JP7552701B2 - Variable magnification optical system and optical equipment - Google Patents

Description

The present invention relates to a variable magnification optical system and an optical instrument .

Variable magnification optical systems suitable for photo cameras, electronic still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). In such variable magnification optical systems, it is difficult to suppress aberration fluctuations during focusing.

JP 2019-12243 A

The variable magnification optical system according to the present invention is composed of, in order from the object side along the optical axis, a front lens group having positive refractive power and composed of one lens group, a first intermediate lens group having negative refractive power and composed of one or two lens groups, a second intermediate lens group having positive refractive power and composed of two or three lens groups, and a rear lens group composed of three or four lens groups, and during magnification, the front lens group and the first intermediate lens group, the first intermediate lens group and the second intermediate lens group, and the second intermediate lens group and the rear lens group are arranged in the order of the object side along the optical axis. The distance between the lens groups changes, and when the first intermediate lens group, the second intermediate lens group and the subsequent lens group are composed of multiple lens groups, the distance between each of the adjacent lens groups that constitute the multiple lens groups also changes, and the subsequent lens group includes a first focusing lens group that is arranged closest to the object of the subsequent lens groups and moves along the optical axis during focusing, and at least one other focusing lens group that is arranged closer to the image than the first focusing lens group and moves along the optical axis on a trajectory different from that of the first focusing lens group during focusing, and satisfies the following conditional expression.
5.00<f1/(-fM1w)<10.00
0.10<BFw/fw<1.00
ft/fw>3.50
where f1 is the focal length of the front lens group, fM1w is the focal length of the first intermediate lens group in the wide-angle end state, BFw is the back focus of the variable magnification optical system in the wide-angle end state, and fw is the focal length of the variable magnification optical system in the wide-angle end state.
ft: focal length of the variable magnification optical system in the telephoto end state

The optical device according to the present invention is configured with the variable magnification optical system described above.

FIG. 2 is a diagram showing a lens configuration of a variable magnification optical system according to a first example. 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. 3A and 3B are diagrams showing various aberrations of the variable magnification optical system according to Example 1 when focused on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to a second example. 5A and 5B 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. 6A and 6B are diagrams showing various aberrations of the variable magnification optical system according to the second example when focused on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to a third example. 8A and 8B 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. 9A and 9B are diagrams showing various aberrations of the variable magnification optical system according to the third example when focused on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to a fourth example. 11A and 11B 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. 12A and 12B are diagrams showing various aberrations in the variable magnification optical system according to Example 4 when focusing on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to a fifth example. 14A and 14B are diagrams showing various aberrations of the variable magnification optical system according to Example 5 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. 15A and 15B are diagrams showing various aberrations of the variable magnification optical system according to Example 5 when focusing on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing the lens configuration of a variable magnification optical system according to Example 6. 17A and 17B are diagrams showing various aberrations of the variable magnification optical system according to Example 6 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. 18A and 18B are diagrams showing various aberrations of the variable magnification optical system according to Example 6 when focusing on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 13 is a diagram showing a lens configuration of a variable magnification optical system according to a seventh example. 20A and 20B are diagrams showing various aberrations of the variable magnification optical system according to Example 7 when focused on infinity in the wide-angle end state and the telephoto end state, respectively. 21A and 21B are diagrams showing various aberrations of the variable magnification optical system according to Example 7 when focusing on a close object in the wide-angle end state and the telephoto end state, respectively. FIG. 1 is a diagram showing the configuration of a camera equipped with a variable magnification optical system according to an embodiment of the present invention. 5 is a flowchart showing a method of manufacturing a variable magnification optical system according to the present embodiment.

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. 22. As shown in FIG. 22, 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 an LCD screen 5. The photographing lens 3 is equipped with 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 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.

Light from the 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's operation. Note that this camera may be a mirrorless camera or a single-lens reflex camera with a quick-return mirror. Also, the variable magnification optical system ZL shown in FIG. 22 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.

Next, the variable magnification optical system according to this 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 this embodiment is configured to have a front lens group GA having a positive refractive power, a first intermediate lens group GM1 having a negative refractive power, a second intermediate lens group GM2 having a positive refractive power, and a rear lens group GR, which are arranged in order from the object side along the optical axis, as shown in FIG. 1. When changing the magnification, the interval between adjacent lens groups changes. The rear lens group GR includes a first focusing lens group GF1, which is arranged closest to the object side of the rear lens group GR and moves along the optical axis when focusing, and at least one other focusing lens group, which is arranged closer to the image side than the first focusing lens group GF1 and moves along the optical axis on a different trajectory from the first focusing lens group GF1 when focusing.

With the above-mentioned configuration, the variable-magnification optical system ZL according to this embodiment satisfies the following conditional expressions (1) and (2).
4.30<f1/(-fM1w)<10.00...(1)
0.10<BFw/fw<1.00...(2)
where f1 is the focal length of the front lens group GA, fM1w is the focal length of the first intermediate lens group GM1 in the wide-angle end state, BFw is the back focus of the variable magnification optical system ZL in the wide-angle end state, and fw is the focal length of the variable magnification optical system ZL in the wide-angle end state.

According to this embodiment, it is possible to obtain a variable magnification optical system with little aberration fluctuation during focusing, and an optical device equipped with this variable magnification optical system. In addition, since the subsequent lens group GR has multiple focusing lens groups, it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing without increasing the size of the focusing lens group. In addition, by changing the spacing between adjacent lens groups during magnification, aberration correction during magnification can be performed well.

The variable magnification optical system ZL according to this embodiment may be the variable magnification optical system ZL(2) shown in Fig. 4, the variable magnification optical system ZL(3) shown in Fig. 7, or the variable magnification optical system ZL(4) shown in Fig. 10. The variable magnification optical system ZL according to this embodiment may be the variable magnification optical system ZL(5) shown in Fig. 13, the variable magnification optical system ZL(6) shown in Fig. 16, or the variable magnification optical system ZL(7) shown in Fig. 19.

Conditional expression (1) specifies the appropriate relationship between the focal length of the front lens group GA and the focal length of the first intermediate lens group GM1 in the wide-angle end state. By satisfying conditional expression (1), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during zooming.

When the corresponding value of conditional expression (1) exceeds the upper limit, the refractive power of the first intermediate lens group GM1 becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during zooming. By setting the upper limit of conditional expression (1) to 9.50, 9.00, 8.80, 8.50, 8.30, 8.00, or even 7.80, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (1) falls below the lower limit, the refractive power of the front lens group GA becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during zooming. By setting the lower limit of conditional expression (1) to 4.50, 4.80, 5.00, or even 5.40, the effect of this embodiment can be made more certain.

Conditional expression (2) specifies the appropriate relationship between the back focus of the variable magnification optical system ZL in the wide-angle end state and the focal length of the variable magnification optical system ZL in the wide-angle end state. By satisfying conditional expression (2), various aberrations, including coma aberration in the wide-angle end state, can be effectively corrected.

If the corresponding value of conditional expression (2) exceeds the upper limit, the back focus of the variable magnification optical system ZL in the wide-angle end state becomes large relative to the focal length of the variable magnification optical system ZL in the wide-angle end state, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the upper limit of conditional expression (2) to 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, or even 0.60, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (2) falls below the lower limit, the back focus of the variable magnification optical system ZL in the wide-angle end state becomes small relative to the focal length of the variable magnification optical system ZL in the wide-angle end state, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. It also becomes difficult to arrange the mechanical components of the lens barrel. By setting the lower limit of conditional expression (2) to 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or even 0.43, the effect of this embodiment can be made more certain.

In the variable magnification optical system ZL according to this embodiment, it is desirable that the second intermediate lens group GM2 includes at least two lens groups having positive refractive power, and satisfies the following conditional expression (3).
1.50<f1/fM21<7.00...(3)
where fM21 is the focal length of the lens group closest to the object among the lens groups included in the second intermediate lens group GM2.

Conditional expression (3) specifies the appropriate relationship between the focal length of the front lens group GA and the focal length of the lens group closest to the object among the lens groups included in the second intermediate lens group GM2. By satisfying conditional expression (3), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing.

If the corresponding value of conditional expression (3) exceeds the upper limit, the refractive power of the lens group closest to the object among the lens groups included in the second intermediate lens group GM2 becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the upper limit of conditional expression (3) to 6.80, 6.50, 6.30, 6.00, 5.80, 5.00, 4.50, 4.00, or even 3.50, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (3) falls below the lower limit, the refractive power of the front lens group GA becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (3) to 1.60, 1.80, 2.00, 2.10, or even 2.20, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (4).
2.00<f1/fw<8.00...(4)

Conditional expression (4) specifies the appropriate relationship between the focal length of the front lens group GA and the focal length of the variable magnification optical system ZL in the wide-angle end state. By satisfying conditional expression (4), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during magnification change without increasing the size of the lens barrel.

When the corresponding value of conditional expression (4) exceeds the upper limit, the refractive power of the front lens group GA becomes weak, so the amount of movement of the front lens group GA during magnification change increases, and the lens barrel becomes larger. By setting the upper limit of conditional expression (4) to 7.80, 7.50, 7.40, 7.00, 6.50, 6.30, or even 6.00, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (4) falls below the lower limit, the refractive power of the front lens group GA becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during zooming. By setting the lower limit of conditional expression (4) to 2.30, 2.50, 2.80, 3.00, 3.30, 3.50, or even 3.80, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (5).
0.20<|fFs|/f1<2.00 (5)
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group GR.

Conditional expression (5) specifies the appropriate relationship between the focal length of the focusing lens group with the strongest refractive power among the focusing lens groups included in the rear lens group GR and the focal length of the front lens group GA. By satisfying conditional expression (5), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing without increasing the size of the lens barrel. In addition, it is possible to suppress fluctuations in various aberrations, including spherical aberration, during magnification change without increasing the size of the lens barrel.

When the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the focusing lens group becomes weak, so the amount of movement of the focusing lens group during focusing increases, and the lens barrel becomes larger. Also, the refractive power of the front lens group GA becomes strong, so it becomes difficult to suppress the fluctuation of various aberrations, including spherical aberration, during zooming. By setting the upper limit of conditional expression (5) to 1.80, 1.50, 1.30, 1.00, 0.85, 0.70, 0.65, 0.60, or even 0.58, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (5) falls below the lower limit, the refractive power of the focusing lens group becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. In addition, the refractive power of the front lens group GA becomes weak, so the amount of movement of the front lens group GA during magnification change increases, and the lens barrel becomes larger. By setting the lower limit of conditional expression (5) to 0.22, 0.24, 0.25, or even 0.26, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (6).
1.50<|fFs|/(-fM1w)<5.00 (6)
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group GR.

Conditional expression (6) specifies the appropriate relationship between the focal length of the focusing lens group with the strongest refractive power among the focusing lens groups included in the rear lens group GR and the focal length of the first intermediate lens group GM1 in the wide-angle end state. By satisfying conditional expression (6), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing. In addition, it is possible to effectively correct various aberrations, including coma aberration, in the wide-angle end state.

If the corresponding value of conditional expression (6) exceeds the upper limit, the refractive power of the first intermediate lens group GM1 in the wide-angle end state becomes strong, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the upper limit of conditional expression (6) to 4.85, 4.70, 4.50, 4.35, 4.25, 3.85, 3.50, 3.00, or even 2.50, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (6) falls below the lower limit, the refractive power of the focusing lens group becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (6) to 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, or even 1.83, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (7).
0.90<|fFs|/fM2w<4.00 (7)
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the rear lens group GR, and fM2w is the focal length of the second intermediate lens group GM2 in the wide-angle end state.

Conditional expression (7) specifies the appropriate relationship between the focal length of the focusing lens group with the strongest refractive power among the focusing lens groups included in the rear lens group GR and the focal length of the second intermediate lens group GM2 in the wide-angle end state. By satisfying conditional expression (7), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing. In addition, it is possible to effectively correct various aberrations, including coma aberration, in the wide-angle end state.

If the corresponding value of conditional expression (7) exceeds the upper limit, the refractive power of the second intermediate lens group GM2 in the wide-angle end state becomes strong, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the upper limit of conditional expression (7) to 3.80, 3.50, 3.30, 3.00, 2.80, 2.60, 2.00, 1.80, or even 1.50, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (7) falls below the lower limit, the refractive power of the focusing lens group becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (7) to 0.95, 0.98, 1.00, 1.03, or even 1.05, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (8).
0.20<f1/(-fRw)<5.00...(8)
where fRw is the focal length of the rear lens group GR in the wide-angle end state.

Conditional expression (8) specifies the appropriate relationship between the focal length of the front lens group GA and the focal length of the rear lens group GR in the wide-angle end state. By satisfying conditional expression (8), it is possible to effectively correct various aberrations, including coma aberration in the wide-angle end state, without increasing the size of the lens barrel.

If the corresponding value of conditional expression (8) exceeds the upper limit, the refractive power of the rear lens group GR in the wide-angle end state becomes strong, making it difficult to correct various aberrations, including coma aberration in the wide-angle end state. In addition, the refractive power of the front lens group GA becomes weak, so the amount of movement of the front lens group GA during magnification change becomes large, and the lens barrel becomes large. By setting the upper limit of conditional expression (8) to 4.50, 4.00, 3.80, 3.50, 3.30, 3.00, 2.80, or even 2.50, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (8) falls below the lower limit, the refractive power of the rear lens group GR in the wide-angle end state becomes weak, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the lower limit of conditional expression (8) to 0.40, 0.50, 0.60, 0.65, 0.68, or even 0.70, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (9).
0.10<MTF1/MTF2<3.00 (9)
where MTF1 is the absolute value of the amount of movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance in the telephoto end state, and MTF2 is the absolute value of the amount of movement of the focusing lens group that is closest to the first focusing lens group GF1 among the other focusing lens groups when focusing from an object at infinity to an object at a close distance in the telephoto end state.

Conditional expression (9) specifies the appropriate relationship between the amount of movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance in the telephoto end state and the amount of movement of the focusing lens group closest to the first focusing lens group GF1. By satisfying conditional expression (9), it is possible to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance in the telephoto end state.

If the corresponding value of conditional expression (9) exceeds the upper limit, the amount of movement of the first focusing lens group GF1 becomes too large when focusing from an object at infinity to an object at a close distance in the telephoto end state, making it difficult to suppress fluctuations in various aberrations, including spherical aberration. By setting the upper limit of conditional expression (9) to 2.80, 2.50, 2.30, 2.00, 1.80, 1.65, or even 1.50, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (9) falls below the lower limit, when focusing from an object at infinity to an object at a close distance in the telephoto end state, the amount of movement of the focusing lens group closest to the first focusing lens group GF1 becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration. By setting the lower limit of conditional expression (9) to 0.13, 0.15, 0.18, 0.20, 0.23, or even 0.25, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (10).
0.10<βF1w/βF2w<3.00 (10)
where βF1w is the combined lateral magnification of the focusing lens group included in the subsequent lens group GR, which is located closer to the object side than the focusing lens group closest to the image side, when focusing on an object at infinity in the wide-angle end state; and βF2w is the lateral magnification of the focusing lens group included in the subsequent lens group GR, which is located closer to the image side, when focusing on an object at infinity in the wide-angle end state.

Conditional expression (10) specifies the appropriate relationship between the lateral magnification of the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the wide-angle end state, and the combined lateral magnification of the focusing lens group located closer to the object side than the focusing lens group closest to the image when focusing on an object at infinity in the wide-angle end state. By satisfying conditional expression (10), it is possible to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object in the wide-angle end state.

If the corresponding value of conditional expression (10) exceeds the upper limit, the composite lateral magnification of the focusing lens group located closer to the object than the focusing lens group closest to the image becomes too large when focusing on an object at infinity in the wide-angle end state. Therefore, it becomes difficult to suppress the fluctuation of various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance in the wide-angle end state. The effect of this embodiment can be made more certain by setting the upper limit of conditional expression (10) to 2.80, 2.50, 2.30, 2.00, 1.80, 1.50, 1.30, 1.00, or even 0.90.

If the corresponding value of conditional expression (10) falls below the lower limit, the lateral magnification of the focusing lens group closest to the image when focusing on an object at infinity in the wide-angle end state becomes too large. Therefore, it becomes difficult to suppress the fluctuation of various aberrations, including spherical aberration, when focusing from an object at infinity to a close object in the wide-angle end state. By setting the lower limit of conditional expression (10) to 0.20, 0.35, 0.50, 0.55, 0.58, or even 0.60, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (11).
0.10<βF1t/βF2t<3.00 (11)
where βF1t is the combined lateral magnification of the focusing lens group included in the subsequent lens group GR, which is located closer to the object side than the focusing lens group closest to the image side, when focusing on an object at infinity in the telephoto end state; and βF2t is the lateral magnification of the focusing lens group included in the subsequent lens group GR, which is located closer to the image side, when focusing on an object at infinity in the telephoto end state.

Conditional expression (11) specifies the appropriate relationship between the lateral magnification of the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the telephoto end state, and the combined lateral magnification of the focusing lens group located closer to the object side than the focusing lens group closest to the image when focusing on an object at infinity in the telephoto end state. By satisfying conditional expression (11), it is possible to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object in the telephoto end state.

If the corresponding value of conditional expression (11) exceeds the upper limit, the composite lateral magnification of the focusing lens group located closer to the object side than the focusing lens group closest to the image side when focusing on an object at infinity in the telephoto end state becomes too large. Therefore, it becomes difficult to suppress the fluctuation of various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance in the telephoto end state. The effect of this embodiment can be made more certain by setting the upper limit of conditional expression (11) to 2.80, 2.50, 2.30, 2.00, 1.80, 1.50, 1.30, 1.00, or even 0.80.

If the corresponding value of conditional expression (11) falls below the lower limit, the lateral magnification of the focusing lens group closest to the image when focusing on an object at infinity in the telephoto end state becomes too large. Therefore, it becomes difficult to suppress the fluctuation of various aberrations, including spherical aberration, when focusing from an object at infinity to a close object in the telephoto end state. The effect of this embodiment can be made more certain by setting the lower limit of conditional expression (11) to 0.13, 0.15, 0.18, 0.20, 0.23, or even 0.25.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (12).
0.50<βF1w<2.60 (12)
where βF1w is the combined lateral magnification of the focusing lens group included in the subsequent lens group GR, the focusing lens group located closer to the object side than the focusing lens group closest to the image side, when focusing on an object at infinity in the wide-angle end state.

Conditional expression (12) specifies an appropriate range for the composite lateral magnification when focusing on an object at infinity in the wide-angle end state of the focusing lens group located closer to the object than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR. By satisfying conditional expression (12), it is possible to suppress fluctuations in various aberrations, including spherical aberration and coma aberration, during focusing.

If the corresponding value of conditional expression (12) exceeds the upper limit, it becomes difficult to suppress the fluctuation of various aberrations during focusing. By setting the upper limit of conditional expression (12) to 2.58, 2.55, 2.00, 1.80, 1.50, 1.30, or even 1.20, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (12) falls below the lower limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the lower limit of conditional expression (12) to 0.55, 0.60, 0.65, 0.70, or even 0.73, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (13).
0.20<βF2w<1.80 (13)
where βF2w is the lateral magnification of the focusing lens group that is closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the wide-angle end state.

Conditional expression (13) specifies an appropriate range for the lateral magnification of the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the wide-angle end state. By satisfying conditional expression (13), it is possible to suppress fluctuations in various aberrations, including spherical aberration and coma aberration, during focusing.

If the corresponding value of conditional expression (13) exceeds the upper limit, it becomes difficult to suppress the fluctuation of various aberrations during focusing. By setting the upper limit of conditional expression (13) to 1.78, 1.75, 1.73, 1.70, 1.68, or even 1.60, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (13) falls below the lower limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the lower limit of conditional expression (13) to 0.23, 0.25, or even 0.28, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (14).
{βF1w+(1/βF1w)} ^-2 ≦0.25 ... (14)
where βF1w is the combined lateral magnification of the focusing lens group included in the subsequent lens group GR, the focusing lens group located closer to the object side than the focusing lens group closest to the image side, when focusing on an object at infinity in the wide-angle end state.

Conditional expression (14) specifies an appropriate range for the composite lateral magnification when focusing on an object at infinity in the wide-angle end state of the focusing lens group that is located closer to the object than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR. By satisfying conditional expression (14), it is possible to suppress the fluctuation of various aberrations, including spherical aberration and coma aberration, during focusing. If the corresponding value of conditional expression (14) exceeds the upper limit, it becomes difficult to suppress the fluctuation of various aberrations during focusing.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (15).
{βF2w+(1/βF2w)} ^-2 ≦0.25 ... (15)
where βF2w is the lateral magnification of the focusing lens group that is closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the wide-angle end state.

Conditional expression (15) specifies an appropriate range for the lateral magnification of the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group GR when focusing on an object at infinity in the wide-angle end state. By satisfying conditional expression (15), it is possible to suppress fluctuations in various aberrations, including spherical aberration and coma aberration, during focusing. If the corresponding value of conditional expression (15) exceeds the upper limit value, it becomes difficult to suppress fluctuations in various aberrations during focusing.

In the variable magnification optical system ZL according to this embodiment, it is desirable that the rear lens group GR includes at least one lens group that is arranged closer to the image side than the focusing lens group closest to the image side among the focusing lens groups included in the rear lens group GR. This makes it possible to effectively suppress fluctuations in various aberrations, including spherical aberration, during focusing.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (16).
0.10<|fFs|/|fRF|<4.00...(16)
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group GR, and fRF is the focal length of the lens group arranged adjacent to the image side of the focusing lens group closest to the image side among the at least one lens group.

Conditional expression (16) specifies the appropriate relationship between the focal length of the focusing lens group with the strongest refractive power among the focusing lens groups included in the rear lens group GR and the focal length of the lens group arranged adjacent to the image side of the focusing lens group closest to the image side. By satisfying conditional expression (16), it is possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing.

If the corresponding value of conditional expression (16) exceeds the upper limit, the refractive power of the lens group arranged adjacent to the image side of the focusing lens group closest to the image side becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the upper limit of conditional expression (16) to 3.80, 3.50, 3.30, 3.00, 2.80, 2.50, 2.30, 2.00, 1.50, 1.30, or even 1.00, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (16) falls below the lower limit, the refractive power of the focusing lens group becomes strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (16) to 0.13, 0.15, or even 0.18, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (17).
2ωw>75.0°...(17)
where 2ωw is the total angle of view of the variable magnification optical system ZL in the wide-angle end state.

Conditional expression (17) 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 expression (17), a variable magnification optical system with a wide angle of view can be obtained, which is preferable. By setting the lower limit of conditional expression (17) to 78.0°, 80.0°, or even 83.0°, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (18).
ft/fw>3.50...(18)
where ft is the focal length of the variable magnification optical system ZL in the telephoto end state.

Conditional expression (18) specifies the appropriate relationship between the focal length 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 wide-angle end state. By satisfying conditional expression (18), a variable magnification optical system with a high variable magnification ratio can be obtained, which is preferable. By setting the lower limit of conditional expression (18) to 3.80, 4.00, 4.20, or even 4.40, the effect of this embodiment can be made more certain.

It is desirable for the variable magnification optical system ZL according to this embodiment to satisfy the following conditional expression (19).
0.10<(-fN)/fL<1.00 (19)
where fN is the focal length of the second lens in the variable magnification optical system ZL, counting from the image side, and fL is the focal length of the lens in the variable magnification optical system ZL that is located closest to the image side.

Conditional expression (19) specifies the appropriate relationship between the focal length of the second lens from the image side of the variable magnification optical system ZL and the focal length of the lens closest to the image side of the variable magnification optical system ZL. By satisfying conditional expression (19), various aberrations, including coma aberration in the wide-angle end state, can be effectively corrected.

If the corresponding value of conditional expression (19) exceeds the upper limit, the refractive power of the lens arranged closest to the image side of the variable magnification optical system ZL becomes strong, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the upper limit of conditional expression (19) to 0.95, 0.90, 0.85, 0.83, 0.80, 0.78, 0.75, 0.73, or even 0.70, the effect of this embodiment can be made more certain.

If the corresponding value of conditional expression (19) falls below the lower limit, the refractive power of the lens arranged second from the image side of the variable magnification optical system ZL becomes strong, making it difficult to correct various aberrations, including coma aberration, in the wide-angle end state. By setting the lower limit of conditional expression (19) to 0.13, 0.15, or even 0.18, the effect of this embodiment can be made more certain.

Next, referring to FIG. 23, the manufacturing method of the variable magnification optical system ZL described above will be outlined. First, in order from the object side along the optical axis, a front lens group GA having a positive refractive power, a first intermediate lens group GM1 having a negative refractive power, a second intermediate lens group GM2 having a positive refractive power, and a rear lens group GR are arranged (step ST1). Next, a configuration is made in which the interval between adjacent lens groups changes during magnification (step ST2). Next, a first focusing lens group GF1 that moves along the optical axis during focusing is arranged on the most object side of the rear lens group GR, and at least one other focusing lens group that moves along the optical axis on a different trajectory from the first focusing lens group GF1 during focusing is arranged on the image side of the first focusing lens group GF1 in the rear lens group GR (step ST3). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditional formula (1) and conditional formula (2) (step ST4). According to this manufacturing method, it is possible to manufacture a variable magnification optical system with little aberration fluctuation during focusing.

The variable magnification optical system ZL according to the embodiment of the present invention will be described below with reference to the drawings. Figures 1, 4, 7, 10, 13, 16, and 19 are cross-sectional views showing the configuration and refractive power distribution of the variable magnification optical system ZL {ZL(1) to ZL(7)} according to the first to seventh embodiments. In the cross-sectional views of the variable magnification optical systems ZL(1) to ZL(7) according to the first to seventh embodiments, 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 along with the word "focus". In the cross-sectional views of the variable magnification optical systems ZL(1) to ZL(7) according to the first to seventh embodiments, 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.

1, 4, 7, 10, 13, 16, and 19, 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 using 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.

Tables 1 to 7 are shown below, with Table 1 showing data on the various elements in the first embodiment, Table 2 showing data on the second embodiment, Table 3 showing data on the third embodiment, Table 4 showing data on the fourth embodiment, Table 5 showing data on the fifth embodiment, Table 6 showing data on the sixth embodiment, and Table 7 showing data on the seventh 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.

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 (in ° (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. Note that these values are shown for each of the magnification change states at the wide-angle end (W) and telephoto end (T).

In the table of [Overall Specifications], fM1w indicates the focal length of the first intermediate lens group in the wide-angle end state. fM2w indicates the focal length of the second intermediate lens group in the wide-angle end state. MTF1 indicates the absolute value of the movement amount of the first focusing lens group when focusing from an infinite object to a close object in the telephoto end state. MTF2 indicates the absolute value of the movement amount of the focusing lens group closest to the first focusing lens group among the other focusing lens groups when focusing from an infinite object to a close object in the telephoto end state. βF1w indicates the composite lateral magnification when focusing on an infinite object in the wide-angle end state of the focusing lens group located closer to the object side than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens groups. βF2w indicates the lateral magnification when focusing on an infinite object in the wide-angle end state of the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens groups. βF1t indicates the combined lateral magnification of the focusing lens group located closer to the object side than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the telephoto end state. βF2t indicates the lateral magnification of the focusing lens group located closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the telephoto end state. fN indicates the focal length of the lens located second from the image side of the variable magnification optical system. fL indicates the focal length of the lens located closest to the image side of the variable magnification optical system. fRw indicates the focal length of the subsequent lens group in the wide angle end state.

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 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 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.

In the table of [Aspherical Data], 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. "E-n" indicates "×10 ^-n ". For example, 1.234E-05 = 1.234×10 ^-5 . The second-order aspherical coefficient A2 is 0, and is omitted.

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)

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.

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

For all specifications below, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally given in "mm" unless otherwise specified, but this is not limited to the units listed, as the optical system will provide the same optical performance even if it is enlarged or reduced proportionally.

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

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 3 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, 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 negative refractive power, and a seventh lens group G7 having positive 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 to seventh lens groups G1 to G7 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture stop S moves along the optical axis together with the third lens group G3. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the lens group, and this is the same in all the following embodiments.

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 positive meniscus lens L12 with its convex surface facing the object side, and a positive meniscus lens L13 with its convex surface facing the object side.

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

The third lens group G3 is composed of a biconvex positive lens L31. The lens surface facing the object side of the positive lens L31 is aspheric.

The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens of a negative meniscus lens L41 with a convex surface facing the object side and a biconvex positive lens L42, a cemented positive lens of a biconvex positive lens L43 and a negative meniscus lens L44 with a concave surface facing the object side, and a positive meniscus lens L45 with a concave surface facing the object side. The lens surface facing the object side of the positive meniscus lens L45 is aspheric.

The fifth lens group G5 is composed of a positive meniscus lens L51 with its concave surface facing the object side, and a negative lens L52 with a biconcave shape, arranged in order from the object side along the optical axis.

The sixth lens group G6 is composed of a biconcave negative lens L61. The lens surface facing the object side of the negative lens L61 is aspheric.

The seventh lens group G7 is composed of a positive meniscus lens L71 with its convex surface facing the object side. An image surface I is located on the image side of the seventh lens group G7.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having a negative refractive power. The third lens group G3 and the fourth lens group G4 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an infinite object to a close object, the fifth lens group G5 and the sixth lens group G6 constituting the rear lens group GR move toward the image side along the optical axis with different trajectories (movement amounts). That is, the fifth lens group G5 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The sixth lens group G6 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 1 below lists the values of the specifications of the variable magnification optical system in the first embodiment.

(Table 1)
[Overall specifications]
Magnification ratio = 4.74
fM1w=-17.655 fM2w=29.833
MTF1=0.344 MTF2=0.846
βF1w=1.071 βF2w=1.577
βF1t=1.111 βF2t=3.094
fN=-38.218 fL=129.310
fRw = -46.388
W.M.T.
f 24.700 84.962 116.999
FNO 4.07 4.07 4.07
2ω 85.22 27.40 20.32
Ymax 21.60 21.60 21.60
T.L. 128.45 162.37 178.87
BF 13.699 35.087 35.287
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 164.9399 2.000 1.73800 32.26
2 56.4260 7.579 1.59319 67.90
3 329.6967 0.200
4 61.7045 5.273 1.81600 46.59
5 267.7629 (D5)
6* 242.3772 1.500 1.81600 46.59
7 16.6184 5.149
8 879.6675 1.000 1.58913 61.22
9 18.5708 4.233 1.95000 29.37
10 79.8132 2.602
11 -27.5163 1.000 1.77250 49.62
12 -60.4508 (D12)
13 ∞ 2.000 (Aperture S)
14* 33.9421 3.661 1.74310 49.44
15 -231.3985 (D15)
16 30.3875 1.000 1.88300 40.66
17 15.6459 6.192 1.49782 82.57
18 -453.7663 0.776
19 575.4338 5.622 1.51680 64.14
20 -18.7425 1.000 2.00069 25.46
21 -32.0090 1.264
22* -70.8783 5.056 1.55332 71.67
23 -21.6449 (D23)
24 -90.7732 3.558 1.94595 17.98
25 -39.1419 0.200
26 -156.1339 1.000 1.90366 31.27
27 79.8952 (D27)
28* -85.4924 1.500 1.81600 46.59
29 49.4815 (D29)
30 55.2902 3.197 1.90200 25.26
31 102.2388 BF
Image plane ∞
[Aspheric data]
6th face κ=1.0000,A4=5.35995E-06,A6=-8.27153E-09,A8=2.12565E-11,A10=-2.60526E-14
14th side κ=1.0000,A4=-7.33442E-06,A6=4.81859E-09,A8=-4.26147E-11,A10=-2.53196E-14
22nd side κ=1.0000,A4=-2.36052E-05,A6=6.01748E-09,A8=1.01789E-10,A10=1.24064E-13
28th side κ=1.0000,A4=-5.15978E-06,A6=-5.92439E-09,A8=4.45911E-12,A10=-6.10897E-15
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.000 31.270 39.333 2.000 31.270 39.333
D12 17.917 3.226 2.000 17.917 3.226 2.000
D15 13.739 3.651 2.000 13.739 3.651 2.000
D23 6.364 2.978 2.000 6.466 3.278 2.344
D27 4.416 6.716 5.540 5.042 7.231 6.042
D29 3.757 12.879 26.147 3.029 12.064 25.302
[Lens group data]
Group Initial surface Focal length
G1 1 97.130
G2 6 -17.655
G3 14 40.069
G4 16 35.478
G5 24 -320.573
G6 28 -38.218
G7 30 129.310

Figure 2 (A) is a diagram of various aberrations when the variable magnification optical system of the first embodiment is focused on infinity in the wide-angle end state. Figure 2 (B) is a diagram of various aberrations when the variable magnification optical system of the first embodiment is focused on infinity in the telephoto end state. Figure 3 (A) is a diagram of various aberrations when the variable magnification optical system of the first embodiment is focused on a close distance in the wide-angle end state. Figure 3 (B) is a diagram of various aberrations when the variable magnification optical system of the first embodiment is focused on a close distance in the telephoto end state. In each aberration diagram when focusing on infinity, FNO indicates the F-number and Y indicates the image height. In each aberration diagram when focusing on a close distance, NA indicates the numerical aperture and Y indicates the image height. In addition, the spherical aberration diagram shows the value of the F-number or numerical aperture corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum value of the image height, and the coma aberration diagram shows the value of each image height. 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 surface, and the dashed line indicates the meridional image surface. Note that in the aberration diagrams of the following examples, the same symbols as in this example are used, and duplicated explanations will be omitted.

From each of the aberration diagrams, it can be seen that the variable magnification optical system of Example 1 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close distances, from the wide-angle end state to the telephoto end state.

Second Example
The second embodiment will be described with reference to FIGS. 4 to 6 and Table 2. FIG. 4 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, 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 positive refractive power, a sixth lens group G6 having negative refractive power, and a seventh lens group G7 having positive 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 to seventh lens groups G1 to G7 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture stop S moves along the optical axis together with the third lens group G3.

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 positive meniscus lens L12 with its convex surface facing the object side, and a positive meniscus lens L13 with its convex surface facing the object side.

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

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 positive lens consisting of a negative meniscus lens L33 with a convex surface facing the object side and a biconvex positive lens L34, and a negative meniscus lens L35 with a concave surface facing the object side.

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

The fifth lens group G5 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L51, a biconvex positive lens L52, and a cemented positive lens of a negative meniscus lens L53 with its concave surface facing the object side. The lens surface of the negative meniscus lens L53 facing the image side is aspheric.

The sixth lens group G6 is composed of a biconcave negative lens L61. The lens surface facing the object side of the negative lens L61 is aspheric.

The seventh lens group G7 is composed of a biconvex positive lens L71. An image surface I is disposed on the image side of the seventh lens group G7.

In this embodiment, the first lens group G1 constitutes the front lens group GA having positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having negative refractive power. The third lens group G3 and the fourth lens group G4 constitute the second intermediate lens group GM2 having positive refractive power as a whole. The fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 constitute the rear lens group GR having negative refractive power as a whole. When focusing from an infinite object to a close object, the fifth lens group G5 constituting the rear lens group GR moves toward the object side along the optical axis, and the sixth lens group G6 constituting the rear lens group GR moves toward the image side along the optical axis. That is, the fifth lens group G5 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The sixth lens group G6 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 2 below lists the values of the parameters of the variable magnification optical system in the second embodiment.

(Table 2)
[Overall specifications]
Magnification ratio = 4.74
fM1w=-17.052 fM2w=29.062
MTF1=0.279 MTF2=0.983
βF1w=1.045 βF2w=1.670
βF1t=1.038 βF2t=3.943
fN=-31.580 fL=78.519
fRw = -61.009
W.M.T.
f 24.700 69.988 117.001
FNO 4.06 4.06 4.07
2ω 85.22 33.90 20.18
Ymax 21.60 21.60 21.60
T.L. 134.46 162.88 189.46
BF 11.455 31.812 35.779
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 158.1192 2.000 1.73800 32.36
2 69.8101 6.421 1.59319 67.90
3 308.6050 0.200
4 66.9111 5.695 1.81600 46.59
5 207.3443 (D5)
6* 78.5237 1.500 1.81600 46.59
7 16.7218 5.684
8 -172.8187 1.000 1.80400 46.60
9 21.0165 4.905 1.90200 25.26
10 -209.4912 1.624
11 -33.2740 1.000 1.81600 46.59
12 -156.9568 (D12)
13 ∞ 2.000 (Aperture S)
14 37.1973 2.686 1.80518 25.45
15 73.4737 0.200
16 49.8914 3.509 1.59319 67.90
17 -304.2612 0.200
18 35.7712 1.000 1.84850 43.79
19 16.8712 7.999 1.59319 67.90
20 -57.2564 1.355
21 -36.5767 1.000 2.00069 25.46
22 -90.8325 (D22)
23 39.2071 1.000 2.00069 25.46
24 25.6545 6.685 1.59319 67.90
25 -38.5079 (D25)
26 -38.3881 1.000 1.94595 17.98
27 96.5319 0.415
28 37.3704 7.406 1.89286 20.36
29 -30.3636 1.000 1.68893 31.16
30* -185.8364 (D30)
31* -42.4996 1.500 1.81600 46.59
32 66.5016 (D32)
33 148.1143 4.377 1.89286 20.36
34 -131.2552 BF
Image plane ∞
[Aspheric data]
6th face κ=1.0000,A4=1.23369E-06,A6=-3.23247E-09,A8=-1.36560E-12,A10=3.42111E-15
30th side κ=1.0000,A4=2.14045E-05,A6=-7.56199E-10,A8=-2.61800E-11,A10=1.98882E-13
Page 31 κ=1.0000,A4=-3.01641E-06,A6=-1.16781E-08,A8=-5.08849E-11,A10=3.00363E-13
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.000 26.048 41.130 2.000 26.048 41.130
D12 21.130 5.163 2.000 21.130 5.163 2.000
D22 12.345 4.345 2.000 12.345 4.345 2.000
D25 2.023 7.035 9.889 2.000 6.858 9.610
D30 7.665 6.668 3.602 8.357 7.660 4.865
D32 4.476 8.453 21.695 3.807 7.637 20.712
[Lens group data]
Group Initial surface Focal length
G1 1 111.149
G2 6 -17.052
G3 14 34.545
G4 23 40.961
G5 26 915.545
G6 31 -31.580
G7 33 78.519

Figure 5 (A) is a diagram of various aberrations when the variable magnification optical system of Example 2 is focused on infinity in the wide-angle end state. Figure 5 (B) is a diagram of various aberrations when the variable magnification optical system of Example 2 is focused on infinity in the telephoto end state. Figure 6 (A) is a diagram of various aberrations when the variable magnification optical system of Example 2 is focused on a close distance in the wide-angle end state. Figure 6 (B) is a diagram of various aberrations when the variable magnification optical system of Example 2 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 2 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

(Third Example)
The third embodiment will be described with reference to FIGS. 7 to 9 and Table 3. FIG. 7 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, 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 positive refractive power, a sixth lens group G6 having positive refractive power, and a seventh lens group G7 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 to seventh lens groups G1 to G7 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture stop S moves along the optical axis together with the third lens group G3.

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 plano-concave negative lens L11 with its flat surface facing the object side and a biconvex positive lens L12, and a positive meniscus lens L13 with its convex surface facing the object side.

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

The third lens group G3 is composed of a positive meniscus lens L31 with a convex surface facing the object side, a biconvex positive lens L32, and a negative meniscus lens L33 with a concave surface facing the object side, arranged in order from the object side along the optical axis. The lens surface facing the object side of the positive meniscus lens L31 is aspheric.

The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a biconvex positive lens L41, a cemented positive lens consisting of a negative meniscus lens L42 with its convex surface facing the object side and a biconvex positive lens L43.

The fifth lens group G5 is composed of a negative meniscus lens L51 with its concave surface facing the object side, and a positive lens L52 with a biconvex shape, arranged in order from the object side along the optical axis.

The sixth lens group G6 is composed of a positive meniscus lens L61 with its concave surface facing the object side. The lens surface facing the image side of the positive meniscus lens L61 is aspheric.

The seventh lens group G7 is composed of a biconcave negative lens L71 and a positive meniscus lens L72 with a convex surface facing the object side, arranged in order from the object side along the optical axis. An image surface I is located on the image side of the seventh lens group G7.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having a negative refractive power. The third lens group G3 and the fourth lens group G4 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an infinite object to a close object, the fifth lens group G5 and the sixth lens group G6 constituting the rear lens group GR move toward the object side along the optical axis with different trajectories (movement amounts). That is, the fifth lens group G5 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The sixth lens group G6 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 3 below lists the values of the parameters of the variable magnification optical system in the third embodiment.

(Table 3)
[Overall specifications]
Magnification ratio = 4.56
fM1w=-21.004 fM2w=33.500
MTF1=1.413 MTF2=0.980
βF1w=0.770 βF2w=0.954
βF1t=0.658 βF2t=0.946
fN=-29.642 fL=97.753
fRw = -158.485
W.M.T.
f 22.600 70.008 103.000
FNO 4.08 4.08 4.08
2ω 91.54 32.98 22.38
Ymax 21.60 21.60 21.60
TL 139.45 164.17 199.46
BF 11.455 38.439 39.811
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1∞2.0001.8466623.80
2 205.3318 6.252 1.59319 67.90
3 -265.8961 0.200
4 76.0378 4.794 1.77250 49.62
5 155.1941 (D5)
6* 118.3890 1.500 1.74389 49.53
7 19.9637 7.065
8 -66.8860 1.000 1.59319 67.90
9 24.3441 6.322 1.68893 31.16
10 -44.9916 0.573
11 -35.2853 1.000 1.81600 46.59
12∞(D12)
13 ∞ 2.000 (Aperture S)
14* 53.1253 2.930 1.69343 53.30
15 3836.4092 0.200
16 51.4447 4.772 1.59319 67.90
17 -49.9261 2.897
18 -36.2339 1.000 1.83481 42.73
19 -1562.5863 (D19)
20 41.8346 4.903 1.59319 67.90
21 -69.8682 0.200
22 94.4862 1.000 1.81600 46.59
23 19.6322 7.665 1.49782 82.57
24 -56.1775 (D24)
25 -29.1264 1.000 1.90200 25.26
26 -57.1334 2.304
27 93.4868 5.411 1.80400 46.60
28 -48.3174 (D28)
29 -85.5900 1.691 1.77387 47.25
30* -67.1935 (D30)
31 -56.6426 1.000 1.83481 42.73
32 44.2945 2.378
33 64.6533 3.175 1.94595 17.98
34 209.7975 BF
Image plane ∞
[Aspheric data]
6th face κ=1.0000,A4=2.28381E-06,A6=-1.46352E-09,A8=-1.25256E-12,A10=5.36019E-15
Surface 14 κ=1.0000,A4=-2.87497E-06,A6=1.67465E-09,A8=-4.38683E-12,A10=-1.60647E-15
30th side κ=1.0000,A4=9.04034E-06,A6=8.01114E-10,A8=6.16585E-12,A10=-1.63681E-14
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.000 16.912 51.168 2.000 16.912 51.168
D12 23.202 2.589 2.000 23.202 2.589 2.000
D19 10.189 2.436 2.000 10.189 2.436 2.000
D24 5.554 14.413 18.443 4.619 13.500 17.030
D28 2.044 8.464 8.285 2.513 8.681 8.718
D30 9.778 5.681 2.517 10.245 6.377 3.497
[Lens group data]
Group Initial surface Focal length
G1 1 157.131
G2 6 -22.004
G3 14 59.544
G4 20 43.565
G5 25 84.112
G6 29 388.390
G7 31 -43.760

Figure 8 (A) is a diagram of various aberrations when the variable magnification optical system of Example 3 is focused on infinity in the wide-angle end state. Figure 8 (B) is a diagram of various aberrations when the variable magnification optical system of Example 3 is focused on infinity in the telephoto end state. Figure 9 (A) is a diagram of various aberrations when the variable magnification optical system of Example 3 is focused on a close distance in the wide-angle end state. Figure 9 (B) is a diagram of various aberrations when the variable magnification optical system of Example 3 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 3 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

(Fourth Example)
The fourth embodiment will be described with reference to FIGS. 10 to 12 and Table 4. FIG. 10 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, 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 negative refractive power, and a seventh lens group G7 having positive 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 to sixth lens groups G1 to G6 move toward the object side along the optical axis, and the seventh lens group G7 moves toward the object side once along the optical axis and then moves toward the image side, and the interval between the adjacent lens groups changes. The aperture diaphragm S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture diaphragm S moves along the optical axis together with the third lens group G3.

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 positive meniscus lens L12 with its convex surface facing the object side, and a positive meniscus lens L13 with its convex surface facing the object side.

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

The third lens group G3 is composed of a positive meniscus lens L31 with a convex surface facing the object side, and a positive meniscus lens L32 with a convex surface facing the object side. The lens surface facing the object side of the positive meniscus lens L31 is aspheric.

The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens of a negative meniscus lens L41 with a convex surface facing the object side and a biconvex positive lens L42, a cemented negative lens of a biconvex positive lens L43 and a negative meniscus lens L44 with a concave surface facing the object side, and a positive meniscus lens L45 with a concave surface facing the object side. The lens surface facing the object side of the positive meniscus lens L45 is aspheric.

The fifth lens group G5 is composed of a biconvex positive lens L51 and a biconcave negative lens L52, arranged in order from the object side along the optical axis.

The sixth lens group G6 is composed of a biconcave negative lens L61. The lens surface facing the object side of the negative lens L61 is aspheric.

The seventh lens group G7 is composed of a positive meniscus lens L71 with its convex surface facing the object side. An image surface I is located on the image side of the seventh lens group G7.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having a negative refractive power. The third lens group G3 and the fourth lens group G4 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an infinite object to a close object, the fifth lens group G5 and the sixth lens group G6 constituting the rear lens group GR move toward the image side along the optical axis with different trajectories (movement amounts). That is, the fifth lens group G5 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The sixth lens group G6 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 4 below lists the values of the specifications of the variable magnification optical system in the fourth example.

(Table 4)
[Overall specifications]
Magnification ratio = 7.85
fM1w=-17.910 fM2w=29.807
MTF1=0.411 MTF2=0.952
βF1w=1.005 βF2w=1.561
βF1t=1.019 βF2t=3.610
fN=-35.994 fL=170.661
fRw = -44.489
W.M.T.
f 24.700 104.937 194.000
FNO 4.02 5.60 6.42
2ω 85.20 22.32 12.46
Ymax 21.60 21.60 21.60
TL 130.17 173.77 204.45
BF 12.455 42.064 38.864
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 143.1350 2.000 1.73800 32.33
2 54.4612 7.561 1.59319 67.90
3 300.0372 0.200
4 69.5685 5.062 1.77250 49.62
5 409.0849 (D5)
6* 350.7774 1.500 1.88202 37.22
7 18.4546 4.874
8 680.4222 1.000 1.49782 82.57
9 19.1843 4.572 1.85000 27.03
10 106.5036 1.893
11 -45.6629 1.000 1.77250 49.62
12 1027.7309 (D12)
13 ∞ 2.000 (Aperture S)
14* 29.9260 2.529 1.67798 54.89
15 104.6758 0.200
16 37.9415 1.902 1.80809 22.74
17 50.9616 (D17)
18 24.4645 1.758 1.90265 35.77
19 14.5575 6.153 1.49782 82.57
20 -102.7198 0.611
21 1507.9760 4.275 1.51680 64.13
22 -24.0428 1.000 2.00069 25.46
23 -87.8436 0.355
24* -128.1468 4.545 1.55332 71.68
25 -20.7344 (D25)
26 738.8688 4.696 1.80809 22.74
27 -32.2613 0.200
28 -47.0892 1.000 1.81600 46.59
29 81.3412 (D29)
30* -59.9653 1.500 1.77387 47.25
31 52.5852 (D31)
32 51.1837 3.083 1.68893 31.16
33 88.4174 BF
Image plane ∞
[Aspheric data]
6th face κ=1.0000,A4=3.16658E-06,A6=-5.96049E-09,A8=1.61416E-11,A10=-2.62532E-14
14th side κ=1.0000,A4=-7.64081E-06,A6=-1.02540E-08,A8=8.93373E-11,A10=-6.51264E-13
24th side κ=1.0000,A4=-3.12885E-05,A6=3.71787E-08,A8=-1.70544E-10,A10=1.40544E-12
30th side κ=1.0000,A4=-5.46471E-06,A6=-2.65649E-0,A8=1.47492E-10,A10=-2.98216E-13
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.010 35.817 51.220 2.010 35.817 51.220
D12 21.188 4.932 2.030 21.188 4.932 2.030
D17 13.539 4.497 2.000 13.539 4.497 2.000
D25 7.124 3.715 2.000 7.265 4.018 2.411
D29 4.593 6.548 4.486 5.167 7.059 5.027
D31 3.794 10.730 38.386 3.078 9.916 37.434
[Lens group data]
Group Initial surface Focal length
G1 1 103.273
G2 6 -17.910
G3 14 44.938
G4 18 37.783
G5 26 -980.001
G6 30 -35.994
G7 32 170.661

Figure 11 (A) is a diagram of various aberrations when the variable magnification optical system of Example 4 is focused on infinity in the wide-angle end state. Figure 11 (B) is a diagram of various aberrations when the variable magnification optical system of Example 4 is focused on infinity in the telephoto end state. Figure 12 (A) is a diagram of various aberrations when the variable magnification optical system of Example 4 is focused on a close distance in the wide-angle end state. Figure 12 (B) is a diagram of various aberrations when the variable magnification optical system of Example 4 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 4 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

Fifth Example
The fifth embodiment will be described with reference to Figs. 13 to 15 and Table 5. Fig. 13 is a diagram showing the lens configuration of the variable magnification optical system according to the fifth embodiment. The variable magnification optical system ZL(5) according to the fifth embodiment 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 negative refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, a sixth lens group G6 having negative refractive power, a seventh lens group G7 having negative refractive power, and an eighth lens group G8 having positive refractive power. When changing the magnification from the wide-angle end state (W) to the telephoto end state (T), the first to seventh lens groups G1 to G7 move toward the object side along the optical axis, and the eighth lens group G8 moves once toward the object side along the optical axis and then moves toward the image side, changing the interval between adjacent lens groups. The aperture diaphragm S is disposed between the third lens group G3 and the fourth lens group G4. When changing the magnification, the aperture diaphragm S moves along the optical axis together with the fourth lens group G4.

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 positive meniscus lens L12 with its convex surface facing the object side, and a positive meniscus lens L13 with its convex surface facing the object side.

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 cemented positive lens consisting of a negative meniscus lens L22 with a convex surface facing the object side and a positive meniscus lens L23 with a convex surface facing the object side. The lens surface facing the object side of the negative lens L21 is aspheric.

The third lens group G3 is composed of a biconcave negative lens L31.

The fourth lens group G4 is composed of a positive meniscus lens L41 with a convex surface facing the object side, and a positive meniscus lens L42 with a convex surface facing the object side, arranged in order from the object side along the optical axis. The lens surface facing the object side of the positive meniscus lens L41 is aspheric.

The fifth lens group G5 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens of a negative meniscus lens L51 with a convex surface facing the object side and a biconvex positive lens L52, a cemented negative lens of a positive meniscus lens L53 with a concave surface facing the object side and a negative meniscus lens L54 with a concave surface facing the object side, and a positive meniscus lens L55 with a concave surface facing the object side. The lens surface facing the object side of the positive meniscus lens L55 is aspheric.

The sixth lens group G6 is composed of a biconvex positive lens L61 and a biconcave negative lens L62, arranged in order from the object side along the optical axis.

The seventh lens group G7 is composed of a biconcave negative lens L71. The lens surface facing the object side of the negative lens L71 is aspheric.

The eighth lens group G8 is composed of a positive meniscus lens L81 with its convex surface facing the object side. An image surface I is located on the image side of the eighth lens group G8.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 and the third lens group G3 constitute the first intermediate lens group GM1 having a negative refractive power as a whole. The fourth lens group G4 and the fifth lens group G5 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The sixth lens group G6, the seventh lens group G7, and the eighth lens group G8 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an object at infinity to an object at a close distance, the sixth lens group G6 and the seventh lens group G7 constituting the rear lens group GR move toward the image side along the optical axis with different trajectories (movement amounts). That is, the sixth lens group G6 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The seventh lens group G7 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 5 below lists the values of the parameters of the variable magnification optical system in the fifth embodiment.

(Table 5)
[Overall specifications]
Magnification ratio = 7.85
fM1w=-17.295 fM2w=29.310
MTF1=0.371 MTF2=0.950
βF1w=1.002 βF2w=1.550
βF1t=1.016 βF2t=3.590
fN=-36.530 fL=180.299
fRw = -44.658
W.M.T.
f 24.700 104.916 193.992
FNO 3.98 5.60 6.48
2ω 85.20 22.32 12.46
Ymax 21.60 21.60 21.60
T.L. 129.45 174.02 204.45
BF 12.454 43.256 39.757
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 140.6369 2.000 1.73800 32.33
2 54.2993 7.774 1.59319 67.90
3 306.9344 0.200
4 70.1192 5.137 1.77250 49.62
5 433.0896 (D5)
6* -348.9741 1.500 1.88202 37.22
7 18.5669 4.368
8 132.2861 1.000 1.49782 82.57
9 19.1562 4.619 1.85000 27.03
10 92.2216 (D10)
11 -59.9587 1.000 1.77250 49.62
12 207.6789 (D12)
13 ∞ 2.000 (Aperture S)
14* 29.0382 2.246 1.67798 54.89
15 56.3251 0.200
16 35.5481 2.153 1.80809 22.74
17 64.9456 (D17)
18 22.8201 1.147 1.90265 35.77
19 14.0716 6.794 1.49782 82.57
20 -62.9717 0.250
21 -578.5647 3.866 1.51680 64.13
22 -26.3104 1.000 2.00069 25.46
23 -262.9123 0.400
24* -252.2011 4.807 1.55332 71.68
25 -20.2354 (D25)
26 406.6131 4.916 1.80809 22.74
27 -31.2178 0.200
28 -44.1001 1.000 1.81600 46.59
29 76.8052 (D29)
30* -65.9674 1.500 1.77387 47.25
31 49.9596 (D31)
32 48.7044 2.979 1.68893 31.16
33 78.1205 BF
Image plane ∞
[Aspheric data]
6th side κ=1.0000,A4=6.01924E-06,A6=-9.78216E-09,A8=1.91188E-11,A10=-2.54581E-14
14th side κ=1.0000,A4=-8.67328E-06,A6=-1.41146E-08,A8=1.05557E-10,A10=-7.15518E-13
24th face κ=1.0000,A4=-3.58225E-05,A6=5.16946E-08,A8=-2.69722E-10,A10=2.25425E-12
30th side κ=1.0000,A4=-5.04731E-06,A6=-3.08030E-08,A8=1.84868E-10,A10=-5.03672E-13
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.591 35.849 51.107 2.591 35.849 51.107
D10 2.474 1.925 1.779 2.474 1.925 1.779
D12 19.518 4.834 2.144 19.518 4.834 2.144
D17 13.288 4.561 2.000 13.288 4.561 2.000
D25 7.742 3.790 2.000 7.926 4.060 2.371
D29 4.510 6.280 4.193 5.056 6.817 4.772
D31 3.824 10.476 38.417 3.094 9.669 37.467
[Lens group data]
Group Initial surface Focal length
G1 1 101.843
G2 6 -28.919
G3 11 -60.130
G4 14 45.188
G5 18 37.275
G6 26 -979.922
G7 30 -36.530
G8 32 180.299

Figure 14 (A) is a diagram of various aberrations when the variable magnification optical system of Example 5 is focused on infinity in the wide-angle end state. Figure 14 (B) is a diagram of various aberrations when the variable magnification optical system of Example 5 is focused on infinity in the telephoto end state. Figure 15 (A) is a diagram of various aberrations when the variable magnification optical system of Example 5 is focused on a close distance in the wide-angle end state. Figure 15 (B) is a diagram of various aberrations when the variable magnification optical system of Example 5 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 5 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

(Sixth Example)
The sixth embodiment will be described with reference to FIGS. 16 to 18 and Table 6. FIG. 16 is a diagram showing the lens configuration of the variable magnification optical system according to the sixth embodiment. The variable magnification optical system ZL(6) according to the sixth embodiment is composed of 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, a seventh lens group G7 having positive refractive power, and an eighth lens group G8 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 to eighth lens groups G1 to G8 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. The aperture diaphragm S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture diaphragm S moves along the optical axis together with the third lens group G3.

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.

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

The third lens group G3 is composed of a positive meniscus lens L31 with a convex surface facing the object side, a biconvex positive lens L32, and a negative meniscus lens L33 with a concave surface facing the object side, arranged in order from the object side along the optical axis. The lens surface facing the object side of the positive meniscus lens L31 is aspheric.

The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a biconvex positive lens L41, a cemented negative lens consisting of a negative meniscus lens L42 with its convex surface facing the object side and a biconvex positive lens L43.

The fifth lens group G5 consists of a negative meniscus lens L51 with its concave surface facing the object side.

The sixth lens group G6 is composed of a biconvex positive lens L61.

The seventh lens group G7 is composed of a positive meniscus lens L71 with its concave surface facing the object side. The lens surface facing the image side of the positive meniscus lens L71 is aspheric.

The eighth lens group G8 is composed of a biconcave negative lens L81 and a positive meniscus lens L82 with a convex surface facing the object side, arranged in order from the object side along the optical axis. An image surface I is located on the image side of the eighth lens group G8.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having a negative refractive power. The third lens group G3 and the fourth lens group G4 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The fifth lens group G5, the sixth lens group G6, the seventh lens group G7, and the eighth lens group G8 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an infinite object to a close object, the fifth lens group G5, the sixth lens group G6, and the seventh lens group G7 constituting the rear lens group GR move toward the object side along the optical axis with different trajectories (movement amounts). That is, the fifth lens group G5 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The sixth lens group G6 corresponds to a second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1, and the seventh lens group G7 corresponds to a third focusing lens group GF3, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 6 below lists the specifications of the variable magnification optical system for the sixth embodiment.

(Table 6)
[Overall specifications]
Magnification ratio = 4.70
fM1w=-19.907 fM2w=32.581
MTF1=2.249 MTF2=2.096
βF1w=0.765 βF2w=0.949
βF1t=0.684 βF2t=0.943
fN=-37.608 fL=176.733
fRw = -190.173
W.M.T.
f 24.700 70.009 115.999
FNO 4.06 4.02 4.12
2ω 86.44 32.64 19.92
Ymax 21.60 21.60 21.60
TL 139.45 169.68 199.08
BF 12.344 33.226 39.472
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 462.2978 2.000 1.84666 23.80
2 117.9843 7.772 1.59319 67.90
3 -332.8090 0.200
4 68.5981 5.329 1.77250 49.62
5 140.6044 (D5)
6* 102.1762 1.500 1.74389 49.53
7 20.0193 7.301
8 -53.3166 1.000 1.59319 67.90
9 23.3630 6.829 1.68893 31.16
10 -34.9416 0.488
11 -29.8911 1.000 1.81600 46.59
12 771.9204 (D12)
13 ∞ 2.000 (Aperture S)
14* 64.5221 2.313 1.69343 53.30
15 218.6309 0.200
16 42.2294 5.148 1.59319 67.90
17 -50.9166 0.846
18 -38.4211 1.000 1.83481 42.73
19 -121.6787 (D19)
20 50.5091 4.565 1.59319 67.90
21 -73.4692 0.200
22 144.3902 1.000 1.81600 46.59
23 20.8080 7.069 1.49782 82.57
24 -58.5658 (D24)
25 -36.5746 1.000 1.90200 25.26
26 -88.6629 (D26)
27 78.2651 5.215 1.80400 46.60
28 -61.1685 (D28)
29 -115.4337 1.682 1.77387 47.25
30* -84.6141 (D30)
31 -93.1742 1.000 1.83481 42.73
32 47.5819 1.399
33 51.8920 2.458 1.94594 17.98
34 73.5164 BF
Image plane ∞
[Aspheric data]
6th face κ=1.0000,A4=1.46132E-06,A6=-1.42920E-09,A8=2.79764E-12,A10=5.33710E-15
14th side κ=1.0000,A4=-3.76343E-06,A6=1.16052E-09,A8=-1.11309E-11,A10=1.96066E-14
30th side κ=1.0000,A4=9.30832E-06,A6=3.85397E-09,A8=-9.94633E-12,A10=2.27044E-14
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.000 24.468 49.503 2.000 24.468 49.503
D12 20.478 3.818 2.074 20.478 3.818 2.074
D19 8.916 3.265 2.000 8.916 3.265 2.000
D24 6.612 13.356 22.504 5.023 11.937 20.255
D26 3.664 3.898 2.010 3.909 4.002 2.162
D28 3.789 9.856 8.781 4.421 10.371 9.746
D30 11.138 7.275 2.224 11.850 8.075 3.355
[Lens group data]
Group Initial surface Focal length
G1 1 134.376
G2 6 -19.907
G3 14 53.036
G4 20 55.179
G5 25 -69.654
G6 27 43.428
G7 29 399.999
G8 31 -47.335

Figure 17 (A) is a diagram of various aberrations when the variable magnification optical system of Example 6 is focused on infinity in the wide-angle end state. Figure 17 (B) is a diagram of various aberrations when the variable magnification optical system of Example 6 is focused on infinity in the telephoto end state. Figure 18 (A) is a diagram of various aberrations when the variable magnification optical system of Example 6 is focused on a close distance in the wide-angle end state. Figure 18 (B) is a diagram of various aberrations when the variable magnification optical system of Example 6 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 6 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

Seventh Example
The seventh embodiment will be described with reference to FIGS. 19 to 21 and Table 7. FIG. 19 is a diagram showing the lens configuration of the variable magnification optical system according to the seventh embodiment. The variable magnification optical system ZL(7) according to the seventh embodiment is composed of 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, a sixth lens group G6 having positive refractive power, a seventh lens group G7 having positive refractive power, and an eighth lens group G8 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 to eighth lens groups G1 to G8 move toward the object side along the optical axis, and the interval between the adjacent lens groups changes. The aperture diaphragm S is disposed between the second lens group G2 and the third lens group G3. During magnification change, the aperture diaphragm S moves along the optical axis together with the third lens group G3.

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.

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

The third lens group G3 is composed of a biconvex positive lens L31 and a biconvex positive lens L32 arranged in order from the object side along the optical axis. The lens surface facing the object side of the positive lens L31 is aspheric.

The fourth lens group G4 is composed of a biconcave negative lens L41.

The fifth lens group G5 is composed of, arranged along the optical axis from the object side, a biconvex positive lens L51, a cemented positive lens consisting of a negative meniscus lens L52 with its convex surface facing the object side and a biconvex positive lens L53.

The sixth lens group G6 is composed of a negative meniscus lens L61 with its concave surface facing the object side, and a positive lens L62 with a biconvex shape, arranged in order from the object side along the optical axis.

The seventh lens group G7 is composed of a positive meniscus lens L71 with its concave surface facing the object side. The lens surface facing the image side of the positive meniscus lens L71 is aspheric.

The eighth lens group G8 is composed of a biconcave negative lens L81 and a positive meniscus lens L82 with a convex surface facing the object side, arranged in order from the object side along the optical axis. An image surface I is located on the image side of the eighth lens group G8.

In this embodiment, the first lens group G1 constitutes the front lens group GA having a positive refractive power. The second lens group G2 constitutes the first intermediate lens group GM1 having a negative refractive power. The third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the second intermediate lens group GM2 having a positive refractive power as a whole. The sixth lens group G6, the seventh lens group G7, and the eighth lens group G8 constitute the rear lens group GR having a negative refractive power as a whole. When focusing from an infinite object to a close object, the sixth lens group G6 and the seventh lens group G7 constituting the rear lens group GR move toward the object side along the optical axis with different trajectories (movement amounts). That is, the sixth lens group G6 corresponds to the first focusing lens group GF1 arranged closest to the object side of the rear lens group GR. The seventh lens group G7 corresponds to the second focusing lens group GF2, which is another focusing lens group arranged closer to the image side than the first focusing lens group GF1.

Table 7 below lists the values of the parameters of the variable magnification optical system in the seventh embodiment.

(Table 7)
[Overall specifications]
Magnification ratio = 4.56
fM1w=-20.363 fM2w=33.345
MTF1=1.381 MTF2=0.984
βF1w=0.763 βF2w=0.948
βF1t=0.650 βF2t=0.940
fN=-30.226 fL=100.683
fRw = -177.170
W.M.T.
f 22.600 70.004 103.000
FNO 4.09 4.09 4.08
2ω 91.56 33.96 22.38
Ymax 21.60 21.60 21.60
TL 139.45 165.05 199.45
BF 11.779 38.577 39.906
[Lens specifications]
Surface number R D nd νd
Object plane ∞
1 6659.3699 2.000 1.84666 23.80
2 195.3556 6.352 1.59319 67.90
3 -273.7600 0.200
4 73.6739 4.876 1.77250 49.62
5 149.1863 (D5)
6* 113.0230 1.500 1.74389 49.53
7 19.5406 7.132
8 -63.0618 1.000 1.59319 67.90
9 24.3284 6.267 1.68893 31.16
10 -43.5952 0.573
11 -34.2926 1.000 1.81600 46.59
12∞(D12)
13 ∞ 2.000 (Aperture S)
14* 57.8680 3.090 1.69343 53.30
15 -302.2108 0.200
16 48.4547 4.785 1.59319 67.90
17 -53.3050 (D17)
18 -38.1755 1.000 1.83481 42.730
19 616.7068 (D19)
20 42.1940 4.851 1.59319 67.90
21 -69.0643 0.200
22 98.4698 1.000 1.81600 46.59
23 19.6428 7.597 1.49782 82.57
24 -56.1321 (D24)
25 -29.3608 1.000 1.90200 25.26
26 -58.1915 1.995
27 90.0589 5.380 1.80400 46.60
28 -48.9540 (D28)
29 -85.0115 1.709 1.77387 47.25
30* -65.3126 (D30)
31 -62.1123 1.000 1.83481 42.73
32 42.8077 3.227
33 69.1642 3.143 1.94594 17.98
34 247.0342 BF
Image plane ∞
[Aspheric data]
6th side κ=1.0000,A4=2.33500E-06,A6=-8.92215E-10,A8=-3.76442E-12,A10=9.61354E-15
Side 14 κ=1.0000,A4=-2.41342E-06,A6=1.12249E-09A8=-3.73343E-13,A10=-1.07003E-14
30th side κ=1.0000,A4=9.05002E-06,A6=4.53686E-10,A8=5.24788E-12,A10=-1.61841E-14
[Variable interval data]
Focused at infinity Focused at close range
W.M.T. W.M.T.
D5 2.000 17.263 50.507 2.000 17.263 50.507
D12 22.632 2.617 2.000 22.632 2.617 2.000
D17 2.327 2.925 2.897 2.327 2.925 2.897
D19 10.846 2.372 2.000 10.846 2.372 2.000
D24 5.406 14.281 18.351 4.526 13.387 16.970
D28 2.000 8.343 8.382 2.443 8.546 8.779
D30 9.389 5.598 2.334 9.827 6.289 3.318
[Lens group data]
Group Initial surface Focal length
G1 1 153.821
G2 6 -20.363
G3 14 27.666
G4 18 -43.034
G5 20 44.173
G6 25 84.579
G7 29 350.941
G8 31 -44.997

Figure 20 (A) is a diagram of various aberrations when the variable magnification optical system of Example 7 is focused on infinity in the wide-angle end state. Figure 20 (B) is a diagram of various aberrations when the variable magnification optical system of Example 7 is focused on infinity in the telephoto end state. Figure 21 (A) is a diagram of various aberrations when the variable magnification optical system of Example 7 is focused on a close distance in the wide-angle end state. Figure 21 (B) is a diagram of various aberrations when the variable magnification optical system of Example 7 is focused on a close distance in the telephoto end state. From each aberration diagram, it can be seen that the variable magnification optical system of Example 7 has excellent imaging performance, with various aberrations being well corrected from the wide-angle end state to the telephoto end state not only when focusing on infinity but also when focusing on a close distance.

Next, a table of [Values Corresponding to Conditional Expressions] is shown below. In this table, values corresponding to each of the conditional expressions (1) to (19) are shown for all the examples (Examples 1 to 7).
Conditional expression (1) 4.30<f1/(-fM1w)<10.00
Conditional expression (2) 0.10<BFw/fw<1.00
Conditional expression (3) 1.50<f1/fM21<7.00
Conditional expression (4) 2.00<f1/fw<8.00
Conditional expression (5) 0.20<|fFs|/f1<2.00
Conditional expression (6) 1.50<|fFs|/(-fM1w)<5.00
Conditional expression (7) 0.90<|fFs|/fM2w<4.00
Conditional expression (8) 0.20<f1/(-fRw)<5.00
Conditional expression (9) 0.10<MTF1/MTF2<3.00
Conditional expression (10) 0.10<βF1w/βF2w<3.00
Conditional expression (11) 0.10<βF1t/βF2t<3.00
Conditional expression (12) 0.50<βF1w<2.60
Conditional expression (13) 0.20<βF2w<1.80
Conditional expression (14) {βF1w+(1/βF1w)} ^-2 ≦0.25
Conditional expression (15) {βF2w+(1/βF2w)} ^-2 ≦0.25
Conditional expression (16) 0.10<|fFs|/|fRF|<4.00
Conditional expression (17) 2ωw>75.0°
Conditional expression (18) ft/fw>3.50
Conditional expression (19) 0.10<(-fN)/fL<1.00

[Conditional Expression Corresponding Values] (First to Fourth Examples)
Conditional formula 1st Example 2nd Example 3rd Example 4th Example (1) 5.502 6.518 7.481 5.766
(2) 0.555 0.464 0.507 0.504
(3) 2.424 3.217 2.639 2.298
(4) 3.932 4.500 6.953 4.181
(5) 0.393 0.284 0.535 0.349
(6) 2.165 1.852 4.005 2.010
(7) 1.281 1.087 2.511 1.208
(8) 2.094 1.822 0.991 2.321
(9) 0.407 0.284 1.442 0.432
(10) 0.679 0.626 0.807 0.644
(11) 0.359 0.263 0.695 0.282
(12) 1.071 1.045 0.770 1.005
(13) 1.577 1.670 0.954 1.561
(14) 0.249 0.250 0.234 0.250
(15) 0.205 0.194 0.249 0.206
(16) 0.296 0.402 1.922 0.211
(17) 85.22 85.22 91.54 85.20
(18) 4.737 4.737 4.558 7.854
(19) 0.296 0.402 0.303 0.211
[Conditional Expression Corresponding Values] (Fifth to Seventh Examples)
Conditional formula Fifth embodiment Sixth embodiment Seventh embodiment (1) 5.889 6.750 7.554
(2) 0.504 0.500 0.521
(3) 2.254 2.534 5.560
(4) 4.123 5.440 6.806
(5) 0.359 0.323 0.550
(6) 2.112 2.182 4.154
(7) 1.246 1.333 2.537
(8) 2.280 0.707 0.868
(9) 0.391 1.073 1.403
(10) 0.647 0.806 0.805
(11) 0.283 0.725 0.692
(12) 1.002 0.765 0.763
(13) 1.550 0.949 0.948
(14) 0.250 0.233 0.233
(15) 0.208 0.249 0.249
(16) 0.203 0.917 1.880
(17) 85.20 86.44 91.56
(18) 7.854 4.696 4.558
(19) 0.203 0.213 0.300

According to each of the above embodiments, by making the focusing lens group small and lightweight, it is possible to realize quiet and high-speed focusing without increasing the size of the lens barrel. It is also possible to realize a variable magnification optical system with little aberration fluctuation when changing magnification from the wide-angle end state to the telephoto end state, and when focusing from an object at infinity to an object at close range.

The above examples are merely illustrative of the present invention, and the present invention is not limited to these.

The following contents can be adopted as appropriate to the extent that they do not impair the optical performance of the variable magnification optical system of this embodiment.

Although seven and eight group configurations have been shown as examples of the variable magnification optical system of this embodiment, the present application is not limited thereto, and variable magnification optical systems with other group configurations (e.g., nine 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.

A single or multiple lens groups, or a partial lens group, 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 may also be applied to autofocusing, and is suitable for motor drive (using an ultrasonic motor, etc.) for autofocusing.

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

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 degradation of optical performance due to errors in processing and assembly adjustment. It is also preferable because there is little degradation of imaging performance even if the image plane is misaligned.

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 in which glass is molded into an aspheric shape, or a composite aspheric surface in which resin is formed into an aspheric shape on the surface of glass. The lens surface may also be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

It is preferable that the aperture diaphragm be located between the second and third lens groups, or between the third and fourth lens groups, but it is also possible to use the lens frame to fulfill this role without providing a component serving as an aperture diaphragm.

Each lens surface may be coated with an anti-reflective coating with high transmittance over a wide wavelength range to reduce flare and ghosting and achieve high-contrast optical performance.

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 G8 Eighth lens group I Image surface S Aperture stop

Claims (19)

The optical system is composed of a front lens group having positive refractive power and composed of one lens group, a first intermediate lens group having negative refractive power and composed of one or two lens groups, a second intermediate lens group having positive refractive power and composed of two or three lens groups, and a rear lens group composed of three or four lens groups, which are arranged in order from the object side along the optical axis,
When varying the magnification, the intervals between the front lens group and the first intermediate lens group, between the first intermediate lens group and the second intermediate lens group, and between the second intermediate lens group and the rear lens group change, and when the first intermediate lens group, the second intermediate lens group, and the rear lens group are composed of a plurality of lens groups, the intervals between adjacent lens groups that constitute the plurality of lens groups also change,
the subsequent lens group includes a first focusing lens group that is disposed closest to the object side of the subsequent lens group and moves along the optical axis during focusing, and at least one other focusing lens group that is disposed closer to the image side than the first focusing lens group and moves along the optical axis along a locus different from that of the first focusing lens group during focusing,
A variable magnification optical system that satisfies the following condition:
5.00<f1/(-fM1w)<10.00
0.10<BFw/fw<1.00
ft/fw>3.50
where f1 is the focal length of the front lens group, fM1w is the focal length of the first intermediate lens group in the wide-angle end state, BFw is the back focus of the variable magnification optical system in the wide-angle end state, and fw is the focal length of the variable magnification optical system in the wide-angle end state.
ft: focal length of the variable magnification optical system in the telephoto end state the second intermediate lens group includes at least two lens groups having positive refractive power;
2. The variable magnification optical system according to claim 1, which satisfies the following condition:
1.50<f1/fM21<7.00
where fM21 is the focal length of the lens group closest to the object among the lens groups included in the second intermediate lens group. 3. The variable magnification optical system according to claim 1, wherein the following condition is satisfied:
2.00<f1/fw<8.00 4. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.20<|fFs|/f1<2.00
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group. 5. The variable magnification optical system according to claim 1, which satisfies the following condition:
1.50<|fFs|/(-fM1w)<5.00
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group. 6. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.90<|fFs|/fM2w<4.00
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group, and fM2w is the focal length of the second intermediate lens group in the wide-angle end state. 7. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.20<f1/(-fRw)<5.00
where fRw is the focal length of the rear lens group in the wide-angle end state. 8. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.10<MTF1/MTF2<3.00
where MTF1 is the absolute value of the amount of movement of the first focusing lens group when focusing from an object at infinity to an object at a close distance in the telephoto end state, and MTF2 is the absolute value of the amount of movement of the focusing lens group that is closest to the first focusing lens group among the other focusing lens groups when focusing from an object at infinity to an object at a close distance in the telephoto end state. 9. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.10<βF1w/βF2w<3.00
where βF1w is the combined lateral magnification of the focusing lens group located closer to the object than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the wide-angle end state, and βF2w is the lateral magnification of the focusing lens group located closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the wide-angle end state. 10. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.10<βF1t/βF2t<3.00
where βF1t is a composite lateral magnification of the focusing lens group located closer to the object than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the telephoto end state, and βF2t is a lateral magnification of the focusing lens group located closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the telephoto end state. 11. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.50<βF1w<2.60
where βF1w is the composite lateral magnification when focusing on an object at infinity in the wide-angle end state of the focusing lens group located closer to the object side than the focusing lens group closest to the image side among the focusing lens groups included in the subsequent lens group. 12. The variable magnification optical system according to claim 1, which satisfies the following condition:
0.20<βF2w<1.80
where βF2w is the lateral magnification of the focusing lens group that is closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the wide-angle end state. 13. The variable magnification optical system according to claim 1, which satisfies the following condition:
{βF1w+(1/βF1w)} ^-2 ≦0.25
where βF1w is the composite lateral magnification when focusing on an object at infinity in the wide-angle end state of the focusing lens group located closer to the object side than the focusing lens group closest to the image side among the focusing lens groups included in the subsequent lens group. 14. The variable magnification optical system according to claim 1, which satisfies the following condition:
{βF2w+(1/βF2w)} ^-2 ≦0.25
where βF2w is the lateral magnification of the focusing lens group that is closest to the image among the focusing lens groups included in the subsequent lens group when focusing on an object at infinity in the wide-angle end state. The variable magnification optical system according to any one of claims 1 to 14, wherein the subsequent lens group includes at least one lens group arranged closer to the image than the focusing lens group closest to the image among the focusing lens groups included in the subsequent lens group. 16. The variable magnification optical system according to claim 15, which satisfies the following condition:
0.10<|fFs|/|fRF|<4.00
where fFs is the focal length of the focusing lens group having the strongest refractive power among the focusing lens groups included in the subsequent lens group, and fRF is the focal length of the lens group that is adjacent to the image side of the focusing lens group closest to the image side among the at least one lens group. 17. The variable magnification optical system according to claim 1, which satisfies the following condition:
2ωw＞75.0°
where 2ωw is the total angle of view of the variable magnification optical system in the wide-angle end state. 18. The variable magnification optical system according to claim 1, which satisfies the following condition: 1.5×100 2.0 ...3.0×100 4.0×100 5.0×100 6.0×100
0.10<(-fN)/fL<1.00
where fN is the focal length of the second lens in the variable magnification optical system from the image side, and fL is the focal length of the lens in the variable magnification optical system that is located closest to the image side. An optical instrument comprising the variable magnification optical system according to any one of claims 1 to 18 .

Images