Optical systems and optical instruments

Abstract

Provided are: an optical system which achieves miniaturization, low weight, and favorable optical performance; an optical device; and an optical system manufacturing method.　An optical system OL, which is mounted in an optical device such as a camera 1, comprises the following in order from the object side: a first negative meniscus lens 1 the protruding surface of which faces the object side and which has a negative refractive power; a second negative meniscus lens L2 the protruding surface of which faces the object side and which has a negative refractive power; a third biconcave negative lens L3 having a negative refractive power; and at least one lens (e.g., a biconvex positive lens L4). The optical system is configured to satisfy a condition based on a prescribed conditional formula.

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, compact optical systems with a wide angle of view have been proposed (see, for example, Patent Document 1). However, Patent Document 1 has a problem in that it is desired to achieve both compactness and light weight and good optical performance.

[0003] Japanese Patent Application Laid-Open No. 2020-056995

[0004] An optical system according to a first aspect of the present invention comprises, in order from the object side, a first negative meniscus lens having negative refractive power with a convex surface facing the object side, a second negative meniscus lens having negative refractive power with a convex surface facing the object side, a third biconcave negative lens having negative refractive power, and at least one lens, and satisfies the following condition: 90.0° < ω 0.10 < R12 / (-fL1) < 0.80, where ω: half angle of view of the optical system, fL1: focal length of the first negative meniscus lens, and R12: radius of curvature of the lens surface of the first negative meniscus lens facing the image plane side.

[0005] An optical system according to a second aspect of the present invention comprises, in order from the object side, a first negative meniscus lens having negative refractive power with a convex surface facing the object side, a second negative meniscus lens having negative refractive power with a convex surface facing the object side, a third biconcave negative lens having negative refractive power, and at least one lens, and satisfies the following conditions: 90.0° < ω 1.80 < R12 / D12 < 3.00, where ω: half angle of view of the optical system, D12: axial air spacing between the first negative meniscus lens and the second negative meniscus lens, R12: radius of curvature of the lens surface of the first negative meniscus lens on the image side.

[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 comprising, in order from the object side, a first negative meniscus lens having negative refractive power with a convex surface facing the object side, a second negative meniscus lens having negative refractive power with a convex surface facing the object side, and a third biconcave negative lens having negative refractive power, and at least one lens, which are arranged so as to satisfy the following condition: 90.0° < ω 0.10 < R12 / (-fL1) < 0.80 where, ω: half angle of view of the optical system, fL1: focal length of the first negative meniscus lens, R12: radius of curvature of the lens surface of the first negative meniscus lens facing the image plane side.

[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 comprising, in order from the object side, a first negative meniscus lens having negative refractive power with a convex surface facing the object side, a second negative meniscus lens having negative refractive power with a convex surface facing the object side, and a third biconcave negative lens having negative refractive power, and at least one lens, which are arranged so as to satisfy the following conditions: 90.0° < ω 1.80 < R12 / D12 < 3.00 where, ω: half angle of view of the optical system, D12: axial air spacing between the first negative meniscus lens and the second negative meniscus lens, R12: radius of curvature of the lens surface of the first negative meniscus lens facing the image plane side.

[0008] FIG. 1 is a cross-sectional view showing the lens configuration of the optical system according to Example 1 when focusing on an object at infinity. 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 cross-sectional view showing the lens configuration of the optical system according to Example 2 when focusing on an object at infinity. FIG. 4 is a diagram showing various aberrations of the optical system according to Example 2 when focusing on an object at infinity. FIG. 5 is a cross-sectional view showing the lens configuration of the optical system according to Example 3 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 of a camera equipped with the optical system. FIG. 8 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 configured to include, in order from the object side, a first negative meniscus lens L1 having a convex surface facing the object side and negative refractive power, a second negative meniscus lens L2 having a convex surface facing the object side and negative refractive power, a third biconcave negative lens L3 having negative refractive power, and at least one other lens. By configuring the optical system OL in this manner, it is possible to achieve both a small and lightweight optical system OL and good optical performance.

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

[0012] 90.0° < ω (1) where ω: half angle of view of the optical system OL

[0013] Conditional expression (1) defines the half angle of view of the optical system OL. By satisfying conditional expression (1), the angle of view required for a fisheye lens can be obtained. In order to ensure the effect of conditional expression (1), it is preferable to set the lower limit of conditional expression (1) to 95.0°, and more preferably 100.0°. In order to ensure the effect of conditional expression (1), it is preferable to set the upper limit of conditional expression (1) to 120.0° (ω<120.0°), and even more preferably 110.0°.

[0014] Moreover, it is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (2).

[0015] 0.10<R12 / (-fL1)<0.80 (2) where, fL1: focal length of the first negative meniscus lens L1, and R12: radius of curvature of the lens surface of the first negative meniscus lens L1 on the image side.

[0016] Conditional expression (2) defines the ratio of the radius of curvature of the image-side lens surface of the first negative meniscus lens L1 to the focal length of the first negative meniscus lens L1. By satisfying conditional expression (2), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Below the lower limit of conditional expression (2), the entire optical system OL becomes large, and correction of axial chromatic aberration and lateral chromatic aberration becomes difficult, which is undesirable. To ensure the effect of conditional expression (2), it is more preferable to set the lower limit of conditional expression (2) to 0.15, 0.25, 0.35, or even 0.40. Above the upper limit of conditional expression (2), it is more preferable to set the upper limit of conditional expression (2) to 0.75, 0.65, 0.55, or even 0.50, which is undesirable.

[0017] 1, an optical system OL according to a second embodiment is configured to include, in order from the object side, a first negative meniscus lens L1 having a convex surface facing the object side and negative refractive power, a second negative meniscus lens L2 having a convex surface facing the object side and negative refractive power, and a third biconcave negative lens L3 having negative refractive power, and at least one other lens. By configuring the optical system OL in this manner, it is possible to achieve both a small and lightweight optical system OL and good optical performance.

[0018] It is also desirable that the optical system OL according to the second embodiment satisfy the above-mentioned conditional expression (1). The effects and the like resulting from satisfying this conditional expression (1) are as described above.

[0019] Moreover, it is desirable that the optical system OL according to the second embodiment satisfy the following conditional expression (3).

[0020] 1.80<R12 / D12<3.00 (3) where D12 is the axial air gap between the first negative meniscus lens L1 and the second negative meniscus lens L2, and R12 is the radius of curvature of the lens surface of the first negative meniscus lens L1 on the image side.

[0021] Conditional expression (3) defines the ratio of the radius of curvature of the image-side lens surface of the first negative meniscus lens L1 to the axial air gap between the first negative meniscus lens L1 and the second negative meniscus lens L2. By satisfying conditional expression (3), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (3) is undesirable because it makes it difficult to correct curvature of field and astigmatism. To ensure the effect of conditional expression (3), it is preferable to set the lower limit of conditional expression (3) to 1.90, or even 2.00. Exceeding the upper limit of conditional expression (3) is undesirable because it results in insufficient correction of curvature of field and astigmatism. To ensure the effect of conditional expression (3), it is more preferable to set the upper limit of conditional expression (3) to 2.80, 2.65, or even 2.50.

[0022] (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 (4).

[0023] φ12 / R12<1.90 (4) where R12 is the radius of curvature of the lens surface of the first negative meniscus lens L1 on the image side, and φ12 is the effective diameter of the lens surface of the first negative meniscus lens L1 on the image side.

[0024] Conditional expression (4) defines the ratio of the effective diameter of the image-side lens surface of the first negative meniscus lens L1 to the radius of curvature of the image-side lens surface of the first negative meniscus lens L1. By satisfying conditional expression (4), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Exceeding the upper limit of conditional expression (4) facilitates compactness, but makes it difficult to correct lateral chromatic aberration, makes lens processing difficult, and significantly degrades imaging performance due to manufacturing errors, which is undesirable. To ensure the effect of conditional expression (4), it is more desirable to set the upper limit of conditional expression (4) to 1.88, 1.85, or even 1.83. To ensure the effect of conditional expression (4), it is more desirable to set the lower limit of conditional expression (4) to 1.60 (1.60<φ12 / R12), or even 1.70.

[0025] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5).

[0026] φ22 / R22<1.90 (5) where R22 is the radius of curvature of the lens surface of the second negative meniscus lens L2 on the image side, and φ22 is the effective diameter of the lens surface of the second negative meniscus lens L2 on the image side.

[0027] Conditional expression (5) defines the ratio of the effective diameter of the image-side lens surface of the second negative meniscus lens L2 to the radius of curvature of the image-side lens surface of the second negative meniscus lens L2. By satisfying conditional expression (5), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Exceeding the upper limit of conditional expression (5) facilitates compactness, but makes it difficult to correct lateral chromatic aberration, makes lens processing difficult, and significantly degrades imaging performance due to manufacturing errors, 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 1.88, 1.85, or even 1.83. To ensure the effect of conditional expression (5), it is more desirable to set the lower limit of conditional expression (5) to 1.60 (1.60<φ22 / R22), or even 1.70.

[0028] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (6).

[0029] 7.50<R12 / DL1<11.00 (6) where DL1 is the thickness of the first negative meniscus lens L1 on the optical axis, and R12 is the radius of curvature of the lens surface of the first negative meniscus lens L1 on the image side.

[0030] Conditional expression (6) defines the ratio of the radius of curvature of the image-side lens surface of the first negative meniscus lens L1 to the axial thickness of the first negative meniscus lens L1. Satisfying conditional expression (6) makes it possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (6) is undesirable because it makes it difficult to correct curvature of field and astigmatism. To ensure the effect of conditional expression (6), it is more desirable to set the lower limit of conditional expression (6) to 8.00, 8.50, or even 8.80. Exceeding the upper limit of conditional expression (6) increases the overall size of the optical system OL. Furthermore, reducing the radius of curvature of the object-side lens surface of the first negative meniscus lens L1 to mitigate this effect is undesirable because it makes it difficult to correct astigmatism and curvature of field. In order to ensure the effect of conditional expression (6), it is more desirable to set the upper limit of conditional expression (6) to 10.50, 10.00, or even 9.50.

[0031] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (7).

[0032] −3.50<(R12+R11) / (R12−R11)<−2.00 (7) where R11 is the radius of curvature of the object-side lens surface of the first negative meniscus lens L1, and R12 is the radius of curvature of the image-side lens surface of the first negative meniscus lens L1.

[0033] Conditional expression (7) defines the shape factor of the first negative meniscus lens L1. By satisfying conditional expression (7), it is possible to achieve both a compact and lightweight optical system OL and good optical performance. Falling below the lower limit of conditional expression (7) is undesirable because it makes it difficult to correct spherical aberration, coma, and curvature of field. To ensure the effect of conditional expression (7), it is more desirable to set the lower limit of conditional expression (7) to -3.40, -3.25, or even -3.00. Exceeding the upper limit of conditional expression (7) is undesirable because it makes it difficult to obtain the amount of distortion required for a fisheye lens. To ensure the effect of conditional expression (7), it is more desirable to set the upper limit of conditional expression (7) to -2.20, -2.35, or even -2.50.

[0034] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (8).

[0035] 0.20<R22 / (-fL2)<0.80 (8) where, fL2 is the focal length of the second negative meniscus lens L2, and R22 is the radius of curvature of the lens surface of the second negative meniscus lens L2 on the image side.

[0036] Conditional expression (8) defines the ratio of the radius of curvature of the image-side lens surface of the second negative meniscus lens L2 to the focal length of the second negative meniscus lens L2. By satisfying conditional expression (8), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Below the lower limit of conditional expression (8), the entire optical system OL becomes large, and correction of axial chromatic aberration and lateral chromatic aberration becomes difficult, which is undesirable. To ensure the effect of conditional expression (8), it is more preferable to set the lower limit of conditional expression (8) to 0.30, 0.40, or even 0.50. Exceeding the upper limit of conditional expression (8) makes correction of spherical aberration difficult, which is undesirable. To ensure the effect of conditional expression (8), it is more preferable to set the upper limit of conditional expression (8) to 0.75, 0.70, or even 0.65.

[0037] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (9).

[0038] 6.50<R22 / DL2<12.00 (9) where DL2 is the thickness of the second negative meniscus lens L2 on the optical axis, and R22 is the radius of curvature of the lens surface of the second negative meniscus lens L2 on the image side.

[0039] Conditional expression (9) defines the ratio of the radius of curvature of the image-side lens surface of the second negative meniscus lens L2 to the axial thickness of the second negative meniscus lens L2. Satisfying conditional expression (9) makes it possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (9) is undesirable because it makes it difficult to correct curvature of field and astigmatism. To ensure the effect of conditional expression (9), it is more desirable to set the lower limit of conditional expression (9) to 7.00, 7.50, or even 8.00. Exceeding the upper limit of conditional expression (9) increases the overall size of the optical system OL. Furthermore, reducing the radius of curvature of the object-side lens surface of the second negative meniscus lens L2 to mitigate this effect is undesirable because it makes it difficult to correct astigmatism and curvature of field. In order to ensure the effect of conditional expression (9), it is more desirable to set the upper limit of conditional expression (9) to 11.50, 11.00, 10.50, and more preferably 10.00.

[0040] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (10).

[0041] −2.50<(R22+R21) / (R22−R21)<−1.00 (10) where R21 is the radius of curvature of the object-side lens surface of the second negative meniscus lens L2, and R22 is the radius of curvature of the image-side lens surface of the second negative meniscus lens L2.

[0042] Conditional expression (10) defines the shape factor of the second negative meniscus lens L2. By satisfying conditional expression (10), it is possible to achieve both a compact and lightweight optical system OL and good optical performance. Falling below the lower limit of conditional expression (10) is undesirable because it makes it difficult to correct spherical aberration, coma, and curvature of field. To ensure the effect of conditional expression (10), it is more preferable to set the lower limit of conditional expression (10) to −2.40, −2.25, −2.10, or even −2.00. Exceeding the upper limit of conditional expression (10) is undesirable because it makes it difficult to obtain the amount of distortion required for a fisheye lens. To ensure the effect of conditional expression (10), it is more preferable to set the upper limit of conditional expression (10) to −1.10, −1.20, −1.30, or even −1.40.

[0043] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (11).

[0044] 0.80<R22 / D23<2.00 (11) where D23 is the axial air gap between the second negative meniscus lens L2 and the third biconcave negative lens L3, and R22 is the radius of curvature of the lens surface of the second negative meniscus lens L2 on the image side.

[0045] Conditional expression (11) defines the ratio of the radius of curvature of the image-side lens surface of the second negative meniscus lens L2 to the axial air gap between the second negative meniscus lens L2 and the third biconcave negative lens L3. By satisfying conditional expression (11), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (11) is undesirable because it makes it difficult to correct curvature of field and astigmatism. To ensure the effect of conditional expression (11), it is more preferable to set the lower limit of conditional expression (11) to 0.90, 0.95, 1.00, or even 1.05. Exceeding the upper limit of conditional expression (11) is undesirable because it results in insufficient correction of curvature of field and astigmatism. To ensure the effect of conditional expression (11), it is more preferable to set the upper limit of conditional expression (11) to 1.80, 1.65, 1.50, or even 1.40.

[0046] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (12).

[0047] 2.00 < TL / Ymax < 5.00 (12) where Ymax: maximum image height of the optical system OL TL: total optical length (air equivalent length) when the optical system OL is focused at infinity

[0048] Conditional expression (12) defines the ratio of the total optical length (equivalent to air length) of the optical system OL when focused at infinity to the maximum image height. Satisfying conditional expression (12) allows for both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (12) is undesirable because it makes it difficult to correct aberrations such as spherical aberration and coma. To ensure the effect of conditional expression (12), it is more preferable to set the lower limit of conditional expression (12) to 2.25, 2.50, 2.75, or even 3.00. Exceeding the upper limit of conditional expression (12) is undesirable because it increases the overall size of the optical system OL. To ensure the effect of conditional expression (12), it is more preferable to set the upper limit of conditional expression (12) to 4.75, 4.50, 4.25, 4.00, or even 3.80.

[0049] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (13).

[0050] 1.75<(nd1+nd2) / 2<1.95 (13) where, nd1 is the refractive index of the medium of the first negative meniscus lens L1 for the d-line, and nd2 is the refractive index of the medium of the second negative meniscus lens L2 for the d-line.

[0051] Conditional expression (13) defines the average value of the refractive index of the medium of the first negative meniscus lens L1 and the second negative meniscus lens L2 at the d-line. By satisfying this conditional expression (13), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Below the lower limit of conditional expression (13), the refractive index of the medium of the first negative meniscus lens L1 and the second negative meniscus lens L2 at the d-line becomes low, making it difficult to correct field curvature and astigmatism, which is undesirable. To ensure the effect of conditional expression (13), it is preferable to set the lower limit of conditional expression (13) to 1.78, or even 1.80. Above the upper limit of conditional expression (13), it is undesirable because an appropriate Petzval sum cannot be obtained, making it difficult to correct astigmatism. In order to ensure the effect of conditional expression (13), it is more desirable to set the upper limit of conditional expression (13) to 1.94, 1.92, or even 1.90.

[0052] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (14).

[0053] 30.0<(νd1+νd2) / 2<45.0 (14) where νd1 is the Abbe number for the d-line of the medium of the first negative meniscus lens L1, and νd2 is the Abbe number for the d-line of the medium of the second negative meniscus lens L2.

[0054] Conditional expression (14) defines the average value of the Abbe number at the d-line of the medium of the first negative meniscus lens L1 and the second negative meniscus lens L2. By satisfying conditional expression (14), it is possible to achieve both a compact and lightweight optical system OL and excellent optical performance. Falling below the lower limit of conditional expression (14) is undesirable because it makes it impossible to correct chromatic aberrations generated by the first negative meniscus lens L1 and the second negative meniscus lens L2 with other lenses. To ensure the effect of conditional expression (14), it is preferable to set the lower limit of conditional expression (14) to 31.5, 32.5, 34.0, or even 34.5. Exceeding the upper limit of conditional expression (14) is undesirable because it reduces the Abbe number of the medium of the first negative meniscus lens L1 and the second negative meniscus lens L2, making it difficult to correct field curvature and astigmatism. In order to ensure the effect of conditional expression (14), it is more desirable to set the upper limit of conditional expression (14) to 43.0, 41.5, 40.0, and more preferably 38.0.

[0055] Furthermore, the optical system OL according to this embodiment preferably includes a diaphragm (aperture diaphragm S) and a positive lens (for example, in FIG. 1, a biconvex positive lens L4 and a biconvex positive lens L5) disposed adjacent to the diaphragm on the object side or the image plane side. By configuring the optical system OL in this manner, it is possible to achieve both a small and lightweight optical system OL and good optical performance.

[0056] Moreover, it is desirable that the optical system OL according to this embodiment has a stop (aperture stop S) and satisfies the following conditional expression (15).

[0057] −0.80<f / fa<0.10 (15) where, fa is the focal length of the cemented lens CLa that is located closest to the object among the cemented lenses located closer to the image plane than the aperture stop (aperture stop S), and f is the focal length of the entire optical system OL when focused at infinity.

[0058] Conditional expression (15) defines the ratio of the focal length of the entire system in an infinity-focused state to the focal length of the cemented lens CLa, which is located closest to the object among the cemented lenses located closer to the image plane than the aperture stop (aperture stop S). By satisfying conditional expression (15), it is possible to achieve both a compact and lightweight optical system OL and good optical performance. Falling below the lower limit of conditional expression (15) is undesirable because it makes it difficult to correct axial chromatic aberration. To ensure the effect of conditional expression (15), it is more desirable to set the lower limit of conditional expression (15) to −0.75, −0.70, −0.65, or even −0.60. Exceeding the upper limit of conditional expression (15) is undesirable because it makes it difficult to correct spherical aberration. In order to ensure the effect of conditional expression (15), it is more preferable to set the upper limit of conditional expression (15) to 0.05, 0.01, -0.01, -0.05, -0.10, -0.15, -0.20, -0.25, and more preferably -0.28.

[0059] Moreover, it is desirable that the optical system OL according to this embodiment has a stop (aperture stop S) and satisfies the following conditional expression (16).

[0060] −0.30<f / fb<0.30 (16) where, fb: focal length of the second cemented lens CLb from the object side among the cemented lenses located closer to the image plane than the aperture stop (aperture stop S), and f: focal length of the entire optical system OL when focused at infinity.

[0061] Conditional expression (16) defines the ratio of the focal length of the entire system in an infinity-focused state to the focal length of the second cemented lens CLb from the object side among the cemented lenses located closer to the image plane than the aperture stop (aperture stop S). By satisfying conditional expression (16), it is possible to achieve both a compact and lightweight optical system OL and good optical performance. Falling below the lower limit of conditional expression (16) is undesirable because it makes it difficult to correct chromatic aberration of magnification. To ensure the effect of conditional expression (16), it is more preferable to set the lower limit of conditional expression (16) to −0.25, −0.20, −0.15, or even −0.10. Exceeding the upper limit of conditional expression (16) is undesirable because it makes it difficult to correct coma and curvature of field. To ensure the effect of conditional expression (16), it is more preferable to set the upper limit of conditional expression (16) to 0.25, 0.20, 0.15, or even 0.10.

[0062] In the optical system OL according to this embodiment, it is desirable that the lens Ln arranged closest to the image plane has at least one lens surface that is an aspherical surface with inverted curvature. It is also desirable that the lens Ln-1 arranged adjacent to the lens Ln arranged closest to the image plane has at least one lens surface that is an aspherical surface with inverted curvature. This configuration makes it possible to achieve both a compact and lightweight optical system OL and good optical performance.

[0063] 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.

[0064] 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. 7 . This camera 1 is a so-called mirrorless camera with an interchangeable lens system 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 passes through an OLPF (Optical Low Pass Filter) (not shown) to form a subject image on the imaging surface of the imaging unit 3. 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.

[0065] 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.

[0066] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0067] In this embodiment, the optical system OL is configured with 9 or 10 lens components, but the above configuration conditions and the like are also applicable to a configuration with 8 or less lens components or 11 or more lens components. Note that the lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0068] Alternatively, a single lens group, 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 object. In this case, the focusing group can be used for autofocusing and is also suitable for driving a motor (such as an ultrasonic motor) for autofocusing.

[0069] Furthermore, the lens group or 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.

[0070] 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.

[0071] The aperture stop S is preferably located near the center of the optical axis of the optical system OL, but it is also possible to use the lens frame to fulfill that role without providing a member serving as an aperture stop.

[0072] 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.

[0073] An outline of a manufacturing method for the optical system OL according to this embodiment will be described below with reference to Fig. 8. First, at least one lens is prepared (step S100): a first negative meniscus lens L1 having a convex surface facing the object side and negative refractive power; a second negative meniscus lens L2 having a convex surface facing the object side and negative refractive power; and a third biconcave negative lens L3 having negative refractive power. Then, each lens is arranged so as to satisfy predetermined conditions (for example, the above-mentioned conditional expressions (1) and (2) in the first embodiment, and the above-mentioned conditional expressions (1) and (3) in the second embodiment) (step S200).

[0074] As described above, it is possible to provide an optical system, an optical device, and a method for manufacturing this optical system that achieve both small size and light weight and good optical performance.

[0075] Each embodiment will be described below with reference to the drawings. Figures 1, 3, and 5 are cross-sectional views showing the configuration of an optical system OL (OL1 to OL3) according to each embodiment. The arrows at the bottom of these cross-sectional views indicate the direction of movement of the focusing group along the optical axis when focusing from an object at infinity (∞) to a close object.

[0076] In each example, the aspherical surface is expressed by the following formula (a), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance along the optical axis from the tangent plane of the vertex of each aspherical surface at the height y to each aspherical surface (amount of sag), r is the radius of curvature of the reference spherical surface (paraxial radius of curvature), K is the conic constant, and An is the n-th order aspherical coefficient. Note that in the following examples, "e-n" is "×10 -n " indicates.

[0077] S(y)=(y 2 / r) / {1+(1-K×y 2 / r 2 ) 1 / 2} + A4 × y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 (a)

[0078] 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.

[0079] 1 shows the configuration of an optical system OL1 according to Example 1. This optical system OL1 includes, in order from the object side, a meniscus negative lens (first negative meniscus lens) L1 with a convex surface facing the object side, a meniscus negative lens (second negative meniscus lens) L2 with a convex surface facing the object side, a biconcave negative lens (third biconcave negative lens) L3 with aspherical lens surfaces on the object side and the image side, a biconvex positive lens L4, a biconvex positive lens L5 with aspherical lens surfaces on the object side and the image side, and a biconvex positive lens L6. The lens element is made up of a cemented negative lens CLa cemented with a biconcave negative lens L7, a cemented negative lens CLb cemented with a meniscus positive lens L8 with a concave surface facing the object side and a meniscus negative lens L9 with a concave surface facing the object side, a meniscus positive lens L10 (Ln-1) with a convex surface facing the object side and whose object-side and image-side lens surfaces are aspherical, and a biconvex positive lens L11 (Ln) with an aspherical object-side and image-side lens surfaces. Note that the object-side and image-side lens surfaces of the positive lens L10 (Ln-1) and the object-side and image-side lens surfaces of the positive lens L11 (Ln) are aspherical with inverted curvature.

[0080] An aperture stop S is disposed between the positive lens L4 and the positive lens L5. An optical filter FL is disposed between the image plane I and the positive lens L11 (Ln) closest to the image plane.

[0081] Furthermore, when focusing from an object at infinity to an object at a close distance, the entire optical system OL1 moves toward the object side.

[0082] 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, which represent values ​​when focused at infinity. Here, the back focus Bf represents the air-equivalent length on the optical axis from the lens surface closest to the image plane (surface No. 22) 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. 22) plus the air-equivalent length of the back focus. In the lens data, the first column m indicates the order of the lens surfaces (surface number) from the object side along the direction of light 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), the fourth column nd and the fifth column vd indicate the refractive index and Abbe number for the d-line (λ = 587.6 nm), and the sixth column ip indicates the position of the inflection point. The position of the inflection point indicates the height perpendicular to the optical axis at which the curvature of an aspheric surface with curvature inversion is inverted. The radius of curvature ∞ indicates a flat surface, and the refractive index of air, 1.000000, is omitted.

[0083] 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.

[0084] (Table 1) First Example [Overall specifications] f = 10.184 FNo = 4.08 ω = 108.1 Ymax = 21.630 TL (equivalent length in air) = 75.604 Bf (equivalent length in air) = 10.185 [Lens data] mr d nd νd ip Object surface ∞ 1 38.8086 2.0000 1.846660 23.80 2 18.1489 7.5089 3 34.8073 1.2000 1.804000 46.60 4 10.7528 7.9956 5* -24.4955 3.4882 1.516800 64.13 6* 17.7105 1.3476 7 26.8728 6.2548 1.846660 23.80 8 -41.7098 6.2175 9 ∞ 0.1000 Aperture Stop S 10* 16.1802 2.2961 1.516800 64.13 11* -15.4891 1.4138 12 39.9385 3.8403 1.516800 64.13 13 -11.1383 1.0000 1.846660 23.80 14 63.9809 3.3773 15 -72.2609 5.2297 1.516800 64.13 16 -8.3676 1.0000 1.804000 46.60 17 -22.2128 0.1010 18* 28.8319 3.0944 1.536497 55.98 5.0 19* 35.9760 3.3991 4.7 20* 36.7332 4.5549 1.536497 55.98 14.3 21* -925.9246 8.6297 14.4 22 ∞ 1.6000 1.516800 64.13 23 ∞ 0.5000 Image plane ∞

[0085] In this optical system OL1, surfaces 5, 6, 10, 11, 18, 19, 20, and 21 are aspherical. 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 A12.

[0086] (Table 2) [Aspherical data] m K A4 A6 A8 A10 A12 5 0.382 1.953e-05 1.097e-07 1.814e-10 -4.272e-12 0.000e-00 6 1.963 6.745e-05 6.621e-07 -4.961e-09 5.269e-11 0.000e-00 10 0.000 1.872e-05 1.106e-07 -6.243e-09 3.857e-10 0.000e-00 11 0.000 5.263e-05 -2.331e-07 2.395e-08 -2.410e-10 0.000e-00 18 -0.695 -1.261e-04 4.100e-07 -7.949e-09 4.776e-11 0.000e-00 19 1.410 -1.184e-04 2.742e-07 -4.418e-09 3.123e-11 0.000e-00 20 0.000 3.542e-05 -4.594e-07 1.939e-09 -3.017e-12 0.000e-00 21 0.000 9.243e-05 -4.616e-07 1.417e-09 -2.044e-12 0.000e-00

[0087] FIG. 2 shows spherical aberration, astigmatism, and coma diagrams of this optical system OL1 when focused at infinity. In each aberration diagram, FNo indicates the F-number, and A indicates the half angle of view. Note that in the spherical aberration diagram, the F-number value corresponding to the maximum aperture is shown, in the astigmatism diagram, the maximum value of the half angle of view is shown, and in the coma diagram, the value of each half angle of view 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 of the following examples. These aberration diagrams demonstrate that this optical system OL1 effectively corrects various aberrations and has excellent imaging performance.

[0088] 3 shows the configuration of an optical system OL2 according to Example 2. This optical system OL2 comprises, in order from the object side, a meniscus negative lens (first negative meniscus lens) L1 with a convex surface facing the object side, a meniscus negative lens (second negative meniscus lens) L2 with a convex surface facing the object side, a biconcave negative lens (third biconcave negative lens) L3 with an aspherical surface formed on the image side lens surface, a biconvex positive lens L4, a biconvex positive lens L5 with aspherical surfaces formed on the object side lens surface and the image side lens surface, and a biconvex positive lens L6. The lens element is composed of a cemented negative lens CLa formed by cementing a biconvex positive lens L8 and a biconcave negative lens L7, a cemented positive lens CLb formed by cementing a biconvex positive lens L8 and a meniscus negative lens L9 with a concave surface facing the object side, a biconvex positive lens L10 (Ln-1) with aspherical object-side and image-side lens surfaces, and a meniscus positive lens L11 (Ln) with aspherical object-side and image-side lens surfaces. The negative lens L3 is a composite lens in which a resin layer is provided on the image-side lens surface of a glass lens body to form an aspherical surface. The image-side lens surface of the positive lens L10 (Ln-1) and the object-side and image-side lens surfaces of the positive lens L11 (Ln) are aspherical with inverted curvature.

[0089] An aperture stop S is disposed between the positive lens L4 and the positive lens L5. An optical filter FL is disposed between the image plane I and the positive lens L11 (Ln) closest to the image plane.

[0090] In addition, in this optical system OL1, when focusing from an object at infinity to an object at a close distance, the negative lens L2, the negative lens L3, and the positive lens L4 move toward the object side.

[0091] Table 3 below lists the specifications of the optical system OL2.

[0092] (Table 3) Second Example [Overall specifications] f = 10.800 FNo = 4.31 ω = 108.2 Ymax = 21.630 TL (equivalent length in air) = 75.681 Bf (equivalent length in air) = 13.589 [Lens data] mr d nd νd ip Object surface ∞ 1 38.4930 2.0000 1.846660 23.80 2 18.1994 7.7453 3 31.3266 1.2000 1.804000 46.60 4 10.1212 7.4845 5 -28.2828 1.8745 1.516800 64.13 6 13.5367 0.3000 1.517417 52.43 7* 16.0189 1.1415 8 23.1082 4.1597 1.846660 23.80 9 -1133.8574 6.4898 10 ∞ 0.1000 Aperture Stop S 11* 13.8921 5.2227 1.516800 64.13 12* -17.8409 2.4747 13 15.8353 5.4988 1.516800 64.13 14 -9.4885 1.0000 1.850260 32.35 15 23.3720 0.9227 16 53.5359 5.6247 1.516800 64.13 17 -10.7038 1.0000 1.850260 32.35 18 -37.2536 1.5633 19* 28.3105 4.1472 1.536497 55.98 20* -73.6320 0.5924 11.4 21* 38.4645 1.5494 1.536497 55.98 15.3 22* 37.9324 12.0345 13.1 23 ∞ 1.6000 1.516800 64.13 24 ∞ 0.5000 Image plane ∞

[0093] In this optical system OL2, surfaces 7, 11, 12, 19, 20, 21, and 22 are formed aspherical surfaces. Table 4 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0094] (Table 4) [Aspherical data] m K A4 A6 A8 A10 A12 7 0.000 5.864e-05 4.236e-07 1.341e-09 4.009e-11 0.000e-00 11 0.000 -2.348e-06 4.229e-07 -1.794e-08 4.158e-10 0.000e-00 12 0.000 4.274e-05 5.241e-07 -1.154e-08 2.520e-10 0.000e-00 19 0.000 -4.102e-05 -5.807e-08 6.132e-10 -1.064e-12 0.000e-00 20 0.000 -3.901e-05 3.288e-07 2.259e-10 -1.272e-12 0.000e-00 21 0.000 6.497e-06 -1.613e-07 9.567e-10 -1.754e-12 0.000e-00 22 0.000 8.431e-05 -7.162e-07 2.374e-09 -3.132e-12 0.000e-00

[0095] 4 shows diagrams of spherical aberration, astigmatism, and coma when the optical system OL2 is focused at infinity. These diagrams show that the optical system OL2 has excellent correction for various aberrations and has excellent imaging performance.

[0096] 5 shows the configuration of an optical system OL3 according to Example 3. This optical system OL3 comprises, in order from the object side, a meniscus negative lens (first negative meniscus lens) L1 with a convex surface facing the object side, a meniscus negative lens (second negative meniscus lens) L2 with a convex surface facing the object side, a biconcave negative lens (third biconcave negative lens) L3, a biconvex positive lens L4, a meniscus positive lens L5 with a convex surface facing the object side and whose object-side and image-plane-side lens surfaces are aspherical, a biconvex positive lens L6, and a biconvex negative lens L7. The lens element is made up of a cemented negative lens CLa formed by cementing a biconvex positive lens L7 to a biconcave negative lens L8, a cemented negative lens CLb formed by cementing a biconvex positive lens L9 to a meniscus negative lens L10 with its concave surface facing the object side, a biconvex positive lens L11 (Ln-1) whose object-side and image-side lens surfaces are aspherical, and a biconvex positive lens L12 (Ln) whose object-side and image-side lens surfaces are aspherical. Note that the object-side lens surface of the positive lens L11 (Ln-1) and the object-side and image-side lens surfaces of the positive lens L12 (Ln) are aspherical with inverted curvature.

[0097] An aperture stop S is disposed between the positive lens L5 and the positive lens L6. An optical filter FL is disposed between the image plane I and the positive lens L12 (Ln) closest to the image plane.

[0098] In addition, in this optical system OL3, when focusing from an object at infinity to an object at a close distance, the negative lens L3 and the positive lens L4 move toward the image plane side.

[0099] Table 5 below lists the specifications of the optical system OL3.

[0100] (Table 5) Third Example [Overall specifications] f = 10.320 FNo = 4.10 ω = 108.2 Ymax = 21.630 TL (equivalent length in air) = 80.453 Bf (equivalent length in air) = 9.555 [Lens data] mr d nd νd ip Object surface ∞ 1 38.1536 2.0000 2.000690 25.46 2 18.7162 8.8900 3 64.8953 1.2000 1.772500 49.62 4 11.6510 10.7371 5 -22.3206 1.1044 1.772500 49.62 6 81.7597 0.1000 7 56.6242 7.6127 1.850260 32.35 8 -25.9653 3.6583 9* 12.0383 1.9489 1.647690 33.72 10* 14.5775 4.1023 11 ∞ 1.3075 Aperture Stop S 12 20.1343 3.3377 1.563840 60.71 13 -14.2563 0.1559 14 21.0384 4.5506 1.487490 70.32 15 -10.4332 1.0000 1.850260 32.35 16 16.6449 1.0524 17 47.3014 4.7935 1.487490 70.32 18 -9.9926 1.0000 1.850260 32.35 19 -39.8171 3.8396 20* 46.6429 4.3398 1.536497 55.98 10.2 21* -89.6813 2.4988 22* 87.3093 1.6690 1.536497 55.98 7.1 23* -330.4666 8.0000 8.7 24 ∞ 1.6000 1.516800 64.13 25 ∞ 0.5000 Image plane ∞

[0101] In this optical system OL3, surfaces 9, 10, 20, 21, 22, and 23 are formed aspherical surfaces. Table 6 below shows data on the aspherical surfaces, i.e., the values ​​of the conic constant K and each of the aspherical constants A4 to A12.

[0102] (Table 6) [Aspherical data] m K A4 A6 A8 A10 A12 9 0.000 -9.573e-06 1.487e-07 -3.046e-08 -3.922e-10 1.654e-22 10 0.000 8.932e-05 2.650e-06 -9.717e-08 5.604e-10 -7.248e-23 20 0.000 -3.454e-06 2.602e-07 -2.664e-09 7.746e-12 -1.048e-14 21 0.000 -2.187e-05 1.976e-07 1.281e-09 -1.957e-11 5.433e-14 22 0.000 1.165e-04 -1.656e-06 7.400e-09 -1.612e-11 1.530e-14 23 0.000 2.077e-04 -2.071e-06 9.243e-09 -2.025e-11 1.649e-14

[0103] 6 shows diagrams of spherical aberration, astigmatism, and coma when the optical system OL3 is focused at infinity. These diagrams show that the optical system OL3 has excellent imaging performance with various aberrations well corrected.

[0104] [Values ​​Corresponding to Conditional Expressions] Table 7 below shows the values ​​corresponding to conditional expressions (1) to (16) in the first to third embodiments.

[0105] (Table 7) (1) ω (2) R12 / (-fL1) (3) R12 / D12 (4) φ12 / R12 (5) φ22 / R22 (6) R12 / DL1 (7) (R12+R11) / (R12-R11) (8) R22 / (-fL2) (9) R22 / DL2 (10) (R22+R21) / (R22-R21) (11) R22 / D23 (12) TL / Ymax (13) (nd1+nd2) / 2 (14) (νd1+νd2) / 2 (15) f / fa (16) f / fb Example 1 Example 2 Example 3 fL1 -42.137 -42.702 -38.704 fL2 -19.793 -19.078 -18.565 φ12 32.666 32.759 33.696 φ22 19.353 18.262 20.987 fa -34.945 -32.903 -17.591 fb -228.098 533.836 -258.987 (1) 108.1 108.2 108.2 (2) 0.431 0.426 0.484 (3) 2.417 2.350 2.105 (4) 1.800 1.800 1.800 (5) 1.800 1.804 1.801 (6) 9.074 9.100 9.358 (7) -2.757 -2.794 -2.926 (8) 0.543 0.531 0.628 (9) 8.961 8.434 9.709 (10) -1.894 -1.955 -1.438 (11) 1.345 1.352 1.085 (12) 3.495 3.499 3.720 (13) 1.825 1.825 1.887 (14) 35.200 35.200 37.540 (15) -0.291 -0.328 -0.587 (16) -0.045 0.020 -0.040

[0106] 1 Camera (optical equipment) OL (OL1 to OL3) Optical system L1 First negative meniscus lens L2 Second negative meniscus lens L3 Third double concave negative lens S Aperture stop (aperture)

Claims

1. The optical system comprises, in order from the object side, a first negative meniscus lens having a convex surface facing the object side and negative refractive power, a second negative meniscus lens having a convex surface facing the object side and negative refractive power, and a third biconcave negative lens having negative refractive power, and at least one lens; An optical system that satisfies the following condition: 90.0° < ω 0.10 < R12 / (-fL1) < 0.80 however, ω: half angle of view of the optical system fL1: focal length of the first negative meniscus lens R12: radius of curvature of the image-side lens surface of the first negative meniscus lens

2. The optical system comprises, in order from the object side, a first negative meniscus lens having a convex surface facing the object side and negative refractive power, a second negative meniscus lens having a convex surface facing the object side and negative refractive power, and a third biconcave negative lens having negative refractive power, and at least one lens; An optical system that satisfies the following condition: 90.0° < ω 1.80 < R12 / D12 < 3.00 however, ω: half angle of view of the optical system D12: On-axis air gap between the first negative meniscus lens and the second negative meniscus lens R12: radius of curvature of the image-side lens surface of the first negative meniscus lens

3. 3. The optical system according to claim 1, wherein the following condition is satisfied: φ12 / R12 < 1.90 however, R12: radius of curvature of the image-side lens surface of the first negative meniscus lens φ12: effective diameter of the lens surface of the first negative meniscus lens on the image plane side

4. 3. The optical system according to claim 1, wherein the following condition is satisfied: φ22 / R22 < 1.90 however, R22: radius of curvature of the image-side lens surface of the second negative meniscus lens φ22: effective diameter of the lens surface on the image plane side of the second negative meniscus lens

5. 3. The optical system according to claim 1, wherein the following condition is satisfied: 7.50 < R12 / DL1 < 11.00 however, DL1: the thickness of the first negative meniscus lens on the optical axis R12: radius of curvature of the image-side lens surface of the first negative meniscus lens

6. 3. The optical system according to claim 1, wherein the following condition is satisfied: -3.50 < (R12+R11) / (R12-R11) < -2.00 however, R11: radius of curvature of the object-side lens surface of the first negative meniscus lens R12: radius of curvature of the image-side lens surface of the first negative meniscus lens

7. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.20 < R22 / (-fL2) < 0.80 however, fL2: focal length of the second negative meniscus lens R22: radius of curvature of the image-side lens surface of the second negative meniscus lens

8. 3. The optical system according to claim 1, wherein the following condition is satisfied: 6.50 < R22 / DL2 < 12.00 however, DL2: the thickness of the second negative meniscus lens on the optical axis R22: radius of curvature of the image-side lens surface of the second negative meniscus lens

9. 3. The optical system according to claim 1, wherein the following condition is satisfied: -2.50 < (R22+R21) / (R22-R21) < -1.00 however, R21: radius of curvature of the object-side lens surface of the second negative meniscus lens R22: radius of curvature of the image-side lens surface of the second negative meniscus lens

10. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.80 < R22 / D23 < 2.00 however, D23: an air gap on the axis between the second negative meniscus lens and the third biconcave negative lens R22: radius of curvature of the image-side lens surface of the second negative meniscus lens

11. 3. The optical system according to claim 1, wherein the following condition is satisfied: 2.00 < TL / Ymax < 5.00 however, Ymax: maximum image height of the optical system TL: total optical length of the optical system when focused at infinity

12. 3. The optical system according to claim 1, wherein the following condition is satisfied: 1.75 < (nd1+nd2) / 2 < 1.95 however, nd1: refractive index of the medium of the first negative meniscus lens at the d line nd2: refractive index of the medium of the second negative meniscus lens at the d line

13. 3. The optical system according to claim 1, wherein the following condition is satisfied: 30.0 < (νd1+νd2) / 2 < 45.0 however, νd1: Abbe number of the medium of the first negative meniscus lens at the d line νd2: Abbe number of the medium of the second negative meniscus lens at the d line

14. 3. The optical system according to claim 1, further comprising: a stop; and a positive lens disposed adjacent to the stop on the object side or the image plane side.

15. having an aperture, 3. The optical system according to claim 1, wherein the following condition is satisfied: -0.80 < f / fa < 0.10 however, fa: the focal length of the cemented lens closest to the object among the cemented lenses closer to the image plane than the aperture stop f: focal length of the entire optical system when the optical system is focused at infinity

16. having an aperture, 3. The optical system according to claim 1, wherein the following condition is satisfied: -0.30 < f / fb < 0.30 however, fb: focal length of the second cemented lens from the object side among the cemented lenses closer to the image plane than the stop f: focal length of the entire optical system when the optical system is focused at infinity

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