Optical system and image capturing device

Abstract

To provide an optical system which is bright with a small F-number, has a large aperture, and yet offers suppressed image plane variation and chromatic aberration while shifting focus, and to provide an image capturing device.SOLUTION: An optical system is provided, comprising, in order from the object side, a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, a third lens group (G3) having positive refractive power, and a fourth lens group (G4) having negative refractive power, the second lens group having at least one positive lens and at least one negative lens. When shifting focus from infinity to a shortest distance, the first and fourth lens groups are stationary relative to the image plane while the second and third lens groups move along an optical axis. The optical system satisfies given conditional expressions. An image capturing device comprising such optical system is also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, as demand for full-frame mirrorless cameras has grown, lenses that can support higher resolutions are required in response to the increasing pixel count of sensors and higher resolution monitors.

[0003] Generally, bright, large-aperture lenses with an F-number of around 1.4 have a shallow depth of field, so it is necessary to further suppress image plane fluctuations when focusing from infinity to the closest object distance.In addition, it is becoming more important to correct axial chromatic aberration and lateral chromatic aberration, such as color bleeding of the image on the sensor imaging plane and color bleeding of blurred images in out-of-focus areas.

[0004] Optical systems with bright large-aperture lenses having an F-number of about 1.4 have been known for some time. For example, the optical systems disclosed in Patent Documents 1 and 2 are composed of, in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, and employ an inner focus focusing system in which the second lens group is moved along the optical axis to achieve focusing. The optical system disclosed in Patent Document 3 is composed of, in order from the object side to the image 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, and employs a floating focus focusing system in which the second and third lens groups are moved along the optical axis to achieve focusing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-30383 [Patent Document 2] International Publication No. 2016 / 056310 [Patent Document 3] Patent No. 6631412 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the optical system described in Patent Document 1, the power distribution between the first and second lens groups is inappropriate, which results in the diameter of the lenses constituting the first lens group becoming relatively large. This results in an increase in the overall size of the product. Furthermore, the correction of image plane fluctuation and chromatic aberration during focusing is insufficient, and improvements in optical performance are required.

[0007] In the optical system described in Patent Document 2, focusing is performed using a single lens group, so image plane fluctuations become large when focusing from infinity to the closest object. Therefore, it is necessary to suppress image plane fluctuations throughout the entire focusing range.

[0008] The optical system described in Patent Document 3 focuses using a floating focus method. The lenses used in the lens group that moves during focusing are made of glass with low anomalous dispersion. As a result, correction of axial chromatic aberration and lateral chromatic aberration is insufficient throughout the entire focusing range, resulting in noticeable color bleeding on the imaging surface.

[0009] An object of the present invention is to provide an optical system and an imaging device that have a bright large-aperture lens with a small F-number, yet suppresses image plane fluctuation and chromatic aberration over the entire focusing range. [Means for solving the problem]

[0010] In order to solve the above problem, the optical system of the present invention is composed of, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, wherein the second lens group has at least one positive lens and at least one negative lens, and when focusing from infinity to the closest point, the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group each move along the optical axis direction, and is characterized in that the following formula is satisfied: -0.55 ≦ f1 / f2 ≦ -0.01 (1) ν2 ≦ 25.0 (2) however, f1: focal length of the first lens group f2: focal length of the second lens group ν2: Abbe number at the d-line of any one of the positive lenses included in the second lens group

[0011] In addition, in order to solve the above problem, the imaging device of the present invention is characterized by comprising the above optical system and an imaging element on the image side of the optical system that converts the optical image formed by the optical system into an electrical signal. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view of the lens of the optical system of Example 1 when focused at infinity. [Figure 2] FIG. 2 is a longitudinal aberration diagram of the optical system of Example 1 when focused at infinity. [Figure 3] 4A to 4C are diagrams showing lateral aberrations of the optical system of Example 1 when focused at infinity. [Figure 4] FIG. 2 is a longitudinal aberration diagram of the optical system of Example 1 at the closest focusing point. [Figure 5] 4A and 4B are diagrams illustrating lateral aberrations at the closest focusing point of the optical system of Example 1. FIG. [Figure 6] FIG. 10 is a cross-sectional view of the lens of the optical system of Example 2 when focused at infinity. [Figure 7] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 2 when focused at infinity. [Figure 8] FIG. 10 is a diagram illustrating lateral aberration of the optical system of Example 2 when focused at infinity. [Figure 9] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 2 when focused at the closest distance. [Figure 10] FIG. 10 is a diagram illustrating lateral aberration when the optical system of Example 2 is focused at the closest distance. [Figure 11] FIG. 10 is a cross-sectional view of the lens of the optical system of Example 3 when focused at infinity. [Figure 12] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 3 when focused at infinity. [Figure 13] FIG. 10 is a diagram illustrating lateral aberration of the optical system of Example 3 when focused at infinity. [Figure 14] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 3 when focused at the closest distance. [Figure 15] FIG. 10 is a diagram illustrating lateral aberration when the optical system of Example 3 is focused at the closest distance. [Figure 16] FIG. 10 is a cross-sectional view of the lens of the optical system of Example 4 when focused at infinity. [Figure 17] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 4 when focused at infinity. [Figure 18] FIG. 10 is a diagram illustrating lateral aberration of the optical system of Example 4 when focused at infinity. [Figure 19] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 4 when focused at the closest distance. [Figure 20] FIG. 10 is a diagram illustrating lateral aberration when the optical system of Example 4 is focused at the closest distance. [Figure 21] FIG. 10 is a cross-sectional view of the lens of the optical system of Example 5 when focused at infinity. [Figure 22] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 5 when focused at infinity. [Figure 23] FIG. 10 is a diagram illustrating lateral aberration of the optical system of Example 5 when focused at infinity. [Figure 24] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 5 when focused at the closest distance. [Figure 25] FIG. 10 is a diagram illustrating lateral aberration when the optical system of Example 5 is focused at the closest point. [Figure 26] FIG. 10 is a cross-sectional view of the lens of the optical system of Example 6 when focused at infinity. [Figure 27] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 6 when focused at infinity. [Figure 28] FIG. 13 is a diagram illustrating lateral aberration of the optical system of Example 6 when focused at infinity. [Figure 29] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 6 when focused at the closest distance. [Figure 30] FIG. 13 is a diagram showing lateral aberration at the closest focusing point of the optical system of Example 6. [Figure 31] FIG. 11 is a cross-sectional view of the lens of the optical system of Example 7 when focused at infinity. [Figure 32] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 7 when focused at infinity. [Figure 33] FIG. 11 is a diagram showing lateral aberration of the optical system of Example 7 when focused at infinity. [Figure 34] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 7 when focused at the closest distance. [Figure 35] FIG. 13 is a diagram showing lateral aberration at the closest focusing point of the optical system of Example 7. [Figure 36] FIG. 13 is a cross-sectional view of the lens of the optical system of Example 8 when focused at infinity. [Figure 37] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 8 when focused at infinity. [Figure 38] FIG. 13 is a diagram showing lateral aberration of the optical system of Example 8 when focused at infinity. [Figure 39] FIG. 13 is a longitudinal aberration diagram of the optical system of Example 8 when focused at the closest distance. [Figure 40] FIG. 13 is a diagram showing lateral aberration at the closest focusing point of the optical system of Example 8. [Figure 41] 1 is a diagram schematically illustrating an example of the configuration of an imaging device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the optical system and the imaging device according to the present invention will be described. However, the optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects.

[0014] 1.Optical system 1-1.Optical configuration The optical system of this embodiment is composed of, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power.

[0015] By adopting the refractive power arrangement described above, the optical system can easily correct aberrations in a bright, large-aperture optical system with a small F-number of about 1.4.

[0016] (1) First lens group The specific configuration of the first lens group is not particularly limited, except that it is a lens group having positive refractive power. Having the first lens group having positive refractive power can suppress various aberrations and facilitate compactness. Furthermore, for example, if the first lens group has a negative lens, it is preferable because it can easily suppress chromatic aberration and achieve good optical performance. Furthermore, if the first lens group has a cemented lens of a positive lens and a negative lens, it is preferable because it can easily suppress chromatic aberration and reduce the sensitivity of each lens. It is preferable that the first lens group has the largest air gap among the air gaps disposed between the lens surface of the first lens group closest to the object and the lens surface of the fourth lens group closest to the image, it can easily correct coma aberration.

[0017] Here, "lens group" refers to a group consisting of one or more adjacent lenses. Furthermore, the distance between adjacent lenses in a lens group along the optical axis changes during focusing. When a lens group is composed of multiple lenses, the distance on the optical axis between each lens in that lens group does not change during focusing.

[0018] (2) Second lens group The second 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 with negative refractive power. The second lens group may have one or more lenses with positive refractive power and one or more lenses with negative refractive power. Furthermore, if the second lens group is configured, from the object side, with a negative lens and a positive lens, chromatic aberration can be effectively suppressed, which is preferable.

[0019] (3) Third lens group The third lens group is a lens group having positive refractive power, and its specific configuration is not particularly limited as long as it includes one or more lenses with positive refractive power. For example, the third lens group may include one or more lenses with positive refractive power and one or more lenses with negative refractive power. Furthermore, if the third lens group includes a cemented lens consisting of a positive lens and a negative lens, this configuration is preferable because it makes it easier to suppress chromatic aberration and reduce the sensitivity of each lens. In order to suppress various aberrations, it is preferable that the lens located closest to the object side of the third lens group has a convex shape on the object side. It is also preferable that the lens located closest to the image side has a convex shape on the image side.

[0020] (3) Fourth lens group The fourth lens group is a lens group having negative refractive power, and its specific configuration is not particularly limited as long as it includes one or more lenses with negative refractive power. Furthermore, including at least one negative lens makes it easier to suppress chromatic aberration and achieve good optical performance, which is preferable. For example, if the fourth lens group includes a positive lens, it makes it easier to suppress chromatic aberration and achieve good optical performance, which is preferable. Furthermore, if the fourth lens group includes a cemented lens consisting of a positive lens and a negative lens, it makes it easier to suppress chromatic aberration and reduce the sensitivity of each lens, which is preferable. Furthermore, if the fourth lens group includes, in order from the object side, a positive lens, a negative lens, and a negative lens, it makes it easier to correct various aberrations, which is preferable.

[0021] (4) Aperture diaphragm In this optical system, the location of the aperture diaphragm is not particularly limited. However, the aperture diaphragm referred to here refers to the aperture diaphragm that determines the diameter of the light beam in the optical system, i.e., the aperture diaphragm that determines the F-number of the optical system. However, it is preferable to locate the aperture diaphragm within the first lens group in order to reduce the size of the diaphragm unit.

[0022] 1-2.Focus In this optical system, when focusing from infinity to the closest distance, the first and fourth lens groups are fixed relative to the image plane, and the second and third lens groups move along the optical axis, respectively, so long as their specific movements are not particularly limited. Furthermore, when focusing from infinity to the closest distance, a configuration in which the second lens group moves along the optical axis toward the image side and the third lens group moves along the optical axis toward the object side is preferable because it minimizes image plane fluctuations. Furthermore, when focusing from infinity to the closest distance, it is more preferable that the second and third lens groups move along the optical axis by different amounts. This configuration enables high optical performance when focusing from infinity to the closest distance. Furthermore, it is more preferable that the second lens group moves a larger amount along the optical axis relative to the image plane than the third lens group when focusing from infinity to the closest distance. This configuration enables even higher optical performance when focusing from infinity to the closest distance.

[0023] 1-3.Formula In this optical system, it is preferable to employ the above-mentioned configuration and also satisfy one or more of the following expressions.

[0024] 1-3-1.Formula (1) -0.55 ≦ f1 / f2 ≦ -0.01 (1) however, f1: focal length of the first lens group f2: focal length of the second lens group

[0025] Formula (1) defines the ratio of the focal lengths of the first and second lens groups. By satisfying formula (1), it is possible to effectively correct various aberrations while shortening the overall optical length, making it easier to miniaturize the second lens group.

[0026] On the other hand, if the value of formula (1) is below the lower limit, the power of the first lens group becomes weak, making it difficult to reduce the size of the optical system. On the other hand, if the value of formula (1) exceeds the upper limit, the power of the first lens group becomes strong, causing large fluctuations in coma and distortion occurring within the first lens group, making it difficult to correct various aberrations.

[0027] In order to obtain the above effects, the lower limit of formula (1) is preferably −0.53, more preferably −0.50, and the upper limit of formula (1) is preferably −0.02, more preferably −0.03.

[0028] 1-3-2.Formula (2) ν2 ≦ 25.0 (2) however, ν2: Abbe number at the d-line of any one of the positive lenses included in the second lens group

[0029] Equation (2) defines the Abbe number at the d-line of any one of the positive lenses included in the second lens group. Satisfying equation (2) makes it possible to correct axial chromatic aberration and lateral chromatic aberration during focusing, from an object at infinity to a close-up object. Note that when the second lens group has multiple positive lenses, the effect can be obtained if only one of the lenses satisfies equation (2). Furthermore, it is more preferable for the effect to be obtained if multiple lenses satisfy equation (2).

[0030] On the other hand, if the numerical value of the formula (2) exceeds the upper limit, the correction of the axial chromatic aberration and the chromatic aberration of magnification becomes insufficient, and the color bleeding of the image on the imaging plane and the color bleeding of the blurred image in the out-of-focus portion become conspicuous, which is undesirable.

[0031] In order to obtain the above effects, the lower limit of formula (2) is preferably 10.0, more preferably 15.0, and the upper limit of formula (2) is preferably 24.0, more preferably 22.0.

[0032] 1-3-3.Formula (3) -0.50 ≦ f / f2 ≦ -0.01 ····(3) however, f: focal length of the optical system when focused at infinity

[0033] Equation (3) defines the ratio between the focal length of the optical system when focused at infinity and the focal length of the second lens group. By satisfying equation (3), it is possible to effectively correct various aberrations while shortening the overall optical length, making it easier to miniaturize the second lens group.

[0034] On the other hand, if the value of formula (3) falls below the lower limit, the power of the second lens group weakens and the amount of movement increases, making it difficult to achieve compactness while correcting various aberrations. On the other hand, if the value of formula (3) exceeds the upper limit, the power of the second lens group becomes strong, making the second lens group more susceptible to lens manufacturing errors, resulting in increased sensitivity to decentering. Also, image plane fluctuations become significant. Also, it becomes difficult to suppress aberration fluctuations when focusing from infinity to the closest object.

[0035] To obtain the above effects, the lower limit of formula (3) is preferably −0.45, more preferably −0.40, and the upper limit of formula (3) is preferably −0.05, more preferably −0.10.

[0036] 1-3-4.Formula (4) ν1 ≦ 25.0 (4) however, ν1: Abbe number at the d-line of the negative lens included in the first lens group

[0037] Equation (4) defines the Abbe number at the d-line of the negative lens included in the first lens group. By including at least one negative lens that satisfies equation (4) in the first lens group, it becomes possible to correct axial chromatic aberration and chromatic aberration of magnification during focusing from infinity to the closest object.

[0038] On the other hand, if the value of formula (4) exceeds the upper limit, sagittal coma flare increases, and further, correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient, resulting in noticeable color bleeding of the image on the imaging plane and noticeable color bleeding of the blurred image in the out-of-focus area, which is undesirable.

[0039] In order to obtain the above effects, the lower limit of formula (4) is preferably 10.0, more preferably 15.0, and the upper limit of formula (4) is preferably 24.0, more preferably 22.0.

[0040] 1-3-5.Formula (5) 39.0 ≦ f1R ≦ 85.0 (5) however, f1R: The composite focal length (mm) of the lens in the first lens group located closer to the image than the aperture stop

[0041] Equation (5) defines the composite focal length of the lens in the first lens group that is closer to the image than the aperture stop. Satisfying equation (5) limits the light rays that enter the second lens group, suppressing fluctuations in aberrations during focusing by the second lens group, enabling good correction.

[0042] On the other hand, if the value of formula (5) falls below the lower limit, the angle of incidence of the light beam on the second lens group becomes large. Furthermore, the aberration sensitivity of the second lens group increases, and the decentering sensitivity of the lens group due to lens manufacturing errors increases, making it difficult to achieve an optical system with high optical performance. On the other hand, if the value of formula (5) exceeds the upper limit, the angle of incidence of the light beam on the second lens group becomes small. Furthermore, while it is possible to reduce the aberration sensitivity of the lens group, this undesirably leads to an increase in the size and weight of the second lens group, and further increases the outer diameter of the product.

[0043] To obtain the above effects, the lower limit of formula (5) is preferably 40.0, more preferably 41.0, and the upper limit of formula (5) is preferably 83.0, more preferably 80.0, and even more preferably 75.0.

[0044] 1-3-6.Formula (6) -10.0≦(R1f+R1r) / (R1f-R1r)≦1.2 (6) however, R1f: Radius of curvature of the image side of the lens located closest to the object across the largest air gap in the first lens group R1r: Radius of curvature of the object-side surface of the lens located on the image side across the largest air gap in the first lens group

[0045] Equation (6) defines the radii of curvature of the object-side and image-side lens surfaces across the maximum air gap in the first lens group. Satisfying equation (6) enables excellent correction of sagittal coma and lateral chromatic aberration that occur in the first lens group.

[0046] On the other hand, if the value of formula (6) falls below the lower limit, the angle of incidence of off-axial rays will change. Furthermore, the change will be particularly large for the g-line, resulting in increased chromatic aberration of magnification. Furthermore, sagittal coma, which is a problem with large-diameter lenses, will increase, making aberration correction difficult. On the other hand, if the value of formula (6) exceeds the upper limit, fluctuations in sagittal coma and distortion will increase, making aberration correction difficult.

[0047] To obtain the above effect, the lower limit of formula (6) is preferably −9.5, more preferably −9.3, and the upper limit of formula (6) is preferably 1.0, more preferably 0.8.

[0048] 1-3-7.Formula (7) 0.5 ≦ BF / Y ≦ 1.3 (7) however, BF: The distance on the optical axis from the apex of the surface of the fourth lens group closest to the image plane Y: Maximum image height of the optical system

[0049] Equation (7) defines the distance from the apex of the surface of the fourth lens group closest to the image to the image plane and the maximum image height of the image plane in the optical system. Satisfying equation (7) minimizes the effects of peripheral illumination. Furthermore, the overall length of the optical system can be shortened, making it easier to make it more compact.

[0050] On the other hand, if the value of formula (7) falls below the lower limit, the angle of incidence of the chief ray incident on the image plane from the side closest to the image of the optical system (the angle of incidence of the chief ray that the pixels on the sensor's light receiving surface can tolerate) becomes tight, resulting in the effects of peripheral light deficiency (shading) and color fringing. On the other hand, if the value of formula (7) exceeds the upper limit, the back focus becomes long and the overall length of the optical system becomes long. This also makes it difficult to miniaturize the optical system, making it unsuitable for mirrorless cameras.

[0051] To obtain the above effects, the lower limit of formula (7) is preferably 0.52, more preferably 0.55, and the upper limit of formula (7) is preferably 1.2, more preferably 1.1.

[0052] 1-3-8.Formula (8) 0.80 ≦ FD / f ≦ 1.50 (8) however, FD: The distance on the optical axis from the lens surface in the second lens group closest to the object to the lens surface in the fourth lens group closest to the image when focusing at infinity f: focal length of the optical system when focused at infinity

[0053] Equation (8) defines the ratio of the axial distance from the lens surface of the second lens group closest to the object to the lens surface of the fourth lens group closest to the image to the focal length of the optical system when focusing at infinity. Satisfying equation (8) makes it possible to optimize the size of the second lens group while suppressing aberration fluctuations during focusing. Furthermore, the effect of peripheral illumination is minimized. Furthermore, the overall length of the optical system can be shortened, making it easier to make it more compact.

[0054] On the other hand, if the value of formula (8) is below the lower limit, the overall length cannot be suppressed, making it difficult to achieve compactness.On the other hand, if the value of formula (8) is above the upper limit, aberration fluctuations during focusing become large, making it difficult to correct various aberrations.

[0055] To obtain the above effects, the lower limit of formula (8) is preferably 0.85, more preferably 0.90, and the upper limit of formula (8) is preferably 1.45, more preferably 1.40.

[0056] 1-3-9.Formula (9) 1.45 ≦ F1_F2 / f ≦ 2.55 (9) however, F1_F2: Combined focal length of the second and third lens groups when focusing at infinity

[0057] Equation (9) defines the ratio between the combined focal length of the second and third lens groups and the focal length of the optical system when focused at infinity. By satisfying equation (9), aberration fluctuations during focusing can be effectively corrected.

[0058] On the other hand, if the value of formula (9) is below the lower limit, the overall length cannot be suppressed, making it difficult to achieve a compact size.On the other hand, if the value of formula (9) is above the upper limit, aberration fluctuations during focusing become large, making it difficult to correct various aberrations.

[0059] In order to obtain the above effects, the lower limit of formula (9) is preferably 1.48, more preferably 1.50, and the upper limit of formula (9) is preferably 2.52, more preferably 2.49.

[0060] 1-3-10.Formula (10) 0.95 ≦ βb ≦ 1.50 (10) however, βb: Lateral magnification of the fourth lens group when focusing at infinity

[0061] Expression (10) defines the lateral magnification of the fourth lens group. Satisfying expression (10) makes it possible to reduce the size of the optical system and correct various aberrations.

[0062] On the other hand, if the value of formula (10) is below the lower limit, the overall length cannot be suppressed, making it difficult to achieve compactness.On the other hand, if the value of formula (10) is above the upper limit, aberration fluctuations during focusing become large, making it difficult to correct various aberrations.

[0063] In order to obtain the above effects, the lower limit of formula (10) is preferably 0.98, more preferably 1.00, and the upper limit of formula (10) is preferably 1.48, more preferably 1.46.

[0064] 2. Imaging device Next, the 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 provided on the image side of the optical system, which converts an optical image formed by the optical system into an electrical signal.

[0065] Here, there are no particular limitations on the imaging element, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also 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. Furthermore, the imaging device may be a fixed-lens imaging device in which the lens is fixed to the housing, or a lens-interchangeable imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

[0066] 41 is a diagram schematically illustrating an example of the configuration of the imaging device 1. The camera 2 has a detachable optical system 3, an imaging element 21 (CCD sensor or CMOS sensor) arranged on an image plane IP of the optical system 3, and a cover glass 22 arranged on the object side of the imaging element 21. The optical system 3 has an aperture stop 31.

[0067] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples. [Example]

[0068] (1) Optical configuration of the optical system FIG. 1 is a cross-sectional view of a lens showing the lens configuration of an optical system according to a first embodiment of the present invention when focused at infinity.

[0069] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0070] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens with positive refractive power formed by cementing a positive meniscus lens L1 with a concave surface facing the object side and a negative meniscus lens L2 with a concave surface facing the object side, a negative meniscus lens L3 with a convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with a convex surface facing the object side, a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0071] The second lens group G2 is composed of a plano-concave lens L9 with a flat surface on the object side, and a biconvex lens L10.

[0072] The third lens group G3 is composed of a positive meniscus lens L11 with its concave surface facing the object side.

[0073] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with its convex surface facing the object side.

[0074] "IP" in Figure 1 denotes an image plane, specifically 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. A parallel plate with no substantial refractive power, such as a cover glass CG, is provided on the object side of the image plane IP. These points are the same in the lens cross-sectional views shown in other embodiments, and therefore will not be described below.

[0075] (2) Numerical examples Next, we will explain numerical examples that apply specific numerical values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system. In addition, the values of each formula (values corresponding to the conditional formulas) are listed after Example 8.

[0076] In the "Surface Data" section, the "Surface Number" indicates the order of the lens surface counted from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the axial spacing of the lens surface, "Nd" indicates the refractive index for the d-line (wavelength λ=587.6 nm), and "νd" indicates the Abbe number for the d-line. The "ASPH" next to the surface number indicates that the lens surface is aspherical, and "STOP" indicates the aperture stop. Furthermore, "D(15)," "D(19)," etc., in the axial spacing column of the lens surface indicate that the axial spacing of the lens surface is variable, changing when focusing at the subject distance. All length values in each table are in millimeters, and all angle of view values are in degrees. In the radius of curvature column, "0.0000" indicates a flat surface. Surfaces 29 and 30 in Table 1 represent the surface data for the cover glass CG.

[0077] "Various data" indicates the "F" focal length, "Fno" F-number, "W" half angle of view, "Y" image height, and "BF" back focus of the optical system when focused at infinity and at the closest possible distance. Note that the "BF" value of the optical system includes a 2.5 mm thick cover glass (Nd=1.5168), and the same applies to the back focus shown in other examples.

[0078] "Variable intervals (in focus)" indicate the variable intervals when in focus at a predetermined shooting distance.

[0079] "Focal length of each lens group" indicates the focal length of each lens group that constitutes the optical system.

[0080] "Aspherical surface data" indicates the aspherical coefficients of each aspherical surface. Note that the aspherical surface is defined by the following equation, where x is the amount of displacement from the vertex of the surface in the optical axis direction. x=(h 2 / r) / [1+{1-(1+k)×(h / r) 2} 1 / 2 )] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In the above formula, h is the height from the optical axis, r is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th order aspheric coefficient. Also, "E±XX" represents exponential notation, and is expressed as "×10 ±XX The matters relating to these tables are the same as those in the tables shown in the other examples, and therefore will not be described below.

[0081] 2, 3, 4, and 5 show longitudinal and lateral aberration diagrams of the optical system when focused at infinity and when focused at the closest possible distance. The longitudinal aberration diagrams shown in each diagram, from left to right, show spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the spherical aberration diagrams, the solid line shows spherical aberration at the d-line (wavelength 587.6 nm) and the dashed line shows spherical aberration at the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the vertical axis shows half angle of view (ω) and the horizontal axis shows defocus. The solid line shows the sagittal image plane (ds) for the d-line and the dashed line shows the meridional image plane (dm) for the d-line. In the distortion diagrams, the vertical axis shows half angle of view (ω) and the horizontal axis shows distortion. The lateral aberration diagrams shown in each figure, from left to right, respectively show coma aberration (mm) in the meridional direction and coma aberration (mm) in the sagittal direction. From top to bottom of the figure, they show coma aberration at half angles of view (ω) with a ratio of 1.0 to 0.0. The solid line shows coma aberration at the d-line, and the dashed line shows coma aberration at the g-line. These matters are the same in the aberration diagrams shown in other examples, so explanations will be omitted below.

[0082] [Face Data] Surface number RD Nd νd 1 -1112.3474 5.8449 1.83481 42.72 2 -76.9745 1.3000 1.92286 20.88 3 -210.0000 0.2000 4 912.7674 1.5500 1.72947 51.78 5 29.2979 12.6247 6 37.4056 8.0335 1.77012 24.46 7 -184.3239 9.3213 8ASPH 73.0859 1.3200 1.58313 59.42 9ASPH 26.8077 5.9985 10 -44.5673 1.2500 1.84666 23.78 11 26.5193 10.3945 1.74126 51.15 12 -39.7111 2.0000 13STOP 0.0000 2.0000 14 78.5899 7.1050 1.77250 49.62 15 -55.6186 D(15) 16 0.0000 1.2000 1.74167 32.84 17 37.9326 4.3916 18 81.4598 3.7061 1.92286 20.88 19 -538.5562 D(19) 20 -1603.1667 4.9642 1.70802 53.04 21 -49.8250 D(21) 22 32.7713 9.4981 1.49700 81.61 23 -69.7355 0.2000 24 -241.3847 1.0000 1.65620 29.82 25 28.7255 4.6346 26ASPH 107.2719 1.8500 1.85108 40.12 27ASPH 42.7204 3.0998 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0083] [Various items] Shooting distance INF: Closest F 33.3896 32.2974 Fno 1.4500 1.4500 W 32.8185 31.2228 Y 21.633 21.633 BF 17.500 17.500

[0084] [Variable interval (when focusing)] Shooting distance INF: Closest D( 0) ∞ 320.0288 D(15) 2.1937 8.9177 D(19) 9.5193 2.2299 D(21) 0.4000 0.9654 D(30) 1.0000 1.0000

[0085] [Focus distance of each レンズ group] Group face number focus distance G1 1-15 37.8392 G2 16-19 -186.367 G3 20-21 72.5337 G4 22-27 -85.4053

[0086] [Aspherical surface] Face number k A4 A6 A8 A10 8 0.00000E+00 -1.64135E-05 -2.94174E-08 8.96861E-11 8.35605E-14 9 -8.23823E-01 1.20196E-06 -2.58683E-08 3.11021E-11 3.67239E-13 26 0.00000E+00 -1.75503E-05 -8.41385E-09 -3.09446E-11 6.41687E-14 27 0.00000E+00 -5.70161E-06 7.86503E-10 4.91575E-13 4.95011E-14 Face number A12 8 -5.23312E-16 9 -1.28157E-15 26 0.00000E+00 27 0.00000E+00 [Example]

[0087] (1) Optical configuration of the optical system FIG. 6 is a lens cross-sectional view showing the lens configuration of the optical system of Example 2 according to the present invention when focused at infinity.

[0088] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0089] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens with negative refractive power formed by cementing a positive meniscus lens L1 with its concave surface facing the object side and a biconcave lens L2, a biconvex lens L3, a negative meniscus lens L4 with its convex surface facing the object side, a cemented lens with positive refractive power formed by cementing a biconcave lens L5 and a biconvex lens L6, an aperture stop S, and a biconvex lens L7.

[0090] The second lens group G2 is composed of, in order from the object side, a cemented lens having negative refractive power, in which a biconvex lens L8 and a biconcave lens L9 are cemented together, and a biconvex lens L10.

[0091] The third lens group G3 is composed of a biconvex lens L11.

[0092] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a biconcave lens L14.

[0093] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0094] [Face Data] Surface number RD Nd νd 1 -3861.4979 8.0746 1.61692 56.07 2 -45.3488 1.6500 1.59867 38.84 3 31.5068 6.7310 4 38.0602 6.9105 1.92119 23.96 5 -324.9412 7.5142 6ASPH 114.7520 1.3200 1.58313 59.42 7ASPH 25.8590 7.0110 8 -57.4174 1.2500 1.82140 22.97 9 26.6490 0.0010 1.56732 42.84 10 26.6490 11.7877 1.74320 49.34 11 -48.3089 2.0000 12STOP 0.0000 2.0000 13 74.6318 8.5601 1.77250 49.62 14 -57.8627 D(14) 15 552.0331 3.0000 1.72916 54.67 16 -179.6380 1.0000 1.94728 29.07 17 40.8417 4.1464 18 123.9079 4.0082 1.94595 17.98 19 -163.8626 D(19) 20 75.5778 7.9360 1.77250 49.62 21 -64.1003 D(21) 22 53.6737 6.6944 1.49700 81.61 23 -103.7803 0.2000 24 -295.5789 1.0000 1.68893 31.16 25 30.1757 5.7954 26ASPH 997.7596 1.8500 1.85108 40.12 27ASPH 81.6478 3.0987 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0095] [Various items] Shooting distance INF Closest F 40.3989 38.4571 Fno 1.4100 1.4726 W 27.8608 26.1523 Y 21.633 21.633 BF 17.4987 17.4987

[0096] [Variable Interval (in Focus)] Shooting distance INF Closest D(0)∞320.0781 D(14) 1.9972 8.4486 D(19) 9.0634 2.0835 D(21) 1.0000 1.5285 D(30) 1.0000 1.0000

[0097] [Focal length of each lens group] Group Surface number Focal length G1 1-14 42.3197 G2 15-19 -121.959 G3 20-21 46.0380 G4 22-27 -50.5631

[0098] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -1.15559E-05 -1.81351E-08 4.30716E-11 8.09943E-14 7 -6.15033E-01 3.84438E-06 -1.43478E-08 -1.90530E-11 3.35123E-13 26 0.00000E+00 -1.51181E-05 -1.31262E-08 4.54774E-11 -2.16222E-14 27 0.00000E+00 -5.12939E-06 -7.00821E-09 7.14763E-11 -4.60828E-14 Face number A12 6 -2.64140E-16 7 -7.75048E-16 26 0.00000E+00 27 0.00000E+00 [Example]

[0099] (1) Optical configuration of the optical system FIG. 11 is a lens cross-sectional view showing the lens configuration of an optical system according to Example 3 of the present invention when focused at infinity.

[0100] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0101] The configuration of each lens group will be described below. The first lens group G1 is composed of a cemented lens with negative refractive power formed by cementing a positive meniscus lens L1 with its concave surface facing the object side and a negative meniscus lens L2 with its concave surface facing the object side, a biconvex lens L3, a negative meniscus lens L4 with its convex surface facing the object side, a cemented lens with positive refractive power formed by cementing a biconcave lens L5 and a biconvex lens L6, an aperture stop S, and a biconvex lens L7.

[0102] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L8 with its concave surface facing the image side, and a biconvex lens L9.

[0103] The third lens group G3 is composed of a biconvex lens L10.

[0104] The fourth lens group G4 is composed of, in order from the object side, a cemented lens having negative refractive power, in which a biconvex lens L11 and a biconcave lens L12 are cemented together, and a biconcave lens L13.

[0105] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0106] [Face Data] Surface number RD Nd νd 1 -85.0429 8.0000 1.90366 31.31 2 -29.9056 1.6500 1.93211 23.42 3 -153.0497 0.2000 4 67.2583 6.9594 1.92119 23.96 5 -144.6815 1.2881 6ASPH 78.8292 1.3200 1.58313 59.42 7ASPH 26.5688 16.2436 8 -35.0794 1.2500 1.70287 27.15 9 41.0964 10.8441 1.77250 49.62 10 -43.8325 2.0000 11STOP 0.0000 2.0000 12 79.2385 5.2508 1.77250 49.62 13 -159.3262 D(13) 14 17575.3702 1.2000 1.74317 47.32 15 42.0250 3.5969 16 206.9434 3.0697 1.92286 20.88 17 -225.6701 D(17) 18 69.3808 8.5634 1.77250 49.62 19 -68.0892 D(19) 20 64.9150 8.1710 1.77250 49.62 21 -56.1403 1.0000 1.71823 26.74 22 32.8244 6.4330 23ASPH -535.2130 1.8500 1.85135 40.10 24ASPH 99.5002 3.7462 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0107] [Various items] Shooting distance INF: Closest F 48.5017 45.4920 Fno 1.4399 1.5474 W 23.7670 21.4597 Y 21.633 21.633 BF 18.1462 18.1462

[0108] [Variable interval (when focusing)] Shooting distance INF: Closest D( 0) ∞ 324.8170 D(13) 1.9888 12.4470 D(17) 13.4766 2.1062 D(19) 0.7500 1.6622 D(27) 1.0000 1.0000

[0109] [Focus distance of each レンズ group] Group face number focus distance G1 1-13 55.2474 G2 14-17 -118.122 G3 18-19 45.7261 G4 20-24 -56.1795

[0110] [Aspherical surface] Face number k A4 A6 A8 A10 6 0.00000E+00 -3.08885E-06 -6.33741E-09 4.04863E-14 8.15307E-15 7 -3.99165E-01 4.84256E-06 1.26947E-09 5.26078E-12 -4.27315E-15 23 0.00000E+00 -2.43881E-05 2.84540E-08 -2.26609E-11 6.28328E-14 24 0.00000E+00 -1.62108E-05 3.28709E-08 -6.10781E-12 2.73903E-14 Face number A12 6 -7.30680E-18 7 3.48953E-17 23 0.00000E+00 24 0.00000E+00 [Example]

[0111] (1) Optical configuration of the optical system FIG. 16 is a lens cross-sectional view showing the lens configuration of the optical system of Example 4 according to the present invention when focused at infinity.

[0112] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0113] The configuration of each lens group will be described below. The first lens group G1 is composed of a cemented lens with negative refractive power, formed by cementing a negative meniscus lens L1 with its concave surface facing the object side and a biconcave lens L2 with its object side cemented together, a biconvex lens L3, a negative meniscus lens L4 with its convex surface facing the object side, a cemented lens with positive refractive power, formed by cementing a biconcave lens L5 and a biconvex lens L6, an aperture stop S, and a biconvex lens L7.

[0114] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L8 whose object side is flat, and a biconvex lens L9.

[0115] The third lens group G3 is composed of a biconvex lens L10.

[0116] The fourth lens group G4 is composed of, in order from the object side, a cemented lens having negative refractive power, in which a biconvex lens L11 and a biconcave lens L12 are cemented together, and a biconcave lens L13.

[0117] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0118] [Face Data] Surface number RD Nd νd 1 -228.0707 9.2744 1.61207 56.13 2 -33.4559 1.6500 1.62434 32.26 3 52.8155 2.1424 4 49.1826 6.8951 1.92119 23.96 5 -138.7195 5.0245 6ASPH 76.0775 1.3200 1.82115 24.06 7ASPH 32.4415 10.4748 8 -26.6038 1.2500 1.64863 30.34 9 79.7838 8.9693 1.83559 40.92 10 -33.6165 2.0000 11STOP 0.0000 2.0000 12 52.7128 6.4330 1.49700 81.61 13 -115.2491 D(13) 14 0.0000 1.2000 1.86485 38.15 15 44.1417 2.5752 16 128.7199 3.3271 1.92286 20.88 17 -235.1172 D(17) 18 77.2245 8.0235 1.77250 49.62 19 -61.2723 D(19) 20 68.9607 8.6126 1.77250 49.62 21 -43.5976 1.1129 1.73256 25.83 22 35.5320 5.8861 23ASPH -846.2459 1.8500 1.85108 40.12 24ASPH 81.3907 3.1015 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0119] [Various data] Shooting distance INF Closest F 45.5424 42.9123 Fno 1.4500 1.5435 W 25.1291 22.9702 Y 21.633 21.633 BF 17.5015 17.5015

[0120] [Variable Interval (in Focus)] Shooting distance INF Closest D(0)∞326.9244 D(13) 1.9931 12.2469 D(17) 13.0915 2.0952 D(19) 0.5500 1.2926 D(27) 1.0000 1.0000

[0121] [Focal length of each lens group] Group Surface number Focal length G1 1-13 53.0404 G2 14-17 -127.289 G3 18-19 45.3719 G4 20-24 -53.7838

[0122] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -4.62733E-06 -1.30739E-08 -5.66238E-12 -1.65355E-14 7 -5.18276E-01 4.17552E-06 -3.40382E-09 -1.61178E-11 1.30079E-15 23 0.00000E+00 -3.32507E-05 5.31909E-08 -2.74049E-11 -5.47803E-15 24 0.00000E+00 -2.46297E-05 6.19703E-08 -2.71967E-11 -2.86687E-15 Face number A12 6 4.04711E-17 7 -2.40030E-17 23 0.00000E+00 24 0.00000E+00 [Example]

[0123] (1) Optical configuration of the optical system FIG. 21 is a lens cross-sectional view showing the lens configuration of the optical system of Example 5 according to the present invention when focused at infinity.

[0124] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0125] The configuration of each lens group will be described below. The first lens group G1 is composed of a cemented lens with positive refractive power formed by cementing a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object side, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0126] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L9 whose object side is flat, and a biconvex lens L10.

[0127] The third lens group G3 is composed of a biconvex lens L11.

[0128] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a biconcave lens L14.

[0129] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0130] [Face Data] Surface number RD Nd νd 1 771.1109 7.4367 1.83481 42.72 2 -55.3704 1.3000 1.92119 23.96 3 -212.2186 0.2000 4 -7833.9757 1.5500 1.48749 70.44 5 21.9033 15.3480 6 30.4735 6.6151 1.82898 23.95 7 -141.9773 1.2819 8ASPH 71.4042 1.3200 1.83441 37.28 9ASPH 23.2956 6.8381 10 -36.8428 1.2500 1.84666 23.78 11 26.3609 9.7232 1.75746 50.33 12 -37.4388 2.0000 13STOP 0.0000 2.0000 14 96.1773 6.5028 1.77250 49.62 15 -48.8457 D(15) 16 0.0000 1.2000 1.74218 36.71 17 39.5754 2.5352 18 91.1801 3.3773 1.92286 20.88 19 -413.4901 D(19) 20 318.6990 4.5321 1.75198 50.60 21 -55.4532 D(21) 22 31.2848 8.6005 1.49700 81.61 23 -64.8295 0.2000 24 -172.0204 1.0000 1.73842 25.60 25 29.9718 4.4796 26ASPH -271.4701 1.8500 1.85108 40.12 27ASPH 115.4858 3.1000 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0131] [Various data] Shooting distance INF Closest F 31.4732 30.5281 Fno 1.4601 1.4852 W 34.5150 32.9635 Y 21.633 21.633 BF 17.5000 17.5000

[0132] [Variable Interval (in Focus)] Shooting distance INF Closest D(0)∞330.0319 D(15) 1.9878 8.2936 D(19) 8.8217 2.0595 D(21) 0.5500 1.0064 D(30) 1.0000 1.0000

[0133] [Focal length of each lens group] Group Surface number Focal length G1 1-15 37.3918 G2 16-19 -172.976 G3 20-21 63.1415 G4 22-27 -79.3352

[0134] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.36185E-05 -2.39755E-08 8.40427E-11 -2.51782E-15 9 -5.83033E-01 3.26236E-06 -2.06282E-08 3.20478E-11 1.59786E-13 26 0.00000E+00 1.12564E-05 -6.68072E-08 -1.23570E-11 1.55764E-13 27 0.00000E+00 2.47794E-05 -5.75350E-08 1.93230E-11 1.39863E-13 Face number A12 8 -2.32666E-16 9 -6.55543E-16 26 0.00000E+00 27 0.00000E+00 [Example]

[0135] (1) Optical configuration of the optical system FIG. 26 is a lens cross-sectional view showing the lens configuration of the optical system of Example 6 according to the present invention when focused at infinity.

[0136] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0137] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens with positive refractive power formed by cementing a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object side, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0138] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L9 whose object side is flat, and a biconvex lens L10.

[0139] The third lens group G3 is composed of a biconvex lens L11.

[0140] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with its convex surface facing the object side.

[0141] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0142] [Face Data] Surface number RD Nd νd 1 173.7978 8.9679 1.83481 42.72 2 -63.9488 1.3000 1.92119 23.96 3 -240.3604 1.5000 4 -220.5721 1.5500 1.48749 70.44 5 20.4720 16.0381 6 30.4538 5.9926 1.83284 23.72 7 -116.2805 0.2000 8ASPH 82.5260 1.3200 1.83441 37.28 9ASPH 23.7204 6.4492 10 -35.5547 1.2500 1.84666 23.78 11 26.7926 0.0010 1.56732 42.84 12 26.7926 9.2332 1.77250 49.62 13 -37.0378 2.0000 14STOP 0.0000 2.0000 15 91.7715 6.2826 1.77250 49.62 16 -51.1134 D(16) 17 0.0000 1.2000 1.74265 41.05 18 40.4868 2.4271 19 108.4402 3.2198 1.92119 23.96 20 -295.8316 D(20) 21 492.4813 4.2604 1.77250 49.62 22 -55.8168 D(22) 23 31.0567 8.5715 1.49700 81.61 24 -66.4032 0.2000 25 -193.7372 1.0000 1.71466 26.60 26 28.4787 4.7194 27ASPH 1926.3038 1.8500 1.85108 40.12 28ASPH 106.5676 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0143] [Various items] Shooting distance INF Closest F 31.0124 30.1903 Fno 1.4400 1.4856 W 34.9133 33.3701 Y 21.633 21.633 BF 17.500 17.500

[0144] [Changeable interval (when focusing)] Shooting distance INF Closest D( 0) ∞ 330.0363 D(16) 1.9737 7.6918 D(20) 8.4445 2.0906 D(22) 0.5500 1.1858 D(31) 1.0000 1.0000

[0145] [Focal length of each lens group] Group Surface number Focal length G1 1-16 37.6960 G2 17-20 -162.130 G3 21-22 65.1197 G4 23-28 -102.190

[0146] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.01087E-05 -3.35865E-08 9.33889E-11 2.32372E-13 9 -4.61533E-01 5.22094E-06 -2.94241E-08 -9.54051E-12 8.66882E-13 27 0.00000E+00 -7.90613E-06 -1.41361E-09 -8.38477E-11 1.35651E-13 28 0.00000E+00 4.50209E-06 5.24274E-09 -4.18014E-11 1.14135E-13 Face number A12 8 -9.34433E-16 9 -2.41711E-15 27 0.00000E+00 28 0.00000E+00 [Example]

[0147] (1) Optical configuration of the optical system FIG. 31 is a lens cross-sectional view showing the lens configuration of the optical system of Example 7 according to the present invention when focused at infinity.

[0148] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0149] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens with positive refractive power formed by cementing a negative meniscus lens L1 with a convex surface facing the object side and a biconvex lens L2, a negative meniscus lens L3 with a convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with a convex surface facing the object side, a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0150] The second lens group G2 is composed of, in order from the object side, a plano-concave lens L9 whose object side is flat, and a biconvex lens L10.

[0151] The third lens group G3 is composed of a biconvex lens L11.

[0152] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, and a negative meniscus lens L14 with its convex surface facing the object side.

[0153] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0154] [Face Data] Surface number RD Nd νd 1 250.0000 1.5000 1.92286 20.88 2 91.3371 5.4833 1.66386 56.12 3 -284.4015 0.5000 4 864.4431 1.6500 1.49700 81.61 5 21.6476 20.8072 6 28.5497 6.1373 1.93107 23.11 7 -660.6291 0.2000 8ASPH 90.6064 1.3200 1.83441 37.28 9ASPH 23.9800 6.4664 10 -42.6079 1.2500 1.84666 23.78 11 24.0973 9.8154 1.77250 49.62 12 -40.4448 2.0000 13STOP 0.0000 2.0000 14 59.6619 5.2243 1.77250 49.62 15 -118.9867 D(15) 16 0.0000 1.2000 1.74077 27.76 17 42.1415 2.9042 18 212.5356 3.8056 1.92286 20.88 19 -83.7584 D(19) 20 52.7404 4.3972 1.77250 49.62 21 -1579.0980 D(21) 22 39.8190 7.1079 1.49700 81.61 23 -70.5632 0.2000 24 152.5886 1.0000 1.78322 24.04 25 23.2826 5.9758 26ASPH 378.8394 1.8500 1.85108 40.12 27ASPH 135.9702 3.1003 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0155] [Various items] Shooting distance INF: Closest F 29.0222 28.0795 Fno 1.4432 1.4628 W 36.7181 35.8784 Y 21.633 21.633 BF 17.5003 17.5003

[0156] [Variable interval (when focusing)] Shooting distance INF: Closest D( 0) ∞ 330.0427 D(15) 1.9754 4.8815 D(19) 7.1799 2.3193 D(21) 0.5500 2.5044 D(30) 1.0000 1.0000

[0157] [Focus distance of each レンズ group] Group face number focus distance G1 1-15 41.5286 G2 16-19 -869.596 G3 20-21 66.1435 G4 22-27 -90.4289

[0158] [Aspherical surface] Face number k A4 A6 A8 A10 8 0.00000E+00 -4.28786E-06 -2.52717E-08 9.50604E-11 -1.29592E-14 9 -3.35657E-01 6.46108E-06 -1.37717E-08 -5.13782E-11 9.09925E-13 26 0.00000E+00 -4.23342E-05 7.45101E-08 -2.48716E-10 7.05368E-13 27 0.00000E+00 -3.10941E-05 8.91765E-08 -1.49046E-10 6.40234E-13 Face number A12 8 -2.99395E-16 9 -2.08971E-15 26 0.00000E+00 27 0.00000E+00 [Example]

[0159] (1) Optical configuration of the optical system FIG. 36 is a lens cross-sectional view showing the lens configuration of the optical system of Example 8 according to the present invention when focused at infinity.

[0160] The optical system is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side, while the first lens group G1 and the fourth lens group G4 remain fixed in the optical axis direction. An aperture stop S is located inside the first lens group G1.

[0161] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens with positive refractive power formed by cementing a biconcave lens L1 and a biconvex lens L2 together, a negative meniscus lens L3 with its convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7, an aperture stop S, and a biconvex lens L8.

[0162] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L9 with its convex surface facing the object side, and a biconvex lens L10.

[0163] The third lens group G3 is composed of a biconvex lens L11.

[0164] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, and a negative meniscus lens L14 with its convex surface facing the object side.

[0165] (2) Numerical examples Next, we will explain numerical examples that apply specific values of the optical system. The following shows the "surface data," "various data," "variable spacing (when in focus)," "focal length of each lens group," and "aspherical surface data" of the optical system.

[0166] [Face Data] Surface number RD Nd νd 1 -383.2756 1.5000 1.92286 20.88 2 159.6775 4.6368 1.89930 35.51 3 -206.6054 0.5000 4 192.7697 1.6500 1.49700 81.61 5 21.7668 17.9391 6 0.0000 2.8000 7 29.9836 6.1586 1.92439 23.96 8 -332.8322 0.2000 9ASPH 89.8504 1.3200 1.85135 40.10 10ASPH 24.7941 6.4858 11 -39.1059 1.2500 1.84666 23.78 12 25.8283 9.5478 1.77250 49.62 13 -39.9770 2.0000 14STOP 0.0000 2.0000 15 63.5839 5.5981 1.77250 49.62 16 -96.0612 D(16) 17 390.3404 1.2000 1.74077 27.76 18 40.4417 3.3313 19 237.4962 3.7739 1.92286 20.88 20 -89.6564 D(20) 21 56.9933 4.2450 1.77250 49.62 22 -1377.1300 D(22) 23 41.5995 7.1973 1.49700 81.61 24 -71.5673 0.2000 25 125.8501 1.5449 1.78667 23.94 26 24.2525 5.6791 27ASPH 424.4833 1.8500 1.85108 40.12 28ASPH 115.8130 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0167] [Various items] Shooting distance INF Closest F 29.0933 28.1356 Fno 1.4500 1.4733 W 36.9290 36.0637 Y 21.633 21.633 BF 17.5000 17.5000

[0168] [Changeable interval (when focusing)] Shooting distance INF Closest D( 0) ∞ 330.0429 D(16) 1.9719 4.9204 D(20) 7.3703 2.3161 D(22) 0.5500 2.6557 D(31) 1.0000 1.0000

[0169] [Focal length of each lens group] Group Surface number Focal length G1 1-16 40.9541 G2 17-20 -825.245 G3 21-22 70.9373 G4 23-28 -95.2085

[0170] [Aspherical data] Surface number k A4 A6 A8 A10 9 0.00000E+00 -4.12277E-06 -2.81947E-08 8.70743E-11 3.56984E-14 10 -3.50599E-01 6.46480E-06 -1.84803E-08 -4.39047E-11 7.82031E-13 27 0.00000E+00 -3.82861E-05 8.62244E-08 -1.91624E-10 3.68250E-13 28 0.00000E+00 -2.72470E-05 1.02161E-07 -1.33095E-10 3.82708E-13 Face number A12 9 -3.35643E-16 10 -1.67421E-15 27 0.00000E+00 28 0.00000E+00

[0171] [Conditional expression corresponding value] Example 1 Example 2 Example 3 Example 4 Conditional expression (1) f1 / f2 -0.20 -0.35 -0.47 -0.42 Conditional expression (2) ν2 20.88 17.98 20.88 20.88 Conditional expression (3) f / f2 -0.18 -0.33 -0.41 -0.36 Conditional expression (4) ν1 20.88 22.97 23.42 24.06 Conditional expression (5) f1R 43.16 43.41 69.17 73.71 Conditional formula (6) (R1f + R1r) / (R1f -R1r) -8.23 0.48 -0.14 0.10 Conditional expression (7) BF / Y 0.81 0.81 0.84 0.81 Condition (8) FD / f 1.24 1.13 0.99 1.02 Conditional expression (9) F1_F2 / f 1.69 1.88 2.23 2.12 Conditional expression (10) βb 1.08 1.35 1.30 1.30 Example 5 Example 6 Example 7 Example 8 Conditional expression (1) f1 / f2 -0.22 -0.23 -0.05 -0.05 Conditional expression (2) ν2 20.88 23.96 20.88 20.88 Conditional expression (3) f / f2 -0.18 -0.19 -0.03 -0.04 Conditional expression (4) ν1 23.78 23.78 20.88 20.88 Conditional expression (5) f1R 42.77 43.33 52.10 50.30 Conditional formula (6) (R1f + R1r) / (R1f -R1r) -6.11 -5.10 -7.27 -6.30 Conditional expression (7) BF / Y 0.81 0.81 0.81 0.81 Condition (8) FD / f 1.18 1.18 1.25 1.27 Conditional expression (9) F1_F2 / f 1.76 1.85 1.65 1.63 Conditional expression (10) βb 1.12 1.07 1.16 1.13 [Industrial Applicability]

[0172] According to the present invention, it is possible to provide an optical system and an imaging device that have a bright large-aperture lens with a small F-number, yet suppresses image plane fluctuations and chromatic aberrations over the entire focusing range. [Explanation of symbols]

[0173] G1: First lens group G2: Second lens group G3: Third lens group G4: Fourth lens group S Aperture CG...Cover glass IP: Image plane

Claims

1. The lens comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; the second lens group has at least one positive lens and at least one negative lens; an optical system in which, during focusing from infinity to a closest point, the first lens group and the fourth lens group are fixed with respect to an image plane, and the second lens group and the third lens group each move along an optical axis direction, and the following formula is satisfied: -0.55 ≦ f1 / f2 ≦ -0.01 (1) ν2 ≦ 25.0 (2) however, f1: focal length of the first lens group f2: focal length of the second lens group ν2: Abbe number at the d-line of any one of the positive lenses included in the second lens group

2. 2. The optical system according to claim 1, wherein the following formula is satisfied: -0.50 ≦ f / f2 ≦ -0.01 (3) however, f: focal length of the optical system when focused at infinity

3. 3. The optical system according to claim 1, wherein the first lens group comprises at least one negative lens that satisfies the following formula: ##EQU1## however, ν1 ≦ 25.0 (4) ν1: Abbe number at the d-line of the negative lens included in the first lens group

4. 4. The optical system according to claim 1, wherein the first lens group has a diaphragm, and the following formula is satisfied: 39.0 ≦ f1R ≦ 85.0 (5) however, f1R: composite focal length (mm) of the lens in the first lens group located closer to the image than the aperture stop

5. 5. The optical system according to claim 1, wherein the first lens group has the largest air gap among air gaps disposed between a lens surface of the first lens group closest to the object and a lens surface of the fourth lens group closest to the image.

6. 6. The optical system according to claim 1, wherein the first lens group satisfies the following formula: -10.0≦(R1f+R1r) / (R1f-R1r)≦1.2...(6) however, R1f: the radius of curvature of the image-side surface of the lens located on the object side across the largest air gap in the first lens group R1r: the radius of curvature of the object-side surface of the lens located on the image side across the largest air gap in the first lens group

7. 7. The optical system according to claim 1, wherein the following formula is satisfied: 0.5 ≦ BF / Y ≦ 1.3 (7) however, BF: the distance on the optical axis from the apex of the surface of the fourth lens group closest to the image side to the image plane Y: Maximum image height of the optical system

8. 8. The optical system according to claim 1, wherein the first lens group includes at least one cemented lens.

9. 9. The optical system according to claim 1, wherein the following formula is satisfied: 0.80≦FD / f≦1.50 (8) however, FD: the distance on the optical axis from the lens surface of the second lens group closest to the object to the lens surface of the fourth lens group closest to the image when focusing at infinity f: focal length of the optical system when focused at infinity

10. 10. The optical system according to claim 1, wherein the following formula is satisfied: 1.45 ≦ F1_F2 / f ≦ 2.55 (9) however, F1_F2: composite focal length of the second lens group and the third lens group when focusing at infinity

11. 11. The optical system according to claim 1, wherein the following formula is satisfied: 0.95 ≦ βb ≦ 1.50 (10) however, βb: lateral magnification of the fourth lens group when focused at infinity

12. 12. An imaging apparatus comprising: the optical system according to claim 1; 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