Variable magnification optical system and optical equipment

Abstract

Provided is a small-size and lightweight variable magnification optical system suitable for moving image photography and capable of obtaining excellent optical performance, an optical device, and a method for manufacturing the variable magnification optical system.　A variable magnification optical system ZL for use in an optical device such as a camera 1 includes, in order from the object side: a first lens group G1 having negative refractive power; a second lens group G2 having positive refractive power; a third lens group G3; and a fourth lens group G4 having positive refractive power. During zooming, the distance between adjacent lens groups changes, the first lens group G1 is fixed with respect to the image plane, and the fourth lens group G4 moves along the optical axis. During focusing, at least the second lens group G2 moves along the optical axis and satisfies a condition represented by a predetermined conditional expression.

Description

[Technical Field]

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

[0002] Variable magnification optical systems that can also be used for video shooting have been proposed (see, for example, Patent Document 1). However, there is a demand for further miniaturization and weight reduction, as well as further improvement in optical performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-120823 Summary of the Invention

[0004] The variable magnification optical system according to the first aspect of the present invention comprises, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group, and a fourth lens group having positive refractive power. It essentially consists of four lens groups: During zooming, the distance between adjacent lens groups changes, the first lens group is fixed relative to the image plane, the fourth lens group moves along the optical axis, and during focusing, at least the second lens group moves along the optical axis, and the following condition is satisfied: 0.050 < (-f1) / f2 < 0.650 0.600 < ft / Bft < 1.500 0.010 < f4 / |f3| < 1.000 however, f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire variable magnification optical system in the telephoto end state Bft: back focus of the variable magnification optical system in the telephoto end state f3: focal length of the third lens group f4: focal length of the fourth lens group A variable magnification optical system according to a second aspect of the present invention substantially comprises four lens groups: a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group, and a fourth lens group having positive refractive power, in that order from the object side; the spacing between adjacent lens groups changes during magnification variation; the first lens group is fixed with respect to the image plane; the fourth lens group moves along the optical axis; and during focusing, at least the second lens group moves along the optical axis, and the following condition is satisfied: 0.050 < (-f1) / f2 < 0.800 0.600 < ft / Bft < 1.500 0.010 < f4 / |f3| < 0.550 however, f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire variable magnification optical system in the telephoto end state Bft: back focus of the variable magnification optical system in the telephoto end state f3: focal length of the third lens group f4: focal length of the fourth lens group

[0005] The present invention three The variable magnification optical system according to the aspect of the present invention comprises, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group, and a fourth lens group having positive refractive power. It essentially consists of four lens groups: During zooming, the distance between adjacent lens groups changes, the first lens group is fixed relative to the image plane, the fourth lens group moves along the optical axis, and during focusing, at least the second lens group moves along the optical axis, and the following condition is satisfied: 0.010 < (-f1) / |f3| < 0.250 0.100 < f4 / f2 < 1.200 however, f1: focal length of the first lens group f2: focal length of the second lens group f3: focal length of the third lens group f4: focal length of the fourth lens group [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing the lens configuration of a variable magnification optical system according to a first example. [Figure 2] 1A and 1B are diagrams showing various aberrations of the variable magnification optical system according to Example 1, in which FIG. 1A shows the wide-angle end state and FIG. 1B shows the telephoto end state. [Figure 3] FIG. 10 is a cross-sectional view showing the lens configuration of a variable magnification optical system according to Example 2. [Figure 4] 10A and 10B are diagrams showing various aberrations of the variable magnification optical system according to Example 2, in which FIG. 10A shows the wide-angle end state and FIG. [Figure 5] FIG. 10 is a cross-sectional view showing the lens configuration of a variable magnification optical system according to Example 3. [Figure 6] 10A and 10B are diagrams showing various aberrations of the variable magnification optical system according to Example 3, in which FIG. 10A shows the wide-angle end state and FIG. [Figure 7] FIG. 10 is a cross-sectional view showing the lens configuration of a variable magnification optical system according to Example 4. [Figure 8] 10A and 10B are diagrams showing various aberrations of the variable magnification optical system according to Example 4, in which FIG. 10A shows the wide-angle end state and FIG. [Figure 9] FIG. 2 is a cross-sectional view of a camera equipped with the variable magnification optical system. [Figure 10] 10 is a flowchart illustrating a method for manufacturing the variable magnification optical system. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments will now be described with reference to the drawings.

[0010] (First embodiment) As shown in FIG. 1, the variable-magnification optical system ZL according to the first embodiment includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3, and a fourth lens group G4 having positive refractive power. Furthermore, during zooming, the spacing between adjacent lens groups changes, with the first lens group G1 being fixed relative to the image plane and the fourth lens group G4 moving along the optical axis. Furthermore, during focusing, at least the second lens group G2 moves along the optical axis. This configuration allows for zooming and focusing to be performed by lens groups other than the first lens group G1, which has a large diameter and is heavy, making it possible to easily move each lens group, making the system suitable for video recording and other applications.

[0011] Furthermore, it is desirable that the variable magnification optical system ZL according to the first embodiment satisfy the following conditional expression (1).

[0012] 0.050 < (-f1) / f2 < 1.500 (1) however, f1: focal length of the first lens group G1 f2: Focal length of the second lens group G2

[0013] Conditional expression (1) 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 (1), the variable magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (1) undesirably shortens the focal length of the second lens group G2, increasing the spherical aberration, coma, and curvature of field generated by the second lens group G2. This results in poor optical performance during zooming. To ensure the effectiveness of conditional expression (1), it is desirable to set the upper limit of conditional expression (1) to 0.800, or even 0.650. Falling below the lower limit of conditional expression (1) undesirably shortens the focal length of the first lens group G1, increasing the coma and curvature of field generated by the first lens group G1. This results in poor optical performance during zooming. In order to ensure the effect of conditional expression (1), it is more desirable to set the lower limit of conditional expression (1) to 0.100, and more preferably 0.150.

[0014] Furthermore, it is desirable that the variable magnification optical system ZL according to the first embodiment satisfy the following conditional expression (2).

[0015] 0.100 < ft / Bft < 1.500 (2) however, ft: focal length of the entire system when the variable magnification optical system ZL is focused at infinity in the telephoto end state Bft: Back focus (air equivalent length) of the variable magnification optical system ZL at the telephoto end

[0016] Conditional expression (2) defines the ratio of the focal length of the entire system when focused at infinity to the back focus of the variable magnification optical system ZL in the telephoto end state. By satisfying this conditional expression (2), it is possible to achieve a compact variable magnification optical system ZL while obtaining good optical performance. In order to ensure the effect of conditional expression (2), it is preferable to set the upper limit of conditional expression (2) to 1.300, and more preferably 1.100. In addition, in order to ensure the effect of conditional expression (2), it is preferable to set the lower limit of conditional expression (2) to 0.300, and more preferably 0.600.

[0017] (Second embodiment) As shown in FIG. 1, the variable-magnification optical system ZL according to the second embodiment includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3, and a fourth lens group G4 having positive refractive power. Furthermore, during zooming, the spacing between adjacent lens groups changes, with the first lens group G1 being fixed relative to the image plane and the fourth lens group G4 moving along the optical axis. Furthermore, during focusing, at least the second lens group G2 moves along the optical axis. This configuration allows for zooming and focusing to be performed by lens groups other than the first lens group G1, which has a large diameter and is heavy, making it possible to easily move each lens group, making the system suitable for video recording and other applications.

[0018] Furthermore, it is desirable that the variable magnification optical system ZL according to the second embodiment satisfy the following conditional expression (3).

[0019] 0.010 < (-f1) / |f3| < 1.000 (3) however, f1: focal length of the first lens group G1 f3: Focal length of the third lens group G3

[0020] Conditional expression (3) defines the ratio of the focal length of the first lens group G1 to the focal length of the third lens group G3. By satisfying conditional expression (3), the variable magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (3) undesirably shortens the focal length of the third lens group G3, increasing the spherical aberration, coma, and curvature of field generated in the third lens group G3. This results in poor optical performance during zooming. To ensure the effectiveness of conditional expression (3), it is preferable to set the upper limit of conditional expression (3) to 0.500, or even 0.250. Falling below the lower limit of conditional expression (3) undesirably shortens the focal length of the first lens group G1, increasing the coma and curvature of field generated in the first lens group G1. This results in poor optical performance during zooming. In order to ensure the effect of conditional expression (3), it is more desirable to set the lower limit of conditional expression (3) to 0.040, and more preferably 0.070.

[0021] Furthermore, it is desirable that the variable magnification optical system ZL according to the second embodiment satisfy the following conditional expression (4).

[0022] 0.100 < f4 / f2 < 1.200 (4) however, f2: Focal length of the second lens group G2 f4: Focal length of the fourth lens group G4

[0023] Conditional expression (4) defines the ratio of the focal length of the fourth lens group G4 to the focal length of the second lens group G2. By satisfying conditional expression (4), the variable magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (4) undesirably shortens the focal length of the second lens group G2, increasing the spherical aberration, coma, and curvature of field generated by the second lens group G2. This results in poor optical performance during zooming. To ensure the effectiveness of conditional expression (4), it is desirable to set the upper limit of conditional expression (4) to 1.000, or even 0.950. Falling below the lower limit of conditional expression (4) undesirably shortens the focal length of the fourth lens group G4, increasing the curvature of field generated by the fourth lens group G4. This results in poor optical performance during zooming. In order to ensure the effect of conditional expression (4), it is more desirable to set the lower limit of conditional expression (4) to 0.250, and more preferably 0.350.

[0024] (Regarding the first and second embodiments) Furthermore, it is desirable that the variable magnification optical system ZL according to the first embodiment satisfy the above-mentioned conditional expression (3). The effects and the like resulting from satisfying this conditional expression (3) are as described above.

[0025] Furthermore, it is desirable that the variable magnification optical system ZL according to the first embodiment satisfy the above-mentioned conditional expression (4). The effects and the like resulting from satisfying this conditional expression (4) are as described above.

[0026] Furthermore, it is desirable that the variable magnification optical system ZL according to the first and second embodiments (hereinafter referred to as "the present embodiment") satisfy the following conditional expression (5).

[0027] 0.010 < f4 / |f3| < 1.000 (5) however, f3: Focal length of the third lens group G3 f4: Focal length of the fourth lens group G4

[0028] Conditional expression (5) defines the ratio of the focal length of the fourth lens group G4 to the focal length of the third lens group G3. By satisfying conditional expression (5), the variable magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (5) undesirably shortens the focal length of the third lens group G3, increasing the spherical aberration, coma, and curvature of field generated by the third lens group G3. This results in poor optical performance during zooming. To ensure the effectiveness of conditional expression (5), it is preferable to set the upper limit of conditional expression (5) to 0.800, or even 0.550. Falling below the lower limit of conditional expression (5) undesirably shortens the focal length of the fourth lens group G4, increasing the curvature of field generated by the fourth lens group G4. This results in poor optical performance during zooming. In order to ensure the effect of conditional expression (5), it is more desirable to set the lower limit of conditional expression (5) to 0.070, and more preferably 0.130.

[0029] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (6).

[0030] 0.150 < (-f1) / f4 < 1.500 (6) however, f1: focal length of the first lens group G1 f4: Focal length of the fourth lens group G4

[0031] Conditional expression (6) defines the ratio of the focal length of the first lens group G1 to the focal length of the fourth lens group G4. By satisfying conditional expression (6), the variable-magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (6) undesirably shortens the focal length of the fourth lens group G4, increasing the curvature of field generated by the fourth lens group G4 and thereby preventing good optical performance during zooming. To ensure the effectiveness of conditional expression (6), it is preferable to set the upper limit of conditional expression (6) to 1.000, or even 0.700. Falling below the lower limit of conditional expression (6) undesirably shortens the focal length of the first lens group G1, increasing the coma and curvature of field generated by the first lens group G1 and thereby preventing good optical performance during zooming. To ensure the effectiveness of conditional expression (6), it is preferable to set the lower limit of conditional expression (6) to 0.300, or even 0.400.

[0032] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (7).

[0033] 0.010 < f2 / |f3| < 2.000 (7) however, f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3

[0034] Conditional expression (7) defines the ratio of the focal length of the second lens group G2 to the focal length of the third lens group G3. By satisfying conditional expression (7), the variable magnification optical system ZL can be made compact while still achieving good optical performance. Exceeding the upper limit of conditional expression (7) undesirably shortens the focal length of the third lens group G3, increasing the spherical aberration, coma, and curvature of field generated in the third lens group G3. This results in poor optical performance during zooming. To ensure the effectiveness of conditional expression (7), it is desirable to set the upper limit of conditional expression (7) to 1.500, or even 1.200. Falling below the lower limit of conditional expression (7) undesirably shortens the focal length of the second lens group G2, increasing the spherical aberration, coma, and curvature of field generated in the second lens group G2. This results in poor optical performance during zooming. In order to ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to 0.100, and more preferably 0.200.

[0035] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (8).

[0036] 0.010 < ft / TL < 1.000 (8) however, ft: focal length of the entire system when the variable magnification optical system ZL is focused at infinity in the telephoto end state TL: Total optical length (equivalent to air) of variable magnification optical system ZL

[0037] Conditional expression (8) defines the ratio of the focal length of the entire system when focused at infinity to the total optical length of the variable magnification optical system ZL in the telephoto end state. By satisfying this conditional expression (8), it is possible to achieve a compact variable magnification optical system ZL while obtaining good optical performance. In order to ensure the effect of conditional expression (8), it is preferable to set the upper limit of conditional expression (8) to 0.750, and more preferably 0.380. In addition, in order to ensure the effect of conditional expression (8), it is preferable to set the lower limit of conditional expression (8) to 0.100, and more preferably 0.150.

[0038] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (9).

[0039] 0.300 < fw / Bfw < 4.000 (9) however, fw: focal length of the entire system when focusing at infinity on the variable magnification optical system ZL in the wide-angle end state Bfw: Back focus (air equivalent length) of the variable magnification optical system ZL in the wide-angle end state

[0040] Conditional expression (9) defines the ratio of the focal length of the entire system when focused at infinity to the back focus of the variable magnification optical system ZL in the wide-angle end state. By satisfying this conditional expression (9), it is possible to achieve a compact variable magnification optical system ZL while obtaining good optical performance. In order to ensure the effect of conditional expression (9), it is preferable to set the upper limit of conditional expression (9) to 3.000, and more preferably 2.000. In addition, in order to ensure the effect of conditional expression (9), it is preferable to set the lower limit of conditional expression (9) to 0.500, and more preferably 0.650.

[0041] Furthermore, it is desirable that the variable magnification optical system ZL according to this embodiment satisfy the following conditional expression (10).

[0042] 0.100 < ft / TLGt < 1.000 (10) however, ft: focal length of the entire system when the variable magnification optical system ZL is focused at infinity in the telephoto end state TLGt: The distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plane of the variable magnification optical system ZL in the telephoto end state

[0043] Conditional expression (10) defines the ratio of the focal length of the entire system when focused at infinity to the axial distance from the lens surface closest to the object to the lens surface closest to the image plane of the variable magnification optical system ZL in the telephoto end state. By satisfying conditional expression (10), the variable magnification optical system ZL can be made compact while still achieving good optical performance. To ensure the effectiveness of conditional expression (10), it is preferable to set the upper limit of conditional expression (10) to 0.800, and more preferably 0.700. To ensure the effectiveness of conditional expression (10), it is preferable to set the lower limit of conditional expression (10) to 0.250, and even more preferably 0.500.

[0044] In the variable magnification optical system ZL according to this embodiment, it is desirable that the third lens group G3 has positive refractive power. By adopting such a configuration, it is possible to achieve a compact variable magnification optical system ZL while obtaining good optical performance.

[0045] In the variable magnification optical system ZL according to this embodiment, it is desirable that the second lens group G2 be composed of a single lens component. By adopting such a configuration, it is possible to achieve a compact variable magnification optical system ZL while obtaining good optical performance.

[0046] In the variable magnification optical system ZL according to this embodiment, the second lens group G2 is preferably composed of one positive lens and one negative lens, which allows the variable magnification optical system ZL to be compact while still achieving good optical performance.

[0047] 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.

[0048] 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. 9. 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 plane 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 (imaging 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.

[0049] Furthermore, when the photographer presses a release button (not shown), the 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.

[0050] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0051] In this embodiment, a variable magnification optical system ZL having a four-group configuration is shown, but the above-described configuration conditions can also be applied to other group configurations, such as five groups or six 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 change is added closest to the image plane, may be considered. Furthermore, unless a specific boundary is specified, a lens group refers to a portion having at least one lens separated by an air gap that changes during magnification change or focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0052] 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 a close-up object. In this case, the focusing group can be used for autofocusing and is suitable for driving a motor (such as an ultrasonic motor) for autofocusing. In particular, it is preferable to use at least one of the second lens group G2 and the third lens group G3 (or a part of these lens groups) as a focusing group, with the remaining lenses fixed in position relative to the image plane during focusing.

[0053] Alternatively, a lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization group that corrects image blur caused by camera shake. It is particularly preferable to use at least a portion of the third lens group G3 as an image stabilization group.

[0054] The lens surface may be spherical, 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 degradation of imaging performance is minimal 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.

[0055] It is preferable that the aperture stop S is located within or near the third lens group G3, but it is also possible to use the lens frame to fulfill that role without providing a member serving as an aperture stop.

[0056] 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.

[0057] A manufacturing method for the variable-magnification optical system ZL according to this embodiment will be outlined below with reference to FIG. 10. First, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power are prepared (Step S100). Next, the lens groups are arranged so that the spacing between adjacent lens groups changes during magnification, the first lens group G1 is fixed relative to the image plane, and the fourth lens group G4 moves along the optical axis (Step S200). Furthermore, at least the second lens group G2 moves along the optical axis during focusing (Step S300). These lens groups are then arranged to satisfy predetermined conditions (e.g., the above-mentioned conditional expressions (1), (2), and (3), (4)) (Step S400).

[0058] As described above, 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 suitable for video shooting, is small, lightweight, and provides good optical performance. [Example]

[0059] Each embodiment will be described below with reference to the drawings. Figures 1, 3, 5, and 7 are cross-sectional views showing the configuration and refractive index distribution of the variable magnification optical system ZL (ZL1 to ZL4) according to each embodiment. In addition, in the cross-sectional views of these variable magnification optical systems ZL1 to ZL4, arrows indicate the direction of movement of each lens group G1 to G4 along the optical axis when changing magnification from the wide-angle end state (W) to the telephoto end state (T) and when focusing from infinity (∞) to a close-up object.

[0060] In each embodiment, 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 (amount of sag) along the optical axis from the tangent plane of the vertex of each aspherical surface at the height y to each aspherical surface, r is the radius of curvature (paraxial radius of curvature) of the reference spherical surface, K is the conic constant, and An is the n-th order aspherical coefficient. Note that in the following embodiments, "En" is expressed as "×10 -n " indicates.

[0061] 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)

[0062] In each example, the second-order aspherical coefficient A2 is 0. In the table for each example, aspherical surfaces are marked with an * to the right of the surface number.

[0063] [First Example] 1 shows the configuration of a variable magnification optical system ZL1 according to Example 1. This variable magnification optical system ZL1 is composed of, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

[0064] The first lens group G1 is composed of, in order from the object side, an aspherical negative lens L11 whose object side lens surface and image side lens surface are formed aspherically and which has a negative meniscus lens shape with its convex surface facing the object side; an aspherical negative lens L12 whose image side lens surface is formed aspherically and which has a negative meniscus lens shape with its convex surface facing the object side; a biconcave negative lens L13; and a positive meniscus lens L14 whose convex surface faces the object side.

[0065] The second lens group G2 is composed of, in order from the object side, a cemented positive lens formed by cementing together a negative meniscus lens L21 with its convex surface facing the object side and a biconvex positive lens L22.

[0066] The third lens group G3 is composed of, in order from the object side, a positive meniscus lens L31 with a convex surface facing the object side, a cemented positive lens formed by cementing a negative meniscus lens L32 with a convex surface facing the object side and a biconvex positive lens L33, a negative meniscus lens L34 with a concave surface facing the object side, a biconcave negative lens L35, and a positive meniscus lens L36 with a convex surface facing the object side.

[0067] The fourth lens group G4 is composed of, in order from the object side, a cemented positive lens formed by cementing a negative meniscus lens L41 with a convex surface facing the object side and a biconvex positive lens L42, a cemented negative lens formed by cementing a biconvex positive lens L43 and a biconcave negative lens L44, a biconvex positive lens L45, an aspherical negative lens L46 having a spherical lens surface facing the image side and a negative meniscus lens shape with a convex surface facing the object side, and an aspherical negative lens L47 having an aspherical lens surface facing the image side and a concave surface facing the object side.

[0068] In this variable magnification optical system ZL1, the spacing between adjacent lens groups changes when the magnification is changed from the wide-angle end state to the telephoto end state. Also, in the variable magnification optical system ZL1, when the magnification is changed, the first lens group G1 is fixed with respect to the image plane I, and the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis.

[0069] In addition, in this variable magnification optical system ZL1, when focusing from infinity to a close-distance object, the second lens group G2 moves toward the image plane side.

[0070] In addition, in this variable magnification optical system ZL1, the aperture stop S is disposed between the cemented positive lens formed by cementing the negative meniscus lens L32 and the biconvex positive lens L33 of the third lens group G3 and the negative meniscus lens L34, and moves along the optical axis together with the third lens group G3 during magnification variation.

[0071] 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 [°], Y, the maximum image height, TL, the total optical length, and Bf, the back focus, which represent values ​​when focusing on infinity in the wide-angle end state, the mid-focal length state, and the telephoto end state. Here, the total optical length TL indicates the distance on the optical axis from the lens surface closest to the object (surface No. 1) to the image plane I. The back focus Bf indicates the distance on the optical axis from the lens surface closest to the image (surface No. 35) to the image plane I. The values ​​of the total optical length TL and the back focus Bf are air-equivalent lengths. 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 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. The lens group focal length indicates the surface number and focal length of the first surface of each lens group.

[0072] Here, the focal length f, radius of curvature r, surface spacing d, and other length units listed in the following specifications are generally in millimeters, but this is not a limitation because the optical system can achieve the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and specifications tables also apply to the following examples.

[0073] (Table 1) First Example [Overall specifications] Wide-angle end Mid-range focal length Telephoto end f = 16.375 ~ 24.000 ~ 34.000 Fno = 2.910 ~ 2.910 ~ 2.910 ω[°] = 53.330 ~ 42.239 ~ 32.570 Y = 20.397 ~ 21.055 ~ 21.599 TL (air equivalent length) = 159.455 ~ 159.455 ~ 159.455 Bf (air equivalent length) = 10.355 ~ 22.514 ~ 35.756 [Lens data] mrd nd νd Object surface ∞ D0 1* 35.0582 2.800 1.82098 42.50 2* 16.7377 10.337 3 31.7067 2.000 1.82098 42.50 4* 21.6441 13.766 5 -40.1091 1.700 1.45600 91.37 6 60.9680 0.541 7 53.2492 4.453 2.00069 25.46 8 485.8307 D8 9 88.0588 1.100 1.96300 24.11 10 35.4164 5.224 1.67270 32.18 11 -110.5143 D11 12 29.3371 3.943 1.81666 29.30 13 56.1980 0.468 14 44.5698 1.232 1.84666 23.80 15 24.6119 8.231 1.48749 70.32 16 -77.0710 1.416 17 ∞ 1.853 Aperture S 18 -229.7187 1.100 1.95375 32.33 19 -284.2053 1.377 20 -51.4494 1.100 1.95375 32.33 21 95.9749 0.100 22 30.9572 2.006 1.92286 20.88 23 38.9406 D23 24 28.4971 1.100 1.95375 32.33 25 19.4010 6.575 1.49782 82.57 26 -173.7622 0.401 27 33.6267 6.625 1.49782 82.57 28 -28.3420 1.200 1.95375 32.33 29 149.7072 3.576 30 36.7805 5.550 1.80809 22.74 31 -77.2223 0.608 32 97.7931 1.512 1.85108 40.12 33* 44.1538 8.527 34 -27.8483 1.400 1.82098 42.50 35* -59.3344 Bf Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 -24.581 Second lens group G2 9 113.817 Third lens group G3 12 120.097 4th lens group G4 24 50.673

[0074] In this variable magnification optical system ZL1, surfaces 1, 2, 4, 33, and 35 are aspherical. Table 2 below shows aspherical surface data for each surface number, i.e., the values ​​of the conic constant K and each of the aspherical surface constants A4 to A12.

[0075] (Table 2) [Aspherical data] Front page K=1 A4 =-1.18404E-06 A6 =-1.78487E-08 A8 = 2.04398E-11 A10=-9.10242E-15 A12=-1.60620E-19 2nd page K=1 A4 = 2.17668E-05 A6 = -1.32250E-08 A8 = 7.55812E-11 A10=-3.29409E-13 A12= 5.66430E-16 4th page K=1 A4 =-8.57708E-06 A6 =-1.43980E-08 A8 =-1.85528E-12 A10=5.78174E-14 A12=-3.00240E-16 Page 33 K=1 A4 = 1.80937E-05 A6 = 4.76381E-08 A8=-2.53185E-10 A10=2.50614E-12 A12=-3.69680E-15 Page 35 K=1 A4 = 1.19645E-06 A6 = -3.91842E-08 A8 = 3.08087E-10 A10=-1.89993E-12 A12= 3.16740E-15

[0076] In this variable magnification optical system ZL1, the axial air spacing D8 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 D23 between the third lens group G3 and the fourth lens group G4, 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-up object. Note that D0 represents the distance from the lens surface (first surface) closest to the object in the variable magnification optical system ZL1 to the object, f represents the focal length, and β represents the magnification ratio. This explanation also applies to the following examples.

[0077] (Table 3) [Variable Interval Data] Infinity Near object Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 16.375 24.000 34.000 - - - β - - - -0.033 -0.033 -0.033 D0 ∞ ∞ ∞ 461.130 691.430 992.394 D8 30.850 10.327 1.500 32.194 11.408 2.351 D11 10.026 22.536 18.877 8.682 21.455 18.026 D23 6.402 2.255 1.500 6.402 2.255 1.500 Bf 10.355 22.514 35.756 10.355 22.514 35.756

[0078] FIG. 2 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this variable magnification optical system ZL1 when focused at infinity in the wide-angle and telephoto end states. 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 corresponding to the maximum aperture, the astigmatism and distortion diagrams indicate the maximum image height, and the coma diagram indicates the value of each image height. d represents the d-line (λ=587.6 nm), and g represents the g-line (λ=435.8 nm). In the astigmatism diagram, the solid line represents the sagittal image plane, and the dashed line represents the meridional image plane. The same symbols as in this embodiment are used in the aberration diagrams for each embodiment shown below. These aberration diagrams demonstrate that this variable magnification optical system ZL1 provides excellent correction for various aberrations and exhibits excellent imaging performance.

[0079] [Second Example] 3 shows the configuration of a variable magnification optical system ZL2 according to Example 2. This variable magnification optical system ZL2 is composed of, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive refractive power.

[0080] The first lens group G1 is composed of, in order from the object side, an aspherical negative lens L11 whose object side lens surface and image side lens surface are formed aspherically and which has a negative meniscus lens shape with its convex surface facing the object side; an aspherical negative lens L12 whose image side lens surface is formed aspherically and which has a negative meniscus lens shape with its convex surface facing the object side; a biconcave negative lens L13; and a positive meniscus lens L14 whose convex surface faces the object side.

[0081] The second lens group G2 is composed of, in order from the object side, a cemented positive lens formed by cementing together a negative meniscus lens L21 with its convex surface facing the object side and a biconvex positive lens L22.

[0082] The third lens group G3 is composed of, in order from the object side, a positive meniscus lens L31 with a convex surface facing the object side, a cemented positive lens formed by cementing a negative meniscus lens L32 with a convex surface facing the object side and a biconvex positive lens L33, and a biconcave negative lens L34.

[0083] The fourth lens group G4 is composed of, in order from the object side, a cemented positive lens formed by cementing a negative meniscus lens L41 with its convex surface facing the object side and a biconvex positive lens L42 together, a cemented negative lens formed by cementing a biconvex positive lens L43 and a biconcave negative lens L44 together, a biconvex positive lens L45, an aspherical negative lens L46 whose lens surface facing the image side is formed in an aspherical shape and which is formed in the shape of a biconcave negative lens, and an aspherical negative lens L47 whose lens surface facing the image side is formed in an aspherical shape and which is formed in the shape of a negative meniscus lens with its concave surface facing the object side.

[0084] In this variable magnification optical system ZL2, the spacing between adjacent lens groups changes when the magnification is changed from the wide-angle end state to the telephoto end state. Also, in the variable magnification optical system ZL2, when the magnification is changed, the first lens group G1 is fixed with respect to the image plane I, and the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis.

[0085] In addition, in this variable magnification optical system ZL2, when focusing from infinity to a close-distance object, the second lens group G2 moves toward the image plane side.

[0086] In addition, in this variable magnification optical system ZL2, the aperture stop S is disposed between the cemented positive lens formed by cementing the negative meniscus lens L32 and the biconvex positive lens L33 of the third lens group G3 and the biconcave negative lens L34, and moves along the optical axis together with the third lens group G3 during magnification variation.

[0087] Table 4 below lists the specifications of the variable magnification optical system ZL2.

[0088] (Table 4) Second Example [Overall specifications] Wide-angle end Mid-range focal length Telephoto end f = 16.500 ~ 24.000 ~ 34.000 Fno = 2.910 ~ 2.910 ~ 2.910 ω[°] = 53.244 ~ 42.298 ~ 32.588 Y = 20.529 ~ 21.114 ~ 21.632 TL (air equivalent length) = 164.455 ~ 164.455 ~ 164.455 Bf (air equivalent length) = 10.355 ~ 21.907 ~ 34.932 [Lens data] mrd nd νd Object surface ∞ D0 1* 67.9718 2.800 1.82098 42.50 2* 21.3995 9.567 3 37.6575 2.000 1.82098 42.50 4* 27.3158 13.974 5 -47.1653 1.700 1.45600 91.37 6 50.0315 0.571 7 46.3866 4.818 2.00069 25.46 8 157.7521 D8 9 75.2773 1.100 1.96300 24.11 10 32.6428 6.697 1.67270 32.18 11 -109.8274 D11 12 29.9845 4.494 1.81666 29.30 13 57.3435 0.100 14 41.9240 1.200 1.84666 23.80 15 27.0265 8.346 1.48749 70.32 16 -109.6222 1.545 17 ∞ 2.766 Aperture S 18 -72.0021 1.100 1.95375 32.33 19 74.7453 D19 20 24.4218 1.100 1.95375 32.33 21 18.4764 8.090 1.49782 82.57 22 -102.1447 0.100 23 40.6595 6.855 1.49782 82.57 24 -25.2216 2.393 1.95375 32.33 25 239.9117 3.670 26 34.1200 6.761 1.80809 22.74 27 -45.7105 0.136 28 -91.2255 1.400 1.85108 40.12 29* 82.4416 6.029 30 -23.6589 1.400 1.82098 42.50 31* -63.9793 Bf Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 -24.240 Second lens group G2 9 100.531 Third lens group G3 12 156.969 4th lens group G4 20 47.722

[0089] In this variable magnification optical system ZL2, surfaces 1, 2, 4, 29, and 31 are aspherical. Table 5 below shows aspherical surface data for each surface number, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0090] (Table 5) [Aspherical data] Front page K=1 A4 = 8.17319E-06 A6 = -1.88149E-08 A8 = 1.87871E-11 A10=-7.74503E-15 A12= 1.03020E-18 2nd page K=1 A4 = 1.63234E-05 A6 = 2.32356E-09 A8 =-2.20036E-11 A10=-6.34872E-14 A12= 1.82740E-16 4th page K=1 A4 = 2.20421E-06 A6 = -1.28194E-08 A8 = 6.50777E-11 A10=-8.76509E-14 A12= 4.81690E-17 Page 29 K=1 A4 = 1.17598E-05 A6 =-1.00073E-08 A8 = 2.62820E-11 A10=8.49715E-13 A12=-3.69680E-15 Page 31 K=1 A4 = 6.90553E-06 A6 = 2.29334E-08 A8 =-1.90581E-11 A10=-7.45460E-13 A12= 3.16740E-15

[0091] In this variable magnification optical system ZL2, the axial air distance D8 between the first lens group G1 and the second lens group G2, the axial air distance D11 between the second lens group G2 and the third lens group G3, the axial air distance D19 between the third lens group G3 and the fourth lens group G4, and the back focal length Bf change during magnification change and focusing. Table 6 below shows the variable distances in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity and a close distance.

[0092] (Table 6) [Variable Interval Data] Infinity Near object Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 16.500 24.000 34.000 - - - β - - - -0.033 -0.033 -0.033 D0 ∞ ∞ ∞ 465.588 692.044 993.025 D8 28.510 10.140 1.500 29.763 11.126 2.270 D11 17.764 29.157 25.812 16.511 28.172 25.042 D19 7.115 2.540 1.500 7.115 2.540 1.500 Bf 10.355 21.907 34.932 10.355 21.907 34.932

[0093] Figure 4 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma when this variable magnification optical system ZL2 is focused at infinity in the wide-angle end state and the telephoto end state. These aberration diagrams show that this variable magnification optical system ZL2 has excellent correction for various aberrations and has excellent imaging performance.

[0094] [Third Example] 5 is a diagram showing the configuration of a variable magnification optical system ZL3 according to Example 3. This variable magnification optical system ZL3 is configured to include, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0095] The first lens group G1 is composed of, in order from the object side, an aspherical negative lens L11 whose lens surface on the image side is formed in an aspherical shape and which has a negative meniscus lens shape with its convex surface facing the object side, a biconcave negative lens L12, and an aspherical positive lens L13 whose lens surface on the image side is formed in an aspherical shape and which has a positive meniscus lens shape with its convex surface facing the object side.

[0096] The second lens group G2 is composed of, in order from the object side, a cemented positive lens formed by cementing together an aspherical negative lens L21 having a negative meniscus lens shape with its object side surface formed aspherical and its convex surface facing the object side, and a biconvex positive lens L22.

[0097] The third lens group G3 is composed of, in order from the object side, a negative meniscus lens L31 with a convex surface facing the object side, a negative meniscus lens L32 with a concave surface facing the object side, and a biconvex positive lens L33.

[0098] The fourth lens group G4 is composed of, in order from the object side, a cemented positive lens formed by cementing a biconvex positive lens L41 and a negative meniscus lens L42 with its concave surface facing the object side, a biconvex positive lens L43, a cemented negative lens formed by cementing a positive meniscus lens L44 with its concave surface facing the object side and a biconcave negative lens L45, and an aspherical negative lens L46 whose lens surfaces facing the object side and the image plane side are formed into aspherical shapes and which has a negative meniscus lens shape with its convex surface facing the object side.

[0099] In this variable magnification optical system ZL3, the spacing between adjacent lens groups changes when the magnification is changed from the wide-angle end state to the telephoto end state. In addition, in the variable magnification optical system ZL3, when the magnification is changed, the first lens group G1 is fixed with respect to the image plane I, and the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis.

[0100] In addition, in this variable magnification optical system ZL3, when focusing from infinity to a close-distance object, the second lens group G2 moves toward the image plane side, and the third lens group G3 moves toward the object side.

[0101] In addition, in this variable magnification optical system ZL3, the aperture stop S is disposed between the negative meniscus lens L31 and the negative meniscus lens L32 of the third lens group G3, and moves along the optical axis together with the third lens group G3 during magnification and focusing.

[0102] Table 7 below lists the specifications of the variable magnification optical system ZL3.

[0103] (Table 7) Third Example [Overall specifications] Wide-angle end Mid-range focal length Telephoto end f = 18.500 ~ 28.001 ~ 48.473 Fno = 1.974 ~ 2.508 ~ 4.120 ω[°] = 50.726 ~ 37.607 ~ 23.903 Y = 20.799 ~ 21.700 ~ 21.700 TL (air equivalent length) = 139.484 ~ 139.484 ~ 139.484 Bf (air equivalent length) = 24.098 ~ 35.551 ~ 58.886 [Lens data] mrd nd νd Object surface ∞ D0 1 138.6428 3.000 1.54449 56.33 2* 19.3464 14.626 3 -116.1278 2.000 1.77250 49.46 4 46.8544 0.100 5 37.5275 4.434 1.94594 17.98 6* 66.5532 D6 7* 39.5868 1.100 1.82115 24.06 8 27.4793 5.497 1.64000 60.20 9 -91.3357 D9 10 1660.8371 1.200 1.80625 40.91 11 115.4552 2.174 12 ∞ 4.192 Aperture stop S 13 -29.8167 1.247 1.76385 48.49 14 -140.2473 0.200 15 66.1759 3.651 1.68893 31.16 16 -80.2468 D16 17 29.0393 8.658 1.59282 68.62 18 -31.0177 1.000 2.00330 28.27 19 -69.5190 0.100 20 27.7549 6.701 1.55032 75.49 21 -89.6746 0.636 22 -347.6865 4.652 2.00272 19.32 23 -26.8868 1.000 2.00330 28.27 24 65.0833 2.088 25* 61.7639 1.600 1.95150 29.83 26* 28.1094 Bf Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 -24.310 Second lens group G2 7 48.034 Third lens group G3 10 -148.331 4th lens group G4 17 41.035

[0104] In this variable magnification optical system ZL3, surfaces 2, 6, 7, 25, and 26 are aspherical. Table 8 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.

[0105] (Table 8) [Aspherical data] 2nd page K=1 A4 = 9.51553E-06 A6 = 1.21754E-08 A8 =-5.92398E-11 A10=2.46358E-13 A12=-3.27160E-16 Page 6 K=1 A4 = 1.51701E-07 A6 = 3.95534E-09 A8 =-2.06177E-11 A10=7.48105E-14 A12=-7.38860E-17 Page 7 K=1 A4 =-2.10374E-06 A6 =-1.68231E-09 A8 = 2.88731E-13 A10=3.11082E-14 A12=-7.40790E-17 Page 25 K=1 A4 =-9.20691E-05 A6 = 3.33506E-07 A8 =-3.76359E-10 A10=-3.03908E-12 A12= 9.58650E-15 Page 26 K=1 A4 =-5.96955E-05 A6 = 4.23747E-07 A8 =-3.95963E-10 A10=-3.68864E-12 A12= 1.18830E-14

[0106] In this variable magnification optical system ZL3, the axial air distance D6 between the first lens group G1 and the second lens group G2, the axial air distance D9 between the second lens group G2 and the third lens group G3, the axial air distance D16 between the third lens group G3 and the fourth lens group G4, and the back focal length Bf change during magnification change and focusing. Table 9 below shows the variable distances 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 distance object.

[0107] (Table 9) [Variable Interval Data] Infinity Near object Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 18.500 28.001 48.473 - - - β - - - -0.033 -0.033 -0.033 D0 ∞ ∞ ∞ 516.893 808.024 1424.067 D6 23.309 10.765 1.300 24.476 11.449 1.677 D9 8.266 18.006 7.942 6.281 17.151 7.302 D16 13.956 5.306 1.500 14.773 5.477 1.763 Bf 24.098 35.551 58.886 24.098 35.551 58.886

[0108] Figure 6 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this variable magnification optical system ZL3 when focused at infinity in the wide-angle end state and the telephoto end state. These aberration diagrams show that this variable magnification optical system ZL3 has excellent correction for various aberrations and has excellent imaging performance.

[0109] [Fourth Example] 7 is a diagram showing the configuration of a variable magnification optical system ZL4 according to Example 4. This variable magnification optical system ZL4 is configured to include, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

[0110] The first lens group G1 is composed of, in order from the object side, an aspherical negative lens L11 having an aspherical shape on both the object side lens surface and the image plane side lens surface, and a cemented negative lens formed by cementing a biconcave negative lens L12 and a positive meniscus lens L13.

[0111] The second lens group G2 is composed of, in order from the object side, a cemented positive lens formed by cementing together an aspherical negative lens L21 having a negative meniscus lens shape with its object side surface formed aspherical and its convex surface facing the object side, and a biconvex positive lens L22.

[0112] The third lens group G3 is composed of, in order from the object side, a biconcave negative lens L31 and a biconvex positive lens L32.

[0113] The fourth lens group G4 is composed of, in order from the object side, a cemented positive lens formed by cementing a biconvex positive lens L41 and a negative meniscus lens L42 with its concave surface facing the object side, a biconvex positive lens L43, a cemented negative lens formed by cementing a biconvex positive lens L44 and a biconcave negative lens L45, and an aspherical negative lens L46 whose object-side lens surface and image-plane-side lens surface are formed into aspherical shapes and which has a biconcave negative lens shape.

[0114] In this variable magnification optical system ZL4, the spacing between adjacent lens groups changes when the magnification is changed from the wide-angle end state to the telephoto end state. Also, in the variable magnification optical system ZL4, when the magnification is changed, the first lens group G1 is fixed with respect to the image plane I, and the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis.

[0115] In addition, in this variable magnification optical system ZL4, when focusing from infinity to a close-distance object, the second lens group G2 moves toward the image plane side, and the third lens group G3 moves toward the object side.

[0116] In this variable magnification optical system ZL4, the aperture stop S is disposed on the object side of the third lens group G3, and moves along the optical axis together with the third lens group G3 during magnification and focusing.

[0117] Table 10 below lists the specifications of the variable magnification optical system ZL4.

[0118] (Table 10) Fourth Example [Overall specifications] Wide-angle end Mid-range focal length Telephoto end f = 18.500 ~ 28.005 ~ 48.404 Fno = 2.185 ~ 2.751 ~ 4.120 ω[°] = 50.767 ~ 37.878 ~ 23.996 Y = 20.889 ~ 21.700 ~ 21.700 TL (air equivalent length) = 143.391 ~ 143.391 ~ 143.391 Bf (air equivalent length) = 24.159 ~ 35.193 ~ 57.555 [Lens data] mrd nd νd Object surface ∞ D0 1* 157.2879 3.000 1.74310 49.44 2* 22.0380 16.576 3 -199.2673 2.000 1.59319 67.90 4 25.5366 7.872 1.73037 32.23 5 99.6228 D5 6* 43.3190 1.100 1.80810 22.76 7 32.2106 4.322 1.62263 58.16 8 -225.4283 D8 9 ∞ 3.496 Aperture S 10 -34.4195 1.247 1.77250 49.50 11 603.2210 0.200 12 55.8216 3.500 1.68893 31.16 13 -100.0706 D13 14 30.7766 8.643 1.59282 68.62 15 -36.1075 1.000 2.00272 19.32 16 -116.9050 0.238 17 31.0442 6.556 1.49731 82.51 18 -76.9724 0.100 19 3216.6555 5.257 1.94594 17.98 20 -27.0690 1.000 2.00330 28.27 21 1357.0901 5.237 22* -74.9653 1.600 1.95150 29.83 23* 69.0499 Bf Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 -27.114 Second lens group G2 6 64.115 Third lens group G3 9 -252.229 4th lens group G4 14 44.503

[0119] In this variable magnification optical system ZL4, surfaces 1, 2, 6, 22, and 23 are aspherical. Table 11 below shows aspherical surface data for surface numbers, that is, the values ​​of the conic constant K and each of the aspherical surface constants A4 to A12.

[0120] (Table 11) [Aspherical data] Front page K=1 A4 = 5.19274E-06 A6 = -1.00509E-08 A8 = 1.02480E-11 A10=-5.31168E-15 A12= 1.19070E-18 2nd page K=1 A4 = 1.28094E-05 A6 = 1.20928E-11 A8 = 2.73339E-12 A10=-4.51231E-14 A12= 9.30290E-17 Page 6 K=1 A4 =-1.06769E-06 A6 =-1.76220E-09 A8 = 9.37521E-12 A10=-5.63577E-14 A12= 1.14190E-16 Page 22 K=1 A4 =-9.16321E-05 A6 = 8.51953E-07 A8 =-5.15501E-09 A10= 1.88158E-11 A12=-3.03680E-14 Page 23 K=1 A4 =-5.49884E-05 A6 = 8.85063E-07 A8 =-5.14130E-09 A10= 1.86307E-11 A12=-2.95090E-14

[0121] In this variable magnification optical system ZL4, the axial air distance D5 between the first lens group G1 and the second lens group G2, the axial air distance D8 between the second lens group G2 and the third lens group G3, the axial air distance D13 between the third lens group G3 and the fourth lens group G4, and the back focal length Bf change during magnification change and focusing. Table 12 below shows the variable distances in the wide-angle end state, the intermediate focal length state, and the telephoto end state when focusing on an object at infinity and a close distance.

[0122] (Table 12) [Variable Interval Data] Infinity Near object Wide-angle end Mid-range Telephoto end Wide-angle end Mid-range Telephoto end f 18.500 28.005 48.404 - - - β - - - -0.033 -0.033 -0.033 D0 ∞ ∞ ∞ 519.839 808.763 1422.941 D5 27.325 12.324 0.974 28.665 13.186 1.485 D8 5.785 18.263 10.258 3.707 17.185 9.491 D13 13.178 4.667 1.660 13.915 4.883 1.916 Bf 24.159 35.193 57.555 24.159 35.193 57.555

[0123] Fig. 8 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this variable magnification optical system ZL4 when focused at infinity in the wide-angle end state and the telephoto end state. These aberration diagrams show that this variable magnification optical system ZL4 has excellent correction for various aberrations and has excellent imaging performance.

[0124] [Conditional expression corresponding value] The values ​​corresponding to the conditional expressions (1) to (10) in the first to fourth examples are shown in Table 13 below.

[0125] (Table 13) (1)(-f1) / f2 (2)ft / Bft (3)(-f1) / |f3| (4) f4 / f2 (5)f4 / |f3| (6)(-f1) / f4 (7)f2 / |f3| (8)ft / TL (9)fw / Bfw (10)ft / TLGt First Example Second Example Third Example Fourth Example TLGt 123.699 129.523 80.598 85.836 (1) 0.216 0.241 0.506 0.423 (2) 0.951 0.973 0.823 0.841 (3) 0.205 0.154 0.164 0.107 (4) 0.445 0.475 0.854 0.694 (5) 0.422 0.304 0.277 0.176 (6) 0.485 0.508 0.592 0.609 (7) 0.948 0.640 0.324 0.254 (8) 0.213 0.207 0.348 0.338 (9) 1.581 1.593 0.768 0.766 (10) 0.275 0.263 0.601 0.564 [Explanation of symbols]

[0126] 1 Camera (Optical Equipment) ZL (ZL1~ZL4) Variable Magnification Optical System G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group

Claims

1. From the object side, a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group; and The fourth lens unit has a positive refractive power, and the fourth lens unit has a positive refractive power. During magnification change, the interval between adjacent lens groups changes, the first lens group is fixed relative to the image plane, and the fourth lens group moves along the optical axis, During focusing, at least the second lens group moves along the optical axis, A variable magnification optical system that satisfies the following condition: 0.050 < (-f1) / f2 < 0.650 0.600 < ft / Bft < 1.500 0.010 < f4 / | f3 | < 1.000 however, f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire variable magnification optical system in the telephoto end state Bft: back focus of the variable magnification optical system in the telephoto end state f3: focal length of the third lens group f4: focal length of the fourth lens group

2. From the object side, a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group; and The fourth lens unit has a positive refractive power, and the fourth lens unit has a positive refractive power. During magnification change, the interval between adjacent lens groups changes, the first lens group is fixed relative to the image plane, and the fourth lens group moves along the optical axis, During focusing, at least the second lens group moves along the optical axis, A variable magnification optical system that satisfies the following condition: 0.050 < (-f1) / f2 < 0.800 0.600 < ft / Bft < 1.500 0.010 < f4 / | f3 | < 0.550 however, f1: focal length of the first lens group f2: focal length of the second lens group ft: focal length of the entire variable magnification optical system in the telephoto end state Bft: back focus of the variable magnification optical system in the telephoto end state f3: focal length of the third lens group f4: focal length of the fourth lens group

3. From the object side, a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group; and The fourth lens unit has a positive refractive power, and the fourth lens unit has a positive refractive power. During magnification change, the interval between adjacent lens groups changes, the first lens group is fixed relative to the image plane, and the fourth lens group moves along the optical axis, During focusing, at least the second lens group moves along the optical axis, A variable magnification optical system that satisfies the following condition: 0.010 < (-f1) / |f3| < 0.250 0.100 < f4 / f2 < 1.200 however, f1: focal length of the first lens group f2: focal length of the second lens group f3: focal length of the third lens group f4: focal length of the fourth lens group

4. 3. A variable magnification optical system according to claim 1, wherein the following condition is satisfied: .times. ... 0.010 < (-f1) / |f3| < 1.000 however, f1: focal length of the first lens group f3: focal length of the third lens group

5. 3. A variable magnification optical system according to claim 1, wherein the following condition is satisfied: .times. ... 0.100 < f4 / f2 < 1.200 however, f2: focal length of the second lens group f4: focal length of the fourth lens group

6. 4. A variable magnification optical system according to claim 3, which satisfies the following condition: ##EQU1## 0.010 < f4 / | f3 | < 1.000 however, f3: focal length of the third lens group f4: focal length of the fourth lens group

7. 4. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.150 < (-f1) / f4 < 1.500 however, f1: focal length of the first lens group f4: focal length of the fourth lens group

8. 4. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.010 < f2 / | f3 | < 2.000 however, f2: focal length of the second lens group f3: focal length of the third lens group

9. 4. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.010 < ft / TL < 1.000 however, ft: focal length of the entire variable magnification optical system in the telephoto end state TL: total optical length of the variable magnification optical system

10. 4. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.300 < fw / Bfw < 4.000 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

11. 4. The variable magnification optical system according to claim 1, wherein the following condition is satisfied: 0.100 < ft / TLGt < 1.000 however, ft: focal length of the entire variable magnification optical system in the telephoto end state TLGt: the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plane in the variable magnification optical system in the telephoto end state

12. 4. The variable magnification optical system according to claim 1, wherein the third lens group has a positive refractive power.

13. 4. The variable magnification optical system according to claim 1, wherein the second lens group is composed of one lens component.

14. 4. The variable magnification optical system according to claim 1, wherein the second lens group is composed of one positive lens and one negative lens.

15. An optical instrument comprising the variable magnification optical system according to any one of claims 1 to 3.

Images