JP7627444B2 - Optical systems and optical instruments - Google Patents

Description

The present invention relates to an optical system and an optical instrument.

Conventionally, optical systems have been proposed that use aspherical lenses to achieve a small size and a wide angle of view (see, for example, Patent Document 1). However, Patent Document 1 has an issue in that further improvements in optical performance are required.

International Publication No. WO 2016/056310

An optical system according to a first aspect of the present invention essentially 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°
0.80 < f1/fR < 3.00
0.90 < (-fn123)/f < 1.15
0.00 < fp/f1 < 0.55
50.0 <νp
however,
2ω: total angle of view of the optical system f1: focal length of the first lens group fR: composite focal length of the lens group of the optical system closer to the image surface than the first lens group in the infinity focused state f: focal length of the entire optical system in the infinity focused state fn123: 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

In addition, an optical system according to a second aspect of the present invention essentially consists of 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: total angle of view of the optical system f: focal length of the entire optical system in an infinity focused state fp: focal length of the positive lens component arranged closest to the image surface side of the first lens group fn123: 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

FIG. 2 is a cross-sectional view showing the lens configuration of the optical system according to the first example when focused on infinity. 5A to 5C are diagrams illustrating various aberrations in the optical system according to the first example when focused on an object at infinity. FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 2 when focused on infinity. 13A to 13C are diagrams illustrating various aberrations in the optical system according to the second example when focused on an object at infinity. FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 3 when focused at infinity. 13A to 13C are diagrams illustrating various aberrations in the optical system according to Example 3 when focused at infinity. FIG. 2 is a cross-sectional view of a camera equipped with the optical system. 4 is a flowchart illustrating a method for manufacturing the optical system.

The preferred embodiment will be described below with reference to the drawings. As shown in FIG. 1, the optical system OL according to the first embodiment has, 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 surface 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.

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

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

Conditional formula (1) specifies 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 furthermore 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 furthermore to 170°, 165°, 160°, or 150°.

In addition, in the optical system OL according to the first embodiment, it is desirable that the first lens group G1 has a positive refractive power and the rear group GR has a positive refractive power. With this configuration, it is possible to suppress aberration fluctuations that occur during focusing.

Furthermore, it is desirable that the optical system OL according to the first embodiment satisfies the following conditional expression (2).

0.50 < (-fn123)/f < 1.50 (2)
however,
f: focal length of the entire optical system OL in a state 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.

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 relative to the focal length of the entire optical system OL in the infinity focused state. By satisfying this conditional expression (2), it is possible to obtain an optical system that is small and has well-corrected aberrations while ensuring a long back focus relative to the focal length. If the lower limit of conditional expression (2) is exceeded, it is not preferable because it becomes difficult to correct chromatic aberration of magnification. 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, and if it is forcibly made small, it is not preferable because it becomes difficult to correct curvature of field and distortion. In order to ensure the effect of conditional expression (2), it is more preferable 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.

In addition, in the optical system OL according to the first embodiment, it is desirable for the first lens group G1 to have at least one positive lens component (for example, the biconvex positive lens L16 in FIG. 1) closest to the image surface. This configuration satisfies the need for compactness and allows for good correction of spherical aberration, coma aberration, and aberration fluctuations associated with focusing.

Furthermore, it is desirable that the optical system OL according to the first embodiment satisfies the following conditional expression (3).

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 disposed closest to the image surface in the first lens group G1;

Conditional formula (3) specifies the composite focal length of the three negative meniscus lenses arranged on the most object side of the first lens group G1 relative to the focal length of the positive lens component arranged on the most image side of the first lens group G1. By satisfying this conditional formula (3), it is possible to achieve compactness and suppress aberration fluctuations due to focusing while satisfactorily correcting spherical aberration, axial chromatic aberration, lateral chromatic aberration, etc. If the lower limit of conditional formula (3) is exceeded, it is not preferable because it is difficult to correct lateral chromatic aberration, curvature of field, and distortion aberration. In order to ensure the effect of conditional formula (3), it is more preferable to set the lower limit of conditional formula (3) to 0.10, and further to 0.15, 0.20, 0.25, and 0.28. Also, if the upper limit of conditional formula (3) is exceeded, it is not preferable because it is difficult to suppress aberration fluctuations due to focusing. In order to ensure the effect of conditional expression (3), it is more preferable to set the upper limit value 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.

The optical system OL according to the second embodiment has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power, and the second lens group G2 is a focusing lens group Gfo that moves in the optical axis direction when focusing. With this configuration, it is possible to suppress fluctuations in field curvature and distortion aberration that accompany focusing.

Furthermore, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (1).

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

Conditional formula (1) specifies 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 furthermore 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 furthermore to 170°, 165°, 160°, or 150°.

Furthermore, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (4).

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

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 the infinity focus 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. In addition, 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. In addition, 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 preferable 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.

In addition, in the optical system OL according to the second embodiment, it is preferable that the first lens group G1 has, 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 field curvature and distortion.

Furthermore, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (5).

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

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 the infinity focus 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 exceeded, the variation of the 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 preferable to set the upper limit value 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.

In addition, in the optical system OL according to the second embodiment, it is desirable 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 associated with focusing while effectively correcting spherical aberration, coma, and axial chromatic aberration.

Furthermore, it is desirable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (6).

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 the optical system OL

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 on the optical axis from the lens surface closest to the image surface of the optical system OL to the image surface I when focused at infinity (air-equivalent length). By satisfying this conditional expression (6), it is possible to obtain a long back focus suitable for a single-lens reflex camera equipped with a mirror box 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.

Furthermore, it is preferable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (7).

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

Conditional expression (7) specifies the focal length of the first lens group G1 with respect to the composite focal length of the lens group 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 by simplifying the optical system on the image side of the first lens group G1, it is possible to obtain good optical performance while miniaturizing the entire optical system. If the lower limit of conditional expression (7) 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 formula (7), it is more preferable to set the lower limit of conditional formula (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 formula (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 formula (7) in order to obtain good optical performance while making the entire optical system compact. In order to ensure the effect of conditional formula (7), it is more preferable to set the upper limit of conditional formula (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.

Furthermore, it is desirable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (8).

1.00 < fp/f < 5.00 (8)
however,
f: focal length of the entire optical system OL in a state of focusing at infinity fp: focal length of the positive lens component arranged closest to the image surface in the first lens group G1

Conditional expression (8) 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 entire optical system OL in the 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 not preferable 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 not preferable because the aberration fluctuation associated with focusing increases. In order to ensure the effect of conditional expression (8), it is more preferable 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.

Furthermore, it is desirable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (9).

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 arranged closest to the image surface in the first lens group G1

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 curvature of field 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, curvature of field, axial chromatic aberration, and chromatic aberration of magnification. In order to ensure the effect of conditional expression (9), it is more preferable to set the upper limit value 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.

Furthermore, it is preferable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (10).

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

Conditional formula (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 formula (10), axial chromatic aberration, spherical aberration, and coma aberration can be corrected in the first lens group G1, and aberration fluctuations 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 while obtaining good optical performance. If the lower limit of conditional formula (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 formula (10), it is more preferable to set the lower limit of conditional formula (10) to 1.00, and further to 2.00, 3.00, 4.00, 5.00, 5.50, 6.00, 6.50, and 7.00. Moreover, exceeding the upper limit of conditional expression (10) is undesirable because it becomes difficult to ensure good optical performance while miniaturizing the entire optical system. In order to ensure the effect of conditional expression (10), it is more preferable 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.

In addition, in the optical system OL according to the first and second embodiments, it is preferable that the focusing lens group Gfo is a cemented lens in which a negative lens and a positive lens are cemented together. By making the focusing lens group Gfo a cemented lens in which a positive lens and a negative lens are cemented together, it is possible to suppress aberration fluctuations, particularly axial fluctuations, that accompany focusing.

In the optical system OL according to the first and second embodiments, it is preferable that the first lens group 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.

In addition, in the optical system OL according to the first and second embodiments of the present invention, 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 chromatic aberration of magnification.

Here, it is preferable that the positive lens L14 and the fourth negative lens L15 are cemented lenses. With this configuration, it is possible to suppress various aberrations, particularly chromatic aberration of magnification.

It is also desirable that the first negative lens L11 be a negative meniscus lens with a convex surface facing the object side. With this configuration, various aberrations, particularly field curvature and distortion, can be effectively corrected.

The second negative lens L12 is preferably a negative meniscus lens with a convex surface facing the object side. With this configuration, various aberrations, particularly field curvature and distortion, can be effectively corrected.

It is also preferable that the third negative lens L13 is a negative meniscus lens with a convex surface facing the object side. With this configuration, various aberrations, particularly field curvature and distortion, can be effectively corrected.

Furthermore, it is desirable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (11).

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

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 must be made tight to correct the chromatic aberration, which is undesirable because 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 further to 40.0, 35.0, or 32.0.

Furthermore, it is desirable that the optical system OL according to the first and second embodiments of the present invention satisfy the following conditional expression (12).

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

Conditional expression (12) specifies 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 as it makes it 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.

In addition, in the optical system OL according to the first and second embodiments, it is preferable that the first lens group G1 has a negative meniscus lens that satisfies the following conditional expression (13).

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

Conditional expression (13) specifies the Abbe number for the d-line of the medium of the negative meniscus lens included in the first lens group G1. By having the first lens group G1 have 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 exceeded, it becomes difficult to correct the lateral chromatic aberration. In addition, the difference in the field curvature 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.

In addition, in the optical system OL according to the first and second embodiments, it is preferable that the first lens group G1 has a negative meniscus lens that satisfies the following conditional expression (14).

nsp < 1.70 (14)
however,
nsp: refractive index of the medium of the negative meniscus lens included in the first lens group G1 with respect to the d-line

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 the Petzval sum increases and it becomes difficult to correct the curvature of field. Note that 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 further to 1.55 or 1.50.

In addition, in the optical systems OL according to the first and second embodiments of the present invention, 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 conditional formula (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 effectively corrected.

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

The conditions and configurations described above each provide the above-mentioned effects, and are not limited to those that satisfy all of the conditions and configurations. The above-mentioned effects can be obtained by satisfying any of the conditions or configurations, or any combination of the conditions or configurations.

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

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 it may be a compact camera without a quick return mirror or a mirrorless single-lens reflex camera.

Below, an outline of a manufacturing method for the optical system OL according to this embodiment will be described with reference to FIG. 8, using 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, each lens group is arranged so as to satisfy a condition according to a predetermined conditional formula (for example, the above-mentioned conditional formula (1)) (step S300).

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 are arranged to form a first lens group G1. 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 then arranged in the above-mentioned procedure to manufacture the optical system OL.

The above configuration makes it possible to provide an optical system with good imaging performance, an optical device having this optical system, and a method for manufacturing the optical system.

Each embodiment of the present application will be described below with reference to the drawings. Note that Figs. 1, 3, and 5 are cross-sectional views showing the configuration and refractive power distribution of the optical system OL (OL1 to OL3) in each embodiment.

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 height y to each aspheric surface (amount of sag), r is the radius of curvature (paraxial radius of curvature) of the reference spherical surface, K is the conic constant, and An is the n-th order aspheric coefficient. Note that in the following embodiments, "E-n" represents "×10 ^-n ".

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)

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

[First embodiment]
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 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.

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.

The second lens group G2 is composed of a cemented lens consisting of, in order from the object side, a negative meniscus lens L21 with its convex surface facing the object side and a positive meniscus lens L22 with its convex surface facing the object side.

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-shaped positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus-shaped 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-shaped negative lens L36 with its convex surface facing the object side and a biconvex positive lens L37, and a meniscus-shaped negative lens L38 with its convex surface facing the image plane side.

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

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 second lens group G2, the focusing lens group Gfo, along the optical axis from the image plane side to the object side.

The following Table 1 lists the values of the specifications of the optical system OL1. In this 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 total length. Here, the total 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, the first column m in the lens data indicates the order (surface number) of the lens surfaces from the object side along the direction in which the light rays travel (surface number), the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and the fourth column 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 of 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, the rear group GR, the second lens group G2, and the third lens group G3 (the focal length of the rear group GR is the value when focused at infinity).

The focal length f, radius of curvature r, surface spacing d, and other length units listed in the following specifications are generally 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 table also apply to the following examples.

(Table 1) First Example [Overall Specifications]
f = 14.36
FNO = 2.88
ω [°] = 56.4
Y = 21.60
TL = 159.9

[Lens data]
m r d ν d 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

In this optical system OL1, the third, fourth, sixth and twenty-eighth surfaces are aspheric. The following Table 2 shows the aspheric data, i.e., the conic constant K and the values of each of the aspheric constants A4 to A10.

(Table 2)
[Aspheric data]
Face 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

In this optical system OL1, the axial distance D0 from the surface (first surface) of 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. The following Table 3 shows the variable distances when focused at infinity and when focused on a close object. Note that β indicates the shooting magnification.

(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

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 of 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 first negative meniscus lens L22, and fn123 is the focal length of the second negative meniscus lens L23. In the first embodiment, fp is the focal length of the biconvex positive 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 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.

(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) vj = 31.85
(12) vp = 91.37
(13) vsp=82.57
(14) nsp = 1.50

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

Figure 2 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, 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. These aberration diagrams show that the various aberrations of the optical system OL1 are well corrected.

[Second embodiment]
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.

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.

The second lens group G2 is composed of a cemented lens consisting of, in order from the object side, a negative meniscus lens L21 with its convex surface facing the object side and a positive meniscus lens L22 with its convex surface facing the object side.

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-shaped positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus-shaped 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-shaped negative lens L36 with its convex surface facing the object side and a biconvex positive lens L37, and a biconcave negative lens L38.

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

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 second lens group G2, the focusing lens group Gfo, along the optical axis from the image plane side to the object side.

The specifications of optical system OL2 are listed in Table 5 below.

(Table 5) Second Example [Overall Specifications]
f = 12.36
FNO = 2.88
ω [°] = 61.2
Y = 21.60
TL = 165.6

[Lens data]
m r d ν d 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

In this optical system OL2, the first, third, fourth, sixth and twenty-eighth surfaces are aspheric. The following Table 6 shows the aspheric data, i.e., the conic constant K and the values of each of the aspheric constants A4 to A10.

(Table 6)
[Aspheric data]
Face 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

In this optical system OL2, the axial distance D0 from the surface (first surface) of 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. The following Table 7 shows the variable distances when focused on infinity and when focused on a close object. Note that β indicates the shooting magnification.

(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

The following Table 8 shows the corresponding values of each conditional expression in this optical system OL2. 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.

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) vj = 26.90
(12) vp = 91.37
(13) vsp = 87.13
(14) nsp = 1.50

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

Figure 4 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration diagrams for this optical system OL2 when focused at infinity. From these aberration diagrams, it can be seen that various aberrations are well corrected in the optical system OL2.

[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 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.

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.

The second lens group G2 is composed of a cemented lens consisting of, in order from the object side, a negative meniscus lens L21 with its convex surface facing the object side and a positive meniscus lens L22 with its convex surface facing the object side.

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-shaped positive lens L33 with its convex surface facing the object side, a cemented lens formed by cementing a meniscus-shaped 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.

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

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 second lens group G2, the focusing lens group Gfo, along the optical axis from the image plane side to the object side.

The specifications of optical system OL3 are listed in Table 9 below.

(Table 9) Third Example [Overall Specifications]
f = 16.48
FNO = 2.88
ω [°] = 52.8
Y = 21.60
TL = 160.0

[Lens data]
m r d ν d 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

In this optical system OL3, surfaces 3, 4, 6, and 28 are aspheric. Table 10 below shows the data for the aspheric surfaces, i.e., the conic constant K and the values of each of the aspheric constants A4 to A10.

(Table 10)
[Aspheric data]
Face 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

In this optical system OL3, the axial distance D0 from the surface (first surface) of 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. The following Table 11 shows the variable distances when focused on infinity and when focused on a close object. Note that β indicates the shooting magnification.

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

The following Table 12 shows the corresponding values of each conditional expression in this optical system OL3. 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.

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) vj = 30.08
(12) vp = 91.37
(13) vsp=82.57
(14) nsp = 1.50

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

Figure 6 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration diagrams for this optical system OL3 when focused at infinity. From these aberration diagrams, it can be seen that various aberrations are well corrected in the optical system OL3.

The contents described below can be adopted as appropriate as long as they do not impair optical performance.

In this embodiment, an optical system OL having a three-group configuration is shown, but the above configuration conditions can also be applied to other group configurations such as four groups or five groups. 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, is also acceptable. Specifically, a configuration in which a lens group whose position relative to the image surface is fixed when changing magnification or focusing is added closest to the image surface side is considered. Furthermore, a lens group refers to a portion having at least one lens separated by an air gap that changes when changing magnification or focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

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 also be applied to autofocusing, and is 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 for the focusing lens group to be composed of a single lens.

In addition, the lens group or 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 portion of the third lens group G3 as an anti-vibration lens group.

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 errors in processing and assembly adjustment. It is also preferable because there is little deterioration in depiction performance even if the image plane is shifted. If the lens surface is aspheric, the aspheric surface may be any of the following aspheric surfaces: an aspheric surface formed by grinding, a glass molded aspheric surface in which glass is formed into an aspheric shape using a mold, and a composite aspheric surface in which resin is formed 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.

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

In addition, each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range to reduce flare and ghosting and achieve high-contrast optical performance.

1 Camera (optical device) OL (OL1 to OL3) Optical system G1 First lens group GR Rear group G2 Second lens group (Gfo Focusing lens group) G3 Third lens group L11 First negative meniscus lens, first negative lens L12 Second negative meniscus lens, second negative lens L13 Third negative meniscus lens, third negative lens CL1 Cemented lens L14 Biconvex positive lens L16 Biconvex positive lens (positive lens component)

Claims (12)

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: total angle of view of the optical system f1: focal length of the first lens group fR: composite focal length of the lens group of the optical system closer to the image surface than the first lens group in the infinity focused state f: focal length of the entire optical system in the infinity focused state fn123: 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 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: total angle of view of the optical system f: focal length of the entire optical system in an infinity focused state fp: focal length of the positive lens component arranged closest to the image surface side of the first lens group fn123: 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 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 located closest to the image surface in the first lens group, 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 in an infinity focused state 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. 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: a focal length of the positive lens component disposed closest to the image surface side of the first lens group. 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. 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 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. 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 negative meniscus lens medium for the d-line nsp: refractive index of the negative meniscus lens medium for the d-line 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. An optical instrument comprising the optical system according to any one of claims 1 to 11 .