Imaging optical system and imaging apparatus having the same

Abstract

To provide an imaging optical system that has a small size, a large diameter, and high optical performance.SOLUTION: An imaging optical system has a maximum aperture, and a first transmission and reflection surface, a 1 / 4 wavelength plate, and a second transmission and reflection surface, which are arranged in order from an object side to an image side. Light from the object side passes in order through the first transmission and reflection surface and 1 / 4 wavelength plate, is reflected on the second transmission and reflection surface to the object side, passes through the 1 / 4 wavelength plate, is reflected on the first transmission and reflection surface to the image side, passes in order through the 1 / 4 wavelength plate and second transmission and reflection surface, and is directed to an image surface. The entire optical length, the distance on an optical axis from the first transmission and reflection surface to the image surface, the diameter of the maximum aperture, and the distance on an optical axis from the maximum aperture to the image surface.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, a configuration called a Gaussian type is 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, the curvature of field occurs significantly 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, the light that passes through the negative lens enters the image sensor at a large angle with respect to the optical axis, so that so-called vignetting by the image sensor occurs, resulting in an image that becomes darker toward the periphery.

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

[0004] [Patent Document 1] JP 2005-352273 A [Patent Document 2] JP 2013-218078 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the configuration of Patent Document 1 can be made compact, but the number of lenses is small, making it difficult to correct aberrations and making it impossible to accommodate large-diameter specifications. Also, in the configuration of Patent Document 2, the light flux is thin from the on-axis to the most off-axis light rays in order to accommodate the observation system, making it difficult to accommodate large-diameter specifications with the lens diameter configured. Furthermore, the overall lens length is long, and the distance from the lens located closest to the object to the aperture is far, so the lens diameter of the lens located closest to the object is very large.

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

[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 transmissive-reflective surface, a quarter-wave plate, and a second transmissive-reflective surface, wherein light from the object side passes through the first transmissive-reflective surface and the quarter-wave plate in this order, is reflected by the second transmissive-reflective surface towards the object side, passes through the quarter-wave plate, is reflected by the first transmissive-reflective surface towards the image side, passes through the quarter-wave plate and the second transmissive-reflective surface in this order, and proceeds towards the image plane; when the total optical length is L, the distance on the optical axis from the first transmissive-reflective surface to the image plane is Lh, the diameter of the open aperture is D, and the distance on the optical axis from the open aperture to the image plane is LD, 2.2≦L / Lh≦100.0 0.15≦D / LD≦2.00 The present invention is characterized in that the following conditional expression is satisfied: Effect of the Invention

[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. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram showing an optical path of an optical system. [Diagram 2] FIG. 2 is a schematic diagram showing an optical path of an optical system. [Diagram 3]1 is a cross-sectional view of an imaging optical system according to a first embodiment. [Figure 4] 4A to 4C are aberration diagrams of the imaging optical system of Example 1 when focusing at infinity. [Diagram 5] FIG. 11 is a cross-sectional view of an imaging optical system according to a second embodiment. [Figure 6] 11A to 11C are aberration diagrams of the imaging optical system of Example 2 when focusing at infinity. [Figure 7] FIG. 11 is a cross-sectional view of an imaging optical system according to a third embodiment. [Figure 8] 11A to 11C are aberration diagrams of the imaging optical system of Example 3 when focusing at infinity. [Figure 9] FIG. 11 is a cross-sectional view of an imaging optical system according to a fourth embodiment. [Figure 10] 13A to 13C are aberration diagrams of the imaging optical system of Example 4 when focusing at infinity. [Figure 11] FIG. 13 is a cross-sectional view of an imaging optical system according to a fifth embodiment. [Figure 12] 13A to 13C are aberration diagrams of the imaging optical system of Example 5 when focusing at infinity. [Figure 13] FIG. 13 is a cross-sectional view of an imaging optical system according to a sixth embodiment. [Figure 14] 13A to 13C are aberration diagrams of the imaging optical system of Example 6 when focusing at infinity. [Figure 15] FIG. 23 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 7. [Figure 16] 13A to 13C are diagrams showing cross-sectional views and movement trajectories of an imaging optical system according to a seventh embodiment at infinity from a wide-angle end to a telephoto end. [Figure 17] 13A to 13C are aberration diagrams at the wide-angle end when focusing at infinity in the imaging optical system of Example 7. [Figure 18] 13A to 13C are aberration diagrams in the intermediate range when the imaging optical system of Example 7 is focused at infinity. [Figure 19] 13A to 13C are aberration diagrams at the telephoto end when focusing at infinity in the imaging optical system of Example 7. [Figure 20] FIG. 13 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 8. [Figure 21] 13A to 13C are diagrams showing cross-sectional views and movement trajectories of an imaging optical system according to an eighth embodiment at infinity from a wide-angle end to a telephoto end. [Figure 22] 13A to 13C are aberration diagrams at the wide-angle end when focusing at infinity in the imaging optical system of Example 8. [Diagram 23] 13A to 13C are aberration diagrams in the intermediate range when the imaging optical system of Example 8 is focused at infinity. [Figure 24] 13A to 13C are aberration diagrams at the telephoto end when focusing at infinity in the imaging optical system of Example 8. [Diagram 25] FIG. 13 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 9. [Figure 26] 13A to 13C are diagrams showing cross-sectional views and movement trajectories of an imaging optical system according to a ninth embodiment at infinity from a wide-angle end to a telephoto end. [Figure 27] 13A to 13C are aberration diagrams at the wide-angle end when focusing at infinity in the imaging optical system of Example 9. [Figure 28] 13A to 13C are aberration diagrams in the intermediate range when the imaging optical system of Example 9 is focused at infinity. [Figure 29] 13A to 13C are aberration diagrams at the telephoto end when focusing at infinity in the imaging optical system of Example 9. [Diagram 30] FIG. 23 is a cross-sectional view of the wide-angle end of the imaging optical system of Example 10. [Diagram 31] 23A to 23C are diagrams showing cross-sectional views and movement trajectories of an imaging optical system according to a tenth embodiment at infinity from a wide-angle end to a telephoto end. [Diagram 32] 23A to 23C are aberration diagrams at the wide-angle end when focusing at infinity in the imaging optical system of Example 10. [Diagram 33] 13A to 13C are aberration diagrams in the intermediate range when the imaging optical system of Example 10 is focused at infinity. [Diagram 34] 23A to 23C are aberration diagrams at the telephoto end when focusing at infinity in the imaging optical system of Example 10. [Diagram 35] FIG. 23 is a cross-sectional view of an imaging optical system according to an eleventh embodiment. [Diagram 36] 13A to 13C are aberration diagrams of the imaging optical system of Example 11 when focusing at infinity. [Figure 37] FIG. 23 is a cross-sectional view of an imaging optical system according to a twelfth embodiment. [Figure 38] 23A to 23C are aberration diagrams of the imaging optical system of Example 12 when focusing at infinity. [Figure 39]FIG. 1 is an explanatory diagram of an off-axis ray passing through the center of an open aperture. [Diagram 40] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred 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 refer to the same components, and duplicated descriptions will be omitted.

[0011] The imaging optical system in each embodiment is an optical system that forms an image of an object on an image plane, and is an optical system for acquiring an image by a solid-state imaging element or a 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 having an imaging element that receives an image formed by the imaging optical system, distance detection cameras, fixed lens cameras, disposable film cameras, etc. 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, facial expression recognition, etc. Also, it may be used for external environment recognition applications such as XR devices and automatic robots.

[0014] The imaging optical system of each embodiment has an open aperture, and a first transmissive-reflective surface, a quarter-wave plate (QWP), and a second transmissive-reflective surface arranged in this order from the object side to the image side. The open aperture means the state in which the aperture diaphragm is most open, and in each embodiment, the state in which the aperture diaphragm is most open is the value of the open aperture, and at that time, the width of the axial light beam is determined by the open aperture diameter. In a lens system without an aperture that can change the aperture opening, the aperture that determines the axial light beam may be determined as the open aperture, and if there is an aperture that determines the axial light beam that falls within the range of conditional formula (3) described later, the aperture is determined as the open aperture. Light from the object side passes through the first transmissive-reflective surface and the QWP in order, and is reflected by the second transmissive-reflective surface. The light then passes through the QWP, is reflected by the first transmissive-reflective surface, passes through the QWP, and the second transmissive-reflective surface, and heads toward an imaging unit such as a solid-state imaging element or a photosensitive film.

[0015] Here, the first transmissive-reflective surface and the second transmissive-reflective surface do not necessarily 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 bonded to either or both sides of each of the transmission / reflection surfaces.

[0017] As the QWP, for example, a polymer film having birefringence or a liquid crystal alignment layer can be used. Also, a laminate of such polymer films or liquid crystal alignment layers can be used as the QWP. By appropriately laminating these, a phase difference close to a quarter of the wavelength can be obtained in a wide wavelength range. In addition to the above, for example, an inorganic wave plate from Dexerials Corporation can be used as the QWP.

[0018] The QWP can be arranged, for example, by bonding with the first transmissive-reflective surface or the second transmissive-reflective surface. The QWP can also be arranged separately from these transmissive-reflective surfaces. For example, the film can be inserted directly into the optical path, or a film bonded to a glass plate can be inserted into the optical path. A lens can be formed or bonded on one or both sides of the QWP. For example, a lens can be molded on one or both sides of the inorganic waveplate using wafer-level optics technology with the inorganic waveplate 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) Here, L is the total optical length. Lh is the distance on the optical axis from the first transmissive-reflecting surface to the image plane. D is the open aperture diameter. LD is the distance on the optical axis from the open aperture to the image plane.

[0022] Conditional formula (1) is a conditional formula that specifies the position of the first transmissive-reflective surface relative to the total optical length, and is a conditional formula that expresses the position in the entire lens system (imaging optical system) at which the angle of incidence of off-axis light with respect to the optical axis when it is incident on the imaging element is relaxed. Also, by specifying the distance on the optical axis from the first transmissive-reflective surface to the image plane, it leads to specifying the width of the light beam passing through the first transmissive-reflective surface, and expresses high performance. If the distance on the optical axis from the first transmissive-reflective surface to the image plane becomes long below the lower limit of conditional formula (1), the total lens length becomes too large, which is not preferable. In addition, the entire lens system will be separated from the imaging element, but the incidence angle to the imaging element will become sharp, which is not preferable because the incidence angle constraint cannot be satisfied. Furthermore, the width of the light beam passing through the front and rear surfaces adjacent to the first transmissive-reflective surface will become large, and the amount of aberration generated when passing through the surfaces will become large, which is not preferable. In addition, if the upper limit of conditional formula (1) is exceeded, it is easy to accommodate the angle of incidence to the imaging element, but it is not preferable because the final surface of the entire lens system will interfere with the imaging element.

[0023] Conditional formula (2) is a conditional formula that specifies the open aperture diameter of the open aperture that determines the axial Fno light beam diameter and the distance on the optical axis from the open aperture 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 open aperture where the axial light beam diameter (corresponding to the open aperture diameter) will be thicker than the axial light beam diameter at the aperture position. When the negative refractive power is strong and sagittal coma flare occurs significantly, the value of the conditional formula will be smaller than when the negative refractive power is weak and sagittal coma flare is good. Also, 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 open aperture diameter on the image side of the open aperture, so the value of the conditional formula will be large. Therefore, conditional formula (2) can be said to be a conditional formula that specifies the brightness of Fno and the negative refractive power in the entire lens system. If the lower limit of conditional formula (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 as it increases coma flare in the sagittal direction.If the upper limit of conditional formula (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 as it becomes impossible to aim for a larger lens and higher performance.

[0024] By simultaneously satisfying conditional expressions (1) and (2), it is possible to realize a large-diameter lens, a weak negative refractive power within the entire lens system, and high performance while mitigating the angle of incidence to the image sensor.

[0025] It is preferable that the numerical ranges of the conditional expressions (1) and (2) are 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 further preferable that the numerical ranges of the conditional expressions (1) and (2) be within 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, a description will be given of configurations that are preferably satisfied in the imaging optical system of each embodiment.

[0028] It is preferable that one of the first and second transmission-reflection surfaces is a surface that separates incident light into reflected light and transmitted light according to the polarization state. Specifically, as described later, it is preferable to use a polarization-selective transmission-reflection element as one of the first and second transmission-reflection surfaces. Examples of the polarization-selective transmission-reflection element include "WGF" manufactured by Asahi Kasei Corporation and "IQPE" manufactured by 3M Company. In addition, an optical element may be used as the polarization-selective transmission-reflection element, which is created by forming a grid on the lens reflection surface during lens molding and depositing, printing, or lithography a metal or dielectric thereon. A half mirror, a cholesteric liquid crystal, a holographic optical element, or the like may be used as the other. When a half mirror is used, the amount of randomly polarized light incident from the object side is 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 to about twice the amount when a half mirror is used.

[0029] The imaging optical system in 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 lens surface on the object side of the negative lens arranged adjacent to the object side of the first transmission-reflection surface to the second transmission-reflection surface is arranged at a position closest to the image sensor in the lens system. Therefore, there is a concern that ghosts may occur, and in order to avoid ghosts, it is preferable that the shape from the lens surface on the object side of the negative lens arranged adjacent to the object side of the first transmission-reflection surface to the second transmission-reflection surface is configured with a surface having a convex surface facing the image side.

[0033] It is preferable that the lens surface on the object side of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface is arranged on the image side of the open aperture from the second transmissive-reflective surface to the second transmissive-reflective surface, and that the lens surface is arranged as close as possible to the image sensor where the light beam width becomes small. If the lens surface is arranged at a position where the light beam is thick, the change in the surface shape relative to the light beam will affect the aberration.

[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 light ray passing through the center of the open aperture relative to the optical axis when it is incident on the first transmission-reflection surface. θ2 is the angle of the most off-axis light ray passing through the center of the open aperture relative to the optical axis after it is reflected by the second transmission-reflection surface and then reflected by the first transmission-reflection surface. fp is the focal length of the structure surrounded by the first transmission-reflection surface and the second transmission-reflection surface arranged adjacent to the image side of the first transmission-reflection surface. f is the focal length of the imaging optical system. nd is the refractive index of the material other than air that is filled between the first transmission-reflection surface and the second transmission-reflection surface. Li is the distance on the optical axis from the second transmission-reflection surface to the image surface. fN is the focal length of the negative lens arranged adjacent to the object side of the first transmission-reflection surface. R1 is the radius of curvature of the lens surface on the object side 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 transmissive-reflective surface to the second transmissive-reflective surface. ndN is the refractive index of the negative lens arranged adjacent to the object side of the first transmissive-reflective 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 of the imaging optical system. Ie is the outer diameter of the lens arranged closest to the image side of the imaging optical system.

[0036] Conditional formula (3) is a conditional formula that specifies where the open aperture is located in the entire lens system, and also specifies the size of the entire lens system. If the open aperture is located in the center of the entire lens system, off-axis rays can pass through the lenses before and after the open aperture in a well-balanced manner, centered around the open aperture, so that the entire lens system can be made compact. If the lower limit of conditional formula (3) is exceeded, the open aperture approaches the image plane, which is undesirable because the diameter of the front lens increases and the size becomes large. In addition, the approach of the open aperture to the image plane makes the angle of incidence to the image sensor too sharp, and even if the angle of incidence is reduced by reflection on the first and second transmissive reflecting surfaces, the angle of incidence to the image sensor cannot be reduced, which is undesirable. If the upper limit of conditional formula (3) is exceeded, the angle of incidence to the image sensor is easily reduced, but the angle of incidence is excessively corrected with respect to the optical axis by reflection on the first and second transmissive reflecting surfaces, which is undesirable because it goes too far in the direction of incidence from the outside toward the optical axis (the direction in which the subject is located at infinity).

[0037] Conditional formula (4) shows the change in angle of a ray when it is incident on the first transmissive-reflective surface and when it is emitted from the first transmissive-reflective surface, and expresses the refractive power due to passing through the first transmissive-reflective surface. Here, angles θ1 and θ2 will be specifically described. 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 toward the maximum image height of the image sensor, and is a ray passing through the center of the open aperture SP. Angle θ1 is the angle of the ray P with respect to the optical axis immediately before it is incident on the first transmissive surface, and angle θ2 is the angle of the ray P with respect to the optical axis after it passes through the first transmissive surface, is reflected by the second transmissive-reflective surface, and is reflected by the first transmissive-reflective surface. If the lower limit of conditional formula (4) is exceeded, the change in angle at the first transmissive-reflective surface becomes small, the effect of setting the first and second transmissive-reflective surfaces becomes small, and the negative refractive power in the entire lens system becomes strong, which is undesirable because it increases the occurrence of coma flare in the sagittal direction. If the upper limit of condition (4) is exceeded, the angle of incidence on the image sensor with respect to the optical axis will be in a direction toward the optical axis from the outside, and the light 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 formula (5) specifies the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface, and is a conditional formula corresponding to the refractive power of the second transmissive-reflective surface. If the lower limit of conditional formula (5) is not satisfied, the curvature of the second transmissive-reflective surface is reduced, so that the angle of incidence on the image sensor is increased in a direction from the outside toward the optical axis, and the light beam is outside the effective light receiving sensor area in front of the light receiving sensor of the image sensor (is vignetted), which is undesirable. If the upper limit of conditional formula (5) is exceeded, the curvature of the second transmissive-reflective surface is increased, so that the angle of incidence on the image sensor is increased with respect to the optical axis, which is undesirable.

[0039] Conditional formula (6) indicates that the space between the first transmissive-reflective surface and the second transmissive-reflective surface is filled with a refractive index medium other than air. If there is no refractive index medium and the surface is made of air alone, the relative positional relationship between the first transmissive-reflective surface and the second transmissive-reflective surface will cause changes in the angle of incidence on the image sensor and performance degradation such as one-sided blur. The accuracy of the relative positional relationship can be ensured by a structure that can be processed as an integral part such as a lens. If the lower limit of conditional formula (6) is exceeded, the surface cannot be processed with glass material, so the relative positional relationship between the first transmissive-reflective surface and the second transmissive-reflective surface is likely to shift, which is undesirable as it affects optical performance such as one-sided blur. If the upper limit of conditional formula (6) is exceeded, there is no glass material and there is an air gap, which requires the surface to be constructed with a reflecting surface or the like, so it is necessary to suppress the gap with a mechanical structure, and the relative positional relationship between the first transmissive-reflective surface and the second transmissive-reflective surface is likely to shift, which is undesirable as it 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 large, which is not preferable. In addition, the entire lens system is moved away from the image sensor, which is not preferable because the angle of incidence from the optical axis to the image sensor becomes steep. 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 not preferable because the amount of aberration generated when passing through the surfaces increases. If the upper limit of conditional expression (7) is exceeded, the angle of incidence to the image sensor can be easily accommodated, but the second transmissive-reflective surface interferes with the image sensor, which is not preferable.

[0041] Conditional formula (8) specifies the refractive power of the negative lens near the image side for correcting the curvature of field. The strong refractive power of the negative lens corrects the curvature of field, while the reflection of the structure surrounded by the first and second transmissive-reflective surfaces reduces the angle of incidence to the image sensor, and the negative lens is mainly responsible for correcting the curvature of field. If the refractive power of the negative lens is weaker than the lower limit of conditional formula (8), the correction of the curvature of field is insufficient, and the insufficient negative refractive power must be borne by the lens system closer to the object than the negative lens, which results in a large coma flare in the sagittal direction, which is undesirable. If the refractive power of the negative lens is strong beyond the upper limit of conditional formula (8), it is advantageous for correcting the curvature of field, but it is undesirable because the correction of the curvature of field becomes excessive and the angle of incidence to the image sensor with respect to the optical axis becomes large.

[0042] Conditional formula (9) specifies the refractive power of the negative lens near the image side with respect to the entire lens system in order to correct the field curvature. If the refractive power of the negative lens is weak below the lower limit of conditional formula (9), the correction of the 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, which results in a large amount of 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 formula (9), this is advantageous for correcting the field curvature, but is undesirable because the correction of the field curvature becomes excessive and the angle of incidence to the image sensor with respect to the optical axis becomes large.

[0043] Conditional formula (10) specifies the shape factor of the structure surrounded by the object side surface of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface and the second transmissive-reflective surface. Specifically, conditional formula (10) specifies that the object side surface of the negative lens has a strong concave curvature to correct the field curvature, and that the second transmissive-reflective surface has a convex shape from a flat surface to the image side to reduce the angle of incidence. If the lower limit of conditional formula (10) is exceeded, the second transmissive-reflective surface has a shape with a concave surface facing the image side, and if the second transmissive-reflective surface faces the image side, light rays originating from the image sensor are likely to be reflected by the second transmissive-reflective surface and return to the image sensor, which is a concern, and this is not preferable. If the upper limit of conditional formula (10) is exceeded, the curvature of the object side surface of the negative lens arranged adjacent to the object side of the first transmissive-reflective surface becomes gentle, which is not preferable because it makes it difficult to correct the field.

[0044] Conditional expression (11) prescribes 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 prescribes the correction of curvature of field. If the refractive power of the negative lens is weak below the lower limit of conditional expression (11), the correction of curvature of field is insufficient, and the insufficient negative refractive power must be borne by the lens closer to the object than the negative lens, which results in large 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), it is advantageous for the correction of curvature of field, but is undesirable because the correction of curvature of field becomes excessive.

[0045] Conditional expression (12) specifies 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 object side of the first transmissive-reflective surface, and the higher the refractive index of the negative lens, the longer the optical path length of off-axis light rays can be, which is advantageous for correcting curvature of field. If the refractive index of the negative lens becomes higher below the lower limit of conditional expression (12), the correction of curvature of field becomes excessive, which is undesirable. If the refractive index of the negative lens becomes lower above the upper limit of conditional expression (12), the amount of correction of curvature of field becomes insufficient, and the curvature of the object side surface of the negative lens becomes sharp to compensate for the insufficient amount, or the lens closer to the object side than the negative lens must bear the insufficient negative refractive power. As a result, a large amount of coma flare occurs in the sagittal direction, which is undesirable.

[0046] Conditional expression (13) specifies 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 with respect 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. In addition, the width of the light beam passing through each surface becomes large. In particular, since the lens surface on the object side 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 becomes large, and the change in the surface shape of the negative lens with respect to the light beam becomes large, which is undesirable because aberration worsens.

[0047] Conditional formula (14) is a conditional formula that specifies the focal length of the entire lens system and the position of the first transmissive-reflective surface, and specifies at what position in the entire lens system the reflection of the off-axis light beam is mitigated with respect to the angle of incidence of the off-axis light beam on the imaging element. If the lower limit of conditional formula (14) is exceeded, the position from the first transmissive-reflective surface to the image plane becomes far away, and the total lens length becomes too long, which is not preferable. In addition, the entire lens system becomes farther away from the imaging element, which is not preferable because the angle of incidence of the imaging element becomes sharp. In addition, if the upper limit of conditional formula (14) is exceeded, the angle of incidence of the imaging element can be easily accommodated, but the final surface of the entire lens system interferes with the imaging element, which is not preferable.

[0048] Conditional formula (15) is a conditional formula regarding the outer diameter of the lens arranged closest to the object side and the outer diameter of the lens arranged closest to the image side, and is a conditional formula 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 formula (15) is exceeded, the outer diameter of the lens arranged closest to the object side becomes too small, the specified Fno light flux does not enter, and it becomes difficult to increase the aperture, which is undesirable. If the upper limit of conditional formula (15) is exceeded, the outer diameter of the lens arranged closest to the object side becomes too large, which is undesirable because it becomes heavy.

[0049] In the imaging optical system of each embodiment, a loss of light occurs due to the first and second transmissive-reflective surfaces. If the F-number is large, the amount of light that reaches the image sensor becomes very small. Therefore, it is preferable that the imaging optical system of each embodiment satisfies 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) It is further preferable that the numerical ranges of the 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) In addition, in the imaging optical system of each embodiment, for example, by applying the following configuration, 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 the optical path that transmits without reflecting even once on the transmissive-reflective surface. [Polarized Configuration 1] A configuration using polarized light will be described with reference to FIG. 1. The imaging optical system of this configuration has two transmissive and reflective surfaces. Here, the transmissive and reflective surface disposed on the object side of the imaging optical system of this configuration is configured by disposing a polarization-selective transmissive and reflective element (PBS):A. The transmissive and reflective surface disposed 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 transmissive and reflective element PBS and the half mirror HM. Furthermore, a second quarter-wave plate (QWP2):D and a linear polarizer (POL):E are disposed between the half mirror HM and the imaging plane IM, in that 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 was transmitted through the linear polarizing plate E, and transmit linearly polarized light perpendicular to the direction. The polarization selective transmission reflection element A is, for example, a wire grid polarizer or a reflective polarizer having a retardation film laminated structure. In this case, the wire grid forming surface or retardation film surface of the polarization selective transmission reflection element A functions as a transmission reflection surface. Note that the wire grid polarizer does not necessarily have to be one in which metal wires are aligned, and it is sufficient that it has thin metal or dielectric layers at a predetermined interval 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 a light beam passes through the first quarter-wave plate B and the second quarter-wave plate D, the wavelength dispersion characteristics of the wave plates are offset.

[0055] The half mirror C is a half mirror formed by, for example, a dielectric multilayer film or metal deposition, and the mirror surface of the half mirror C functions as a transmission / reflection surface. The linear polarizing plate 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 entering the imaging optical system from the object side becomes linearly polarized light by the polarization-selective transflective element A, becomes circularly polarized light by the first quarter-wave plate B, and enters the half mirror C. A part of the light that reaches the half mirror C is reflected and becomes circularly polarized in the reverse direction, returning to the first quarter-wave plate B.

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

[0059] On the other hand, a portion of the light that reaches the half mirror C is transmitted through 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 transflector A is converted to 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 transflector 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 are aligned, so most of the light is transmitted and directed to the imaging plane IM.

[0061] Due to the above-mentioned 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 using a cholesteric liquid crystal instead of the half mirror C, it is preferable to set 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. In this way, it is possible to increase the amount of light on the normal optical path while reducing ghost light.

[0063] In addition, 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. After that, the light that leaves the second quarter-wave plate D is 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 the direction immediately after passing through the linear polarizer E immediately before. Since 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 manner, in this configuration, most of the light reflected by the imaging surface IM and the half mirror C in this order is cut, so ghosts and flares related to the imaging surface IM are less noticeable. In order to obtain such a reflection reduction effect, it is preferable that an optical low-pass filter using birefringence does not exist between the imaging surface IM and the linear polarizer E. This is because the optical low pass filter causes the polarization state to deviate from the desired polarization state.

[0064] In this configuration, a quarter-wave plate may be disposed between the polarization-selective transflector A and the object. In this case, the quarter-wave plate is disposed so that the fast axis or slow axis of the quarter-wave plate forms an angle of 45° with the transmission axis of the polarization-selective transflector A. In this way, even if the light incident from the object side is linearly polarized, it is possible to capture an image regardless of its polarization direction. Also, a depolarizing element may be disposed instead of the quarter-wave plate. For example, "Cosmoshine SRF" by Toyobo Co., Ltd. can be used as the depolarizing element. [Polarized Configuration 2] A configuration using polarized light will be described with reference to FIG. 2. The imaging optical system of this configuration has two transmissive and reflective surfaces. Here, the transmissive and reflective surface disposed on the object side of the imaging optical system of this configuration is configured by disposing a half mirror (HM):C. The transmissive and reflective surface disposed on the image surface side of the imaging optical system of this configuration is configured by disposing a polarization selective transmissive and reflective element (PBS):A. In addition, a first quarter-wave plate (QWP1):B is disposed between the polarization selective transmissive and reflective element PBS and the half mirror HM. Furthermore, a linear polarizer (POL):E and a second quarter-wave plate (QWP2):D are disposed between the half mirror HM and the object surface, in that order from the object side to the image side.

[0065] Here, the configuration of each polarizing element and the suitable arrangement of the optical axis orientation are similar to those in the polarized light utilization 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 becomes linearly polarized light by linear polarizer E, becomes circularly polarized light by second quarter-wave plate D, and enters half mirror C. Part of the light that reaches half mirror C is reflected and becomes circularly polarized in the reverse direction, 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 polarized by the second quarter-wave plate D as linearly polarized light in a direction perpendicular to the direction that it was when it passed through the linear polarizer E, and is then incident on and absorbed by the linear polarizer E.

[0069] Meanwhile, the light that passes through half mirror C becomes linearly polarized light by first quarter-wave plate B, polarized in the same direction as the light immediately after passing through linear polarizer E. This linearly polarized light is reflected by polarization-selective transmission / reflection element A and returns to first quarter-wave plate B. The light is then converted into circularly polarized light by first quarter-wave plate B, and part of it is reflected by half mirror C. The light reflected by half mirror C enters first quarter-wave plate B again and is converted into linearly polarized light whose polarization direction is orthogonal to that when it was reflected by polarization-selective transmission / reflection element A. This linearly polarized light passes through 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 is transmitted through the half mirror C, reflected by the polarization-selective transmission / reflection element PBS, reflected by the half mirror C, and transmitted 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 transflector A and the imaging plane IM. In this case, the transmission axes of the linear polarizer A' and the polarization-selective transflector A are made to coincide with each other. In this way, it is possible to absorb light that is reflected by the imaging plane IM, reflected by the polarization-selective transflector A, and then enters the imaging plane IM again to cause ghosts and flares.

[0072] In this configuration, a quarter-wave plate may be disposed between the linear polarizer E and the object. In this case, the quarter-wave plate is disposed so that the fast axis or slow axis of the quarter-wave plate forms an angle of 45° with the transmission axis of the linear polarizer E. In this way, even if the light incident from the object side is linearly polarized, it is possible to capture an image regardless of its polarization direction. Also, a depolarizing element may be disposed 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 have to be strictly 90°, 0°, and 45°. However, these should be within ±5° of the desired angle, preferably within ±2°, and more preferably within ±1°.

[0074] In the imaging optical system of each embodiment, the lens may be made of a polymer material or a glass material. However, 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. EXAMPLES

[0076] FIG. 3 is a cross-sectional view of the imaging optical system 100 of this embodiment. The imaging optical system 100 has, 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, an open 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 as a unit in the optical axis direction. The imaging optical system 100 also has, in order from the object side to the image side, a cemented lens of a seventh lens 107 having a first transmission-reflection surface HM1 and an eighth lens 108 having a second transmission-reflection 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 transmissive / reflective surface HM1.

[0077] FIG. 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 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). EXAMPLES

[0078] FIG. 5 is a cross-sectional view of the imaging optical system 200 of this embodiment. The imaging optical system 200 has, 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, an open 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 as a unit in the optical axis direction. The imaging optical system 200 also has, in order from the object side to the image side, a cemented lens of a seventh lens 207 having a first transmission-reflection surface HM1 and an eighth lens 208 having a second transmission-reflection surface HM2, and a sensor protection glass G. The seventh lens 207 is provided with a quarter-wave plate QWP on the image side of the first transmissive / reflective 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). EXAMPLES

[0080] FIG. 7 is a cross-sectional view of the imaging optical system 300 of this embodiment. The imaging optical system 300 has a first positive lens 301, a second negative lens 302, an open aperture SP, and a third positive lens 303, which are arranged in this order from the object side to the image side. 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 has a cemented lens of a fourth positive lens 204, a fifth negative lens 305 having a first transmission-reflection surface HM1, and a sixth positive lens 308 having a second transmission-reflection surface HM2, which are arranged in this order from the object side to the image side, and a sensor protective glass G. The fifth negative lens 305 has a quarter-wave plate QWP on the image side of the first transmission-reflection 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 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). EXAMPLES

[0082] FIG. 9 is a cross-sectional view of the imaging optical system 400 of this embodiment. The imaging optical system 400 has, in order from the object side to the image side, a first positive lens 401, a cemented lens of a second negative lens 402 and a third positive lens 403, an open aperture SP, a fourth positive lens 404, and a cemented lens of 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 has, in order from the object side to the image side, a cemented lens of a seventh negative lens 407 having a first transmission-reflection surface HM1 and an eighth positive lens 408 having a second transmission-reflection surface HM2, and a sensor protection 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 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). EXAMPLES

[0084] FIG. 11 is a cross-sectional view of the imaging optical system 500 of this embodiment. The imaging optical system 500 has, in order from the object side to the image side, a first positive lens 501, a cemented lens of a second positive lens 502 and a third negative lens 503, an open aperture 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 as a unit in the optical axis direction. The imaging optical system 500 also has a cemented lens of a fifth negative lens 505 and a sixth positive lens 506. The imaging optical system 500 further has, in order from the object side to the image side, a cemented lens of a seventh negative lens 507 having a first transmission-reflection surface HM1 and an eighth positive lens 508 having a second transmission-reflection surface HM2, and a sensor protection 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). EXAMPLES

[0086] FIG. 13 is a cross-sectional view of the imaging optical system 600 of this embodiment. The imaging optical system 600 has, in order from the object side to the image side, a first positive lens 601, a cemented lens of a second positive lens 602 and a third negative lens 603, an open 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 as a unit in the optical axis direction. The imaging optical system 600 also has a cemented lens of a fifth negative lens 605 and a sixth positive lens 606. The imaging optical system 600 further has a cemented lens of a seventh negative lens 607 having a first transmission-reflection surface HM1 and an eighth positive lens 608 having a second transmission-reflection surface HM2, and a sensor protection 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 aberration diagrams 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 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 aberration 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). EXAMPLES

[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 has a first negative lens 701, a second negative lens 702, a third positive lens 703, and a flare cut aperture e1, which are arranged in this order from the object side to the image side. The imaging optical system 700 also has a fourth positive lens 704, an open aperture SP, a fifth positive lens 705, a sixth negative lens 706, a flare cut aperture e2, and a seventh positive lens 707, which are arranged in this order from the object side to the image side. 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 has a cemented lens of an eighth positive lens 708, a ninth negative lens 709, and a tenth positive lens 710. Furthermore, the imaging optical system 700 includes, 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 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 are lens groups that move together during zooming. 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 is a diagram showing cross-sectional views and movement trajectories of the imaging optical system 700 from the wide-angle end to the telephoto end at infinity. 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 group L1 moves toward the image side, the flare cut aperture e1 moves toward the image side, the second lens group L2 moves toward the object side, and the third lens group L3 is fixed.

[0091] 17, 18, and 19 are aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the imaging optical system 700 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 g-line (wavelength 435.8 nm). In the astigmatism diagrams, 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 aberration diagrams, the amount of distortion aberration for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration at the g-line is shown. ω is the imaging half angle of view (degrees). EXAMPLES

[0092] FIG. 20 is a cross-sectional view of the imaging optical system 800 of this embodiment at the wide-angle end. The imaging optical system 800 has a first negative lens 801, a second negative lens 802, a third positive lens 803, and a fourth negative lens 804 arranged in this order from the object side to the image side. The imaging optical system 800 also has a fifth positive lens 805, an open aperture SP, a sixth positive lens 806, a seventh negative lens 807, a flare cut aperture e1, and an eighth positive lens 808 arranged in this order from the object side to the image side. 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 has a cemented lens of a ninth positive lens 809, a tenth negative lens 810, and an eleventh positive lens 811. Furthermore, the imaging optical system 800 includes, in order from the object side to the image side, a cemented lens of a twelfth negative lens 812 having a first transmission-reflection surface HM1 and a thirteenth positive lens 813 having a second transmission-reflection 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 transmission-reflection 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 are lens groups that 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 is a diagram showing cross-sectional views and movement trajectories of the imaging optical system 800 from the wide-angle end to the telephoto end at infinity. 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 group L1 moves toward the image side, the second lens group L2 moves toward the object side, and the third lens group L3 is fixed.

[0095] 22, 23, and 24 are aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the imaging optical system 800 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 g-line (wavelength 435.8 nm). In the astigmatism diagrams, 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 aberration diagrams, the amount of distortion aberration 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). EXAMPLES

[0096] FIG. 25 is a cross-sectional view of the imaging optical system 900 of this embodiment at the wide-angle end. The imaging optical system 900 has a first negative lens 901, a second positive lens 902, and a third positive lens 903 arranged in this order from the object side to the image side. The imaging optical system 900 also has a fourth negative lens 904, a fifth positive lens 905, a sixth positive lens 906, and a seventh negative lens 907 arranged in this order from the object side to the image side. The imaging optical system 900 also has an open aperture SP, an eighth positive lens 908, a ninth positive lens 909, a tenth negative lens 910, and an eleventh positive lens 911 arranged in this order from the object side to the image side. 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 as a unit in the optical axis direction. The imaging optical system 900 also has, 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 has, arranged in order from the object side to the image side, a cemented lens of a fourteenth negative lens 914 having a first transmission-reflection surface HM1 and a fifteenth positive lens 915 having a second transmission-reflection surface HM2, and a sensor protection glass G. The fourteenth negative lens 914 has a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0097] The imaging optical system 900 has 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 as lens groups that 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 L 4 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 is a diagram showing cross-sectional views and movement trajectories of the imaging optical system 900 from the wide-angle end to the telephoto end at infinity. 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 group L1 moves once toward the image side and then moves toward the object side, the second lens group L2 moves toward the image side, the third lens group L3 moves toward the image side, and the fourth lens group L4 is fixed.

[0099] 27, 28, and 29 are aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the imaging optical system 900 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 g-line (wavelength 435.8 nm). In the astigmatism diagrams, 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 aberration 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). EXAMPLES

[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 has a first negative lens 1001, a second positive lens 1002, and a third positive lens 1003 arranged in this order from the object side to the image side. The imaging optical system 900 also has a fourth negative lens 1004, a fifth negative lens 1005, a sixth positive lens 1006, and a seventh negative lens 1007 arranged in this order from the object side to the image side. The imaging optical system 1000 also has an open aperture SP, an eighth positive lens 1008, a ninth positive lens 1009, a tenth negative lens 1010, and an eleventh positive lens 1011 arranged in this order from the object side to the image side. 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 has a twelfth negative lens 1012 and a thirteenth positive lens 1013, which are arranged in this order from the object side to the image side. The imaging optical system 1000 also has a cemented lens of a fourteenth negative lens 1014 having a first transmission-reflection surface HM1 and a fifteenth positive lens 1015 having a second transmission-reflection surface HM2, which are arranged in this order from the object side to the image side, and a sensor protective glass G. The fourteenth negative lens 1014 has a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0101] The imaging optical system 1000 has 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 as lens groups that 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 from the wide-angle end to the telephoto end at infinity. 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 group L1 moves once toward the image side and then moves toward the object side, the second lens group L2 moves toward the image side, the third lens group L3 moves toward the image side, and the fourth lens group L4 is fixed.

[0103] 32, 33, and 34 are aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the imaging optical system 1000 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 g-line (wavelength 435.8 nm). In the astigmatism diagrams, 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 aberration diagrams, the amount of distortion aberration for the d-line is shown. In the chromatic aberration diagrams, the amount of chromatic aberration at the g-line is shown. ω is the imaging half angle of view (degrees). EXAMPLES

[0104] FIG. 35 is a cross-sectional view of the imaging optical system 1100 of this embodiment. The imaging optical system 1100 has a first positive lens 1101, a second negative lens 1102, an open aperture SP, and a third positive lens 1103, which are arranged in this order from the object side to the image side. 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 has a cemented lens of a fourth negative lens 1104 having a first transmission-reflection surface HM1 and a fifth positive lens 1105 having a second transmission-reflection surface HM2, and a sensor protective glass G. The fourth negative lens 1104 has a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0105] 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). EXAMPLES

[0106] FIG. 37 is a cross-sectional view of the imaging optical system 1200 of this embodiment. The imaging optical system 1200 has a first positive lens 1201, a second negative lens 1202, an open aperture SP, and a third positive lens 1203, which are arranged in this order from the object side to the image side. 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 has a cemented lens of a fourth negative lens 1204 having a first transmission-reflection surface HM1 and a fifth positive lens 1205 having a second transmission-reflection surface HM2, and a sensor protective glass G. The fourth negative lens 1204 has a quarter-wave plate QWP on the image side of the first transmission-reflection surface HM1.

[0107] Figure 38 is aberration diagrams of the imaging optical system 1200 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 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 aberration 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 the first to twelfth embodiments, respectively, are given 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. Additionally, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is given by the following, when 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 are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[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 surface expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the foreground (the lens surface closest to the object) of the imaging optical system to the final surface plus the back focus. The term "lens group" is not limited to cases where the group is composed of multiple lenses, but also includes cases where the group is composed of a single lens.

[0111] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in the 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 the aspheric coefficients of each order: X = (h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 In addition, "e±XX" in each aspheric coefficient is "×10± XX " It 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 them is described.

[0113] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 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 plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4= 2.68200e-06 A 6= 4.08072e-09 A 8= 2.50665e-11 Side 4 K = 0.00000e+00 A 4=-1.05832e-06 A 6=-9.32302e-10 A 8=-2.25900e-11 5th page K = 0.00000e+00 A 4=-1.11685e-05 A 6=-1.56567e-08 A 8=-1.66515e-10 9th page K = 0.00000e+00 A 4=-5.72921e-06 A 6= 9.84264e-09 Page 12 K = 0.00000e+00 A 4= 8.38497e-06 A 6= 2.02585e-10 A 8= 5.15363e-12 Various 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(in AIR) 6.65 Single lens data Lens starting 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 Effective diameter 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 plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4= 1.93351e-07 A 6= 1.40310e-09 A 8= 1.63609e-11 Side 4 K = 0.00000e+00 A 4=-1.40320e-05 A 6= 1.57528e-08 A 8=-1.95261e-11 5th page K = 0.00000e+00 A 4=-1.49134e-05 A 6=-8.19704e-09 A 8=-5.11549e-11 9th page K = 0.00000e+00 A 4=-1.86854e-07 A 6= 1.61960e-08 Page 12 K = 0.00000e+00 A 4= 4.86104e-06 A 6= 2.81753e-09 A 8= 4.38490e-12 Various 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(in AIR) 7.85 Single lens data Lens starting 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 Effective diameter 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 plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4= 1.30583e-05 A 6=-1.65551e-08 A 8= 5.12331e-12 Side 4 K = 0.00000e+00 A 4= 1.80379e-05 A 6=-1.14415e-08 Page 6 K = 0.00000e+00 A 4= 3.41178e-06 A 6= 4.14610e-09 Side 7 K = 0.00000e+00 A 4= 2.79360e-06 A 6= 5.80781e-09 Various 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(in AIR) 9.32 Single lens data Lens starting 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 Effective 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 plane ∞ Aspheric Data 5th page K = 0.00000e+00 A 4= 3.46583e-06 A 6= 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 total length 80.00 BF(in AIR) 11.45 Single lens data Lens starting 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 Effective diameter 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 plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4=-9.17893e-07 A 6=-3.55927e-10 Page 1 K = 0.00000e+00 A 4= 2.93531e-07 A 6= 4.60080e-11 Various data Zoom ratio 1.00 Focal length 82.92 F-number 1.03 Half angle of view (degrees) 14.62 Image height 21.64 Lens length 133.09 BF(in AIR) 13.00 Single lens data Lens starting 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 plane ∞ Aspheric Data 3rd page K = 0.00000e+00 A 4=-5.70475e-07 A 6=-1.67302e-10 Page 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 Lens length 159.85 BF(in AIR) 13.60 Single lens data Lens starting 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 plane ∞ Aspheric Data Side 4 K =-9.69697e-01 A 4= 6.81233e-07 A 6=-1.55549e-10 A 8= 1.32810e-13 Side 8 K = 0.00000e+00 A 4=-3.32737e-06 A 6=-2.58459e-09 A 8=-2.84899e-12 Page 14 K = 0.00000e+00 A 4= 4.05263e-06 A 6= 9.13264e-10 Page 16 K = 0.00000e+00 A 4= 5.81408e-07 A 6=-1.96531e-09 Various data Zoom ratio 1.40 Wide Angle Mid-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 Lens length 163.41 141.33 126.34 BF(in AIR) 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 starting plane Focal length Lens length Front principal point position Rear principal point position 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 starting 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 Effective 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 plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.13593e-06 A 6=-1.31682e-09 A 8=-1.13405e-12 Page 5 K = 0.00000e+00 A 4= 6.52079e-06 A 6= 6.92491e-09 Page 7 K = 0.00000e+00 A 4= 3.32630e-06 A 6= 6.16101e-09 Various data Zoom ratio 1.36 Wide Angle Mid-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 Lens length 171.50 147.73 133.49 BF(in AIR) 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 starting plane 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 Single lens data Lens starting 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 Effective 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 plane ∞ Aspheric Data Side 8 K = 0.00000e+00 A 4= 4.09477e-07 A 6= 1.99886e-10 A 8= 6.08231e-13 Page 5 K = 0.00000e+00 A 4=-1.01011e-06 A 6=-1.56970e-09 A 8=-2.18854e-14 Page 20 K = 0.00000e+00 A 4= 3.32477e-06 A 6= 1.01917e-09 2nd page 1 K = 0.00000e+00 A 4=-7.69683e-07 A 6= 8.64044e-10 2nd page 6 K = 0.00000e+00 A 4= 1.13781e-07 A 6= 1.32293e-10 Various data Zoom ratio 1.60 Wide Angle Mid-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 Lens length 180.50 174.98 176.93 BF(in AIR) 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 starting plane Focal length Lens length Front principal point position Rear principal point position 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 Single lens data Lens starting 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 Effective 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 plane ∞ Aspheric Data Side 8 K = 0.00000e+00 A 4= 3.43387e-07 A 6= 4.32489e-10 A 8= 6.35316e-13 Page 5 K = 0.00000e+00 A 4=-1.35390e-06 A 6=-1.83822e-09 A 8= 9.03689e-14 Page 20 K = 0.00000e+00 A 4= 3.59093e-06 A 6= 9.83623e-10 2nd page 1 K = 0.00000e+00 A 4=-1.88335e-06 A 6= 9.09329e-10 2nd page 6 K = 0.00000e+00 A 4=-6.13989e-06 A 6=-4.79014e-10 Various data Zoom ratio 1.60 Wide Angle Mid-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 Lens length 156.83 151.14 156.37 BF(in AIR) 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 starting plane Focal length Lens length Front principal point position Rear principal point position 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 starting 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 Effective diameter 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 plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-5.98397e-08 A 6=-4.69065e-09 second side K = 0.00000e+00 A 4=-1.72753e-05 A 6= 6.66460e-09 3rd page K = 0.00000e+00 A 4=-7.97584e-05 A 6= 1.55610e-07 A 8= 5.12331e-12 Side 4 K = 0.00000e+00 A 4=-6.47253e-05 A 6= 1.88884e-07 Page 6 K = 0.00000e+00 A 4=-8.81099e-06 A 6= 6.90546e-09 Side 7 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 length 62.82 BF(in AIR) 22.81 Single lens data Lens starting 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 plane ∞ Aspheric Data Front page 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 3rd page K = 0.00000e+00 A 4=-6.70571e-05 A 6= 5.26611e-08 A 8= 5.12331e-12 Side 4 K = 0.00000e+00 A 4=-4.86355e-05 A 6= 1.74615e-07 Page 6 K = 0.00000e+00 A 4=-7.99779e-06 A 6= 1.58276e-08 Side 7 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 Lens length 62.82 BF(in AIR) 22.97 Single lens data Lens starting 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] [Table 1]

[0115] [Imaging device] An image pickup device having the photographing optical system of each embodiment will be described. Fig. 40 is a schematic diagram of a digital camera, which is an example of an image pickup device. Reference numeral 20 denotes a digital camera body, 21 denotes an image pickup optical system which is one of the image pickup optical systems of each embodiment, and 22 denotes an image pickup element such as a CCD that receives a subject image through the image pickup optical system 21. Reference numeral 23 denotes a recording means that records the subject image received by the image pickup 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 imaging element 22. Reference numeral 25 denotes a liquid crystal display panel having the same function as the viewfinder 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] The disclosure of each embodiment includes the following configuration. (Configuration 1) An imaging optical system having an open aperture, and a first transmissive / reflective surface, a quarter-wave plate, and a second transmissive / reflective surface, which are arranged in this order from an object side to an image side, light from the object side passes through the first transmission-reflection surface and the quarter-wave plate in this order, is reflected by the second transmission-reflection surface toward the object side, passes through the quarter-wave plate, is reflected by the first transmission-reflection surface toward the image side, passes through the quarter-wave plate and the second transmission-reflection surface in this order, and proceeds toward the image plane; When the total optical length is L, the distance on the optical axis from the first transmitting-reflecting surface to the image plane is Lh, the diameter of the open aperture is D, and the distance on the optical axis from the open aperture to the image plane is LD, 2.2≦L / Lh≦100.0 0.15≦D / LD≦2.00 An imaging optical system characterized by satisfying the following conditional expression: (Configuration 2) the open aperture is disposed closer to the image side than the lens disposed closest to the object side among the lenses included in the imaging optical system, 0.35≦LD / L≦0.85 2. The imaging optical system according to configuration 1, wherein the following condition is satisfied: (Configuration 3) 3. The imaging optical system according to configuration 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. (Configuration 4) Let θ1 be 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-reflecting surface, and θ2 be 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-reflecting surface and then by the first transmitting-reflecting surface. 1.20≦θ1 / θ2≦20.00 4. The imaging optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) the second transmissive-reflective surface is disposed adjacent to an image side of the first transmissive-reflective surface, When the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface is fP and the focal length of the imaging optical system is f, 2.00≦fP / f≦15.00 5. The imaging optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) a space between the first transmissive-reflective surface and the second transmissive-reflective surface is filled with a material other than air; When the refractive index of the material is nd, 1.45≦nd≦2.30 6. The imaging optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the distance on the optical axis from the second transmissive-reflective surface to the image plane is Li, 1.00≦L / Li≦200.00 7. The imaging optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) The imaging optical system according to any one of configurations 1 to 7, wherein the second transmissive reflective surface is a lens surface of the imaging optical system closest to the image side. (Configuration 9) 9. The imaging optical system according to any one of configurations 1 to 8, wherein one of the first transmissive-reflective surface and the second transmissive-reflective surface is a flat surface. (Configuration 10) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, the second transmissive-reflective surface is disposed adjacent to an image side of the first transmissive-reflective surface, When the focal length of the negative lens is fN and the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface is fP, -1.00≦fN / fP≦-0.10 10. The imaging optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the focal length of the negative lens is fN and the focal length of the imaging optical system is f, -10.00≦fN / f≦-0.30 11. The imaging optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the radius of curvature of the lens surface on the object side of the negative lens is R1 and the radius of curvature of the second transmissive-reflective surface is R2, -1.00≦(R1-R2) / (R1+R2)≦0.30 12. The imaging optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the focal length from the object side lens surface of the negative lens to the second transmitting / reflecting surface is fF and the focal length of the imaging optical system is f, -30.00≦fF / f≦-0.30 13. The imaging optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, a space between the first transmissive-reflective surface and the second transmissive-reflective surface is filled with a material other than air; When the refractive index of the material is nd and the refractive index of the negative lens is ndN, 0.65≦nd / ndN≦1.10 14. The imaging optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the distance on the optical axis from the object side lens surface of the negative lens to the second transmitting / reflecting surface is d, 0.01≦d / L≦0.15 15. The imaging optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) a negative lens disposed adjacent to the object side of the first transmission-reflection surface, 16. The imaging optical system according to any one of configurations 1 to 15, wherein there is no air gap between the object-side lens surface of the negative lens and the second transmitting and reflecting surface. (Configuration 17) When the focal length of the imaging optical system is f, 0.01≦Lh / f≦0.90 17. The imaging optical system according to any one of configurations 1 to 16, wherein the following condition is satisfied: (Configuration 18) When the outer diameter of the lens arranged closest to the object side in the imaging optical system is Oe and the outer diameter of the lens arranged closest to the image side in the imaging optical system is Ie, 0.30≦Oe / Ie≦4.00 18. The imaging optical system according to any one of configurations 1 to 17, wherein the following condition is satisfied: (Configuration 19) 19. The imaging optical system according to any one of configurations 1 to 18, wherein 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 according to a polarization state. (Configuration 20) 20. The imaging optical system according to configuration 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. (Configuration 21) The imaging optical system according to any one of configurations 1 to 20, wherein the imaging optical system is rotationally symmetric with respect to an optical axis. (Configuration 22) When the F-number of the imaging optical system is Fno, 0.50≦Fno≦8.0 22. The imaging optical system according to any one of configurations 1 to 21, wherein the following condition is satisfied: (Configuration 23) 23. An imaging apparatus comprising: an imaging optical system according to any one of structures 1 to 22; and an imaging element that receives an image formed by the imaging optical system.

[0119] 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. [Explanation of symbols]

[0120] HM1 First transflective surface QWP 1 / 4 wave plate HM2 Second transflective surface SP Maximum aperture IM image plane

Claims

1. An imaging optical system having an open aperture, and a first transmissive / reflective surface, a quarter-wave plate, and a second transmissive / reflective surface, which are arranged in this order from an object side to an image side, light from the object side passes through the first transmission-reflection surface and the quarter-wave plate in this order, is reflected by the second transmission-reflection surface toward the object side, passes through the quarter-wave plate, is reflected by the first transmission-reflection surface toward the image side, passes through the quarter-wave plate and the second transmission-reflection surface in this order, and proceeds toward the image plane; When the total optical length is L, the distance on the optical axis from the first transmitting-reflecting surface to the image plane is Lh, the diameter of the open aperture is D, and the distance on the optical axis from the open aperture to the image plane is LD, 2.2≦L / Lh≦100.0 0.15≦D / LD≦2.00 An imaging optical system characterized by satisfying the following conditional expression:

2. the open aperture is disposed closer to the image side than the lens disposed closest to the object side among the lenses included in the imaging optical system, 0.35≦LD / L≦0.85 2. The imaging optical system according to claim 1, wherein the following condition is satisfied:

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

4. Let θ1 be 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 be 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. 1.20≦θ1 / θ2≦20.00 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

5. the second transmissive-reflective surface is disposed adjacent to an image side of the first transmissive-reflective surface, When the focal length of a structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface is fP and the focal length of the imaging optical system is f, 2.00≦fP / f≦15.00 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

6. a space between the first transmissive-reflective surface and the second transmissive-reflective surface is filled with a material other than air; When the refractive index of the material is n, 1.45≦nd≦2.30 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

7. When the distance on the optical axis from the second transmissive-reflective surface to the image plane is Li, 1.00≦L / Li≦200.00 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

8. 3. The imaging optical system according to claim 1, wherein the second transmissive reflective surface is a lens surface of the imaging optical system that is closest to an image side.

9. 3. The imaging optical system according to claim 1, wherein one of the first transmissive-reflective surface and the second transmissive-reflective surface is a flat surface.

10. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, the second transmissive-reflective surface is disposed adjacent to an image side of the first transmissive-reflective surface, When the focal length of the negative lens is fN and the focal length of the structure surrounded by the first transmissive-reflective surface and the second transmissive-reflective surface is fP, -1.00≦fN / fP≦-0.10 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

11. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the focal length of the negative lens is fN and the focal length of the imaging optical system is f, −10.00≦fN / f≦−0.30 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

12. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the radius of curvature of the lens surface on the object side of the negative lens is R1 and the radius of curvature of the second transmissive-reflective surface is R2, -1.00≦(R1-R2) / (R1+R2)≦0.30 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

13. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the focal length from the object side lens surface of the negative lens to the second transmissive-reflective surface is fF and the focal length of the imaging optical system is f, −30.00≦fF / f≦−0.30 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

14. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, a space between the first transmissive-reflective surface and the second transmissive-reflective surface is filled with a material other than air; When the refractive index of the material is nd and the refractive index of the negative lens is ndN, 0.65≦nd / ndN≦1.10 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

15. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, When the distance on the optical axis from the object side lens surface of the negative lens to the second transmitting / reflecting surface is d, 0.01≦d / L≦0.15 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

16. a negative lens disposed adjacent to the object side of the first transmission-reflection surface, 3. The imaging optical system according to claim 1, wherein there is no air gap between the object-side lens surface of the negative lens and the second transmitting / reflecting surface.

17. When the focal length of the imaging optical system is f, 0.01≦Lh / f≦0.90 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

18. When the outer diameter of the lens arranged closest to the object side in the imaging optical system is Oe and the outer diameter of the lens arranged closest to the image side in the imaging optical system is Ie, 0.30≦Oe / Ie≦4.00 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

19. 3. The imaging optical system according to claim 1, wherein 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 according to a polarization state.

20. 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. 3. The imaging optical system according to claim 1, wherein the imaging optical system is rotationally symmetric with respect to an optical axis.

22. When the F-number of the imaging optical system is Fno, 0.50≦Fno≦8.0 3. The imaging optical system according to claim 1, wherein the following condition is satisfied:

23. 3. An imaging apparatus comprising: the imaging optical system according to claim 1; and an imaging element that receives an image formed by the imaging optical system.

Images