Imaging optical system, imaging device, and moving object

Abstract

An imaging optical system, an imaging device, and a moving body, which can realize a new imaging optical system that reduces the influence of ghost light. The imaging optical system forms an image of an object set as an imaging subject on an imaging surface, and the imaging optical system is configured with a lens system and a filter from the object side toward the image side, the lens system is a five-group structure, the filter is a parallel plate and is configured in a manner orthogonal to the optical axis of the lens system, the first group of the lens system is composed of a first lens that is a negative meniscus lens with a convex surface facing the object side, the curvature radius of the object side surface of the first lens: R11, the focal length of the entire system: f, the distance between the object side surface of the filter and the image surface: Df, and the total length of the entire system: L satisfy the conditional expression 0.55<(R11 / f)×(Df / L)<1.00.

Description

Technical Field

[0001] The present invention relates to an imaging optical system, an imaging device and a moving object. Background Art

[0002] Various optical systems are known in the art for imaging optical systems that form an image of an object set as an imaging subject on an imaging plane, including imaging optical systems used in photographic cameras. In recent years, imaging devices using various area sensors are being mounted on surveillance cameras, cameras for inspection, or mobile objects such as automobiles, airplanes, and drones (Patent Document 1).

[0003] When an area sensor is used for imaging, the "light receiving surface of the area sensor" that becomes the imaging surface reflects a portion of the imaging light beam based on the lens system. It is known that the light reflected on the imaging surface enters the imaging lens system, is reflected on the lens surface of the lens system, and returns to the imaging surface, acting as ghost light with respect to the image to be captured by the area sensor.

[0004] In addition, usually, the imaging optical system uses filters such as "infrared cut filter and optical low-pass filter" together with the lens system. Such filters are generally parallel plate-shaped and are arranged orthogonally to the optical axis of the lens system, that is, parallel to the imaging surface. Therefore, the "reflected light from the filter surface" of the imaging light beam is also incident on the lens system and reflected by the lens surface, and can act as ghost light.

[0005] <Prior Art Literature>

[0006] <Patent Documents>

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-211598 Summary of the invention

[0008] <Problems to be Solved by the Invention>

[0009] An object of the present invention is to realize a new imaging optical system which can reduce the influence of ghost light as described above.

[0010] <Methods used to solve the problem>

[0011] The imaging optical system of the present invention forms an image of an object set as an imaging subject on an imaging plane. The imaging optical system is provided with a lens system and a filter from the object side toward the image side. The lens system is a 5-group structure. The filter is a parallel plate and is arranged in a manner orthogonal to the optical axis of the lens system. The first group of the lens system is composed of a first lens which is a negative meniscus lens with a convex surface facing the object side. The radius of curvature of the object side surface of the first lens: R11, the focal length of the entire system: f, the distance between the object side surface of the filter and the image plane: Df, and the total length of the entire system: L satisfy the conditional expression 0.55<(R11 / f)×(Df / L)<1.00.

[0012] <Effects of the Invention>

[0013] According to the present invention, a new imaging optical system capable of reducing the influence of ghost light can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing the optical structure of Example 1 of the imaging optical element.

[0015] Figure 2 This is a diagram showing data of Example 1.

[0016] Figure 3 1 and 2 are diagrams showing aspherical surface data in the imaging optical system of Example 1.

[0017] Figure 4 It is a diagram showing parameters and the like of the imaging optical system of Example 1.

[0018] Figure 5 1 and 2 are aberration diagrams of the imaging optical system of Example 1.

[0019] Figure 6 1 is a diagram showing the reduction in the influence of ghost light by the imaging optical system of Example 1.

[0020] Figure 7 It is a diagram showing the optical structure of Example 2 of the imaging optical element.

[0021] Figure 8 This is a diagram showing data of Example 2.

[0022] Fig. 9 This is a diagram showing aspherical surface data in the imaging optical system of Example 2.

[0023] Fig.10 It is a diagram showing parameters and the like of the imaging optical system of Example 2.

[0024] Fig.11 1 and 10 are aberration diagrams of the imaging optical system of Example 2.

[0025] Fig.12 1 and 2 are diagrams showing how the influence of ghost light is reduced by the imaging optical system of Example 2.

[0026] Fig.13 It is a diagram showing the optical structure of Example 3 of the imaging optical element.

[0027] Fig.14 This is a diagram showing data of Example 3.

[0028] Fig.15 1 and 2 are diagrams showing aspherical surface data in the imaging optical system of Example 3.

[0029] Fig.16 It is a diagram showing parameters and the like of the imaging optical system of Example 3.

[0030] Fig.17 1 and 1 are aberration diagrams of the imaging optical system of Example 3.

[0031] Fig.18 Graphs showing reduction in the influence of ghost light by the imaging optical system of Example 3.

[0032] Fig.19 This is a diagram for explaining a digital camera which is one embodiment of the imaging device.

[0033] Fig. 20 yes Fig.19 System structure diagram of a digital camera.

[0034] Fig.21 This is a diagram for explaining a stereo camera which is an example of implementation of the imaging device.

[0035] Description of Reference Numerals

[0036] G1 Group 1

[0037] G2 Group 2

[0038] G3 Group 3

[0039] G4 Group 4

[0040] G5 Group 5

[0041] S Aperture stop

[0042] F1 Filter

[0043] IS camera area

[0044] CG Glass Cover

[0045] L1 First lens

[0046] L2 Second lens

[0047] L3 Third lens

[0048] L4 Fourth lens

[0049] L5 Fifth lens

[0050] L45 Cemented lens of the fourth and fifth lenses

[0051] L6 Sixth lens DETAILED DESCRIPTION

[0052] Hereinafter, description will be given based on the implementation modes with reference to the drawings.

[0053] exist Figure 1 , Figure 7 , Fig.13 In the figure, three examples of implementation of the imaging optical system of the present invention are shown.

[0054] The embodiments shown in these drawings correspond to the imaging optical systems of Example 1, Example 2, and Example 3 described later in the order of the figure numbers.

[0055] In order to avoid cluttering the figures, reference numerals are used in common in these figures.

[0056] exist Figure 1 , Figure 7 , Fig.13 In the figure, the left side is the object side and the right side is the image side.

[0057] The imaging optical system of the present invention is to make the Figure 1 , Figure 7 , Fig.13 The imaging optical system which forms an image of an imaging subject (not shown) on the left side of the image sensor as an object on the imaging plane IS has a lens system and a filter F1 arranged from the object side toward the image side.

[0058] The "lens system" has a five-group structure, and the filter F1 is a parallel plate. The group structure of the lens system will be described later. The filter F1 is arranged to be orthogonal to the optical axis of the lens system.

[0059] The first group G1 of the lens system is composed of a first lens L1 which is a negative meniscus lens having a convex surface facing the object side.

[0060] The radius of curvature of the object side of the first lens L1: R11, the focal length of the entire system: f, the distance between the object side surface of the filter F1 and the image surface IS: Df, and the total length of the entire system: L satisfy the conditional formula:

[0061] (1)0.55<(R11 / f)×(Df / L)<1.00.

[0062] The focal length of the entire system: f is the focal length of the system including the lens system and the filter F1, and the total length of the entire system: L is the distance from the object side of the first lens L1 forming the first group G1 to the optical axis of the imaging surface IS. Figure 7 , Fig.13 Medium length: L is not shown in the figure.

[0063] Figure 1 , Figure 7 , Fig.13 The embodiments shown in the drawings all assume that an image of an object based on an imaging optical system is read by an area sensor (imaging element). Figure 1 , Figure 7 , Fig.13 The imaging surface IS in FIG. 1 is an "image plane" and is consistent with the light receiving surface of the area sensor. In addition, reference numeral CG shows a glass cover disposed close to the light receiving surface of the area sensor.

[0064] In addition to the above-mentioned configuration, the imaging optical system of the present invention preferably has a focal length of the entire system: f, a total length of the entire system: L, and a half viewing angle: W (degrees) satisfying the conditional formula:

[0065] (2)4.0 <W×(L / f) / 100<6.0。

[0066] In addition to the conditional expressions (1) and (2), it is preferred that the focal length of the entire system: f, the distance between the object side of the filter F1 and the image plane IS: Df, the half angle of view: W (degrees), and the total length of the entire system: L satisfy the conditional expression:

[0067] (3)14.0 <W×(Df / L)。

[0068] In addition to the conditional expressions (1) to (3), it is further preferred that the curvature radius R11 on the object side of the first lens L1, the focal length f of the entire system, and the half angle of view W (degrees) satisfy the conditional expression:

[0069] (4)1.5 <W×(R11 / f)<4.0。

[0070] It is preferred that the imaging optical system of the present invention satisfies the following conditional expression (5) together with the above-mentioned conditional expression (1), or satisfies the following conditional expression (5) together with the conditional expressions (1) and (2), and further satisfies the following conditional expression (5) together with the conditional expressions (1) to (3), or the conditional expressions (1) to (4).

[0071] (5)0.2 <R12 / R11<0.4

[0072] Here, R11 is the curvature radius of the object side surface of the first lens L1, which is the "negative meniscus lens with the convex surface facing the object side" as described above, and R12 is the curvature radius of the image side surface of the first lens L1.

[0073] Since the first lens L1 is a "negative meniscus lens with its convex surface facing the object side", both R11 and R12 are "positive", and "R11>R12".

[0074] Here, the group structure of the "lens system" that constitutes the imaging optical system is explained. Although the first group of the lens system is the "negative meniscus lens with the convex surface facing the object side" as described above, the following structure can be cited as a preferred example of the second to fifth groups.

[0075] The second group is composed of a "negative lens, i.e., the second lens", the third group is composed of a "positive lens, i.e., the third lens", the fourth group is composed of a "cemented lens in which a positive or negative fourth lens is bonded to a positive or negative fifth lens and has positive refractive power", and the fifth group is composed of a "positive lens, i.e., the sixth lens", and the structure can be set so that the first group to the fifth group are arranged in sequence from the object side to the image side.

[0076] exist Figure 1 , Figure 7 , Fig.13 In the illustrated embodiment, the second lens L2 constituting the second group G2 is a "negative meniscus lens with a concave surface facing the object side", and the third lens L3 constituting the third group G3 is a "biconvex lens".

[0077] The fourth group G4 is formed by having a "fourth lens" having a positive refractive power, that is, a biconvex lens L4, as the object side, and a "fifth lens" having a negative refractive power, that is, a biconcave lens L5, which is joined to the image side. The joined lens of the fourth lens L4 and the fifth lens L5 constituting the fourth group G4 is called a joined lens L45.

[0078] The sixth lens L6 constituting the fifth group G5 is a “paraxially biconvex lens.” It should be noted that an aperture stop S is disposed between the third lens L3 constituting the third group and the cemented lens L45 constituting the fourth group.

[0079] In the lens system in the imaging optical system of the present invention, the first lens L1 constituting the first group 1G may have at least one aspherical surface, and the sixth lens L6 constituting the fifth group may have at least one aspherical surface.

[0080] In addition, the second lens L2 constituting the second group G2 may have at least one aspherical surface, and the sixth lens L6 constituting the fifth group G5 may have at least one aspherical surface.

[0081] It should be noted that the radius of curvature in an aspheric surface: R11, etc. is the "paraxial curvature radius".

[0082] By combining the imaging optical system of the present invention with an area sensor and using the light receiving surface of the area sensor as an imaging surface, a "camera device" can be formed. The imaging device can be formed as a "camera device such as a digital camera or a stereo camera", a "sensor camera such as a surveillance camera or an inspection camera", or a "vehicle-mounted imaging device".

[0083] In addition, the camera device of the present invention can constitute a "mobile body" mounted on a car, an airplane, an unmanned aerial vehicle, etc.

[0084] The meanings of conditional expressions (1) to (5) are explained below.

[0085] Conditional expression (1) is a condition for effectively reducing the influence of "ghost light caused by reflection by the imaging surface IS" and "ghost light caused by reflection by the object side surface of the filter F1".

[0086] Hereinafter, ghost light in which the imaging light of the imaging optical system is reflected by the imaging surface IS and travels backward in the imaging optical system and is reflected by the object side surface of the first lens to become ghost light is referred to as “ghost light from the imaging surface”.

[0087] In addition, hereinafter, the ghost light in which the imaging light based on the lens system is reflected on the object side surface of the filter F1 and travels backward in the lens system and is reflected on the object side surface of the first lens to become the ghost light is referred to as “filter-derived ghost light”.

[0088] The influence of ghost light originating from the imaging plane appears most strongly when the ghost light is focused on the imaging plane IS.

[0089] Likewise, the influence of ghost light from the filter is most significant when the ghost light is focused on the imaging surface IS.

[0090] In the imaging optical system of the present invention, the influence of ghost light is reduced by making the convergence positions of "ghost light from the imaging surface" and "ghost light from the filter" that are reflected on the object side of the first lens L1 and directed toward the imaging surface IS side via the lens system and the filter F1 "shift from the imaging surface position", thereby reducing the influence of ghost light.

[0091] When the radius of curvature R11 of the object side surface of the first lens L1 increases (decreases) and when the distance Df between the imaging surface IS and the object side surface of the filter F1 increases (decreases), the parameter of the conditional expression (1) increases (decreases).

[0092] When the parameter of conditional expression (1) decreases and exceeds the lower limit, the resolution near the optical axis can be improved and the "influence of ghost light from the imaging surface" can be easily suppressed.

[0093] However, if the radius of curvature R11 of the object side surface of the first lens L1 becomes smaller, "various aberrations such as coma and field curvature" increase, and the imaging performance of the imaging optical system decreases.

[0094] In addition, the "ghost light from the filter" is focused into a small-diameter light spot near the imaging surface, and the influence of the ghost light from the filter is increased.

[0095] On the contrary, if the parameter of conditional expression (1) increases and exceeds the upper limit of conditional expression (1), the radius of curvature of the object side surface of the first lens L1 increases, and the ghost light from the imaging surface is focused into a small-diameter light spot near the imaging surface IS, thereby increasing the influence of the ghost light from the imaging surface.

[0096] In the range satisfying conditional expression (1), the “converging position of ghost light from the imaging plane” is shifted toward the object side compared to the imaging plane IS, and the “converging position of ghost light from the filter” is shifted toward the image side compared to the imaging plane SI.

[0097] In this way, the respective convergence positions of the ghost light from the imaging plane and the ghost light from the filter are shifted from the imaging plane IS to the “opposite sides” in the optical axis direction, so that the influence of both ghost lights is reduced.

[0098] Under the condition that conditional expression (1) is satisfied, by satisfying conditional expression (2), when the imaging optical system is widened in angle, it is possible to suppress "the focal length from being shortened and the distortion from being increased as the angle is widened".

[0099] Under the condition that conditional expressions (1) and (2) are satisfied at the same time, by satisfying conditional expression (3), the filter F1 can be arranged at a position away from the imaging surface IS, thereby effectively suppressing the influence of ghost light from the filter.

[0100] Under the condition that conditional expressions (1) to (3) are satisfied, if conditional expression (4) is satisfied, when the imaging optical system is widened, the "radius of curvature of the object side surface of the first lens L1" will not be set too small, and good distortion can be achieved. In addition, the influence of ghost light originating from the imaging surface and the filter can be suppressed more effectively.

[0101] If conditional expression (5) is satisfied, it is possible to effectively prevent the reflected light on the imaging surface IS and the object side surface of the filter F1 from being reflected on the “image side surface” of the first lens L1 and becoming ghost light.

[0102] In the imaging optical system of the present invention, the first lens L1 of the first group G1 constituting the lens system is a “negative meniscus lens having a convex surface facing the object side”.

[0103] In this way, by setting the first lens L1 as a negative meniscus lens with the convex surface facing the object side, it is possible to prevent the light reflected by the filter F1, the glass cover CG, and the imaging surface IS from being re-reflected on the object side of the first lens L1 (ghost light from the imaging surface and the filter) from converging into a smaller light spot on the imaging surface IS.

[0104] In addition, the image side surface of the first lens L1 is also concave, which maintains negative refractive power, and adjustment of distortion is possible.

[0105] If one wants to ensure a "wide viewing angle and back focal length", the first lens L1 needs to have a certain degree of function to "bend the off-axis principal light ray away from the optical axis", so the first lens L1 needs to have a certain degree of negative refractive power.

[0106] like Figure 1 , Figure 7 , Fig.13 As in the embodiment shown, by also setting the object side surface of the second lens L2 to be a concave surface, the negative refractive power can be dispersed in the first lens L1 and the second lens L2, thereby suppressing the generation of various aberrations and improving the resolution performance with a small refractive power.

[0107] By setting the third lens L3 as a positive lens, the spherical aberration generated in the first lens L1 can be effectively corrected.

[0108] By setting the fourth lens L4 and the fifth lens L5 as a cemented lens L45, chromatic aberration and high-order aberration can be effectively suppressed. In addition, since the two lenses L4 and L5 can be configured as a lens group G4 by cementing, the image height change of the optical axis can be suppressed relative to the eccentricity that is easy to occur when the ambient temperature changes. Moreover, by cementing, the number of lens groups is reduced, thereby improving the ease of manufacturing.

[0109] By using an aspherical surface in "at least one lens surface" of the sixth lens L6 constituting the fifth group G5, light can be split according to the viewing angle, various aberrations (distortion, spherical aberration, field curvature, coma) can be corrected, and the total length of the lens can be set shorter than that of a structure with only a spherical lens. In addition, the refractive power of the final lens will not become extremely strong.

[0110] The imaging optical system of the present invention can adjust the radius of curvature by using an aspherical surface in either the first lens L1 or the second lens L2, thereby suppressing the generation of ghost light based on reflection on the object side surface of the first lens L1 and maintaining "wide viewing angle and good imaging performance".

[0111] (Example)

[0112] Three specific embodiments of the imaging optical system are given below.

[0113] The following examples 1 to 3 are based on Figure 1 , Figure 7 , Fig.13 The filter F1 is assumed to be an "infrared cut filter" in each embodiment.

[0114] The meanings of the symbols in the embodiments are as follows.

[0115] f: focal length of the entire system

[0116] fi: focal length of the i-th lens

[0117] Fno: aperture value

[0118] L: The total length of the entire system

[0119] W: half viewing angle (degrees)

[0120] R: Radius of curvature (for aspherical surfaces, the radius of curvature is the paraxial radius)

[0121] D: Surface spacing

[0122] Df: Distance from the imaging surface to the object side of the filter

[0123] Nd: Refractive index

[0124] νd: Abbe number

[0125] E: effective diameter of lens

[0126] For the aspheric surface, the aspheric amount in the direction parallel to the optical axis is set to X, the distance in the direction orthogonal to the optical axis is set to y, the paraxial curvature radius: R, the cone coefficient: K, the 4th, 6th, 8th, 10th, 12th, and 14th aspheric coefficients are set to A4, A6, A8, A10, A12, and A14, which are expressed by the well-known formula below, and K, R, A4, etc. are assigned to determine the shape.

[0127] X=(y2 / R) / [1+√(1-(K+1)(y / R)2)]+A4·y4+A6·y6+A8·y8+A10·y10+A12·y12+A14·y14

[0128] (Example 1)

[0129] Example 1 is based on Figure 1 A specific example of the embodiment is described.

[0130] Figure 2 Data of the imaging optical system of Example 1 is shown.

[0131] exist Figure 2 In the figure, the "leftmost column" is the "surface number" calculated from the object side, including the surface of the aperture stop S.

[0132] In addition, the curvature radius: R=∞(inf) indicates a flat surface, and the surface number corresponding to the aspherical surface is given an "*" mark. This also applies to Examples 2 and 3 described later.

[0133] (Aspherical data)

[0134] exist Figure 3 2 shows data of the aspherical surface in the imaging optical system of Example 1.

[0135] In Example 1, both surfaces of the first lens and both surfaces of the sixth lens are aspherical surfaces.

[0136] For example, in the figure, "3.7005E-08" is displayed as "3.7005×10 -8 The same also applies to Examples 2 and 3 described later.

[0137] exist Figure 4 In (a), the focal length of the entire imaging optical system of Example 1: f, Fno, total length: L, and viewing angle: W are shown, and in (b), the focal lengths of the first group G1 to the fifth group G5: f1 to f5 and the effective diameters of the lenses: E1 to E5 are shown.

[0138] In addition, Figure 4 In (c), the values ​​of the parameters of conditional expressions (1) to (5) of the imaging optical system of Example 1 are shown.

[0139] exist Figure 5 2 and 3 show aberration diagrams of the imaging optical system of Example 1.

[0140] Figure 5 The left figure shows "spherical aberration", the center figure shows "astigmatism (solid line is sagittal, dotted line is meridian)", and the right figure shows "distortion". D represents d-line (λ=587.6nm), and g represents g-line (λ=435.8nm).

[0141] Figure 6 1 is a diagram showing the behavior of ghost light in the imaging optical system of Example 1.

[0142] Figure 6 (a) shows the behavior of "ghost light from the imaging surface" in which the imaging light beam from the object side is reflected on the imaging surface IS and further reflected on the object side surface of the first lens L1 for the paraxial light.

[0143] As shown in the figure, the ghost light in this case converges on the front side of the imaging surface IS, that is, the "object side", and enters the imaging surface IS while diverging. Therefore, the light is prevented from converging on the imaging surface IS, and the influence of the ghost light from the imaging surface is reduced.

[0144] Figure 6 (b) shows the behavior of "filter-derived ghost light" in which the imaging light beam from the object side is reflected on the object side surface of the filter F1 and further reflected on the object side surface of the first lens L1 for the paraxial light.

[0145] As shown in the figure, the "ghost light from the filter" converges toward the back side of the imaging surface IS, that is, the "image side", and enters the imaging surface IS in the middle of the convergence. Therefore, the convergence of light to the imaging surface IS is avoided, and the influence of the ghost light from the filter is reduced.

[0146] That is, the focusing positions of ghost light from the imaging plane and the ghost light from the filter are separated on the object side and the image side of the imaging plane IS. Since they are not focused into a small-diameter light spot on the imaging plane IS, the influence of the ghost light is effectively reduced.

[0147] (Example 2)

[0148] Example 2 is based on Figure 7 A specific example of the embodiment is described.

[0149] Figure 8 Follow Figure 2 Data of the imaging optical system of Example 2 is shown.

[0150] (Aspherical data)

[0151] Fig. 9 Follow Figure 3 Data of the aspherical surface in the imaging optical system of Example 2 are shown.

[0152] In Example 2, both surfaces of the first lens and both surfaces of the sixth lens are also aspherical surfaces.

[0153] exist Fig.10 (a) shows the focal length of the entire system of the imaging optical system of Example 2: f, Fno, total length: L, and viewing angle: W, and (b) shows the respective focal lengths of the first group G1 to the fifth group G5: f1 to f5 and the lens effective diameters: E1 to E5.

[0154] In addition, Fig.10 In (c), the values ​​of the parameters of conditional expressions (1) to (5) of the imaging optical system of Example 2 are shown.

[0155] Fig.11 Follow Figure 5 Aberration diagrams of the imaging optical system of Example 2 are shown.

[0156] Fig.12 It is modeled after Figure 6 The diagram shows the behavior of ghost light originating from the imaging plane and the behavior of ghost light originating from the filter in the imaging optical system of Example 2.

[0157] Fig.12 (a) shows the behavior of ghost light from the imaging surface for the paraxial light. As shown in the figure, the ghost light in this case converges on the front side of the imaging surface IS, that is, the "object side", and enters the imaging surface IS while diverging. Therefore, the convergence of light to the imaging surface IS is avoided, and the influence of the ghost light from the imaging surface is reduced.

[0158] Fig.12 (b) shows the behavior of the ghost light from the filter, which is reflected on the object side of the filter F1 and further reflected on the object side of the first lens L1, for the paraxial light. As shown in the figure, the ghost light in this case converges toward the back side of the imaging surface IS, that is, the "image side", and enters the imaging surface IS in the middle of the convergence. Therefore, the convergence of light to the imaging surface IS is avoided, and the influence of the ghost light from the filter is reduced.

[0159] That is, the focusing positions of ghost light from the imaging plane and the ghost light from the filter are separated on the object side and the image side of the imaging plane IS, and a small-diameter light spot is not focused on the imaging plane IS, thereby effectively reducing the influence of ghost light.

[0160] (Example 3)

[0161] Example 3 is based on Fig.13 A specific example of the embodiment is described.

[0162] Fig.14 Follow Figure 2 Data of the imaging optical system of Example 3 is shown.

[0163] (Aspherical data)

[0164] Fig.15 Follow Figure 3 Data of the aspherical surface in the imaging optical system of Example 3 are shown.

[0165] In Example 3, both surfaces of the second lens and both surfaces of the sixth lens are aspherical surfaces.

[0166] exist Fig.16In (a), the focal length of the entire system of the imaging optical system of Example 3 is shown: f, Fno, total length: L, and viewing angle: W, and in (b), the respective focal lengths of the first group G1 to the fifth group G5: f1 to f5 and the lens effective diameters: E1 to E5 are shown.

[0167] In addition, Fig.16 (c) shows the values ​​of the parameters of the conditional expressions (1) to (5) of the imaging optical system of Example 3.

[0168] Fig.17 Follow Figure 5 Aberration diagrams of the imaging optical system of Example 3 are shown.

[0169] Fig.18 It is modeled after Figure 6 A diagram showing the behavior of ghost light in the imaging optical system of Example 3.

[0170] Fig.18 (a) shows the behavior of ghost light from the imaging surface IS, which is reflected by the imaging beam from the object side and further reflected by the object side of the first lens L1, for the paraxial light. As shown in the figure, the ghost light in this case converges on the front side of the imaging surface IS, that is, the "object side", and enters the imaging surface IS while diverging. Therefore, the convergence of light to the imaging surface IS is avoided, and the influence of the ghost light from the imaging surface is reduced.

[0171] Fig.18 (b) shows the behavior of the ghost light from the filter, which is reflected on the object side of the filter F1 and further reflected on the object side of the first lens L1, for the paraxial light. As shown in the figure, the ghost light in this case also converges toward the back side of the imaging surface IS, that is, the "image side", and enters the imaging surface IS in the middle of the convergence. Therefore, the convergence of light to the imaging surface IS is avoided, and the influence of the ghost light from the filter is reduced.

[0172] That is, the ghost light from the imaging surface and the ghost light from the filter converge at separate positions on the object side and the image side of the imaging surface IS. Since a small-diameter light spot is not converged on the imaging surface IS, the influence of ghost light is effectively reduced.

[0173] As shown in the aberration diagrams, the imaging optical systems of Examples 1 to 3 have all aberrations corrected at a high level, and spherical aberration and axial chromatic aberration are small and do not pose a problem. Astigmatism and field curvature are also sufficiently small, and although not shown, lateral chromatic aberration is also sufficiently small, and coma and chromatic aberration disturbances are well suppressed even at the most peripheral parts.

[0174] In addition, Examples 1 to 3 all achieve "half viewing angle: wide viewing angle of 65 degrees or more".

[0175] Hereinafter, as specific examples of an imaging device using the imaging optical system of the present invention, an embodiment of a digital camera implemented as a camera device and an embodiment of a stereo camera implemented as a camera device will be described.

[0176] like Fig.19 As shown in (a) and (b), the digital camera 100 is equipped with a camera optical system, namely a photographic lens 1, a viewfinder 2, a flash (electronic flash) 3, a shutter button 4, a power switch 6, a liquid crystal display 7, an operation button 8 and a memory card slot 9 on a housing (camera body) 5.

[0177] like Fig. 20 As shown, the system structure of the digital camera 100 includes a central processing unit (CPU) 11, an image processing device 12, an area sensor, i.e., a light receiving element 13, a signal processing device 14, a semiconductor memory 15, and a communication card 16 in a housing 5.

[0178] The digital camera 100 has a photographic lens 1 as an imaging optical system, and an area sensor, i.e., a light receiving element 13, which is constructed as an image sensor using a (complementary metal oxide semiconductor) imaging element such as a CMOS or a CCD (charge coupled device) imaging element, and the subject image formed by the imaging optical system 1 is read by the light receiving element 13.

[0179] As the imaging optical system 1, the imaging optical systems of the above-mentioned Embodiments 1 to 3 can be used. In this case, the light receiving surface of the light receiving element 13 is the imaging surface in the above description.

[0180] The output of the light receiving element 13 is processed by the signal processing device 14 controlled by the central processing unit 11 and converted into digital image information.

[0181] The image information digitized by the signal processing device 14 is subjected to predetermined image processing by the image processing device 12 which is also controlled by the central processing unit 11, and then stored in a semiconductor memory 15 such as a nonvolatile memory.

[0182] In this case, the semiconductor memory 15 may use a memory card loaded in the memory card slot 9 or a semiconductor memory built into the digital camera body in an integrated manner.

[0183] The image being photographed can be displayed on the liquid crystal display 7, and the image stored in the semiconductor memory 15 can also be displayed. In addition, the image stored in the semiconductor memory 15 can also be sent to the outside through the communication card 16 loaded in the communication card slot (which can also be used as the memory card slot 9).

[0184] The imaging optical system, namely the photographic lens 1, is configured such that when the camera is carried, its object surface is covered by a lens cover (not shown). When the user operates the power switch 6 to turn on the power, the lens cover opens to expose the object surface.

[0185] The image stored in the semiconductor memory 15 is displayed on the liquid crystal display 7 and transmitted to the outside through the communication card 16, etc., by operating the operation button 8. The semiconductor memory 15 and the communication card 16, etc. are loaded in dedicated or common slots such as the memory card slot 9 and the communication card slot for use.

[0186] exist Fig.21 In the figure, a stereo camera is shown as one embodiment of a camera device using the imaging optical system of the present invention.

[0187] like Fig.21 As shown, the stereo camera 200 has two camera devices 100a and 100b, and as the imaging optical systems of these camera devices 100a and 100b, the imaging optical systems such as those in Examples 1 to 3 are used.

[0188] As the camera devices 100a and 100b, for example, although the camera device 100a and 100b can be used, Fig.18 , Fig.19 The camera device described above has the same structure as the camera device 100, but is not limited to this.

[0189] By appropriately correcting and processing the digital image information output from the camera devices 100a and 100b in the image processing unit provided in the stereo camera 200, and then outputting the image, the sensing technology can be used for production line, vehicle control, etc.

[0190] As described above, the imaging optical system of the present invention can effectively reduce the influence of ghost light not only from the imaging surface, but also from the filter. In addition, as in Examples 1 to 3, the imaging optical system has a half viewing angle: a wide viewing angle of more than 65 degrees, and has good performance. The imaging optical system can be used to constitute an imaging device such as a camera device, and the imaging device can be mounted on various mobile objects such as vehicles and drones as a vehicle-mounted imaging device.

[0191] It should be noted that the camera device of the present invention is not limited to digital cameras, and animation photography can of course be implemented as a video camera mainly used for animation photography, as well as a camera device mainly dedicated to photography, including a conventional film camera using so-called silver halide film.

[0192] In addition, not only camera devices, but also various information devices including mobile phones, portable information terminal devices called PDAs (personal data assistants), and portable terminal devices including these functions, such as so-called smart phones and tablet terminals, often have built-in camera functions equivalent to digital cameras, and such information devices also include essentially the same functions and structures as digital cameras, and the above-mentioned camera optical systems of Examples 1 to 3 can also be used in such information devices.

[0193] Although preferred embodiments of the invention have been described above, the present invention is not limited to the above-mentioned specific embodiments, and various modifications / changes are possible within the scope of the gist of the invention described in the claims unless otherwise specified in the above description.

[0194] The effects described in the embodiments of the present invention are merely examples of preferred effects produced by the invention, and the effects of the invention are not limited to "the descriptions in the embodiments."

Claims

1. An imaging optical system that forms an image of an object, which is a subject to be imaged, on an imaging surface. The imaging optical system is provided with a lens system and a filter arranged from the object side toward the image side. The lens system has a five-group structure and is arranged with a first group, a second group, a third group, a fourth group, and a fifth group from the object side toward the image side. Among them, the first group is composed of a first lens, which is a negative meniscus lens with its convex surface facing the object side; the second group is composed of a second lens, which is a negative lens; the third group is composed of a third lens, which is a positive lens; the fourth group is composed of a cemented lens formed by cementing a fourth lens, which is a positive lens, and a fifth lens, which is a negative lens, and has a positive refractive power as a whole; the fifth group is composed of a sixth lens, which is a positive lens. The filter is in the shape of a parallel flat plate and is arranged on the image side of the fifth group in a manner orthogonal to the optical axis of the lens system. The radius of curvature R11 of the object-side surface of the first lens, the focal length f of the entire system, the distance Df between the object-side surface of the filter and the imaging surface, and the overall length L of the entire system satisfy the conditional expression 0.55 < (R11 / f) × (Df / L) < 1.

00. The focal length f of the entire system, the overall length L of the entire system, and the half-angle of view W satisfy the conditional expression 4.0 < W × (L / f) / 100 < 6.0, where the unit of the half-angle of view W is degrees. The focal length f of the entire system, the distance Df between the object-side surface of the filter and the imaging surface, the half-angle of view W, and the overall length L of the entire system satisfy the conditional expression 14.0 < W × (Df / L).

2. The imaging optical system according to claim 1, wherein the radius of curvature R11 of the object-side surface of the first lens, the focal length f of the entire system, and the half-angle of view W satisfy the conditional expression 1.5 < W × (R11 / f) < 4.

0.

3. The imaging optical system according to claim 1, wherein the radius of curvature R11 of the object-side surface of the first lens and the radius of curvature R12 of the image-side surface of the first lens satisfy the conditional expression 0.2 < R12 / R11 < 0.

4.

4. The imaging optical system according to any one of claims 1 to 3, wherein the first lens has at least one aspherical surface, and the sixth lens has at least one aspherical surface.

5. The imaging optical system according to any one of claims 1 to 3, wherein the second lens has at least one aspherical surface, and the sixth lens has at least one aspherical surface.

6. An imaging device that has the imaging optical system according to any one of claims 1 to 5 and uses the light-receiving surface of an area sensor as the imaging surface.

7. The imaging device according to claim 6, wherein the imaging device is configured as a camera device.

8. The imaging device according to claim 6, wherein the imaging device is configured as an in-vehicle imaging device.

9. A moving body that is equipped with the imaging device according to any one of claims 6 to 8.

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