Optical system and image pickup apparatus including the same

Abstract

To obtain an optical system having high optical performance by satisfactorily correcting various aberrations including chromatic aberration of magnification in spite of a wide angle and a large aperture ratio.SOLUTION: The optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit, a third lens unit having a positive refractive power, and a fourth lens unit having a negative refractive power, and an interval between adjacent lens units changes during focusing and satisfies a predetermined condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device having the same, which is suitable for use in electronic cameras such as video cameras and digital still cameras, film cameras, broadcast cameras, and the like. [Background technology]

[0002] Imaging optical systems used in imaging devices using image sensors are required to have not only high image quality (high resolution) but also good image blur. Large aperture imaging optical systems are known as imaging optical systems that satisfy these requirements. Since large aperture imaging optical systems have a shallow depth of field, it is necessary to effectively correct various aberrations, including chromatic aberration, in order to achieve high image quality and beautiful image blur.

[0003] BACKGROUND ART Conventionally, various imaging optical systems with a large aperture ratio that are designed to effectively correct various aberrations including chromatic aberration have been proposed (Patent Document 1).

[0004] Patent Document 1 discloses an optical system that is composed of a first lens group with positive refractive power and a second lens group with positive refractive power, arranged in that order from the object side to the image side, in which the first lens group moves during focusing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-74631 Summary of the Invention [Problem to be solved by the invention]

[0006] In optical systems with large aperture ratios, the depth of field is shallow, which increases the impact that aberrations such as axial chromatic aberration, lateral chromatic aberration, spherical aberration, coma, and astigmatism have on image quality.In order to effectively correct aberrations such as spherical aberration, coma, and astigmatism while achieving overall compactness in optical systems with large aperture ratios, it is effective to use a multi-group focus group (floating focus) and to use a low-dispersion material for the positive lens element on the image side of the aperture stop.

[0007] In Patent Document 1, the second lens group uses a material with a relatively high refractive index and low dispersion, but a small partial dispersion ratio, which makes it difficult to correct chromatic aberration of magnification when the angle of view is widened. Also, the weight of the focus lens group is not sufficiently reduced. [Means for solving the problem]

[0008] An optical system according to one aspect of the present invention comprises, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, in which the spacing between adjacent lens groups changes during focusing, and the fourth lens group has at least one positive lens.

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

[0010] According to the above-mentioned means, various aberrations including chromatic aberration of magnification can be well corrected even with a wide angle and a large aperture ratio, and high optical performance can be easily obtained. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of the lens when the optical system of Example 1 is focused on an object at infinity. [Figure 2] Longitudinal aberration diagram when the optical system of Example 1 is focused on an object at infinity [Figure 3] Longitudinal aberration diagram when the optical system of Example 1 is focused on a close-up object (0.28 m) [Figure 4] 10 is a cross-sectional view of the lens when the optical system of Example 2 is focused on an object at infinity. [Figure 5] Longitudinal aberration diagram when the optical system of Example 2 is focused on an object at infinity [Figure 6] Longitudinal aberration diagram when focusing on a close-up object (0.28 m) in the optical system of Example 2 [Figure 7] 10 is a cross-sectional view of the lens when the optical system of Example 3 is focused on an object at infinity. [Figure 8] Longitudinal aberration diagram when the optical system of Example 3 is focused on an object at infinity [Figure 9] Longitudinal aberration diagram when focusing on a close-up object (0.28 m) in the optical system of Example 3 [Figure 10] 10 is a cross-sectional view of the lens when the optical system of Example 4 is focused on an object at infinity. [Figure 11] Longitudinal aberration diagram when the optical system of Example 4 is focused on an object at infinity [Figure 12] Longitudinal aberration diagram when focusing on a close-up object (0.28 m) in the optical system of Example 4 [Figure 13] 1 is a schematic diagram of a main part of a camera (image capture device) equipped with the optical system of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] Fig. 1 is a lens cross-sectional view of the optical system of Example 1 when focused on an object at infinity, and Fig. 2 is a longitudinal aberration diagram of the optical system of Example 1 when focused on an object at infinity.

[0014] Fig. 3 is a longitudinal aberration diagram when the optical system of Example 1 is focused on a close object (0.28 m), and Fig. 4 is a lens cross-sectional view when the optical system of Example 2 is focused on an object at infinity.

[0015] Fig. 5 is a longitudinal aberration diagram when the optical system of Example 2 is focused on an object at infinity. Fig. 6 is a longitudinal aberration diagram when the optical system of Example 2 is focused on an object at a close distance (0.28 m). Fig. 7 is a lens cross-sectional view when the optical system of Example 3 is focused on an object at infinity. Fig. 8 is a longitudinal aberration diagram when the optical system of Example 3 is focused on an object at infinity.

[0016] Fig. 9 is a longitudinal aberration diagram when the optical system of Example 3 is focused on a close object (0.28 m). Fig. 10 is a lens cross-sectional view when the optical system of Example 4 is focused on an object at infinity. Fig. 11 is a longitudinal aberration diagram when the optical system of Example 4 is focused on an object at infinity. Fig. 12 is a longitudinal aberration diagram when the optical system of Example 4 is focused on a close object (0.28 m).

[0017] FIG. 13 is a schematic diagram of the main parts of a camera (image pickup device) equipped with the optical system of this embodiment.

[0018] The optical system of each embodiment is a photographic lens system used in image pickup devices such as video cameras, digital cameras, and silver halide film cameras.

[0019] In the lens cross-sectional view, the left is the object side (front) and the right is the image side (rear). In the lens cross-sectional view, i indicates the order of the lens groups from the object side, and Li is the ith lens group. SP denotes an aperture stop, which is arranged on the image side of the first lens unit L1.

[0020] IP is the image plane, and when used as the imaging optical system of a video camera or digital still camera, it is placed on the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor, and in the case of a silver halide film camera, it is placed on the photosensitive surface equivalent to the film surface. In the aberration diagram, d and g represent the d-line and g-line, respectively. ΔM and ΔS represent the meridional and sagittal image planes, and lateral chromatic aberration is represented by the g-line.

[0021] ω is the half angle of view, and Fno is the F-number.

[0022] In Examples 1 to 4 of FIGS. 1, 4, 7, and 10, focusing is performed by moving the second lens group L2 and the third lens group L3 in the optical axis direction.

[0023] The arrows indicate the movement locus of each lens group during focusing from an object at infinity to a close object. Note that focusing may be performed by moving the entire optical system or any one of the lens groups.

[0024] Next, features of each embodiment other than those described above will be described.

[0025] In optical systems with large aperture ratios, the depth of field is shallow, which increases the impact of various aberrations on image quality, such as axial chromatic aberration, lateral chromatic aberration, spherical aberration, coma, and astigmatism. In optical systems with large aperture ratios, it is important to achieve good optical performance over the entire object distance while miniaturizing the entire lens system.

[0026] To solve this problem, it is important to properly set the refractive power and lens configuration of each lens group, as well as the movement conditions of each lens group during focusing. Without proper configuration, it becomes difficult to obtain an optical system that has high optical performance over the entire object distance while maintaining a large aperture ratio. Correcting lateral chromatic aberration becomes particularly difficult as the focal length becomes shorter.

[0027] In order to effectively correct various aberrations, such as chromatic aberration, spherical aberration, coma, and astigmatism, while also achieving a compact overall size, it is effective to use a multi-group focus group (floating focus) and to use a crystalline material for the positive lens element on the image side of the aperture stop.

[0028] The optical system according to the first embodiment will be described.

[0029] The optical system according to the first embodiment is composed of a first lens group L1 with a positive refractive power, a second lens group L2, a third lens group L3 with a positive refractive power, and a fourth lens group L4 with a negative refractive power, arranged in this order from the object side to the image side. The spacing between adjacent lens groups changes during focusing, and the following conditions are set:

[0030] When the focal length of the entire optical system is f and the focal length of the second lens unit L2 is f2, -0.40 <f / f2<0.15 ···(1) The present invention is characterized in that the following conditional expressions are satisfied:

[0031] Conditional formula (1) defines the focal length of the second lens unit L2.

[0032] If the upper limit of conditional expression (1) is exceeded and the refractive power of the second lens group becomes positive, it becomes difficult to adopt a retrofocus type power arrangement, making it difficult to achieve a wide angle of view, and it also becomes difficult to suppress fluctuations in field curvature during focusing.

[0033] If the lower limit of conditional expression (1) is exceeded and the negative refractive power of the second lens unit becomes too strong, the performance change due to decentering of the second lens unit L2 and the third lens unit L3 becomes large, which is undesirable.

[0034] The third lens group L3 has a positive lens, and when the refractive index of the positive lens G3p having the lowest refractive index is ndG3p, 1.400 <ndG3p<1.700 ···(2) The present invention is characterized in that the following conditional expressions are satisfied:

[0035] Conditional expression (2) defines the refractive index of the positive lens G3p, which has the lowest refractive index, in the third lens unit L3.

[0036] If the upper limit of conditional expression (2) is exceeded and the refractive index of the positive lens element G3p becomes too high, the second-order dispersion of the positive lens element becomes small, making it difficult to correct axial chromatic aberration and chromatic aberration of magnification. Furthermore, lenses with high refractive index tend to have a high specific gravity, which is undesirable because it makes it difficult to reduce the weight of the focus lens group.

[0037] If the lower limit of conditional expression (2) is exceeded and the refractive index of the positive lens element G3p becomes too low, it becomes difficult to correct spherical aberration and lateral chromatic aberration.

[0038] Next, an optical system according to a second embodiment will be described.

[0039] The optical system according to the second embodiment comprises, arranged in order from the object side to the image side, a first lens group L1 with a positive refractive power, a second lens group L2, a third lens group L3 with a positive refractive power, and a fourth lens group L4 with a negative refractive power, and the spacing between adjacent lens groups changes during focusing. By moving at least two lens groups during focusing, fluctuations in various aberrations that occur during focusing can be easily suppressed.

[0040] Furthermore, the fourth lens unit L4 has at least one positive lens, which makes it easier to correct chromatic aberration of magnification and the like that is likely to occur in the fourth lens unit L4.

[0041] In the optical system of each embodiment, it is preferable to satisfy one or more of the following conditions. This will provide an effect that corresponds to each condition.

[0042] The first lens unit L1 preferably has two negative lenses in order from the object side. The above-described configuration makes it easy to correct curvature of field and sagittal coma flare. In addition, the diameter of the front lens can be reduced, making it easy to make the lens smaller in diameter and lighter in weight.

[0043] When the Abbe number of the positive lens G3p is vdG3p, 60.0 <vdG3p<100.0 ···(3) It is preferable to satisfy the following conditional expression.

[0044] Conditional expression (3) defines the Abbe number of the positive lens G3p, which has the lowest refractive index, in the third lens unit L3.

[0045] By satisfying conditional expression (3), axial chromatic aberration and lateral chromatic aberration can be corrected satisfactorily.

[0046] When the focal length of the third lens unit L3 is f3, 0.8 <f3 / f<2.0 ···(4) It is preferable to satisfy the following conditional expression.

[0047] Conditional expression (4) defines the focal length of the third lens unit L3. By satisfying conditional expression (4), it is possible to suppress aberration fluctuations during focusing. If the refractive power of the third lens unit L3 becomes too strong by falling below the lower limit of conditional expression (4), it becomes difficult to correct spherical aberration, which is undesirable. If the refractive power of the third lens unit L3 becomes too weak by exceeding the upper limit of conditional expression (4), the amount of movement of the third lens unit L3 during focusing increases. This makes it difficult to shorten the overall lens length, which is undesirable.

[0048] When the focal length of the first lens unit L1 is f1, 2.5 <f1 / f<5.0 ···(5) It is preferable to satisfy the following conditional expression.

[0049] Conditional expression (5) defines the refractive power of the first lens unit L1. By satisfying conditional expression (5), the axial light rays incident on the focus group can be made closer to afocal, making it possible to suppress aberration fluctuations during focusing. If the refractive power of the first lens unit L1 becomes too weak and the conditional expression is violated, the lens diameter of the focus lens group becomes too large, making the focus lens group heavy.

[0050] This makes it difficult to achieve rapid autofocusing. It is also undesirable because it makes it difficult to correct longitudinal chromatic aberration and spherical aberration. If the refractive power of the first lens unit L1 becomes too strong and the conditional expression is violated, the refractive power of the focus lens unit weakens, increasing the amount of movement during focusing. This makes it difficult to shorten the overall lens length. It is also undesirable because it makes it difficult to correct longitudinal chromatic aberration and spherical aberration.

[0051] When the focal length of the fourth lens unit L4 is f4, -6.0 <f4 / f<―2.0···(6) It is preferable to satisfy the following conditional expression.

[0052] Conditional expression (6) defines the focal length f4 of the fourth lens unit L4. By satisfying conditional expression (6), it is possible to suppress fluctuations in coma aberration during focusing.

[0053] By giving the fourth lens unit L4 negative refractive power, it is possible to configure the optical system to be nearly symmetrical, making it easier to correct coma and chromatic aberration of magnification. Furthermore, it is possible to strengthen the refractive power of the focus unit, reducing the amount of movement during focusing. This makes it possible to suppress fluctuations in coma during focusing.

[0054] If the refractive power of the fourth lens group L4 becomes too strong, exceeding the upper limit of conditional expression (6), the refractive power of the focus group becomes too strong, making it difficult to correct spherical aberration. Also, the entrance pupil position moves toward the image plane, making it difficult to ensure telecentricity of the light beam incident on the image sensor, which is undesirable.

[0055] If the refractive power of the fourth lens unit L4 becomes too weak by going below the lower limit of conditional expression (6), the refractive power of the focus unit becomes too weak, and the amount of movement during focusing increases, which makes it difficult to shorten the overall lens length, which is undesirable.

[0056] When the back focus at an object at infinity is sk, -0.20 <sk / f4<0.00 ···(7) It is preferable to satisfy the following conditional expression.

[0057] Condition (7) defines the back focus of the optical system and the focal length f4 of the fourth lens unit L4.

[0058] By satisfying conditional expression (7), it is possible to suppress fluctuations in coma aberration during focusing.

[0059] By giving the fourth lens unit L4 negative refractive power, it is possible to configure the optical system to be nearly symmetrical, making it easier to correct coma and chromatic aberration of magnification. Furthermore, it is possible to strengthen the refractive power of the focus unit, reducing the amount of movement during focusing. This makes it possible to suppress fluctuations in coma during focusing.

[0060] If the refractive power of the fourth lens group L4 becomes too strong, exceeding the upper limit of conditional expression (7), the refractive power of the focus group becomes too strong, making it difficult to correct spherical aberration. Also, the entrance pupil position moves toward the image plane, making it difficult to ensure telecentricity of the light beam incident on the image sensor, which is undesirable.

[0061] If the refractive power of the fourth lens unit L4 becomes too weak by going below the lower limit of conditional expression (7), the refractive power of the focus unit becomes too weak, and the amount of movement during focusing increases, which makes it difficult to shorten the overall lens length, which is undesirable.

[0062] When the focal length of the positive lens G3p is f3p, 1.6 <f3p / f<4.0 ···(8) It is preferable to satisfy the following conditional expression.

[0063] Condition (8) defines the focal length of the positive lens G3p, which has the lowest refractive index, in the third lens unit L3.

[0064] If the upper limit of conditional expression (8) is exceeded and the refractive power of the positive lens G3p becomes too weak, it becomes difficult to correct axial chromatic aberration and chromatic aberration of magnification.

[0065] If the refractive power of the positive lens G3p becomes too strong, falling below the lower limit of conditional expression (8), it becomes difficult to correct spherical aberration and curvature of field.

[0066] moreover, 1.3 <f3p / f3<2.5 ···(9) It is preferable to satisfy the following conditional expression.

[0067] Condition (9) defines the focal length of the positive lens G3p, which has the lowest refractive index, in the third lens unit L3.

[0068] If the upper limit of conditional expression (9) is exceeded and the refractive power of the positive lens G3p becomes too weak, it becomes difficult to correct axial chromatic aberration and chromatic aberration of magnification.

[0069] If the refractive power of the positive lens G3p becomes too strong, falling below the lower limit of conditional expression (9), it becomes difficult to correct spherical aberration and curvature of field.

[0070] The second lens unit L2 is preferably made up of two or less lenses. By configuring the second lens group L2, which is a focus lens group, with a small number of lenses, the focus lens group can be made lighter even in a lens with a large aperture ratio, in which the lens diameter is large, and quick autofocusing is possible.

[0071] The second lens unit L2 preferably comprises, in order from the object side, a negative lens having a concave surface facing the object side, and a positive lens.

[0072] By configuring the second lens unit L2 as described above, it has a shape concentric with the aperture stop, which makes it possible to suppress field of view changes (focus breathing) during focusing, and also makes it possible to suppress focus fluctuations due to chromatic aberration.

[0073] It is best for the third lens group to consist of two or fewer lenses. By using a small number of lenses in the third lens group, which is the focus lens group, the weight of the focus lens group can be reduced even in a lens with a large aperture ratio, which means that the lens diameter becomes large, enabling quick autofocusing.

[0074] It is desirable for the third lens group to consist of, from the object side, a positive lens and a positive lens. By configuring the third lens group with only positive lenses, it is possible to make the focus lens group relatively lightweight even if it has strong positive refractive power.

[0075] It is preferable that the second lens unit L2 and the third lens unit L3 move toward the object side during focusing from infinity to a close distance.

[0076] By moving both the second lens unit L2 and the third lens unit L3 toward the object side, it is possible to reduce changes in the field of view during focusing (focus breathing).

[0077] -1.20 <f1 / f2<0.30 ···(10) It is preferable to satisfy the following conditional expression.

[0078] Condition (10) defines the ratio of the refractive power of the first lens group to that of the second lens group.

[0079] If the upper limit of conditional expression (10) is exceeded and the refractive power of the second lens group becomes positive, it becomes difficult to adopt a retrofocus type power arrangement, making it difficult to achieve a wide angle of view, and it also becomes difficult to suppress fluctuations in field curvature during focusing.

[0080] If the lower limit of conditional expression (10) is exceeded and the negative refractive power of the second lens unit becomes too strong, the performance change due to decentering of the second lens unit L2 and the third lens unit L3 becomes large, which is undesirable.

[0081] -0.45 <f3 / f2<0.15 ···(11) It is preferable to satisfy the following conditional expression.

[0082] Condition (11) defines the ratio of the refractive power of the third lens unit L3 to the refractive power of the second lens unit L2.

[0083] If the upper limit of conditional expression (11) is exceeded and the refractive power of the second lens unit L2 becomes positive, it becomes difficult to adopt a retrofocus type power arrangement, making it difficult to achieve a wide angle of view, and it also becomes difficult to suppress fluctuations in field curvature during focusing.

[0084] If the lower limit of conditional expression (11) is exceeded and the negative refractive power of the second lens unit becomes too strong, the performance change due to decentering of the second lens unit L2 and the third lens unit L3 becomes large, which is undesirable.

[0085] When the distance between the first lens unit L1 and the second lens unit L2 at infinity is d12, 0.30 <d12 / f<0.70 ···(12) It is preferable to satisfy the following conditional expression.

[0086] Condition (12) defines the distance between the first lens unit L1 and the second lens unit L2 at infinity.

[0087] If the upper limit of conditional expression (12) is exceeded and the distance between the first lens unit L1 and the second lens unit L2 at infinity becomes too large, this is not desirable because it increases the size of the optical system and also increases the fluctuation in field curvature during focusing.

[0088] If the lower limit of conditional expression (12) is exceeded and the distance between the first lens unit L1 and the second lens unit L2 at infinity becomes too small, it becomes impossible to ensure the amount of movement during focusing, making it difficult to shorten the minimum shooting distance. Also, the refractive power of the focus lens unit becomes too strong, making it difficult to reduce fluctuations in spherical aberration during focusing.

[0089] Let m2 be the amount of movement of the second lens unit L2 from infinity to the closest point, and m3 be the amount of movement of the third lens unit L3 from infinity to the closest point, then 0.9 <m2 / m3<2.5 ···(13) It is preferable to satisfy the following conditional expression.

[0090] Condition (13) defines the ratio of the movement amounts of the second lens unit L2 and the third lens unit L3 during focusing.

[0091] If the upper limit of conditional expression (13) is exceeded and the amount of movement of the second lens group becomes too large relative to the third lens group, the amount of movement of the third lens group, which has a strong refractive power, becomes small, making it difficult to shorten the minimum shooting distance.

[0092] If the lower limit of conditional expression (13) is not reached and the amount of movement of the second lens group becomes too small relative to the third lens group, the fluctuation of coma aberration during focusing becomes too large.

[0093] 2.0 <f1 / f3<4.5 ···(14) It is preferable to satisfy the following conditional expression.

[0094] Condition (14) defines the ratio of the refractive power of the first lens unit L1 to the refractive power of the third lens unit L3.

[0095] If the upper limit of conditional expression (14) is exceeded and the refractive power of the third lens unit L3 becomes too strong, it becomes difficult to correct spherical aberration, which is undesirable. If the lower limit of conditional expression (14) is exceeded and the refractive power of the third lens unit L3 becomes too weak, the amount of movement of the third lens unit L3 during focusing becomes large, which makes it difficult to shorten the overall lens length, which is undesirable.

[0096] -2.00 <f1 / f4<-0.30 ···(15) It is preferable to satisfy the following conditional expression.

[0097] Condition (15) defines the ratio of the refractive power of the first lens unit L1 to the refractive power of the fourth lens unit L4.

[0098] If the upper limit of conditional expression (15) is exceeded and the refractive power of the fourth lens unit L4 becomes too weak, the amount of movement during focusing increases, which makes it difficult to shorten the overall lens length, which is undesirable.

[0099] If the refractive power of the fourth lens unit L4 is too strong, falling below the lower limit of conditional expression (15), the refractive power of the focus unit will be too strong, making it difficult to correct spherical aberration. Also, the entrance pupil position will move toward the image plane, making it difficult to ensure telecentricity of the light beam incident on the image sensor, which is undesirable.

[0100] -0.30 <f4 / f2<1.70 ···(16) It is preferable to satisfy the following conditional expression.

[0101] Condition (16) defines the ratio of the refractive power of the fourth lens unit L4 to the refractive power of the second lens unit L2.

[0102] If the lower limit of conditional expression (16) is exceeded and the refractive power of the second lens unit L2 becomes positive, it becomes difficult to adopt a retrofocus type power arrangement, making it difficult to achieve a wide angle of view, and it also becomes difficult to suppress fluctuations in field curvature during focusing.

[0103] If the upper limit of conditional expression (16) is exceeded and the negative refractive power of the second lens unit becomes too strong, the change in performance due to decentering of the second lens unit L2 and the third lens unit L3 becomes large, which is undesirable.

[0104] -0.70 <f3 / f4<-0.10 ···(17) It is preferable to satisfy the following conditional expression.

[0105] Condition (17) defines the ratio of the refractive power of the third lens unit L3 to the refractive power of the fourth lens unit L4.

[0106] If the upper limit of conditional expression (17) is exceeded and the refractive power of the third lens unit L3 becomes too strong, it becomes difficult to correct spherical aberration, which is undesirable. If the lower limit of conditional expression (17) is exceeded and the refractive power of the third lens unit L3 becomes too weak, the amount of movement of the third lens unit L3 during focusing becomes large, which makes it difficult to shorten the overall lens length, which is undesirable.

[0107] It is preferable that the first lens unit L1 has three or more positive lenses. By having three or more positive lenses, it becomes easier to correct spherical aberration even if the refractive power is strong. By increasing the refractive power, it becomes possible to reduce the diameter of the aperture and the diameter of the focus lens unit.

[0108] It is desirable for the optical system to have four or fewer groups in which the spacing between adjacent lens groups changes during zooming or focusing. Reducing the number of groups in which the spacing changes simplifies the mechanical configuration and makes it easier to reduce the size of the lens in the outer diameter direction.

[0109] In each embodiment, it is preferable to set the numerical ranges of the above-mentioned conditional expressions (1) to (17) as follows:

[0110] -0.35 <f / f2<0.10 ···(1a) 1.430 <ndG3p<1.670 ···(2a) 62.0 <vdG3p<96.0 ···(3a) 0.9 <f3 / f<1.8 ···(4a) 2.7 <f1 / f<4.5 ···(5a) -5.7 <f4 / f<-2.2 ···(6a) -0.18 <sk / f4<-0.02 ···(7a) 1.7 <f3p / f<3.5 ···(8a) 1.4 <f3p / f3<2.3 ···(9a) -1.10 <f1 / f2<0.20 ···(10a) -0.40 <f3 / f2<0.10 ···(11a) 0.35 <d12 / f<0.65 ···(12a) 1.1 <m2 / m3<2.2 ···(13a) 2.2 <f1 / f3<4.0 ···(14a) -1.70 <f1 / f4<-0.50 ···(15a) -0.20 <f4 / f2<1.50 ···(16a) -0.60 <f3 / f4<-0.15 ···(17a) It is more preferable to set the numerical ranges of the above-mentioned conditional expressions (1) to (17) as follows:

[0111] -0.30 <f / f2<0.05 ···(1b) 1.460 <ndG3p<1.630 ···(2b) 63.0 <vdG3p<91.0 ···(3b) 1.0 <f3 / f<1.5 ···(4b) 2.8 <f1 / f<4.2 ···(5b) -5.5 <f4 / f<-2.3 ···(6b) -0.17 <sk / f4<-0.04 ···(7b) 1.8 <f3p / f<3.0 ···(8b) 1.5 <f3p / f3<2.1 ···(9b) -1.00 <f1 / f2<0.10 ···(10b) -0.35 <f3 / f2<0.05 ···(11b) 0.40 <d12 / f<0.60 ···(12b) 1.2 <m2 / m3<2.0 ···(13b) 2.4 <f1 / f3<3.5 ···(14b) -1.50 <f1 / f4<-0.70 ···(15b) -0.10 <f4 / f2<1.30 ···(16b) -0.50 <f3 / f4<-0.20 ···(17b) As described above, according to each embodiment, it is possible to obtain an optical system having a wide angle and a large aperture ratio, while still being able to effectively correct various aberrations including chromatic aberration of magnification, and having high optical performance. [Example] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below. In each numerical example, i indicates the order of the surface from the object side, ri indicates the radius of curvature of the ith surface (i-th surface), di indicates the distance between the ith surface and the (i+1)th surface, ndi and vdi indicate the refractive index and Abbe number based on the d-line, respectively. f indicates the focal length, and Fno indicates the F-number.

[0112] In addition, when the refractive indices at the d line (wavelength 587.6 nm), F line (wavelength 486.1 nm), and C line (wavelength 656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively, νd is expressed as follows: νd=(Nd-1) / (NF-NC) It is expressed as:

[0113] BF is the back focus. The back focus is the air-equivalent distance from the lens surface located closest to the object in optical system L0 to the image plane. The total lens length is the sum of the back focus and the distance on the optical axis from the lens surface located closest to the object in optical system L0 to the lens surface closest to the image.

[0114] (Aspherical surface data) shows the aspherical surface coefficients when the aspherical surface is expressed by the following formula.

[0115]

number

[0116] however, x: Displacement from the reference plane in the optical axis direction h: Height perpendicular to the optical axis R: Radius of the base quadratic surface k: conic constant C n :nth-order aspheric coefficient The "EZ" display is "10 -Z " means. [Example 1] In the lens cross-sectional view of FIG. 1, L1 is a first lens group having a positive refractive power, L2 is a second lens group, L3 is a third lens group having a positive refractive power, and L4 is a fourth lens group having a negative refractive power.

[0117] The first lens group L1 includes, in order from the object side, a negative meniscus lens having a meniscus shape with a convex surface facing the object side and an aspheric surface formed on the image side, and a cemented negative lens formed by cementing together a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side.

[0118] Furthermore, it is composed of a biconcave negative lens, a cemented positive lens formed by cementing a biconvex positive lens and a negative meniscus lens with its concave surface facing the object side, a biconvex positive lens, and a cemented negative lens formed by cementing a biconcave negative lens and a positive meniscus lens with its convex surface facing the object side.

[0119] The second lens unit L2 is composed of a negative meniscus lens with a concave surface facing the object side, and a positive meniscus lens with a convex surface facing the object side.

[0120] The third lens group L3 is composed of a biconvex positive lens (positive lens G3p) with an aspherical surface formed on the object side surface, and a biconvex positive lens with an aspherical surface formed on the image side surface.

[0121] The fourth lens group L4 is composed of a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, and a cemented negative lens formed by cementing a biconvex positive lens and a biconcave negative lens together.

[0122] SP denotes an aperture stop, which is arranged on the image side of the first lens unit L1.

[0123] Focusing is performed by moving the intermediate lens unit Lm toward the object side.

[0124] During focusing from infinity to a close distance, the second lens unit L2 moves toward the object side as shown by the arrow, and the third lens unit L3 moves toward the object side while increasing the distance between it and the third lens unit.

[0125] Numerical values ​​corresponding to the first embodiment are hereinafter referred to as Numerical Example 1.

[0126] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 49.250 2.80 1.58313 59.4 54.49 2* 25.748 10.41 45.24 3 91.875 1.40 1.51633 64.1 44.82 4 27.517 6.24 2.00069 25.5 40.51 5 32.273 13.09 37.51 6 -31.122 1.40 1.51742 52.4 37.10 7 167.205 0.20 39.18 8 77.066 15.83 1.76385 48.5 40.96 9 -28.044 1.50 1.85478 24.8 42.44 10 -49.833 0.20 45.41 11 52.217 9.24 2.00100 29.1 46.69 12 -175.727 2.91 45.73 13 -83.034 1.30 1.77047 29.7 43.66 14 25.756 10.87 1.59522 67.7 38.86 15 326.441 2.29 38.39 16 (Aperture) ∞ (Variable) 38.01 17 -46.467 1.40 1.77047 29.7 34.83 18 -268.162 0.20 35.79 19 46.945 3.88 1.59522 67.7 37.18 20 98.394 (variable) 36.93 21* 48.067 7.58 1.59522 67.7 36.94 22 -186.725 2.69 36.81 23 251.279 3.25 1.76450 49.1 37.23 24* -109.420 (variable) 37.21 25 45.812 5.15 1.79631 22.6 37.98 26 424.301 0.20 37.52 27 71.316 1.20 1.61340 44.3 36.40 28 26.464 4.46 33.82 29 72.240 10.39 1.43875 94.7 33.86 30 -27.204 1.20 1.85478 24.8 33.70 31 5790.447 13.45 35.75 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-1.16066e-06 A 6=-3.03244e-09 A 8=-4.46652e-13 A10= 3.41317e-15 A12=-1.75072e-17 Page 21 K = 0.00000e+00 A 4=-1.70638e-06 A 6= 4.96073e-09 A 8= 1.12011e-11 A10=-2.59322e-14 A12= 2.53729e-17 Page 24 K = 0.00000e+00 A 4= 6.13353e-06 A 6= 5.14223e-09 A 8=-1.07393e-13 A10= 1.29861e-14 A12= 8.20741e-18 Various data Focal length 34.00 F-number 1.24 Half angle of view: 32.47 Image height 21.64 Lens length 154.96 BF 13.45 Infinity 0.28m d16 17.85 6.06 d20 1.20 4.43 d24 1.19 9.76 Group Data Group starting plane focal length 1 1 135.15 2 17 -143.94 3 21 41.37 4 25 -180.31 [Example 2] In the lens cross-sectional view of FIG. 4, L1 is a first lens group with positive refractive power, L2 is a second lens group, L3 is a third lens group with positive refractive power, and L4 is a fourth lens group with negative refractive power.

[0127] The first lens group L1 includes, in order from the object side, a negative meniscus lens having a meniscus shape with a convex surface facing the object side and an aspheric surface formed on the image side, and a cemented negative lens formed by cementing together a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side.

[0128] Furthermore, it is composed of a biconcave negative lens, a cemented positive lens formed by cementing a biconvex positive lens and a negative meniscus lens with its concave surface facing the object side, a biconvex positive lens, and a cemented negative lens formed by cementing a biconcave negative lens and a biconvex positive lens.

[0129] The second lens unit L2 is composed of a negative meniscus lens with a concave surface facing the object side, and a positive meniscus lens with a convex surface facing the object side.

[0130] The third lens group L3 is composed of a biconvex positive lens (positive lens G3p) with an aspherical surface formed on the object side surface, and a biconvex positive lens with an aspherical surface formed on the image side surface.

[0131] The fourth lens group L4 is composed of a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, and a cemented negative lens formed by cementing a biconvex positive lens and a biconcave negative lens together.

[0132] SP denotes an aperture stop, which is arranged on the image side of the first lens unit L1.

[0133] Focusing is performed by moving the intermediate lens unit Lm toward the object side.

[0134] During focusing from infinity to a close distance, the second lens unit L2 moves toward the object side as shown by the arrow. The third lens unit L3 moves toward the object side while increasing the distance between it and the third lens unit. Numerical values ​​corresponding to Example 2 are shown below as Numerical Example 2.

[0135] (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 62.837 2.80 1.58313 59.4 55.11 2* 28.303 9.96 45.48 3 136.845 1.40 1.51633 64.1 44.99 4 37.622 2.93 2.00069 25.5 41.31 5 50.790 10.90 40.28 6 -36.110 1.40 1.51742 52.4 39.18 7 131.738 0.20 41.17 8 78.795 12.72 1.76385 48.5 42.73 9 -37.220 1.50 1.85478 24.8 43.95 10 -66.905 0.20 46.45 11 61.160 7.16 2.00100 29.1 47.00 12 -308.481 5.13 45.91 13 -100.536 1.30 1.77047 29.7 43.27 14 29.265 11.46 1.59522 67.7 38.86 15 -119.475 1.00 38.43 16 (Aperture) ∞ (Variable) 38.01 17 -38.857 1.40 1.77047 29.7 35.03 18 -106.130 0.20 36.38 19 45.912 3.15 1.59522 67.7 38.09 20 85.580 (variable) 37.90 21* 65.526 6.78 1.55332 71.7 36.31 22 -153.621 3.46 35.73 23 500.204 3.28 1.76450 49.1 35.94 24* -90.398 (variable) 35.56 25 36.959 5.00 1.77830 23.9 35.63 26 149.776 0.20 35.19 27 67.697 1.20 1.61340 44.3 34.52 28 25.062 9.23 31.81 29 143.338 7.77 1.43875 94.7 31.96 30 -29.960 1.20 1.85478 24.8 32.25 31 288.732 14.94 34.68 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-3.81875e-07 A 6=-1.77711e-09 A 8= 6.18998e-12 A10=-1.59599e-14 A12= 1.44372e-17 Page 21 K = 0.00000e+00 A 4= 5.75900e-07 A 6= 6.03605e-09 A 8= 5.42166e-12 A10=-9.22343e-15 A12= 7.97029e-18 Page 24 K = 0.00000e+00 A 4= 5.65424e-06 A 6= 5.91887e-09 A 8=-9.92448e-13 A10= 2.08698e-14 A12=-2.51766e-18 Various data Focal length 42.38 F-number 1.52 Half angle of view 27.04 Image height 21.64 Lens length 152.96 BF 14.94 Infinity 0.28m d16 22.71 6.96 d20 1.20 5.21 d24 1.20 12.94 Group Data Group starting plane focal length 1 1 123.27 2 17 -158.07 3 21 47.82 4 25 -102.07 [Example 3] In the lens cross-sectional view of FIG. 7, L1 is the first lens group with positive refractive power, L2 is the second lens group, L3 is the third lens group with positive refractive power, and L4 is the fourth lens group with negative refractive power.

[0136] The first lens group L1 includes, in order from the object side, a negative meniscus lens with a meniscus shape convex toward the object side and an aspheric surface formed on the image side, a cemented negative lens formed by cementing a negative meniscus lens with a convex surface toward the object side and a positive meniscus lens with a convex surface toward the object side, a biconcave negative lens, a cemented positive lens formed by cementing a biconvex positive lens and a negative meniscus lens with a concave surface toward the object side, a biconvex positive lens, and a cemented negative lens formed by cementing a biconcave negative lens and a biconvex positive lens.

[0137] The second lens unit L2 is composed of a negative meniscus lens with a concave surface facing the object side, and a positive meniscus lens with a convex surface facing the object side.

[0138] The third lens group L3 is composed of a biconvex positive lens (positive lens G3p) with an aspherical surface formed on the object side surface, and a biconvex positive lens with an aspherical surface formed on the image side surface.

[0139] The fourth lens group L4 is composed of a biconvex positive lens, a negative meniscus lens with a convex surface facing the object side, and a cemented negative lens formed by cementing a biconvex positive lens and a negative meniscus lens with a concave surface facing the object side.

[0140] SP denotes an aperture stop, which is arranged on the image side of the first lens unit L1. Focusing is performed by moving the intermediate lens unit Lm toward the object side.

[0141] During focusing from infinity to a close distance, the second lens unit L2 moves toward the object side as shown by the arrow. The third lens unit L3 moves toward the object side while increasing the distance between it and the third lens unit. Numerical values ​​corresponding to Example 3 are shown below as Numerical Example 3.

[0142] (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 54.657 2.80 1.58313 59.4 56.17 2* 25.434 11.70 45.10 3 113.067 1.40 1.51633 64.1 44.62 4 26.749 4.42 2.00069 25.5 40.27 5 32.139 15.23 38.73 6 -31.675 1.40 1.51742 52.4 37.92 7 219.944 0.28 40.47 8 88.731 14.47 1.76385 48.5 41.49 9 -28.600 1.50 1.85478 24.8 41.75 10 -47.807 3.69 44.28 11 56.321 11.48 2.00100 29.1 46.20 12 -162.905 2.82 44.32 13 -79.829 1.30 1.77047 29.7 42.56 14 27.506 10.42 1.59522 67.7 38.76 15 -11558.899 1.68 38.40 16 (Aperture) ∞ (Variable) 38.00 17 -45.259 1.40 1.77047 29.7 35.46 18 -204.255 0.20 36.46 19 50.234 4.88 1.59522 67.7 37.79 20 841.378 (variable) 37.61 21* 48.125 7.93 1.49700 81.5 36.64 22 -339.413 0.20 35.02 23 66.186 4.20 1.76450 49.1 34.51 24* -544.156 (variable) 33.86 25 49.370 4.43 1.75575 24.7 33.98 26 -5095.117 0.19 33.57 27 128.162 1.20 1.61340 44.3 32.89 28 23.425 5.04 30.45 29 110.349 9.26 1.43875 94.7 30.62 30 -23.798 1.20 1.85883 30.0 30.99 31 -121.247 13.45 33.73 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-5.19506e-07 A 6=-3.96549e-09 A 8= 9.07553e-12 A10=-1.67303e-14 A12= 3.06982e-18 Page 21 K = 0.00000e+00 A 4= 2.97105e-06 A 6= 6.99504e-09 A 8= 1.64275e-11 A10=-3.89622e-14 A12= 4.86661e-17 Page 24 K = 0.00000e+00 A 4= 1.06794e-05 A 6= 3.72319e-09 A 8= 2.78295e-11 A10=-6.58023e-14 A12= 1.80633e-16 Various data Focal length 30.00 F-number 1.24 Half angle of view 35.79 Image height 21.64 Lens length 93.73 BF 13.45 Infinity 0.28m d16 14.39 6.18 d20 1.20 4.70 d24 1.20 5.90 Group Data Group starting plane focal length 1 1 108.48 2 17 -531.24 3 21 41.93 4 25 -90.76 [Example 4] In the lens cross-sectional view of FIG. 1, L1 is a first lens group having a positive refractive power, L2 is a second lens group, L3 is a third lens group having a positive refractive power, and L4 is a fourth lens group having a negative refractive power.

[0143] The first lens group L1 includes, in order from the object side, a negative meniscus lens with a meniscus shape convex toward the object side and an aspheric surface formed on the image side, a cemented negative lens formed by cementing a negative meniscus lens with a convex surface toward the object side and a positive meniscus lens with a convex surface toward the object side, a biconcave negative lens, a cemented positive lens formed by cementing a biconvex positive lens and a negative meniscus lens with a concave surface toward the object side, a biconvex positive lens, and a cemented negative lens formed by cementing a biconcave negative lens and a positive meniscus lens with a convex surface toward the object side.

[0144] The second lens unit L2 is composed of a negative meniscus lens with a concave surface facing the object side, and a positive meniscus lens with a convex surface facing the object side. The third lens group L3 is composed of a biconvex positive lens (positive lens G3p) with an aspherical surface formed on the object-side surface, and a biconvex positive lens with an aspherical surface formed on the image-side surface.

[0145] The fourth lens group L4 is composed of a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, and a negative meniscus lens with a concave surface facing the object side.

[0146] SP denotes an aperture stop, which is arranged on the image side of the first lens unit L1.

[0147] Focusing is performed by moving the intermediate lens unit Lm toward the object side.

[0148] During focusing from infinity to a close distance, the second lens unit L2 moves toward the object side as shown by the arrow, and the third lens unit L3 moves toward the object side while increasing the distance between it and the third lens unit.

[0149] Numerical values ​​corresponding to the fourth embodiment are hereinafter referred to as the fourth numerical embodiment.

[0150] (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 51.616 2.80 1.58313 59.4 56.10 2* 26.628 8.90 46.44 3 57.709 1.40 1.76385 48.5 46.12 4 23.785 7.12 2.00069 25.5 40.76 5 33.469 16.86 39.08 6 -35.492 1.40 1.51742 52.4 36.89 7 582.720 1.01 38.85 8 75.366 17.97 1.76385 48.5 44.20 9 -28.721 1.50 1.85478 24.8 45.33 10 -57.261 0.19 48.30 11 60.154 8.68 2.00100 29.1 48.14 12 -151.485 3.38 47.37 13 -80.629 1.30 1.77047 29.7 44.02 14 26.819 10.01 1.59522 67.7 39.01 15 238.603 2.51 38.47 16 (Aperture) ∞ (Variable) 38.01 17 -30.758 1.40 1.77047 29.7 34.72 18 -47.438 0.20 36.10 19 45.828 4.04 1.59522 67.7 37.22 20 145.005 (variable) 36.92 21* 91.312 7.65 1.49700 81.5 37.42 22 -64.145 4.45 38.04 23 84.332 3.29 1.76450 49.1 38.21 24* -826.769 (variable) 37.84 25 62.960 3.06 1.79631 22.6 37.91 26 182.404 0.19 37.62 27 43.277 1.20 1.61340 44.3 36.61 28 25.661 9.65 34.55 29 -67.750 1.20 1.77047 29.7 34.68 30 -502.271 13.45 35.73 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-4.53964e-07 A 6=-2.81876e-09 A 8= 5.57099e-12 A10=-9.85220e-15 A12= 2.29695e-18 Page 21 K = 0.00000e+00 A 4=-6.77933e-07 A 6= 5.55648e-10 A 8= 9.21152e-12 A10=-3.25029e-14 A12= 2.86790e-17 Page 24 K = 0.00000e+00 A 4= 6.90962e-06 A 6= 1.59512e-09 A 8= 8.82941e-12 A10=-8.70854e-15 A12= 1.07094e-17 Various data Focal length 34.97 F-number 1.24 Half angle of view 31.75 Image height 21.64 Lens length 88.52 BF 13.45 Infinity 0.28m d16 17.78 8.56 d20 1.20 4.15 d24 1.19 7.45 Group Data Group starting plane focal length 1 1 125.63 2 17 1567.48 3 21 45.30 4 25 -97.66 [Variations] Unlike Example 1, the second lens unit L2 may be configured with one positive or negative lens. By configuring the second lens unit L2 with one lens, it becomes easier to reduce the weight of the second lens unit L2.

[0151] In the optical systems of each embodiment, it is advisable to vapor-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 prone to contact with the outside world, vapor-depositing a fluorine coating can improve water and oil repellency, suppress flare, and achieve high optical performance.

[0152] In particular, since the lens surface closest to the object side of the lens positioned closest to the object side has a large diameter, it is preferable to vapor-deposit a fluorine coating on it.

[0153] In the cemented lenses arranged in the optical systems of the respective embodiments, 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 cemented lens 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 axial thickness be 0.008 mm or more and 0.02 mm or less.

[0154] At least one lens in the optical system of each example 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, it is preferable that the anti-reflection coating PC has Nd of 1.32 or less.

[0155] By setting Nd to 1.32 or less, the difference in refractive index with air can be reduced, which makes it possible to further reduce light reflection and reduce ghosting.

[0156] 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.

[0157] Here, it is preferable to apply an anti-reflection coating PC to the image-side lens surface of the negative lens with a concave surface facing the image side among the negative lenses arranged in the optical system. 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 ghosting more noticeable. Therefore, ghosting 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.

[0158] The various values ​​in each numerical example are summarized in Table 1 below.

[0159] [Table 1]

[0160] Next, an example in which the optical system of each example is used as an imaging optical system will be described with reference to Fig. 13. In Fig. 13, 10 is a diagram showing an example of an imaging device, 11 is an imaging optical system configured using the optical system of this embodiment, and 12 is a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that receives the subject image formed by the imaging optical system 11. Also, 13 is a recording means that records the subject image received by the imaging element 12, and 14 is a finder for observing the subject image displayed on a display element (not shown). The display element is configured using a liquid crystal panel or the like, and displays the subject image formed on the imaging element 12.

[0161] In this way, by applying the optical system of this embodiment to an optical device such as a digital camera, an optical device with high optical performance can be realized.

[0162] This embodiment can also be applied to an SLR (Single Lens Reflex) camera that does not have a quick return mirror.

[0163] The optical system of this embodiment can also be applied to a video camera.

[0164] The disclosure of each embodiment includes the following configuration. (Configuration 1) An optical system comprising a first lens group having a positive refractive power, a second lens group, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, arranged in this order from the object side to the image side, in which the spacing between adjacent lens groups changes during focusing, the third lens group has at least one positive lens; Let f be the focal length of the entire system, f2 be the focal length of the second lens group, and ndG3p be the refractive index of the positive lens G3p having the lowest refractive index among the materials of the positive lenses arranged in the third lens group. -0.40 <f / f2<0.15 1.400 <ndG3p<1.700 An optical system characterized by satisfying the following conditional expression: (Configuration 2) An optical system comprising a first lens group having a positive refractive power, a second lens group, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, arranged in this order from the object side to the image side, in which the spacing between adjacent lens groups changes during focusing, An optical system characterized in that the fourth lens group has at least one positive lens. (Configuration 3) 3. The optical system according to configuration 1 or 2, wherein the first lens group has two negative lenses arranged in this order from the most object side to the most image side. (Configuration 4) When the Abbe number of the material of the positive lens G3p is vdG3p, 60.0 <vdG3p<100.0 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the focal length of the third lens group is f3, 0.8 <f3 / f<2.0 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the focal length of the first lens group is f1, 2.5 <f1 / f<5.0 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the focal length of the fourth lens group is f4, -6.0 <f4 / f<―2.0 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When the back focus when focusing on an object at infinity is sk and the focal length of the fourth lens group is f4, -0.20 <sk / f4<0.00 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) When the focal length of the positive lens G3p is f3p, 1.6 <f3p / f<4.0 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) When the focal length of the positive lens G3p is f3p and the focal length of the third lens group is f3, 1.3 <f3p / f3<2.5 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) 11. The optical system according to claim 10, wherein the second lens group is made up of two or less lenses. (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the second lens group comprises a negative lens, both concave on the object side, and a positive lens, arranged in this order from the object side to the image side. (Configuration 13) 13. The optical system according to any one of configurations 1 to 12, wherein the third lens group is made up of two or less lenses. (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the third lens group is made up of two positive lenses. (Configuration 15) 15. The optical system according to any one of configurations 1 to 14, wherein the second lens group and the third lens group move toward the object side during focusing from infinity to a close distance. (Configuration 16) When the focal length of the first lens group is f1, -1.20 <f1 / f2<0.30 16. The optical system according to any one of configurations 1 to 15, wherein the following condition is satisfied: (Configuration 17) When the focal length of the third lens group is f3, -0.45 <f3 / f2<0.15 17. The optical system according to any one of configurations 1 to 16, wherein the following condition is satisfied: (Configuration 18) When the distance on the optical axis between the first lens group and the second lens group when focused on an object at infinity is d12, 0.30 <d12 / f<0.70 18. The optical system according to any one of configurations 1 to 17, wherein the following condition is satisfied: (Configuration 19) Let m2 be the amount of movement of the second lens group from infinity to the closest distance, and m3 be the amount of movement of the third lens group from infinity to the closest distance, 0.9 <m2 / m3<2.5 19. The optical system according to any one of configurations 1 to 18, wherein the following condition is satisfied: (Configuration 20) When the focal length of the first lens group is f1 and the focal length of the third lens group is f3, 2.0 <f1 / f3<4.5 19. The optical system according to any one of configurations 1 to 19, wherein the following condition is satisfied: (Configuration 21) When the focal length of the first lens group is f1 and the focal length of the fourth lens group is f4, -2.00 <f1 / f4<-0.30 21. The optical system according to any one of configurations 1 to 20, wherein the following condition is satisfied: (Configuration 22) When the focal length of the fourth lens group is f4, -0.30 <f4 / f2<1.70 22. The optical system according to any one of configurations 1 to 21, wherein the following condition is satisfied: (Configuration 23) When the focal length of the third lens group is f3 and the focal length of the fourth lens group is f4, -0.70 <f3 / f4<-0.10 23. The optical system according to any one of configurations 1 to 22, wherein the following condition is satisfied: (Configuration 24) 24. The optical system according to any one of configurations 1 to 23, wherein the first lens group has a stop arranged closest to the image side. (Configuration 25) The optical system according to any one of configurations 1 to 24, wherein the first lens group has three or more positive lenses. (Configuration 26) 26. The optical system according to any one of configurations 1 to 25, wherein the optical system has four or less groups in which the spacing between adjacent lens groups changes during zooming or focusing. (Configuration 27) 27. An imaging device comprising: an optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

[0165] Although the 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 the gist of the present invention. [Explanation of symbols]

[0166] L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group

Claims

1. An optical system comprising a first lens group having a positive refractive power, a second lens group, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during focusing, An optical system characterized in that the fourth lens group has at least one positive lens.

2. 2. The optical system according to claim 1, wherein the first lens group has two negative lenses arranged in this order from the object side to the image side.

3. the third lens group has at least one positive lens; When the Abbe number of the material of the positive lens G3p having the lowest refractive index among the materials of the positive lenses arranged in the third lens group is vdG3p, 60.0<vdG3p<100.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the entire system is f and the focal length of the third lens group is f3, 0.8<f3 / f<2.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the focal length of the entire system is f and the focal length of the first lens group is f1, 2.5<f1 / f<5.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the focal length of the entire system is f and the focal length of the fourth lens group is f4, -6.0<f4 / f<-2.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. When the back focus when focusing on an object at infinity is sk and the focal length of the fourth lens group is f4, -0.20<sk / f4<0.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

8. the third lens group has at least one positive lens; When the focal length of the positive lens G3p having the lowest refractive index among the materials of the positive lenses arranged in the third lens group is f3p and the focal length of the entire system is f, 1.6<f3p / f<4.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

9. the third lens group has at least one positive lens; When the focal length of the positive lens G3p having the lowest refractive index among the materials of the positive lenses arranged in the third lens group is f3p and the focal length of the third lens group is f3, 1.3<f3p / f3<2.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. 2. The optical system according to claim 1, wherein the second lens group is composed of two or less lenses.

11. 2. The optical system according to claim 1, wherein the second lens group comprises, in order from the object side to the image side, a negative lens having a concave surface facing the object side and a positive lens.

12. 2. The optical system according to claim 1, wherein the third lens group is made up of two or less lenses.

13. 13. The optical system according to claim 12, wherein the third lens group is made up of two positive lenses.

14. 2. The optical system according to claim 1, wherein the second lens group and the third lens group move toward the object side during focusing from infinity to a close distance.

15. When the focal length of the second lens group is f2 and the focal length of the first lens group is f1, -1.20<f1 / f2<0.30 2. The optical system according to claim 1, wherein the following condition is satisfied:

16. When the focal length of the second lens group is f2 and the focal length of the third lens group is f3, -0.45<f3 / f2<0.15 2. The optical system according to claim 1, wherein the following condition is satisfied:

17. When the focal length of the entire system is f and the distance on the optical axis between the first lens group and the second lens group when focused on an object at infinity is d12, 0.30<d12 / f<0.70 2. The optical system according to claim 1, wherein the following condition is satisfied:

18. Let m2 be the amount of movement of the second lens group from infinity to the closest distance, and m3 be the amount of movement of the third lens group from infinity to the closest distance, 0.9<m2 / m3<2.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

19. When the focal length of the first lens group is f1 and the focal length of the third lens group is f3, 2.0<f1 / f3<4.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

20. When the focal length of the first lens group is f1 and the focal length of the fourth lens group is f4, -2.00<f1 / f4<-0.30 2. The optical system according to claim 1, wherein the following condition is satisfied:

21. When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, -0.30<f4 / f2<1.70 2. The optical system according to claim 1, wherein the following condition is satisfied:

22. When the focal length of the third lens group is f3 and the focal length of the fourth lens group is f4, -0.70<f3 / f4<-0.10 2. The optical system according to claim 1, wherein the following condition is satisfied:

23. 2. The optical system according to claim 1, wherein the first lens group has a stop disposed closest to the image side.

24. 2. The optical system according to claim 1, wherein the first lens group includes three or more positive lenses.

25. 2. The optical system according to claim 1, wherein the optical system has four or less groups in which the spacing between adjacent lens groups changes during zooming or focusing.

26. 26. An imaging device comprising: the optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

Images