Imaging optical system and image pickup apparatus having same

Abstract

The invention discloses an imaging optical system and an image pickup apparatus having the same. The imaging optical system sequentially comprises at least one lens, an aperture diaphragm, a first transmission and reflection surface, a quarter-wave plate and a second transmission and reflection surface from an object side to an image side, the imaging optical system is arranged such that light from an object side sequentially passes through a first transmissive-reflective surface and a quarter-wave plate, is reflected toward the object side by a second transmissive-reflective surface, passes through the quarter-wave plate, is reflected toward an image side by the first transmissive-reflective surface, and sequentially passes through the quarter-wave plate and the second transmissive-reflective surface. And travels toward the image side. A predetermined inequality is satisfied.

Description

Technical Field

[0001] One aspect of the embodiments relates to an imaging optical system adapted for a wide angle configuration. Background Art

[0002] Due to the widespread popularity of smartphone cameras and the shift from single-lens reflex cameras to mirrorless cameras in the high-end camera market, imaging optical systems have recently been increasingly required to have reduced size. In addition to the reduced size of cameras, in the drone and vehicle-mounted camera markets, imaging optical systems have also been increasingly required to have a wider angle configuration for capturing a wider field of view. Japanese Patent Publication No. 2005-352273 discloses a compact imaging optical system using two transflective surfaces.

[0003] However, the imaging optical system disclosed in Japanese Patent Laid-Open No. 2005-352273 is insufficient in wide-angle configuration or excellent optical performance. Summary of the invention

[0004] An imaging optical system according to one aspect of the present disclosure includes at least one lens, an aperture stop, a first transmissive reflective surface, a quarter wave plate, and a second transmissive reflective surface in sequence from the object side to the image side, and the imaging optical system is arranged so that light from the object side sequentially passes through the first transmissive reflective surface and the quarter wave plate, is reflected toward the object side by the second transmissive reflective surface, passes through the quarter wave plate, is reflected toward the image side by the first transmissive reflective surface, sequentially passes through the quarter wave plate and the second transmissive reflective surface, and travels toward the image side. The following inequality is satisfied:

[0005] 0.55≤zm1 / f≤4.80

[0006] Wherein zm1 is the distance on the optical axis from the first transflective surface to the image plane, and f is the focal length of the imaging optical system. An image pickup device having the above-described imaging optical system also constitutes another aspect of the present disclosure.

[0007] An imaging optical system according to another aspect of the present disclosure includes an aperture stop, a first transflective surface, a quarter wave plate, and a second transflective surface in order from the object side to the image side, and the imaging optical system is arranged so that light from the object side sequentially passes through the first transflective surface and the quarter wave plate, is reflected toward the object side by the second transflective surface, passes through the quarter wave plate, is reflected toward the image side by the first transflective surface, sequentially passes through the quarter wave plate and the second transflective surface, and proceeds toward the image side. The following inequality is satisfied:

[0008] 0.80≤zm1 / f≤4.80

[0009] Wherein zm1 is the distance on the optical axis from the first transflective surface to the image plane, and f is the focal length of the imaging optical system. An image pickup device having the above-described imaging optical system also constitutes another aspect of the present disclosure.

[0010] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram illustrating the light path of the optical system.

[0012] Figure 2 is a schematic diagram illustrating the light path of the optical system.

[0013] Figure 3 is a cross-sectional view of an imaging optical system according to Example 1.

[0014] Figure 4 is a longitudinal aberration diagram of the imaging optical system according to Example 1 in an infinity focused state (on the object).

[0015] Figure 5 is a longitudinal aberration diagram of the imaging optical system according to Example 1 in a focused state (on the object) at a close distance.

[0016] Figure 6 is a cross-sectional view of an imaging optical system according to Example 2.

[0017] Figure 7 is a longitudinal aberration diagram of the imaging optical system according to Example 2 in an infinity focused state.

[0018] Figure 8 is a longitudinal aberration diagram of the imaging optical system according to Example 2 in a focused state at a close distance.

[0019] Fig. 9 is a cross-sectional view of an imaging optical system according to Example 3.

[0020] Fig.10 is a longitudinal aberration diagram of the imaging optical system according to Example 3 in an infinity focused state.

[0021] Fig.11 is a longitudinal aberration diagram of the imaging optical system according to Example 3 in a focused state at a close distance.

[0022] Fig.12 is a cross-sectional view of an imaging optical system according to Example 4.

[0023] Fig.13 is a longitudinal aberration diagram of the imaging optical system according to Example 4 in an infinity focused state.

[0024] Fig.14 is a schematic diagram of an image pickup device. DETAILED DESCRIPTION

[0025] Now, with reference to the accompanying drawings, a detailed description of embodiments according to the present disclosure will be given. Corresponding elements in the various drawings will be represented by the same reference numerals, and their repeated description will be omitted.

[0026] The imaging optical system according to each example is an optical system configured to form an object image on an image plane and acquire the image using a solid-state image sensor or a photosensitive film disposed on the image plane.

[0027] The imaging optical system according to each example includes a first transflective surface, a quarter wave plate (QWP), and a second transflective surface arranged in sequence from the object side to the image side. Light from the object side sequentially transmits the first transflective surface and the QWP, and is reflected by the second transflective surface. The light then transmits the QWP and is reflected by the first transflective surface, and then transmits the QWP and the second transflective surface, and travels toward an imaging unit (such as a solid-state image sensor or a photosensitive film).

[0028] Each of the first transflective surface and the second transflective surface does not necessarily have a transmittance of 50% and a reflectance of 50%. For randomly polarized light, the ratio of transmittance to reflectance may be in the range of 1:3 to 3:1. Randomly polarized light is light having Stokes parameters of S0=1, S1=S2=S3=0. Each of the first transflective surface and the second transflective surface may absorb light.

[0029] Lenses or cemented lenses are formed on both sides or one side of each transflective surface.

[0030] QWP can use, for example, a polymer film or a liquid crystal alignment layer with birefringence. It is also possible to use a laminate of such polymer films or liquid crystal alignment layers as QWP. Properly laminating them can provide a phase difference close to a quarter of the wavelength over a wide wavelength range. In addition to the above, inorganic wave plates from Dexerials can also be used as QWP.

[0031] For example, the QWP can be bonded to the first transflective surface or the second transflective surface. The QWP can also be deployed separately from these transflective surfaces. For example, the film can be directly inserted into the light path, or the film can be bonded to a glass plate and inserted into the light path. Lenses can be formed or bonded to both sides or one side of the QWP. For example, a lens can be molded on one or both sides of an inorganic wave plate as a substrate using wafer-level optical technology.

[0032] A characteristic configuration of the imaging optical system according to each example will be described below.

[0033] The imaging optical system according to each example includes an aperture stop on the object side of the first transflective surface. This configuration can satisfactorily correct coma aberration and field curvature in particular.

[0034] The imaging optical system according to each example further includes at least one concave lens on the object side of the aperture stop. This configuration can reduce the focal length of the imaging optical system and achieve a wider viewing angle.

[0035] The imaging optical system according to each example satisfies the following inequality (1-1):

[0036] 0.55≤zm1 / f≤4.80 (1-1)

[0037] Where zm1 is the distance on the optical axis from the first transflective surface to the image plane, and f is the focal length of the imaging optical system.

[0038] In the case where the distance zm1 decreases and the value of zm1 / f becomes lower than the lower limit of the inequality (1-1), it becomes difficult to ensure the back focus of the imaging optical system. In the case where the focal length f increases and the value of zm1 / f becomes lower than the lower limit of the inequality (1-1), it becomes difficult to achieve a wide-angle configuration of the imaging optical system. In the case where the distance zm1 increases and the value of zm1 / f becomes higher than the upper limit of the inequality (1-1), the size of the lens device increases and it becomes particularly difficult to correct the field curvature.

[0039] The imaging optical system according to each example does not necessarily include at least one concave lens on the object side of the aperture stop. In this case, the optical system according to each example satisfies the following inequality (1-2).

[0040] 0.80≤zm1 / f≤4.80 (1-2)

[0041] This configuration can realize a compact imaging optical system with a wide angle and a bright F number.

[0042] Inequalities (1-1) and (1-2) can be replaced by the following inequality (1a):

[0043] 0.80≤zm1 / f≤4.50(1a)

[0044] Inequalities (1-1) and (1-2) can be replaced by the following inequality (1b):

[0045] 0.85≤zm1 / f≤4.20(1b)

[0046] A description will now be given of configurations that may be satisfied in the imaging optical system according to each example.

[0047] The second transflective surface may have a concave shape on the object side. This configuration can particularly satisfactorily correct for curvature of field.

[0048] A description will now be given of inequalities that may be satisfied in the imaging optical system according to each example. The imaging optical system according to each example may satisfy one or more of the following inequalities (2) to (9).

[0049] 1.2≤zp / f≤6.5 (2)

[0050] 1.0≤Dp / f≤6.5 (3)

[0051] 0.005≤Dm / L≤0.060 (4)

[0052] 0.50≤zm2 / f≤4.50 (5)

[0053] 0.07≤Dm1 / L≤0.40 (6)

[0054] 0.09≤Dm2 / L≤0.42 (7)

[0055] 2.5≤L / f≤11.5 (8)

[0056] 0.55≤Fno≤2.50 (9)

[0057] Here, zp is the distance on the optical axis from the aperture stop to the image plane. Dp is the distance on the optical axis from the lens surface closest to the object in the imaging optical system to the aperture stop. L is the total length of the imaging optical system (the distance on the optical axis from the lens surface closest to the object to the image plane). Dm is the distance on the optical axis from the first transflective surface to the second transflective surface. zm2 is the distance on the optical axis from the second transflective surface to the image plane. Dm1 is the distance on the optical axis from the aperture stop to the first transflective surface. Dm2 is the distance on the optical axis from the aperture stop to the second transflective surface. Fno is the F number of the imaging optical system.

[0058] When the distance zp decreases and the value of zp / f becomes lower than the lower limit of inequality (2), it becomes difficult to correct the curvature of field. When the focal length f increases and the value of zp / f becomes lower than the lower limit of inequality (2), it becomes difficult to achieve a wide-angle configuration of the imaging optical system. When the distance zp increases and the value of zp / f becomes higher than the upper limit of inequality (2), the size of the lens device increases.

[0059] In the case where the distance Dp decreases and the value of Dp / f becomes lower than the lower limit of inequality (3), it becomes particularly difficult to correct distortion. In the case where the focal length f increases and the value of Dp / f becomes lower than the lower limit of inequality (3), it becomes difficult to achieve a wide-angle configuration of the imaging optical system. In the case where the distance Dp increases and the value of Dp / f becomes higher than the upper limit of inequality (3), the size of the lens device increases.

[0060] When the distance Dm decreases and the value of Dm / L becomes lower than the lower limit of inequality (4), interference may occur between the transmissive reflective surfaces. When the distance Dm increases and the value of Dm / L becomes higher than the upper limit of inequality (4), it becomes particularly difficult to correct coma aberration.

[0061] In the case where the distance zm2 decreases and the value of zm2 / f becomes lower than the lower limit of inequality (5), it becomes difficult to ensure the back focus of the imaging optical system. In the case where the focal length f increases and the value of zm2 / f becomes lower than the lower limit of inequality (5), it becomes difficult to achieve a wide-angle configuration of the imaging optical system. In the case where the distance zm2 increases and the value of zm2 / f becomes higher than the upper limit of inequality (5), the size of the lens device increases and it becomes particularly difficult to correct the field curvature.

[0062] When the distance Dm1 decreases and the value of Dm1 / L becomes lower than the lower limit of inequality (6), it becomes particularly difficult to correct field curvature. When the distance Dm1 increases and the value of Dm1 / L becomes higher than the upper limit of inequality (6), the size of the lens apparatus increases.

[0063] When the distance Dm2 decreases and the value of Dm2 / L becomes lower than the lower limit of inequality (7), it becomes particularly difficult to correct the field curvature. When the distance Dm2 increases and the value of Dm2 / L becomes higher than the upper limit of inequality (7), the size of the lens device increases.

[0064] When the focal length f increases and the value of L / f becomes lower than the lower limit of inequality (8), it becomes difficult to achieve a wide-angle configuration of the imaging optical system. When the distance L increases and the value of L / f becomes higher than the upper limit of inequality (8), the size of the lens device increases.

[0065] In the case where the F number Fno becomes lower than the lower limit of the inequality (9), it becomes particularly difficult to correct spherical aberration and coma aberration. In the case where the F number Fno becomes higher than the upper limit of the inequality (9), the imaging optical system lacks brightness.

[0066] Inequalities (2) to (9) can be replaced by the following inequalities (2a) to (9a):

[0067] 1.4≤zp / f≤6.0(2a)

[0068] 1.2≤Dp / f≤6.0(3a)

[0069] 0.008≤Dm / L≤0.055(4a)

[0070] 0.60≤zm2 / f≤4.30(5a)

[0071] 0.08≤Dm1 / L≤0.35(6a)

[0072] 0.10≤Dm2 / L≤0.37(7a)

[0073] 2.8≤L / f≤10.5(8a)

[0074] 0.60≤Fno≤2.30(9a)

[0075] Inequalities (2) to (9) can be replaced by the following inequalities (2b) to (9b):

[0076] 1.6≤zp / f≤5.5(2b)

[0077] 1.4≤Dp / f≤5.5(3b)

[0078] 0.011≤Dm / L≤0.050(4b)

[0079] 0.70≤zm2 / f≤4.10(5b)

[0080] 0.09≤Dm1 / L≤0.25(6b)

[0081] 0.11≤Dm2 / L≤0.29(7b)

[0082] 3.1≤L / f≤10.0(8b)

[0083] 0.65≤Fno≤2.10(9b)

[0084] Configuration 1 using polarization

[0085] Reference now Figure 1, a description of a configuration utilizing polarization will be given. An imaging optical system having such a configuration includes two transmissive reflective surfaces. Here, the transmissive reflective surface disposed on the object side of the imaging optical system having such a configuration includes a polarization-selective transmissive reflective element (polarization beam splitter: PBS): A. The transmissive reflective surface disposed on the image plane side of the imaging optical system having such a configuration includes a half mirror (HM): C. A first quarter wave plate (QWP1): B is disposed between the polarization-selective transmissive reflective element PBS and the half mirror HM. A second quarter wave plate (QWP2): D and a linear polarizer (POL): E are disposed in sequence from the object side to the image side between the half mirror HM and the imaging surface IM.

[0086] Here, the polarization selective transflective element A is an element configured to reflect linear polarized light polarized in the same direction as when it passes through the linear polarizer E and transmit linear polarized light perpendicular to this direction. The polarization selective transflective element A is, for example, a wire grid polarizer or a reflective polarizer having a laminated retardation film configuration. In this case, the wire grid forming surface or the retardation film surface of the polarization selective transflective element A serves as a transflective surface. The wire grid polarizer does not necessarily have to be made of aligned metal wires, but may be any material including a thin metal layer or dielectric layer arranged at predetermined intervals, as long as it can be used as a polarization selective transflective element. For example, an element having a metal layer or a dielectric layer aligned by vapor deposition may be used.

[0087] The first quarter wave plate B and the second quarter wave plate D are arranged with their slow axes tilted 45° relative to the polarization transmission axis of the linear polarizer E. Here, the first quarter wave plate B and the second quarter wave plate D may be arranged with their slow axes tilted 90°. Due to this arrangement, in the case where light is transmitted through the first quarter wave plate B and the second quarter wave plate D, the wavelength dispersion characteristics of the wave plates are offset.

[0088] The half mirror C is a half mirror formed of, for example, a dielectric multilayer film or metal deposition, and a mirror surface of the half mirror C serves as a transflective surface. The linear polarizer plate E is, for example, an absorptive linear polarizer.

[0089] A description will now be given of optical path selection and functionality in a configuration utilizing polarization.

[0090] Light incident on the imaging optical system from the object side is changed into linear polarized light by the polarization selective transflective element A, changed into circular polarized light by the first quarter wave plate B, and enters the half mirror C. Part of the light reaching the half mirror C is reflected, changed into circular polarization in the opposite direction, and returns to the first quarter wave plate B.

[0091] The reverse circularly polarized light that has returned to the first quarter wave plate B returns to the polarization selective transflective element A through the first quarter wave plate B as linearly polarized light polarized in a direction perpendicular to the direction in which the light first passed through the polarization selective transflective element A. The light that has returned to the polarization selective transflective element A is reflected by the polarization selective transflective element A. Here, due to the polarization selectivity of the polarization selective transflective element A, the linearly polarized light polarized in a direction perpendicular to the direction in which the light first passed through the polarization selective transflective element A is reflected.

[0092] Part of the light that has reached the half mirror C passes through the half mirror C, is converted by the second quarter wave plate D into linearly polarized light polarized in the same direction as the direction when the light passes through the polarization selective transmission reflection element A, enters the linear polarizer E, and is absorbed by the linear polarizer E.

[0093] The light reflected by the polarization selective transflective element A is changed into circular polarized light by the first quarter wave plate B and enters the half mirror C. A part of the light having reached the half mirror C is transmitted through the half mirror C, and enters the second quarter wave plate D. Due to the second quarter wave plate D, the incident light is changed into linear polarized light polarized in a direction parallel to the direction of the linear polarized light reflected by the polarization selective transflective element A. The light transmitted through the second quarter wave plate D enters the linear polarizer E. Here, the polarization of the light matches the transmission axis of the linear polarizer E, so most of the light is transmitted and guided to the imaging surface IM.

[0094] Due to the above-mentioned action, only the light that transmits the polarization selective transflective element PBS, is reflected by the half mirror C, is reflected by the polarization selective transflective element PBS, and transmits the half mirror C is guided to the imaging surface IM.

[0095] In the case of using cholesteric liquid crystal instead of the half mirror C, the cholesteric liquid crystal can be installed so that it reflects a large amount of circularly polarized light in the direction of the incident light during the first reflection. Therefore, the amount of light on the normal light path can be increased while reducing ghost light.

[0096] Solid-state image sensors and charge-coupled devices (CCDs) that can be used for imaging surface IM generally have high surface reflectivity. In this configuration, the light reflected by imaging surface IM passes through linear polarizer E again and is converted into circular polarized light by second quarter wave plate D. The light emitted from second quarter wave plate D is then reflected by half mirror C, becomes circular polarized light in the opposite direction, and passes through second quarter wave plate D again. At this time, circular polarized light is converted by second quarter wave plate D into linear polarized light polarized in a direction perpendicular to the direction of light just passing through linear polarizer E. Since the direction of this linear polarized light is orthogonal to the transmission axis of linear polarizer E, most of the light is absorbed by linear polarizer E. Therefore, in this configuration, most of the light reflected by imaging surface IM and half mirror C in turn is cut off, and ghosting and glare associated with imaging surface IM are not obvious. In order to obtain such a reflection reduction effect, an optical low-pass filter using birefringence may not be placed between imaging surface IM and linear polarizer E. This is because the optical low-pass filter causes the polarization state to deviate from the desired polarization state.

[0097] In this configuration, a quarter wave plate may be placed between the polarization selective transflective element A and the object. In this case, the quarter wave plate and the polarization selective transflective element A are arranged so that the fast axis or slow axis of the quarter wave plate forms an angle of 45° with the transmission axis of the polarization selective transflective element A.

[0098] Therefore, even if the light incident from the object side is linearly polarized, imaging can be performed regardless of its polarization direction. A depolarizing element may be placed instead of the quarter wave plate. For example, "Cosmoshine SRF" manufactured by Toyobo Co., Ltd. may be used as the depolarizing element.

[0099] Configuration 2 using polarization

[0100] Reference now Figure 2 , a description of a configuration utilizing polarization will be given. An imaging optical system having such a configuration includes two transmissive reflective surfaces. Here, the transmissive reflective surface placed on the object side of the imaging optical system having such a configuration includes a half mirror (HM): C. The transmissive reflective surface disposed on the image side of the imaging optical system having such a configuration includes a polarization selective transmissive reflective element (PBS): A. The first quarter wave plate (QWP1): B is disposed between the polarization selective transmissive reflective element PBS and the half mirror HM. A linear polarizer (POL): E and a second quarter wave plate (QWP2): D are arranged in sequence from the object side to the image side between the half mirror HM and the object plane.

[0101] The configuration of each polarization element and the appropriate arrangement of the optical axis orientation are similar to those of Configuration 1 utilizing polarization.

[0102] A description will now be given of the optical path selection and action in a configuration utilizing polarization.

[0103] Light incident on the imaging optical system from the object side is changed into linear polarized light by the linear polarizer E, changed into circular polarized light by the second quarter wave plate D, and enters the half mirror C. Part of the light that has reached the half mirror C is reflected, changed into circular polarized light in the opposite direction, and returns to the second quarter wave plate D.

[0104] The light reaching and reflected by the half mirror C becomes circularly polarized light in the direction opposite to the incident direction. This light is converted by the second quarter wave plate D into linearly polarized light polarized in a direction perpendicular to the direction when it passes through the linear polarizer E, enters the linear polarizer E, and is absorbed by the linear polarizer E.

[0105] The light transmitted through the half mirror C is converted by the first quarter wave plate B into linearly polarized light polarized in the same direction as the light just transmitted through the linear polarizer E. This linearly polarized light is reflected by the polarization selective transflective element A and returns to the first quarter wave plate B. The light is then converted into circularly polarized light by the first quarter wave plate B, and a portion thereof is reflected by the half mirror C. The light reflected by the half mirror C enters the first quarter wave plate B again and is converted into linearly polarized light having a polarization direction perpendicular to that when reflected by the polarization selective transflective element A. This linearly polarized light transmits the polarization selective transflective element A and is guided to the imaging surface IM.

[0106] Due to the above-mentioned effects, only the light that transmits the half mirror C, is reflected by the polarization selective transflective element PBS, is reflected by the half mirror C and transmits the polarization selective transflective element PBS is guided to the imaging surface IM.

[0107] Due to this arrangement, the linear polarizer A' can be placed between the polarization selective transflective element A and the imaging surface IM. In this case, the linear polarizer A' is matched with the transmission axis of the polarization selective transflective element A. In this way, light reflected by the imaging surface IM, reflected by the polarization selective transflective element A, enters the imaging surface IM again, and becomes ghost and glare can be absorbed.

[0108] In this configuration, a quarter wave plate can be placed between the linear polarizer E and the object. In this case, the quarter wave plate and the linear polarizer E are arranged so that the fast axis or slow axis of the quarter wave plate forms an angle of 45° with the transmission axis of the linear polarizer E. In this way, even if the light incident from the object side is linearly polarized light, imaging can be performed regardless of its polarization direction. A depolarizing element may be placed instead of the quarter wave plate. As an example of a depolarizing element, "Cosmoshine SRF" manufactured by Toyobo Co., Ltd. can be used.

[0109] In the description of the above configuration, terms such as orthogonal (perpendicular), parallel, and 45° do not necessarily have to be strictly 90°, 0°, and 45°. However, these angles should be within ±5° of the desired angle, and may be within ±2° of the desired angle, and may be within ±1° of the desired angle.

[0110] In the imaging optical system according to each example, a polymer material or a glass material may be used as a material of the lens. However, the lens placed between the first transflective surface and the second transflective surface may have low birefringence.

[0111] The configuration of the imaging optical system according to each example will be described below.

[0112] Example 1

[0113] Figure 3 : is a cross-sectional view of an imaging optical system according to this example. The imaging optical system according to this example includes at least one concave lens, an F number determining member (aperture stop) STO, a first transmissive reflective surface HM1, a quarter wave plate QWP, and a second transmissive reflective surface HM2 in order from the object side to the image side. The imaging optical system according to this example is an optical system having an aperture ratio of about 0.7 and a half viewing angle of about 42 degrees.

[0114] The first focus lens unit F1 is movable along the optical axis OA during focusing. The F number determination member STO determines (limits) a light beam of a minimum F number (Fno). IM is an image plane on which an imaging surface of an image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is disposed.

[0115] Figure 4 : is a longitudinal aberration diagram of the imaging optical system according to this example in an infinity focused state (on the object). Figure 5It is a longitudinal aberration diagram of the imaging optical system according to this example in a focused state (on the object) at a close distance. In the spherical aberration diagram, Fno represents the F number. The spherical aberration diagram illustrates the spherical aberration amount for the d-line (wavelength 587.6nm) and the g-line (wavelength 435.8nm). In the astigmatism diagram, S indicates the astigmatism amount on the sagittal image plane, and M indicates the astigmatism amount on the meridional image plane. The distortion diagram illustrates the distortion amount for the d-line. The chromatic aberration diagram illustrates the chromatic aberration amount for the g-line. ω is the half viewing angle (°).

[0116] Example 2

[0117] Figure 6 : is a cross-sectional view of an imaging optical system according to this example. The basic configuration of the imaging optical system according to this example is similar to that of the imaging optical system according to Example 1, so a detailed description thereof will be omitted. The imaging optical system according to this example is an optical system having an aperture ratio of about 1.0 and a half viewing angle of about 50.2 degrees.

[0118] The first and second focus lens units F1 and F2 are independently movable along the optical axis OA during focusing.

[0119] Figure 7 is a longitudinal aberration diagram of the imaging optical system according to this example in a state in which the imaging optical system is focused at infinity. Figure 8 3 is a longitudinal aberration diagram of the imaging optical system according to this example in a focused state at a close distance.

[0120] Example 3

[0121] Fig. 9 : is a cross-sectional view of an imaging optical system according to this example. The basic configuration of the imaging optical system according to this example is similar to that according to Example 1, so its description will be omitted. The imaging optical system according to this example has an aperture ratio of 2.03 and a half viewing angle of about 63 degrees.

[0122] The first and second focus lens units F1 and F2 are independently movable along the optical axis OA during focusing.

[0123] Fig.10 is a longitudinal aberration diagram of the imaging optical system according to this example in a state in which the imaging optical system is focused at infinity. Fig.11 3 is a longitudinal aberration diagram of the imaging optical system according to this example in a focused state at a close distance.

[0124] Example 4

[0125] Fig.12: is a cross-sectional view of an imaging optical system according to this example. The basic configuration of the imaging optical system according to this example is similar to that of the imaging optical system according to Example 1, so a description thereof will be omitted. The imaging optical system according to this example is an optical system having an aperture ratio of about 2.0 and a half viewing angle of about 105 degrees.

[0126] Fig.13 is a longitudinal aberration diagram of the imaging optical system according to this example in a state in which the imaging optical system is focused at infinity.

[0127] A description will now be given of numerical values ​​corresponding to Examples 1 to 4, respectively.

[0128] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the on-axis distance (distance on the optical axis) between the mth surface and the (m+1)th surface, where m is the surface number counted from the light incident side. nd represents the refractive index of each optical element for the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material can be expressed by:

[0129] νd=(Nd-1) / (NF-NC)

[0130] Wherein Nd, NF and NC are the refractive indices for the d-line (587.6 nm), F-line (486.1 nm) and C-line (656.3 nm) of the Fraunhofer line, respectively. STO represents an aperture stop.

[0131] In each numerical example, d, focal length (mm), F number (Fno) and half angle of view (°) are values ​​when the optical system according to each example is in focus on an object at infinity. "Back focal length (BF)" is the distance on the optical axis from the last lens surface (lens surface closest to the image plane) to the paraxial image plane expressed in air equivalent length. "Total lens length" is the distance on the optical axis from the frontmost lens surface (lens surface closest to the object) to the last surface of the optical system plus the back focal length. "Lens unit" includes one or more lenses.

[0132] In the case where the optical surface is aspherical, an asterisk * is added to the right of the surface number. The aspherical shape is expressed as follows:

[0133] X=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8

[0134] +A10×h 10+A12×h 12 +A14×h 14 +A16×h 16

[0135] Where X is the displacement from the surface vertex in the direction of the optical axis, h is the height from the optical axis in the direction orthogonal to the optical axis, R is the paraxial radius of curvature, K is the cone constant, and A4, A6, A8, A10, A12, A14, A16 are the aspheric coefficients of each order. The "e±XX" in each aspheric coefficient means "×10 ±XX ”.

[0136] Numerical Example 1

[0137] Unit: mm

[0138] Surface data

[0139]

[0140]

[0141] Aspheric surface data

[0142] Surface 3

[0143] K=0.00000e+00A4=6.90310e-06A6=-1.18669e-10A8=-1.45462e-14A10=1.85849e-15A12=-1.90182e-19

[0144] Surface 4

[0145] K=0.00000e+00A4=1.07004e-05A6=-5.16331e-09A8=9.53971e-12A10=-6.99885e-15A12=7.47937e-18

[0146] Surface 5

[0147] K=0.00000e+00A4=6.23717e-06A6=-1.03357e-08A8=6.34562e-12A10=3.18774e-14A12=-3.17854e-17

[0148] Surface 6

[0149] K=0.00000e+00A4=-8.13525e-07A6=-5.00015e-09A8=1.68190e-11A10=-1.88163e-14A12=6.32007e-18

[0150] Surface 8

[0151] K=0.00000e+00A4=-1.43963e-05A6=-3.55063e-09A8=-5.68413e-11A10=1.68695e-13A12=-4.12289e-16

[0152] Surface 9

[0153] K=0.00000e+00A4=-1.55561e-06A6=1.09550e-08A8=-1.24225e-10A10=2.97939e-13A12=-2.92015e-16

[0154] Surface 10

[0155] K=0.00000e+00A4=-1.22186e-05A6=5.22298e-09A8=-1.27765e-10A10=1.32336e-13A12=-9.94539e-17

[0156] Surface 11

[0157] K=0.00000e+00A4=-1.06247e-05A6=-4.24834e-09A8=-1.49135e-11A10=-3.70202e-14A12=7.22317e-17

[0158] Surface 12

[0159] K=0.00000e+00A4=-6.52096e-06A6=2.60342e-09A8=-4.67165e-11A10=6.11641e-14A12=-3.22546e-17

[0160] Surface 13

[0161] K=0.00000e+00A4=-1.06247e-05A6=-4.24834e-09A8=-1.49135e-11A10=-3.70202e-14A12=7.22317e-17

[0162] Surface 14

[0163] K=0.00000e+00A4=-6.52096e-06A6=2.60342e-09A8=-4.67165e-11A10=6.11641e-14A12=-3.22546e-17

[0164] Surface 15

[0165] K=0.00000e+00A4=3.96573e-07A6=-1.25386e-08A8=7.36277e-12A10=-4.81591e-15A12=-2.78757e-17

[0166] Various data

[0167]

[0168]

[0169] First focusing lens unit F1

[0170] Starting surface 8

[0171] End surface 15

[0172] F1 drive amount during focusing at a close distance (-0.6m from the image plane): -1.26 Numerical Example 2

[0173] Unit: mm

[0174] Surface data

[0175]

[0176]

[0177] Aspheric surface data

[0178] Surface 3

[0179] K=0.00000e+00A4=7.18789e-05A6=-2.67733e-07A8=7.79197e-10A10=-1.30731e-12A12=1.01400e-15

[0180] Surface 4

[0181] K=0.00000e+00A4=5.88394e-05A6=-1.66317e-07A8=-1.61763e-09A10=1.04955e-11A12=-3.01415e-14

[0182] Surface 7

[0183] K=0.00000e+00A4=-1.19790e-04A6=-6.17280e-07A8=4.41932e-09A10=-3.35374e-11A12=1.10260e-13

[0184] Surface 8

[0185] K=0.00000e+00A4=-1.24953e-04A6=-3.77720e-07A8=3.14488e-09A10=-1.52028e-11A12=5.44430e-14

[0186] Surface 16

[0187] K=0.00000e+00A4=1.94438e-05A6=4.18663e-08A8=-1.44043e-09A10=9.06092e-12A12=-1.92562e-14

[0188] Surface 18

[0189] K=0.00000e+00A4=1.94438e-05A6=4.18663e-08A8=-1.44043e-09A10=9.06092e-12A12=-1.92562e-14

[0190] Surface 19

[0191] K=0.00000e+00A4=5.98622e-05A6=-6.63837e-08A8=5.55235e-09A10=-3.24060e-11A12=1.35603e-13

[0192] Various data

[0193]

[0194] First focusing lens unit F1

[0195] Starting surface 12

[0196] End surface 19

[0197] Second focusing lens unit F2

[0198] Starting surface 9

[0199] End surface 10

[0200] F1 drive amount during focusing at close distance (-0.2m from the image plane): -1.11

[0201] F2 drive amount during focusing at close distance (-0.2m from image plane): 1.38

[0202] Numerical Example 3

[0203] Unit: mm

[0204] Surface data

[0205]

[0206] Aspheric surface data

[0207] Surface 1

[0208] K=0.00000e+00A4=6.35973e-06A6=-4.69667e-09A8=2.56033e-12A10=-7.77952e-16A12=1.12638e-19

[0209] Surface 5

[0210] K=0.00000e+00A4=8.12933e-05A6=-2.98011e-07A8=7.85905e-10A10=-2.20542e-12A12=2.68019e-15

[0211] Surface 6

[0212] K=0.00000e+00A4=8.52668e-05A6=-2.16917e-07A8=-1.25803e-10A10=-2.48945e-12A12=4.79686e-15

[0213] Surface 15

[0214] K=0.00000e+00A4=7.55612e-06A6=5.10821e-08A8=-3.59935e-10A10=1.35344e-12A12=-2.35031e-15

[0215] Surface 17

[0216] K=0.00000e+00A4=7.55612e-06A6=5.10821e-08A8=-3.59935e-10A10=1.35344e-12A12=-2.35031e-15

[0217] Surface 18

[0218] K=0.00000e+00A4=8.49549e-06A6=7.19326e-08A8=-8.15232e-10A10=2.85603e-12A12=-3.66330e-15

[0219] Surface 19

[0220] K=0.00000e+00A4=-5.26526e-05A6=4.46114e-07A8=-1.98536e-09A10=4.22671e-12A12=-3.60703e-15

[0221] Surface 20

[0222] K=0.00000e+00A4=-1.24404e-05A6=3.08673e-07A8=-9.40054e-10A10=1.39679e-12A12=-4.24441e-16

[0223] Various data

[0224]

[0225] First focusing lens unit F1

[0226] Starting surface 10

[0227] End surface 18

[0228] Second focusing lens unit F2

[0229] Starting surface 7

[0230] End Surface 8

[0231] F1 drive amount during focusing at a close distance (-0.4m from the image plane): -1.12 F2 drive amount during focusing at a close distance (-0.4m from the image plane): -0.20 Numerical Example 4

[0232] Unit: mm

[0233] Surface data

[0234]

[0235]

[0236] Aspheric surface data

[0237] Surface 5

[0238] K=0.00000e+00A4=9.41582e-05A6=1.58368e-06A8=-1.22848e-07A10=2.37154e-09A12=-1.69053e-11

[0239] Surface 6

[0240] K=0.00000e+00A4=1.88314e-06A6=4.96667e-06A8=-3.28152e-07A10=7.32711e-09A12=-6.13397e-11

[0241] Surface 14

[0242] K=0.00000e+00A4=2.42656e-05A6=2.89608e-07A8=8.23640e-09A10=-1.25973e-09A12=2.83740e-11

[0243] Surface 16

[0244] K=0.00000e+00A4=2.42656e-05A6=2.89608e-07A8=8.23640e-09A10=-1.25973e-09A12=2.83740e-11

[0245] Surface 17

[0246] K=0.00000e+00A4=1.86570e-04A6=7.03375e-07A8=-3.75096e-09A10=-4.21870e-10A12=9.23085e-12

[0247] Various data

[0248]

[0249] Table 1 summarizes the various values ​​in each numerical example.

[0250] Table 1

[0251]

[0252] Image pickup device

[0253] Reference now Fig.14 , a description will be given of an image pickup device having an imaging optical system according to any of the above-described examples. Fig.14is a schematic diagram of a single-lens reflex camera as an example of an image pickup device. The lens device 10 includes an imaging lens 1 as one of the imaging optical systems according to any one of Examples 1 to 4, and a lens barrel 2 configured to hold the imaging lens 1. The camera body 20 has a quick return mirror 3 configured to reflect a light beam from the lens device 10 upward, a focusing screen 4 disposed at an imaging position of the lens device 10, and a pentaprism 5 that converts an inverted image formed on the focusing screen 4 into an erect image. The camera body 20 also includes an eyepiece 6 configured to enable a user to observe the erect image.

[0254] An image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is disposed on the imaging surface 7. During imaging, the quick return mirror 3 is moved out of the optical path, and an image is formed on the imaging surface 7 by the lens device 10. The image sensor receives the optical image formed by the imaging lens 1, photoelectrically converts it, and outputs image data. The imaging lens 1 can also be applied to an image pickup device that does not have the quick return mirror 3.

[0255] Therefore, applying the imaging optical system according to each example to an image pickup device such as a video camera or a digital camera can realize an image pickup device with high optical performance.

[0256] Although the disclosure has described example embodiments, it is to be understood that some embodiments are not limited to the disclosed embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

[0257] Each example can provide a compact imaging optical system having a wide angle and a bright F number.

Claims

1. An imaging optical system, comprising, from the object side to the image side, the following components: at least one lens; Aperture diaphragm; a first transflective surface; quarter wave plate; as well as a second transflective surface, The imaging optical system is arranged so that light from the object side sequentially transmits the first transflective surface and the quarter-wave plate, is reflected toward the object side by the second transflective surface, transmits the quarter-wave plate, is reflected toward the image side by the first transflective surface, sequentially transmits the quarter-wave plate and the second transflective surface, and proceeds toward the image side, It is characterized by the following inequality being satisfied: 0.55≤zm1 / f≤4.80 Where zm1 is the distance on the optical axis from the first transflective surface to the image plane, and f is the focal length of the imaging optical system. 2 . The imaging optical system according to claim 1 , wherein the at least one lens is a negative lens.

3. The imaging optical system according to claim 1, wherein the following inequality is satisfied: 0.80≤zm1 / f≤4.80 Where zm1 is the distance on the optical axis from the first transflective surface to the image plane, and f is the focal length of the imaging optical system.

4. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 1.2≤zp / f≤6.5 where zp is the distance on the optical axis from the aperture stop to the image plane.

5. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 1.0≤Dp / f≤6.5 where Dp is the distance on the optical axis from the lens surface of the imaging optical system closest to the object to the aperture stop.

6. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 0.005≤Dm / L≤0.060 Wherein L is the total length of the imaging optical system, and Dm is the distance on the optical axis from the first transflective surface to the second transflective surface.

7. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 0.50≤zm2 / f≤4.50 where zm2 is the distance on the optical axis from the second transflective surface to the image plane.

8. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 0.07≤Dm1 / L≤0.40 Wherein L is the total length of the imaging optical system, and Dm1 is the distance on the optical axis from the aperture stop to the first transflective surface.

9. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 0.09≤Dm2 / L≤0.42 Wherein L is the total length of the imaging optical system, and Dm2 is the distance on the optical axis from the aperture stop to the second transflective surface.

10. The imaging optical system according to claim 1, characterized in that The following inequalities are satisfied: 2.5≤L / f≤11.5 Where L is the total length of the imaging optical system.

11. The imaging optical system according to claim 1, characterized in that the following The inequality is satisfied: 0.55≤Fno≤2.50 Where Fno is the F number of the imaging optical system.

12. The imaging optical system according to claim 1, characterized in that The second transflective surface has a concave shape on the object side.

13. An image pickup device, comprising: The imaging optical system according to any one of claims 1 to 12; as well as The image sensor is configured to receive an image formed by the imaging optical system.

Images