Fixed-focus optical system and imaging device

Abstract

The present invention provides a fixed-focus optical system in which chromatic aberration and other aberrations are corrected in a well-balanced manner, and an imaging device equipped with this fixed-focus optical system. [Solution] The fixed-focus optical system consists of a front group, an aperture, and a rear group, arranged in order from the object side to the image side. When the refractive index and Abbe number of the lenses included in the fixed-focus optical system are Nd and νd, respectively, the fixed-focus optical system is 2.435

Description

Technical Field

[0001] The technology of the present disclosure relates to a fixed-focus optical system and an imaging device.

Background Art

[0002] Conventionally, as a lens system that can be used in an imaging device such as a digital camera, a single-focus lens system described in Patent Document 1 below is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a demand for a fixed-focus optical system in which chromatic aberration and other various aberrations are corrected in a well-balanced manner, and the required level is increasing year by year.

[0005] The present disclosure provides a fixed-focus optical system in which chromatic aberration and other various aberrations are corrected in a well-balanced manner, and an imaging device including this fixed-focus optical system.

Means for Solving the Problems

[0006] A first aspect of the present disclosure is a fixed-focus optical system including, in order from the object side to the image side, a front group, an aperture stop, and a rear group, 2.435 < Nd + 0.01425 × νd < 2.75 (1) 15 < νd < 39 (2) including at least one specific lens that satisfies the conditional expressions (1) and (2) represented by. Here, the refractive index with respect to the d-line of the lens included in the fixed-focus optical system is Nd. The Abbe number based on the d-line of the lens included in the fixed-focus optical system is νd.

[0007] A second aspect of this disclosure relates to the fixed-focus optical system of the first aspect, where θgF is the partial dispersion ratio between the g-line and the F-line of the lens included in the fixed-focus optical system, and a specific lens is 0.65<θgF+0.00316×νd<0.85 (3) The condition (3) expressed by is satisfied.

[0008] A third aspect of this disclosure is a fixed-focus optical system of the first aspect, in which the focal length of the front group when in focus on an object at infinity is fF, and the focal length of the rear group when in focus on an object at infinity is fR, -5 <fR / fF<10 (4) The condition (4) expressed by is satisfied.

[0009] A fourth aspect of the present disclosure is a fixed-focus optical system of the first aspect, wherein at least one focusing lens group that moves along the optical axis when focusing is arranged.

[0010] A fifth aspect of this disclosure is a fixed-focus optical system of the fourth aspect, in which, if the focal length of the focusing lens group with the strongest refractive power among the focusing lens group included in the fixed-focus optical system is ffocmax, and the focal length of the fixed-focus optical system when in focus on an object at infinity is f, 0.2 < |ffocmax / f| < 3.5 (5) The condition (5) expressed by is satisfied.

[0011] A sixth aspect of this disclosure is a fixed-focus optical system of the fourth aspect, wherein the fixed-focus optical system includes two focusing lens groups, and of the two focusing lens groups, the focal length of the object-side focusing lens group is ff1, and the focal length of the image-side focusing lens group is ff2. 0.1 < |ff1 / ff2| < 10 (6) The condition (6) expressed by is satisfied.

[0012] A seventh aspect of this disclosure is a fixed-focus optical system of the fourth aspect, in which the combined focal length of all lenses closer to the object than the object-side focusing lens group in the focusing lens group included in the fixed-focus optical system is ffocF, and the focal length of the fixed-focus optical system when in focus on an object at infinity is f, -2 <f / ffocF<6 (7) The condition (7) expressed by is satisfied.

[0013] An eighth aspect of this disclosure is a fixed-focus optical system of the fourth aspect, in which the combined focal length of all lenses on the image side of the focusing lens group included in the fixed-focus optical system is ffocR, and the focal length of the fixed-focus optical system when in focus on an object at infinity is f, -6 <f / ffocR<2 (8) The condition (8) expressed by is satisfied.

[0014] A ninth aspect of this disclosure is a fixed-focus optical system of the fourth aspect, wherein two focusing lens groups are arranged in the rear group, each moving on a different trajectory when focusing.

[0015] A tenth aspect of this disclosure is a fixed-focus optical system of the fourth aspect, wherein one focusing lens group is arranged in the front group and one in the rear group, and the focusing lens group of the front group and the focusing lens group of the rear group move on different trajectories when focusing. 0.1 < |ffocF / fM| < 2 (9) The condition expressed in equation (9) is satisfied. Here, ffocF is the combined focal length of all lenses on the object side of the focusing lens group closest to the object in the fixed-focus optical system. fM is the combined focal length from the lens adjacent to the image side of the front focusing lens group to the lens adjacent to the object side of the rear focusing lens group.

[0016] An eleventh aspect of this disclosure is a fixed-focus optical system of the fourth aspect, wherein at least one focusing lens group includes at least one specific lens.

[0017] In the 12th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, the rear group includes at least one specific lens.

[0018] In the 13th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, the front group includes at least one specific lens.

[0019] In the 14th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, each of the front group and the rear group includes at least one specific lens.

[0020] In the 15th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, it includes at least one cemented lens, and at least one cemented lens includes at least one specific lens.

[0021] In the 16th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, the rear group includes an anti-vibration group that moves in a direction intersecting the optical axis during image blur correction. Let the focal length of the anti-vibration group be fIS, and the focal length of the fixed-focus optical system in the state of focusing on an infinite object be f. 0.05 < |fIS / f| < 2 (10) It satisfies the conditional expression (10) represented by the above.

[0022] In the 17th aspect of the present disclosure, in the fixed-focus optical system of the 16th aspect, the anti-vibration group includes at least one specific lens.

[0023] In the 18th aspect of the present disclosure, in the fixed-focus optical system of the 1st aspect, the maximum half field angle in the state of focusing on an infinite object is 7 degrees or less, 0.2 < Amax / TLf < 0.8 (11) It satisfies the conditional expression (11) represented by the above. Here, the maximum value of the air interval on the optical axis within the front group in the state of focusing on an infinite object is defined as Amax. The distance on the optical axis from the most object-side lens surface to the most image-side lens surface of the front group in the state of focusing on an infinite object is defined as TLf.

[0024] A 19th aspect of this disclosure relates to a fixed-focus optical system of the first aspect, in which, when the system is focused on an object at the longest possible object distance, the angle with respect to the optical axis at which the principal ray of the maximum field of view enters the image plane is θc, and the unit of θc is degrees, 0 < |θc| < 30 (12) The condition (12) expressed by is satisfied.

[0025] A 20th aspect of this disclosure is an imaging device comprising a fixed-focus optical system of any one of the first to 19th aspects.

[0026] Furthermore, the terms "~consisting of" and "~consisting of" in this specification are intended to include, in addition to the listed components, lenses that substantially have no refractive power, optical elements other than lenses such as apertures, filters, and cover glass, and mechanical parts such as lens flanges, lens barrels, image sensors, and image stabilization mechanisms.

[0027] In this specification, "a group of lenses having positive refractive power" means that the group as a whole has positive refractive power. Similarly, "a group of lenses having negative refractive power" means that the group as a whole has negative refractive power. "A lens having positive refractive power" and "a positive lens" are synonymous. "A lens having negative refractive power" and "a negative lens" are synonymous. In this specification, "a group of lenses" is not limited to a configuration consisting of multiple lenses, but may also consist of a single lens.

[0028] A "single lens" refers to a single, unbonded lens. However, a composite aspherical lens (a lens in which a lens (e.g., a spherical lens) and an aspherical film formed on that lens are integrally constructed and function as a single aspherical lens as a whole) is not considered a bonded lens and is treated as a single lens. Unless otherwise specified, the radius of curvature, the sign of the refractive power, and the surface shape for lenses including aspherical surfaces are those of the paraxial region. The sign of the radius of curvature is positive for the surface with the convex shape facing the object, and negative for the surface with the convex shape facing the image.

[0029] The "focal length" used in the conditional formulas refers to the paraxial focal length. Unless otherwise specified, the "distance on the optical axis" used in the conditional formulas refers to the geometric distance. Unless otherwise specified, the values ​​used in the conditional formulas are those with the d-line as the reference when the lens is in focus on an object at infinity. In this specification, "object distance" refers to the distance on the optical axis from the object to the lens surface closest to the object.

[0030] The terms "d-line," "C-line," "F-line," and "g-line" used herein are emission lines. The wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line as 656.27 nm (nanometers), the wavelength of the F-line as 486.13 nm (nanometers), and the wavelength of the g-line as 435.84 nm (nanometers). [Effects of the Invention]

[0031] According to this disclosure, it is possible to provide a fixed-focus optical system in which chromatic aberration and other aberrations are corrected in a well-balanced manner, and an imaging device equipped with this fixed-focus optical system. [Brief explanation of the drawing]

[0032] [Figure 1] This is a cross-sectional view corresponding to the fixed-focus optical system of Example 1, showing the configuration of a fixed-focus optical system according to one embodiment. [Figure 2] Figure 1 is a cross-sectional view showing the configuration and light beam of a fixed-focus optical system in each state. [Figure 3] These are aberration diagrams for the fixed-focus optical system of Example 1. [Figure 4] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 2. [Figure 5] These are aberration diagrams for the fixed-focus optical system of Example 2. [Figure 6] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 3. [Figure 7] These are aberration diagrams for the fixed-focus optical system of Example 3. [Figure 8] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 4. [Figure 9]These are aberration diagrams for the fixed-focus optical system of Example 4. [Figure 10] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 5. [Figure 11] These are aberration diagrams for the fixed-focus optical system of Example 5. [Figure 12] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 6. [Figure 13] These are aberration diagrams for the fixed-focus optical system of Example 6. [Figure 14] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 7. [Figure 15] These are aberration diagrams for the fixed-focus optical system of Example 7. [Figure 16] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 8. [Figure 17] These are aberration diagrams for the fixed-focus optical system of Example 8. [Figure 18] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 9. [Figure 19] These are aberration diagrams for the fixed-focus optical system of Example 9. [Figure 20] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 10. [Figure 21] These are aberration diagrams for the fixed-focus optical system of Example 10. [Figure 22] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 11. [Figure 23] These are aberration diagrams for the fixed-focus optical system of Example 11. [Figure 24] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 12. [Figure 25] These are aberration diagrams for the fixed-focus optical system of Example 12. [Figure 26] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 13. [Figure 27] These are aberration diagrams for the fixed-focus optical system of Example 13. [Figure 28] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 14. [Figure 29] These are aberration diagrams for the fixed-focus optical system of Example 14. [Figure 30] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 15. [Figure 31] These are aberration diagrams for the fixed-focus optical system of Example 15. [Figure 32] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 16. [Figure 33] These are aberration diagrams for the fixed-focus optical system of Example 16. [Figure 34] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 17. [Figure 35] These are aberration diagrams for the fixed-focus optical system of Example 17. [Figure 36] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 18. [Figure 37] These are aberration diagrams for the fixed-focus optical system of Example 18. [Figure 38] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 19. [Figure 39] These are aberration diagrams for the fixed-focus optical system of Example 19. [Figure 40] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 20. [Figure 41] These are aberration diagrams for the fixed-focus optical system of Example 20. [Figure 42] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 21. [Figure 43] These are aberration diagrams for the fixed-focus optical system of Example 21. [Figure 44] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 22. [Figure 45] These are aberration diagrams for the fixed-focus optical system of Example 22. [Figure 46] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 23. [Figure 47] These are aberration diagrams for the fixed-focus optical system of Example 23. [Figure 48]This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 24. [Figure 49] These are aberration diagrams for the fixed-focus optical system of Example 24. [Figure 50] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 25. [Figure 51] These are aberration diagrams for the fixed-focus optical system of Example 25. [Figure 52] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 26. [Figure 53] These are aberration diagrams for the fixed-focus optical system of Example 26. [Figure 54] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 27. [Figure 55] These are aberration diagrams for the fixed-focus optical system of Example 27. [Figure 56] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 28. [Figure 57] These are aberration diagrams for the fixed-focus optical system of Example 28. [Figure 58] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 29. [Figure 59] These are aberration diagrams for the fixed-focus optical system of Example 29. [Figure 60] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 30. [Figure 61] These are aberration diagrams for the fixed-focus optical system of Example 30. [Figure 62] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 31. [Figure 63] These are aberration diagrams for the fixed-focus optical system of Example 31. [Figure 64] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 32. [Figure 65] These are aberration diagrams for the fixed-focus optical system of Example 32. [Figure 66] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 33. [Figure 67]These are aberration diagrams for the fixed-focus optical system of Example 33. [Figure 68] This is a cross-sectional view showing the configuration and light beam of the fixed-focus optical system of Example 34. [Figure 69] These are aberration diagrams for the fixed-focus optical system of Example 34. [Figure 70] This is a front perspective view of an imaging device according to one embodiment. [Figure 71] This is a perspective view of the rear side of an imaging device according to one embodiment. [Modes for carrying out the invention]

[0033] Embodiments of this disclosure will be described below with reference to the drawings. In the following description, to avoid redundant explanations, "the fixed-focus optical system of this disclosure" may be simply referred to as "the fixed-focus optical system."

[0034] Figure 1 shows a cross-sectional view of the configuration of a fixed-focus optical system according to one embodiment of the present disclosure. Figure 2 shows a cross-sectional view of the configuration of the fixed-focus optical system and the light beam of Figure 1. In Figure 2, the upper section labeled "Infinity" shows the state in focus on an object at infinity, and the lower section labeled "Near Distance" shows the state in focus on an object at near distance. In Figure 2, the light beams shown are the on-axial light beam 2 and the light beam 3 with the maximum half-angle of view ωm when in focus on an object at infinity, and the on-axial light beam and the light beam with the maximum half-angle of view when in focus on an object at near distance. In Figures 1 and 2, the left side is the object side, and the right side is the image side. The examples shown in Figures 1 and 2 correspond to the fixed-focus optical system of Embodiment 1 described later. The following explanation will mainly refer to Figure 1.

[0035] The fixed-focus optical system of this disclosure consists of a front group GF, an aperture diaphragm St, and a rear group GR, arranged in order from the object side to the image side along the optical axis Z.

[0036] As an example, each group in Figure 1 is configured as follows: The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of seven lenses, L21 to L27, arranged in order from the object side to the image side. The aperture diaphragm St in Figure 1 indicates its position in the optical axis direction, rather than its size or shape. This method of illustrating the aperture diaphragm St is the same in other cross-sectional views.

[0037] The fixed-focus optical system of this disclosure is configured to include at least one of the specified lenses described below. The specified lens is defined as a lens that satisfies the following conditions (1) and (2). Here, Nd is the refractive index of the lens included in the fixed-focus optical system with respect to the d line. νd is the d-line reference Abbe number of the lens included in the fixed-focus optical system. 2.435 <Nd+0.01425×νd<2.75 (1) 15 < νd < 39 (2) The material for the specific lens may be glass, for example. Pages 40-42 of the proceedings of the 49th Optical Symposium (held June 20-21, 2024, organized by the Optical Society of Japan) describe optical glass that satisfies conditions (1) and (2) and its manufacturing method.

[0038] Ensuring that the corresponding value in condition (1) does not fall below the lower limit is advantageous for achieving good correction of spherical aberration and chromatic aberration. Ensuring that the corresponding value in condition (1) does not exceed the upper limit helps to prevent the correction of field curvature from becoming highly difficult.

[0039] To obtain better characteristics, the lower limit of conditional expression (1) is more preferably 2.445, even more preferably 2.455, even more preferably 2.468, even more preferably 2.48, even more preferably 2.49, even more preferably 2.5, even more preferably 2.51, and even more preferably 2.52. To obtain better characteristics, the upper limit of conditional expression (1) is more preferably 2.74, even more preferably 2.73, even more preferably 2.72, even more preferably 2.71, even more preferably 2.7, even more preferably 2.69, even more preferably 2.68, and even more preferably 2.67.

[0040] By ensuring that the corresponding value in conditional equation (2) does not fall below the lower limit, in addition to correcting the first-order aberration, the second-order spectrum can be corrected effectively. By ensuring that the corresponding value in conditional equation (2) does not exceed the upper limit, the second-order spectrum can be corrected more reliably and effectively.

[0041] To obtain better characteristics, the lower limit of conditional equation (2) is more preferably 15.5, even more preferably 16, even more preferably 16.5, even more preferably 16.8, even more preferably 17.1, and even more preferably 17.3. To obtain better characteristics, the upper limit of conditional equation (2) is more preferably 36, even more preferably 34, even more preferably 33.5, even more preferably 33, even more preferably 32.5, and even more preferably 32.

[0042] By using a specific lens that satisfies conditions (1) and (2) simultaneously, chromatic aberration correction becomes easier, thus reducing the burden of chromatic aberration correction for each lens compared to not using a specific lens. This also benefits the correction of other aberrations, making it easier to correct chromatic aberration and other aberrations in a balanced manner.

[0043] When θgF is the partial dispersion ratio between the g-line and F-line of a lens included in a fixed-focus optical system, it is preferable that a particular lens satisfies the following condition (3). 0.65<θgF+0.00316×νd<0.85 (3)

[0044] Furthermore, if the refractive indices of a lens for the g-line, F-line, and C-line are Ng, NF, and NC, respectively, and the partial dispersion ratio between the g-line and F-line of that lens is θgF, then θgF is defined by the following formula. θgF = (Ng - NF) / (NF - NC)

[0045] By ensuring that the corresponding value in conditional equation (3) does not fall below the lower limit, in addition to correcting the first-order aberration, the second-order spectrum can be corrected effectively. By ensuring that the corresponding value in conditional equation (3) does not exceed the upper limit, the second-order spectrum can be corrected more reliably and effectively.

[0046] To obtain better characteristics, the lower limit of conditional equation (3) is more preferably 0.67, even more preferably 0.675, even more preferably 0.68, even more preferably 0.683, even more preferably 0.689, and even more preferably 0.692. To obtain better characteristics, the upper limit of conditional equation (3) is more preferably 0.8, even more preferably 0.78, even more preferably 0.76, even more preferably 0.74, even more preferably 0.73, and even more preferably 0.725.

[0047] In the example in Figure 2, lens L11 is a specific lens. However, in the art of this disclosure, the specific lens may be positioned in a different location than in the example in Figure 2, and the fixed-focus optical system may include multiple specific lenses.

[0048] For example, a fixed-focus optical system may include at least one cemented lens, and the at least one cemented lens of the fixed-focus optical system may be configured to include at least one specific lens. Using a specific lens in the lenses that make up the cemented lens is advantageous in suppressing chromatic aberration. It is preferable that the specific lens included in the cemented lens satisfies the above condition (3).

[0049] The front group GF preferably includes at least one specific lens. This is advantageous for correcting axial chromatic aberration. In this case, the specific lens included in the front group GF preferably satisfies the above condition (3).

[0050] The front group GF may be configured to have a specific lens with positive refractive power placed on the object side. Since the specific lens is made of a material with a high refractive index, placing a specific lens with positive refractive power on the object side of the front group GF is advantageous for shortening the overall optical length and correcting spherical aberration. In the case of a variable magnification optical system, the above advantages may not be effective depending on the magnification state, and the high refractive index may act as a disadvantage, but this is not the case with a fixed-focus optical system.

[0051] The front group GF may be configured to have a specific lens with negative refractive power placed on the object side. Since the specific lens is made of a high refractive index material, placing a specific lens with negative refractive power on the object side of the front group GF is advantageous for achieving both wide-angle correction and distortion correction. In the case of a variable magnification optical system, the above advantages may not apply depending on the magnification state, and the high refractive index may act as a disadvantage, but this is not the case with a fixed-focus optical system.

[0052] The rear group GR preferably includes at least one specific lens element. This is advantageous for correcting chromatic aberration. In this case, the specific lens element included in the rear group GR preferably satisfies the above condition (3).

[0053] The front group GF and the rear group GR may each be configured to include at least one specific lens element. This configuration is advantageous for correcting axial chromatic aberration and lateral chromatic aberration. In this case, it is preferable that both the specific lens included in the front group GF and the specific lens included in the rear group GR satisfy the above condition (3).

[0054] Specific lenses may be arranged in a series. Lenses made of high refractive index materials, such as specific lenses, can have strong refractive power even if the difference in thickness between the vicinity of the optical axis and the periphery is small. Therefore, if the specific lens is a positive lens, the central thickness can be reduced, and if it is a negative lens, the lenses adjacent to its concave side can be placed closer together. If specific lenses with such shape and arrangement characteristics are arranged in a series regardless of the sign of their refractive power, these arranged specific lenses can have strong refractive power while reducing the thickness in the optical axis direction, which is advantageous for miniaturization. Such arranged specific lenses generally have high assembly sensitivity, which can be disadvantageous in variable magnification optical systems with moving parts, but this is not the case in fixed-focus optical systems.

[0055] A specific lens with positive refractive power may be placed adjacent to the object side of the aperture diaphragm St. Using a high refractive index material, such as a specific lens, as the positive lens and placing it adjacent to the object side of the aperture diaphragm St is advantageous in suppressing the size of the diaphragm diameter. On the other hand, lenses adjacent to the aperture diaphragm St generally have high sensitivity in the optical axis direction, and in the case of a variable magnification optical system, the interplanar spacing on the object side of the aperture diaphragm St often fluctuates, making the sensitivity even greater. Therefore, this arrangement of a specific lens is more desirable in a fixed-focus optical system than in a variable-magnification optical system.

[0056] A specific lens may be placed adjacent to the image side of the aperture diaphragm St. This arrangement is advantageous for suppressing axial chromatic aberration. In the case of a variable magnification optical system, the correction of axial chromatic aberration changes depending on the magnification state, but this is not the case with a fixed-focus optical system.

[0057] A fixed-focus optical system preferably satisfies the following condition (4). Here, fF is the focal length of the front group GF when in focus on an object at infinity. fR is the focal length of the rear group GR when in focus on an object at infinity. By ensuring that the corresponding value in condition (4) does not fall below the lower limit, various aberrations such as spherical aberration can be suppressed. By ensuring that the corresponding value in condition (4) does not exceed the upper limit, it is advantageous to achieve a wide angle of view. -5 <fR / fF<10 (4)

[0058] To obtain better characteristics, the lower limit of conditional equation (4) is more preferably -3, even more preferably -1.8, even more preferably -1.4, even more preferably -1, and even more preferably -0.5. To obtain better characteristics, the upper limit of conditional equation (4) is more preferably 7, even more preferably 4, even more preferably 3, even more preferably 2, and even more preferably 1.

[0059] In a fixed-focus optical system, it is preferable to include at least one focusing lens group that moves along the optical axis Z when focusing. In this case, focusing can be achieved according to the distance to the object. The focusing lens group may be configured as a part of the front group GF, a part of the rear group GR, an aperture diaphragm St and a part of the rear group GR, a part of the front group GF, an aperture diaphragm St and a part of the rear group GR, the entire front group GF, an aperture diaphragm St and a part of the rear group GR, or the entire fixed-focus optical system.

[0060] Preferably, at least one focusing lens group includes at least one specific lens. This configuration is advantageous in suppressing fluctuations in chromatic aberration during focusing. Preferably, the specific lens included in the focusing lens group satisfies the above condition (3).

[0061] As an example, the focusing lens group in Figure 1 consists of lenses L11 to L13, an aperture diaphragm St, and lenses L21 to L24. The parentheses and left-pointing arrows above lenses L11 to L24 in Figure 1 indicate that these are the focusing lens group and the direction in which the focusing lens group moves when focusing from an object at infinity to an object at a close distance. The above method of illustrating the focusing lens group is the same in the figures of other embodiments. In addition, in the drawings of this application, multiple components enclosed in a single parenthese accompanying an arrow indicating movement indicate that they move as a whole. "Moving as a whole" means moving simultaneously in the same direction and by the same amount.

[0062] Figure 1 shows an example of a fixed-focus optical system with only one focusing lens group. However, a fixed-focus optical system may be configured to include two focusing lens groups that move along different trajectories during focusing. Note that "moving along different trajectories" for multiple focusing lens groups is synonymous with "moving while changing the distance between them." Having the two focusing lens groups move by different amounts is advantageous in suppressing aberration variations during focusing.

[0063] For example, the rear lens group GR may be configured to have two focusing lens groups that move along different trajectories when focusing. In this case, in addition to the effect of suppressing the aberration fluctuations during focusing mentioned above, it is also possible to suppress the diameter of the focusing lens group by positioning the focusing lens group closer to the image than the front lens group GF.

[0064] Alternatively, one focusing lens group may be arranged in both the front group GF and the rear group GR, and the focusing lens groups of the front group GF and the rear group GR may be configured to move along different trajectories during focusing. This configuration is even more advantageous in suppressing aberration fluctuations during focusing.

[0065] It is preferable that the fixed-focus optical system satisfies the following condition (5). Here, ffocmax is defined as the focal length of the focusing lens group with the strongest refractive power among the focusing lens groups included in the fixed-focus optical system. f is defined as the focal length of the fixed-focus optical system when focused on an object at infinity. Ensuring that the corresponding value in condition (5) does not fall below the lower limit is advantageous for correcting various aberrations. Ensuring that the corresponding value in condition (5) does not exceed the upper limit ensures that the refractive power of the focusing lens group is secured, making it easier to suppress the amount of movement of the focusing group during focusing, which is advantageous for miniaturization. 0.2 < |ffocmax / f| < 3.5 (5)

[0066] To obtain better characteristics, the lower limit of conditional equation (5) is more preferably 0.3, even more preferably 0.35, even more preferably 0.4, even more preferably 0.45, and even more preferably 0.5. To obtain better characteristics, the upper limit of conditional equation (5) is more preferably 3, even more preferably 2.5, even more preferably 2, even more preferably 1.5, and even more preferably 1.

[0067] It is preferable that the fixed-focus optical system satisfies the following condition (7). Here, ffocF is the combined focal length of all lenses on the object side of the focusing lens group closest to the object in the fixed-focus optical system. f is the focal length of the fixed-focus optical system when in focus on an object at infinity. By ensuring that the corresponding value of condition (7) does not fall below the lower limit, the negative combined refractive power of all lenses on the object side of the focusing lens group closest to the object does not become too strong, thus suppressing an increase in the overall optical length and providing an advantage in securing peripheral illumination. By ensuring that the corresponding value of condition (7) does not exceed the upper limit, the positive combined refractive power of all lenses on the object side of the focusing lens group closest to the object does not become too strong, thus providing an advantage in correcting distortion and field curvature. -2 <f / ffocF<6 (7)

[0068] To obtain better characteristics, the lower limit of conditional equation (7) is more preferably -1.5, even more preferably -1.2, even more preferably -0.9, even more preferably -0.7, even more preferably -0.5, even more preferably -0.4, and even more preferably -0.3. To obtain better characteristics, the upper limit of conditional equation (7) is more preferably 4.5, even more preferably 3.5, even more preferably 2.5, even more preferably 2, even more preferably 1.5, even more preferably 1.2, and even more preferably 0.9.

[0069] It is preferable that the fixed-focus optical system satisfies the following condition (8). Here, ffocR is the combined focal length of all lenses on the image side of the focusing lens group included in the fixed-focus optical system that are closer to the image. f is the focal length of the fixed-focus optical system when in focus on an object at infinity. By ensuring that the corresponding value of condition (8) does not fall below the lower limit, the negative combined refractive power of all lenses on the image side of the focusing lens group mentioned above does not become too strong, which is advantageous for correcting chromatic aberration. By ensuring that the corresponding value of condition (8) does not exceed the upper limit, the positive combined refractive power of all lenses on the image side of the focusing lens group mentioned above does not become too strong, which is advantageous for correcting distortion and field curvature. -6 <f / ffocR<2 (8)

[0070] To obtain better characteristics, the lower limit of conditional equation (8) is more preferably -4.5, even more preferably -3.5, even more preferably -2.5, even more preferably -2, even more preferably -1.5, even more preferably -1.2, and even more preferably -0.9. To obtain better characteristics, the upper limit of conditional equation (8) is more preferably 1.5, even more preferably 1.2, even more preferably 0.9, even more preferably 0.7, even more preferably 0.5, even more preferably 0.4, and even more preferably 0.3.

[0071] In a fixed-focus optical system configuration that includes two focusing lens groups, it is preferable that the fixed-focus optical system satisfies the following condition (6). Here, of these two focusing lens groups, the focal length of the object-side focusing lens group is denoted as ff1, and the focal length of the image-side focusing lens group is denoted as ff2. By ensuring that the corresponding value in condition (6) does not fall below the lower limit, the refractive power of the object-side focusing lens group does not become too strong, making it easier to correct astigmatism. By ensuring that the corresponding value in condition (6) does not exceed the upper limit, the refractive power of the object-side focusing lens group does not become too weak, making it easier to correct field curvature. 0.1 < |ff1 / ff2| < 10 (6)

[0072] To obtain better characteristics, the lower limit of conditional equation (6) is more preferably 0.2, even more preferably 0.3, even more preferably 0.4, even more preferably 0.45, and even more preferably 0.5. To obtain better characteristics, the upper limit of conditional equation (6) is more preferably 5, even more preferably 4, even more preferably 3, even more preferably 2, and even more preferably 1.

[0073] In a configuration where one focusing lens group is arranged in the front group GF and one focusing lens group GR, and the focusing lens groups of the front group GF and the rear group GR move along different trajectories when focusing, it is preferable that the fixed-focus optical system satisfies the following condition (9). Here, ffocF is defined as the combined focal length of all lenses on the object side of the focusing lens group closest to the object among the focusing lens groups included in the fixed-focus optical system. fM is defined as the combined focal length from the lens adjacent to the image side of the focusing lens group of the front group GF to the lens adjacent to the object side of the focusing lens group of the rear group GR. That is, fM is defined as the combined focal length of all lenses located between the focusing lens group of the front group GF and the focusing lens group of the rear group GR. By ensuring that the corresponding value of condition (9) does not fall below the lower limit, the combined refractive power of all lenses on the object side of the focusing lens group closest to the object does not become too strong, which is advantageous for correcting various aberrations. By ensuring that the corresponding value in conditional equation (9) does not exceed the upper limit, it is possible to suppress the increase in diameter of the lens on the object side compared to the object-side focusing lens group mentioned above. 0.1 < |ffocF / fM| < 2 (9)

[0074] To obtain better characteristics, the lower limit of conditional equation (9) is more preferably 0.4, even more preferably 0.5, even more preferably 0.6, and even more preferably 0.65. To obtain better characteristics, the upper limit of conditional equation (9) is more preferably 1.2, even more preferably 1, even more preferably 0.9, and even more preferably 0.85.

[0075] In a fixed-focus optical system, the rear group GR may be configured to include an image stabilization group that moves in a direction intersecting the optical axis Z during image blur correction. By placing the image stabilization group in the rear group GR, it becomes easier to suppress the diameter of the image stabilization group. The image stabilization group may be configured to include at least one specific lens. In this case, it is advantageous to suppress fluctuations in chromatic aberration during image blur correction. It is preferable that the specific lens included in the image stabilization group satisfies the above condition equation (3).

[0076] In a configuration where the rear group GR includes an image stabilization group, it is preferable that the fixed-focus optical system satisfies the following condition (10). Here, the focal length of the image stabilization group is denoted as fIS. The focal length of the fixed-focus optical system when in focus on an object at infinity is denoted as f. Ensuring that the corresponding value in condition (10) does not fall below the lower limit is advantageous for correcting various aberrations. Ensuring that the corresponding value in condition (10) does not exceed the upper limit ensures that the refractive power of the image stabilization group is secured, making it easier to suppress the amount of movement of the image stabilization group during image blur correction, which is advantageous for miniaturization. 0.05 < |fIS / f| < 2 (10)

[0077] To obtain better characteristics, the lower limit of conditional expression (10) is more preferably 0.1, even more preferably 0.15, even more preferably 0.2, even more preferably 0.25, and even more preferably 0.3. To obtain better characteristics, the upper limit of conditional expression (10) is more preferably 1.5, even more preferably 1, even more preferably 0.7, even more preferably 0.5, and even more preferably 0.4.

[0078] In a fixed-focus optical system, it is preferable that the following condition (11) is satisfied in a configuration where the maximum half-angle of view when focused on an object at infinity is 7 degrees or less. Here, Amax is the maximum value of the air gap on the optical axis within the front group GF when focused on an object at infinity. TLf is the distance on the optical axis from the lens surface closest to the object in the front group GF to the lens surface closest to the image in the front group GF when focused on an object at infinity. Figure 22 shows the configuration of a fixed-focus optical system of Example 11 in which the maximum half-angle of view when focused on an object at infinity is 7 degrees or less, and as an example, the maximum value of the air gap Amax and the distance TLf are shown. By ensuring that the corresponding value of condition (11) does not fall below the lower limit, it is possible to suppress the weight of the entire optical system from becoming too heavy. By ensuring that the corresponding value of condition (11) does not exceed the upper limit, it becomes easier to suppress spherical aberration and axial chromatic aberration. 0.2 <Amax / TLf<0.8 (11)

[0079] To obtain better characteristics, the lower limit of conditional equation (11) is more preferably 0.3, even more preferably 0.4, and even more preferably 0.45. To obtain better characteristics, the upper limit of conditional equation (11) is more preferably 0.7, even more preferably 0.65, and even more preferably 0.6.

[0080] It is preferable that the fixed-focus optical system satisfies the following condition (12). Here, θc is the angle with respect to the optical axis Z when the principal ray of the maximum field of view enters the image plane Sim when the fixed-focus optical system is in focus on an object at the longest possible object distance for which it can be focused. The unit of θc is degrees. As an example, in the fixed-focus optical system of Figure 1, the longest possible object distance for which it can be focused is infinity. However, condition (12) is also applicable to optical systems where the longest possible object distance for which it can be focused is a finite value. As an example, the upper part of Figure 2 shows the principal ray 3c of the maximum field of view and the angle θc mentioned above. In Figure 2, the axis Zp parallel to the optical axis Z is shown by a dashed line. By ensuring that the corresponding value of condition (12) does not fall below the lower limit, it becomes easier to reduce the diameter of the lens near the image plane and shorten the overall optical length. By ensuring that the corresponding value of condition (12) does not exceed the upper limit, it is possible to suppress the reduction in the amount of light incident on the image plane Sim. 0 < |θc| < 30 (12)

[0081] To obtain better characteristics, the lower limit of conditional expression (12) is more preferably 0.4, even more preferably 0.8, even more preferably 1.2, even more preferably 1.6, even more preferably 2, even more preferably 2.3, and even more preferably 2.5. To obtain better characteristics, the upper limit of conditional expression (12) is more preferably 26, even more preferably 23, even more preferably 20, even more preferably 17, even more preferably 14, even more preferably 12, and even more preferably 10.

[0082] The fixed-focus optical system preferably satisfies the following condition (13). Here, L1f is defined as the paraxial radius of curvature of the object-side surface of the lens closest to the object in the front group GF. L1r is defined as the paraxial radius of curvature of the image-side surface of the lens closest to the object in the front group GF. Condition (13) is an equation that defines the shape factor of the lens. By ensuring that the corresponding value of condition (13) does not fall below the lower limit, it becomes easier to correct astigmatism. By ensuring that the corresponding value of condition (13) does not exceed the upper limit, it becomes easier to correct spherical aberration well, and the refractive power of the lens does not become too weak, making it easier to widen the angle of view. -3 < (L1r - L1f) / (L1r + L1f) < 1 (13)

[0083] To obtain better characteristics, the lower limit of conditional equation (13) is more preferably -2, even more preferably -1, even more preferably -0.7, and even more preferably -0.5. To obtain better characteristics, the upper limit of conditional equation (13) is more preferably 0.8, even more preferably 0.6, even more preferably 0.4, and even more preferably 0.2.

[0084] When the open aperture F-number of a fixed-focus optical system is focused on an object at infinity, denoted as Fno, it is preferable that the fixed-focus optical system satisfies the following condition (14). By ensuring that the corresponding value in condition (14) does not fall below the lower limit, it becomes easier to correct various aberrations and shorten the overall optical length. By ensuring that the corresponding value in condition (14) does not exceed the upper limit, the brightness of the optical system can be ensured. 0.8 <Fno<3 (14)

[0085] To obtain better characteristics, the lower limit of conditional expression (14) is more preferably 0.9, even more preferably 0.95, even more preferably 1, even more preferably 1.05, and even more preferably 1.1. To obtain better characteristics, the upper limit of conditional expression (14) is more preferably 2.4, even more preferably 2.1, even more preferably 1.8, even more preferably 1.5, and even more preferably 1.3.

[0086] When the maximum half-angle of view of a fixed-focus optical system is in focus on an object at infinity, let ωm be the maximum half-angle of view. Preferably, the fixed-focus optical system satisfies the following condition (15). The unit of ωm is degrees. As an example, the upper part of Figure 2 shows the above maximum half-angle of view ωm. By ensuring that the corresponding value of condition (15) does not fall below the lower limit, a wide angle of view can be secured, thus providing high added value as an imaging lens system. By ensuring that the corresponding value of condition (15) does not exceed the upper limit, it becomes easier to balance optical performance and miniaturization. 20 < ωm < 50 (15)

[0087] To obtain better characteristics, the lower limit of conditional expression (15) is more preferably 21, even more preferably 22, even more preferably 23, even more preferably 24, and even more preferably 25. To obtain better characteristics, the upper limit of conditional expression (15) is more preferably 47, even more preferably 44, even more preferably 41, even more preferably 38, and even more preferably 36.

[0088] The example shown in Figure 1 is just one example, and the fixed-focus optical system of this disclosure can be modified in various ways without departing from the spirit of the technology of this disclosure. For example, the number and configuration of lenses included in the front group GF, the rear group GR, and the focusing lens group may differ from the example in Figure 1.

[0089] The front group GF may be configured to include a first lens component having positive refractive power and a second lens component having positive refractive power, arranged sequentially from the object side to the image side. In this specification, one single lens or one cemented lens is considered as one lens component. In a configuration in which the front group GF includes the above-mentioned first lens component and second lens component, arranged sequentially from the object side to the image side, it is preferable that the fixed-focus optical system satisfies the following conditional equation (16). Here, the combined focal length of the above-mentioned first lens component and second lens component is defined as fp2. By ensuring that the corresponding value of conditional equation (16) does not fall below the lower limit, it is advantageous for correcting spherical aberration. By ensuring that the corresponding value of conditional equation (16) does not exceed the upper limit, excessive correction of spherical aberration can be suppressed. 0.8 <f / fp2<10 (16)

[0090] To obtain better characteristics, the lower limit of conditional expression (16) is more preferably 1, even more preferably 1.2, even more preferably 1.4, even more preferably 1.6, and even more preferably 1.8. To obtain better characteristics, the upper limit of conditional expression (16) is more preferably 8, even more preferably 6, even more preferably 5, even more preferably 4, and even more preferably 3.

[0091] The front lens group GF may be configured to include a first lens component having positive refractive power, a second lens component having positive refractive power, and a third lens component having positive refractive power, in a continuous sequence from the object side to the image side. In a configuration where the front lens group GF includes the above-mentioned first, second, and third lens components in a continuous sequence from the object side to the image side, it is preferable that the fixed-focus optical system satisfies the following conditional equation (17). Here, the combined focal length of the above-mentioned first, second, and third lens components is defined as fp3. By ensuring that the corresponding value of conditional equation (17) does not fall below the lower limit, it is advantageous for correcting spherical aberration. By ensuring that the corresponding value of conditional equation (17) does not exceed the upper limit, excessive correction of spherical aberration can be suppressed. 1 <f / fp3<10 (17)

[0092] To obtain better characteristics, the lower limit of conditional expression (17) is more preferably 1.1, even more preferably 1.2, even more preferably 1.3, even more preferably 1.4, and even more preferably 1.5. To obtain better characteristics, the upper limit of conditional expression (17) is more preferably 7.5, even more preferably 5.5, even more preferably 4, even more preferably 3, and even more preferably 2.

[0093] The front group GF may be configured to include a fourth lens component having negative refractive power and a fifth lens component having negative refractive power, in a continuous sequence from the object side to the image side. In a configuration in which the front group GF includes the above-mentioned fourth lens component and fifth lens component in a continuous sequence from the object side to the image side, it is preferable that the fixed-focus optical system satisfies the following conditional equation (18). Here, the combined focal length of the above-mentioned fourth lens component and fifth lens component is denoted as fn2. By ensuring that the corresponding value of conditional equation (18) does not fall below the lower limit, it is advantageous to effectively correct chromatic aberration. By ensuring that the corresponding value of conditional equation (18) does not exceed the upper limit, it is advantageous to effectively correct various aberrations such as distortion and field curvature. -4 <f / fn2<-0.2 (18)

[0094] To obtain better characteristics, the lower limit of conditional equation (18) is more preferably -3, even more preferably -2, even more preferably -1.5, even more preferably -1.3, and even more preferably -1.1. To obtain better characteristics, the upper limit of conditional equation (18) is more preferably -0.4, even more preferably -0.5, even more preferably -0.55, even more preferably -0.6, and even more preferably -0.65.

[0095] The front group GF may be configured to include a fourth lens component having negative refractive power, a fifth lens component having negative refractive power, and a sixth lens component having negative refractive power, in a continuous sequence from the object side to the image side. In a configuration where the front group GF includes the above-mentioned fourth, fifth, and sixth lens components in a continuous sequence from the object side to the image side, it is preferable that the fixed-focus optical system satisfies the following conditional equation (19). Here, the combined focal length of the above-mentioned fourth, fifth, and sixth lens components is defined as fn3. By ensuring that the corresponding value of conditional equation (19) does not fall below the lower limit, it is advantageous to effectively correct chromatic aberration. By ensuring that the corresponding value of conditional equation (19) does not exceed the upper limit, it is advantageous to effectively correct various aberrations such as distortion and field curvature. -4 <f / fn3<-0.2 (19)

[0096] To obtain better characteristics, the lower limit of conditional equation (19) is more preferably -3, even more preferably -2, even more preferably -1.5, even more preferably -1.3, and even more preferably -1.1. To obtain better characteristics, the upper limit of conditional equation (19) is more preferably -0.4, even more preferably -0.5, even more preferably -0.55, even more preferably -0.6, and even more preferably -0.65.

[0097] When the maximum magnification is β, it is preferable that the fixed-focus optical system satisfies the following condition (20). The maximum magnification is the magnification when photographing the nearest object (i.e., the object at the shortest distance that can be focused). By ensuring that the corresponding value in condition (20) does not fall below the lower limit, the narrowing of the area that can be photographed by the optical system can be suppressed, thereby securing a suitable added value as an imaging lens system. By ensuring that the corresponding value in condition (20) does not exceed the upper limit, the amount of movement of the focusing lens group during focusing can be suppressed, thereby contributing to the miniaturization of the optical system. 0.05 < |β| < 1.1 (20)

[0098] To obtain better characteristics, the lower limit of conditional expression (20) is more preferably 0.09, even more preferably 0.12, even more preferably 0.15, even more preferably 0.18, even more preferably 0.21, even more preferably 0.24, and even more preferably 0.27. To obtain better characteristics, the upper limit of conditional expression (20) is more preferably 1, even more preferably 0.9, even more preferably 0.8, even more preferably 0.75, even more preferably 0.7, even more preferably 0.67, and even more preferably 0.65.

[0099] The preferred and possible configurations described above can be combined in any way as long as they are not contradictory, and it is preferable to select and adopt them as appropriate according to the required specifications.

[0100] As an example, a preferred embodiment of the fixed-focus optical system of the present disclosure is a fixed-focus optical system comprising, in order from the object side to the image side, a front group GF, an aperture diaphragm St, and a rear group GR, and including at least one specific lens that satisfies the above-mentioned conditions (1) and (2).

[0101] Next, each embodiment of the fixed-focus optical system of this disclosure will be described with reference to the drawings. Note that the reference numerals assigned to each lens and group in the cross-sectional view of each embodiment are used independently for each embodiment to avoid complexity in the explanation and drawings due to the increasing number of digits in the reference numerals. Therefore, even if the same reference numerals are used in the drawings of different embodiments, they do not necessarily represent a common configuration.

[0102] [Example 1] A cross-sectional view of the fixed-focus optical system configuration of Example 1 is shown in Figure 1, and its illustration method and configuration are as described above, so some redundant explanations will be omitted here. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L11 to L13, an aperture diaphragm St, and lenses L21 to L24, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0103] Table 1 shows the basic lens data for the fixed-focus optical system of Example 1, Table 2 shows the specifications and variable plane spacing, and Table 3 shows the aspherical coefficient.

[0104] The basic lens data table is as follows: The "Sn" column shows the surface number, where the surface closest to the object is designated as the 1st surface, and the number increases by one as you move towards the image side. The "R" column shows the radius of curvature of each surface. The "D" column shows the interplanar spacing on the optical axis between each surface and the surface adjacent to it on the image side. The "Nd" column shows the refractive index of each lens with respect to the d line. The "νd" column shows the Abbe number of each lens with respect to the d line. The "θgF" column shows the partial dispersion ratio between the g line and the F line of each lens. The "ED" column shows the effective diameter of each surface.

[0105] The "Material" column in the basic lens data table, including the table of examples described later, is written as follows. The "Material" column for a specific lens lists one of the following: "N231. Glass", "N216. Glass", and "N200. Glass". For "N231. Glass", "N216. Glass", and "N200. Glass", the glass described on pages 40-42 of the proceedings of the 49th Optical Symposium (held June 20-21, 2024, organized by the Optical Society of Japan) can be used.

[0106] For lenses other than specific lenses, in the "Material" column, resin lenses are listed as "Plastic," and for other lenses, the material name is listed before the "." and the manufacturer's name is listed after the ".". In the table, the manufacturer's name is generally shown as follows: "OHARA" refers to Ohara Corporation. "CDGM" refers to Chengdu Guangming Optoelectronics Co., Ltd. "HOYA" refers to HOYA Corporation. "HIKARI" refers to Hikari Glass Co., Ltd. "SUMITA" refers to Sumida Optical Glass Co., Ltd. "NHG" refers to Hubei Xinhua Optics Information Materials Co., Ltd.

[0107] In the basic lens data table, the sign of the radius of curvature of a surface with a convex shape facing the object is positive, and the sign of the radius of curvature of a surface with a convex shape facing the image is negative. In the column for the surface number of the surface corresponding to the aperture diaphragm St, the surface number and the phrase (St) are entered. The value in the bottom column of column D in the table is the distance between the image-side surface in the table and the image plane Sim. For the variable surface spacing when focusing, the symbol DD[ ] is used, and the object-side surface number for this spacing is placed inside the [ ] and entered in the surface spacing column.

[0108] Table 2 shows the focal length, back focus, maximum aperture F-number, maximum field of view, and variable plane spacing of the fixed-focus optical system, relative to the d-line. The [°] in the maximum field of view column indicates that the unit is degrees. In Table 2, the "Infinity" column shows the values ​​when focused on an object at infinity, and the "Close Range -0.1x" column shows the values ​​when focused on a close-range object with a magnification of -0.1x. In the specifications table, the magnification when focused on the closest object is indicated with "times" after the term "close range".

[0109] In the basic lens data, the aspherical surface numbers are marked with an asterisk (*), and the column for the radius of curvature of the aspherical surface lists the value of the paraxial radius of curvature. In Table 3, the row labeled Sn shows the aspherical surface number, and the rows labeled KA and Am show the aspherical coefficient values ​​for each aspherical surface. Note that m in Am is an integer greater than or equal to 3 and varies depending on the surface. For example, in the 13th surface of Example 1, m = 4, 6, 8, 10, 12, 14, 16, 18. The "E±n" (n: integer) values ​​for the aspherical coefficient in Table 3 represent "×10 ±nThis means "[...]. KA and Am are the aspheric coefficients in the aspheric equation expressed by the following formula. Zd = C × h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspherical depth (length of the perpendicular line drawn from a point on the aspherical surface at height h to a plane perpendicular to the optical axis Z to which the aspherical surface tangent is located). h: Height (distance from the optical axis Z to the lens surface) C: Reciprocal of the radius of paraxial curvature KA, Am: Aspherical coefficients Therefore, the Σ in aspherical formulas represents the summation with respect to m.

[0110] In the data in each table, degrees are used as the unit for angles and millimeters (mm) as the unit for lengths. However, since optical systems can be used with proportional magnification or reduction, other appropriate units can also be used. Furthermore, the values ​​in the tables below are rounded to a predetermined number of decimal places.

[0111] [Table 1]

[0112] [Table 2]

[0113] [Table 3]

[0114] Figure 3 shows the aberration diagrams for the fixed-focus optical system of Example 1. From left to right in Figure 3, the diagrams show spherical aberration, astigmatism, distortion, and chromatic aberration. In Figure 3, the upper section labeled "Infinity" shows the aberration diagrams when the camera is focused on an object at infinity, and the lower section labeled "Near Distance -0.1x" shows the aberration diagrams when the camera is focused on a nearby object with a magnification of -0.1x. Thus, the lower section of the aberration diagrams shows the aberrations when the camera is focused on the magnification shown in the specifications table. In the spherical aberration diagram, the aberrations on the d, C, F, and g lines are shown as solid lines, long dashed lines, short dashed lines, and dashed lines, respectively. In the astigmatism diagram, the aberration on the d line in the sagittal direction is shown as a solid line, and the aberration on the d line in the tangential direction is shown as a short dashed line. In the distortion diagram, the aberration on the d line is shown as a solid line. In the chromatic aberration diagram, the aberrations along the C, F, and g lines are shown by long dashed lines, short dashed lines, and dashed lines, respectively. In the spherical aberration diagram, the value of the wide-open F number is shown after "FNo.=". In other aberration diagrams, the value of the maximum half-angle of view is shown after "ω=".

[0115] The symbols, meanings, methods of description, and methods of illustration for each data point in Example 1 described above are basically the same in the following examples unless otherwise specified, so redundant explanations will be omitted below.

[0116] [Example 2] Figure 4 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 2. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of seven lenses, L21 to L27, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L11 to L13, an aperture diaphragm St, and lenses L21 to L24, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0117] For the fixed-focus optical system of Example 2, the basic lens data is shown in Table 4, the specifications and variable plane spacing are shown in Table 5, and the aberration diagrams are shown in Figure 5.

[0118] [Table 4]

[0119] [Table 5]

[0120] [Example 3] Figure 6 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 3. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of four lenses, L11 to L14, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L11 to L14, an aperture diaphragm St, and lenses L21 to L22, and moves towards the object side when focusing from an object at infinity to an object at a close distance. The vibration isolation group consists of lenses L25 to L26. In Figure 6, brackets and upward arrows are placed above the lenses corresponding to the vibration isolation group. The above method of illustrating the vibration isolation group is the same in the figures of the other examples.

[0121] For the fixed-focus optical system of Example 3, the basic lens data is shown in Table 6, the specifications and variable plane spacing in Table 7, the aspherical coefficient in Table 8, and the aberration diagrams in Figure 7.

[0122] [Table 6]

[0123] [Table 7]

[0124] [Table 8]

[0125] [Example 4] Figure 8 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 4. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of four lenses, L11 to L14, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L11 to L14, an aperture diaphragm St, and lenses L21 to L22, and moves towards the object side when focusing from an object at infinity to an object at a close distance. The vibration isolation group consists of lenses L25 to L26.

[0126] For the fixed-focus optical system of Example 4, the basic lens data is shown in Table 9, the specifications and variable plane spacing in Table 10, the aspherical coefficient in Table 11, and the aberration diagrams in Figure 9.

[0127] [Table 9]

[0128] [Table 10]

[0129] [Table 11]

[0130] [Example 5] Figure 10 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 5. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of eight lenses, L11 to L18, arranged in order from the object side to the image side. The rear group GR consists of six lenses, L21 to L26, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L21 to L24 and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0131] For the fixed-focus optical system of Example 5, the basic lens data is shown in Table 12, the specifications and variable plane spacing in Table 13, the aspherical coefficient in Table 14, and the aberration diagrams in Figure 11.

[0132] [Table 12]

[0133] [Table 13]

[0134] [Table 14]

[0135] [Example 6] Figure 12 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 6. The fixed-focus optical system consists of a front group GF with negative refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of seven lenses, L21 to L27, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lens L26 and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0136] For the fixed-focus optical system of Example 6, the basic lens data is shown in Table 15, the specifications and variable plane spacing in Table 16, the aspherical coefficient in Table 17, and the aberration diagrams in Figure 13.

[0137] [Table 15]

[0138] [Table 16]

[0139] [Table 17]

[0140] [Example 7] Figure 14 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 7. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of seven lenses, L11 to L17, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L21 to L26 and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0141] For the fixed-focus optical system of Example 7, the basic lens data is shown in Table 18, the specifications and variable plane spacing in Table 19, the aspherical coefficient in Table 20, and the aberration diagrams in Figure 15.

[0142] [Table 18]

[0143] [Table 19]

[0144] [Table 20]

[0145] [Example 8] Figure 16 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 8. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of six lenses, L21 to L26, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L21 to L23 and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0146] For the fixed-focus optical system of Example 8, the basic lens data is shown in Table 21, the specifications and variable plane spacing in Table 22, the aspheric coefficient in Table 23, and the aberration diagrams in Figure 17. In the table of basic lens data, an asterisk (*) is placed on both sides of the plane number corresponding to the composite aspheric surface of the composite aspheric lens.

[0147] [Table 21]

[0148] [Table 22]

[0149] [Table 23]

[0150] [Example 9] Figure 18 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 9. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L21 to L22 and moves towards the image side when focusing from an object at infinity to an object at a close distance.

[0151] For the fixed-focus optical system of Example 9, the basic lens data is shown in Table 24, the specifications and variable plane spacing are shown in Table 25, and the aberration diagrams are shown in Figure 19.

[0152] [Table 24]

[0153] [Table 25]

[0154] [Example 10] Figure 20 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 10. The fixed-focus optical system consists of a front group GF with negative refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of seven lenses, L11 to L17, arranged in order from the object side to the image side. The rear group GR consists of seven lenses, L21 to L27, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L21 to L26 and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0155] For the fixed-focus optical system of Example 10, the basic lens data is shown in Table 26, the specifications and variable plane spacing in Table 27, the aspherical coefficients in Tables 28A and 28B, and the aberration diagrams are shown in Figure 21.

[0156] [Table 26]

[0157] [Table 27]

[0158] [Table 28A]

[0159] [Table 28B]

[0160] [Example 11] Figure 22 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 11. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with negative refractive power, arranged in order from the object side to the image side. The front group GF consists of seven lenses, L11 to L17, arranged in order from the object side to the image side. The rear group GR consists of eighteen lenses, L21 to L38, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lens L21 and moves towards the image side when focusing from an object at infinity to an object at a close distance. The vibration isolation group consists of lenses L24 to L26.

[0161] For the fixed-focus optical system of Example 11, the basic lens data is shown in Tables 29A and 29B, the specifications and variable plane spacing are shown in Table 30, and the aberration diagrams are shown in Figure 23. Here, to avoid making a single table too long, the basic lens data is shown in two separate tables.

[0162] [Table 29A]

[0163] [Table 29B]

[0164] [Table 30]

[0165] [Example 12] Figure 24 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 12. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of five lenses, L11 to L15, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of an aperture diaphragm St and lenses L21 to L27, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0166] For the fixed-focus optical system of Example 12, the basic lens data is shown in Table 31, the specifications and variable plane spacing in Table 32, the aspherical coefficient in Table 33, and the aberration diagrams in Figure 25.

[0167] [Table 31]

[0168] [Table 32]

[0169] [Table 33]

[0170] [Example 13] Figure 26 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 13. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of five lenses, L11 to L15, arranged in order from the object side to the image side. The rear group GR consists of nine lenses, L21 to L29, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L13 to L15, an aperture diaphragm St, and lenses L21 to L25, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0171] For the fixed-focus optical system of Example 13, the basic lens data is shown in Table 34, the specifications and variable surface intervals are shown in Table 35, the aspherical coefficients are shown in Table 36, and each aberration diagram is shown in FIG. 27.

[0172]

Table 34

[0173]

Table 35

[0174]

Table 36

[0175] [[ID=~30]]][Example 14] The configuration of the fixed-focus optical system of Example 14 and the cross-sectional view of the light beam are shown in FIG. 28. The fixed-focus optical system consists of a front group GF having a positive refractive power, an aperture stop St, and a rear group GR having a positive refractive power, in order from the object side to the image side. The front group GF consists of five lenses L11 to L15 in order from the object side to the image side. The rear group GR consists of eight lenses L21 to L28 in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L13 to L15, the aperture stop St, and lenses L21 to L25, and moves toward the object side when focusing from an infinite object to a close-distance object.

[0176] For the fixed-focus optical system of Example 14, the basic lens data is shown in Table 37, the specifications and variable surface intervals are shown in Table 38, the aspherical coefficients are shown in Table 39, and each aberration diagram is shown in FIG. 29.

[0177]

Table 37

[0178]

Table 38

[0179] [Table 39]

[0180] [Example 15] Figure 30 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 15. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with negative refractive power, arranged in order from the object side to the image side. The front group GF consists of seven lenses, L11 to L17, arranged in order from the object side to the image side. The rear group GR consists of fourteen lenses, L21 to L34, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lens L16 and moves towards the image side when focusing from an object at infinity to an object at a close distance. The vibration isolation group consists of lenses L23 to L25.

[0181] For the fixed-focus optical system of Example 15, the basic lens data is shown in Table 40, the specifications and variable plane spacing are shown in Table 41, and the aberration diagrams are shown in Figure 31.

[0182] [Table 40]

[0183] [Table 41]

[0184] [Example 16] The configuration of the fixed-focus optical system of Example 16 and a cross-sectional view of the light beam are shown in FIG. 32. The fixed-focus optical system includes, in order from the object side to the image side, a front group GF having a positive refractive power, an aperture stop St, and a rear group GR having a positive refractive power. The front group GF consists of seven lenses L11 to L17 in order from the object side to the image side. The rear group GR consists of seven lenses L21 to L27 in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L22 to L25, and the focusing lens group on the image side consists of lens L26. When focusing from an infinite object to a close object, the focusing lens group on the object side and the focusing lens group on the image side move toward the object side while changing the mutual distance therebetween.

[0185] Regarding the fixed-focus optical system of Example 16, the basic lens data is shown in Table 42, the specifications and variable surface intervals are shown in Table 43, the aspherical coefficients are shown in Tables 44A and 44B, and each aberration diagram is shown in FIG. 33.

[0186] [Table 42]

[0187] [Table 43]

[0188] [Table 44A]

[0189] [Table 44B]

[0190] [Example 17] Figure 34 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 17. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of seven lenses, L21 to L27, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L21 to L24, and the focusing lens group on the image side consists of lenses L25 to L26. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side and the focusing lens group on the image side change their relative distance and move toward the object side.

[0191] For the fixed-focus optical system of Example 17, the basic lens data is shown in Table 45, the specifications and variable plane spacing in Table 46, the aspherical coefficient in Table 47, and the aberration diagrams in Figure 35. In the table of basic lens data, an asterisk (*) is placed on both sides of the plane number corresponding to the composite aspherical surface of the composite aspherical lens.

[0192] [Table 45]

[0193] [Table 46]

[0194] [Table 47]

[0195] [Example 18] Figure 36 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 18. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of seven lenses, L11 to L17, arranged in order from the object side to the image side. The rear group GR consists of four lenses, L21 to L24, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L21, and the focusing lens group on the image side consists of lens L22. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0196] For the fixed-focus optical system of Example 18, the basic lens data is shown in Table 48, the specifications and variable plane spacing in Table 49, the aspherical coefficient in Table 50, and the aberration diagrams in Figure 37.

[0197] [Table 48]

[0198] [Table 49]

[0199] [Table 50]

[0200] [Example 19] Figure 38 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 19. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of 10 lenses, L11 to L20, arranged in order from the object side to the image side. The rear group GR consists of 8 lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L21 to L22, and the focusing lens group on the image side consists of lenses L23 to L24. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side and the focusing lens group on the image side change their relative distance and move toward the object side.

[0201] For the fixed-focus optical system of Example 19, the basic lens data is shown in Table 51, the specifications and variable plane spacing in Table 52, the aspherical coefficient in Table 53, and the aberration diagrams in Figure 39.

[0202] [Table 51]

[0203] [Table 52]

[0204] [Table 53]

[0205] [Example 20] Figure 40 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 20. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of eight lenses, L11 to L18, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L21 to L22, and the focusing lens group on the image side consists of lenses L23 to L24. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side and the focusing lens group on the image side change their relative distance and move toward the object side.

[0206] For the fixed-focus optical system of Example 20, the basic lens data is shown in Table 54, the specifications and variable plane spacing in Table 55, the aspherical coefficient in Table 56, and the aberration diagrams in Figure 41.

[0207] [Table 54]

[0208] [Table 55]

[0209] [Table 56]

[0210] [Example 21] Figure 42 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 21. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of six lenses, L21 to L26, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L15 to L16, and the focusing lens group on the image side consists of lens L21. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0211] For the fixed-focus optical system of Example 21, the basic lens data is shown in Table 57, the specifications and variable plane spacing are shown in Table 58, and the aberration diagrams are shown in Figure 43.

[0212] [Table 57]

[0213] [Table 58]

[0214] [Example 22] Figure 44 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 22. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with negative refractive power, arranged in order from the object side to the image side. The front group GF consists of five lenses, L11 to L15, arranged in order from the object side to the image side. The rear group GR consists of nine lenses, L21 to L29, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L22, and the focusing lens group on the image side consists of lens L26. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0215] For the fixed-focus optical system of Example 22, the basic lens data is shown in Table 59, the specifications and variable plane spacing in Table 60, the aspherical coefficients in Table 61, and the aberration diagrams in Figure 45.

[0216] [Table 59]

[0217] [Table 60]

[0218] [Table 61]

[0219] [Example 23] Figure 46 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 23. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with negative refractive power, arranged in order from the object side to the image side. The front group GF consists of five lenses, L11 to L15, arranged in order from the object side to the image side. The rear group GR consists of nine lenses, L21 to L29, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L22, and the focusing lens group on the image side consists of lens L26. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0220] For the fixed-focus optical system of Example 23, the basic lens data is shown in Table 62, the specifications and variable plane spacing in Table 63, the aspherical coefficient in Table 64, and the aberration diagrams in Figure 47.

[0221] [Table 62]

[0222] [Table 63]

[0223] [Table 64]

[0224] [Example 24] Figure 48 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 24. The fixed-focus optical system consists of a front group GF with negative refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of four lenses, L11 to L14, arranged in order from the object side to the image side. The rear group GR consists of eleven lenses, L21 to L31, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L14, and the focusing lens group on the image side consists of lens L29. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0225] For the fixed-focus optical system of Example 24, the basic lens data is shown in Table 65, the specifications and variable plane spacing in Table 66, the aspherical coefficients in Tables 67A and 67B, and the aberration diagrams are shown in Figure 49.

[0226] [Table 65]

[0227] [Table 66]

[0228] [Table 67A]

[0229] [Table 67B]

[0230] [Example 25] Figure 50 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 25. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of nine lenses, L11 to L19, arranged in order from the object side to the image side. The rear group GR consists of six lenses, L21 to L26, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lenses L16 to L17, and the focusing lens group on the image side consists of lenses L21 to L24. When focusing from an object at infinity to a nearby object, the object-side focusing lens group and the image-side focusing lens group change their relative distance and move toward the object side.

[0231] For the fixed-focus optical system of Example 25, the basic lens data is shown in Table 68, the specifications and variable plane spacing in Table 69, the aspherical coefficient in Table 70, and the aberration diagrams in Figure 51.

[0232] [Table 68]

[0233] [Table 69]

[0234] [Table 70]

[0235] [Example 26] Figure 52 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 26. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of eight lenses, L11 to L18, arranged in order from the object side to the image side. The rear group GR consists of six lenses, L21 to L26, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L16, and the focusing lens group on the image side consists of lenses L21 to L24. When focusing from an object at infinity to a nearby object, the object-side focusing lens group and the image-side focusing lens group change their relative distance and move toward the object side.

[0236] For the fixed-focus optical system of Example 26, the basic lens data is shown in Table 71, the specifications and variable plane spacing in Table 72, the aspherical coefficient in Table 73, and the aberration diagrams in Figure 53.

[0237] [Table 71]

[0238] [Table 72]

[0239] [Table 73]

[0240] [Example 27] Figure 54 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 27. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of ten lenses, L21 to L30, arranged in order from the object side to the image side. The fixed-focus optical system includes two focusing lens groups. The focusing lens group on the object side consists of lens L16, and the focusing lens group on the image side consists of lenses L26 to L27. When focusing from an object at infinity to a nearby object, the focusing lens group on the object side moves towards the image side, and the focusing lens group on the image side moves towards the object side.

[0241] For the fixed-focus optical system of Example 27, the basic lens data is shown in Table 74, the specifications and variable plane spacing in Table 75, the aspherical coefficient in Table 76, and the aberration diagrams in Figure 55.

[0242] [Table 74]

[0243] [Table 75]

[0244] [Table 76]

[0245] [Example 28] Figure 56 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 28. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of five lenses, L21 to L25, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of an aperture diaphragm St and the rear group GR, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0246] For the fixed-focus optical system of Example 28, the basic lens data is shown in Table 77, the specifications and variable plane spacing in Table 78, the aspherical coefficient in Table 79, and the aberration diagrams in Figure 57.

[0247] [Table 77]

[0248] [Table 78]

[0249] [Table 79]

[0250] [Example 29] Figure 58 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 29. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of eight lenses, L21 to L28, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of lenses L26 to L28 and moves towards the image side when focusing from an object at infinity to an object at a close distance.

[0251] For the fixed-focus optical system of Example 29, the basic lens data is shown in Table 80, the specifications and variable plane spacing are shown in Table 81, and the aberration diagrams are shown in Figure 59.

[0252] [Table 80]

[0253] [Table 81]

[0254] [Example 30] Figure 60 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 30. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of six lenses, L11 to L16, arranged in order from the object side to the image side. The rear group GR consists of five lenses, L21 to L25, arranged in order from the object side to the image side. The fixed-focus optical system includes only one focusing lens group. The focusing lens group consists of an aperture diaphragm St and the rear group GR, and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0255] For the fixed-focus optical system of Example 30, the basic lens data is shown in Table 82, the specifications and variable plane spacing are shown in Table 83, and the aberration diagrams are shown in Figure 61.

[0256] [Table 82]

[0257] [Table 83]

[0258] [Example 31] Figure 62 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 31. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of five lenses, L21 to L25, arranged in order from the object side to the image side. The focusing lens group consists of the entire fixed-focus optical system and moves towards the object side when focusing from an object at infinity to an object at a close distance.

[0259] For the fixed-focus optical system of Example 31, the basic lens data is shown in Table 84, the specifications and variable plane spacing are shown in Table 85, and the aberration diagrams are shown in Figure 63.

[0260] [Table 84]

[0261] [Table 85]

[0262] [Example 32] Figure 64 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 32. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of two lenses, L11 to L12, arranged in order from the object side to the image side. The rear group GR consists of three lenses, L21 to L23, arranged in order from the object side to the image side.

[0263] For the fixed-focus optical system of Example 32, the basic lens data is shown in Table 86, the specifications in Table 87, and the aberration diagrams are shown in Figure 65.

[0264] [Table 86]

[0265] [Table 87]

[0266] [Example 33] Figure 66 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 33. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of two lenses, L11 to L12, arranged in order from the object side to the image side. The rear group GR consists of four lenses, L21 to L24, arranged in order from the object side to the image side.

[0267] For the fixed-focus optical system of Example 33, the basic lens data is shown in Table 88, the specifications in Table 89, and the aberration diagrams are shown in Figure 67.

[0268] [Table 88]

[0269] [Table 89]

[0270] [Example 34] Figure 68 shows the configuration and cross-sectional view of the light beam of the fixed-focus optical system of Example 34. The fixed-focus optical system consists of a front group GF with positive refractive power, an aperture diaphragm St, and a rear group GR with positive refractive power, arranged in order from the object side to the image side. The front group GF consists of three lenses, L11 to L13, arranged in order from the object side to the image side. The rear group GR consists of three lenses, L21 to L23, arranged in order from the object side to the image side.

[0271] For the fixed-focus optical system of Example 34, the basic lens data is shown in Table 90, the specifications in Table 91, and the aberration diagrams are shown in Figure 69.

[0272] [Table 90]

[0273] [Table 91]

[0274] Table 92 shows the corresponding values ​​for conditional formulas (1) to (3) for "N231. Glass", "N216. Glass", and "N200. Glass" used in the above examples. Tables 93 to 99 show the corresponding values ​​for conditional formulas (4) to (20) for the fixed-focus optical systems of Examples 1 to 34 described above. The corresponding values ​​shown in Tables 92 to 99 may be used as the upper or lower limits of the conditional formulas to set a preferred range for the conditional formulas.

[0275] [Table 92]

[0276] [Table 93]

[0277] [Table 94]

[0278] [Table 95]

[0279] [Table 96]

[0280] [Table 97]

[0281] [Table 98]

[0282] [Table 99]

[0283] Next, an imaging device according to an embodiment of the present disclosure will be described. Figures 70 and 71 show external views of a camera 30, which is an imaging device according to one embodiment of the present disclosure. Figure 70 shows a perspective view of the camera 30 from the front, and Figure 71 shows a perspective view of the camera 30 from the rear. The camera 30 is a so-called mirrorless type digital camera, and an interchangeable lens 20 can be detachably attached. The interchangeable lens 20 is configured to include a fixed-focus optical system 1 according to one embodiment of the present disclosure, which is housed in the lens barrel. In this example, the fixed-focus optical system 1 functions as an imaging lens.

[0284] The camera 30 comprises a camera body 31. A shutter button 32 and a power button 33 are provided on the top surface of the camera body 31. An operation unit 34, an operation unit 35, and a display unit 36 ​​are provided on the back surface of the camera body 31. The display unit 36 ​​can display captured images and images within the field of view before the image was captured.

[0285] A shooting aperture is provided in the center of the front of the camera body 31, through which light from the subject being photographed enters. A mount 37 is provided at a position corresponding to the shooting aperture, and the interchangeable lens 20 is attached to the camera body 31 via the mount 37.

[0286] An image sensor 38 is provided inside the camera body 31. The image sensor 38 outputs an imaging signal corresponding to the subject image formed by the interchangeable lens 20. For example, a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) can be used as the image sensor 38. The camera body 31 also contains a signal processing circuit (not shown) and a recording medium (not shown). The signal processing circuit processes the imaging signal output from the image sensor 38 to generate an image. The recording medium is for recording the generated image. With the camera 30, still images or videos can be taken by pressing the shutter button 32, and the image data obtained from this shooting is recorded on the recording medium.

[0287] Although the technology of this disclosure has been described above with reference to embodiments and examples, the technology of this disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, interplanar spacing, refractive index, Abbe number, and aspheric coefficient of each lens are not limited to the values ​​shown in each of the above embodiments, but can take other values.

[0288] Furthermore, the imaging device according to the embodiments of this disclosure is not limited to the above examples, and can take various forms, such as cameras other than mirrorless types, cameras in which the imaging lens and camera body are integrally configured, film cameras, video cameras, surveillance cameras, broadcast cameras, movie cameras, FA (Factory Automation) cameras, and MV (Machine Vision) cameras.

[0289] The following additional information is disclosed regarding the above embodiments and examples. [Note 1] A fixed-focus optical system consisting of a front group, an aperture, and a rear group, arranged in order from the object side to the image side, The refractive index of the lens included in the fixed-focus optical system with respect to the d line is Nd. If the Abbe number of the lens included in the fixed-focus optical system is νd, then 2.435 <Nd+0.01425×νd<2.75 (1) 15 < νd < 39 (2) A fixed-focus optical system including at least one specific lens that satisfies the conditions (1) and (2) represented by . [Note 2] When the partial dispersion ratio between the g-line and the F-line of the lens included in the aforementioned fixed-focus optical system is denoted as θgF, The aforementioned specific lens is 0.65<θgF+0.00316×νd<0.85 (3) A fixed-focus optical system as described in Appendix 1 that satisfies the conditional equation (3) represented by . [Note 3] The focal length of the front group when in focus on an object at infinity is fF. If the focal length of the rear group when in focus on an object at infinity is fR, -5 <fR / fF<10 (4) A fixed-focus optical system according to Appendix 1 or Appendix 2 that satisfies the conditional expression (4) represented by . [Note 4] A fixed-focus optical system according to any one of the appendices 1 to 3, wherein at least one focusing lens group that moves along the optical axis when focusing is arranged. [Note 5] Among the group of focusing lenses included in the fixed-focus optical system, the focal length of the group of focusing lenses with the strongest refractive power is defined as ffocmax. When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, 0.2 < |ffocmax / f| < 3.5 (5) A fixed-focus optical system as described in Appendix 4 that satisfies the conditional equation (5) represented by . [Note 6] The fixed-focus optical system includes two groups of focusing lenses. Of the two focusing lens groups, the focal length of the focusing lens group on the object side is set to ff1. If the focal length of the image-side focusing lens group among the two focusing lens groups is set to ff2, 0.1 < |ff1 / ff2| < 10 (6) A fixed-focus optical system described in Appendix 4 or Appendix 5 that satisfies the conditional expression (6) represented by . [Note 7] The combined focal length of all lenses on the object side of the focusing lens group included in the fixed-focus optical system is ffocF. When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, -2 <f / ffocF<6 (7) A fixed-focus optical system described in any one of the appendices 4 to 6 that satisfies the conditional equation (7) represented by . [Note 8] The combined focal length of all lenses on the image side of the focusing lens group included in the fixed-focus optical system is ffocR. When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, -6 <f / ffocR<2 (8) A fixed-focus optical system described in any one of the appendices 4 to 7 that satisfies the conditional equation (8) represented by . [Note 9] The fixed-focus optical system according to any one of the appendices 4 to 8, wherein two focusing lens groups are arranged in the rear group, moving along different trajectories when focusing. [Note 10] The front group and the rear group each have one of the focusing lens groups. The focusing lens group of the front group and the focusing lens group of the rear group move along different trajectories when focusing. The combined focal length of all lenses on the object side of the focusing lens group included in the fixed-focus optical system is ffocF. If fM is the combined focal length from the lens adjacent to the image side of the focusing lens group in the front group to the lens adjacent to the object side of the focusing lens group in the rear group, 0.1 < |ffocF / fM| < 2 (9) A fixed-focus optical system described in any one of the appendices 4 to 9 that satisfies the conditional equation (9) represented by . [Note 11] The fixed-focus optical system according to any one of the appendices 4 to 10, wherein at least one of the focusing lens groups includes at least one of the specified lenses. [Note 12] The aforementioned rear group is a fixed-focus optical system according to any one of Appendix 1 to Appendix 11, which includes at least one of the specified lenses. [Note 13] The aforementioned front group is a fixed-focus optical system according to any one of Appendix 1 to Appendix 12, including at least one of the specified lenses. [Note 14] The front group and the rear group each include at least one of the specified lenses, as described in any one of Appendix 1 to Appendix 13. [Note 15] Includes at least one cemented lens, At least one of the cemented lenses is a fixed-focus optical system according to any one of Appendix 1 to Appendix 14, comprising at least one of the specified lenses. [Note 16] The aforementioned rear group includes an anti-vibration group that moves in a direction intersecting the optical axis during image blur correction. The focal length of the aforementioned vibration isolation group is fIS, When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, 0.05 < |fIS / f| < 2 (10) A fixed-focus optical system described in any one of the appendices 1 to 15 that satisfies the conditional equation (10) represented by . [Note 17] The vibration isolation group is a fixed-focus optical system as described in Appendix 16, which includes at least one of the specified lenses. [Note 18] The maximum half-angle of view when focused on an object at infinity is 7 degrees or less. Amax is the maximum value of the air gap along the optical axis within the front group when in focus on an object at infinity. When the lens group is in focus on an object at infinity, if TLf is the distance along the optical axis from the lens surface closest to the object in the front group to the lens surface closest to the image in the front group, 0.2 <Amax / TLf<0.8 (11) A fixed-focus optical system described in any one of the appendices 1 to 17 that satisfies the conditional expression (11) represented by . [Note 19] When the image is focused on the object with the longest possible distance for focusing, the angle with respect to the optical axis at which the principal ray of the widest field of view enters the image plane is θc. If the unit of θc is degrees, 0 < |θc| < 30 (12) A fixed-focus optical system described in any one of the appendices 1 to 18 that satisfies the conditional equation (12) represented by . [Note 20] An imaging device equipped with a fixed-focus optical system as described in any one of the appendices 1 through 19. [Explanation of Symbols]

[0290] 1 Fixed focus optical system 2 On-axis luminous flux 3 Luminous flux 3c chief ray 20 interchangeable lenses 30 Cameras 31 Camera Body 32 Shutter button 33 Power button 34 Control section 35 Control section 36 Display section 37 Mount 38 Image sensor Amax: Maximum air gap GF front group GR rear group L11~L38 Lenses Sim image plane St aperture diaphragm TLf distance Z optical axis Zp axis θc angle ωm Maximum half-angle

Claims

1. A fixed-focus optical system consisting of a front group, an aperture, and a rear group, arranged in order from the object side to the image side, The refractive index of the lens included in the fixed-focus optical system with respect to the d line is Nd. If the Abbe number of the lens included in the fixed-focus optical system is νd, then 2.435<Nd+0.01425×νd<2.75 (1) 15<νd<39 (2) A fixed-focus optical system including at least one specific lens that satisfies the conditions (1) and (2) represented by .

2. When the partial dispersion ratio between the g-line and the F-line of the lens included in the fixed-focus optical system is denoted as θgF, The aforementioned specific lens is 0.65<θgF+0.00316×νd<0.85 (3) A fixed-focus optical system according to claim 1 that satisfies the conditional expression (3) represented by .

3. The focal length of the front group when in focus on an object at infinity is fF. If the focal length of the rear group when in focus on an object at infinity is fR, -5<fR / fF<10 (4) A fixed-focus optical system according to claim 1 that satisfies the conditional expression (4) represented by .

4. The fixed-focus optical system according to claim 1, wherein at least one focusing lens group that moves along the optical axis when focusing is arranged.

5. Among the group of focusing lenses included in the fixed-focus optical system, the focal length of the focusing lens group with the strongest refractive power is ffocmax. When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, 0.2<|ffocmax / f|<3.5 (5) A fixed-focus optical system according to claim 4 that satisfies the conditional expression (5) represented by .

6. The fixed-focus optical system includes two groups of focusing lenses. Of the two focusing lens groups, the focal length of the focusing lens group on the object side is set to ff1. If the focal length of the image-side focusing lens group among the two focusing lens groups is set to ff2, 0.1<|ff1 / ff2|<10 (6) A fixed-focus optical system according to claim 4 that satisfies the conditional expression (6) represented by .

7. The combined focal length of all lenses on the object side of the focusing lens group included in the fixed-focus optical system is ffocF, When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, -2<f / ffocF<6 (7) A fixed-focus optical system according to claim 4 that satisfies the conditional expression (7) represented by .

8. The combined focal length of all lenses on the image side of the focusing lens group included in the fixed-focus optical system is ffocR. When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, -6<f / ffocR<2 (8) A fixed-focus optical system according to claim 4 that satisfies the conditional expression (8) represented by .

9. The fixed-focus optical system according to claim 4, wherein two focusing lens groups are arranged in the rear group, each moving along a different trajectory when focusing.

10. The front group and the rear group each have one of the focusing lens groups arranged in them. The focusing lens group of the front group and the focusing lens group of the rear group move along different trajectories when focusing. The combined focal length of all lenses on the object side of the focusing lens group included in the fixed-focus optical system is ffocF, When fM is the combined focal length from the lens adjacent to the image side of the focusing lens group in the front group to the lens adjacent to the object side of the focusing lens group in the rear group, 0.1<|ffocF / fM|<2 (9) A fixed-focus optical system according to claim 4 that satisfies the conditional expression (9) represented by .

11. The fixed-focus optical system according to claim 4, wherein at least one of the focusing lens groups includes at least one of the specific lenses.

12. The fixed-focus optical system according to claim 1, wherein the rear group includes at least one of the specified lenses.

13. The fixed-focus optical system according to claim 1, wherein the front group includes at least one of the specified lenses.

14. The fixed-focus optical system according to claim 1, wherein the front group and the rear group each include at least one of the specified lenses.

15. Includes at least one cemented lens, The fixed-focus optical system according to claim 1, wherein at least one of the cemented lenses includes at least one of the specific lenses.

16. The aforementioned rear group includes an anti-vibration group that moves in a direction intersecting the optical axis during image blur correction. The focal length of the aforementioned vibration isolation group is fIS, When the focal length of the fixed-focus optical system is f in the state where it is in focus on an object at infinity, 0.05<|fIS / f|<2 (10) A fixed-focus optical system according to claim 1 that satisfies the conditional expression (10) represented by .

17. The fixed-focus optical system according to claim 16, wherein the vibration isolation group includes at least one of the specified lenses.

18. The maximum half-angle of view when focused on an object at infinity is 7 degrees or less. Amax is the maximum value of the air gap along the optical axis within the front group when in focus on an object at infinity. When the lens group is in focus on an object at infinity, if TLf is the distance along the optical axis from the lens surface closest to the object in the front group to the lens surface closest to the image in the front group, 0.2<Amax / TLf<0.8 (11) A fixed-focus optical system according to claim 1 that satisfies the conditional expression (11) represented by .

19. When the image is focused on the object with the longest possible distance for focusing, the angle with respect to the optical axis at which the principal ray of the widest field of view enters the image plane is θc. If the unit of θc is degrees, 0<|θc|<30 (12) A fixed-focus optical system according to claim 1 that satisfies the conditional expression (12) represented by .

20. An imaging device comprising a fixed-focus optical system according to any one of claims 1 to 19.

Images