Imaging optical system and imaging device

Abstract

To balance resolution between a center portion and a peripheral portion around an optical axis.SOLUTION: An imaging optical system 10 comprises, in order from an object side, a first lens group LG1, an aperture diaphragm S, and a second lens group LG2. The first lens group LG1 includes at least one aspherical lens AL having negative power. In the aspherical lens AL, a surface angle of an object-side surface has an extreme value between an optical axis Ax and an effective diameter position. The first lens group LG1 includes three or more lenses including a positive lens and a negative lens. The second lens group LG2 includes four or more lenses including a positive lens and a negative lens. A final lens closest to an image side in the second lens group LG2 has a convex object-side surface and a concave image-side surface. The imaging optical system 10 satisfies the following conditional expression: 3.0<CD / OD<8.0 ...(1), where CD is a change amount per unit angle of view of normalized image height at a position in the minimum angle of view, and OD is a change amount per unit angle of view of the normalized image height at the effective diameter position.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging optical system and an imaging apparatus. [Background Art]

[0002] For example, in imaging optical systems for vehicle front sensing, higher resolution to improve sensing accuracy and wider angle to cover a wider range are required. In contrast, for example, in the imaging lens system described in Patent Document 1, the incident side surface (object side) of the first lens is an aspherical surface having an inflection point. This achieves both high-resolution imaging of long distances in the direction of the optical axis center and wide-angle imaging of nearby areas. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2019 / 093377 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the technique described in Patent Document 1 leaves room for improvement in terms of balancing the resolution between the central portion around the optical axis and the peripheral portion. An object of the present invention is to suitably achieve resolution balance between the central portion around the optical axis and the peripheral portion. [Means for Solving the Problem]

[0005] To achieve the above object, the present invention One embodiment is an imaging optical system, wherein: in order from the object side, a first lens group, an aperture stop, a second lens group, Combination , the first lens group includes at least one aspherical lens having negative power, The aforementioned aspherical lens has an extreme value in the surface angle of the object's side surface between the optical axis and the effective diameter position. The first lens group includes three or more lenses, including positive and negative lenses. The second lens group includes four or more lenses, including positive and negative lenses. The final lens in the second lens group, closest to the image, has a convex side on the object side and a concave side on the image side. It is characterized by satisfying the following conditional expression. 3.0 <CD / OD<8.0 ···(1) 3.0 <TTL / f<4.0 ···(3) however, CD: Change in normalized image height per unit field of view at the minimum field of view position. OD: The change in normalized image height per unit field of view at the effective aperture position. TTL: Total optical length from the side of the object on the first lens to the image plane f: Focal length of the entire imaging optical system [Effects of the Invention]

[0006] According to the present invention, it is possible to suitably balance the resolution between the central and peripheral parts around the optical axis. [Brief explanation of the drawing]

[0007] [Figure 1] (a) A schematic cross-sectional view of the imaging device according to the embodiment. [Figure 2] This is a block diagram showing a schematic control configuration of the imaging device according to the embodiment. [Figure 3] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 1. [Figure 4] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 2. [Figure 5] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 3. [Figure 6] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 4. [Figure 7](a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 5. [Figure 8] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 6. [Figure 9] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 7. [Figure 10] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 8. [Figure 11] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 9. [Figure 12] (a) is a cross-sectional view and (b) is a longitudinal aberration diagram of the imaging optical system of Example 10. [Figure 13] It is a diagram showing an example of calculation of CD and OD. MODE FOR CARRYING OUT THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0009] [Overall Configuration of Imaging Apparatus] FIG. 1 is a schematic cross-sectional view of an imaging apparatus 100 according to the present embodiment. As shown in this figure, the imaging apparatus 100 includes a camera module 30 for forming image signals. The camera module 30 includes the imaging optical system 10 and a sensor unit 50.

[0010] The imaging optical system 10 is a single-focus optical system for forming a subject image on the imaging surface (projected surface) I of the image sensor 51, and is accommodated in a lens barrel 41. The imaging optical system 10 includes a plurality of lenses (in the present embodiment, from the first lens L1 to the seventh lens L7). Details of the configuration of the imaging optical system 10 will be described later.

[0011] The lens barrel 41 that accommodates the imaging optical system 10 has an aperture OP through which light from the object side enters. Furthermore, the lens barrel 41 is provided with a drive mechanism 42 (see Figure 2) that moves at least some of the lenses or lens groups among the first lens L1 to the seventh lens L7 along the optical axis Ax. The drive mechanism 42 enables the focusing operation of the imaging optical system 10 by moving the said some lenses or lens groups along the optical axis Ax. The drive mechanism 42 comprises, for example, a voice coil motor and a guide. Note that the drive mechanism 42 may be configured with a stepping motor or the like instead of a voice coil motor.

[0012] The sensor unit 50 includes an image sensor (solid-state image sensor) 51 that detects the subject image formed by the imaging optical system 10 and converts it into photoelectric energy. The image sensor 51 is, for example, a CMOS type image sensor. The image sensor 51 is fixed in a position relative to the optical axis Ax. The image sensor 51 has a photoelectric conversion unit as the imaging surface I, and a signal processing circuit (not shown) around it. Pixels, or photoelectric conversion elements, are arranged two-dimensionally in the photoelectric conversion unit. Note that the image sensor 51 is not limited to the CMOS type image sensor described above, but may also incorporate other image sensors such as a CCD. A cover glass P is positioned immediately to the object side of the image sensor 51 to protect the imaging surface I.

[0013] Figure 2 is a block diagram showing the schematic control configuration of the imaging device 100. As shown in this figure, the imaging device 100 includes a processing unit 60 that operates the camera module 30. The processing unit 60 includes a lens drive unit 61, an element drive unit 62, an input unit 63, a storage unit 64, an image processing unit 65, a display unit 66, and a control unit 67.

[0014] The lens drive unit 61 operates the drive mechanism 42 to move some of the lenses or lens groups among the first lens L1 to the seventh lens L7 along the optical axis Ax. This allows the lens drive unit 61 to perform operations such as focusing of the imaging optical system 10. The element drive unit 62 receives voltage and clock signals from the control unit 67 to drive the image sensor 51 and outputs them to the circuitry associated with the image sensor 51. This allows the element drive unit 62 to operate the image sensor 51. The input unit 63 accepts user operations or commands from external devices. The memory unit 64 stores information necessary for the operation of the imaging device 100, image data acquired by the camera module 30, lens correction data used for image processing, and the like. The image processing unit 65 performs image processing on the image signal output from the image sensor 51. The image processing unit 65 processes the frame images that make up the image signal, assuming that the image signal corresponds to a moving image. In addition to normal image processing such as color correction, gradation correction, and zooming, the image processing unit 65 performs distortion correction processing on the image signal based on lens correction data read from the storage unit 64. The display unit 66 is the part that displays information to be presented to the user, such as captured images. The display unit 66 can also function as the input unit 63. The control unit 67 comprehensively controls the operation of the lens drive unit 61, element drive unit 62, input unit 63, storage unit 64, image processing unit 65, display unit 66, and the like.

[0015] [Specific configuration of the imaging optical system] Next, we will explain the imaging optical system 10 in more detail. As shown in Figure 1, in this embodiment, the imaging optical system 10 comprises, in order from the object side, a first lens group LG1, an aperture diaphragm S, and a second lens group LG2.

[0016] The first lens group LG1 includes three or more lenses, including positive and negative lenses. In this embodiment, the first lens group LG1 comprises three lenses (first lens L1 to third lens L3).

[0017] The first lens group LG1 includes at least one aspherical lens AL having negative power. In this embodiment, the first lens L1, which is positioned closest to the object in the imaging optical system 10, is the negative lens aspherical lens AL. The aspherical lens AL is a negative meniscus lens with a convex surface on the object side and a concave surface on the image side. The surface angle of the aspherical lens AL has an extreme value between the optical axis Ax (and its vicinity) and the effective aperture position. In other words, the object side of the aspherical lens AL has a shape in which the center around the optical axis Ax has positive power (convex towards the object), and the positive power weakens towards the periphery. Due to this aspherical lens AL, the imaging optical system 10 has a negative lens leading the way. Therefore, by positioning the positive lens closer to the object than the aperture diaphragm S, aberration control within the first lens group LG1 becomes easier. As a result, a larger aperture becomes possible. Furthermore, the aspherical lens AL only needs to be included in the first lens group LG1, and any lens other than the first lens L1 may be the aspherical lens AL. However, it is preferable that the first lens L1 or the second lens L2 be the aspherical lens AL so as to minimize the overlap of light rays at each angle of view.

[0018] The second lens group LG2 includes four or more lenses, including positive and negative lenses. In this embodiment, the second lens group LG2 comprises four lenses (fourth lens L4 to seventh lens L7). The second lens group LG2 includes a cemented lens formed by joining a positive lens and a negative lens. In this embodiment, the fifth negative lens L5 and the sixth positive lens L6 are joined together to form a cemented lens. The final lens in the second lens group LG2, closest to the image (the seventh lens L7 in this embodiment), has a convex surface on the object side and a concave surface on the image side. The final lens may be either a positive or negative lens. The final lens may also have an inflection point on the image side. This allows for a reduced incident angle to the image sensor 51.

[0019] A parallel plate F is positioned between the second lens group LG2 and the image sensor 51 (cover glass P). The parallel plate F is an optical filter, such as an IR cut filter, wavelength selective filter, or optical low-pass filter. While glass is preferable for each lens in the imaging optical system 10 considering its temperature characteristics, it may also be made of plastic through a shape design that takes temperature characteristics into account.

[0020] Furthermore, the imaging optical system 10 satisfies the following condition (1). 3.0 <CD / OD<8.0 ···(1) However, CD is the change in normalized image height per unit field of view at the minimum field of view position (near the optical axis Ax), and OD is the same change at the effective diameter position. More specifically, CD and OD are calculated by normalizing the image height relative to the field of view at the image height corresponding to the maximum field of view, and then calculating the normalized image height as a value per unit field of view (1°) at the minimum field of view position and the effective diameter position. Figure 13 shows an example of CD and OD calculation. In the example in Figure 13, the radial position of the maximum field of view is the effective diameter position.

[0021] Condition (1) is a conditional expression for setting the resolution of the central part around the optical axis Ax and the resolution of the peripheral part in a suitable balance. If CD / OD falls below the lower limit of condition (1), the resolution in the center will be too degraded. If CD / OD exceeds the upper limit of condition (1), the resolution in the peripheral areas will be too degraded.

[0022] Furthermore, the imaging optical system 10 may satisfy the following condition (2) instead of (or in addition to) the above condition (1). 1.6 <f·θ / H<1.95 ···(2) However, f is the focal length [mm] of the entire imaging optical system 10, θ is the maximum angle of view [°], and H is the image height [mm] corresponding to the maximum angle of view.

[0023] Condition (2) is a conditional expression for setting the resolution of the central part around the optical axis Ax and the resolution of the peripheral part in a suitable balance. If f·θ / H falls below the lower limit of condition (2), the resolution in the central area decreases too much. If f·θ / H exceeds the upper limit of condition (2), the resolution in the peripheral area decreases too much.

[0024] Furthermore, it is preferable that the imaging optical system 10 satisfies the following condition (3). 3.0 <TTL / f<4.0 ···(3) However, TTL is the total optical length [mm] from the object side of the first lens L1 to the imaging plane I, and f is the focal length [mm] of the entire imaging optical system 10.

[0025] To increase the resolution in the central area, we want to increase the focal length. However, increasing the focal length increases the overall optical length. Conditional equation (3) is a conditional equation for ensuring central resolution while suitably suppressing the overall optical length. If TTL / f falls below the lower limit of condition (3), the aberration performance deteriorates. If TTL / f exceeds the upper limit of condition (3), the optical length becomes too long.

[0026] Furthermore, it is preferable that the imaging optical system 10 satisfies the following condition (4). 0.06 <Dfl / TTL<0.17 ···(4) However, Dfl is the air gap on the object side of the optical axis Ax of the final lens (the seventh lens L7 in this embodiment), that is, the air gap on the optical axis Ax between the sixth lens L6 and the seventh lens L7. TTL is the total optical length from the object side of the first lens L1 to the imaging plane I.

[0027] In retrofocus optical systems where the negative lens is the primary element, wide-angle lenses are easier to achieve, and the focal length can be increased by bringing the final lens closer to the image sensor I. On the other hand, bringing the final lens closer to the image sensor I makes it difficult to secure a sufficient flange back distance. Conditional equation (4) is the condition for suitably securing both the focal length and the flange back distance.

[0028] [Technical effects of this embodiment] As described above, according to this embodiment, the negative-power aspherical lens AL included in the first lens group LG1 has an extreme value in the surface angle of the object's side surface between the optical axis Ax and the effective diameter position. Therefore, the negative-power aspherical lens AL can suitably capture light with a wide field of view. Furthermore, since the aspherical lens has an extreme value in the surface angle of the object's side surface, it is possible to suitably achieve both expansion of the central region (high resolution) and wide-angle by changing the power between the central and peripheral regions. Furthermore, the first lens group LG1 includes three or more lenses, including positive and negative lenses, and the second lens group LG2 includes four or more lenses, including positive and negative lenses. As a result, the aperture diaphragm S between the first lens group LG1 and the second lens group LG2 is positioned approximately in the center of the imaging optical system 10. Therefore, it is easier to standardize the size of each lens, and consequently, easier to manufacture each lens. Furthermore, the final lens in the second lens group LG2, which is closest to the image, has a convex surface on the object side and a concave surface on the image side. This allows for optimal telecentricity.

[0029] Furthermore, according to this embodiment, the imaging optical system 10 satisfies the above condition (1). This allows for a suitable balance of resolution between the central and peripheral areas around the optical axis Ax.

[0030] Furthermore, according to this embodiment, the imaging optical system 10 satisfies the above condition (2). This allows for a suitable balance of resolution between the central and peripheral areas around the optical axis Ax.

[0031] Furthermore, according to this embodiment, the imaging optical system 10 satisfies the above condition (3). This allows for ensuring resolution in the central area while effectively suppressing the overall optical length.

[0032] Furthermore, according to this embodiment, the aspherical lens AL is positioned closest to the object within the first lens group LG1. This reduces the overlap within the lens for each angle of view, making it easier to control aberration performance.

[0033] Furthermore, according to this embodiment, the aspherical lens AL may be positioned second from the object side in the first lens group LG1. In this case, the first lens L1 can be made into a spherical lens. This increases the variety of glass materials that can be used for the first lens L1 compared to glass molds, thus providing more options in terms of environmental resistance and other factors.

[0034] Furthermore, according to this embodiment, the imaging optical system 10 satisfies the above condition (4). This allows for a suitable length of focal length and flange back distance to be secured.

[0035] Furthermore, according to this embodiment, the second lens group LG2 includes a cemented lens in which a positive lens and a negative lens are joined together. This allows for a favorable reduction in chromatic aberration.

[0036] Although one embodiment of the present invention has been described above, the embodiments to which the present invention can be applied are not limited to those described above and can be modified as appropriate without departing from the spirit of the present invention. [Examples]

[0037] The following are examples of the imaging optical system of the present invention. The symbols used in each example are as follows. f: Focal length of the entire imaging optical system Fno: F number 2Y: Diagonal length of the imaging plane of the solid-state image sensor 2ω: Maximum field of view R: radius of curvature D: Distance between top surfaces of shaft Nd: Refractive index of lens material relative to the d line νd: Abbe number of lens material In each embodiment, the shape of the aspherical surface is represented by "Equation 1" below, where the vertex of the surface is the origin, the X-axis is taken in the direction of the optical axis, and the height perpendicular to the optical axis is h.

number

[0038] (Example 1) Figures 3(a) and 3(b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 1. In the imaging optical system of Example 1, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lens elements, and the second lens group LG2 has 4 lens elements.

[0039] The overall specifications of the imaging optical system in Example 1 are shown below. f=9.00mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0040] The lens surface data for Example 1 is shown in Table 1 below. [Table 1]

[0041] The aspheric coefficients of the lens surface in Example 1 are shown in Table 2 below. In the following data on aspheric coefficients, powers of 10 (e.g., 2.5 × 10⁻⁰²) will be expressed using E (e.g., 2.5E⁻⁰²). [Table 2]

[0042] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 1.

[0043] (Example 2) Figures 4(a) and 4(b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 2. In the imaging optical system of Example 2, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lens elements, and the second lens group LG2 has 4 lens elements.

[0044] The overall specifications of the imaging optical system in Example 2 are shown below. f=9.00mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0045] The lens surface data for Example 2 is shown in Table 3 below. [Table 3]

[0046] The aspheric coefficient of the lens surface in Example 2 is shown in Table 4 below. [Table 4]

[0047] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 2.

[0048] (Example 3) Figures 5(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 3. In the imaging optical system of Example 3, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lenses, and the second lens group LG2 has 4 lenses.

[0049] The overall specifications of the imaging optical system in Example 3 are shown below. f=8.7mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0050] The lens surface data for Example 3 is shown in Table 5 below. [Table 5]

[0051] The aspheric coefficient of the lens surface in Example 3 is shown in Table 6 below. [Table 6]

[0052] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 3.

[0053] (Example 4) Figures 6(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 4. In the imaging optical system of Example 4, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lenses, and the second lens group LG2 has 4 lenses.

[0054] The overall specifications of the imaging optical system in Example 4 are shown below. f = 10.1 mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0055] The lens surface data for Example 4 is shown in Table 7 below. [Table 7]

[0056] The aspheric coefficient of the lens surface in Example 4 is shown in Table 8 below. [Table 8]

[0057] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 4.

[0058] (Example 5) Figures 7(a) and 7(b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 5. In the imaging optical system of Example 5, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lenses, and the second lens group LG2 has 4 lenses.

[0059] The overall specifications of the imaging optical system in Example 5 are shown below. f = 10.0 mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0060] The lens surface data for Example 5 is shown in Table 9 below. [Table 9]

[0061] The aspheric coefficient of the lens surface in Example 5 is shown in Table 10 below. [Table 10]

[0062] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 5.

[0063] (Example 6) Figures 8(a) and 8(b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 6. In the imaging optical system of Example 6, the second lens L2 is an aspherical lens AL, the first lens group LG1 has 3 lens elements, and the second lens group LG2 has 4 lens elements.

[0064] The overall specifications of the imaging optical system in Example 6 are shown below. f=8.9mm Fno=1.65 2Y = 11.088 mm 2ω = 120°

[0065] The lens surface data for Example 6 is shown in Table 11 below. [Table 11]

[0066] The aspheric coefficient of the lens surface in Example 6 is shown in Table 12 below. [Table 12]

[0067] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 6.

[0068] (Example 7) Figures 9(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 7. In the imaging optical system of Example 7, the second lens L2 is an aspherical lens AL, the first lens group LG1 has 3 lens elements, and the second lens group LG2 has 4 lens elements.

[0069] The overall specifications of the imaging optical system in Example 7 are shown below. f=9.0mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0070] The lens surface data for Example 7 is shown in Table 13 below. [Table 13]

[0071] The aspheric coefficient of the lens surface in Example 7 is shown in Table 14 below. [Table 14]

[0072] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 7.

[0073] (Example 8) Figures 10(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 8. In the imaging optical system of Example 8, the second lens L2 is an aspherical lens AL, the first lens group LG1 has 3 lens elements, and the second lens group LG2 has 4 lens elements.

[0074] The overall specifications of the imaging optical system in Example 8 are shown below. f=9.0mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0075] The lens surface data for Example 8 is shown in Table 15 below. [Table 15]

[0076] The aspheric coefficient of the lens surface in Example 8 is shown in Table 16 below. [Table 16]

[0077] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 8.

[0078] (Example 9) Figures 11(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 9. In the imaging optical system of Example 9, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 4 lens elements, and the second lens group LG2 has 4 lens elements.

[0079] The overall specifications of the imaging optical system in Example 9 are shown below. f=9.6mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0080] The lens surface data for Example 9 is shown in Table 17 below. [Table 17]

[0081] The aspheric coefficient of the lens surface in Example 9 is shown in Table 18 below. [Table 18]

[0082] Table 21 shows the numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 9.

[0083] (Example 10) Figures 12(a) and (b) show a cross-sectional view and a longitudinal aberration diagram (spherical aberration, astigmatism, and distortion) of the imaging optical system of Example 10. In the imaging optical system of Example 10, the first lens L1 is an aspherical lens AL, the first lens group LG1 has 3 lenses, and the second lens group LG2 has 4 lenses.

[0084] The overall specifications of the imaging optical system in Example 10 are shown below. f=8.5mm Fno=1.6 2Y = 11.088 mm 2ω = 120°

[0085] The lens surface data for Example 10 is shown in Table 19 below. [Table 19]

[0086] The aspheric coefficient of the lens surface in Example 10 is shown in Table 20 below. [Table 20]

[0087] The numerical values ​​of conditional equations (1) to (4) in the imaging optical system of Example 10 are shown in Table 21 below. [Table 21] [Explanation of Symbols]

[0088] 10 Imaging optical system 41 Telescope Tube 50 Sensor section 51 Image sensor 100 Imaging device AL Aspherical Lenses Ax optical axis I. Imaging surface L1 First Lens L2 Second Lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens (final lens) LG1 1st lens group LG2 2nd lens group S Aperture diaphragm

Claims

1. Starting from the object side, it consists of a first lens group, an aperture diaphragm, and a second lens group. The first lens group includes at least one aspherical lens having negative power, The aforementioned aspherical lens has an extreme value in the surface angle of the object's side surface between the optical axis and the effective diameter position. The first lens group includes three or more lenses, including a positive lens and a negative lens. The second lens group includes four or more lenses, including positive and negative lenses. The final lens in the second lens group, closest to the image, has a convex surface on the object side and a concave surface on the image side. An imaging optical system characterized by satisfying the following conditional equation. 3.0<CD / OD<8.0...(1) 3.0<TTL / f<4.0...(3) however, CD: Change in normalized image height per unit field of view at the minimum field of view position. OD: The change in normalized image height per unit field of view at the effective aperture position. TTL: Total optical length from the side of the object to the image plane of the first lens. f: Focal length of the entire imaging optical system

2. Starting from the object side, it consists of a first lens group, an aperture diaphragm, and a second lens group. The first lens group includes at least one aspherical lens having negative power, The aforementioned aspherical lens has an extreme value in the surface angle of the object's side surface between the optical axis and the effective diameter position. The first lens group includes three or more lenses, including a positive lens and a negative lens. The second lens group includes four or more lenses, including positive and negative lenses. The final lens in the second lens group, closest to the image, has a convex surface on the object side and a concave surface on the image side. An imaging optical system characterized by satisfying the following conditional equation. 1.6<f・θ / H<1.95 (2) 3.0<TTL / f<4.0...(3) however, f: Focal length of the entire imaging optical system θ: Maximum field of view H: Image height corresponding to the maximum field of view TTL: Total optical length from the side of the object to the image plane of the first lens. f: Focal length of the entire imaging optical system

3. The aspherical lens is the lens in the first lens group that is positioned closest to the object. The imaging optical system according to feature 1 or 2.

4. The aspherical lens is the second lens positioned from the object side in the first lens group. The imaging optical system according to feature 1 or 2.

5. The imaging optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression. 0.06<Dfl / TTL<0.17...(4) however, Dfl: Air gap on the optical axis on the object side of the final lens TTL: Total optical length from the side of the object to the image plane of the first lens.

6. The second lens group includes a cemented lens formed by joining a positive lens and a negative lens. The imaging optical system according to feature 1 or 2.

7. The imaging optical system according to claim 1 or 2, A lens barrel that holds the imaging optical system, An imaging device characterized by comprising:

Images