OPTICAL SYSTEM AND IMAGE ACQUISITIONING DEVICE

Abstract

An optical system (L) comprises, in the order from one object side to one image side, a diffracting optical element (L1) with positive refractive power, a diffraction surface with a controlled wavelength dispersion characteristic, and a lens (L2) with negative refractive power. A predetermined inequality is satisfied.

Description

BACKGROUNDTechnical field

[0001] One of the aspects of the embodiments relates to an optical system or optics system suitable for an image recording device, such as a digital camera. Description of the state of the art

[0002] As an optical system for a small camera attached to a smartphone, US Patent No. 10989901 discloses a teletype optical system consisting of six lenses, wherein a first lens with strong positive refractive power is positioned closest to an object. US Patent Publication No. 2021 / 0132256 discloses an optical system consisting of a first lens with positive refractive power and a convex shape facing one side of an object and positioned closest to an object, and a second lens with negative chromatic aberration, which includes a metasurface lens. International Patent Publication No.WO2021 / 170417 discloses an optical system comprising a first lens having strong positive refractive power and positioned closest to the object, and a diffracting optical element (DOE) with at least one surface having an uncontrolled wavelength dispersion characteristic, wherein a focal length and overall length of the optical system as well as a focal length of the DOE are suitably adjusted for size reduction.

[0003] These optical systems contain a first lens with strong positive refractive power, positioned closest to the object. This configuration is effective in reducing the overall length of the optical system, but the first lens introduces strong chromatic and monochromatic aberrations. Therefore, multiple lenses, including an aspherical lens with negative refractive power, correct various aberrations, such as chromatic aberration.

[0004] In a case where the first lens has a strong positive refractive power, it is effective to use a diffraction surface with a negative Abbe number primarily to correct chromatic aberration, thus reducing the overall length and correcting aberrations with a small number of lenses. However, the Abbe number of a normal diffractive surface with an uncontrolled wavelength dispersion characteristic exhibits extremely high dispersion, and therefore this diffraction surface with refractive power (the reciprocal of the focal length) produces strong chromatic aberration. Thus, it is difficult to achieve both a compact optical system and high image quality by reducing the number of lenses. SUMMARY

[0005] The present disclosure in its first aspect provides an optical system as specified in claims 1 to 16.

[0006] The present disclosure in its second aspect provides an image recording device as specified in claim 17.

[0007] Further features of the disclosure will become apparent from the following description of embodiments with reference to the accompanying drawings. Each of the embodiments of the present invention described below can be implemented alone or as a combination of several embodiments. Features of different embodiments can also be combined where necessary or where the combination of elements or features of individual embodiments in a single embodiment is advantageous. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a sectional view of an optical system according to Example 1. Fig. Figure 2 is an aberration diagram of the optical system according to Example 1. Fig.Figure 3 is a sectional view of an optical system according to Example 2. Fig. Figure 4 is an aberration diagram of the optical system according to Example 2. Fig. Figure 5 is a sectional view of an optical system according to Example 3. Fig. Figure 6 is an aberration diagram of the optical system according to Example 3. Fig. Figure 7 is a sectional view of an optical system according to Example 4. Fig. Figure 8 is an aberration diagram of the optical system according to Example 4. Fig. Figure 9 is a sectional view of an optical system according to Example 5. Fig. Figure 10 is an aberration diagram of the optical system according to Example 5. Fig. Figure 11 is a diagram illustrating an image acquisition device which uses the optical system according to one of the examples above. DESCRIPTION OF THE EXECUTION FORMS

[0008] With reference to the accompanying drawings, embodiments according to the disclosure will now be described. First, features common to each example will be described before specific examples 1 to 5 are described. Fig. 1, Fig. 3, Fig. 5, Fig. 7 and Fig.Figure 9 illustrates the configurations of optical systems L according to Examples 1 to 5. O represents an optical axis of the optical system L. MOE represents a diffracting optical element (DOE) containing a diffraction surface with a controlled wavelength dispersion characteristic (hereafter referred to simply 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 (diaphragm), and GB represents a glass block containing an infrared blocking filter, a low-pass filter, etc. IP represents an image plane of the optical system L. On the image plane IP, an imaging surface (light-receiving surface) of an image sensor, such as a CCD sensor or a CMOS sensor, or a film plane (light-sensitive surface) of a silver film is arranged. Fig. 2, Fig. 4, Fig. 6, Fig. 8 and Fig.Figure 10 illustrates diagrams of the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems according to numerical examples 1 to 5, corresponding to examples 1 to 5, in a focused state with respect to an object at infinity (hereinafter referred to as "in the focused state at infinity"). A vertical axis Fno of each diagram for spherical aberration represents an f-stop, and a vertical axis ω of each diagram for astigmatism, distortion, and chromatic aberration represents half an angle of view (°). A horizontal axis represents a corresponding aberration magnitude.

[0009] In the spherical aberration diagram, a solid line represents the amount of spherical aberration for the d-line (wavelength 587.6 nm), and a line drawn with alternating long and twice short dashed lines represents spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, a solid line S represents the amount of astigmatism on a sagittal image plane, and a dashed line M represents the amount of astigmatism on a meridional image plane. The distortion diagrams illustrate the amount of distortion for the d-line. The chromatic aberration diagram illustrates the amount of lateral chromatic aberration for the g-line.

[0010] A description of the properties of the optical system will now be given according to a specific example, which has a reduced size, high optical performance and a small number of lenses.

[0011] The optical system according to each example comprises, in order from the object side to the image side, a DOE having positive refractive power and a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side, and a lens with negative refractive power. A lens or other optical element may be arranged on the object side of the DOE. The following inequality (1) is satisfied: −0.2<1 / v0<0.2 where v0 is an Abbe number of the diffraction area.

[0012] The Abbe number v0 of the dispersion-controlled diffraction area is defined by the following equation: 1v0≡ψ(λF)−ψ(λC)ψ(λd)=λFP(λF)−λCP(λC)λdP(λd)

[0013] Here, the reference wavelength is the d-line (λ). d = 0.58756 µm), the primary dispersion the F-line (λ F = 0.48613 µm) and the C-line (λ C = 0.65627 µm) and ψ(λ d ), ψ(λ F ) and ψ(λ C) optical path difference functions for the respective wavelengths. P(λ) d ), P(λ F ) and P(λ C ) are an optical path difference dispersion of the area for the respective wavelengths.

[0014] As described above, the optical system, according to each example, includes a DOE with positive refractive power, a convex refractive surface on the object side, and a dispersion-controlled diffraction surface on the image side. The convergence of the light rays due to the positive refractive power allows for a reduced size of the optical system. The dispersion-controlled diffraction surface can effectively correct chromatic aberration and provide high optical performance with a small number of lenses.

[0015] Furthermore, according to one example, the optical system includes a second lens with negative refractive power. This second lens can enhance optical performance by correcting various aberrations, primarily monochromatic aberrations, that are generated in a DOE with positive refractive power.

[0016] Inequality (1) defines a condition for effectively correcting chromatic aberration with a dispersion-controlled diffraction surface and providing high optical performance with a small number of lenses. In a case where the negative Abbe number is dispersed too strongly, such that 1 / v0 falls below the lower limit of inequality (1), the chromatic aberration produced by the dispersion-controlled diffraction surface becomes too large. It then becomes difficult to increase the refractive power of the diffraction surface and reduce the size of the optical system. It also becomes difficult to correct chromatic aberration and provide high optical performance.In a case where the positive Abbe number is dispersed too strongly, such that 1 / v0 exceeds the upper limit of inequality (1), the chromatic aberration generated by the dispersion-controlled diffraction surface becomes too large, and it becomes difficult to increase the refractive power of the diffraction surface and reduce the size of the optical system. It also becomes difficult to correct chromatic aberration and provide high optical performance.

[0017] Inequality (1) can be replaced with inequality (1a) below: −0.10<1 / v0<0.02

[0018] Inequality (1) can be replaced with inequality (1b) below: −0.100<1 / v0<0.01

[0019] The optical system according to each example can satisfy at least one of the following inequalities (2) to (8).

[0020] The following inequality (2) can be satisfied: 0.3 <f1 / f<0,8 where f1 is a focal length of a DOE with positive refractive power and f is a focal length of the entire optical system.

[0021] Inequality (2) defines a condition for easily providing an optical system that has a reduced size and high optical power. If f1 / f falls below the lower limit of inequality (2), the focal length of the DOE becomes too short, and it becomes difficult to provide high optical power. If f1 / f exceeds the upper limit of inequality (2), the focal length of the DOE becomes too long, and it becomes difficult to reduce the size of the optical system.

[0022] Inequality (2) can be replaced by inequality (2a) below: 0.4 <f1 / f<0,7

[0023] Inequality (2) can be replaced with inequality (2b) below: 0.45 <f1 / f<0,65

[0024] The following inequality (3) can be satisfied: 2.5 <fmoe / f<10,0 where f moe where f is a focal length of the dispersion-controlled diffraction area and f is a focal length of the entire optical system.

[0025] The focal length f moe The dispersion-controlled diffraction area is calculated using the following equation: 1fmoe=−2U2 where U2 is a quadratic coefficient of the optical path difference function of the area at a design wavelength.

[0026] Inequality (3) defines a condition for the simple provision of an optical system with reduced size and high optical power. In a case where f moeIf f falls below the lower limit of inequality (3), the focal length of the dispersion-controlled diffraction surface becomes too short, large aberrations such as spherical aberration are generated, and it becomes difficult to achieve high optical power. In a case where f moe / f exceeds the upper limit of 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.

[0027] Inequality (3) can be replaced by inequality (3a) below: 3.0 <fmoe / f<9,7

[0028] Inequality (3) can be replaced by inequality (3b) below: 4.0 <fmoe / f<9,4

[0029] The following inequality (4) can be satisfied: 0.6 <TL / f<0,9 where TL is a distance on the optical axis from a lens surface closest to the object to the image surface (hereinafter referred to as the total lens length).

[0030] Inequality (4) defines a condition for easily providing an optical system that has reduced size and high optical performance. If TL / f falls below the lower limit of inequality (4), the overall lens length becomes too short, large aberrations such as spherical aberration are introduced, and it becomes difficult to achieve high optical performance. If TL / f exceeds the upper limit of inequality (4), the overall lens length becomes too long, and it becomes difficult to reduce the size of the optical system.

[0031] Inequality (4) can be replaced by inequality (4a) below: 0.70 <TL / f<0,88

[0032] Inequality (4) can be replaced by inequality (4b) below: 0.75 <TL / f<0,86

[0033] The optical system, according to each example, can include, in order from the object side to the image side, a first optical element (hereinafter referred to as the first DOE) as a DOE with positive refractive power as described above (and located closest to the object), and a second optical element (hereinafter referred to as the second lens) as a lens with negative refractive power as described above. As described above, the first DOE is a DOE with positive refractive power, a convex refracting surface on the object side, and a dispersion-controlled diffraction surface on the image side. Because of this arrangement, the first DOE can effectively converge light rays while adequately 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 aberrations, which are produced by the DOE with positive refractive power.

[0034] The following inequality (5) can be satisfied: 0.08 <D12 / TL<0,40 where D12 is an air gap on the optical axis between the first DOE with positive refractive power and the second lens with negative refractive power.

[0035] Inequality (5) defines a condition for easily providing an optical system that has a reduced size and high optical performance. If the air gap D12 is too short, so that D12 / TL falls below the lower limit of inequality (5), it becomes difficult to sufficiently converge the marginal ray on the axis through the first DOE and allow it to enter the second lens. Consequently, it becomes difficult to achieve high optical performance by correcting various aberrations such as spherical aberration and coma by imparting strong negative refractive power to the second lens. If the air gap D12 is too long, so that D12 / TL exceeds the upper limit of inequality (5), it becomes difficult to reduce the size of the optical system.

[0036] Inequality (5) can be replaced by inequality (5a) below: 0.10 <D12 / TL<0,30

[0037] Inequality (5) can be replaced with inequality (5b) below: 0.11, <D12 / TL<0,25

[0038] The following inequality (6) may be satisfied: 0.15 <D23 / TL<0,50 where D23 is an air gap on the optical axis between the second lens with negative refractive power and the third optical element (hereinafter referred to as the third lens), which serves as a lens located on the image side of and adjacent to the second lens.

[0039] Inequality (6) defines a condition for easily providing an optical system that has a reduced size and high optical performance. If the air gap D23 becomes too short, so that D23 / TL falls below the lower limit of inequality (6), it becomes difficult to adequately separate an off-axis beam of light incident on the third lens. Consequently, it becomes difficult to effectively utilize an aspherical surface of the third lens to correct aberrations and provide high optical performance. If the air gap D23 becomes too long, so that D23 / TL exceeds the upper limit of inequality (6), it becomes difficult to reduce the size of the optical system.

[0040] Inequality (6) can be replaced by inequality (6a) below: 0.18 <D23 / TL<0,40

[0041] Inequality (6) can be replaced by inequality (6b) below: 0.20 <D23 / TL<0,35

[0042] The following inequality (7) can be satisfied: 0.20 <L02 / TL<0,45 where L02 is a distance on the optical axis from a lens surface of the optical system that is closest to the object to a lens surface of the second lens that is closest to the object.

[0043] Inequality (7) defines a condition for easily providing an optical system with high optical performance. If the distance L02 becomes too short, so that L02 / TL falls below the lower limit of inequality (7), the second lens is too close to the first lens. Consequently, it becomes difficult to ensure that the entire optical system has a concentric shape with respect to the second lens as its center, and it becomes difficult to correct various aberrations, such as field curvature and distortion. Conversely, if the distance L02 becomes too long, so that L02 / TL exceeds the upper limit of inequality (7), the second lens is too close to the image-side lens. Consequently, it becomes difficult to ensure that the entire optical system has a concentric shape with respect to the second lens as its center, and it becomes difficult to correct various aberrations, such as field curvature and distortion.

[0044] Inequality (7) can be replaced with inequality (7a) below: 0.24 <L02 / TL<0,40

[0045] Inequality (7) can be replaced by inequality (7b) below: 0.26 <L02 / TL<0,36

[0046] The following inequality (8) can be satisfied: −1.5 <fG3 / f<−0,4 where fG3 is a focal length of the third lens with negative refractive power, which is located on the image side of and adjacent to the second lens with negative refractive power.

[0047] Inequality (8) defines a condition for easily providing an optical system that has reduced size and high optical performance. If the focal length fG3 is too long, such that fG3 / f falls below the lower limit of inequality (8), the effect of the third lens to change the direction of light rays becomes too weak, and it becomes difficult for the third lens to effectively correct various aberrations, such as field curvature and distortion. If the focal length fG3 becomes too short, such that fG3 / f exceeds the upper limit of inequality (8), the light divergence effect of the third lens becomes too strong, and it becomes difficult to reduce the overall length of the optical system.

[0048] Inequality (8) can be replaced with inequality (8a) below: -1.0 <fG3 / F<−0,5

[0049] Inequality (8) can be replaced by inequality (8b) below: -0.70 <fG3 / f<−0,55

[0050] The optical system according to a given example can include, in order from the object side to the image side, a first DOE that has positive refractive power (and is located closest to the object), a second lens with negative refractive power, a third lens with aspherical surfaces on both sides, and a fourth optical element (fourth lens) with aspherical surfaces on both sides.

[0051] The first DOE with positive refractive power and the second lens with negative refractive power, arranged sequentially from the object side, effectively converge the light rays with the first DOE and adequately correct various aberrations, such as chromatic aberration. The second lens with negative refractive power, positioned next to the first DOE with positive refractive power, can easily provide high optical performance by correcting various aberrations, primarily monochromatic aberrations, introduced by the first DOE. A third lens with aspherical surfaces on both sides and a fourth lens with aspherical surfaces on both sides can provide high optical performance with a small number of lenses, namely four.

[0052] A specific description of the optical systems L according to Examples 1 to 5 will now be given. Following Example 5, numerical examples 1 to 5 will be illustrated in accordance with Examples 1 to 5.

[0053] In each numerical example, an area number i represents the sequence of surfaces counted from the object side. r represents a paraxial radius of curvature (mm) of an i-th optical surface (i-th surface), and d represents a distance on the axis (lens thickness or air gap) (mm) along the optical axis between the i-th and (i+1)-th surfaces. nd and vd represent a refractive index for the d-line of the material of the i-th optical element and the Abbe number based on the d-line, respectively.

[0054] The Abbe number vd based on the d-line is expressed as: vd=(Nd−1) / (NF−NC) 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) in the Fraunhofer line. An effective diameter represents a radius (mm) of a region on the i-th surface through which the light rays contributing to imaging pass.

[0055] BF represents a rear focal point (mm). The rear focal point is a distance on the optical axis from the rearmost surface of the zoom lens (the lens surface closest to the image plane) to a paraxial image surface, expressed as an air-equivalent length. The total lens length is a distance on the optical axis from the foremost surface of the zoom lens (the lens surface closest to the object) to the rearmost surface plus the rear focal point and corresponds to TL in inequalities (4) to (7).

[0056] An asterisk “*” appended to an area value indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following expression: x=(h2 / R) / [1+{1−(1+k)(h / R)2}1 / 2]+A4⋅h4+A6⋅h6+A8⋅h8+A10⋅h10 where x is a displacement from a surface vertex in the direction of the optical axis, h is a height from the optical axis in a direction orthogonal to the optical axis, one direction of light propagation is positive, R is a paraxial radius of curvature, k is a conic constant, and A4 to A10 are aspheric coefficients. e±M in the conic constant and the aspheric coefficients means ×10 ±M .

[0057] The optical path difference function of the surface at the design wavelength is expressed by the following expression: ψ0=U2⋅h2+U4⋅h4+U6⋅h6+U8⋅h8+U10⋅h10 where U2 to U10 are coefficients of the optical path difference function of the area.

[0058] The (diffraction) function appended to the area number represents an optically constructed area using the optical path difference function of the area.

[0059] Table 1 summarizes values ​​relating to inequalities (1) to (8) for numerical examples 1 to 5. Example 1

[0060] The in Fig. The illustrated optical system L according to Example 1 (numerical example 1) is an optical system with a focal length of 6.79 mm, an aperture number of 2.7, and a half angle of view of 21.83°. The optical system L comprises, in this order from the object side to the image side, a first DOE L1, which has positive refractive power, an aperture diaphragm SP, a second lens L2, which has negative refractive power, and a third lens unit L3.

[0061] The first DOE, L1, is a DOE that has a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side. The second lens, L2, has aspheric surfaces on both sides and paraxial biconcave lens surfaces. The third lens unit, L3, contains, in order from the object side to the image side, a third lens with negative refractive power, paraxial biconcave lens surfaces, and aspheric surfaces on both sides, and a fourth lens with positive refractive power, a paraxial meniscus shape that is convex on the image side, and aspheric surfaces on both sides. Example 2

[0062] The in Fig.The optical system L illustrated in Example 2 (numerical example 2) is an optical system with a focal length of 5.53 mm, an aperture of f-number of 2.5, and a half angle of view of 26.2°. The optical system L comprises, in this order from the object side to the image side, a first DOE L1, which has positive refractive power, an aperture diaphragm SP, a second lens L2, which has negative refractive power, and a third lens unit L3.

[0063] The first DOE, L1, is a DOE that has a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side. The second lens, L2, has aspheric surfaces on both sides and paraxial biconcave lens surfaces. The third lens unit, L3, contains, in order from the object side to the image side, a third lens with negative refractive power, paraxial biconcave lens surfaces, and aspheric surfaces on both sides, and a fourth lens with negative refractive power, a paraxial meniscus shape that is convex on the image side, and aspheric surfaces on both sides. Example 3

[0064] The in Fig.The optical system L illustrated in Example 3 (numerical example 3) is an optical system with a focal length of 8.70 mm, an aperture of f-number of 2.9, and a half-angle of view of 17.36°. The optical system L comprises, in this order from the object side to the image side, a first DOE L1, which has positive refractive power, an aperture diaphragm SP, a second lens L2, which has negative refractive power, and a third lens unit L3.

[0065] The first DOE 1 is a DOE that has a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side. The second lens L2 has aspheric surfaces on both sides and paraxial biconcave lens surfaces. The third lens unit L3 contains, in order from the object side to the image side, a third lens with negative refractive power, paraxial biconcave lens surfaces and aspheric surfaces on both sides, and a fourth lens with positive refractive power, a paraxial meniscus shape that is convex on the image side, and aspheric surfaces on both sides. Example 4

[0066] The in Fig.The illustrated optical system L according to Example 4 (numerical example 4) is an optical system with a focal length of 8.58 mm, an aperture number of 2.9, and a half angle of view of 17.59°. The optical system L comprises, in this order from the object side to the image side, a first DOE L1, which has positive refractive power, an aperture diaphragm SP, a second lens L2, which has negative refractive power, and a third lens unit L3.

[0067] Similar to Example 1, the first DOE L1 is a DOE that has a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side. The second lens L2 has aspheric surfaces on both sides and paraxial biconcave lens surfaces. The third lens unit L3 contains, in this order from the object side to the image side, a third lens with negative refractive power, paraxial biconcave lens surfaces and aspheric surfaces on both sides, and a fourth lens with positive refractive power, a paraxial meniscus shape that is convex on the image side, and aspheric surfaces on both sides. Example 5

[0068] The in Fig.The optical system L illustrated in Example 5 (numerical example 5) is an optical system with a focal length of 6.79 mm, an aperture of 2.7, and a half angle of view of 21.83°. The optical system L comprises, in this order from the object side to the image side, a first DOE L1, which has positive refractive power, an aperture diaphragm SP, a second lens L2, which has negative refractive power, and a third lens unit L3.

[0069] Similar to Example 1, the first DOE L1 is a DOE that has a convex refractive surface on the object side and a dispersion-controlled diffraction surface on the image side. The second lens L2 has aspheric surfaces on both sides and paraxial biconcave lens surfaces. The third lens unit L3 contains, in this order from the object side to the image side, a third lens with negative refractive power, paraxial biconcave lens surfaces and aspheric surfaces on both sides, and a fourth lens with positive refractive power, a paraxial meniscus shape that is convex on the image side, and aspheric surfaces on both sides.

[0070] In imaging using the optical system L, as described in the respective example, aberration correction can be performed by image processing. The optical path difference function of the DOE can be implemented using a metalens with a so-called single-layer metasurface, where the metasurface consists of a single layer, or a so-called layered metasurface, where the metasurface contains multiple layers. In this case, the metalens has a positive refractive power and a metasurface with a controlled wavelength dispersion characteristic. The metalens can have a convex refractive surface on the object side, and the metasurface can be located on the image side of the metalens. NUMERICAL EXAMPLE 1

[0071] UNIT: mm

[0072] AREA DATA Area number r d and vd Effective diameter 1* 1,684 0,81 1,43875 94,9 2,51 2 (Diffraction) ∞ 0,83 2,37 3 (SP) ∞ 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 1. Area

[0073] K = -8.37714e-01 A 4 = 9.67558e-03 A 6 = -6.23630e-04 A 8 = 2.13482e-03 A10=-8.44847e-04 2. Area (diffraction surface)

[0074] Design wavelength 0.58756 [µm] U2=-9.76396e-03 U4 = 1.46160e-03 U6 = 1.78901e-03 U8 = -1.02999e-03 U10=1.12524e-04 OPTICAL PATHWAY DIFFERENCE DISPERSION OF THE AREA P(λ)=12.24651⋅λ10−119.47404⋅λ9+698.9340⋅λ8−2720.50548⋅λ7+7400.16189⋅λ6−14357 .25933⋅λ5+19873.45822⋅λ4−19240.96797⋅λ3+19240.96797⋅λ2−4807.97026⋅λ+847.47010

[0075] P(λ d ) = 1.000000e+00

[0076] P(λ C ) = 9.061342e-01

[0077] P(λ F ) = 1.194911e+00 4. Area

[0078] 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 5. Area

[0079] K = 9.50000e+01 A 4 = 2.50245e-01 A 6 = -9.99304e-02 A 8 = 1.82022e-01 A10 = -2.06303e-01 6. Area

[0080] K = 3.71S73e+00 A 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 7. Area

[0081] 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 8. Area

[0082] 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 9. Area

[0083] 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 Fno 2,70 Half the angle of view (°) 21,83 Image height 2,72 Total lens length 5,69 BF 0,57 Entrance pupil position 2,21 Exit pupil position -5,42 Position of the front main point 1,08 Position of the rear main point -6,39 DATA OF INDIVIDUAL LENSES lens Launch area Focal length 1 1 3,61 2 4 -7,04 3 6 -4,42 4 8 5,55 NUMERICAL EXAMPLE 2 UNIT: mm AREA DATA Area number r d and vd Effective diameter 1* 1,386 0,77 1,43875 94,9 2,21 2 (Diffraction) ∞ 0,57 2,06 3 (SP) ∞ 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 1. Area

[0084] K = -9.18376e-01 A 4 = 1.89471e-02 A 6 = 1.09143e-03 A 8 = 1.87832e-03 A10 = -2.95422e-03 2. Area (diffraction surface)

[0085] 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 OPTICAL PATHWAY DIFFERENCE DISPERSION OF THE AREA P(λ)=13.87546⋅λ10−153.95668⋅λ9+1009.95630⋅λ8−4356.52716⋅λ7+13006.44877⋅λ6−27470 .79737⋅λ5+41106.88437⋅λ4−42762.08537⋅λ3+29486.82651⋅λ2−12144.39247⋅λ+2266.41068

[0086] P(λ d ) = 1.000000e+00

[0087] P(λ C ) = 9.155559e-01

[0088] P(λ F ) = 1.184181e+00 4. Area

[0089] K = -2.7166Se+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 5. Area

[0090] K = 4.89253e-01 A 4 = 2.25750e-01 A 6 = 6.27068e-01 A 8 = -1.60141e+00 A10 = 1.82728e+00 6. Area

[0091] 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 7. Area

[0092] 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 8. Area

[0093] 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 9. Area

[0094] 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 Fno 2,50 Half the angle of view (°) 26,20 Image height 2,72 Total lens length 4,59 BF 0,57 Entrance pupil position 1,73 Exit pupil position -2,19 Position of the front main point -4,53 Position of the rear main point -5,13 DATA OF INDIVIDUAL LENSES lens Launch area Focal length 1 1 3,00 2 4 -8,98 3 6 -3,37 4 8 -64,19 NUMERICAL EXAMPLE 3 UNIT: mm AREA DATA Area number r d and vd Effective diameter 1* 2,226 0,83 1,43875 94,9 3,00 2 (Diffraction) ∞ 1,43 2,87 3 (SP) ∞ 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 plane ∞ ASPHERICAL DATA 1. Area

[0095] K = 3.28784e-01 A 4 = -1.12717e-02 A 6 = -1.16474e-03 A 8 = -5.88116e-04 A10 = -7.58421e-05 2. Area (diffraction surface)

[0096] Design wavelength 0.58756 [µm]

[0097] U2 = -1.24211e-02 U4 = -9.93242e-04 U6 = 1.10002e-03 U8 = -5.79917e-04 U10 = 1.48671e-04 OPTICAL PATHWAY DIFFERENCE DISPERSION OF THE SURFACE P(λ)=11.97801⋅λ10−113.77083⋅λ9+647.33574⋅λ8−2448.35587⋅λ7+6465.34198⋅λ6−1216 5.39383⋅λ5+16315.44261⋅λ4−15288.88750⋅λ3+9538.09656⋅λ2−3567.44539⋅λ+606.61668

[0098] P(λ d ) = 1.000000e+00

[0099] P(λ C ) = 9.046900e-01

[0100] P(λ F ) = 1.196528e+00 4. Area

[0101] 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 5. Area

[0102] K = 7.49263e+01 A 4 = 1.33691e-01 A 6 = -4.90895e-02 A 8 = 7.52699e-02 A10 = -6.37695e-02 6. Area

[0103] 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 7. Area

[0104] 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 8. Area

[0105] 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 9. Area

[0106] 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 Fno 2,90 Half the angle of view (°) 17,36 Image height 2,72 Total lens length 7,27 BF 1,05 Entrance pupil position 3,46 Exit pupil position -5,58 Position of the front main point -0,50 Position of the rear main point -8,30 DATA OF INDIVIDUAL LENSES lens Launch area Focal length 1 1 4,56 2 4 -7,33 3 6 -5,86 4 8 7,85 NUMERICAL EXAMPLE 4

[0107] UNIT: mm AREA DATA Area number r d and vd Effective diameter 1* 2,246 0,81 1,43875 94,9 2,96 2 (Diffraction) -295,185 1,41 2,83 3 (SP) ∞ 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 1. Area

[0108] K = 2.78962e-01 A 4 = -9.97081e-03 A 6 = -1.16477e-03 A 8 = -6.47121e-04 A10 = -2.00577e-07 2. Area (diffraction surface)

[0109] K = 2.28097e+04

[0110] Design wavelength 0.58756 [µm]

[0111] U 2 = -1.21838e-02 U 4 = 1.63050e-04 U 6 = 2.16299e-04 U 8 = -1.70898e-04 U10 = 7.75164e-05 OPTICAL PATHWAY DIFFERENCE DISPERSION OF THE AREA P(λ)=−434.73044⋅λ10+8122.08910⋅λ9−67394.74965⋅λ8+329209.06586⋅λ7−1049750.44998⋅λ6+228426 0.64803⋅λ5−3435917.19850⋅λ4+3528102.09277⋅λ3−2367044.44179⋅λ2+937029.43952⋅λ−166209.30017

[0112] P(λ d ) = 1.000000e+00

[0113] P(λ C ) = 9.218523e-01

[0114] P(λ F ) = 1.177345e+00 4. Area

[0115] 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 5. Area

[0116] K = 4.21306e+01 A 4 = 1.19464e-01 A 6 = -1.17085e-02 A 8 = 4.56339e-03 A10 = -1.28123e-02 6. Area

[0117] 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 7. Area

[0118] 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 8. Area

[0119] K = 3.74014e+00 A 4 = -3.44508e-03 A 6 = 1.14067e-02 A 8 = -2.17872e-03 A10 = 4.85615e-04 A12 = -5.30278e-05 9. Area

[0120] 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 Fno 2,90 Half the angle of view (°) 17,59 Image height 2,72 Total lens length 7,15 BF 0,81 Entrance pupil position 3,34 Exit pupil position -5,71 Position of the front main point -0,13 Position of the rear main point -8,18 DATA OF INDIVIDUAL LENSES lens Launch area Focal length 1 1 4,61 2 4 -8,09 3 6 -5,48 4 8 7,37 NUMERICAL EXAMPLE 5 UNIT: mm AREA DATA Area number r d and vd Effective diameter 1* 1,679 0,81 1,43875 94,9 2,51 2 (Diffraction) -1201,658 0,80 2,37 3 (SP) ∞ 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 1. Area

[0121] K = -8.31081e-01 A 4 = 9.86364e-03 A 6 = -4.96299e-04 A 8 = 2.14642e-03 A10 = -8.10108e-04 2. Area (diffraction surface)

[0122] K = 8.39004e+05

[0123] Design wavelength 0.58756 [µm]

[0124] U 2 = -9.57924e-03 U 4 = 1.96827e-03 U 6 = 1.84008e-03 U 8 = -1.04244e-03 U10 = 1.26614e-04 OPTICAL PATHWAY DIFFERENCE DISPERSION OF THE AREA

[0125] P(λ) = 0.58756 / λ

[0126] P(λ d ) = 1.000000e+00

[0127] P(λ C ) = 8.953022e-01

[0128] P(λ F ) = 1.208648e+00 4. Area

[0129] 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 5. Area

[0130] K = 9.50000e+01 A 4 = 2.51941e-01 A 6 = -1.04642e-01 A 8 = 1.91332e-01 A10 = -2.07083e-01 6. Area

[0131] K = 3.75305e+00 A 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 7. Area

[0132] 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 8. Area

[0133] K = -8.3767Se+00 A 4 = 2.02048e-02 A 6 = -1.49159e-02 A 8 = 1.26993e-03 A10 = 1.53299e-03 A12 = -3.05658e-04 9. Area

[0134] 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 Fno 2,70 Half the angle of view (°) 21,83 Image height 2,72 Total lens length 5,69 BF 0,57 Entrance pupil position 2,16 Exit pupil position -5,42 Position of the front main point 1,02 Position of the rear main point -6,39 DATA OF INDIVIDUAL LENSES lens Launch area Focal length 1 1 3,60 2 4 -7,07 3 6 -4,31 4 8 5,50 IMAGE ACTING DEVICE

[0135] Fig.Figure 11 illustrates a digital still camera as an image acquisition device, which uses the optical system according to one of the examples described above as the optical imaging system. Reference numeral 20 denotes a camera body, and reference numeral 21 denotes an optical imaging system that includes any of the optical systems according to Examples 1 to 5. Reference numeral 22 denotes an image sensor, such as a CCD sensor or CMOS sensor, which is installed in the camera body 20 and configured to acquire an optical image (object image) produced by the optical imaging system 21. Reference numeral 23 denotes a recording device configured to record image data produced by processing an imaging signal from the image sensor 22, and reference numeral 24 denotes a rear display unit configured to display image data.

[0136] The optical system, based on a given example, can provide a camera with reduced size and high optical performance. The camera can be a single-lens reflex camera with a quick-turn mirror or a mirrorless camera without a quick-turn mirror.

[0137] While the disclosure has described exemplary embodiments, it is understood that some embodiments are not limited to the disclosed embodiments.

[0138] One example is an optical system with reduced size and high optical performance using a diffraction surface with a controlled wavelength dispersion characteristic. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 10989901

[0002] US 2021 / 0132256

[0002] WO 2021 / 170417

[0002]

Claims

[1] Optical system (L) comprising, in order from an object side to an image side: a diffractive optical element (L1) having positive refractive power and a diffraction surface with a controlled wavelength dispersion characteristic; and a lens (L2) with negative refractive power, characterized by that, if v0 is an Abbe number of the diffraction surface, a reference wavelength is the d-line, a primary dispersion is the F-line and the C-line, ψ(λ d ), ψ(λ F ) and ψ(λ C ) optical path difference functions for the d-line, the F-line and the C-line, respectively, P(λ d ), P(λ F ) and P(λ C ) optical path difference dispersions of a surface for the d-line, the F-line and the C-line, respectively, the following equation is satisfied: 1v0≡ψ(λF)−ψ(λC)ψ(λd)=λFP(λF)−λCP(λC)λdP(λd) and the following inequality is satisfied: −0.2<1 / v0<0.

2. [2] Optical system according to claim 1, characterized by that the diffractive optical element has a convex refractive surface on the object side. [3] Optical system according to claim 1 or 2, characterized by that the diffraction surface is arranged on the image side of the diffractive optical element. [4] Optical system according to one of claims 1 to 3, characterized by that the following inequality is satisfied: 0.3 <f1 / f<0,8 where f1 is a focal length of the diffractive optical element and f is a focal length of the optical system. [5] Optical system according to one of claims 1 to 4, characterized by that the following equation is satisfied: 1fmoe=−2U2 where f moe is a focal length of the diffraction surface and U2 is a quadratic coefficient of an optical path difference function of a surface at a design wavelength, and the following inequality is satisfied: 2.5 <fmoe / f<10,0 where f is a focal length of the optical system. [6] Optical system according to one of claims 1 to 5, characterized by that the following inequality is satisfied: 0.6 <TL / f<0,9 where TL is a distance on an optical axis from a lens surface of the optical system closest to an object to an image plane, and f is a focal length of the optical system. [7] Optical system according to one of claims 1 to 6, characterized by that a first optical element serves as the diffractive optical element and is arranged closest to an object, and a second optical element serves as the lens. [8] Optical system according to claim 7, characterized by that the following inequality is satisfied: 0.08 <D12 / TL<0,40 where D12 is an air gap on an optical axis between the first optical element and the second optical element, and TL is a distance on an optical axis from a lens surface of the optical system closest to the object to an image plane. [9] An optical system according to claim 7, further comprising a third optical element as a lens arranged on the image side of and adjacent to the second optical element, characterized by that the following inequality is satisfied: 0.15 <D23 / TL<0,50 where D23 is an air gap on an optical axis between the second optical element and the third optical element, and TL is a distance on the optical axis from a lens surface of the optical system closest to the object to an image plane. [10] Optical system according to claim 7, characterized by that the following inequality is satisfied: 0.20 <L02 / TL<0,45 where L02 is a distance on an optical axis from a lens surface of the optical system closest to the object to a lens surface of the second optical element closest to the object, and TL is a distance on the optical axis from the lens surface of the optical system closest to the object to an image plane. [11] Optical system according to claim 7, characterized by that the optical system comprises a third optical element as a lens with negative refractive power, which is arranged on the image side of and adjacent to the second optical element, wherein the following inequality is satisfied: −1.5 <fG3 / f<−0,4 where fG3 is a focal length of the third optical element and f is a focal length of the optical system. [12] An optical system according to any one of claims 1 to 11, further comprising, in order from the object side to the image side: a first optical element as the diffractive optical element arranged closest to an object; a second optical element as the lens; a third optical element with aspherical surfaces on both sides; and a fourth optical element with aspherical surfaces on both sides. [13] Optical system according to claim 12, characterized by that the third optical element has negative refractive power, wherein the fourth optical element has positive or negative refractive power. [14] Optical system comprising, in order from an object side to an image side: a metal lens with positive refractive power, and a metasurface with a controlled wavelength dispersion characteristic; and a lens with negative refractive power, characterized by that, if v0 is an Abbe number of the metasurface, a reference wavelength is the d-line, a primary dispersion is the F-line and the C-line, ψ(λ d ), ψ(λF ) and ψ(λ C ) optical path difference functions for the d-line, the F-line and the C-line, respectively, P(λ d ), P(λ F ) and P(λ C ) optical path difference dispersions of a surface for the d-line, the F-line and the C-line, respectively, the following equation is satisfied: 1v0≡ψ(λF)−ψ(λC)ψ(λd)=λFP(λF)−λCP(λC)λdP(λd),and the following inequality is satisfied: −0.2<1 / v0<0.

2. [15] Optical system according to claim 14, characterized by that the metal lens has a convex refractive surface on the object side. [16] Optical system according to claim 14 or 15, characterized by that the metasurface is arranged on the image side of the metal lens. [17] Image recording device comprising: the optical system according to one of claims 1 to 16; and an image sensor configured to capture an object image through the optical system.

Images