Optical system and image pickup apparatus

Abstract

The invention discloses an optical system and an image pickup apparatus. An optical system includes, in order from an object side to an image side, a diffractive optical element having a positive refractive power and a diffractive surface having a controlled wavelength dispersion characteristic, and a lens having a negative refractive power. A predetermined inequality is satisfied.

Description

Technical Field

[0001] An aspect of the embodiment relates to an optical system suitable for an image pickup device such as a digital camera. Background Art

[0002] As an optical system for a small camera mounted on a smartphone, U.S. Patent No. 10989901 discloses a telephoto optical system consisting of six lenses, in which a first lens having a strong positive refractive power is deployed closest to an object. U.S. Patent Publication No. 2021 / 0132256 discloses an optical system consisting of a first lens and a second lens, the first lens having a positive refractive power and a convex shape toward the object side and being deployed closest to the object, the second lens having a negative chromatic aberration and including a metasurface lens. International Patent Publication No. WO2021 / 170417 discloses an optical system including a first lens and a diffractive optical element (DOE), the first lens having a strong positive refractive power and being deployed closest to the object, the diffractive optical element (DOE) having at least one surface having an uncontrolled wavelength dispersion characteristic, wherein the focal length and total length of the optical system and the focal length of the DOE are appropriately set to reduce the size.

[0003] These optical systems include a first lens having a strong positive refractive power and arranged closest to the object. This configuration is effective for reducing the overall length of the optical system, but the first lens generates large chromatic aberration and monochromatic aberration, so multiple lenses including an aspherical lens having a negative refractive power correct various aberrations such as chromatic aberration.

[0004] In the case where the first lens has a strong positive refractive power to correct aberrations with a small number of lenses and reduce the total length, it is effective to mainly use a diffractive surface with a negative Abbe number to correct chromatic aberration. However, the Abbe number of a general diffractive surface with uncontrolled wavelength dispersion characteristics shows extremely high dispersion, so the diffractive surface with refractive power (the inverse of the focal length) produces large chromatic aberration. Therefore, it is difficult to achieve both a compact optical system and high image quality by reducing the number of lenses. Summary of the invention

[0005] According to one aspect of the present disclosure, an optical system includes, from the object side to the image side, a diffractive optical element having a positive refractive power and a diffractive surface, the diffractive surface having a controlled wavelength dispersion characteristic; and a lens having a negative refractive power. Where ν0 is the Abbe number of the diffractive surface, the reference wavelength is the d-line, the main dispersion is the F-line and the C-line, ψ(λ d ),ψ(λ F ) and ψ(λ C ) are the optical path difference functions for d-line, F-line and C-line, respectively, P(λd ), P(λ F ) and P(λ C ) are the optical path difference dispersions of the surface for d-line, F-line and C-line respectively, and the following equation is satisfied:

[0006] and

[0007] The following inequality is satisfied:

[0008] -0.2<1 / ν0<0.2.

[0009] According to another aspect of the present disclosure, an optical system includes, from the object side to the image side, a metalens having a positive refractive power and a metasurface having a controlled wavelength dispersion characteristic; and a lens having a negative refractive power. Where ν0 is the Abbe number of the metasurface, the reference wavelength is the d-line, the main dispersion is the F-line and the C-line, ψ(λ d ),ψ(λ F ) and ψ(λ C ) are the optical path difference functions for d-line, F-line and C-line, respectively, P(λ d ), P(λ F ) and P(λ C ) are the optical path difference dispersions of the surface for d-line, F-line and C-line respectively, and the following equation is satisfied:

[0010] and

[0011] The following inequality is satisfied:

[0012] -0.2<1 / ν0<0.2.

[0013] An image pickup device having each of the above optical systems also constitutes another aspect of the present disclosure.

[0014] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a cross-sectional view of an optical system according to Example 1.

[0016] Figure 2 : is an aberration diagram of the optical system according to Example 1.

[0017] Figure 3 is a cross-sectional view of an optical system according to Example 2.

[0018] Figure 4 : is an aberration diagram of the optical system according to Example 2.

[0019] Figure 5 is a cross-sectional view of an optical system according to Example 3.

[0020] Figure 6 : is an aberration diagram of the optical system according to Example 3.

[0021] Figure 7 is a cross-sectional view of an optical system according to Example 4.

[0022] Figure 8 : is an aberration diagram of the optical system according to Example 4.

[0023] Fig. 9 is a cross-sectional view of an optical system according to Example 5.

[0024] Fig.10 : is an aberration diagram of the optical system according to Example 5.

[0025] Fig.11 is a diagram illustrating an image pickup device using the optical system according to any of the above examples. DETAILED DESCRIPTION

[0026] Now, referring to the drawings, a description will be given of an embodiment according to the present disclosure. Now, before describing specific examples 1 to 5, a description is given of matters common to each example. Figure 1 , Figure 3 , Figure 5 , Figure 7 and Fig. 9 Configurations of the optical system L according to Examples 1 to 5 are illustrated respectively. O represents an optical axis of the optical system L. MOE represents a diffractive optical element (DOE) including a diffractive surface having a controlled wavelength dispersion characteristic (hereinafter referred to as controlled dispersion). L1 represents a first lens, L2 represents a second lens, and L3 represents a third lens unit. SP represents an aperture stop (aperture), and GB represents a glass block including an infrared cut filter, a low-pass filter, and the like, and IP represents an image plane of the optical system L. Arranged on the image plane IP is an imaging surface (light receiving surface) of an image sensor such as a CCD sensor or a CMOS sensor, or a film surface (photosensitive surface) of a silver film. Figure 2 , Figure 4 , Figure 6 , Figure 8 and Fig.10 Longitudinal aberration diagrams (spherical aberration, astigmatism, distortion, and chromatic aberration) in a focused state on an object at infinity (hereinafter referred to as “focused state at infinity”) according to the optical systems of numerical examples 1 to 5 corresponding to examples 1 to 5 are illustrated respectively. The vertical axis Fno of each spherical aberration diagram represents the F number, and the vertical axis ω of each of astigmatism, distortion, and chromatic aberration represents the half angle of view (°). The horizontal axis represents the corresponding aberration amount.

[0027] In the spherical aberration diagram, the solid line represents the amount of spherical aberration for the d-line (wavelength 587.6nm), and the alternating one long and two short dashed lines represent the spherical aberration for the g-line (wavelength 435.8nm). In the astigmatism diagram, the solid line S represents the amount of astigmatism on the sagittal image plane, and the dashed line M represents the amount of astigmatism on the meridional image plane. The distortion diagram illustrates the amount of distortion for the d-line. The chromatic aberration diagram illustrates the amount of lateral chromatic aberration for the g-line.

[0028] Now, a description will be given of the characteristics of an optical system according to each example, the optical system having a reduced size, high optical performance, and a small number of lenses.

[0029] The optical system according to each example includes a DOE and a lens having negative refractive power in order from the object side to the image side, the DOE having positive refractive power and a convex refractive surface located on the object side and a controlled dispersion diffractive surface located on the image side. The lens or another optical element may be disposed on the object side of the DOE. The following inequality (1) is satisfied:

[0030] -0.2 < 1 / ν0 < 0.2 (1)

[0031] where ν0 is the Abbe number of the diffractive surface.

[0032] The Abbe number ν0 of a controlled dispersion diffractive surface is defined by the following equation:

[0033]

[0034] Here, the reference wavelength is the d-line (λ d =0.58756μm), the main dispersion is F line (λ F =0.48613μm) and C line (λ C =0.65627 μm), and ψ(λ d ),ψ(λ F ) and ψ(λ C ) is the optical path difference function of the corresponding wavelength. d ), P(λ F ) and P(λ C ) is the optical path difference dispersion of the surface for the corresponding wavelength.

[0035] As described above, the optical system according to each example includes a DOE having a positive refractive power, a convex refractive surface located on the object side, and a controlled dispersion diffractive surface located on the image side. The converging effect of light due to the positive refractive power promotes the size reduction of the optical system. The controlled dispersion diffractive surface can effectively correct chromatic aberration and provide high optical performance with a small number of lenses.

[0036] In addition, the optical system according to each example includes a second lens having a negative refractive power. The second lens can contribute to high optical performance by correcting various aberrations (mainly monochromatic aberration) generated in the DOE having a positive refractive power.

[0037] Inequality (1) defines conditions for effectively correcting chromatic aberration using a diffractive surface with controlled dispersion and for providing high optical performance using a small number of lenses. In the case where the negative Abbe number becomes too highly dispersed so that 1 / ν0 becomes lower than the lower limit of inequality (1), the chromatic aberration generated by the diffractive surface with controlled dispersion becomes too large, and it becomes difficult to increase the refractive power of the diffractive surface and to reduce the size of the optical system. It also becomes difficult to correct chromatic aberration and it is difficult to provide high optical performance. In the case where the positive Abbe number becomes too highly dispersed so that 1 / ν0 becomes higher than the upper limit of inequality (1), the chromatic aberration generated by the diffractive surface with controlled dispersion becomes too large, and it becomes difficult to increase the refractive power of the diffractive surface and to reduce the size of the optical system. It also becomes difficult to correct chromatic aberration and it is difficult to provide high optical performance.

[0038] Inequality (1) can be replaced by the following inequality (1a):

[0039] -0.10<1 / ν0<0.02(1a)

[0040] Inequality (1) can be replaced by the following inequality (1b):

[0041] -0.100<1 / ν0<0.01(1b)

[0042] The optical system according to each example may satisfy at least one of the following inequalities (2) to (8):

[0043] The following inequality (2) can be satisfied:

[0044] 0.3 < f1 / f < 0.8 (2)

[0045] where f1 is the focal length of the DOE with positive refractive power, and f is the focal length of the entire optical system.

[0046] Inequality (2) defines a condition for easily providing an optical system with reduced size and high optical performance. In the case where f1 / f becomes lower than the lower limit of inequality (2), the focal length of DOE becomes too short, and it becomes difficult to provide high optical performance. In the case where f1 / f becomes higher than the upper limit of inequality (2), the focal length of DOE becomes too long, and it becomes difficult to reduce the size of the optical system.

[0047] Inequality (2) can be replaced by the following inequality (2a):

[0048] 0.4 <f1 / f<0.7(2a)

[0049] Inequality (2) can be replaced by the following inequality (2b):

[0050] 0.45 <f1 / f<0.65(2b)

[0051] The following inequality (3) can be satisfied:

[0052] 2.5 < f moe / f < 10.0 (3)

[0053] where f moe is the focal length of the dispersion controlled diffractive surface, and f is the focal length of the entire optical system.

[0054] The focal length f of the controlled dispersion diffractive surface is calculated by the following equation: moe :

[0055]

[0056] where U2 is the quadratic coefficient of the optical path difference function of the surface at the design wavelength.

[0057] Inequality (3) defines a condition for easily providing an optical system with reduced size and high optical performance. moe In the case where / f becomes lower than the lower limit of inequality (3), the focal length of the dispersion-controlled diffraction surface becomes too short, large aberrations such as spherical aberration occur, and it becomes difficult to achieve high optical performance. moe In the case where / f becomes higher than the upper limit of the inequality (3), the focal length of the dispersion-controlled diffraction surface becomes too long, and it becomes difficult to reduce the size of the optical system.

[0058] Inequality (3) can be replaced by the following inequality (3a):

[0059] 3.0 <f moe / f<9.7(3a)

[0060] Inequality (3) can be replaced by the following inequality (3b):

[0061] 4.0 <f moe / f<9.4(3b)

[0062] The following inequality (4) can be satisfied:

[0063] 0.6 < TL / f < 0.9 (4)

[0064] Here, TL is the distance on the optical axis from the lens surface closest to the object to the image plane (hereinafter referred to as the total lens length).

[0065] Inequality (4) defines a condition for easily providing an optical system with reduced size and high optical performance. In the case where TL / f becomes lower than the lower limit of inequality (4), the total lens length becomes too short, large aberrations such as spherical aberration are generated, and it becomes difficult to obtain high optical performance. In the case where TL / f becomes higher than the upper limit of inequality (4), the total lens length becomes too long, and it becomes difficult to reduce the size of the optical system.

[0066] Inequality (4) can be replaced by the following inequality (4a):

[0067] 0.70 <TL / f<0.88(4a)

[0068] Inequality (4) can be replaced by the following inequality (4b):

[0069] 0.75 <TL / f<0.86(4b)

[0070] The optical system according to each example may include the above-mentioned first optical element (hereinafter referred to as the first DOE) as a DOE having positive refractive power (and disposed closest to the object) and the above-mentioned second optical element (hereinafter referred to as the second lens) as a lens having negative refractive power, in order from the object side to the image side. As described above, the first DOE is a DOE having positive refractive power, a convex refractive surface located on the object side, and a dispersion-controlled diffractive surface located on the image side. Due to this arrangement, the first DOE can effectively converge light while appropriately correcting various aberrations such as chromatic aberration. The second lens with negative refractive power can easily provide high optical performance by correcting various aberrations (mainly monochromatic aberration) generated by the DOE with positive refractive power.

[0071] The following inequality (5) can be satisfied:

[0072] 0.08 < D12 / TL < 0.40 (5)

[0073] Where D12 is the air gap on the optical axis between the first DOE with positive refractive power and the second lens with negative refractive power.

[0074] Inequality (5) defines a condition for easily providing an optical system with reduced size and high optical performance. In the case where the air gap D12 is too short so that D12 / TL becomes lower than the lower limit of inequality (5), it becomes difficult to sufficiently converge the on-axis marginal light by the first DOE and make it enter the second lens. As a result, it becomes difficult to obtain high optical performance by correcting various aberrations such as spherical aberration and coma aberration by imparting a strong negative refractive power to the second lens. In the case where the air gap D12 is too long so that D12 / TL becomes higher than the upper limit of inequality (5), it becomes difficult to reduce the size of the optical system.

[0075] Inequality (5) can be replaced by the following inequality (5a):

[0076] 0.10 <D12 / TL<0.30(5a)

[0077] Inequality (5) can be replaced by the following inequality (5b):

[0078] 0.11 <D12 / TL<0.25(5b)

[0079] The following inequality (6) can be satisfied:

[0080] 0.15 < D23 / TL < 0.50 (6)

[0081] Wherein D23 is an air gap on the optical axis between the second lens having negative refractive power and a third optical element (hereinafter referred to as the third lens) serving as a lens disposed on the image side of the second lens and adjacent to the second lens.

[0082] Inequality (6) defines a condition for easily providing an optical system with reduced size and high optical performance. In the case where the air gap D23 becomes too short so that D23 / TL becomes lower than the lower limit of inequality (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 to correct aberrations, and it is difficult to provide high optical performance. In the case where the air gap D23 becomes too long so that D23 / TL becomes higher than the upper limit of inequality (6), it becomes difficult to reduce the size of the optical system.

[0083] Inequality (6) can be replaced by the following inequality (6a):

[0084] 0.18 <D23 / TL<0.40(6a)

[0085] Inequality (6) can be replaced by the following inequality (6b):

[0086] 0.20 <D23 / TL<0.35(6b)

[0087] The following inequality (7) can be satisfied:

[0088] 0.20 < L02 / TL < 0.45 (7)

[0089] Where L02 is the distance on the optical axis from the lens surface of the optical system closest to the object to the lens surface of the second lens closest to the object.

[0090] Inequality (7) defines a condition for easily providing an optical system with high optical performance. When the distance L02 becomes too short so that L02 / TL becomes lower than the lower limit of inequality (7), the second lens becomes too close to the first lens. As a result, it becomes difficult to make the entire optical system have a concentric shape relative to the second lens as the center, and it becomes difficult to correct various aberrations such as field curvature and distortion. When the distance L02 becomes too long so that L02 / TL becomes higher than the upper limit of inequality (7), the second lens becomes too close to the lens on the image side. As a result, it becomes difficult to make the entire optical system have a concentric shape relative to the second lens as the center, and it becomes difficult to correct various aberrations such as field curvature and distortion.

[0091] Inequality (7) can be replaced by the following inequality (7a):

[0092] 0.24 <L02 / TL<0.40(7a)

[0093] Inequality (7) can be replaced by the following inequality (7b):

[0094] 0.26 <L02 / TL<0.36(7b)

[0095] The following inequality (8) can be satisfied:

[0096] -1.5 < fG3 / f < -0.4 (8)

[0097] Wherein fG3 is the focal length of the third lens with negative refractive power disposed on the image side of the second lens with negative refractive power and adjacent to the second lens.

[0098] Inequality (8) defines a condition for easily providing an optical system with reduced size and high optical performance. In the case where the focal length fG3 is too long so that fG3 / f becomes lower than the lower limit of inequality (8), the effect of changing the direction of light by the third lens becomes too weak, and it becomes difficult for the third lens to effectively correct various aberrations such as field curvature and distortion. In the case where the focal length fG3 becomes too long so that fG3 / f becomes higher than the upper limit of inequality (8), the light converging effect of the third lens becomes too strong, and it becomes difficult to reduce the total length of the optical system.

[0099] Inequality (8) can be replaced by the following inequality (8a):

[0100] -1.0 <fG3 / f<-0.5(8a)

[0101] Inequality (8) can be replaced by the following inequality (8b):

[0102] -0.70 <fG3 / f<-0.55(8b)

[0103] The optical system according to each example can include, in sequence from the object side to the image side, a first DOE having positive refractive power (and disposed closest to the object), a second lens having negative refractive power, a third lens having aspherical surfaces on both sides, and a fourth optical element (fourth lens) having aspherical surfaces on both sides.

[0104] The first DOE with positive refractive power and the second lens with negative refractive power arranged in sequence from the object side can effectively use the first DOE to converge light and appropriately correct various aberrations such as chromatic aberration. The second lens with negative refractive power next to the first DOE with positive refractive power can easily provide high optical performance by correcting various aberrations (mainly monochromatic aberration) generated by the first DOE. The third lens with aspherical surfaces on both sides and the fourth lens with aspherical surfaces on both sides can provide high optical performance with a small number of (ie, four) lenses.

[0105] Now, a specific description will be given of the optical system L according to Examples 1 to 5. Following Example 5, Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively, will be illustrated.

[0106] In each numerical example, the surface number i represents the order of the surface counted from the object side. r represents the paraxial curvature radius (mm) of the i-th optical surface (i-th surface), and d represents the axial distance (lens thickness or air gap) along the optical axis between the i-th surface and the (i+1)-th surface (mm). nd and vd represent the refractive index of the material of the i-th optical member for the d-line and the Abbe number based on the d-line, respectively.

[0107] The Abbe number νd based on the d-line is expressed as:

[0108] νd=(Nd-1) / (NF-NC)

[0109] Where Nd, NF and NC are the refractive indices for the d line (587.6 nm), F line (486.1 nm) and C line (656.3 nm) among the Fraunhofer lines. The effective diameter represents the radius (mm) of the region on the i-th surface through which the light that contributes to imaging passes.

[0110] BF represents the back focal length (mm). The back focal length is the distance on the optical axis from the rearmost surface (lens surface closest to the image plane) of the zoom lens to the paraxial image plane expressed by the air equivalent length. The total lens length is the distance on the optical axis from the frontmost surface (lens surface closest to the object) to the rearmost surface of the zoom lens plus the back focal length, and corresponds to TL in inequalities (4) to (7).

[0111] The asterisk "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following expression:

[0112] 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

[0113] Where x is the displacement relative to the surface vertex in the optical axis direction, h is the height from the optical axis in the direction orthogonal to the optical axis, the light travel direction is set to be positive, R is the paraxial curvature radius, k is the cone constant, and A4 to A10 are aspheric coefficients. e±M in the cone constant and aspheric coefficient means ×10 ±M .

[0114] The optical path difference function of the surface at the design wavelength is expressed by the following expression:

[0115] ψ0=U2·h 2 +U4·h 4 +U6·h 6 +U8·h 8 +U10·h 10

[0116] Where U2 to U10 are the optical path difference function coefficients of the surface.

[0117] (Diffraction) appended to the surface number indicates that the surface is optically designed using the optical path difference function of the surface.

[0118] Table 1 summarizes the values ​​of Numerical Examples 1 to 5 related to Inequalities (1) to (8).

[0119] Example 1

[0120] Figure 1The optical system L according to Example 1 (Numerical Example 1) illustrated in FIG. 1 is an optical system having 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 includes, in order from the object side to the image side, a first DOEL1 having a positive refractive power, an aperture stop SP, a second lens L2 having a negative refractive power, and a third lens unit L3.

[0121] The first DOE L1 is a DOE having a convex refractive surface on the object side and a controlled dispersion diffractive surface on the image side. The second lens L2 has aspheric surfaces and paraxial biconcave lens surfaces on both sides. The third lens unit L3 includes a third lens and a fourth lens in order from the object side to the image side, the third lens having negative refractive power, a paraxial biconcave lens surface and aspheric surfaces on both sides, and the fourth lens having positive refractive power, a convex paraxial meniscus shape on the image side and aspheric surfaces on both sides.

[0122] Example 2

[0123] Figure 3 The optical system L according to Example 2 (Numerical Example 2) illustrated in FIG. 1 is an optical system having 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 includes, in order from the object side to the image side, a first DOEL1 having a positive refractive power, an aperture stop SP, a second lens L2 having a negative refractive power, and a third lens unit L3.

[0124] The first DOE L1 is a DOE having a convex refractive surface on the object side and a controlled dispersion diffractive surface on the image side. The second lens L2 has aspheric surfaces and paraxial biconcave lens surfaces on both sides. The third lens unit L3 includes a third lens and a fourth lens in order from the object side to the image side, the third lens having negative refractive power, a paraxial biconcave lens surface and aspheric surfaces on both sides, and the fourth lens having negative refractive power, a convex paraxial meniscus shape on the image side and aspheric surfaces on both sides.

[0125] Example 3

[0126] Figure 5 The optical system L according to Example 3 (Numerical Example 3) illustrated in FIG. 1 is an optical system having 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 includes, in order from the object side to the image side, a first DOEL1 having a positive refractive power, an aperture stop SP, a second lens L2 having a negative refractive power, and a third lens unit L3.

[0127] The first DOE 1 is a DOE having a convex refractive surface on the object side and a controlled dispersion diffractive surface on the image side. The second lens L2 has aspheric surfaces and paraxial biconcave lens surfaces on both sides. The third lens unit L3 includes a third lens and a fourth lens in order from the object side to the image side, the third lens having negative refractive power, a paraxial biconcave lens surface and aspheric surfaces on both sides, and a fourth lens having positive refractive power, a convex paraxial meniscus shape on the image side and aspheric surfaces on both sides.

[0128] Example 4

[0129] Figure 7 The optical system L according to Example 4 (Numerical Example 4) illustrated in FIG. 1 is an optical system having 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 includes, in order from the object side to the image side, a first DOEL1 having a positive refractive power, an aperture stop SP, a second lens L2 having a negative refractive power, and a third lens unit L3.

[0130] Similar to Example 1, the first DOE L1 is a DOE having a convex refractive surface on the object side and a dispersion-controlled diffractive surface on the image side. The second lens L2 has aspheric surfaces and paraxial biconcave lens surfaces on both sides. The third lens unit L3 includes, in order from the object side to the image side, a third lens having negative refractive power, a paraxial biconcave lens surface, and aspheric surfaces on both sides, and a fourth lens having positive refractive power, a convex paraxial meniscus shape on the image side, and aspheric surfaces on both sides.

[0131] Example 5

[0132] Fig. 9 The optical system L according to Example 5 (Numerical Example 5) illustrated in FIG. 1 is an optical system having 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 includes, in order from the object side to the image side, a first DOEL1 having a positive refractive power, an aperture stop SP, a second lens L2 having a negative refractive power, and a third lens unit L3.

[0133] Similar to Example 1, the first DOE L1 is a DOE having a convex refractive surface on the object side and a dispersion-controlled diffractive surface on the image side. The second lens L2 has aspheric surfaces and paraxial biconcave lens surfaces on both sides. The third lens unit L3 includes, in order from the object side to the image side, a third lens having negative refractive power, a paraxial biconcave lens surface, and aspheric surfaces on both sides, and a fourth lens having positive refractive power, a convex paraxial meniscus shape on the image side, and aspheric surfaces on both sides.

[0134] When imaging is performed using the optical system L according to each example, aberration correction can be performed by image processing. The optical path difference function of the DOE can be realized by a metalens having a so-called single-layer metasurface (where the metasurface is composed of a single layer) or a so-called layered metasurface (where the metasurface includes multiple layers). In this case, the metalens has a positive refractive power and a metasurface with controlled wavelength dispersion characteristics. The metalens can have a convex refractive surface located on the object side, and the metasurface can be deployed on the image side of the metalens.

[0135] Numerical Example 1

[0136] Unit: mm

[0137] Surface data

[0138]

[0139] Aspheric surface data

[0140] Surface 1

[0141] K=-8.37714e-01A4=9.67558e-03A6=-6.23630e-04A8=2.13482e-03

[0142] A10=-8.44847e-04

[0143] Second surface (diffraction surface)

[0144] Design wavelength 0.58756[μm]

[0145] U2=-9.76396e-03 U4=1.46160e-03 U6=1.78901e-03 U8=-1.02999e-03

[0146] U10=1.12524e-04

[0147] Surface optical path difference dispersion

[0148] P(λ)=12.24651·λ 10 -119.47404 λ 9 +698.9340 λ 8 -2720.50548 · λ 7 +

[0149] 7400.16189 λ 6 -14357.25933 · λ 5 +19873.45822 λ 4 -19240.96797 · λ 3+19240.96797 λ 2 -4807.97026·λ+847.47010

[0150] P(λ d )=1.000000e+00

[0151] P(λ C ) = 9.061342e-01

[0152] P(λ F )=1.194911e+00

[0153] Surface 4

[0154] K=-7.30312e+02A4=1.11548e-01A6=2.68473e-01A8=-1.02096e+00

[0155] A10=2.20808e+00A12=-2.77979e+00A14=1.80491e+00A16=-4.29895e-01

[0156] Surface 5

[0157] K=9.50000e+01A4=2.50245e-01A6=-9.99304e-02A8=1.82022e-01

[0158] A10=-2.06303e-01

[0159] Surface 6

[0160] K=3.71573e+00A4=-3.10316e-01A6=-1.39954e-01A8=1.08852e+00

[0161] A10=-1.59622e+00A12=1.13582e+00A14=-4.07725e-01A16=6.09779e-02

[0162] Surface 7

[0163] K=5.66804e+01A4=-3.59989e-01A6=2.81360e-01A8=-1.32968e-01

[0164] A10=3.00410e-02A12=-3.03550e-03A14=1.94204e-04

[0165] Surface 8

[0166] K=-7.61381e+00A4=2.25923e-02A6=-1.53447e-02A8=1.29023e-03

[0167] A10=1.54000e-03A12=-3.07319e-04

[0168] Surface 9

[0169] K=-3.68987e+00A4=-2.79819e-03A6=-1.52162e-03A8=-3.47584e-03

[0170] A10=2.02821e-03A12=-2.65856e-04

[0171] Various data

[0172]

[0173] Single lens data

[0174]

[0175] Numerical Example 2

[0176] Unit: mm

[0177] Surface data

[0178]

[0179] Aspheric surface data

[0180] Surface 1

[0181] K=-9.18376e-01A4=1.89471e-02A6=1.09143e-03A8=1.87832e-03

[0182] A10=-2.95422e-03

[0183] Second surface (diffraction surface)

[0184] Design wavelength 0.58756[μm]

[0185] U2=-1.00142e-02 U4=7.40658e-03 U6=-1.02452e-02U8=7.55762e-03

[0186] U10=-2.62698e-03

[0187] Surface optical path difference dispersion

[0188] P(λ) = 13.87546·λ 10 - 153.95668·λ 9 + 1009.95630·λ 8 - 4356.52716·λ 7 +

[0189] 13006.44877·λ 6 - 27470.79737·λ 5 + 41106.88437·λ 4 - 42762.08537·λ 3 + 29486.82651·λ 2 - 12144.39247·λ + 2266.41068

[0190] P(λ d ) = 1.000000e+00

[0191] P(λ C ) = 9.155559e - 01

[0192] P(λ F ) = 1.184181e+00

[0193] Fourth surface

[0194] K = - 2.71665e+02 A4 = 2.02763e - 01 A6 = - 7.20641e - 02 A8 = 8.04897e - 01

[0195] A10 = - 3.05427e+00 A12 = 5.29501e+00 A14 = - 4.14210e+00 A16 = 1.19528e+00

[0196] Fifth surface

[0197] K = 4.89253e - 01 A4 = 2.25750e - 01 A6 = 6.27068e - 01 A8 = - 1.60141e+00

[0198] A10 = 1.82728e+00

[0199] Sixth surface

[0200] K = 2.66010e+00 A4 = - 3.37434e - 01 A6 = - 2.07792e - 01 A8 = 1.03514e+00

[0201] A10=-1.74754e+00A12=1.26306e+00A14=-1.36633e-01A16=-8.95322e-02

[0202] Surface 7

[0203] K=2.89242e+01A4=-3.42912e-01A6=1.98866e-01A8=-9.07270e-02

[0204] A10=7.20873e-03A12=8.78904e-03A14=-1.68521e-03

[0205] Surface 8

[0206] K=-5.53855e+00A4=5.40644e-03A6=7.17144e-03A8=-6.11534e-04

[0207] A10=3.80971e-04A12=-1.54203e-04

[0208] Surface 9

[0209] K=-1.10259e+01A4=-7.33408e-02A6=2.34943e-02A8=-1.14536e-03

[0210] A10=1.23043e-04A12=-8.25915e-05

[0211] Various data

[0212]

[0213]

[0214] Single lens data

[0215] Numerical example 3 Unit: mm Surface data

[0216]

[0217] Aspherical surface data 1st surface

[0218] K=3.28784e-01A4=-1.12717e-02A6=-1.16474e-03A8=-5.88116e-04

[0219] A10=-7.58421e-05

[0220] Second surface (diffraction surface)

[0221] Design wavelength 0.58756[μm]

[0222] U2=-1.24211e-02 U4=-9.93242e-04 U6=1.10002e-03 U8=-5.79917e-04

[0223] U10=1.48671e-04

[0224] Surface optical path difference dispersion

[0225] P(λ)=11.97801·λ 10 -113.77083 · λ 9 +647.33574 λ 8 -2448.35587 · λ 7 +

[0226] 6465.34198 λ 6 -12165.39383 · λ 5 +16315.44261 λ 4 -15288.88750 · λ 3 +9538.09656 λ 2 -3567.44539·λ+606.61668

[0227] P(λ d )=1.000000e+00

[0228] P(λ C ) = 9.046900e-01

[0229] P(λ F )=1.196528e+00

[0230] Surface 4

[0231] K=-7.12739e+02A4=1.93928e-02A6=3.10222e-01A8=-9.88060e-01

[0232] A10=2.03483e+00A12=-2.53536e+00A14=1.71781e+00A16=-4.81247e-01

[0233] Surface 5

[0234] K=7.49263e+01A4=1.33691e-01A6=-4.90895e-02A8=7.52699e-02

[0235] A10 = -6.37695e-02

[0236] Surface 6

[0237] K=4.03729e+01A4=-2.72142e-01A6=-1.27746e-01A8=8.56983e-01

[0238] A10=-1.36860e+00A12=1.08218e+00A14=-4.25757e-01A16=6.72854e-02

[0239] Surface 7

[0240] K=8.34119e+00A4=-3.52878e-01A6=2.40338e-01A8=-1.18592e-01

[0241] A10=2.59296e-02A12=1.55307e-03A14=-1.08217e-03

[0242] Surface 8

[0243] K=2.04857e+00A4=3.67846e-02A6=4.39495e-03A8=-1.50198e-03

[0244] A10=2.19341e-04A12=1.74466e-05

[0245] Surface 9

[0246] K=-8.24113e-02A4=3.88049e-02A6=2.10572e-03A8=-1.59372e-03

[0247] A10=3.89306e-04A12=-3.30176e-05

[0248] Various data

[0249]

[0250]

[0251] Single lens data

[0252] Numerical example 4 Unit: mm Surface data

[0253]

[0254] Aspheric surface data

[0255] Surface 1

[0256] K=2.78962e-01A4=-9.97081e-03A6=-1.16477e-03A8=-6.47121e-04

[0257] A10=-2.00577e-07

[0258] Second surface (diffraction surface)

[0259] K=2.28097e+04

[0260] Design wavelength 0.58756[μm]

[0261] U2=-1.21838e-02 U4=1.63050e-04 U6=2.16299e-04 U8=-1.70898e-04

[0262] U10=7.75164e-05

[0263] Surface optical path difference dispersion

[0264] P(λ)=-434.73044·λ 10 +8122.08910 λ 9 -67394.74965 · λ 8 +

[0265] 329209.06586 · λ 7 -1049750.44998 · λ 6 +2284260.64803 · λ 5 -3435917.19850 · λ 4 +3528102.09277 · λ 3 -2367044.44179 · λ 2 +937029.43952·λ-166209.30017

[0266] P(λ d )=1.000000e+00

[0267] P(λ C ) = 9.218523e-01

[0268] P(λ F )=1.177345e+00

[0269] Surface 4

[0270] K=-3.94370e+03A4=3.63831e-02A6=3.04246e-01A8=-1.00699e+00

[0271] A10=2.05779e+00A12=-2.51896e+00A14=1.67922e+00A16=-4.64464e-01

[0272] Surface 5

[0273] K=4.21306e+01A4=1.19464e-01A6=-1.17085e-02A8=4.56339e-03

[0274] A10=-1.28123e-02

[0275] Surface 6

[0276] K=2.25807e+01A4=-2.40989e-01A6=-1.20292e-01A8=8.48864e-01

[0277] A10=-1.36495e+00A12=1.07826e+00A14=-4.25456e-01A16=6.78933e-02

[0278] Surface 7

[0279] K=1.01704e+01A4=-3.33795e-01A6=2.36754e-01A8=-1.18145e-01

[0280] A10=2.50599e-02A12=1.71424e-03A14=-1.05420e-03

[0281] Surface 8

[0282] K=3.74014e+00A4=-3.44508e-03A6=1.14067e-02A8=-2.17872e-03

[0283] A10=4.85615e-04A12=-5.30278e-05

[0284] Surface 9

[0285] K=3.93746e-02A4=2.66395e-02A6=-1.24811e-03A8=1.05063e-04

[0286] A10=1.52986e-04A12=-2.06204e-05

[0287] Various data

[0288]

[0289]

[0290] Single lens data

[0291] Numerical example 5 Unit: mm Surface data

[0292]

[0293]

[0294] Aspheric surface data

[0295] Surface 1

[0296] K=-8.31081e-01A4=9.86364e-03A6=-4.96299e-04A8=2.14642e-03

[0297] A10=-8.10108e-04

[0298] Second surface (diffraction surface)

[0299] K=8.39004e+05

[0300] Design wavelength 0.58756[μm]

[0301] U2=-9.57924e-03 U4=1.96827e-03 U6=1.84008e-03 U8=-1.04244e-03

[0302] U10=1.26614e-04

[0303] Surface optical path difference dispersion

[0304] P(λ)=0.58756 / λ

[0305] P(λ d )=1.000000e+00

[0306] P(λC ) = 8.953022e-01

[0307] P(λ F )=1.208648e+00

[0308] Surface 4

[0309] K=-7.78980e+02A4=1.13646e-01A6=2.67771e-01A8=-1.02350e+00

[0310] A10=2.21155e+00A12=-2.77374e+00A14=1.79686e+00A16=-4.32428e-01

[0311] Surface 5

[0312] K=9.50000e+01A4=2.51941e-01A6=-1.04642e-01A8=1.91332e-01

[0313] A10=-2.07083e-01

[0314] Surface 6

[0315] K=3.75305e+00A4=-3.17027e-01A6=-1.36568e-01A8=1.09289e+00

[0316] A10=-1.59737e+00A12=1.13434e+00A14=-4.07143e-01A16=6.08155e-02

[0317] Surface 7

[0318] K=4.07551e+01A4=-3.64478e-01A6=2.85375e-01A8=-1.33950e-01

[0319] A10=3.01960e-02A12=-2.92272e-03A14=1.40925e-04

[0320] Surface 8

[0321] K=-8.37675e+00A4=2.02048e-02A6=-1.49159e-02A8=1.26993e-03

[0322] A10=1.53299e-03A12=-3.05658e-04

[0323] Surface 9

[0324] K=-3.76863e+00A4=-2.11771e-03A6=-2.28008e-03A8=-3.46988e-03

[0325] A10=2.07880e-03A12=-2.72202e-04

[0326] Various data

[0327]

[0328]

[0329] Single lens data

[0330] Table 1

[0331]

[0332] Image pickup device

[0333] Fig.11 A digital still camera as an image pickup device using an optical system according to any of the above examples as an imaging optical system is illustrated. Reference numeral 20 denotes a camera body, and reference numeral 21 denotes an imaging optical system including any of the optical systems according to Examples 1 to 5. Reference numeral 22 denotes an image sensor such as a CCD sensor or a CMOS sensor that is built into the camera body 20 and is configured to capture an optical image (object image) formed by the imaging optical system 21. Reference numeral 23 denotes a recorder configured to record image data generated by processing an imaging signal from the image sensor 22, and reference numeral 24 denotes a rear display unit configured to display the image data.

[0334] The optical system according to each example can provide a camera with reduced size and high optical performance.The camera can be a single-lens reflex camera with a fast-turning mirror or a mirrorless camera without a fast-turning mirror.

[0335] Although the present disclosure has described example embodiments, it is to be understood that some embodiments are not limited to the disclosed embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

[0336] Each example may use a diffractive surface with controlled wavelength dispersion characteristics to provide an optical system with reduced size and high optical performance.

Claims

1. An optical system, comprising, from the object side to the image side, the following: a diffractive optical element having a positive refractive power and a diffractive surface having a controlled wavelength dispersion characteristic; and A lens having negative refractive power; It is characterized in that ν0 is the Abbe number of the diffraction surface, the reference wavelength is the d line, the main dispersion is the F line and the C line, ψ(λ d ),ψ(λ F ) and ψ(λ C ) are the optical path difference functions for d-line, F-line and C-line, respectively, P(λ d ), P(λ F ) and P(λ C ) are the optical path difference dispersions of the surface for d-line, F-line and C-line respectively, and the following equation is satisfied: and The following inequality is satisfied: -0.2<1 / ν0<0.

2.

2. The optical system according to claim 1, characterized in that The diffractive optical element has a convex refractive surface on the object side.

3. The optical system according to claim 1, characterized in that The diffractive surface is disposed on the image side of the diffractive optical element.

4. The optical system according to claim 1, characterized in that The following inequality is satisfied: 0.3 <f1 / f<0.8 Wherein f1 is the focal length of the diffractive optical element, and f is the focal length of the optical system.

5. The optical system according to claim 1, characterized in that The following equation is satisfied: where f moe is the focal length of the diffractive surface, and U2 is the quadratic coefficient of the optical path difference function of the surface at the design wavelength, and The following inequality is satisfied: 2.5<f moe / f<10.0 where f is the focal length of the optical system.

6. The optical system according to claim 1, characterized in that The following inequality is satisfied: 0.6 <TL / f<0.9 Where TL is the distance on the optical axis from the lens surface of the optical system closest to the object to the image plane, and f is the focal length of the optical system.

7. The optical system according to claim 1, characterized in that The first optical element serves as the diffractive optical element and is disposed closest to the object, and the second optical element serves as the lens.

8. The optical system according to claim 7, characterized in that The following inequality is satisfied: 0.08 <D12 / TL<0.40 Wherein 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 of the optical system closest to the object to the image plane.

9. The optical system according to claim 7, further comprising a third optical element as a lens disposed on the image side of the second optical element and adjacent to the second optical element, It is characterized in that The following inequality is satisfied: 0.15 <D23 / TL<0.50 Wherein 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 of the optical system closest to the object to the image plane.

10. The optical system according to claim 7, characterized in that The following inequality is satisfied: 0.20 <L02 / TL<0.45 Wherein L02 is the distance on the optical axis from the lens surface of the optical system closest to the object to the lens surface of the second optical element closest to the object, and TL is the distance on the optical axis from the lens surface of the optical system closest to the object to the image plane.

11. The optical system according to claim 7, characterized in that the optical system having a third optical element as a lens having a negative refractive power disposed on the image side of the second optical element and adjacent to the second optical element, Among them, the following inequality is satisfied: -1.5 <fG3 / f<-0.4 Wherein fG3 is the focal length of the third optical element, and f is the focal length of the optical system.

12. The optical system according to claim 1, further comprising, from the object side to the image side: A first optical element as the diffractive optical element, the first optical element being disposed closest to the object; as a second optical element of the lens; a third optical element having aspherical surfaces on both sides; and A fourth optical element has aspherical surfaces on both sides.

13. The optical system according to claim 12, characterized in that The third optical element has negative refractive power, Wherein, the fourth optical element has positive refractive power or negative refractive power.

14. An optical system, comprising, from the object side to the image side, A metalens having a positive refractive power and a metasurface having controlled wavelength dispersion properties; and A lens having negative refractive power; It is characterized in that ν0 is the Abbe number of the metasurface, the reference wavelength is the d line, the main dispersion is the F line and the C line, ψ(λ d ),ψ(λ F ) and ψ(λ C ) are the optical path difference functions for d-line, F-line and C-line, respectively, P(λ d ), P(λ F ) and P(λ C ) are the optical path difference dispersions of the surface for d-line, F-line and C-line respectively, and the following equation is satisfied: and The following inequality is satisfied: -0.2<1 / ν0<0.

2.

15. The optical system according to claim 14, characterized in that The superlens has a convex refractive surface on the object side.

16. The optical system according to claim 14, characterized in that The metasurface is disposed on the image side of the metalens.

17. An image pickup device, comprising: An optical system according to any one of claims 1 to 16; and An image sensor is configured to capture an image of an object through the optical system.

Images