Optical systems and optical instruments

Abstract

Provided are an optical system, an optical device, and a method for manufacturing an optical system which achieve miniaturization, widen the angle of view, reduce distortion aberration, and ensure an amount of peripheral light.　An optical system OL to be used in an optical device such as a camera 1 is configured from, in order from an object side, a front group GA, an aperture stop S, and a rear group GB. The rear group GB includes a focusing group Gf that moves along the optical axis during focusing, and an image-side group Gr that is fixed during focusing and arranged closer to the image surface side than the focusing group Gf. The optical system is configured to satisfy a condition according to a prescribed conditional expression.

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] In recent years, large-aperture ultra-wide-angle lenses have been developed, with numerical apertures of less than 2 (see, for example, Patent Document 1). However, these lenses are required to strike a balance between further performance improvement and miniaturization.

[0003] International Publication No. 2021 / 199923

[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, a stop, and a rear group, the rear group having a focusing group that moves along the optical axis during focusing, and an image-side group that is positioned closer to the image plane than the focusing group and is fixed during focusing, and satisfies the following condition: 0.10 < fr / ff < 4.00, where fr is the focal length of the image-side group, and ff is the focal length of the focusing group.

[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, a stop, and a rear group having positive refractive power, and the front group has, in order from the most object side, a first negative lens, a second negative lens, and a third negative lens, and satisfies the following condition: 0.10 < (-fL123) / fB < 0.65, where fL123 is the composite focal length of the first negative lens, the second negative lens, and the third negative lens, and fB is the focal length of the rear group.

[0006] A manufacturing method for an optical system according to a first aspect of the present invention is a manufacturing method for an optical system composed of, in order from the object side, a front group, a stop, and a rear group, in which the rear group includes a focusing group that moves along the optical axis during focusing, and an image-side group that is located closer to the image plane than the focusing group and is fixed during focusing, and the arrangement is such that the following condition is satisfied: 0.10 < fr / ff < 4.00, where fr is the focal length of the image-side group, and ff is the focal length of the focusing group.

[0007] A manufacturing method for an optical system according to a second aspect of the present invention is a manufacturing method for an optical system configured of, in order from the object side, a front group, a stop, and a rear group having positive refractive power, in which, in order from the most object side, a first negative lens, a second negative lens, and a third negative lens are arranged in the front group so as to satisfy the following condition: 0.10 < (-fL123) / f2 < 0.65 where fL123 is the composite focal length of the first negative lens, the second negative lens, and the third negative lens, and f2 is the focal length of the rear group.

[0008] FIG. 1 is a sectional view showing the lens configuration of an optical system according to Example 1 when focusing on an object at infinity. FIG. 2 is a diagram showing various aberrations of an optical system according to Example 1 when focusing on an object at infinity. FIG. 3 is a diagram showing various aberrations of an optical system according to Example 1 when focusing on a close object. FIG. 4 is a sectional view showing the lens configuration of an optical system according to Example 2 when focusing on an object at infinity. FIG. 5 is a diagram showing various aberrations of an optical system according to Example 2 when focusing on an object at infinity. FIG. 6 is a diagram showing various aberrations of an optical system according to Example 2 when focusing on a close object. FIG. 7 is a sectional view showing the lens configuration of an optical system according to Example 3 when focusing on an object at infinity. FIG. 8 is a diagram showing various aberrations of an optical system according to Example 3 when focusing on an object at infinity. FIG. 9 is a diagram showing various aberrations of an optical system according to Example 3 when focusing on a close object. FIG. 10 is a sectional view showing the lens configuration of an optical system according to Example 4 when focusing on an object at infinity in the wide-angle end state. FIG. 11 is a diagram showing various aberrations of an optical system according to Example 4 when focusing on an object at infinity in the wide-angle end state. FIG. 12 is a diagram showing various aberrations of an optical system according to Example 4 when focusing on a close object at wide-angle end state. FIG. 13 is a diagram showing various aberrations of an optical system according to Example 4 when focusing on an object at infinity in the telephoto end state. FIG. 10 is a diagram illustrating various aberrations when the optical system according to Example 4 is in a telephoto end state and focuses on a close-up object. FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 5 when focusing on an object at infinity. FIG. 12 is a diagram illustrating various aberrations when the optical system according to Example 5 is focused on an object at infinity. FIG. 13 is a cross-sectional view of a camera equipped with the optical system. FIG. 14 is a flowchart for explaining a method for manufacturing the optical system, where (a) shows a first embodiment and (b) shows a second embodiment.

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

[0010] In a general wide-angle lens using the central projection method, the reduction in peripheral illumination becomes a problem as the angle of view increases. With respect to the angle of view θ, if the object luminance is B, the size of the entrance pupil is S(θ), the distance between the object and the entrance pupil is L, the infinitesimal area on the object is ds, and the infinitesimal area on the image plane is ds', the image plane illuminance E is related by the so-called fourth power cosine law on the entrance side, as shown in the following equation (b):

[0011]

[0012] Therefore, when considering an optical system in which the size of the entrance pupil and ds / ds' are constant regardless of the angle of view θ, cos 4 For example, when the half angle of view θ is 57.1° (equivalent to a focal length of 14 mm), the peripheral light intensity at the diagonal of the 35 mm format falls to 8.7% of the central level even without vignetting.

[0013] To solve this problem, a method is known in which the loss of light is corrected by generating negative distortion. For example, one possible method is to generate large negative distortion, which will allow the optical system to be made smaller, assuming that the distortion will be corrected by image processing.

[0014] Furthermore, it is known that, in principle, vignetting does not occur with fisheye lenses that employ an orthogonal projection method. This corresponds to compressing the peripheral image by generating distortion (as viewed from the central projection), and increasing the ds / ds' ratio in equation (b) above to increase the image plane illuminance. Because generating a large negative distortion reduces the image circle, this method makes it possible to miniaturize the optical system and suppress vignetting. However, the process of electronically correcting the image to that of a central projection method stretches the peripheral image, resulting in problems such as reduced resolution and elliptical deformation of point light sources.

[0015] Another method for suppressing vignetting without relying on distortion is to increase the area S(θ) of the entrance pupil according to the angle of view. It is known that in so-called retrofocus wide-angle lenses that have a strong negative lens element on the object side, pupil aberration occurs in the off-axis entrance pupil, which suppresses vignetting.

[0016] According to the present embodiment, which will be described below, by appropriately setting the various conditions of the optical system, it is possible to control the occurrence of pupil aberration, and to achieve correction of peripheral illumination and a compact optical system without relying on distortion.

[0017] In the following description, when the value of a conditional expression changes depending on the focusing state, it is assumed to be the value when an object at infinity is focused. Also, when the optical system OL is a variable magnification optical system that changes magnification from the wide-angle end state to the telephoto end state, when the value of a conditional expression changes depending on the focusing state, it is assumed to be the value in the wide-angle end state.

[0018] 1, an optical system OL according to a first embodiment is composed of, in order from the object side, a front group GA, a diaphragm (aperture diaphragm S), and a rear group GB, and the rear group GB is composed of a focusing group Gf that moves along the optical axis during focusing, and an image-side group Gr that is positioned closer to the image plane than the focusing group Gf and is fixed during focusing. This configuration makes it possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral illumination.

[0019] Moreover, it is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (1).

[0020] 0.10 < fr / ff < 4.00 (1) where fr is the focal length of the image-side group Gr, and ff is the focal length of the focusing group Gf.

[0021] Conditional expression (1) defines the ratio of the focal length of the image-side group Gr to the focal length of the focusing group Gf in the rear group GB of the optical system OL. When the focusing group Gf is composed of multiple lens groups, the focal length of the focusing group Gf is the combined focal length of those lens groups when focusing on an object at infinity. By satisfying conditional expression (1), it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral illumination. Exceeding the upper limit of conditional expression (1) is undesirable because it becomes difficult to move the exit pupil away from the image plane, which reduces pupil aberration and makes it difficult to ensure sufficient peripheral illumination. To ensure the effect of conditional expression (1), it is preferable to set the upper limit of conditional expression (1) to 3.65, 3.50, 2.50, 2.00, 1.50, 1.30, or even 1.00. Furthermore, if the lower limit of conditional expression (1) is not reached, the focal length of the image-side group Gr, which has positive refractive power and is located closest to the image plane, becomes short, making it impossible to ensure sufficient back focus. Ensuring sufficient back focus requires increasing the refractive power of the negative lens element located closer to the object than the image-side group Gr (mainly the front group GA, which is closer to the object than the aperture stop S), which is undesirable because it increases the size of the optical system OL. To ensure the effect of conditional expression (1), it is more desirable to set the lower limit of conditional expression (1) to 0.20, 0.25, 0.30, 0.35, 0.40, or even 0.45.

[0022] In the optical system OL according to the first embodiment, the front group GA has, in order from the object side, a first negative lens Ln1, a second negative lens Ln2, and a third negative lens Ln3, and it is desirable that the front group GA satisfy the following conditional expression (2):

[0023] 0.10<(-fL123) / fB<0.65 (2) where, fL123 is the combined focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3, and fB is the focal length of the rear group GB.

[0024] Conditional expression (2) defines the ratio of the composite focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3 to the focal length of the rear group GB. By satisfying conditional expression (2), it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral light intensity. Exceeding the range of conditional expression (2) results in significant distortion. Attempting to reduce the size of the optical system OL while maintaining the peripheral light intensity is undesirable because it makes it difficult to correct distortion. To ensure the effect of conditional expression (2), it is preferable to set the upper limit of conditional expression (2) to 0.60, 0.55, 0.51, 0.45, 0.40, 0.37, or even 0.35. To ensure the effect of conditional expression (2), it is preferable to set the lower limit of conditional expression (2) to 0.15, 0.20, 0.25, or even 0.29.

[0025] 1, an optical system OL according to a second embodiment is composed of, in order from the object side, a front group GA, a diaphragm (aperture stop S), and a rear group GB having positive refractive power, and the front group GA is composed of, in order from the object side, a first negative lens Ln1, a second negative lens Ln2, and a third negative lens Ln3. With this configuration, it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral light amount.

[0026] It is also desirable that the optical system OL according to the second embodiment satisfy the above-mentioned conditional expression (2). The effects and the like resulting from satisfying this conditional expression (2) are as described above.

[0027] (First and Second Embodiments) It is desirable that the optical system OL according to the first and second embodiments (hereinafter referred to as "the present embodiment") satisfy the following conditional expression (3).

[0028] 0.50 < DSI / DL1S < 1.00 (3) where DSI is the distance on the optical axis from the stop (aperture stop S) to the image plane I, and DL1S is the distance on the optical axis from the lens surface of the front group GA closest to the object to the stop (aperture stop S).

[0029] Conditional expression (3) defines the ratio of the axial distance from the aperture stop (aperture stop S) to the axial distance from the aperture stop (aperture stop S) to the image plane I to the axial distance from the lens surface closest to the object in the front group GA to the aperture stop (aperture stop S). Note that DSI represents the axial distance from the aperture stop (aperture stop S) to the lens surface closest to the image plane in the optical system OL, plus the air-equivalent back focus length (this also applies in the following explanations). Satisfying conditional expression (3) not only achieves compactness but also provides an optical system OL with a wide angle of view, reduced distortion, and sufficient peripheral illumination. Exceeding the upper limit of conditional expression (3) is undesirable because it increases the distance between the aperture stop (aperture stop S) and the image plane I and increases the overall optical length of the optical system OL. Note that, to ensure the effect of conditional expression (3), it is more desirable to set the upper limit of conditional expression (3) to 0.90, 0.85, 0.80, or even 0.78. Furthermore, if the lower limit of conditional expression (3) is not reached, it becomes difficult to move the exit pupil away from the image plane, and the pupil aberration decreases, which undesirably reduces the amount of peripheral illumination. In order to ensure the effect of conditional expression (3), it is more desirable to set the lower limit of conditional expression (3) to 0.55, 0.60, 0.65, or even 0.70.

[0030] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (4).

[0031] 0.40 < DSLR / DL1S < 0.95 (4) where, DSLR is the distance on the optical axis from the aperture stop (aperture stop S) to the lens surface of the rear group GB that is closest to the image plane, and DL1S is the distance on the optical axis from the lens surface of the front group GA that is closest to the object to the aperture stop (aperture stop S).

[0032] Conditional expression (4) defines the ratio of the axial distance from the aperture stop (aperture stop S) to the axial distance from the lens surface of the rear group GB closest to the image plane to the distance from the aperture stop (aperture stop S) to the lens surface of the front group GA closest to the object. By satisfying conditional expression (4), it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral illumination. Exceeding the upper limit of conditional expression (4) is undesirable because it increases the distance between the aperture stop (aperture stop S) and the image plane I, thereby increasing the overall optical length of the optical system OL. To ensure the effect of conditional expression (4), it is preferable to set the upper limit of conditional expression (4) to 0.90, 0.85, 0.80, 0.75, 0.70, or even 0.65. Furthermore, falling below the lower limit of conditional expression (4) is undesirable because it becomes difficult to move the exit pupil away from the image plane, reducing pupil aberration and reducing peripheral illumination. In order to ensure the effect of conditional expression (4), it is more desirable to set the lower limit of conditional expression (4) to 0.45, 0.50, or even 0.53.

[0033] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5).

[0034] 0.75 < fA / fB < 4.20 (5) where fA is the focal length of the front group GA, and fB is the focal length of the rear group GB.

[0035] Conditional expression (5) defines the ratio of the focal length of the front group GA to the focal length of the rear group GB. By satisfying conditional expression (5), it is possible to provide an optical system OL that is compact, has a wide angle of view, little distortion, and ensures sufficient peripheral illumination. Exceeding the upper limit of conditional expression (5) is undesirable because it becomes difficult to move the entrance pupil away from the lens surface closest to the object in the optical system OL, which reduces the height of the chief ray passing through the negative lens positioned on the object side, thereby reducing pupil aberration and reducing peripheral illumination. To ensure the effect of conditional expression (5), it is preferable to set the upper limit of conditional expression (5) to 4.10, 3.50, 3.00, 2.45, 2.40, 2.30, 2.25, or even 2.10. Furthermore, falling below the lower limit of conditional expression (5) is undesirable because it becomes difficult to move the exit pupil away from the image plane I, which reduces pupil aberration and reduces peripheral illumination. In order to ensure the effect of conditional expression (5), it is more desirable to set the lower limit of conditional expression (5) to 0.80, 0.85, or even 0.90.

[0036] In the optical system OL according to this embodiment, the front group GA has, in order from the object side, a first negative lens Ln1, a second negative lens Ln2, and a third negative lens Ln3, and it is desirable that the front group GA satisfy the following conditional expression (6):

[0037] 0.05<(-fL123) / fA<0.55 (6) where fL123 is the combined focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3, and fA is the focal length of the front group GA.

[0038] Conditional expression (6) defines the ratio of the composite focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3 to the focal length of the front group GA. By satisfying conditional expression (6), it is possible to realize a compact optical system OL, and provide an optical system OL that has a wide angle of view, effectively corrects distortion, and ensures sufficient peripheral light intensity. Exceeding the range of conditional expression (6) is undesirable because distortion becomes significant, making it difficult to effectively correct distortion when attempting to compact the optical system OL while maintaining peripheral light intensity. To ensure the effect of conditional expression (6), it is more desirable to set the upper limit of conditional expression (6) to 0.53, 0.50, 0.45, 0.40, 0.35, 0.33, or even 0.30. In order to ensure the effect of conditional expression (6), it is more desirable to set the lower limit of conditional expression (6) to 0.07, 0.10, 0.12, and more preferably 0.15.

[0039] Furthermore, in the optical system OL according to this embodiment, the front group GA has, in order from the object side, a first negative lens Ln1, a second negative lens Ln2, and a third negative lens Ln3, and the rear group GB has a focusing group Gf that moves along the optical axis during focusing, and an image side group Gr that is positioned closer to the image plane than the focusing group Gf and is fixed during focusing, and it is desirable that the following conditional expression (7) be satisfied:

[0040] 0.10<(-fL123) / fr<0.40 (7) where fL123 is the combined focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3, and fr is the focal length of the image-side group Gr.

[0041] Conditional expression (7) defines the ratio of the composite focal length of the first negative lens Ln1, the second negative lens Ln2, and the third negative lens Ln3 to the focal length of the image-side group Gr. By satisfying conditional expression (7), it is possible to realize a compact optical system OL, and provide an optical system OL that has a wide angle of view, excellent correction of distortion, and ensures sufficient peripheral light intensity. Exceeding the range of conditional expression (7) increases the amount of distortion, making it difficult to effectively correct distortion when attempting to reduce the size of the optical system OL while maintaining the amount of peripheral light intensity, which is undesirable. Exceeding the upper limit of conditional expression (7) also makes it difficult to ensure the back focus of the optical system OL, which is undesirable. To ensure the effect of conditional expression (7), it is preferable to set the upper limit of conditional expression (7) to 0.35, and even more preferably 0.30. Falling below the lower limit of conditional expression (7) also increases the overall optical length of the optical system OL, resulting in a large optical system OL. In order to ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to 0.13, and more preferably 0.15.

[0042] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (8).

[0043] 0.10<fA / TL<0.70 (8) where, fA: focal length of the front group GA, TL: total optical length (equivalent to air length) of the optical system OL.

[0044] Conditional expression (8) defines the ratio of the focal length of the front group GA to the total optical length of the optical system OL. By satisfying conditional expression (8), it is possible to realize a compact optical system OL, provide an optical system OL with a wide angle of view, excellent correction of distortion, and ensure sufficient peripheral illumination. Exceeding the upper limit of conditional expression (8) is undesirable because it becomes difficult to move the entrance pupil away from the lens surface closest to the object in the optical system OL, thereby lowering the height of the chief ray passing through the negative lens disposed on the object side, thereby reducing pupil aberration and reducing peripheral illumination. To ensure the effect of conditional expression (8), it is more desirable to set the upper limit of conditional expression (8) to 0.65, 0.60, or even 0.58. Furthermore, falling below the lower limit of conditional expression (8) is undesirable because it becomes difficult to move the exit pupil away from the image plane I, thereby reducing pupil aberration and reducing peripheral illumination. In order to ensure the effect of conditional expression (8), it is more desirable to set the lower limit of conditional expression (8) to 0.15, 0.20, or even 0.25.

[0045] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (9).

[0046] 50.00° < ω < 67.00° (9) where ω: half angle of view of the optical system OL

[0047] Conditional expression (9) defines an appropriate range for the half angle of view of the optical system OL. By satisfying conditional expression (9), it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral illumination. Exceeding the upper limit of conditional expression (9) is undesirable because the angle of view becomes wider than appropriate, making it difficult to ensure sufficient peripheral illumination. To ensure the effect of conditional expression (9), it is more preferable to set the upper limit of conditional expression (9) to 65.00°, 63.00°, 61.00°, or even 59.00°. Falling below the lower limit of conditional expression (9) is undesirable because the optical system OL becomes large. To ensure the effect of conditional expression (9), it is more preferable to set the lower limit of conditional expression (9) to 52.00°, 54.00°, or even 56.00°.

[0048] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (10).

[0049] 0.27 < BF / Ymax < 1.84 (10) where BF is the back focus (air-equivalent length) of the optical system OL, and Ymax is the maximum image height of the optical system OL.

[0050] Conditional expression (10) defines the ratio of the back focus to the maximum image height of the optical system OL. By satisfying conditional expression (10), it is possible to provide an optical system OL that is compact, has a wide angle of view, has little distortion, and ensures sufficient peripheral illumination. Exceeding the upper limit of conditional expression (10) is undesirable because it increases the size of the optical system OL. To ensure the effect of conditional expression (10), it is preferable to set the upper limit of conditional expression (10) to 1.38, 0.92, 0.83, or even 0.69. Falling below the lower limit of conditional expression (10) is undesirable because it physically interferes with the optical system OL and makes it difficult to install an optical filter near the lens mount, thereby impairing the functionality of the optical system OL. To ensure the effect of conditional expression (10), it is more preferable to set the lower limit of conditional expression (10) to 0.37, 0.46, or even 0.55.

[0051] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (11).

[0052] −0.10 < D (11) where D: amount of distortion at the outermost periphery

[0053] Conditional expression (11) defines an appropriate range for the amount of distortion of the optical system OL. Here, the amount of distortion at the outermost periphery is the amount of distortion at the maximum image height Ymax, and is expressed as D = (Ymax - Ymax') / Ymax', where Ymax is the actual image height and Ymax' is the ideal image height. By satisfying conditional expression (11), it is possible to realize a compact optical system OL, and to provide an optical system OL that has a wide angle of view, excellently corrects distortion, and ensures sufficient peripheral illumination. Falling below the lower limit of conditional expression (11) is undesirable because it significantly deteriorates the image when distortion is corrected by image processing or the like. To ensure the effect of conditional expression (11), it is more desirable to set the lower limit of conditional expression (11) to -0.08, -0.06, -0.04, or even -0.02. In order to ensure the amount of peripheral light in the optical system OL, it is preferable that the amount of distortion at the outermost periphery be a negative value (D<0.00).

[0054] 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.

[0055] 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. 12 . 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.

[0056] 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.

[0057] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0058] In this embodiment, the optical system OL is shown to be composed of a front group GA and a rear group GB, with the front group GA consisting of one or two lens groups and the rear group GB consisting of three lens groups. However, the above-described structural conditions can also be applied to other group structures, such as a rear group GB consisting of two or four lens groups. Furthermore, a structure in which a lens or lens group is added closest to the object or closest to the image plane may also be used. Specifically, a structure in which a lens group is added closest to the image plane, the position of which relative to the image plane is fixed during focusing or zooming, 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 focusing or zooming. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0059] 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 a portion of the rear group GB as a focusing group, with the remaining lenses fixed in position relative to the image plane during focusing. Considering the load on the motor, it is preferable for the focusing group to be composed of a single lens or one lens component.

[0060] Furthermore, a lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or may be rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization group that corrects image blur caused by camera shake.

[0061] 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.

[0062] The aperture stop S is preferably disposed between the front group GA and the rear group GB, but it is also possible to use the lens frame to perform the role of the aperture stop instead of providing a member serving as the aperture stop.

[0063] 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.

[0064] Hereinafter, an outline of a method for manufacturing the optical system OL according to this embodiment will be described with reference to FIG.

[0065] 13A, the manufacturing method of the optical system OL according to the first embodiment begins by preparing, in order from the object side, a front group GA, an aperture stop S, and a rear group GB (Step S100). Next, a focusing group Gf that moves along the optical axis during focusing and an image-side group Gr that is stationary during focusing and positioned closer to the image plane than the focusing group Gf are arranged in the rear group GB (Step S110). These lens groups are then arranged so as to satisfy a predetermined condition (for example, the above-mentioned conditional expression (1)) (Step S120).

[0066] 13B, the method for manufacturing the optical system OL according to the second embodiment begins by preparing, from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power (Step S200). Next, from the object side, a first negative lens Ln1, a second negative lens Ln2, and a third negative lens Ln3 are arranged in the front group GA (Step S210). These lens groups are then arranged so as to satisfy a predetermined condition (e.g., the above-mentioned conditional expression (2)) (Step S220).

[0067] As a result, it is possible to provide an optical system, an optical device, and a method for manufacturing an optical system that is compact, has a wide angle of view, little distortion, and ensures sufficient peripheral light.

[0068] Each example will be described below with reference to the drawings, in which Figures 1, 3, 5, 7, and 10 are cross-sectional views showing the configuration and refractive index distribution of the optical system OL (OL1 to OL5) according to each example.

[0069] In each embodiment, the aspherical surface is expressed by the following equation (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 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.

[0070] 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 +A16×y 16 (a)

[0071] 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. In each example, "E-n" is expressed as "×10 -n " indicates.

[0072] 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 GA having positive refractive power, an aperture stop S, and a rear group GB having positive refractive power. The rear group GB is also composed of, in order from the object side, a focusing group Gf having positive refractive power that moves along the optical axis during focusing, and an image-side group Gr that is positioned closer to the image plane than the focusing group Gf and has fixed positive refractive power during focusing.

[0073] The front group GA is composed of, in order from the object side, a meniscus negative lens L11 (Ln1) whose image side lens surface is aspherical and whose convex surface faces the object side, a meniscus negative lens L12 (Ln2) whose object side lens surface and image side lens surfaces are aspherical and whose convex surface faces the object side, a biconcave negative lens L13 (Ln3), a meniscus negative lens L14 whose convex surface faces the object side, a biconvex positive lens L15, a cemented negative lens formed by cementing together a meniscus negative lens L16 whose convex surface faces the image side and a meniscus positive lens L17 whose convex surface faces the image side, a biconvex positive lens L18, and a cemented negative lens formed by cementing together a biconvex positive lens L19 and a meniscus negative lens L20 whose convex surface faces the image side.

[0074] The focusing group Gf constituting the rear group GB is composed of, from the object side, a first focusing group Gf1 having negative refractive power and a second focusing group Gf2 having positive refractive power. The first focusing group Gf1 is composed of, from the object side, a biconcave negative lens L21 and a meniscus positive lens L22 with its convex surface facing the object side. The second focusing group Gf2 is composed of, from the object side, a biconvex positive lens L23 with an aspherical lens surface facing the image plane side and a biconcave negative lens L24 with an aspherical lens surface facing the object side.

[0075] The image side group Gr that constitutes the rear group GB is composed of, in order from the object side, a meniscus positive lens L25 with its convex surface facing the object side, a cemented negative lens formed by cementing a biconvex positive lens L26 and a biconcave negative lens L27, and a cemented positive lens formed by cementing a biconvex positive lens L28 with its object side surface formed in an aspherical shape and a meniscus negative lens L29 with its convex surface facing the image plane side.

[0076] In addition, a filter group FL is disposed between the optical system OL1 and the image plane I.

[0077] Furthermore, the optical system OL1 is configured so that, when focusing from an object at infinity to an object at a close distance, the first focusing group Gf1 and the second focusing group Gf2 move toward the object along the optical axis.

[0078] Table 1 below lists 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 [°], Ymax, the maximum image height, TL, the total optical length, and BF, the back focus, all of which represent values ​​when focused on an object at infinity. Here, the back focus BF represents the air-equivalent distance on the optical axis from the lens surface (surface No. 35) of the optical system OL closest to the image plane to the image plane I. The total optical length TL represents the distance on the optical axis from the lens surface (surface No. 1) of the optical system OL closest to the object plane to the lens surface (surface No. 35) closest to the image plane, plus the air-equivalent distance of the back focus. In the lens data, the first column m indicates the order of the lens surfaces (surface numbers) from the object side along the direction of light ray travel, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the axial distance 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 lengths indicate the numbers and focal lengths of the initial surfaces of the front group GA, rear group GB, focusing group Gf (first focusing group G1 and second focusing group Gf2), and image-side group Gr.

[0079] 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.

[0080] (Table 1) First Example [Overall specifications] f = 14.420 FNO = 1.456 ω [°] = 56.927 Ymax = 21.700 TL (equivalent length in air) = 160.0190 BF (equivalent length in air) = 12.4549 [Lens data] m r d nd νd Object surface ∞ D0 1 61.2275 3.0000 1.55332 71.68 2* 16.1879 20.0000 3* 56.0763 2.5000 1.69343 53.30 4* 31.6978 15.1486 5 -43.4072 2.5000 1.49710 81.56 6 123.8683 1.0000 7 135.7992 2.0000 1.59319 67.90 8 50.9373 1.0000 9 41.4691 12.2827 1.75520 27.57 10 -50.0453 2.4512 11 -35.7106 2.1000 1.92286 20.88 12 -371.3218 4.6455 2.00272 19.32 13 -72.4758 2.7212 14 64.3642 8.6709 1.59319 67.90 15 -54.4247 0.2000 16 105.0379 10.3425 1.51860 69.89 17 -25.1120 1.6000 1.73800 32.33 18 -1672.7244 1.9272 19 ∞ d1 Aperture Stop S 20 -79.2502 1.5000 1.73800 32.33 21 97.9582 0.1000 22 31.1309 4.8320 1.49700 81.61 23 255.5008 d2 24 44.4785 7.2319 1.59255 67.86 25* -54.2006 2.9982 26* -132.3383 2.0000 1.85108 40.12 27 124.6201 d3 28 28.7986 3.6122 2.00272 19.32 29 36.2066 3.2703 30 156.4438 2.8110 2.00272 19.32 31 -889.0851 1.4000 1.78880 28.43 32 45.5270 1.6704 33* 42.0691 8.7812 1.59255 67.86 34 -31.9376 1.4000 1.78880 28.43 35 -110.6798 11.2226 36 ∞ 1.6000 1.51680 64.13 37 ∞ 0.1774 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GA 1 47.796 Rear group GB 20 48.086 Focusing group Gf 20 104.849 First focusing group Gf1 20 -362.893 Second focusing group Gf2 24 81.927 Image side group Gr 28 77.994.

[0081] In this optical system OL1, surfaces 2, 3, 4, 25, 26, and 33 are formed aspherical surfaces. Table 2 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A16.

[0082] (Table 2) [Aspherical surface data] Surface 2 K = 0.0707 A4 = 2.9763E-06 A6 = -6.2035E-09 A8 = 9.0406E-11 A10 = -4.1678E-13 A12 = 1.0452E-15 A14 = -1.4364E-18 A16 = 7.6036E-22 Surface 3 K = 3.1738 A4 = -5.2412E-05 A6 = 2.3143E-07 A8 = -6.7187E-10 A10 = 1.3014E-12 A12 = -1.6179E-15 A14 = 1.1384E-18 A16=-3.3817E-22 4th side K=-0.8420 A4=-3.8009E-05 A6=2.7111E-07 A8=-8.3703E-10 A10=1.9656E-12 A12=-2.9480E-15 A14= 2.9090E-18 A16=-9.9641E-22 25th side K= 1.0000 A4=-6.1249E-06 A6=2.4810E-08 A8=-2.4042E-10 A10= 2.4634E-12 A12=-1.3370E-14 A14= 3.7671E-17 A16=-4.3106E-20 26th side K= 1.0000 A4=-1.8671E-05 A6=-1.0986E-11 A8=-4.7552E-11 A10= 8.5315E-13 A12=-4.4553E-15 A14= 1.2996E-17 A16=-1.5998E-20 33rd side K= 1.0000 A4=-1.0735E-05 A6=5.1680E-08 A8 =-8.7619E-10 A10= 5.9170E-12 A12=-2.5007E-14 A14= 5.4912E-17 A16=-5.2022E-20

[0083] Furthermore, in this optical system OL1, the axial air spacing d1 between the front group GA (aperture stop S) and the rear group GB (first focusing group Gf1), the axial air spacing d2 between the first focusing group Gf1 and the second focusing group Gf2, and the axial air spacing d3 between the second focusing group Gf2 and the image-side group Gr change during focusing. Table 3 below shows the variable spacings during focusing on an object at infinity and during focusing on a close-up object. Note that D0 indicates the distance from the lens surface (first surface) closest to the object in the optical system OL1 to the object, f indicates the focal length, and β indicates the magnification. This explanation also applies to the following examples.

[0084] (Table 3) [Variable distance data] Focused object Infinity Close distance f 14.420 - β - -0.125 D0 ∞ 94.3844 d1 8.6605 6.2591 d2 2.7066 0.1000 d3 0.5000 5.5080

[0085] 2A and 2B show 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 represents the F-number, NA represents the numerical aperture, and Y represents the image height. Note that the spherical aberration diagram indicates the F-number or numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and distortion diagram 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), g represents the g-line (λ=435.8 nm), F represents the F-line (λ=486.1 nm), and C represents the C-line (λ=656.3 nm). In the astigmatism diagrams, 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 of each embodiment shown below. From these aberration diagrams, it can be seen that the optical system OL1 has excellent correction of various aberrations and has excellent imaging performance.

[0086] 3 is a diagram showing 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 GA having positive refractive power, an aperture stop S, and a rear group GB having positive refractive power. The rear group GB is also composed of, in order from the object side, a focusing group Gf having positive refractive power that moves along the optical axis during focusing, and an image-side group Gr that is positioned closer to the image plane than the focusing group Gf and has fixed positive refractive power during focusing.

[0087] The front group GA is composed of, in order from the object side, a meniscus negative lens L11 (Ln1) having a convex surface facing the object side and whose object-side and image-side lens surfaces are aspherical, a meniscus negative lens L12 (Ln2) having a convex surface facing the object side and whose object-side and image-side lens surfaces are aspherical, a biconcave negative lens L13 (Ln3), a meniscus negative lens L14 having a convex surface facing the object side and whose object-side and image-side lens surfaces are aspherical, a biconvex positive lens L15, a cemented negative lens formed by cementing together a plano-concave negative lens L16 having a concave surface facing the object side and a plano-convex positive lens L17 having a convex surface facing the image side, a biconvex positive lens L18, and a cemented positive lens formed by cementing together a biconvex positive lens L19 and a meniscus negative lens L20 having a convex surface facing the image side.

[0088] The focusing group Gf constituting the rear group GB is composed of, from the object side, a first focusing group Gf1 having positive refractive power and a second focusing group Gf2 having positive refractive power. The first focusing group Gf1 is composed of, from the object side, a biconcave negative lens L21 and a biconvex positive lens L22. The second focusing group Gf2 is composed of, from the object side, a biconvex positive lens L23 whose image-side lens surface is aspherical, and a meniscus negative lens L24 whose object-side lens surface is aspherical and whose convex surface faces the image side.

[0089] The image side group Gr that constitutes the rear group GB is composed of, in order from the object side, a meniscus positive lens L25 with a convex surface facing the object side, a cemented negative lens formed by cementing together a meniscus positive lens L26 with a convex surface facing the object side and a meniscus negative lens L27 with a convex surface facing the object side, and a cemented positive lens formed by cementing together a biconvex positive lens L28 with an aspherical lens surface facing the object side and a meniscus negative lens L29 with a convex surface facing the image side.

[0090] In addition, a filter group FL is disposed between the optical system OL2 and the image plane I.

[0091] Furthermore, the optical system OL2 is configured so that, when focusing from an object at infinity to an object at a close distance, the first focusing group Gf1 and the second focusing group Gf2 move toward the object along the optical axis.

[0092] Table 4 below lists the specifications of the optical system OL2.

[0093] (Table 4) Second Example [Overall specifications] f = 14.420 FNO = 1.456 ω [°] = 56.927 Ymax = 21.700 TL (equivalent length in air) = 159.4670 BF (equivalent length in air) = 12.4549 [Lens data] m r d nd νd Object surface ∞ D0 1* 83.5711 3.0000 1.55332 71.68 2* 16.1426 20.0000 3* 60.5381 2.5000 1.59319 67.90 4* 30.7805 12.6544 5 -207.1091 2.5000 1.49710 81.56 6 65.1894 3.8416 7* 94.2727 2.3209 1.49731 82.51 8* 35.7996 1.0000 9 34.3991 11.3438 1.72825 28.38 10 -76.7072 3.5449 11 -36.8658 2.1000 1.92286 20.88 12 ∞ 4.4151 2.00272 19.32 13 -68.7000 0.1000 14 80.1796 5.9753 1.59319 67.90 15 -97.1926 0.2000 16 61.3271 12.0016 1.51860 69.89 17 -22.7068 1.6000 1.73800 32.26 18 -665.2635 1.8158 19 ∞ d1 Aperture Stop S 20 -69.7018 1.5000 1.73800 32.26 21 94.2346 0.1000 22 34.1075 6.5745 1.49700 81.61 23 -129.3048 d2 24 46.8054 7.8011 1.59255 67.86 25* -59.8437 2.7001 26* -63.9084 2.0000 1.85108 40.12 27 -409.2237 d3 28 30.0815 3.9690 2.00272 19.32 29 39.5799 4.5842 30 188.4016 2.4542 2.00272 19.32 31 7492.6644 1.4000 1.78880 28.42 32 50.9351 3.2325 33* 73.3772 8.7054 1.59255 67.86 34 -26.4682 1.4000 1.78880 28.42 35 -59.6844 11.2830 36 ∞ 1.6000 1.51680 64.13 37 ∞ 0.1169 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GA 1 75.725 Rear group GB 20 43.653 Focusing group Gf 20 79.532 First focusing group Gf1 20 5266.86 Second focusing group Gf2 24 82.989 Image side group Gr 28 78.881.

[0094] In this optical system OL2, surfaces 1, 2, 3, 4, 7, 8, 25, 26, and 33 are formed aspherical surfaces. Table 5 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A16.

[0095] (Table 5) [Aspherical surface data] Surface 1 K = 1.6641 A4 = 2.2919E-06 A6 = -4.1452E-09 A8 = 7.0290E-12 A10 = -7.4436E-15 A12 = 4.5088E-18 A14 = -1.4511E-21 A16 = 2.0470E-25 Surface 2 K = 0.1219 A4 = 9.1272E-07 A6 = -1.9461E-08 A8 = 2.2494E-10 A10 = -1.0561E-12 A12 = 2.8193E-15 A14 = -3.8568E-18 A16 = 2.0170E-21 3rd side K = 2.6581 A4 = -3.1022E-05 A6 = 1.3787E-07 A8 = -3.5571E-10 A10 = 4.5309E-13 A12=-2.7628E-16 A14= 6.6618E-20 A16=-5.9652E-24 4th side K= 1.3335 A4=-1.1834E-05 A6=1.5372E-07 A8=-3.1653E-10 A10= 5.6630E-13 A12 = -1.8111E-15 A14 = 6.8805E-18 A16 = -9.2049E-21 7th side K = 1.0000 A4 = 3.9335E-06 A6 = 2.0359E-08 A8 = 1.4757E-10 A10=-7.7880E-13 A12= 2.1206E-15 A14=-3.3066E-18 A16= 2.4552E-21 8th side K= 1.0000 A4=-8.4668E-06 A6=1.5292E-08 A8= 1.6616E-10 A10=-1.1188E-12 A12= 3.6221E-15 A14=-6.3205E-18 A16= 4.9439E-21 25th side K= 1.0000 A4=-1.1189E-05 A6=-1.2772E-08 A8 =-4.3965E-11 A10= 1.3861E-12 A12=-6.0446E-15 A14= 1.2113E-17 A16=-1.0118E-20 26th side K= 1.0000 A4 = -1.9838E-05 A6 = -4.3603E-08 A8 = 2.8627E-10 A10 = -1.4994E-12 A12 = 9.0404E-15 A14 = -2.6130E-17 A16 = 2.7283E-20 Page 33 K = 1.0000 A4 = -1.4000E-05 A6 = 9.5057E-08 A8 = -1.2228E-09 A10 = 8.0801E-12 A12 = -3.3962E-14 A14 = 7.5390E-17 A16=-7.1256E-20.

[0096] In this optical system OL2, the axial air distance d1 between the front group GA (aperture stop S) and the rear group GB (first focusing group Gf1), the axial air distance d2 between the first focusing group Gf1 and the second focusing group Gf2, and the axial air distance d3 between the second focusing group Gf2 and the image-side group Gr change during focusing. Table 6 below shows the variable distances when focusing on an object at infinity and when focusing on a close object.

[0097] (Table 6) [Variable distance data] Focused object Infinity Close distance f 14.420 - β - -0.100 D0 ∞ 124.6057 d1 7.5359 5.4495 d2 1.6418 0.1000 d3 0.5000 4.1282

[0098] 4A and 4B show 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 correction for various aberrations and has excellent imaging performance.

[0099] 5 is a diagram showing 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 GA having positive refractive power, an aperture stop S, and a rear group GB having positive refractive power. The rear group GB is also composed of, in order from the object side, a focusing group Gf having positive refractive power that moves along the optical axis during focusing, and an image-side group Gr that is positioned closer to the image plane than the focusing group Gf and has fixed positive refractive power during focusing.

[0100] The front group GA is composed of, in order from the object side, a meniscus negative lens L11 (Ln1) whose image side lens surface is aspherical and whose convex surface faces the object side, a meniscus negative lens L12 (Ln2) whose object side lens surface and image side lens surfaces are aspherical and whose convex surface faces the object side, a biconvex negative lens L13 (Ln3), a biconcave negative lens L14, a cemented positive lens formed by cementing together a biconvex positive lens L15, a biconcave negative lens L16, and a biconvex positive lens L17, and a cemented positive lens formed by cementing together a biconvex positive lens L18 and a meniscus negative lens L19 whose convex surface faces the image side.

[0101] The focusing group Gf constituting the rear group GB is composed of, from the object side, a first focusing group Gf1 having positive refractive power and a second focusing group Gf2 having positive refractive power. The first focusing group Gf1 is composed of, from the object side, a biconcave negative lens L21 and a biconvex positive lens L22. The second focusing group Gf2 is composed of, from the object side, a biconvex positive lens L23 and a meniscus negative lens L24 whose object-side lens surface is aspherical and whose convex surface faces the image plane.

[0102] The image side group Gr that constitutes the rear group GB is composed of, in order from the object side, a meniscus positive lens L25 with a convex surface facing the object side, a cemented negative lens formed by cementing together a meniscus positive lens L26 with a convex surface facing the object side and a meniscus negative lens L27 with a convex surface facing the object side, and a cemented positive lens formed by cementing together a biconvex positive lens L28 with an aspherical lens surface facing the object side and a meniscus negative lens L29 with a convex surface facing the image side.

[0103] In addition, a filter group FL is disposed between the optical system OL3 and the image plane I.

[0104] Furthermore, the optical system OL3 is configured so that, when focusing from an object at infinity to an object at a close distance, the first focusing group Gf1 and the second focusing group Gf2 move toward the object along the optical axis.

[0105] Table 7 below lists the specifications of the optical system OL3.

[0106] (Table 7) Third Example [Overall specifications] f = 14.420 FNO = 1.855 ω [°] = 56.926 Ymax = 21.700 TL (air equivalent length) = 158.2815 BF (air equivalent length) = 12.4574 [Lens data] m r d nd νd Object surface ∞ D0 1 57.3653 3.0000 1.55332 71.68 2* 15.4294 20.0000 3* 45.9812 2.5000 1.62291 58.30 4* 29.1000 11.8748 5 -96.2896 2.5000 1.49782 82.57 6 62.5248 7.2059 7 -829.6276 2.5000 1.49782 82.57 8 55.1883 1.0000 9 36.3188 10.7524 1.85478 24.80 10 -40.3484 2.1000 2.00272 19.32 11 57.3517 6.6941 1.92286 20.88 12 -84.1131 7.9905 13 41.2330 9.6546 1.52841 76.45 14 -21.5267 1.6000 1.73800 32.33 15 -322.6085 1.7522 16 ∞ d1 Aperture Stop S 17 -138.5362 1.5000 1.73800 32.33 18 60.5580 0.1000 19 31.0430 5.0222 1.49700 81.61 20 -134.8423 d2 21 58.3757 4.8366 1.53775 74.70 22 -58.9721 8.6941 23* -37.1708 2.0000 1.85108 40.12 24 -90.2846 d3 25 35.9212 3.7159 2.00272 19.32 26 47.7741 3.2469 27 77.3038 3.7439 2.00272 19.32 28 258.8871 1.4000 1.78880 28.43 29 42.4147 1.6131 30* 41.6838 10.0699 1.59255 67.86 31 -32.0979 1.4000 1.78880 28.43 32 -105.4076 11.2866 33 ∞ 1.6000 1.51680 64.13 34 ∞ 0.1157 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GA 1 90.039 Rear group GB 17 45.087 Focusing group Gf 17 103.030 First focusing group Gf1 17 440.701 Second focusing group Gf2 21 140.679 Image side group Gr 25 61.160.

[0107] In this optical system OL3, surfaces 2, 3, 4, 23, and 30 are formed aspherical surfaces. Table 8 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A16.

[0108] (Table 8) [Aspherical surface data] Surface 2 K = 0.0917 A4 = 5.9305E-06 A6 = -3.1451E-08 A8 = 3.5053E-10 A10 = -1.6458E-12 A12 = 4.2871E-15 A14 = -5.8639E-18 A16 = 3.1181E-21 Surface 3 K = 2.2689 A4 = -5.6376E-05 A6 = 2.5506E-07 A8 = -8.4703E-10 A10 = 1.8782E-12 A12 = -2.6054E-15 A14 = 2.0050E-18 A16=-6.4571E-22 4th side K=-1.1262 A4=-3.6982E-05 A6=2.9305E-07 A8=-9.4435E-10 A10=1.8120E-12 A12=-2.4787E-16 A14=-4.5471E-18 A16= 6.6560E-21 23rd side K= 1.0000 A4=-1.1430E-05 A6=-4.0275E-09 A8=-1.6921E-10 A10= 1.9532E-12 A12=-1.2468E-14 A14= 3.8296E-17 A16=-4.6118E-20 30th side K= 1.4814 A4=-9.1406E-06 A6=2.9005E-08 A8=-5.4883E-10 A10= 3.6224E-12 A12=-1.4680E-14 A14= 3.1383E-17 A16=-2.8888E-20

[0109] In this optical system OL3, the axial air distance d1 between the front group GA (aperture stop S) and the rear group GB (first focusing group Gf1), the axial air distance d2 between the first focusing group Gf1 and the second focusing group Gf2, and the axial air distance d3 between the second focusing group Gf2 and the image-side group Gr change during focusing. Table 9 below shows the variable distances when focusing on an object at infinity and when focusing on a close object.

[0110] (Table 9) [Variable distance data] Focused object Infinity Close distance f 14.420 - β - -0.100 D0 ∞ 125.7633 d1 6.1076 1.6572 d2 0.7494 0.1000 d3 0.5000 5.5998

[0111] 6A and 6B show 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.

[0112] [Fourth Example] Figure 7 shows the configuration of an optical system OL4 according to a fourth example. This optical system OL4 is composed of, from the object side, a front group GA having positive refractive power, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed, from the object side, of a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power. The rear group GB is composed, from the object side, of a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having positive refractive power. The third lens group G3 and the fourth lens group G4 form a focusing group Gf having positive refractive power that moves along the optical axis during focusing. The fifth lens group G5 forms an image-side group Gr having fixed positive refractive power during focusing, which is located closer to the image plane than the focusing group Gf.

[0113] The first lens group G1 is composed of, from the object side, a meniscus negative lens L11 (Ln1) whose image-side lens surfaces are aspherical and whose convex surface faces the object side, a meniscus negative lens L12 (Ln2) whose object-side and image-side lens surfaces are aspherical and whose convex surface faces the object side, and a meniscus negative lens L13 (Ln3) whose convex surface faces the image side. The second lens group G2 is composed of, from the object side, a biconcave negative lens L21, a cemented positive lens formed by cementing a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex positive lens L24, and a cemented positive lens formed by cementing a biconvex positive lens L25 and a meniscus negative lens L26 whose convex surface faces the image side. The third lens group G3 is composed of, from the object side, a meniscus negative lens L31 with a convex surface facing the image side and a biconvex positive lens L32. The fourth lens group G4 is composed of, from the object side, a biconvex positive lens L41 and a meniscus negative lens L42 with an aspherical lens surface facing the object side and a convex surface facing the image side. The fifth lens group G5 is composed of, from the object side, a meniscus positive lens L51 with a convex surface facing the object side, a cemented negative lens formed by cementing a meniscus positive lens L52 with a convex surface facing the image side and a biconcave negative lens L53, and a cemented positive lens formed by cementing a biconvex positive lens L54 with an aspherical lens surface facing the object side and a meniscus negative lens L55 with a convex surface facing the image side.

[0114] In addition, a filter group FL is disposed between the optical system OL4 and the image plane I.

[0115] In this optical system OL4, the spacing between adjacent lens groups changes when the magnification is changed from the wide-angle end state to the telephoto end state. Furthermore, in the optical system OL4, when the magnification is changed from the wide-angle end state to the telephoto end state, the first lens group G1 and the fifth lens group G5 are fixed with respect to the image plane I, while the second lens group G2, the third lens group G3, and the fourth lens group G4 move toward the object along the optical axis. The aperture stop S moves in the optical axis direction together with the second lens group G2. In Figure 7 , arrows are shown at the bottom of the cross-sectional view of the optical system OL4 indicating the movement directions of the second lens group G2, the third lens group G3, and the fourth lens group G4 along the optical axis when the magnification is changed from the wide-angle end state (W) to the telephoto end state (T).

[0116] In addition, the optical system OL4 is configured so that the third lens group G3 is the first focusing group Gf1 and the fourth lens group G4 is the second focusing group Gf2, and when focusing from an object at infinity to an object at close range, the first focusing group Gf1 and the second focusing group Gf2 are moved toward the object along the optical axis.

[0117] Table 10 below lists the specifications of optical system OL4. In Table 10, the overall specifications show values ​​when focusing on an object at infinity in the wide-angle end state and the telephoto end state. Surface 5 in the lens data is a virtual surface and is not shown in FIG. 7 .

[0118] (Table 10) Fourth Example [Overall specifications] Wide-angle end to telephoto end f = 14.421 to 15.519 FNO = 2.010 to 2.080 ω [°] = 56.927 to 53.728 Ymax = 21.700 to 21.700 TL (air-equivalent length) = 158.2469 to 158.2469 BF (air-equivalent length) = 15.2281 to 15.2281 [Lens data] m r d nd νd Object plane ∞ D0 1 60.2631 3.0000 1.55332 71.68 2* 16.1854 19.6248 3* 42.7995 2.5000 1.62291 58.30 4* 25.4410 10.1836 5 ∞ 3.1872 6 -58.3967 2.5000 1.49782 82.57 7 -69.0503 d1 8 -51.9578 2.5000 1.49782 82.57 9 44.9537 1.2463 10 34.1197 10.9019 1.85478 24.80 11 -40.3484 2.1000 2.00272 19.32 12 57.3517 5.4520 1.92286 20.88 13 -107.0241 8.8533 14 42.4729 7.8908 1.52841 76.45 15 -22.5767 1.6000 1.73800 32.33 16 -79.1879 1.1478 17 ∞ d2 Aperture Stop S 18 -31.3117 1.5000 1.73800 32.33 19 -316.6461 0.1000 20 30.8365 6.1816 1.49700 81.61 21 -89.8241 d3 22 138.0937 5.5942 1.53775 74.70 23 -39.4904 0.6211 24* -101.9502 2.0000 1.85108 40.12 25 -150.1828 d4 26 27.9600 2.7892 2.00272 19.32 27 32.1909 5.2989 28 -84.1452 4.7568 2.00272 19.32 29 -32.3444 1.4000 1.78880 28.43 30 75.0448 1.0000 31* 49.6862 8.6402 1.59255 67.86 32 -28.4109 1.4000 1.78880 28.43 33 -90.5596 13.8933 34 ∞ 1.6000 1.51680 64.13 35 ∞ 0.2800 Image plane ∞ [Lens group focal lengths] Lens group Initial surface Focal length Front group GA 1 47.511 First lens group G1 1 -24.410 Second lens group G2 8 49.130 Rear group GB 18 48.392 Focusing group Gf 18 61.626 Third lens group G3 (Gf1) 18 949.841 Fourth lens group G4 (Gf2) 22 68.269 Image side group Gr (fifth lens group G5) 26 218.754.

[0119] In this optical system OL4, surfaces 2, 3, 4, 24, and 31 are formed aspherical surfaces. Table 11 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A16.

[0120] (Table 11) [Aspherical surface data] Surface 2 K = 0.0644 A4 = 4.7662E-06 A6 = -1.7507E-08 A8 = 2.1692E-10 A10 = -1.0407E-12 A12 = 2.7170E-15 A14 = -3.7099E-18 A16 = 1.9503E-21 Surface 3 K = 1.8614 A4 = -7.2307E-05 A6 = 3.2106E-07 A8 = -9.4929E-10 A10 = 1.8183E-12 A12 = -2.2097E-15 A14 = 1.5310E-18 A16=-4.5126E-22 4th side K=-1.9321 A4=-4.6492E-05 A6=3.4267E-07 A8=-9.3765E-10 A10=9.8371E-13 A12= 3.1926E-15 A14=-1.1809E-17 A16= 1.2892E-20 24th side K= 1.0000 A4 =-1.1434E-05 A6 =-1.2826E-08 A8 = 5.3259E-11 A10=-8.9548E-13 A12= 6.8882E-15 A14=-2.6482E-17 A16= 3.9313E-20 31st side K= 1.6749 A4=-1.2900E-05 A6=4.6234E-08 A8=-7.9652E-10 A10= 5.6051E-12 A12=-2.5013E-14 A14= 5.9672E-17 A16=-6.2408E-20

[0121] In this optical system OL4, 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 (front group GA) and the third lens group G3 (first focusing group Gf1), the axial air distance d3 between the third lens group G3 (first focusing group Gf1) and the fourth lens group G4 (second focusing group Gf2), and the axial air distance d4 between the fourth lens group G4 (second focusing group Gf2) and the fifth lens group G5 (image side group Gr) change during magnification change and focusing. Table 12 below shows the variable distances when focusing on an object at infinity and when focusing on a close object in the wide-angle end state and the telephoto end state.

[0122] (Table 12) [Variable distance data] Magnification state Wide-angle end Telephoto end Focused object Infinity Close distance Infinity Close distance f 14.421 - 15.519 - β - -0.100 - -0.100 D0 ∞ 120.0375 ∞ 131.4709 d1 5.1151 5.1151 1.6543 1.6543 d2 10.7512 10.1170 13.1865 12.4111 d3 2.6828 1.0363 2.1283 0.5000 d4 0.5000 2.7807 2.0800 4.4837

[0123] 8A and 8B show 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 a close distance in the wide-angle end state, and Fig. 9A and 9B show diagrams of spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma when focused on an object at infinity and a close distance in the telephoto end state. These aberration diagrams show that this optical system OL4 has excellent imaging performance with various aberrations well corrected.

[0124] 10 is a diagram showing 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 GA having positive refractive power, an aperture stop S, and a rear group GB having positive refractive power. The rear group GB is also composed of, in order from the object side, a focusing group Gf having positive refractive power that moves along the optical axis during focusing, and an image-side group Gr that is positioned closer to the image plane than the focusing group Gf and has fixed positive refractive power during focusing.

[0125] The front group GA is composed of, in order from the object side, a meniscus negative lens L11 (Ln1) whose image side lens surface is aspherical and whose convex surface faces the object side, a meniscus negative lens L12 (Ln2) whose object side lens surface and image side lens surfaces are aspherical and whose convex surface faces the object side, a biconcave negative lens L13 (Ln3), a meniscus negative lens L14 whose convex surface faces the object side, a cemented positive lens formed by cementing a biconvex positive lens L15, a biconcave negative lens L16, and a biconvex positive lens L17, and a cemented positive lens formed by cementing a biconvex positive lens L18 and a biconcave negative lens L19.

[0126] The focusing group Gf constituting the rear group GB is composed of, from the object side, a first focusing group Gf1 having positive refractive power and a second focusing group Gf2 having positive refractive power. The first focusing group Gf1 is composed of, from the object side, a biconcave negative lens L21 and a biconvex positive lens L22. The second focusing group Gf2 is composed of, from the object side, a biconvex positive lens L23 and a meniscus negative lens L24 whose object-side lens surface is aspherical and whose convex surface faces the image plane.

[0127] The image side group Gr that constitutes the rear group GB is composed of, in order from the object side, a meniscus positive lens L25 with its convex surface facing the object side, and a cemented positive lens formed by cementing together a meniscus negative lens L26 with its convex surface facing the object side and a biconvex positive lens L27 whose lens surface on the image side is formed into an aspherical shape.

[0128] In addition, a filter group FL is disposed between the optical system OL5 and the image plane I.

[0129] Furthermore, the optical system OL5 is configured so that, when focusing from an object at infinity to an object at a close distance, the first focusing group Gf1 and the second focusing group Gf2 move toward the object along the optical axis.

[0130] Table 13 below lists the specifications of the optical system OL5.

[0131] (Table 13) Fifth Example [Overall specifications] f = 14.420 FNO = 1.881 ω [°] = 56.928 Ymax = 21.700 TL (equivalent length in air) = 164.6007 BF (equivalent length in air) = 12.4547 [Lens data] m r d nd νd Object surface ∞ D0 1 60.0020 3.0000 1.55332 71.68 2 * 16.1004 19.5299 3 * 45.9358 2.5000 1.62291 58.30 4 * 24.8219 12.5146 5 -94.5402 2.5000 1.49782 82.57 6 101.2638 9.3244 7 1015.4016 2.5000 1.49782 82.57 8 54.0224 1.0000 9 38.1589 11.0563 1.85478 24.80 10 -40.3484 2.1000 2.00272 19.32 11 57.3517 6.8513 1.92286 20.88 12 -80.8393 8.7094 13 42.3038 9.3121 1.52841 76.45 14 -23.0556 1.6000 1.73800 32.33 15 401.4012 2.2032 16 ∞ d1 Aperture Stop S 17 -265.1697 1.5000 1.73800 32.33 18 53.7798 0.1000 19 31.2577 5.2879 1.49700 81.61 20 -100.5943 d2 21 59.8974 4.0342 1.53775 74.70 22 -90.7796 11.7926 23* -37.2220 2.0000 1.85108 40.12 24 -74.2456 d3 25 37.6348 5.2999 2.00272 19.32 26 75.4222 4.3588 27 112.7979 1.4000 1.78880 28.43 28 23.7856 12.0000 1.59255 67.86 29* -99.7663 11.2935 30 ∞ 1.6000 1.51680 64.13 31 ∞ 0.1064 Image plane ∞ [Lens group focal length] Lens group Initial surface Focal length Front group GA 1 176.936 Rear group GB 17 43.720 Focusing group Gf 17 93.824 First focusing group Gf1 17 227.456 Second focusing group Gf2 21 176.744 Image side group Gr 25 56.222.

[0132] In this optical system OL5, surfaces 2, 3, 4, 23, and 29 are formed aspherical surfaces. Table 14 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A16.

[0133] (Table 14) [Aspherical surface data] Surface 2 K = 0.0757 A4 = 3.7732E-06 A6 = -1.6525E-08 A8 = 2.1561E-10 A10 = -9.9755E-13 A12 = 2.5508E-15 A14 = -3.4193E-18 A16 = 1.7852E-21 Surface 3 K = 2.2621 A4 = -6.6865E-05 A6 = 3.3902E-07 A8 = -1.1260E-09 A10 = 2.3370E-12 A12 = -2.9582E-15 A14 = 2.0854E-18 A16=-6.2899E-22 4th side K=-0.7881 A4=-4.6005E-05 A6=3.8336E-07 A8=-1.2778E-09 A10=2.8422E-12 A12=-4.0218E-15 A14= 4.4995E-18 A16=-2.1720E-21 23rd side K= 1.0000 A4=-1.1352E-05 A6=1.7422E-09 A8=-2.8899E-10 A10= 2.9714E-12 A12 = -1.7526E-14 A14 = 5.1029E-17 A16 = -6.3491E-20 29th side K = 14.3273 A4 = 1.1255E-05 A6 = -4.1754E-08 A8 = 5.0341E-10 A10=-2.5125E-12 A12= 8.1305E-15 A14=-1.4505E-17 A16= 1.1060E-20

[0134] In this optical system OL5, the axial air distance d1 between the front group GA (aperture stop S) and the rear group GB (first focusing group Gf1), the axial air distance d2 between the first focusing group Gf1 and the second focusing group Gf2, and the axial air distance d3 between the second focusing group Gf2 and the image-side group Gr change during focusing. Table 15 below shows the variable distances when focusing on an object at infinity and when focusing on a close object.

[0135] (Table 15) [Variable distance data] Focused object Infinity Close distance f 14.420 - β - -0.100 D0 ∞ 126.7802 d1 6.7859 1.3508 d2 0.1760 0.4462 d3 2.7094 7.8744

[0136] 11A and 11B show 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 correction for various aberrations and has excellent imaging performance.

[0137] [Values ​​Corresponding to Conditional Expressions] The values ​​corresponding to conditional expressions (1) to (11) in the first to fifth examples are shown in Table 16 below.

[0138] (Table 16) (1) fr / ff (2) (-fL123) / fB (3) DSI / DL1S (4) DSLR / DL1S (5) fA / fB (6) (-fL123) / fA (7) (-fL123) / fr (8) fA / TL (9) ω (10) Bfa / Ymax (11) D Example 1 Example 2 Example 3 Example 4 Example 5 fL123 -14.045 -15.727 -15.716 -24.410 -16.065 (1) 0.744 0.992 0.594 3.550 0.599 (2) 0.292 0.360 0.349 0.504 0.367 (3) 0.701 0.754 0.737 0.802 0.738 (4) 0.568 0.617 0.600 0.629 0.607 (5) 0.994 1.735 1.997 0.982 4.047 (6) 0.294 0.208 0.175 0.514 0.091 (7) 0.180 0.199 0.257 0.112 0.286 (8) 0.299 0.475 0.569 0.300 1.075 (9) 56.927 56.927 56.926 56.927 56.928 (10) 0.574 0.574 0.574 0.702 0.574 (11) -2.000 -2.003 -2.000 -2.006 -2.000

[0139] 1 Camera (optical device) OL (OL1 to OL5) Optical system GA Front group GB Rear group Gf Focusing group Gr Image side group S Aperture stop (aperture) Ln1 First negative lens Ln2 Second negative lens Ln3 Third negative lens

Claims

1. From the object side, it is composed of a front group, a stop, and a rear group. the rear group includes a focusing group that moves along the optical axis during focusing, and an image-side group that is located closer to the image plane than the focusing group and is fixed during focusing, An optical system that satisfies the following condition: 0.10 < fr / ff < 4.00 however, fr: focal length of the image-side lens group ff: focal length of the focusing group

2. It is composed of, in order from the object side, a front group, a stop, and a rear group having positive refractive power, the front group includes, in order from the object side, a first negative lens, a second negative lens, and a third negative lens; An optical system that satisfies the following condition: 0.10 < (-fL123) / fB < 0.65 however, fL123: a composite focal length of the first negative lens, the second negative lens, and the third negative lens fB: focal length of the rear group

3. the front group includes, in order from the object side, a first negative lens, a second negative lens, and a third negative lens; 2. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < (-fL123) / fB < 0.65 however, fL123: a composite focal length of the first negative lens, the second negative lens, and the third negative lens fB: focal length of the rear group

4. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.50 < DSI / DL1S < 1.00 however, DSI: Distance on the optical axis from the aperture to the image plane DL1S: the distance on the optical axis from the lens surface in the front group closest to the object to the stop

5. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.40 < DSLR / DL1S < 0.95 however, DSLR: the distance on the optical axis from the stop to the lens surface in the rear group closest to the image plane DL1S: the distance on the optical axis from the lens surface in the front group closest to the object to the stop

6. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.75 < fA / fB < 4.20 however, fA: focal length of the front group fB: focal length of the rear group

7. the front group includes, in order from the object side, a first negative lens, a second negative lens, and a third negative lens; 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.05 < (-fL123) / fA < 0.55 however, fL123: a composite focal length of the first negative lens, the second negative lens, and the third negative lens fA: focal length of the front group

8. the front group includes, in order from the object side, a first negative lens, a second negative lens, and a third negative lens; the rear group includes a focusing group that moves along the optical axis during focusing, and an image-side group that is located closer to the image plane than the focusing group and is fixed during focusing, 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < (-fL123) / fr < 0.40 however, fL123: a composite focal length of the first negative lens, the second negative lens, and the third negative lens fr: focal length of the image-side lens group

9. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < fA / TL < 0.70 however, fA: focal length of the front group TL: total optical length of the optical system

10. 4. The optical system according to claim 1, wherein the following condition is satisfied: 50.00° < ω < 67.00° however, ω: half angle of view of the optical system

11. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.27 < BF / Ymax < 1.84 however, BF: back focus of the optical system Ymax: maximum image height of the optical system

12. 4. The optical system according to claim 1, wherein the following condition is satisfied: -0.10 < D however, D: Amount of distortion at the outermost periphery

13. An optical instrument comprising the optical system according to any one of claims 1 to 3.