Optical system and imaging device

Abstract

[PROBLEM] To provide an optical system which has been made low-profile. [Solution] This optical system L includes: an optical element provided with a diffraction surface for which the wavelength dispersion characteristics are controlled; and a reflection element provided with a reflection surface M1. Light incident from the object side is reflected by the reflection surface and guided to the image side. When the Abbe number of the diffraction surface is defined as ν0, condition │1 / ν0│<0.2 is satisfied.

Description

Optical system and imaging device

[0001] This disclosure relates to an optical system suitable for imaging.

[0002] As described above, a thin telephoto lens is needed for this type of optical system. Patent documents 1 and 2 disclose optical systems using two reflective surfaces that bend the optical path. The optical system in patent document 2 includes a flat diffracting lens.

[0003] U.S. Patent No. 1,1762,174, U.S. Patent Publication No. 2022 / 0121016

[0004] There is a demand for optical systems that are thinner than conventional ones.

[0005] One aspect of this disclosure is an optical system comprising an optical element having a diffracting surface with controlled wavelength dispersion characteristics and a reflecting element having a reflective surface, which reflects light incident from the object side onto the image side using the reflective surface. The Abbe number of the diffracting surface is ν ０ When this is the case, |1 / ν| ０ It is characterized by satisfying the condition that | < 0.2. The Abbe number of the diffraction plane will be described later. An imaging device having the above optical system also constitutes another aspect of this disclosure.

[0006] A thin optical system can be provided using a diffraction plane with controlled wavelength dispersion characteristics.

[0007] Cross-sectional view of the optical system of Example 1. Aberration diagram of the optical system of Example 1. Cross-sectional view of the optical system of Example 2. Aberration diagram of the optical system of Example 2. Cross-sectional view of the optical system of Example 3. Aberration diagram of the optical system of Example 3. Diagram showing a smartphone using the optical systems of Examples 1 to 3.

[0008] The embodiments of this disclosure will be described below with reference to the drawings. First, before describing the specific embodiments 1 to 3, we will explain the matters common to each embodiment. Figures 1, 3, and 5 show the configuration of the optical system L of embodiments 1 to 3, respectively.

[0009] O indicates the optical axis of optical system L. L1 indicates the first lens group, and L2 indicates the second lens group. F1 indicates a planar optical element that includes a diffraction plane with controlled wavelength dispersion characteristics (hereinafter referred to as "dispersion-controlled").

[0010] P represents a right-angle prism (reflective element) that bends the optical axis O by 90°, and M1 represents a reflective surface provided on the inclined surface of the right-angle prism P. The right-angle prism P is a prism element filled with a light-transmitting medium inside, with an incident surface and an exit surface perpendicular to each other and the inclined surface making an angle (45°) with respect to the incident surface and the exit surface. SP represents an aperture stop, and GB represents a glass block including an infrared cut filter, a low-pass filter, etc. IP represents the image plane of the optical system L. On the image plane IP, an imaging surface (light-receiving surface) of an imaging element such as a CCD sensor or a CMOS sensor or a film surface (photosensitive surface) of a silver halide film is arranged.

[0011] Next, in the optical system L having a reflective surface, the features of the optical systems of each embodiment that achieve thinning and high optical performance by using a diffraction surface with dispersion control will be described.

[0012] The optical system of each embodiment has at least one diffraction surface with dispersion control and a reflective surface. The light rays incident from the object side are condensed by diffraction at the diffraction surface with dispersion control and reflected by the reflective surface and directed toward the image side.

[0013] When the Abbe number of the diffraction surface with dispersion control is ν ０ it satisfies the condition of the following formula (1).

[0014] |1 / ν ０ [[ID=I6]]|<0.2 (1) The Abbe number ν of the diffraction surface with dispersion control ０ is defined by the following formula. The reference wavelength is the d line (λ ｄ = 0.58756 [μm]), the principal dispersions are the F line (λ F = 0.48613 [μm]) and the C line (λ Ｃ = 0.65627 [μm]), and the optical path difference dispersions of the surface at each wavelength are P(λ ｄ ), P(λ Ｆ ), P(λ Ｃ ). At this time,

[0015]

[0016] By including at least one diffraction surface with dispersion control in the optical system of each embodiment, it becomes easy to effectively correct chromatic aberration and obtain high optical performance. Further, since the optical system of each embodiment has a reflective surface and the optical path from the object side is bent by the reflective surface, thinning is facilitated. The condition of Equation (1) is a condition for effectively correcting chromatic aberration with a diffraction surface having dispersion control and obtaining high optical performance. 1 / ν ０ If the negative Abbe number has too high dispersion such that 1 / ν is below the upper limit of Equation (1), the chromatic aberration generated by the diffraction surface with dispersion control becomes too large. As a result, it becomes difficult to increase the refractive power of the diffraction surface to miniaturize the optical system, which is not preferable. Also, it becomes difficult to correct chromatic aberration and high optical performance cannot be obtained, which is not preferable. 1 / ν ０ If the positive Abbe number has too high dispersion such that 1 / ν exceeds the upper limit of Equation (1), the chromatic aberration generated by the diffraction surface with dispersion control becomes too large. As a result, it becomes difficult to increase the refractive power of the diffraction surface to miniaturize the optical system, which is not preferable. Also, it becomes difficult to correct chromatic aberration and high optical performance cannot be obtained, which is not preferable.

[0017] It is more preferable that the upper limit of Equation (1) is 0.15, 0.12, 0.08 or 0.05.

[0018] It is preferable that the optical system of each embodiment satisfies at least one of the following configurations and conditions.

[0019] The reflective surface M1 preferably has a planar shape. When the reflective surface M1 has a planar shape, even if the optical path is bent to facilitate thinning of the optical system, the rotational symmetry of the entire optical system is maintained. As a result, the aberrations generated in the optical system are limited to those generated in a rotationally symmetric optical system. As a result, it becomes easy to obtain high optical performance.

[0020] It is preferable that there is one reflective surface included in the optical system of each embodiment. This is because the reflective surface has a high sensitivity to manufacturing errors, and an optical system including a plurality of reflective surfaces is likely to generate aberrations due to manufacturing errors, making it difficult to obtain high optical performance.

[0021] In each embodiment, it is preferable to place the planar optical element F1 closest to the object, and to place a dispersion-controlled diffraction surface with positive refractive power on the image-side surface of the planar optical element F1. Placing the planar optical element F1 closest to the object facilitates the thinning of the optical system. Furthermore, by placing a dispersion-controlled diffraction surface with positive refractive power on the image-side surface of the planar optical element F1, it is possible to avoid contact between the microstructure, such as a so-called metasurface that realizes the dispersion-controlled diffraction surface, and the outside world. In addition, the dispersion-controlled diffraction surface has positive refractive power and deflects the light rays in the converging direction, which facilitates thinning. Moreover, by using a dispersion-controlled diffraction surface, it is possible to suppress the occurrence of chromatic aberration even though it is a planar optical element with positive refractive power. This makes it easier to achieve high optical performance.

[0022] The optical system of the embodiment is preferably composed of, in order from the object side to the image side, a first group L1 having a planar optical element F1 and a reflective surface M1, and a second group L2 having an aperture diaphragm SP and at least one refractive lens. By arranging the first group L1, it is easy to achieve a thin profile and high optical performance. Furthermore, by arranging the second group L2, off-axis aberrations using the first group L1 and the second group L2 can be corrected, making it easy to achieve high optical performance.

[0023] In the optical systems of each embodiment, it is preferable that the dispersion-controlled diffraction planes are included in the first group L1. This effectively suppresses the occurrence of axial chromatic aberration, making it easier to achieve high optical performance.

[0024] In the optical system of each embodiment, when the focal length of the dispersion-controlled diffraction surface provided on the planar optical element F1 is fm and the focal length of the entire optical system is f, it is preferable to set the focal length fm such that the following condition (2) is satisfied.

[0025] 0.5 < fm / f < 7.0 (2) The focal length fm of the dispersion-controlled diffraction plane is calculated using the following formula.

[0026]

[0027] C ２is the coefficient of the second order when the surface shape of the optical surface is expanded into a power series. When the radius of curvature of the optical surface is r, it is related to C² = 1 / (2r). N is the refractive index of the incident medium, N' is the refractive index of the exit medium, m is the order of diffraction, and λ is the coefficient of the second order. ０ λ is the design wavelength, λ is the incident wavelength, P is the optical path difference dispersion of the surface at the incident wavelength, U ２ is the quadratic coefficient of the optical path difference function of the surface at the design wavelength. ２ This is the coefficient of the second order when the optical path difference function of the surface at the design wavelength, which is added to the optical surface, is expanded into a power series.

[0028] The conditions in equation (2) are designed to facilitate the thinning of the optical system while achieving high optical performance. If fm / f falls below the lower limit of equation (2), the focal length of the dispersion-controlled diffraction surface becomes too short, making it difficult to obtain high optical performance, which is undesirable. If fm / f exceeds the upper limit of equation (2), the focal length of the dispersion-controlled diffraction surface becomes too long, making it difficult to effectively focus the light rays. As a result, it becomes difficult to thin the optical system, which is also undesirable.

[0029] Furthermore, it is more preferable to set the lower limit of formula (2) to 0.8, 1.0, or 1.2. Also, it is more preferable to set the upper limit of formula (2) to 5.0, 4.0, 3.0, 2.5, or 2.0.

[0030] In each embodiment, the focal length of the optical system from the object-side surface to the incident light on the reflective surface M1 (for example, the portion from the planar optical element F1 to the incident surface side of the right-angle prism P) is defined as f1. In this case, it is preferable to set the focal length f1 so as to satisfy the following condition (3).

[0031] 0.5 < f1 / f < 5.0 (3) The conditions in equation (3) are designed to facilitate the thinning of the optical system while maintaining high optical performance. If f1 / f falls below the lower limit of equation (3), the focal length f1 becomes too short, making it difficult to obtain high optical performance, which is undesirable. If f1 / f exceeds the upper limit of equation (3), the focal length f1 becomes too long, making it difficult to effectively focus the light rays. As a result, it becomes difficult to thin the optical system, which is undesirable.

[0032] Furthermore, it is more preferable to set the lower limit of formula (3) to 0.8, 1.0, or 1.2. Also, it is more preferable to set the upper limit of formula (3) to 3.0, 2.0, or 1.5.

[0033] In the optical system of each embodiment, the second group L2 has a positive refractive power, and when the focal length of the second group L2 is f2, it is preferable to set the focal length f2 such that the following equation (4) is satisfied.

[0034] 1.0 < f² / f < 25.0 (4) The conditions in equation (4) are designed to facilitate miniaturization of the optical system while obtaining high optical performance. If f² / f falls below the lower limit of equation (4), the focal length f² of the second group L2 becomes too short, making it difficult to obtain high optical performance, which is undesirable. If f² / f exceeds the upper limit of equation (4), the focal length of the second group L2 becomes too long, making it difficult to miniaturize the optical system, which is also undesirable.

[0035] Furthermore, it is more preferable to set the lower limit of formula (4) to 2.0, 2.5, or 3.0. Also, it is more preferable to set the upper limit of formula (4) to 20.0, 18.0, or 16.0.

[0036] In the optical systems of each embodiment, it is preferable to form the reflective surface M1 on the right-angle prism P. By providing the reflective surface M1 on the right-angle prism P, the reflective surface M1 can be positioned with high precision, making it easier to achieve high optical performance while making the optical system thinner.

[0037] In the optical systems of each embodiment, it is preferable to provide a dispersed diffraction surface on the incident or exit surface of the right-angle prism P. This allows refractive power to be imparted to the right-angle prism P, making it even easier to achieve high optical performance while making the optical system thinner.

[0038] The optical systems L of Examples 1 to 3 will be described in detail below. After Example 3, numerical examples 1 to 3 corresponding to each of Examples 1 to 3 are shown.

[0039] The optical system L of Embodiment 1 (Numerical Example 1) shown in Figure 1 is an optical system with a focal length of 1.0 mm, an F-number of 2.88, and a half-angle of view of 9.64°. The optical system L is composed of a first group L1 having positive refractive power, an aperture diaphragm SP, and a second group L2 having positive refractive power, arranged in order from the object side to the image side.

[0040] The first group L1 consists of a planar optical element F1 and a right-angle prism P having a reflective surface M1. The image-side surface of the planar optical element F1 is provided with a dispersion-controlled diffraction surface. The incident and exit surfaces of the right-angle prism P are also provided with dispersion-controlled diffraction surfaces.

[0041] The second group L2 consists of a double-sided aspherical lens with a biconvex shape at the center near the optical axis and a double-sided aspherical lens with a biconcave shape at the center, arranged sequentially from the object side to the image side.

[0042] Figure 2 shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L in numerical example 1 when it is in focus on an object at infinity (hereinafter referred to as the infinity focus state). Figure 2 shows the longitudinal aberrations when the optical system L is magnified 17 times.

[0043] In the spherical aberration diagram, the vertical axis Fno represents the F-number, and the vertical axis ω for astigmatism, distortion, and chromatic aberration represents the half-angle of view (°). The horizontal axis represents the amount of each aberration. In the spherical aberration diagram, the solid line represents the spherical aberration with respect to the d-line (wavelength 587.6 nm), and the dashed line represents the spherical aberration with respect to the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S represents astigmatism at the sagittal image plane, and the dashed line M represents astigmatism at the meridional image plane. The distortion diagram shows distortion at the d-line. The chromatic aberration diagram shows lateral chromatic aberration at the g-line. Note that the explanations for these aberration diagrams are the same for other numerical examples described later.

[0044] The optical system L of Embodiment 2 (Numerical Example 2) shown in Figure 3 is an optical system with a focal length of 1.0 mm, an F-number of 2.47, and a half-angle of view of 11.89°. The optical system L is composed of a first group L1 with positive refractive power, an aperture diaphragm SP, and a second group L2 with positive refractive power, arranged in order from the object side to the image side. The first group L1 is composed of a planar optical element F1, a right-angle prism P having a reflective surface M1, and a double-sided aspherical lens having a meniscus shape that is convex toward the object side near the optical axis. A dispersion-controlled diffraction surface is provided on the image-side surface of the planar optical element F1.

[0045] The second group L2 consists of a double-sided aspherical lens with a biconvex shape at its center and a double-sided aspherical lens with a biconcave shape at its center, arranged in order from the object side to the image side.

[0046] Figure 4 shows the longitudinal aberration of the optical system L in numerical example 2 when it is in focus at infinity. Figure 4 also shows the longitudinal aberration when the optical system L is magnified 13 times.

[0047] The optical system L of Embodiment 3 (Numerical Example 3) shown in Figure 5 is an optical system with a focal length of 1.0 mm, an F-number of 4.5, and a half-angle of view of 6.18°. The optical system L is composed of a first group L1 with positive refractive power, an aperture diaphragm SP, and a second group L2 with positive refractive power, arranged in order from the object side to the image side.

[0048] The first group L1 consists of a planar optical element F1, a right-angle prism P having a reflective surface M1, and a double-sided aspherical lens having a meniscus shape with its center convex towards the image side. The image-side surface of the planar optical element F1 is provided with a dispersion-controlled diffraction surface. The incident surface of the right-angle prism P is also provided with a dispersion-controlled diffraction surface.

[0049] The second group L2 consists of a double-sided aspherical lens with a biconvex shape at its center and a double-sided aspherical lens with a biconcave shape at its center, arranged in order from the object side to the image side.

[0050] Figure 6 shows the longitudinal aberration of the optical system L in numerical example 3 when it is in focus at infinity. Figure 6 also shows the longitudinal aberration when the optical system L is magnified 26 times.

[0051] Furthermore, a metasurface may be used as (or instead of) the diffraction surface. The metasurface is constructed by calculating the phase delay amount of metaatoms for each wavelength and arranging the metaatoms to control the wavelength dispersion characteristics. The metasurface may be a so-called single-layer metasurface consisting of one layer, or a so-called stacked metasurface consisting of multiple layers.

[0052] The following shows the numerical values ​​for numerical examples 1 to 3. In each numerical example, the surface number i indicates the order of the surfaces when counted from the object side. r is the radius of paraxial curvature (mm) of the i-th optical surface (the i-th surface), and d is the distance (lens thickness or air gap) (mm) on the optical axis between the i-th surface and the (i+1)-th surface. nd is the refractive index of the optical material between the i-th surface and the (i+1)-th surface at the d-line. νd is the Abbe number of the optical material between the i-th surface and the (i+1)-th surface with respect to the d-line. The Abbe number νd with respect to the d-line is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm), respectively.

[0053] BF indicates the back focus (mm). The back focus is the air-equivalent distance along the optical axis from the image-side surface (final surface) of the optical system to the paraxial image plane. The total length of the lens is the distance along the optical axis from the object-side surface (frontmost surface) to the final surface of the optical system, plus the back focus.

[0054] The asterisk (*) next to the surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement from the surface vertex in the direction of the optical axis, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the radius of paraxial curvature, k is the cone constant, and A4 to A10 are the aspherical coefficients. Note that "e±M" in the cone constant and aspherical coefficients means ×10±M.

[0055] x = (h ２ / R) / [1+√{1-(1+k)(h / R) ２}] + A4 × h4 + A6 × h6 + A8 × h8 + A10 × h10 The optical path difference function of a surface at the design wavelength is expressed by the following formula, when U2 to U10 are the coefficients of the optical path difference function of the surface. The coefficients of the optical path difference function "e ± M" mean × 10 ± M.

[0056] F0 = U2 × h2 + U4 × h4 + U6 × h6 + U8 × h8 + U10 × h10 The (diffraction) appended to the surface number indicates a surface for which optical design has been performed using the optical path difference function of the surface. [Numerical Example 1] Unit: mm Surface Data Surface Number rd nd νd 1 ∞ 0.03 1.51633 64.1 2 (Diffraction) ∞ 0.04 3 (Diffraction) ∞ 0.20 1.51633 64.1 4 (Reflection) ∞ 0.20 1.51633 64.1 5 (Diffraction) ∞ 0.09 6 (Aperture) ∞ 0.12 7* 0.501 0.08 1.54450 56.0 8* -0.605 0.05 9* -0.339 0.03 1.56918 40.0 10* 1.904 0.40 11 (GB) ∞ 0.01 1.51633 64.1 12 ∞ 0.02 Image plane ∞ Aspherical data Second plane (diffraction plane) Diffraction order 1 Design wavelength 0.58756 [μm] U2 = -2.67821e-01 U4 = 5.09058e+00 U6 = -1.45264e+00 U8 = 9.95778e+01 Unit of optical path difference dispersion wavelength of the plane [μm] P(λ) = 0.58756 / λ P(λ d) = 1.0000e+00 P(λ C ) = 8.9530e-01 P(λ F = 1.2086e+00 3rd face (folded face) Folding count 1 Design wavelength 0.58756 [μm] U2=-1.27483e-01 U4=-5.51664e+00 U6= 9.48205e+00 U8=-1.02284e+02 Optical path difference of the face, wavelength unit [μm] P(λ) = 0.58756 / λ P(λ d ) = 1.0000e+00 P(λ C ) = 8.9530e-01 P(λ F = 1.2086e+00 5th face (folded face) Folding count 1 Design wavelength 0.58756 [μm] U2= 5.16570e-02 U4= 7.68697e-01 U6= 9.64945e-01 U8=-1.13271e+01 Optical path difference of the face, wavelength unit [μm] P(λ) = 2.13777486e+03・λ 10 - 1.27052337e+04・λ 9 + 3.40956124e+04・λ 8 - 5.44848734e+04・λ 7 + 5.75291455e+04・λ 6 - 4.20575803e+04・λ 5 + 2.16529322e+04・λ 4 - 7.80721794e+03・λ 3 + 1.91173823e+03・λ 2 - 2.95804794e+02·λ + 2.43577393e+01 P(λ d ) = 1.0000e+00 P(λ C ) = 8.9129e-01 P(λ F) = 1.2211e+00 7th side K = 8.80894e+00 A 4= 4.39045e+00 A 6= 1.39913e+02 A 8= 3.89036e+02 A10=-2.95342e+05 8th side K =-3.97410e+00 A 4= 2.62925e+01 A 6= 1.80040e+02 A 8=-2.13393e+04 A10= 5.89322e+05 9th side K =-2.26427e+00 A 4= 7.85439e+01 A 6=-6.46253e+03 A 8= 2.28632e+05 A10 = -4.79006e+06 10th surface K = 9.50000e+01 A4 = 6.48893e+01 A6 = -5.68040e+03 A8 = 2.19969e+05 A10 = -4.04013e+06 Various data Focal length 1.00 F-number 2.88 Half angle of view (°) 9.64 Image height 0.17 Lens length 1.26 BF 0.43 Entrance pupil position 0.56 Exit pupil position -0.61 Front principal point position -0.03 Rear principal point position -0.98 Lens group data Group Starting surface Focal length Lens construction length Front principal point position Rear principal point position L1 1 1.42 0.45 -0.01 -0.31 L2 7 3.53 0.16 -0.58 -0.61 Single Lens Data Lens Starting Surface Focal Length 1 1 1.87 2 3 6.32 3 7 0.52 4 9 -0.50 [Numerical Example 2] Unit: mm Surface Data Surface Number rd nd νd 1 ∞ 0.03 1.51633 64.1 2 (Diffraction) ∞ 0.01 3 (Reflection) ∞ 0.24 1.51633 64.1 4 ∞ 0.24 1.51633 64.1 4 ∞ 0.01 5* 1.547 0.07 1.43875 94.9 6* 3.686 0.08 7 (Twisting) ∞ 0.32 8* 0.630 0.08 1.54450 56.0 9* -0.651 0.05 10* -0.342 0.02 1.59614 33.2 11* 8.566 0.19 12 ∞ 0.01 1.51633 64.1 13 ∞ 0.03 Image plane ∞ Aspherical Data 2nd Surface (Reflection Surface) Reflection Count 1 Design Wavelength 0.58756 [μm] U2=-3.58853e-01 U4= 2.18845e-01 U6=-4.74947e-01 U8= 1.06441e+00 Surface Optical Path Difference Dispersion Wavelength Unit [μm] P(λ) = 0.58756 / λ P(λ). d ) = 1.0000e+00 P(λ C ) = 8.9530e-01 P(λ F) = 1.2086e+00 5th side K = 1.08861e+01 A 4=-6.52209e+00 A 6=-5.87935e+01 A 8=-2.89487e+02 A10=-2.52623e+03 6th side K =-4.11003e+01 A 4=-9.29083e+00 A 6=-4.47223e+01 A 8=-3.90456e+02 A10= 5.86234e+03 8th side K = 8.78283e+00 A 4=-3.79848e+00 A 6= 1.79987e+02 A 8=-8.49121e+03 A10= 1.37827e+05 9th side K = 1.11579e+01 A 4= 1.39442e+01 A 6= 4.24303e+02 A 8=-2.83351e+04 A10= 5.28172e+05 10th side K = 2.30828e+00 A 4= 2.79912e+01 A 6=-1.26675e+03 A 8= 3.21612e+03 A10= 3.22826e+05 11th side K =-9.50000e+01 A 4= 1.06954e+01 A 6=-1.50858e+03 A 8= 3.17166e+04 A10 = -2.35272e+05 Various Data Focal Length 1.00 F-number 2.47 Half-angle of view (°) 11.89 Image height 0.21 Lens length 1.38 BF 0.23 Entrance pupil position 0.73 Exit pupil position -0.55 Front principal point position 0.00 Rear principal point position -0.97 Lens Group Data Group Starting plane Focal length Lens construction length Front principal point position Rear principal point position L1 1 1.18 0.59 0.08 -0.33 L2 8 11.48 0.15 -1.61 -1.51 Single Lens Data Lens Starting plane Focal length 1 1 1.39 3 5 6.01 4 8 0.60 5 10 -0.55 [Numerical Example 3] Unit: mm Surface Data Surface Number rd nd νd 1 ∞ 0.03 1.51633 64.1 2 (Diffraction) ∞ 0.02 3 (Diffraction) ∞ 0.13 1.62041 60.3 4 (Reflection) ∞ 0.13 1.62041 60.3 5 ∞ 0.24 6* -19.614 0.03 1.53563 55.8 7* -4.151 0.02 8 (Aperture) ∞ 0.12 9* 0.551 0.04 1.54308 55.9 10* -0.754 0.04 11* -0.353 0.04 1.55833 41.1 12* 2.690 0.37 13 ∞ 0.01 1.51633 64.1 14 ∞ 0.02 Image plane ∞ Aspheric data 2nd surface (diffraction surface) Diffraction order 1 Design wavelength 0.58756[μm] U2=-4.07171e-01 U4= 8.05746e-01 U6= 9.58828e+00 U8=-4.87345e+02 Surface optical path difference dispersion wavelength unit [μm] P(λ) = 0.58756 / λ P(λ. d ) = 1.0000e+00 P(λ C ) = 8.9530e-01 P(λ F= 1.2086e+00 3rd face (folded face) Folding count 1 Design wavelength 0.58756 [μm] U2= 4.04610e-03 U4=-3.32625e-01 U6=-1.19140e+01 U8= 6.44928e+02 Optical path difference of the face, wavelength unit [μm] P(λ) = 2266.41068・λ 10 - 12144.39247・λ 9 + 29486.82651・λ 8 - 42762.08537・λ 7 + 41106.88437・λ 6 - 27470.79737・λ 5 + 13006.44877・λ 4 - 4356.52716・λ 3 + 1009.95630・λ 2 - 153.95668・λ + 13.87546 P(λ d ) = 1.0000e+00 P(λ C ) = 9.1556e-01 P(λ F) = 1.1842e+00 6th side K = 9.50000e+01 A 4=-4.41769e+00 A 6=-1.09040e+03 A 8=-2.91673e+04 A10= 1.18025e+07 7th side K =-9.50000e+01 A 4=-1.19641e+01 A 6=-1.42859e+03 A 8=-1.76546e+04 A10= 1.41815e+07 9th side K = 2.78229e+01 A 4= 3.15741e+01 A 6=-2.71933e+03 A 8=-5.98522e+05 A10= 5.38312e+07 10th side K =-8.70300e+01 A 4= 8.51595e+01 A 6=-3.28158e+03 A 8=-1.26675e+06 A10= 1.28843e+08 11th side K =-7.56413e+00 A 4= 8.96239e+01 A 6=-1.47171e+04 A 8=-2.72480e+03 A10= 5.54760e+07 12th side K = 9.50000e+01 A 4= 4.97947e+01 A 6=-8.59803e+03 A 8= 2.59653e+05 A10= 1.18989e+07 Various Data Focal Length 1.00 F-number 4.50 Half-angle of view (°) 6.18 Image height 0.11 Lens length 1.22 BF 0.40 Entrance pupil position 0.74 Exit pupil position -0.56 Front principal point position 0.00 Rear principal point position -0.98 Lens Group Data Group Starting plane Focal length Lens construction length Front principal point position Rear principal point position L1 1 1.15 0.57 0.07 -0.40 L2 9 14.67 0.12 -1.54 -1.48 Single Lens Data Lens Starting plane Focal length 1 1 1.23 2 3 -123.Table 1 shows the values ​​of equations (1) to (4) for numerical examples 1 to 3. The value of equation (1) represents the largest absolute value among the reciprocals of the Abbe numbers of at least one dispersion-controlled diffraction plane. The optical system L in each numerical example satisfies all the conditions of equations (1) to (4).

[0057]

[0058] [Imaging Device] Figure 7 shows a smartphone 10 as an imaging device including the optical system L of Examples 1 to 3. A display 11, a microphone 12, and a speaker 13 are arranged on the front of the smartphone 10. The optical system L takes in light from the subject from the back of the smartphone 10, bends the light path to form an image on an image sensor (imaging surface) not shown. This allows the subject to be imaged. By using the optical system L of Examples 1 to 3, a thin smartphone that can obtain high-quality images can be provided.

[0059] The embodiments described above are merely representative examples, and various modifications and changes are possible for each embodiment.

Claims

1. An optical system comprising an optical element having a diffraction surface with controlled wavelength dispersion characteristics and a reflective element having a reflective surface, wherein light incident from the object side is reflected by the reflective surface and guided to the image side, wherein the Abbe number of the diffraction surface is ν ０ Let the reference wavelength of the diffraction plane be the d-line, and the principal dispersions be the F-line and C-line, and the optical path difference function at each wavelength be ψ ｄ ψ Ｆ ψ Ｃ P(λ) is the optical path difference dispersion of the surface at each wavelength. ｄ ), P(λ Ｆ ), P(λ Ｃ ) as, When this is the case, |1 / ν| ０ An optical system characterized by satisfying the condition | < 0.

2.

2. The optical system according to claim 1, characterized in that the reflective surface has a planar shape.

3. The optical system according to claim 1 or 2, characterized in that the optical system includes one reflective surface.

4. The optical system according to any one of claims 1 to 3, characterized in that the optical element is located closest to the object, and the diffraction surface having a positive refractive power is provided on the surface of the optical element.

5. Let the focal length of the diffractive surface be \(f_m\), and let the second-order coefficient when the surface shape of the optical surface is expanded in a power series be \(C\). ２ , the refractive index of the incident medium be \(N\), the refractive index of the exit medium be \(N'\), the diffraction order be \(m\), the design wavelength be \(\lambda\). ０ , the incident wavelength be \(\lambda\), the optical path difference dispersion of the surface at the incident wavelength be \(P\), and the second-order coefficient of the optical path difference function of the surface at the design wavelength be \(U\). ２ Then, where the focal length of the optical system is \(f\), the optical system according to any one of claims 1 to 4, characterized in that it satisfies the condition \(0.5 < f_m / f < 7.0\).

6. The optical system according to any one of claims 1 to 5, characterized in that, when f1 is the focal length of the portion of the optical system from the surface closest to the object to the point where light enters the reflective surface, and f is the focal length of the optical system, the condition 0.5 < f1 / f < 5.0 is satisfied.

7. The optical system according to any one of claims 1 to 6, characterized in that the optical system comprises, in order from the object side to the image side, a first group having the diffraction surface and the reflection surface, an aperture diaphragm, and a second group including a lens.

8. The optical system according to claim 7, characterized in that the second group has a positive refractive power, and when the focal length of the second group is f2 and the focal length of the optical system is f, the condition 1.0 < f2 / f < 25.0 is satisfied.

9. The optical system according to any one of claims 1 to 8, characterized in that the reflective surface is provided on an inclined surface having an angle with respect to the incident surface and the exit surface of the prism element as the reflective element, which is filled inside with a light-transmitting medium.

10. The optical system according to claim 9, characterized in that the diffraction surface is provided on at least one of the incident surface and the exit surface of the prism element.

11. An imaging device comprising an optical system according to any one of claims 1 to 10, and an image sensor that receives an image formed by the optical system.

Images