Image pickup optical system and image pickup apparatus

Abstract

To provide an imaging optical system and an imaging apparatus capable of more efficiently suppressing light reflected on the surface of the inner wall of a lens barrel from reaching an imaging device.SOLUTION: The imaging optical system 10 is an imaging optical system including a plurality of lenses, a stop St, and a lens barrel in which the plurality of lenses are included, and when a minimum radius of an inner wall of the lens barrel around an optical axis at an attachment position of the plurality of lenses attached closer to an object side than the stop is FDmin, a groove is provided in at least a part of the inner wall that satisfies a relationship of the following expression (1). 1 ≤ H / FDmin ≤ 1.15 (1) In Expression (1), H is a distance from the optical axis of the imaging optical system to the inner wall.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an imaging optical system and an imaging device. [Background technology]

[0002] BACKGROUND ART Conventionally, a technique for forming a groove to prevent light reflected from the inner wall of a lens barrel of an imaging optical system from reaching an imaging element (image sensor) is known.

[0003] Patent Documents 1 and 2 disclose a technique in which grooves are formed in the inner wall of the lens barrel to prevent light reflected on the surface of the inner wall of the lens barrel from reaching the imaging element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-27960 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-177293 Summary of the Invention

[0005] An embodiment of the technique of the present disclosure can more efficiently prevent light reflected on the surface of the inner wall of the lens barrel from reaching the imaging element. [Means for solving the problem]

[0006] An imaging optical system according to one aspect of the present invention is an imaging optical system including a plurality of lenses, an aperture, and a lens barrel containing the plurality of lenses, and the minimum radius of the inner wall of the lens barrel, centered on the optical axis, at the mounting position of the plurality of lenses mounted on the object side of the aperture, is defined as FDmin. In this case, grooves are provided on at least a part of the inner wall that satisfies the relationship of the following formula (1).

[0007] 1≦H / FDmin≦1.15…(1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall.

[0008] Preferably, the groove is provided on the inner wall that satisfies the relationship of formula (1).

[0009] Preferably, when the Nth adjacent lens gap among the plurality of lenses, in order from the object side, is defined as the Nth adjacent lens gap, and the distance between adjacent lenses in the Nth adjacent lens gap is defined as dN, a groove is provided on at least a part of the inner wall surrounding the lens gap that satisfies the relationship of the following formula (2).

[0010] 0.3 <dN / f<0.4…(2) In addition, f in the formula (2) is the focal length of the imaging optical system.

[0011] Preferably, among the plurality of lenses, in a lens group that moves as a single group during magnification variation, grooves are provided on at least a part of an inner wall between lenses that satisfies the relationship of the following formula (3), where D is the distance between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image, and d is the distance between adjacent lenses in the lens group: 0.55 <d / D<0.65…(3) Preferably, the angle of view is 90° or more.

[0012] An imaging device according to another aspect of the present invention includes the imaging optical system described above. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an overall view of an imaging optical system. [Figure 2] FIG. 2 is an enlarged view of area A in FIG. [Figure 3] FIG. 3 is a diagram showing the main positions at which the lens barrel radius of the imaging optical system is measured. [Figure 4] FIG. 4 is a diagram showing the values ​​of the main lens barrel radii shown in FIG. [Figure 5] FIG. 5 is a diagram showing H / FDmin at the main lens barrel radii shown in FIG. [Figure 6] FIG. 6 is a diagram showing the lens arrangement at the wide end (distance INF) of the imaging optical system. [Figure 7] FIG. 7 is a diagram showing the layout of the middle (distance INF) lenses in the imaging optical system. [Figure 8] FIG. 8 is a diagram showing the lens arrangement at the telephoto end (distance INF) of the imaging optical system. [Figure 9] FIG. 9 is a diagram showing the appearance of the imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of an imaging optical system and an imaging device according to the present invention will now be described with reference to the accompanying drawings.

[0015] In recent years, wide-angle lenses mounted on mirrorless cameras have become increasingly compact, taking advantage of their short back focus. Because of their wide angle of view, wide-angle lenses allow light to enter from various angles. This inevitably results in a large amount of light being reflected by the inner walls of the lens barrel. The larger outer diameter of the front portion of a wide-angle lens results in a large amount of light being reflected by the inner walls of the lens barrel. In wide-angle lenses, the first lens group, located closest to the object, has a large outer diameter for the lens and the lens barrel housing it. On the other hand, the second and third lens groups, located closer to the object than the first lens group, are located near the aperture, so their lens and lens barrel diameters are relatively small. As such, light is more likely to strike the inner walls of the lens barrel (lens frame, lens barrel) at the locations where the lens and lens barrel diameters are small. If light reflected by the inner walls of the lens barrel reaches the image sensor, it can affect the image quality of the captured image, such as reducing contrast. Therefore, in order to obtain images with good image quality, it is important to prevent light reflected from the inner wall of the lens barrel from reaching the image sensor.

[0016] In the present invention disclosed below, the internal structure of the imaging optical system can efficiently prevent light incident from a wide range of angles from being reflected by the inner wall of the lens barrel and reaching the imaging element.

[0017] <Imaging optical system> Fig. 1 is an overall view of an imaging optical system of the present invention. Fig. 1 shows the configuration of an imaging optical system 10 according to one embodiment of the present invention in a cross section including an optical axis Z. In Fig. 1, the left side is the object side and the right side is the image side. Note that Fig. 1 mainly shows the multiple lenses, aperture stop, and lens barrel (lens holding frame) that directly hold the lenses that make up the imaging optical system 10, with other components omitted or simplified.

[0018] 1 also shows an example in which a parallel-plate-shaped optical member PP is arranged between the imaging optical system 10 and an image plane Sim, assuming that the imaging optical system 10 is applied to an imaging device 110 (see FIG. 9). The optical member PP is a member that is assumed to include various filters and / or cover glass. Examples of various filters include a low-pass filter, an infrared cut filter, and a filter that cuts off a specific wavelength range. The optical member PP is a member that does not have refractive power, and a configuration in which the optical member PP is omitted is also possible.

[0019] The imaging optical system 10 is, for example, an interchangeable lens, and is a variable imaging optical system (zoom lens) with a focal length of 20 mm to 35 mm, and is capable of setting an angle of view of 90° or more. The imaging optical system 10 comprises a first lens group G1, a second lens group G2, an aperture stop St, a third lens group G The imaging optical system 10 is composed of a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. Each lens group is composed of one or more lenses and a lens barrel that holds the lenses. The lens barrel as used herein encompasses a lens holding frame and a lens barrel that hold the lenses. The imaging optical system 10 is composed of, in order from the object side to the image side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. As will be explained later with reference to FIGS. 6 to 8, during magnification, the second lens group G2, the third lens group G3, and the fourth lens group G4 move along the optical axis L while changing the distance between adjacent groups in the optical axis direction. The first lens group G1 and the fifth lens group G5 are fixed.

[0020] The first lens group G1 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a lens barrel T1, and a lens barrel T2. The first lens L1 is disposed closest to the object and is held by the lens barrel T1 and the lens barrel T2. The second lens L2 is disposed on the image side of the first lens L1 and is held by the lens barrel T2. The third lens L3 and the fourth lens L4 are disposed on the image side of the second lens L2. The third lens L3 and the fourth lens L4 are cemented together and held by the lens barrel T2.

[0021] The second lens group G2 is made up of a fifth lens L5, a sixth lens L6, and a lens barrel T3.

[0022] The fifth lens L5 is disposed closest to the object in the second lens group G2 and is held by the lens barrel T3. The sixth lens L6 is disposed on the image side of the fifth lens L5 and is held by the lens barrel T3. The second lens group G2 is disposed closest to the aperture stop St on the object side.

[0023] The aperture stop St is disposed on the image side of the sixth lens L6. The aperture stop St is held by an aperture holding mechanism MSt, and the opening diameter of the aperture stop St is increased or decreased automatically or in response to a user operation.

[0024] The third lens group G3 is made up of a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, a lens barrel T4, a lens barrel T5, and a lens barrel T6.

[0025] The seventh lens L7 is disposed closest to the object in the third lens group G3. Furthermore, the eighth lens L8, the ninth lens L9, and the tenth lens L10 are disposed in that order on the image side of the seventh lens L7, and the seventh lens L7, the eighth lens L8, and the ninth lens L9 are cemented together. The cemented seventh lens L7, the eighth lens L8, and the ninth lens L9 are held by the lens barrels T4 and T5. Furthermore, the tenth lens L10 is held by the lens barrels T4, T5, and T6. The third lens group G3 is disposed closest to the aperture stop St on the image side.

[0026] The fourth lens group G4 is made up of an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a lens barrel T7.

[0027] The eleventh lens L11 is disposed closest to the object in the fourth lens group G4. The twelfth lens L12 is disposed on the image side of the eleventh lens L11, and the eleventh lens L11 and the twelfth lens L12 are cemented together and held by the lens barrel T7. The thirteenth lens L13 is disposed on the image side of the twelfth lens L12 and is held by the lens barrel T7.

[0028] The fifth lens group G5 is made up of a fourteenth lens L14 and a lens barrel T8. The fourteenth lens L14 is disposed closest to the image side and is held by the lens barrel T8.

[0029] As described above, the imaging optical system 10 is made up of the first lens group G1, the second lens group G2, the aperture stop St, the third lens group G3, the fourth lens group G4, and the fifth lens group G5.

[0030] Next, Table 1 shows lens data of the imaging optical system 10 described in FIG. 1, Table 2 shows data related to specifications, Table 3 shows data related to variable surface spacing, and Table 4 shows data related to aspherical coefficients.

[0031] In the lens data in Table 1, the surface number column indicates the surface number, beginning with the surface closest to the magnification side and increasing sequentially toward the image side. The radius of curvature column indicates the radius of curvature (unit: mm) of each surface. The surface spacing column indicates the spacing (unit: mm) along the optical axis Z between each surface and the next surface. The n column indicates the refractive index of each optical element at the d-line, and the v column indicates the Abbe number of each optical element at the d-line. The sign of the radius of curvature is positive when the surface shape is convex toward the object side and negative when the surface shape is convex toward the image side. The lens data also includes the aperture stop St (surface number 12) and optical element PP (surface numbers 26 and 27). The surface number column for the surface corresponding to aperture stop St includes the surface number and the term (aperture). In the lens data in Table 1, the surface spacing column for surfaces whose spacing changes during focusing lists DD [surface number]. The numerical values ​​corresponding to this DD [surface number] are shown in Table 3.

[0032] The data on the specifications in Table 2 shows the zoom magnification, focal length f (mm), back focus Bf (mm), F-number FNo., and total angle of view 2ω [°].

[0033] In the lens data of Table 1, the aspherical surface number is marked with an *, and the paraxial radius of curvature is shown as the radius of curvature of the aspherical surface. The data on aspherical coefficients in Table 4 shows the aspherical surface number, KA and Am (m = 3, 4, 5, 6, 7, 8, 9, 10), and the aspherical coefficients for these aspherical surfaces. The numerical values ​​of the aspherical coefficients in Table 4, "E±n" (n: integer), are expressed as "×10 ±n The aspherical coefficients are the values ​​of the coefficients KA and Am in the aspherical formula given below.

[0034] Zd = C·h 2 / {1+(1-KA·C 2 h 2 ) 1 / 2}+ΣAm·h m however, Zd: Aspheric depth (length of the perpendicular line drawn from a point on the aspheric surface at height h to a plane perpendicular to the optical axis where the vertex of the aspheric surface touches) h: Height (distance from the optical axis) C: Reciprocal of paraxial radius of curvature KA, Am: aspherical coefficients and Σ at the aspherical depth Zd means the summation with respect to m.

[0035] Lens data and specifications are normalized to the focal length at the wide-angle end. The angle is expressed in degrees.

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] <Shape of the groove on the lens barrel> Next, we will explain the grooves provided in the lens barrel T2 of the imaging optical system 10. In the imaging optical system 10, by providing grooves in the lens barrel T2, light reflected on the inner wall of the lens barrel T2 is prevented from reaching the imaging element 120 (see FIG. 9).

[0041] FIG. 2 is an enlarged view of area A in FIG. 1, and is a diagram illustrating the grooves provided on the inner wall of the lens barrel T2.

[0042] As shown in FIG. 2, a groove R is provided on the inner wall of the lens barrel T3, which holds the fifth lens L5 and sixth lens L6 that make up the second lens group G2, to prevent light reflected on the inner wall from reaching the image sensor 120. FIG. 2 schematically shows an incident ray S1 that is incident on the fifth lens L5. After entering and passing through the fifth lens L5, the incident ray S1 is reflected on the inner wall of the lens barrel T2 and becomes a reflected ray S2. The groove R is provided on the inner wall of the lens barrel T2. 2. By reflecting the reflected light S2 from the groove R, the light based on the reflected light S2 is prevented from reaching the image sensor 120.

[0043] The groove R shown in FIG. 2 has a sawtooth shape. The sawtooth shape of the groove R can efficiently prevent reflected light (reflected light ray S2) from reaching the image sensor 120. Specifically, the front slope R(a) is provided so that when the incident light ray S1 is reflected, the reflected light ray S2 is reflected toward the object side. The rear slope R(b) is provided so that the incident light ray S1 does not strike the front slope R(a). The angle of each slope can be determined by appropriately modifying known techniques (e.g., Japanese Patent Application Laid-Open No. 7-27960 and Japanese Patent Application Laid-Open No. 2003-177293). The surface of the groove R can be textured to further prevent reflection of incident light.

[0044] Next, how to determine the position of the groove R on the lens barrel in the imaging optical system 10 will be described.

[0045] <Position of the groove on the lens barrel (1)> Next, the first criterion for determining the position where the groove R is provided will be explained. When the minimum radius of the inner wall of the lens barrel centered on the optical axis L is FDmin at the attachment position of the lens attached closer to the object side than the aperture stop St, the groove R is determined by the smallest radius of the inner wall that satisfies the following formula (1): At least in part,

[0046] 1≦H / FDmin≦1.15…(1) In addition, H in the formula (1) is the distance from the optical axis L of the imaging optical system 10 to the inner wall.

[0047] 3, 4, and 5 are diagrams for explaining the minimum radius FDmin of the inner wall of the lens barrel. Fig. 3 is a diagram showing positions for measuring the main lens barrel radii of the imaging optical system 10 described in Fig. 1. Fig. 4 is a diagram showing values ​​of the main lens barrel radii shown in Fig. 3. The radii shown in Fig. 3 are H shown in equation (1). Fig. 5 is a diagram showing H / FDmin at the main lens barrel radii shown in Fig. 3.

[0048] The barrel radius (I) is formed by the inner wall of the barrel T2 that holds the fourth lens L4 of the first lens group G1. The barrel radius (I) has a radius of 14.8 mm and a diameter of 29.6 mm. The barrel radius (II) is formed by the inner wall of the barrel T3 that holds the fifth lens L5 of the second lens group G2. The barrel radius (II) has a radius of 9.9 mm and a diameter of 19.8 mm. The barrel radius (III) is formed by the inner wall of the barrel T3 that holds the sixth lens L6 of the second lens group G2. The barrel radius (III) has a radius of 8.6 mm and a diameter of 17.2 mm. The barrel radius (IV) is the aperture corresponding to the aperture St. The barrel radius (IV) is when the aperture St is fully open, and has a radius of 8.72 mm and a diameter of 17.44 mm. The barrel radius (V) is formed by the inner wall of the barrel T4 that holds the seventh lens L7 of the third lens group G3. The inner wall of the lens barrel T4 (lens barrel) has a radius of 10.3 mm and a diameter of 20.6 mm. The outer diameter of the seventh lens L7 is 10 mm and 20 mm. The lens barrel radius (VI) is determined by the inner wall of the lens barrel T5, which holds the ninth lens L9 of the third lens group G3. The lens barrel radius (VI) is 9.45 mm and 18.9 mm.

[0049] As explained above, among the lens barrel radii (I) to (VI), the lens barrel radius (III) is the smallest, at 8.6 mm, which is the minimum radius FDmin.

[0050] Figure 5 shows the H of each lens barrel radius when the lens barrel radius (III) is 8.6 mm and FDmin is set as FDmin. / FDmin.

[0051] As shown in Figure 5, the lens barrel radius (I) / lens barrel radius (III) = 1.72093, the lens barrel radius (II) / lens barrel radius (III) = 1.151163, the lens barrel radius (III) / lens barrel radius (III) = 1.000000, the lens barrel radius (IV) / lens barrel radius (III) = 1.013953, the lens barrel radius (V) / lens barrel radius (III) = 1.197674, 1.162791, and the lens barrel radius (VI) / lens barrel radius (III) = 1.098837. When entering the values ​​into formula (1), the above values ​​are rounded to two decimal places and determined based on the values ​​to two decimal places.

[0052] From the above, the lens barrel radii (II) and (III) are located closer to the object side than the aperture stop St and have lens barrel radii that satisfy formula (1). Therefore, a groove R is provided on a portion of the inner wall of the lens barrel T3 from the lens barrel radius (II) to the lens barrel radius (III). This makes it possible to efficiently prevent reflected light from reaching the image sensor 120. Alternatively, grooves R may be provided on the inner wall of the lens barrel T3 from the lens barrel radius (II) to the lens barrel radius (III). This makes it possible to more efficiently prevent reflected light from reaching the image sensor 120.

[0053] <Position of the groove on the lens barrel (2)> Next, we will explain the second criterion for determining the position of groove R. When the gap between the Nth adjacent lenses in order from the object side is defined as the Nth gap, and the distance between adjacent lenses in the Nth gap is defined as dN, groove R is provided in at least a part of the inner wall of the lens barrel surrounding the gap between lenses that satisfies the relationship of the following formula (2):

[0054] 0.3 <dN / f<0.4…(2) In equation (2), f is the focal length of the imaging optical system 10. In the case of a variable magnification optical system (zoom lens) like the imaging optical system 10, the focal length at the wide-angle end is f, and dN is only considered between lenses that do not change even when the magnification is changed.

[0055] 6 to 8 are diagrams showing the arrangement of lenses when the magnification is changed from the wide end to the middle end and to the telephoto end of the imaging optical system 10. Note that in Figs. 6 to 8, only the first lens L1 to the fourteenth lens L14, the optical member PP, and the image plane Sim are shown, and the lens barrel and the like are omitted.

[0056] Fig. 6 is a lens layout diagram at the wide end (focused on the distance INF) of the imaging optical system 10. Fig. 7 is a lens layout diagram at the middle end (focused on the distance INF) of the imaging optical system 10. Fig. 8 is a lens layout diagram at the telephoto end (focused on the distance INF) of the imaging optical system 10.

[0057] 6 to 8, when the lenses are moved between the wide-angle, middle, and telephoto ends, the distance d1 between the first lens L1 and the second lens L2, the distance d2 between the second lens L2 and the third lens L3, the distance d5 between the fifth lens L5 and the sixth lens L6, the distance d9 between the ninth lens L9 and the tenth lens L10, and the distance d12 between the twelfth lens L12 and the thirteenth lens L13 remain constant. Here, d1 = 6.3511 (see the surface spacing of surface number 2), d2 = 9.1788 (see the surface spacing of surface number 4), d5 = 7.0374 (see the surface spacing of surface number 9), d9 = 1.4526 (see the surface spacing of surface number 16), and d12 = 4.7645 (see the surface spacing of surface number 21). The focal length f at the wide-angle end of the imaging optical system 10 is 20.6 mm. Therefore, d1 / f = 0.3083, d2 / f = 0.4456, d5 / f = 0.3416, d9 / f = 0.0705, and d12 / f = 0.2313.

[0058] From the above, it is d5 between the fifth lens L5 and the sixth lens L6 and d12 between the first lens L1 and the second lens L2 that satisfy the formula (2). Therefore, by providing a groove R on at least a part of the inner wall of the lens barrel T3 that surrounds the gap between the fifth lens L5 and the sixth lens L6, and the inner wall of the lens barrel T1 or T2 that surrounds the gap between the first lens L1 and the second lens L2, it is possible to efficiently prevent reflected light from reaching the image sensor 120. As in the imaging optical system 10 shown in FIG. 1, the lens barrel T3 surrounding the space between the fifth lens L5 and the sixth lens L6 is located in front of the aperture stop St and has a narrow lens barrel radius, so by providing a groove R on the inner wall of the lens barrel T3, it is possible to more efficiently prevent reflected light from reaching the imaging element 120.

[0059] <Position of the groove on the lens barrel (3)> Next, we will explain a third different criterion for determining the position at which groove R is provided. Groove R is provided in at least a part of the inner wall of the lens barrel that satisfies the relationship of the following formula (3), where D is the distance between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image, and d is the distance between adjacent lenses in the lens group, in a lens group that moves as a single group when the magnification of imaging optical system 10 is changed.

[0060] 0.55 <d / D<0.65…(3) As described above, the second lens group G2, the third lens group G3, and the fourth lens group G4 are lens groups that move as a single group when the magnification of the imaging optical system 10 is varied (see FIGS. 6 to 8). In the second lens group G2, the third lens group G3, and the fourth lens group G4, the distances between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image are as follows: D2 = 12.2374 for the second lens group G2 (see the surface spacings of surface numbers 8, 9, and 10); D3 = 19.8826 for the third lens group G3 (see the surface spacings of surface numbers 13, 14, 15, 16, and 17); and D4 = 12.2645 for the fourth lens group G4 (see the surface spacings of surface numbers 19, 20, 21, and 22). Furthermore, since the distance between the lenses in the second lens group G2 is d5, d5 / D2 = 0.5750. Furthermore, since the distance between the lenses in the third lens group G3 is d9, d9 / D3 = 0.0730. Furthermore, since the distance between the lenses in the fourth lens group G4 is d12, d12 / D4 = 0.3884. Note that the distance between lenses here refers to the distance between lenses that are substantially spaced apart.

[0061] From the above, the lens group that satisfies formula (3) is the second lens group G2. A groove R is provided between the fifth lens L5 and the sixth lens L6 that constitute the second lens group G2. This makes it possible to efficiently prevent reflected light from reaching the image sensor 120.

[0062] As explained above, the position of the groove R on the lens barrel is determined by the first, second, and third criteria. Here, the groove R may be provided at a position that satisfies all of the first, second, and third criteria, or at a position that satisfies two of the first, second, and third criteria, or at a position that satisfies any one of the first, second, and third criteria.

[0063] <Imaging device> Next, an imaging device equipped with the imaging optical system 10 described above will be described.

[0064] FIG. 9 is a diagram showing the appearance of the imaging device.

[0065] As shown in Fig. 9, imaging device 110 is a mirrorless digital single-lens camera made up of imaging optical system 10, which is an interchangeable lens, and camera body 150 to which the interchangeable lens can be attached or detached. Note that imaging device 110 is not limited to the digital single-lens camera shown in Fig. 9, and may be a mirrorless digital single-lens camera in which the lens and camera body are integrally configured.

[0066] A body mount 160 is provided on the front surface of the camera body 150, to which the imaging optical system 10 is attached. The camera body 150 is provided with an imaging element 120, which acquires an image formed by the imaging optical system 10. The top surface of the camera body 150 is provided with a A shutter release button 122, a shutter speed dial 123, an exposure compensation dial 124, and a power lever 125 are provided.

[0067] By using the imaging optical system 10 of this embodiment as an interchangeable lens in such an imaging device 110, it is possible to acquire images in which degradation of image quality due to reflected light from the lens barrel is suppressed.

[0068] <Other> An anti-reflection sheet may be attached to the inner wall of the lens barrel included in the imaging optical system 10. This will suppress internal reflection in the lens barrels T1 to T8.

[0069] The imaging optical system 10 may include an FPC (Flexible Printed Circuit: flex cable). In this case, the surface of the FPC has a high reflectivity, so by attaching an anti-reflection sheet to the surface of the FPC, it is possible to further suppress internal reflection in the imaging optical system 10.

[0070] For example, the metal actuator of the stepping motor is mounted so that it faces the image sensor 120. The surface of the metal actuator has a shiny metallic surface with high reflectivity and a black painted surface with low reflectivity. If the metal actuator is positioned on the object side, light will be incident on the highly reflective surface. Therefore, the actuator may be positioned on the image sensor 120 side to prevent light from being incident on the highly reflective surface of the actuator. This can reduce the incidence of harmful light on the second lens group G2.

[0071] From the above description, the imaging optical systems described in Supplementary Items 1 to 3 below can be understood.

[0072] [Additional note 1] An imaging optical system including a plurality of lenses, a diaphragm, and a lens barrel containing the plurality of lenses, When the minimum radius of the inner wall of the lens barrel centered on the optical axis at the mounting position of the plurality of lenses mounted on the object side of the diaphragm is FDmin, the relationship of the following formula (1) is satisfied: a groove is provided in at least a portion of the inner wall that satisfies the relationship.

[0073] 1≦H / FDmin≦1.15…(1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall.

[0074] [Additional note 2] An imaging optical system in which the groove is provided on at least a part of the inner wall surrounding the gap between the lenses that satisfies the following formula (2), where the gap between the N-th adjacent lenses among the plurality of lenses, in order from the object side, is defined as the N-th adjacent gap, and the distance between adjacent lenses in the N-th adjacent gap is dN.

[0075] 0.3 <dN / f<0.4…(2) In addition, f in the formula (2) is the focal length of the imaging optical system.

[0076] [Additional note 3] Among the plurality of lenses, in a lens group that moves as a single group during magnification variation, when the distance between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image is defined as D and the distance between adjacent lenses in the lens group is defined as d, a groove is provided on at least a part of the inner wall of the lens barrel having a gap between the lenses that satisfies the relationship of the following formula (3):

[0077] 0.55 <d / D<0.65…(3) Although examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0078] L1: First lens L2: Second lens L3: Third lens L4: Fourth lens L5: Fifth lens L6: Sixth lens L7: Seventh lens L8: 8th lens L9: 9th lens L10: 10th lens L11: 11th lens element L12: 12th lens element L13: 13th lens L14: 14th lens element T1~T8: Telescope tube 10: Imaging optical system 110: Imaging device 120: Image sensor St: Aperture

Claims

1. An imaging optical system including a plurality of lenses, a diaphragm, and a lens barrel containing the plurality of lenses, an imaging optical system in which a concave portion is provided on at least a part of the inner wall of the lens barrel that satisfies the relationship of the following formula (1), where FDmin is a minimum radius of the inner wall of the lens barrel centered on the optical axis at a mounting position of the plurality of lenses that are mounted on the object side of the aperture stop, An imaging optical system in which the recess is provided on at least a part of the inner wall surrounding the space between the lenses that satisfies the relationship of the following formula (2), where the space between the Nth adjacent lenses among the plurality of lenses, in order from the object side, is defined as the Nth adjacent space, and the distance between adjacent lenses in the Nth adjacent space is defined as dN. 1≦H / FDmin≦1.15 (1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall. 0.3<dN / f<0.4...(2) In addition, f in the formula (2) is the focal length of the imaging optical system.

2. An imaging optical system including a plurality of lenses, a diaphragm, and a lens barrel containing the plurality of lenses, an imaging optical system in which a concave portion is provided on at least a part of the inner wall of the lens barrel that satisfies the relationship of the following formula (1), where FDmin is a minimum radius of the inner wall of the lens barrel centered on the optical axis at a mounting position of the plurality of lenses that are mounted on the object side of the aperture stop, an imaging optical system in which, among the plurality of lenses, in a lens group that moves as a single group during magnification variation, the recess is provided on at least a part of the inner wall having a gap between the lenses that satisfies the relationship of the following formula (3), where D is the distance between the object-side surface of the lens closest to the object and the image-side surface of the lens closest to the image, and d is the distance between adjacent lenses in the lens group: 1≦H / FDmin≦1.15 (1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall. 0.55<d / D<0.65...(3)

3. An imaging optical system including a plurality of lenses, a diaphragm, and a lens barrel containing the plurality of lenses, an imaging optical system in which a concave portion is provided on at least a part of the inner wall of the lens barrel that satisfies the relationship of the following formula (1), where FDmin is a minimum radius of the inner wall of the lens barrel centered on the optical axis at a mounting position of the plurality of lenses that are mounted on the object side of the aperture stop, An imaging optical system having an angle of view of 90° or more. 1≦H / FDmin≦1.15 (1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall.

4. An imaging optical system including a plurality of lenses, a diaphragm, and a lens barrel containing the plurality of lenses, An imaging optical system in which, when the minimum radius of the inner wall of the lens barrel centered on the optical axis at the mounting position of the plurality of lenses mounted on the object side of the aperture is defined as FDmin, a recess is provided in at least a part of the inner wall that satisfies the relationship of the following formula (1), the recess suppressing light reflected on the inner wall from reaching an imaging element. 1≦H / FDmin≦1.15 (1) In addition, H in the formula (1) is the distance from the optical axis of the imaging optical system to the inner wall.

5. 5. The imaging optical system according to claim 2, wherein the recess is provided on at least a part of the inner wall surrounding the gap between the lenses that satisfies the following relationship (2): 0.3<dN / f<0.4...(2) In addition, f in the formula (2) is the focal length of the imaging optical system.

6. 5. The imaging optical system according to claim 1, wherein, in a lens group among the plurality of lenses that moves as a single group during magnification variation, when a distance between an object-side surface of a lens closest to the object side and an image-side surface of a lens closest to the image side are defined as D and a distance between adjacent lenses in the lens group is defined as d, the recess is provided in at least a part of the inner wall having a gap between the lenses that satisfies the relationship of the following formula (3): 0.55<d / D<0.65...(3)

7. 5. The imaging optical system according to claim 1, wherein the imaging optical system has an angle of view of 90 degrees or more.

8. The imaging optical system according to claim 1 , wherein the recess is provided on the inner wall that satisfies the relationship of the formula (1).

9. An imaging device comprising the imaging optical system according to claim 1 .

Images