Optical systems and optical instruments

Abstract

To provide an optical system including good optical performance, and an optical device including the optical system.SOLUTION: An optical system OL comprises, in order from the closest to an object side, substantially two lens groups: a first lens group G1 having a first negative meniscus lens L11, a second negative meniscus lens L12, and a third negative meniscus lens L13; and a rear group GR disposed on an image surface side of the first lens group G1 and having a focusing lens group Gfo which moves in an optical axis direction when focusing on the closest side to the object. The first lens group G1 has a positive lens component L16 on the closest side to the image surface, the third negative meniscus lens L13 is a single lens, and the positive lens component L16 is a single lens. The optical system is configured to satisfy conditions represented by predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system and an optical instrument. [Background technology]

[0002] Conventionally, optical systems that use aspherical lenses to achieve a small size and a wide angle of view have been proposed (see, for example, Patent Document 1). However, Patent Document 1 has a problem in that further improvement in optical performance is required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 056310 Summary of the Invention

[0004] The optical system according to the first aspect of the present invention substantially comprises two lens groups: a first lens group having, in order from the most object side, a first negative meniscus lens, a second negative meniscus lens, and a third negative meniscus lens; and a rear group which is disposed closer to the image surface than the first lens group and has a focusing lens group which moves in the optical axis direction when focusing closest to the object surface. The first lens group has a positive lens component closest to the image surface. A positive lens and the third negative meniscus lens is a single lens and satisfies the condition of the following formula: 80° < 2ω < 180° 0.80 < f1 / fR < 3.00 0.90 < (-fn123) / f < 1.15 0.00 < fp / f1 < 0.55 50.0 < νp however, 2ω: full angle of view of the optical system f1: focal length of the first lens group fR: the composite focal length of the lens group on the image side of the first lens group in the optical system when focused at infinity f: focal length of the entire optical system when focused at infinity fn123: a composite focal length of the first negative meniscus lens, the second negative meniscus lens, and the third negative meniscus lens fp: focal length of the positive lens component arranged closest to the image plane in the first lens group νp: Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group

[0005] Moreover, an optical system according to a second aspect of the present invention substantially comprises two lens groups: a first lens group having, in order from the most object side, a first negative meniscus lens, a second negative meniscus lens, and a third negative meniscus lens; and a rear group which is arranged closer to the image surface than the first lens group and has a focusing lens group that moves in the optical axis direction when focusing closest to the object, wherein the first lens group has a positive lens that is a positive lens component closest to the image surface, and the third negative meniscus lens is a single lens, and satisfies the condition of the following equation: 80° < 2ω < 180° 2.50 < fp / f < 5.00 0.95 < (-fn123) / f < 1.15 0.00 < fp / f1 < 0.55 50.0 < νp however, 2ω: full angle of view of the optical system f: focal length of the entire optical system when focused at infinity fp: focal length of the positive lens component arranged closest to the image plane in the first lens group fn123: a composite focal length of the first negative meniscus lens, the second negative meniscus lens, and the third negative meniscus lens f1: focal length of the first lens group νp: Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group [Brief description of the drawings]

[0006] [Figure 1] 1 is a cross-sectional view showing a lens configuration of an optical system according to a first example when focused on infinity. [Diagram 2]5A to 5C are diagrams illustrating various aberrations in the optical system according to the first example when focused on an object at infinity. [Diagram 3] FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 2 when focused on infinity. [Figure 4] 13A to 13C are diagrams illustrating various aberrations in the optical system according to Example 2 when focused on an object at infinity. [Diagram 5] FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 3 when focused on infinity. [Figure 6] 13A to 13C are diagrams illustrating various aberrations in the optical system according to Example 3 when focused on an object at infinity. [Figure 7] FIG. 2 is a cross-sectional view of a camera equipped with the optical system. [Figure 8] 4 is a flowchart illustrating a method for manufacturing the optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, preferred embodiments will be described with reference to the drawings. As shown in Fig. 1, the optical system OL according to the first embodiment includes, in order from the object side, a first lens group G1 having a first negative meniscus lens L11, a second negative meniscus lens L12, and a third negative meniscus lens L13, and a rear group GR arranged closer to the image plane than the first lens group G1 and having a focusing lens group Gfo that moves in the optical axis direction during focusing. With this configuration, it is possible to realize an optical system that suppresses the occurrence of field curvature and distortion, has small fluctuations in aberrations associated with focusing, and has a long back focus relative to the focal length.

[0008] It is desirable for the optical system OL according to the first embodiment to satisfy the following conditional expression (1).

[0009] 80° < 2ω < 180° (1) however, 2ω: Full angle of view of optical system OL

[0010] Conditional formula (1) defines the full angle of view of the optical system OL. By satisfying this conditional formula (1), it is possible to obtain good optical performance over the entire image circle while being small and lightweight. If the lower limit of conditional formula (1) is exceeded, it is undesirable because it becomes difficult to correct spherical aberration and axial chromatic aberration. In order to ensure the effect of conditional formula (1), it is more preferable to set the lower limit of conditional formula (1) to 85°, and more preferably to 90°, 95°, or 100°. In order to ensure the effect of conditional formula (1), it is more preferable to set the upper limit of conditional formula (1) to 175°, and more preferably to 170°, 165°, 160°, or 150°.

[0011] In the optical system OL according to the first embodiment, it is preferable that the first lens group G1 has a positive refractive power and the rear lens group GR has a positive refractive power, which can suppress aberration fluctuations that occur during focusing.

[0012] Moreover, it is desirable for the optical system OL according to the first embodiment to satisfy the following conditional expression (2).

[0013] 0.50 < (-fn123) / f < 1.50 (2) however, f: focal length of the entire optical system OL when focused at infinity fn123: composite focal length of the first negative meniscus lens L11, the second negative meniscus lens L12, and the third negative meniscus lens L13

[0014] Conditional expression (2) specifies the composite focal length of the three negative meniscus lenses arranged on the most object side of the first lens group G1 with respect to the focal length of the entire optical system OL in an infinity focused state. By satisfying this conditional expression (2), it is possible to obtain an optical system that is small in size and has a good correction of various aberrations while ensuring a long back focus relative to the focal length. If the lower limit of conditional expression (2) is exceeded, it is undesirable because it becomes difficult to correct lateral chromatic aberration. In order to ensure the effect of conditional expression (2), it is more preferable to set the lower limit of conditional expression (2) to 0.55, and further to 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 1.00. In addition, if the upper limit of conditional expression (2) is exceeded, the optical system becomes large in size, and if it is forcibly made small, it is undesirable because it becomes difficult to correct curvature of field and distortion. In order to ensure the effect of conditional expression (2), it is more desirable to set the upper limit of conditional expression (2) to 1.45, and more preferably to 1.40, 1.35, 1.30, 1.25, 1.20 or 1.15.

[0015] In the optical system OL according to the first embodiment, it is preferable that the first lens group G1 has at least one positive lens component (for example, the biconvex positive lens L16 in FIG. 1) closest to the image surface. With this configuration, it is possible to satisfy the need for compactness and to satisfactorily correct spherical aberration, coma aberration, and aberration fluctuations associated with focusing.

[0016] Moreover, it is desirable for the optical system OL according to the first embodiment to satisfy the following conditional expression (3).

[0017] 0.05 < (-fn123) / fp < 1.00 (3) however, fn123: composite focal length of the first negative meniscus lens L11, the second negative meniscus lens L12, and the third negative meniscus lens L13 fp: focal length of the positive lens component located closest to the image plane in the first lens group G1

[0018] Conditional expression (3) specifies the composite focal length of the three negative meniscus lenses arranged closest to the object side of the first lens group G1 relative to the focal length of the positive lens component arranged closest to the image surface side of the first lens group G1. By satisfying this conditional expression (3), it is possible to achieve compactness, and to suppress aberration fluctuations due to focusing while satisfactorily correcting spherical aberration, axial chromatic aberration, lateral chromatic aberration, etc. If the lower limit of conditional expression (3) is exceeded, it is undesirable because it is difficult to correct lateral chromatic aberration, curvature of field, and distortion aberration. In order to ensure the effect of conditional expression (3), it is more preferable to set the lower limit of conditional expression (3) to 0.10, and further to 0.15, 0.20, 0.25, and 0.28. In addition, if the upper limit of conditional expression (3) is exceeded, it is undesirable because it is difficult to suppress aberration fluctuations due to focusing. In order to ensure the effect of conditional expression (3), it is more desirable to set the upper limit of conditional expression (3) to 0.90, and more preferably to 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, 0.45 or 0.42.

[0019] The optical system OL according to the second embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, and the second lens group G2 is a focusing lens group Gfo that moves in the optical axis direction during focusing. With this configuration, it is possible to suppress the fluctuation of the field curvature and distortion aberration accompanying focusing.

[0020] Moreover, it is desirable for the optical system OL according to the second embodiment to satisfy the following conditional expression (1).

[0021] 80° < 2ω < 180° (1) however, 2ω: Full angle of view of optical system OL

[0022] Conditional formula (1) defines the full angle of view of the optical system OL. By satisfying this conditional formula (1), it is possible to obtain good optical performance over the entire image circle while being small and lightweight. If the lower limit of conditional formula (1) is exceeded, it is undesirable because it becomes difficult to correct spherical aberration and axial chromatic aberration. In order to ensure the effect of conditional formula (1), it is more preferable to set the lower limit of conditional formula (1) to 85°, and more preferably to 90°, 95°, or 100°. In order to ensure the effect of conditional formula (1), it is more preferable to set the upper limit of conditional formula (1) to 175°, and more preferably to 170°, 165°, 160°, or 150°.

[0023] Moreover, it is desirable for the optical system OL according to the second embodiment to satisfy the following conditional expression (4).

[0024] 1.00 < f3 / f < 4.00 (4) however, f: focal length of the entire optical system OL when focused at infinity f3: focal length of the third lens group G3

[0025] Conditional expression (4) specifies the focal length of the third lens group G3 relative to the focal length of the entire optical system OL in an infinity focused state. By satisfying this conditional expression (4), a long back focus can be ensured relative to the focal length. If the lower limit of conditional expression (4) is exceeded, the refractive power of the negative lens in the first lens group G1 must be increased to ensure the back focus, resulting in a large size. Also, it becomes difficult to correct spherical aberration and coma aberration in the third lens group G3. In order to ensure the effect of conditional expression (4), it is more preferable to set the lower limit of conditional expression (4) to 1.20, and further to 1.40, 1.60, 1.70, 1.80, 1.90, or 1.95. Also, if the upper limit of conditional expression (4) is exceeded, the lens becomes large, and if it is forcibly made small, it becomes difficult to correct off-axis aberrations such as field curvature and coma aberration, which is not preferable. In order to ensure the effect of conditional expression (4), it is more desirable to set the upper limit of conditional expression (4) to 3.70, and more preferably to 3.50, 3.40, 3.20, 3.00, 2.90 or 2.85.

[0026] In the optical system OL according to the second embodiment, the first lens group G1 preferably includes, in order from the object side, a first negative lens L11, a second negative lens L12, and a third negative lens L13. With this configuration, it is possible to satisfactorily correct curvature of field and distortion.

[0027] Moreover, it is desirable for the optical system OL according to the second embodiment to satisfy the following conditional expression (5).

[0028] 2.00 < (-f2) / f < 9.00 (5) however, f: focal length of the entire optical system OL when focused at infinity f2: focal length of the second lens group G2

[0029] Conditional expression (5) specifies the focal length of the second lens group G2 relative to the focal length of the entire optical system OL in an infinity focused state. By satisfying this conditional expression (5), it is possible to suppress the variation of aberrations accompanying focusing. If the lower limit of conditional expression (5) is not satisfied, the variation of field curvature, axial chromatic aberration, and lateral chromatic aberration accompanying focusing is large, which is undesirable. In order to ensure the effect of conditional expression (5), it is more preferable to set the lower limit of conditional expression (5) to 2.30, and further to 2.50, 2.80, 3.00, 3.30, 3.50, 3.70, 3.80, 3.90, 4.00, or 4.10. In addition, if the upper limit of conditional expression (5) is exceeded, the amount of movement of the focusing lens group Gfo accompanying focusing increases, which is undesirable because it leads to the size of the entire optical system. In order to ensure the effect of conditional expression (5), it is more desirable to set the upper limit of conditional expression (5) to 8.80, and more preferably to 8.50, 8.30, 8.00, 7.80, 7.50, 7.30, 7.00, 6.90, 6.80, 6.70, or 6.60.

[0030] In the optical system OL according to the second embodiment, it is preferable that the first lens group G1 has at least one positive lens component (for example, the biconvex positive lens L16 in FIG. 1) closest to the image surface. With this configuration, it is possible to suppress aberration fluctuations accompanying focusing while satisfactorily correcting spherical aberration, coma, and axial chromatic aberration.

[0031] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (6).

[0032] 1.00 < bfa / f (6) however, f: focal length of the entire optical system OL when focused at infinity bfa: Air-equivalent back focus of optical system OL

[0033] Conditional expression (6) specifies the air-equivalent back focus of the optical system OL with respect to the focal length of the entire optical system OL in the infinity-focused state. The back focus bfa indicates the distance (air-equivalent length) on the optical axis from the lens surface closest to the image surface of the optical system OL to the image surface I when the optical system OL is focused at infinity. By satisfying this conditional expression (6), a long back focus suitable for a single-lens reflex camera having a mirror box can be obtained while ensuring a wide angle of view. If the lower limit of conditional expression (6) is exceeded, the focal length must be lengthened to ensure the back focus, which is not preferable because a wide angle of view cannot be ensured. In order to ensure the effect of conditional expression (6), it is more preferable to set the lower limit of conditional expression (6) to 1.30, and further to 1.50, 1.80, 2.00, 2.10, 2.20, or 2.30.

[0034] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (7).

[0035] 0.20 < f1 / fR (7) however, f1: focal length of the first lens group G1 fR: the composite focal length of the lens group on the image side of the first lens group G1 in the optical system OL when focused at infinity

[0036] Conditional expression (7) specifies the focal length of the first lens group G1 with respect to the composite focal length of the lens groups on the image side of the first lens group G1 of the optical system OL in the infinity focused state (corresponding to the focal length of the rear group GR in the first embodiment, and corresponding to the composite focal length of the second lens group G2 and the third lens group G3 in the second embodiment). By satisfying this conditional expression (7), it is possible to correct axial chromatic aberration, spherical aberration, and coma aberration in the first lens group G1, and it is possible to suppress aberration fluctuations due to focusing, and it is possible to obtain good optical performance while miniaturizing the entire optical system by simplifying the optical system on the image side of the first lens group G1. If the lower limit of conditional expression (7) is not satisfied, the Petzval sum increases, making it difficult to correct the curvature of field, which is not preferable. In order to ensure the effect of conditional expression (7), it is more preferable to set the lower limit of conditional expression (7) to 0.50, and more preferably to 0.80, 1.00, 1.30, 1.40, or 1.50. If the upper limit of conditional expression (7) is to be lowered, it is preferable to set it to 12.00, and it is preferable to be within the range of conditional expression (7) in order to obtain good optical performance while making the entire optical system compact. In order to ensure the effect of conditional expression (7), it is more preferable to set the upper limit of conditional expression (7) to 10.00, and more preferably to 9.00, 8.00, 7.00, 6.00, 5.00, 4.50, 4.00, 3.80, 3.50, 3.30, 3.00, 2.80, or 2.50.

[0037] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (8).

[0038] 1.00 < fp / f < 5.00 (8) however, f: focal length of the entire optical system OL when focused at infinity fp: focal length of the positive lens component located closest to the image plane in the first lens group G1

[0039] Conditional expression (8) specifies the focal length of the positive lens component arranged closest to the image surface in the first lens group G1 with respect to the focal length of the entire optical system OL in an infinity focused state. By satisfying this conditional expression (8), various aberrations, particularly field curvature and spherical aberration, can be corrected well. If the lower limit of conditional expression (8) is exceeded, it is undesirable because it becomes difficult to correct spherical aberration. In order to ensure the effect of conditional expression (8), it is more preferable to set the lower limit of conditional expression (8) to 1.30, and further to 1.50, 1.80, 2.00, 2.30, 2.40, 2.50, 2.60, or 2.70. In addition, if the upper limit of conditional expression (8) is exceeded, it is undesirable because the aberration fluctuation associated with focusing becomes large. In order to ensure the effect of conditional expression (8), it is more desirable to set the upper limit of conditional expression (8) to 4.80, and more preferably to 4.50, 4.30, 4.00, 3.90, 3.80, 3.70 or 3.60.

[0040] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (9).

[0041] 0.00 < fp / f1 < 1.50 (9) however, f1: focal length of the first lens group G1 fp: focal length of the positive lens component located closest to the image plane in the first lens group G1

[0042] Conditional expression (9) specifies the focal length of the positive lens component arranged closest to the image surface in the first lens group G1 relative to the focal length of the first lens group G1. By satisfying this conditional expression (9), various aberrations, particularly field curvature and spherical aberration, can be corrected well. In order to ensure the effect of conditional expression (9), it is more preferable to set the lower limit of conditional expression (9) to 0.10, and further to 0.15, 0.20, 0.23, 0.25, 0.28, 0.30, 0.31, 0.32, or 0.33. In addition, if the upper limit of conditional expression (9) is exceeded, it is not preferable because it becomes difficult to correct spherical aberration, field curvature, axial chromatic aberration, and chromatic aberration of magnification. In order to ensure the effect of conditional expression (9), it is more desirable to set the upper limit of conditional expression (9) to 1.40, and more preferably to 1.30, 1.20, 1.10, 1.00, 0.90, 0.80, 0.70, 0.60, or 0.55.

[0043] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (10).

[0044] 0.80 < f1 / f < 15.00 (10) however, f: focal length of the entire optical system OL when focused at infinity f1: focal length of the first lens group G1

[0045] Conditional expression (10) specifies the focal length of the first lens group G1 relative to the focal length of the entire optical system OL in the infinity focus state. By satisfying this conditional expression (10), the axial chromatic aberration, spherical aberration, and coma aberration can be corrected in the first lens group G1, and the aberration fluctuation due to focusing can be suppressed. In addition, by simplifying the optical system on the image side of the first lens group G1, the entire optical system can be made small and good optical performance can be obtained. If the lower limit of conditional expression (10) is exceeded, the Petzval sum increases, making it difficult to correct the curvature of field, which is not preferable. In order to ensure the effect of conditional expression (10), it is more preferable to set the lower limit of conditional expression (10) to 1.00, and further to 2.00, 3.00, 4.00, 5.00, 5.50, 6.00, 6.50, or 7.00. Moreover, exceeding the upper limit of conditional expression (10) is undesirable because it becomes difficult to ensure good optical performance while reducing the size of the entire optical system. In order to ensure the effect of conditional expression (10), it is more desirable to set the upper limit of conditional expression (10) to 14.00, and further to 13.00, 12.00, 11.00, 10.00, 9.50, or 9.00.

[0046] In the optical systems OL according to the first and second embodiments, the focusing lens group Gfo is preferably a cemented lens formed by cementing a negative lens and a positive lens together. By using a cemented lens formed by cementing a positive lens and a negative lens together as the focusing lens group Gfo, it is possible to suppress aberration fluctuations, particularly axial fluctuations, that occur during focusing.

[0047] In the optical system OL according to the first and second embodiments, the first lens group desirably has a cemented lens in which a positive lens and a negative lens are cemented together (for example, the cemented lens CL1 in FIG. 1 in which the biconvex positive lens L14 and the biconcave negative lens L15 are cemented together). With this configuration, various aberrations, particularly chromatic aberration of magnification, can be suppressed.

[0048] In the optical systems OL according to the first and second embodiments, the first lens group G1 has, from the object side, a first negative lens L11, a second negative lens L12, a third negative lens L13, a positive lens L14, and a fourth negative lens L15, thereby enabling excellent correction of field curvature, distortion, and lateral chromatic aberration.

[0049] Here, it is preferable that the positive lens L14 and the fourth negative lens L15 are a cemented lens, which can suppress various aberrations, particularly lateral chromatic aberration.

[0050] Moreover, it is desirable that the first negative lens L11 is a negative meniscus lens with a convex surface facing the object side, which makes it possible to effectively correct various aberrations, particularly curvature of field and distortion.

[0051] Moreover, it is preferable that the second negative lens L12 is a negative meniscus lens with a convex surface facing the object side, which makes it possible to effectively correct various aberrations, particularly curvature of field and distortion.

[0052] Moreover, it is preferable that the third negative lens L13 is a negative meniscus lens with a convex surface facing the object side, which makes it possible to effectively correct various aberrations, particularly curvature of field and distortion.

[0053] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (11).

[0054] νj < 50.0 (11) however, Abbe number for the d-line of the medium of the positive lens constituting the cemented lens included in the first lens group G1

[0055] Conditional expression (11) specifies the Abbe number for the d-line of the medium of the positive lens constituting the cemented lens included in the first lens group G1. By satisfying this conditional expression (11), various aberrations, particularly lateral chromatic aberration, can be suppressed. If the upper limit of conditional expression (11) is exceeded, the curvature of the positive lens needs to be increased in order to correct the chromatic aberration, which is undesirable since it makes the cemented lens thicker and makes it difficult to make the entire optical system compact. In order to ensure the effect of conditional expression (11), it is more preferable to set the upper limit of conditional expression (11) to 45.0, and more preferably 40.0, 35.0, or 32.0.

[0056] Moreover, it is desirable for the optical systems OL according to the first and second embodiments to satisfy the following conditional expression (12).

[0057] 50.0 < νp (12) however, νp: Abbe number for the d-line of the medium of the positive lens in the first lens group G1 closest to the image surface

[0058] Conditional expression (12) defines the Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group G1. By satisfying this conditional expression (12), various aberrations, particularly axial chromatic aberration and lateral chromatic aberration, can be corrected well. If the lower limit of conditional expression (12) is exceeded, the refractive power of the positive lens becomes strong, which is undesirable since it becomes difficult to correct spherical aberration and Petzval sum. In order to ensure the effect of conditional expression (12), it is more preferable to set the lower limit of conditional expression (12) to 55.0, and further to 60.0, 65.0, 70.0, 75.0, 80.0, 85.0, or 90.0.

[0059] In the optical systems OL according to the first and second embodiments, it is desirable for the first lens group G1 to have a negative meniscus lens that satisfies the following conditional expression (13).

[0060] 50.0 < vsp (13) however, νsp: Abbe number for the d-line of the medium of the negative meniscus lens included in the first lens group G1

[0061] Conditional expression (13) defines the Abbe number for the d-line of the medium of the negative meniscus lens included in the first lens group G1. When the first lens group G1 has a negative meniscus lens that satisfies this conditional expression (13), various aberrations, particularly lateral chromatic aberration, can be corrected well. If the lower limit of conditional expression (13) is not satisfied, it becomes difficult to correct the lateral chromatic aberration. In addition, the difference in the curvature of field due to the wavelength also becomes large. In order to force the correction, it is necessary to provide a positive lens on the object side of the first lens group G1, which significantly increases the size of the optical system. In order to ensure the effect of conditional expression (13), it is more preferable to set the lower limit of conditional expression (13) to 55.0, and further to 60.0, 65.0, 70.0, 75.0, or 80.0.

[0062] In the optical systems OL according to the first and second embodiments, it is desirable for the first lens group G1 to have a negative meniscus lens that satisfies the following conditional expression (14).

[0063] nsp < 1.70 (14) however, nsp: the refractive index of the medium of the negative meniscus lens included in the first lens group G1 at the d line

[0064] Conditional expression (14) specifies the refractive index for the d-line of the medium of the negative meniscus lens included in the first lens group G1. When the first lens group G1 has a negative meniscus lens that satisfies this conditional expression (14), various aberrations, particularly lateral chromatic aberration, can be corrected well. Exceeding the upper limit of conditional expression (14) is undesirable because it increases the Petzval sum and makes it difficult to correct curvature of field. In order to ensure the effect of conditional expression (14), it is more preferable to set the upper limit of conditional expression (14) to 1.60, and more preferably 1.55 or 1.50.

[0065] In the optical systems OL according to the first and second embodiments, it is desirable that the negative meniscus lens included in the first lens group G1 and satisfying at least one of the above-mentioned conditional formula (13) or (14) has an aspheric lens surface on the object side and a lens surface on the image side. With this configuration, various aberrations, particularly field curvature and distortion, can be well corrected.

[0066] In addition, in the optical systems OL according to the first and second embodiments, it is desirable that the focusing lens group Gfo moves toward the object side along the optical axis when focusing from infinity to a close object. With this configuration, it is possible to suppress fluctuations in spherical aberration and axial chromatic aberration that accompany focusing.

[0067] It should be noted that the conditions and configurations described above each provide 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 any combination of the conditions or configurations.

[0068] 7 shows a schematic cross-sectional view of a single-lens reflex camera 1 (hereinafter simply referred to as camera) as an imaging device equipped with the above-mentioned optical system OL. In this camera 1, light from an object (subject) (not shown) is collected by a photographing lens 2 (optical system OL) and an image is formed on a focusing screen 4 via a quick return mirror 3. The light imaged on the focusing screen 4 is then reflected multiple times in a pentaprism 5 and directed to an eyepiece 6. This allows the photographer to observe the object (subject) image as an erect image through the eyepiece 6.

[0069] When the photographer presses a release button (not shown), the quick return mirror 3 moves out of the optical path, and the light of an object (subject) (not shown) collected by the photographing lens 2 forms an image of the object on the image sensor 7. As a result, the light from the object (subject) is captured by the image sensor 7 and recorded in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph the object (subject) with the camera 1. The camera 1 shown in FIG. 7 may detachably hold the photographing lens 2, or may be molded integrally with the photographing lens 2. The camera 1 may be a so-called single-lens reflex camera, or may be a compact camera without a quick return mirror or a mirrorless single-lens reflex camera.

[0070] Hereinafter, the manufacturing method of the optical system OL according to the present embodiment will be outlined with reference to FIG. 8, taking the optical system OL according to the second embodiment as an example. First, the first lens group G1, the second lens group G2, and the third lens group G3 of the optical system OL are prepared by arranging the respective lenses (step S100). In addition, the second lens group G2 is arranged as a focusing lens group Gfo that moves in the optical axis direction during focusing (step S200). Then, the respective lens groups are arranged so as to satisfy a condition according to a predetermined conditional formula (for example, the above-mentioned conditional formula (1)) (step S300).

[0071] Specifically, in this embodiment, as shown in FIG. 1, the optical system OL includes, in order from the object side, a first negative lens L11 having a meniscus shape with a convex surface facing the object side, a second negative lens L12 having a meniscus shape with a convex surface facing the object side, a third negative lens L13 having a meniscus shape with a convex surface facing the object side, a cemented lens CL1 in which a biconvex positive lens L14 and a biconcave negative lens L15 are cemented together, and a biconvex positive lens L16, which are arranged as a first lens group G1, and a meniscus negative lens L21 having a convex surface facing the object side and a meniscus negative lens L22 having a convex surface facing the object side. The second lens group G2 is a cemented lens formed by cementing a biconvex positive lens L31 and a biconcave negative lens L32, a meniscus-shaped positive lens L33 with a convex surface facing the object side, a cemented lens formed by cementing a meniscus-shaped negative lens L34 with a convex surface facing the object side and a biconvex positive lens L35, a cemented lens formed by cementing a meniscus-shaped negative lens L36 with a convex surface facing the object side and a biconvex positive lens L37, and a meniscus-shaped negative lens L38 with a convex surface facing the image surface side are arranged to form a third lens group G3. The second lens group G2 is a focusing lens group Gfo. The lens groups prepared in this way are arranged in the above-mentioned procedure to manufacture the optical system OL.

[0072] With the above-described configuration, it is possible to provide an optical system having good imaging performance, an optical device having this optical system, and a method for manufacturing the optical system. EXAMPLES

[0073] Each embodiment of the present invention will be described below with reference to the drawings, in which Fig. 1, Fig. 3, and Fig. 5 are cross-sectional views showing the configuration and refractive power distribution of an optical system OL (OL1 to OL3) according to each embodiment.

[0074] In each embodiment, the aspheric 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 apex of each aspheric surface at the height y to each aspheric surface (amount of sag), r is the radius of curvature (paraxial radius of curvature) of the reference sphere, K is the conic constant, and An is the n-th order aspheric coefficient. Note that in the following embodiments, "En" is expressed as "×10 -n".

[0075] 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 (a)

[0076] In each embodiment, the second-order aspheric coefficient A2 is 0. In the table of each embodiment, aspheric surfaces are marked with an * to the right of the surface number.

[0077] [First Example] 1 is a diagram showing the configuration of an optical system OL1 according to Example 1. This optical system OL1 is composed of, from the object side, a first lens group G1 having positive refractive power and a rear group GR having positive refractive power. The rear group GR is composed of, from the object side, a second lens group G2 having negative refractive power and a third lens group G3 having positive refractive power.

[0078] The first lens group G1 is composed of, in order from the object side, a first negative lens (or first negative meniscus lens) L11 having a meniscus shape with a convex surface facing the object side, a second negative lens (or second negative meniscus lens) L12 having a meniscus shape with a convex surface facing the object side, a third negative lens (or third negative meniscus lens) L13 having a meniscus shape with a convex surface facing the object side, a cemented lens CL1 consisting of a biconvex positive lens L14 and a biconcave negative lens L15 cemented together, and a biconvex positive lens L16.

[0079] The second lens group G2 is composed of a cemented lens in which, from the object side, a negative meniscus lens L21 with a convex surface facing the object side and a positive meniscus lens L22 with a convex surface facing the object side are cemented together.

[0080] The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a biconvex positive lens L31 and a biconcave negative lens L32, a meniscus positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus negative lens L34 with its convex surface facing the object side and a biconvex positive lens L35, a cemented lens formed by cementing a meniscus negative lens L36 with its convex surface facing the object side and a biconvex positive lens L37, and a meniscus negative lens L38 with its convex surface facing the image side.

[0081] In the optical system OL1, an aperture stop S is disposed between the second lens group G2 and the third lens group G3. In the optical system OL1, a filter FL is disposed between the third lens group G3 and the image plane I.

[0082] In addition, in this optical system OL1, focusing from an object at infinity to an object at a close distance is performed by fixing the first lens group G1 and the third lens group G3 with respect to the image plane I and moving the focusing lens group Gfo, which is the second lens group G2, from the image plane side to the object side along the optical axis.

[0083] The values ​​of the specifications of the optical system OL1 are shown in Table 1 below. In Table 1, f in the overall specifications indicates the focal length of the entire system in the infinity focused state, FNO indicates the F-number, ω indicates the half angle of view [°], Y indicates the maximum image height, and TL indicates the overall length. Here, the overall length TL indicates the distance on the optical axis from the lens surface closest to the object (the first surface in FIG. 1) to the image surface I when focused on infinity. In addition, in the lens data, the first column m indicates the order (surface number) of the lens surfaces from the object side along the direction in which the light ray travels, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance (surface spacing) on ​​the optical axis from each optical surface to the next optical surface, and the fourth column νd and the fifth column nd indicate the Abbe number and refractive index for the d-line (λ=587.6 nm). In addition, a radius of curvature of 0.00000 indicates a flat surface, and the refractive index of air, 1.00000, is omitted. The lens group focal length indicates the surface number and focal length of the first surface of each of the first lens group G1, rear group GR, second lens group G2, and third lens group G3 (the focal length of the rear group GR is the value when focused at infinity).

[0084] Here, the focal length f, radius of curvature r, surface spacing d, and other length units listed in all the following specifications are generally in "mm," but the optical system is not limited to this because the same optical performance can be obtained even if it is proportionally enlarged or reduced. The explanations of these symbols and the specifications tables also apply to the following examples.

[0085] (Table 1) First Example [Overall specifications] f = 14.36 FNO = 2.88 ω[°] = 56.4 Y = 21.60 TL = 159.9 [Lens data] mrd νd nd Object surface ∞ D0 1 47.0219 2.5000 59.95 1.631835 2 26.9000 8.6766 3* 37.7100 2.5000 82.57 1.497820 4* 13.9470 16.4215 5 125.3586 2.3000 52.67 1.741000 6* 28.0288 7.9769 7 384.3276 6.4852 31.85 1.826164 8 -32.1222 3.0000 81.47 1.487469 9 32.0024 10.9635 10 84.4517 9.4797 91.37 1.456000 11 -25.7140 D1 12 152.3955 1.2000 33.60 1.862086 13 13.3320 4.3737 30.37 1.899345 14 40.8063 D2 15 0.0000 0.0500 Aperture S 16 21.4627 5.6551 53.56 1.507742 17 -29.7782 1.0000 25.46 2.000690 18 39.2894 0.1000 19 24.3575 2.3131 23.94 1.768502 20 98.6099 0.1000 21 17.1858 1.0000 31.10 1.897498 22 12.1955 5.3161 70.32 1.487490 23 -53.4117 0.1592 24 2408.9184 1.0000 32.26 1.737999 25 11.7446 5.2963 26.87 1.659398 26 -45.7195 0.3474 27 -68.6279 1.2000 47.25 1.773870 28* -986.9537 38.0908 29 0.0000 2.0000 64.13 1.516800 30 0.0000 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 127.4216 Rear group GR 12 55.3436 Second lens group G2 12 -76.3989 Third lens group G3 16 33.6830

[0086] In this optical system OL1, the third, fourth, sixth and twenty-eighth surfaces are formed aspheric surfaces. Table 2 below shows data on the aspheric surfaces, that is, the values ​​of the conic constant K and each of the aspheric constants A4 to A10.

[0087] (Table 2) [Aspheric data] Surface K A4 A6 A8 A10 3 1.0000 -2.84128E-06 1.77032E-08 -1.78479E-11 1.20562E-14 4 0.1703 -1.57086E-06 8.88007E-09 9.96821E-11 -7.62152E-14 6 1.0000 2.01863E-05 1.95042E-08 2.45909E-11 -2.94950E-14 28 1.0000 3.93832E-05 5.20934E-08 8.66287E-10 -5.91381E-12

[0088] In this optical system OL1, the axial distance D0 from the surface (first surface) of the optical system OL1 closest to the object to the object, the axial distance D1 between the first lens group G1 and the second lens group G2, the axial distance D2 between the second lens group G2 and the aperture stop S (third lens group G3), and the axial distance BF between the filter FL and the image plane I change during focusing. Table 3 below shows the variable distances when focused at infinity and when focused on a close object. Note that β indicates the shooting magnification.

[0089] (Table 3) [Variable interval data] Infinity Near distance f 14.35999 - β - -0.03330 D0∞392.93110 D1 18.06566 16.30623 D2 2.42023 4.15465 BF 0.00000 -0.00603

[0090] The following Table 4 shows the corresponding values ​​of each conditional expression in this optical system OL1. In this Table 4, 2ω is the total angle of view of the optical system OL1, f is the focal length of the entire optical system OL1 when focused at infinity, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, fR is the composite focal length of the lens group closer to the image surface than the first lens group G1 in the optical system OL1 when focused at infinity (the focal length of the rear group GR), fp is the focal length of the positive lens component arranged closest to the image surface in the first lens group G1, fn123 is the focal length of the first negative meniscus lens L11, the second negative meniscus lens L23 is the focal length of the second negative meniscus lens L24, and fn123 is the focal length of the first negative meniscus lens L25. The composite focal length of the lens L12 and the third negative meniscus lens L13, bfa is the air-equivalent back focus of the optical system OL1, νj is the Abbe number for the d-line of the medium of the positive lens constituting the cemented lens included in the first lens group G1, νp is the Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group G1, νsp is the Abbe number for the d-line of the medium of the negative meniscus lens included in the first lens group G1, and nsp is the refractive index for the d-line of the medium of the negative meniscus lens included in the first lens group G1. The explanation of these symbols is the same in the following examples. In this first example, fp is the focal length of the double-convex positive lens L16, νj is the Abbe number of the double-convex positive lens L14, νp is the Abbe number of the double-convex positive lens L16, and νsp and nsp are the Abbe number and refractive index of the negative lens L12.

[0091] (Table 4) fp=44.4254 fn123=-14.9537 bfa=39.4093 (1) 2ω = 112.8 (2)(-fn123) / f=1.041 (3)(-fn123) / fp=0.337 (4) f3 / f=2.346 (5)(-f2) / f=5.320 (6) bfa / f=2.744 (7) f1 / fR=2.302 (8) fp / f=3.094 (9) fp / f1=0.349 (10) f1 / f=8.873 (11)νj=31.85 (12)νp=91.37 (13)νsp=82.57 (14) nsp=1.50

[0092] In this way, the optical system OL1 satisfies all of the above conditional expressions (1) to (14).

[0093] FIG. 2 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma diagrams of this optical system OL1 when focused at infinity. In each aberration diagram, FNO indicates the F-number, and Y indicates the image height. In the spherical aberration diagram, the F-number value corresponding to the maximum aperture is shown, in the astigmatism diagram and the distortion diagram, the maximum value of the image height is shown, and in the coma diagram, the value of each image height is shown. d indicates the d-line (λ=587.6 nm), and g indicates the g-line (λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image surface, and the dashed line indicates the meridional image surface. In the coma diagram, the solid line indicates the meridional coma, and the dashed line indicates the Y direction (meridional) and Z direction (sagittal) of the skew ray, respectively. In the aberration diagrams of each embodiment shown below, the same symbols as in this embodiment are used. From these aberration diagrams, it is apparent that various aberrations are well corrected in the optical system OL1.

[0094] [Second Example] 3 is a diagram showing the configuration of an optical system OL2 according to Example 2. This optical system OL2 is composed of, from the object side, a first lens group G1 having positive refractive power and a rear lens group GR having positive refractive power. The rear lens group GR is composed of, from the object side, a second lens group G2 having negative refractive power and a third lens group G3 having positive refractive power.

[0095] The first lens group G1 is composed of, in order from the object side, a first negative lens (or first negative meniscus lens) L11 having a meniscus shape with a convex surface facing the object side, a second negative lens (or second negative meniscus lens) L12 having a meniscus shape with a convex surface facing the object side, a third negative lens (or third negative meniscus lens) L13 having a meniscus shape with a convex surface facing the object side, a cemented lens CL1 consisting of a biconvex positive lens L14 and a biconcave negative lens L15 cemented together, and a biconvex positive lens L16.

[0096] The second lens group G2 is composed of a cemented lens in which, from the object side, a negative meniscus lens L21 with a convex surface facing the object side and a positive meniscus lens L22 with a convex surface facing the object side are cemented together.

[0097] The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a biconvex positive lens L31 and a biconcave negative lens L32, a meniscus positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus negative lens L34 with its convex surface facing the object side and a biconvex positive lens L35, a cemented lens formed by cementing a meniscus negative lens L36 with its convex surface facing the object side and a biconvex positive lens L37, and a biconcave negative lens L38.

[0098] In the optical system OL2, an aperture stop S is disposed between the second lens group G2 and the third lens group G3. In the optical system OL2, a filter FL is disposed between the third lens group G3 and the image plane I.

[0099] In addition, in this optical system OL2, focusing from an object at infinity to an object at a close distance is performed by fixing the first lens group G1 and the third lens group G3 with respect to the image plane I and moving the focusing lens group Gfo, which is the second lens group G2, from the image plane side to the object side along the optical axis.

[0100] Table 5 below lists the specifications of the optical system OL2.

[0101] (Table 5) Second Example [Overall specifications] f = 12.36 FNO = 2.88 ω[°] = 61.2 Y = 21.60 TL = 165.6 [Lens data] mrd νd nd Object surface ∞ D0 1* 123.6764 3.0000 43.81 1.837208 2 26.9000 10.8592 3* 34.1255 2.5000 87.13 1.468099 4* 17.5865 13.7281 5 72.2114 2.3000 40.66 1.883000 6* 28.0288 9.3790 7 209.6969 9.2128 26.90 1.755328 8 -29.5048 2.5559 84.24 1.477461 9 31.8373 8.9410 10 60.9536 12.1981 91.37 1.456000 11 -28.3539 D1 12 297.1761 1.0226 30.08 1.806044 13 12.2150 5.9179 28.04 1.813749 14 51.2545 D2 15 0.0000 0.0500 Aperture S 16 22.5323 4.6551 56.39 1.500845 17 -33.5240 1.0000 25.38 1.994547 18 37.3510 0.1000 19 25.0529 2.1694 25.77 1.720823 20 90.6318 0.1000 21 17.7582 1.0000 33.75 1.865872 22 12.8125 5.0030 70.32 1.487490 23 -54.9085 0.9159 24 326.9572 1.0000 32.26 1.737999 25 11.6430 5.2310 26.87 1.659398 26 -50.9878 0.0500 27 -96.5889 1.1078 47.25 1.773870 28* 4697.2424 38.0937 29 0.0000 2.0000 64.13 1.516800 30 0.0000 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 89.3772 Rear group GR 12 55.0687 Second lens group G2 12 -81.0572 Third lens group G3 16 34.7892

[0102] In this optical system OL2, surfaces 1, 3, 4, 6 and 28 are formed aspheric. Table 6 below shows data on the aspheric surfaces, that is, the conic constant K and the values ​​of each of the aspheric constants A4 to A10.

[0103] (Table 6) [Aspheric data] Surface K A4 A6 A8 A10 1 2.9452 8.50155E-06 -6.55314E-09 2.83916E-12 -4.23824E-16 3 1.0000 -1.17482E-05 2.74323E-08 -1.86417E-11 -1.88477E-15 4 0.5619 -4.26615E-06 7.98631E-08 -2.70962E-10 1.56850E-13 6 1.0000 1.13709E-05 1.60615E-09 1.49741E-10 -3.77636E-13 28 1.0000 3.40787E-05 4.23370E-08 7.46077E-10 -4.31808E-12

[0104] In this optical system OL2, the axial distance D0 from the surface (first surface) of the optical system OL1 closest to the object to the object, the axial distance D1 between the first lens group G1 and the second lens group G2, the axial distance D2 between the second lens group G2 and the aperture stop S (third lens group G3), and the axial distance BF between the filter FL and the image plane I change during focusing. Table 7 below shows the variable distances when focused at infinity and when focused on a close object. Note that β indicates the shooting magnification.

[0105] (Table 7) [Variable interval data] Infinity Near distance f 12.36000 - β - -0.02500 D0∞460.73750 D1 19.32015 17.66124 D2 2.21228 3.87119 BF 0.00000 -0.01285

[0106] The corresponding values ​​of each conditional expression in this optical system OL2 are shown in Table 8. In this second embodiment, fp is the focal length of the biconvex positive lens L16, νj is the Abbe number of the biconvex positive lens L14, νp is the Abbe number of the biconvex positive lens L16, and νsp and nsp are the Abbe number and refractive index of the negative lens L12.

[0107] (Table 8) fp=44.3349 fn123=-13.1306 bfa=39.4122 (1) 2ω = 122.4 (2)(-fn123) / f=1.062 (3)(-fn123) / fp=0.296 (4) f3 / f=2.815 (5)(-f2) / f=6.558 (6) bfa / f=3.189 (7) f1 / fR=1.623 (8) fp / f=3.587 (9) fp / f1=0.496 (10) f1 / f=7.231 (11)νj=26.90 (12)νp=91.37 (13) vsp=87.13 (14) nsp=1.50

[0108] In this way, the optical system OL2 satisfies all of the above conditional expressions (1) to (14).

[0109] 4 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration for this optical system OL2 when focused at infinity. These aberration diagrams show that various aberrations are well corrected for in the optical system OL2.

[0110] [Third Example] 5 is a diagram showing the configuration of an optical system OL3 according to Example 3. This optical system OL3 is composed of, from the object side, a first lens group G1 having positive refractive power and a rear group GR having positive refractive power. The rear group GR is composed of, from the object side, a second lens group G2 having negative refractive power and a third lens group G3 having positive refractive power.

[0111] The first lens group G1 is composed of, in order from the object side, a first negative lens (or first negative meniscus lens) L11 having a meniscus shape with a convex surface facing the object side, a second negative lens (or second negative meniscus lens) L12 having a meniscus shape with a convex surface facing the object side, a third negative lens (or third negative meniscus lens) L13 having a meniscus shape with a convex surface facing the object side, a cemented lens CL1 consisting of a biconvex positive lens L14 and a biconcave negative lens L15 cemented together, and a biconvex positive lens L16.

[0112] The second lens group G2 is composed of a cemented lens in which, from the object side, a negative meniscus lens L21 with a convex surface facing the object side and a positive meniscus lens L22 with a convex surface facing the object side are cemented together.

[0113] The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a biconvex positive lens L31 and a biconcave negative lens L32, a meniscus positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus negative lens L34 with its convex surface facing the object side and a biconvex positive lens L35, a cemented lens formed by cementing a biconcave negative lens L36 and a biconvex positive lens L37, and a biconcave negative lens L38.

[0114] In the optical system OL3, an aperture stop S is disposed between the second lens group G2 and the third lens group G3. In the optical system OL3, a filter FL is disposed between the third lens group G3 and the image plane I.

[0115] In addition, in this optical system OL3, focusing from an object at infinity to an object at a close distance is performed by fixing the first lens group G1 and the third lens group G3 with respect to the image plane I and moving the focusing lens group Gfo, which is the second lens group G2, from the image plane side to the object side along the optical axis.

[0116] Table 9 below lists the specifications of the optical system OL3.

[0117] (Table 9) Third Example [Overall specifications] f = 16.48 FNO = 2.88 ω[°] = 52.8 Y = 21.60 TL = 160.0 [Lens data] mrd νd nd Object surface ∞ D0 1 39.6142 5.0000 52.34 1.755000 2 27.3858 8.5477 3* 33.2055 2.5000 82.57 1.497820 4* 13.1996 15.9987 5 83.3700 2.3000 52.67 1.741000 6* 28.0288 7.4882 7 903.1304 8.3689 30.08 1.911918 8 -41.4440 3.0000 80.65 1.490638 9 33.5455 10.7750 10 84.0718 10.1279 91.37 1.456000 11 -26.2853 D1 12 446.9940 1.2000 33.67 1.861126 13 15.7892 4.2607 29.37 1.922788 14 44.2919 D2 15 0.0000 0.0500 Aperture S 16 22.0269 4.2536 53.81 1.507088 17 -35.1767 1.0000 25.32 1.989791 18 41.4549 0.1000 19 28.1065 2.5043 22.74 1.808090 20 464.3428 0.1000 21 17.9194 1.0000 30.30 1.908654 22 12.7733 5.3094 70.32 1.487490 23 -52.2422 1.5697 24 -75.1921 1.0000 32.26 1.737999 25 12.5296 5.1199 26.87 1.659398 26 -75.7013 0.1000 27 -2698.6076 1.2000 47.25 1.773870 28* 598.3062 38.3669 29 0.0000 2.0000 64.13 1.516800 30 0.0000 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 132.8313 Rear group GR 12 57.2616 Second lens group G2 12 -67.9699 Third lens group G3 16 32.6991

[0118] In this optical system OL3, surfaces 3, 4, 6 and 28 are formed aspheric. Table 10 below shows data on the aspheric surfaces, that is, the values ​​of the conic constant K and each of the aspheric constants A4 to A10.

[0119] (Table 10) [Aspheric data] Surface K A4 A6 A8 A10 3 1.0000 -6.10454E-06 1.37878E-08 -1.88319E-11 1.07993E-14 4 0.3686 -4.34076E-06 -1.36341E-08 1.07882E-10 -2.38693E-13 6 1.0000 1.36143E-05 2.57728E-08 -9.18517E-12 2.04898E-13 28 1.0000 3.36113E-05 3.50988E-08 5.15560E-10 -3.38548E-12

[0120] In this optical system OL3, the axial distance D0 from the surface (first surface) of the optical system OL1 closest to the object to the object, the axial distance D1 between the first lens group G1 and the second lens group G2, the axial distance D2 between the second lens group G2 and the aperture stop S (third lens group G3), and the axial distance BF between the filter FL and the image plane I change during focusing. Table 11 below shows the variable distances when focused at infinity and when focused on a close object. Note that β indicates the shooting magnification.

[0121] (Table 11) [Variable interval data] Infinity Near distance f 16.48000 - β - -0.03300 D0∞ 450.56370 D1 14.28467 12.81127 D2 2.47799 3.95140 BF 0.00000 -0.00671

[0122] The corresponding values ​​of each conditional expression in this optical system OL3 are shown in Table 12. In this third embodiment, fp is the focal length of the biconvex positive lens L16, νj is the Abbe number of the biconvex positive lens L14, νp is the Abbe number of the biconvex positive lens L16, and νsp and nsp are the Abbe number and refractive index of the negative lens L12.

[0123] (Table 8) fp=45.2130 fn123=-17.9914 bfa=39.6855 (1) 2ω = 105.6 (2)(-fn123) / f=1.092 (3)(-fn123) / fp=0.398 (4) f3 / f=1.984 (5)(-f2) / f=4.124 (6) bfa / f=2.408 (7) f1 / fR=2.320 (8) fp / f=2.744 (9) fp / f1=0.340 (10) f1 / f=8.060 (11)νj=30.08 (12)νp=91.37 (13)νsp=82.57 (14) nsp=1.50

[0124] In this way, the optical system OL3 satisfies all of the above conditional expressions (1) to (14).

[0125] Fig. 6 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration for this optical system OL3 when focused at infinity. These aberration diagrams show that various aberrations are well corrected in the optical system OL3.

[0126] The contents described below can be appropriately adopted as long as they do not impair optical performance.

[0127] In this embodiment, the optical system OL is configured with three groups, but the above configuration conditions can be applied to other group configurations such as four groups and five groups. In addition, a configuration in which a lens or lens group is added closest to the object side, or a configuration in which a lens or lens group is added closest to the image surface side, may be used. Specifically, a configuration in which a lens group whose position relative to the image surface is fixed when zooming or focusing is added closest to the image surface side is considered. In addition, the lens group refers to a portion having at least one lens separated by an air gap that changes when zooming or focusing. In addition, the lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0128] Also, a single or multiple lens groups, or a partial lens group may be moved in the optical axis direction to form a focusing lens group that focuses from an object at infinity to an object at a close distance. In this case, the focusing lens group can be applied to autofocusing, and is also suitable for driving a motor (such as an ultrasonic motor) for autofocusing. In particular, as described above, it is preferable to use the second lens group GR as the focusing lens group Gfo, and to fix the positions of the other lenses relative to the image plane during focusing. Considering the load on the motor, it is preferable that the focusing lens group is composed of a single lens.

[0129] In addition, the lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (rocked) in a plane including the optical axis to serve as an anti-vibration lens group that corrects image blur caused by camera shake. In particular, it is preferable to use at least a part of the third lens group G3 as an anti-vibration lens group.

[0130] The lens surface may be spherical or flat, or aspheric. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment, and prevents deterioration of optical performance due to processing and assembly adjustment errors. It is also preferable because there is little deterioration in depiction performance even if the image plane is shifted. When the lens surface is aspheric, the aspheric surface may be any of aspheric surfaces such as an aspheric surface formed by grinding, a glass molded aspheric surface formed by molding glass into an aspheric shape, and a composite aspheric surface formed by forming a resin into an aspheric shape on the surface of glass. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0131] It is preferable that the aperture stop S is disposed near or within the third lens group G3, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as the aperture stop.

[0132] Furthermore, each lens surface may be coated with an anti-reflection coating having high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high contrast and high optical performance. [Explanation of symbols]

[0133] 1 Camera (optical equipment) OL (OL1~OL3) Optical system G1 First lens group GR Rear group G2 2nd lens group (Gfo focusing lens group) G3 3rd lens group L11 1st negative meniscus lens, 1st negative lens L12 2nd negative meniscus lens, 2nd negative lens L13 3rd negative meniscus lens, 3rd negative lens CL1 Cemented Lens L14 Biconvex Positive Lens L16 Biconvex positive lens (positive lens component)

Claims

1. Starting from the object side, A first negative meniscus lens; and A second negative meniscus lens; and a third negative meniscus lens; and a rear lens group having a focusing lens group that is disposed closer to the object side than the first lens group and moves in the optical axis direction when focusing, and the first lens group has a positive lens that is a positive lens component closest to an image surface, the third negative meniscus lens is a single lens, An optical system that satisfies the following condition: 80° < 2ω < 180° 0.80 < f1 / fR < 3.00 0.90 < (-fn123) / f < 1.15 0.00 < fp / f1 < 0.55 50.0 <νp however, 2ω: full angle of view of the optical system f1: focal length of the first lens group fR: composite focal length of the lens group on the image side of the first lens group in the optical system when focused at infinity f: focal length of the entire optical system when focused at infinity fn123: a composite focal length of the first negative meniscus lens, the second negative meniscus lens, and the third negative meniscus lens fp: focal length of the positive lens component arranged closest to the image surface in the first lens group νp: Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group

2. Starting from the object side, A first negative meniscus lens; and A second negative meniscus lens; and a third negative meniscus lens; and a rear lens group having a focusing lens group that is disposed closer to the object side than the first lens group and moves in the optical axis direction when focusing, and the first lens group has a positive lens that is a positive lens component closest to an image surface, the third negative meniscus lens is a single lens, An optical system that satisfies the following condition: 80° < 2ω < 180° 2.50 < fp / f < 5.00 0.95 < (-fn123) / f < 1.15 0.00 < fp / f1 < 0.55 50.0 <νp however, 2ω: full angle of view of the optical system f: focal length of the entire optical system when focused at infinity fp: focal length of the positive lens component arranged closest to the image surface in the first lens group fn123: a composite focal length of the first negative meniscus lens, the second negative meniscus lens, and the third negative meniscus lens f1: focal length of the first lens group νp: Abbe number for the d-line of the medium of the positive lens closest to the image surface in the first lens group

3. 2. The optical system according to claim 1, which satisfies the following condition: 1.00 < fp / f < 5.00 however, f: focal length of the entire optical system when focused at infinity fp: focal length of the positive lens component arranged closest to the image surface in the first lens group

4. 3. The optical system according to claim 2, which satisfies the following condition: 0.20 < f1 / fR however, f1: focal length of the first lens group fR: composite focal length of the lens group on the image side of the first lens group in the optical system when focused at infinity

5. the first lens group has a positive refractive power, 5. The optical system according to claim 1, wherein the rear group has a positive refractive power.

6. 6. The optical system according to claim 1, which satisfies the following condition: 0.05 < (-fn123) / fp < 1.00 however, fn123: a composite focal length of the first negative meniscus lens, the second negative meniscus lens, and the third negative meniscus lens fp: focal length of the positive lens component arranged closest to the image surface in the first lens group

7. 7. The optical system according to claim 1, which satisfies the following condition: 1.00 < bfa / f however, f: focal length of the entire optical system when focused at infinity bfa: air-equivalent back focus of the optical system

8. 8. The optical system according to claim 1, which satisfies the following condition: 0.80 < f1 / f < 15.00 however, f: focal length of the entire optical system when focused at infinity f1: focal length of the first lens group

9. the first lens group includes a cemented lens in which a positive lens and a negative lens are cemented together, 9. The optical system according to claim 1, which satisfies the following condition: νj < 50.0 however, the Abbe number of the medium of the positive lens constituting the cemented lens included in the first lens group with respect to the d-line

10. 10. The optical system according to claim 1, wherein the first lens group has a negative meniscus lens that satisfies the following condition: 50.0 < vsp nsp < 1.70 however, νsp: Abbe number of the medium of the negative meniscus lens with respect to the d line nsp: refractive index of the medium of the negative meniscus lens with respect to the d line

11. 11. The optical system according to claim 1, wherein, when focusing from infinity to a close-distance object, the focusing lens group moves toward the object along the optical axis.

12. An optical instrument comprising the optical system according to any one of claims 1 to 11.

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