Optical system and imaging apparatus having same

Abstract

[Problem] To provide a compact optical system. [Solution] The optical system includes: a first lens disposed closest to an object; an aperture stop disposed between the first lens and an image plane; and an air lens disposed closer to the object than the aperture stop and having a negative refractive power. At least one of lens surfaces constituting the air lens includes a diffraction surface subjected to dispersion control. The effective diameter of the diffraction surface and the aperture diameter of the aperture stop are each set appropriately.

Description

Optical system and imaging device having the same

[0001] This disclosure relates to optical systems and imaging devices having the same.

[0002] In recent years, with the spread of VR systems, fisheye lenses capable of capturing a range exceeding 180 degrees have attracted attention. Patent Document 1 discloses a fisheye lens that uses an aspherical surface to achieve miniaturization and high resolution.

[0003] U.S. Patent Application Publication No. 2019 / 0187442

[0004] In a fisheye lens, in order to guide light from a range exceeding 180 degrees to the image plane, the lens positioned closest to the object must have a convex shape toward the object, and a strong negative refractive force is required on the object side. In the fisheye lens of Patent Document 1, the curvature of the image-side lens surface of the meniscus lens with a strong negative refractive force positioned closest to the object is small, so the distance between the meniscus lens and the lens positioned adjacent to the image side of the meniscus lens must be large, making miniaturization difficult.

[0005] An optical system, as one aspect of the present invention, comprises a first lens positioned closest to the object, an aperture diaphragm positioned between the first lens and the image plane, and an air lens with negative refractive power positioned closer to the object than the aperture diaphragm, wherein at least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffraction surface, and when the effective diameter of the diffraction surface is EAmoe and the open diameter of the aperture diaphragm is EAstto, the following condition is satisfied: 2.0 < EAmoe / EAstto < 10.0.

[0006] Furthermore, as another aspect of the present invention, the optical system comprises a first lens positioned closest to the object, an aperture diaphragm positioned between the first lens and the image plane, and an air lens positioned closer to the object than the aperture diaphragm, wherein at least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffraction surface.

[0007] We can provide a compact optical system.

[0008] It is a cross-sectional view of the optical system of Example 1. It is an aberration diagram of the optical system of Example 1. It is a cross-sectional view of the optical system of Example 2. It is an aberration diagram of the optical system of Example 2. It is a cross-sectional view of the optical system of Example 3. It is an aberration diagram of the optical system of Example 3. It is a cross-sectional view of the optical system of Example 4. It is an aberration diagram of the optical system of Example 4. It is a schematic diagram of a main part of an imaging apparatus.

[0009] Hereinafter, the examples disclosed in the present specification will be described in detail with reference to the drawings. In each drawing, identical members are assigned identical reference numerals, and redundant descriptions are omitted.

[0010] FIGS. 1, 3, 5, and 7 are respectively cross-sectional views of the optical systems of Examples 1 to 4. The optical system of each example is an optical system used in imaging apparatuses such as digital video cameras, digital still cameras, broadcast cameras, silver-halide film cameras, and surveillance cameras.

[0011] In each cross-sectional view, the left side is the object side, and the right side is the image side. Note that the optical system of each example may be used as a projection lens for a projector or the like. In this case, the left side is the screen side, and the right side is the projected image side.

[0012] In each cross-sectional view, Li represents the i-th (i is a natural number) lens counted from the object side among the lenses included in the optical system.

[0013] O is the optical axis. MOE is a dispersion-controlled diffraction surface. SP is a stop (aperture stop). IP is an image plane, and when the optical system of each example is used as an imaging optical system of a digital still camera or a digital video camera, the imaging surface of an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is disposed. When the optical system of each example is used as the optical system of a silver-halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP. GB is a glass block, which is disposed as a protective glass for the imaging element or a UV-IR cut filter.

[0014] FIG. 2, FIG. 4, FIG. 6, and FIG. 8 are respectively longitudinal aberration diagrams of the optical systems of Examples 1 to 4 at the time of infinite focus. In the spherical aberration diagrams, Fno is the F-number, which indicates the spherical aberration amounts for the d-line (wavelength 587.56 nm) and the g-line (wavelength 435.83 nm). In the astigmatism diagrams, S indicates the astigmatism amount on the sagittal image plane, and M indicates the astigmatism amount on the meridional image plane. The distortion diagrams show the distortion amount for the d-line. The chromatic aberration diagrams show the chromatic aberration amount for the g-line. ω is the imaging half angle of view (°).

[0015] Hereinafter, characteristic configurations of the optical systems of the respective examples will be described.

[0016] The optical system of each example includes a first lens L1 disposed closest to the object side, a stop SP disposed between the first lens L1 and the image plane, and an air lens with negative refractive power disposed closer to the object side than the stop SP.

[0017] At least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffractive surface.

[0018] Here, the definition of the air lens will be explained. In a fisheye lens, in order to guide light from a range exceeding 180 degrees to the image plane, the first lens L1 disposed closest to the object side needs to have a shape convex toward the object side. In addition, in order to bend light from a range exceeding 180 degrees and guide it to the image plane, a strong negative refractive power is required on the object side of the optical system. For this reason, the object-side lens surface of the first lens L1 has a convex shape. When an aspherical surface is disposed on the object side of the first lens L1, the object-side lens surface of the first lens L1 has a convex or concave shape in the paraxial region and a convex shape in the peripheral region. In either case, the image-side lens surface of the first lens L1 has a concave shape facing the image side, and the first lens L1 is a biconcave lens or a meniscus lens with negative refractive power that is convex toward the object side.

[0019] The object-side lens surface of the second lens L2, which is positioned adjacent to the image-side lens surface of the first lens L1, has a concave shape or a convex shape with a greater curvature than the image-side lens surface of the first lens L1. The air lens formed by the image-side lens surface of the first lens L1 and the object-side lens surface of the second lens L2 has a biconvex shape or a meniscus shape with a convex object-side lens surface and has a negative refractive power. Due to the negative refractive action of the air lens, distortion and field curvature can be well corrected while obtaining the refractive power to guide light from a range exceeding 180 degrees to the image plane. However, if the refractive power of the air lens becomes strong and the curvature of the image-side lens surface of the first lens L1 becomes small, it becomes necessary to increase the distance between these lenses in order to suppress interference with the second lens L2. As a result, it becomes difficult to shorten the overall optical length of the optical system.

[0020] Furthermore, the position of the air lens can be any position that satisfies the conditional equation (1) described later, and is not limited to the space between the first lens L1 and the second lens L2.

[0021] Therefore, in this disclosure, at least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffraction surface. The dispersion-controlled diffraction surface has a negative refractive power and contributes to the refractive power of the air lens. This allows the absolute value of the radius of curvature of the air lens to be increased, making it possible to reduce the distance between the first lens L1 and the second lens L2, and thus shortening the overall optical length of the optical system. Conventional blazed diffractive optical elements have a very high dispersion, expressed as an Abbe number of -3.45. Therefore, if the refractive power of the diffraction surface is increased, large chromatic aberrations occur, and the refractive effect cannot be greatly contributed. In this disclosure, since the dispersion-controlled diffraction surface is included, it is possible to increase the refractive power of the diffraction surface and contribute to the refractive power of the air lens while still being able to effectively correct the lateral chromatic aberration and axial chromatic aberration of the optical system.

[0022] Here, we will explain the definition of aperture SP. Aperture SP has an aperture shape that determines the upper and lower lines of axial rays and determines the Fno of the optical system. Aperture SP may be a symmetrical aperture with blades, or a fixed aperture consisting of a sheet-like aperture. Furthermore, if the ray range is determined by the shape of the holder frame that holds the lens, it is also defined as an aperture if it achieves the above effect.

[0023] As described above, in the disclosure herein, at least one of the lens surfaces constituting the air lens has a dispersion-controlled diffraction surface, and the dispersion-controlled diffraction surface is responsible for the refractive action of the air lens. This makes it possible to increase the absolute value of the radius of curvature of the air lens and shorten the lens spacing while controlling dispersion and effectively correcting chromatic aberration.

[0024] The following describes the preferred configurations for the optical systems of each embodiment.

[0025] In the optical systems of each embodiment, it is preferable that the optical system or a part of the optical system moves during focusing and vibration damping. This makes it possible to acquire higher-resolution images in various shooting scenes and expand the shooting range.

[0026] The simplest diffraction plane, made from a cylindrical pillar of a single material, lacks freedom in color phase dispersion. Therefore, it essentially exhibits the same dispersion characteristics as conventional diffraction lenses. However, by employing techniques such as preparing metaatoms with various structures, it is possible to achieve different phase delays at other wavelengths depending on the metaatom structure, even if the phase delay at the reference wavelength remains the same. In other words, by having pillar shapes with varying sizes or shapes of irregularities, a dispersion-controlled diffraction plane can be realized.

[0027] The following describes the conditions that the optical systems of each embodiment preferably satisfy. The optical systems of each embodiment preferably satisfy one or more of the following conditional formulas (1) to (13).

[0028] 2.0<EAmoe / EAsto<10.0 (1) -0.1<1 / νd<0.2 (2) 0.1<L1s / EAmoe<1.5 (3) 0.5<Lms / L1s<1.0 (4) 0.05<fa / fmoe<0.80 (5) -3.5<fa / f<-0.5 (6) 0.05<fN / fmoe<1.50 (7) -0.02<Σφ ｉ / ν ｄｉ +φ ｍｅｔａ / ν ｄ <0.02 (8) 1.5<r12 / f<5.0 (9) -10.0<(r12+r21) / (r12-r21)<1.0 (10) -30.0<f1s / f<-0.5 (11) 0.5<f / imgH<1.0 (12) 1.5<TDL / imgH<8.0 (13) Here, EAmoe is the effective diameter of the dispersion-controlled diffractive surface (the diameter of the effective region through which the light beam contributing to image formation passes). EAsto is the open diameter of the stop SP. ν ｄ is the Abbe number of the dispersion-controlled diffractive surface. The Abbe number of the dispersion-controlled diffractive surface is defined by the following formula.

[0029] 1 / ν ｄ ={ψ(λ Ｆ )-ψ(λ Ｃ )} / ψ(λ ｄ ) ={λ Ｆ ×P(λ Ｆ )-λ Ｃ ×P(λ Ｃ )} / λ ｄ ×P(λ ｄ ) Note that the reference wavelength is the d-line, and the main dispersions are the F-line and C-line, with their respective wavelengths denoted as λ ｄ , λ Ｆ , λ Ｃ , and the optical path difference function at each respective wavelength is denoted as ψ(λ ｄ ), ψ(λ Ｆ ), ψ(λ Ｃ), and the optical path difference dispersion of the surface at each wavelength is P(λ) ｄ ), P(λ Ｆ ), P(λ Ｃ ) is defined as follows: L1s is the distance along the optical axis from the object-side lens surface of the optical system (the object-side lens surface of the first lens L1) to the aperture SP. Lms is the distance along the optical axis from the dispersion-controlled diffraction surface to the aperture SP. fa is the focal length of the air lens including the refractive power of the dispersion-controlled diffraction surface. fmoe is the focal length of the dispersion-controlled diffraction surface. f is the focal length of the optical system. fN is the focal length of the lens equipped with the dispersion-controlled diffraction surface including the refractive power of the diffraction surface. Here, φ ｉ , v ｄｉ These are the reciprocal of the focal length and the Abbe number of the i-th lens (where i is a natural number) from the object side, among the lenses positioned on the object side of aperture SP. ｍｅｔａ r is the reciprocal of the focal length of the dispersion-controlled diffraction plane. r12 is the radius of curvature of the object-side lens surface of the air lens. r21 is the radius of curvature of the image-side lens surface of the air lens. f1s is the combined focal length of the lenses positioned closer to the object than aperture SP. imgH is the image height, which is the height from the optical axis to the position of the ray with the maximum field of view of the optical system on the imaging plane of the image sensor. TDL is the distance along the optical axis from the lens surface closest to the object in the optical system to the image sensor.

[0030] If the effective diameter of the dispersed diffraction surface exceeds the upper limit of condition (1) and becomes too large relative to the aperture SP, it is advantageous for correcting distortion, field curvature, and chromatic aberration, but it leads to an increase in the size of the optical system because the front element diameter becomes too large. If the effective diameter of the dispersed diffraction surface falls below the lower limit of condition (1) and becomes too small relative to the aperture SP, the refractive power of the air lens becomes too weak, making it difficult to correct distortion, field curvature, and chromatic aberration while bending light from a range exceeding 180 degrees.

[0031] When refractive power is applied to an optical element, the light beam can be bent in a desired direction at a specific wavelength. However, if the light beam at different wavelengths is not properly controlled, chromatic aberration occurs, making it difficult to obtain high-resolution images. Satisfying condition (2) is preferable because it allows for the acquisition of images with good chromatic aberration correction even if the dispersion-controlled diffraction plane contributes a large amount of negative refractive power. If the positive dispersion becomes too large, exceeding the upper limit of condition (2), the lateral chromatic aberration at short wavelengths becomes excessive, making it difficult to correct. Also, if the dispersion becomes too strong on the positive side, inward-directed coma aberration at short wavelengths occurs, degrading imaging performance. If the negative dispersion becomes too large, falling below the lower limit of condition (2), the lateral chromatic aberration at short wavelengths becomes under-directed, making it difficult to correct. Also, if the dispersion becomes too strong on the negative side, outward-directed coma aberration at short wavelengths occurs, degrading imaging performance.

[0032] If the upper limit of condition (3) is exceeded, the distance along the optical axis from the object-side lens surface of the first lens L1 to the aperture SP becomes too large, making it difficult to miniaturize the optical system. If the lower limit of condition (3) is exceeded, the effective diameter of the dispersion-controlled diffraction surface becomes too large relative to the distance along the optical axis from the object-side lens surface of the first lens L1 to the aperture SP, resulting in a decrease in the refractive power of the air lens and making it difficult to obtain a shooting range exceeding 180 degrees.

[0033] To correct distortion, field curvature, and chromatic aberration, it is preferable to position the dispersed diffraction plane at a high position of the pupil's paraxial ray, i.e., at a position far from the aperture SP. Conditional equation (4) defines the arrangement of the dispersed diffraction plane. Since the dispersed diffraction plane is positioned on the image side of the first lens L1's object-side lens surface, it will not exceed the upper limit of conditional equation (4). If it falls below the lower limit of conditional equation (4), the dispersed diffraction plane will be positioned close to the aperture SP, making it difficult to correct distortion, field curvature, and chromatic aberration, and resulting in a deterioration of imaging performance.

[0034] If the upper limit of condition (5) is exceeded, the refractive power of the dispersed diffraction surface becomes too strong, complicating the microstructure that makes up the diffraction surface and making manufacturing difficult. If the lower limit of condition (5) is exceeded, the refractive power of the dispersed diffraction surface cannot be obtained, making it difficult to miniaturize the optical system, or aberrations cannot be sufficiently corrected, resulting in poor imaging performance.

[0035] If the upper limit of condition (6) is exceeded, the refractive power of the air lens becomes too weak, making it difficult to guide light from a range exceeding 180 degrees to the image plane, or requiring the use of other lenses to obtain refractive power, which increases the number of lenses and leads to a larger optical system. If the lower limit of condition (6) is exceeded, the refractive power of the air lens becomes too strong, making it difficult to correct aberrations even when using a dispersion-controlled diffraction surface, or making manufacturing difficult due to the increased complexity of the microstructure constituting the diffraction surface.

[0036] A dispersed diffraction surface is formed on at least one of the lens surfaces constituting the air lens. However, since it is effective to correct distortion and field curvature not only on the air lens but also on the lens surface, it is preferable that the lens with the diffraction surface has negative refractive power. Condition (7) specifies the amount of refractive power contributed by the diffraction surface to the focal length of a lens with a dispersed diffraction surface. If the upper limit of condition (7) is exceeded, the refractive power of the dispersed diffraction surface becomes too strong, making manufacturing difficult due to the complexity of the microstructure constituting the diffraction surface. Alternatively, the refractive power of the lens with the dispersed diffraction surface becomes too weak, making it difficult to guide light from a range exceeding 180 degrees to the image plane. If the lower limit of condition (7) is exceeded, the refractive power of the dispersed diffraction surface becomes too weak, making it impossible to shorten the spacing between the air lenses and making it difficult to miniaturize the optical system.

[0037] Conditional equation (8) specifies the aberration conditions for the lens positioned on the object side of the aperture SP. In a fisheye lens, the sign of the refractive power differs before and after the aperture SP, making it difficult to cancel out aberrations. Therefore, it is preferable to correct chromatic aberration with the lenses on the object side and the image side of the aperture SP, respectively. If the upper limit of conditional equation (8) is exceeded, excessive lateral chromatic aberration occurs, degrading the imaging performance. If the lower limit of conditional equation (8) is fallen below, under-lateral chromatic aberration occurs, degrading the imaging performance.

[0038] If the upper limit of condition (9) is exceeded, the radius of curvature of the object-side lens surface of the air lens becomes too gentle, resulting in insufficient refractive power to guide light from a range exceeding 180 degrees to the image plane, making wide-angle viewing difficult. If the lower limit of condition (9) is exceeded, the radius of curvature of the object-side lens surface of the air lens becomes too strong, preventing the thickness of the air lens from being reduced, making it difficult to shorten the overall optical length.

[0039] Condition (10) defines the shape factor of the air lens. If the upper limit of condition (10) is exceeded, the air lens becomes meniscus-shaped, and its refractive power weakens. This makes it difficult to guide light from a range exceeding 180 degrees to the image plane, or it becomes necessary to obtain refractive power from other lenses, leading to an increase in the number of lenses and a larger optical system. If the lower limit of condition (10) is exceeded, the air lens becomes strongly biconvex, and its refractive power strengthens. This makes it difficult to correct aberrations even when using a dispersion-controlled diffraction surface, or it becomes difficult to manufacture because the microstructure constituting the diffraction surface becomes complex.

[0040] A fisheye lens has a strong negative refractive power on the object side of the aperture SP in order to guide light from a range exceeding 180 degrees to the image plane. Condition (11) specifies the value of the ratio of the combined focal length of the lenses positioned on the object side of the aperture SP to the focal length of the optical system. If the value exceeds the upper limit of condition (11), the negative refractive power of the lenses positioned on the object side of the aperture SP is insufficient, making it difficult to achieve a wide-angle view exceeding 180 degrees. If the value falls below the lower limit of condition (11), the negative refractive power of the lenses positioned on the object side of the aperture SP becomes too strong, making it difficult to correct distortion and field curvature, or making miniaturization difficult due to the increased number of lenses.

[0041] Conditional equation (12) specifies the value of the ratio of the focal length of the optical system to the image height, and is a conditional equation that represents the shooting range of the optical system. If the upper limit of conditional equation (12) is exceeded, the focal length of the optical system becomes too large relative to the image height, making it impossible to obtain a field of view greater than 180 degrees. If the lower limit of conditional equation (12) is exceeded, the focal length of the optical system becomes too small relative to the image height, making it difficult to correct aberrations, which is undesirable.

[0042] Conditional equation (13) specifies the value of the ratio of the total optical length of the optical system to the image height, and is a conditional equation that represents the size of the optical system. If the ratio exceeds the upper limit of conditional equation (13), the total optical length becomes too large relative to the image height, making it difficult to miniaturize the optical system. If the ratio falls below the lower limit of conditional equation (13), the total optical length becomes too small relative to the image height, resulting in strong refractive power in each lens and making it difficult to correct aberrations.

[0043] Furthermore, it is more preferable that the lower limit of conditional expression (1) be set to 2.10, 2.20, 2.30, 2.35, 2.40, 2.45, 2.50, 2.55, 2.60, or 2.65. It is more preferable that the upper limit of conditional expression (1) be set to 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, or 4.5.

[0044] Furthermore, it is more preferable that the lower limit of conditional expression (2) be set to -0.090, -0.080, -0.070, -0.060, -0.050, -0.040, -0.030, -0.020, -0.015, or -0.010. It is more preferable that the upper limit of conditional expression (2) be set to 0.18, 0.16, 0.14, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, or 0.06.

[0045] Furthermore, it is more preferable that the lower limit of conditional expression (3) be set to 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, or 0.60. It is more preferable that the upper limit of conditional expression (3) be set to 1.48, 1.45, 1.42, 1.39, 1.36, 1.33, 1.30, 1.27, 1.25, or 1.23.

[0046] Furthermore, it is more preferable that the lower limit of conditional expression (4) be set to 0.52, 0.54, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, or 0.63.

[0047] Furthermore, it is more preferable that the lower limit of condition expression (5) be set to 0.052, 0.054, 0.056, 0.058, 0.060, 0.061, 0.062, 0.063, 0.064, or 0.065. It is more preferable that the upper limit of condition expression (5) be set to 0.75, 0.70, 0.65, 0.60, 0.57, 0.55, 0.53, 0.51, 0.49, or 0.47.

[0048] Furthermore, it is more preferable that the lower limit of condition expression (6) be set to -3.4, -3.2, -3.0, -2.8, -2.7, -2.6, -2.5, -2.4, -2.3, or -2.2. It is more preferable that the upper limit of condition expression (6) be set to -0.510, -0.515, -0.520, -0.525, -0.530, -0.535, -0.540, -0.545, -0.540, or -0.535.

[0049] Furthermore, it is more preferable that the lower limit of condition expression (7) be set to 0.052, 0.054, 0.056, 0.058, 0.060, 0.062, 0.064, 0.066, 0.067, or 0.068. It is more preferable that the upper limit of condition expression (7) be set to 1.40, 1.30, 1.20, 1.10, 1.05, 1.00, 0.95, 0.90, 0.85, or 0.80.

[0050] Furthermore, it is more preferable that the lower limit of condition expression (8) be set to -0.018, -0.016, -0.014, -0.012, -0.011, -0.010, -0.009, -0.008, -0.007, or -0.006. It is more preferable that the upper limit of condition expression (8) be set to 0.018, 0.016, 0.014, 0.012, 0.010, 0.008, 0.006, 0.004, 0.002, or 0.001.

[0051] Furthermore, it is more preferable that the lower limit of condition expression (9) be set to 1.55, 1.60, 1.65, 1.70, 1.75, 1.77, 1.79, 1.81, 1.83, or 1.85. It is more preferable that the upper limit of condition expression (9) be set to 4.8, 4.6, 4.4, 4.2, 4.0, 3.8, 3.6, 3.4, 3.2, or 3.0.

[0052] Furthermore, it is more preferable that the lower limit of condition expression (10) be set to -9.0, -8.0, -7.0, -6.0, -5.0, -4.0, -3.0, -2.0, -1.7, or -1.5. It is more preferable that the upper limit of condition expression (10) be set to 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, or 0.50.

[0053] Furthermore, it is more preferable that the lower limit of condition expression (11) be set to -28.0, -27.0, -26.0, -25.0, -24.0, -23.0, -22.0, -21.0, -20.0, or -19.0. It is more preferable that the upper limit of condition expression (11) be set to -0.55, -0.60, -0.65, -0.70, -0.75, -0.80, -0.85, -0.90, -0.93, or -0.95.

[0054] Furthermore, it is more preferable that the lower limit of condition expression (12) be set to 0.510, 0.520, 0.530, 0.540, 0.550, 0.560, 0.565, 0.570, 0.575, or 0.580. It is more preferable that the upper limit of condition expression (12) be set to 0.97, 0.94, 0.91, 0.88, 0.85, 0.82, 0.79, 0.76, 0.73, or 0.70.

[0055] Furthermore, it is more preferable that the lower limit of condition expression (13) be set to 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or 2.6. It is more preferable that the upper limit of condition expression (13) be set to 7.8, 7.6, 7.4, 7.2, 7.0, 6.9, 6.8, 6.7, 6.6, or 6.5.

[0056] Next, the optical systems of each embodiment will be described in detail.

[0057] The optical system of Example 1 has a focal length of 2.64 mm, an F-number of 2.88, and a half-angle of view of 98.86 degrees. The optical system of Example 1 has multiple lenses. The multiple lenses consist of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in order from the object side to the image side. The positive and negative refractive powers of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are negative, negative, positive, positive, negative, and positive, respectively.

[0058] In the optical system of Example 1, the first lens L1 has a meniscus shape that is convex towards the object. The image-side lens surface of the first lens L1 includes a diffraction surface with dispersed control of negative refractive power. The dispersed control of the diffraction surface distributes the negative refractive power and can reduce the curvature of the image-side lens surface of the first lens L1. The second lens L2 has a meniscus shape that is convex towards the object. The third lens L3 has a biconvex shape. The fourth lens L4 has a biconvex shape. Both the object-side and image-side lens surfaces of the fourth lens L4 are aspherical. The aspherical surface near the aperture SP can effectively correct spherical aberration and coma aberration. The fifth lens L5, which has a meniscus shape that is convex towards the object, and the sixth lens L6, which has a biconvex shape, are joined together, and the achromatic effect of the joining surface can effectively correct chromatic aberration.

[0059] The optical system of Example 2 has a focal length of 2.65 mm, an F-number of 2.88, and a half-angle of view of 98.80 degrees. The optical system of Example 2 has multiple lenses. The multiple lenses consist of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in order from the object side to the image side. The positive and negative refractive powers of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are negative, negative, positive, positive, negative, and positive, respectively.

[0060] In the optical system of Example 2, the first lens L1 has a meniscus shape that is convex towards the object. The second lens L2 has a plano-concave shape. The object-side lens surface of the second lens L2 includes a diffraction surface with dispersed and controlled negative refractive power. The dispersed and controlled diffraction surface shares the negative refractive power, allowing the curvature of the image-side lens surface of the first lens L1 to be increased. Furthermore, by providing a dispersed and controlled diffraction surface on a plane, the difficulty of forming the diffraction surface is reduced, making it easier to manufacture. The third lens L3 has a biconvex shape. The fourth lens L4 has a biconvex shape. The lens surfaces on both sides of the fourth lens L4 are aspherical. The aspherical surface near the aperture SP allows for good correction of spherical aberration and coma aberration. The fifth lens L5, which has a meniscus shape that is convex towards the object, and the sixth lens L6, which has a biconvex shape, are joined together, and the achromatic effect of the joining surface allows for good correction of chromatic aberration.

[0061] The optical system of Example 3 has a focal length of 2.88 mm, an F-number of 2.88, and a half-angle of view of 93.02 degrees. The optical system of Example 3 has multiple lenses. The multiple lenses consist of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6, arranged in order from the object side to the image side. The positive and negative refractive powers of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are negative, negative, positive, negative, positive, and negative, respectively.

[0062] In the optical system of Embodiment 3, the first lens L1 has a meniscus shape that is convex towards the object side. The image-side lens surface of the first lens L1 includes a dispersion-controlled diffraction surface with negative refractive power. The dispersion-controlled diffraction surface distributes the negative refractive power and can reduce the curvature of the image-side lens surface of the first lens L1. The second lens L2 has a meniscus shape that is convex towards the image side. The lens surfaces on both sides of the second lens L2 are aspherical. The third lens L3 has a biconvex shape. The lens surfaces on both sides of the third lens L3 are aspherical. The fourth lens L4 has a meniscus shape that is convex towards the image side. The lens surfaces on both sides of the fourth lens L4 are aspherical. The fifth lens L5 has a biconvex shape. The lens surfaces on both sides of the fifth lens L5 are aspherical. The sixth lens L6 has a biconcave shape. The lens surfaces on both sides of the sixth lens L6 are aspherical. The sixth lens L6 has a critical point on the image-side lens surface, which corrects field curvature.

[0063] The optical system of Example 4 has a focal length of 3.07 mm, an F-number of 2.88, and a half-angle of view of 89.08 degrees. The optical system of Example 4 has multiple lenses. The multiple lenses consist of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7, arranged in order from the object side to the image side. The positive and negative refractive powers of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are negative, negative, positive, positive, negative, positive, and negative, respectively.

[0064] In the optical system of Embodiment 4, the first lens L1 has a meniscus shape that is convex towards the object side. The image-side lens surface of the first lens L1 includes a dispersion-controlled diffraction surface with negative refractive power. The dispersion-controlled diffraction surface distributes the negative refractive power and can reduce the curvature of the image-side lens surface of the first lens L1. The second lens L2 has a meniscus shape that is convex towards the image side. The surfaces on both sides of the second lens L2 are aspherical. The second lens L2 has critical points on the object side and the image side, and effectively corrects field curvature. The third lens L3 has a meniscus shape that is convex towards the image side. The lens surfaces on both sides of the third lens L3 are aspherical. The fourth lens L4 has a biconvex shape. The lens surfaces on both sides of the fourth lens L4 are aspherical. The fifth lens L5 has a meniscus shape that is convex towards the image side. The lens surfaces on both sides of the fifth lens L5 are aspherical. The sixth lens L6 has a biconvex shape. The lens surfaces on both sides of the sixth lens L6 are aspherical. The seventh lens L7 has a biconcave shape. The lens surfaces on both sides of the seventh lens L7 are aspherical. The object-side lens surface of the fifth lens L5 or the image-side lens surface of the sixth lens L6 has a critical point, and the refractive power at the periphery is controlled to correct field curvature.

[0065] In the optical systems of Examples 1 to 2 and 4, the aperture SP is positioned between the third lens L3 and the fourth lens L4. This allows light from a range exceeding 180 degrees to be directed to the aperture SP, enabling ultra-wide-angle photography.

[0066] In the optical system of Example 3, the aperture SP is positioned between the second lens L2 and the third lens L3. In the optical system of Example 3, the aperture SP is positioned close to the object. This makes it possible to capture an ultra-wide-angle range exceeding 180 degrees while keeping the front element small. Positioning the aperture SP at approximately 20-40% of the front of the total optical length allows for both wide-angle and compact design.

[0067] In the optical systems of each embodiment, the entire optical system is moved toward the object when focusing on a nearby object. This allows for simplification of the mechanical structure. However, since fisheye lenses have a wide pan-focus range, it is also possible to use them with the focus fixed depending on the shooting distance range used.

[0068] Furthermore, in the optical systems of each embodiment, aberration correction may be performed by image processing. Also, the structure that realizes the optical path difference function of the diffracting element may be a so-called single-layer metasurface consisting of one layer, or a so-called stacked metasurface consisting of multiple layers. In addition, the glass block GB may be replaced with a component such as a low-pass filter or an IR cut filter.

[0069] The numerical values ​​corresponding to Examples 1 to 4 are shown below.

[0070] In the surface data for each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the on-axial spacing (distance along the optical axis) between the m-th surface and the (m+1)-th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical component with respect to the d line, and νd represents the Abbe number of each optical component with respect to the d line. Note that the Abbe number νd of a certain material is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer lines d line (587.56 nm), F line (486.13 nm), and C line (656.27 nm).

[0071] In each numerical example, d, focal length (mm), F-number, and half-angle of view [°] are all values ​​when the optical system of each example is focused on an object at infinity. The half-angle of view is a value obtained by ray tracing. "Lens length" is expressed as the distance along the optical axis from the lens surface closest to the object among the optically powerful lens surfaces to the paraxial image plane, expressed as the air-equivalent length (length excluding the glass block GB). "BF" is the back focus, expressed as the distance along the optical axis from the lens surface closest to the image among the optically powerful lens surfaces to the paraxial image plane, expressed as the air-equivalent length.

[0072] Furthermore, if the optical surface is aspherical, the symbol * is added to the right of the surface number. The aspherical shape is given by x = (h) where x is the displacement from the surface vertex in the direction of the optical axis, h is the height from the optical axis perpendicular to the optical axis, R is the radius of paraxial curvature, k is the cone constant, and A4, A6, A8, and A10 are the aspherical coefficients of each order. 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ] + A4 x h 4 + A6 × h 6 +A8×h 8 +A10×h 10 This is expressed as follows. Note that "e±XX" in each aspherical coefficient is "×10± ＸＸ It means "...".

[0073] Furthermore, the optical path difference function ψ0 of the surface at the design wavelength is given by ψ0 = U2 × h, where U2, U4, U6, U8, and U10 are coefficients of the optical path difference function of the surface. ２ +U4×h ４ +U6×h ６ +U8×h ８ +U10×h 10 It is expressed as follows:

[0074] [Numerical Example 1] Surface Data Surface Number rd nd νd Effective Diameter 1 17.120 0.60 1.61800 63.3 14.23 2 (Diffraction) 6.352 3.00 9.65 3 825.655 0.50 1.61800 63.3 7.75 4 4.094 3.91 5.87 5 14.759 1.25 2.00069 25.5 4.12 6 -20.402 1.58 3.66 8* 14.754 1.76 1.75501 51.2 6.14 9* -9.096 0.10 6.56 10 64.764 0.50 1.92286 18.9 6.74 11 4.351 5.38 1.85150 40.8 6.89 12 -371.572 (Variable) 7.55 13 ∞ 1.00 1.51633 64.1 10.00 14 ∞ (Variable) 10.00 Image plane ∞ Aspherical data second plane (diffraction plane) U 2 = 4.09441e-02 U 4 = 2.51217e-04 U 6 = -2.63854e-06 Optical path difference dispersion second plane P(λ) = 99.2922 × λ 6 - 447.9397 × λ 5 + 838.3518 × λ 4 - 836.5424 × λ 3+ 473.1175×λ 2- 146.5441×λ+ 20.8227 P(d)= 1.000432E+00 P(C)= 8.816019E-01 P(F)= 1.256261E+00 8th surface K =0.00000e+00 A 4=-8.80872e-04 9th surface K =0.00000e+00 A 4= 1.56247e-04 A 6=-1.22736e-05 A 8= 2.58874e-07 Various data Focal length 2.64 F-number 2.88 Half angle of view [°] 98.86 Image height 4.53 Lens length 27.17 BF 1.00 d12 2.80 d14 1.00 [Numerical Example 2] Face Number rd nd νd Effective Diameter 1 12.536 0.60 2.00100 29.1 11.07 2 5.005 2.27 7.78 3 (Diffraction) ∞ 0.50 1.65670 62.3 6.46 4 3.363 2.12 4.68 5 13.377 1.77 2.00100 29.1 3.59 6 -15.508 0.59 2.73 7 (Aperture) ∞ 2.81 2.17 8* 17.587 1.93 1.69350 53.2 6.06 9* -6.305 0.10 6.53 10 16.194 0.50 2.00272 19.3 6.88 11 4.051 5.22 1.77250 49.6 6.73 12 -19.223 (variable) 7.77 13 ∞ 1.00 1.51633 64.1 10.00 14 ∞ (variable) 10.00 Image plane ∞ Aspherical data third plane (diffraction plane) U2= 7.24279e-03 U4=-8.86729e-04 U6= 4.84785e-05 U8=-1.60348e-06 Optical path difference dispersion third plane P(λ)= 12.05455. - 113.49269 × λ + 639.22010 × λ ２ - 2391.27356 × λ ３ + 6239.37313 × λ ４ - 11587.26285 × λ 5 + 15317.57049 × λ ６ - 14126.71848 × λ ７ + 8657.89741 × λ ８ -3174.20584 × λ ９ + 527.57827 × λ １０P(d) = 1.000000e+00 P(C) = 8.993327e-01 P(F) = 1.203222e+00 Surface 8 K = 0.00000e+00 A 4 = -3.28172e-04 A 6 = 9.35486e-06 A 8 = -3.32727e-07 Surface 9 K = 0.00000e+00 A 4 = 1.24637e-03 Various data Focal length 2.65 F number 2.88 Half angle of view [°] 98.80 Image height 4.53 Lens length 22.57 BF 1.00 d12 2.17 d14 1.00 [Numerical example 3] Surface data Surface number rd nd νd Effective diameter 1 8.343 0.60 1.53775 74.7 7.37 2 (diffraction) 2.875 1.84 4.40 3* -2.502 0.50 1.53500 55.7 2.38 4* -4.468 0.15 1.69 5 (aperture) ∞ 0.10 1.66 6* 4.411 1.36 1.53500 55.7 1.76 7* -2.819 0.34 2.04 8* -2.020 0.60 1.67070 19.3 2.29 9* -3.046 0.09 2.88 10* 3.709 2.00 1.53500 55.7 3.83 11* -3.149 1.00 4.43 12* -6.889 0.80 1.67070 19.3 4.65 13* 4.065 (Variable) 6.40 14 ∞ 1.00 1.51633 64.1 10.00 15 ∞ (Variable) 10.00 Image plane ∞ Aspherical data second plane (diffraction plane) U 2 = 6.34622e-02 U 4 = 2.96035e-03 U 6 = -2.77175e-04 Optical path difference dispersion second plane P(λ) = 18.3669 × λ. 6 - 86.4710 × λ 5 + 171.0092 × λ 4 - 183.7005 × λ 3 + 115.2804 × λ 2- 41.9174×λ+ 8.0117 P(d)= 1.000110E+00 P(C)= 8.919978E-01 P(F)= 1.218926E+00 3rd surface K = 0.00000e+00 A 4= 9.16491e-02 A 6=-2.17527e-02 A 8= 3.33794e-03 4th side K = 0.00000e+00 A 4= 1.51065e-01 A 6=-4.55273e-02 A 8= 1.75417e-02 6th side K = 0.00000e+00 A 4= 3.04525e-02 A 6=-3.07428e-02 A 8=-6.48484e-03 7th side K = 0.00000e+00 A 4=-4.41231e-02 A 6= 6.24746e-03 A 8=-9.54924e-03 8th side K = 0.00000e+00 A 4= 3.57043e-02 A 6=-1.16360e-03 A 8=-5.90531e-05 9th side K = 0.00000e+00 A 4= 2.15762e-02 A 6=-7.12243e-04 A 8= 1.33531e-03 10th side K = 0.00000e+00A 4=-1.70109e-02 A 6= 9.96021e-04 A 8=-1.02251e-04 11th side K = 0.00000e+00 A 4= 2.54288e-02 A 6=-5.20297e-03 A 8= 4.26235e-04 12th side K = 0.00000e+00 A 4=-1.63829e-03 A 6=-5.18884e-03 A 8= 4.89865e-04 13th side K = 0.00000e+00 A 4=-2.18294e-02 A 6= 1.38743e-03 A 8=-5.03137e-05 Various data: Focal length 2.88, F-number 2.88, Half-angle of view [°] 93.02, Image height 4.53, Lens length 11.78, BF 1.00, d13 0.40, d15 1.00 [Numerical Example 4] Surface Data Surface Number rd nd νd Effective Diameter 1 16.368 0.50 1.48749 70.2 11.18 2 (Diffraction) 8.878 2.09 8.88 3* -3.099 0.50 1.53500 55.7 4.81 4* -17.596 0.92 3.22 5* -5.238 1.53 1.53500 55.7 2.21 6* -3.578 0.00 2.12 7 (Aperture) ∞ 0.10 2.15 8* 3.433 1.94 1.53500 55.7 2.22 9* -3.867 0.46 2.74 10* -2.155 0.50 1.67070 19.3 2.75 11* -2.893 0.35 3.31 12* 4.848 0.94 1.53500 55.7 4.38 13* -7.881 0.36 4.75 14* -4.484 0.65 1.67070 19.3 4.77 15* 8.004 (variable) 6.00 16 ∞ 1.00 1.51633 64.1 7.07 17 ∞ (Variable) 7.78 Image plane ∞ Aspherical data second plane (diffraction plane) U 2 = 3.85324e-02 U 4 = -6.30562e-04 U 6 = -1.15857e-05 U 8 = 3.31814e-07 Optical path difference dispersion of the second plane P(λ) = 27.6800 × λ. 6 - 128.8525 × λ 5 + 251.0673 × λ 4 - 264.2896 × λ 3 + 161.0859 × λ 2- 55.9552×λ+ 9.8364 P(d)= 1.000046E+00 P(C)= 8.887143E-01 P(F)= 1.229330E+00 Face 3 K =-1.73048e+01 A 4= 2.12676e-02 A 6=-3.13790e-03 A 8= 2.16909e-04 A10=-5.26476e-06 Face 4 K =-1.69606e+03 A 4= 6.28774e-02 A 6=-9.13206e-03 A 8= 2.31295e-03 A10=-4.21986e-04 Face 5 K = 0.00000e+00 A4 = -1.89879e-02 A6 = 3.15834e-03 A8 = -1.57859e-03 A10 = 5.11998e-04 Page 6 K = 0.00000e+00 A4 = 5.40335e-03 A6 = 1.11832e-03 A8 = 3.07931e-04 A10 = 1.58414e-04 Page 8 K = 0.00000e+00 A4 = 1.07554e-02 A6 = -7.18611e-03 A8 = 5.46231e-03 A10 = -2.90184e-03 Page 9 K = 0.00000e+00 A 4 = -2.41777e-02 A 6 = -9.29614e-03 A 8 = 3.37803e-03 A10 = -1.01183e-03 Page 10 K = 0.00000e+00 A 4 = 2.74744e-02 A 6 = -1.64616e-02 A 8 = 3.18441e-03 A10 = -1.42187e-03 Page 11 K = 0.00000e+00 A 4 = 3.66280e-02 A 6 = -2.01029e-04 A 8 = -1.37353e-03 A10 = 3.39200e-04 Page 12 K = 0.00000e+00 A 4 = -1.20630e-02 A 6 = 8.75806e-04 A 8 = -1.30581e-04 A10 = -8.00035e-06 Page 13 K = 0.00000e+00 A 4 = 1.45678e-02 A 6 = -2.50361e-03 A 8 = 2.60142e-04 A10 = -2.34191e-05 14th surface K = 0.00000e+00 A 4 = 1.54752e-02 A 6 = -2.87348e-03 A 8 = 1.65165e-04 A10 = -2.17999e-06 15th surface K = 0.00000e+00 A 4 = -7.47986e-03 A 6 = 3.10979e-04 A 8 = -2.98333e-05 A10 = 6.12170e-07 Various data Focal length 3.07 F-number 2.88 Half angle of view [°] 89.08 Image height 4.53 Lens length 13.77 BF 1.00 d15 0.94 d17 1.00 The various values ​​in each numerical example are summarized in Table 1 below.

[0075]

[0076] [Imaging Device] Next, an example of a digital still camera (imaging device) using the optical system of each embodiment as the imaging optical system will be described with reference to Figure 9. In Figure 9, 20 is the camera body, and 21 is the imaging optical system composed of one of the optical systems described in Examples 1 to 4. 22 is an image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which is built into the camera body and receives the optical image formed by the imaging optical system 21 and performs photoelectric conversion. 23 is a memory that records information corresponding to the subject image photoelectrically converted by the image sensor 22. 24 is a viewfinder composed of a liquid crystal display panel or the like, for observing the subject image formed on the image sensor 22.

[0077] By applying the optical systems of each embodiment to imaging devices such as digital still cameras, it is possible to realize imaging devices that can effectively correct chromatic aberration while mitigating the angle of incidence to the image sensor.

[0078] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist.

Claims

1. An optical system comprising: a first lens positioned closest to the object; an aperture diaphragm positioned between the first lens and the image plane; and an air lens with negative refractive power positioned closer to the object than the aperture diaphragm, wherein at least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffraction surface, and the condition 2.0 < EAmoe / EAst < 10.0 is satisfied when the effective diameter of the diffraction surface is EAmoe and the open diameter of the aperture diaphragm is EAst.

2. An optical system comprising a first lens positioned closest to the object, an aperture diaphragm positioned between the first lens and the image plane, and an air lens positioned closer to the object than the aperture diaphragm, wherein at least one of the lens surfaces constituting the air lens includes a dispersion-controlled diffraction surface.

3. The Abbe number of the diffraction surface is denoted as ν ｄ , the reference wavelength is the d-line, the main dispersion is defined by the F-line and the C-line, and the respective wavelengths are denoted as λ ｄ , λ Ｆ , λ Ｃ , the optical path difference function at each wavelength is denoted as ψ(λ ｄ ), ψ(λ Ｆ ), ψ(λ Ｃ ), and the optical path difference dispersion of the surface at each wavelength is denoted as P(λ ｄ ), P(λ Ｆ ), P(λ Ｃ ), the Abbe number is expressed by the following formula: 1 / ν ｄ ={ψ(λ Ｆ )-ψ(λ Ｃ )} / ψ(λ ｄ ) ={λ Ｆ ×P(λ Ｆ )-λ Ｃ ×P(λ Ｃ )} / λ ｄ ×P(λ ｄ ), and satisfies the conditional expression of -0.1<1 / νd<0.2, the optical system according to claim 1 or 2.

4. The optical system according to any one of claims 1 to 3, characterized in that, when L1s is the distance along the optical axis from the object-side lens surface of the first lens to the aperture diaphragm, the condition 0.1 < L1s / EAmoe < 1.5 is satisfied.

5. The optical system according to any one of claims 1 to 4, characterized in that, when Lms is the distance along the optical axis from the diffraction plane to the aperture diaphragm, and L1s is the distance along the optical axis from the object-side lens surface of the first lens to the aperture diaphragm, the condition 0.5 < Lms / L1s < 1.0 is satisfied.

6. The optical system according to any one of claims 1 to 5, characterized in that when the focal length of the air lens including the refractive power of the diffraction plane is fa and the focal length of the diffraction plane is fmoe, the condition 0.05 < fa / fmoe < 0.80 is satisfied.

7. The optical system according to any one of claims 1 to 6, characterized in that, when the focal length of the air lens including the refractive power of the diffraction plane is fa and the focal length of the optical system is f, the condition -3.5 < fa / f < -0.5 is satisfied.

8. An optical system according to any one of claims 1 to 7, characterized in that, when the focal length of the lens having the diffraction surface including the refractive power of the diffraction surface is fN and the focal length of the diffraction surface is fmoe, the condition 0.05 < fN / fmoe < 1.50 is satisfied.

9. φ is the reciprocal of the focal length and the Abbe number of the i-th lens (where i is a natural number) from the object side, among the lenses positioned on the object side of the aperture diaphragm. ｉ , v ｄｉ , the reciprocal of the focal length of the diffraction plane is φ ｍｅｔａ In this case, -0.02 < Σφ ｉ / ν ｄｉ +φ ｍｅｔａ / ν ｄ The optical system according to any one of claims 1 to 8, characterized in that it satisfies the conditional expression < 0.

02.

10. The optical system according to any one of claims 1 to 9, characterized in that, when the radius of curvature of the object-side lens surface of the air lens is r12 and the focal length of the optical system is f, the condition 1.5 < r12 / f < 5.0 is satisfied.

11. The optical system according to any one of claims 1 to 10, characterized in that, when the radius of curvature of the object-side lens surface of the air lens is r12 and the radius of curvature of the image-side lens surface of the air lens is r21, the following condition is satisfied: -10.0 < (r12 + r21) / (r12 - r21) < 1.

0.

12. The optical system according to any one of claims 1 to 11, characterized in that, when the combined focal length of the lens positioned closer to the object than the aperture diaphragm is f1s and the focal length of the optical system is f, the condition -30.0 < f1s / f < -0.5 is satisfied.

13. The optical system according to any one of claims 1 to 12, characterized in that the diffraction surface has a pillar shape due to uneven shapes of different sizes or shapes.

14. The optical system according to any one of claims 1 to 13, characterized in that the diffraction plane is formed on the image-side lens surface of the first lens.

15. The optical system according to any one of claims 1 to 14, characterized in that the diffraction plane is formed on the object-side lens surface of a second lens which is arranged adjacent to the image side of the first lens.

16. An optical system according to any one of claims 1 to 15, comprising, arranged in order from the object side to the image side, a first lens with negative refractive power, a second lens with negative refractive power, a third lens with positive refractive power, the aperture diaphragm, a fourth lens with positive refractive power, a fifth lens with negative refractive power, and a sixth lens with positive refractive power, wherein at least one of the image-side lens surface of the first lens or the object-side lens surface of the second lens includes the diffraction surface.

17. The optical system according to any one of claims 1 to 15, comprising, arranged in order from the object side to the image side, a first lens with negative refractive power, a second lens with negative refractive power, the aperture diaphragm, a third lens with positive refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, and a sixth lens with negative refractive power, wherein the image-side lens surface of the first lens includes the diffraction surface.

18. An optical system according to any one of claims 1 to 15, comprising, arranged in order from the object side to the image side, a first lens with negative refractive power, a second lens with negative refractive power, a third lens with positive refractive power, the aperture diaphragm, a fourth lens with positive refractive power, a fifth lens with negative refractive power, a sixth lens with positive refractive power, and a seventh lens with negative refractive power, wherein the image-side lens surface of the first lens includes the diffraction surface.

19. An imaging device comprising an optical system according to any one of claims 1 to 18, and an image sensor that receives an image formed by the optical system.

20. The imaging apparatus according to claim 19, characterized in that, when the focal length of the optical system is f and the distance from the optical axis to the position of the light ray of the optical system with the maximum field of view on the imaging surface of the image sensor is imgH, the condition 0.5 < f / imgH < 1.0 is satisfied.

21. The imaging apparatus according to claim 19 or 20, characterized in that, when TDL is the distance along the optical axis from the object-side lens surface of the first lens to the image sensor, and imgH is the distance from the optical axis to the position of the light ray of the maximum field of view of the optical system on the imaging surface of the image sensor, the following condition is satisfied: 1.5 < TDL / imgH < 8.0.

Images