Optical system and imaging device

Abstract

To provide an optical system which is compact and has high optical performance.SOLUTION: An optical system reflects light from an object side by a first reflection surface M1 and further reflects light by a second reflection surface M2, then leads light to the image side. The optical system includes a diffraction surface Lm whose wavelength dispersion characteristic is controlled. Assuming that ν0 represents the Abbe number of the diffraction surface, the condition -0.2<1 / ν0<0.2 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] There is a demand for reducing the number of lenses and shortening the overall optical length of optical systems used in small imaging devices. Patent Document 1 discloses an optical system that achieves miniaturization by reducing the number of lenses using a flat lens with a diffractive surface and folding the optical path using two reflecting surfaces. Patent Document 2 discloses an optical system that shortens the overall optical length by folding the optical path using two semi-transmissive reflecting surfaces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Publication No. 2022 / 0121016 [Patent Document 2] Patent No. 6778823 Summary of the Invention [Problem to be solved by the invention]

[0004] If a normal diffractive surface with uncontrolled wavelength dispersion characteristics is used as in Patent Document 1, the Abbe number will be -3.45, which is an extremely high dispersion. Considering the chromatic aberration that occurs in this case, it is difficult to give the diffractive surface a large optical power (the reciprocal of the focal length), and there is a limit to further reducing the number of lenses and shortening the overall optical length.

[0005] Furthermore, in Patent Document 2, the semi-transmissive reflective surface is configured as a flat surface in order to shorten the lens back, so that it is difficult to reduce the number of lenses in the optical system and to achieve high specifications.

[0006] The present invention provides an optical system that can be made compact by reducing the number of lenses and the total optical length, and that has high optical performance. [Means for solving the problem]

[0007] According to one aspect of the present invention, an optical system reflects light from an object side by a first reflecting surface, and then reflects the light by a second reflecting surface and guides the light to an image side. The optical system includes a diffractive surface or metasurface with controlled wavelength dispersion characteristics. When the Abbe number of the diffractive surface or metasurface is ν0, -0.2<1 / ν0<0.2 The optical system according to the present invention is characterized in that it satisfies the following conditions: An image pickup apparatus including the optical system described above also constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, it is possible to provide an optical system that is compact by reducing the number of lenses and the total optical length, and that has high optical performance. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] FIG. 4 is a longitudinal aberration diagram of the optical system of the first embodiment. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 6A to 6C are longitudinal aberration diagrams of the optical system of Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of the optical system of the third embodiment. [Figure 6] 11A to 11C are longitudinal aberration diagrams of the optical system of Example 3. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 4. [Figure 9] FIG. 13 is a cross-sectional view of the optical system of the fifth embodiment. [Figure 10] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 5. [Figure 11] FIG. 13 is a cross-sectional view of the optical system of the sixth embodiment. [Figure 12] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 6. [Figure 13] FIG. 13 is a cross-sectional view of the optical system of Example 7. [Figure 14] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 7. [Figure 15] FIG. 13 is a cross-sectional view of the optical system of Example 8. [Figure 16] 13A to 13C are longitudinal aberration diagrams of the optical system of Example 8. [Figure 17] FIG. 13 is a cross-sectional view of the optical system of the ninth embodiment. [Figure 18] 13 is a spot diagram of the optical system of Example 9. [Figure 19] 1A and 1B are diagrams illustrating a configuration in which polarized light is used. [Figure 20] FIG. 1 is a diagram showing an imaging device equipped with an optical system according to any one of Examples 1 to 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing specific embodiments 1 to 9, matters common to the embodiments will be described.

[0011] 1, 3, 5, 7, 9, 11, 13, 15, and 17 show the configurations of the optical systems of Examples 1 to 9, respectively. The optical systems of the examples are used as imaging optical systems in imaging devices such as digital cameras and film cameras, and further in imaging devices mounted on smartphones, tablets, etc. In each figure, the left side is the object side (subject side), and the right side is the image side.

[0012] In each embodiment, Lm denotes a diffractive surface with controlled wavelength dispersion characteristics (hereinafter simply referred to as dispersion controlled). M1 denotes a first reflecting surface, and M2 denotes a second reflecting surface. CG denotes a glass block equivalent to a cover glass, low-pass filter, IR cut filter, etc. IM denotes the image plane of the optical system. On the image plane IM, the imaging surface (light receiving surface) of an imaging element such as a CCD sensor or CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is disposed.

[0013] The optical system of each embodiment is an optical system that reflects light from the object side by a first reflecting surface M1, and then reflects it further by a second reflecting surface M2 to guide it to the image side, and includes a dispersion-controlled diffractive surface Lm. The optical path is folded by the first and second reflecting surfaces M1 and M2, thereby shortening the total optical length of the optical system. In an optical system configured in this way, the Abbe number ν0 of the dispersion-controlled diffractive surface Lm satisfies the condition shown in the following formula (1).

[0014] -0.2<1 / ν0<0.2 (1) The Abbe number ν0 of the dispersion-controlled diffractive surface Lm is defined by the following formula. Here, the reference wavelength is the d line (λ d =0.58756μm), main dispersion is F line (λ F =0.48613μm) and C line (λ C = 0.65627 μm, and the optical path difference function at each wavelength is 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 ) In this case,

[0015]

number

[0016] It is.

[0017] The condition of formula (1) is a condition related to the wavelength dispersion characteristic (corresponding to the Abbe number in a refractive lens) of the dispersion-controlled diffractive surface Lm, and indicates the appropriate range of 1 / ν0 for achieving high optical performance by achieving both achromatization and reduction in the number of lenses in the entire optical system. If 1 / ν0 is below the lower limit of formula (1), the wavelength dispersion characteristic of the diffractive surface Lm becomes too high dispersion as a negative Abbe number, and the chromatic aberration generated at the diffractive surface Lm increases, making it impossible to strengthen the optical power of the diffractive surface Lm. As a result, it becomes difficult to downsize the optical system and reduce the number of lenses, which is undesirable. If 1 / ν0 is above the upper limit of formula (1), the wavelength dispersion characteristic of the diffractive surface Lm becomes too high dispersion as a positive Abbe number, and the chromatic aberration generated at the diffractive surface Lm increases, making it impossible to strengthen the optical power of the diffractive surface Lm, which is undesirable. In addition, when realizing a dispersion-controlled diffraction surface Lm using a metasurface, it is not preferable because it is difficult to design a metastructure with high diffraction efficiency in order to obtain high dispersion characteristics corresponding to a positive Abbe number.

[0018] It is more preferable that the numerical range of the formula (1) is as follows:

[0019] -0.1<1 / ν0<0.1 (1a) Moreover, it is more preferable that the numerical range of the formula (1) is set to the following range.

[0020] -0.05<1 / ν0<0.08 (1b) In each embodiment, an optical system includes a dispersion-controlled diffractive surface and two reflecting surfaces, and by optimizing the wavelength dispersion characteristics of the diffractive surface, the number of lenses in the optical system is reduced and the overall optical length of the optical system is shortened, thereby realizing an optical system that is small in size and has high optical performance.

[0021] It is preferable that the optical system of each embodiment has the following configuration and satisfies at least one of the conditions of expressions (2) to (5).

[0022] In each embodiment, it is preferable that at least one of the first and second reflecting surfaces M1 and M2 is a concave mirror having a positive optical power. With this configuration, by using a reflecting surface that does not generate chromatic aberration and a dispersion-controlled diffractive surface Lm, it is possible to suppress chromatic aberration in the entire optical system while realizing a compact optical system. In particular, by making the dispersion-controlled diffractive surface Lm zero dispersion (1 / ν0=0), the optical system can be configured to generate almost no chromatic aberration in combination with the reflecting surface.

[0023] In each embodiment, when the focal length of the dispersion-controlled diffractive surface Lm is fm and the focal length of the entire optical system is f, it is preferable to satisfy the condition of the following formula (2). When there are multiple diffractive surfaces Lm, the focal length fm of the diffractive surface Lm is the focal length of the diffractive surface with the strongest optical power.

[0024] 0.01 <f / |fm|<5.00 (2) Here, the focal length fm of the dispersion-controlled diffractive surface Lm is calculated by the following formula, where U2 is the quadratic coefficient of the optical path difference function of the surface at the wavelength used (design wavelength).

[0025]

number

[0026] The condition of formula (2) indicates the appropriate power sharing of the dispersion-controlled diffractive surface Lm in the optical system. When f / |fm| exceeds the upper limit of formula (2), the focal length of the dispersion-controlled diffractive surface Lm becomes too short relative to the focal length of the entire optical system, which causes large monochromatic aberrations such as spherical aberration, making it difficult to obtain high optical performance, which is undesirable. When f / |fm| falls below the lower limit of formula (2), the focal length of the dispersion-controlled diffractive surface Lm becomes too long relative to the focal length of the entire optical system, which causes the total optical length of the optical system to increase, making it difficult to miniaturize the optical system, which is undesirable.

[0027] It is more preferable that the numerical range of the formula (2) is as follows:

[0028] 0.05 <f / |fm|<4.00 (2a) Moreover, it is more preferable that the numerical range of the formula (2) is set to the following range.

[0029] 0.1 <f / |fm|<3.0 (2b) In each embodiment, when the focal length of the dispersion-controlled diffractive surface Lm is denoted by fm and the focal length of the reflecting surface having the strongest optical power among the first and second reflecting surfaces M1, M2 is denoted by fr, it is preferable to satisfy the condition of the following equation (3):

[0030] |fm / fr|<10.0 (3) The condition of formula (3) indicates the appropriate power sharing within the optical system between the dispersion-controlled diffractive surface Lm and the reflecting surface with the strongest optical power. If |fm / fr| exceeds the upper limit of formula (3), the optical power of the dispersion-controlled diffractive surface Lm becomes too strong relative to the optical power of the reflecting surface. As a result, monochromatic aberrations such as spherical aberration are generated significantly on the diffractive surface Lm, making it difficult to obtain high optical performance, which is not preferable.

[0031] It is more preferable that the numerical range of the formula (3) is as follows:

[0032] |fm / fr|<8.0 (3a) Moreover, it is more preferable that the numerical range of the formula (3) is set to the following range.

[0033] |fm / fr|<6.0 (3b) In each embodiment, it is preferable to arrange the dispersion-controlled diffractive surface Lm closer to the object side than the first reflecting surface M1. In this case, it is preferable to satisfy the condition of the following formula (4), where D1 is the optically effective diameter of the first reflecting surface M1, f is the focal length of the entire optical system, and Fno is the maximum aperture ratio of the optical system. The optically effective diameter is the radius (mm) of the area of ​​the first reflecting surface M1 through which light rays that contribute to image formation on the image plane pass. The maximum aperture ratio is the aperture ratio (F-number) when the diaphragm is in the maximum aperture state.

[0034] 0.1 <D1 / (f / Fno)<1.1 (4) Equation (4) shows the appropriate relationship between the entrance pupil diameter of the optical system and the optical effective diameter of the first reflecting surface M1. By arranging the dispersion-controlled diffractive surface Lm on the object (light ray incidence) side of the first reflecting surface M1 to converge the incident light beam to the first reflecting surface M1, the optical effective diameter of the first reflecting surface M1 can be reduced and the optical system can be made compact. This arrangement is particularly advantageous for telephoto optical systems with a large entrance pupil diameter and a large aperture ratio. If D1 / (f / Fno) is below the lower limit of Equation (4), the optical effective diameter of the first reflecting surface M1 becomes too small relative to the entrance pupil diameter. As a result, the dispersion-controlled diffractive surface Lm is given strong optical power, and monochromatic aberrations such as spherical aberrations are generated significantly in the diffractive surface Lm, making it difficult to obtain high optical performance, which is not preferable. If D1 / (f / Fno) is above the upper limit of Equation (4), the optical effective diameter of the first reflecting surface M1 becomes too large relative to the entrance pupil diameter, which is not preferable, because the optical effective diameter of the first reflecting surface M1 becomes too large relative to the entrance pupil diameter, and the optical system becomes large.

[0035] It is more preferable that the numerical range of the formula (4) is as follows:

[0036] 0.2 <D1 / (f / Fno)<0.8 (4a) Moreover, it is more preferable that the numerical range of the formula (4) is set to the following range.

[0037] 0.3 <D1 / (f / Fno)<0.7 (4b) In each embodiment, it is preferable to satisfy the condition of the following formula (5), where OAL is the total optical length of the optical system and f is the focal length of the entire optical system. The total optical length OAL is the distance on the optical axis from the lens surface (frontmost) closest to the object in the optical system to the image plane. Note that the total optical length OAL for the portion of the glass block CG such as the cover glass is an air-equivalent value.

[0038] 0.1 <OAL / f<1.4 (5) The condition of formula (5) indicates the appropriate telephoto ratio of the optical system. When OAL / f is below the lower limit of formula (5), the total optical length becomes too short for the focal length of the optical system. As a result, even if the optical path is folded at the first and second reflecting surfaces M1 and M2, the dispersion-controlled diffractive surface Lm and each reflecting surface share strong optical power. Therefore, it becomes difficult to correct monochromatic aberrations other than chromatic aberration such as spherical aberration and curvature of field, and it becomes difficult to obtain high optical performance, which is not preferable. When OAL / f is above the upper limit of formula (5), the total optical length becomes too long for the focal length of the optical system, which is not preferable because the optical system becomes large.

[0039] It is more preferable that the numerical range of the formula (5) is as follows:

[0040] 0.2 <OAL / f<1.0 (5a) Moreover, it is more preferable that the numerical range of the formula (5) is set to the following range.

[0041] 0.2 <OAL / f<0.6 (5b) As in each embodiment, it is preferable that the dispersion-controlled diffractive surface Lm has a positive optical power. When there are a plurality of dispersion-controlled diffractive surfaces Lm, at least one of the diffractive surfaces Lm should have a positive optical power. By making the dispersion-controlled diffractive surface Lm have a positive optical power, the diffractive surface Lm can share a part of the positive power of the entire optical system, and the optical system can be made compact. In particular, by making the diffractive surface Lm having a positive optical power low dispersion, the configuration that previously required two lenses, a positive lens and a negative lens, for achromatization can be replaced with one diffractive surface Lm.

[0042] As in Examples 1 to 7, both the first and second reflecting surfaces M1 and M2 may be semi-transmissive reflecting surfaces. In this case, it is preferable that light from an object is transmitted through the second reflecting surface M2, reflected by the first reflecting surface M1, reflected by the second reflecting surface M2, and transmitted through the first reflecting surface M1 to be guided to the image surface. By folding the optical path at two semi-transmissive reflecting surfaces as in this configuration, the total optical length can be shortened. In addition, by adopting a configuration using polarized light, which will be described later, it is possible to prevent unnecessary light that is not reflected even once by the two semi-transmissive reflecting surfaces from reaching the image surface.

[0043] As in Example 8, the first reflecting surface M1 may have a non-reflective portion (for example, a hole through which light passes). In this case, it is preferable that light from an object is reflected by the reflective portion of the first reflecting surface M1, reflected by the second reflecting surface M2, and passed (or transmitted) through the non-reflective portion of the first reflecting surface M1 to be guided to the image surface. By folding the optical path at two reflecting surfaces as in this configuration, the total optical length can be shortened.

[0044] As in each embodiment, at least one refractive lens may be disposed in the optical system. By disposing a refractive lens, it is possible to achieve high optical performance by correcting monochromatic aberration that cannot be corrected by the dispersion-controlled diffractive surface Lm and the first and second reflecting surfaces M1 and M2. The Petzval term generated by the dispersion-controlled diffractive surface Lm is zero. Therefore, when optical power is given to each reflecting surface in order to reduce the size of the optical system, the Petzval term generated by the reflecting surface is corrected by the Petzval term generated by the refractive lens, thereby allowing the field curvature to be corrected satisfactorily.

[0045] As in Examples 2 to 9, the optical system may include at least one positive refractive lens and a negative refractive lens. By including a positive and a negative refractive lens, it is possible to correct monochromatic aberration that cannot be corrected by the diffractive surface Lm and the first and second reflecting surfaces M1 and M2, and also correct chromatic aberration, thereby achieving high optical performance.

[0046] Furthermore, when the optical system includes positive and negative refractive lenses, the optical power of the i-th refractive lens from the object side among all the refractive lenses in the optical system is Φi, the Abbe number of the i-th refractive lens based on the d-line is νdi, and the sum of Φi / νdi of all the refractive lenses is Σ(Φi / νdi). The focal length of the entire optical system is f. In this case, it is preferable to satisfy the condition of the following formula (6). The Abbe number νd based on the d-line is expressed as νd=(Nd-1) / (NF-NC) when the refractive indices at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm) of the Fraunhofer line are Nd, NF, and NC, respectively.

[0047] 1000×|Σ(Φi / νdi)| / f<1.0 (6) The condition of formula (6) indicates the appropriate achromatic state of the refractive lens included in the optical system. Since the first and second reflecting surfaces M1 and M2 do not generate chromatic aberration, when the dispersion characteristic of the dispersion-controlled diffractive surface Lm is set to zero dispersion or low dispersion, the refractive lens combined with them is arranged in an appropriate position for achromatization, and the chromatic aberration is well corrected in the entire optical system to achieve high optical performance. If 1000×|Σ(Φi / νdi)| / f exceeds the upper limit of formula (6), the chromatic aberration generated by the refractive lens becomes too large and chromatic aberration remains, making it difficult to obtain high optical performance, which is not preferable.

[0048] It is more preferable that the numerical range of the formula (6) is as follows:

[0049] 1000×|Σ(Φi / νdi)| / f<0.8 (6a) Moreover, it is more preferable that the numerical range of the formula (6) is set to the following range.

[0050] 1000×|Σ(Φi / νdi)| / f<0.4 (6b) [Polarized Configuration] FIG. 19 shows an optical configuration using polarized light in the optical system of Examples 1 to 7. In these Examples, both the first and second reflecting surfaces M1 and M2 are semi-transmissive reflecting surfaces, and at least one of them is configured by a polarization-selective semi-transmissive reflecting element. In the configuration of FIG. 19, the first reflecting surface M1 is a half mirror (HM) C, and the second reflecting surface M2 arranged on the object OBJ side of the first reflecting surface M1 is a polarization-selective semi-transmissive reflecting element A. The half mirror C is formed by a dielectric multilayer film or metal deposition, and functions as a semi-transmissive reflecting surface in the wavelength region of the light to be imaged. In addition, examples of the polarization-selective semi-transmissive reflecting element A include a wire grid element such as WGF (registered trademark) manufactured by Asahi Kasei Corporation, a reflective linear polarizing element such as IQP-E manufactured by 3M, and a circularly polarized reflecting element using cholesteric liquid crystal. In the configuration of FIG. 19, the polarization-selective semi-transmissive reflecting element A transmits linearly polarized light with a polarization direction parallel to the paper surface of the figure, and reflects linearly polarized light with a polarization direction perpendicular to the paper surface.

[0051] A first λ / 4 plate B is disposed between the two semi-transmissive reflective surfaces (A, C). The first λ / 4 plate B is disposed so that its slow axis is inclined at 45° with respect to the polarized light transmission axis of the polarization-selective semi-transmissive reflector A. When a circular polarized light reflector is used as the polarization-selective semi-transmissive reflector A, the first λ / 4 plate B is not necessary.

[0052] In the configuration of Fig. 19, the second λ / 4 plate D is disposed closer to the image side than the half mirror C. The second λ / 4 plate D is disposed so that its slow axis is inclined at 45° to the polarized light transmission axis of the polarization-selective semi-transmissive reflector A. Furthermore, the first λ / 4 plate B and the second λ / 4 plate D are preferably disposed so that their slow axes are inclined at 90° to each other. In this arrangement, when light passes through the first λ / 4 plate B and the second λ / 4 plate D, the wavelength dispersion characteristics of each λ / 4 are offset.

[0053] 19, an absorptive linear polarizing element E is disposed on the image side of the second λ / 4 plate D. When the orientations of the slow axes of the first and second λ / 4 plates B and D are set as described above, the polarization transmission axis of the absorptive linear polarizing element E extends in a direction perpendicular to the plane of the drawing.

[0054] Although the illustration of the above-mentioned elements is omitted in the figures showing Examples 1 to 7, methods for arranging the elements can include bonding a film-like element to the optical surface of the lens, or molding a wire grid structure integrally with the lens base material when molding the resin lens.

[0055] By adopting the above-described configuration using polarized light, it is possible to suppress a decrease in the amount of light that reaches the image plane IM from the object OBJ via the normal optical path, while reducing unwanted light (ghost light and leakage light) that reaches the image plane IM without reflecting once through the two semi-transmissive reflective surfaces (A, C).

[0056] The optical path of normal imaging light in the above configuration using polarized light will now be described. Imaging light incident as non-polarized light from an object OBJ passes through the polarization-selective semi-transmissive reflector A and is converted into linearly polarized light with a polarization direction parallel to the paper surface of the figure. The linearly polarized light is then converted into circularly polarized light by the first λ / 4 plate B, and the circularly polarized light enters the half mirror C.

[0057] A portion of the circularly polarized light that enters the half mirror C is transmitted and converted by the second λ / 4 plate D into linearly polarized light with a polarization direction parallel to the plane of the drawing. This linearly polarized light is absorbed by the absorbing linear polarization element E. Meanwhile, the remainder of the circularly polarized light that enters the half mirror C is reflected by the half mirror C and converted into reverse circularly polarized light, which returns to the second λ / 4 plate D and is converted into linearly polarized light with a polarization direction perpendicular to the plane of the drawing. This linearly polarized light enters the polarization-selective semi-transmissive reflector A and is reflected by the polarization selectivity of the polarization-selective semi-transmissive reflector A.

[0058] The linearly polarized light reflected by the polarization-selective semi-transmissive reflector A is converted by the first λ / 4 plate B into circularly polarized light in the opposite direction to the circularly polarized light originally converted by the first λ / 4 plate B, and this circularly polarized light then enters the half mirror C. The circularly polarized light that passes through the half mirror C is converted by the second λ / 4 plate D into linearly polarized light with a polarization direction perpendicular to the paper surface of the figure. The linearly polarized light passes through the absorbing linear polarizer E and reaches the image plane IM.

[0059] In this way, the normal imaging light is reflected by the half mirror C, reflected by the polarization-selective semi-transmissive reflector A, and transmitted through the half mirror C to be guided to the image plane IM. When a reflective linear polarizing element is used as the polarization-selective semi-transmissive reflector A, it is preferable to place an absorptive polarizing element having a polarization transmission axis in the same direction as the polarization transmission axis of the reflective linear polarizing element A on the object side of the polarization-selective semi-transmissive reflector A. With this configuration, the reflection by the reflective linear polarizing element (A) of the linearly polarized component of the light incident on the polarization-selective semi-transmissive reflector A from the object OBJ with the polarization direction perpendicular to the paper surface of the figure can be absorbed by the absorptive polarizing element.

[0060] Moreover, the optical system of each embodiment can have a focusing function and an anti-shake function for correcting image blur caused by camera shake or the like, using a known configuration. The focusing function is realized, for example, by a configuration in which the whole or a part of the optical system, or the image sensor, is moved in the direction of the optical axis. The anti-shake function is realized by a configuration in which the whole or a part of the optical system, or the image sensor, is moved eccentrically with respect to the optical axis. Furthermore, the focusing function and the anti-shake function may be realized by using an optical element whose refractive power is variable by mechanical or electrical action, such as a shape-changing lens or a liquid crystal lens that utilizes pressure or electrowetting, or the like.

[0061] Furthermore, when an image of a subject formed by the optical system of each embodiment is photoelectrically converted (captured) by an imaging element to generate image data, various aberrations such as distortion may be electronically corrected by image processing of the image data.

[0062] Furthermore, an optical path difference function equivalent to that of the diffractive surface Lm may be realized by a metalens having a so-called single-layer metasurface, in which the metasurface consists of one layer, or by a metalens having a so-called stacked metasurface, in which the metasurface consists of multiple layers. EXAMPLES

[0063] The optical system of Example 1 (Numerical Example 1) shown in FIG. 1 is a medium telephoto optical system with a diagonal half angle of view of about 10° and an aperture ratio of about 2.

[0064] The optical system has a dispersion-controlled diffractive surface Lm arranged closest to the object, and a second reflecting surface M2 and a first reflecting surface M1 arranged in order toward the image side. The optical path is folded by the first and second reflecting surfaces M1 and M2, thereby shortening the overall optical length. In addition, the dispersion-controlled diffractive surface Lm is given a positive refractive power, thereby reducing the optical effective diameter of the first reflecting surface M1, and the second reflecting surface M2 is configured as a concave mirror to have a positive optical power, thereby further miniaturizing the optical system. Furthermore, a refractive lens having an aspheric surface is arranged in the optical system, and the correction of monochromatic aberration is appropriately shared among the aspheric surface, the diffractive surface Lm, and the first and second reflecting surfaces M1 and M2, thereby obtaining high optical performance. EXAMPLES

[0065] The optical system of Example 2 (Numerical Example 2) shown in Figure 3 has the same basic configuration and optical specifications as Example 1, but is different in the wavelength dispersion characteristics and optical path difference function of the diffractive surface Lm, the shapes of the first and second reflecting surfaces M1 and M2 and the refractive lens, etc.

[0066] In the second embodiment, achromatization of the refractive system is achieved by arranging a positive refractive lens and a negative refractive lens within the optical system, and further, excellent achromatization is achieved throughout the optical system by combining a zero-dispersion diffractive surface Lm with the first and second reflecting surfaces M1 and M2. EXAMPLES

[0067] The optical system of Example 3 (Numerical Example 3) shown in FIG. 5 is a large-aperture standard optical system with a diagonal half angle of view of about 23° and an aperture ratio of about 0.8.

[0068] The optical system of this embodiment has the same basic configuration as that of the second embodiment, but differs from the second embodiment in the optical specifications, the wavelength dispersion characteristics and optical path difference function of the diffractive surface Lm, the shapes of the first and second reflecting surfaces M1, M2 and the refractive lens, etc. EXAMPLES

[0069] The optical system of Example 4 (Numerical Example 4) shown in FIG. 7 is a large-aperture wide-angle optical system with a diagonal half angle of view of about 35° and an aperture ratio of about 0.8.

[0070] The optical system of this embodiment has the same basic configuration as that of the second embodiment, but differs from that of the second embodiment in the optical specifications, the wavelength dispersion characteristics and optical path difference function of the diffractive surface Lm, the shapes of the first and second reflecting surfaces M1 and M2 and the refractive lens, etc. EXAMPLES

[0071] The optical system of Example 5 (Numerical Example 5) shown in Figure 9 has the same optical specifications as Example 4, but a dispersion-controlled diffractive surface Lm is disposed between the first and second reflecting surfaces M1, M2, making the wavelength dispersion characteristics of the diffractive surface Lm different from those of Example 4.

[0072] In this embodiment, the imaging light passes through the diffractive surface Lm three times, which makes it possible to make greater use of the characteristics of the diffractive surface Lm, which has a zero Petzval term and controllable wavelength dispersion characteristics. EXAMPLES

[0073] The optical system of Example 6 (Numerical Example 6) shown in Figure 11 has the same optical specifications as Example 4, but a dispersion-controlled diffractive surface Lm is positioned on the image side of the first and second reflecting surfaces M1, M2, making the wavelength dispersion characteristics of the diffractive surface Lm different from those of Example 4.

[0074] In this embodiment, by arranging the diffractive surface Lm at a position where the height of the pupil paraxial ray is high, it is possible to selectively control the lateral chromatic aberration and the exit pupil position without significantly affecting the axial chromatic aberration and spherical aberration. EXAMPLES

[0075] 13 is a super telephoto optical system with a diagonal half angle of view of about 2.5° and an aperture ratio of about 2.8. The basic configuration of the optical system of this embodiment and the wavelength dispersion characteristics of the diffractive surface Lm are the same as those of the second embodiment. In this embodiment, the diffractive surface Lm is disposed closer to the object side than the first and second reflecting surfaces M1 and M2, and the optical specifications of the optical system, the optical path difference function of the diffractive surface Lm, and the shapes of the first and second reflecting surfaces M1 and M2 and the refractive lens are different from those of the second embodiment. EXAMPLES

[0076] The optical system of Example 8 (Numerical Example 8) shown in Fig. 15 is an ultra-telephoto optical system with a diagonal half angle of view of about 2.5° and an aperture ratio of about 5.6. The basic configuration of the optical system of this example and the wavelength dispersion characteristics of the diffractive surface Lm are the same as those of Example 7. This example employs a so-called catadioptric configuration in which the total optical length is shortened by folding the optical path by combining a first reflecting surface M1 and a second reflecting surface M2 having a non-reflective portion (hole). EXAMPLES

[0077] 17 is a medium telephoto optical system with a half angle of view of about 7° and an aperture ratio of about 4. In the optical system of this embodiment, the arrangement of the diffractive surface Lm and the wavelength dispersion characteristics are the same as those of the seventh embodiment.

[0078] In this embodiment, the first reflecting surface M1 and the second reflecting surface M2 are formed of free-form surfaces (aspheric surfaces), and an optical path is formed with an eccentric optical axis, thereby reducing the volume of the optical system.

[0079] The drop in the T number of the optical system is about 3 steps in the coaxial folding configuration and the polarized light utilization configuration of Examples 1 to 7, and about 1 step in the catadioptric configuration of Example 8. Furthermore, there is no drop in the T number in the decentered configuration of the free curved surface mirror of Example 9.

[0080] Although the coaxial folding configuration and the use of polarized light have a large drop in the T number, the optical path folding configuration can shorten the overall optical length from wide-angle to super telephoto, and is also advantageous for increasing the aperture from wide-angle to medium telephoto. In addition, the catadioptric configuration has issues such as ring blur due to pupil shading and vignetting of imaging light from wide-angle to standard optical systems, but in super telephoto optical systems, a balance can be achieved between shortening the overall optical length and the drop in the T number. Furthermore, the free-form mirror decentering configuration has an advantage over others in terms of the drop in the T number, but the manufacturing difficulty of the reflective surface is high, and the effect of shortening the overall optical length is not as good as the coaxial folding configuration.

[0081] Taking these factors into consideration, one of the above three optical configurations can be selected according to the required optical specifications to realize an optical system that is compact and has high optical performance.

[0082] Numerical examples 1 to 9 are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, and d is the lens thickness or air space (mm) on the optical axis between the i-th and (i+1)-th surfaces. nd is the refractive index at the d-line of the optical material between the i-th and (i+1)-th surfaces. νd is the Abbe number based on the d-line of the optical material between the i-th and (i+1)-th surfaces, and is expressed as described above. The effective diameter (mm) corresponds to the optical effective diameter described above, and indicates the radius (mm) of the area through which light rays that contribute to image formation pass on the i-th surface.

[0083] BF stands for back focus (mm). Back focus is the distance on the optical axis from the surface closest to the image (last surface) of the optical system to the paraxial image surface, expressed as an air-equivalent length. The total lens length corresponds to the optical length mentioned above, and is the distance on the optical axis from the front surface to the last surface of the optical system plus the back focus.

[0084] An "*" next to a surface number means that the surface has an aspheric shape. An aspheric shape is expressed by the following formula, where x is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the conic constant, and A4 to A10 are aspheric coefficients. Note that the conic constant and the aspheric coefficients "e±M" are expressed as x10 ±M means.

[0085] x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ] +A4·h 4 +A6·h 6 +A8·h 8 +A10·h 10 Moreover, the optical path difference function of the surface at the design wavelength is expressed by the following formula, where U2 to U10 are the optical path difference function coefficients of the surface.

[0086] ψ0=U2 h 2 +U4·h 4 +U6·h 6 +U8·h 8 +U10·h 10 The (diffraction) affixed to the surface number means that the surface is optically designed according to the optical path difference function of the surface.

[0087] The values ​​of Numerical Examples 1 to 9 relating to the above-mentioned formulas (1) to (6) are summarized in Table 1. As can be seen from Table 1, the optical systems of Numerical Examples 1 to 8 satisfy the conditions of formulas (1) to (6). The optical system of Numerical Example 9 also satisfies the conditions of formulas (1), (2), and (6).

[0088] 2, 4, 6, 8, 10, 12, 14, and 16 respectively show longitudinal aberration diagrams (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Numerical Examples 1 to 8 corresponding to Examples 1 to 8 in a state where the optical systems are focused on an object at infinity (hereinafter referred to as an infinity focused state). The vertical axis Fno of the spherical aberration diagram indicates the F-number, and the vertical axis ω of the astigmatism, distortion, and chromatic aberration indicates the half angle of view (°). The horizontal axis indicates the amount of each aberration.

[0089] In the spherical aberration diagram, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S indicates the astigmatism on the sagittal image plane, and the dashed line M indicates the astigmatism on the meridional image plane. The distortion diagram shows the distortion aberration at the d-line. The chromatic aberration diagram shows the lateral chromatic aberration at the g-line.

[0090] FIG. 18 is a spot diagram for d-line and g-line in the optical system of Numerical Example 9 corresponding to Example 9, in a state where the optical system is focused at infinity. (Numerical example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1(diffraction) ∞ 0.40 1.45867 67.9 7.60 2 ∞ 0.50 1.49171 57.4 7.35 3* 18.177 0.50 6.94 4* 4.626 0.50 1.64220 22.4 5.94 5* 4.200 2.72 5.54 6* 15.045 0.50 1.49171 57.4 3.73 7* 11.523 -0.50 3.41 8* 15.045 -2.72 3.37 9* 4.200 -0.50 1.64220 22.4 4.38 10* 4.626 -0.50 4.67 11* 18.177 0.50 5.08 12* 4.626 0.50 1.64220 22.4 5.21 13* 4.200 2.72 5.10 14* 15.045 0.50 1.49171 57.4 5.50 15* 11.523 0.77 5.52 16 ∞ 0.11 1.51633 64.1 10.00 17 ∞ 0.00 10.00 Image plane∞ Aspheric surface Side 1 (folded side) Design wavelength: 0.58756 [μm] U 2=-7.04145e-02 U 4= 4.29237e-04 U 6= 2.36760e-06 U 8=-1.38378e-07 U10 = 8.49695e-09 Surface optical path difference dispersion 1 / ν0= 0.0033 P(λ) = -8.15777e+00·λ 3 +1.73588e+01 λ 2 -1.36506e+01 · λ +4.68253e+00 P(λd) = 1.000000e+00 P(λC) = 8.945633e-01 P(λF) = 1.211667e+00 Page 3 K = 0.00000e+00 A 4=-7.31335e-04 A 6=-2.07839e-05 Page 4 K = 0.00000e+00 A 4=-2.69396e-03 A 6=-1.27809e-04 A 8=-4.88912e-06 A10 = 2.01970e-07 Page 5 K = 0.00000e+00 A 4=-3.52870e-03 A 6=-1.91524e-04 A 8=-1.80392e-07 Page 6 K = 0.00000e+00 A 4= 3.03962e-04 A 6= 6.15251e-05 A 8=-1.70049e-05 Page 7 K = 0.00000e+00 A 4=-9.61651e-04 A 6= 4.43089e-05 A 8=-1.16768e-05 A10= 3.28426e-07 Side 8 K = 0.00000e+00 A 4= 3.03962e-04 A 6= 6.15251e-05 A 8=-1.70049e-05 9th page K = 0.00000e+00 A 4=-3.52870e-03 A 6=-1.91524e-04 A 8=-1.80392e-07 Side 10 K = 0.00000e+00 A 4=-2.69396e-03 A 6=-1.27809e-04 A 8=-4.88912e-06 A10 = 2.01970e-07 Page 11 K = 0.00000e+00 A 4=-7.31335e-04 A 6=-2.07839e-05 Side 12 K = 0.00000e+00 A 4=-2.69396e-03 A 6=-1.27809e-04 A 8=-4.88912e-06 A10 = 2.01970e-07 Page 13 K = 0.00000e+00 A 4=-3.52870e-03 A 6=-1.91524e-04 A 8=-1.80392e-07 Side 14 K = 0.00000e+00 A 4= 3.03962e-04 A 6= 6.15251e-05 A 8=-1.70049e-05 Page 15 K = 0.00000e+00 A 4=-9.61651e-04 A 6= 4.43089e-05 A 8=-1.16768e-05 A10= 3.28426e-07 Various data Focal length 15.20 F-number 2.00 Half angle of view (°) 10.51 Image height 2.82 Lens length 5.96 (in Air) BF 0.84 (in Air) Entrance pupil position 0.00 Exit pupil position -18.44 Front principal point position 2.67 Back principal point position -15.20 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 15.20 6.00 2.67 -15.20 Single lens data Lens starting surface focal length 1 1 7.10 2 2 -36.97 3 4 -131.41 4 6 -105.05 CGI 16 0.00 (Numerical example 2) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1(diffraction) ∞ 0.40 1.45867 67.9 7.60 2 ∞ 0.65 1.49171 57.4 7.52 3* -873.868 0.20 7.42 4* 4.350 0.50 1.68100 18.2 6.58 5* 3.939 3.54 6.11 6* 53.819 0.61 1.49171 57.4 5.34 7* 16101.975 -0.61 5.18 8* 53.819 -3.54 5.00 9* 3.939 -0.50 1.68100 18.2 4.33 10* 4.350 -0.20 4.57 11* -873.868 0.20 4.62 12* 4.350 0.50 1.68100 18.2 4.81 13* 3.939 3.54 4.61 14* 53.819 0.61 1.49171 57.4 5.48 15* 16101.975 0.50 5.54 16 ∞ 0.11 1.51633 64.1 10.00 17 ∞ 0.00 10.00 Image plane∞ Aspheric surface Side 1 (folded side) Design wavelength: 0.58756 [μm] U 2=-3.20489e-02 U 4= 3.80728e-04 U 6=-3.85874e-06 U 8= 3.60971e-07 U10=-1.62009e-09 Surface optical path difference dispersion 1 / ν0= 0 P(λ) = 0.58756 / λ P(λd) = 1.000000e+00 P(λC) = 8.953022e-01 P(λF) = 1.208648e+00 Page 3 K = 0.00000e+00 A 4=-5.98573e-04 A 6=-9.59531e-06 Page 4 K = 0.00000e+00 A 4= 5.60733e-05 A 6=-1.76965e-05 A 8=-6.21435e-06 A10 = 1.32369e-09 Page 5 K = 0.00000e+00 A 4= 1.04101e-04 A 6= 2.53936e-06 A 8=-9.38371e-06 Page 6 K = 0.00000e+00 A 4= 4.53344e-04 A 6=-1.03391e-04 A 8= 1.43491e-05 Side 7 K = 0.00000e+00 A 4=-1.51804e-04 A 6=-3.85332e-05 A 8= 4.52831e-06 A10=-1.33895e-08 Side 8 K = 0.00000e+00 A 4= 4.53344e-04 A 6=-1.03391e-04 A 8= 1.43491e-05 9th page K = 0.00000e+00 A 4= 1.04101e-04 A 6= 2.53936e-06 A 8=-9.38371e-06 Side 10 K = 0.00000e+00 A 4= 5.60733e-05 A 6=-1.76965e-05 A 8=-6.21435e-06 A10= 1.32369e-09 Page 11 K = 0.00000e+00 A 4=-5.98573e-04 A 6=-9.59531e-06 Side 12 K = 0.00000e+00 A 4= 5.60733e-05 A 6=-1.76965e-05 A 8=-6.21435e-06 A10= 1.32369e-09 Page 13 K = 0.00000e+00 A 4= 1.04101e-04 A 6= 2.53936e-06 A 8=-9.38371e-06 Side 14 K = 0.00000e+00 A 4= 4.53344e-04 A 6=-1.03391e-04 A 8= 1.43491e-05 Page 15 K = 0.00000e+00 A 4=-1.51804e-04 A 6=-3.85332e-05 A 8= 4.52831e-06 A10=-1.33895e-08 Various data Focal length 15.20 F-number 2.00 Half angle of view (°) 10.51 Image height 2.82 Lens length 6.46 (in Air) BF 0.57 (in Air) Entrance pupil position 0.00 Exit pupil position -14.83 Front principal point position -0.38 Back principal point position -15.20 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 15.20 6.50 -0.38 -15.20 Single lens data Lens starting surface focal length 1 1 15.60 2 2 1777.20 3 4 -120.59 4 6 109.82 CGI 16 0.00 (Numerical example 3) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1(diffraction) ∞ 0.40 1.45867 67.9 8.25 2 ∞ 0.67 1.49171 57.4 8.17 3* 25.682 0.76 8.00 4* 8.141 0.60 1.64220 22.4 7.88 5* 5.422 0.50 7.87 6* 6.270 2.47 1.49171 57.4 7.98 7 ∞ -2.47 7.66 8* 6.270 -0.50 7.30 9* 5.422 -0.60 1.64220 22.4 7.24 10* 8.141 -0.76 7.35 11* 25.682 0.76 7.49 12* 8.141 0.60 1.64220 22.4 7.08 13* 5.422 0.50 6.80 14* 6.270 2.47 1.49171 57.4 6.70 15 ∞ 0.50 6.02 16 ∞ 0.11 1.51633 64.1 10.00 17 ∞ 0.00 10.00 Image plane∞ Aspheric surface Side 1 (folded side) Design wavelength: 0.58756 [μm] U 2=-2.14859e-02 U 4= 3.05969e-04 U 6=-8.39039e-06 U 8= 1.40702e-07 U10=-2.28891e-09 Surface optical path difference dispersion 1 / ν0= 0.0250 P(λ) = -1.08847e+01·λ 3 +2.26307e+01 λ 2 -1.71261e+01·λ +5.45778e+00 P(λd) = 1.000000e+00 P(λC) = 8.886774e-01 P(λF) = 1.229922e+00 Page 3 K = 0.00000e+00 A 4=-1.78071e-04 A 6= 7.05292e-06 Page 4 K = 0.00000e+00 A 4=-1.73243e-03 A 6=-1.06953e-05 A 8=-8.24978e-07 A10=-2.01336e-08 Page 5 K = 0.00000e+00 A 4=-2.75919e-03 A 6=-1.90134e-05 A 8=-1.23270e-06 Side 6 K = 0.00000e+00 A 4=-6.32397e-04 A 6=-2.33184e-05 A 8= 5.75123e-08 Side 8 K = 0.00000e+00 A 4=-6.32397e-04 A 6=-2.33184e-05 A 8= 5.75123e-08 9th page K = 0.00000e+00 A 4=-2.75919e-03 A 6=-1.90134e-05 A 8=-1.23270e-06 Side 10 K = 0.00000e+00 A 4=-1.73243e-03 A 6=-1.06953e-05 A 8=-8.24978e-07 A10=-2.01336e-08 Page 11 K = 0.00000e+00 A 4=-1.78071e-04 A 6= 7.05292e-06 Side 12 K = 0.00000e+00 A 4=-1.73243e-03 A 6=-1.06953e-05 A 8=-8.24978e-07 A10=-2.01336e-08 Page 13 K = 0.00000e+00 A 4=-2.75919e-03 A 6=-1.90134e-05 A 8=-1.23270e-06 Side 14 K = 0.00000e+00 A 4=-6.32397e-04 A 6=-2.33184e-05 A 8= 5.75123e-08 Various data Focal length 6.60 F-number: 0.80 Half angle of view (°) 23.14 Image height 2.82 Lens length 5.96 (in Air) BF 0.57 (in Air) Entrance pupil position 0.00 Exit pupil position 59.62 Front principal point position 7.33 Back principal point position -6.60 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 6.60 6.00 7.33 -6.60 Single lens data Lens starting surface focal length 1 1 23.27 2 2 -52.23 3 4 -27.64 4 6 12.75 CGI 16 0.00 (Numerical example 4) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1(diffraction) ∞ 0.40 1.45867 67.9 6.42 2 ∞ 0.51 1.64220 22.4 5.97 3* 12.670 0.50 5.23 4* 124.437 0.50 1.64220 22.4 4.95 5* 11.977 0.50 4.95 6* 4.215 1.60 1.54390 56.0 5.34 7* 53.899 -1.60 5.18 8* 4.215 -0.50 5.75 9* 11.977 -0.50 1.64220 22.4 6.12 10* 124.437 -0.50 6.60 11* 12.670 0.50 6.80 12* 124.437 0.50 1.64220 22.4 6.71 13* 11.977 0.50 6.41 14* 4.215 1.60 1.54390 56.0 6.59 15* 53.899 0.79 6.36 16 ∞ 0.11 1.51633 64.1 10.00 17 ∞ 0.00 10.00 Image plane∞ Aspheric surface Side 1 (folded side) Design wavelength: 0.58756 [μm] U 2=-2.21744e-02 U 4= 9.45811e-04 U 6=-2.95602e-05 U 8= 1.27738e-06 U10=-2.90765e-08 Surface optical path difference dispersion 1 / ν0= 0.0667 P(λ) = -2.26691e+01·λ 3 +4.43986e+01 λ 2 -3.06505e+01 · λ +8.27965e+00 P(λd) = 1.000000e+00 P(λC) = 8.792962e-01 P(λF) = 1.267609e+00 Page 3 K = 0.00000e+00 A 4=-2.07649e-04 A 6= 2.92887e-05 Page 4 K = 0.00000e+00 A 4= 1.17727e-03 A 6=-4.71275e-05 A 8= 1.82894e-05 A10=-1.28976e-06 Page 5 K = 0.00000e+00 A 4=-2.62526e-03 A 6= 4.91910e-04 A 8=-9.16917e-06 Page 6 K = 0.00000e+00 A 4=-4.66606e-03 A 6= 2.97579e-04 A 8=-1.64321e-05 Page 7 K = 0.00000e+00 A 4= 2.78015e-04 A 6=-6.43271e-05 A 8= 5.59188e-06 A10=-2.21629e-07 Page 8 K = 0.00000e+00 A 4=-4.66606e-03 A 6= 2.97579e-04 A 8=-1.64321e-05 Page 9 K = 0.00000e+00 A 4=-2.62526e-03 A 6= 4.91910e-04 A 8=-9.16917e-06 Page 10 K = 0.00000e+00 A 4= 1.17727e-03 A 6=-4.71275e-05 A 8= 1.82894e-05 A10=-1.28976e-06 Page 11 K = 0.00000e+00 A 4=-2.07649e-04 A 6= 2.92887e-05 Page 12 K = 0.00000e+00 A 4= 1.17727e-03 A 6=-4.71275e-05 A 8= 1.82894e-05 A10=-1.28976e-06 Page 13 K = 0.00000e+00 A 4=-2.62526e-03 A 6= 4.91910e-04 A 8=-9.16917e-06 Page 14 K = 0.00000e+00 A 4=-4.66606e-03 A 6= 2.97579e-04 A 8=-1.64321e-05 Page 15 K = 0.00000e+00 A 4= 2.78015e-04 A 6=-6.43271e-05 A 8= 5.59188e-06 A10=-2.21629e-07 Various data Focal length 4.00 F-number: 0.80 Half angle of view (°) 35.18 Image height 2.82 Lens length 4.87 (in Air) BF 0.87 (in Air) Entrance pupil position 0.00 Exit pupil position 10.49 Front principal point position 5.53 Back principal point position -4.00 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 4.00 4.91 5.53 -4.00 Single lens data Lens starting surface focal length 1 1 22.55 2 2 -19.73 3 4 -20.67 4 6 8.31 CGI 16 0.00 (Numerical example 5) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* 10.403 1.00 1.64220 22.4 5.26 2* 10.904 0.86 4.86 3(Diffraction) ∞ 0.50 1.45867 67.9 4.89 4 ∞ 0.50 1.64220 22.4 4.86 5* 36.372 0.20 4.83 6* 5.855 1.22 1.49171 57.4 4.83 7* 31.031 -1.22 5.36 8* 5.855 -0.20 5.98 9* 36.372 -0.50 1.64220 22.4 6.71 10 ∞ -0.50 1.45867 67.9 7.13 11(Diffraction) ∞ -0.86 7.51 12* 10.904 0.86 7.73 13 (Diffraction) ∞ 0.50 1.45867 67.9 7.62 14 ∞ 0.50 1.64220 22.4 7.38 15* 36.372 0.20 7.11 16* 5.855 1.22 1.49171 57.4 6.65 17* 31.031 0.50 6.31 18 ∞ 0.11 1.51633 64.1 10.00 19∞0.00 10.00 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-7.52738e-04 A 6=-4.03305e-05 A 8= 5.55786e-07 2nd side K = 0.00000e+00 A 4=-7.93443e-05 A 6=-9.43615e-06 Surfaces 3 / 11 / 12 (diffractive surfaces) Design wavelength: 0.58756 [μm] U 2=-1.18555e-02 U 4= 1.11307e-04 U 6=-2.55520e-05 U 8=-1.43329e-06 U10 = 1.29144e-07 Surface optical path difference dispersion 1 / ν0= -0.0104 P(λ) = -6.91918e+00 λ 3+1.51415e+01 λ 2 -1.22523e+01 · λ +4.37524e+00 P(λd) = 1.000000e+00 P(λC) = 8.999832e-01 P(λF) = 1.202378e+00 Page 5 K = 0.00000e+00 A 4=-1.67159e-03 A 6= 2.58566e-04 A 8=-1.01678e-05 Page 6 K = 0.00000e+00 A 4=-1.49376e-03 A 6= 2.45797e-04 A 8=-2.13874e-05 Page 7 K = 0.00000e+00 A 4= 3.36050e-04 A 6=-4.64461e-05 A 8= 2.42199e-06 A10=-3.04106e-07 Page 8 K = 0.00000e+00 A 4=-1.49376e-03 A 6= 2.45797e-04 A 8=-2.13874e-05 Page 9 K = 0.00000e+00 A 4=-1.67159e-03 A 6= 2.58566e-04 A 8=-1.01678e-05 Page 12 K = 0.00000e+00 A 4=-7.93443e-05 A 6=-9.43615e-06 Page 15 K = 0.00000e+00 A 4=-1.67159e-03 A 6= 2.58566e-04 A 8=-1.01678e-05 Page 16 K = 0.00000e+00 A 4=-1.49376e-03 A 6= 2.45797e-04 A 8=-2.13874e-05 Page 17 K = 0.00000e+00 A 4= 3.36050e-04 A 6=-4.64461e-05 A 8= 2.42199e-06 A10=-3.04106e-07 Various data Focal length 4.00 F-number: 0.80 Half angle of view (°) 35.18 Image height 2.82 Lens length 4.86 (in Air) BF 0.57 (in Air) Entrance pupil position 0.00 Exit pupil position 6.69 Front principal point position 6.39 Back principal point position -4.00 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 4.00 4.89 6.39 -4.00 Single lens data Lens starting surface focal length 1 1 197.99 2 3 42.17 3 4 -56.64 4 6 14.44 CGI 18 0.00 (Numerical Example 6) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* -8.037 0.63 1.54390 56.0 5.00 2* -10.909 0.30 5.14 3* 54.622 0.85 1.49171 57.4 5.18 4* -20.791 0.64 5.32 5* -9.996 -0.64 5.28 6* -20.791 -0.85 1.49171 57.4 4.93 7* 54.622 -0.30 4.94 8* -10.909 0.30 5.05 9* 54.622 0.85 1.49171 57.4 5.55 10* -20.791 0.64 6.07 11* -9.996 0.50 1.63550 23.9 6.65 12 ∞ 0.50 1.45867 67.9 7.36 13(Diffraction) ∞ 1.46 7.77 14 ∞ 0.11 1.51633 64.1 10.00 15∞0.0010.00 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4= 3.11162e-05 A 6= 1.05670e-04 A 8=-3.66147e-06 2nd side K = 0.00000e+00 A 4= 3.87022e-05 A 6= 4.03111e-05 3rd page K = 0.00000e+00 A 4=-1.31161e-03 A 6=-2.84377e-04 A 8=-6.06880e-06 A10 = 1.12407e-07 Side 4 K = 0.00000e+00 A 4=-5.36099e-04 A 6=-3.08553e-04 A 8=-1.18226e-07 5th page K = 0.00000e+00 A 4= 2.55938e-04 A 6= 4.45923e-05 A 8= 4.95630e-07 A10=-1.08627e-07 Side 6 K = 0.00000e+00 A 4=-5.36099e-04 A 6=-3.08553e-04 A 8=-1.18226e-07 Page 7 K = 0.00000e+00 A 4=-1.31161e-03 A 6=-2.84377e-04 A 8=-6.06880e-06 A10 = 1.12407e-07 Page 8 K = 0.00000e+00 A 4= 3.87022e-05 A 6= 4.03111e-05 Page 9 K = 0.00000e+00 A 4=-1.31161e-03 A 6=-2.84377e-04 A 8=-6.06880e-06 A10 = 1.12407e-07 Page 10 K = 0.00000e+00 A 4=-5.36099e-04 A 6=-3.08553e-04 A 8=-1.18226e-07 Page 11 K = 0.00000e+00 A 4= 2.55938e-04 A 6= 4.45923e-05 A 8= 4.95630e-07 A10=-1.08627e-07 Side 13 (folded side) Design wavelength: 0.58756 [μm] U 2=-1.73168e-01 U 4= 3.37949e-04 U 6= 7.44346e-05 U 8=-2.93620e-06 U10= 2.85092e-08 Surface optical path difference dispersion 1 / ν0= 0 P(λ) = 0.58756 / λ P(λd) = 1.000000e+00 P(λC) = 8.953022e-01 P(λF) = 1.208648e+00 Various データ Focus distance 4.00 F-number: 0.80 Half angle of view (°) 35.18 Image height 2.82 Lens length 4.96 (in Air) BF 1.53 (in Air) Entrance pupil position 0.00 Exit pupil position 7.48 Front principal point position 6.14 Back principal point position -4.00 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 4.00 5.00 6.14 -4.00 Single lens data Lens starting surface focal length 1 1 -60.83 2 3 30.74 5 11 -15.73 6 12 2.89 CGI 14 0.00 (Numerical Example 7) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1(Aperture) ∞ 0.50 1.45867 67.9 24.79 2(diffraction) ∞ 0.84 24.79 3 20.508 2.25 1.59551 39.2 20.47 4 31.689 2.16 19.27 5* 10.215 2.66 1.54390 56.0 14.19 6* 8.799 1.60 11.89 7 51.373 4.28 1.72047 34.7 10.64 8 10.184 -4.28 5.50 9 51.373 -1.60 5.65 10* 8.799 -2.66 1.54390 56.0 5.62 11* 10.215 -2.16 6.64 12 31.689 2.16 7.29 13* 10.215 2.66 1.54390 56.0 6.79 14* 8.799 1.60 5.87 15 51.373 4.28 1.72047 34.7 5.55 16 10.184 0.91 4.69 17* 7.085 1.20 1.67000 19.4 4.69 18* 10.281 1.16 5.27 19* -3.784 1.65 1.54390 56.0 5.26 20* -8.550 0.50 6.00 21 ∞ 0.30 1.51633 64.1 10.00 22 ∞ 0.00 10.00 Image plane∞ Aspheric surface Side 2 (folded side) Design wavelength: 0.58756 [μm] U 2=-2.65530e-02 U 4= 2.90505e-05 U 6=-6.86760e-08 U 8= 1.36253e-10 U10=-1.21830e-13 Surface optical path difference dispersion 1 / ν0= 0 P(λ) = 0.58756 / λ P(λd) = 1.000000e+00 P(λC) = 8.953022e-01 P(λF) = 1.208648e+00 Page 5 K = 0.00000e+00 A 4=-9.62169e-05 A 6=-2.08297e-07 A 8= 5.98344e-09 A10=-3.57905e-10 Side 6 K = 0.00000e+00 A 4=-6.56587e-04 A 6=-3.21660e-06 A 8= 1.51282e-08 Side 10 K = 0.00000e+00 A 4=-6.56587e-04 A 6=-3.21660e-06 A 8= 1.51282e-08 Page 11 K = 0.00000e+00 A 4=-9.62169e-05 A 6=-2.08297e-07 A 8= 5.98344e-09 A10=-3.57905e-10 Page 13 K = 0.00000e+00 A 4=-9.62169e-05 A 6=-2.08297e-07 A 8= 5.98344e-09 A10=-3.57905e-10 Side 14 K = 0.00000e+00 A 4=-6.56587e-04 A 6=-3.21660e-06 A 8= 1.51282e-08 Page 17 K = 0.00000e+00 A 4=-1.30286e-02 A 6=-2.43684e-04 A 8=-1.07847e-04 Page 18 K = 0.00000e+00 A 4=-1.49050e-02 A 6= 3.90560e-04 A 8=-3.68580e-05 Page 19 K = 0.00000e+00 A 4= 1.20727e-03 A 6=-3.33745e-04 A 8= 5.26975e-05 Page 20 K = 0.00000e+00 A 4=-1.42199e-02 A 6= 6.11571e-04 A 8= 1.61765e-05 Various data Focal length 69.40 F-number 2.80 Half angle of view (°) 2.48 Image height 3.00 Lens length 19.90 (in Air) BF 0.70 (in Air) Entrance pupil position 0.00 Exit pupil position -11.52 Front principal point position -348.65 Back principal point position -69.40 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 69.40 20.00 -348.65 -69.40 Single lens data Lens starting surface focal length 1 1 18.83 2 3 90.80 3 5 -345.41 4 7 -18.43 9 17 29.58 10 19 -14.22 C.G. 21 0.00 (Numerical Example 8) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.50 1.45867 67.9 12.39 2(Diffraction) ∞ 0.00 12.39 3∞ 10.12 4.00 4* -43.204 1.17 1.49171 57.4 11.19 5* -40.745 -1.17 11.20 6* -43.204 -9.12 10.54 7* -17.227 9.12 3.76 8* -43.204 1.17 1.49171 57.4 2.83 9* -40.745 0.90 3.10 10* -3.574 0.50 1.54390 56.0 3.69 11* 8.821 1.37 4.31 12* 6.791 2.20 1.58517 34.6 5.89 13* -20.712 0.93 5.90 14 ∞ 0.30 1.51633 64.1 20.00 15 ∞ 0.00 20.00 Image plane∞ Aspheric surface Side 2 (folded side) Design wavelength: 0.58756 [μm] U 2=-6.28884e-03 U 4= 1.57913e-05 U 6= 1.90677e-08 Surface optical path difference dispersion 1 / ν0= 0 P(λ) = 0.58756 / λ P(λd) = 1.000000e+00 P(λC) = 8.953022e-01 P(λF) = 1.208648e+00 Page 4 K = 0.00000e+00 A 4=-2.96836e-05 A 6= 6.97712e-07 A 8=-1.21276e-08 Page 5 K = 0.00000e+00 A 4=-1.61527e-05 A 6= 1.90480e-07 A 8=-2.93181e-09 A10=-4.24214e-12 Page 6 K = 0.00000e+00 A 4=-2.96836e-05 A 6= 6.97712e-07 A 8=-1.21276e-08 Page 7 K = 0.00000e+00 A 4=-9.38573e-05 A 6=-2.17370e-07 Page 8 K = 0.00000e+00 A 4=-2.96836e-05 A 6= 6.97712e-07 A 8=-1.21276e-08 9th page K = 0.00000e+00 A 4=-1.61527e-05 A 6= 1.90480e-07 A 8=-2.93181e-09 A10=-4.24214e-12 Side 10 K = 0.00000e+00 A 4= 7.25779e-03 Page 11 K = 0.00000e+00 A 4= 3.36181e-03 Side 12 K = 0.00000e+00 A 4= 2.08687e-03 Page 13 K = 0.00000e+00 A 4= 5.08988e-03 A 6= 1.15441e-04 A 8=-2.92779e-05 Various data Focal length 69.40 F-number 5.60 Half angle of view (°) 2.48 Image height 3.00 Lens length 17.90 (in Air) BF 1.13 (in Air) Entrance pupil position 51.54 Exit pupil position -14.60 Front principal point position -208.86 Back principal point position -69.40 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 69.40 18.00 -208.86 -69.40 Single lens data Lens starting surface focal length 1 1 79.51 2 4 1258.33 5 10 -4.61 6 12 9.01 CGI 14 0.00 (Numerical Example 9) Unit: mm Surface Data Surface number rd nd νd Azimuth Effective diameter 1 ∞ 0.50 1.45867 67.9 0.0 5.20 2(Diffraction) ∞ 7.53 0.0 5.02 3(Reflection) FFS -6.53 -25.0 4.68 4(Reflection) FFS 10.99 -20.0 5.38 5* 6.105 0.50 1.66691 19.6 0.0 7.12 6* 4.522 0.23 0.0 6.81 7* 4.582 2.03 1.54390 56.0 0.0 6.91 8* 19.200 0.84 0.0 6.78 9 ∞ 0.40 1.51633 64.1 0.0 10.00 10*∞ 0.00 0.0 10.00 Image plane ∞ Aspheric Data Surface 2 (diffractive surface) Design wavelength: 0.58756 [μm] U 2=-1.45535e-02 U 4= 2.85585e-05 U 6= -2.47330e-07 Dispersion of optical path difference of the surface 1 / ν0= 0 P(λ) = 0.58756 / λ P(λd) = 1.000000e+00 P(λC) = 8.953022e-01 P(λF) = 1.208648e+00 (free-form surface) "FFS" means that the surface has a free-form curved shape. The shape of a free-form curved surface is expressed by the following formula, where x is the displacement from the vertex of the surface in the optical axis direction, Y and Z are the distances from the optical axis in the Y and Z directions of a plane perpendicular to the optical axis, and C20 to C44 are free-form curved surface coefficients. Note that "e±M" of the free-form curved surface coefficients is expressed as x x 10 ±M means.

[0091] x=C02·Z 2 +C04·Z 4 +C20·Y 2 +C22·Y 2 Z 2 +C24·Y 2 Z 4 +C30·Y 3 +C32·Y 3 Z 2 +C34·Y 3 Z 4 +C40·Y 4 +C42·Y 4 Z 2 +C44·Y 4 Z 4 In addition, azimuth is the angle between a plane when all the free-form surface coefficients are set to 0 and the optical axis incident on the origin of the free-form surface. 3rd page C 02 =-1.31302E-03 C 04 =-3.81789E-05 C 20 =-1.05275E-03 C 22 =-6.10650E-05 C 24 =-2.97892E-07 C 30 =-2.05445E-05 C 32 =-1.56703E-06 C 34 =-8.57809E-07 C 40 =-2.59432E-05 C 42 =-1.50453E-06 C 44 = 2.32575E-07 Side 4 C02=2.69410E-03 C04=-2.87723E-05 C20 = 2.42249E-03 C22 =-5.17626E-05 C24 = 3.07669E-07 C 30 =-4.31712E-05 C 32 =-6.84351E-06 C 34 =-7.21633E-07 C 40 =-2.28556E-05 C 42 =-1.20457E-06 C 44 = 3.27461E-07 (Rotationally symmetric aspheric surface) 5th page K = 0.00000e+00 A 4= 1.86068e-03 A 6=-1.02002e-04 Side 6 K = 0.00000e+00 A 4= 3.26723e-03 A 6=-2.47320e-04 Side 7 K = 0.00000e+00 A 4= 1.16271e-03 A 6=-1.57151e-04 Side 8 K = 0.00000e+00 A 4= 4.02193e-05 A 6=-4.57636e-05 Various data Focal length 20.80 F-number 4.00 Half angle of view (°) 8.21 Image height 1.80 Single lens data Lens starting surface focal length 1 1 34.36 2 5 -29.93 5 7 10.55 C.G.9 0.00

[0092] [Table 1]

[0093] [Imaging device] Fig. 20 shows a digital still camera as an imaging device using the optical system of each of the above-mentioned embodiments as an imaging optical system. Reference numeral 20 denotes a camera body, and 21 denotes an imaging optical system constituted by any of the optical systems of embodiments 1 to 9. Reference numeral 22 denotes an imaging element such as a CCD sensor or a CMOS sensor that is built into the camera body 20 and captures an optical image (i.e., a subject) formed by the imaging optical system 21. Reference numeral 23 denotes a recording unit that records image data generated by processing an imaging signal from the imaging element 22, and 24 denotes a rear display that displays the image data.

[0094] By using the optical system of each embodiment, a small-sized camera having high optical performance can be obtained. The camera may be a single-lens reflex camera having a quick-turn mirror, or a mirrorless camera having no quick-turn mirror.

[0095] The above embodiment includes the following configurations.

[0096] (Configuration 1) An optical system in which light from an object side is reflected by a first reflecting surface and then further reflected by a second reflecting surface to be guided to an image side, the optical system includes a diffractive surface having controlled wavelength dispersion characteristics; The Abbe number of the diffractive surface is ν0, the reference wavelength is d-line, the primary dispersion is F-line and C-line, and the optical path difference function at each wavelength is 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 ) as

[0097]

number

[0098] When -0.2<1 / ν0<0.2 An optical system characterized in that the following conditions are satisfied. (Configuration 2) 2. The optical system according to configuration 1, wherein at least one of the first and second reflecting surfaces is a concave mirror having positive optical power. (Configuration 3) Let f be the focal length of the optical system, and fm be the focal length of the diffractive surface. 0.01 <f / |fm|<5.00 3. The optical system according to configuration 1 or 2, which satisfies the following condition: (Configuration 4) Let fm be the focal length of the diffractive surface, and fr be the focal length of the reflecting surface having the strongest optical power among the first and second reflecting surfaces. |fm / fr|<10.0 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) the diffractive surface is disposed on the object side of the first reflecting surface, When the optical effective diameter of the first reflecting surface is D1, the focal length of the optical system is f, and the maximum aperture ratio of the optical system is Fno, 0.1 <D1 / (f / Fno)<1.1 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the total optical length of the optical system is OAL and the focal length of the optical system is f, 0.1 <OAL / f<1.4 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) The optical system according to any one of configurations 1 to 6, wherein the diffractive surface has a positive optical power. (Configuration 8) the first reflecting surface and the second reflecting surface are both semi-transmissive reflecting surfaces; 8. The optical system according to any one of configurations 1 to 7, characterized in that light from an object side is transmitted through the first reflecting surface, reflected by the second reflecting surface, reflected by the first reflecting surface, transmitted through the second reflecting surface, and guided to the image side. (Configuration 9) the first reflecting surface has a non-reflecting portion that transmits light; 8. The optical system according to any one of configurations 1 to 7, characterized in that light from an object side is reflected by the first reflecting surface, reflected by the second reflecting surface, and guided to the image side through the non-reflecting portion. (Configuration 10) 10. The optical system according to any one of configurations 1 to 9, characterized in that it has at least one refractive lens. (Configuration 11) 11. The optical system according to configuration 10, characterized in that the refractive lenses include a positive lens and a negative lens. (Configuration 12) Let Φi be the optical power of the i-th refractive lens from the object side among all the refractive lenses included in the optical system, νdi be the Abbe number of the i-th refractive lens based on the d-line, Σ(Φi / νdi) be the sum of Φi / νdi of all the refractive lenses, and f be the focal length of the optical system. 1000×|Σ(Φi / νdi)| / f<1.0 12. The optical system according to any one of configurations 1 to 11, characterized in that the following condition is satisfied: (Configuration 13) An optical system in which light from an object side is reflected by a first reflecting surface and then reflected by a second reflecting surface to be guided to an image side, The optical system includes a metasurface having a controlled wavelength dispersion characteristic; The Abbe number of the metasurface is ν0, the reference wavelength is the d-line, the primary dispersion is the F-line and the C-line, and the optical path difference function at each wavelength is 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 ) as

[0099]

number

[0100] When -0.2<1 / ν0<0.2 An optical system characterized by satisfying the following conditions. (Configuration 14) An optical system according to any one of configurations 1 to 13; and an image sensor for capturing an image of a subject through the optical system.

[0101] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0102] IM image plane Lm Diffractive surface with controlled wavelength dispersion characteristics M1 1st reflective surface M2 2nd reflective surface

Claims

1. An optical system in which light from an object side is reflected by a first reflecting surface and then further reflected by a second reflecting surface to be guided to an image side, the optical system includes a diffractive surface having controlled wavelength dispersion characteristics; The Abbe number of the diffractive surface is ν ０ The reference wavelength is the d-line, the primary dispersion is the F-line and the C-line, and the optical path difference function at each wavelength is 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 ) as [0010] When -0.2<1 / n ０ <0.2 An optical system characterized by satisfying the following conditions.

2. 2. The optical system according to claim 1, wherein at least one of the first and second reflecting surfaces is a concave mirror having positive optical power.

3. When the focal length of the optical system is f and the focal length of the diffractive surface is fm, 0.01<f / |fm|<5.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the diffractive surface is fm and the focal length of the reflecting surface having the strongest optical power among the first and second reflecting surfaces is fr, |fm / fr|<10.0 2. The optical system according to claim 1, which satisfies the following condition:

5. the diffractive surface is disposed on the object side of the first reflecting surface, When the optical effective diameter of the first reflecting surface is D1, the focal length of the optical system is f, and the maximum aperture ratio of the optical system is Fno, 0.1<D1 / (f / Fno)<1.1 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the total optical length of the optical system is OAL and the focal length of the optical system is f, 0.1<OAL / f<1.4 2. The optical system according to claim 1, which satisfies the following condition:

7. The optical system of claim 1 , wherein the diffractive surface has positive optical power.

8. the first reflecting surface and the second reflecting surface are both semi-transmissive reflecting surfaces, 2. The optical system according to claim 1, wherein light from an object side is transmitted through the first reflecting surface, reflected by the second reflecting surface, reflected by the first reflecting surface, and transmitted through the second reflecting surface to be guided to the image side.

9. the first reflecting surface has a non-reflecting portion that transmits light; 2. The optical system according to claim 1, wherein light from an object side is reflected by the first reflecting surface, reflected by the second reflecting surface, and guided to the image side through the non-reflecting portion.

10. 2. The optical system of claim 1, comprising at least one refractive lens.

11. 11. The optical system according to claim 10, wherein the refractive lenses include a positive lens and a negative lens.

12. Let Φi be the optical power of the i-th refractive lens from the object side among all the refractive lenses included in the optical system, νdi be the Abbe number of the i-th refractive lens based on the d-line, Σ(Φi / νdi) be the sum of Φi / νdi of all the refractive lenses, and f be the focal length of the optical system. 1000×|Σ(Φi / νdi)| / f<1.0 2. The optical system according to claim 1, which satisfies the following condition:

13. An optical system in which light from an object side is reflected by a first reflecting surface and then further reflected by a second reflecting surface to be guided to an image side, The optical system includes a metasurface having a controlled wavelength dispersion characteristic; The Abbe number of the metasurface is v ０ The reference wavelength is the d-line, the primary dispersion is the F-line and the C-line, and the optical path difference function at each wavelength is 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 ) as [0025] When -0.2<1 / n ０ <0.2 An optical system characterized by satisfying the following conditions.

14. An optical system according to any one of claims 1 to 13; and an image sensor for capturing an image of a subject through the optical system.

Images