Optical system and imaging device

Abstract

[Problem] To achieve both size reduction and high optical performance by using a diffraction surface that has controlled wavelength dispersion characteristics. [Solution] An optical system L has a diffractive optical element L1 that has a positive refractive power, which has a convex refractive surface on the object side and a diffraction surface having controlled wavelength dispersion characteristics on the image side, and a lens L2 that has a negative refractive power, said diffractive optical element L1 and said lens L2 being disposed in order from the object side to the image side. The Abbe number ν0 of the diffraction surface satisfies the condition -0.2<1 / ν0<0.2.

Description

Optical System and Imaging Device

[0001] The present invention relates to an optical system suitable for an imaging device such as a digital camera.

[0002] As an optical system for a small camera mounted on a smartphone, Patent Document 1 discloses a telephoto-type optical system in which the entire system is composed of six lenses and a first lens having a strong positive refractive power on the object side is arranged. Further, Patent Document 2 discloses an optical system composed of a first lens having a convex positive refractive power facing the object side arranged on the object side and a second lens having a negative chromatic aberration including a metasurface lens. Furthermore, Patent Document 3 discloses an optical system in which a first lens having a strong positive refractive power is arranged on the object side, and a diffractive optical element whose wavelength dispersion characteristics of at least one surface are not controlled is provided, and the focal length, the overall length of the entire optical system, and the focal length of the diffractive optical element are set to be suitable for miniaturization.

[0003] These optical systems arrange a first lens having a strong positive refractive power on the object side. This configuration is effective for shortening the overall length of the optical system, but large chromatic aberration and monochromatic aberration occur in the first lens. Therefore, various aberrations such as chromatic aberration are corrected by arranging a large number of lenses including an aspherical lens having a negative refractive power.

[0004] U.S. Patent No. 10,989,901, U.S. Patent Publication No. 2021 / 0132256, International Patent Publication No. WO2021 / 170417

[0005] When a strong positive refractive power is arranged in the first lens and the overall length is shortened and aberration correction is performed with a small number of lenses, it is effective to use a diffractive surface having a negative Abbe number mainly for correcting chromatic aberration. However, since the Abbe number of a normal diffractive surface whose wavelength dispersion characteristics are not controlled is very highly dispersive, when a refractive power (reciprocal of the focal length) is given to the diffractive surface, a large chromatic aberration occurs. Therefore, it is difficult to achieve both miniaturization and high image quality of the optical system by reducing the number of lenses.

[0006] The present invention provides an optical system capable of achieving both miniaturization and high optical performance by using a diffractive surface whose wavelength dispersion characteristics are controlled.

[0007] An optical system, as one aspect of the present invention, comprises a positive refractive power diffractive optical element (or metalens) arranged sequentially from the object side to the image side, having a convex refractive surface on the object side and a diffractive surface (or metasurface) with controlled wavelength dispersion characteristics on the image side, and a negative refractive power lens. The Abbe number of the diffractive surface (or metasurface) is ν ０ In this case, -0.2 < 1 / ν ０ The present invention is characterized by satisfying the condition < 0.2. Furthermore, an imaging device having the above optical system also constitutes another aspect of the present invention.

[0008] According to the present invention, by using a diffraction surface with controlled wavelength dispersion characteristics, it is possible to achieve both miniaturization of the optical system and high optical performance.

[0009] Cross-sectional view of the optical system of Example 1. Aberration diagram of the optical system of Example 1. Cross-sectional view of the optical system of Example 2. Aberration diagram of the optical system of Example 2. Cross-sectional view of the optical system of Example 3. Aberration diagram of the optical system of Example 3. Cross-sectional view of the optical system of Example 4. Aberration diagram of the optical system of Example 4. Cross-sectional view of the optical system of Example 5. Aberration diagram of the optical system of Example 5. Diagram showing an imaging device using the optical system of the example.

[0010] The embodiments of the present invention will be described below with reference to the drawings. First, before describing the specific embodiments 1 to 5, matters common to each embodiment will be explained. Figures 1, 3, 5, 7, and 9 show the configuration of the optical system L of embodiments 1 to 5, respectively. O indicates the optical axis of the optical system L. MOE indicates a diffractive optical element including a diffractive surface whose wavelength dispersion characteristics are controlled (hereinafter simply referred to as dispersion controlled). L1 indicates the first lens, L2 indicates the second lens, and L3 indicates the third lens group. SP indicates the aperture diaphragm, and GB indicates a glass block including an infrared cut filter, a low-pass filter, etc. IP indicates the image plane of the optical system L. The image plane IP is where the imaging surface (light-receiving surface) of an image sensor such as a CCD sensor or a CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is arranged.

[0011] Figures 2, 4, 6, 8, and 10 each show the longitudinal aberration diagrams (spherical aberration, astigmatism, distortion, and chromatic aberration) in the state of focusing on an infinite object of the optical systems of numerical examples 1 to 5 corresponding to Examples 1 to 5 (hereinafter referred to as the infinite focusing state). The vertical axis Fno of the spherical aberration diagram indicates the F-number, and the vertical axis ω of the astigmatism, distortion, and chromatic aberration diagrams indicates the semi-field angle (°). The horizontal axis indicates the aberration amount of each aberration.

[0012] In the spherical aberration diagram, the solid line indicates the spherical aberration with respect to the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration with respect to the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S indicates the astigmatism in the sagittal image plane, and the broken line M indicates the astigmatism in the meridional image plane. The distortion aberration diagram shows the distortion aberration at the d-line. The chromatic aberration diagram shows the longitudinal chromatic aberration at the g-line.

[0013] Next, the characteristics of the optical systems of each example, which are small in size and have high optical performance and are composed of a small number of lenses, will be described.

[0014] The optical system of each example has a diffractive optical element with a positive refractive power having a convex refractive surface on the object side and a diffractive surface with dispersion control on the image side, and a lens with a negative refractive power, which are arranged in order from the object side to the image side. Note that a lens or other optical element may be arranged on the object side of the diffractive optical element. When the Abbe number of the diffractive surface is ν ０ it satisfies the condition of the following formula (1).

[0015] -0.2 < 1 / ν ０ < 0.2 (1) Here, the Abbe number ν ０ of the diffractive surface with dispersion control is defined by the following formula. The reference wavelength is the d-line (λ ｄ = 0.58756 μm), the principal dispersion is the F-line (λ Ｆ = 0.48613 μm) and the C-line (λ Ｃ = 0.65627 μm), and the optical path difference functions at each wavelength are ψ(λ ｄ ), ψ(λ Ｆ ), ψ(λ Ｃ ). Also, the optical path difference dispersions of the surface at each wavelength are P(λ ｄ ), P(λ Ｆ ), P(λ Ｃ) Let it be so.

[0016]

[0017] As described above, the optical system of each embodiment includes a diffractive optical element with a positive refractive power, having a convex refractive surface on the object side and a dispersed and controlled diffractive surface on the image side. The convergence effect of light rays due to the positive refractive power facilitates miniaturization of the optical system. Furthermore, by including a dispersed and controlled diffractive surface, chromatic aberration can be effectively corrected, making it easy to obtain high optical performance with a small number of lenses.

[0018] Furthermore, the optical system of each embodiment includes a second lens with negative refractive power. This second lens makes it easy to correct various aberrations, mainly monochromatic aberrations, generated by the positive refractive power diffractive optical element, thereby obtaining high optical performance.

[0019] The conditions in equation (1) are necessary to effectively correct chromatic aberration with a dispersion-controlled diffraction plane and to obtain high optical performance with a small number of lenses. 1 / ν ０ If the negative Abbe number becomes too highly dispersed so that it falls below the lower limit of equation (1), the chromatic aberration generated at the dispersion-controlled diffraction surface becomes too large, making it difficult to increase the refractive power of the diffraction surface and miniaturize the optical system, which is undesirable. Furthermore, chromatic aberration correction becomes difficult, making it difficult to obtain high optical performance, which is also undesirable. 1 / ν ０ If the positive Abbe number becomes too highly dispersed, exceeding the upper limit of equation (1), the chromatic aberration generated at the dispersion-controlled diffraction plane becomes too large, making it difficult to increase the refractive power of the diffraction plane and miniaturize the optical system, which is undesirable. Furthermore, chromatic aberration correction becomes difficult, making it difficult to obtain high optical performance, which is also undesirable.

[0020] It is more preferable to set the numerical range of equation (1) as follows.

[0021] -0.10 < 1 / ν ０ <0.02 (1a) It is even more preferable to set the numerical range of equation (1) as follows.

[0022] -0.100 < 1 / ν ０<0.011 (1b) The optical system of each embodiment preferably satisfies at least one of the following conditions of formulas (2) to (8).

[0023] When the focal length of a diffractive optical element with positive refractive power is f1 and the focal length of the entire optical system is f, it is preferable to set the focal length f1 of the diffractive optical element so as to satisfy the condition in the following equation (2).

[0024] 0.3 < f1 / f < 0.8 (2) The conditions in equation (2) are conditions that facilitate obtaining a compact optical system with high optical performance. If f1 / f falls below the lower limit of equation (2), the focal length of the diffractive optical element becomes too short, making it difficult to obtain high optical performance, which is undesirable. If f1 / f exceeds the upper limit of equation (2), the focal length of the diffractive optical element becomes too long, making it difficult to miniaturize the optical system, which is also undesirable.

[0025] It is more preferable to set the numerical range of equation (2) as follows.

[0026] 0.4 < f1 / f < 0.7 (2a) It is even more preferable to set the numerical range of equation (2) as follows.

[0027] 0.45 < f1 / f < 0.65 (2b) When the focal length of the dispersion-controlled diffraction plane is fmoe and the focal length of the entire optical system is f, it is preferable to set the focal length of the diffraction plane fmoe to satisfy the following condition (3).

[0028] 2.5 < fmoe / f < 10.0 (3) The focal length fmoe of the dispersion-controlled diffraction plane is the quadratic coefficient of the optical path difference function of the plane at the design wavelength U ２ In that case, it is calculated using the following formula.

[0029]

[0030] The conditions in equation (3) are also conditions that facilitate obtaining a compact optical system with high optical performance. If fmoe / f falls below the lower limit of equation (3), the focal length of the dispersion-controlled diffraction surface becomes too short, causing large aberrations such as spherical aberration, making it difficult to obtain high optical performance, which is undesirable. If fmoe / f exceeds the upper limit of equation (3), the focal length of the dispersion-controlled diffraction surface becomes too long, making it difficult to miniaturize the optical system, which is also undesirable.

[0031] It is more preferable to set the numerical range of equation (3) as follows.

[0032] 3.0 < fmoe / f < 9.7 (3a) It is even more preferable to set the numerical range of equation (3) as follows.

[0033] 4.0 < fmoe / f < 9.4 (3b) When TL is the distance along the optical axis from the lens surface closest to the object to the image plane (hereinafter referred to as the total lens length), it is preferable to set the total lens length such that the following equation (4) is satisfied.

[0034] 0.6 < TL / f < 0.9 (4) The conditions in equation (4) are also conditions that facilitate obtaining a compact optical system with high optical performance. If TL / f falls below the lower limit of equation (4), the overall length of the lens becomes too short, causing large aberrations such as spherical aberration, making it difficult to obtain high optical performance, which is undesirable. If TL / f exceeds the upper limit of equation (4), the overall length of the lens becomes too long, making it difficult to miniaturize the optical system, which is also undesirable.

[0035] It is more preferable to set the numerical range of equation (4) as follows.

[0036] 0.70 < TL / f < 0.88 (4a) It is even more preferable to set the numerical range of equation (4) as follows.

[0037] 0.75 < TL / f < 0.86 (4b) In the optical system of each embodiment, it is preferable to arrange, from the object side to the image side, a first optical element as a diffractive optical element with positive refractive power (hereinafter referred to as the first diffractive optical element) and a second optical element as a lens with negative refractive power (hereinafter referred to as the second lens) as described above. The first diffractive optical element is a diffractive optical element with positive refractive power that has a convex refractive surface on the object side and a dispersed and controlled diffractive surface on the image side, as described above. With this arrangement, the first diffractive optical element can effectively converge light rays while appropriately correcting various aberrations such as chromatic aberration. Furthermore, the second lens with negative refractive power can easily correct various aberrations, mainly monochromatic aberration, generated by the diffractive optical element with positive refractive power, thereby obtaining high optical performance.

[0038] When D12 is the air gap on the optical axis between the first diffractive optical element with positive refractive power and the second lens with negative refractive power, it is preferable to set the air gap D12 such that the following equation (5) is satisfied.

[0039] 0.08 < D12 / TL < 0.40 (5) The conditions in equation (5) are also conditions that facilitate obtaining a compact optical system with high optical performance. If the air gap D12 becomes too short so that D12 / TL falls below the lower limit of equation (5), it becomes difficult to sufficiently converge the on-axial marginal rays at the first diffracting optical element and have them incident on the second lens. As a result, it becomes difficult to give the second lens a strong negative refractive force to correct various aberrations such as spherical aberration and coma aberration and obtain high optical performance, which is undesirable. If the air gap D12 becomes too long so that D12 / TL exceeds the upper limit of equation (5), it becomes difficult to miniaturize the optical system, which is undesirable.

[0040] It is more preferable to set the numerical range of equation (5) as follows.

[0041] 0.10 < D12 / TL < 0.30 (5a) It is even more preferable to set the numerical range of equation (5) as follows.

[0042] 0.11 < D12 / TL < 0.25 (5b) When D23 is the air gap on the optical axis between a second lens with negative refractive power and a third optical element (hereinafter referred to as the third lens) which is adjacent to the second lens on the image side, it is preferable to set the air gap D23 so as to satisfy the following condition of equation (6).

[0043] 0.15 < D23 / TL < 0.50 (6) The conditions in equation (6) are also conditions that facilitate obtaining a compact optical system with high optical performance. If the air gap D23 becomes too short so that D23 / TL falls below the lower limit of equation (6), it becomes difficult to sufficiently separate the off-axis light beam incident on the third lens. As a result, it becomes difficult to effectively utilize the aspherical surface of the third lens for aberration correction, making it difficult to obtain high optical performance, which is undesirable. If the air gap D23 becomes too long so that D23 / TL exceeds the upper limit of equation (6), it becomes difficult to miniaturize the optical system, which is undesirable.

[0044] It is more preferable to set the numerical range of equation (6) as follows.

[0045] 0.18 < D23 / TL < 0.40 (6a) It is even more preferable to set the numerical range of equation (6) as follows.

[0046] 0.20 < D23 / TL < 0.35 (6b) When L02 is the distance on the optical axis from the lens surface closest to the object of the optical system to the lens surface closest to the object of the second lens, it is preferable to set the distance L02 such that the following equation (7) is satisfied.

[0047] 0.20 < L02 / TL < 0.45 (7) The conditions in equation (7) are conditions to facilitate obtaining an optical system with high optical performance. If the distance L2 becomes too short so that L02 / TL falls below the lower limit of equation (7), the second lens comes too close to the first lens. As a result, it becomes difficult to make the entire optical system a concentric shape with the second lens as the center, and it becomes difficult to correct aberrations such as field curvature and distortion, which is undesirable. If the distance L2 becomes too long so that L02 / TL exceeds the upper limit of equation (7), the second lens comes too close to the image-side lens. As a result, it becomes difficult to make the entire optical system a concentric shape with the second lens as the center, and it becomes difficult to correct aberrations such as field curvature and distortion, which is undesirable.

[0048] It is more preferable to set the numerical range of equation (7) as follows.

[0049] 0.24 < L02 / TL < 0.40 (7a) It is even more preferable to set the numerical range of equation (7) as follows.

[0050] 0.26 < L02 / TL < 0.36 (7b) When the focal length of a third lens with negative refractive power adjacent to a second lens with negative refractive power on the image side is fG3, it is preferable to set the focal length fG3 of the third lens so as to satisfy the condition of the following equation (8).

[0051] -1.5 < fG3 / f < -0.4 (8) The conditions in equation (8) are also conditions that facilitate obtaining a compact optical system with high optical performance. If the focal length fG3 becomes too long so that fG3 / f falls below the lower limit of equation (8), the effect of the third lens in changing the direction of light rays becomes too weak, making it difficult to effectively correct aberrations such as field curvature and distortion with the third lens, which is undesirable. If the focal length fG3 becomes too short so that fG3 / f exceeds the upper limit of equation (8), the divergence effect of the third lens becomes too strong, making it difficult to shorten the overall length of the optical system, which is also undesirable.

[0052] It is more preferable to set the numerical range of equation (8) as follows.

[0053] -1.0 < fG3 / f < -0.5 (8a) It is even more preferable to set the numerical range of equation (8) as follows.

[0054] -0.70 < fG3 / f < -0.55 (8b) The optical system of the embodiment is preferably composed of a first diffractive optical element with positive refractive power, a second lens with negative refractive power, a third lens which is a double-sided aspherical lens, and a fourth optical element (fourth lens) which is a double-sided aspherical lens, arranged in order from the object side to the image side.

[0055] By arranging a positive first diffractive optical element and a negative second lens in order from the object side, the first diffractive optical element can effectively converge light rays while appropriately correcting various aberrations such as chromatic aberration. Furthermore, by arranging the negative second lens immediately following the positive first diffractive optical element, it becomes easier to correct various aberrations, mainly monochromatic aberration, generated by the first diffractive optical element, and obtain high optical performance. In addition, by arranging a double-sided aspherical third lens and a double-sided aspherical fourth lens, it becomes easier to obtain high optical performance with a small number of lenses, just four.

[0056] The optical systems L of Examples 1 to 5 will be described in detail below. After Example 5, numerical examples 1 to 5 corresponding to each of Examples 1 to 5 are shown.

[0057] In each numerical example, the surface number i indicates the order of the surfaces when counted from the object side. r is the paraxial radius of curvature (mm) of the i-th optical surface (the i-th surface), and d is the on-axial spacing (lens thickness or air gap) (mm) along the optical axis between the i-th surface and the (i+1)-th surface. Furthermore, nd and νd represent the refractive index of the i-th optical component material at line d and the Abbe number with respect to line d, respectively.

[0058] The Abbe number νd, with respect to the d-line, is given by νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices of the Fraunhofer lines d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm), respectively. The effective diameter indicates the radius (mm) of the region through which the light rays contributing to imaging pass in the i-th plane.

[0059] BF represents the back focus (mm). The back focus is the distance along the optical axis from the final surface of the zoom lens (the lens surface closest to the image) to the paraxial image plane, expressed in terms of air-equivalent length. The total length of the lens is the distance along the optical axis from the frontmost lens surface (the lens surface closest to the object) to the final surface of the zoom lens, plus the back focus, and corresponds to TL in equations (4) to (7).

[0060] The asterisk (*) next to the surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the radius of paraxial curvature, k is the cone constant, and A4 to A10 are the aspherical coefficients. Note that the cone constant and the aspherical coefficients "e±M" are multiplied by 10. ±Ｍ It means...

[0061] x = (h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ] + A4・h 4 +A6・h 6 +A8・h 8 +A10・h 10 Furthermore, the optical path difference function of the surface at the design wavelength is expressed by the following equation, where U2 to U10 are the optical path difference function coefficients of the surface.

[0062] ψ0 = U²h ２ +U4・h ４ +U6・h ６ +U8・h ８ +U10・h １０ The (diffraction) designation next to the surface number indicates a surface whose optical design has been performed using the optical path difference function.

[0063] Table 1 summarizes the values ​​related to the aforementioned equations (1) to (8) for numerical examples 1 to 5.

[0064] The optical system L of Embodiment 1 (Numerical Example 1) shown in Figure 1 is an optical system with a focal length of 6.79 mm, an F-number of 2.7, and a half-angle of view of 21.83°. The optical system L is composed of a first diffractive optical element L1 with positive refractive power, an aperture diaphragm SP, a second lens L2 with negative refractive power, and a third lens group L3, which are arranged in order from the object side to the image side.

[0065] The first diffractive optical element L1 is a diffractive optical element having a convex refractive surface on the object side and a dispersed and controlled diffractive surface on the image side. The second lens L2 is a double-sided aspherical lens with a biconcave shape in the paraxial lens surface. The third lens group L3 is composed of a third double-sided aspherical lens having negative refractive power and a biconcave shape in the paraxial radius of curvature, and a fourth double-sided aspherical lens having positive refractive power and a meniscus shape in the paraxial radius of curvature that is convex towards the image side, arranged in order from the object side to the image side.

[0066] The optical system L of Embodiment 2 (Numerical Example 2) shown in Figure 3 is an optical system with a focal length of 5.53 mm, an F-number of 2.5, and a half-angle of view of 26.2°. The optical system L is composed of a first diffractive optical element L1 with positive refractive power, an aperture diaphragm SP, a second lens L2 with negative refractive power, and a third lens group L3.

[0067] The first diffractive optical element L1 is a diffractive optical element having a convex refractive surface on the object side and a dispersed and controlled diffractive surface on the image side. The second lens L2 is a double-sided aspherical lens with a biconcave shape for its paraxial radius of curvature. The third lens group L3 is composed of a third double-sided aspherical lens with negative refractive power and a biconcave shape for its paraxial radius of curvature, and a fourth double-sided aspherical lens with negative refractive power and a meniscus shape with a convex paraxial radius of curvature on the image side, arranged sequentially from the object side to the image side.

[0068] The optical system L of Embodiment 3 (Numerical Example 3) shown in Figure 5 is an optical system with a focal length of 8.70 mm, an F-number of 2.9, and a half-angle of view of 17.36°. The optical system L is composed of a first diffractive optical element L1 with positive refractive power, an aperture diaphragm SP, a second lens L2 with negative refractive power, and a third lens group L3, which are arranged in order from the object side to the image side.

[0069] The first diffractive optical element L1 is a diffractive optical element having a convex refractive surface on the object side and a dispersed and controlled diffractive surface on the image side. The second lens L2 is a double-sided aspherical lens with a biconcave shape for its paraxial radius of curvature. The third lens group L3 is composed of a third double-sided aspherical lens with negative refractive power and a biconcave shape for its paraxial radius of curvature, and a fourth double-sided aspherical lens with positive refractive power and a meniscus shape for its paraxial radius of curvature that is convex towards the image side, arranged sequentially from the object side to the image side.

[0070] The optical system L of Embodiment 4 (Numerical Example 4) shown in Figure 7 is an optical system with a focal length of 8.58 mm, an F-number of 2.9, and a half-angle of view of 17.59°. The optical system L is composed of a first diffractive optical element L1 with positive refractive power, an aperture diaphragm SP, a second lens L2 with negative refractive power, and a third lens group L3, which are arranged in order from the object side to the image side.

[0071] Similar to Example 1, the first diffractive optical element L1 is a diffractive optical element having a convex refractive surface on the object side and a dispersed diffractive surface on the image side. The second lens L2 is a double-sided aspherical lens with a biconcave shape for its paraxial radius of curvature. The third lens group L3 is composed of a third double-sided aspherical lens having negative refractive power and a biconcave shape for its paraxial radius of curvature, and a fourth double-sided aspherical lens having positive refractive power and a meniscus shape with a convex paraxial radius of curvature on the image side, arranged sequentially from the object side to the image side.

[0072] The optical system L of Embodiment 5 (Numerical Example 5) shown in Figure 9 is an optical system with a focal length of 6.79 mm, an F-number of 2.7, and a half-angle of view of 21.83°. The optical system L is composed of a first diffractive optical element L1 with positive refractive power, an aperture diaphragm SP, a second lens L2 with negative refractive power, and a third lens group L3, which are arranged in order from the object side to the image side.

[0073] Similar to Example 1, the first diffractive optical element L1 is a diffractive optical element having a convex refractive surface on the object side and a dispersed diffractive surface on the image side. The second lens L2 is a double-sided aspherical lens with a biconcave shape for its paraxial radius of curvature. The third lens group L3 is composed of a third double-sided aspherical lens having negative refractive power and a biconcave shape for its paraxial radius of curvature, and a fourth double-sided aspherical lens having positive refractive power and a meniscus shape with a convex paraxial radius of curvature on the image side, arranged sequentially from the object side to the image side.

[0074] Furthermore, in imaging using the optical system L of each embodiment, aberration correction may be performed by image processing. In addition, the optical path difference function of the diffractive optical element may be realized by a metalens having a so-called single-layer metasurface, where the metasurface consists of one layer, or a so-called stacked metasurface, where the metasurface consists of multiple layers.[Numerical Example 1] Unit: mm Surface Data Surface Number rd nd νd Effective Diameter 1* 1.684 0.81 1.43875 94.9 2.51 2 (Diffraction) ∞ 0.83 2.37 3 (Aperture) ∞ 0.10 1.74 4* -9.488 0.30 1.59946 25.8 1.63 5* 7.691 1.82 1.39 6* -2.930 0.40 1.53504 55.7 2.56 7* 12.835 0.12 3.25 8* -1.910 0.74 1.64025 19.3 3.75 9* -1.431 0.03 4.11 10 ∞ 0.21 1.51633 64.1 5.50 11 ∞ 0.40 5.50 Image plane ∞ Aspherical data 1st plane K = -8.37714e-01 A 4 = 9.67558e-03 A 6 = -6.23630e-04 A 8 = 2.13482e-03 A10 = -8.44847e-04 2nd plane (diffraction plane) Design wavelength 0.58756 [μm] U 2 = -9.76396e-03 U 4 = 1.46160e-03 U 6 = 1.78901e-03 U 8 = -1.02999e-03 U 10 = 1.12524e-04 Units of optical path difference dispersion wavelength of the plane [μm] P(λ) = 847.47010・λ. 10 - 4807.97026・λ 9 + 12415.11872・λ8 - 19240.96797・l 7 + 19873.45822・l 6 - 14357.25933・l 5 + 7400.16189・l 4 - 2720.50548・l 3 + 698.93940・l 2 - 119.47404・λ + 12.24651 P(λ d ) = 1.0000e+00 P(λ C ) = 9.0614e-01 P(λ F) = 1.1949e+00 4th surface K =-7.30312e+02 A 4= 1.11548e-01 A 6= 2.68473e-01 A 8=-1.02096e+00 A10= 2.20808e+00 A12=-2.77979e+00 A14= 1.80491e+00 A16=-4.29895e-01 5th side K = 9.50000e+01 A 4= 2.50245e-01 A 6=-9.99304e-02 A 8= 1.82022e-01 A10=-2.06303e-01 6th side K = 3.71573e+00A 4=-3.10316e-01 A 6=-1.39954e-01 A 8= 1.08852e+00 A10=-1.59622e+00 A12= 1.13582e+00 A14=-4.07725e-01 A16= 6.09779e-02 7th side K = 5.66804e+01 A 4=-3.59989e-01 A 6= 2.81360e-01 A 8=-1.32968e-01 A10= 3.00410e-02 A12=-3.03550e-03 A14= 1.94204e-04 8th side K =-7.61381e+00 A 4= 2.25923e-02 A 6=-1.53447e-02 A 8= 1.29023e-03 A10= 1.54000e-03 A12=-3.07319e-04 9th surface K =-3.68987e+00 A 4=-2.79819e-03 A 6=-1.52162e-03 A 8=-3.47584e-03 A10= 2.02821e-03 A12=-2.65856e-04 Various data Focal length 6.79 F-number 2.70 Half angle of view (°) 21.83 Image height 2.72 Lens length 5.69 BF 0.57 Entrance pupil position 2.21 Exit pupil position -5.42 Front principal point position 1.08 Rear principal point position -6.39 Single Lens Data Lens Starting Surface Focal Length 1 1 3.61 2 4 -7.04 3 6 -4.42 4 8 5.55 [Numerical Example 2] Unit: mm Surface Data Surface Number rd nd νd Effective Aperture 1* 1.386 0.77 1.43875 94.9 2.21 2 (Diffraction) ∞ 0.57 2.06 3 (Aperture) ∞ 0.11 1.60 4* -10.233 0.30 1.60586 24.5 1.48 5* 11.746 1.17 1.25 6* -2.121 0.40 1.53504 55.7 2.08 7* 12.818 0.09 2.88 8* -2.090 0.61 1.63085 20.4 3.65 9* -2.454 0.03 4.06 10 ∞ 0.21 1.51633 64.1 5.50 11 ∞ 0.40 5.50 Image plane ∞ Aspherical data 1st plane K = -9.18376e-01 A 4 = 1.89471e-02 A 6 = 1.09143e-03 A 8 = 1.87832e-03 A10 = -2.95422e-03 2nd plane (diffraction plane) Design wavelength 0.58756 [μm] U 2 = -1.00142e-02 U 4 = 7.40658e-03 U 6 = -1.02452e-02 U 8 = 7.55762e-03 U10=-2.62698e-03 Unit of optical path difference dispersion wavelength of the surface [μm] P(λ) = 2266.41068・λ. 10 - 12144.39247・λ 9 + 29486.82651・λ 8 - 42762.08537・λ 7 + 41106.88437・λ 6 - 27470.79737・λ 5 + 13006.44877・λ 4 - 4356.52716・λ 3 + 1009.95630・λ 2 - 153.95668・λ + 13.87546 P(λ d ) = 1.0000e+00 P(λ C ) = 9.1556e-01 P(λ F) = 1.1842e+00 4th side K =-2.71665e+02 A 4= 2.02763e-01 A 6=-7.20641e-02 A 8= 8.04897e-01 A10=-3.05427e+00 A12= 5.29501e+00 A14=-4.14210e+00 A16= 1.19528e+00 5th side K = 4.89253e-01 A 4= 2.25750e-01 A 6= 6.27068e-01 A 8=-1.60141e+00 A10= 1.82728e+00 6th side K = 2.66010e+00 A 4=-3.37434e-01 A 6=-2.07792e-01 A 8= 1.03514e+00 A10=-1.74754e+00 A12= 1.26306e+00 A14=-1.36633e-01 A16=-8.95322e-02 7th side K = 2.89242e+01 A 4=-3.42912e-01 A 6= 1.98866e-01 A 8=-9.07270e-02 A10= 7.20873e-03 A12= 8.78904e-03 A14=-1.68521e-03 8th side K =-5.53855e+00 A 4= 5.40644e-03 A 6 = 7.17144e-03 A 8 = -6.11534e-04 A10 = 3.80971e-04 A12 = -1.54203e-04 9th surface K = -1.10259e+01 A 4 = -7.33408e-02 A 6 = 2.34943e-02 A 8 = -1.14536e-03 A10 = 1.23043e-04 A12 = -8.25915e-05 Various data Focal length 5.53 F-number 2.50 Half angle of view (°) 26.20 Image height 2.72 Lens length 4.59 BF 0.57 Entrance pupil position 1.73 Exit pupil position -2.19 Front principal point position -4.53 Rear principal point position -5.13 Single Lens Data Lens Starting Surface Focal Length 1 1 3.00 2 4 -8.98 3 6 -3.37 4 8 -64.19 [Numerical Example 3] Unit: mm Surface Data Surface Number rd nd νd Effective Aperture 1* 2.226 0.83 1.43875 94.9 3.00 2 (Diffraction) ∞ 1.43 2.87 3 (Aperture) ∞ 0.10 1.86 4* -9.383 0.30 1.58172 30.3 1.77 5* 7.917 2.01 1.56 6* -8.482 0.40 1.53504 55.7 2.53 7* 5.062 0.15 3.12 8* -3.299 1.00 1.63648 19.7 3.52 9* -2.221 0.51 4.19 10 ∞ 0.21 1.51633 64.1 5.50 11 ∞ 0.40 5.50 Image surface ∞ Aspheric data 1st surface K = 3.28784e-01 A 4=-1.12717e-02 A 6=-1.16474e-03 A 8=-5.88116e-04 A10=-7.58421e-05 2nd surface (diffraction surface) Design wavelength 0.58756 [μm] U 2=-1.24211e-02 U 4=-9.93242e-04 U 6= 1.10002e-03 U 8=-5.79917e-04 U10 = 1.48671e-04 Unit of optical path difference dispersion wavelength of the surface [μm] P(λ) = 606.61668・λ. 10 - 3567.44539・λ 9 + 9538.09656・λ 8 - 15288.88750・λ 7 + 16315.44261・λ 6 - 12165.39383・λ 5 + 6465.34198・λ 4 - 2448.35587・λ 3 + 647.33574・λ 2 - 113.77083・λ + 11.97801 P(λ d ) = 1.0000e+00 P(λ C ) = 9.0469e-01 P(λ F) = 1.1965e+00 4th side K =-7.12739e+02 A 4= 1.93928e-02 A 6= 3.10222e-01 A 8=-9.88060e-01 A10= 2.03483e+00 A12=-2.53536e+00 A14= 1.71781e+00 A16=-4.81247e-01 5th side K = 7.49263e+01 A 4= 1.33691e-01 A 6=-4.90895e-02 A 8= 7.52699e-02 A10=-6.37695e-02 6th side K = 4.03729e+01 A 4=-2.72142e-01 A 6=-1.27746e-01 A 8= 8.56983e-01 A10=-1.36860e+00 A12= 1.08218e+00 A14=-4.25757e-01 A16= 6.72854e-02 7th side K = 8.34119e+00 A 4=-3.52878e-01 A 6= 2.40338e-01 A 8=-1.18592e-01 A10= 2.59296e-02 A12= 1.55307e-03 A14=-1.08217e-03 8th side K = 2.04857e+00 A 4= 3.67846e-02 A 6 = 4.39495e-03 A 8 = -1.50198e-03 A10 = 2.19341e-04 A12 = 1.74466e-05 9th surface K = -8.24113e-02 A 4 = 3.88049e-02 A 6 = 2.10572e-03 A 8 = -1.59372e-03 A10 = 3.89306e-04 A12 = -3.30176e-05 Various data Focal length 8.70 F-number 2.90 Half angle of view (°) 17.36 Image height 2.72 Lens length 7.27 BF 1.05 Entrance pupil position 3.46 Exit pupil position -5.58 Front principal point position -0.50 Rear principal point position -8.30 Single Lens Data Lens Starting Surface Focal Length 1 1 4.56 2 4 -7.33 3 6 -5.86 4 8 7.85 [Numerical Example 4] Unit: mm Surface Data Surface Number rd nd νd Effective Aperture 1* 2.246 0.81 1.43875 94.9 2.96 2 (Diffraction) -295.185 1.41 2.83 3 (Aperture) ∞ 0.10 1.87 4* -17.662 0.30 1.56422 36.5 1.77 5* 6.188 1.99 1.56 6* -6.412 0.40 1.53504 55.7 2.52 7* 5.517 0.33 3.11 8* -4.293 1.00 1.61957 22.1 3.65 9* -2.411 0.28 4.28 10 ∞ 0.21 1.51633 64.1 5.50 11 ∞ 0.40 5.50 Image plane ∞ Aspherical data 1st plane K = 2.78962e-01 A 4=-9.97081e-03 A 6=-1.16477e-03 A 8=-6.47121e-04 A10=-2.00577e-07 2nd plane (diffraction plane) K = 2.28097e+04 Design wavelength 0.58756 [μm] U 2=-1.21838e-02 U 4= 1.63050e-04 U 6= 2.16299e-04 U 8=-1.70898e-04 U10= 7.75164e-05 Unit of optical path difference dispersion wavelength of the surface [μm] P(λ) = -166210.38186・λ. 10 + 937035.34298・λ 9 - 2367058.88337・λ 8 + 3528122.94489・λ 7 - 3435936.87755・λ 6 + 2284273.33127・λ 5 - 1049756.10330・λ 4 + 329210.78659・λ 3 - 67395.09192・λ 2 + 8122.12927・λ - 434.73255 P(λ d ) = 1.0000e+00 P(λ C ) = 9.2186e-01 P(λ F) = 1.1773e+00 4th side K =-3.94370e+03 A 4= 3.63831e-02 A 6= 3.04246e-01 A 8=-1.00699e+00 A10= 2.05779e+00 A12=-2.51896e+00 A14= 1.67922e+00 A16=-4.64464e-01 5th side K = 4.21306e+01 A 4= 1.19464e-01 A 6=-1.17085e-02 A 8= 4.56339e-03 A10=-1.28123e-02 6th side K = 2.25807e+01 A 4=-2.40989e-01 A 6=-1.20292e-01 A 8= 8.48864e-01 A10=-1.36495e+00 A12= 1.07826e+00 A14=-4.25456e-01 A16= 6.78933e-02 7th side K = 1.01704e+01 A 4=-3.33795e-01 A 6= 2.36754e-01 A 8=-1.18145e-01 A10= 2.50599e-02 A12= 1.71424e-03 A14=-1.05420e-03 8th side K = 3.74014e+00A 4=-3.44508e-03 A 6= 1.14067e-02 A 8=-2.17872e-03 A10= 4.85615e-04 A12=-5.30278e-05 9th surface K = 3.93746e-02 A 4= 2.66395e-02 A 6=-1.24811e-03 A 8= 1.05063e-04 A10= 1.52986e-04 A12=-2.06204e-05 Various data Focal length 8.58 F-number 2.90 Half angle of view (°) 17.59 Image height 2.72 Lens length 7.15 BF 0.81 Entrance pupil position 3.34 Exit pupil position -5.71 Front principal point position -0.13 Back principal point position -8.18 Single Lens Data Lens Starting Surface Focal Length 1 1 4.61 2 4 -8.09 3 6 -5.48 4 8 7.37 [Numerical Example 5] Unit: mm Surface Data Surface Number rd nd νd Effective Aperture 1* 1.679 0.81 1.43875 94.9 2.51 2(Diffraction) -120 1.658 0.80 2.37 3(Aperture) ∞ 0.10 1.76 4* -9.679 0.30 1.60444 24.8 1.65 5* 7.743 1.84 1.40 6* -2.952 0.40 1.53504 55.7 2.57 7* 11.054 0.11 3.28 8* -1.909 0.75 1.64475 19.1 3.74 9* -1.431 0.03 4.10 10 ∞ 0.21 1.51633 64.1 5.50 11 ∞ 0.40 5.50 Image plane ∞ Aspherical data 1st plane K = -8.31081e-01 A 4 = 9.86364e-03 A 6 = -4.96299e-04 A 8 = 2.14642e-03 A10 = -8.10108e-04 2nd plane (diffraction plane) K = 8.39004e+05 Design wavelength 0.58756 [μm] U 2 = -9.57924e-03 U 4 = 1.96827e-03 U 6 = 1.84008e-03 U 8=-1.04244e-03 U10= 1.26614e-04 Surface optical path difference dispersion P(λ) = 0.58756 / λ P(λ). d ) = 1.0000e+00 P(λ C ) = 8.9530e-01 P(λ F) = 1.2086e+00 4th side K =-7.78980e+02 A 4= 1.13646e-01 A 6= 2.67771e-01 A 8=-1.02350e+00 A10= 2.21155e+00 A12=-2.77374e+00 A14= 1.79686e+00 A16=-4.32428e-01 5th side K = 9.50000e+01 A 4= 2.51941e-01 A 6=-1.04642e-01 A 8= 1.91332e-01 A10=-2.07083e-01 6th side K = 3.75305e+00A 4=-3.17027e-01 A 6=-1.36568e-01 A 8= 1.09289e+00 A10=-1.59737e+00 A12= 1.13434e+00 A14=-4.07143e-01 A16= 6.08155e-02 7th side K = 4.07551e+01 A 4=-3.64478e-01 A 6= 2.85375e-01 A 8=-1.33950e-01 A10= 3.01960e-02 A12=-2.92272e-03 A14= 1.40925e-04 8th side K =-8.37675e+00 A 4= 2.02048e-02 A 6=-1.49159e-02 A 8= 1.26993e-03 A10= 1.53299e-03 A12=-3.05658e-04 9th surface K =-3.76863e+00 A 4=-2.11771e-03 A 6=-2.28008e-03 A 8=-3.46988e-03 A10= 2.07880e-03 A12=-2.72202e-04 Various data Focal length 6.79 F-number 2.70 Half angle of view (°) 21.83 Image height 2.72 Lens length 5.69 BF 0.57 Entrance pupil position 2.16 Exit pupil position -5.42 Front principal point position 1.02 Rear principal point position -6.39 Single-lens data lens: Starting plane, Focal length 1 1 3.60 2 4 -7.07 3 6 -4.31 4 8 5.50.

[0075]

[0076] [Imaging Device] Figure 11 shows a digital still camera as an imaging device using the optical systems of each of the above embodiments as imaging optical systems. 20 is the camera body, and 21 is the imaging optical system composed of any of the optical systems of Embodiments 1 to 3. 22 is an image sensor such as a CCD sensor or CMOS sensor built into the camera body 20 that captures the optical image (subject image) formed by the imaging optical system 21. 23 is a recording unit that records image data generated by processing the imaging signal from the image sensor 22, and 24 is a rear display that displays the image data.

[0077] By using the optical systems of each embodiment, a compact camera with high optical performance can be obtained. The camera may be a single-lens reflex camera with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0078] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention.

Claims

1. A diffractive optical element with positive refractive power, having a convex refractive surface on the object side and a diffractive surface with controlled wavelength dispersion characteristics on the image side, arranged sequentially from the object side to the image side, and a lens with negative refractive power, wherein the Abbe number of the diffractive surface is ν ０ Let the reference wavelength be the d-line and the principal dispersion be the F-line and C-line, and the optical path difference function at each wavelength be ψ(λ). ｄ ), ψ(λ Ｆ ), ψ(λ Ｃ Let P(λ) be the optical path difference dispersion of the surface at each wavelength. ｄ ), P(λ Ｆ ), P(λ Ｃ ) as, When this is the case, -0.2 < 1 / ν ０ An optical system characterized by satisfying the condition < 0.

2.

2. The optical system according to claim 1, characterized in that, when the focal length of the diffractive optical element is f1 and the focal length of the optical system is f, the condition 0.3 < f1 / f < 0.8 is satisfied.

3. Let the focal length of the diffraction surface be \(f_{moe}\), the focal length of the optical system be \(f\), and the second-order coefficient of the optical path difference function of the surface at the design wavelength be \(U\). ２ When it is, the optical system according to claim 1 or 2, characterized in that it satisfies the condition \(2.5 < f_{moe} / f < 10.0\).

4. The optical system according to any one of claims 1 to 3, characterized in that, when TL is the distance on the optical axis from the lens surface closest to the object to the image plane of the optical system, and f is the focal length of the optical system, the condition 0.6 < TL / f < 0.9 is satisfied.

5. The optical system according to any one of claims 1 to 4, characterized in that the first optical element as a diffractive optical element and the second optical element as a lens are arranged in order from the object side to the image side in the optical system.

6. The optical system according to claim 5, characterized in that when D12 is the air gap on the optical axis between the first optical element and the second optical element, and TL is the distance on the optical axis from the lens surface on the object side of the optical system to the image plane, the condition 0.08 < D12 / TL < 0.40 is satisfied.

7. The optical system according to claim 5 or 6, wherein a third optical element is provided as a lens adjacent to the second optical element on the image side, and when D23 is the air gap on the optical axis between the second optical element and the third optical element, and TL is the distance on the optical axis from the lens surface on the object side of the optical system to the image plane, the condition 0.15 < D23 / TL < 0.50 is satisfied.

8. The optical system according to any one of claims 5 to 7, characterized in that, when L02 is the distance along the optical axis from the lens surface on the object side of the optical system to the lens surface on the object side of the second optical element, and TL is the distance along the optical axis from the lens surface on the object side of the optical system to the image plane, the condition 0.20 < L02 / TL < 0.45 is satisfied.

9. The optical system according to any one of claims 5 to 8, wherein the second optical element has a third optical element as a negative refractive lens adjacent to it on the image side, and when the focal length of the third optical element is fG3 and the focal length of the optical system is f, the condition -1.5 < fG3 / f < -0.4 is satisfied.

10. The optical system according to any one of claims 1 to 9, characterized in that it comprises a first optical element as a diffractive optical element, a second optical element as a lens, a third optical element as a double-sided aspherical lens, and a fourth optical element as a double-sided aspherical lens, all arranged in order from the object side to the image side in the optical system.

11. The optical system according to claim 10, characterized in that the third optical element has a negative refractive power, and the fourth optical element has a positive or negative refractive power.

12. A positive refractive power metalens and a negative refractive power lens are arranged sequentially from the object side to the image side, with a convex refractive surface on the object side and a metasurface with controlled wavelength dispersion characteristics on the image side, wherein the Abbe number of the metasurface is ν ０ Let the reference wavelength be the d-line and the principal dispersion be the F-line and C-line, and the optical path difference function at each wavelength be ψ(λ). ｄ ), ψ(λ Ｆ ), ψ(λ Ｃ Let P(λ) be the optical path difference dispersion of the surface at each wavelength. ｄ ), P(λ Ｆ ), P(λ Ｃ ) as, When this is the case, -0.2 < 1 / ν ０ An optical system characterized by satisfying the condition < 0.

2.

13. An imaging device characterized by having an optical system according to any one of claims 1 to 12, and an image sensor that images a subject through the optical system.

Images