optical system to an image surface while being focused on the infinite object as TTL, conditions of -0.37≤f3 / f2<0 and 0<LB2B3 / TTL≤0.24 are satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system suitable for imaging.

Background Art

[0002] When a focus lens group is driven in an optical system, fluctuations in the angle of view, so-called breathing, may occur. Patent Document 1 discloses an optical system that suppresses the occurrence of breathing by adopting a so-called floating focus method in which a plurality of focus lens groups are driven to reduce the amount of movement of each focus lens group.

[0003] In addition, the optical system is also required to have high optical performance with reduced aberrations. Patent Document 2 discloses an optical system that suppresses fluctuations in optical performance (various aberrations) during focusing by moving a negative focus lens group and a positive focus lens group in different directions from each other.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the optical system of Patent Document 1, the imaging magnification at the shortest imaging distance is less than 0.1 times, and the optical performance, particularly the variation in spherical aberration, during zooming is large. On the other hand, in the optical system of Patent Document 2, breathing during focusing is large.

[0006] The present invention provides an optical system capable of suppressing breathing and fluctuations in optical performance during focusing, and an imaging device equipped with the same.

Means for Solving the Problem

[0007] The optical system as one aspect of the present invention is composed of a first lens group, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group, which are arranged in order from the object side to the image side. During focusing, the distance between adjacent lens groups changes. The third lens group includes a plurality of lenses. The second lens group and the third lens group move during focusing. Let the focal length of the second lens group be f2, the focal length of the third lens group be f3, the air interval on the optical axis from the most image-side lens surface of the second lens group to the most object-side lens surface of the third lens group in the state of focusing on an infinite object be LB2B3, and the distance on the optical axis from the object-side lens surface of the most object-side lens of the optical system to the image surface in the state of focusing on an infinite object be TTL. Then, -0.37 ≦ f3 / f2 < 0 0 < LB2B3 / TTL ≦ 0.24 It is characterized by satisfying the following conditions. Note that the imaging device equipped with the above optical system also constitutes another aspect of the present invention.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide an optical system that suppresses bleeding and fluctuations in optical performance during focusing.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIGS. 1, 3, 5, 7, and 9 each show the configuration of the optical systems L0 of Examples 1 to 5 in a state focused on an object at infinity (hereinafter referred to as the infinity focus state). In each figure, the left side is the object side (front side) and the right side is the image side (rear side).

[0011] The optical system L0 of each embodiment has a plurality of lens groups. A lens group is a collection of one or more lenses that move integrally or do not move during zooming (variation) and focusing (focus adjustment). The lens group may include an aperture stop.

[0012] In each figure, Li represents the i-th (i is a natural number) lens group counted from the object side of the optical system L0. Also, on the lens group that moves during focusing, the moving direction of the lens group during focusing from infinity to the closest distance is indicated by an arrow focus.

[0013] SP is the aperture stop, and IP is the image plane. On the image plane IP, the imaging surface of an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is arranged. GB is a glass block such as an optical filter arranged in front of the image plane IP. The glass block GB is composed of a parallel flat plate or a prism having no effective refractive power and is not included in the optical system L0.

[0014] Next, the features common to the optical systems L0 of Examples 1 to 5 will be described. In the optical system L0 of each example, a plurality of lens groups arranged in order from the object side to the image side are composed of a first lens group L1, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4.

[0015] During focusing, at least the second lens group L2 and the third lens group L3 move. Different signs of refractive power are given to the second lens group L2 and the third lens group L3 that move during focusing in this way. Thereby, various aberrations such as field curvature, longitudinal chromatic aberration, and coma aberration that vary during focusing are corrected well, and breathing during focusing (hereinafter referred to as focus breathing) is suppressed.

[0016] Also, the third lens group L3 includes a plurality of lenses. Thereby, the occurrence of various aberrations such as spherical aberration and axial chromatic aberration is suppressed without significantly refracting the light rays incident on the third lens group L3.

[0017] Also, by arranging the fourth lens group L4 on the image side of the third lens group L3, various aberrations such as field curvature and longitudinal chromatic aberration are corrected well.

[0018] Furthermore, the optical system L0 of each example satisfies the conditions of the following formulas (1) and (2). In formulas (1) and (2), let the focal length of the second lens group L2 be f2, the focal length of the third lens group L3 be f3, and the air interval on the optical axis from the most image-side lens surface of the second lens group L2 to the most object-side lens surface of the third lens group L3 in the infinitely focused state be LB2B3. Also, let the distance on the optical axis from the object-side lens surface of the most object-side lens (frontmost lens) of the optical system L0 in the infinitely focused state to the image plane IP (overall optical length) be TTL.

[0019] -0.37 ≦ f3 / f2 < 0 (1) 0 < LB2B3 / TTL ≦ 0.24 (2) The condition of Equation (1) shows an appropriate relationship between the focal length of the second lens group L2 and the focal length of the third lens group L3. When f3 / f2 is below the lower limit value of Equation (1), the refractive power of the second lens group L2 becomes too strong, making it difficult to suppress focus breathing, which is not preferable. When f3 / f2 exceeds the upper limit value of Equation (1), the refractive powers of the second lens group L2 and the third lens group L3 have the same sign, making it difficult to correct various aberrations such as field curvature, longitudinal chromatic aberration, and coma aberration and to suppress focus breathing, which is not preferable.

[0020] The condition of Equation (2) shows an appropriate relationship between the air gap between the second lens group L2 and the third lens group L3 and the overall optical length of the optical system L0. When LB2B3 / TTL exceeds the upper limit value of Equation (2), the air gap between the second lens group L2 and the third lens group L3 becomes too long with respect to the overall optical length, making it difficult to correct various aberrations such as field curvature, longitudinal chromatic aberration, and coma aberration that vary during focusing and to suppress focus breathing, which is not preferable. When LB2B3 / TTL is below the lower limit value of Equation (2), the second lens group L2 and the third lens group L3 interfere with each other, which is not preferable.

[0021] Note that it is more preferable to set the numerical ranges of Equations (1) and (2) as follows.

[0022] -0.35 ≦ f3 / f2 ≦ -0.06 (1a) 0.02 ≦ LB2B3 / TTL ≦ 0.23 (2a) Also, it is even more preferable to set the numerical ranges of Equations (1) and (2) as follows.

[0023] -0.33 ≦ f3 / f2 ≦ -0.10 (1b) 0.03 ≦ LB2B3 / TTL ≦ 0.22 (2b) By satisfying the above configuration and conditions, it is possible to realize an optical system that can suppress focus breathing and fluctuations in optical performance (various aberrations) during focusing.

[0024] Furthermore, the optical system L0 of each embodiment preferably satisfies at least one of the conditions of the following formulas (3) to (11).

[0025] -12.0 ≦ f2 / f ≦ -3.0 (3) 1.50 ≦ |(R21 + R22) / (R21 - R22)| ≦ 10.00 (4) -10.0 ≦ (R31 + R32) / (R31 - R32) ≦ -2.0 (5) -0.50 ≦ f123 / f2 ≦ -0.01 (6) -0.50 ≦ f34 / f2 ≦ -0.05 (7) 0.20 ≦ BF / f ≦ 1.50 (8) 0.40 ≦ Do / TTL ≦ 0.70 (9) 1.50 ≦ |ES3 / ES2| ≦ 20.00 (10) 1.55 ≦ Nd4L ≦ 2.20 (11) In formulas (3) to (11), let f be the focal length of the optical system L0 in the infinity focus state. Let R21 be the radius of curvature of the most object-side lens surface of the second lens group L2, R22 be the radius of curvature of the most image-side lens surface of the second lens group L2, R31 be the radius of curvature of the most object-side lens surface of the third lens group L2, and R32 be the radius of curvature of the most image-side lens surface of the third lens group L3. Also, let f123 be the combined focal length from the most object-side lens (frontmost lens) of the first lens group L1 to the most image-side lens of the third lens group L3 (including the focal length of the air lens between the lens groups), and f34 be the combined focal length from the most object-side lens of the third lens group L3 to the most image-side lens of the fourth lens group L4. Also, let BF be the air-equivalent value (back focus) of the distance on the optical axis from the most image-side lens surface of the optical system L0 to the image plane IP in the infinity focus state, and Do be the distance on the optical axis from the aperture stop SP to the image plane IP in the infinity focus state.

[0026] Also, let the focus sensitivity of the second lens group L2, which is a focus lens group that moves during focusing, be ES2, and the focus sensitivity of the third lens group L3 be ES3. The focus sensitivity is the amount of movement of the image plane IP with respect to the unit movement amount of the focus lens group that moves during focusing. Specifically, when the lateral magnification of the focus lens group is βf and the combined lateral magnification of all the lenses arranged on the image side with respect to the focus lens group is βR, it is defined by the following formula.

[0027] ES=(1-βf 2 )×βR 2 Furthermore, let the refractive index of the convex lens having the lowest refractive index at the d-line among the convex lenses included in the fourth lens group L4 be Nd4L.

[0028] The condition of Equation (3) shows an appropriate relationship between the focal length of the optical system L0 in the infinitely far focused state and the focal length of the second lens group. When f2 / f is below the lower limit value of Equation (3), the refractive power of the second lens group L2 becomes too weak, which is advantageous for suppressing focus breathing, but the movement amount of the second lens group L2 during focusing increases, making it difficult to correct field curvature, so it is not preferable. When f2 / f exceeds the upper limit value of Equation (3), the refractive power of the second lens group L2 becomes too strong, making it difficult to suppress focus breathing, so it is not preferable.

[0029] Equation (4) shows an appropriate shape of the second lens group L2. When the shape factor |(R21 + R22) / (R21 - R22)| is below the lower limit value of Equation (4), the curvature of the other concave surface also becomes strong with respect to the concave surface with a strong curvature in the second lens group L2, and the second lens group L2 deviates from a concentric shape. As a result, it becomes difficult to suppress focus breathing, so it is not preferable. On the other hand, when |(R21 + R22) / (R21 - R22)| exceeds the upper limit value of Equation (4), the meniscus shape of the second lens group L2 becomes too strong, making it difficult to correct various aberrations such as field curvature and coma aberration, so it is not preferable.

[0030] The condition of Equation (5) indicates the appropriate shape of the third lens group L3. When the shape factor (R31 + R32) / (R31 - R32) is lower than the lower limit value of Equation (5), the meniscus shape of the third lens group L3 becomes too strong, making it difficult to correct various aberrations such as field curvature and coma aberration, which is not preferable. When (R31 + R32) / (R31 - R32) exceeds the upper limit value of Equation (5), the meniscus shape of the third lens group L3 becomes too weak, making it difficult to suppress focus breathing, which is not preferable.

[0031] The condition of Equation (6) indicates the appropriate relationship between the combined focal length of the first lens group L1, the second lens group L2, and the third lens group L3 and the focal length of the second lens group L2. When f123 / f2 is lower than the lower limit value of Equation (6), the refractive power of the second lens group L2 becomes too strong, making it difficult to suppress focus breathing, which is not preferable. When f123 / f2 exceeds the upper limit of Equation (6), the combined refractive power of the first to third lens groups L1 to L3 becomes too strong, making it difficult to correct various aberrations such as spherical aberration and axial chromatic aberration, which is not preferable.

[0032] The condition of Equation (7) indicates the appropriate relationship between the combined focal length of the third lens group L3 and the fourth lens group L4 and the focal length of the second lens group L2. When f34 / f2 is lower than the lower limit value of Equation (7), the refractive power of the second lens group L2 becomes too strong, making it difficult to suppress focus breathing, which is not preferable. When f34 / f2 exceeds the upper limit of Equation (7), the combined refractive power of the third and fourth lens groups L3 and L4 becomes too strong, making it difficult to correct various aberrations such as field curvature and magnification chromatic aberration, which is not preferable.

[0033] The condition of Equation (8) shows an appropriate relationship between the back focus of the optical system L0 and the focal length of the optical system L0 in the infinitely focused state. When BF / f is below the lower limit value of Equation (8), it is advantageous in terms of correcting various aberrations such as field curvature and lateral chromatic aberration and miniaturizing the optical system L0. However, the incident angle of the light rays incident on the image sensor disposed on the image plane IP increases, and the light collection efficiency of the image sensor decreases, which is not preferable. When BF / f exceeds the upper limit value of Equation (8), the back focus becomes too long, making it difficult to correct various aberrations such as field curvature and lateral chromatic aberration and miniaturize the optical system L0, which is not preferable.

[0034] The condition of Equation (9) shows an appropriate relationship between the distance from the aperture stop SP to the image plane IP in the infinitely focused state and the overall optical length of the optical system L0. When Do / TTL is below the lower limit value of Equation (9), the aperture stop SP approaches too close to the image sensor disposed on the image plane IP, the incident angle of the light rays incident on the image sensor increases, and the light collection efficiency of the image sensor decreases, which is not preferable. Also, the diameter of the frontmost lens of the optical system L0 increases, making it difficult to miniaturize the optical system L0, which is not preferable. When Do / TTL exceeds the upper limit value of Equation (9), the aperture stop SP moves too close to the object side, the diameter of the aperture stop SP increases, and it becomes difficult to miniaturize the optical system L0, which is not preferable.

[0035] The condition of Equation (10) shows an appropriate relationship between the focus sensitivity of the second lens group L2 and the focus sensitivity of the third lens group L3. When |ES3 / ES2| is below the lower limit value of Equation (10), the focus sensitivity of the third lens group L3 becomes too small, the movement amount of the third lens group L3 during focusing increases, and the optical system L0 becomes larger, which is not preferable. On the other hand, when |ES3 / ES2| exceeds the upper limit value of Equation (10), the focus sensitivity of the second lens group L2 becomes too small, the movement amount of the second lens group L2 during focusing increases, and the optical system L0 becomes larger or it becomes difficult to correct field curvature, which is not preferable.

[0036] The condition of Equation (11) indicates the appropriate refractive index of the convex lens with the lowest refractive index within the fourth lens group L4. When Nd4L is below the lower limit value of Equation (11), the curvature radius of the convex lens for obtaining the necessary refractive power becomes too strong, making it difficult to correct various aberrations such as field curvature and lateral chromatic aberration, which is not preferable. When Nd4L exceeds the upper limit of Equation (11), the curvature radius of the convex lens for obtaining the necessary refractive power becomes too weak, making it difficult to correct various aberrations such as field curvature and lateral chromatic aberration, which is not preferable.

[0037] Note that it is more preferable if the numerical ranges of Equations (3) to (11) are as follows.

[0038] -11.0 ≦ f2 / f ≦ -3.4 (3a) 2.00 ≦ |(R21 + R22) / (R21 - R22)| ≦ 8.00 (4a) -9.80 ≦ (R31 + R32) / (R31 - R32) ≦ -2.50 (5a) -0.32 ≦ f123 / f2 ≦ -0.04 (6a) -0.40 ≦ f34 / f2 ≦ -0.12 (7a) 0.25 ≦ BF / f ≦ 1.30 (8a) 0.50 ≦ Do / TTL ≦ 0.67 (9a) 2.00 ≦ |ES3 / ES2| ≦ 18.50 (10a) 1.70 ≦ Nd4L ≦ 2.10 (11a) Also, it is even more preferable if the numerical ranges of Equations (3) to (11) are as follows.

[0039] -10.0 ≦ f2 / f ≦ -3.5 (3b) 2.10 ≦ |(R21 + R22) / (R21 - R22)| ≦ 7.00 (4b) -9.60 ≦ (R31 + R32) / (R31 - R32) ≦ -2.80 (5b) -0.28 ≦ f123 / f2 ≦ -0.06 (6b) -0.38 ≦ f34 / f2 ≦ -0.14 (7b) 0.30 ≦ BF / f ≦ 1.20 (8b) 0.55 ≦ Do / TTL ≦ 0.66 (9b) 2.20 ≦ |ES3 / ES2| ≦ 17.50 (10b) 1.75 ≦ Nd4L ≦ 2.05 (11b) Furthermore, the optical system L0 of each embodiment preferably has at least one of the following configurations.

[0040] The third lens group L3 preferably includes, on the object side, a cemented lens of a positive meniscus lens with a concave surface facing the object side and a negative lens. This can correct various aberrations such as spherical aberration and axial chromatic aberration, and suppress aberration variations during focusing.

[0041] The second lens group L2 preferably has a negative lens on the object side. This allows a negative lens to be placed near the first lens group where the on-axis light beam is relatively high, and can correct various aberrations such as spherical aberration and axial chromatic aberration well.

[0042] The third lens group L3 preferably includes a plurality of convex lenses. This can increase the refractive power of the third lens group L3, so that the curvature of the convex lens does not become too strong, and the occurrence of various aberrations such as spherical aberration and axial chromatic aberration can be suppressed.

[0043] The fourth lens group L4 preferably includes a plurality of lenses. This can prevent the curvature of the lenses in the fourth lens group L4 from becoming too strong, and suppress the occurrence of various aberrations such as field curvature and lateral chromatic aberration. Moreover, by arranging lenses with different refractive powers, various aberrations such as field curvature and lateral chromatic aberration can be corrected well.

[0044] The first lens group L1 preferably has a plurality of concave lenses. This can prevent the curvature of the concave lenses in the first lens group L1 from becoming too strong, and can correct or suppress various aberrations such as field curvature and lateral chromatic aberration well.

[0045] Next, the optical system L0 of each embodiment will be specifically described.

[0046] The optical system L0 of Example 1 shown in FIG. 1 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with negative refractive power, which are arranged in order from the object side to the image side. An aperture stop SP is arranged between the second lens group L2 and the third lens group L3. When focusing from infinity to the nearest distance, the second lens group L2 moves toward the image side and the third lens group L3 moves toward the object side.

[0047] The optical system L0 of Example 2 shown in FIG. 3 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with negative refractive power, which are arranged in order from the object side to the image side. An aperture stop SP is arranged between the first lens group L1 and the second lens group L2. When focusing from infinity to the nearest distance, both the second lens group L2 and the third lens group L3 move toward the object side.

[0048] The optical system L0 of Example 3 shown in FIG. 5 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with negative refractive power, which are arranged in order from the object side to the image side. An aperture stop SP is arranged between the second lens group L2 and the third lens group L3. When focusing from infinity to the nearest distance, both the second lens group L2 and the third lens group L3 move toward the object side.

[0049] The optical system L0 of Example 4 shown in FIG. 7 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with negative refractive power, which are arranged in order from the object side to the image side. An aperture stop SP is arranged between the second lens group L2 and the third lens group L3. When focusing from infinity to the nearest distance, the second lens group L2 moves toward the image side and the third lens group L3 moves toward the object side.

[0050] The optical system L0 of Example 5 shown in Fig. 9 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with positive refractive power, which are arranged in order from the object side to the image side. An aperture stop SP is arranged between the second lens group L2 and the third lens group L3. When focusing from infinity to the nearest point, the second lens group L2 moves toward the image side and the third lens group L3 moves toward the object side, respectively.

[0051] The following shows numerical examples 1 to 5 corresponding to Examples 1 to 5 respectively. In the surface data of each numerical example, the surface number m indicates the order of the surface (lens surface or aperture surface) when counted from the object side. r (mm) represents the radius of curvature of the m-th surface, and d (mm) represents the distance on the optical axis between the m-th surface and the (m + 1)-th surface. Also, nd represents the refractive index of the optical material between the m-th surface and the (m + 1)-th surface at the d-line, and νd represents the Abbe number of the optical material between the m-th surface and the (m + 1)-th surface with respect to the d-line. The Abbe number νd with respect to the d-line is defined as follows when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, νd=(Nd - 1) / (NF - NC) and is represented by.

[0052] In addition, in each numerical example, d, focal length (mm), F-number, and half field angle (°) are all values when the optical system of each numerical example is in an infinitely focused state. The back focus (BF) is the distance on the optical axis from the most image-side lens surface (the final surface) of the optical system to the paraxial image plane, expressed in air-equivalent length. The overall length of the lens is the length obtained by adding the back focus to the distance on the optical axis from the most object-side lens surface (the front surface) of the optical system to the final surface, which corresponds to the overall optical length. The object distance (mm) in the state of focusing on a finite-distance object in each numerical example represents the distance on the optical axis from the object to the image plane IP.

[0053] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is defined by the formula where 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, A12 are the aspherical coefficients of each order.

[0054]

Number

[0055] It is represented by the following formula. "e±Z" in each aspherical coefficient means "×10 ±Z ".

[0056] Also, the values related to the conditions of the above-mentioned formulas (1) to (11) in Numerical Examples 1 to 5 are summarized in Tables 1 and 2. The optical systems L0 in Numerical Examples 1 to 5 satisfy all the conditions of formulas (1) to (11). [Numerical Example 1] Unit: mm Surface Data Surface Number r d nd νd 1 53.181 1.30 1.69349 50.8 2 23.707 11.39 3 -44.340 1.21 1.49700 81.5 4 38.487 7.34 5 48.142 10.53 1.76385 48.5 6 -28.586 1.30 1.85478 24.8 7 -70.693 0.19 8 52.079 3.71 2.00069 25.5 9 7495.352 (Variable) 10 52.308 1.29 1.77047 29.7 11 34.606 (Variable) 12 (Aperture) ∞ (Variable) 13 -24.759 5.63 1.49700 81.5 14 -15.000 1.00 1.77047 29.7 15 -175.025 0.59 16 63.764 7.59 1.49700 81.5 17 -27.632 1.10 18* 67.630 7.39 1.80400 46.5 19* -47.978 (variable) 20 181.048 7.22 1.95375 32.3 21 -34.114 1.25 1.77047 29.7 22 54.736 4.74 23 -71.318 1.19 1.65412 39.7 24 138.028 2.75 1.92286 20.9 25 -500.035 15.20 26 ∞ 1.00 1.51633 64.1 27 ∞ 1.00 Image plane ∞ Aspherical data The 18th surface K = 0.00000e+00 A 4=-5.65304e-06 A 6= 5.53536e-09 A 8=-3.00386e-11 A10= 9.16452e-14 A12=-2.01097e-16 The 19th surface K = 0.00000e+00 A 4= 6.31684e-06 A 6= 4.51680e-09 A 8=-2.25389e-11 A10= 9.25935e-14 A12=-1.87097e-16 Various data Zoom ratio 1.00 Focal length 24.72 F-number 1.44 Half field angle (°) 37.03 Image height 18.64 Overall length of the lens 117.81 BF 17.20 Object distance Infinity - 240 d9 1.30 4.19 d11 9.12 6.23 d12 9.81 6.91 d19 2.00 4.90 Lens group data Group Starting surface Focal length 1 1 38.12 2 10 - 137.06 3 13 31.69 4 20 - 118.82 [Numerical example 2] Unit: mm Surface data Surface number r d nd νd 1 84.764 1.30 1.60311 60.6 2 27.757 11.00 3 - 35.589 1.21 1.49700 81.5 4 46.961 3.50 5 54.948 10.94 1.76385 48.5 6 - 27.209 1.30 1.85478 24.8 7 - 234.377 0.20 8 209.866 4.51 2.00069 25.5 9 - 96.169 0.20 10 295.467 3.76 1.76385 48.5 11 - 123.342 10.04 12 (Aperture) ∞ (Variable) 13 - 31.294 2.00 1.67300 38.3 14 43.809 6.79 1.89190 37.1 15 - 76.299 (Variable) 16 - 42.414 6.23 1.43875 94.7 17 - 21.158 1.00 1.77047 29.7 18 -35.162 0.20 19 35.666 9.77 1.43875 94.7 20 -52.978 0.20 21* 195.038 4.44 1.80400 46.5 22* -84.967 (Variable) 23 56.435 5.11 1.91082 35.3 24 -165.698 1.25 1.77047 29.7 25 28.523 8.85 26 -38.320 1.20 1.65160 58.5 27 -57.201 11.54 28 ∞ 1.00 1.51633 64.1 29 ∞ 1.00 Image plane ∞ Aspherical data Surface 21 K = 0.00000e+00 A 4=-9.08036e-06 A 6= 2.48605e-09 A 8= 4.53982e-12 A10= 1.97345e-13 A12=-2.97642e-16 Surface 22 K = 0.00000e+00 A 4=-5.91166e-07 A 6= 5.59824e-09 A 8= 4.96338e-12 A10= 1.93055e-13 A12=-2.48779e-16 Various data Zoom ratio 1.00 Focal length 27.62 F-number 1.24 Half field angle (°) 34.33 Image height 18.86 Overall lens length 124.66 BF 13.54 Object distance Infinity - 300 d12 10.03 5.48 d15 5.00 6.81 d22 1.45 4.18 Lens group data Group start surface Focal length 1 1 78.63 2 13 -270.00 3 16 32.51 4 23 -70.97 [Numerical example 3] Unit: mm Surface data Surface number r d nd νd 1 68.591 1.30 1.85150 40.8 2 23.921 8.81 3 216.106 1.22 1.49700 81.5 4 23.000 8.95 1.88300 40.8 5 224.462 0.19 6 34.721 1.99 2.00100 29.1 7 44.344 0.19 8 44.356 1.99 1.49700 81.5 9 25.687 (Variable) 10 21.924 1.29 1.49700 81.5 11 15.850 (Variable) 12 (Aperture) ∞ (Variable) 13 -55.083 8.57 1.49700 81.5 14 -15.165 1.16 1.85478 24.8 15 -28.994 7.49 16 55.800 11.13 1.49700 81.5 17 -30.538 2.01 18* 181.350 5.25 1.80400 46.5 19* -68.044 (Variable) 20 123.519 10.33 1.80400 46.5 21 -26.172 1.20 1.61340 44.3 22 23.632 23.58 23 ∞ 1.00 1.51633 64.1 24 ∞ 1.00 Image plane ∞ Aspherical data Surface 18 K = 0.00000e+00 A 4=-4.84049e-06 A 6= 6.66659e-09 A 8=-9.57538e-11 A10= 3.49919e-13 A12=-7.42226e-16 Surface 19 K = 0.00000e+00 A 4= 6.01015e-06 A 6= 5.60753e-09 A 8=-4.96845e-11 A10= 1.97676e-13 A12=-4.44356e-16 Various data Zoom ratio 1.00 Focal length 24.34 F-number 1.80 Half field angle (°) 37.81 Image height 18.89 Overall lens length 120.16 BF 25.58 Object distance Infinity - 240 d 9 8.59 1.99 d11 7.10 13.71 d12 3.74 1.44 d19 2.41 4.71 Lens group data Group Starting surface Focal length 1 1 -181.58 2 10 -123.85 3 13 25.42 4 20 -89.22 [Numerical Example 4] Unit: mm Surface data Surface number r d nd νd 1 -77.699 1.10 1.72047 34.7 2 65.828 6.03 3 717.957 1.50 1.77047 29.7 4 33.249 13.60 1.76385 48.5 5 -117.421 0.21 6 54.033 7.93 2.00069 25.5 7 -320.908 (Variable) 8 99.154 1.30 1.65412 39.7 9 58.728 (Variable) 10 (Aperture) ∞ (Variable) 11 -28.460 5.37 1.49700 81.5 12 -21.800 1.00 1.85478 24.8 13 -125.854 0.10 14 53.605 8.84 1.49700 81.5 15 -43.060 3.29 16* 131.304 6.95 1.80400 46.5 17* -47.702 (Variable) 18 68.927 8.62 1.83481 42.7 19 -36.506 1.25 1.74951 35.3 20 30.422 7.72 21 -46.017 1.20 1.61340 44.3 22 38.811 5.73 1.92286 20.9 23 -5026.441 13.98 24 ∞ 1.00 1.51633 64.1 25 ∞ 1.00 Image plane ∞ Aspherical data Page 16 K = 0.00000e+00 A 4=-5.58992e-06 A 6=-5.81792e-10 A 8= 2.77849e-12 A10=-3.56043e-15 A12= 8.74910e-17 Page 17 K = 0.00000e+00 A 4= 2.98915e-06 A 6=-2.19539e-09 A 8= 1.86567e-11 A10=-5.02691e-14 A12= 1.50963e-16 Various data Zoom ratio 1.00 Focal length 48.61 F number 1.44 Half angle of view (°) 23.99 Image height 21.64 Overall lens length 129.72 BF 15.98 Object distance Infinity - 400 d 7 3.37 11.15 d 9 14.26 6.48 d10 12.72 8.46 d17 2.01 6.27 Lens group data Group Starting surface Focal length 1 1 58.89 2 8 -223.05 3 11 42.47 4 18 -73.00 [Numerical example 5] Unit mm Surface data Surface number r d nd νd 1 92.543 1.30 1.48749 70.2 2 28.922 10.96 3 -36.379 1.22 1.51742 52.4 4 50.223 3.55 5 61.042 13.56 1.76385 48.5 6 -27.661 1.30 1.85478 24.8 7 -54.624 0.19 8 52.026 5.07 2.00069 25.5 9 -946.627 (variable) 10 95.124 1.50 1.77047 29.7 11 47.562 (variable) 12 (aperture) ∞ (variable) 13 -28.511 5.23 1.49700 81.5 14 -17.984 1.00 1.77047 29.7 15 -246.706 2.42 16 66.332 7.83 1.49700 81.5 17 -31.411 0.19 18* 171.715 5.50 1.85400 40.4 19* -50.789 (variable) 20 93.764 9.02 1.78800 47.4 21 -29.378 1.25 1.77047 29.7 22 36.043 8.36 23 -33.721 1.19 1.61340 44.3 24 60.722 9.69 2.00069 25.5 25 -47.682 13.50 26 ∞ 1.00 1.51633 64.1 27 ∞ 1.00 Image plane ∞ Aspherical data The 18th surface K = 0.00000e+00 A 4=-4.97076e-06 A 6= 3.30627e-09 A 8= 2.12404e-11 A10 = -4.09579e-15 A12 = 8.64092e-17 Page 19 K = 0.00000e+00 A4 = 3.12399e-06 A6 = 4.44051e-09 A8 = 1.96810e-11 A10 = 3.19130e-15 A12 = 1.15698e-16 Various data Zoom ratio 1.00 Focal length 34.00 F-number 1.44 Half field angle (°) 30.34 Image height 19.90 Overall lens length 129.94 BF 15.50 Object distance Infinity - 280 d9 2.25 6.43 d11 11.29 7.11 d12 8.92 4.67 d19 2.00 6.25 Lens group data Group Starting surface Focal length 1 1 39.71 2 10 -125.18 3 13 38.73 4 20 800.02

[0057]

Table 1

[0058]

Table 2

[0059] Figures 2(A), 4(A), 6(A), 8(A) and 10(A) are the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L0 in the infinity focus state for numerical examples 1 to 5, respectively.

[0060] Figures 2(B), 4(B), 6(B), 8(B), and 10(B) each show the longitudinal aberration in the state of focusing on the nearest object (nearest focusing state) of the optical systems L0 of Numerical Examples 1 to 5.

[0061] The nearest object is an object that is 240 mm away from the image plane IP on the optical axis in Figure 2(B), an object that is 300 mm away from the image plane IP on the optical axis in Figure 4(B), and an object that is 240 mm away from the image plane IP on the optical axis in Figure 6(B). Also, in Figure 8(B), it is an object that is 400 mm away from the image plane IP on the optical axis, and in Figure 10(B), it is an object that is 280 mm away from the image plane IP on the optical axis.

[0062] In the spherical aberration diagram, the solid line indicates the spherical aberration with respect to the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration with respect to the g-line (wavelength 435.8 nm). In the astigmatism diagram, the dashed line M indicates the astigmatism in the meridional image plane, and the solid line S indicates the astigmatism in the sagittal image plane. The distortion aberration diagram shows the amount of distortion aberration with respect to the d-line. The chromatic aberration diagram shows the longitudinal chromatic aberration with respect to the g-line. ω represents the half field angle (°), and Fno represents the F-number.

[0063] [Imaging device] Figure 11 shows a digital still camera (imaging device) 10 that uses the optical systems L0 of Examples 1 to 5 as an imaging optical system. In Figure 11, 13 is the camera body, and 11 is the imaging optical system as one of the optical systems L0 of Examples 1 to 5. 12 is an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body 13 and photoelectrically converts the optical image formed by the imaging optical system 11 (i.e., captures the subject).

[0064] The camera body 13 may be a single-lens reflex camera having a quick-return mirror or a mirrorless camera without a quick-return mirror. Also, the camera body 13 may be a lens-exchangeable camera in which the imaging optical system 11 is detachable, or a lens-integrated camera that integrally has the imaging optical system 11.

[0065] By using the optical system L0 of each embodiment as an imaging optical system 11 in an imaging device such as a digital still camera, it is possible to suppress deterioration of the imaging image quality associated with focus blurring and focusing.

[0066] The above embodiments include the following configurations.

[0067] (Configuration 1) An optical system composed of a first lens group, a second lens group with a negative refractive power, a third lens group with a positive refractive power, and a fourth lens group, which are arranged in order from the object side to the image side, and in which the distance between adjacent lens groups changes during focusing. The third lens group includes a plurality of lenses. The second lens group and the third lens group move during focusing. When the focal length of the second lens group is f2, the focal length of the third lens group is f3, the air interval on the optical axis from the most image-side lens surface of the second lens group to the most object-side lens surface of the third lens group in a state of focusing on an infinite object is LB2B3, and the distance on the optical axis from the object-side lens surface of the most object-side lens of the optical system to the image surface in a state of focusing on an infinite object is TTL. -0.37 ≦ f3 / f2 < 0 0 < LB2B3 / TTL ≦ 0.24 An optical system characterized by satisfying the following conditions. (Configuration 2) When the focal length of the optical system in a state of focusing on an infinite object is f. -12.0 ≦ f2 / f ≦ -3.0 The optical system according to Configuration 1, characterized by satisfying the following conditions. (Configuration 3) When the radius of curvature of the most object-side lens surface of the second lens group is R21 and the radius of curvature of the most image-side lens surface of the second lens group is R22. 1.50 ≦ |(R21 + R22) / (R21 - R22)| ≦ 10.00 The optical system according to Configuration 1 or 2, characterized by satisfying the following conditions. (Configuration 4) When the radius of curvature of the lens surface on the object side of the third lens group is R31 and the radius of curvature of the lens surface on the image side of the third lens group is R32, -10.0 ≦ (R31 + R32) / (R31 - R32) ≦ -2.0 The optical system according to any one of Configurations 1 to 3, characterized by satisfying the following condition. (Configuration 5) When the combined focal length from the lens on the object side of the first lens group to the lens on the image side of the third lens group is f123, -0.50 ≦ f123 / f2 ≦ -0.01 The optical system according to any one of Configurations 1 to 4, characterized by satisfying the following condition. (Configuration 6) When the combined focal length from the lens on the object side of the third lens group to the lens on the image side of the fourth lens group is f34, -0.50 ≦ f34 / f2 ≦ -0.05 The optical system according to any one of Configurations 1 to 5, characterized by satisfying the following condition. (Configuration 7) When the air-converted value of the distance on the optical axis from the lens surface on the image side of the optical system to the image plane in the state of focusing on an infinite object is BF and the focal length of the optical system in the state of focusing on an infinite object is f, 0.20 ≦ BF / f ≦ 1.50 The optical system according to any one of Configurations 1 to 6, characterized by satisfying the following condition. (Configuration 8) The optical system has a diaphragm, When the distance from the diaphragm to the image plane in the state of focusing on an infinite object is Do and the distance on the optical axis from the lens surface on the object side of the most object-side lens of the optical system to the image plane in the state of focusing on an infinite object is TTL, 0.40 ≦ Do / TTL ≦ 0.70 The optical system according to any one of Configurations 1 to 7, characterized by satisfying the following condition. (Configuration 9) The amount of movement of the image plane with respect to the unit movement amount of each of the second lens group and the third lens group is defined as the focus sensitivity. When the focus sensitivity of the second lens group is ES2 and the focus sensitivity of the third lens group is ES3, 1.50 ≦ |ES3 / ES2| ≦ 20.00 The optical system according to any one of Configurations 1 to 8, characterized by satisfying the condition. (Configuration 10) The fourth lens group includes at least one convex lens, When the refractive index of the convex lens having the lowest refractive index among the at least one convex lens at d-line is Nd4L, 1.55 ≦ Nd4L ≦ 2.20 The optical system according to any one of Configurations 1 to 9, characterized by satisfying the condition. (Configuration 11) The third lens group includes, on the object side, a cemented lens of a positive meniscus lens having a concave surface facing the object side and a negative lens, and the optical system according to any one of Configurations 1 to 10. (Configuration 12) The second lens group has a negative lens on the object side, and the optical system according to any one of Configurations 1 to 11. (Configuration 13) The third lens group includes a plurality of convex lenses, and the optical system according to any one of Configurations 1 to 12. (Configuration 14) The fourth lens group includes a plurality of lenses, and the optical system according to any one of Configurations 1 to 13. (Configuration 15) The first lens group includes a plurality of concave lenses, and the optical system according to any one of Configurations 1 to 14. (Configuration 16) The first lens group has a positive refractive power, The fourth lens group has a negative refractive power, and the optical system according to any one of Configurations 1 to 15. (Configuration 17) The first lens group has a positive refractive power, The fourth lens group has a positive refractive power, and the optical system according to any one of Configurations 1 to 15. (Configuration 18) The first lens group has a negative refractive power, The fourth lens group has a negative refractive power, and the optical system according to any one of Configurations 1 to 15. (Configuration 19) An imaging device, comprising: the optical system according to any one of Configurations 1 to 18; and an imaging element that images a subject through the optical system.

[0068] Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to each embodiment when implementing the present invention.

Description of Reference Numerals

[0069] L0 Optical system L1 First lens group L2 Second lens group L3 Third lens group L4 Fourth lens group SP Aperture stop IP Image plane

Claims

1. An optical system composed of a first lens group, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group, arranged in order from the object side to the image side, and in which the distance between adjacent lens groups changes during focusing, wherein the third lens group includes a plurality of lenses, the second lens group and the third lens group move during focusing, when the focal length of the second lens group is f2, the focal length of the third lens group is f3, the air space on the optical axis from the most image-side lens surface of the second lens group to the most object-side lens surface of the third lens group in the state of focusing on an infinite object is LB2B3, and the distance on the optical axis from the object-side lens surface of the most object-side lens of the optical system to the image surface in the state of focusing on an infinite object is TTL, -0.37 ≤ f3 / f2 < 0 0 < LB2B3 / TTL ≤ 0.24 An optical system characterized by satisfying the following conditions.

2. When the focal length of the optical system in the state of focusing on an infinite object is f, -12.0 ≤ f2 / f ≤ -3.0 The optical system according to claim 1, characterized by satisfying the following conditions.

3. When the radius of curvature of the most object-side lens surface of the second lens group is R21 and the radius of curvature of the most image-side lens surface of the second lens group is R22, 1.50 ≤ |(R21 + R22) / (R21 - R22)| ≤ 10.00 The optical system according to claim 1, characterized by satisfying the following conditions.

4. When the radius of curvature of the most object-side lens surface of the third lens group is R31 and the radius of curvature of the most image-side lens surface of the third lens group is R32, -10.0 ≤ (R31 + R32) / (R31 - R32) ≤ -2.0 The optical system according to claim 1, characterized by satisfying the following conditions.

5. When the combined focal length from the most object-side lens of the first lens group to the most image-side lens of the third lens group is f123, -0.50 ≤ f123 / f2 ≤ -0.01 The optical system according to claim 1, characterized by satisfying the following conditions.

6. When the combined focal length from the most object-side lens of the third lens group to the most image-side lens of the fourth lens group is f34, -0.50 ≤ f34 / f2 ≤ -0.05 The optical system according to claim 1, characterized by satisfying the following conditions.

7. When the air-equivalent value of the distance on the optical axis from the most image-side lens surface of the optical system to the image plane in the state of focusing on an infinitely distant object is BF and the focal length of the optical system in the state of focusing on an infinitely distant object is f, 0.20 ≤ BF / f ≤ 1.50 The optical system according to claim 1, characterized in that the condition is satisfied.

8. The optical system has a diaphragm, When the distance from the diaphragm to the image plane in the state of focusing on an infinitely distant object is Do and the distance on the optical axis from the object-side lens surface of the most object-side lens of the optical system to the image plane in the state of focusing on an infinitely distant object is TTL, 0.40 ≤ Do / TTL ≤ 0.70 The optical system according to claim 1, characterized in that the condition is satisfied.

9. Regarding the movement amount of the image plane with respect to the single movement amount of each of the second lens group and the third lens group as the focus sensitivity, when the focus sensitivity of the second lens group is ES2 and the focus sensitivity of the third lens group is ES3, 1.50 ≤ |ES3 / ES2| ≤ 20.00 The optical system according to claim 1, characterized in that the condition is satisfied.

10. The fourth lens group includes at least one convex lens, When the refractive index of the convex lens having the lowest refractive index among the at least one convex lens at the d line is Nd4L, 1.55 ≤ Nd4L ≤ 2.20 The optical system according to claim 1, characterized in that the condition is satisfied.

11. The optical system according to claim 1, characterized in that the third lens group includes, on the most object side, a cemented lens of a positive meniscus lens with a concave surface facing the object side and a negative lens.

12. The optical system according to claim 1, characterized in that the second lens group has a negative lens on the most object side.

13. The optical system according to claim 1, characterized in that the third lens group includes a plurality of convex lenses.

14. The optical system according to claim 1, characterized in that the fourth lens group includes a plurality of lenses.

15. The optical system according to claim 1, characterized in that the first lens group includes a plurality of concave lenses.

16. The first lens group has a positive refractive power, The optical system according to claim 1, characterized in that the fourth lens group has a negative refractive power.

17. The first lens group has a positive refractive power, The optical system according to claim 1, characterized in that the fourth lens group has a positive refractive power.

18. The first lens group has a negative refractive power, The optical system according to claim 1, wherein the fourth lens group has a negative refractive power.

19. An imaging device comprising: the optical system according to any one of claims 1 to 18; and an image sensor that images a subject through the optical system.

Images