Imaging optical system and imaging device having same

Abstract

[Problem] To provide an imaging optical system having a small size, a large aperture, and high optical performance. [Solution] An imaging optical system according to the present invention has an aperture diaphragm, as well as a first transmissive reflective surface, a quarter-wave plate, and a second transmissive reflective surface arranged in order from the object side to the image side. Light coming from the object side is transmitted through the first transmissive reflective surface and the quarter-wave plate in order, is reflected toward the object side by the second transmissive reflective surface, is transmitted through the quarter-wave plate, is reflected toward the image side by the first transmissive reflective surface, and is transmitted through the quarter-wave plate and the second transmissive reflective surface in order toward the image surface. The total optical length, the distance on the optical axis from the first transmissive reflective surface to the image surface, the aperture diaphragm diameter, and the distance on the optical axis from the aperture diaphragm to the image surface are each set suitably.

Description

Imaging optical system and imaging device having the same

[0001] The present invention relates to an imaging optical system.

[0002] Conventionally, a configuration known as a Gaussian type has been known for realizing a large-diameter lens with a small number of lenses, but when the sagittal coma flare that occurs in this configuration is corrected, a large curvature of field occurs on the underside. If a lens with a strong negative refractive power is placed immediately before the image sensor to correct the large curvature of field on the underside, light rays that pass through the negative lens will enter the image sensor at a large angle with respect to the optical axis, causing so-called vignetting of light rays by the image sensor, resulting in an image that is darker toward the periphery.

[0003] In recent years, optical systems capable of controlling reflection and transmission at lens surfaces by using polarization have been proposed. Patent Document 1 discloses a configuration having two or three lenses and utilizing surface reflection within the lenses. Patent Document 2 discloses a configuration that utilizes surface reflection within the lenses, and enables switching from an imaging system to an observation system by rearranging lenses near a reflecting surface located on the image side while keeping the front lens group in common.

[0004] JP 2005-352273 A JP 2013-218078 A

[0005] However, while the configuration of Patent Document 1 allows for miniaturization, the number of lenses is small, making aberration correction difficult and preventing support for large-aperture specifications. Furthermore, the configuration of Patent Document 2 requires a narrow luminous flux from the on-axis to the most off-axis ray to accommodate the observation system, making it difficult to support large-aperture specifications with the lens diameters configured. Furthermore, the overall lens length is long and the distance from the lens located closest to the object to the aperture is far, resulting in a very large lens diameter for the lens located closest to the object.

[0006] An object of the present invention is to provide an imaging optical system that is small, has a large aperture, and has high optical performance.

[0007] An imaging optical system according to one aspect of the present invention is an imaging optical system having an open aperture and, arranged in this order from the object side to the image side, a first transmitting-reflecting surface, a quarter-wave plate, and a second transmitting-reflecting surface, wherein light from the object side passes through the first transmitting-reflecting surface and the quarter-wave plate in this order, is reflected by the second transmitting-reflecting surface towards the object side, passes through the quarter-wave plate, is reflected by the first transmitting-reflecting surface towards the image side, passes through the quarter-wave plate and the second transmitting-reflecting surface in this order, and proceeds towards the image plane, satisfying the following conditional expressions: 2.2≦L / Lh≦100.0 0.15≦D / LD≦2.00, where L is the total optical length, Lh is the distance on the optical axis from the first transmitting-reflecting surface to the image plane, D is the diameter of the open aperture, and LD is the distance on the optical axis from the open aperture to the image plane.

[0008] According to the present invention, it is possible to provide an imaging optical system that is small in size, has a large aperture, and has high optical performance.

[0009] 1 is a schematic diagram showing an optical path of an optical system. FIG. 1 is a schematic diagram showing an optical path of an optical system. FIG. 2 is a cross-sectional view of an imaging optical system of Example 1. FIG. 3 is aberration diagrams of the imaging optical system of Example 1 when focusing at infinity. FIG. 4 is a cross-sectional view of an imaging optical system of Example 2. FIG. 5 is aberration diagrams of the imaging optical system of Example 2 when focusing at infinity. FIG. 6 is a cross-sectional view of an imaging optical system of Example 3. FIG. 7 is aberration diagrams of the imaging optical system of Example 3 when focusing at infinity. FIG. 8 is a cross-sectional view of an imaging optical system of Example 4. FIG. 9 is aberration diagrams of the imaging optical system of Example 4 when focusing at infinity. FIG. 10 is a cross-sectional view of an imaging optical system of Example 5. FIG. 11 is aberration diagrams of the imaging optical system of Example 5 when focusing at infinity. FIG. 11 is a cross-sectional view of an imaging optical system of Example 6. FIG. 12 is aberration diagrams of the imaging optical system of Example 6 when focusing at infinity. FIG. 13 is a cross-sectional view of the wide-angle end of an imaging optical system of Example 7. FIG. 14 is a diagram showing cross-sectional views and movement locus of the imaging optical system of Example 7 from the wide-angle end to the telephoto end at infinity. FIG. 15 is aberration diagrams at the wide-angle end when focusing at infinity for the imaging optical system of Example 7. FIG. 16 is aberration diagrams in the intermediate range when focusing at infinity for the imaging optical system of Example 7. FIG. 11 is a diagram illustrating aberration diagrams at the telephoto end when focusing at infinity for the imaging optical system of Example 7. FIG. 12 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 8. FIG. 13 is a diagram illustrating a cross-sectional view from the wide-angle end to the telephoto end at infinity and a movement locus for the imaging optical system of Example 8 at the wide-angle end when focusing at infinity for the imaging optical system of Example 8. FIG. 14 is a diagram illustrating aberration diagrams in the intermediate range when focusing at infinity for the imaging optical system of Example 8. FIG. 15 is a diagram illustrating aberration diagrams at the telephoto end when focusing at infinity for the imaging optical system of Example 8. FIG. 16 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 9. FIG. 17 is a diagram illustrating a cross-sectional view from the wide-angle end to the telephoto end at infinity and a movement locus for the imaging optical system of Example 9 at the wide-angle end when focusing at infinity for the imaging optical system of Example 9. FIG. 18 is a diagram illustrating aberration diagrams at the wide-angle end of the imaging optical system of Example 9 at the intermediate range when focusing at infinity for the imaging optical system of Example 9. FIG. 19 is a diagram illustrating aberration diagrams at the telephoto end when focusing at infinity for the imaging optical system of Example 9. FIG. 19 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 10. 10A and 10B are diagrams showing cross-sectional views and movement loci from the wide-angle end to the telephoto end at infinity of the imaging optical system of Example 10. 10B are aberration diagrams at the wide-angle end when focusing at infinity of the imaging optical system of Example 10. 10C are aberration diagrams in the intermediate range when focusing at infinity of the imaging optical system of Example 10. 10D are aberration diagrams at the telephoto end when focusing at infinity of the imaging optical system of Example 10.Fig. 11 is a cross-sectional view of an imaging optical system of Example 11. Fig. 12 is a cross-sectional view of an imaging optical system of Example 12. Fig. 13 is a cross-sectional view of an imaging optical system of Example 13. Fig. 14 is a cross-sectional view of an imaging optical system of Example 14. Fig. 15 is a cross-sectional view of an imaging optical system of Example 15. Fig. 16 is a cross-sectional view of an imaging optical system of Example 16. Fig. 17 is a cross-sectional view of an imaging optical system of Example 17. Fig. 18 is a cross-sectional view of an imaging optical system of Example 18. Fig. 19 is a cross-sectional view of an imaging optical system of Example 19. Fig. 20 is a cross-sectional view of an imaging optical system of Example 20. Fig. 21 is a cross-sectional view of an imaging optical system of Example 21. Fig. 22 is a cross-sectional view of an imaging optical system of Example 22. Fig. 23 is a cross-sectional view of an imaging optical system of Example 23.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same components, and redundant explanations will be omitted.

[0011] The imaging optical system of each embodiment is an optical system that forms an image of an object on an image plane, and is an optical system that acquires an image using a solid-state imaging element or photosensitive film arranged on the image plane.

[0012] The imaging optical system of each embodiment can be used in imaging devices such as imaging cameras for smartphones, distance detection cameras, fixed-lens cameras, disposable film cameras, etc., which have an imaging element that receives an image formed by the imaging optical system. The imaging optical system of each embodiment can also be used in video cameras, digital still cameras, and interchangeable lenses for interchangeable-lens cameras.

[0013] The imaging optical system of each embodiment may be used in a camera viewfinder or an XR device for, for example, gaze detection, biometric recognition, or facial expression recognition. It may also be used for external environment recognition purposes in an XR device or an automatic robot.

[0014] The imaging optical system in each embodiment includes an open aperture, and, arranged in this order from the object side to the image side, a first transmissive-reflective surface, a quarter-wave plate (QWP), and a second transmissive-reflective surface. The open aperture refers to the state in which the aperture diaphragm is most open. In each embodiment, the open aperture value is the state in which the aperture diaphragm is most open, and at this time, the width of the axial ray is determined by the open aperture diameter. In a lens system without a variable aperture, the aperture that determines the axial ray bundle may be determined as the open aperture. If there is an aperture that determines the axial ray bundle within the range of conditional expression (3) described below, that aperture is determined as the open aperture. Light from the object side passes through the first transmissive-reflective surface and the QWP in that order, and is reflected by the second transmissive-reflective surface. The light then passes through the QWP, reflects off the first transmissive-reflective surface, and then passes through the QWP and the second transmissive-reflective surface, and proceeds toward an imaging unit such as a solid-state image sensor or a photosensitive film.

[0015] Here, the first transmissive-reflective surface and the second transmissive-reflective surface do not necessarily have to have a transmittance of 50% and a reflectance of 50%. The ratio of the transmittance to the reflectance for randomly polarized light is preferably in the range of 1:3 to 3:1. Randomly polarized light is light with Stokes parameters S0 = 1, S1 = S2 = S3 = 0. Furthermore, the first transmissive-reflective surface and the second transmissive-reflective surface may absorb light.

[0016] Furthermore, a lens may be formed or cemented to one or both sides of each of the transmission / reflection surfaces.

[0017] For example, a polymer film or liquid crystal alignment layer having birefringence can be used as a QWP. Furthermore, a stack of such polymer films or liquid crystal alignment layers can also be used as a QWP. By appropriately stacking these, a phase difference close to one-quarter of the wavelength can be obtained over a wide wavelength range. In addition to the above, an inorganic wave plate from Dexerials Corporation can also be used as a QWP.

[0018] The QWP can be arranged by bonding, for example, the first transflective surface or the second transflective surface. Alternatively, the QWP can be arranged separately from these transflective surfaces. For example, the film itself can be inserted into the optical path, or a film bonded to a glass plate can be inserted into the optical path. Alternatively, lenses can be formed or bonded to one or both sides of the QWP. For example, lenses can be molded on one or both sides of an inorganic waveplate using wafer-level optics technology as a substrate.

[0019] The characteristic configuration of the imaging optical system of each embodiment will be described below.

[0020] The imaging optical system of each embodiment satisfies the following conditional expressions (1) and (2).

[0021] 2.2≦L / Lh≦100.0 (1) 0.15≦D / LD≦2.00 (2) where L is the total optical length, Lh is the distance on the optical axis from the first transmissive-reflective surface to the image plane, D is the open aperture diameter, and LD is the distance on the optical axis from the open aperture to the image plane.

[0022] Conditional formula (1) defines the position of the first transmissive-reflective surface relative to the overall optical length, and also defines the position within the entire lens system (image pickup optical system) at which the angle of incidence of off-axial light rays relative to the optical axis when they enter the image sensor is reduced. Furthermore, defining the distance on the optical axis from the first transmissive-reflective surface to the image plane leads to defining the width of the light beam passing through the first transmissive-reflective surface, thereby achieving high performance. If the distance on the optical axis from the first transmissive-reflective surface to the image plane becomes longer below the lower limit of conditional formula (1), the overall lens length becomes too long, which is undesirable. Furthermore, the entire lens system would be farther away from the image sensor, which would result in a sharper angle of incidence at the image sensor and would make it impossible to satisfy the angle of incidence constraint, which is undesirable. Furthermore, the width of the light beam passing through the front and rear surfaces adjacent to the first transmissive-reflective surface would increase, which would increase the amount of aberration generated when the light beam passes through the surfaces, which is undesirable. Furthermore, exceeding the upper limit of conditional formula (1) makes it easier to accommodate the angle of incidence at the image sensor, but is undesirable because the final surface of the entire lens system would interfere with the image sensor.

[0023] Conditional expression (2) defines the maximum aperture diameter of the aperture stop, which determines the axial F-number light beam diameter, and the distance on the optical axis from the aperture stop to the image plane. If there is a location with strong negative refractive power near the center of the entire lens system, there will be a location on the image side of the aperture stop where the axial light beam diameter (corresponding to the maximum aperture diameter) is thicker than the axial light beam diameter at the aperture position. When the negative refractive power is strong and significant sagittal coma flare occurs, the value of the conditional expression becomes smaller than when the negative refractive power is weak and sagittal coma flare is good. Furthermore, when the negative refractive power in the entire lens system is weak and sagittal coma flare is good, the axial light beam gradually becomes thinner than the maximum aperture diameter on the image side of the aperture stop, and the value of the conditional expression becomes larger. Therefore, conditional expression (2) can be said to be a conditional expression that defines the F-number brightness and the negative refractive power in the entire lens system. If the lower limit of conditional expression (2) is exceeded, the F-number that can be targeted in the specifications becomes dark, or the negative refractive power in the entire lens system becomes strong, which is undesirable because coma flare in the sagittal direction becomes large. If the upper limit of conditional expression (2) is exceeded, the lens becomes bright and coma flare in the sagittal direction is well corrected, but it becomes too bright, which is undesirable because it becomes impossible to aim for a larger lens size and high performance.

[0024] By simultaneously satisfying conditional expressions (1) and (2), a large-diameter lens can be achieved, the negative refractive power of the entire lens system can be weak, and high performance can be achieved while mitigating the angle of incidence onto the image sensor.

[0025] It is preferable that the numerical ranges of the conditional expressions (1) and (2) be set to the numerical ranges of the following conditional expressions (1a) to (2a).

[0026] 2.3≦L / Lh≦85.0 (1a) 0.21≦D / LD≦1.50 (2a) It is more preferable that the numerical ranges of the conditional expressions (1) and (2) be set to the numerical ranges of the following conditional expressions (1b) to (2b).

[0027] 2.4≦L / Lh≦70.0 (1b) 0.25≦D / LD≦1.00 (2b) Next, configurations that are preferably satisfied in the imaging optical systems of the respective examples will be described.

[0028] Preferably, one of the first transflective surface and the second transflective surface is a surface that separates incident light into reflected light and transmitted light according to the polarization state. Specifically, as described below, it is preferable to use a polarization-selective transflective element as one of the first transflective surface and the second transflective surface. Examples of polarization-selective transflective elements include those manufactured by Asahi Kasei Corporation under the trade name "WGF" and 3M Company under the trade name "IQPE." Alternatively, an optical element may be used as the polarization-selective transflective element by forming a grid on the lens reflective surface during lens molding and then depositing, printing, or lithographically depositing a metal or dielectric thereon. Other examples of the polarization-selective transflective element include a half mirror, a cholesteric liquid crystal, and a holographic optical element. When a half mirror is used, the amount of randomly polarized light incident from the object side is reduced to 12.5% ​​or less by the time it reaches the image plane. By using a cholesteric liquid crystal or a holographic optical element, the amount of light on the image plane can be significantly increased, approximately doubled, compared to when a half mirror is used.

[0029] The imaging optical system of each embodiment is preferably rotationally symmetric with respect to the optical axis.

[0030] At least one of the first transmissive-reflective surface and the second transmissive-reflective surface is preferably a flat surface, which is preferable because it makes it easier to manufacture the imaging optical system.

[0031] It is preferable that the area from the object-side lens surface of the negative lens disposed adjacent to the object side of the first transmission-reflection surface to the second transmission-reflection surface be processed with a glass medium, i.e., that the area is formed into an integrated cemented lens, which is preferable because it simplifies the assembly of the lenses.

[0032] The portion from the object-side lens surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface is disposed at a position closest to the image sensor in the lens system. Therefore, there is a concern that ghost images may occur. In order to avoid ghost images, it is preferable that the shape from the object-side lens surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface be configured with a surface having a convex surface facing the image side.

[0033] The distance from the object-side lens surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface is preferably closer to the image side than the open aperture, and is preferably as close as possible to the image sensor where the light beam width becomes narrow. If the lens is disposed at a position where the light beam is thick, changes in the surface shape relative to the light beam will affect aberrations.

[0034] Next, conditions that the imaging optical system of each embodiment should preferably satisfy will be described. The imaging optical system of each embodiment should preferably satisfy one or more of the following conditional expressions (3) to (16).

[0035] 0.35≦LD / L≦0.85 (3) 1.20≦θ2 / θ1≦20.00 (4) 2.00≦fP / f≦15.00 (5) 1.45≦nd≦2.30 (6) 1.00≦L / Li≦200.00 (7) -1.00≦fN / fP≦-0.10 (8) -10.00≦fN / f≦-0.30 (9) -1.00≦(R1-R2) / (R1+R2)≦0.30 (10) -30.00≦fF / f≦-0.30 (11) 0.65≦nd / ndN≦1.10 (12) 0.01≦d / L≦0.15 (13) 0.01≦Lh / f≦0.90 (14) 0.30≦Oe / Ie≦4.00 (15) 0.5≦Fno≦8.0 (16) Here, θ1 is the angle of the most off-axis ray passing through the center of the open aperture relative to the optical axis when it is incident on the first transmissive-reflective surface. θ2 is the angle of the most off-axis ray passing through the center of the open aperture relative to the optical axis after it is reflected by the second transmissive-reflective surface and then reflected by the first transmissive-reflective surface. fp is the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface arranged adjacent to the image side of the first transmissive-reflective surface. f is the focal length of the imaging optical system. nd is the refractive index of the material other than air that fills between the first transmissive-reflective surface and the second transmissive-reflective surface. Li is the distance on the optical axis from the second transmissive-reflective surface to the image plane. fN is the focal length of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface. R1 is the radius of curvature of the object-side lens surface of the negative lens arranged adjacent to the object side of the first transmission-reflection surface. R2 is the radius of curvature of the second transmission-reflection surface. fF is the focal length from the object-side lens surface of the negative lens arranged adjacent to the object side of the first transmission-reflection surface to the second transmission-reflection surface. ndN is the refractive index of the negative lens arranged adjacent to the object side of the first transmission-reflection surface.d is the distance on the optical axis from the object-side lens surface of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface. Oe is the outer diameter of the lens arranged closest to the object side in the imaging optical system. Ie is the outer diameter of the lens arranged closest to the image side in the imaging optical system.

[0036] Conditional expression (3) not only defines the position of the maximum aperture stop within the entire lens system, but also defines the size of the entire lens system. If the maximum aperture stop is located in the center of the entire lens system, off-axial light rays can pass through the lenses before and after the maximum aperture stop in a balanced manner, centered around the maximum aperture stop, thereby enabling the entire lens system to be made more compact. Falling below the lower limit of conditional expression (3) is undesirable because the maximum aperture stop approaches the image plane, increasing the diameter of the front lens element and resulting in a larger lens size. Furthermore, the proximity of the maximum aperture stop to the image plane makes the angle of incidence on the image sensor too steep, which is undesirable because attempts to reduce the angle of incidence through reflection at the first and second transflective surfaces are unable to reduce the angle of incidence on the image sensor. Exceeding the upper limit of conditional expression (3) is undesirable because, while the angle of incidence on the image sensor is more easily reduced, the angle of incidence is overcorrected with respect to the optical axis through reflection at the first and second transflective surfaces, resulting in excessive incidence toward the optical axis from the outside (i.e., toward the subject being positioned at infinity).

[0037] Conditional expression (4) indicates the change in angle of a light ray when it enters the first transmissive-reflective surface and when it exits from the first transmissive-reflective surface, and expresses the refractive power resulting from passage through the first transmissive-reflective surface. Here, angles θ1 and θ2 will be described in detail. FIG. 39 is an explanatory diagram of the most off-axis ray passing through the center of the open aperture. P is the most off-axis ray traveling toward the maximum image height of the image sensor and passing through the center of the open aperture SP. Angle θ1 is the angle of light ray P relative to the optical axis immediately before it enters the first transmissive-reflective surface, and angle θ2 is the angle of light ray P relative to the optical axis after it passes through the first transmissive-reflective surface, is reflected by the second transmissive-reflective surface, and is then reflected by the first transmissive-reflective surface. Falling below the lower limit of conditional expression (4) reduces the change in angle at the first transmissive-reflective surface, diminishing the effect of providing the first and second transmissive-reflective surfaces. This is undesirable because it increases the negative refractive power of the entire lens system and increases the occurrence of sagittal coma flare. If the upper limit value of conditional expression (4) is exceeded, the angle of incidence on the image sensor relative to the optical axis will be in a direction that is incident from the outside toward the optical axis, and the light rays will be outside the effective light-receiving sensor area in front of the light-receiving sensor of the image sensor (will be vignetted), which is not preferable.

[0038] Conditional expression (5) defines the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface, and corresponds to the refractive power of the second transmissive-reflective surface. If the lower limit of conditional expression (5) is exceeded, the curvature of the second transmissive-reflective surface becomes small, which increases the angle of incidence on the image sensor in a direction from the outside toward the optical axis, undesirably causing light rays to fall outside the effective light-receiving sensor area in front of the light-receiving sensor of the image sensor (vignetting). If the upper limit of conditional expression (5) is exceeded, the curvature of the second transmissive-reflective surface becomes large, which undesirably increases the angle of incidence on the image sensor relative to the optical axis.

[0039] Conditional expression (6) indicates that the space between the first transmissive-reflective surface and the second transmissive-reflective surface must be filled with a refractive index medium other than air. If the first transmissive-reflective surface and the second transmissive-reflective surface were constructed solely from air without a refractive index medium, the relative positional relationship between them would result in changes in the angle of incidence at the image sensor and performance degradation such as one-sided blur. The precision of the relative positional relationship can be ensured by using a structure that can be processed as an integrated unit, such as a lens. If the lower limit of conditional expression (6) is exceeded, glass material cannot be used for processing, and the relative positional relationship between the first transmissive-reflective surface and the second transmissive-reflective surface is likely to be distorted, which undesirably affects optical performance such as one-sided blur. If the upper limit of conditional expression (6) is exceeded, there is no glass material and an air gap is formed, which requires the construction of a reflective surface or the like, which requires a mechanical structure to suppress this. This undesirably affects optical performance such as one-sided blur, which undesirably affects optical performance such as one-sided blur.

[0040] If the lower limit of conditional expression (7) is exceeded, the total lens length becomes too long, which is undesirable. Furthermore, the entire lens system becomes farther away from the image sensor, which is undesirable because the angle of incidence from the optical axis to the image sensor becomes steeper. Furthermore, the width of the light beam passing through the front and rear surfaces adjacent to the first transmissive-reflective surface becomes large, which is undesirable because it increases the amount of aberration generated when passing through the surfaces. If the upper limit of conditional expression (7) is exceeded, it becomes easier to accommodate the angle of incidence to the image sensor, but it is undesirable because the second transmissive-reflective surface interferes with the image sensor.

[0041] Conditional expression (8) defines the refractive power of the negative lens near the image side for correcting field curvature. While the strong refractive power of the negative lens corrects field curvature, the structure reduces the angle of incidence on the image sensor through reflection from the structure surrounded by the first and second transmissive-reflective surfaces, with the negative lens primarily responsible for correcting field curvature. If the refractive power of the negative lens is weaker than the lower limit of conditional expression (8), the correction of field curvature is insufficient, and the insufficient negative refractive power must be borne by the lens system closer to the object than the negative lens. As a result, significant coma flare in the sagittal direction occurs, which is undesirable. If the refractive power of the negative lens is strong enough to exceed the upper limit of conditional expression (8), this is advantageous for correcting field curvature, but is undesirable because the correction of field curvature becomes excessive and the angle of incidence on the image sensor relative to the optical axis becomes large.

[0042] Conditional expression (9) defines the refractive power of the negative lens near the image side of the entire lens system in order to correct field curvature. If the refractive power of the negative lens is weak below the lower limit of conditional expression (9), the correction of field curvature will be insufficient, and the insufficient negative refractive power will have to be borne by the lens system closer to the object than the negative lens. As a result, significant coma flare will occur in the sagittal direction, which is undesirable. If the refractive power of the negative lens is strong above the upper limit of conditional expression (9), this will be advantageous for correcting field curvature, but will be excessively corrected and the angle of incidence on the image sensor with respect to the optical axis will be large, which is undesirable.

[0043] Conditional expression (10) defines the shape factor of the structure surrounded by the object-side surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface and the second transmissive-reflective surface. Specifically, conditional expression (10) defines a configuration in which the object-side surface of the negative lens has a strong concave curvature to correct field curvature, and the second transmissive-reflective surface has a shape that is convex from a flat surface toward the image side to reduce the angle of incidence. If the value falls below the lower limit of conditional expression (10), the second transmissive-reflective surface will have a shape that faces the concave surface toward the image side. If the second transmissive-reflective surface faces the concave surface toward the image side, light rays originating from the image sensor will be easily reflected by the second transmissive-reflective surface and return to the image sensor, which is likely to cause ghosting, which is undesirable. If the value exceeds the upper limit of conditional expression (10), the curvature of the object-side surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface will become gentle, which makes field correction difficult, which is undesirable.

[0044] Conditional expression (11) defines the refractive power of the entire lens system from the object-side lens surface of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface, and defines the correction of field curvature. If the refractive power of the negative lens is weak below the lower limit of conditional expression (11), the correction of field curvature will be insufficient, and the insufficient negative refractive power will need to be borne by a lens closer to the object than the negative lens, which will result in significant coma flare in the sagittal direction, which is undesirable. If the refractive power of the negative lens is strong above the upper limit of conditional expression (11), this will be advantageous for correcting field curvature, but will be undesirable because the field curvature will be over-corrected.

[0045] Conditional expression (12) defines the refractive index between the first transmissive-reflective surface and the second transmissive-reflective surface and the refractive index of the negative lens disposed adjacent to the first transmissive-reflective surface on the object side. The higher the refractive index of the negative lens, the longer the optical path length of off-axial light rays, which is advantageous for correcting field curvature. If the refractive index of the negative lens becomes high below the lower limit of conditional expression (12), excessive correction of field curvature will occur, which is undesirable. If the refractive index of the negative lens becomes low above the upper limit of conditional expression (12), the amount of field curvature correction will be insufficient, and either the curvature of the object-side surface of the negative lens will become stronger to compensate for the insufficient amount, or the insufficient negative refractive power will need to be borne by a lens closer to the object than the negative lens. As a result, significant coma flare will occur in the sagittal direction, which is undesirable.

[0046] Conditional expression (13) defines the distance on the optical axis from the object-side lens surface of the negative lens disposed adjacent to the object side of the first transmissive-reflective surface to the second transmissive-reflective surface relative to the total optical length. If the lower limit of conditional expression (13) is exceeded, the negative lens becomes too thin and cannot be machined, which is undesirable. If the upper limit of conditional expression (13) is exceeded, the total lens length becomes too long, which is undesirable. Furthermore, the width of the light beam passing through each surface increases. In particular, since the object-side lens surface of the negative lens has a strong curvature and is located on the object side, the width of the light beam passing through the negative lens increases, which increases the range of change in the surface shape of the negative lens relative to the light beam, undesirably worsening aberrations.

[0047] Conditional expression (14) defines the focal length of the entire lens system and the position of the first transmissive-reflective surface, and also defines the position within the entire lens system at which the angle of incidence of off-axial light rays onto the image sensor is mitigated. Falling below the lower limit of conditional expression (14) is undesirable because the distance from the first transmissive-reflective surface to the image plane becomes too far, resulting in an excessively long overall lens length. Furthermore, the entire lens system becomes farther away from the image sensor, which is undesirable because the angle of incidence onto the image sensor becomes too steep. Furthermore, exceeding the upper limit of conditional expression (14) is undesirable because, although it is easier to accommodate the angle of incidence onto the image sensor, the final surface of the entire lens system interferes with the image sensor.

[0048] Conditional expression (15) is a conditional expression relating to the outer diameter of the lens positioned closest to the object and the outer diameter of the lens positioned closest to the image, and is a conditional expression that regulates compactness. The outer diameter is set to a value obtained by adding 2 mm to the effective diameter. If the lower limit of conditional expression (15) is exceeded, the outer diameter of the lens positioned closest to the object becomes too small, preventing the entrance of a predetermined F-number light beam and making it difficult to increase the aperture, which is undesirable. If the upper limit of conditional expression (15) is exceeded, the outer diameter of the lens positioned closest to the object becomes too large, resulting in a heavy lens, which is undesirable.

[0049] In the imaging optical system of each embodiment, a loss of light occurs due to the first and second transmissive-reflective surfaces, and therefore, if the F-number is large, the amount of light reaching the image sensor becomes very small. Therefore, it is preferable that the imaging optical system of each embodiment satisfy conditional expression (16).

[0050] It is preferable that the numerical ranges of the conditional expressions (3) to (16) be the numerical ranges of the following conditional expressions (3a) to (16a).

[0051] 0.38≦LD / L≦0.82 (3a) 1.30≦θ1 / θ2≦16.00 (4a) 2.20≦fP / f≦12.00 (5a) 1.47≦nd≦2.20 (6a) 2.00≦L / Li≦185.00 (7a) -0.80≦fN / fP≦-0.12 (8a) -7.00≦fN / f≦-0.34 (9a) -1.00≦(R1-R2) / (R1+R2)≦0.20 (10a) -25.00≦fF / f≦-0.40 (11a) 0.70≦nd / ndN≦1.05 (12a) 0.01≦d / L≦0.12 (13a) 0.01≦Lh / f≦0.85 (14a) 0.40≦Oe / Ie≦3.00 (15a) 0.60≦Fno≦4.00 (16a) Furthermore, it is more preferable that the numerical ranges of conditional expressions (3) to (16) be the numerical ranges of the following conditional expressions (3b) to (16b).

[0052] 0.40≦LD / L≦0.80 (3b) 1.40≦θ1 / θ2≦13.00 (4b) 2.40≦fP / f≦9.00 (5b) 1.49≦nd≦2.10 (6b) 2.50≦L / Li≦170.0 (7b) -0.75≦fN / fP≦-0.15 (8b) -6.00≦fN / f≦-0.38 (9b) -1.00≦(R1-R2) / (R1+R2)≦0.15 (10b) -6.00≦fF / f≦-0.45 (11b) 0.75≦nd / ndN≦1.02 (12b) 0.01≦d / L≦0.09 (13b) 0.01≦Lh / f≦0.80 (14b) 0.50≦Oe / Ie≦2.00 (15b) 0.70≦Fno≦2.50 (16b) Furthermore, by applying the following configuration to the imaging optical system of each embodiment, for example, it is possible to suppress a decrease in the amount of light in the normal imaging optical path while reducing ghost light (unwanted light leakage) from an optical path that passes through a transmission-reflection surface without ever reflecting off the transmission-reflection surface. [Configuration 1 Using Polarization] A configuration using polarization will be described with reference to FIG. 1 . The imaging optical system of this configuration has two transmission-reflection surfaces. Here, the transmission-reflection surface located on the object side of the imaging optical system of this configuration is configured by disposing a polarization-selective transmission-reflection element (PBS):A. The transmission-reflection surface located on the image plane side of the imaging optical system of this configuration is configured by disposing a half mirror (HM):C. In addition, a first quarter-wave plate (QWP1):B is disposed between the polarization-selective transmission-reflection element PBS and the half mirror HM. Furthermore, a second quarter-wave plate (QWP2): D and a linear polarizer (POL): E are arranged between the half mirror HM and the imaging surface IM in this order from the object side to the image side.

[0053] Here, the polarization-selective transmission / reflection element A is an element configured to reflect linearly polarized light polarized in the same direction as when it passed through the linear polarizer E, and to transmit linearly polarized light perpendicular to that. The polarization-selective transmission / reflection 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-formed surface or retardation film surface of the polarization-selective transmission / reflection element A functions as the transmission / reflection surface. Note that the wire grid polarizer does not necessarily have to be one in which metal wires are aligned, but may be one that has thin metal or dielectric layers at predetermined intervals and functions as a polarization-selective transmission / reflection element. For example, an element in which metal or dielectric layers are aligned by vapor deposition can be used.

[0054] The first quarter-wave plate B and the second quarter-wave plate D are arranged with their slow axes tilted at 45° with respect to the polarization transmission axis of the linear polarizer E. Here, the first quarter-wave plate B and the second quarter-wave plate D are preferably arranged with their slow axes tilted at 90°. With this arrangement, when light passes through the first quarter-wave plate B and the second quarter-wave plate D, the wavelength dispersion characteristics of the wave plates are canceled out.

[0055] The half mirror C is formed of, for example, a dielectric multilayer film or metal vapor deposition, and the mirror surface of the half mirror C functions as a transmission / reflection surface. The linear polarizer E is, for example, an absorptive linear polarizer.

[0056] Next, the optical path selection and operation in the polarization utilization configuration will be described.

[0057] Light incident on the imaging optical system from the object side is converted into linearly polarized light by the polarization-selective transflective element A, then converted into circularly polarized light by the first quarter-wave plate B, and then incident on the half mirror C. A portion of the light that reaches the half mirror C is reflected and converted into reverse circularly polarized light, and returns to the first quarter-wave plate B.

[0058] The counter-circularly polarized light that has returned to the first quarter-wave plate B is returned to the polarization selective transmission reflector A by the first quarter-wave plate B as linearly polarized light polarized in a direction perpendicular to the direction when the light first passed through the polarization selective transmission reflector A. The light that has returned to the polarization selective transmission reflector A is reflected by the polarization selective transmission reflector A. Here, due to the polarization selectivity of the polarization selective transmission reflector A, linearly polarized light polarized in a direction perpendicular to the direction when the light first passed through the polarization selective transmission reflector A is reflected.

[0059] On the other hand, a portion of the light that reaches the half mirror C is transmitted and becomes linearly polarized light polarized in the same direction as when it passed through the polarization-selective transmission / reflection element A by the second quarter-wave plate D, and is incident on the linear polarizer E and absorbed by the linear polarizer E.

[0060] The light reflected by the polarization-selective transmission / reflection element A is converted into circularly polarized light by the first quarter-wave plate B and enters the half mirror C. A portion of the light that reaches the half mirror C is transmitted and enters the second quarter-wave plate D. The second quarter-wave plate D converts the incident light into linearly polarized light that is oriented parallel to the linearly polarized light reflected by the polarization-selective transmission / reflection element A. The light that passes through the second quarter-wave plate D enters the linear polarizer E. Here, the polarization of the light and the transmission axis of the linear polarizer E coincide, so most of the light is transmitted and directed to the imaging plane IM.

[0061] Due to the above-described action, only the light that has been transmitted through the polarization-selective transmission / reflection element PBS, reflected by the half mirror C, reflected by the polarization-selective transmission / reflection element PBS, and transmitted through the half mirror C is guided to the imaging plane IM.

[0062] When a cholesteric liquid crystal is used instead of the half mirror C, it is preferable to arrange the cholesteric liquid crystal so that it reflects a large amount of circularly polarized light in the direction of the incident light during the first reflection of the cholesteric liquid crystal. This makes it possible to reduce ghost light while increasing the amount of light in the normal optical path.

[0063] Furthermore, solid-state imaging elements and CCDs (Charge Coupled Devices) that can be used as the imaging surface IM generally have high surface reflectance. In this configuration, the light reflected by the imaging surface IM passes through the linear polarizer E again and is converted into circularly polarized light by the second quarter-wave plate D. The light exiting the second quarter-wave plate D is then reflected by the half mirror C to become circularly polarized light in the opposite direction and passes through the second quarter-wave plate D again. At this time, the circularly polarized light is converted by the second quarter-wave plate D into linearly polarized light in a direction perpendicular to that of the light immediately after passing through the linear polarizer E. Because the direction of this linearly polarized light is orthogonal to the transmission axis of the linear polarizer E, most of the light is absorbed by the linear polarizer E. In this configuration, most of the light reflected by the imaging surface IM and the half mirror C in this order is cut off, making ghosts and flares associated with the imaging surface IM less noticeable. In order to obtain such a reflection-reducing effect, it is preferable that no optical low-pass filter utilizing birefringence be present between the imaging plane IM and the linear polarizer E. This is because an optical low-pass filter would cause the polarization state to deviate from the desired polarization state.

[0064] In this configuration, a quarter-wave plate may be placed between the polarization-selective transmission / reflection element A and the object. In this case, the quarter-wave plate is placed so that the fast axis or slow axis of the quarter-wave plate forms a 45° angle with the transmission axis of the polarization-selective transmission / reflection element A. This allows imaging regardless of the polarization direction, even if the light incident from the object side is linearly polarized. A depolarizing element may also be placed instead of the quarter-wave plate. For example, Toyobo Co., Ltd.'s "Cosmoshine SRF" can be used as the depolarizing element. [Polarized Light-Utilizing Configuration 2] A configuration using polarized light will be described with reference to FIG. 2 . The imaging optical system of this configuration has two transmission / reflection surfaces. Here, the transmission / reflection surface located on the object side of the imaging optical system of this configuration is constituted by a half mirror (HM):C. The transmission / reflection surface located on the image plane side of the imaging optical system of this configuration is constituted by a polarization-selective transmission / reflection element (PBS):A. A first quarter-wave plate (QWP1):B is placed between the polarization-selective transmission / reflection element PBS and the half mirror HM. Furthermore, a linear polarizer (POL): E and a second quarter-wave plate (QWP2): D are arranged between the half mirror HM and the object surface in this order from the object side to the image side.

[0065] Here, the configuration of each polarizing element and the preferred arrangement of the optical axis direction are the same as in the polarized light-using configuration 1.

[0066] Next, the optical path selection and operation in the polarization utilization configuration will be described.

[0067] Light entering the imaging optical system from the object side is converted to linearly polarized light by the linear polarizer E, converted to circularly polarized light by the second quarter-wave plate D, and then enters the half mirror C. A portion of the light that reaches the half mirror C is reflected and converted to reverse circularly polarized light, returning to the second quarter-wave plate D.

[0068] The light that reaches and is reflected by the half mirror C is circularly polarized in the opposite direction to the incident direction. This light is then converted by the second quarter-wave plate D into linearly polarized light that is polarized in a direction perpendicular to the direction when it passed through the linear polarizer E, and is then incident on and absorbed by the linear polarizer E.

[0069] On the other hand, the light that has passed 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 immediately after passing through the linear polarizer E. This linearly polarized light is reflected by the polarization-selective transmission / reflection 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 of this light is reflected by the half mirror C. The light reflected by the half mirror C is again incident on the first quarter-wave plate B and converted into linearly polarized light whose polarization direction is orthogonal to that when it was reflected by the polarization-selective transmission / reflection element A. This linearly polarized light passes through the polarization-selective transmission / reflection element A and is guided to the imaging plane IM.

[0070] Due to the above-mentioned action, only the light that passes through the half mirror C, is reflected by the polarization selective transmission / reflection element PBS, is reflected by the half mirror C, and is passed through the polarization selective transmission / reflection element PBS is guided to the imaging plane IM.

[0071] In this arrangement, a linear polarizer A' may be placed between the polarization-selective transmission / reflection element A and the imaging plane IM. In this case, the transmission axes of the linear polarizer A' and the polarization-selective transmission / reflection element A are aligned. By doing so, it is possible to absorb light that is reflected by the imaging plane IM, reflected by the polarization-selective transmission / reflection element A, and then re-enters the imaging plane IM to cause ghosts and flares.

[0072] In this configuration, a quarter-wave plate may be placed between the linear polarizer E and the object. In this case, the quarter-wave plate is placed so that the fast axis or slow axis of the quarter-wave plate forms a 45° angle with the transmission axis of the linear polarizer E. By doing so, even if the light incident from the object side is linearly polarized, it is possible to capture an image regardless of its polarization direction. Furthermore, a depolarizing element may be placed instead of the quarter-wave plate. For example, "Cosmoshine SRF" by Toyobo Co., Ltd. can be used as the depolarizing element.

[0073] In the above description of the configuration, terms such as orthogonal, parallel, and 45° are used, but these do not necessarily have to be strictly 90°, 0°, or 45°. However, these should be within ±5° of the desired angle, preferably within ±2°, and even more preferably within ±1°.

[0074] In the imaging optical system of each embodiment, the lenses may be made of either a polymer material or a glass material, but it is preferable that the lens disposed between the first transmissive-reflective surface and the second transmissive-reflective surface has low birefringence.

[0075] The configuration of the imaging optical system in each embodiment will be described below.

[0076] FIG. 3 is a cross-sectional view of the imaging optical system 100 of this embodiment. The imaging optical system 100 includes, arranged in order from the object side to the image side, a first negative lens 101, a second positive lens 102, a cemented lens of a third negative lens 103 and a fourth positive lens 104, a maximum aperture SP, a fifth positive lens 105, and a sixth negative lens 106. The first negative lens 101, the second positive lens 102, the third negative lens 103, the fourth positive lens 104, and the fifth positive lens 105 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 100 also includes, arranged in order from the object side to the image side, a cemented lens of a seventh lens 107 having a first transmissive-reflective surface HM1 and an eighth lens 108 having a second transmissive-reflective surface HM2, and a sensor protection glass G. The seventh lens 107 includes a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0077] 4 is a diagram showing aberrations of the imaging optical system 100 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0078] FIG. 5 is a cross-sectional view of the imaging optical system 200 of this embodiment. The imaging optical system 200 includes, arranged in order from the object side to the image side, a first negative lens 201, a second positive lens 202, a cemented lens of a third negative lens 203 and a fourth positive lens 204, a maximum aperture SP, a fifth positive lens 205, and a sixth negative lens 206. The first negative lens 201, the second positive lens 202, the third negative lens 203, the fourth positive lens 204, the fifth positive lens 205, and the sixth negative lens 206 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 200 also includes, arranged in order from the object side to the image side, a cemented lens of a seventh lens 207 having a first transmissive-reflective surface HM1 and an eighth lens 208 having a second transmissive-reflective surface HM2, and a sensor protection glass G. The seventh lens 207 includes a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0079] 6 is a diagram showing aberrations of the imaging optical system 200 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0080] FIG. 7 is a cross-sectional view of an imaging optical system 300 according to this embodiment. The imaging optical system 300 includes, arranged in order from the object side to the image side, a first positive lens 301, a second negative lens 302, a maximum aperture stop SP, and a third positive lens 303. The first positive lens 301, the second negative lens 302, and the third positive lens 303 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 300 also includes, arranged in order from the object side to the image side, a cemented lens including a fourth positive lens 204, a fifth negative lens 305 having a first transmissive-reflective surface HM1, and a sixth positive lens 308 having a second transmissive-reflective surface HM2, as well as a sensor protective glass G. The fifth negative lens 305 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0081] 8 is a diagram showing aberrations of the imaging optical system 300 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0082] FIG. 9 is a cross-sectional view of an imaging optical system 400 according to this embodiment. The imaging optical system 400 includes, arranged in order from the object side to the image side, a first positive lens 401, a cemented lens formed by a second negative lens 402 and a third positive lens 403, a maximum aperture SP, a fourth positive lens 404, and a cemented lens formed by a fifth negative lens 405 and a sixth positive lens 406. The first positive lens 401, the second negative lens 402, the third positive lens 403, and the fourth positive lens 404 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 400 also includes, arranged in order from the object side to the image side, a cemented lens formed by a seventh negative lens 407 having a first transmissive-reflective surface HM1 and an eighth positive lens 408 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The seventh negative lens 407 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0083] 10 is a diagram showing aberrations of the imaging optical system 400 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0084] FIG. 11 is a cross-sectional view of an imaging optical system 500 according to this embodiment. The imaging optical system 500 includes, arranged in order from the object side to the image side, a first positive lens 501, a cemented lens formed by a second positive lens 502 and a third negative lens 503, a maximum aperture stop SP, and a fourth positive lens 504. The first positive lens 501, the second positive lens 502, the third negative lens 503, and the fourth positive lens 504 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 500 also includes a cemented lens formed by a fifth negative lens 505 and a sixth positive lens 506. The imaging optical system 500 also includes, arranged in order from the object side to the image side, a cemented lens formed by a seventh negative lens 507 having a first transmissive-reflective surface HM1 and an eighth positive lens 508 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The seventh negative lens 507 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0085] 12 is a diagram showing aberrations of the imaging optical system 500 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0086] FIG. 13 is a cross-sectional view of an imaging optical system 600 according to this embodiment. The imaging optical system 600 includes, arranged in order from the object side to the image side, a first positive lens 601, a cemented lens formed by a second positive lens 602 and a third negative lens 603, a maximum aperture SP, and a fourth positive lens 604. The first positive lens 601, the second positive lens 602, the third negative lens 603, and the fourth positive lens 604 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 600 also includes a cemented lens formed by a fifth negative lens 605 and a sixth positive lens 606. The imaging optical system 600 also includes a cemented lens formed by a seventh negative lens 607 having a first transmissive-reflective surface HM1 and an eighth positive lens 608 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The seventh negative lens 607 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0087] 14 is a diagram showing aberrations of the imaging optical system 600 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0088] FIG. 15 is a cross-sectional view of the imaging optical system 700 of this embodiment at the wide-angle end. The imaging optical system 700 includes, arranged in order from the object side to the image side, a first negative lens 701, a second negative lens 702, a third positive lens 703, and a flare-cutting aperture e1. The imaging optical system 700 also includes, arranged in order from the object side to the image side, a fourth positive lens 704, a maximum aperture aperture SP, a fifth positive lens 705, a sixth negative lens 706, a flare-cutting aperture e2, and a seventh positive lens 707. The fourth positive lens 704, the fifth positive lens 705, the sixth negative lens 706, and the seventh positive lens 707 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 700 also includes a cemented lens consisting of an eighth positive lens 708, a ninth negative lens 709, and a tenth positive lens 710. The imaging optical system 700 further includes, arranged in order from the object side to the image side, a cemented lens of an eleventh negative lens 711 having a first transmission-reflection surface HM1 and a twelfth positive lens 712 having a second transmission-reflection surface HM2, and a sensor protection glass G. The eleventh negative lens 711 includes a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0089] The imaging optical system 700 has three lens groups that move together during zooming: a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power. The first lens group L1 is composed of a first negative lens 701, a second negative lens 702, and a third positive lens 703. The second lens group L2 is composed of a fourth positive lens 704, a fifth positive lens 705, a sixth negative lens 706, and a seventh positive lens 707. The third lens group L3 is composed of an eighth positive lens 708, a ninth negative lens 709, a tenth positive lens 710, an eleventh negative lens 711, and a twelfth positive lens 712.

[0090] 16 shows cross-sectional views and movement trajectories of the imaging optical system 700 at infinity from the wide-angle end to the telephoto end. The cross-sectional view in (A) shows the wide-angle end, the cross-sectional view in (B) shows the intermediate region, and the cross-sectional view in (C) shows the telephoto end. The first lens unit L1 moves toward the image side, the flare-cutting stop e1 moves toward the image side, the second lens unit L2 moves toward the object side, and the third lens unit L3 is fixed.

[0091] 17, 18, and 19 are aberration diagrams of the imaging optical system 700 at the wide-angle end, intermediate range, and telephoto end when focusing at infinity, respectively. In the spherical aberration diagrams, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagrams, S shows the amount of astigmatism in the sagittal image plane, and M shows the amount of astigmatism in the meridional image plane. In the distortion diagrams, the amount of distortion for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0092] FIG. 20 is a cross-sectional view of an imaging optical system 800 of this embodiment at the wide-angle end. The imaging optical system 800 includes, arranged in order from the object side to the image side, a first negative lens 801, a second negative lens 802, a third positive lens 803, and a fourth negative lens 804. The imaging optical system 800 also includes, arranged in order from the object side to the image side, a fifth positive lens 805, a maximum aperture SP, a sixth positive lens 806, a seventh negative lens 807, a flare-cut aperture e1, and an eighth positive lens 808. The fifth positive lens 805, the sixth positive lens 806, the seventh negative lens 807, and the eighth positive lens 808 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 800 also includes a cemented lens consisting of a ninth positive lens 809, a tenth negative lens 810, and an eleventh positive lens 811. The imaging optical system 800 further includes, arranged in order from the object side to the image side, a cemented lens of a twelfth negative lens 812 having a first transmissive-reflective surface HM1 and a thirteenth positive lens 813 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The twelfth negative lens 812 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0093] The imaging optical system 800 has a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power, which move together during zooming. The first lens group L1 is composed of a first negative lens 801, a second negative lens 802, a third positive lens 803, and a fourth negative lens 804. The second lens group L2 is composed of a fifth positive lens 805, a sixth positive lens 806, a seventh negative lens 807, and an eighth positive lens 808. The third lens group L3 is composed of a ninth positive lens 809, a tenth negative lens 810, an eleventh positive lens 811, a twelfth negative lens 812, and a thirteenth positive lens 813.

[0094] 21 shows cross-sectional views and movement trajectories of the imaging optical system 800 at infinity from the wide-angle end to the telephoto end. The cross-sectional view in (A) shows the wide-angle end, the cross-sectional view in (B) shows the intermediate region, and the cross-sectional view in (C) shows the telephoto end. The first lens unit L1 moves toward the image side, the second lens unit L2 moves toward the object side, and the third lens unit L3 is fixed.

[0095] 22, 23, and 24 are aberration diagrams of the imaging optical system 800 at the wide-angle end, intermediate range, and telephoto end when focusing at infinity, respectively. In the spherical aberration diagrams, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagrams, S shows the amount of astigmatism in the sagittal image plane, and M shows the amount of astigmatism in the meridional image plane. In the distortion diagrams, the amount of distortion for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0096] FIG. 25 is a cross-sectional view of an imaging optical system 900 of this embodiment at the wide-angle end. The imaging optical system 900 includes, in order from the object side to the image side, a first negative lens 901, a second positive lens 902, and a third positive lens 903. The imaging optical system 900 also includes, in order from the object side to the image side, a fourth negative lens 904, a fifth positive lens 905, a sixth positive lens 906, and a seventh negative lens 907. The imaging optical system 900 also includes, in order from the object side to the image side, an open aperture stop SP, an eighth positive lens 908, a ninth positive lens 909, a tenth negative lens 910, and an eleventh positive lens 911. The eighth positive lens 908, the ninth positive lens 909, the tenth negative lens 910, and the eleventh positive lens 911 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 900 also includes, arranged in order from the object side to the image side, a twelfth negative lens 912 and a thirteenth positive lens 913. The imaging optical system 900 also includes, arranged in order from the object side to the image side, a cemented lens of a fourteenth negative lens 914 having a first transmissive-reflective surface HM1 and a fifteenth positive lens 915 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The fourteenth negative lens 914 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0097] The imaging optical system 900 includes a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with positive refractive power, which move together during zooming. The first lens group L1 is composed of a first negative lens 901, a second positive lens 902, and a third positive lens 903. The second lens group L2 is composed of a fourth negative lens 904, a fifth positive lens 905, a sixth positive lens 906, and a seventh negative lens 907. The third lens group L3 is composed of an eighth positive lens 908, a ninth positive lens 909, a tenth negative lens 910, and an eleventh positive lens 911. The fourth lens group L4 is composed of a twelfth negative lens 912 , a thirteenth positive lens 913 , a fourteenth negative lens 914 , and a fifteenth positive lens 915 .

[0098] 26 shows cross-sectional views and movement trajectories of the imaging optical system 900 at infinity from the wide-angle end to the telephoto end. The cross-sectional view in (A) shows the wide-angle end, the cross-sectional view in (B) shows the intermediate region, and the cross-sectional view in (C) shows the telephoto end. The first lens unit L1 moves toward the image side and then moves toward the object side, the second lens unit L2 moves toward the image side, the third lens unit L3 moves toward the image side, and the fourth lens unit L4 is fixed.

[0099] 27, 28, and 29 are aberration diagrams of the imaging optical system 900 at the wide-angle end, intermediate range, and telephoto end when focusing at infinity, respectively. In the spherical aberration diagrams, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagrams, S shows the amount of astigmatism in the sagittal image plane, and M shows the amount of astigmatism in the meridional image plane. In the distortion diagrams, the amount of distortion for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0100] 30 is a cross-sectional view of the imaging optical system 1000 of this embodiment at the wide-angle end. The imaging optical system 1000 includes, arranged in order from the object side to the image side, a first negative lens 1001, a second positive lens 1002, and a third positive lens 1003. The imaging optical system 900 also includes, arranged in order from the object side to the image side, a fourth negative lens 1004, a fifth negative lens 1005, a sixth positive lens 1006, and a seventh negative lens 1007. The imaging optical system 1000 also includes, arranged in order from the object side to the image side, an open aperture stop SP, an eighth positive lens 1008, a ninth positive lens 1009, a tenth negative lens 1010, and an eleventh positive lens 1011. The eighth positive lens 1008, the ninth positive lens 1009, the tenth negative lens 1010, and the eleventh positive lens 1011 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 1000 also includes, arranged in order from the object side to the image side, a twelfth negative lens 1012 and a thirteenth positive lens 1013. The imaging optical system 1000 also includes, arranged in order from the object side to the image side, a cemented lens of a fourteenth negative lens 1014 having a first transmissive-reflective surface HM1 and a fifteenth positive lens 1015 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The fourteenth negative lens 1014 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0101] The imaging optical system 1000 includes a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with positive refractive power, which move together during zooming. The first lens group L1 is composed of a first negative lens 1001, a second positive lens 1002, and a third positive lens 1003. The second lens group L2 is composed of a fourth negative lens 1004, a fifth negative lens 1005, a sixth positive lens 1006, and a seventh negative lens 1007. The third lens group L3 is composed of an eighth positive lens 1008, a ninth positive lens 1009, a tenth negative lens 1010, and an eleventh positive lens 1011. The fourth lens group L4 is composed of a twelfth negative lens 1012 , a thirteenth positive lens 1013 , a fourteenth negative lens 1014 , and a fifteenth positive lens 1015 .

[0102] 31 shows cross-sectional views and movement trajectories of the imaging optical system 1000 at infinity from the wide-angle end to the telephoto end. The cross-sectional view in (A) shows the wide-angle end, the cross-sectional view in (B) shows the intermediate region, and the cross-sectional view in (C) shows the telephoto end. The first lens unit L1 moves toward the image side and then moves toward the object side, the second lens unit L2 moves toward the image side, the third lens unit L3 moves toward the image side, and the fourth lens unit L4 is fixed.

[0103] 32, 33, and 34 are aberration diagrams of the imaging optical system 1000 at the wide-angle end, intermediate range, and telephoto end when focusing at infinity. In the spherical aberration diagrams, Fno is the F-number and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagrams, S shows the amount of astigmatism in the sagittal image plane, and M shows the amount of astigmatism in the meridional image plane. In the distortion diagrams, the amount of distortion for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0104] FIG. 35 is a cross-sectional view of an imaging optical system 1100 according to this embodiment. The imaging optical system 1100 includes, in order from the object side to the image side, a first positive lens 1101, a second negative lens 1102, a maximum aperture SP, and a third positive lens 1103. The first positive lens 1101, the second negative lens 1102, and the third positive lens 1103 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 1100 also includes a cemented lens consisting of a fourth negative lens 1104 having a first transmissive-reflective surface HM1 and a fifth positive lens 1105 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The fourth negative lens 1104 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0105] Figure 36 is a diagram showing aberrations of the imaging optical system 1100 when focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0106] FIG. 37 is a cross-sectional view of the imaging optical system 1200 of this embodiment. The imaging optical system 1200 includes, arranged in order from the object side to the image side, a first positive lens 1201, a second negative lens 1202, a maximum aperture SP, and a third positive lens 1203. The first positive lens 1201, the second negative lens 1202, and the third positive lens 1203 form a focusing group f. Focusing is performed by moving these lenses together in the optical axis direction. The imaging optical system 1200 also includes a cemented lens consisting of a fourth negative lens 1204 having a first transmissive-reflective surface HM1 and a fifth positive lens 1205 having a second transmissive-reflective surface HM2, and a sensor protective glass G. The fourth negative lens 1204 includes a quarter-wave plate QWP on the image side of the first transmissive-reflective surface HM1.

[0107] Figure 38 is a diagram of aberrations when the imaging optical system 1200 is focused at infinity. In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the imaging half angle of view (degrees).

[0108] Numerical Examples 1 to 12 corresponding to Examples 1 to 12, respectively, are shown below.

[0109] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Furthermore, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is expressed as follows, where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines.

[0110] In each numerical example, d, focal length (mm), F-number, and half angle of view (degrees) are all values ​​when the imaging optical system of each example is focused on an object at infinity. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the length on the optical axis from the foremost lens surface (the lens surface closest to the object) of the imaging optical system to the final surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

[0111] If the optical surface is aspherical, a * symbol is added to the right of the surface number. The aspherical shape is expressed as follows, where X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, and A10 are aspherical coefficients of each order: X=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 ]+A4×h 4 + A6 x h 6 +A8 x h 8 + A10 x h 10 In addition, "e±XX" in each aspherical coefficient is "×10± ＸＸ " means.

[0112] The effective diameter is described for the first transmissive-reflective surface and the second transmissive-reflective surface. These transmissive-reflective surfaces act on the light beam multiple times, but the diameter that is the largest among these is described.

[0113] (Numerical Example 1) Unit: mm Surface data Surface number rd nd νd Clear aperture 1 47.127 2.00 1.53775 74.7 60.09 2 23.850 18.04 45.00 3* 29.239 10.23 1.49710 81.6 34.61 4* 114.591 5.82 27.78 5* 51.788 1.00 1.88202 37.2 26.24 6 28.911 4.59 1.51742 52.4 25.77 7 741.525 1.13 25.82 8 (Aperture) ∞ 3.56 25.89 9* 77.668 10.51 1.55332 71.7 26.19 10 -26.066 1.02 30.49 11 -226.514 2.07 1.83481 42.7 34.14 12* -457.836 3.36 35.56 13 -67.625 1.00 1.89286 20.4 36.05 14 ∞ 3.97 1.49700 81.5 39.28 15 -67.674 -3.97 40.41 16 ∞ 3.97 40.34 17 -67.674 5.50 40.26 18 ∞ 1.00 1.51633 64.1 50.00 19 ∞ 0.50 50.00 Image surface ∞ Aspheric surface data Surface 3 K = 0.00000e+00 A 4= 2.68200e-06 A 6= 4.08072e-09 A 8= 2.50665e-11 Surface 4 K = 0.00000e+00 A 4=-1.05832e-06 A 6=-9.32302e-10 A 8=-2.25900e-11 Surface 5 K = 0.00000e+00 A 4=-1.11685e-05 A 6=-1.56567e-08 A 8=-1.66515e-10 Surface 9 K = 0.00000e+00 A4=-5.72921e-06 A6= 9.84264e-09 Surface 12 K = 0.00000e+00 A4= 8.38497e-06 A6= 2.02585e-10 A8= 5.15363e-12 Data Zoom ratio 1.00 Focal length 18.19 F-number 0.77 Half angle of view (degrees) 44.54 Image height 17.90 Lens length 75.29 BF (inAIR) 6.65 Single lens data Lens First surface Focal length 1 1 -92.57 2 3 75.95 3 5 -75.75 4 6 58.02 5 9 36.59 6 11 -539.23 7 13 -75.74 8 14 136.17 9 15 136.17 10 16 136.17 11 18 0.00 (Numerical Example 2) Unit: mm Surface data Surface number rd nd νd Clear aperture 1 34.920 2.00 1.49700 81.5 53.56 2 24.436 13.52 44.93 3* 29.483 8.67 1.49710 81.6 37.46 4* 54.330 4.16 32.52 5* 35.329 1.00 1.80400 46.6 30.82 6 23.085 6.05 1.49700 81.5 29.57 7 72.829 3.79 29.44 8 (Aperture) ∞ 0.17 29.70 9* 126.462 14.50 1.60738 56.8 29.84 10 -34.158 1.66 29.12 11 -98.308 2.07 1.72916 54.7 32.60 12* -114.637 2.58 34.43 13 -106.158 1.00 1.95906 17.5 36.75 14 ∞ 5.10 1.49700 81.5 38.83 15 -81.272 -5.10 41.50 16 ∞ 5.10 41.46 17 -81.272 6.70 41.42 18 ∞ 1.00 1.51633 64.1 50.00 19 ∞ 0.50 50.00 Image surface ∞ Aspheric surface data Surface 3 K = 0.00000e+00 A 4= 1.93351e-07 A 6= 1.40310e-09 A 8= 1.63609e-11 Surface 4 K = 0.00000e+00 A 4=-1.40320e-05 A 6= 1.57528e-08 A 8=-1.95261e-11 Surface 5 K = 0.00000e+00 A 4=-1.49134e-05 A 6=-8.19704e-09 A 8=-5.11549e-11 Surface 9 K = 0.00000e+00 A 4=-1.86854e-07 A 6= 1.61960e-08 Surface 12 K = 0.00000e+00 A 4= 4.86104e-06 A 6= 2.81753e-09 A 8= 4.38490e-12 Data Zoom ratio 1.00 Focal length 24.02 F-number 0.77 Half angle of view (degrees) 38.52 Image height 19.12 Lens length 74.46 BF(inAIR) 7.85 Single lens data Lens First surface Focal length 1 1 -174.85 2 3 116.22 3 5 -85.97 4 6 65.36 5 9 45.84 6 11 -1000.00 7 13 -110.69 8 14 163.52 9 15 163.52 10 16 163.52 11 18 0.00 (Numerical Example 3) Unit: mm Surface data Surface number rd nd νd Clear aperture 1 32.864 8.88 1.49700 81.5 41.70 2 1368.694 2.58 40.89 3* 391.069 2.80 1.95375 32.3 37.87 4* 107.203 10.39 35.40 5 (Aperture) ∞ 0.52 33.12 6* 78.254 18.01 1.51633 64.1 32.35 7* -89.131 1.00 28.91 8 940.768 10.10 1.57135 53.0 34.99 9 -24.514 1.00 1.83481 42.7 36.27 10 ∞ 3.77 1.49700 81.5 43.92 11 -87.122 -3.77 44.84 12 ∞ 3.77 44.80 13 -87.122 8.16 44.76 14 ∞ 1.00 1.51633 64.1 50.00 15 ∞ 0.50 50.00 Image surface ∞ Aspheric surface data Surface 3 K = 0.00000e+00 A 4= 1.30583e-05 A 6=-1.65551e-08 A 8= 5.12331e-12 Surface 4 K = 0.00000e+00 A4= 1.80379e-05 A6=-1.14415e-08 Surface 6 K = 0.00000e+00 A4= 3.41178e-06 A6= 4.14610e-09 Surface 7 K = 0.00000e+00 A4= 2.79360e-06 A6= 5.80781e-09 Data Zoom ratio 1.00 Focal length 35.02 F-number 0.84 Half angle of view (degrees) 29.40 Image height 19.73 Lens length 68.71 BF(inAIR) 9.32 Single lens data Lens First surface Focal length 1 1 67.60 2 3 -155.60 3 6 83.77 4 8 41.98 5 9 -29.37 6 10 175.30 7 11 175.30 8 12 175.30 9 14 0.00 (Numerical Example 4) Unit: mm Surface data Surface number rd nd νd Pitch diameter 1 38.891 9.25 1.61997 63.9 49.50 2 268.113 12.53 48.64 3 186.733 3.31 1.89286 20.4 37.86 4 53.469 1.56 1.85135 40.1 35.01 5* 78.364 4.54 34.51 6(Aperture) ∞ 11.62 33.53 7 137.484 2.63 1.60342 38.0 28.10 8 -143.025 2.66 27.67 9 -603.030 1.50 1.59282 68.6 36.70 10 41.251 12.62 1.58144 40.8 40.00 11 -45.071 1.00 41.20 12 -38.805 1.00 1.77830 23.9 41.21 13 ∞ 4.00 1.63980 34.5 45.59 14 -136.851 -4.00 46.95 15 ∞ 4.00 46.90 16 -136.851 10.29 46.86 17 ∞ 1.00 1.51633 64.1 50.00 18 ∞ 0.50 50.00 Image surface ∞ Aspheric surface data 5th surface K = 0.00000e+00 A4= 3.46583e-06 A6= 2.99436e-09 Various data Zoom ratio 1.00 Focal length 50.99 F-number 1.03 Half angle of view (degrees) 22.99 Image height 21.64 Lens length 80.00 BF(inAIR) 11.45 Single lens data Lens First surface Focal length 1 1 72.26 2 3 -84.91 3 4 192.15 4 7 116.58 5 9 -65.07 6 10 39.15 7 12 -49.86 8 13 213.90 9 14 213.90 10 15 213.90 11 17 0.00 (Numerical Example 5) Unit: mm Surface data Surface number rd nd νd Clear aperture 1 59.672 17.42 1.49700 81.5 80.50 2 722.281 15.00 78.89 3* 81.327 12.53 1.49700 81.5 63.44 4 -249.811 4.99 1.70154 41.2 59.55 5 62.175 13.22 52.42 6(Aperture) ∞ 9.18 49.98 7 134.805 6.40 1.49700 81.5 46.30 8 -133.525 13.27 45.48 9 -134.752 1.50 1.76182 26.5 35.73 10 53.339 7.49 1.95150 29.8 38.44 11* -152.685 14.74 39.26 12 -116.988 1.00 1.85025 30.1 44.31 13 ∞ 3.00 1.64769 33.8 45.48 14 -207.078 -3.00 46.20 15 ∞ 3.00 46.15 16 -207.078 11.84 46.09 17 ∞ 1.00 1.51633 64.1 43.50 18 ∞ 0.50 43.37 Image surface ∞ Aspheric data Surface 3 K = 0.00000e+00 A 4=-9.17893e-07 A 6=-3.55927e-10 Surface 1 K = 0.00000e+00 A 4= 2.93531e-07 A 6= 4.60080e-11 Other data Zoom ratio 1.00 Focal length 82.92 F-number 1.03 Half angle of view (degrees) 14.62 Image height 21.64 Total lens length 133.09 BF(inAIR) 13.00 Single lens data Lens Initial surface Focal length 1 1 129.74 2 3 125.02 3 4 -70.50 4 7 136.05 5 9 -49.99 6 10 42.29 7 12 -137.59 8 13 319.72 9 14 319.72 10 15 319.72 11 17 0.00 (Numerical Example 6) Unit: mm Surface data Surface number rd nd νd Effective diameter 1 69.284 19.84 1.49700 81.5 94.27 2 722.539 19.54 92.67 3* 94.913 10.25 1.49700 81.5 73.24 4 -217.337 2.00 1.74400 44.8 72.33 5 78.844 14.68 65.85 6(Aperture) ∞ 16.68 63.93 7 190.708 6.77 1.49700 81.5 59.05 8 -143.750 17.32 58.65 9 -577.102 2.00 1.54072 47.2 45.40 10 55.848 6.29 1.71300 53.9 42.80 11* -648.673 24.98 42.05 12 -110.958 1.00 1.80518 25.4 47.98 13 ∞ 4.55 1.80610 33.3 49.22 14 -218.870 -4.55 50.28 15 ∞ 4.55 49.90 16 -218.870 12.44 49.52 17 ∞ 1.00 1.51633 64.1 50.00 18 ∞ 0.50 50.00 Image surface ∞ Aspheric surface data Surface 3 K = 0.00000e+00 A 4=-5.70475e-07 A 6=-1.67302e-10 Surface 1 K = 0.00000e+00 A 4= 1.42663e-07 A 6= 6.55028e-11 Various data Zoom ratio 1.00 Focal length 97.10 F-number 1.03 Half angle of view (degrees) 12.56 Image height 21.64 Total lens length 159.85 BF(inAIR) 13.60 Single lens data Lens First surface Focal length 1 1 152.65 2 3 134.39 3 4 -77.54 4 7 166.04 5 9 -94.07 6 10 72.39 7 12 -137.81 8 13 271.52 9 14 271.52 10 15 271.52 11 17 0.00 (Numerical Example 7) Unit: mm Surface data Surface number rd nd νd Effective diameter 1 74.855 1.50 2.00330 28.3 72.00 2 38.980 15.88 61.69 3 8731.995 1.50 1.49710 81.6 61.26 4* 40.949 0.63 57.02 5 45.281 8.40 1.91650 31.6 57.10 6 131.225 (Variable) 56.27 7 ∞ (Variable) 35.31 8* 77.497 2.52 1.76802 49.2 36.89 9 636.111 11.25 36.96 10(Aperture) ∞ 1.00 38.82 11 -5038.428 6.26 1.58913 61.1 38.98 12 -42.662 4.92 39.15 13 -185.603 1.50 2.00330 28.3 34.96 14* 184.694 7.00 34.49 15 ∞ (Variable) 35.10 16* 71.683 8.63 1.49710 81.6 35.42 17 -36.820 (Variable) 35.24 18 142.633 6.83 1.84666 23.8 35.64 19 -55.989 1.50 1.95375 32.3 35.51 20 36.259 15.19 1.43875 94.7 35.45 21 -26.254 1.60 36.75 22 -25.869 1.00 2.00100 29.1 36.40 23 ∞ 3.00 2.00069 25.5 43.24 24 -125.535 -3.00 44.09 25 ∞ 3.00 44.15 26 -125.535 (variable) 44.21 27 ∞ 1.00 1.51633 64.1 50.00 28 ∞ (variable) 50.00 Image surface ∞ Aspheric surface data Surface 4 K =-9.69697e-01 A 4= 6.81233e-07 A 6=-1.55549e-10 A 8= 1.32810e-13 Surface 8 K = 0.00000e+00 A 4=-3.32737e-06 A 6=-2.58459e-09 A 8=-2.84899e-12 Surface 14 K = 0.00000e+00 A 4= 4.05263e-06 A 6= 9.13264e-10 Surface 16 K = 0.00000e+00 A 4= 5.81408e-07 A 6=-1.96531e-09 Various data Zoom ratio 1.40 Wide-angle Mid-range Telephoto Focal length 25.01 30.00 34.99 F-number 1.24 1.24 1.24 Half angle of view (degrees) 37.96 33.46 29.93 Image height 19.51 19.83 20.15 Total lens length 163.41 141.33 126.34 BF(inAIR) 14.01 14.01 14.01 d 6 33.25 16.19 2.00 d 7 14.71 7.06 3.54 d15 0.00 0.39 0.87 d17 1.00 3.23 5.47 d26 12.85 12.85 12.85 d28 0.50 0.50 0.50 Zoom lens group data Group Initial surface Focal length Lens length Front principal point Rear principal point 1 1 -95.10 27.91 1.34 -20.86 2 7 ∞ 0.00 0.00 -0.00 3 8 81.45 34.45 0.41 -28.74 4 16 50.26 8.63 3.91 -2.01 5 18 83.23 29.12 29.08 10.13 6 27 ∞ 1.00 0.33 -0.33 Single Lens Data Lens Initial Surface Focal Length 1 1 -82.80 2 3 -82.77 3 5 72.07 4 8 114.68 5 11 73.00 6 13 -92.08 7 16 50.26 8 18 48.25 9 19 -22.89 10 20 37.49 11 22 -25.84 12 23 125.45 13 24 125.45 14 25 125.45 15 27 0.00 (Numerical Example 8) Unit: mm Surface data Surface number rd nd νd Pitch diameter 1 82.906 1.50 2.00330 28.3 60.19 2 47.948 12.23 55.60 3 -280.351 1.50 1.72916 54.1 54.42 4 172.581 0.71 53.27 5 77.195 7.52 1.85478 24.8 52.67 6 -224.262 1.81 52.08 7 -117.811 1.50 1.95375 32.3 51.54 8 -1484.341 (Variable) 50.43 9* 43.712 10.42 1.49710 81.6 53.30 10 -214.406 3.00 53.19 11(Aperture) ∞ 3.27 52.12 12 45.679 12.76 1.49700 81.5 49.68 13 -91.143 3.24 48.48 14 231.687 1.50 2.00100 29.1 38.15 15* 41.564 7.09 34.47 16 ∞ (Variable) 34.04 17* 7841.280 4.89 1.53775 74.7 33.70 18 -49.823 (Variable) 33.43 19 201.845 6.85 1.85026 32.3 33.45 20 -31.488 1.50 1.76845 41.2 33.56 21 40.703 6.96 1.49700 81.5 33.87 22 -261.989 5.31 34.49 23 -44.129 1.00 2.00330 28.3 35.47 24 ∞ 3.00 1.92119 24.0 38.59 25 -166.656 -3.00 39.84 26 ∞ 3.00 40.17 27 -166.656 (variable) 40.51 28 ∞ 1.00 1.51633 64.1 50.00 29 ∞ (variable) 50.00 Image surface ∞ Aspheric surface data Surface 9 K = 0.00000e+00 A 4=-2.13593e-06 A 6=-1.31682e-09 A 8=-1.13405e-12 Surface 15 K = 0.00000e+00 A 4= 6.52079e-06 A 6= 6.92491e-09 1st 7th surface K = 0.00000e+00 A4= 3.32630e-06 A6= 6.16101e-09 Various data Zoom ratio 1.36 Wide angle Mid-range Telephoto Focal length 36.00 43.00 49.00 F-number 1.24 1.24 1.24 Half angle of view (degrees) 28.19 25.16 22.93 Image height 19.29 20.20 20.72 Total lens length 171.50 147.73 133.49 BF(inAIR) 11.49 11.49 11.49 d 8 58.96 32.16 15.33 d16 2.14 1.81 1.56 d18 1.00 4.35 7.19 d27 10.33 10.33 10.33 d29 0.50 0.50 0.50 Zoom Lens Group Data Group Initial Surface Focal Length Lens Length Front Principal Point Position Rear Principal Point Position 1 1 -126.63 26.77 3.06 -17.60 2 9 64.16 41.29 -12.17 -36.78 3 17 92.08 4.89 3.16 -0.02 4 19 112.85 24.62 20.00 -0.35 5 28 ∞ 1.00 0.33 -0.33 Singlet Lens Data Lens Initial Surface Focal Length 1 1 -115.82 2 3 -146.30 3 5 67.97 4 7 -134.24 5 9 74.04 6 12 63.18 7 14 -50.80 8 17 92.08 9 19 32.47 10 20 -22.90 11 21 71.43 12 23 -43.98 13 24 180.91 14 25 180.91 15 26 180.91 16 28 0.00 (Numerical Example 9) Unit: mm Surface data Surface number rd nd νd Pitch diameter 1 131.213 2.40 2.00069 25.5 74.00 2 68.682 8.94 1.72916 54.7 70.30 3 346.172 0.50 69.83 4 70.119 6.87 1.75500 52.3 65.99 5 230.471 (variable) 65.51 6 78.661 1.50 1.78800 47.4 47.02 7 33.678 10.84 43.25 8* -150.561 1.50 1.76802 49.2 43.35 9 114.246 0.45 44.03 10 60.690 10.89 1.74077 27.8 45.61 11 -93.611 3.24 45.44 12 -51.294 1.50 1.81600 46.6 45.04 13 -342.865 (Variable) 46.36 14(Aperture) ∞ (Variable) 51.51 15* 74.722 6.50 1.49710 81.6 54.75 16 -379.157 2.54 54.94 17 81.670 13.12 1.49700 81.5 55.90 18 -64.887 2.54 55.58 19 147.596 1.50 1.63540 23.9 46.44 20* 59.113 (Variable) 43.47 21* 671.400 8.06 1.55332 71.7 48.97 22 -52.233 (variable) 49.38 23 193.868 1.50 2.00330 28.3 47.89 24 77.484 3.55 47.12 25 665.553 5.14 1.49710 81.6 47.18 26* -83.120 5.75 47.35 27 -50.955 1.50 1.90525 35.0 47.01 28 ∞ 3.50 1.78472 25.7 50.12 29 -172.444 -3.50 50.86 30 ∞ 3.50 50.63 31 -172.444 (variable) 50.40 32 ∞ 1.00 1.51633 64.1 50.00 33 ∞ (variable) 50.00 Image surface ∞ Aspheric surface data Surface 8 K = 0.00000e+00 A 4= 4.09477e-07 A 6= 1.99886e-10 A 8= 6.08231e-13 Surface 15 K = 0.00000e+00 A 4=-1.01011e-06 A 6=-1.56970e-09 A 8=-2.18854e-14 Surface 20 K = 0.00000e+00 A 4= 3.32477e-06 A 6= 1.01917e-09 2nd side 1 K = 0.00000e+00 A 4=-7.69683e-07 A 6= 8.64044e-10 2nd side 6 K = 0.00000e+00 A 4= 1.13781e-07 A 6= 1.32293e-10 Various data Zoom ratio 1.60 Wide angle Mid-range Telephoto Focal length 51.50 64.34 82.51 F-number 1.20 1.20 1.20 Half angle of view (degrees) 22.79 18.59 14.69 Image height 21.64 21.64 21.64 Total lens length 180.50 174.98 176.93 BF(inAIR) 12.32 12.32 12.32 d 5 0.31 11.06 26.20 d13 25.14 16.13 10.20 d14 6.50 1.97 1.31 d20 24.85 22.35 21.73 d22 7.21 6.99 1.00 d31 11.16 11.16 11.16 d33 0.50 0.50 0.50 Zoom lens group data Group Initial surface Focal length Lens construction length Front principal point Rear principal point 1 1 110.00 18.71 2.35 -8.42 2 6 -51.13 29.92 7.60 -13.72 3 14 ∞ 0.00 0.00 0.00 4 15 65.43 26.20 2.93 -15.82 5 21 87.93 8.06 4.83 -0.38 6 23 118.24 20.95 28.15 10.76 7 32 ∞ 1.00 0.33 -0.33 Singlet Lens Data Lens Initial Surface Focal Length 1 1 -146.84 2 2 115.93 3 4 131.07 4 6 -75.85 5 8 -84.37 6 10 51.24 7 12 -74.09 8 15 126.17 9 17 74.98 10 19 -156.21 11 21 87.93 12 23 -129.48 13 25 148.98 14 27 -56.29 15 28 219.75 16 29 219.75 17 30 219.75 18 32 0.00 (Numerical Example 10) Unit: mm Surface data Surface number rd nd νd Pitch diameter 1 142.069 2.40 2.00069 25.5 68.50 2 66.558 8.65 1.67790 55.3 65.09 3 576.692 0.50 64.66 4 62.418 6.01 1.78800 47.4 60.22 5 170.503 (Variable) 59.50 6 110.473 1.50 1.77250 49.6 39.84 7 35.677 6.70 37.64 8* -180.308 1.50 1.76802 49.2 37.71 9 136.211 0.48 38.33 10 58.865 11.64 1.72151 29.2 39.71 11 -73.590 2.07 39.63 12 -49.898 1.50 1.83481 42.7 39.29 13 -353.817 (Variable) 40.08 14(Aperture) ∞ (Variable) 40.87 15* 68.326 5.36 1.49710 81.6 43.04 16 -200.750 3.25 43.06 17 56.773 8.45 1.49700 81.5 42.44 18 -75.641 3.25 42.01 19 244.132 1.50 1.63540 23.9 36.15 20* 55.164 (Variable) 34.00 21* 315.543 6.65 1.55332 71.7 43.38 22 -52.972 (Variable) 43.77 23 95.103 1.50 2.00069 25.5 42.99 24 52.813 1.64 42.05 25 80.038 6.90 1.61340 44.3 42.08 26* -148.434 7.04 42.05 27 -36.126 1.00 1.91650 31.6 40.02 28 182.394 1.81 1.88202 37.2 43.10 29 ∞ -1.81 43.31 30 182.394 1.81 43.50 31 ∞ 0.50 1.51633 64.1 43.45 32 ∞ (variable) 43.39 Image surface ∞ Aspheric surface data Surface 8 K = 0.00000e+00 A 4= 3.43387e-07 A 6= 4.32489e-10 A 8= 6.35316e-13 Surface 15 K = 0.00000e+00 A 4=-1.35390e-06 A 6=-1.83822e-09 A 8= 9.03689e-14 2nd surface 0 K = 0.00000e+00 A 4= 3.59093e-06 A 6= 9.83623e-10 2nd surface 1 K = 0.00000e+00 A 4=-1.88335e-06 A 6= 9.09329e-10 2nd surface 6 K = 0.00000e+00 A 4=-6.13989e-06 A 6=-4.79014e-10 Various data Zoom ratio 1.60 Wide angle Medium Telephoto Focal length 51.50 64.00 82.52 F-number 1.44 1.44 1.44 Half angle of view (degrees) 22.79 18.68 14.69 Image height 21.64 21.64 21.64 Total lens length 156.83 151.14 156.37 BF(inAIR) 3.37 3.37 3.37 d 5 1.35 13.41 28.99 d13 23.74 12.43 8.52 d14 6.02 2.60 1.00 d20 23.54 21.73 24.57 d22 9.89 8.68 1.00 d32 0.50 0.50 0.50 Zoom lens group data Group Initial surface Focal length Lens construction length Front principal point Rear principal point 1 1 109.52 17.56 3.01 -7.20 2 6 -58.36 25.39 4.81 -12.56 3 14 ∞ 0.00 0.00 0.00 4 15 59.13 21.80 0.40 -15.27 5 21 82.50 6.65 3.69 -0.62 6 23 -6334.37 20.39 -200.09 -225.15 Single Lens Data Lens Initial Surface Focal Length 1 1 -127.16 2 2 110.24 3 4 121.96 4 6 -68.81 5 8 -100.82 6 10 47.06 7 12 -69.74 8 15 103.23 9 17 66.67 10 19 -112.51 11 21 82.50 12 23 -120.83 13 25 85.76 14 27 -32.83 15 28 206.79 16 29 206.79 17 30 206.79 18 31 0.00 (Numerical Example 11) Unit: mm Surface data Surface number rd nd νd Clear aperture 1* 41.238 8.16 1.49700 81.5 25.00 2* 143.259 4.37 23.70 3* 84.062 2.47 1.76802 49.2 22.37 4* 46.408 2.17 22.19 5(Aperture) ∞ 5.00 22.24 6* 336.902 13.20 1.49700 81.5 22.41 7* -25.213 1.31 29.98 8 -67.450 1.00 1.88300 40.8 33.04 9 ∞ 1.98 1.49700 81.5 34.94 10 -126.165 -1.98 35.52 11 ∞ 1.98 35.66 12 -126.165 21.65 35.81 13 ∞ 1.00 1.51633 64.1 40.39 14 ∞ 0.50 40.55 Image surface ∞ Aspheric surface data First surface K = 0.00000e+00 A 4=-5.98397e-08 A 6=-4.69065e-09 2nd side K = 0.00000e+00 A 4=-1.72753e-05 A 6= 6.66460e-09 3rd side K = 0.00000e+00 A 4=-7.97584e-05 A 6= 1.55610e-07 A 8= 5.12331e-12 4th side K = 0.00000e+00 A 4=-6.47253e-05 A 6= 1.88884e-07 6th side K = 0.00000e+00 A 4=-8.81099e-06 A 6= 6.90546e-09 7th side K = 0.00000e+00 A 4= 1.10940e-06 A 6=-5.37594e-09 Various data Zoom ratio 1.00 Focal length 32.50 F-number 1.30 Half angle of view (degrees) 31.19 Image height 19.68 Lens overall length 62.82 BF(inAIR) 22.81 Single lens data Lens First surface Focal length 1 1 113.50 2 3 -138.86 3 6 47.78 4 8 -76.39 5 9 253.85 6 10 253.85 7 11 253.85 8 13 0.00 (Numerical Example 12) Unit: mm Surface data Surface number rd nd νd Effective diameter 1* 33.057 4.67 1.49700 81.5 19.13 2* 219.507 4.76 16.76 3* 349.408 2.76 1.76802 49.2 15.56 4* 42.910 1.69 15.33 5(Aperture) ∞ 5.00 15.41 6* -382.974 9.91 1.49700 81.5 17.16 7* -21.374 7.90 23.37 8 -76.290 1.00 1.88300 40.8 32.20 9 ∞ 1.82 1.49700 81.5 33.88 10 -135.143 -1.82 34.45 11 ∞ 1.82 34.63 12 -135.143 21.81 34.80 13 ∞ 1.00 1.51633 64.1 40.41 14 ∞ 0.50 40.57 Image surface ∞ Aspheric surface data First surface K = 0.00000e+00 A 4= 1.11113e-05 A 6= 2.80371e-08 Second side K = 0.00000e+00 A 4= 3.71379e-06 A 6=-3.33873e-08 Third side K = 0.00000e+00 A 4=-6.70571e-05 A 6= 5.26611e-08 A 8= 5.12331e-12 4th side K = 0.00000e+00 A 4=-4.86355e-05 A 6= 1.74615e-07 6th side K = 0.00000e+00 A 4=-7.99779e-06 A 6= 1.58276e-08 7th surface K = 0.00000e+00 A 4=-1.62333e-06 A 6=-9.03039e-09 Various data Zoom ratio 1.00 Focal length 35.00 F-number 2.00 Half angle of view (degrees) 29.34 Image height 19.67 Total lens length 62.82 BF (in AIR) 22.97 Single lens data Lens Initial surface Focal length 1 1 77.66 2 3 -63.94 3 6 45.14 4 8 -86.40 5 9 271.92 6 10 271.92 7 11 271.92 8 13 0.00 Various values ​​in each numerical example are summarized in Table 1 below.

[0114]

[0115] [Imaging Device] An imaging device having the imaging optical system of each embodiment will now be described. Fig. 40 is a schematic diagram of a digital camera, which is an example of an imaging device. Reference numeral 20 denotes a digital camera body, 21 denotes an imaging optical system that is one of the imaging optical systems of each embodiment, and 22 denotes an imaging element such as a CCD that receives a subject image via the imaging optical system 21. Reference numeral 23 denotes a recording means that records the subject image received by the imaging element 22, and 24 denotes a finder for observing the subject image displayed on a display element (not shown).

[0116] The display element is composed of a liquid crystal panel or the like, and displays the subject image formed on the image pickup element 22. Reference numeral 25 denotes a liquid crystal display panel having the same function as the finder 24.

[0117] In this way, by applying the imaging optical system of each embodiment to an imaging device, it is possible to realize an imaging device that is small in size and has high optical performance.

[0118] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

Claims

1. An imaging optical system having an open aperture, and a first transmitting / reflecting surface, a quarter-wave plate, and a second transmitting / reflecting surface arranged in this order from the object side to the image side, wherein light from the object side passes through the first transmitting / reflecting surface and the quarter-wave plate in that order, is reflected by the second transmitting / reflecting surface towards the object side, passes through the quarter-wave plate, is reflected by the first transmitting / reflecting surface towards the image side, passes through the quarter-wave plate and the second transmitting / reflecting surface in that order towards the image surface, and wherein the imaging optical system satisfies the following conditional expressions: 2.2≦L / Lh≦100.0 0.15≦D / LD≦2.00, where L is the total optical length, Lh is the distance on the optical axis from the first transmitting / reflecting surface to the image surface, D is the diameter of the open aperture, and LD is the distance on the optical axis from the open aperture to the image surface.

2. The imaging optical system according to claim 1, characterized in that the open aperture is positioned closer to the image side than the lens positioned furthest to the object side among the lenses included in the imaging optical system, and satisfies the condition: 0.35≦LD / L≦0.

85.

3. The imaging optical system according to claim 1 or 2, wherein the first transmissive reflective surface and the second transmissive reflective surface are disposed on the image side of the open aperture.

4. An imaging optical system as described in any one of claims 1 to 3, characterized in that the following condition is satisfied: 1.20≦θ1 / θ2≦20.00, where θ1 is the angle of the most off-axis ray passing through the center of the open aperture with respect to the optical axis when it is incident on the first transmitting and reflecting surface, and θ2 is the angle of the most off-axis ray passing through the center of the open aperture with respect to the optical axis after it is reflected by the second transmitting and reflecting surface and then by the first transmitting and reflecting surface.

5. An imaging optical system according to any one of claims 1 to 4, characterized in that the second transmitting and reflecting surface is arranged adjacent to the image side of the first transmitting and reflecting surface, and satisfies the condition: 2.00≦fP / f≦15.00, where fP is the focal length of a structure surrounded by the first transmitting and reflecting surface and the second transmitting and reflecting surface, and f is the focal length of the imaging optical system.

6. An imaging optical system as claimed in any one of claims 1 to 5, characterized in that the space between the first transmissive reflective surface and the second transmissive reflective surface is filled with a material other than air, and the following condition is satisfied, where nd is the refractive index of the material: 1.45≦nd≦2.

30.

7. The imaging optical system according to any one of claims 1 to 6, characterized in that the following condition is satisfied: 1.00≦L / Li≦200.00, where Li is the distance on the optical axis from the second transmissive-reflective surface to an image plane.

8. The imaging optical system according to any one of claims 1 to 7, characterized in that the second transmissive reflective surface is a lens surface of the imaging optical system that is closest to the image side.

9. The imaging optical system according to any one of claims 1 to 8, characterized in that one of the first transmissive-reflective surface and the second transmissive-reflective surface is a flat surface.

10. An imaging optical system according to any one of claims 1 to 9, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, the second transmitting and reflecting surface being arranged adjacent to the image side of the first transmitting and reflecting surface, and satisfying the condition: -1.00≦fN / fP≦-0.10, where fN is the focal length of the negative lens and fP is the focal length of a structure surrounded by the first transmitting and reflecting surface and the second transmitting and reflecting surface.

11. An imaging optical system according to any one of claims 1 to 10, further comprising a negative lens arranged adjacent to the object side of the first transmitting / reflecting surface, wherein the imaging optical system satisfies the condition: -10.00≦fN / f≦-0.30, where fN is the focal length of the negative lens and f is the focal length of the imaging optical system.

12. An imaging optical system according to any one of claims 1 to 11, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, wherein the following condition is satisfied: -1.00≦(R1-R2) / (R1+R2)≦0.30, where R1 is the radius of curvature of the lens surface on the object side of the negative lens, and R2 is the radius of curvature of the second transmitting and reflecting surface.

13. An imaging optical system according to any one of claims 1 to 12, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, wherein the imaging optical system satisfies the condition: -30.00≦fF / f≦-0.30, where fF is the focal length from the object side lens surface of the negative lens to the second transmitting and reflecting surface, and f is the focal length of the imaging optical system.

14. An imaging optical system as described in any one of claims 1 to 13, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, the space between the first transmitting and reflecting surface and the second transmitting and reflecting surface being filled with a material other than air, and satisfying the condition: 0.65≦nd / ndN≦1.10, where nd is the refractive index of the material and ndN is the refractive index of the negative lens.

15. An imaging optical system as described in any one of claims 1 to 14, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, wherein when the distance on the optical axis from the object side lens surface of the negative lens to the second transmitting and reflecting surface is d, the following condition is satisfied: 0.01≦d / L≦0.

15.

16. An imaging optical system as described in any one of claims 1 to 15, further comprising a negative lens arranged adjacent to the object side of the first transmitting and reflecting surface, and there is no air gap between the object side lens surface of the negative lens and the second transmitting and reflecting surface.

17. The imaging optical system according to any one of claims 1 to 16, characterized in that the following condition is satisfied: 0.01≦Lh / f≦0.90, where f is a focal length of the imaging optical system.

18. An imaging optical system according to any one of claims 1 to 17, characterized in that the following condition is satisfied: 0.30≦Oe / Ie≦4.00, where Oe is the outer diameter of the lens arranged closest to the object side of the imaging optical system, and Ie is the outer diameter of the lens arranged closest to the image side of the imaging optical system.

19. An imaging optical system described in any one of claims 1 to 18, characterized in that one of the first transmissive reflective surface and the second transmissive reflective surface is a surface that separates incident light into reflected light and transmitted light depending on the polarization state.

20. The imaging optical system according to claim 19, wherein the other of the first transmissive-reflective surface and the second transmissive-reflective surface is a half mirror or a cholesteric liquid crystal surface.

21. The imaging optical system according to any one of claims 1 to 20, characterized in that the imaging optical system is rotationally symmetric with respect to an optical axis.

22. The imaging optical system according to any one of claims 1 to 21, characterized in that, when the F-number of the imaging optical system is Fno, the following condition is satisfied: 0.50≦Fno≦8.

0.

23. An imaging device comprising: an imaging optical system according to any one of claims 1 to 22; and an imaging element for receiving an image formed by the imaging optical system.

Images