JP7515321B2 - Optical system and imaging device - Google Patents

Description

This invention relates to an optical system and an imaging device.

In recent years, small imaging devices using solid-state imaging elements such as digital still cameras have become widespread. Accordingly, there is a high demand for small imaging systems, and there is a demand for miniaturization of the optical systems they are equipped with. There is also a high demand for high performance, and optical systems capable of close-up photography with high shooting magnification require high optical performance from infinity to close range. For this reason, a so-called floating method is adopted, which suppresses aberration fluctuations by moving multiple lens groups when focusing. However, in optical systems that adopt the floating method, reducing the stroke amount of each focus lens group required when focusing greatly contributes to the miniaturization of the optical system and, ultimately, the lens barrel, so the challenge is how to reduce the stroke amount.

Patent Document 1 discloses an invention that employs a floating system in which, from the object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power are arranged, and the second and third lens groups are moved in the optical axis direction during focusing.

Patent document 2 discloses an invention that employs a floating system in which, from the object side, a first lens group has positive refractive power, a second lens group has negative refractive power, a third lens group has negative refractive power, and a fourth lens group has positive refractive power, and that moves the second and third lens groups in the optical axis direction when focusing.

Patent document 3 discloses an invention that employs a floating system in which, from the object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power are arranged, and the second and fourth lens groups are moved in the optical axis direction during focusing.

Japanese Patent Application Laid-Open No. 9-211319 Japanese Patent Application Laid-Open No. 62-231918 Japanese Patent Application Laid-Open No. 59-215513

In the optical system of Patent Document 1, the focus sensitivity of the third lens group, which has a positive refractive power, is small, so the stroke amount is large, which hinders miniaturization of the optical system.

In the optical system of Patent Document 2, the focus sensitivity of the third lens group, which has a negative refractive power, is small, so the stroke amount is large, which hinders miniaturization of the optical system.

In the optical system of Patent Document 3, the combined focal length of the first lens group and onwards is large compared to the focal length of the entire system, so the overall lens length is not sufficiently shortened.

Therefore, the objective of the present invention is to provide a compact optical system that has high optical performance from infinity to close range.

In order to solve the above-mentioned problems, the optical system of the present invention is composed of, in order from the object side, a front group and a rear group, and the rear group is composed of, in order from the object side, a first focus lens group having negative refractive power, an intermediate group, a second focus lens group having negative refractive power, and a final group, and when focusing, the front group is fixed with respect to the image plane, and the first focus lens group and the second focus lens group move along the optical axis, and is characterized in that the following conditional formula is satisfied:
−0.90≦fr/f≦−0.05 (1)
however,
fr: focal length of the rear group when focusing on infinity f: focal length of the optical system when focusing on infinity

In order to solve the above problem, the imaging device according to the present invention is characterized by having the above optical system and an imaging element that converts the optical image formed by the optical system into an electrical signal.

This invention makes it possible to provide a compact optical system and imaging device that has high optical performance from infinity to close range.

FIG. 2 is a cross-sectional view of the optical system of the first embodiment. 5A to 5C are aberration diagrams of the optical system of Example 1 in a state where the optical system is focused at infinity. 4A to 4C are aberration diagrams of the optical system of Example 1 in a close-up focus state. FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. 11A and 11B are aberration diagrams of the optical system of Example 2 in a state where the optical system is focused at infinity. 11A and 11B are aberration diagrams of the optical system of Example 2 in a close-up focus state. FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. 13A to 13C are aberration diagrams of the optical system of Example 3 in a state where the optical system is focused at infinity. 13A to 13C are aberration diagrams of the optical system of Example 3 in a close-up focus state. FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. 13A to 13C are aberration diagrams of the optical system of Example 4 in a state where the optical system is focused at infinity. 13A to 13C are aberration diagrams of the optical system of Example 4 in a close-up focus state. FIG. 13 is a cross-sectional view of an optical system according to a fifth embodiment. 13A to 13C are aberration diagrams of the optical system of Example 5 in a state where the optical system is focused at infinity. 13A to 13C are aberration diagrams of the optical system of Example 5 in a close-up focus state. 1 is a diagram illustrating an example of a configuration of an imaging device according to an embodiment of the present invention.

The following describes an embodiment of the optical system and imaging device according to the present invention. However, the optical system and imaging device described below are one aspect of the optical system and imaging device according to the present invention, and the optical system and imaging device according to the present invention are not limited to the following aspects.

1. Optical system 1-1. Optical configuration The optical system according to the present invention is composed of, in order from the object side, a front group that is fixed with respect to the image plane during focusing, and a rear group, and the rear group is composed of, in order from the object side, a first focus lens group having negative refractive power, an intermediate group, a second focus lens group having negative refractive power, and a final group. At least the first focus lens group and the second focus lens group move along the optical axis during focusing in a so-called floating manner, which allows the optical system to be made compact.

(1) Front Group The specific configuration of the front group is not particularly limited as long as it is a lens group (front lens group) that is fixed with respect to the image plane during focusing. It is preferable that the front group has at least one positive lens, since it is easy to suppress chromatic aberration and achieve good optical performance. It is preferable that the front group has a negative lens, since it is easy to suppress chromatic aberration and achieve good optical performance. It is preferable that the front group has at least one cemented lens of a positive lens and a negative lens, since it is easy to suppress chromatic aberration and reduce the sensitivity of each lens. It is also preferable that the front group is a lens group with positive refractive power, since it is easy to suppress various aberrations and achieve compactness. It is also preferable that the front group has at least three positive lenses and one negative lens. It is also preferable that the front group has at least a positive lens, a positive lens, a negative lens, and a positive lens in order from the object side.

Here, a "lens group" is composed of one lens or multiple adjacent lenses, and the distance between adjacent lens groups along the optical axis changes when focusing. When a lens group is composed of multiple lenses, the distance on the optical axis between the lenses included in that lens group does not change when focusing.

(2) Rear Group The rear group is composed of, in order from the object side, a first focus lens group having negative refractive power, an intermediate group, a second focus lens group having negative refractive power, and a final group, which enables miniaturization.

(3) First focus lens group The first focus lens group is a lens group having negative refractive power, and the specific configuration is not particularly limited as long as it has one or more lenses having negative refractive power. The first focus lens group may have one or more lenses having positive refractive power and one or more lenses having negative refractive power. In addition, it is preferable that the first focus lens group has at least one cemented lens of a positive lens and a negative lens, since it is easy to suppress chromatic aberration and the sensitivity of each lens.

(4) Intermediate group The intermediate group is not particularly limited in its specific configuration, as long as it is a lens group (intermediate lens group) having refractive power, with the first focus lens group disposed on the object side and the second focus lens group disposed on the image side. It is also preferable that the intermediate group is a lens group having positive refractive power. With this configuration, the light rays incident on the second focus lens group are converged, so that the second focus lens group can be made more compact. It is also preferable that the intermediate group is fixed relative to the image plane during focusing in order to reduce the overall lens length.

(5) Second focus lens group The second focus lens group is a lens group having negative refractive power, and its specific configuration is not particularly limited as long as it has one or more lenses having negative refractive power. The second focus lens group may have one or more lenses having positive refractive power and one or more lenses having negative refractive power. In addition, it is preferable that the second focus lens group has at least one cemented lens of a positive lens and a negative lens, because it is easy to suppress chromatic aberration and the sensitivity of each lens.

(6) Final lens group The final lens group is not particularly limited in its specific configuration, as long as it is the lens group (final lens group) that is disposed closest to the image and has refractive power. In addition, it is preferable for the final lens group to be a lens group with positive refractive power in order to facilitate compactness. Furthermore, it is preferable for the final lens group to be fixed relative to the image plane during focusing, which facilitates compactness of the lens barrel.

(7) Aperture Stop In the optical system, the arrangement of the aperture stop is not particularly limited. However, the aperture stop here refers to an aperture stop that defines the light beam diameter of the optical system, that is, an aperture stop that defines the Fno of the optical system. However, it is preferable to arrange the aperture stop in the rear group in order to miniaturize the aperture unit. Furthermore, when the rear group includes a lens group having a negative refractive power, it is preferable to arrange the aperture stop on the object side of the lens group having the negative refractive power. In order to cancel the negative distortion and negative curvature of field generated in the front group, it is sufficient to generate aberrations in the same direction before and after the aperture stop. Therefore, by arranging the aperture stop on the image side of the first focus lens group and on the object side of the lens group having a negative refractive power in the rear group, aberrations before and after the aperture stop can be efficiently canceled out, which is preferable in obtaining an optical system with high optical performance.

The aperture stop is preferably disposed between the first and second focus lens groups, and more preferably disposed before or after the intermediate group or within the intermediate group. This configuration allows for good aberration correction when in close focus, making it possible to construct a high-performance optical system.

1-2. Operation (1) Focusing The specific operation of the optical system is not particularly limited as long as at least the first focus lens group and the second focus lens group move on the optical axis when focusing from infinity to a close distance. For example, it is preferable that the first focus lens group and the second focus lens group move toward the image side along the optical axis when focusing from infinity to a close distance. It is more preferable that the first focus lens group and the second focus lens group move on the optical axis by different amounts when focusing from infinity to a close distance. This configuration makes it possible to have higher optical performance from infinity to a close distance. Furthermore, it is more preferable that the second focus lens group has a larger amount of movement on the optical axis relative to the image surface than the first focus lens group when focusing from infinity to a close distance. This configuration makes it possible to have even higher optical performance from infinity to a close distance.

1-3. Conditional Expressions It is desirable that the optical system employs the above-mentioned configuration and satisfies at least one of the following conditional expressions.

1-3-1. Conditional formula (1)
−0.90≦fr/f≦−0.05 (1)
however,
fr: focal length of the rear group when focused on infinity; f: focal length of the optical system when focused on infinity.

Conditional formula (1) specifies the ratio of the focal length of the rear group when focused at infinity to the focal length of the optical system when focused at infinity. By satisfying conditional formula (1), various aberrations can be well corrected while the overall optical length can be shortened by achieving a high telephoto performance, making it easier to reduce the size.

On the other hand, if the value of conditional formula (1) falls below the lower limit, the negative power of the rear group becomes weak and the total optical length becomes long, making it difficult to make the lens barrel compact. On the other hand, if the value of conditional formula (1) exceeds the upper limit, the negative power of the rear group becomes strong, making it difficult to correct various aberrations.

To obtain the above effect, the lower limit of conditional formula (1) is preferably -0.80, and more preferably -0.70. The upper limit of conditional formula (1) is preferably -0.10, more preferably -0.20, and even more preferably -0.30. When adopting these preferred lower or upper limits, the inequality sign with equality (≦) in conditional formula (1) may be replaced with an inequality sign (<). The same principle applies to the other conditional formulas.

1-3-2. Conditional Expression (2)
2.00≦|(1−βfO1×βfO1)×βfO1r×βfO1r| ・・・・(2)
however,
βfO1: lateral magnification of the first focus lens group when focused on infinity βfO1r: combined lateral magnification of all lenses arranged on the image side of the first focus lens group when focused on infinity

The above conditional formula (2) specifies the focus sensitivity of the first focus lens group. By satisfying conditional formula (2), the amount of movement during focusing can be reduced, making it easier to reduce the overall length. Here, focus sensitivity refers to the amount of change in the image plane relative to the amount of movement of the focus group (first focus lens group and/or second focus lens group) during focusing.

On the other hand, if the value of conditional expression (2) falls below the lower limit, the focus sensitivity of the first focus lens group decreases and the amount of movement required for focusing increases, making it difficult to achieve a compact size.

To obtain the above effect, the lower limit of conditional formula (2) is preferably 2.10, and more preferably 2.20. The upper limit of conditional formula (2) is preferably 20.00, and more preferably 10.00, and even more preferably 8.00.

1-3-3. Conditional expression (3)
2.00 ≦ |(1-βfO2×βfO2)×βfO2r×βfO2r| ... (3)
however,
βfO2: lateral magnification of the second focus lens group when focusing on infinity βfO2r: lateral magnification of the final group when focusing on infinity

The above conditional expression (3) defines the focus sensitivity of the second focus lens group. By satisfying conditional expression (3), the amount of movement during focusing can be reduced, making it easier to reduce the size of the lens barrel.

On the other hand, if the value of conditional expression (3) falls below the lower limit, the focus sensitivity of the second focus lens group decreases and the amount of movement required for focusing increases, making it difficult to achieve a compact size.

To obtain the above effect, the lower limit of conditional formula (3) is preferably 2.10, and more preferably 2.20. The upper limit of conditional formula (3) is preferably 20.00, and more preferably 10.00, and even more preferably 8.00.

1-3-4. Conditional expression (4)
0.005≦dPgF (4)
however,
dPgF: Anomalous dispersion of a lens having positive refractive power at the g-line (435.83 nm) and F-line (486.13 nm), and is expressed by the following formula.
dPgF = PgF + 0.0018 × vd - 0.6483
here,
vd: Abbe number of a lens having positive refractive power PgF: partial dispersion ratio of a lens having positive refractive power at g line and F line The partial dispersion ratio is PgF = (ng-nF) / (nF-nC) where ng, nF, and nC represent the refractive indices for the g-line, F-line, and C-line (656.28 nm), respectively.

Conditional formula (4) specifies the anomalous dispersion of the positive lenses in the front group. If at least one of the positive lenses in the front group satisfies conditional formula (4), chromatic aberration can be corrected well, making it easier to realize a high-performance optical system.

On the other hand, if the value of conditional expression (4) falls below the lower limit, the anomalous dispersion of the positive lens becomes small, and chromatic aberration cannot be corrected well, making it difficult to achieve high performance.

In order to obtain the above effect, the lower limit of conditional formula (4) is preferably 0.007, and more preferably 0.009. The upper limit of conditional formula (4) is preferably 0.060, and more preferably 0.050, and even more preferably 0.040.

1-3-4. Conditional expression (5)
0.05≦ff/f≦0.70 (5)
however,
ff: focal length of the front group f: focal length of the optical system when focused at infinity

Conditional formula (5) specifies the ratio of the focal length of the front group to the focal length of the optical system when focused at infinity. By satisfying conditional formula (5), it is possible to shorten the overall optical length while effectively correcting various aberrations, making it easier to reduce the size of the lens.

On the other hand, if the value of conditional expression (5) falls below the lower limit, the power of the front group becomes strong, making it difficult to correct various aberrations. On the other hand, if the value of conditional expression (5) exceeds the upper limit, the power of the front group becomes weak, and the total optical length becomes long, making it difficult to achieve compact size.

In order to obtain the above effect, the lower limit of conditional formula (5) is preferably 0.10, and more preferably 0.20. The upper limit of conditional formula (5) is preferably 0.60, and more preferably 0.50, and even more preferably 0.45.

1-3-6. Conditional expression (6)
−1.00≦ffO1/f≦−0.05 (6)
however,
ffO1: focal length of the first focus lens group f: focal length of the optical system when focused at infinity

Conditional expression (6) is a conditional expression that specifies the ratio of the focal length of the first focus lens group to the focal length of the optical system when focused at infinity. By satisfying conditional expression (6), it is possible to effectively correct various aberrations while suppressing the amount of movement during focusing, making it easier to reduce the size.

On the other hand, if the value of conditional expression (6) falls below the lower limit, the refractive power of the first focus lens group becomes weak, and the amount of movement during focusing becomes large, making it difficult to achieve a compact size. On the other hand, if the value of conditional expression (6) exceeds the upper limit, the negative refractive power of the first focus lens group becomes strong, making it difficult to correct various aberrations.

To obtain the above effect, the lower limit of conditional formula (6) is preferably -0.90, more preferably -0.80, even more preferably -0.60, and even more preferably -0.50. The upper limit of conditional formula (6) is preferably -0.10, more preferably -0.20, and even more preferably -0.30.

1-3-7. Conditional expression (7)
−1.00≦ffO2/f≦−0.05 (7)
however,
ffO2: focal length of the second focus lens group f: focal length of the optical system when focused at infinity

The above conditional expression (7) is a conditional expression for defining the ratio of the focal length of the second focus lens group to the focal length of the optical system when focused at infinity. By satisfying conditional expression (7), it is possible to effectively correct various aberrations while suppressing the amount of movement during focusing, making it easier to miniaturize the lens barrel.

On the other hand, if the value of conditional expression (7) falls below the lower limit, the refractive power of the second focus lens group becomes weak, and the amount of movement during focusing becomes large, making it difficult to miniaturize the lens barrel. On the other hand, if the value of conditional expression (7) exceeds the upper limit, the negative refractive power of the second focus lens group becomes strong, making it difficult to correct various aberrations.

To obtain the above effect, the lower limit of conditional formula (7) is preferably -0.90, more preferably -0.80, and even more preferably -0.60. The upper limit of conditional formula (7) is preferably -0.10, more preferably -0.20, and even more preferably -0.30.

1-3-8. Conditional expression (8)
−2.50≦ff/ffO1≦−0.80 (8)
however,
ff: focal length of the front group ffO1: focal length of the first focus lens group

The above conditional expression (8) is a conditional expression for defining the ratio of the focal length of the front group to the focal length of the first focus lens group. By satisfying conditional expression (8), it is possible to shorten the total optical length while satisfactorily correcting various aberrations, making it easier to miniaturize the lens barrel.

On the other hand, if the value of conditional expression (8) falls below the lower limit, the refractive power of the front group will be weak and the total optical length will be long, making it difficult to miniaturize the lens barrel. On the other hand, if the value of conditional expression (8) exceeds the upper limit, the refractive power of the front group will be strong, making it difficult to correct various aberrations.

To obtain the above effect, the lower limit of conditional formula (8) is preferably -2.40, more preferably -2.30, even more preferably -2.00, and even more preferably -1.60. The upper limit of conditional formula (8) is preferably -0.85, more preferably -0.90, even more preferably -0.95, and even more preferably -1.00.

2. Imaging device Next, an imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the optical system according to the present invention described above and an imaging element that converts an optical image formed by the optical system into an electrical signal. It is preferable that the imaging element is provided on the image side of the optical system.

Here, the imaging element is not particularly limited, and solid-state imaging elements such as a CCD (Charge Coupled Device) sensor and a CMOS (Complementary Metal Oxide Semiconductor) sensor can be used. The imaging device according to the present invention is suitable for imaging devices using these solid-state imaging elements, such as digital cameras and video cameras. The imaging device can be applied to various imaging devices, such as single-lens reflex cameras, mirrorless single-lens cameras, digital still cameras, surveillance cameras, car-mounted cameras, and drone-mounted cameras. These imaging devices may be lens-interchangeable imaging devices, or lens-fixed imaging devices in which the lens is fixed to the housing. In particular, the optical system according to the present invention is suitable for an optical system of an imaging device equipped with a large-sized imaging element such as a full-size. The optical system is small and lightweight overall, and has high optical performance, so that a high-quality image can be obtained even when used as an optical system for such an imaging device.

Fig. 16 is a diagram showing a schematic example of the configuration of an imaging device according to this embodiment. As shown in Fig. 16, a mirrorless single-lens camera 1 has a camera body 2 and a lens barrel 3 that is detachable from the camera body 2. The mirrorless single-lens camera 1 is one form of an imaging device.

The camera body 2 has a CCD sensor 21 as an image sensor and a cover glass 22. The CCD sensor 21 is disposed in the camera body 2 at a position where the optical axis of the optical system 30 in the lens barrel 3 attached to the camera body 2 is the central axis. Instead of the cover glass 22, the camera body 2 may have an IR cut filter or a parallel plate that has no substantial refractive power.

Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples.

(1) Optical Configuration Fig. 1 is a cross-sectional view of an optical system according to a first embodiment of the present invention when focusing at infinity and when focusing at close range. The optical system is composed of, in order from the object side, a first lens group G1 (front group) having positive refractive power, a second lens group G2 (first focus lens group) having negative refractive power, a third lens group G3 (middle group) having positive refractive power, a fourth lens group G4 (second focus lens group) having negative refractive power, and a fifth lens group G5 (last group) having positive refractive power. The rear group is composed of the second lens group G2 to the fifth lens group G5.

When focusing from an object at infinity to a close object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts.

The aperture stop S is located within the third lens group G3.

The first lens group G1 is composed of, from the object side, a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconvex lens with aspheric surfaces on both sides.

The second lens group G2 is composed of, from the object side, a cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented together.

The third lens group G3 is composed of, in order from the object side, a cemented lens in which a biconvex lens having an aspheric surface on the object side is cemented to a biconcave lens, an aperture stop S, and a biconvex lens.

The fourth lens group G4 is composed of, from the object side, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together.

The fifth lens group G5 is composed of, from the object side, a cemented lens in which a biconvex lens and a biconcave lens are cemented together, and a negative meniscus lens.

In FIG. 1, "IP" stands for image plane, and more specifically, it indicates the imaging surface of a solid-state imaging device such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. In addition, on the object side of the image plane IP, there is a parallel plate such as a cover glass CG that has no substantial refractive power. These points are the same in the lens cross-sectional views shown in the other embodiments, so further explanation will be omitted.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the optical system are applied will be described. The "lens data", "specification table", "variable interval", "aspheric coefficient", and "lens group data" are shown below. In addition, the values of each conditional expression (Table 1) are summarized after Example 5.

In (Lens Data), "Surface Number" is the order of the lens surface counted from the object side, "R" is the radius of curvature of the lens surface, "D" is the lens thickness or air space on the optical axis, "Nd" is the refractive index at the d line (wavelength λ = 587.56 nm), "ABV" is the Abbe number at the d line, and "dPgF" indicates the anomalous dispersion of the lens at the g line (435.83 nm) and F line (486.13 nm). In the "Surface Number" column, "ASP" next to the surface number indicates that the lens surface is aspheric, and "S" indicates that the surface is an aperture stop. In the "D" column, "D(7)", "D(10)", etc. indicate that the spacing on the optical axis of the lens surface is a variable spacing that changes when focusing. In the "Radius of Curvature" column, "∞" means infinity, and that the lens surface is flat.

In the specification table, "f" is the focal length of the optical system, "Fno." is the F-number, and "ω" is the half angle of view. They show the values when focused at infinity and when focused at close range, respectively.

(Variable interval) shows the values when focusing at infinity and when focusing at close range. The same applies to other examples.

(Aspherical coefficient) indicates the aspherical coefficient when the aspherical shape is defined as follows, where x is the amount of displacement from the reference surface in the optical axis direction, r is the paraxial radius of curvature, H is the height from the optical axis in a direction perpendicular to the optical axis, k is the conical coefficient, and An is the n-th order aspherical coefficient. In the "Aspherical coefficient" table, "E±XX" indicates exponential notation, meaning "×10 ^±XX ".

The details in these tables are the same as those in the tables shown in the other examples, so we will not repeat the explanation below.

2 and 3 show longitudinal aberration diagrams of the optical system when it is focused on an object at infinity and when it is focused on a close object. The longitudinal aberration diagrams shown in each diagram are, from the left side of the drawing, spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the spherical aberration diagram, the solid line shows the spherical aberration at the d-line (wavelength 587.56 nm), the long dashed line shows the spherical aberration at the F-line (wavelength 486.13 nm), and the short dashed line shows the spherical aberration at the C-line (wavelength 656.28 nm). In the astigmatism diagram, the vertical axis shows the half angle of view (ω) and the horizontal axis shows the defocus, the solid line shows the sagittal image plane (S) of the d-line, and the dashed line shows the meridional image plane (T) of the d-line. In the distortion diagram, the vertical axis shows the half angle of view (ω) and the horizontal axis shows the distortion aberration. These matters are the same in each aberration diagram shown in the other examples, so explanations will be omitted below.

(Lens data)
Surface number RD Nd ABV dPgF
1 171.4013 2.7631 1.72916 54.67 -0.0046
2 -1000.0000 0.2000
3 95.9189 3.6739 1.55032 75.50 0.0276
4 -250.0000 1.0000 1.85478 24.80 0.0109
5 226.7927 0.2000
6 ASP 35.6576 5.8752 1.72903 54.04 -0.0064
7 ASP -381.8040 D(7)
8 141.2492 1.0000 1.90366 31.31 0.0028
9 15.8498 4.1995 1.92286 20.88 0.0283
10 25.1238 D(10)
11 ASP 39.5777 3.5181 1.69350 53.20 -0.0059
12 -500.0000 1.0000 1.92286 20.88 0.0283
13 26.8989 3.3113
14 S∞1.1976
15 51.0382 4.2713 1.83400 37.34 -0.0021
16 -42.7075 D(16)
17 -77.0778 0.8000 1.83481 42.72 -0.0067
18 23.8300 2.5173 1.94595 17.98 0.0386
19 68.7591 D(19)
20 53.6265 8.7466 1.90366 31.31 0.0028
21 -26.7844 1.0000 1.84666 23.78 0.0137
22 113.4251 4.8576
23 -43.7301 1.2000 1.92286 20.88 0.0283
24 -92.7988 17.0000
25 ∞ 2.5000 1.51680 64.20 0.0015
26∞1.0000
27∞

(Specifications table)
Infinity Close
f 102.2339 39.8108
Fno. 2.8880 5.7689
ω 11.8820 5.8028

(variable interval)
Infinity Close magnification 0.0 -1.0
D(7) 2.0000 11.0111
D(10) 12.6717 3.6606
D(16) 2.0026 22.4652
D(19) 26.4943 6.0318

(Aspherical coefficients)
Face number K A4 A6 A8 A10
6 0.00000E+00 -1.80303E-06 -2.10543E-09 -3.92885E-12 1.36903E-14
7 0.00000E+00 2.52733E-06 -3.68416E-09 7.29622E-12 -6.87823E-16
11 0.00000E+00 7.50686E-06 1.10467E-08 0.00000E+00 0.00000E+00

(Lens group data)
Group Surface Number Focal Length
G1 1-7 36.7952
G2 8-10 -35.2189
G3 11-16 47.4922
G4 17-19 -49.8092
G5 20-24 398.3370

(1) Optical configuration Fig. 4 is a cross-sectional view of an optical system according to Example 2 of the present invention when focusing at infinity and when focusing at close range. The optical system is composed of, in order from the object side, a first lens group G1 (front group) having positive refractive power, a second lens group G2 (first focus lens group) having negative refractive power, a third lens group G3 (middle group) having positive refractive power, a fourth lens group G4 (second focus lens group) having negative refractive power, and a fifth lens group G5 (last group) having positive refractive power. In this example, the rear group is composed of the second lens group G2 to the fifth lens group G5.

When focusing from an object at infinity to a close object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts.

The aperture stop S is located within the third lens group G3.

The first lens group G1 is composed of, from the object side, a positive meniscus lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconvex lens with aspheric surfaces on both sides.

The second lens group G2 is composed of, from the object side, a cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented together.

The third lens group G3 is composed of, in order from the object side, a cemented lens in which a biconvex lens having an aspheric surface on the object side is cemented to a biconcave lens, an aperture stop S, and a biconvex lens.

The fourth lens group G4 is composed of, from the object side, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together.

The fifth lens group G5 is composed of, from the object side, a cemented lens in which a biconvex lens and a biconcave lens are cemented together, and a negative meniscus lens.

(2) Numerical Examples Next, as numerical examples to which specific numerical values of the optical system are applied, the "lens data", "specification table", "variable interval", "aspheric coefficient", and "lens group data" are shown. Also, longitudinal aberration diagrams at infinity focusing and close focusing of the optical system are shown in Figs. 5 and 6.

(Lens data)
Surface number RD Nd ABV dPgF
1 80.1532 3.6897 1.77250 49.62 -0.0086
2 1281.0701 0.2000
3 79.2615 3.9667 1.49700 81.61 0.0374
4 -250.0000 1.0000 1.85478 24.80 0.0109
5 111.0033 0.2000
6 ASP 38.7366 5.2499 1.72903 54.04 -0.0064
7 ASP -418.3984 D(7)
8 169.8641 1.0000 1.80610 33.27 0.0000
9 16.7170 3.3642 1.92286 20.88 0.0283
10 23.5208 D(10)
11 ASP 40.2066 3.3972 1.69350 53.20 -0.0059
12 -500.0000 1.0000 1.85478 24.80 0.0109
13 25.2141 3.3413
14 S∞ 1.0000
15 45.0181 3.9282 1.83400 37.34 -0.0021
16 -53.1787 D(16)
17 -88.2090 0.8000 1.87070 40.73 -0.0068
18 27.2074 2.6377 1.94595 17.98 0.0386
19 89.8202 D(19)
20 59.1913 7.6069 1.91082 35.25 -0.0027
21 -31.2701 1.0000 1.84666 23.78 0.0137
22 201.8194 3.6712
23 -63.1766 1.2000 1.92286 20.88 0.0283
24 -332.6113 17.0000
25 ∞ 2.5000 1.51680 64.20 0.0015
26∞1.0000
27∞

(Specifications table)
Infinity Close
f 101.8435 39.6709
Fno. 2.8838 5.7633
ω 11.9328 5.3990

(variable interval)
Infinity Close magnification 0.0 -1.0
D(7) 2.0000 12.7555
D(10) 14.4191 3.6636
D(16) 2.0025 27.7731
D(19) 27.8254 2.0548

(Aspherical coefficients)
Face number K A4 A6 A8 A10
6 0.00000E+00 -2.01936E-06 -1.05940E-09 0.00000E+00 0.00000E+00
7 0.00000E+00 1.64396E-06 -2.18612E-10 0.00000E+00 0.00000E+00
11 0.00000E+00 9.02556E-06 9.92993E-09 0.00000E+00 0.00000E+00

(Lens group data)
Group Surface Number Focal Length
G1 1-7 38.9863
G2 8-10 -37.5697
G3 11-16 51.5095
G4 17-19 -56.2712
G5 20-24 333.3760

(1) Optical configuration Fig. 7 is a cross-sectional view of an optical system according to a third embodiment of the present invention when focusing at infinity and at close range. The optical system is composed of, in order from the object side, a first lens group G1 (front group) having positive refractive power, a second lens group G2 (first focus lens group) having negative refractive power, a third lens group G3 (middle group) having positive refractive power, a fourth lens group G4 (second focus lens group) having negative refractive power, and a fifth lens group G5 (last group) having positive refractive power. The rear group is composed of the second lens group G2 to the fifth lens group G5.

When focusing from an object at infinity to a close object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts.

The aperture stop S is located within the third lens group G3.

The first lens group G1 is composed of, from the object side, a biconvex lens, a cemented lens in which a biconvex lens and a negative meniscus lens are cemented together, and a biconvex lens with aspheric surfaces on both sides.

The second lens group G2 is composed of, from the object side, a cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented together.

The third lens group G3 is composed of, in order from the object side, a cemented lens in which a biconvex lens having an aspheric surface on the object side is cemented to a biconcave lens, an aperture stop S, and a biconvex lens.

The fourth lens group G4 is composed of, from the object side, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together.

The fifth lens group G5 is composed of, from the object side, a cemented lens in which a biconvex lens and a biconcave lens are cemented together, and a negative meniscus lens.

(2) Numerical Examples Next, as numerical examples to which specific numerical values of the optical system are applied, the "lens data", "specification table", "variable interval", "aspheric coefficient", and "lens group data" are shown. Also, Figs. 8 and 9 show longitudinal aberration diagrams of the optical system when focused at infinity and when focused at close range.

(Lens data)
Surface number RD Nd ABV dPgF
1 171.4013 2.7631 1.72916 54.67 -0.0046
2 -1000.0000 0.2000
3 223.5505 3.6355 1.48749 70.44 0.0090
4 -103.9143 1.0000 1.85478 24.80 0.0109
5 -1318.3983 0.2000
6 ASP 34.8759 6.4925 1.72903 54.04 -0.0064
7 A.S.P. -189.5284 D(7)
8 144.1868 1.0000 1.90366 31.31 0.0028
9 15.8364 4.1749 1.92286 20.88 0.0283
10 24.7739 D(10)
11 ASP 42.0875 3.6227 1.69350 53.20 -0.0059
12 -207.5991 1.0000 1.92286 20.88 0.0283
13 28.2828 3.2181
14 S∞ 1.0000
15 54.1668 4.3281 1.83400 37.34 -0.0021
16 -40.1656 D(16)
17 -71.8888 0.8000 1.83481 42.72 -0.0067
18 22.5817 2.6630 1.94595 17.98 0.0386
19 67.7407 D(19)
20 50.7789 8.9947 1.90366 31.31 0.0028
21 -26.3723 1.0000 1.84666 23.78 0.0137
22 105.4155 4.2533
23 -42.9986 1.2000 1.92286 20.88 0.0283
24 -101.3139 17.2536
25 ∞ 2.5000 1.51680 64.20 0.0015
26∞1.0000
27∞

(Specifications table)
Infinity Close
f 103.0119 39.6323
Fno. 2.9099 5.7631
ω 11.7947 5.9312

(variable interval)
Infinity Close magnification 0.0 -1.0
D(7) 2.0000 10.3740
D(10) 12.1146 3.7407
D(16) 2.0022 20.7626
D(19) 26.5836 7.8232

(Aspherical coefficients)
Face number K A4 A6 A8 A10
6 0.00000E+00 -2.07070E-06 -2.05319E-09 -5.07994E-12 1.31403E-14
7 0.00000E+00 3.30845E-06 -4.59751E-09 7.06002E-12 -5.12319E-16
11 0.00000E+00 7.21661E-06 9.98081E-09 0.00000E+00 0.00000E+00

(Lens group data)
Group Surface Number Focal Length
G1 1-7 35.6813
G2 8-10 -34.4254
G3 11-16 47.1619
G4 17-19 -48.0117
G5 20-24 496.9200

(1) Optical configuration Fig. 10 is a cross-sectional view of an optical system according to a fourth embodiment of the present invention when focusing at infinity and when focusing at close range. The optical system is composed of, in order from the object side, a first lens group G1 (front group) having positive refractive power, a second lens group G2 (first focus lens group) having negative refractive power, a third lens group G3 (middle group) having positive refractive power, a fourth lens group G4 (second focus lens group) having negative refractive power, and a fifth lens group G5 (last group) having positive refractive power. The rear group is composed of the second lens group G2 to the fifth lens group G5.

When focusing from an object at infinity to a close object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts.

The aperture stop S is located within the third lens group G3.

The first lens group G1 is composed of, from the object side, a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconvex lens with aspheric surfaces on both sides.

The second lens group G2 is composed of, from the object side, a cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented together.

The third lens group G3 is composed of, in order from the object side, a cemented lens in which a biconvex lens having an aspheric surface on the object side is cemented to a biconcave lens, an aperture stop S, and a biconvex lens.

The fourth lens group G4 is composed of, from the object side, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together.

The fifth lens group G5 is composed of, from the object side, a cemented lens in which a biconvex lens and a biconcave lens are cemented together, and a biconcave lens.

(2) Numerical Examples Next, as numerical examples to which specific numerical values of the optical system are applied, the "lens data", "specification table", "variable interval", "aspheric coefficient", and "lens group data" are shown. Also, longitudinal aberration diagrams when the optical system is focused at infinity and when it is focused at close range are shown in Figs. 11 and 12.

(Lens data)
Surface number RD Nd ABV dPgF
1 49.3632 5.5713 1.77250 49.62 -0.0086
2 -1000.0000 0.2000
3 151.9132 2.8975 1.59282 68.62 0.0192
4 -250.0000 1.0000 1.85478 24.80 0.0109
5 80.6388 0.2000
6 ASP 46.6041 4.2065 1.72903 54.04 -0.0064
7 ASP -826.3704 D(7)
8 238.0739 1.0000 1.80610 33.27 0.0000
9 17.3814 3.3426 1.92286 20.88 0.0283
10 25.8138 D(10)
11 ASP 38.8126 3.2238 1.69350 53.20 -0.0059
12 -500.0000 1.0000 1.85478 24.80 0.0109
13 26.2754 3.6337
14 S∞ 1.0000
15 50.3398 3.5538 1.83400 37.34 -0.0021
16 -53.0192 D(16)
17 -94.1255 0.8000 1.87070 40.73 -0.0068
18 26.2903 2.3148 1.94595 17.98 0.0386
19 80.1791 D(19)
20 52.4560 8.0439 1.91082 35.25 -0.0027
21 -32.6715 1.0000 1.84666 23.78 0.0137
22 203.0088 2.4065
23 -92.0448 1.2000 1.92286 20.88 0.0283
24 342.3205 18.1500
25 ∞ 2.5000 1.51680 64.20 0.0015
26∞1.0000
27∞

(Specifications table)
Infinity Close
f 101.8612 40.4397
Fno. 2.8843 5.7582
ω 12.0274 4.5873

(variable interval)
Infinity Close magnification 0.0 -1.0
D(7) 2.0000 15.0789
D(10) 16.5952 3.5163
D(16) 2.0006 26.1259
D(19) 26.1596 2.0344

(Aspherical coefficients)
Face number K A4 A6 A8 A10
6 0.00000E+00 -2.11926E-06 9.97877E-10 -4.80270E-12 -8.50359E-15
7 0.00000E+00 1.53597E-06 2.40122E-09 -1.19942E-11 6.80915E-15
11 0.00000E+00 6.64629E-06 5.28865E-09 0.00000E+00 0.00000E+00

(Lens group data)
Group Surface Number Focal Length
G1 1-7 41.0151
G2 8-10 -40.0550
G3 11-16 51.9196
G4 17-19 -54.6110
G5 20-24 239.0820

(1) Optical configuration Fig. 13 is a cross-sectional view of an optical system according to a fifth embodiment of the present invention when focusing at infinity and at close range. The optical system is composed of, in order from the object side, a first lens group G1 (front group) having positive refractive power, a second lens group G2 (first focus lens group) having negative refractive power, a third lens group G3 (middle group) having positive refractive power, a fourth lens group G4 (second focus lens group) having negative refractive power, and a fifth lens group G5 (last group) having positive refractive power. The rear group is composed of the second lens group G2 to the fifth lens group G5.

When focusing from an object at infinity to a close object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts.

The aperture stop S is located within the third lens group G3.

The first lens group G1 is composed of, from the object side, a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconvex lens with aspheric surfaces on both sides.

The second lens group G2 is composed of, from the object side, a cemented lens in which a negative meniscus lens and a positive meniscus lens are cemented together.

The third lens group G3 is composed of, in order from the object side, a cemented lens in which a biconvex lens having an aspheric surface on the object side is cemented to a biconcave lens, an aperture stop S, and a biconvex lens.

The fourth lens group G4 is composed of, from the object side, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together.

The fifth lens group G5 is composed of, from the object side, a cemented lens in which a biconvex lens and a biconcave lens are cemented together, and a negative meniscus lens.

(2) Numerical Examples Next, as numerical examples to which specific numerical values of the optical system are applied, the "lens data", "specification table", "variable interval", "aspheric coefficient", and "lens group data" are shown. Also, Figs. 14 and 15 show longitudinal aberration diagrams when the optical system is focused at infinity and at close range.

(Lens data)
Surface number RD Nd ABV dPgF
1 48.7581 5.6238 1.77250 49.62 -0.0086
2 -1000.0000 0.2000
3 172.6299 2.8093 1.59282 68.62 0.0192
4 -239.9458 1.0000 1.85478 24.80 0.0109
5 88.0228 0.2000
6 ASP 46.5557 4.2754 1.72903 54.04 -0.0064
7 A.S.P. -822.8805 D(7)
8 333.5663 1.0000 1.80610 33.27 0.0000
9 16.7517 3.1620 1.92286 20.88 0.0283
10 24.6010 D(10)
11 ASP 37.2415 3.7039 1.69350 53.20 -0.0059
12 -123.1039 1.0000 1.85478 24.80 0.0109
13 27.1730 2.9761
14 S∞ 1.0000
15 50.6631 3.6043 1.83400 37.34 -0.0021
16 -49.8218 D(16)
17 -82.1795 1.0000 1.87070 40.73 -0.0068
18 24.7577 2.5144 1.94595 17.98 0.0386
19 87.6948 D(19)
20 56.1066 8.6934 1.91082 35.25 -0.0027
21 -28.2709 1.0000 1.84666 23.78 0.0137
22 904.4829 4.7543
23 -59.1395 1.0000 1.92286 20.88 0.0283
24 -1194.0700 18.7452
25 ∞ 2.5000 1.51680 64.20 0.0015
26∞1.0000
27∞

(Specifications table)
Infinity Close
f 97.0157 40.7187
Fno. 2.8845 5.7567
ω 12.6238 4.7035

(variable interval)
Infinity Close magnification 0.0 -1.0
D(7) 2.0000 14.7241
D(10) 16.2567 3.5326
D(16) 2.0017 22.9675
D(19) 22.9796 2.0138

(Aspherical coefficients)
Face number K A4 A6 A8 A10
6 0.00000E+00 -2.11926E-06 9.97877E-10 -4.80270E-12 -8.50359E-15
7 0.00000E+00 1.53597E-06 2.40122E-09 -1.19942E-11 6.80915E-15
11 0.00000E+00 6.64629E-06 5.28865E-09 0.00000E+00 0.00000E+00

(Lens group data)
Group Surface Number Focal Length
G1 1-7 40.1514
G2 8-10 -36.3542
G3 11-16 48.6743
G4 17-19 -54.0779
G5 20-24 195.3350

[Table 1]
Conditional Expression Example 1 Example 2 Example 3 Example 4 Example 5
Condition (1) fr/f -0.400 -0.500 -0.350 -0.600 -0.650
Conditional formula (2)｜(1-βfO1 ² )×βfO1r ² ｜ 7.306 6.420 7.871 5.751 5.612
Conditional formula (3)｜(1-βfO2 ² )×βfO2r ² ｜ 2.999 2.500 3.199 2.400 2.300
Condition (4) dPgF 0.028 0.037 0.009 0.019 0.019
Condition (5) ff/f 0.359 0.382 0.345 0.402 0.413
Condition (6) ffO1/f -0.343 -0.367 -0.333 -0.392 -0.373
Conditional formula (7) ffO2/f -0.489 -0.555 -0.468 -0.538 -0.560
Condition (8) ff/ffO1 -1.046 -1.040 -1.038 -1.026 -1.107

The optical system according to the present invention can be suitably applied as an optical system for imaging devices such as film cameras, digital still cameras, and digital video cameras.

S ... aperture stop CG ... cover glass IP ... image surface G1 ... first lens group G2 ... second lens group G3 ... third lens group G4 ... fourth lens group G5 ... fifth lens group 1 ... mirrorless single-lens camera 2 ... camera body 3 ... lens barrel 21 ... CCD sensor 22 ... cover glass

Claims (8)

From the object side, it is composed of a front group and a rear group,
the rear group is composed of, in order from the object side, a first focus lens group having negative refractive power, an intermediate group, a second focus lens group having negative refractive power, and a final group;
During focusing, the front group is fixed relative to an image plane, and the first focus lens group and the second focus lens group move along an optical axis,
An optical system characterized by satisfying the following conditional expression:
−0.650 ≦fr/f≦−0.05 (1)
however,
fr: focal length of the rear group when focusing on infinity f: focal length of the optical system when focusing on infinity 2. The optical system according to claim 1, which satisfies the following condition:
2.00 ≦ |(1-βfO1×βfO1)×βfO1r×βfO1r| ・・・・(
2)
however,
βfO1: lateral magnification of the first focus lens group when focused on infinity βfO1r: composite lateral magnification of all lenses arranged on the image side of the first focus lens group when focused on infinity 3. The optical system according to claim 1, wherein the front group has one or more lenses having positive refractive power that satisfy the following condition: 1<x<1/2;
0.005≦dPgF (4)
however,
dPgF: Anomalous dispersion of the lens having the positive refractive power at the g-line and F-line 4. The optical system according to claim 1, which satisfies the following condition:
0.05≦ff/f≦0.70 (5)
however,
ff: focal length of the front group 5. The optical system according to claim 1, which satisfies the following condition:
−1.00≦ffO1/f≦−0.05 (6)
however,
ffO1: focal length of the first focus lens group 6. The optical system according to claim 1, which satisfies the following condition:
−1.00≦ffO2/f≦−0.05 (7)
however,
ffO2: focal length of the second focus lens group 7. The optical system according to claim 1, which satisfies the following condition:
−2.50≦ff/ffO1≦−0.80 (8)
however,
ff: focal length of the front group ffO1: focal length of the first focus lens group An imaging device comprising the optical system according to any one of claims 1 to 7, and an imaging element on the image side of the optical system that converts an optical image formed by the optical system into an electrical signal.

Images