Variable magnification optical system, optical apparatus, and variable magnification optical system manufacturing method

Abstract

A variable magnification optical system (ZL) comprises, arranged in order from the object side and along the optical axis: an object-side lens group (GA) having a positive refractive power; an intermediate group (GM) having a positive refractive power; and a rear group (GR). The intermediate group (GM) includes at least one lens group. The rear group (GR) includes, arranged in order from the object side and along the optical axis: a first succeeding lens group (GR1) having a negative refractive power; a second succeeding lens group (GR2) having a positive refractive power; and a third succeeding lens group (GR3) having a negative refractive power. When varying magnification, the interval between the adjacent lens groups changes, and the second succeeding lens group (GR2) moves along the optical axis when focusing, and as a result thereof, the following formula is satisfied.　Formula: １．０５＜ｆ１／ＴＬｗ＜２．０, wherein f1 is the focal distance of the object-side lens group (GA), and TLw is the total length of the variable magnification optical system (ZL) when the same is in the wide-angle state.

Description

Variable magnification optical system, optical device, and method for manufacturing variable magnification optical system

[0001] The present invention relates to a variable magnification optical system, an optical instrument, and a method for manufacturing a variable magnification optical system.

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

[0003] Japanese Patent Application Laid-Open No. 2021-43375

[0004] A variable magnification optical system according to a first aspect comprises, arranged in order from the object side along the optical axis, an object-side lens group having positive refractive power, an intermediate group having positive refractive power, and a rear group, the intermediate group having at least one lens group, the rear group having, arranged in order from the object side along the optical axis, a first subsequent lens group having negative refractive power, a second subsequent lens group having positive refractive power, and a third subsequent lens group having negative refractive power, the spacing between adjacent lens groups changes during magnification variation, and the second subsequent lens group moves along the optical axis during focusing, and satisfies the following conditional expression: 1.05<f1 / TLw<2.00, where f1 is the focal length of the object-side lens group, and TLw is the total length of the variable magnification optical system in the wide-angle end state.

[0005] A variable magnification optical system according to a second aspect comprises, arranged along the optical axis from the object side, an object-side lens group having positive refractive power, an intermediate lens group having positive refractive power, and a rear lens group, the intermediate lens group having at least one lens group, and the rear lens group having, arranged along the optical axis from the object side, a first subsequent lens group having negative refractive power, a second subsequent lens group having positive refractive power, and a third subsequent lens group having negative refractive power, the spacing between adjacent lens groups changes during magnification variation, and at least some of the lens groups in the intermediate lens group are fixed with respect to the image plane, and the variable magnification optical system satisfies the following condition: 2.00<f1 / fMw<7.00, where f1 is the focal length of the object-side lens group, and fMw is the composite focal length of the intermediate lens group in the wide-angle end state.

[0006] An optical apparatus according to a third aspect is configured to include the variable magnification optical system described above.

[0007] A manufacturing method for a variable magnification optical system according to a fourth aspect is a manufacturing method for a variable magnification optical system comprising, arranged in order from the object side along the optical axis, an object-side lens group having positive refractive power, an intermediate group having positive refractive power, and a rear group, wherein the intermediate group has at least one lens group, and the rear group has, arranged in order from the object side along the optical axis, a first subsequent lens group having negative refractive power, a second subsequent lens group having positive refractive power, and a third subsequent lens group having negative refractive power, wherein a distance between adjacent lens groups changes during magnification variation, and the second subsequent lens group moves along the optical axis during focusing, and the method comprises the step of arranging each lens within a lens barrel so as to satisfy the following conditional expression: 1.05<f1 / TLw<2.00, where f1 is the focal length of the object-side lens group, and TLw is the total length of the variable magnification optical system in the wide-angle end state.

[0008] A manufacturing method for a variable magnification optical system according to a fifth aspect is a manufacturing method for a variable magnification optical system comprising, arranged in order from the object side along the optical axis, an object-side lens group having positive refractive power, an intermediate group having positive refractive power, and a rear group, wherein the intermediate group has at least one lens group, and the rear group has, arranged in order from the object side along the optical axis, a first subsequent lens group having negative refractive power, a second subsequent lens group having positive refractive power, and a third subsequent lens group having negative refractive power, and the manufacturing method includes the step of arranging the lenses in a lens barrel so that, during magnification variation, the spacing between adjacent lens groups changes, at least some of the lens groups in the intermediate group are fixed with respect to an image plane, and the following condition is satisfied: 2.00<f1 / fMw<7.00, where f1 is the focal length of the object-side lens group, and fMw is the composite focal length of the intermediate group in the wide-angle end state.

[0009] FIG. 2A is a diagram showing the lens configuration of a variable magnification optical system according to Example 1. FIG. 2A and FIG. 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. FIG. 2B is a diagram showing the lens configuration of a variable magnification optical system according to Example 2. FIG. 4A and FIG. 4B are diagrams showing various aberrations of the variable magnification optical system according to Example 2 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. FIG. 2C is a diagram showing the lens configuration of a variable magnification optical system according to Example 3. FIG. 6A and FIG. 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. FIG. 2D is a diagram showing the configuration of a camera equipped with a variable magnification optical system according to each embodiment. FIG. 2E is a flowchart showing a method for manufacturing a variable magnification optical system according to Example 1. FIG. 2F is a flowchart showing a method for manufacturing a variable magnification optical system according to Example 2.

[0010] Preferred embodiments of the present invention will now be described. First, a camera (optical device) equipped with a variable magnification optical system according to each embodiment will be described with reference to FIG. 7. As shown in FIG. 7, this camera 1 comprises a body 2 and a photographic lens 3 attached to the body 2. The body 2 comprises an image sensor 4, a body control unit (not shown) that controls the operation of the digital camera, and an LCD screen 5. The photographic lens 3 comprises a variable magnification optical system ZL consisting of multiple lens groups, and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism comprises a sensor that detects the position of the lens groups, a motor that moves the lens groups back and forth along the optical axis, a control circuit that drives the motor, and the like.

[0011] 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 LCD screen 5 in response to a user operation. Note that this camera may be a mirrorless camera or a single-lens reflex camera with a quick-return mirror. Furthermore, the variable magnification optical system ZL shown in FIG. 7 is a schematic representation 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.

[0012] 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 comprises, arranged along the optical axis from the object side, an object-side lens group GA having positive refractive power, an intermediate lens group GM having positive refractive power, and a rear lens group GR. The intermediate lens group GM has at least one lens group. The rear lens group GR has, arranged along the optical axis from the object side, a first rear lens group GR1 having negative refractive power, a second rear lens group GR2 having positive refractive power, and a third rear lens group GR3 having negative refractive power. When varying magnification, the spacing between adjacent lens groups changes. The second rear lens group GR2 moves along the optical axis during focusing.

[0013] With the above-described configuration, the variable magnification optical system ZL according to the first embodiment satisfies the following conditional expression (1): 1.05<f1 / TLw<2.00 (1) where f1 is the focal length of the object-side lens group GA, and TLw is the total length of the variable magnification optical system ZL in the wide-angle end state.

[0014] 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 Figure 3 or the variable magnification optical system ZL(3) shown in Figure 5.

[0015] Condition (1) defines an appropriate relationship between the focal length of the object-side lens group GA and the overall length of the variable-magnification optical system ZL in the wide-angle end state. By satisfying condition (1), spherical aberration can be effectively corrected.

[0016] If the corresponding value of conditional expression (1) exceeds the upper limit, the refractive power of the object-side lens group GA becomes weak, making it difficult to make the variable-magnification optical system ZL compact while correcting spherical aberration. By setting the upper limit of conditional expression (1) to 1.90, 1.80, 1.70, 1.60, or even 1.50, the effect of this embodiment can be made more certain.

[0017] If the value corresponding to conditional expression (1) falls below the lower limit, the refractive power of the object-side lens group GA becomes strong, making it difficult to correct spherical aberration that occurs in the telephoto end state. By setting the lower limit of conditional expression (1) to 1.10, 1.15, 1.20, 1.25, or even 1.30, the effect of this embodiment can be made more certain.

[0018] Next, a variable magnification optical system according to the second embodiment will be described. The variable magnification optical system ZL according to the second embodiment has the same configuration as the variable magnification optical system ZL according to the first embodiment, and will therefore be described using the same reference numerals as in the first embodiment. As shown in FIG. 1 , a variable magnification optical system ZL(1) as an example of the variable magnification optical system (zoom lens) ZL according to the second embodiment comprises, arranged along the optical axis in order from the object side, an object-side lens group GA having positive refractive power, an intermediate lens group GM having positive refractive power, and a rear lens group GR. The intermediate lens group GM has at least one lens group. The rear lens group GR has, arranged along the optical axis in order from the object side, a first subsequent lens group GR1 having negative refractive power, a second subsequent lens group GR2 having positive refractive power, and a third subsequent lens group GR3 having negative refractive power. During magnification change, the spacing between adjacent lens groups changes, and at least some of the lens groups in the intermediate lens group GM are fixed relative to the image plane I.

[0019] With the above-described configuration, the variable magnification optical system ZL according to the second embodiment satisfies the following conditional expression (2): 2.00<f1 / fMw<7.00 (2) where f1 is the focal length of the object-side lens group GA, and fMw is the combined focal length of the middle group GM in the wide-angle end state.

[0020] 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 apparatus 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 Figure 3 or the variable magnification optical system ZL(3) shown in Figure 5.

[0021] Condition (2) defines an appropriate relationship between the focal length of the object-side lens group GA and the combined focal length of the middle lens group GM at the wide-angle end. By satisfying condition (2), coma and curvature of field can be effectively corrected.

[0022] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive power of the middle group GM in the wide-angle end state becomes strong, making it difficult to suppress fluctuations in coma and field curvature during magnification. By setting the upper limit of conditional expression (2) to 6.75, 6.50, 6.25, 6.00, 5.75, or even 5.50, the effects of this embodiment can be made even more certain.

[0023] If the corresponding value of conditional expression (2) falls below the lower limit, the refractive power of the middle group GM in the wide-angle end state will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting coma and curvature of field. By setting the lower limit of conditional expression (2) to 2.25, 2.50, 2.75, 3.00, 3.25, or even 3.50, the effects of this embodiment can be made even more certain.

[0024] In the variable magnification optical system ZL according to the second embodiment, it is desirable that the second subsequent lens group GR2 move along the optical axis during focusing.

[0025] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (3): 1.50<f1 / (-fn1)<6.00 (3), where fn1 is the focal length of the lens group that has negative refractive power and is located closest to the object side in the variable magnification optical system ZL.

[0026] Conditional expression (3) defines an appropriate relationship between the focal length of the object-side lens group GA and the focal length of the lens group having negative refractive power and located closest to the object in the variable magnification optical system ZL. By satisfying conditional expression (3), spherical aberration can be effectively corrected.

[0027] If the corresponding value of conditional expression (3) exceeds the upper limit, the refractive power of the object-side lens group GA becomes weak, making it difficult to make the variable-magnification optical system ZL compact while correcting spherical aberration. By setting the upper limit of conditional expression (3) to 5.50, 5.00, 4.50, 4.00, or even 3.50, the effects of each embodiment can be made more certain.

[0028] If the corresponding value of conditional expression (3) falls below the lower limit, the refractive power of the object-side lens group GA becomes strong, making it difficult to correct spherical aberration that occurs in the telephoto end state. By setting the lower limit of conditional expression (3) to 1.75, 2.00, 2.25, or even 2.50, the effects of each embodiment can be made more certain.

[0029] It is desirable that the variable magnification optical system ZL according to the first and second embodiments satisfy the following conditional expression (4): 0.05<(-fR3) / ft<1.00 (4) where fR3 is the focal length of the third subsequent lens group GR3, and ft is the focal length of the variable magnification optical system ZL in the telephoto end state.

[0030] Conditional expression (4) defines an appropriate relationship between the focal length of the third subsequent lens group GR3 and the focal length of the variable magnification optical system ZL in the telephoto end state. By satisfying conditional expression (4), distortion can be effectively corrected while maintaining a compact size.

[0031] If the corresponding value of conditional expression (4) exceeds the upper limit, the refractive power of the third subsequent lens group GR3 will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting distortion. By setting the upper limit of conditional expression (4) to 0.80, 0.60, 0.50, or even 0.40, the effects of each embodiment can be made more certain.

[0032] If the corresponding value of conditional expression (4) falls below the lower limit, the refractive power of the third subsequent lens group GR3 becomes strong, making it difficult to suppress fluctuations in distortion during zooming. By setting the lower limit of conditional expression (4) to 0.10, 0.15, 0.20, or even 0.25, the effects of each embodiment can be made more certain.

[0033] It is desirable that the variable magnification optical system ZL according to the first and second embodiments satisfy the following conditional expression (5): 0.00<(-fR3) / fw<2.00 (5) where fR3 is the focal length of the third subsequent lens group GR3, and fw is the focal length of the variable magnification optical system ZL in the wide-angle end state.

[0034] Condition (5) defines an appropriate relationship between the focal length of the third subsequent lens group GR3 and the focal length of the variable magnification optical system ZL in the wide-angle end state. By satisfying condition (5), distortion can be effectively corrected while maintaining a compact size.

[0035] If the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the third subsequent lens group GR3 will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting distortion. By setting the upper limit of conditional expression (5) to 1.75, 1.50, 1.25, or even 1.00, the effects of each embodiment can be made more certain.

[0036] If the corresponding value of conditional expression (5) falls below the lower limit, the refractive power of the third subsequent lens group GR3 becomes strong, making it difficult to suppress fluctuations in distortion during zooming. By setting the lower limit of conditional expression (5) to 0.20, 0.40, 0.50, or even 0.60, the effects of each embodiment can be made more certain.

[0037] It is desirable that the variable magnification optical system ZL according to the first and second embodiments satisfy the following conditional expression (6): 0.15<(TLt-TLw) / TLw<1.00 (6) where TLt is the total length of the variable magnification optical system ZL in the telephoto end state, and TLw is the total length of the variable magnification optical system ZL in the wide-angle end state.

[0038] Condition (6) defines an appropriate relationship between the overall length of the variable magnification optical system ZL in the telephoto end state and the overall length of the variable magnification optical system ZL in the wide-angle end state. By satisfying condition (6), spherical aberration can be effectively corrected.

[0039] If the corresponding value of conditional expression (6) exceeds the upper limit, the refractive power of the object-side lens group GA will be weak, making it difficult to make the variable-magnification optical system ZL compact while correcting spherical aberration. By setting the upper limit of conditional expression (6) to 0.90, 0.80, 0.70, or even 0.60, the effects of each embodiment can be made more certain.

[0040] If the value corresponding to conditional expression (6) falls below the lower limit, the refractive power of the object-side lens group GA becomes strong, making it difficult to correct spherical aberration that occurs in the telephoto end state. By setting the lower limit of conditional expression (6) to 0.20, 0.25, 0.30, or even 0.35, the effects of each embodiment can be made more certain.

[0041] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (7): 1.50<f1 / (-fR3)<6.00 (7) where fR3 is the focal length of the third subsequent lens group GR3.

[0042] Conditional expression (7) defines an appropriate relationship between the focal length of the object-side lens group GA and the focal length of the third subsequent lens group GR3. By satisfying conditional expression (7), coma can be effectively corrected.

[0043] If the value corresponding to conditional expression (7) exceeds the upper limit, the refractive power of the object-side lens group GA becomes weaker than the refractive power of the third subsequent lens group GR3, making it difficult to correct coma. By setting the upper limit of conditional expression (7) to 5.50, 5.00, 4.50, or even 4.00, the effects of each embodiment can be further ensured.

[0044] If the corresponding value of conditional expression (7) falls below the lower limit, the refractive power of the third subsequent lens group GR3 will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting coma aberration. By setting the lower limit of conditional expression (7) to 1.60, 1.70, 1.80, 1.90, or even 2.00, the effects of each embodiment can be made more certain.

[0045] In the variable magnification optical systems ZL according to the first and second embodiments, it is desirable that the third subsequent lens group GR3 has a lens that satisfies the following conditional expressions (8) and (9): 50.0<νd3<80.0 (8) 1.45<nd3<1.58 (9) where νd3 is the Abbe number of the lens in the third subsequent lens group GR3, and nd3 is the refractive index for the d-line of the lens in the third subsequent lens group GR3.

[0046] Conditional expression (8) defines an appropriate range for the Abbe number of the lens in the third subsequent lens group GR3. Conditional expression (9) defines an appropriate range for the refractive index at the d-line of the lens in the third subsequent lens group GR3. By satisfying conditional expressions (8) and (9), lateral chromatic aberration can be effectively corrected.

[0047] If the value corresponding to conditional expression (8) exceeds the upper limit, the lenses in the third subsequent lens group GR3 will have to be made of special glass, which will increase manufacturing costs. By setting the upper limit of conditional expression (8) to 79.0, 78.0, 77.0, or even 75.0, the effects of each embodiment can be made more certain.

[0048] If the corresponding value of conditional expression (8) falls below the lower limit, it becomes difficult to correct lateral chromatic aberration. By setting the lower limit of conditional expression (8) to 51.0, 52.0, 53.0, 54.0, or even 55.0, the effects of each embodiment can be more reliably achieved.

[0049] If the value corresponding to conditional expression (9) exceeds the upper limit, the material of the lenses in the third subsequent lens group GR3 will be a high refractive index material, resulting in an increase in weight. By setting the upper limit of conditional expression (9) to 1.57, 1.56, or even 1.55, the effects of each embodiment can be further ensured.

[0050] If the value corresponding to conditional expression (9) is below the lower limit, the material of the lens in the third subsequent lens group GR3 will be a low refractive index material, and the curvature of the surface of this lens will need to be increased, making it difficult to correct distortion. By setting the lower limit of conditional expression (9) to 1.46, 1.47, or even 1.48, the effects of each embodiment can be made more certain.

[0051] It is desirable that the variable magnification optical system ZL according to the first and second embodiments satisfy the following conditional expression (10): 1.80<TLw / (-fR3)<2.70 (10) where TLw is the total length of the variable magnification optical system ZL in the wide-angle end state, and fR3 is the focal length of the third subsequent lens group GR3.

[0052] Conditional expression (10) defines an appropriate relationship between the overall length of the variable magnification optical system ZL in the wide-angle end state and the focal length of the third subsequent lens group GR3. By satisfying conditional expression (10), it is possible to shorten the overall length of the variable magnification optical system ZL while maintaining good optical performance.

[0053] If the corresponding value of conditional expression (10) exceeds the upper limit, the refractive power of the third subsequent lens group GR3 becomes strong, making it difficult to suppress fluctuations in distortion during zooming. By setting the upper limit of conditional expression (10) to 2.65, 2.60, 2.55, or even 2.50, the effects of each embodiment can be made more certain.

[0054] If the corresponding value of conditional expression (10) falls below the lower limit, the overall length of the variable magnification optical system ZL in the wide-angle end state becomes long, making it difficult to shorten the overall length of the variable magnification optical system ZL. By setting the lower limit of conditional expression (10) to 1.85, 1.90, 1.95, or even 2.00, the effects of each embodiment can be made more certain.

[0055] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (11): 0.30<(-fR1) / fR2<1.30 (11) where fR1 is the focal length of the first subsequent lens group GR1 and fR2 is the focal length of the second subsequent lens group GR2.

[0056] Conditional expression (11) defines an appropriate relationship between the focal length of the first subsequent lens group GR1 and the focal length of the second subsequent lens group GR2. By satisfying conditional expression (11), spherical aberration can be effectively corrected.

[0057] If the corresponding value of conditional expression (11) exceeds the upper limit, the refractive power of the first subsequent lens group GR1 will be weak, making it difficult to make the variable-magnification optical system ZL compact while correcting spherical aberration. By setting the upper limit of conditional expression (11) to 1.20, 1.10, 1.00, or even 0.90, the effects of each embodiment can be made more certain.

[0058] If the corresponding value of conditional expression (11) falls below the lower limit, the refractive power of the first subsequent lens group GR1 becomes strong, making it difficult to correct spherical aberration. By setting the lower limit of conditional expression (11) to 0.40, 0.50, or even 0.60, the effects of each embodiment can be made more certain.

[0059] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (12): 0.70<(-fR1) / fMw<2.00 (12) where fR1 is the focal length of the first subsequent lens group GR1, and fMw is the combined focal length of the middle group GM in the wide-angle end state.

[0060] Condition (12) defines an appropriate relationship between the focal length of the first subsequent lens group GR1 and the combined focal length of the middle group GM at the wide-angle end state. By satisfying condition (12), spherical aberration can be effectively corrected.

[0061] If the corresponding value of conditional expression (12) exceeds the upper limit, the refractive power of the first subsequent lens group GR1 will be weak, making it difficult to make the variable-magnification optical system ZL compact while correcting spherical aberration. By setting the upper limit of conditional expression (12) to 1.90, 1.80, 1.70, or even 1.65, the effects of each embodiment can be made more certain.

[0062] If the corresponding value of conditional expression (12) falls below the lower limit, the refractive power of the first subsequent lens group GR1 becomes strong, making it difficult to suppress fluctuations in spherical aberration during magnification. By setting the lower limit of conditional expression (12) to 0.80, 0.90, 1.00, or even 1.10, the effects of each embodiment can be made more certain.

[0063] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (13): 1.00<fR2 / fMw<3.00 (13) where fR2 is the focal length of the second subsequent lens group GR2, and fMw is the combined focal length of the middle group GM in the wide-angle end state.

[0064] Conditional expression (13) defines an appropriate relationship between the focal length of the second subsequent lens group GR2 and the combined focal length of the middle group GM at the wide-angle end state. By satisfying conditional expression (13), it is possible to effectively correct curvature of field.

[0065] If the corresponding value of conditional expression (13) exceeds the upper limit, the refractive power of the second subsequent lens group GR2 will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting the curvature of field. By setting the upper limit of conditional expression (13) to 2.90, 2.80, 2.70, 2.60, or even 2.50, the effects of each embodiment can be made more certain.

[0066] If the corresponding value of conditional expression (13) falls below the lower limit, the refractive power of the second subsequent lens group GR2 becomes strong, making it difficult to correct curvature of field. By setting the lower limit of conditional expression (13) to 1.10, 1.20, 1.30, 1.35, or even 1.40, the effects of each embodiment can be made more certain.

[0067] It is desirable that the variable magnification optical systems ZL according to the first and second embodiments satisfy the following conditional expression (14): 1.00<(-fR3) / fMw<3.50 (14) where fR3 is the focal length of the third subsequent lens group GR3, and fMw is the combined focal length of the middle group GM in the wide-angle end state.

[0068] Conditional expression (14) defines an appropriate relationship between the focal length of the third subsequent lens group GR3 and the combined focal length of the middle group GM in the wide-angle end state. By satisfying conditional expression (14), distortion can be effectively corrected while maintaining a compact size.

[0069] If the corresponding value of conditional expression (14) exceeds the upper limit, the refractive power of the third subsequent lens group GR3 will be weak, making it difficult to reduce the size of the variable-magnification optical system ZL while correcting distortion. By setting the upper limit of conditional expression (14) to 3.00, 2.50, 2.25, or even 2.00, the effects of each embodiment can be made more certain.

[0070] If the corresponding value of conditional expression (14) falls below the lower limit, the refractive power of the third subsequent lens group GR3 becomes strong, making it difficult to correct distortion. By setting the lower limit of conditional expression (14) to 1.10, 1.15, 1.20, or even 1.25, the effects of each embodiment can be made more certain.

[0071] It is desirable that the variable magnification optical system ZL according to the first and second embodiments satisfy the following conditional expression (15): 0.10<Bft / ft<0.80 (15) where Bft is the back focus of the variable magnification optical system ZL in the telephoto end state, and ft is the focal length of the variable magnification optical system ZL in the telephoto end state.

[0072] Conditional expression (15) defines an appropriate relationship between the back focus of the variable magnification optical system ZL in the telephoto end state and the focal length of the variable magnification optical system ZL in the telephoto end state. By satisfying conditional expression (15), it is possible to obtain a variable magnification optical system that is compact yet bright and has excellent optical performance. By setting the upper limit of conditional expression (15) to 0.75, 0.70, 0.65, 0.60, or even 0.50, the effects of this embodiment can be further ensured. Furthermore, by setting the lower limit of conditional expression (15) to 0.15, 0.20, 0.25, or even 0.30, the effects of this embodiment can be further ensured.

[0073] In the variable magnification optical systems ZL according to the first and second embodiments, it is desirable that, during magnification variation, the third subsequent lens group GR3 be fixed relative to the image plane I. This makes it possible to simplify the structure of the parts that hold each lens group, and to reduce the weight of the variable magnification optical system ZL.

[0074] In the variable-magnification optical systems ZL according to the first and second embodiments, it is desirable that the first subsequent lens group GR1 move along the optical axis during focusing, which makes it possible to effectively suppress fluctuations in field curvature during focusing.

[0075] Next, a manufacturing method for the variable magnification optical system ZL according to the first embodiment will be outlined with reference to FIG. 8 . First, an object-side lens group GA having positive refractive power, an intermediate lens group GM having positive refractive power, and a rear lens group GR are arranged, in order from the object side along the optical axis (Step ST1). At this time, at least one lens group is arranged in the intermediate lens group GM. The rear lens group GR is arranged, in order from the object side along the optical axis, with a first rear lens group GR1 having negative refractive power, a second rear lens group GR2 having positive refractive power, and a third rear lens group GR3 having negative refractive power. Next, the arrangement is such that the spacing between adjacent lens groups changes during magnification (Step ST2). Next, the second rear lens group GR2 is arranged to move along the optical axis during focusing (Step ST3). Finally, the lenses are arranged within the lens barrel so as to satisfy at least conditional expression (1) above (Step ST4). According to this manufacturing method, it is possible to manufacture a variable magnification optical system that is small in size, yet bright and has good optical performance.

[0076] Next, with reference to FIG. 9 , a manufacturing method for the variable-magnification optical system ZL according to the second embodiment will be outlined. First, an object-side lens group GA having positive refractive power, an intermediate lens group GM having positive refractive power, and a rear lens group GR are arranged, in order from the object side along the optical axis (step ST11). At this time, at least one lens group is arranged in the intermediate lens group GM. The rear lens group GR is arranged, in order from the object side along the optical axis, with a first subsequent lens group GR1 having negative refractive power, a second subsequent lens group GR2 having positive refractive power, and a third subsequent lens group GR3 having negative refractive power. Next, the spacing between adjacent lens groups is changed during magnification variation, and at least some of the lens groups in the intermediate lens group GM are fixed relative to the image plane I (step ST12). Then, the lenses are arranged in the lens barrel so as to satisfy at least the above-mentioned conditional expression (2) (step ST13). This manufacturing method makes it possible to manufacture a variable-magnification optical system that is compact, yet bright and has excellent optical performance.

[0077] Variable magnification optical systems ZL according to examples of each embodiment will be described below with reference to the drawings. FIGS. 1, 3, and 5 are cross-sectional views showing the configuration and refractive power distribution of variable magnification optical systems ZL {ZL(1) to ZL(3)} according to first to third examples. In the cross-sectional views of the variable magnification optical systems ZL(1) to ZL(3) according to first to third examples, arrows indicate the movement direction of each lens group when changing magnification from the wide-angle end state (W) to the telephoto end state (T). Additionally, the movement direction of the focusing lens group when focusing from infinity to a close-distance object is indicated by an arrow along with the word "focusing."

[0078] 1, 3, and 5, each lens group is represented by a combination of a symbol G and a number, and each lens is represented by a combination of a symbol L and a number. In this case, to prevent the symbols and numbers from becoming too numerous and complicated, each example uses its own independent combination of symbols and numbers to represent the lens groups, etc. Therefore, even if the same combination of symbols and numbers is used between examples, this does not mean that the examples have the same configuration.

[0079] Tables 1 to 3 are shown below, with Table 1 showing data on various elements in Example 1, Table 2 showing data on various elements in Example 2, and Table 3 showing data on various elements in Example 3. In each example, the d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating aberration characteristics.

[0080] In the table of [Overall Specifications], f denotes the focal length of the entire lens system, FNO denotes the F-number, 2ω denotes the angle of view (unit: ° (degrees), where ω is half the angle of view), and Y denotes the image height. TL denotes the distance on the optical axis from the lens surface closest to the object in the variable magnification optical system to the lens surface closest to the image plane when focused at infinity, plus Bf (back focus), and Bf denotes the distance on the optical axis from the lens surface closest to the image plane in the variable magnification optical system to the image plane when focused at infinity (air-equivalent distance). Note that these values ​​are shown for each of the magnification states: the wide-angle end (W), the intermediate focal length (M), and the telephoto end (T). Also, in the table of [Overall Specifications], fMw denotes the composite focal length of the middle group in the wide-angle end state.

[0081] In the "Lens Specifications" table, the surface number indicates the order of the optical surface from the object side along the direction of light ray travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is located on the image side have 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 plane), nd is the refractive index of the material of the optical element with respect to the d-line, and vd is the Abbe number of the material of the optical element with respect to the d-line. The "∞" next to 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, is omitted. If the optical surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the "radius of curvature R" column.

[0082] In the table of [Aspherical Surface Data], the shape of the aspherical surface shown in [Lens Specifications] is expressed by the following formula (A). X(y) is the distance (amount of sag) along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, R is the radius of curvature of the reference spherical surface (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "E-n" is "×10 -n For example, 1.234E-05 = 1.234 x 10 -5 The second-order aspherical coefficient A2 is 0, and is therefore omitted.

[0083] 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 +A12×y 12 …(A)

[0084] 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 close range. D0 indicates the distance from the object to the lens surface closest to the object in the variable magnification optical system.

[0085] The table of [Lens Group Data] shows the first surface (the surface closest to the object) and focal length of each lens group.

[0086] In the following, for all specifications, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this, as the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0087] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0088] First Example The first example will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 shows the lens configuration of a variable magnification optical system according to the first example. The variable magnification optical system ZL(1) according to the first example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power. When varying magnification from the wide-angle end state (W) to the telephoto end state (T), the first lens group G1 and the fourth lens group G4 move toward the object side along the optical axis, and the second lens group G2 and the fifth lens group G5 move toward the image plane side along the optical axis, changing the spacing between adjacent lens groups. During magnification variation, the third lens group G3 and the sixth lens group G6 are fixed relative to the image plane I. An aperture stop S is disposed between the second lens group G2 and the third lens group G3, and during magnification variation, the aperture stop S moves along the optical axis together with the second lens group G2. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of that lens group, and this is the same in all of the following examples.

[0089] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens consisting of a negative meniscus lens L11 with its convex surface facing the object side and a biconvex positive lens L12, and a biconvex positive lens L13.

[0090] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens of a biconcave negative lens L21 and a positive meniscus lens L22 with its convex surface facing the object side, and a biconcave negative lens L23.

[0091] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with a convex surface facing the object side, a biconvex positive lens L32, a cemented negative lens consisting of a biconcave negative lens L33 and a positive meniscus lens L34 with a convex surface facing the object side, a positive lens L35 with a convex surface facing the object side, and a biconvex positive lens L36. Both lens surfaces of the positive lens L35 are aspherical.

[0092] The fourth lens group G4 is composed of a cemented negative lens consisting of a positive meniscus lens L41 with a convex surface facing the object side and a negative meniscus lens L42 with a convex surface facing the object side.

[0093] The fifth lens group G5 is composed of a positive meniscus lens L51 with its concave surface facing the object side, and both lens surfaces of the positive meniscus lens L51 are aspherical.

[0094] The sixth lens group G6 is composed of a negative meniscus lens L61 with a concave surface facing the object side. The negative meniscus lens L61 has an aspherical lens surface facing the object side. An image surface I is located on the image side of the sixth lens group G6.

[0095] In this embodiment, the first lens group G1 corresponds to the object-side lens group GA. The second lens group G2 and the third lens group G3 together form an intermediate group GM having positive refractive power as a whole. The fourth lens group G4 corresponds to the first subsequent lens group GR1 that forms the rear group GR. The fifth lens group G5 corresponds to the second subsequent lens group GR2 that forms the rear group GR. The sixth lens group G6 corresponds to the third subsequent lens group GR3 that forms the rear group GR. When focusing from an object at infinity to a close object, the first subsequent lens group GR1 (fourth lens group G4) moves toward the image plane along the optical axis, and the second subsequent lens group GR2 (fifth lens group G5) moves toward the object along the optical axis.

[0096] Table 1 below lists the values ​​of the specifications of the variable magnification optical system according to the first example.

[0097] (Table 1) [Overall specifications] Magnification ratio = 2.354 fMw = 45.030 W M T f 82.400 115.000 194.000 FNO 2.910 2.910 2.910 2ω 28.655 20.555 12.452 Y 21.600 21.600 21.600 TL 142.000 183.500 223.700 Bf 16.055 16.055 16.055 [Lens specifications] Surface number R D nd νd 1 171.877 2.200 1.90366 31.27 2 114.587 7.087 1.43700 95.10 3 -1237.212 0.100 4 123.415 6.288 1.43700 95.10 5 -6347.604 (D5) 6 -177.063 1.500 1.48749 70.32 7 32.128 3.865 1.66382 27.35 8 55.335 3.525 9 -129.581 1.500 1.56384 60.71 10 268.506 1.997 11 ∞ (D11) (Aperture S) 12 46.856 3.567 1.94595 17.98 13 107.185 2.885 14 49.829 4.450 1.51860 69.89 15 -1266.722 2.161 16 -255.399 1.491 1.92286 20.88 17 29.834 4.780 1.43700 95.10 18 151.838 0.329 19* 48.160 3.811 1.59245 66.92 20* ∞ 8.140 21 91.502 4.163 1.79952 42.09 22 -76.369 (D22) 23 68.549 2.667 1.94595 17.98 24 229.390 1.234 1.76684 46.78 25 23.740 (D25) 26* -90.743 5.919 1.59245 66.92 27* -28.235 (D27) 28* -27.328 1.800 1.48749 70.32 29 -1984.395 Bf [Aspheric surface] Surface 19: κ=0.000,A4=1.504E-09,A6=-6.079E-09,A8=4.173E-11,A10=-1.301E-13 A12=1.109E-16 Surface 20: κ=0.000,A4=5.705E-06,A6=-4.363E-09,A8=2.313E-11,A10=-5.797E-14 A12=0.000E+00 Surface 26: κ=0.000,A4=3.822E-07,A6=2.351E-08,A8=-1.490E-10,A10=5.248E-13 A12=-1.193E-15 Surface 27: κ=0.000, A4=8.257E-06, A6=2.275E-08, A8=-1.369E-10, A10=4.522E-13 A12=-9.834E-16 Surface 28: κ=0.000, A4=1.670E-05, A6=3.104E-09, A8=4.253E-12, A10=-5.342E-14 A12=1.371E-16 [Variable interval key] Infinity focus W M T Focus distance 82.400 115.000 194.000 Object distance ∞ ∞ ∞ D5 2.268 45.455 74.464 D11 8.943 7.215 5.299 D22 12.359 9.050 5.044 D25 18.808 24.308 30.596 D27 7.608 5.416 3.135 Close focus state W M T Magnification 0.0906 0.1207 0.1786 Object distance 858.088 816.520 776.229 D5 2.268 45.455 74.464 D11 8.943 7.215 5.299 D22 15.090 14.130 12.840 D25 14.310 16.930 20.630 D27 9.370 7.710 5.300 [Lens group data] Group Start plane Focal length G1 1 195.199 G2 6 -63.022 G3 12 39.950 G4 23 -54.456 G5 26 66.832 G6 28 -56.858.

[0098] FIG. 2A shows various aberration diagrams of the variable magnification optical system of Example 1 when focused at infinity in the wide-angle end state. FIG. 2B shows various aberration diagrams of the variable magnification optical system of Example 1 when focused at infinity in the telephoto end state. In each aberration diagram, FNO indicates the F-number, and A indicates the half angle of view. Note that the spherical aberration diagrams indicate the F-number value corresponding to the maximum aperture, the astigmatism diagrams and distortion diagrams indicate the maximum half angle of view, and the coma diagrams indicate the values ​​of each half angle of view. d indicates the d-line (wavelength λ=587.6 nm), and g indicates the g-line (wavelength λ=435.8 nm). In the astigmatism diagrams, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. Note that the same symbols as in this example are used in the aberration diagrams of each example shown below, and redundant explanations will be omitted.

[0099] From the various aberration diagrams, it can be seen that the variable magnification optical system according to Example 1 has excellent correction of various aberrations from the wide-angle end state to the telephoto end state, and has excellent imaging performance.

[0100] Second Example The second example will be described with reference to FIGS. 3 and 4 and Table 2. FIG. 3 shows the lens configuration of a variable magnification optical system according to the second example. The variable magnification optical system ZL(2) according to the second example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having negative refractive power. When varying 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 fourth lens group G4 moves toward the image plane along the optical axis, changing the spacing between adjacent lens groups. Note that the second lens group G2 and the fifth lens group G5 are fixed relative to the image plane I during magnification. An aperture stop S is disposed inside the second lens group G2, and is fixed relative to the image plane I during zooming.

[0101] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens consisting of a negative meniscus lens L11 with a convex surface facing the object side and a positive meniscus lens L12 with a convex surface facing the object side, and a biconvex positive lens L13.

[0102] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens consisting of a biconcave negative lens L21 and a positive meniscus lens L22 with its convex surface facing the object side, a biconcave negative lens L23, a biconvex positive lens L24, a biconvex positive lens L25, a cemented negative lens consisting of a biconcave negative lens L26 and a biconvex positive lens L27, a biconvex positive lens L28, and a biconvex positive lens L29. Both lens surfaces of the positive lens L28 are aspherical. An aperture stop S is disposed between the negative lens L23 and the positive lens L24 in the second lens group G2.

[0103] The third lens group G3 is composed of a cemented negative lens consisting of a biconvex positive lens L31 and a biconcave negative lens L32.

[0104] The fourth lens group G4 is composed of a positive meniscus lens L41 with its concave surface facing the object side, and both lens surfaces of the positive meniscus lens L41 are aspherical.

[0105] The fifth lens group G5 is composed of a negative meniscus lens L51 with its concave surface facing the object side. Both lens surfaces of the negative meniscus lens L51 are aspheric. An image surface I is located on the image side of the fifth lens group G5.

[0106] In this embodiment, the first lens group G1 corresponds to the object-side lens group GA. The second lens group G2 constitutes the middle group GM, which has positive refractive power overall. The third lens group G3 corresponds to the first subsequent lens group GR1 that constitutes the rear group GR. The fourth lens group G4 corresponds to the second subsequent lens group GR2 that constitutes the rear group GR. The fifth lens group G5 corresponds to the third subsequent lens group GR3 that constitutes the rear group GR. When focusing from an object at infinity to a close object, the first subsequent lens group GR1 (third lens group G3) moves toward the image plane along the optical axis, and the second subsequent lens group GR2 (fourth lens group G4) moves toward the object along the optical axis.

[0107] Table 2 below lists the values ​​of the specifications of the variable magnification optical system according to the second example.

[0108] (Table 2) [Overall specifications] Magnification ratio = 2.354 fMw = 44.470 W M T f 82.400 115.000 194.000 FNO 2.910 2.910 2.910 2ω 28.666 20.520 12.390 Y 21.600 21.600 21.600 TL 141.300 181.600 223.000 Bf 17.580 17.580 17.580 [Lens specifications] Surface number R D nd νd 1 140.242 2.500 1.95375 32.33 2 93.845 7.711 1.43700 95.10 3 3243.579 0.100 4 115.926 7.006 1.49700 81.64 5 -1142.670 (D5) 6 -107.638 1.500 1.49700 81.64 7 44.592 3.895 1.66382 27.35 8 154.097 3.169 9 -52.031 1.500 1.51823 58.82 10 343.677 6.157 11 ∞ 2.955 (Aperture S) 12 215.864 4.047 1.94595 17.98 13 -76.395 1.807 14 301.612 3.389 1.59319 67.90 15 -91.000 0.595 16 -64.738 1.474 1.92286 20.88 17 37.030 5.294 1.43700 95.10 18 -201.403 1.095 19* 44.800 4.784 1.59255 67.86 20* -258.339 0.100 21 121.430 3.915 1.79950 42.34 22 -95.231 (D22) 23 121.448 2.670 1.94595 17.98 24 -383.141 1.224 1.72000 43.61 25 25.672 (D25) 26* -73.480 5.620 1.67790 54.89 27* -28.683 (D27) 28* -30.014 1.900 1.48749 70.32 29* -317.720 Bf [Aspheric surface データ] Surface 19: κ=0.000,A4=-2.580E-06,A6=-2.781E-09,A8=6.087E-12,A10=-1.542E-14 A12=1.672E-17 Surface 20: κ=0.000,A4=9.392E-08,A6=-2.660E-09,A8=2.889E-12,A10=-4.235E-15 A12=0.000E+00 Surface 26: κ=0.000,A4=-1.401E-06,A6=8.643E-09,A8=-1.465E-11,A10=-2.254E-14 A12=-1.063E-16 Surface 27: κ=0.000,A4=5.349E-06,A6=7.127E-09,A8=-1.507E-11,A10=7.454E-15 A12=-1.405E-16 Surface 28: κ=0.000,A4=2.023E-05,A6=-3.714E-08,A8=1.151E-10,A10=-1.819E-13 A12=1.124E-16 Surface 29: κ=0.000,A4=7.556E-06,A6=-3.415E-08,A8=1.029E-10,A10=-1.477E-13 A12=6.108E-17 [Changing interval] Infinity focus state W M T Focus distance 82.400 115.000 194.000 Object distance ∞ ∞ ∞ D5 2.685 42.953 84.443 D22 12.981 9.243 1.500 D25 23.498 29.829 43.044 D27 9.566 6.973 1.500 Close focus W M T Magnification 0.0916 0.1229 0.1796 Object distance 858.824 818.461 776.971 D5 2.685 42.953 84.443 D22 15.210 13.450 10.380 D25 19.410 23.250 29.550 D27 11.430 9.340 6.120 [Lens group data] Group Initial surface Focal length G1 1 171.084 G2 6 44.469 G3 23 -52.063 G4 26 66.055 G5 28 -68.139.

[0109] 4A is a diagram showing various aberrations when the variable magnification optical system according to Example 2 is focused at infinity in the wide-angle end state. Fig. 4B is a diagram showing various aberrations when the variable magnification optical system according to Example 2 is focused at infinity in the telephoto end state. It can be seen from the various aberration diagrams 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.

[0110] Third Example A third example will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 is a diagram showing the lens configuration of a variable magnification optical system according to the third example. The variable magnification optical system ZL(3) according to the third example is composed of, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having negative refractive power, a sixth lens group G6 having positive refractive power, and a seventh lens group G7 having negative refractive power. When changing 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 fifth lens group G5 move toward the object along the optical axis, and the second lens group G2 and the sixth lens group G6 move toward the image plane along the optical axis, changing the spacing between adjacent lens groups. During magnification change, the fourth lens group G4 and the seventh lens group G7 are fixed with respect to the image plane I. An aperture diaphragm S is disposed between the second lens group G2 and the third lens group G3, and during magnification change, the aperture diaphragm S moves along the optical axis together with the third lens group G3.

[0111] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens consisting of a negative meniscus lens L11 with a convex surface facing the object side and a biconvex positive lens L12, and a positive meniscus lens L13 with a convex surface facing the object side.

[0112] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens of a biconcave negative lens L21 and a positive meniscus lens L22 with its convex surface facing the object side, and a biconcave negative lens L23.

[0113] The third lens group G3 is composed of a positive meniscus lens L31 with its convex surface facing the object side.

[0114] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with a convex surface facing the object side, a cemented negative lens consisting of a negative meniscus lens L42 with a convex surface facing the object side and a positive meniscus lens L43 with a convex surface facing the object side, a positive meniscus lens L44 with a convex surface facing the object side, and a biconvex positive lens L45. Both lens surfaces of the positive meniscus lens L44 are aspherical.

[0115] The fifth lens group G5 is composed of a cemented negative lens consisting of a positive meniscus lens L51 with a convex surface facing the object side and a negative meniscus lens L52 with a convex surface facing the object side.

[0116] The sixth lens group G6 is composed of a positive meniscus lens L61 with its concave surface facing the object side, and both lens surfaces of the positive meniscus lens L61 are aspherical.

[0117] The seventh lens group G7 is composed of a negative lens L71 having a plano-concave shape with a flat surface facing the image surface side. The negative lens L71 has an aspherical lens surface facing the object surface. An image surface I is located on the image side of the seventh lens group G7.

[0118] In this embodiment, the first lens group G1 corresponds to the object-side lens group GA. The second lens group G2, the third lens group G3, and the fourth lens group G4 together form an intermediate group GM having positive refractive power as a whole. The fifth lens group G5 corresponds to the first subsequent lens group GR1 that forms the rear group GR. The sixth lens group G6 corresponds to the second subsequent lens group GR2 that forms the rear group GR. The seventh lens group G7 corresponds to the third subsequent lens group GR3 that forms the rear group GR. When focusing from an object at infinity to a close object, the first subsequent lens group GR1 (fifth lens group G5) moves toward the image plane along the optical axis, and the second subsequent lens group GR2 (sixth lens group G6) moves toward the object along the optical axis.

[0119] Table 3 below lists the values ​​of the specifications of the variable magnification optical system according to the third example.

[0120] (Table 3) [Overall specifications] Magnification ratio = 2.691 fMw = 36.199 W M T f 82.400 115.000 194.000 FNO 2.910 2.910 2.910 2ω 33.525 21.010 12.536 Y 21.600 21.600 21.600 TL 160.100 211.900 223.700 Bf 16.055 16.055 16.055 [Lens specifications] Surface number R D nd νd 1 199.073 2.200 1.90366 31.27 2 126.494 8.129 1.43700 95.10 3 -719.999 0.100 4 116.402 7.427 1.43700 95.10 5 6813.349 (D5) 6 -338.526 1.500 1.49700 81.14 7 34.249 3.505 1.66382 27.35 8 56.082 3.516 9 -106.736 1.500 1.59349 67.00 10 335.611 (D10) 11 ∞ 3.047 (Aperture S) 12 39.818 3.718 1.94595 17.98 13 78.706 (D13) 14 41.584 4.793 1.49782 82.57 15 1846.157 1.539 16 1852.423 1.471 1.92286 20.88 17 25.361 4.747 1.43700 95.10 18 84.999 0.100 19* 38.841 3.249 1.59255 67.86 20* 109.734 10.867 21 77.691 3.955 1.80611 40.73 22 -82.716 (D22) 23 51.729 2.629 1.94595 17.98 24 104.337 1.205 1.78590 44.17 25 22.293 (D25) 26* -58.828 4.495 1.59245 66.92 27* -28.061 (D27) 28* -33.565 1.800 1.48749 70.32 29 ∞ Bf [Aspheric surface] Surface 19: κ=0.000,A4=3.529E-06,A6=7.180E-09,A8=1.864E-11,A10=0.000E+00 A12=0.000E+00 Surface 20: κ=0.000,A4=1.102E-05,A6=8.970E-09,A8=1.747E-11,A10=0.000E+00 A12=0.000E+00 Surface 26: κ=0.000,A4=-5.680E-07,A6=7.802E-09,A8=5.979E-12,A10=-4.891E-13 A12=1.108E-15 Surface 27: κ=0.000, A4=9.289E-06, A6=5.070E-09, A8=8.783E-11, A10=-7.537E-13 A12=1.362E-15 Surface 28: κ=0.000, A4=1.899E-05, A6=2.021E-08, A8=1.589E-11, A10=-1.257E-13 A12=3.238E-16 [Variable interval date] Infinity focus W M T Focus distance 82.400 115.000 194.000 Object distance ∞ ∞ ∞ D5 1.933 55.833 90.777 D10 26.678 24.269 1.502 D13 2.794 3.106 2.766 D22 10.272 6.444 1.500 D25 19.265 26.828 33.592 D27 7.054 3.319 1.500 Close focus W M T Magnification 0.00796 0.116 0.1758 Object distance 840.025 788.167 776.252 D5 1.933 55.833 90.777 D10 26.678 24.269 1.502 D13 2.794 3.106 2.766 D22 12.447 11.588 15.168 D25 14.990 18.456 15.465 D27 9.160 6.549 5.959 [Lens group data] Group Initial surface Focal length G1 1 195.158 G2 6 -62.952 G3 12 81.410 G4 14 55.746 G5 23 -58.164 G6 26 85.895 G7 28 -68.853.

[0121] 6A is a diagram showing various aberrations of the variable magnification optical system according to Example 3 when focused at infinity in the wide-angle end state. Fig. 6B is a diagram showing various aberrations of the variable magnification optical system according to Example 3 when focused at infinity in the telephoto end state. It can be seen from the various aberration diagrams 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.

[0122] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below, which summarizes the values ​​corresponding to each of the conditional expressions (1) to (15) for all the examples (first to third examples). Conditional expression (1) 1.05<f1 / TLw<2.00 Conditional expression (2) 2.00<f1 / fMw<7.00 Conditional expression (3) 1.50<f1 / (-fn1)<6.00 Conditional expression (4) 0.05<(-fR3) / ft<1.00 Conditional expression (5) 0.00<(-fR3) / fw<2.00 Conditional expression (6) 0.15<(TLt-TLw) / TLw<1.00 Conditional expression (7) 1.50<f1 / (-fR3)<6.00 Conditional expression (8) 50.0<νd3<80.0 Conditional expression (9) 1.45<nd3<1.58 Conditional expression (10) 1.80<TLw / (-fR3)<2.70 Conditional Expression (11) 0.30<(-fR1) / fR2<1.30 Conditional Expression (12) 0.70<(-fR1) / fMw<2.00 Conditional Expression (13) 1.00<fR2 / fMw<3.00 Conditional Expression (14) 1.00<(-fR3) / fMw<3.50 Conditional expression (15) 0.10<Bft / ft<0.80

[0123] [Conditional Expression Corresponding Values] (Examples 1 to 3) Conditional Expression Example 1 Example 2 Example 3 (1) 1.3795 1.2152 1.2231 (2) 4.3349 3.8475 5.3924 (3) 3.0984 3.2841 3.0984 (4) 0.2933 0.3510 0.3552 (5) 0.6905 0.8265 0.9556 (6) 0.5774 0.5803 0.3985 (7) 3.4306 2.5125 2.8331 (8) 1.4875 1.4875 1.4875 (9) 70.32 70.32 70.32 (10) 2.4868 2.0675 2.3164 (11) 0.8148 0.7881 0.6772 (12) 1.2093 1.1707 1.6068 (13) 1.4842 1.4854 2.3729 (14) 1.2627 1.5323 1.9020 (15) 0.3564 0.3953 0.4437

[0124] According to the above-described embodiments, it is possible to realize a variable-magnification optical system that is small in size, yet bright and has good optical performance.

[0125] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0126] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the variable magnification optical system of each embodiment.

[0127] Although examples of the variable magnification optical system of each embodiment have been shown with a five-group configuration, a six-group configuration, and a seven-group configuration, the present application is not limited to these, and variable magnification optical systems with other group configurations (e.g., eight groups, nine groups, ten groups, etc.) may also be configured. For example, a variable magnification optical system of each embodiment may have a configuration in which a lens or lens group is added to the most object-side or most image-side of the variable magnification optical system. Also, for example, a variable magnification optical system of each embodiment may have a configuration in which a lens or lens group is added to the most object-side or most image-side of the intermediate group. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during magnification variation.

[0128] In the variable magnification optical systems of each embodiment, instead of the first and second subsequent lens groups (i.e., the fourth and fifth lens groups, or the third and fourth lens groups, or the fifth and sixth lens groups), a single lens group, multiple lens groups, or partial lens groups may be moved in the optical axis direction to serve 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 motor drive (using an ultrasonic motor, etc.) for autofocusing.

[0129] 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 (oscillated) in a plane including the optical axis, to serve as an image stabilization lens group that corrects image blur caused by camera shake.

[0130] The lens surface may be spherical, flat, or aspherical. Spherical or flat lens surfaces are preferred because they facilitate lens processing and assembly adjustment, and prevent degradation of optical performance due to errors in processing and assembly adjustment. Furthermore, they are preferred because they minimize degradation of imaging performance even when the image plane is misaligned.

[0131] When the lens surface is aspherical, the aspherical surface may be any of a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, and a hybrid aspherical surface in which a resin is formed into an aspherical 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.

[0132] It is preferable that the aperture stop be located inside the intermediate lens group (i.e., between the second and third lens groups, or inside the second lens group), but it is also possible to use the lens frame to fulfill that role without providing a member serving as an aperture stop.

[0133] Each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance.

[0134] G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G5 Fifth lens group G6 Sixth lens group G7 Seventh lens group I Image plane S Aperture stop

Claims

1. the optical system comprises, in order from the object side along the optical axis, an object-side lens group having positive refractive power, an intermediate lens group having positive refractive power, and a rear lens group; the intermediate group has at least one lens group, the rear group includes, arranged in order from the object side along the optical axis, a first rear lens group having negative refractive power, a second rear lens group having positive refractive power, and a third rear lens group having negative refractive power; When changing magnification, the spacing between adjacent lens groups changes, the second subsequent lens group moves along the optical axis during focusing; A variable magnification optical system that satisfies the following condition: 1.05<f1 / TLw<2.00 where f1 is the focal length of the object-side lens group. TLw: total length of the variable magnification optical system in the wide-angle end state

2. the optical system comprises, in order from the object side along the optical axis, an object-side lens group having positive refractive power, an intermediate lens group having positive refractive power, and a rear lens group; the intermediate group has at least one lens group, the rear group includes, arranged in order from the object side along the optical axis, a first rear lens group having negative refractive power, a second rear lens group having positive refractive power, and a third rear lens group having negative refractive power; During magnification change, the interval between adjacent lens groups changes, and at least a part of the lens groups in the intermediate group is fixed with respect to the image plane; A variable magnification optical system that satisfies the following condition: 2.00<f1 / fMw<7.00 where f1 is the focal length of the object-side lens group. fMw: the composite focal length of the intermediate group in the wide-angle end state

3. The variable magnification optical system according to claim 2 , wherein the second subsequent lens group moves along the optical axis during focusing.

4. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 1.50<f1 / (-fn1)<6.00 where fn1 is the focal length of the lens group having negative refractive power and arranged closest to the object side in the variable magnification optical system.

5. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.05<(-fR3) / ft<1.00 where fR3 is the focal length of the third subsequent lens group. ft: focal length of the variable magnification optical system in the telephoto end state

6. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.00<(-fR3) / fw<2.00 where fR3 is the focal length of the third subsequent lens group. fw: focal length of the variable magnification optical system in the wide-angle end state

7. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.15<(TLt-TLw) / TLw<1.00 where TLt is the total length of the variable magnification optical system in the telephoto end state. TLw: total length of the variable magnification optical system in the wide-angle end state

8. 3. A variable magnification optical system according to claim 1, which satisfies the following condition: 1.0≦n≦1.0; 1.50<f1 / (-fR3)<6.00 where fR3 is the focal length of the third subsequent lens group.

9. 3. The variable magnification optical system according to claim 1, wherein the third subsequent lens group has a lens that satisfies the following condition: 1 / 2<1 / 2<1. 50.0<νd3<80.0 1.45<nd3<1.58 where νd3 is the Abbe number of the lens in the third subsequent lens group. nd3: refractive index of the lens in the third subsequent lens group with respect to the d line

10. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 1.80<TLw / (-fR3)<2.70 where TLw is the total length of the variable magnification optical system in the wide-angle end state. fR3: focal length of the third subsequent lens group

11. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.30<(-fR1) / fR2<1.30 where fR1 is the focal length of the first subsequent lens group. fR2: the focal length of the second subsequent lens group

12. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.70<(-fR1) / fMw<2.00 where fR1 is the focal length of the first subsequent lens group. fMw: the composite focal length of the intermediate group in the wide-angle end state

13. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 1.00<fR2 / fMw<3.00 where fR2 is the focal length of the second subsequent lens group. fMw: the composite focal length of the intermediate group in the wide-angle end state

14. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 1.00<(-fR3) / fMw<3.50 where fR3 is the focal length of the third subsequent lens group. fMw: the composite focal length of the intermediate group in the wide-angle end state

15. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.10<Bft / ft<0.80 where Bft is the back focus of the variable magnification optical system in the telephoto end state. ft: focal length of the variable magnification optical system in the telephoto end state

16. 3. A variable magnification optical system according to claim 1, wherein the third subsequent lens group is fixed relative to an image plane during magnification variation.

17. 3. The variable magnification optical system according to claim 1, wherein the first subsequent lens group moves along the optical axis during focusing.

18. An optical instrument comprising a variable magnification optical system according to claim 1 or 2.