Optical system and imaging apparatus

Abstract

To provide a small-sized optical system that can satisfactorily correct various aberrations despite its large aperture ratio.SOLUTION: An optical system consists of a first lens group L1 having a positive refractive power, a second lens group L2 having a negative refractive power, and a rear lens group LR. The first lens group has a first partial lens group L1A, a second partial lens group L1B, and a third partial lens group L1C. The first partial lens group and the second partial lens group have therebetween the maximum air gap on an optical axis in the first lens group. The second partial lens group and the third partial lens group have therebetween the second largest air gap on the optical axis in the first lens group. The second lens group L2 moves in focusing. The focal length f1 of the first lens group, the focal length f1A of the first partial lens group, and the focal length f1B of the second partial lens group satisfy the conditions of 1.0≤f1A / f1≤2.0 and -0.6≤f1A / f1B<0.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for imaging devices such as digital still cameras, video cameras, surveillance cameras, and vehicle-mounted cameras. [Background technology]

[0002] As a small telephoto lens, an optical system is disclosed that has a first lens group with positive refractive power, a second lens group with negative refractive power that moves during focusing, and a third lens group with positive refractive power, which are arranged in this order from the object side to the image side. In addition, as an optical system that is advantageous for video shooting and dustproofing and drip-proofing, an optical system that employs an inner focus method or a rear focus method in which focusing is performed by moving a lens group on the image side rather than the first lens group that is the closest to the object side is disclosed. These optical systems effectively correct various aberrations such as spherical aberration and chromatic aberration. In addition, the optical system may have an anti-vibration function for reducing (correcting) image blur caused by camera shake such as hand shake. Furthermore, these optical systems are also required to have a large aperture ratio and high optical performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6961441 [Patent Document 2] International Publication No. 2021 / 220612 Summary of the Invention [Problem to be solved by the invention]

[0004] The optical system of Patent Document 1 has a large aperture ratio but is large overall. It is difficult to reduce the size of the optical system while keeping the aperture ratio appropriately set.

[0005] The optical system of Patent Document 2 is small but has a small aperture ratio. Increasing the aperture ratio leads to an increase in spherical aberration and chromatic aberration, making it difficult to ensure high optical performance.

[0006] The present invention provides a small and lightweight optical system that has a sufficient aperture ratio and can satisfactorily correct various aberrations. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention comprises a first lens group having positive refractive power, a second lens group having negative refractive power, and a rear lens group, arranged in this order from the object side to the image side. The first lens group has a first partial lens group, a second partial lens group, and a third partial lens group, arranged in this order from the object side to the image side, and the first partial lens group and the second partial lens group have the largest air gap on the optical axis in the first lens group, and the second partial lens group and the third partial lens group have the second largest air gap on the optical axis in the first lens group. The second lens group L2 moves during focusing. When the focal length of the first lens group is f1, the focal length of the first partial lens group is f1A, and the focal length of the second partial lens group is f1B, 1.0≦f1A / f1≦2.0 -0.6≦f1A / f1B<0 The present invention is characterized in that the following conditions are satisfied: Note that an imaging apparatus for imaging a subject through the above optical system constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, it is possible to provide a small and lightweight optical system that has a sufficient aperture ratio and can satisfactorily correct various aberrations. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the optical system of Example 1. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 6A to 6C are aberration diagrams of the optical system of Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6]11A to 11C are aberration diagrams of the optical system of Example 3. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 11A to 11C are aberration diagrams of the optical system of Example 4. [Figure 9] FIG. 13 is a cross-sectional view of the optical system of the fifth embodiment. [Figure 10] 13A to 13C are aberration diagrams of the optical system of Example 5. [Figure 11] FIG. 13 is a cross-sectional view of the optical system of the sixth embodiment. [Figure 12] 13A to 13C are aberration diagrams of the optical system of Example 6. [Figure 13] FIG. 13 is a cross-sectional view of the optical system of the seventh embodiment. [Figure 14] 13A to 13C are aberration diagrams of the optical system of Example 7. [Figure 15] FIG. [Figure 16] 5A and 5B are diagrams for explaining a method of calculating a conditional expression for an aspheric shape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Prior to describing specific embodiments 1 to 7, matters common to the embodiments will be described with reference to FIG. 1 showing the optical system of embodiment 1.

[0011] The optical system of each embodiment is used as an imaging optical system in an imaging device such as a video camera, a digital still camera, a broadcast camera, a surveillance camera, an in-vehicle camera, or a silver halide film camera. However, the optical system of each embodiment can also be used as a projection optical system of an image projection device (projector).

[0012] In the optical system of each embodiment, a lens group is a group of one or more lenses that are stationary or move during focusing or zooming, and the distance between adjacent lens groups changes during focusing or zooming. The lens group may include an aperture stop. The infinity end and the close-up end during focusing respectively indicate the states where the lens group that moves during focusing is located at both ends of the range in which it can move mechanically or controllably on the optical axis.

[0013] In Fig. 1, in the imaging optical system, the left side is the object side (front side) and the right side is the image side (rear side). If i is the order of the lens groups counted from the object side, Li indicates the i-th lens group. In the projection optical system, the object side is referred to as the enlargement conjugate side, and the image side is referred to as the reduction conjugate side.

[0014] The optical system of each embodiment has a first lens group L1 with positive refractive power (refractive power is the reciprocal of the focal length), a second lens group L2 with negative refractive power, and a rear lens group LR, arranged in order from the object side to the image side. The first lens group L1 has a first partial lens group L1A, a second partial lens group L1B, and a third partial lens group L1C, arranged in order from the object side to the image side. The first partial lens group L1A and the second partial lens group L1B are arranged with the largest air gap on the optical axis in the first lens group L1, and the second partial lens group L1B and the third partial lens group L1C are arranged with the second largest air gap on the optical axis in the optical system. The optical system of each embodiment is a single focus lens.

[0015] During focusing from infinity to a close distance, the second lens group L2 moves from the object side to the image side. The arrow labeled "Focus" indicates the direction of movement of the second lens group during focusing from infinity to a close distance.

[0016] SP is the aperture stop that determines (limits) the light flux at the maximum F-number (Fno). IP is the image plane. On the image plane IP, a photosensitive surface equivalent to the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film, is located.

[0017] The optical system of each embodiment having the above configuration satisfies the following condition when the focal length of the first lens group L1 is f1, the focal length of the first partial lens group L1A is f1A, and the focal length of the second partial lens group L1B is f1B.

[0018] 1.0≦f1A / f1≦≦2.0 (1) -0.6≦f1A / f1B<0 (2) The optical system of each embodiment has a configuration in which lens groups having positive, negative and positive refractive powers are arranged in order from the object side in order to shorten the total optical length (hereinafter referred to as the total lens length) and to satisfactorily correct various aberrations. The first lens group L1 effectively corrects spherical aberration, coma aberration and chromatic aberration (such as chromatic aberration of magnification). In addition, since the lens closer to the object side has a larger diameter, the number of lenses constituting the first partial lens group L1A is reduced in order to reduce the weight of the optical system, and a large number of lenses are arranged in the second partial lens group L1B and the third partial lens group L1C, thereby achieving both correction of spherical aberration and chromatic aberration and weight reduction. In addition, an aspherical lens made of a glass material with a high Abbe number and partial dispersion ratio is arranged in the third partial lens group L1C, which provides a strong correction effect against spherical aberration and chromatic aberration. This further reduces the number of lenses included in the first lens group L1, making it even smaller and lighter.

[0019] In addition, by using the second lens group L2, which has negative refractive power, as the focusing group, the weight of the focusing group is reduced. In particular, by effectively suppressing the occurrence of spherical aberration and axial chromatic aberration in the first lens group L1, the focusing group can be constructed from a single lens, enabling further weight reduction.

[0020] The condition of formula (1) indicates an appropriate range of the ratio between the focal length f1A of the first partial lens group L1A in the first lens group L1 and the focal length f1 of the first lens group L1, and is a condition that should be satisfied in order to ensure both compactness and high optical performance. When f1A / f1 exceeds the upper limit of formula (1), it is possible to suppress spherical aberration, etc., but it is not preferable because the refractive power of the first partial lens group L1A becomes too weak and it becomes difficult to reduce the size of the entire optical system. When f1A / f1 falls below the lower limit of formula (1), it is not preferable because the refractive power of the first partial lens group L1A becomes too strong and it becomes possible to reduce the size, but it is difficult to suppress spherical aberration, etc.

[0021] Formula (2) indicates an appropriate range of the ratio of the focal length f1A of the first partial lens group L1A to the focal length f1B of the second partial lens group L1B in the first lens group L1, and is a condition that should be satisfied in order to ensure both compactness and high optical performance. If f1A / f1B exceeds the upper limit of formula (2), it is possible to suppress spherical aberration, etc., but it is not preferable because the telephoto effect of the first partial lens group L1A and the second partial lens group L1B is weakened and it becomes difficult to reduce the size of the entire optical system. If f1A / f1B falls below the lower limit of formula (2), it is possible to reduce the size by strengthening the telephoto effect of the first partial lens group L1A and the second partial lens group L1B, but it is not preferable because it becomes difficult to suppress spherical aberration, etc.

[0022] It is more preferable to set the numerical ranges of the formulas (1) and (2) as follows:

[0023] 1.10≦f1A / f1≦1.95 (1a) -0.56≦f1A / f1B≦-0.05 (2a) It is more preferable to set the numerical ranges of the formulas (1) and (2) as follows:

[0024] 1.15≦f1A / f1≦1.90 (1b) -0.52≦f1A / f1B≦-0.10 (2b) By satisfying the conditions of formulas (1a) and (1b), it is possible to obtain a greater effect of suppressing spherical aberration and coma aberration while suppressing axial chromatic aberration, while satisfying the conditions of formulas (2a) and (2b), it is possible to obtain a greater effect of shortening the overall lens length while suppressing the occurrence of chromatic aberration.

[0025] As described above, by appropriately arranging and configuring each lens group and simultaneously satisfying the conditions of expressions (1) and (2), it is possible to realize a small, lightweight optical system that has a sufficient aperture ratio and is capable of satisfactorily correcting various aberrations, such as spherical aberration and chromatic aberration.

[0026] In addition to the conditions of formulas (1) and (2), it is preferable that the optical system of each embodiment satisfies at least one of the conditions of the following formulas (1) to (13). Hereinafter, the focal length of the optical system is denoted as f, and the focal length of the second lens group L2 is denoted as f2. The air distance on the optical axis between the first partial lens group L1A and the second partial lens group L1B in the first lens group L1 is denoted as D1AB, and the air distance on the optical axis between the second partial lens group L1B and the third partial lens group L1C is denoted as D1BC.

[0027] The total lens length, which is the total length of the optical system, is defined as LD. The total lens length is the distance on the optical axis from the lens surface closest to the object (the frontmost surface) in the optical system to the image surface IP. The sum of the air spaces D1AB and D1BC within the first lens group L1 is defined as D1Air, and the thickness of the first lens group L1 on the optical axis is defined as D1.

[0028] The refractive index at the d-line of the lens having positive refractive power arranged closest to the object in the first partial lens group L1C is nd1CP, and the Abbe number of the lens based on the d-line is νd1CP. The Abbe number based on the d-line is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are 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.

[0029] The maximum absolute value of the aspheric amount of the aspheric lens included in the first lens group L1 is DRMAX. The lens with the strongest positive refractive power among the lenses included in the first lens group L1 is GP, and the shape factor of the lens GP is SF1AP. The radius of curvature of the lens GP on the object side is GPR1, and the radius of curvature of the lens GP on the image side is GPR2. The aspheric amount and shape factor will be described later.

[0030] The back focus of the optical system when focused at infinity is sk. The back focus is the distance on the optical axis from the lens surface (last surface) closest to the image side of the optical system to the image surface IP. If a glass block (optical filter, prism, etc.) with no or very weak refractive power is placed between the optical system and the image surface IP, the back focus is calculated by converting the length of the glass block into air.

[0031] 0.30≦f1A / f≦0.75 (3) 1.3≦D1AB / D1BC≦7.0 (4) -0.95≦f2 / f1≦-0.40 (5) 0.5≦LD / f≦1.2 (6) 0.20≦f1 / f≦0.50 (7) 0.6≦D1Air / D1<1.0 (8) 1.30≦Nd1CP≦1.65 (9) 65.00≦νd1CP≦100.00 (10) 0.000 <DRMAX≦0.080 (11) -2.00≦(R2+R1) / (R2-R1)≦-0.08 (12) 0.05≦sk / LD≦0.24 (13) The aspheric amount will be explained with reference to Fig. 16. The aspheric amount DR is the difference in the optical axis direction between an arbitrary position X on a reference spherical surface, which is a spherical surface connecting the effective diameter position P on the aspheric surface of the lens and the surface vertex of the lens, and a position Xr on the aspheric surface at the same height as that position. The aspheric amount is expressed as DR=X-Xr as shown in Fig. 16. In each embodiment, the maximum absolute value of the aspheric amount of the aspheric lens is defined as DRMAX.

[0032] Furthermore, the shape factor SF1AP of the lens GP having the strongest positive refractive power among the lenses included in the first lens group L1 is defined by the following equation, where R1 is the radius of curvature of the lens surface on the object side of the lens GP and R2 is the radius of curvature of the lens surface on the image side of the lens GP.

[0033] SF1AP = (R2 + R1) / (R2 - R1) When the lens surface is aspheric, the radius of curvature is the base radius of the lens surface (the radius of the reference quadratic surface).

[0034] The condition of formula (3) indicates an appropriate range of the ratio between the focal length f1A of the first partial lens group L1A in the first lens group L1 and the focal length f of the entire optical system, and is a condition for achieving both compactness and high optical performance. When f1A / f exceeds the upper limit of formula (3), it is possible to suppress spherical aberration, etc., but it is not preferable because the refractive power of the first partial lens group L1A becomes too weak and it becomes difficult to reduce the size of the entire optical system. When f1A / f falls below the lower limit of formula (3), it is not preferable because the refractive power of the first partial lens group L1A becomes too strong and it becomes possible to reduce the size, but it is difficult to suppress spherical aberration, etc.

[0035] The condition of formula (4) shows an appropriate range of the ratio of the air gap D1AB between the first partial lens group L1A and the second partial lens group L1B in the first lens group L1 to the air gap D1BC between the second partial lens group L1B and the third partial lens group L1C, and is a condition for achieving both compactness and high optical performance. If D1AB / D1BC exceeds the upper limit of formula (4), the first partial lens group L1B is disposed on the image side, which allows compactness, but is not preferable because the height of the light beam incident on the first partial lens group L1B is low, making it difficult to suppress spherical aberration, etc. If D1AB / D1BC falls below the lower limit of formula (4), the first partial lens group L1B is disposed on the object side, which makes the height of the light beam incident on the first partial lens group L1B high. As a result, it is possible to suppress spherical aberration, etc., but is not preferable because it is difficult to compact the optical system.

[0036] The condition of formula (5) indicates an appropriate range of the focal lengths f1 and f2 of the first lens group L1 and the second lens group L2, and is a condition for achieving both compactness and high optical performance. When f2 / f1 exceeds the upper limit of formula (5), the telephoto effect becomes strong, and although it is possible to compact the optical system, it is undesirable because it becomes difficult to suppress chromatic aberration and the like. When f2 / f1 falls below the lower limit of formula (5), the telephoto effect becomes weak, and although it is possible to suppress chromatic aberration and the like, it is undesirable because it becomes difficult to compact the optical system.

[0037] Equation (6) indicates the appropriate range of the ratio between the total lens length LD and the focal length f of the entire optical system, and is a condition for achieving both compactness and high optical performance. If LD / f exceeds the upper limit of equation (6), the total lens length becomes long, which is effective in suppressing various aberrations such as spherical aberration, but it is undesirable because it makes it difficult to compact the optical system. If LD / f falls below the lower limit of equation (6), the total lens length becomes short, which makes it possible to compact the optical system, but it is undesirable because it makes it difficult to suppress various aberrations such as spherical aberration.

[0038] Equation (7) indicates an appropriate range of the ratio of the focal lengths f1 and f of the first lens group L1 and the entire optical system, and is a condition for achieving both compactness and high optical performance. When f1 / f exceeds the upper limit of equation (7), it is possible to suppress spherical aberration, etc., but it is undesirable because the refractive power of the first lens group L1 becomes weak and it becomes difficult to compact the optical system. When f1 / f falls below the lower limit of equation (7), it is undesirable because the refractive power of the first lens group L1 becomes strong and it becomes possible to compact the optical system, but it is undesirable because it becomes difficult to suppress spherical aberration, etc.

[0039] Equation (8) indicates an appropriate range of the ratio of the sum of the air gaps (D1AB+D1BC)D1Air in the first lens group L1 to the thickness D1 of the first lens group L1, and is a condition for achieving both weight reduction and high optical performance. If D1Air / D1 exceeds the upper limit of equation (8), weight reduction can be expected by reducing the number of lenses, but it is not preferable because it becomes difficult to suppress various aberrations such as spherical aberration and chromatic aberration. Also, if D1Air / D1 falls below the lower limit of equation (8), it is not preferable because it becomes difficult to suppress various aberrations such as spherical aberration and chromatic aberration by increasing the number of lenses.

[0040] Equation (9) indicates an appropriate range of the refractive index nd1CP of the positive lens closest to the object in the first partial lens group L1C in the first lens group L1, and is a condition for achieving compactness while suppressing spherical aberration and coma aberration well. If the refractive index of the material of the positive lens becomes high so that Nd1CP exceeds the upper limit of equation (9), it is advantageous for correcting various aberrations, but the Abbe number becomes insufficient, making it difficult to correct axial chromatic aberration and lateral chromatic aberration, especially secondary spectrum. As a result, in order to ensure the desired optical performance, it is undesirable because it leads to an increase in the size of the entire system and an increase in the number of lenses. If the refractive index of the material of the positive lens becomes low so that Nd1CP falls below the lower limit of equation (9), it is advantageous for correcting axial chromatic aberration, but it is undesirable because it makes it difficult to correct field curvature and distortion aberration.

[0041] Equation (10) indicates an appropriate range of the Abbe number νd1CP of the positive lens closest to the object in the first partial lens unit L1C in the first lens unit L1, and is a condition for achieving compactness while effectively suppressing spherical aberration and coma aberration. If νd1CP exceeds the upper limit of equation (10), it is advantageous for correcting axial chromatic aberration, but it is undesirable because it becomes difficult to ensure the necessary refractive power for the glass material. If νd1CP falls below the lower limit of equation (10), it is undesirable because it becomes difficult to achieve first-order achromatization of axial chromatic aberration and lateral chromatic aberration.

[0042] The condition of formula (11) indicates an appropriate range of the maximum aspheric amount (absolute value) DRMAX of the aspheric lens included in the rear lens group LR. If DRMAX exceeds the upper limit of formula (11), the aspheric amount becomes too large, which is undesirable because it becomes difficult to manufacture the aspheric lens. Also, if DRMAX falls below the lower limit of formula (11), the aspheric amount becomes too small, which is undesirable because it becomes difficult to correct spherical aberration and coma aberration.

[0043] Equation (12) indicates an appropriate range of the shape factor in which the refractive index of the lens with the strongest positive refractive power among the one or more lenses included in the first partial lens group LIA in the first lens group L1 is maximized. This condition is for effectively correcting spherical aberration and coma aberration in the wide-angle range. If the shape factor exceeds the upper limit of equation (12), it becomes difficult to effectively correct spherical aberration, and coma aberration generated when the lens is decentered increases, which is undesirable. If the shape factor falls below the lower limit of equation (12), spherical aberration and axial chromatic aberration increase, which is undesirable.

[0044] Equation (13) shows the appropriate range of the ratio of the back focus sk when focusing at infinity to the total lens length LD. If sk / LD exceeds the upper limit of equation (13), the back focus relative to the total lens length becomes too long, which is undesirable because it is difficult to secure a space for appropriately arranging the lens to suppress the occurrence of various aberrations. Also, if sk / LD falls below the lower limit of equation (13), the back focus relative to the total lens length becomes too short, which is undesirable because it is difficult to arrange the mechanical members for mounting the optical system (interchangeable lens, etc.) to the imaging device.

[0045] It is more preferable to set the numerical ranges of the formulas (3) to (13) as follows:

[0046] 0.35≦f1A / f≦0.70 (3a) 1.1≦D1AB / D1BC≦6.5 (4a) -0.90≦f2 / f1≦-0.45 (5a) 0.55≦LD / f≦1.00 (6a) 0.25≦f1 / f≦0.45 (7a) 0.65≦D1Air / D1≦0.97 (8a) 1.35≦Nd1CP≦1.60 (9a) 70.00≦νd1CP≦97.00 (10a) 0.01≦DRMAX≦0.07 (11a) -1.90≦(R2+R1) / (R2-R1)≦-0.9 (12a) 0.06≦sk / LD≦0.22 (13a) It is more preferable to set the numerical ranges of the formulas (3) to (13) as follows:

[0047] 0.385≦f1A / f≦0.680 (3b) 1.25≦D1AB / D1BC≦6.00 (4b) -0.85≦f2 / f1≦-0.50 (5b) 0.625≦LD / f≦0.850 (6b) 0.30≦f1 / f≦0.42 (7b) 0.70≦D1Air / D1≦0.93 (8b) 1.4≦Nd1CP≦1.55 (9b) 72.00≦νd1CP≦95.00 (10b) 0.020≦DRMAX≦0.062 (11b) -1.80≦(R2+R1) / (R2-R1)≦-0.10 (12b) 0.08≦sk / LD≦0.20 (13b) Furthermore, it is preferable that the optical system of each embodiment satisfies at least one of the following conditions:

[0048] In the first lens group L1, it is preferable that the first partial lens group L1A has a positive refractive power, the second partial lens group L1B has a negative refractive power, and the third partial lens group L1C has a positive refractive power. This results in a positive and negative lens group arrangement from the object side, a so-called telephoto arrangement, which makes it possible to reduce the size of the entire optical system and reduce chromatic aberration. In addition, by arranging the positive first partial lens group L1C, it becomes possible to appropriately set the positive refractive power of the first partial lens group L1A.

[0049] The second lens subgroup L1B is preferably composed of one negative lens and two positive lenses. This allows for good correction of spherical aberration and coma while suppressing axial chromatic aberration. In addition, by configuring the second lens subgroup L1B with three lens groups, the freedom of glass material selection when performing achromatization in the second lens subgroup L1B increases, making it easier to achieve both correction of various aberrations and achromatization within the group.

[0050] It is preferable that the third partial lens group L1C has an aspherical lens. By disposing the aspherical lens in the first lens group L1, it is possible to reduce the number of lenses in the first lens group L1 while satisfactorily correcting spherical aberration and coma aberration, thereby making it possible to reduce the weight of the optical system. In addition, by disposing the aspherical lens in the third partial lens group L1C, it is possible to reduce the size of the aspherical lens, making it easier to manufacture. Furthermore, it is preferable that the aspherical lens is disposed closest to the object in the third partial lens group L1C.

[0051] It is preferable that the second lens group L2 as the focusing group is composed of one negative lens, which allows the focusing group to be lightweight and allows the focusing group to move faster during focusing.

[0052] It is preferable that the lens closest to the image side in the rear lens group has a convex surface on the image side (a surface that is convex toward the image side). This makes it relatively easy to ensure the back focus and also makes it possible to suppress the collection of unwanted light (ghosts) caused by the image sensor.

[0053] In each embodiment, a protective glass for protecting the lens closest to the object side of the optical system may be arranged on the object side of the first lens group L1. Furthermore, a protective glass or a low-pass filter may be arranged between the lens closest to the image side of the optical system and the image surface IP. Members with no or very weak refractive power, such as protective glass and a low-pass filter arranged on the most object side and the most image side of the optical system, are not treated as lenses constituting the optical system. Note that "very weak refractive power" refers to, for example, a member whose absolute value of the focal length is 5 times or more the focal length of the entire optical system.

[0054] It is preferable that the aperture diaphragm SP is disposed closest to the object in the second lens unit L2, which makes it easier to achieve both a small diameter of the aperture diaphragm SP and a sufficient amount of light at the peripheral angles of view.

[0055] It is preferable that the lens adjacent to the aperture stop SP on the image side is a cemented lens of a positive lens and a negative lens, which makes it easier to correct both the curvature of field and the chromatic aberration of magnification.

[0056] The whole or a part of any of the lens groups in the optical system may be moved as an anti-vibration group in a direction including a component perpendicular to the optical axis to reduce image blur caused by camera shake or the like. This movement includes rotation about a point on the optical axis. In this case, it is particularly preferable to use a part of the rear lens group LR as the anti-vibration group. There is no particular restriction on the number or shape of the lenses in the anti-vibration group, but it is preferable that the anti-vibration group has negative refractive power. It is also preferable that the anti-vibration group has at least two negative lenses.

[0057] It is preferable that the optical system does not include a diffractive optical element. If the optical system includes a diffractive optical element, this is advantageous for correcting chromatic aberration, but is not preferable because the diffractive optical element generates diffraction flare.

[0058] Below, a specific description will be given of Examples 1 to 7. In the following description, the arrangement of the lens groups and lenses is from the object side to the image side. EXAMPLES

[0059] The optical system of the first embodiment shown in FIG. 1 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a positive refractive power.

[0060] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0061] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0062] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a convex surface.

[0063] Numerical Example 1 corresponding to Example 1 is shown after Example 7. In Numerical Example 1, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air space (mm) between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νdi is the Abbe number based on the d-line of the optical material between the i-th and (i+1)-th surfaces.

[0064] The half angle of view indicates the half angle of view (°) by paraxial calculation. BF is the back focus (mm) and corresponds to sk in formula (13). The total lens length corresponds to LD in formula (13).

[0065] An "*" next to a surface number means that the surface has an aspheric shape. An aspheric shape is expressed by the following formula, where X is the displacement from the apex of the surface in the optical axis direction, H is the height from the optical axis in a direction perpendicular to the optical axis, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, and A8 are aspheric coefficients. The conic constant and the aspheric coefficients "e±x" are multiplied by 10 ±x means...

[0066]

number

[0067] Values ​​corresponding to formulas (1) to (13) in Numerical Example 1 are summarized in Table 1. Note that (R2+R1) / (R2-R1) in formula (12) is recorded as SF1AP in Table 1. Numerical Example 1 satisfies all of the conditions in formulas (1) to (13).

[0068] FIG. 2 shows longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system of Numerical Example 1 when focused at infinity. In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S indicates the astigmatism at the sagittal image plane, and the dashed line M indicates the astigmatism at the meridional image plane. The distortion diagram shows the distortion at the d-line. The chromatic aberration diagram shows the chromatic aberration of magnification at the g-line. ω is the half angle of view (°).

[0069] The above-mentioned explanations regarding the numerical examples and longitudinal aberration diagrams also apply to other numerical examples described later. EXAMPLES

[0070] The optical system of the second embodiment shown in FIG. 3 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a positive refractive power.

[0071] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of a cemented lens in which a positive lens and a negative lens are cemented together, and one positive lens. The third partial lens group L1C is composed of a positive lens with aspherical surfaces on both sides, and a cemented lens in which a negative lens and a positive lens are cemented together.

[0072] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0073] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a convex surface.

[0074] Numerical Example 2 corresponding to Example 2 will be shown after Example 7. Values ​​corresponding to formulas (1) to (13) in Numerical Example 2 are summarized in Table 1. Numerical Example 2 satisfies all of the conditions in formulas (1) to (13).

[0075] FIG. 4 shows longitudinal aberration of the optical system of Numerical Example 2 when focused at infinity. EXAMPLES

[0076] The optical system of Example 3 shown in FIG. 5 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a negative refractive power.

[0077] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0078] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0079] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a convex surface.

[0080] Numerical Example 3 corresponding to Example 3 will be shown after Example 7. Values ​​corresponding to formulas (1) to (13) in Numerical Example 3 are summarized in Table 1. Numerical Example 3 satisfies all of the conditions in formulas (1) to (13).

[0081] FIG. 6 shows longitudinal aberration of the optical system of Numerical Example 3 when focused at infinity. EXAMPLES

[0082] The optical system of Example 4 shown in FIG. 7 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a negative refractive power.

[0083] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0084] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0085] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a concave surface.

[0086] Numerical Example 4 corresponding to Example 4 will be shown after Example 7. Values ​​corresponding to formulas (1) to (13) in Numerical Example 4 are summarized in Table 1. Numerical Example 4 satisfies all of the conditions in formulas (1) to (13).

[0087] FIG. 8 shows longitudinal aberration of the optical system of Numerical Example 4 when focused at infinity. EXAMPLES

[0088] The optical system of Example 5 shown in FIG. 9 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a negative refractive power.

[0089] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0090] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0091] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a convex surface.

[0092] Numerical Example 5 corresponding to Example 5 is shown after Example 7. Values ​​corresponding to formulas (1) to (13) in Numerical Example 5 are summarized in Table 1. Numerical Example 5 satisfies all of the conditions in formulas (1) to (13).

[0093] FIG. 10 shows longitudinal aberration of the optical system of Numerical Example 5 when focused at infinity. EXAMPLES

[0094] The optical system of Example 6 shown in FIG. 11 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a negative refractive power.

[0095] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0096] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0097] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a positive lens and a negative lens are cemented together, and the lens surface closest to the image side is a concave surface.

[0098] Numerical Example 6 corresponding to Example 6 will be shown after Example 7. Values ​​corresponding to formulas (1) to (13) in Numerical Example 6 are summarized in Table 1. Numerical Example 6 satisfies all of the conditions in formulas (1) to (13).

[0099] FIG. 12 shows longitudinal aberration of the optical system of Numerical Example 6 when focused at infinity. EXAMPLES

[0100] The optical system of Example 7 shown in FIG. 13 is made up of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, and a rear lens unit LR having a negative refractive power.

[0101] The first lens group L1 is composed of a first partial lens group L1A with positive refractive power, a second partial lens group L1B with negative refractive power, and a third partial lens group L1C with positive refractive power. The second partial lens group L1B is composed of one positive lens and a cemented lens in which a negative lens and a positive lens are cemented together. The third partial lens group L1C is composed of one positive lens with aspherical surfaces on both sides.

[0102] The second lens group L2 is composed of an aperture stop SP arranged closest to the object side, and one negative lens arranged on the image side thereof.

[0103] In the rear lens group LR, the lens closest to the image side is a cemented lens in which a negative lens and a positive lens are cemented together, and the lens surface closest to the image side is a convex surface.

[0104] Following this embodiment, Numerical Example 7 corresponding to this embodiment will be shown. Values ​​corresponding to formulas (1) to (13) in Numerical Example 7 are summarized in Table 1. Numerical Example 7 satisfies all of the conditions in formulas (1) to (13).

[0105] FIG. 14 shows longitudinal aberration of the optical system of Numerical Example 7 when focused at infinity.

[0106] [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1 138.407 10.73 1.59349 67.0 2 2654.662 80.97 3 75.053 12.27 1.43875 94.7 4 -135.148 0.87 5 -128.318 2.50 1.61340 44.3 6 38.286 0.05 7 38.229 10.39 1.43875 94.7 8 234.203 39.50 9* 89.902 6.53 1.49700 81.5 10* -141.385 3.73 11 (Aperture) ∞ (Variable) 12 427.087 1.30 1.72916 54.7 13 58.076 (variable) 14 123.001 4.28 1.80810 22.8 15 -48.164 1.50 1.63930 44.9 16 62.467 8.12 17 73.025 3.19 1.72047 34.7 18 -98.066 1.50 1.52841 76.5 19 41.109 2.35 20 -92.421 1.50 1.72916 54.7 21 63.599 2.14 22 85.669 2.57 1.59551 39.2 23 -1173.093 1.30 24 132.455 4.55 1.68893 31.1 25 -34.098 1.80 1.92286 20.9 26 2362.365 23.25 27 87.936 8.56 1.73800 32.3 28 -54.431 1.80 1.92286 20.9 29 -161.546 (variable) Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.38789e-06 A 6= 4.93152e-10 A 8= 1.04009e-12 Side 10 K = 0.00000e+00 A 4=-1.53131e-06 A 6= 1.42620e-09 A 8= 5.66619e-14 Various data Focal length 388.73 F-number: 4.08 Half angle of view (°) 3.19 Image height 21.64 Lens length 310.74 BF 55.06 d11 2.00 d13 16.45 d29 55.06 Lens Group Data Group starting plane focal length 1 1 145.31 2 12 -92.32 3 14 993.19 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1 121.224 9.95 1.59349 67.0 2 617.686 101.59 3 84.722 10.64 1.43875 94.7 4 -100.890 2.50 1.73800 32.3 5 65.208 0.02 6 44.339 8.29 1.43875 94.7 7 263.256 17.46 8* 58.770 8.52 1.43875 94.7 9* -61.943 0.02 10 -82.556 1.50 1.88100 40.1 11 46.947 8.16 1.77830 23.9 12 -165.105 4.11 13 (Aperture) ∞ (Variable) 14 479.548 1.30 1.53775 74.7 15 38.920 (variable) 16 34.650 5.31 1.58144 40.8 17 -81.081 1.50 1.48749 70.2 18 29.016 2.92 19 82.260 3.61 1.72047 34.7 20 -71.571 1.50 1.52841 76.5 21 44.399 2.69 22 -77.374 1.50 1.72916 54.7 23 66.797 2.08 24 58.807 5.29 1.78880 28.4 25 -47.521 1.80 1.92286 20.9 26 245.871 18.91 27 126.124 8.86 1.73800 32.3 28 -37.407 1.80 1.92286 20.9 29 -99.229 (variable) Image plane ∞ Aspheric Data Side 8 K = 0.00000e+00 A 4=-8.29406e-07 A 6=-2.98580e-10 9th page K = 0.00000e+00 A 4= 1.08069e-06 A 6= 3.34995e-10 Various data Focal length 389.12 F-number: 4.08 Half angle of view (°) 3.18 Image height 21.64 Lens total length 310.56 BF 60.09 d13 2.00 d15 16.62 d29 60.09 Lens Group Data Group starting plane focal length 1 1 155.61 2 14 -78.85 3 16 501.29 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1 132.665 8.52 1.59349 67.0 2 2107.440 66.58 3 81.063 10.57 1.43875 94.7 4 -170.759 2.79 5 -144.718 2.50 1.61340 44.3 6 41.583 0.05 7 41.532 8.86 1.43875 94.7 8 214.811 50.00 9* 167.363 5.60 1.43875 94.7 10* -92.989 3.26 11 (Aperture) ∞ (Variable) 12 204.486 1.30 1.55200 70.7 13 51.773 (variable) 14 120.972 4.58 1.80518 25.4 15 -42.301 1.50 1.79952 42.2 16 105.985 14.90 17 77.053 3.16 1.72047 34.7 18 -73.504 1.50 1.53775 74.7 19 44.508 3.63 20 -77.141 1.50 1.72916 54.7 21 69.069 1.98 22 74.389 2.74 1.62004 36.3 23 -285.860 1.30 24 81.067 3.09 1.65412 39.7 25 -69.459 1.80 1.92286 20.9 26 138.431 48.76 27 82.964 5.36 1.67300 38.3 28 -155.295 1.80 1.92286 20.9 29 -2564.862 (variable) Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.53309e-06 A 6=-2.58260e-10 Side 10 K = 0.00000e+00 A 4=-1.34677e-06 Various data Focal length 479.13 F-number: 5.65 Half angle of view (°) 2.59 Image height 21.64 Lens total length 331.00 BF 55.35 d11 2.00 d13 16.02 d29 55.35 Lens Group Data Group starting plane focal length 1 1 160.43 2 12 -125.97 3 14 -1443.93 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1 119.231 12.36 1.59349 67.0 2 859.310 69.59 3 70.151 12.13 1.43875 94.7 4 -461.124 0.53 5 -329.909 2.50 1.61340 44.3 6 37.506 0.05 7 37.459 11.98 1.43875 94.7 8 158.144 49.36 9* 428.674 4.78 1.49700 81.5 10* -143.738 3.79 11 (Aperture) ∞ (Variable) 12 231.481 1.30 1.74100 52.6 13 69.656 (variable) 14 -232.122 4.64 1.80518 25.4 15 -31.586 1.50 1.91082 35.2 16 -124.083 2.00 17 -1807.348 3.29 1.80810 22.8 18 -61.899 1.50 1.72916 54.7 19 73.075 1.94 20 -60.615 1.50 1.55200 70.7 21 1269.310 2.03 22 52.078 3.26 1.48749 70.2 23 336.184 64.76 24 177.383 8.95 1.66680 33.0 25 -32.902 1.50 1.92286 20.9 26 -197.247 0.20 27 81.419 10.41 1.65412 39.7 28 -37.449 1.80 1.59282 68.6 29 102.430 (variable) Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.39739e-06 A 6= 1.88178e-09 A 8= 3.82317e-12 Side 10 K = 0.00000e+00 A 4=-2.61242e-06 A 6= 2.50565e-09 A 8= 3.02575e-12 Various data Focal length 583.80 F-number: 5.65 Half angle of view (°) 2.12 Image height 21.64 Lens length 366.23 BF 67.52 d11 2.00 d13 19.08 d29 67.52 Lens Group Data Group starting plane focal length 1 1 187.70 2 12 -134.93 3 14 -595.54 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd 1 203.414 5.08 1.48749 70.2 2 405.216 1.00 3 132.587 12.21 1.43387 95.1 4 8940.857 72.63 5 86.012 8.93 1.43875 94.7 6 -1957.221 0.87 7 -468.482 2.50 1.61340 44.3 8 43.356 0.05 9 43.329 9.58 1.49700 81.5 10 139.785 55.47 11* 275.586 4.78 1.49700 81.5 12* -159.475 3.88 13 (Aperture) ∞ (Variable) 14 370.153 1.30 1.48749 70.2 15 55.031 (variable) 16 -143.016 4.13 1.76182 26.5 17 -33.026 1.50 1.91082 35.2 18 -83.255 2.00 19 260.012 2.72 1.80810 22.8 20 -84.289 1.50 1.72916 54.7 21 59.132 2.00 22 -61.057 1.50 1.55200 70.7 23 330.747 2.08 24 53.630 2.83 1.48749 70.2 25 3212.424 58.10 26 313.855 8.29 1.72825 28.5 27 -29.387 1.50 1.92286 20.9 28 -930.109 4.29 29 135.569 10.43 1.65412 39.7 30 -31.386 1.80 1.59282 68.6 31 -839.737 (variable) Image plane ∞ Aspheric Data Page 11 K = 0.00000e+00 A 4=-2.29610e-06 A 6=-5.34837e-10 A 8= 9.93691e-14 Side 12 K = 0.00000e+00 A 4=-2.27700e-06 A 6=-2.15977e-10 A 8= 1.36594e-13 Various data Focal length 584.53 F-number: 5.65 Half angle of view (°) 2.12 Image height 21.64 Lens total length 365.61 BF 60.55 d13 2.00 d15 20.10 d31 60.55 Lens Group Data Group starting plane focal length 1 1 192.73 2 14 -132.78 3 16 -883.66 [Numerical example 6] Unit: mm Surface Data Surface number rd nd νd 1 134.242 9.20 1.61800 63.4 2 1314.075 74.00 3 89.773 9.82 1.43875 94.7 4 -218.240 2.51 5 -181.652 2.50 1.65412 39.7 6 44.867 0.05 7 44.707 8.80 1.49700 81.5 8 207.287 57.67 9* 347.816 3.48 1.55032 75.5 10* -123.287 3.62 11 (Aperture) ∞ (Variable) 12 242.034 1.30 1.51633 64.1 13 58.445 (variable) 14 -599.803 4.40 1.85478 24.8 15 -32.731 1.50 1.95375 32.3 16 -199.504 2.00 17 177.666 3.09 1.80810 22.8 18 -82.435 1.50 1.74100 52.6 19 61.999 2.97 20 -66.219 1.50 1.55200 70.7 21 298.123 2.08 22 47.661 3.19 1.48749 70.2 23 1188.446 61.13 24 169.445 7.23 1.68893 31.1 25 -28.142 1.50 1.92286 20.9 26 -782.884 0.35 27 63.393 8.63 1.65412 39.7 28 -32.047 1.80 1.59282 68.6 29 63.322 (variable) Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.48098e-06 A 6=-8.95562e-10 A 8= 2.84884e-13 Side 10 K = 0.00000e+00 A 4=-1.39622e-06 A 6=-8.34937e-10 A 8= 4.87796e-13 Various data Focal length 584.06 F-number 6.40 Half angle of view (°) 2.12 Image height 21.64 Lens total length 366.13 BF 69.91 d11 2.00 d13 18.41 d29 69.91 Lens Group Data Group starting plane focal length 1 1 185.68 2 12 -149.59 3 14 -165.54 [Numerical example 7] Unit: mm Surface Data Surface number rd nd νd 1 226.622 8.41 1.59349 67.0 2 831.115 240.34 3 87.828 11.24 1.43875 94.7 4 -712.862 0.94 5 -312.895 2.50 1.61340 44.3 6 62.670 0.05 7 61.068 9.03 1.43875 94.7 8 281.341 76.82 9* 172.010 4.14 1.43875 94.7 10* -164.740 3.73 11 (Aperture) ∞ (Variable) 12 181.320 1.30 1.69895 30.1 13 64.810 (variable) 14 162.527 5.14 1.69895 30.1 15 -43.999 1.50 1.91082 35.2 16 -184.598 2.00 17 595.345 2.87 1.80810 22.8 18 -97.125 1.50 1.72916 54.7 19 62.351 2.80 20 -69.032 1.50 1.55200 70.7 21 446.782 2.07 22 60.561 4.72 1.48749 70.2 23 -131.715 90.50 24 68.400 11.19 1.85478 24.8 25 -33.210 1.50 1.92286 20.9 26 74.621 8.74 27 -37.445 1.80 1.49700 81.5 28 55.303 9.08 1.65412 39.7 29 -57.050 (variable) Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.06341e-06 A 6= 2.00501e-10 A 8= 4.39704e-13 Side 10 K = 0.00000e+00 A 4=-9.60571e-07 A 6= 4.27979e-10 A 8= 2.91278e-13 Various data Focal length 789.38 F-number 6.40 Half angle of view (°) 1.57 Image height 21.64 Lens total length 600.18 BF 62.06 d11 2.00 d13 30.68 d29 62.06 Lens Group Data Group starting plane focal length 1 1 282.01 2 12 -144.97 3 14 -2505.05

[0107] [Table 1]

[0108] [Imaging device] 15 shows a digital still camera 10 as an imaging device using the optical system of each of the above-mentioned embodiments as an imaging optical system. Reference numeral 13 denotes a camera body, and reference numeral 11 denotes an imaging optical system constituted by any of the optical systems of embodiments 1 to 7. Reference numeral 12 denotes a solid-state imaging element such as a CCD sensor or a CMOS sensor that is built into the camera body 10 and captures an optical image (subject image) formed by the imaging optical system 11.

[0109] By using the optical system of each embodiment, it is possible to obtain a small-sized camera that is bright and capable of acquiring images of good quality.

[0110] The camera may be a single-lens reflex camera having a quick-turn mirror, or a mirrorless camera having no quick-turn mirror. As described above, the zoom lenses of Examples 1 to 7 can be used in various imaging devices such as video cameras, broadcast cameras, and surveillance cameras.

[0111] The above embodiment includes the following configurations.

[0112] (Configuration 1) An optical system including a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a rear lens group, which are arranged in this order from the object side to the image side, the first lens group has a first partial lens group, a second partial lens group, and a third partial lens group, which are arranged in this order from the object side to the image side, and between the first partial lens group and the second partial lens group, there is a maximum air gap on the optical axis in the first lens group, and between the second partial lens group and the third partial lens group, there is a second largest air gap on the optical axis in the first lens group, The second lens group L2 moves during focusing, When the focal length of the first lens group is f1, the focal length of the first partial lens group is f1A, and the focal length of the second partial lens group is f1B, 1.0≦f1A / f1≦2.0 -0.6≦f1A / f1B<0 An optical system characterized by satisfying the following conditions. (Configuration 2) When the focal length of the optical system is f, 0.30≦f1A / f≦0.75 2. The optical system according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the air gap between the first partial lens group and the second partial lens group is defined as D1AB, and the air gap between the second partial lens group and the third partial lens group is defined as D1BC, 1.3≦D1AB / D1BC≦7.0 3. The optical system according to configuration 1 or 2, which satisfies the following condition: (Configuration 4) The focal length of the second lens group L2 is f2.

[0113] -0.95≦f2 / f1≦-0.40 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the total optical length of the optical system is LD and the focal length of the optical system is f, 0.5≦LD / f≦1.2 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 optical system is f, 0.20≦f1 / f≦0.50 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the air distance between the first partial lens group and the second partial lens group is D1AB, the air distance between the second partial lens group and the third partial lens group is D1BC, the sum of the air distances D1AB and D1BC is D1Air, and the thickness of the first lens group on the optical axis is D1, 0.6≦D1Air / D1<1.0 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When a positive lens is disposed closest to the object side in the third lens subgroup and the refractive index of the positive lens at the d-line is nd1CP, 1.30≦Nd1CP≦1.65 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) When a positive lens is disposed closest to the object side in the third lens subgroup and the Abbe number of the positive lens based on the d-line is νd1CP, 65.00≦νd1CP≦90.00 9. The optical system according to any one of configurations 1 to 8, which satisfies the following condition: (Configuration 10) When the third lens group includes a lens having an aspheric surface, and the absolute value of the maximum aspheric amount of the aspheric surface is DRMAX, 0.000 <DRMAX≦0.080 10. The optical system according to any one of configurations 1 to 9, which satisfies the following condition: (Configuration 11) The focal length of the lens is fL, the radius of curvature of the lens surface on the object side of the lens is R1, the radius of curvature of the lens surface on the image side of the lens is R2, and a sign function sgn that takes +1 when the focal length fL is a positive value and takes -1 when the focal length fL is a negative value is sgn. The shape factor of the lens is expressed as follows: SF = sgn(fL) × (R2 + R1) / (R2 - R1) year, When the shape factor of the lens having the strongest positive refractive power among the one or more lenses included in the first lens group is SF1AP, -2.00≦SF1AP≦-0.08 11. The optical system according to any one of configurations 1 to 10, which satisfies the following condition: (Configuration 12) When the back focus of the optical system is sk and the total optical length of the optical system is LD, 0.05≦sk / LD≦0.24 12. The optical system according to any one of configurations 1 to 11, characterized in that the following condition is satisfied: (Configuration 13) The optical system described in any one of configurations 1 to 12, characterized in that the first partial lens group has positive refractive power, the second partial lens group has negative refractive power, and the third partial lens group has positive refractive power. (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the second partial lens group is composed of one negative lens and two positive lenses. (Configuration 15) The optical system according to any one of configurations 1 to 14, wherein the third partial lens group has an aspheric lens closest to the image side. (Configuration 16) The optical system according to any one of configurations 1 to 15, wherein the second lens group L2 is composed of one negative lens. (Configuration 17) 17. The optical system according to any one of configurations 1 to 16, wherein the image-side lens surface of the lens closest to the image side in the rear lens group is a surface having a convex shape facing the image side. (Configuration 18) 18. The optical system according to any one of configurations 1 to 17, wherein the second lens group has an aperture stop closest to the object side. (Configuration 19) 19. The optical system according to configuration 18, wherein the lens adjacent to the aperture stop on the image side is a cemented lens of a positive lens and a negative lens. (Configuration 20) 20. The optical system according to any one of configurations 1 to 19, wherein the rear lens group has a positive or negative refractive power. (Configuration 21) An optical system according to any one of configurations 1 to 20; and an image sensor for capturing an image of a subject through the optical system.

[0114] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0115] L1 First lens group L2 Second lens group LR rear lens group L1A First lens group L1B Second lens group L1C 3rd lens group

Claims

1. An optical system consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, and a rear lens group, arranged in order from the object side to the image side, The first lens group comprises a first partial lens group, a second partial lens group, and a third partial lens group, arranged in order from the object side to the image side, wherein there is the largest air gap on the optical axis within the first lens group between the first partial lens group and the second partial lens group, and there is the second largest air gap on the optical axis within the first lens group between the second partial lens group and the third partial lens group. The second lens group L2 moves during focusing. When the focal length of the first lens group is f1, the focal length of the first partial lens group is f1A, the focal length of the second partial lens group is f1B, the total optical length of the optical system is LD, and the focal length of the optical system is f, 1.0 ≤ f1A / f1 ≤ 2.0 -0.6≦f1A / f1B<0 0.5 ≤ LD / f ≤ 1.0 An optical system characterized by satisfying the following conditions.

2. When the focal length of the optical system is f, 0.30 ≤ f1A / f ≤ 0.75 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When the air gap between the first partial lens group and the second partial lens group is D1AB, and the air gap between the second partial lens group and the third partial lens group is D1BC, 1.3 ≤ D1AB / D1BC ≤ 7.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. When the focal length of the second lens group L2 is f2, -0.95 ≤ f² / f¹ ≤ -0.40 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. When the focal length of the optical system is f, 0.20 ≤ f1 / f ≤ 0.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. When the air gap between the first and second partial lens groups is D1AB, the air gap between the second and third partial lens groups is D1BC, the sum of the air gaps D1AB and D1BC is D1Air, and the thickness of the first lens group along the optical axis is D1, 0.6≦D1Air / D1<1.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When the positive lens is positioned closest to the object in the third partial lens group, and the refractive index of the positive lens at the d-line is Nd1CP, 1.30 ≤ Nd1CP ≤ 1.65 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When the positive lens is positioned closest to the object in the third sublens group, and the Abbe number with respect to the d-line of the positive lens is νd1CP, 65.00 ≤ νd1CP ≤ 90.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. The third lens group includes a lens having an aspherical surface, and when DRMAX is the absolute value of the maximum aspherical amount of the aspherical surface, 0.000 < DRMAX ≤ 0.080 The optical system according to claim 1, characterized in that it satisfies the following conditions.

10. When one or more lenses included in the first lens group have the strongest positive refractive power, and the radius of curvature of the lens surface on the object side is R1, and the radius of curvature of the lens surface on the image side is R2, -2.00≦(R2+R1) / (R2-R1)≦-0.08 The optical system according to claim 1, characterized in that it satisfies the following conditions.

11. When the optical system is in focus at infinity, the back focus of the optical system is sk, and the total optical length of the optical system is LD. 0.05 ≤ sk / LD ≤ 0.24 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. The optical system according to claim 1, characterized in that the first partial lens group has a positive refractive power, the second partial lens group has a negative refractive power, and the third partial lens group has a positive refractive power.

13. The optical system according to claim 1, characterized in that the second partial lens group comprises one negative lens and two positive lenses.

14. The optical system according to claim 1, characterized in that the third partial lens group has an aspherical lens on the image side.

15. The optical system according to claim 1, characterized in that the second lens group L2 consists of a single negative lens.

16. The optical system according to claim 1, characterized in that the image-side lens surface of the lens closest to the image in the rear lens group is a convex surface toward the image side.

17. The optical system according to claim 1, characterized in that the second lens group has an aperture diaphragm closest to the object.

18. The optical system according to claim 1, characterized in that the lens adjacent to the aperture diaphragm on the image side is a cemented lens of a positive lens and a negative lens.

19. The optical system according to claim 1, characterized in that the rear lens group has a positive or negative refractive power.

20. An optical system according to any one of claims 1 to 19, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

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