Variable magnification optical system and optical equipment

Abstract

Provided are: a variable magnification optical system having good optical performance while being reduced in weight and size; an optical device; and a method for manufacturing a variable magnification optical system.　A variable magnification optical system ZL used in an optical device such as a camera 1 comprises, in order from the object side: a first lens group G1 having positive refractive power; a second lens group G2 having negative refractive power; an intermediate lens group GM comprising one or two lens groups and having positive refractive power as a whole; a focusing lens group GF having negative refractive power and moving in an optical axis direction during focusing; and a final lens group GR having positive refractive power. When magnification is changed, the distances between lens groups adjacent to each other change. The first lens group G1 is composed of one single-lens, and satisfies conditions by predetermined conditional expressions.

Description

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

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

[0002] In recent years, there has been a demand for lighter and smaller variable magnification optical systems (see Patent Document 1), and there is a demand for further improvement in optical performance while achieving lighter and smaller sizes.

[0003] Japanese Patent Application Laid-Open No. 2022-096075

[0004] A variable magnification optical system according to a first aspect of the present invention comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, an intermediate lens group consisting of one or two lens groups and having positive refractive power as a whole, a focusing lens group having negative refractive power and moving in the optical axis direction during focusing, and a final lens group having positive refractive power, wherein the spacing between adjacent lens groups changes during magnification, the first lens group is composed of one single lens, and satisfies the following conditions: 1.45 < nd1 < 1.63 62.50 < νd1 < 85.00 where nd1: refractive index for the d-line of the medium of the single lens constituting the first lens group νd1: Abbe number for the d-line of the medium of the single lens constituting the first lens group

[0005] A manufacturing method for a variable magnification optical system according to a first aspect of the present invention is a manufacturing method for a variable magnification optical system having, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, an intermediate lens group consisting of one or two lens groups and having positive refractive power as a whole, a focusing lens group having negative refractive power and moving in the optical axis direction during focusing, and a final lens group having positive refractive power, wherein the lens groups are arranged so that the interval between adjacent lens groups changes during magnification variation, and the first lens group is arranged to be composed of one single lens that satisfies the following conditions: 1.45 < nd1 < 1.63 62.50 < νd1 < 85.00 where nd1: refractive index for the d-line of the medium of the single lens that constitutes the first lens group νd1: Abbe number for the d-line of the medium of the single lens that constitutes the first lens group

[0006] 1 is a sectional view showing the lens configuration of the variable magnification optical system of Example 1 when focused on an object at infinity in the wide-angle end state. FIG. 2 is a diagram showing various aberrations of the variable magnification optical system of Example 1 when focused on an object at infinity in the wide-angle end state. FIG. 3 is a sectional view showing the lens configuration of the variable magnification optical system of Example 2 when focused on an object at infinity in the wide-angle end state. FIG. 4 is a diagram showing various aberrations of the variable magnification optical system of Example 2 when focused on an object at infinity in the wide-angle end state. FIG. 5 is a sectional view of a camera equipped with the variable magnification optical system. FIG. 6 is a flowchart for explaining a method for manufacturing the variable magnification optical system.

[0007] Preferred embodiments will now be described with reference to the drawings.

[0008] As shown in Figure 1, the variable magnification optical system ZL according to this embodiment comprises, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an intermediate lens group GM consisting of one or two lens groups and having positive refractive power as a whole, a focusing lens group GF having negative refractive power and moving in the optical axis direction during focusing, and a final lens group GR having positive refractive power, and the spacing between adjacent lens groups changes during magnification. Furthermore, the first lens group G1 is composed of a single lens L11. This configuration allows for a variable magnification optical system ZL that is lightweight and compact, while also exhibiting excellent optical performance.

[0009] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expressions (1) and (2).

[0010] 1.45<nd1<1.63 (1) 62.50<νd1<85.00 (2) where, nd1: refractive index for d-line of the medium of the single lens L11 constituting the first lens group G1, and νd1: Abbe number for d-line of the medium of the single lens L11 constituting the first lens group G1.

[0011] Conditional expressions (1) and (2) define the refractive index and Abbe number of the medium of the single lens L11 constituting the first lens group G1 at the d-line. By disposing a single lens L11 that satisfies conditional expressions (1) and (2) in the first lens group G1, a variable magnification optical system ZL can be realized that is lightweight and compact, while also exhibiting excellent optical performance. To ensure the effect of conditional expression (1), it is preferable to set the upper limit of conditional expression (1) to 1.62, and more preferably 1.60. To ensure the effect of conditional expression (1), it is preferable to set the lower limit of conditional expression (1) to 1.46, and more preferably 1.47. To ensure the effect of conditional expression (2), it is preferable to set the upper limit of conditional expression (2) to 82.56, and more preferably 80.00. To ensure the effect of conditional expression (2), it is preferable to set the lower limit of conditional expression (2) to 64.00, and more preferably 65.50.

[0012] In the variable magnification optical system ZL according to this embodiment, it is desirable that the final lens group GR moves along the optical axis when the magnification is changed.

[0013] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (3).

[0014] 4.80 < f1 / (-f2) < 7.50 (3) where f1 is the focal length of the first lens group G1, and f2 is the focal length of the second lens group G2.

[0015] Conditional expression (3) defines the ratio of the focal length of the first lens group G1 to the focal length of the second lens group G2. By satisfying conditional expression (3), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (3) is undesirable, since the focal length of the second lens group G2 becomes short, which increases the spherical aberration, coma, and curvature of field generated in the second lens group G2, making it difficult to achieve good optical performance. To ensure the effect of conditional expression (3), it is preferable to set the upper limit of conditional expression (3) to 7.25, or even 7.00. Furthermore, falling below the lower limit of conditional expression (3) is undesirable, since the focal length of the first lens group G1 becomes short, which increases the spherical aberration, coma, and curvature of field generated in the first lens group G1, making it difficult to achieve good optical performance. In order to ensure the effect of conditional expression (3), it is more desirable to set the lower limit of conditional expression (3) to 5.00, and more preferably 5.10.

[0016] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (4).

[0017] 3.80<f1 / fMw<6.00 (4) where, f1: focal length of the first lens group G1, and fMw: focal length of the middle lens group GM in the wide-angle end state.

[0018] Conditional expression (4) defines the ratio of the focal length of the first lens group G1 to the focal length of the intermediate lens group GM in the wide-angle end state. When the intermediate lens group GM consists of two lens groups, fMw is the combined focal length of the two lens groups in the wide-angle end state. By satisfying conditional expression (4), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (4) is undesirable, since the focal length of the intermediate lens group GM becomes short, which increases the spherical aberration and coma aberration generated in the intermediate lens group GM, making it impossible to achieve good optical performance. To ensure the effect of conditional expression (4), it is more desirable to set the upper limit of conditional expression (4) to 5.80, or even 5.50. Furthermore, if the lower limit of conditional expression (4) is not satisfied, the focal length of the first lens group G1 becomes short, and the spherical aberration, coma, and curvature of field generated in the first lens group G1 become large, making it impossible to obtain good optical properties, which is undesirable. In order to ensure the effect of conditional expression (4), it is more desirable to set the lower limit of conditional expression (4) to 4.00, and even more desirably 4.30.

[0019] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (5).

[0020] 2.00<f1 / (-fF)<4.00 (5) where, f1: focal length of the first lens group G1, and fF: focal length of the focusing lens group GF.

[0021] Conditional expression (5) defines the ratio of the focal length of the first lens group G1 to the focal length of the focusing lens group GF. By satisfying conditional expression (5), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (5) is undesirable, since the focal length of the focusing lens group GF becomes short, which increases the spherical aberration, coma, and curvature of field generated in the focusing lens group GF, making it difficult to achieve good optical performance. To ensure the effect of conditional expression (5), it is preferable to set the upper limit of conditional expression (5) to 3.85, or even 3.70. Furthermore, falling below the lower limit of conditional expression (5) is undesirable, since the focal length of the first lens group G1 becomes short, which increases the spherical aberration, coma, and curvature of field generated in the first lens group G1, making it difficult to achieve good optical performance. In order to ensure the effect of conditional expression (5), it is more desirable to set the lower limit of conditional expression (5) to 2.25, and more preferably 2.45.

[0022] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (6).

[0023] 1.10<f1 / fR<1.75 (6) where f1 is the focal length of the first lens group G1, and fR is the focal length of the final lens group GR.

[0024] Conditional expression (6) defines the ratio of the focal length of the first lens group G1 to the focal length of the final lens group GR. By satisfying conditional expression (6), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (6) is undesirable, since the focal length of the final lens group GR becomes short, the curvature of field generated in the final lens group GR becomes large, and good optical performance cannot be achieved. To ensure the effect of conditional expression (6), it is preferable to set the upper limit of conditional expression (6) to 1.65, or even 1.45. Falling below the lower limit of conditional expression (6) is undesirable, since the focal length of the first lens group G1 becomes short, the spherical aberration, coma, and curvature of field generated in the first lens group G1 become large, and good optical performance cannot be achieved. To ensure the effect of conditional expression (6), it is more preferable to set the lower limit of conditional expression (6) to 1.20, or even 1.35.

[0025] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (7).

[0026] 0.40<f2 / fF<0.65 (7) where, f2: focal length of the second lens group G2, and fF: focal length of the focusing lens group GF.

[0027] Conditional expression (7) defines the ratio of the focal length of the second lens group G2 to the focal length of the focusing lens group GF. By satisfying conditional expression (7), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (7) is undesirable, since the focal length of the focusing lens group GF becomes short, which increases the spherical aberration, coma, and curvature of field generated in the focusing lens group GF, making it difficult to achieve good optical performance. To ensure the effect of conditional expression (7), it is preferable to set the upper limit of conditional expression (7) to 0.60, or even 0.55. Furthermore, falling below the lower limit of conditional expression (7) is undesirable, since the focal length of the second lens group G2 becomes short, which increases the spherical aberration, coma, and curvature of field generated in the second lens group G2, making it difficult to achieve good optical performance. In order to ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to 0.43, and more preferably 0.45.

[0028] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (8).

[0029] 0.10<(-f2) / fR<0.35 (8) where, f2: focal length of the second lens group G2, and fR: focal length of the final lens group GR.

[0030] Conditional expression (8) defines the ratio of the focal length of the second lens group G2 to the focal length of the final lens group GR. By satisfying conditional expression (8), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (8) is undesirable, since the focal length of the final lens group GR becomes short, the curvature of field generated in the final lens group GR becomes large, and good optical performance cannot be achieved. To ensure the effect of conditional expression (8), it is preferable to set the upper limit of conditional expression (8) to 0.33, and even more preferably 0.30. Falling below the lower limit of conditional expression (8) is undesirable, since the focal length of the second lens group G2 becomes short, the spherical aberration, coma, and curvature of field generated in the second lens group G2 become large, and good optical performance cannot be achieved. To ensure the effect of conditional expression (8), it is more preferable to set the lower limit of conditional expression (8) to 0.15, and even more preferably 0.19.

[0031] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (9).

[0032] 0.20<fMw / fR<0.40 (9) where, fMw: focal length of the middle lens group GM in the wide-angle end state, and fR: focal length of the final lens group GR.

[0033] Conditional expression (9) defines the ratio of the focal length of the intermediate lens group GM in the wide-angle end state to the focal length of the final lens group GR. When the intermediate lens group GM consists of two lens groups, fMw is the combined focal length of the two lens groups in the wide-angle end state. By satisfying conditional expression (9), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. Exceeding the upper limit of conditional expression (9) is undesirable, since the focal length of the final lens group GR becomes short, the curvature of field generated in the final lens group GR becomes large, and good optical performance cannot be achieved. To ensure the effect of conditional expression (9), it is preferable to set the upper limit of conditional expression (9) to 0.37, or even 0.35. Furthermore, falling below the lower limit of conditional expression (9) is undesirable, since the focal length of the intermediate lens group GM becomes short, the spherical aberration and coma generated in the intermediate lens group GM become large, and good optical performance cannot be achieved. In order to ensure the effect of conditional expression (9), it is more desirable to set the lower limit of conditional expression (9) to 0.23, and more preferably 0.25.

[0034] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (10).

[0035] 0.20<(-fF) / fR<0.65 (10) where, fF: focal length of the focusing lens group GF, and fR: focal length of the final lens group GR.

[0036] Conditional expression (10) defines the ratio of the focal length of the focusing lens group GF to the focal length of the final lens group GR. By satisfying conditional expression (10), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting excellent optical performance. Exceeding the upper limit of conditional expression (10) is undesirable, since the focal length of the final lens group GR becomes short, the curvature of field generated by the final lens group GR increases, and excellent optical performance cannot be achieved. To ensure the effect of conditional expression (10), it is preferable to set the upper limit of conditional expression (10) to 0.60, or even 0.58. Falling below the lower limit of conditional expression (10) is undesirable, since the focal length of the focusing lens group GF becomes short, the spherical aberration, coma, and curvature of field generated by the focusing lens group GF increase, and excellent optical performance cannot be achieved. To ensure the effect of conditional expression (10), it is more preferable to set the lower limit of conditional expression (10) to 0.25, or even 0.30.

[0037] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (11).

[0038] 1.00<fw / Bfw<1.80 (11) where, fw: focal length of the entire variable magnification optical system ZL in the wide-angle end state, and Bfw: back focus (air-equivalent length) of the variable magnification optical system ZL in the wide-angle end state.

[0039] Conditional expression (11) defines the ratio of the focal length of the entire system to the back focus of the variable magnification optical system ZL in the wide-angle end state. By satisfying this conditional expression (11), a variable magnification optical system ZL can be obtained that is lightweight and compact while also having good optical performance. In order to ensure the effect of conditional expression (11), it is preferable to set the upper limit of conditional expression (11) to 1.70, and more preferably 1.65. In addition, in order to ensure the effect of conditional expression (11), it is preferable to set the lower limit of conditional expression (11) to 1.10, and more preferably 1.20.

[0040] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (12).

[0041] 0.75<f1 / TLw<1.35 (12) where, f1: focal length of the first lens group G1, TLw: total optical length (air-equivalent length) of the variable magnification optical system ZL in the wide-angle end state.

[0042] Conditional expression (12) defines the ratio of the focal length of the first lens group G1 to the total optical length of the variable-magnification optical system ZL in the wide-angle end state. By satisfying this conditional expression (12), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting good optical performance. To ensure the effect of conditional expression (12), it is preferable to set the upper limit of conditional expression (12) to 1.30, and more preferably 1.20. To ensure the effect of conditional expression (12), it is preferable to set the lower limit of conditional expression (12) to 0.80, and even more preferably 0.90.

[0043] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (13).

[0044] 0.70<f1 / TLt<1.00 (13) where, f1: focal length of the first lens group G1, TLt: total optical length (air-equivalent length) of the variable magnification optical system ZL in the telephoto end state.

[0045] Conditional expression (13) defines the ratio of the focal length of the first lens group G1 to the total optical length of the variable-magnification optical system ZL in the telephoto end state. By satisfying this conditional expression (13), a variable-magnification optical system ZL can be achieved that is lightweight and compact, while also exhibiting excellent optical performance. To ensure the effect of conditional expression (13), it is preferable to set the upper limit of conditional expression (13) to 0.95, and more preferably 0.90. To ensure the effect of conditional expression (13), it is preferable to set the lower limit of conditional expression (13) to 0.73, and even more preferably 0.75.

[0046] It should be noted that the conditions and configurations described above each exert the effects described above, and are not limited to those that satisfy all of the conditions and configurations; the effects described above can be obtained by satisfying any one of the conditions or configurations, or a combination of any one of the conditions or configurations.

[0047] Next, a camera, which is an optical device equipped with the variable magnification optical system ZL according to this embodiment, will be described with reference to FIG. 7 . This camera 1 is a so-called mirrorless camera with interchangeable lenses that uses the variable magnification optical system ZL according to this embodiment as a photographing lens 2. In this camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and forms a subject image on the imaging surface of the imaging unit 3 via an OLPF (Optical Low Pass Filter) (not shown). The subject image is then photoelectrically converted by a photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic Viewfinder) 4 provided in the camera 1. This allows the photographer to observe the subject through the EVF 4.

[0048] Furthermore, when the photographer presses a release button (not shown), an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph a subject using this camera 1. Note that although an example of a mirrorless camera has been described in this embodiment, the same effects as those of the camera 1 can be achieved even when the variable magnification optical system ZL according to this embodiment is installed in a single-lens reflex camera that has a quick-return mirror in the camera body and observes a subject through a viewfinder optical system.

[0049] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0050] In this embodiment, as will be described later, a variable magnification optical system ZL having a five-group or six-group configuration is shown, but the above configurations, conditions, etc. can also be applied to other group configurations, such as seven groups or eight groups. Furthermore, a configuration in which a lens or lens group is added closest to the object, or a configuration in which a lens or lens group is added closest to the image plane, may also be used. Specifically, a configuration in which a lens group whose position relative to the image plane is fixed during magnification or focusing is added closest to the image plane, may be considered. Furthermore, a lens group refers to a portion having at least one lens separated by an air gap that changes during magnification or focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0051] Alternatively, a single or multiple lens groups, or a partial lens group, may be moved in the optical axis direction to function as a focusing group that focuses from an object at infinity to an object at close range. In this case, the focusing group can be used for autofocusing and is suitable for driving an autofocus motor (such as an ultrasonic motor). In particular, it is preferable to use the fourth lens group G4 (first and second embodiments) or the fifth lens group G5 (third embodiment) as the focusing group. It is also preferable that the positions of the lenses other than the focusing group be fixed relative to the image plane during focusing. Considering the load on the motor, it is preferable that the focusing group be composed of a single lens or one lens component.

[0052] Furthermore, a lens group or a partial lens group may be moved so as to have a displacement component in a direction perpendicular to the optical axis, or may be rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization group that corrects image blur caused by camera shake. In particular, it is preferable to use at least a portion of the third lens group G3 (first and second embodiments) or the fourth lens group G4 (third embodiment) as an image stabilization group.

[0053] The lens surface may be spherical, flat, or aspherical. A spherical or flat lens surface is preferred 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 preferred because it minimizes degradation of imaging performance even when the image plane is misaligned. If the lens surface is aspherical, the aspherical surface may be any of the following aspherical surfaces: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is molded into an aspherical 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.

[0054] The aperture stop S is preferably disposed between the second lens group G2 and the third lens group G3, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as an aperture stop.

[0055] Furthermore, each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high contrast and high optical performance.

[0056] A manufacturing method for the variable-magnification optical system ZL according to this embodiment will be outlined below with reference to Fig. 8. First, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a middle lens group GM consisting of one or two lens groups and having positive refractive power as a whole, a focusing lens group GF having negative refractive power and moving in the optical axis direction during focusing, and a final lens group GR having positive refractive power are prepared (Step S100). Then, the lens groups are arranged so that the spacing between adjacent lens groups changes during magnification (Step S200), and the first lens group G1 is arranged so that it is composed of a single lens L11 that satisfies predetermined conditional expressions (e.g., the above-mentioned conditional expressions (1) and (2)) (Step S300).

[0057] With the above-described configuration, it is possible to provide a variable magnification optical system, an optical device, and a method for manufacturing a variable magnification optical system that is lightweight, compact, and has good optical performance.

[0058] Each embodiment will be described below with reference to the drawings. Figures 1, 3, and 5 are cross-sectional views showing the configuration and refractive power distribution of the variable-magnification optical system ZL (ZL1 to ZL3) according to each embodiment. The bottom of each figure also shows the movement locus of each lens group of the variable-magnification optical system ZL as it changes magnification from the wide-angle end state (W) to the telephoto end state (T).

[0059] In each example, the aspherical surface is expressed by the following formula (a), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance along the optical axis from the tangent plane of the vertex of each aspherical surface at the height y to each aspherical surface (amount of sag), r is the radius of curvature of the reference spherical surface (paraxial radius of curvature), K is the conic constant, and An is the n-th order aspherical coefficient. Note that in the following examples, "E-n" is expressed as "×10 -n " indicates.

[0060] S(y)=(y 2 / r) / {1+(1-K×y 2 / r 2 ) 1 / 2} + A4 × y 4 +A6×y 6 +A8×y 8 +A10×y 10+A12×y 12 (a)

[0061] In each embodiment, the second-order aspherical coefficient A2 is zero.

[0062] Furthermore, the following examples show specific examples of the present invention, and the present invention is not limited to these examples.

[0063] [First Example] Figure 1 shows the configuration of a variable magnification optical system ZL1 according to the first example. This variable magnification optical system ZL1 is composed of, in order from the object side, 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 focusing lens group GF which is a fourth lens group G4 having negative refractive power and which moves in the optical axis direction during focusing, and a final lens group GR which is a fifth lens group G5 having positive refractive power. In the variable magnification optical system ZL1, the third lens group G3 corresponds to the intermediate lens group GM.

[0064] The first lens group G1 is composed of a single positive meniscus lens L11 with a convex surface facing the object side. The second lens group G2 is composed of, from the object side, a negative meniscus lens L21 with a convex surface facing the object side, a biconcave negative lens L22, a positive biconvex lens L23, and a negative meniscus lens L24 with a concave surface facing the object side. The third lens group G3 is composed of, from the object side, a positive biconvex lens L31, a negative meniscus lens L32 with a convex surface facing the object side, a cemented negative lens formed by cementing a negative biconcave lens L33 and a positive biconvex lens L34, and a positive biconvex lens L35. The fourth lens group G4 is composed of a negative meniscus lens L41 with a convex surface facing the object side. The fifth lens group G5 is composed of, in order from the object side, a meniscus-shaped negative lens L51 with its concave surface facing the object side, and a biconvex positive lens L52. The negative lens L21 is a compound lens in which a dendritic layer is provided on the object-side lens surface of the glass lens body to form an aspherical surface. The positive lens L31 also has aspherical surfaces on its object-side and image-plane-side lens surfaces. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

[0065] In this variable magnification optical system ZL1, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 (the final lens group GR) move along the optical axis so that the spacing between the lens groups changes during magnification. Note that the aperture stop S moves together with the third lens group G3.

[0066] In this variable magnification optical system ZL1, image position correction (vibration prevention) when camera shake occurs is performed by moving the positive lens L35 of the third lens group G3 so that it has a displacement component in a direction perpendicular to the optical axis.

[0067] In this variable magnification optical system ZL1, focusing from an object at infinity to an object at a close distance is performed by moving the fourth lens group G4, which is the focusing lens group GF, toward the image side along the optical axis.

[0068] Table 1 below lists the specifications of the variable magnification optical system ZL1. In Table 1, the overall specifications include f, the focal length of the entire system, Fno, the F-number, ω, the half angle of view (maximum angle of incidence, measured in degrees), Y, the maximum image height, TL, the total optical length, and Bf, the back focus, which are expressed as values ​​in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity. Here, the back focus Bf indicates the air-equivalent length on the optical axis from the lens surface closest to the image plane (surface No. 27) to the image plane I. The total optical length TL indicates the distance on the optical axis from the lens surface closest to the object plane (surface No. 1) to the lens surface closest to the image plane (surface No. 27) plus the air-equivalent length of the back focus. In the lens data, the first column m indicates the order of the lens surfaces (surface number) from the object side along the direction of light ray travel, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and the fourth column nd and fifth column vd indicate the refractive index and Abbe number for the d-line (λ=587.6 nm). A radius of curvature of ∞ indicates a flat surface, and the refractive index of air, 1.00000, is omitted. If the lens surface is aspherical, an asterisk (*) is added to the right of the surface number, and the column for the radius of curvature r indicates the paraxial radius of curvature. The lens group focal lengths indicate the number and focal length of the first surface of each of the first through fifth lens groups G1 through G5.

[0069] Here, the focal length f, radius of curvature r, surface spacing d, and other length values ​​listed in all of the following specifications are generally expressed in units of "mm," but this is not limited to this because the optical system can achieve the same optical performance even when proportionally enlarged or reduced.

[0070] The explanations of these symbols and the specifications tables also apply to the following examples.

[0071] (Table 1) First Example [Overall specifications] Wide-angle end Mid-focal length Telephoto end f 16.480 35.000 48.500 Fno 2.912 2.912 2.912 ω 42.697 21.877 16.021 Y 13.703 14.200 14.200 TL (air equivalent length) 100.155 107.321 126.930 Bf (air equivalent length) 10.852 15.002 20.124 [Lens data] m r d nd νd Object plane ∞ 1 46.5018 7.272 1.48749 70.32 2 408.3816 D2 3* 136.5101 0.050 1.56093 36.64 4 66.8522 1.300 1.83481 42.73 5 14.6653 7.584 6 -45.3757 1.000 1.79500 45.31 7 61.3801 0.529 8 34.9234 3.918 1.84666 23.80 9 -49.9980 1.473 10 -20.2084 1.226 1.83400 37.18 11 -33.8168 D11 12 ∞ 1.500 Aperture Stop S 13* 20.1310 5.426 1.85108 40.12 14* -47.1968 0.966 15 41.3577 3.151 1.79504 28.69 16 18.7104 2.515 17 -47.4062 0.900 1.80518 25.45 18 15.4271 6.106 1.49782 82.57 19 -17.9780 1.429 20 33.5686 2.364 1.80400 46.60 21 -826.3821 D21 22 106.6457 1.060 1.85026 32.35 23 25.1644 D23 24 -33.1197 1.000 1.75500 52.34 25 -85.8550 0.100 26 74.7201 4.479 1.86966 20.02 27 -58.0572 Bf Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length 1st lens group G1 1 106.944 2nd lens group G2 3 -18.564 3rd lens group G3 12 21.446 4th lens group G4 22 -38.969 5th lens group G5 24 75.827.

[0072] In this variable magnification optical system ZL1, surfaces 3, 13, and 14 are aspherical. Table 2 below shows the aspherical data for the surface numbers, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0073] (Table 2) [Aspherical surface data] Surface 3 K = 1.00000 A4 = 1.59272E-05 A6 = -3.39148E-08 A8 = 1.14126E-10 A10 = -5.80834E-14 A12 = 0.00000E-00 Surface 13 K = 1.00000 A4 = -1.62725E-05 A6 = -9.04684E-09 A8 = 5.95302E-11 A10 = -1.31075E-12 A12 = 0.00000E-00 Surface 14 K = 1.00000 A4 = 2.50810E-05 A6 =-4.76238E-08 A8 = 6.96628E-11 A10=-8.53155E-13 A12= 0.00000E-00

[0074] In this variable magnification optical system ZL1, the axial air spacing D2 between the first lens group G1 and the second lens group G2, the axial air spacing D11 between the second lens group G2 and the third lens group G3, the axial air spacing D21 between the third lens group G3 and the fourth lens group G4, the axial air spacing D23 between the fourth lens group G4 and the fifth lens group G5, and the back focal length Bf change during magnification and focusing. Table 3 below shows the variable spacings in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity and when focusing on a close object. In Table 3, f represents the focal length of the entire system, β represents the magnification, and D0 represents the axial distance from the lens surface closest to the object (surface No. 1) to the object. The same explanations of these symbols apply to the following examples.

[0075] (Table 3) [Variable distance data] When focusing on an object at infinity When focusing on an object at close range Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 16.480 35.000 48.500 - - - β - - - - -0.221 -0.221 -0.245 D0 ∞ ∞ ∞ 49.845 112.679 123.070 D2 1.150 15.983 29.891 1.150 15.983 29.891 D11 21.701 3.424 2.000 21.701 3.424 2.000 D21 2.122 5.358 2.000 5.338 10.686 8.015 D23 8.982 12.206 17.567 5.766 6.877 11.552 Bf 10.852 15.002 20.124 10.852 15.002 20.124

[0076] FIG. 2 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma when this variable magnification optical system ZL1 is focused on an object at infinity in the wide-angle end state. In each aberration diagram, FNO represents the F-number, and Y represents the image height. Note that the spherical aberration diagram indicates the F-number value relative to the maximum aperture, the astigmatism diagram and distortion diagram indicate the image height value, and the coma diagram indicates the value of each image height. Also, in the spherical aberration diagram and coma diagram, d represents the d-line (λ=587.6 nm) and g represents the g-line (λ=435.8 nm), respectively. In the astigmatism diagram, the solid line represents the sagittal image plane, and the dashed line represents the meridional image plane. In the coma diagram, the solid line represents the meridional image plane, and the dashed line represents the sagittal image plane. The same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below. From these aberration diagrams, it can be seen that the variable magnification optical system ZL1 has excellent correction of various aberrations and has excellent imaging performance.

[0077] [Second Example] Figure 3 shows the configuration of a variable magnification optical system ZL2 according to the second example. This variable magnification optical system ZL2 is composed of, in order from the object side, 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 focusing lens group GF which is a fourth lens group G4 having negative refractive power and which moves in the optical axis direction during focusing, and a final lens group GR which is a fifth lens group G5 having positive refractive power. In the variable magnification optical system ZL2, the third lens group G3 corresponds to the intermediate lens group GM.

[0078] The first lens group G1 is composed of a single positive meniscus lens L11 with a convex surface facing the object side. The second lens group G2 is composed of, from the object side, a negative meniscus lens L21 with a convex surface facing the object side, a biconcave negative lens L22, a positive biconvex lens L23, and a negative meniscus lens L24 with a concave surface facing the object side. The third lens group G3 is composed of, from the object side, a positive biconvex lens L31, a negative meniscus lens L32 with a convex surface facing the object side, a cemented negative lens formed by cementing a negative biconcave lens L33 and a positive biconvex lens L34, and a positive biconvex lens L35. The fourth lens group G4 is composed of a negative meniscus lens L41 with a convex surface facing the object side. The fifth lens group G5 is composed of, in order from the object side, a meniscus-shaped negative lens L51 with its concave surface facing the object side, and a biconvex positive lens L52. The negative lens L21 is a compound lens in which a dendritic layer is provided on the object-side lens surface of the glass lens body to form an aspherical surface. The positive lens L31 also has aspherical surfaces on its object-side and image-plane-side lens surfaces. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

[0079] In this variable magnification optical system ZL2, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 (the final lens group GR) move along the optical axis so that the spacing between the lens groups changes during magnification. Note that the aperture stop S moves together with the third lens group G3.

[0080] In this variable magnification optical system ZL2, image position correction (vibration prevention) when camera shake occurs is performed by moving the positive lens L35 of the third lens group G3 so that it has a displacement component in a direction perpendicular to the optical axis.

[0081] In this variable magnification optical system ZL2, focusing from an object at infinity to an object at a close distance is performed by moving the fourth lens group G4, which is the focusing lens group GF, toward the image side along the optical axis.

[0082] The specifications of the variable magnification optical system ZL2 are listed in Table 4. In Table 4, the lens group focal lengths indicate the number and focal length of the first surface of each of the first to fifth lens groups G1 to G5.

[0083] (Table 4) Second Example [Overall specifications] Wide-angle end Mid-focal length Telephoto end f 16.480 35.000 48.500 Fno 2.912 2.912 2.912 ω 42.664 22.015 16.180 Y 13.703 14.200 14.200 TL (air equivalent length) 100.155 107.705 125.373 Bf (air equivalent length) 11.697 16.622 21.303 [Lens data] m r d nd νd Object plane ∞ 1 44.5814 6.848 1.59349 67.00 2 185.5658 D2 3* 153.8319 0.050 1.56093 36.64 4 69.6014 1.300 1.83481 42.73 5 14.6513 7.801 6 -55.6723 1.000 1.80440 39.61 7 49.5009 0.593 8 32.5138 3.921 1.84666 23.80 9 -64.9436 2.054 10 -19.6826 1.500 1.75500 52.34 11 -31.2494 D11 12 ∞ 1.500 Aperture Stop S 13* 18.6861 5.444 1.85108 40.12 14* -52.9303 1.074 15 29.4394 1.619 1.85026 32.35 16 16.4311 2.797 17 -41.0732 0.900 1.80518 25.45 18 15.2459 6.073 1.49782 82.57 19 -17.7821 0.697 20 31.7706 2.403 1.78800 47.35 21 -4370.0352 D21 22 153.8425 0.900 1.85026 32.35 23 26.4287 D23 24 -30.6834 1.000 1.75500 52.34 25 -60.5124 0.100 26 90.3717 4.499 1.86966 20.02 27 -52.7177 Bf Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length 1st lens group G1 1 97.114 2nd lens group G2 3 -18.342 3rd lens group G3 12 21.211 4th lens group G4 22 -37.653 5th lens group G5 24 68.262.

[0084] In this variable magnification optical system ZL2, surfaces 3, 13, and 14 are aspherical. Table 5 below shows the aspherical data for the surface numbers, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0085] (Table 5) [Aspherical surface data] Surface 3 K = 1.0000 A4 = 1.68417E-05 A6 = -3.56538E-08 A8 = 1.08569E-10 A10 = -7.12771E-14 A12 = 0.00000E-00 Surface 13 K = 1.0000 A4 = -1.80545E-05 A6 = -1.77998E-08 A8 = 8.38042E-11 A10 = -8.62163E-13 A12 = 0.00000E-00 Surface 14 K = 1.0000 A4 = 2.57593E-05 A6 =-5.94339E-08 A8 = 2.20073E-10 A10=-8.59413E-13 A12= 0.00000E-00

[0086] In this variable magnification optical system ZL2, the axial air spacing D2 between the first lens group G1 and the second lens group G2, the axial air spacing D11 between the second lens group G2 and the third lens group G3, the axial air spacing D21 between the third lens group G3 and the fourth lens group G4, the axial air spacing D23 between the fourth lens group G4 and the fifth lens group G5, and the back focal length Bf change during magnification change and focusing. Table 6 below shows the variable spacings in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity and when focusing on a close object.

[0087] (Table 6) [Variable distance data] When focusing on an object at infinity When focusing on an object at close range Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 16.480 35.000 48.500 - - - β - - - - -0.222 -0.219 -0.244 D0 ∞ ∞ ∞ 49.845 112.295 124.627 D2 1.150 16.385 28.332 1.150 16.385 28.332 D11 21.464 3.601 2.000 21.464 3.601 2.000 D21 2.862 5.191 2.000 5.915 10.214 7.803 D23 8.909 11.832 17.664 5.856 6.809 11.861 Bf 11.697 16.622 21.303 11.697 16.622 21.303

[0088] 4 shows diagrams of spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma when this variable magnification optical system ZL2 is focused on an object at infinity in the wide-angle end state. These aberration diagrams show that the variable magnification optical system ZL2 has excellent correction for various aberrations and has excellent imaging performance.

[0089] [Third Example] Figure 5 shows the configuration of a variable magnification optical system ZL3 according to a third example. This variable magnification optical system ZL3 is composed of, in order from the object side, 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 focusing lens group GF which is a fifth lens group G5 having negative refractive power and moving in the optical axis direction during focusing, and a final lens group GR which is a sixth lens group G6 having positive refractive power. In the variable magnification optical system ZL3, the third lens group G3 and the fourth lens group G4 correspond to the intermediate lens group GM. The composite focal length of the third lens group G3 and the fourth lens group G4 has positive refractive power over the entire focal length range from the wide-angle end state to the telephoto end state.

[0090] The first lens group G1 is composed of a single positive meniscus lens L11 with a convex surface facing the object side. The second lens group G2 is composed of, from the object side, a negative meniscus lens L21 with a convex surface facing the object side, a negative biconcave lens L22, 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 third lens group G3 is composed of, from the object side, a positive biconvex lens L31, a positive meniscus lens L32 with a convex surface facing the object side, and a negative biconcave lens L33. The fourth lens group G4 is composed of, from the object side, a biconvex positive lens L41, a cemented positive lens formed by cementing a biconcave negative lens L42 and a biconvex positive lens L43, and a meniscus positive lens L44 with its convex surface facing the object side. The fifth lens group G5 is composed of a meniscus negative lens L51 with its convex surface facing the object side. The sixth lens group G6 is composed of, from the object side, a meniscus negative lens L61 with its concave surface facing the object side, and a biconvex positive lens L62. The object-side lens surface of the negative lens L21 and the object-side lens surface of the positive lens L41 are aspheric. An aperture stop S is disposed between the second lens group G2 and the third lens group G3.

[0091] In this variable magnification optical system ZL3, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 (the final lens group GR) move along the optical axis so that the spacing between the lens groups changes during magnification. Note that the aperture stop S moves together with the third lens group G3.

[0092] In this variable magnification optical system ZL3, image position correction (vibration prevention) when camera shake occurs is performed by moving the positive lens L44 of the fourth lens group G4 so that it has a displacement component in a direction perpendicular to the optical axis.

[0093] In this variable magnification optical system ZL3, focusing from an object at infinity to an object at a close distance is performed by moving the fifth lens group G5, which is the focusing lens group GF, toward the image side along the optical axis.

[0094] The specifications of the variable magnification optical system ZL3 are listed in Table 7. In Table 7, the lens group focal lengths indicate the number and focal length of the first surface of each of the first to sixth lens groups G1 to G6.

[0095] (Table 7) Third Example [Overall specifications] Wide-angle end Mid-focal length Telephoto end f 16.482 28.000 48.459 Fno 2.880 2.880 2.880 ω 42.653 26.682 15.902 Y 13.885 14.200 14.200 TL (air equivalent length) 100.014 106.921 128.169 Bf (air equivalent length) 10.302 16.621 27.268 [Lens data] m r d nd νd Object plane ∞ 1 61.0909 5.996 1.59349 67.00 2 686.9805 D2 3* 85.9734 1.100 1.71300 53.96 4 14.0683 5.455 5 -178.7274 1.000 1.71300 53.96 6 33.5456 0.150 7 23.8666 3.751 1.80518 25.45 8 172.4103 2.499 9 -18.6039 1.000 1.83481 42.73 10 -30.4955 D10 11 ∞ 1.500 Aperture Stop S 12 30.3961 3.509 1.84850 43.79 13 -99.0853 0.150 14 25.9460 2.573 1.49782 82.57 15 52.3273 2.620 16 -38.1600 0.900 1.64769 33.72 17 62.0567 D17 18* 58.5455 2.763 1.59349 67.00 19 -59.2707 0.150 20 -207.7349 0.900 1.64769 33.72 21 18.0774 5.697 1.49782 82.57 22 -23.2115 0.642 23 35.1108 2.828 1.81600 46.59 24 717.6419 D24 25 74.7293 0.900 1.85026 32.35 26 19.5842 D26 27 -18.4123 1.000 1.83481 42.73 28 -33.2771 0.100 29 958.0302 4.829 1.84666 23.80 30 -29.1663 Bf Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length 1st lens group G1 1 112.581 2nd lens group G2 3 -16.515 3rd lens group G3 11 38.095 4th lens group G4 18 20.269 5th lens group G5 25 -31.449 Sixth lens group G6 27 80.009.

[0096] In this variable magnification optical system ZL3, surfaces 3 and 18 are aspherical. Table 8 below shows aspherical data for surface numbers, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0097] (Table 8) [Aspherical surface data] Surface 3 K = 1.00000 A4 = 9.25982E-06 A6 = -6.14077E-09 A8 = 7.75003E-11 A10 = -3.97760E-13 A12 = 1.20510E-15 Surface 18 K = 1.00000 A4 = -4.40876E-05 A6 = 4.98433E-08 A8 = -4.06429E-10 A10 = 5.67993E-12 A12 = -2.68170E-14

[0098] In this variable magnification optical system ZL3, the axial air spacing D2 between the first lens group G1 and the second lens group G2, the axial air spacing D10 between the second lens group G2 and the third lens group G3, the axial air spacing D17 between the third lens group G3 and the fourth lens group G4, the axial air spacing D24 between the fourth lens group G4 and the fifth lens group G5, the axial air spacing D26 between the fifth lens group G5 and the sixth lens group G6, and the back focal length Bf change during magnification change and focusing. Table 9 below shows the variable spacings in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity and when focusing on a close object.

[0099] (Table 9) [Variable distance data] When focusing on an object at infinity When focusing on an object at close range Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 16.482 28.000 48.459 - - - β - - - - -0.220 -0.224 -0.249 D0 ∞ ∞ ∞ 49.986 83.079 121.831 D2 1.490 13.884 30.784 1.490 13.884 30.784 D10 19.755 7.956 1.644 19.755 7.956 1.644 D17 4.727 2.512 1.493 4.727 2.512 1.493 D24 1.992 2.828 1.997 4.191 5.757 6.123 D26 9.734 11.105 12.969 7.535 8.177 8.843 Bf 10.302 16.621 27.268 10.302 16.621 27.268

[0100] 6 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma when the variable magnification optical system ZL3 is focused on an object at infinity in the wide-angle end state. These aberration diagrams show that the variable magnification optical system ZL3 has excellent imaging performance with various aberrations well corrected.

[0101] [Values ​​of Conditional Expressions] The values ​​of conditional expressions (1) to (13) in Examples 1 to 3 are shown in Table 10. In Table 10, the focal length fMw of the middle lens group GM in the wide-angle end state is the focal length of the third lens group G3 in Examples 1 and 2, and is the combined focal length of the third lens group G3 and the fourth lens group G4 in the wide-angle end state in Example 3.

[0102] (Table 10) Example 1 Example 2 Example 3 fMw 21.446 21.211 20.866 (1) nd1 1.487 1.593 1.593 (2) νd1 70.32 67.00 67.00 (3) f1 / (-f2) 5.761 5.295 6.817 (4) f1 / fMw 4.987 4.578 5.395 (5) f1 / (-fF) 2.744 2.579 3.580 (6) f1 / fR 1.410 1.423 1.407 (7) f2 / fF 0.476 0.487 0.525 (8) (-f2) / fR 0.245 0.269 0.206 (9) fMw / fR 0.283 0.311 0.261 (10) (-fF) / fR 0.514 0.552 0.393 (11) fw / Bfw 1.519 1.409 1.600 (12) f1 / TLw 1.068 0.970 1.126 (13) f1 / TLt 0.843 0.775 0.878

[0103] 1 Camera (optical equipment) ZL (ZL1 to ZL3) Variable magnification optical system G1 First lens group G2 Second lens group GM Intermediate lens group GF Focusing lens group GR Last lens group

Claims

1. The optical system has, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, an intermediate lens group consisting of one or two lens groups and having positive refractive power as a whole, a focusing lens group having negative refractive power and moving in the optical axis direction during focusing, and a final lens group having positive refractive power, When changing magnification, the spacing between adjacent lens groups changes, the first lens group is composed of one single lens, A variable magnification optical system that satisfies the following condition: 1.45 < nd1 < 1.63 62.50 < νd1 < 85.00 however, nd1: refractive index of the medium of the single lens constituting the first lens group with respect to the d line νd1: Abbe number of the medium of the single lens constituting the first lens group with respect to the d line

2. 2. A variable magnification optical system according to claim 1, wherein the final lens group moves along the optical axis during magnification variation.

3. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 4.80 < f1 / (-f2) < 7.50 however, f1: focal length of the first lens group f2: focal length of the second lens group

4. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 3.80 < f1 / fMw < 6.00 however, f1: focal length of the first lens group fMw: focal length of the intermediate lens group in the wide-angle end state

5. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 2.00 < f1 / (-fF) < 4.00 however, f1: focal length of the first lens group fF: focal length of the focusing lens group

6. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 1.10 < f1 / fR < 1.75 however, f1: focal length of the first lens group fR: focal length of the final lens group

7. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.40 < f2 / fF < 0.65 however, f2: focal length of the second lens group fF: focal length of the focusing lens group

8. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.10 < (-f2) / fR < 0.35 however, f2: focal length of the second lens group fR: focal length of the final lens group

9. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.20 < fMw / fR < 0.40 however, fMw: focal length of the intermediate lens group in the wide-angle end state fR: focal length of the final lens group

10. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.20 < (-fF) / fR < 0.65 however, fF: focal length of the focusing lens group fR: focal length of the final lens group

11. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 1.00 < fw / Bfw < 1.80 however, fw: focal length of the entire variable magnification optical system in the wide-angle end state Bfw: back focus of the variable magnification optical system in the wide-angle end state

12. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.75 < f1 / TLw < 1.35 however, f1: focal length of the first lens group TLw: total optical length of the variable magnification optical system in the wide-angle end state

13. 2. A variable magnification optical system according to claim 1, which satisfies the following condition: .times. ... 0.70 < f1 / TLt < 1.00 however, f1: focal length of the first lens group TLt: total optical length of the variable magnification optical system in the telephoto end state

14. An optical instrument comprising the variable magnification optical system according to any one of claims 1 to 13.