Zoom optical system and optical device

Abstract

To provide a zoom optical system which is compact and bright and offers good optical performance.SOLUTION: A zoom optical system ZL provided herein consists of a first lens group G1 having positive refractive power and a rear group GR comprising multiple lens groups, and is configured such that a distance between adjacent lens groups changes while zooming. The multiple lens groups of the rear group GR include a second lens group G2 having positive refractive power disposed on the most object side in the rear group GR. The zoom lens satisfies the following conditional expressions: 0.15<f2 / f1<0.80, 1.00<(L1r2+L1r1) / (L1r2-L1r1)<2.50, 1.50<(LEr2+LEr1) / (LEr2-LEr1)<3.00.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a variable magnification optical system and an optical instrument. [Background technology]

[0002] Conventionally, variable magnification optical systems suitable for photo cameras, electronic still cameras, video cameras, etc. have been proposed (for example, see Patent Document 1). In such variable magnification optical systems, it is difficult to obtain bright and good optical performance while making them compact. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-132675 A Summary of the Invention

[0004] A variable magnification optical system according to the present invention comprises, arranged in order from the object side along an optical axis, a first lens group having positive refractive power and a rear group having a plurality of lens groups, wherein the spacing between adjacent lens groups changes during magnification variation, and the plurality of lens groups of the rear group include a second lens group having positive refractive power that is arranged closest to the object side of the rear group, and satisfies the following conditional expression: 0.15 <f2 / f1<0.80 1.00<(L1r2+L1r1) / (L1r2-L1r1)<2.50 1.50<(LEr2+LEr1) / (LEr2-LEr1)<3.00 where f1 is the focal length of the first lens group. f2: focal length of the second lens group L1r1: the radius of curvature of the object-side lens surface of the lens arranged closest to the object side of the variable magnification optical system L1r2: the radius of curvature of the image-side lens surface of the lens arranged closest to the object side of the variable magnification optical system LEr1: the radius of curvature of the object-side lens surface of the lens arranged closest to the image side in the variable magnification optical system LEr2: radius of curvature of the image-side lens surface of the lens arranged closest to the image side of the variable magnification optical system

[0005] An optical device according to the present invention includes the variable magnification optical system described above. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a diagram showing a lens configuration of a variable magnification optical system according to a first example. [Diagram 2] 2A and 2B are diagrams showing various aberrations of the variable magnification optical system according to Example 1 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. [Diagram 3] FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to Example 2. [Figure 4] 4A and 4B are diagrams showing various aberrations of the variable magnification optical system according to the second example when focused on infinity in the wide-angle end state and the telephoto end state, respectively. [Diagram 5] FIG. 13 is a diagram showing the lens configuration of a variable magnification optical system according to Example 3. [Figure 6] 6A and 6B are diagrams showing various aberrations of the variable magnification optical system according to Example 3 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. [Figure 7] FIG. 13 is a diagram showing the lens configuration of a variable magnification optical system according to Example 4. [Figure 8] 8A and 8B are diagrams showing various aberrations of the variable magnification optical system according to Example 4 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. [Figure 9] FIG. 1 is a diagram showing the configuration of a camera equipped with a variable magnification optical system according to each embodiment. [Figure 10] 5 is a flowchart showing a method for manufacturing the variable magnification optical system according to the first embodiment. [Figure 11] 10 is a flowchart showing a method for manufacturing a variable magnification optical system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] A preferred embodiment of the present invention will be described below. First, a camera (optical device) equipped with a variable magnification optical system according to this embodiment will be described with reference to FIG. 9. As shown in FIG. 9, this camera 1 is composed of a body 2 and a photographing lens 3 attached to the body 2. The body 2 is equipped with an image sensor 4, a body control unit (not shown) that controls the operation of the digital camera, and a liquid crystal screen 5. The photographing lens 3 is equipped with a variable magnification optical system ZL consisting of a plurality of lens groups, and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism is composed of a sensor that detects the position of the lens group, a motor that moves the lens group back and forth along the optical axis, a control circuit that drives the motor, and the like.

[0008] Light from a subject is collected by the variable magnification optical system ZL of the photographing lens 3 and reaches the image plane I of the image sensor 4. The light from the subject that reaches the image plane I is photoelectrically converted by the image sensor 4 and recorded as digital image data in a memory (not shown). The digital image data recorded in the memory can be displayed on the liquid crystal screen 5 in response to a user's operation. This camera may be a mirrorless camera or a single-lens reflex camera having a quick return mirror. The variable magnification optical system ZL shown in FIG. 9 is a schematic diagram of a variable magnification optical system provided in the photographing lens 3, and the lens configuration of the variable magnification optical system ZL is not limited to this configuration.

[0009] Next, a variable magnification optical system according to the first embodiment will be described. As shown in FIG. 1, the variable magnification optical system ZL(1) as an example of the variable magnification optical system (zoom lens) ZL according to the first embodiment is composed of a first lens group G1 having positive refractive power and a rear group GR having multiple lens groups, which are arranged in order from the object side along the optical axis. When varying the magnification, the interval between adjacent lens groups changes. The multiple lens groups in the rear group GR include a second lens group G2 having positive refractive power that is arranged closest to the object side of the rear group GR.

[0010] With the above-mentioned configuration, the variable magnification optical system ZL according to the first embodiment satisfies the following conditional expression (1). 0.15 <f2 / f1<0.80 ···(1) where f1 is the focal length of the first lens group G1 f2: focal length of the second lens group G2

[0011] According to the first embodiment, it is possible to obtain a variable magnification optical system that is small yet bright and has good optical performance, and an optical device equipped with this variable magnification optical system. The variable magnification optical system ZL according to the first embodiment may be the variable magnification optical system ZL(2) shown in Fig. 3, the variable magnification optical system ZL(3) shown in Fig. 5, or the variable magnification optical system ZL(4) shown in Fig. 7.

[0012] Conditional expression (1) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the second lens group G2. The focal length of the first lens group G1 is the focal length of the first lens group G1 when focused at infinity. By satisfying conditional expression (1), good optical performance can be obtained over the entire range of magnification.

[0013] If the corresponding value of conditional expression (1) falls outside the above range, it becomes difficult to obtain good optical performance in at least a part of the range of magnification. By setting the upper limit of conditional expression (1) to 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45, or even 0.40, the effect of this embodiment can be made more certain. Also, by setting the lower limit of conditional expression (1) to 0.18, 0.20, 0.23, 0.25, 0.28, or even 0.30, the effect of this embodiment can be made more certain.

[0014] Next, a variable magnification optical system according to the second embodiment will be described. The variable magnification optical system ZL(1) as an example of the variable magnification optical system (zoom lens) ZL according to the second embodiment is composed of a first lens group G1 having a positive refractive power and a rear group GR having a plurality of lens groups, which are arranged in order from the object side along the optical axis, as shown in FIG. 1. When changing magnification from the wide-angle end state to the telephoto end state, the first lens group G1 moves along the optical axis toward the object side, and the interval between adjacent lens groups changes. The first lens group G1 has a front fixed group GP1, which is fixed in position relative to the image surface I during focusing, and a front focusing group GF1, which moves along the optical axis during focusing, which are arranged in order from the object side along the optical axis.

[0015] With the above-mentioned configuration, the variable magnification optical system ZL according to the second embodiment satisfies the following conditional expressions (2) and (3). 0.60 <fP1 / (-fF1)<1.00 ···(2) 0.80<(-fF1) / fw<1.40 (3) where fP1 is the focal length of the front fixed group GP1 fF1: focal length of the front focusing group GF1 fw: focal length of the variable magnification optical system ZL at the wide-angle end

[0016] According to the second embodiment, it is possible to obtain a variable magnification optical system that is small yet bright and has good optical performance, and an optical device equipped with this variable magnification optical system. The variable magnification optical system ZL according to the second embodiment may be the variable magnification optical system ZL(2) shown in Fig. 3, the variable magnification optical system ZL(3) shown in Fig. 5, or the variable magnification optical system ZL(4) shown in Fig. 7.

[0017] Conditional formula (2) specifies the appropriate relationship between the focal length of the front fixed group GP1 and the focal length of the front focusing group GF1. Conditional formula (3) specifies the appropriate relationship between the focal length of the front focusing group GF1 and the focal length of the variable magnification optical system ZL in the wide-angle end state. By satisfying conditional formulas (2) and (3), good optical performance can be obtained even when focusing on close objects, despite the compact size.

[0018] If the corresponding value of conditional expression (2) falls outside the above range, it becomes difficult to obtain good optical performance when focusing on a close object. By setting the upper limit of conditional expression (2) to 0.98, 0.96, 0.95, 0.93, 0.90, 0.88, or even 0.85, the effect of this embodiment can be made more certain. Also, by setting the lower limit of conditional expression (2) to 0.63, 0.65, 0.68, 0.70, 0.73, 0.75, 0.76, or even 0.80, the effect of this embodiment can be made more certain.

[0019] If the corresponding value of conditional expression (3) is out of the above range, it becomes difficult to obtain good optical performance when focusing on a close object. By setting the upper limit of conditional expression (3) to 1.35, 1.33, 1.30, 1.26, 1.25, 1.23, or even 1.20, the effect of this embodiment can be made more certain. Also, by setting the lower limit of conditional expression (3) to 0.83, 0.85, 0.88, 0.90, 0.93, 0.95, 0.96, or even 1.00, the effect of this embodiment can be made more certain.

[0020] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (4). 1.20 <ft / fw<2.00 ···(4) Where ft is the focal length of the variable magnification optical system ZL at the telephoto end fw: focal length of the variable magnification optical system ZL at the wide-angle end

[0021] Condition (4) defines an appropriate range for the zoom ratio of the variable-magnification optical system ZL. By satisfying condition (4), various aberrations such as field curvature can be effectively corrected over the entire range of zoom ratio.

[0022] If the corresponding value of conditional expression (4) exceeds the upper limit, it becomes difficult to correct the field curvature in at least a part of the range of magnification. By setting the upper limit of conditional expression (4) to 1.90, 1.80, 1.70, or even 1.60, the effects of each embodiment can be more reliably achieved.

[0023] If the corresponding value of conditional expression (4) falls below the lower limit, the variable magnification optical system ZL will have an excessively small variable magnification ratio, making it useless as a variable magnification optical system (zoom lens). By setting the lower limit of conditional expression (4) to 1.25, 1.30, 1.35, 1.40, 1.43, 1.45, or even 1.48, the effects of each embodiment can be more reliably achieved.

[0024] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (5). 0.01 <Bfw / TLw<0.20 ···(5) where Bfw is the back focus of the variable magnification optical system ZL in the wide-angle end state. TLw: Total length of the variable magnification optical system ZL in the wide-angle end state

[0025] Condition (5) defines an appropriate relationship between the back focus of the variable magnification optical system ZL in the wide-angle end state and the overall length of the variable magnification optical system ZL in the wide-angle end state. By satisfying condition (5), it is possible to satisfactorily correct curvature of field.

[0026] When the corresponding value of conditional expression (5) exceeds the upper limit, the relative length of the back focus with respect to the overall length of the variable magnification optical system ZL becomes large, making it difficult to correct the curvature of field. By setting the upper limit of conditional expression (5) to 0.18, 0.15, 0.12, or even 0.10, the effects of each embodiment can be made more certain.

[0027] If the corresponding value of conditional expression (5) falls below the lower limit, the overall length of the variable magnification optical system ZL becomes large, making it difficult to correct the field curvature while keeping the variable magnification optical system ZL small. By setting the lower limit of conditional expression (5) to 0.02, 0.04, 0.05, 0.06, or even 0.07, the effects of each embodiment can be made more certain.

[0028] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (6). 0.60 <YLE / IHw<1.00 ···(6) However, YLE is the effective diameter of the lens located closest to the image side in the variable magnification optical system ZL. IHw: Maximum image height of the variable magnification optical system ZL in the wide-angle end state

[0029] Conditional formula (6) specifies an appropriate relationship between the effective diameter of the lens arranged closest to the image side of the variable magnification optical system ZL and the maximum image height of the variable magnification optical system ZL in the wide-angle end state. Hereinafter, the lens arranged closest to the image side of the variable magnification optical system ZL may be referred to as the final lens. In each embodiment, the effective diameter of the final lens refers to the effective diameter of the lens surface on the image side of the final lens in the wide-angle end state. By satisfying conditional formula (6), it is possible to satisfactorily correct the curvature of field.

[0030] When the corresponding value of conditional expression (6) exceeds the upper limit, the effective diameter of the final lens becomes large, making it difficult to correct the field curvature while keeping the variable magnification optical system ZL small. By setting the upper limit of conditional expression (6) to 0.96, 0.95, 0.93, 0.90, 0.88, or even 0.85, the effects of each embodiment can be made more certain.

[0031] When the corresponding value of conditional expression (6) falls below the lower limit, the effective diameter of the final lens becomes small, making it difficult to correct the curvature of field. By setting the lower limit of conditional expression (6) to 0.65, 0.70, 0.73, 0.75, 0.78, or even 0.80, the effects of each embodiment can be more reliably achieved.

[0032] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (7). FNOw<2.8 (7) However, FNOw: F-number of the variable magnification optical system ZL at the wide-angle end

[0033] Conditional expression (7) defines an appropriate range for the F-number of the variable magnification optical system ZL in the wide-angle end state. By satisfying conditional expression (7), a bright variable magnification optical system can be obtained, which is preferable. By setting the upper limit value of conditional expression (7) to 2.50, 2.40, 2.20, 2.00, or even 1.90, the effects of each embodiment can be made more certain. The lower limit value of conditional expression (7) may be set to 1.20, 1.40, 1.50, or even greater than 1.80.

[0034] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (8). 10.00°<2ωw<35.00° ···(8) However, 2ωw: the total angle of view of the variable magnification optical system ZL in the wide-angle end state

[0035] Conditional formula (8) specifies an appropriate range for the total angle of view of the variable magnification optical system ZL in the wide-angle end state. By satisfying conditional formula (8), a variable magnification optical system in the medium telephoto range is obtained, which is preferable. By setting the upper limit of conditional formula (8) to 32.00°, 30.00°, 29.00°, or even 28.00°, the effects of each embodiment can be made more certain. By setting the lower limit of conditional formula (8) to 15.00°, 20.00°, 24.00°, or even 27.00°, the effects of each embodiment can be made more certain.

[0036] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (9). 0.30 <fw / f1<0.70 ···(9) where fw is the focal length of the variable magnification optical system ZL at the wide-angle end f1: focal length of the first lens group G1

[0037] Condition (9) defines an appropriate relationship between the focal length of the variable magnification optical system ZL in the wide-angle end state and the focal length of the first lens group G1. By satisfying condition (9), spherical aberration can be effectively corrected throughout the entire variable magnification range.

[0038] If the corresponding value of conditional expression (9) exceeds the upper limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct spherical aberration. By setting the upper limit of conditional expression (9) to 0.68, 0.65, 0.62, 0.58, or even 0.55, the effects of each embodiment can be made more certain.

[0039] If the corresponding value of conditional expression (9) falls below the lower limit, the refractive power of the first lens group G1 becomes too weak, and the variable magnification optical system ZL becomes large. Therefore, it becomes difficult to correct spherical aberration while making the variable magnification optical system ZL small. By setting the lower limit of conditional expression (9) to 0.33, 0.35, 0.38, 0.42, or even 0.45, the effects of each embodiment can be more reliably achieved.

[0040] In the variable magnification optical systems ZL according to the first and second embodiments, it is desirable that the multiple lens groups in the rear group GR include a second lens group G2 having positive refractive power that is arranged closest to the object in the rear group GR, and that the following conditional expression (10) be satisfied: 0.30 <f2 / fRw<0.65 ···(10) where f2 is the focal length of the second lens group G2 fRw: The composite focal length of the rear group GR at the wide-angle end

[0041] Condition (10) defines an appropriate relationship between the focal length of the second lens group G2 and the combined focal length of the rear group GR in the wide-angle end state. By satisfying condition (10), spherical aberration can be effectively corrected throughout the entire zoom range.

[0042] If the corresponding value of conditional expression (10) exceeds the upper limit, the refractive power of the second lens group G2 becomes too weak, making it difficult to correct the curvature of field. By setting the upper limit of conditional expression (10) to 0.62, 0.60, 0.58, 0.55, or even 0.52, the effects of each embodiment can be made more certain.

[0043] If the corresponding value of conditional expression (10) falls below the lower limit, the refractive power of the second lens group G2 becomes too strong, making it difficult to correct spherical aberration. By setting the lower limit of conditional expression (10) to 0.32, 0.34, 0.35, 0.36, 0.38, or even 0.40, the effects of each embodiment can be made more certain.

[0044] In the variable magnification optical systems ZL according to the first and second embodiments, it is desirable that the multiple lens groups in the rear group GR include a final lens group GE arranged closest to the image side of the rear group GR, and that the following conditional expression (11) be satisfied: 0.50<(-fGE) / fw<1.00 ···(11) where fGE is the focal length of the final lens group GE. fw: focal length of the variable magnification optical system ZL at the wide-angle end

[0045] Condition (11) defines an appropriate relationship between the focal length of the final lens group GE and the focal length of the variable magnification optical system ZL in the wide-angle end state. By satisfying condition (11), the variable magnification optical system ZL can be made compact and curvature of field can be effectively corrected.

[0046] If the corresponding value of conditional expression (11) exceeds the upper limit, the refractive power of the final lens group GE becomes too weak, making it difficult to correct the curvature of field. By setting the upper limit of conditional expression (11) to 0.98, 0.95, 0.93, 0.90, 0.88, 0.85, 0.83, or even 0.80, the effects of each embodiment can be made more certain.

[0047] If the corresponding value of conditional expression (11) falls below the lower limit, the refractive power of the final lens group GE becomes too strong, making it difficult to correct distortion and lateral chromatic aberration. By setting the lower limit of conditional expression (11) to 0.53, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, or even 0.72, the effects of each embodiment can be more reliably achieved.

[0048] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (12). 1.00<(L1r2+L1r1) / (L1r2-L1r1)<2.50 (12) where L1r1 is the radius of curvature of the lens surface on the object side of the lens arranged closest to the object side in the variable magnification optical system ZL. L1r2: Radius of curvature of the image-side lens surface of the lens located closest to the object in the variable magnification optical system ZL

[0049] Condition (12) defines an appropriate range for the shape factor of the lens located closest to the object in the variable magnification optical system ZL. By satisfying condition (12), various aberrations such as coma can be effectively corrected throughout the entire range of magnification.

[0050] When the corresponding value of conditional expression (12) exceeds the upper limit, it becomes difficult to correct spherical aberration. By setting the upper limit of conditional expression (12) to 2.40, 2.25, 2.10, 2.00, 1.95, 1.90, 1.85, or further to 1.80, the effects of each embodiment can be more reliably achieved.

[0051] When the corresponding value of conditional expression (12) falls below the lower limit, it becomes difficult to correct coma aberration. By setting the lower limit of conditional expression (12) to 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, or even 1.40, the effects of each embodiment can be more reliably achieved.

[0052] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (13). 1.50<(LEr2+LEr1) / (LEr2-LEr1)<3.00 (13) where LEr1 is the radius of curvature of the lens surface on the object side of the lens arranged closest to the image side in the variable magnification optical system ZL. LEr2: Radius of curvature of the image-side lens surface of the lens located closest to the image side in the variable magnification optical system ZL

[0053] Condition (13) defines an appropriate range for the shape factor of the lens (final lens) located closest to the image side in the variable magnification optical system ZL. By satisfying condition (13), various aberrations such as field curvature can be effectively corrected throughout the entire range of magnification.

[0054] When the corresponding value of conditional expression (13) exceeds the upper limit, it becomes difficult to correct spherical aberration. By setting the upper limit of conditional expression (13) to 2.90, 2.80, 2.70, 2.60, 2.50, 2.45, 2.40, 2.35, or further to 2.30, the effects of each embodiment can be more reliably achieved.

[0055] When the corresponding value of conditional expression (13) falls below the lower limit, it becomes difficult to correct coma aberration. By setting the lower limit of conditional expression (13) to 1.60, 1.65, 1.75, 1.80, 1.85, 1.90, 1.95, or even 2.00, the effects of each embodiment can be more reliably achieved.

[0056] It is desirable for the variable magnification optical system ZL according to the first and second embodiments to satisfy the following conditional expression (14). 1.00 <f1 / fRw<1.80 ···(14) where f1 is the focal length of the first lens group G1 fRw: The composite focal length of the rear group GR at the wide-angle end

[0057] Condition (14) defines an appropriate relationship between the focal length of the first lens group G1 and the combined focal length of the rear group GR in the wide-angle end state. By satisfying condition (14), spherical aberration can be effectively corrected throughout the entire zoom range.

[0058] When the corresponding value of conditional expression (14) exceeds the upper limit, the refractive power of the first lens group G1 becomes too weak, and the variable magnification optical system ZL becomes large. Therefore, it becomes difficult to correct spherical aberration while making the variable magnification optical system ZL small. By setting the upper limit of conditional expression (14) to 1.75, 1.70, 1.68, 1.65, 1.63, or even 1.60, the effects of each embodiment can be more reliably achieved.

[0059] If the corresponding value of conditional expression (14) falls below the lower limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct spherical aberration. By setting the lower limit of conditional expression (14) to 1.03, 1.05, 1.08, or even 1.10, the effects of each embodiment can be more reliably achieved.

[0060] In the variable magnification optical system ZL according to the first and second embodiments, the multiple lens groups of the rear group GR include a second lens group G2 having positive refractive power that is arranged closest to the object of the rear group GR, and a third lens group G3 that is arranged adjacent to the image side of the second lens group G2, and it is desirable that the distance between the second lens group G2 and the third lens group G3 decreases when changing magnification from the wide-angle end state to the telephoto end state.

[0061] The variable magnification optical system ZL according to the first and second embodiments has an aperture stop S disposed between the first lens group G1 and the rear group GR, and it is desirable that, during magnification change, the first lens group G1 moves along the optical axis together with the aperture stop S.

[0062] In the variable magnification optical system ZL according to the first and second embodiments, the first lens group G1 has a front focusing group GF1 that moves along the optical axis during focusing, and the rear group GR has a rear focusing group GF2 that moves along the optical axis along a trajectory different from that of the front focusing group GF1 during focusing, and it is desirable that at least a portion of any one of the multiple lens groups in the rear group GR constitutes the rear focusing group GF2.

[0063] In the variable magnification optical system ZL according to the first and second embodiments, the front focusing group GF1 and the rear focusing group GF2 may satisfy the following conditional expression (15). -0.30 <fF2 / fF1<0.30 ···(15) where fF1 is the focal length of the front focusing group GF1 fF2: focal length of rear focusing group GF2

[0064] Condition (15) defines an appropriate relationship between the focal length of the front focusing group GF1 and the focal length of the rear focusing group GF2. By satisfying condition (15), fluctuations in field curvature during focusing can be effectively suppressed throughout the entire zoom range.

[0065] When the corresponding value of conditional expression (15) exceeds the upper limit, it becomes difficult to suppress the fluctuation of the field curvature during focusing. By setting the upper limit of conditional expression (15) to 0.28, 0.25, 0.23, 0.20, or further to 0.18, the effects of each embodiment can be more reliably achieved.

[0066] If the corresponding value of conditional expression (15) falls below the lower limit, it becomes difficult to suppress fluctuations in field curvature during focusing. By setting the lower limit of conditional expression (15) to -0.25, -0.15, -0.10, -0.05, -0.01, 0.01, or even 0.02, the effects of each embodiment can be made more certain.

[0067] In the variable magnification optical system ZL according to the first and second embodiments, the front focusing group GF1 and the rear focusing group GF2 may satisfy the following conditional expression (16). 0.01 <fF2 / (-fF1)<0.30 ···(16) where fF1 is the focal length of the front focusing group GF1 fF2: focal length of rear focusing group GF2

[0068] Condition (16) defines an appropriate relationship between the focal length of the front focusing group GF1 and the focal length of the rear focusing group GF2. By satisfying condition (16), fluctuations in field curvature during focusing can be effectively suppressed throughout the entire zoom range.

[0069] When the corresponding value of conditional expression (16) exceeds the upper limit, it becomes difficult to suppress the fluctuation of the field curvature during focusing. By setting the upper limit of conditional expression (16) to 0.28, 0.25, 0.23, 0.20, or further to 0.18, the effects of each embodiment can be more reliably achieved.

[0070] If the corresponding value of conditional expression (16) falls below the lower limit, it becomes difficult to suppress fluctuations in field curvature during focusing. By setting the lower limit of conditional expression (16) to 0.02, the effects of each embodiment can be more reliably achieved.

[0071] Next, referring to FIG. 10, a manufacturing method of the variable magnification optical system ZL according to the first embodiment will be outlined. First, a first lens group G1 having a positive refractive power and a rear group GR having a plurality of lens groups are arranged in order from the object side along the optical axis (step ST1). Next, the arrangement is made so that the interval between adjacent lens groups changes during magnification (step ST2). Next, among the lens groups in the rear group GR, a second lens group G2 having a positive refractive power is arranged closest to the object side of the rear group GR (step ST3). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditional formula (1) (step ST4). According to this manufacturing method, it is possible to manufacture a variable magnification optical system that is small yet bright and has good optical performance.

[0072] Next, referring to FIG. 11, a manufacturing method of the variable magnification optical system ZL according to the second embodiment will be outlined. First, a first lens group G1 having a positive refractive power and a rear group GR having a plurality of lens groups are arranged in order from the object side along the optical axis (step ST11). Next, when the magnification is changed from the wide-angle end state to the telephoto end state, the first lens group G1 is configured to move along the optical axis toward the object side, and the interval between each of the adjacent lens groups is changed (step ST12). Next, in the first lens group G1, a front fixed group GP1 whose position is fixed with respect to the image surface I during focusing and a front focusing group GF1 whose position is moved along the optical axis during focusing are arranged in order from the object side along the optical axis (step ST13). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditional expressions (2) and (3) (step ST14). According to such a manufacturing method, it is possible to manufacture a variable magnification optical system that is small yet bright and has good optical performance. EXAMPLES

[0073] The variable magnification optical system ZL according to the examples of each embodiment will be described below with reference to the drawings. Figs. 1, 3, 5, and 7 are cross-sectional views showing the configuration and refractive power distribution of the variable magnification optical system ZL {ZL(1)-ZL(4)} according to the first to fourth examples. In the cross-sectional views of the variable magnification optical systems ZL(1)-ZL(4) according to the first to fourth examples, the movement direction along the optical axis of the focusing group when focusing from infinity to a close-distance object is indicated by an arrow together with the word "focusing". In the cross-sectional views of the variable magnification optical systems ZL(1)-ZL(4) according to the first to fourth examples, the movement direction along the optical axis of each lens group when changing magnification from the wide-angle end state (W) to the telephoto end state (T) is indicated by an arrow.

[0074] 1, 3, 5, and 7, each lens group is represented by a combination of the symbol G and a number, and each lens is represented by a combination of the symbol L and a number. In this case, to prevent the symbols and numbers from becoming too large and becoming complicated in number, the lens groups, etc. are represented by different combinations of symbols and numbers for each embodiment. Therefore, even if the same combinations of symbols and numbers are used between embodiments, this does not mean that they have the same configuration.

[0075] Tables 1 to 4 are shown below, with Table 1 showing data on various elements in the first embodiment, Table 2 showing data on various elements in the second embodiment, Table 3 showing data on various elements in the third embodiment, and Table 4 showing data on various elements in the fourth embodiment. In each embodiment, the d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) are selected as the targets for calculating the aberration characteristics.

[0076] In the [Overall Specifications] table, f is the focal length of the entire lens system, FNO is the F-number, 2ω is the angle of view (units are ° (degrees), where ω is half the angle of view), and Ymax is the maximum image height. TL is the distance from the frontmost lens surface to the final lens surface on the optical axis when focused at infinity plus BF, and BF is the distance (back focus) from the final lens surface to image plane I on the optical axis when focused at infinity. These values ​​are shown for both the wide-angle end (W) and the telephoto end (T) magnification settings.

[0077] In addition, in the table of [Overall Specifications], YLE indicates the effective diameter of the lens (final lens) located closest to the image side of the variable magnification optical system. IHw indicates the maximum image height of the variable magnification optical system in the wide-angle end state. fP1 indicates the focal length of the front fixed group. fF1 indicates the focal length of the front focusing group. fRw indicates the composite focal length of the rear group in the wide-angle end state. fF2 indicates the focal length of the rear focusing group.

[0078] In the [Lens specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction of light travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is located on the image side are given a positive value), D is the surface spacing which is the distance on the optical axis from each optical surface to the next optical surface (or image surface), nd is the refractive index of the material of the optical component with respect to the d-line, and νd is the Abbe number based on the d-line of the material of the optical component. The "∞" in the radius of curvature indicates a plane or an aperture, and (stop S) indicates the aperture stop S. The refractive index of air, nd=1.00000, has been omitted. If the optical surface is aspheric, an * is added to the surface number, and the paraxial radius of curvature is shown in the column for radius of curvature R.

[0079] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following formula (A). X(y) is the distance (sag amount) along the optical axis direction from the tangent plane at the apex of the aspherical surface to the position on the aspherical surface at height y, R is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "En" is the ratio of "×10 -n For example, 1.234E-05=1.234×10 -5 In addition, the second-order aspheric coefficient A2 is 0, and is omitted.

[0080] X(y)=(y 2 / R) / {1+(1-κ×y 2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 …(A)

[0081] The [Variable Distance Data] table shows the surface spacing for surface number i, which has a surface spacing of (Di) in the [Lens Specifications] table. The [Variable Distance Data] table also shows the surface spacing when focused at infinity and when focused at the closest distance.

[0082] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0083] In the following, for all specifications, the focal length f, radius of curvature R, surface separation D, and other lengths are generally in "mm" unless otherwise specified; however, this is not limited to this because the optical system can provide the same optical performance even when proportionally enlarged or reduced.

[0084] The above explanation of the tables is common to all the embodiments, and therefore, duplicate explanations will be omitted below.

[0085] (First embodiment) The first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 is a diagram showing the lens configuration of the variable magnification optical system according to the first embodiment. The variable magnification optical system ZL(1) according to the first embodiment is composed of a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, which are arranged in order from the object side along the optical axis. When changing the magnification from the wide-angle end state (W) to the telephoto end state (T), the first lens group G1 and the third lens group G3 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. In addition, when changing the magnification, the aperture stop S moves along the optical axis together with the first lens group G1, and the position of the second lens group G2 is fixed with respect to the image surface I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of each lens group, and this is the same in all the following embodiments.

[0086] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with a convex surface facing the object side, a cemented lens of a positive meniscus lens L12 with a convex surface facing the object side and a negative meniscus lens L13 with a convex surface facing the object side, a positive meniscus lens L14 with a convex surface facing the object side, and a cemented lens of a biconvex positive lens L15 and a biconcave negative lens L16.

[0087] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21, a biconvex positive lens L22, and a cemented lens of a biconvex positive lens L23 and a negative meniscus lens L24 with its concave surface facing the object side. The lens surface facing the object side of the positive lens L23 is aspheric.

[0088] The third lens group G3 is composed of, in order from the object side along the optical axis, a cemented lens of a positive meniscus lens L31 with a concave surface facing the object side and a biconcave negative lens L32, and a negative meniscus lens L33 with a concave surface facing the object side. The lens surface of the negative lens L32 facing the image side is aspheric. An image surface I is disposed on the image side of the third lens group G3.

[0089] In this embodiment, the second lens group G2 and the third lens group G3 constitute the rear group GR having a positive refractive power as a whole. The third lens group G3 corresponds to the final lens group GE arranged on the most image side of the rear group GR. The negative meniscus lens L33 of the third lens group G3 corresponds to the final lens. The positive meniscus lens L11 of the first lens group G1, the cemented lens of the positive meniscus lens L12 and the negative meniscus lens L13, and the positive meniscus lens L14 constitute the front fixed group GP1 whose position is fixed with respect to the image surface I during focusing. The cemented lens of the positive lens L15 and the negative lens L16 of the first lens group G1 constitutes the front focusing group GF1 that moves along the optical axis during focusing. When focusing from an object at infinity to an object at a close distance, the front focusing group GF1 (the cemented lens of the positive lens L15 and the negative lens L16 of the first lens group G1) moves toward the image side along the optical axis.

[0090] Table 1 below lists the values ​​of the specifications of the variable magnification optical system according to the first example.

[0091] (Table 1) [Overall specifications] Magnification ratio=1.497 YLE=18.000 IHw=21.600 fP1=84.022 fF1=-101.078 fRw=119.920 W.T. f 87.497 130.992 FNO 1.859 2.788 2ω 27.50 18.79 Ymax 21.600 21.600 TL 119.454 149.236 Bf 9.103 24.335 [Lens specifications] Surface number RD nd νd 1 46.914 6.995 1.846660 23.8 2 166.537 0.200 3 47.658 7.580 1.593190 67.9 4 33336.213 2.000 1.846660 23.8 5 30.363 2.896 6 40.058 5.343 1.593190 67.9 7 165.681 (D7) 8 362.425 3.014 1.945944 18.0 9 -100.065 1.100 1.850000 27.0 10 62.769 (D10) 11∞ (D11) (Aperture S) 12 -39.802 1.100 1.720000 43.6 13 5040.621 0.200 14 65.807 6.882 1.696800 55.5 15 -83.001 7.355 16* 254.149 7.210 1.772500 49.6 17 -39.577 1.100 1.846660 23.8 18 -60.083 (D18) 19 -412.223 4.304 1.846660 23.8 20 -59.324 1.600 1.487490 70.3 21* 87.613 8.473 22 -37.483 1.600 1.834000 37.2 23 -96.128 Bf [Aspheric data] Page 16 κ=1.0000,A4=-4.16377E-06,A6=1.34984E-10,A8=-2.63295E-12,A10=2.51738E-15 Page 21 κ=1.0000,A4=-3.27383E-06,A6=-4.18982E-09,A8=2.10935E-12,A10=-1.03143E-14 [Variable interval data] Focused at infinity WMT Focal length 87.497 104.995 130.992 Object distance ∞ ∞ ∞ D7 2.675 2.675 2.675 D10 13.768 13.768 13.768 D11 4.479 17.898 34.262 D18 16.479 9.390 1.246 Bf 9.103 16.191 24.335 Closest focusing state W M T Magnification -0.085 -0.103 -0.131 Object distance 1080.047 1066.880 1050.516 D7 11.703 11.826 11.983 D10 4.740 4.617 4.460 D11 4.479 17.898 34.262 D18 16.479 9.390 1.246 Bf 9.103 16.191 24.335 [Lens group data] Group Starting surface Focal length G1 1 186.610 G2 12 59.317 G3 19 -66.172

[0092] FIG. 2(A) is a diagram showing various aberrations when the variable magnification optical system according to the first embodiment is focused on infinity in the wide-angle end state. FIG. 2(B) is a diagram showing various aberrations when the variable magnification optical system according to the first embodiment is focused on infinity in the telephoto end state. In each aberration diagram, FNO indicates the F-number, and Y indicates the image height. In the spherical aberration diagram, the F-number value corresponding to the maximum aperture is shown, in the astigmatism diagram and the distortion aberration diagram, the maximum value of the image height is shown, and in the coma aberration diagram, the value of each image height is shown. d indicates the d-line (wavelength λ=587.6 nm), and g indicates the g-line (wavelength λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image surface, and the dashed line indicates the meridional image surface. In the aberration diagrams of each embodiment shown below, the same symbols as in this embodiment are used, and duplicated explanations are omitted.

[0093] It can be seen from each of the aberration diagrams that the variable magnification optical system according to Example 1 has excellent imaging performance, with the various aberrations being well corrected from the wide-angle end state to the telephoto end state.

[0094] (Second Example) The second embodiment will be described with reference to FIGS. 3 to 4 and Table 2. FIG. 3 is a diagram showing the lens configuration of the variable magnification optical system according to the second embodiment. The variable magnification optical system ZL(2) according to the second embodiment is composed of a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, which are arranged in order from the object side along the optical axis. When changing the magnification from the wide-angle end state (W) to the telephoto end state (T), the first lens group G1 and the third lens group G3 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. Also, when changing the magnification, the aperture stop S moves along the optical axis together with the first lens group G1, and the position of the second lens group G2 is fixed with respect to the image surface I.

[0095] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with a convex surface facing the object side, a cemented lens of a biconvex positive lens L12 and a biconcave negative lens L13, a positive meniscus lens L14 with a convex surface facing the object side, and a cemented lens of a biconvex positive lens L15 and a biconcave negative lens L16.

[0096] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21, a biconvex positive lens L22, and a cemented lens of a biconvex positive lens L23 and a negative meniscus lens L24 with its concave surface facing the object side. The lens surface facing the object side of the positive lens L23 is aspheric.

[0097] The third lens group G3 is composed of, in order from the object side along the optical axis, a cemented lens of a positive meniscus lens L31 with a concave surface facing the object side and a biconcave negative lens L32, and a negative meniscus lens L33 with a concave surface facing the object side. The lens surface of the negative lens L32 facing the image side is aspheric. An image surface I is disposed on the image side of the third lens group G3.

[0098] In this embodiment, the second lens group G2 and the third lens group G3 constitute the rear group GR having a positive refractive power as a whole. The third lens group G3 corresponds to the final lens group GE arranged on the most image side of the rear group GR. The negative meniscus lens L33 of the third lens group G3 corresponds to the final lens. The positive meniscus lens L11 of the first lens group G1, the cemented lens of the positive lens L12 and the negative lens L13, and the positive meniscus lens L14 constitute the front fixed group GP1 whose position is fixed with respect to the image surface I during focusing. The cemented lens of the positive lens L15 and the negative lens L16 of the first lens group G1 constitutes the front focusing group GF1 that moves along the optical axis during focusing. The cemented lens of the positive lens L23 and the negative meniscus lens L24 of the second lens group G2 constitutes the rear focusing group GF2 that moves along the optical axis during focusing. When focusing from an object at infinity to an object at a close distance, the front focusing group GF1 (a cemented lens of a positive lens L15 and a negative lens L16 in the first lens group G1) moves toward the image side along the optical axis, and the rear focusing group GF2 (a cemented lens of a positive lens L23 and a negative meniscus lens L24 in the second lens group G2) moves toward the object side along the optical axis.

[0099] Table 2 below lists the values ​​of the specifications of the variable magnification optical system according to the second example.

[0100] (Table 2) [Overall specifications] Magnification ratio=1.499 YLE=18.000 IHw=21.600 fP1=82.997 fF1=-99.080 fRw=118.936 fF2=671.573 W.T. f 87.387 131.002 FNO 1.859 2.791 2ω 27.48 18.77 Ymax 21.600 21.600 TL 115.452 145.326 Bf 9.106 24.310 [Lens specifications] Surface number RD nd νd 1 48.237 6.840 1.846660 23.8 2 176.058 0.201 3 47.311 7.706 1.593190 67.9 4 -10977.113 2.000 1.846660 23.8 5 30.989 2.743 6 40.022 5.341 1.593190 67.9 7 158.515 (D7) 8 288.236 3.092 1.945944 18.0 9 -101.965 1.100 1.850000 27.0 10 58.937 (D10) 11∞ (D11) (Aperture S) 12 -38.826 1.100 1.720000 43.6 13 1908.000 0.200 14 63.919 7.360 1.696800 55.5 15 -78.285 (D15) 16* 305.745 7.228 1.772500 49.6 17 -38.870 1.100 1.846660 23.8 18 -58.392 (D18) 19 -329.356 4.313 1.846660 23.8 20 -57.876 1.600 1.487490 70.3 21* 88.263 8.353 22 -38.199 1.600 1.834000 37.2 23 -96.156 Bf [Aspherical data] The 16th surface κ = 1.0000, A4 = -4.42907E-06, A6 = 2.27606E-10, A8 = -3.87693E-12, A10 = 4.36472E-15 The 21st surface κ = 1.0000, A4 = -3.09349E-06, A6 = -4.12964E-09, A8 = 3.11255E-12, A10 = -9.85811E-15 [Variable interval data] Infinity focus state W M T Focal length 87.387 105.000 131.002 Object distance ∞ ∞ ∞ D7 2.600 2.600 2.600 D10 13.859 13.859 13.859 D11 4.529 18.085 34.404 D15 6.736 6.736 6.736 D18 16.744 9.652 1.541 Bf 9.106 16.198 24.310 Closest focus state W M T Magnification -0.105 -0.128 -0.160 Object distance 880.077 866.739 850.411 D7 12.676 13.336 12.579 D10 3.783 3.123 3.881 D11 4.529 18.085 34.404 D15 6.092 6.334 5.007 D18 17.389 10.053 3.269 Bf 9.106 16.199 24.310 [Lens group data] Group starting plane focal length G1 1 185.733 G2 12 58.900 G3 19 -66.353

[0101] Fig. 4(A) is a diagram showing various aberrations of the variable magnification optical system according to Example 2 when focused on infinity in the wide-angle end state. Fig. 4(B) is a diagram showing various aberrations of the variable magnification optical system according to Example 2 when focused on infinity in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system according to Example 2 has excellent imaging performance with various aberrations being well corrected from the wide-angle end state to the telephoto end state.

[0102] (Third Example) The third embodiment will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 is a diagram showing the lens configuration of the variable magnification optical system according to the third embodiment. The variable magnification optical system ZL(3) according to the third embodiment is composed of a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, which are arranged in order from the object side along the optical axis. When changing the magnification from the wide-angle end state (W) to the telephoto end state (T), the first lens group G1, the third lens group G3, and the fourth lens group G4 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. Also, when changing the magnification, the aperture stop S moves along the optical axis together with the first lens group G1, and the position of the second lens group G2 is fixed with respect to the image surface I.

[0103] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with a convex surface facing the object side, a cemented lens of a biconvex positive lens L12 and a biconcave negative lens L13, a biconvex positive lens L14, and a cemented lens of a positive meniscus lens L15 with a concave surface facing the object side and a biconcave negative lens L16.

[0104] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21, a biconvex positive lens L22, and a cemented lens of a biconvex positive lens L23 and a negative meniscus lens L24 with its concave surface facing the object side. The lens surface facing the object side of the positive lens L23 is aspheric.

[0105] The third lens group G3 is composed of a cemented lens of a positive meniscus lens L31 with a concave surface facing the object side and a negative meniscus lens L32 with a concave surface facing the object side, arranged in order from the object side along the optical axis. The lens surface facing the image side of the negative meniscus lens L32 is aspheric.

[0106] The fourth lens group G4 is composed of a negative meniscus lens L41 with its concave surface facing the object side. An image surface I is disposed on the image side of the fourth lens group G4.

[0107] In this embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR having a positive refractive power as a whole. The fourth lens group G4 corresponds to the final lens group GE arranged on the most image side of the rear group GR. The negative meniscus lens L41 of the fourth lens group G4 corresponds to the final lens. The positive meniscus lens L11 of the first lens group G1, the cemented lens of the positive lens L12 and the negative lens L13, and the positive lens L14 constitute the front fixed group GP1 whose position is fixed with respect to the image surface I during focusing. The cemented lens of the positive meniscus lens L15 and the negative lens L16 of the first lens group G1 constitute the front focusing group GF1 that moves along the optical axis during focusing. The entire third lens group G3 constitutes the rear focusing group GF2 that moves along the optical axis during focusing. When focusing from an object at infinity to an object at a close distance, the front focusing group GF1 (a cemented lens of the positive meniscus lens L15 and the negative lens L16 in the first lens group G1) moves along the optical axis toward the image side, and the rear focusing group GF2 (the entire third lens group G3) moves along the optical axis toward the image side on a trajectory (movement amount) different from that of the front focusing group GF1.

[0108] Table 3 below lists the values ​​of the specifications of the variable magnification optical system according to the third example.

[0109] (Table 3) [Overall specifications] Magnification ratio=1.497 YLE=18.000 IHw=21.600 fP1=74.366 fF1=-90.157 fRw=147.649 fF2=2886.045 W.T. f 87.500 131.001 FNO 1.858 2.786 2ω 27.43 18.80 Ymax 21.600 21.600 TL 116.222 142.023 Bf 9.251 25.667 [Lens specifications] Surface number RD nd νd 1 56.682 6.478 1.846660 23.8 2 318.773 0.200 3 50.234 8.612 1.593190 67.9 4 -271.667 1.200 1.854779 24.8 5 37.409 4.817 6 44.054 6.278 1.497820 82.6 7 -2142.172 (D7) 8 -369.420 3.507 1.922860 20.9 9 -52.787 1.100 1.770470 29.7 10 67.323 (D10) 11 ∞ (D11) (Diaphragm S) 12 -34.128 1.100 1.723420 38.0 13 306.831 0.200 14 92.900 6.152 1.834810 42.7 15 -56.452 4.410 16* 875.397 9.115 1.693430 53.3 17 -26.311 1.100 1.850260 32.4 18 -44.283 (D18) 19 -132.378 3.586 1.846660 23.8 20 -50.802 1.600 1.588870 61.1 21* -371.956 (D21) 22 -29.395 1.600 1.693500 53.2 23 -86.978 Bf [Aspherical Data] Surface 16 κ = 1.0000, A4 = -4.22271E-06, A6 = -3.12823E-10, A8 = -1.96537E-12, A10 = 2.59367E-15 Surface 21 κ = 1.0000, A4 = -6.06022E-06, A6 = -5.54411E-09, A8 = -1.79582E-12, A10 = -6.81506E-15 [Variable interval data] Infinity focus state W M T Focal length 87.500 105.000 131.001 Object distance ∞ ∞ ∞ D7 2.737 2.737 2.737 D10 12.555 12.555 12.555 D11 4.854 16.294 30.654 D18 17.472 10.297 2.001 D21 8.299 7.849 7.354 Bf 9.251 16.876 25.667 Closest focus state W M T Magnification -0.104 -0.127 -0.161 Object distance 880.418 868.885 854.626 D7 11.412 11.574 11.749 D10 3.881 3.719 3.543 D11 4.854 16.294 30.654 D18 19.896 11.712 3.066 D21 5.875 6.434 6.289 Bf 9.283 16.924 25.744 [Lens group data] Group Starting surface Focal length G1 1 163.682 G2 12 62.062 G3 19 2886.045 G4 22 -64.759

[0110] Fig. 6(A) is a diagram showing various aberrations when the variable magnification optical system according to Example 3 is focused on infinity in the wide-angle end state. Fig. 6(B) is a diagram showing various aberrations when the variable magnification optical system according to Example 3 is focused on infinity in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system according to Example 3 has excellent imaging performance with various aberrations being well corrected from the wide-angle end state to the telephoto end state.

[0111] (Fourth Example) The fourth embodiment will be described with reference to FIGS. 7 to 8 and Table 4. FIG. 7 is a diagram showing the lens configuration of the variable magnification optical system according to the fourth embodiment. The variable magnification optical system ZL(4) according to the fourth embodiment is composed of a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, which are arranged in order from the object side along the optical axis. When changing the magnification from the wide-angle end state (W) to the telephoto end state (T), the first lens group G1 and the third lens group G3 move toward the object side along the optical axis, and the second lens group G2 moves toward the image side along the optical axis, and the interval between the adjacent lens groups changes. In addition, when changing the magnification, the aperture stop S moves along the optical axis together with the first lens group G1.

[0112] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with a convex surface facing the object side, a cemented lens of a positive meniscus lens L12 with a convex surface facing the object side and a negative meniscus lens L13 with a convex surface facing the object side, a positive meniscus lens L14 with a convex surface facing the object side, and a cemented lens of a biconvex positive lens L15 and a biconcave negative lens L16.

[0113] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21, a biconvex positive lens L22, and a cemented lens of a biconvex positive lens L23 and a negative meniscus lens L24 with its concave surface facing the object side. The lens surface facing the object side of the positive lens L23 is aspheric.

[0114] The third lens group G3 is composed of, in order from the object side along the optical axis, a cemented lens of a positive meniscus lens L31 with a concave surface facing the object side and a biconcave negative lens L32, and a negative meniscus lens L33 with a concave surface facing the object side. The lens surface of the negative lens L32 facing the image side is aspheric. An image surface I is disposed on the image side of the third lens group G3.

[0115] In this embodiment, the second lens group G2 and the third lens group G3 constitute the rear group GR having a positive refractive power as a whole. The third lens group G3 corresponds to the final lens group GE arranged on the most image side of the rear group GR. The negative meniscus lens L33 of the third lens group G3 corresponds to the final lens. The positive meniscus lens L11 of the first lens group G1, the cemented lens of the positive meniscus lens L12 and the negative meniscus lens L13, and the positive meniscus lens L14 constitute the front fixed group GP1 whose position is fixed with respect to the image surface I during focusing. The cemented lens of the positive lens L15 and the negative lens L16 of the first lens group G1 constitutes the front focusing group GF1 that moves along the optical axis during focusing. When focusing from an object at infinity to an object at a close distance, the front focusing group GF1 (the cemented lens of the positive lens L15 and the negative lens L16 of the first lens group G1) moves toward the image side along the optical axis.

[0116] Table 4 below lists the values ​​of the specifications of the variable magnification optical system according to the fourth example.

[0117] (Table 4) [Overall specifications] Magnification ratio=1.497 YLE=18.000 IHw=21.600 fP1=82.088 fF1=-96.051 fRw=118.327 W.T. f 87.500 131.000 FNO 1.860 2.785 2ω 27.51 18.80 Ymax 21.600 21.600 TL 115.456 145.509 Bf 9.105 23.679 [Lens specifications] Surface number RD nd νd 1 47.389 6.930 1.846660 23.8 2 168.915 0.200 3 46.629 7.713 1.593190 67.9 4 20954.696 2.000 1.846660 23.8 5 30.529 2.967 6 40.993 5.299 1.593190 67.9 7 183.696 (D7) 8 389.304 3.072 1.945944 18.0 9 -93.280 1.100 1.850000 27.0 10 60.942 (D10) 11∞ (D11) (Aperture S) 12 -40.799 1.100 1.720000 43.6 13 6130.299 0.200 14 65.875 6.929 1.696800 55.5 15 -87.261 7.752 16* 234.100 7.362 1.772500 49.6 17 -40.329 1.100 1.846660 23.8 18 -61.665 (D18) 19 -723.265 4.425 1.846660 23.8 20 -61.965 1.600 1.487490 70.3 21* 82.427 7.649 22 -40.118 1.600 1.834000 37.2 23 -116.183 Bf [Aspheric data] Page 16 κ = 1.0000, A4 = -4.01821E-06, A6 = 3.20252E-10, A8 = -3.12345E-12, A10 = 3.14559E-15 Page 21 κ = 1.0000, A4 = -2.97715E-06, A6 = -3.92189E-09, A8 = 1.79480E-12, A10 = -9.46067E-15 [Variable interval data] Infinity focus state WMT Focal length 87.500 105.000 131.000 Object distance ∞ ∞ ∞ D7 2.689 2.689 2.689 D10 13.153 13.153 13.153 D11 4.613 18.735 35.490 D18 16.898 9.784 1.500 Bf 9.105 15.838 23.679 Closest focus state WMT Magnification -0.085 -0.103 -0.130 Object distance 1084.544 1070.803 1054.491 D7 11.156 11.275 11.422 D10 4.686 4.566 4.420 D11 4.613 18.735 35.490 D18 16.898 9.784 1.500 Bf 9.105 15.838 23.679 [Lens group data] Group Starting surface Focal length G1 1 187.387 G2 12 59.720 G3 19 -67.423

[0118] Fig. 8(A) is a diagram showing various aberrations of the variable magnification optical system according to Example 4 when focused on infinity in the wide-angle end state. Fig. 8(B) is a diagram showing various aberrations of the variable magnification optical system according to Example 4 when focused on infinity in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system according to Example 4 has excellent imaging performance with various aberrations well corrected from the wide-angle end state to the telephoto end state.

[0119] Next, a table of [Values ​​Corresponding to Conditional Expressions] is shown below. This table shows the values ​​corresponding to each of the conditional expressions (1) to (16) for all the examples (Examples 1 to 4). Condition (1) 0.15 <f2 / f1<0.80 Condition (2) 0.60 <fP1 / (-fF1)<1.00 Conditional expression (3) 0.80<(-fF1) / fw<1.40 Condition (4) 1.20 <ft / fw<2.00 Condition (5) 0.01 <Bfw / TLw<0.20 Condition (6) 0.60 <YLE / IHw<1.00 Conditional expression (7) FNOw<2.8 Conditional expression (8) 10.00°<2ωw<35.00° Condition (9) 0.30 <fw / f1<0.70 Condition (10) 0.30 <f2 / fRw<0.65 Conditional expression (11) 0.50<(-fGE) / fw<1.00 Conditional expression (12) 1.00<(L1r2+L1r1) / (L1r2-L1r1)<2.50 Conditional expression (13) 1.50<(LEr2+LEr1) / (LEr2-LEr1)<3.00 Condition (14) 1.00 <f1 / fRw<1.80 Condition (15): -0.30 <fF2 / fF1<0.30 Condition (16) 0.01 <fF2 / (-fF1)<0.30

[0120] [Conditional Expression Corresponding Values] (First to Fourth Examples) Conditional Expression 1st Example 2nd Example 3rd Example 4th Example (1) 0.318 0.317 0.379 0.319 (2) 0.831 0.838 0.825 0.855 (3) 1.155 1.134 1.030 1.098 (4) 1.497 1.499 1.497 1.497 (5) 0.076 0.079 0.080 0.079 (6) 0.833 0.833 0.833 0.833 (7) 1.859 1.859 1.858 1.860 (8) 27.50 27.48 27.43 27.51 (9) 0.469 0.470 0.535 0.467 (10) 0.495 0.495 0.420 0.505 (11) 0.756 0.759 0.740 0.771 (12) 1.784 1.755 1.433 1.780 (13) 2.278 2.278 2.021 2.055 (14) 1.556 1.562 1.109 1.584 (15) ― 0.148 0.031 ― (16) ― 0.148 0.031 ―

[0121] According to each of the above embodiments, it is possible to realize a variable-magnification optical system that is small, yet bright and has good optical performance.

[0122] The above-mentioned embodiments are merely examples of the present invention, and the present invention is not limited to these.

[0123] The following contents can be appropriately adopted within a range that does not impair the optical performance of the variable magnification optical system of this embodiment.

[0124] Although three-group and four-group configurations have been shown as examples of the variable magnification optical system of this embodiment, the present application is not limited thereto, and a variable magnification optical system of other group configurations (e.g., five groups, etc.) can also be configured. Specifically, a lens or lens group may be added to the most object side or the most image side of the variable magnification optical system of this embodiment. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes when the magnification is changed.

[0125] A single or multiple lens groups, or a partial lens group, may be moved in the optical axis direction to function as a focusing lens group that focuses from an object at infinity to an object at a close distance. The focusing lens group can also be applied to autofocusing, and is suitable for driving a motor (using an ultrasonic motor, etc.) for autofocusing.

[0126] The lens group or partial lens group may be moved so as to have a component in a direction perpendicular to the optical axis, or may be rotated (rocked) in a plane including the optical axis to serve as an anti-vibration lens group that corrects image blur caused by camera shake.

[0127] The lens surface may be spherical or flat, or aspherical. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment, and prevents deterioration of optical performance due to errors in processing and assembly adjustment. It is also preferable because there is little deterioration in image quality even if the image plane is shifted.

[0128] When the lens surface is aspheric, the aspheric surface may be any of the following: an aspheric surface formed by grinding, a glass molded aspheric surface formed by molding glass into an aspheric shape, or a composite aspheric surface formed by molding a resin into an aspheric shape on the surface of glass. The lens surface may also be a diffractive surface, or the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0129] The aperture diaphragm is preferably disposed between the first lens group and the second lens group, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as the aperture diaphragm.

[0130] Each lens surface may be coated with an anti-reflection coating having high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance. [Explanation of symbols]

[0131] G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group I Image plane S Aperture stop

Claims

1. the first lens group having a positive refractive power and a rear group having a plurality of lens groups, which are arranged in order from the object side along the optical axis, When changing magnification, the spacing between adjacent lens groups changes, the plurality of lens groups in the rear group include a second lens group having positive refractive power and arranged closest to the object side of the rear group, A variable magnification optical system that satisfies the following condition: 0.15<f2 / f1<0.80 1.00<(L1r2+L1r1) / (L1r2-L1r1)<2.50 1.50<(LEr2+LEr1) / (LEr2-LEr1)<3.00 where f1 is the focal length of the first lens group. f2: focal length of the second lens group L1r1: the radius of curvature of the object-side lens surface of the lens arranged closest to the object side in the variable magnification optical system L1r2: the radius of curvature of the image-side lens surface of the lens arranged closest to the object side in the variable magnification optical system LEr1: the radius of curvature of the object-side lens surface of the lens arranged closest to the image side in the variable magnification optical system LEr2: the radius of curvature of the image-side lens surface of the lens arranged closest to the image side of the variable magnification optical system

2. 2. The variable magnification optical system according to claim 1, which satisfies the following condition: 1.20<ft / fw<2.00 where ft is the focal length of the variable magnification optical system in the telephoto end state. fw: focal length of the variable magnification optical system in the wide-angle end state

3. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.01<Bfw / TLw<0.20 where Bfw is the back focus of the variable magnification optical system in the wide-angle end state. TLw: total length of the variable magnification optical system in the wide-angle end state

4. 4. The variable magnification optical system according to claim 1, which satisfies the following condition: 0.60<YLE / IHw<1.00 where YLE is the effective diameter of the lens arranged closest to the image side in the variable magnification optical system. IHw: maximum image height of the variable magnification optical system in the wide-angle end state

5. 5. The variable magnification optical system according to claim 1, which satisfies the following condition: FNOw<2.8 where FNOw is the F-number of the variable magnification optical system in the wide-angle end state.

6. 6. The variable magnification optical system according to claim 1, which satisfies the following condition: 10.00°<2ωw<35.00° where 2ωw is the total angle of view of the variable magnification optical system in the wide-angle end state.

7. 7. The variable magnification optical system according to claim 1, which satisfies the following condition: 0.30<fw / f1<0.70 where fw is the focal length of the variable magnification optical system in the wide-angle end state. f1: focal length of the first lens group

8. the plurality of lens groups in the rear group include a second lens group having positive refractive power and arranged closest to the object side of the rear group, 8. The variable magnification optical system according to claim 1, which satisfies the following condition: 0.30<f2 / fRw<0.65 where f2 is the focal length of the second lens group. fRw: composite focal length of the rear group in the wide-angle end state

9. the plurality of lens groups in the rear group include a final lens group arranged closest to an image side in the rear group, 9. The variable magnification optical system according to claim 1, which satisfies the following condition: 0.50<(-fGE) / fw<1.00 where fGE is the focal length of the final lens group. fw: focal length of the variable magnification optical system in the wide-angle end state

10. 10. The variable magnification optical system according to claim 1, which satisfies the following condition: 1.00<f1 / fRw<1.80 where f1 is the focal length of the first lens group. fRw: composite focal length of the rear group in the wide-angle end state

11. the plurality of lens groups in the rear group include a second lens group having positive refractive power and arranged closest to the object side of the rear group, and a third lens group arranged adjacent to and on the image side of the second lens group, 11. The variable magnification optical system according to claim 1, wherein the distance between the second lens group and the third lens group decreases when magnification is changed from the wide-angle end state to the telephoto end state.

12. an aperture stop disposed between the first lens group and the rear lens group; 12. The variable magnification optical system according to claim 1, wherein the first lens group moves along the optical axis together with the aperture stop during magnification variation.

13. the first lens group has a front focusing group that moves along an optical axis during focusing; the rear group has a rear focusing group that moves along an optical axis on a different path from that of the front focusing group during focusing; 13. The variable magnification optical system according to claim 1, wherein at least a part of any one of the plurality of lens groups in the rear group constitutes the rear-side focusing group.

14. 14. The variable magnification optical system according to claim 13, which satisfies the following condition: -0.30<fF2 / fF1<0.30 where fF1 is the focal length of the front focusing group fF2: focal length of the rear focusing group

15. 14. The variable magnification optical system according to claim 13, which satisfies the following condition: 0.01<fF2 / (-fF1)<0.30 where fF1 is the focal length of the front focusing group fF2: focal length of the rear focusing group

16. An optical instrument comprising the variable magnification optical system according to any one of claims 1 to 15.

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