Optical systems and optical instruments

Abstract

Provided are: an optical system in which the imaging magnification thereof is 0.5 or greater and good optical performance is ensured while achieving reduced weight and size; an optical device; and a method for manufacturing the optical system.　 An optical system OL used in an optical device such as a camera 1 comprises a front group GF, an intermediate group GM, and a rear group GR in the stated order from the object side, and during focusing, the intermediate group GM moves in the optical axis direction, and satisfies the following condition: 0.54 < d1 / f < 1.00, where d1 is the distance on the optical axis from the lens surface closest to the image surface side of the front group GF to the lens surface closest to the object side of the intermediate group GM when focused on an object at infinity, and f is the focal length of the entire optical system OL when focused on an object at infinity.

Description

Optical system, optical device, and method of manufacturing optical system

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

[0002] Conventionally, small and lightweight macro lenses have been proposed (see, for example, Patent Document 1), but further improvement in optical performance is desired.

[0003] Japanese Patent Application Laid-Open No. 2021-148808

[0004] An optical system according to a first aspect of the present invention is composed of, in order from the object side, a front group, an intermediate group, and a rear group, and during focusing, the intermediate group moves along the optical axis, and satisfies the following condition: 0.54 < d1 / f < 1.00, where d1 is the distance on the optical axis from the lens surface of the front group closest to the image plane to the lens surface of the intermediate group closest to the object when focusing on an object at infinity, and f is the focal length of the entire optical system when focusing on an object at infinity.

[0005] An optical system according to a second aspect of the present invention is composed of, in order from the object side, a front group, an intermediate group, and a rear group, wherein the intermediate group moves in the optical axis direction during focusing, and the following conditions are satisfied: 32.00 < TL / DF < 80.00 1.00 < DM / DR < 4.00 where, TL: total optical length of the optical system when focusing on an object at infinity, DF: distance on the optical axis from the lens surface of the front group closest to the object to the lens surface closest to the image, DM: distance on the optical axis from the lens surface of the intermediate group closest to the object to the lens surface closest to the image when focusing on an object at infinity, DR: distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface closest to the image.

[0006] A method for manufacturing an optical system according to a first aspect of the present invention is a method for manufacturing an optical system composed of, in order from the object side, a front group, an intermediate group, and a rear group, wherein the intermediate group is arranged to move in the optical axis direction during focusing, and is arranged to satisfy the following condition: 0.54 < d1 / f < 1.00, where d1 is the distance on the optical axis from the lens surface of the front group closest to the image plane to the lens surface of the intermediate group closest to the object when focusing on an object at infinity, and f is the focal length of the entire optical system when focusing on an object at infinity.

[0007] A method for manufacturing an optical system according to a second aspect of the present invention is a method for manufacturing an optical system composed of, in order from the object side, a front group, an intermediate group, and a rear group, wherein the intermediate group is arranged to move in the optical axis direction during focusing, and the following conditions are satisfied: 32.00 < TL / DF < 80.00 1.00 < DM / DR < 4.00 where, TL: total optical length of the optical system when focusing on an object at infinity, DF: distance on the optical axis from the lens surface of the front group closest to the object to the lens surface closest to the image plane, DM: distance on the optical axis from the lens surface of the intermediate group closest to the object to the lens surface closest to the image plane when focusing on an object at infinity, DR: distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface closest to the image plane.

[0008] FIG. 1 is a cross-sectional view showing the lens configuration of an optical system according to Example 1. FIG. 2 is a diagram showing various aberrations of the optical system according to Example 1 when focusing on an object at infinity. FIG. 3 is a diagram showing various aberrations of the optical system according to Example 1 when focusing on a close object. FIG. 4 is a cross-sectional view showing the lens configuration of an optical system according to Example 2. FIG. 5 is a diagram showing various aberrations of the optical system according to Example 2 when focusing on an object at infinity. FIG. 6 is a diagram showing various aberrations of the optical system according to Example 3 when focusing on an object at infinity. FIG. 7 is a cross-sectional view showing the lens configuration of an optical system according to Example 4. FIG. 8 is a diagram showing various aberrations of the optical system according to Example 4 when focusing on an object at infinity. FIG. 9 is a cross-sectional view showing the lens configuration of an optical system according to Example 5. FIG. 10 is a diagram showing various aberrations of the optical system according to Example 5 when focusing on an object at infinity. FIG. 11 is a cross-sectional view showing the lens configuration of an optical system according to Example 6. FIG. 10 is a diagram illustrating various aberrations when the optical system according to Example 6 is focused on an object at infinity. FIG. 11 is a diagram illustrating various aberrations when the optical system according to Example 6 is focused on an object at close range. FIG. 12 is a cross-sectional view showing the lens configuration of the optical system according to Example 7. FIG. 13 is a diagram illustrating various aberrations when the optical system according to Example 7 is focused on an object at infinity. FIG. 14 is a diagram illustrating various aberrations when the optical system according to Example 7 is focused on an object at close range. FIG. 15 is a cross-sectional view of a camera incorporating the optical system. FIG. 16 is a flowchart for explaining a method for manufacturing the optical system.

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

[0010] 1, an optical system OL according to a first embodiment is composed of, in order from the object side, a front group GF, a middle group GM, and a rear group GR, with the middle group GM moving in the optical axis direction during focusing. This configuration makes it possible to reduce the weight and size of the optical system OL while ensuring good optical performance at a magnification of 0.5x or greater.

[0011] Moreover, it is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (1).

[0012] 0.54<d1 / f<1.00 (1) where, d1 is the distance on the optical axis from the lens surface of the front group GF closest to the image plane to the lens surface of the middle group GM closest to the object when focusing on an object at infinity, and f is the focal length of the entire optical system OL when focusing on an object at infinity.

[0013] Conditional expression (1) defines the ratio of the axial distance from the lens surface of the front group GF closest to the image plane to the lens surface of the middle group GM closest to the object, relative to the focal length of the entire optical system OL when focusing on an object at infinity, i.e., the spacing between the front group GM and the middle group GM. By satisfying conditional expression (1), the optical system OL can be made lightweight and compact, achieving a magnification of 0.5x or greater, while providing excellent aberration correction during focusing. Exceeding the upper limit of conditional expression (1) allows for excellent correction of spherical aberration, field curvature, coma, and other aberrations during focusing by the middle group GM, but this is undesirable because it makes it difficult to reduce the weight and size of the optical system OL. To ensure the effect of conditional expression (1), it is more desirable to set the upper limit of conditional expression (1) to 0.90, 0.85, 0.80, or even 0.75. Furthermore, if the lower limit of conditional expression (1) is not reached, the optical system OL can be made smaller, but it becomes difficult to correct spherical aberration, curvature of field, coma, etc., when focusing with the middle group GM, which is undesirable. In order to ensure the effect of conditional expression (1), it is more desirable to set the lower limit of conditional expression (1) to 0.58, 0.60, or even 0.63.

[0014] Second Embodiment As shown in Fig. 1, an optical system OL according to a second embodiment is composed of, in order from the object side, a front group GF, a middle group GM, and a rear group GR, with the middle group GM moving in the optical axis direction during focusing. This configuration makes it possible to reduce the weight and size of the optical system OL while ensuring good optical performance at a magnification of 0.5x or greater.

[0015] It is also desirable that the optical system OL according to the second embodiment satisfy the following conditional expression (2).

[0016] 32.00 < TL / DF < 80.00 (2) where, TL: total optical length (equivalent to air length) of the optical system OL when focusing on an object at infinity, DF: distance on the optical axis from the lens surface of the front group GF closest to the object to the lens surface closest to the image plane.

[0017] Conditional expression (2) defines the ratio of the total optical length of the optical system OL when focusing on an object at infinity to the axial distance from the lens surface of the front group GF closest to the object to the lens surface closest to the image (the axial thickness of the front group GF). Satisfying conditional expression (2) facilitates aberration correction while achieving a lightweight and compact optical system OL. Exceeding the upper limit of conditional expression (2) increases the axial thickness of the front group GF (the axial distance from the lens surface closest to the object to the lens surface closest to the image) relative to the total optical length of the optical system OL, resulting in good correction of spherical aberration, chromatic aberration, coma, and other aberrations. However, if the total optical length of the optical system OL becomes too short, this is undesirable because it increases the occurrence of field curvature, astigmatism, and coma during focusing. To ensure the effect of conditional expression (2), it is more desirable to set the upper limit of conditional expression (2) to 75.00, and even more desirably 70.00. Furthermore, if the lower limit of conditional expression (2) is not reached, the thickness on the optical axis of the front group GF becomes thinner relative to the overall optical length of the optical system OL, and so the overall optical length of the optical system OL can be shortened, but this is not preferable because aberration correction by the front group GF becomes insufficient, making it difficult to correct spherical aberration, coma aberration, field curvature, etc. In order to ensure the effect of conditional expression (2), it is more preferable to set the lower limit of conditional expression (2) to 33.50, and even more preferably 35.00.

[0018] Moreover, it is desirable that the optical system OL according to the second embodiment satisfy the following conditional expression (3).

[0019] 1.00 < DM / DR < 4.00 (3) where DM is the distance on the optical axis from the lens surface of the middle group GM closest to the object to the lens surface closest to the image when focusing on an object at infinity, and DR is the distance on the optical axis from the lens surface of the rear group GR closest to the object to the lens surface closest to the image.

[0020] Conditional expression (3) defines the ratio of the axial distance from the lens surface of the middle group GM closest to the object to the lens surface closest to the image plane of the rear group GR (the axial thickness of the rear group GR) to the axial distance from the lens surface of the middle group GM closest to the object to the lens surface closest to the image plane when focusing on an object at infinity (the axial thickness of the middle group GM). By satisfying conditional expression (3), it is possible to achieve a lightweight and compact optical system OL while providing excellent correction of aberrations relative to brightness and the angle of view. Exceeding the upper limit of conditional expression (3) makes the axial thickness of the middle group GM thicker than the axial thickness of the rear group GR, resulting in excellent correction of spherical aberration, coma, and other aberrations. However, this is undesirable because it makes it difficult to correct aberrations relative to the angle of view, such as curvature of field and astigmatism, when the overall length of the optical system OL is shortened. To ensure the effect of conditional expression (3), it is more desirable to set the upper limit of conditional expression (3) to 3.50, 3.00, or even 2.50. Furthermore, if the lower limit of conditional expression (3) is not reached, the axial thickness of the rear group GR becomes thicker than the axial thickness of the intermediate group GM, which makes it possible to satisfactorily correct curvature of field, astigmatism, etc. However, when the overall length of the optical system OL is short, it becomes difficult to correct spherical aberration, coma, etc., which are aberrations relative to brightness, and this is not desirable. In order to ensure the effect of conditional expression (3), it is more desirable to set the lower limit of conditional expression (3) to 1.25, 1.50, or even 1.75.

[0021] Moreover, it is desirable that the optical system OL according to the first and second embodiments (hereinafter simply referred to as "the present embodiment") satisfy the following conditional expression (4).

[0022] 0.20<d1 / TL<0.40 (4) where, d1 is the distance on the optical axis from the lens surface of the front group GF closest to the image plane to the lens surface of the middle group GM closest to the object when focusing on an object at infinity, and TL is the total optical length (equivalent to air length) of the optical system OL when focusing on an object at infinity.

[0023] Conditional expression (4) defines the ratio of the axial distance from the lens surface of the front group GF closest to the image plane to the lens surface of the middle group GM closest to the object (the distance between the front group GF and the middle group GM) to the total optical length of the optical system OL when focusing on an object at infinity. By satisfying conditional expression (4), the optical system OL can be made lightweight and compact, and a magnification of 0.5x or greater can be achieved while still providing excellent correction of aberrations during focusing. Exceeding the upper limit of conditional expression (4) allows for excellent correction of spherical aberration, curvature of field, coma, and other aberrations during focusing with the middle group GM, but makes it difficult to reduce the size of the optical system OL, which is undesirable. To ensure the effect of conditional expression (4), it is desirable to set the upper limit of conditional expression (4) to 0.38, and even more desirably 0.35. Furthermore, if the lower limit of conditional expression (4) is not reached, the optical system OL can be made smaller, but it becomes difficult to correct spherical aberration, curvature of field, coma, etc., when focusing with the intermediate group GM, 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 0.23, and even more desirably 0.25.

[0024] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5).

[0025] 17.00 < (DF+DM+DR) / DF < 40.00 (5) where, DF: the distance on the optical axis from the lens surface of the front group GF closest to the object to the lens surface closest to the image plane, DM: the distance on the optical axis from the lens surface of the middle group GM closest to the object to the lens surface closest to the image plane when focusing on an object at infinity, DR: the distance on the optical axis from the lens surface of the rear group GR closest to the object to the lens surface closest to the image plane.

[0026] Conditional expression (5) defines the ratio of the sum of the axial thicknesses of the front group GF, the intermediate group GM, and the rear group GR to the axial thickness of the front group GF. By satisfying conditional expression (5), curvature of field, astigmatism, spherical aberration, coma, and other aberrations of the optical system OL can be effectively corrected. Exceeding the upper limit of conditional expression (5) makes the axial thickness of the front group GF thinner than the overall thickness (the sum of the axial thicknesses of the front group GF, the intermediate group GM, and the rear group GR). This makes it possible to effectively correct spherical aberration, coma, and other aberrations of the optical system OL, but makes it difficult to effectively correct curvature of field, astigmatism, and other aberrations, which is undesirable. To ensure the effect of conditional expression (5), it is more desirable to set the upper limit of conditional expression (5) to 39.00, 38.00, 37.00, or even 36.50. Furthermore, if the lower limit of conditional expression (5) is not reached, the thickness of the front group GF on the optical axis becomes thicker relative to the overall thickness, and although the curvature of field, astigmatism, etc. of the optical system OL can be well corrected, it becomes difficult to well correct spherical aberration, coma, etc., which is undesirable. In order to ensure the effect of conditional expression (5), it is more desirable to set the lower limit of conditional expression (5) to 17.50, 18.00, 18.50, or even 18.80.

[0027] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (6).

[0028] 0.80 < (1-βM 2 ) × βR 2 < 2.00 (6) where βM is the lateral magnification of the middle group GM when focusing on an object at infinity, and βR is the lateral magnification of the rear group GR when focusing on an object at infinity.

[0029] Conditional expression (6) defines the condition for focusing with the middle group GM. By satisfying conditional expression (6), the optical system OL can be made lighter and more compact while maintaining an appropriate change in image plane position during focusing, and aberration fluctuations during focusing can be suppressed. Exceeding the upper limit of conditional expression (6) makes it possible to suppress aberration fluctuations during focusing and achieve a compact optical system OL, but this is not preferable because it increases the change in image plane position during focusing and limits the selection of actuators for operating the middle group GM, which is the focusing group. To ensure the effect of conditional expression (6), it is more preferable to set the upper limit of conditional expression (6) to 1.90, 1.85, or even 1.80. Furthermore, falling below the lower limit of conditional expression (6) is preferable because it reduces the change in image plane position during focusing of the optical system OL and limits the selection of actuators, but it is not preferable because it becomes difficult to suppress aberration fluctuations during focusing and achieve a compact optical system. In order to ensure the effect of conditional expression (6), it is more desirable to set the lower limit of conditional expression (6) to 0.90, 1.00, or even 1.10.

[0030] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (7).

[0031] −0.50<f / fF<0.30 (7) where, f: focal length of the entire optical system OL when focusing on an object at infinity, and fF: focal length of the front group GF.

[0032] Conditional expression (7) defines the ratio of the focal length of the entire optical system OL when focusing on an object at infinity to the focal length of the front group GF. By satisfying conditional expression (7), various aberrations such as spherical aberration, coma, curvature of field, and astigmatism can be effectively corrected in the optical system OL, and aberration fluctuations during focusing can also be effectively suppressed. To ensure the effect of conditional expression (7), it is more desirable to set the upper limit of conditional expression (7) to 0.25, 0.20, or even 0.15. To ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to -0.40, -0.30, or even -0.20.

[0033] In the optical system OL according to this embodiment, it is desirable that the lens component LL arranged closest to the image plane has negative refractive power. This configuration allows for excellent correction of the field curvature and astigmatism of the optical system OL.

[0034] In the optical system OL according to this embodiment, it is desirable that the front group GF is composed of a single lens. This configuration makes it possible to reduce the weight and size of the optical system OL while effectively suppressing aberration fluctuations during focusing.

[0035] Furthermore, it is desirable that the optical system OL according to this embodiment has a diaphragm (for example, aperture diaphragm S in FIG. 1) in the intermediate group GM, and that the diaphragm moves in the optical axis direction during focusing. By moving the diaphragm along with the intermediate group GM in the optical axis direction during focusing, fluctuations in field curvature, astigmatism, and coma during focusing can be effectively suppressed.

[0036] In the optical system OL according to this embodiment, it is desirable that the middle group GM has positive refractive power. This configuration enables excellent correction of various aberrations such as curvature of field, spherical aberration, coma, and distortion of the optical system OL.

[0037] In the optical system OL according to this embodiment, it is desirable that the rear group GR has negative refractive power. This configuration enables excellent correction of various aberrations such as curvature of field, spherical aberration, coma, and distortion of the optical system OL.

[0038] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (8).

[0039] 0.50<fM / f<1.10 (8) where, fM: focal length of the intermediate group GM when focusing on an object at infinity, and f: focal length of the entire optical system OL when focusing on an object at infinity.

[0040] Conditional expression (8) defines the ratio of the focal length of the middle group GM to the focal length of the entire optical system OL when focusing on an object at infinity. By satisfying conditional expression (8), spherical aberration, coma, and other aberrations can be effectively corrected in the optical system OL. To ensure the effect of conditional expression (8), it is preferable to set the upper limit of conditional expression (8) to 1.05, and more preferably 1.00. To ensure the effect of conditional expression (8), it is more preferable to set the lower limit of conditional expression (8) to 0.55, 0.60, and even more preferably 0.65.

[0041] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (9).

[0042] 0.50<(-fR) / f<3.00 (9) where, fR: focal length of rear group GR, and f: focal length of the entire optical system OL when focusing on an object at infinity.

[0043] Conditional expression (9) defines the ratio of the focal length of the rear group GR to the focal length of the entire optical system OL when focusing on an object at infinity. By satisfying conditional expression (9), the optical system OL can effectively correct curvature of field, chromatic aberration of magnification, distortion, and other aberrations. To ensure the effect of conditional expression (9), it is more desirable to set the upper limit of conditional expression (9) to 2.90, 2.75, 2.60, 2.50, or even 2.40. To ensure the effect of conditional expression (9), it is more desirable to set the lower limit of conditional expression (9) to 0.60, 0.75, 0.90, or even 1.00.

[0044] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (10).

[0045] 1.00<(-fR) / fM<3.00 (10) where, fR: focal length of rear group GR, and fM: focal length of middle group GM when focusing on an object at infinity.

[0046] Conditional expression (10) defines the ratio of the focal length of the rear group GR to the focal length of the middle group GM when focusing on an object at infinity. Satisfying conditional expression (10) effectively suppresses aberration fluctuations during focusing. Exceeding the upper limit of conditional expression (10) weakens the refractive power of the rear group GR relative to the middle group GM in the optical system OL, allowing for effective correction of longitudinal chromatic aberration, lateral chromatic aberration, and other aberrations, but undesirably increases aberration fluctuations during focusing. To ensure the effect of conditional expression (10), it is more desirable to set the upper limit of conditional expression (10) to 2.90, 2.80, 2.70, or even 2.60. Falling below the lower limit of conditional expression (10) strengthens the refractive power of the rear group GR relative to the middle group GM in the optical system OL, effectively suppressing aberration fluctuations during focusing, but undesirably makes it difficult to correct longitudinal chromatic aberrations, lateral chromatic aberrations, and other aberrations. In order to ensure the effect of conditional expression (10), it is more desirable to set the lower limit of conditional expression (10) to 1.10, 1.20, 1.30, 1.40, and more preferably 1.45.

[0047] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (11).

[0048] 0.10<BF / TL<0.30 (11) where BF is the back focus (air-equivalent length) of the optical system OL when focused on an object at infinity, and TL is the total optical length (air-equivalent length) of the optical system OL when focused on an object at infinity.

[0049] Conditional expression (11) defines the ratio of the back focal length to the total optical length of the optical system OL when focusing on an object at infinity. By satisfying conditional expression (11), it is possible to achieve a reduction in the weight and size of the optical system OL while effectively correcting various aberrations such as spherical aberration and curvature of field. To ensure the effect of conditional expression (11), it is preferable to set the upper limit of conditional expression (11) to 0.28, and more preferably 0.25. To ensure the effect of conditional expression (11), it is more preferable to set the lower limit of conditional expression (11) to 0.11, 0.12, and even more preferably 0.13.

[0050] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (12).

[0051] −0.40<f / fL1<0.30 (12) where, f: focal length of the entire optical system OL when focused on an object at infinity, and fL1: focal length of the lens component L1 arranged closest to the object.

[0052] Conditional expression (12) defines the ratio of the focal length of the entire optical system OL when focusing on an object at infinity to the focal length of the lens component L1 located closest to the object in the optical system OL. By satisfying conditional expression (12), various aberrations in the optical system OL, such as spherical aberration, coma, curvature of field, and astigmatism, can be effectively corrected, and aberration fluctuations during focusing can be effectively suppressed. To ensure the effect of conditional expression (12), it is more desirable to set the upper limit of conditional expression (12) to 0.25, 0.20, 0.15, or 0.12. To ensure the effect of conditional expression (12), it is more desirable to set the lower limit of conditional expression (12) to -0.35, -0.30, -0.25, or -0.20.

[0053] 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.

[0054] Next, a camera, which is an optical device equipped with the optical system OL according to this embodiment, will be described with reference to FIG. 15 . This camera 1 is a so-called mirrorless camera with interchangeable lenses that includes the optical system OL 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 (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.

[0055] 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 optical system OL according to this embodiment is mounted on a single-lens reflex camera that has a quick-return mirror in the camera body and observes a subject through a viewfinder optical system.

[0056] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0057] In this embodiment, as will be described later, an optical system OL having a three-group or four-group configuration is shown. However, the above-described configuration conditions and the like can also be applied to other group configurations, such as five-group or six-group configurations. 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 when focusing is added closest to the image plane of the optical system OL, 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 when focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0058] 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 a close distance. 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 the second lens group G2 as the focusing group in a three-group configuration, or at least one of the second lens group G2 and the third lens group G3 in a four-group configuration, while keeping the positions of the other lenses fixed relative to the image plane during focusing.

[0059] 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 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, in the case of a three-group configuration, it is preferable to use at least a portion of the second lens group G2 as an image stabilization group, and in the case of a four-group configuration, it is preferable to use at least a portion of the second lens group G2 or the third lens group G3 as an image stabilization group.

[0060] 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.

[0061] The aperture stop S is preferably disposed within the intermediate group GM, but it is also possible to use the lens frame to fulfill that role without providing a member serving as an aperture stop.

[0062] 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.

[0063] An outline of a manufacturing method for the optical system OL according to this embodiment will be described below with reference to Fig. 16. First, in order from the object side, the front group GF, the middle group GM, and the rear group GR are prepared (Step S100). Next, the middle group GM is arranged so as to move in the optical axis direction during focusing (Step S200). These lens groups are then arranged so as to satisfy a predetermined condition (for example, the above-mentioned conditional expression (1) in the first embodiment, and the above-mentioned conditional expressions (2) and (3) in the second embodiment) (Step S300).

[0064] As a result, it is possible to provide an optical system, optical equipment, and method for manufacturing an optical system that can ensure good optical performance at a magnification of 0.5 or more while achieving lighter weight and smaller size.

[0065] Each embodiment will be described below with reference to the drawings. Figures 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views showing the configuration and refractive power distribution of an optical system OL (OL1 to OL7) according to each embodiment. Arrows at the bottom of the cross-sectional views of these optical systems OL1 to OL7 indicate the direction of movement of each lens group along the optical axis when focusing from an object at infinity (∞) to a close object.

[0066] In the second to seventh embodiments, 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 embodiments, "e-n" is "×10 -n " indicates.

[0067] 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 +A14×y 14 (a)

[0068] In each example, the second-order aspherical coefficient A2 is 0. In the table of each example, aspherical surfaces are marked with an asterisk (*) to the right of the surface number.

[0069] 1 is a diagram showing the configuration of an optical system OL1 according to Example 1. This optical system OL1 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having positive refractive power, an intermediate group GM consisting of a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power, and having positive refractive power as a whole, and a rear group GR consisting of a fourth lens group G4 having negative refractive power.

[0070] The first lens group G1 is composed of a meniscus-shaped positive lens L11 (L1) with a convex surface facing the object side. The second lens group G2 is composed of, from the object side, a meniscus-shaped negative lens L21 with a convex surface facing the object side, and a meniscus-shaped positive lens L22 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a biconcave negative lens L31, a meniscus-shaped positive lens L32 with a concave surface facing the object side, and a biconvex positive lens L33. The fourth lens group G4 is composed of, from the object side, a biconcave negative lens L41, a meniscus-shaped positive lens L42 with a concave surface facing the object side, and a biconcave negative lens L43 (LL).

[0071] In this optical system OL1, an aperture stop S is disposed between the second lens group G2 and the third lens group G3 in the intermediate group GM, and a filter group FL is disposed between the fourth lens group G4 and the image plane I.

[0072] In this optical system OL1, the second and third lens groups G2 and G3, which are the intermediate group GM, move toward the object along the optical axis during focusing from an object at infinity to a close object. The aperture stop S also moves together with the second lens group G2 during focusing.

[0073] Table 1 below lists the values ​​of the specifications of optical system OL1. 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 an object at infinity. Here, the back focus Bf represents the distance on the optical axis from the lens surface closest to the image plane (surface No. 39) to the image plane I. The total optical length TL represents 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. 39) plus the back focus. In addition, the first column m in the lens data 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.

[0074] 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 "mm," but this is not limited to this because the optical system can achieve the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and the specifications tables also apply to the following examples.

[0075] (Table 1) First Example [Overall specifications] f = 39.532 Fno = 2.82 ω [°] = 19.04 Y = 14.200 TL = 91.000 TL (air equivalent length) = 90.455 BF = 13.600 BF (air equivalent length) = 13.055 [Lens data] m r d nd νd Object surface ∞ 1 100.0000 2.5000 1.48749 70.32 2 200.0000 d1 3 17.1714 1.2000 1.62299 58.12 4 13.6956 8.9068 5 22.4494 4.1000 1.60311 60.69 6 152.7709 5.5226 7 ∞ d2 Aperture Stop S 8 -33.8144 1.0000 1.84666 23.80 9 40.4635 0.9000 10 -127.9705 2.5000 1.65160 58.57 11 -21.7834 0.1000 12 32.3448 4.1000 1.80610 40.98 13 -52.6084 d3 14 -135.7811 1.0000 1.48749 70.32 15 34.0082 1.5713 16 -593.0949 3.4000 1.77250 49.62 17 -27.6401 6.2884 18 -16.5865 1.2000 1.51680 64.13 19 214.0528 10.5000 20 ∞ 1.6000 1.51680 64.13 21 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 406.931 Middle group GM 3 27.854 Second lens group G2 3 61.926 Third lens group G3 8 36.238 Rear group GR (fourth lens group G4) 14 -43.251.

[0076] In this optical system OL1, the axial air distance d1 between the first lens group G1 and the second lens group G2, the axial air distance d2 between the second lens group G2 and the third lens group G3, and the axial air distance d3 between the third lens group G3 and the fourth lens group G4 change during focusing. Table 2 below shows the variable distances during focusing on an object at infinity and during focusing on an object at close range. Note that f represents the focal length and β represents the magnification. This explanation also applies to the following examples.

[0077] (Table 2) [Variable distance data] Object at infinity Object at close range f 39.532 - β - -1.00 d1 28.0111 1.5000 d2 3.5000 8.4471 d3 1.6000 23.1639

[0078] FIG. 2 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL1 when focused on an object at infinity and when focused on a close object. In each aberration diagram, FNo indicates the F-number, NA indicates the numerical aperture, and Y indicates the image height. Note that in the spherical aberration diagram, the F-number or numerical aperture value corresponding to the maximum aperture is shown, while in the astigmatism and distortion diagrams, the maximum image height is shown, and in the coma diagram, the value of each image height is shown. "d" indicates the d-line (λ=587.6 nm), and "g" indicates the g-line (λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dashed line indicates 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 optical system OL1 provides excellent correction for various aberrations and exhibits excellent imaging performance.

[0079] 3 shows the configuration of an optical system OL2 according to Example 2. This optical system OL2 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having positive refractive power, a middle group GM consisting of a second lens group G2 having positive refractive power, and a rear group GR consisting of a third lens group G3 having negative refractive power.

[0080] The first lens group G1 is composed of a plano-convex positive lens L11 (L1) with its convex surface facing the object side. The second lens group G2 is composed of, from the object side, a cemented positive lens formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, a cemented negative lens formed by cementing a biconcave negative lens L23 and a biconvex positive lens L24, and a biconvex positive lens L25 with an aspheric surface formed on its image side. The third lens group G3 is composed of, from the object side, a meniscus positive lens L31 with its concave surface facing the object side and a biconcave negative lens L32 (LL).

[0081] In this optical system OL2, an aperture stop S is disposed between the negative lens L22 and the negative lens L23 in the second lens group G2, which is the intermediate group GM. A filter group FL is disposed between the third lens group G3 and the image plane I.

[0082] In this optical system OL2, the second lens group G2, which is the intermediate group GM, moves toward the object along the optical axis when focusing from an object at infinity to a close object. The aperture stop S also moves together with the second lens group G2 when focusing.

[0083] Table 3 below lists the specifications of the optical system OL2.

[0084] (Table 3) Second Example [Overall specifications] f = 41.335 Fno = 2.07 ω [°] = 18.39 Y = 14.200 TL = 85.800 TL (air equivalent length) = 85.255 BF = 13.600 BF (air equivalent length) = 13.055 [Lens data] m r d nd νd Object surface ∞ 1 500.0000 2.0000 1.48749 70.32 2 ∞ d1 3 28.1947 4.6000 1.71999 50.27 4 -61.1236 1.0000 1.80100 34.92 5 74.1433 9.0000 6 ∞ 4.0000 Aperture Stop S 7 -17.6671 1.0000 1.62588 35.72 8 17.0726 5.0000 1.80400 46.60 9 -46.4184 0.1000 10 79.5479 3.3000 1.62263 58.16 11* -30.3176 d2 12 -36.8461 3.0000 1.78590 44.17 13 -25.0125 7.6000 14 -16.0825 1.2000 1.48749 70.32 15 401.0302 10.5000 16 ∞ 1.6000 1.51680 64.13 17 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (1st lens group G1) 1 1025.662 Middle group GM (2nd lens group G2) 3 33.624 Rear group GR (3rd lens group G3) 12 -53.277

[0085] In this optical system OL2, the 11th surface is formed as an aspherical surface. Table 4 below shows data on the aspherical surface, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0086] (Table 4) [Aspherical surface data] Surface 11 K = 1.00000 A4 = 3.71185E-05 A6 = -6.46471E-07 A8 = 3.01332E-08 A10 = -7.16019E-10 A12 = 8.76060E-12 A14 = 4.29930E-14

[0087] In this optical system OL2, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 change during focusing. Table 5 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0088] (Table 5) [Variable distance data] Object at infinity Object at close range f 41.335 - β - -1.00 d1 28.8000 1.3000 d2 1.6000 29.1000

[0089] 4 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this optical system OL2 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL2 has excellent imaging performance with various aberrations well corrected.

[0090] 5 shows the configuration of an optical system OL3 according to Example 3. This optical system OL3 is composed of, in order from the object side, a front group GF consisting of a first lens group G1, an intermediate group GM consisting of a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power, with the result that the entire lens group GM has positive refractive power, and a rear group GR consisting of a fourth lens group G4 having negative refractive power.

[0091] The first lens group G1 is composed of a parallel plate L11 (L1). The second lens group G2 is composed of, from the object side, a cemented positive lens formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22. The third lens group G3 is composed of, from the object side, a cemented negative lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32, and a biconvex positive lens L33 having an aspherical surface formed on the image-side lens surface. The positive lens L33 is a composite lens in which a resin layer is provided on the image-side surface of a glass lens body to form an aspherical surface. The fourth lens group G4 is composed of, from the object side, a cemented positive lens formed by cementing a biconvex positive lens L41 and a biconcave negative lens L42, and a biconcave negative lens L43 (LL) having an aspherical surface formed on the object-side lens surface. The negative lens L43 is a compound lens in which a resin layer is provided on the image-side surface of a glass lens body to form an aspheric surface.

[0092] In this optical system OL3, an aperture stop S is disposed between the second lens group G2 and the third lens group G3 in the intermediate group GM, and a filter group FL is disposed between the fourth lens group G4 and the image plane I.

[0093] In this optical system OL3, the second lens group G2 and the third lens group G3, which are the intermediate group GM, move toward the object along the optical axis during focusing from an object at infinity to a close object. During focusing, the aperture stop S moves together with the third lens group G3.

[0094] Table 6 below lists the specifications of the optical system OL3.

[0095] (Table 6) Third Example [Overall specifications] f = 35.500 Fno = 1.86 ω [°] = 21.09 Y = 14.200 TL = 81.000 TL (equivalent length in air) = 80.455 BF = 13.400 BF (equivalent length in air) = 12.855 [Lens data] m r d nd νd Object surface ∞ 1 ∞ 1.2000 1.48749 70.32 2 ∞ d1 3 32.3113 4.8000 1.70000 48.10 4 -44.7976 1.0000 1.83400 37.18 5 292.5746 d2 6 ∞ 4.5000 Aperture Stop S 7 -16.1414 1.0000 1.71736 29.57 8 40.2209 3.8000 1.80400 46.60 9 -38.4171 0.1000 10 110.7728 3.8000 1.80400 46.60 11 -25.6333 0.2000 1.56093 36.64 12* -25.6333 d3 13 355.6821 5.0000 1.88300 40.66 14 -18.2588 1.0000 1.58144 40.98 15 95.1472 4.8661 16* -20.1725 0.2000 1.56093 36.64 17 -18.0890 1.0000 1.51742 52.20 18 337.3157 10.3000 19 ∞ 1.6000 1.51680 64.13 20 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 ∞ Intermediate group GM 3 32.878 Second lens group G2 3 61.694 Third lens group G3 7 40.089 Rear group GR (fourth lens group G4) 13 -84.292.

[0096] In this optical system OL3, surfaces 12 and 16 are formed aspherical. Table 7 below shows data on the aspherical surfaces, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0097] (Table 7) [Aspherical surface data] Surface 12 K = 1.00000 A4 = 2.46184E-05 A6 = -2.41773E-07 A8 = 1.11585E-08 A10 = -2.69002E-10 A12 = 3.24180E-12 A14 = 1.52330E-14 Surface 16 K = 1.00000 A4 = -3.88298E-05 A6 = 1.22826E-07 A8 = -2.32494E-09 A10 = 9.49732E-12 A12 = 0.00000E+00 A14 = 0.00000E+00

[0098] In this optical system OL3, the axial air distance d1 between the first lens group G1 and the second lens group G2, the axial air distance d2 between the second lens group G2 and the third lens group G3, and the axial air distance d3 between the third lens group G3 and the fourth lens group G4 change during focusing. Table 8 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0099] (Table 8) [Variable distance data] Object at infinity Object at close range f 35.500 - β - -0.70 d1 24.8000 2.6000 d2 8.5000 9.3828 d3 1.8340 23.1512

[0100] 6 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this optical system OL3 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL3 has excellent imaging performance with various aberrations well corrected.

[0101] 7 shows the configuration of an optical system OL4 according to Example 4. This optical system OL4 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having negative refractive power, a middle group GM consisting of a second lens group G2 having positive refractive power, and a rear group GR consisting of a third lens group G3 having negative refractive power.

[0102] The first lens group G1 is composed of a meniscus-shaped negative lens L11 (L1) with a convex surface facing the object side. The second lens group G2 is composed of, from the object side, a meniscus-shaped positive lens L21 with a convex surface facing the object side, a cemented negative lens formed by cementing a biconcave negative lens L22 and a biconvex positive lens L23, and a biconvex positive lens L24 with an aspherical surface formed on the image side. The positive lens L24 is a composite lens in which a resin layer is provided on the image side surface of a glass lens body to form an aspherical surface. The third lens group G3 is composed of, from the object side, a meniscus-shaped positive lens L31 with a concave surface facing the object side, and a meniscus-shaped negative lens L32 (LL) with a concave surface facing the object side.

[0103] In this optical system OL4, an aperture stop S is disposed between a positive lens L21 and a negative lens L22 in the second lens group G2, which is an intermediate group GM. A filter group FL is disposed between the third lens group G3 and the image plane I.

[0104] In this optical system OL4, the second lens group G2, which is the intermediate group GM, moves toward the object along the optical axis when focusing from an object at infinity to a close object. The aperture stop S also moves together with the second lens group G2 when focusing.

[0105] Table 9 below lists the specifications of the optical system OL4.

[0106] (Table 9) Fourth Example [Overall specifications] f = 38.000 Fno = 2.86 ω [°] = 20.18 Y = 14.200 TL = 81.000 TL (air equivalent length) = 80.455 BF = 14.300 BF (air equivalent length) = 13.755 [Lens data] m r d nd νd Object surface ∞ 1 1000.0000 1.2000 1.67270 32.19 2 341.6032 d1 3 26.3938 2.5000 1.61800 63.34 4 104.4847 10.8000 5 ∞ 3.0000 Aperture Stop S 6 -12.9734 1.0000 1.71736 29.57 7 35.4454 3.4000 1.80400 46.60 8 -33.7721 0.1000 9 128.6034 3.5000 1.79500 45.31 10 -20.4927 0.2000 1.56093 36.64 11* -20.4927 d2 12 -30.0289 2.2000 1.74950 35.25 13 -23.0492 9.5978 14 -16.3907 1.2000 1.60311 60.69 15 -110.6686 11.2000 16 ∞ 1.6000 1.51680 64.13 17 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 -771.847 Middle group GM (Second lens group G2) 3 30.796 Rear group GR (Third lens group G3) 12 -47.477

[0107] In this optical system OL4, the 11th surface is formed as an aspherical surface. Table 10 below shows data on the aspherical surface, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0108] (Table 10) [Aspherical surface data] Surface 11 K = 1.00000 A4 = 3.47586E-05 A6 = -1.66949E-07 A8 = 5.09420E-09 A10 = -4.45933E-11 A12 = 0.00000E+00 A14 = 0.00000E+00

[0109] In this optical system OL4, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 change during focusing. Table 11 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0110] (Table 11) [Variable distance data] Object at infinity Object at close range f 38.000 - β - -1.00 d1 26.4022 1.6000 d2 1.6000 26.4022

[0111] 8 shows diagrams of spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma of this optical system OL4 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL4 has excellent imaging performance with various aberrations well corrected.

[0112] 9 shows the configuration of an optical system OL5 according to Example 5. This optical system OL5 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having negative refractive power, a middle group GM consisting of a second lens group G2 having positive refractive power, and a rear group GR consisting of a third lens group G3 having negative refractive power.

[0113] The first lens group G1 is composed of a meniscus negative lens L11 (L1) with a convex surface facing the object side. The second lens group G2 is composed of, in order from the object side, a meniscus positive lens L21 with a convex surface facing the object side, a meniscus negative lens L22 with a convex surface facing the object side and having aspherical surfaces on the object side lens surface and the image plane lens surface, a cemented positive lens formed by cementing a biconcave negative lens L23 and a biconvex positive lens L24, and a meniscus positive lens L25 with a concave surface facing the object side. The third lens group G3 is composed of a meniscus positive lens L31 with a concave surface facing the object side and a meniscus negative lens L32 (LL) with a concave surface facing the object side.

[0114] In this optical system OL5, an aperture stop S is disposed between the negative lens L22 and the negative lens L23 in the second lens group G2, which is the intermediate group GM. A filter group FL is disposed between the third lens group G3 and the image plane I.

[0115] In this optical system OL5, the second lens group G2, which is the intermediate group GM, moves toward the object along the optical axis when focusing from an object at infinity to a close object. The aperture stop S also moves together with the second lens group G2 when focusing.

[0116] Table 12 below lists the specifications of the optical system OL5.

[0117] (Table 12) Fifth Example [Overall specifications] f = 38.257 Fno = 2.88 ω [°] = 20.21 Y = 14.200 TL = 81.000 TL (air equivalent length) = 80.455 BF = 15.800 BF (air equivalent length) = 15.255 [Lens data] m r d nd νd Object surface ∞ 1 1000.0000 1.2000 1.62299 58.12 2 191.9205 d1 3 21.6636 3.2000 1.61800 63.34 4 85.8643 3.9234 5* 5000.0000 1.2000 1.53504 55.71 6* 111.0085 5.4408 7 ∞ 2.5000 Aperture Stop S 8 -13.9656 1.0000 1.75520 27.57 9 70.8048 3.7000 1.80400 46.60 10 -16.9076 0.1000 11 -1132.4588 2.7000 1.80610 40.98 12 -34.9496 d2 13 -33.0000 2.2000 1.69895 30.13 14 -23.5462 8.6359 15 -16.7498 1.2000 1.62299 58.12 16 -115.9839 12.7000 17 ∞ 1.6000 1.51680 64.13 18 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 -381.447 Middle group GM (Second lens group G2) 3 30.882 Rear group GR (Third lens group G3) 13 -48.278

[0118] In this optical system OL5, the fifth and sixth surfaces are formed aspherical. Table 13 below shows data on the aspherical surfaces, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0119] (Table 13) [Aspherical surface data] Surface 5 K = 1.00000 A4 = 2.14608E-04 A6 = -6.37110E-07 A8 = 4.09234E-09 A10 = 0.00000E+00 A12 = 0.00000E+00 A14 = 0.00000E+00 Surface 6 K = 1.00000 A4 = 2.71565E-04 A6 = -6.66060E-07 A8 = 1.26067E-08 A10 = 0.00000E+00 A12 = 0.00000E+00 A14 = 0.00000E+00

[0120] In this optical system OL5, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 change during focusing. Table 14 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0121] (Table 14) [Variable distance data] Object at infinity Object at close range f 38.257 - β - -1.00 d1 26.6000 1.6000 d2 1.6000 26.6000

[0122] 10 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this optical system OL5 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL5 has excellent imaging performance with various aberrations well corrected.

[0123] 11 is a diagram showing the configuration of an optical system OL6 according to Example 6. This optical system OL6 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having negative refractive power, an intermediate group GM consisting of a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power, and having positive refractive power as a whole, and a rear group GR consisting of a fourth lens group G4 having negative refractive power.

[0124] The first lens group G1 is composed of a plano-concave negative lens L11 (L1) with a flat surface facing the object side. The second lens group G2 is composed of a meniscus positive lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented negative lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32 together, a meniscus positive lens L33 with an aspherical surface on the image side and a concave surface facing the object side, and a biconvex positive lens L34. The fourth lens group G4 is composed of, from the object side, a meniscus positive lens L41 with a concave surface facing the object side, a meniscus negative lens L42 with an aspherical surface on the object side and a concave surface facing the object side, and a meniscus negative lens L43 (LL) with a concave surface facing the object side.

[0125] In this optical system OL6, an aperture stop S is disposed between the second lens group G2 and the third lens group G3 in the intermediate group GM, and a filter group FL is disposed between the fourth lens group G4 and the image plane I.

[0126] In this optical system OL6, the second and third lens groups G2 and G3, which are the intermediate group GM, move toward the object along the optical axis during focusing from an object at infinity to a close object. The aperture stop S also moves together with the third lens group G3 during focusing.

[0127] Table 15 below lists the specifications of the optical system OL6.

[0128] (Table 15) Sixth Example [Overall specifications] f = 34.506 Fno = 1.87 ω [°] = 22.613 Y = 14.200 TL = 81.000 TL (equivalent length in air) = 80.455 BF = 13.100 BF (equivalent length in air) = 12.555 [Lens data] m r d nd νd Object surface ∞ 1 ∞ 1.2000 1.60342 38.03 2 137.0000 d1 3 29.7763 3.5000 1.77250 49.62 4 162.6784 d2 5 ∞ 3.9000 Aperture stop S 6 -17.7201 1.0000 1.69895 30.13 7 18.8264 3.6000 1.80400 46.60 8 -368.3266 1.3000 9 -70.0000 1.2000 1.53504 55.71 10* -63.1478 0.1000 11 73.4674 3.8000 1.80400 46.60 12 -24.0859 d3 13 -512.8175 3.0000 1.77250 49.62 14 -53.8371 0.4000 15* -52.0000 1.5000 1.53504 55.71 16 -55.8074 6.8350 17 -18.5196 1.2000 1.51742 52.20 18 -421.4731 10.0000 19 ∞ 1.6000 1.51680 64.13 20 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 -227.039 Middle group GM 3 33.771 Second lens group G2 3 46.646 Third lens group G3 6 43.983 Rear group GR (Fourth lens group G4) 13 -82.053

[0129] In this optical system OL6, surfaces 10 and 15 are formed aspherical. Table 16 below shows data on the aspherical surfaces, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0130] (Table 16) [Aspherical surface data] Surface 10 K = 1.00000 A4 = 4.22622E-05 A6 = -2.61315E-07 A8 = 1.23491E-08 A10 = -2.58085E-10 A12 = 2.70030E-12 A14 = -1.11010E-14 Surface 15 K = 1.00000 A4 = 7.42581E-06 A6 = 4.99661E-08 A8 = -2.94414E-10 A10 = 1.20068E-12 A12 = 0.00000E+00 A14 = 0.00000E+00

[0131] In this optical system OL6, the axial air distance d1 between the first lens group G1 and the second lens group G2, the axial air distance d2 between the second lens group G2 and the third lens group G3, and the axial air distance d3 between the third lens group G3 and the fourth lens group G4 change during focusing. Table 17 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0132] (Table 17) [Variable distance data] Object at infinity Object at close range f 34.506 - β - -0.70 d1 23.1650 1.6000 d2 10.6000 8.6232 d3 1.6000 25.1418

[0133] 12 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this optical system OL6 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL6 has excellent imaging performance with various aberrations well corrected.

[0134] 13 is a diagram showing the configuration of an optical system OL7 according to Example 7. This optical system OL7 is composed of, in order from the object side, a front group GF consisting of a first lens group G1 having negative refractive power, an intermediate group GM consisting of a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power, and having positive refractive power as a whole, and a rear group GR consisting of a fourth lens group G4 having negative refractive power.

[0135] The first lens group G1 is composed of a plano-concave negative lens L11 (L1) with a flat surface facing the object side. The second lens group G2 is composed of a meniscus positive lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented negative lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32 together, a meniscus positive lens L33 with an aspheric lens surface on the image side and a concave surface facing the object side, and a biconvex positive lens L34. The fourth lens group G4 is composed of, from the object side, a meniscus positive lens L41 with a concave surface facing the object side and a biconcave negative lens L42 (LL).

[0136] In this optical system OL7, an aperture stop S is disposed between the second lens group G2 and the third lens group G3 in the intermediate group GM, and a filter group FL is disposed between the fourth lens group G4 and the image plane I.

[0137] In this optical system OL7, the second and third lens groups G2 and G3, which are the intermediate group GM, move toward the object along the optical axis during focusing from an object at infinity to a close object. The aperture stop S also moves together with the third lens group G3 during focusing.

[0138] Table 18 below lists the specifications of the optical system OL7.

[0139] (Table 18) Seventh Example [Overall specifications] f = 34.809 Fno = 1.88 ω [°] = 22.33 Y = 14.200 TL = 81.000 TL (equivalent length in air) = 80.455 BF = 13.100 BF (equivalent length in air) = 12.555 [Lens data] m r d nd νd Object surface ∞ 1 ∞ 1.2000 1.60342 38.03 2 137.0000 d1 3 30.2634 3.5000 1.77250 49.62 4 163.9532 d2 5 ∞ 3.9000 Aperture stop S 6 -17.5242 1.0000 1.69895 30.13 7 19.2332 3.6000 1.80400 46.60 8 -338.5777 1.3000 9 -70.0000 1.2000 1.53504 55.71 10* -59.8040 0.1000 11 78.4773 3.8000 1.80400 46.60 12 -23.8412 d3 13 -125.6395 3.0000 1.77250 49.62 14 -46.8274 8.9114 15 -23.0295 1.2000 1.51742 52.20 16 237.4580 10.0000 17 ∞ 1.6000 1.51680 64.13 18 ∞ 1.5000 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GF (First lens group G1) 1 -227.039 Middle group GM 3 34.000 Second lens group G2 3 47.502 Third lens group G3 6 44.102 Rear group GR (Fourth lens group G4) 13 -82.712

[0140] In this optical system OL7, the tenth surface is formed as an aspherical surface. Table 19 below shows data on the aspherical surface, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A14.

[0141] (Table 19) [Aspherical surface data] Surface 10 K = 1.00000 A4 = 4.27018E-05 A6 = -3.39344E-07 A8 = 1.47524E-08 A10 = -2.99211E-10 A12 = 3.04550E-12 A14 = -1.22760E-14

[0142] In this optical system OL7, the axial air distance d1 between the first lens group G1 and the second lens group G2, the axial air distance d2 between the second lens group G2 and the third lens group G3, and the axial air distance d3 between the third lens group G3 and the fourth lens group G4 change during focusing. Table 20 below shows the variable distances during focusing on an object at infinity and during focusing on a close object.

[0143] (Table 20) [Variable distance data] Object at infinity Object at close range f 34.809 - β - -0.70 d1 22.9886 1.6000 d2 10.6000 8.3141 d3 1.6000 25.2745

[0144] 14 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma of this optical system OL7 when focused on an object at infinity and when focused on a close object. These aberration diagrams show that this optical system OL7 has excellent imaging performance with various aberrations well corrected.

[0145] [Values ​​Corresponding to Conditional Expressions] The values ​​corresponding to conditional expressions (1) to (12) in the first to seventh examples are shown in Table 21 below.

[0146] (Table 21) (1) d1 / f (2) TL / DF (3) DM / DR (4) d1 / TL (5) (DF+DM+DR) / DF (6) (1-βM 2 ) × βR 2(7) f / fF (8) fM / f (9) (-fR) / f (10) (-fR) / fM (11) BF / TL (12) f / fL1 First Example Second Example Third Example Fourth Example (1) 0.709 0.697 0.699 0.695 (2) 36.182 42.627 67.046 67.046 (3) 2.365 2.373 2.296 1.885 (4) 0.310 0.338 0.308 0.328 (5) 19.116 20.900 34.138 32.248 (6) 1.732 1.462 1.166 1.581 (7) 0.097 0.040 0.000 -0.049 (8) 0.705 0.813 0.926 0.810 (9) 1.094 1.289 2.374 1.249 (10) 1.553 1.585 2.564 1.542 (11) 0.144 0.153 0.160 0.171 (12) 0.097 0.040 0.000 -0.049 Fifth Example Sixth Example Seventh Example (1) 0.695 0.671 0.660 (2) 67.046 67.046 67.046 (3) 1.974 2.242 2.212 (4) 0.331 0.288 0.286 (5) 30.833 35.946 36.093 (6) 1.634 1.133 1.135 (7) -0.100 -0.152 -0.153 (8) 0.807 0.979 0.977 (9) 1.262 2.378 2.376 (10) 1.563 2.430 2.433 (11) 0.190 0.156 0.156 (12) -0.100 -0.152 -0.153

[0147] 1 Camera (optical equipment) OL (OL1 to OL7) Optical system GF Front group GM Middle group GR Rear group S Aperture stop (aperture)

Claims

1. It is composed of, in order from the object side, a front group, an intermediate group, and a rear group, During focusing, the intermediate group moves in the optical axis direction, An optical system that satisfies the following condition: 0.54 < d1 / f < 1.00 however, d1: the distance on the optical axis from the lens surface of the front group closest to the image plane to the lens surface of the intermediate group closest to the object when focusing on an object at infinity f: focal length of the entire optical system when focused on an object at infinity

2. It is composed of, in order from the object side, a front group, an intermediate group, and a rear group, During focusing, the intermediate group moves in the optical axis direction, An optical system that satisfies the following condition: 32.00 < TL / DF < 80.00 1.00 < DM / DR < 4.00 however, TL: total optical length of the optical system when focused on an object at infinity DF: the distance on the optical axis from the lens surface of the front group closest to the object to the lens surface closest to the image plane DM: the distance on the optical axis from the lens surface of the intermediate group closest to the object to the lens surface closest to the image plane when focusing on an object at infinity DR: the distance on the optical axis from the lens surface in the rear group closest to the object to the lens surface closest to the image plane

3. 2. The optical system according to claim 1, wherein the following condition is satisfied: 0.20 < d1 / TL < 0.40 however, d1: the distance on the optical axis from the lens surface of the front group closest to the image plane to the lens surface of the intermediate group closest to the object when focusing on an object at infinity TL: total optical length of the optical system when focused on an object at infinity

4. 4. The optical system according to claim 1, wherein the following condition is satisfied: 17.00 < (DF+DM+DR) / DF < 40.00 however, DF: the distance on the optical axis from the lens surface of the front group closest to the object to the lens surface closest to the image plane DM: the distance on the optical axis from the lens surface of the intermediate group closest to the object to the lens surface closest to the image plane when focusing on an object at infinity DR: the distance on the optical axis from the lens surface in the rear group closest to the object to the lens surface closest to the image plane

5. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.80 < (1-βM) 2 )×βR 2 < 2.00 however, βM: lateral magnification of the intermediate group when focusing on an object at infinity βR: lateral magnification of the rear group when focusing on an object at infinity

6. 3. The optical system according to claim 1, wherein the following condition is satisfied: -0.50 < f / fF < 0.30 however, f: focal length of the entire optical system when focused on an object at infinity fF: focal length of the front group

7. 3. The optical system according to claim 1, wherein the lens component arranged closest to the image plane has negative refractive power.

8. 3. The optical system according to claim 1, wherein the front group is composed of a single lens.

9. a diaphragm is provided within the intermediate group, 3. The optical system according to claim 1, wherein the diaphragm moves in the optical axis direction during focusing.

10. 3. The optical system according to claim 1, wherein the intermediate group has positive refractive power.

11. 3. The optical system according to claim 1, wherein the rear group has negative refractive power.

12. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.50 < fM / f < 1.10 however, fM: focal length of the intermediate group when focusing on an object at infinity f: focal length of the entire optical system when focused on an object at infinity

13. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.50 < (-fR) / f < 3.00 however, fR: focal length of the rear group f: focal length of the entire optical system when focused on an object at infinity

14. 3. The optical system according to claim 1, wherein the following condition is satisfied: 1.00 < (-fR) / fM < 3.00 however, fR: focal length of the rear group fM: focal length of the intermediate group when focusing on an object at infinity

15. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < BF / TL < 0.30 however, BF: back focus of the optical system when focused on an object at infinity TL: total optical length of the optical system when focused on an object at infinity

16. 3. The optical system according to claim 1, wherein the following condition is satisfied: -0.40 < f / fL1 < 0.30 however, f: focal length of the entire optical system when focused on an object at infinity fL1: focal length of the lens component located closest to the object

17. An optical instrument comprising the optical system according to claim 1 or 2.