WO2018097287A1 - Imaging optical system, lens unit, and imaging device - Google Patents

Abstract

The present invention provides an imaging optical system having an angle of view of 180° or more and having sufficiently small changes in image formation performance and angle of view between different medium environments although being compact. An imaging optical system 10 substantially comprises a main lens ML, and a supplementary lens SL for use in an aqueous medium or for use in air, wherein an image formation position is located closer to the object side than an imaging surface I in the state of the main lens ML alone, the main lens ML comprises a plurality of lenses, the supplementary lens SL comprises one negative lens, and in a state where the main lens ML and the supplementary lens SL are combined, desired image formation performance is obtained, and the following conditional expression (1) is satisfied: -42≤fA/fM≤-17 where fA is the focal length of the supplementary lens SL, and fM is the focal length of the main lens ML.

Description

Imaging optical system, lens unit, and imaging apparatus

The present invention relates to an imaging optical system, a lens unit, and an imaging apparatus for a camera that can handle different medium environments such as an amphibious camera.

In recent years, there has been a growing demand for amphibious optical systems that have a sufficiently wide angle even in water, have the same angle of view on both land and land, and can obtain the same high imaging performance. Here, an amphibious imaging optical system in which a lens that corrects aberration is combined with a lens system that is a main component is well known. (For example, refer to Patent Documents 1 and 2). In addition, an imaging optical system dedicated to underwater in which a lens in contact with water has a negative meniscus shape with a convex surface facing the object side and collects a light beam of about 180 ° in water is known (for example, Patent Documents). 3).

In the imaging optical system of Patent Document 1, there is almost no change in imaging performance in the air and in water, but there is a problem that the angle of view fluctuates by 15 ° or more in air and in water. The imaging optical system of Patent Document 2 has a problem that the resolution in the air is lower than the resolution in water, and the angle of view also changes by about 10 °. Further, in the imaging optical system of Patent Document 3, an angle of view of 180 ° at maximum is shown in water, but optical performance in air is not considered because of an underwater design.

JP-A-57-4017 JP-A-6-242369 JP-A-7-84180

In view of the above circumstances, an object of the present invention is to provide an imaging optical system that is small in size and has an angle of view of 180 ° or more and sufficiently small in imaging performance change and angle of view change in different medium environments.

Another object of the present invention is to provide a lens unit and an image pickup apparatus that include the image pickup optical system.

In order to achieve at least one of the above objects, an imaging optical system reflecting one aspect of the present invention is substantially composed of a main lens and an auxiliary lens for an aqueous medium or for an air. In the state of the main lens alone, the imaging position is on the object side of the imaging surface, the main lens consists of multiple lenses, the auxiliary lens consists of one negative lens, and the main lens and auxiliary lens are combined Desired imaging performance is obtained, and the following conditional expression is satisfied.
−42 ≦ fA / fM ≦ −17 (1)
Here, the value fA is the focal length of the auxiliary lens, and the value fM is the focal length of the main lens. The desired imaging performance means that the astigmatic difference is reduced by performing sufficient correction with the auxiliary lens, and the imaging position matches the imaging surface. The aqueous medium includes liquid substances in addition to seawater and fresh water.

In order to achieve at least one of the above objects, a lens unit reflecting one aspect of the present invention includes the above-described imaging optical system and a lens barrel that holds the imaging optical system.

In order to achieve at least one of the above objects, an imaging apparatus reflecting one aspect of the present invention includes the above-described imaging optical system and an imaging element that detects an image obtained from the imaging optical system. Prepare.

It is a figure explaining a lens unit and an imaging device provided with an imaging optical system of one embodiment of the present invention. 2A is a cross-sectional view showing an imaging optical system or the like incorporating the in-air auxiliary lens of Example 1, and FIG. 2B shows the imaging optical system or the like incorporating the auxiliary lens for aqueous medium of Example 1. It is sectional drawing. 3A and 3B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 1, and FIGS. 3C and 3D show the imaging optical system of the aqueous medium in-vehicle auxiliary lens incorporated in Example 1. FIG. FIGS. 3E and 3F are aberration diagrams of the imaging optical system of Comparative Example 1. FIG. 4A is a cross-sectional view illustrating an imaging optical system or the like incorporating the in-air auxiliary lens of Example 2, and FIG. 4B illustrates an imaging optical system or the like incorporating the auxiliary lens for aqueous medium of Example 2. It is sectional drawing. FIGS. 5A and 5B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 2. FIGS. 5C and 5D show the imaging optical system of the aqueous medium in Example 2 incorporating the auxiliary lens. FIGS. 5E and 5F are aberration diagrams of the imaging optical system of Comparative Example 2. FIG. 6A is a cross-sectional view showing an imaging optical system and the like incorporating the in-air auxiliary lens of Example 3, and FIG. 6B shows an imaging optical system and the like incorporating the auxiliary lens for aqueous medium of Example 3. It is sectional drawing. FIGS. 7A and 7B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 3. FIGS. 7C and 7D show the imaging optical system of the aqueous medium in Example 3 incorporating the auxiliary lens. FIGS. 7E and 7F are aberration diagrams of the imaging optical system of Comparative Example 3. FIG. FIG. 8A is a cross-sectional view showing an imaging optical system or the like incorporating the in-air auxiliary lens of Example 4, and FIG. 8B shows an imaging optical system or the like incorporating the auxiliary lens for aqueous medium of Example 4. It is sectional drawing. 9A and 9B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 4, and FIGS. 9C and 9D show the imaging optical system of the aqueous medium auxiliary lens of Example 4 incorporated therein. FIGS. 9E and 9F are aberration diagrams of the imaging optical system of Comparative Example 4. FIG. FIG. 10A is a cross-sectional view showing an imaging optical system and the like incorporating the in-air auxiliary lens of Example 5, and FIG. 10B shows the imaging optical system and the like incorporating the auxiliary lens for aqueous medium of Example 5. It is sectional drawing. 11A and 11B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 5, and FIGS. 11C and 11D show the imaging optical system of the aqueous medium in-vehicle auxiliary lens incorporated in Example 5. FIG. FIGS. 11E and 11F are aberration diagrams of the imaging optical system of Comparative Example 5. FIG. 12A is a cross-sectional view showing an imaging optical system and the like incorporating the in-air auxiliary lens of Example 6, and FIG. 12B shows an imaging optical system and the like incorporating the auxiliary lens for aqueous medium of Example 6. It is sectional drawing. 13A and 13B show aberration diagrams of the imaging optical system incorporating the in-air auxiliary lens of Example 6. FIGS. 13C and 13D show the imaging optical system of the aqueous medium in Example 6 incorporating the auxiliary lens. FIGS. 13E and 13F are aberration diagrams of the imaging optical system of Comparative Example 6. FIG.

FIG. 1 is a cross-sectional view showing an imaging apparatus 100 according to an embodiment of the present invention. The imaging apparatus 100 includes a camera module 30 for forming an image signal, and a processing unit 60 that exhibits the function of the imaging apparatus 100 by operating the camera module 30.

The camera module 30 includes a lens unit 40 that incorporates the imaging optical system 10 and a sensor unit 50 that converts a subject image formed by the imaging optical system 10 into an image signal.

The lens unit 40 includes an imaging optical system 10 that is a wide-angle optical system and a lens barrel 41 in which the imaging optical system 10 is incorporated. The total angle of view of the imaging optical system 10 is 180 ° or more. The imaging optical system 10 includes a main lens ML and an auxiliary lens SL. The lens barrel 41 is formed of a resin, a metal, a resin mixed with glass fiber, or the like, and stores and holds a lens or the like therein. When the lens barrel 41 is formed of a metal or a resin in which glass fiber is mixed, the imaging optical system 10 can be stably fixed with less thermal expansion than the resin. The lens barrel 41 has an opening OP through which light from the object side is incident.

The main lens ML and the auxiliary lens SL constituting the imaging optical system 10 are held directly or indirectly on the inner surface side of the lens barrel 41 at the flange portion or the outer peripheral portion of the lenses constituting the imaging optical system 10, and are in the optical axis AX direction. In addition, positioning in a direction perpendicular to the optical axis AX is performed. The lens barrel 41 has a first holder part 41a that holds the main lens ML and a second holder part 41b that holds the auxiliary lens SL. The second holder part 41b has an attachment / detachment mechanism 42 and is attachable / detachable to / from the first holder part 41a, so that the auxiliary lens SL can be replaced as appropriate according to the medium. The connection portions of the respective members such as the first and second holder portions 41a and 41b are appropriately treated with waterproofing and water pressure resistance.

The sensor unit 50 includes an image pickup device (solid-state image pickup device) 51 that photoelectrically converts a subject image formed by the image pickup optical system (wide-angle optical system) 10 and a substrate 52 that supports the image pickup device 51. The image sensor 51 is, for example, a CMOS image sensor. The substrate 52 includes wiring for operating the image sensor 51, peripheral circuits, and the like. The image sensor 51 is positioned and fixed with respect to the optical axis AX by a holder member (not shown). This holder member is fixed in a state of being positioned so as to be fitted to the lens barrel 41 of the lens unit 40.

The imaging element 51 has a photoelectric conversion unit 51a as the imaging surface I, and a signal processing circuit (not shown) is formed around it. Pixels, that is, photoelectric conversion elements are two-dimensionally arranged in the photoelectric conversion unit 51a. Note that the image pickup device 51 is not limited to the above-described CMOS type image sensor, and may include another image pickup device such as a CCD.

In addition, a filter F or the like can be disposed between the lens unit 40 and the sensor unit 50. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of an image sensor, and the like. Although the filter F can be disposed as a separate filter member, the filter F can be imparted to any lens surface constituting the imaging optical system 10 without being disposed separately. For example, in the case of an infrared cut filter, an infrared cut coat may be applied on the surface of one or a plurality of lenses.

The processing unit 60 includes an element driving unit 61, an input unit 62, a storage unit 63, a display unit 64, and a control unit 68. The element driving unit 61 operates the imaging element 51 by receiving supply of a voltage and a clock signal for driving the imaging element 51 from the control unit 68 and outputting them to a circuit associated with the imaging element 51. Further, the element driving unit 61 outputs the YUV and other digital pixel signals from the image sensor 51 as they are or after processing them to the external circuit under the control of the control unit 68. The input unit 62 is a part that receives a user operation or a command from an external device, and the storage unit 63 is a part that stores information necessary for the operation of the imaging device 100, image data acquired by the camera module 30, and the like. The display unit 64 displays information to be presented to the user, captured images, and the like. The control unit 68 comprehensively controls operations of the element driving unit 61, the input unit 62, the storage unit 63, and the like, and can perform various image processing on image data obtained by the camera module 30, for example. .

Although detailed description is omitted, the specific function of the processing unit 60 is appropriately adjusted according to the application of the device in which the imaging apparatus 100 is incorporated. The imaging apparatus 100 can be mounted on an apparatus such as an amphibious camera that is used both in an aqueous medium and in air.

Hereinafter, the imaging optical system (wide-angle optical system) 10 according to the first embodiment will be described with reference to FIG. The imaging optical system 10 illustrated in FIG. 1 has substantially the same configuration as the imaging optical system 10A in which an in-air auxiliary lens SL of Example 1 described later is incorporated.

The imaging optical system (wide-angle optical system) 10 shown in the figure is substantially composed of a main lens ML and an auxiliary lens SL. As already described, the auxiliary lens SL can be attached to and detached from the main lens ML, and can be exchanged according to a medium such as water (or an aqueous medium) or air. In the state of the main lens ML alone, its imaging position is on the object side (or subject side) with respect to the imaging surface I. Although details will be described later, the main lens ML is composed of a plurality of lenses, and the auxiliary lens SL is composed of one negative lens for air and in an aqueous medium, and the main lens ML and the auxiliary lens SL are combined. In this state, desired imaging performance can be obtained. Here, the desired imaging performance means that the astigmatic difference is reduced by performing sufficient correction with the auxiliary lens SL, and the imaging position matches the imaging surface I. The aqueous medium includes liquid substances in addition to seawater and fresh water. When shooting with the same optical system in media with different refractive indexes and dispersions, such as air and aqueous media, the aberrations generated in each medium and the angle of view obtained will differ, and each medium will be sufficient. It becomes difficult to obtain a good optical performance. At this time, by changing the auxiliary lens SL according to the medium, the desired optical performance can be obtained with either medium in the entire optical system. In an aqueous medium, the refractive index is larger than in air, and the angle of view is narrower than in air. In order to prevent this, as described above, the auxiliary lens SL has a negative power to widen the angle of the optical system so as to suppress the angle of view variation between the air and the water.

The main lens ML of the imaging optical system 10 is a main component of the imaging optical system 10, and in order from the object side is a negative first lens L1, a negative second lens L2, a positive third lens L3, and an aperture. It consists essentially of a diaphragm (or diaphragm) ST, a positive fourth lens L4, a positive fifth lens L5, a negative sixth lens L6, and a positive seventh lens L7. By setting the main lens ML as a negative lead, the entrance pupil position can be arranged on the object side, and an optical system with a small front lens diameter can be realized while having a wide angle. Further, by making the first and second lenses L1 and L2 negative, power is divided as compared with the case where only the first lens L1 is negative, and astigmatism and error sensitivity generated in each lens are reduced. Can do. In addition, by setting the third lens L3 to be positive, it is possible to correct distortion aberration, chromatic aberration, spherical aberration, and the like that occur in the negative first and second lenses L1 and L2. In addition, by setting the fourth and fifth lenses L4 and L5 to be positive, the light beam diameter can be converged at a relatively early stage, the optical total length can be shortened, and an increase in spherical aberration can be suppressed. Further, by setting the sixth lens L6 to be negative, distortion generated in the positive lenses in the group behind the aperture stop ST (specifically, the fourth, fifth, and seventh lenses L4, L5, and L7). Aberration, chromatic aberration, spherical aberration, etc. can be corrected. Further, by making the seventh lens L7 a positive lens, the light incident angle on the image sensor can be kept relatively small. With the configuration as described above, the imaging optical system 10 can achieve both wide angle, small size, and high performance.

The object side surface S11 of the first lens L1 has a meniscus shape with the convex surface facing the object side. Thereby, it is possible to reduce the incident angle of the first lens L1 on the object side surface S11 and suppress the generation of astigmatism and the like. Further, the image side S22 of the second lens L2 has a stronger concave surface on the image side than the object side S21. Although the second lens L2 has a negative power as a whole, the second lens L2 has a sufficient negative power by making the concave surface of the image side surface S22 having a small incident angle to the surface of the light ray stronger than the object side surface S21. Astigmatism and the like generated in the second lens L2 can be suppressed to a small level while securing the power. The fifth and sixth lenses L5 and L6 are cemented lenses CS. Thereby, spherical aberration and chromatic aberration can be corrected better than when the fifth and sixth lenses L5 and L6 are single lenses, respectively.

The auxiliary lens SL is attached to the object side from the main lens ML. Thereby, the decentering sensitivity of the auxiliary lens SL can be made lower than the optical system in which the auxiliary lens SL is arranged in the middle of the optical path of the main lens ML, and good optical performance can be maintained. In addition, user operability is improved and the mounting mechanism can be simplified. The object side surface S01 of the auxiliary lens SL has a convex surface facing the object side. As a result, the object side surface S01 of the auxiliary lens SL can capture light rays having a half angle of view of 90 ° or more. Note that the auxiliary lens SL has functions such as waterproof, water pressure resistance, and drop impact resistance in addition to aberration correction in the imaging optical system 10.

The imaging optical system 10 satisfies the following conditional expression (1).
−42 ≦ fA / fM ≦ −17 (1)
Here, the value fA is the focal length of the auxiliary lens SL, and the value fM is the focal length of the main lens ML.

By exceeding the lower limit of the value fA / fM of the conditional expression (1), the power of the auxiliary lens SL is not too weak, so that it is possible to prevent the optical system from being enlarged while ensuring the workability of the auxiliary lens SL. . On the other hand, since the power of the auxiliary lens SL is not too strong by lowering the upper limit of the value fA / fM of the conditional expression (1), the aberration generated in the auxiliary lens SL is reduced or the error sensitivity is reduced. And good optical performance can be obtained in the entire optical system.

In addition to the conditional expression (1), the imaging optical system 10 further satisfies the following conditional expression (2).
−42 ≦ fAA / fM ≦ −28 (2)
Here, the value fAA is the focal length of the in-air auxiliary lens SL, and the value fM is the focal length of the main lens ML.

By exceeding the lower limit of the value fAA / fM of the conditional expression (2), the power of the auxiliary lens SL is not too weak in the air, so that the optical system is enlarged while ensuring the workability of the auxiliary lens SL. Can be prevented. On the other hand, since the power of the auxiliary lens SL is not too strong by falling below the upper limit of the value fAA / fM of the conditional expression (2), the aberration generated in the auxiliary lens SL is reduced or the error sensitivity is reduced. And good optical performance can be obtained in the entire optical system.

In addition to the conditional expression (1), the imaging optical system 10 further satisfies the following conditional expression (3).
−31 ≦ fAW / fM ≦ −17 (3)
Here, the value fAW is the focal length of the auxiliary lens SL for use in an aqueous medium, and the value fM is the focal length of the main lens ML.

By exceeding the lower limit of the value fAW / fM of the conditional expression (3), the power of the auxiliary lens SL is not too weak in the aqueous medium, so that the optical system is enlarged while ensuring the workability of the auxiliary lens SL. Can be prevented. On the other hand, since the power of the auxiliary lens SL is not too strong by lowering the upper limit of the value fAW / fM of the conditional expression (3), the aberration generated in the auxiliary lens SL is reduced or the error sensitivity is reduced. And good optical performance can be obtained in the entire optical system.

In addition to the conditional expression (1), the imaging optical system 10 further satisfies the following conditional expression (4).
−6 ≦ (R2AA + R1AA) / (R2AA−R1AA) ≦ −3 (4)
Here, the value R1AA is the radius of curvature of the object side surface S01 of the in-air auxiliary lens SL, and the value R2AA is the radius of curvature of the image side surface S02 of the in-air auxiliary lens SL.

By exceeding the lower limit of the value (R2AA + R1AA) / (R2AA−R1AA) in the conditional expression (4), there is a certain difference between the curvature radius of the object side surface and the curvature radius of the image side surface. Power is obtained, and the increase in size of the auxiliary lens SL can be prevented, or the processability of the lens can be improved. On the other hand, since the lower limit of the value (R2AA + R1AA) / (R2AA−R1AA) in conditional expression (4) is not reached, there is not too much difference between the curvature radius of the object side surface of the auxiliary lens SL and the curvature radius of the image side surface. Astigmatism generated in the auxiliary lens SL can be reduced.

In addition to the conditional expression (1), the imaging optical system 10 further satisfies the following conditional expression (5).
−9 ≦ (R2AW + R1AW) / (R2AW−R1AW) ≦ −3 (5)
Here, the value R1AW is the radius of curvature of the object side surface S01 of the auxiliary lens SL for aqueous medium, and the value R2AW is the radius of curvature of the image side surface S02 of the auxiliary lens SL for aqueous medium.

Exceeding the lower limit of the value (R2AW + R1AW) / (R2AW−R1AW) in conditional expression (5) creates a certain difference between the curvature radius of the object side surface and the curvature radius of the image side surface. Power is obtained, and the increase in size of the auxiliary lens SL can be prevented, or the processability of the lens can be improved. On the other hand, since the lower limit of the value (R2AW + R1AW) / (R2AW−R1AW) in conditional expression (5) is not reached, there is not too much difference between the curvature radius of the object side surface of the auxiliary lens SL and the curvature radius of the image side surface. Astigmatism generated in the auxiliary lens SL can be reduced.

In addition to the conditional expression (1), the imaging optical system 10 further satisfies the following conditional expression (6).
0.5 ≦ fAW / fAA ≦ 0.9 (6)
Here, the value fAW is the focal length of the auxiliary lens SL for the aqueous medium, and the value fAA is the focal length of the auxiliary lens SL for the air.

By exceeding the lower limit of the value fAW / fAA of the conditional expression (6), the power of the auxiliary lens SL for the aqueous medium does not become too strong compared with the power of the auxiliary lens SL for the air. It is not necessary for the angle of view to be too large compared to the angle of view in air. On the other hand, since the power of the auxiliary lens SL for the aqueous medium does not become too weak compared with the power of the auxiliary lens SL for the air by being below the upper limit of the value fAW / fAA of the conditional expression (6), the aqueous medium It is not necessary for the angle of view in the middle to be too small than the angle of view in the air.

Note that the imaging optical system 10 may further include other optical elements that have substantially no power (for example, a lens, a filter member, and the like).

In the imaging optical system and the like described above, the auxiliary lens SL can be exchanged according to the medium. By thus changing the auxiliary lens SL according to the medium, the entire optical system is refracted like air or an aqueous medium. Desired optical performance can be obtained even in media having different rates and dispersions. Further, by giving negative power to the auxiliary lens SL, the optical system has a wide angle, and it is possible to suppress a change in the angle of view when the auxiliary lens SL for air is switched to the auxiliary lens SL for aqueous medium. . As described above, since the auxiliary lens SL has negative power, the main lens ML alone has a focus position closer to the object side than the imaging surface I so that the imaging surface I is focused in combination with the main lens ML. Further, by using one auxiliary lens SL, the workability when combined with the main lens ML is improved. As described above, the imaging optical system 10 and the imaging apparatus 100 of the present embodiment have a sufficiently wide angle of view of 180 ° or more, such as a fisheye lens, even in an aqueous medium, and the imaging performance changes between the air and the aqueous medium. Is small, and the change in the angle of view is as small as about 5 °, resulting in a small size and high performance.

〔Example〕
Examples of the imaging optical system of the present invention will be described below. Symbols used in each example are as follows.
f: focal length of the entire imaging optical system Fno: F number w: half angle of view ymax: maximum image height TL: total lens length (optical total length) (distance on the optical axis from the lens surface closest to the object side to the imaging surface)
BF: Back focus R: Radius of curvature D: Axial upper surface spacing nd: Refractive index νd of lens material with respect to d-line νd: Abbe number of lens material In each example, a surface with “*” written after each surface number The surface having an aspherical shape, and the aspherical shape is expressed by the following “Equation 1” with the vertex of the surface as the origin, the X axis in the optical axis direction, and the height in the direction perpendicular to the optical axis as h. .

However,
Ai: i-order aspheric coefficient R: reference radius of curvature K: conic constant

Example 1
The overall specifications of the imaging optical system of Example 1 are shown in Table 1 below.
[Table 1]
In the air underwater
f (mm) 1.33 1.03
Fno 2.42 2.42
w (°) 100.0 97.5
ymax (mm) 2.33 2.33
TL (mm) 21.11 27.00
BF (mm) 1.46 1.46

The lens surface data of the imaging optical system of Example 1 is shown in Table 2 below. In Table 1 below, the surface number is represented by “Surf. N”, the aperture stop is represented by “ST”, and the infinity is represented by “INF”. “Image” represents the imaging surface I of the image sensor (or the imaging surface of the imaging optical system). “R1” and “r2” represent the radius of curvature of the auxiliary lens in air or water. “D1” and “d2” represent the axial top surface spacing of the auxiliary lens in air or water. “N1” and “ν1” represent the refractive index and Abbe number for d-line in air or water in the auxiliary lens, respectively.
[Table 2]
Surf.N R (mm) D (mm) nd νd
1 r1 d1 n1 ν1
2 r2 d2
3 10.413 1.00 1.91082 35.3
4 3.326 2.20
5 * -14.343 0.64 1.53048 55.7
6 * 1.899 1.54
7 12.702 1.00 2.00270 19.3
8 -12.538 0.86
9 (ST) INF 0.36
10 13.916 0.85 1.72916 54.7
11 9.485 0.10
12 10.413 1.76 1.72916 54.7
13 3.326 0.01 1.51400 42.8
14 -14.343 0.50 1.92286 20.9
15 1.899 0.58
16 * 12.702 1.93 1.53048 55.7
17 * -12.538 0.43
18 INF 0.61 1.51680 64.2
19 INF 0.63
image

Table 3 below shows the aspheric coefficients of the lens surfaces of the imaging optical system of Example 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed by using E (for example, 2.5E-02).
[Table 3]
5th page
K = 0.000, A4 = 2.6107E-02, A6 = -7.2545E-03, A8 = 1.0482E-03,
A10 = -8.1561E-05, A12 = 2.6580E-06
6th page
K = 0.000, A4 = 3.0016E-02, A6 = 1.3133E-02, A8 = -1.5587E-02,
A10 = 5.4692E-03, A12 = -7.2262E-04
16th page
K = -6.187, A4 = 1.5425E-02, A6 = -1.6216E-03, A8 = 1.7490E-04,
A10 = -8.2247E-06, A12 = 1.9982E-07
17th page
K = 0.611, A4 = 1.0690E-02, A6 = 3.1096E-03, A8 = -6.0656E-04,
A10 = 3.4317E-05, A12 = 7.0148E-08

Table 4 below shows the radius of curvature in air or water in the auxiliary lens of Example 1 shown in Table 2, the distance between the top surfaces of the axes, the refractive index with respect to the d-line, and the Abbe number.
[Table 4]
In the air underwater
r1 13.916 20.614
r2 9.485 15.957
d1 3.00 2.00
d2 3.11 10.00
n1 2.00060 2.00060
ν1 25.5 25.5

In the imaging optical system of Example 1, the screen center imaging position in the case of the main lens alone is shown in Table 5 below. In Table 5, the imaging position when an auxiliary lens is incorporated in the imaging optical system is used as the origin (the same applies to the following examples).
[Table 5]
Image center position of the main lens alone (mm): -0.04

Table 6 below shows the astigmatic difference at the maximum angle of view of the imaging optical systems of Example 1 and Comparative Example 1. Note that Comparative Example 1 is an imaging optical system including only the main lens ML (the same applies to the following comparative examples).
[Table 6]
In the air with an auxiliary lens (Example 1): 0.009
Underwater with auxiliary lens (Example 1): 0.003
Only in air and main lens (Comparative Example 1): 0.104
As shown in Table 6, it can be seen that good optical performance can be obtained by performing aberration correction by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

2A and 2B are cross-sectional views of the imaging optical system 10A and the like of the first embodiment. Specifically, FIG. 2A is a cross-sectional view of the imaging optical system 10A incorporating the in-air auxiliary lens SL, and FIG. 2B is a cross-sectional view of the imaging optical system 10A incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10A substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like. Reference numeral I denotes an imaging surface that is a projection surface of the imaging element 51. The symbols F and I are the same in the following embodiments.

FIGS. 3A and 3B show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10A in which the in-air auxiliary lens SL of Example 1 is incorporated. 3C and 3D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10A in which the underwater auxiliary lens SL of Example 1 is incorporated. 3E and 3F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 1. FIG. In the spherical aberration diagram, “F2.4” represents an F number. In the above astigmatism diagram, the solid line represents the sagittal image plane, and the dotted line represents the meridional image plane.

(Example 2)
Table 7 below shows the overall specifications of the imaging optical system of Example 2.
[Table 7]
In the air underwater
f (mm) 1.34 1.03
Fno 2.42 2.42
w (°) 100.0 97.5
ymax (mm) 2.33 2.33
TL (mm) 20.81 25.23
BF (mm) 1.41 1.41

The data of the lens surface of the imaging optical system of Example 2 is shown in Table 8 below.
[Table 8]
Surf.N R (mm) D (mm) nd νd
1 r1 d1 n1 ν1
2 r2 d2
3 11.224 1.00 1.91082 35.3
4 3.273 2.11
5 * -29.167 0.65 1.53048 55.7
6 * 1.887 1.46
7 24.765 1.39 2.00270 19.3
8 -9.025 0.86
9 (ST) INF 0.30
10 22.240 0.83 1.72916 54.7
11 -3.756 0.10
12 6.083 1.69 1.72916 54.7
13 -2.457 0.01 1.51400 42.8
14 -2.457 0.50 1.92286 20.9
15 5.719 0.66
16 * 3.077 1.82 1.53048 55.7
17 * -4.955 0.40
18 INF 0.61 1.51680 64.2
19 INF 0.61
image

Table 9 below shows the aspheric coefficients of the lens surfaces of the imaging optical system of Example 2.
[Table 9]
5th page
K = 0.000, A4 = 2.4520E-02, A6 = -7.2725E-03, A8 = 1.0574E-03,
A10 = 1.0574E-03, A12 = 1.0574E-03
6th page
K = 0.000, A4 = 3.2707E-02, A6 = 7.0369E-03, A8 = -1.1818E-02,
A10 = 4.2892E-03, A12 = -6.1056E-04
16th page
K = -5.928, A4 = 1.5528E-02, A6 = -1.5478E-03, A8 = 1.8921E-04,
A10 = -8.9726E-06, A12 = 3.4445E-07
17th page
K = 0.183, A4 = 1.2103E-02, A6 = 2.8716E-03, A8 = -5.7878E-04,
A10 = 4.7290E-05, A12 = -1.1043E-06

Table 10 below shows the radius of curvature in air or water in the auxiliary lens of Example 2 shown in Table 8, the axial top surface spacing, the refractive index with respect to the d-line, and the Abbe number.
[Table 10]
In the air underwater
r1 14.073 17.376
r2 9.748 13.565
d1 3.00 2.00
d2 2.81 8.23
n1 1.84666 1.84666
ν1 23.8 23.8

In the imaging optical system of Example 2, the screen center imaging position in the case of the main lens alone is shown in Table 11 below.
[Table 11]
Image center position of the main lens alone (mm): -0.03

Table 12 below shows the astigmatic difference at the maximum angle of view of the imaging optical systems of Example 2 and Comparative Example 2.
[Table 12]
In air with auxiliary lens (Example 2): 0.008
Underwater with auxiliary lens (Example 2): -0.004
Only in air and main lens (Comparative Example 2): 0.086
As shown in Table 12, it can be seen that good optical performance can be obtained by correcting the aberration by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

4A and 4B are cross-sectional views of the imaging optical system 10B and the like of the second embodiment. Specifically, FIG. 4A is a cross-sectional view of the imaging optical system 10B incorporating the in-air auxiliary lens SL, and FIG. 4B is a cross-sectional view of the imaging optical system 10B incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10B substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like.

FIGS. 5A and 5B are aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10B incorporating the in-air auxiliary lens SL of Example 2. FIG. FIGS. 5C and 5D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10B in which the underwater auxiliary lens SL of Example 2 is incorporated. 5E and 5F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 2. FIG.

(Example 3)
Table 13 below shows overall specifications of the imaging optical system of Example 3.
[Table 13]
In the air underwater
f (mm) 1.33 1.07
Fno 2.43 2.43
w (°) 100.0 97.5
ymax (mm) 2.33 2.33
TL (mm) 21.11 27.00
BF (mm) 1.41 1.41

Data of the lens surface of the imaging optical system of Example 3 is shown in Table 14 below.
[Table 14]
Surf.N R (mm) D (mm) nd νd
1 r1 d1 n1 ν1
2 r2 d2
3 10.700 1.00 1.91082 35.3
4 3.388 2.21
5 * -23.656 0.61 1.53048 55.7
6 * 1.979 1.71
7 17.191 1.37 2.00270 19.3
8 -12.377 1.07
9 (ST) INF 0.30
10 14.419 0.84 1.72916 54.7
11 -4.315 0.12
12 6.400 1.80 1.72916 54.7
13 -2.529 0.01 1.51400 42.8
14 -2.529 0.50 1.92286 20.9
15 6.379 0.66
16 * 3.030 1.87 1.53048 55.7
17 * -6.493 0.40
18 INF 0.61 1.51680 64.2
19 INF 0.61
image

Table 15 below shows the aspheric coefficients of the imaging optical system lens surfaces of Example 3.
[Table 15]
5th page
K = 0.000, A4 = 2.4548E-02, A6 = -7.2698E-03, A8 = 1.0701E-03,
A10 = -8.3082E-05, A12 = 2.6679E-06
6th page
K = 0.000, A4 = 2.7299E-02, A6 = 8.3567E-03, A8 = -1.2622E-02,
A10 = 4.3432E-03, A12 = -5.5821E-04
16th page
K = -5.517, A4 = 1.5456E-02, A6 = -1.5504E-03, A8 = 1.8761E-04,
A10 = -9.3742E-06, A12 = 2.2435E-07
17th page
K = 1.415, A4 = 1.0229E-02, A6 = 2.6996E-03, A8 = -5.6199E-04,
A10 = 5.1167E-05, A12 = -2.2542E-06

Table 16 below shows the radius of curvature in air or water, the distance between the upper surfaces of the axes, the refractive index with respect to the d-line, and the Abbe number in the auxiliary lens of Example 3 shown in Table 14.
[Table 16]
In the air underwater
r1 14.297 29.424
r2 9.630 17.772
d1 3.00 2.00
d2 3.15 7.55
n1 1.90366 1.83400
ν1 31.3 37.4

In the imaging optical system of Example 3, the screen center imaging position in the case of the main lens alone is shown in Table 17 below.
[Table 17]
Image center position of the main lens alone (mm): -0.04

Table 18 below shows the astigmatic difference at the maximum angle of view of the imaging optical systems of Example 3 and Comparative Example 3.
[Table 18]
In air / with auxiliary lens (Example 3): 0.007
Underwater with auxiliary lens (Example 3): -0.003
Only in air and main lens (Comparative Example 3): 0.100
As shown in Table 18, it can be seen that good optical performance can be obtained by performing aberration correction by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

6A and 6B are cross-sectional views of the imaging optical system 10C and the like of the third embodiment. Specifically, FIG. 6A is a cross-sectional view of the imaging optical system 10C incorporating the in-air auxiliary lens SL, and FIG. 6B is a cross-sectional view of the imaging optical system 10C incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10C substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like.

7A and 7B show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10C incorporating the in-air auxiliary lens SL of Example 3. FIG. 7C and 7D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10C in which the underwater auxiliary lens SL of Example 3 is incorporated. 7E and 7F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 3.

Example 4
The overall specifications of the imaging optical system of Example 4 are shown in Table 19 below.
[Table 19]
In the air underwater
f (mm) 1.33 1.07
Fno 2.43 2.43
w (°) 100.0 97.5
ymax (mm) 2.33 2.33
TL (mm) 21.79 26.14
BF (mm) 1.41 1.41

Data of the lens surface of the imaging optical system of Example 4 is shown in Table 20 below.
[Table 20]
Surf.N R (mm) D (mm) nd νd
1 r1 d1 n1 ν1
2 r2 d2
3 10.980 1.12 1.91082 35.3
4 3.398 2.22
5 * -23.041 0.61 1.53048 55.7
6 * 1.919 1.61
7 24.575 1.32 2.00270 19.3
8 -10.687 0.95
9 (ST) INF 0.35
10 19.768 0.87 1.72916 54.7
11 -4.004 0.14
12 5.908 1.83 1.72916 54.7
13 -2.616 0.01 1.51400 42.8
14 -2.616 0.50 1.92286 20.9
15 5.762 0.59
16 * 3.034 1.90 1.53048 55.7
17 * -5.281 0.40
18 INF 0.61 1.51680 64.2
19 INF 0.61
image

Table 21 below shows the aspheric coefficients of the lens surfaces of the imaging optical system of Example 4.
[Table 21]
5th page
K = 0.000, A4 = 2.4763E-02, A6 = -7.2354E-03, A8 = 1.0571E-03,
A10 = -8.2628E-05, A12 = 2.7074E-06
6th page
K = 0.000, A4 = 2.9158E-02, A6 = 9.8126E-03, A8 = -1.3791E-02,
A10 = 4.8809E-03, A12 = -6.6456E-04
16th page
K = -5.841, A4 = 1.5554E-02, A6 = -1.5390E-03, A8 = 1.8332E-04,
A10 = -9.3128E-06, A12 = 3.5838E-07
17th page
K = 0.665, A4 = 1.0476E-02, A6 = 3.1216E-03, A8 = -5.7633E-04,
A10 = 4.0517E-05, A12 = -7.8815E-07

Table 22 below shows the curvature radii in air or water in the auxiliary lens of Example 4 shown in Table 20, the axial top surface spacing, the refractive index with respect to the d-line, and the Abbe number.
[Table 22]
In the air underwater
r1 14.213 32.344
r2 9.801 20.620
d1 3.00 2.00
d2 3.16 8.51
n1 1.80610 1.83481
ν1 33.3 42.7

In the imaging optical system of Example 4, the screen center imaging position in the case of the main lens alone is shown in Table 23 below.
[Table 23]
Image center position of the main lens alone (mm): -0.03

Table 24 below shows the astigmatic difference at the maximum angle of view of the imaging optical systems of Example 4 and Comparative Example 4.
[Table 24]
In air / with auxiliary lens (Example 4): 0.001
Underwater with auxiliary lens (Example 4): -0.002
In air only, main lens (Comparative Example 4): 0.079
As shown in Table 24, it can be seen that good optical performance can be obtained by performing aberration correction by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

8A and 8B are sectional views of the imaging optical system 10D and the like of the fourth embodiment. Specifically, FIG. 8A is a cross-sectional view of the imaging optical system 10D incorporating the in-air auxiliary lens SL, and FIG. 8B is a cross-sectional view of the imaging optical system 10D incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10D substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like.

FIGS. 9A and 9B show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10D in which the in-air auxiliary lens SL of Example 4 is incorporated. 9C and 9D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10D in which the underwater auxiliary lens SL of Example 4 is incorporated. 9E and 9F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 4.

(Example 5)
Table 25 below shows the overall specifications of the image pickup optical system of Example 5.
[Table 25]
In the air underwater
f (mm) 1.34 1.06
Fno 2.43 2.43
w (°) 100.0 97.5
ymax (mm) 2.33 2.34
TL (mm) 22.58 24.17
BF (mm) 1.60 1.60

Data on the lens surface of the imaging optical system of Example 5 is shown in Table 26 below.
[Table 26]
Surf.N R (mm) D (mm) nd νd
1 r1 d1 n1 ν1
2 r2 d2
3 11.480 1.00 1.91082 35.3
4 3.285 2.08
5 * -153.424 0.50 1.53048 55.7
6 * 2.176 1.53
7 20.890 2.36 2.00270 19.3
8 -9.481 1.20
9 (ST) INF 0.30
10 24.731 0.71 1.72916 54.7
11 -4.573 0.10
12 4.757 1.32 1.72916 54.7
13 -3.520 0.01 1.51400 42.8
14 -3.520 0.50 1.92286 20.9
15 4.500 0.83
16 * 3.300 1.75 1.53048 55.7
17 * -6.310 0.49
18 INF 0.61 1.51680 64.2
19 INF 0.70
image

Table 27 below shows the aspheric coefficients of the lens surfaces of the imaging optical system of Example 5.
[Table 27]
5th page
K = 0.000, A4 = 2.2915E-02, A6 = -7.2802E-03, A8 = 1.0618E-03,
A10 = -8.0622E-05, A12 = 2.5509E-06
6th page
K = 0.000, A4 = 2.6707E-02, A6 = -7.3507E-04, A8 = -4.7759E-03,
A10 = 1.5042E-03, A12 = -1.6586E-04
16th page
K = -5.491, A4 = 1.3592E-02, A6 = -1.5996E-03, A8 = 1.7021E-04,
A10 = 2.3834E-06, A12 = -1.7387E-06
17th page
K = 2.506, A4 = 1.1759E-02, A6 = 1.2336E-03, A8 = -5.8142E-04,
A10 = 1.0844E-04, A12 = -8.4810E-06

Table 28 below shows the radius of curvature in air or water in the auxiliary lens of Example 5 shown in Table 26, the axial top surface spacing, the refractive index with respect to the d-line, and the Abbe number.
[Table 28]
In the air underwater
r1 14.380 25.700
r2 9.272 13.755
d1 3.00 2.00
d2 3.58 6.17
n1 1.90366 1.83400
ν1 31.3 37.4

In the imaging optical system of Example 5, the center-of-screen imaging position in the case of the main lens alone is shown in Table 29 below.
[Table 29]
Image center position of the main lens alone (mm): -0.05

Table 30 below shows the astigmatic difference at the maximum field angle of the imaging optical systems of Example 5 and Comparative Example 5.
[Table 30]
In air with auxiliary lens (Example 5): 0.016
Underwater with auxiliary lens (Example 5): -0.018
In air only main lens (Comparative Example 5): 0.130
As shown in Table 30, it can be seen that good optical performance can be obtained by performing aberration correction by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

10A and 10B are cross-sectional views of the imaging optical system 10E and the like of the fifth embodiment. Specifically, FIG. 10A is a cross-sectional view of the imaging optical system 10E incorporating the in-air auxiliary lens SL, and FIG. 10B is a cross-sectional view of the imaging optical system 10E incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10E substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like.

11A and 11B show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10E incorporating the in-air auxiliary lens SL of Example 5. FIG. 11C and 11D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10E in which the underwater auxiliary lens SL of Example 5 is incorporated. 11E and 11F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 5.

(Example 6)
The overall specifications of the imaging optical system of Example 6 are shown in Table 31 below.
[Table 31]
In the air underwater
f (mm) 1.34 1.07
Fno 2.43 2.43
w (°) 100.0 97.5
ymax (mm) 2.34 2.33
TL (mm) 21.84 24.85
BF (mm) 1.45 1.45

Data of the lens surface of the imaging optical system of Example 6 is shown in Table 32 below.
[Table 32]
Surf.N R (mm) D (mm) nd νd
1 * r1 d1 n1 ν1
2 * r2 d2
3 11.481 1.01 1.91082 35.3
4 3.281 2.12
5 * -59.464 0.51 1.53048 55.7
6 * 2.194 1.33
7 -266.734 2.09 2.00270 19.3
8 -7.332 1.49
9 (ST) INF 0.30
10 17.929 0.76 1.72916 54.7
11 -4.609 0.22
12 4.845 1.38 1.72916 54.7
13 -3.699 0.01 1.51400 42.8
14 -3.699 0.50 1.92286 20.9
15 4.480 0.77
16 * 3.148 1.85 1.53048 55.7
17 * -5.744 0.42
18 INF 0.61 1.51680 64.2
19 INF 0.63
Image

Table 33 below shows the aspheric coefficients of the lens surfaces of the imaging optical system of Example 6.
[Table 33]
First side (in air)
K = 0, A4 = 1.81E-05, A6 = -1.90E-07, A8 = 6.26E-10,
A10 = -8.37E-13, A12 = 0
Second side (in air)
K = 0, A4 = 1.16E-05, A6 = 3.54E-07, A8 = -2.29E-08,
A10 = 3.68E-11, A12 = 0
First side (underwater)
K = 0, A4 = -8.1055E-08, A6 = -1.2121E-08, A8 = -2.0167E-12,
A10 = 0, A12 = 0
Second side (underwater)
K = 0, A4 = -2.9932E-06, A6 = -2.9891E-07, A8 = 6.3524E-09,
A10 = -1.9722E-11, A12 = 0
5th page
K = 0.000, A4 = 2.4488E-02, A6 = -7.6446E-03, A8 = 1.0547E-03,
A10 = -7.5158E-05, A12 = 2.2437E-06
6th page
K = 0.000, A4 = 3.0291E-02, A6 = -6.6315E-04, A8 = -5.1987E-03,
A10 = 1.5622E-03, A12 = -1.6485E-04
16th page
K = -5.327, A4 = 1.5322E-02, A6 = -1.7361E-03, A8 = 2.1605E-04,
A10 = -7.5695E-06, A12 = -3.2531E-07
17th page
K = 0.651, A4 = 1.4307E-02, A6 = 1.6541E-03, A8 = -6.7327E-04,
A10 = 1.1215E-04, A12 = -7.6886E-06

Table 34 below shows the curvature radius in air or water in the auxiliary lens of Example 6 shown in Table 32, the distance between the top surfaces of the axes, the refractive index with respect to the d-line, and the Abbe number.
[Table 34]
In the air underwater
r1 20.048 25.799
r2 10.791 15.992
d1 4.34 1.40
d2 1.50 7.45
n1 1.63000 1.60000
ν1 23.9 31.1

In the imaging optical system of Example 6, the screen center imaging position in the case of a single main lens is shown in Table 35 below.
[Table 35]
Image center position of the main lens alone (mm): -0.04

Table 36 below shows the astigmatic difference at the maximum field angle of the imaging optical systems of Example 6 and Comparative Example 6.
[Table 36]
In air with auxiliary lens (Example 6): 0.012
Underwater with auxiliary lens (Example 6): 0.027
In air only main lens (Comparative Example 6): 0.122
As shown in Table 36, it can be seen that good optical performance can be obtained by performing aberration correction by incorporating the auxiliary lens SL in the imaging optical system 10. On the other hand, in the case of only the main lens ML, it can be seen that the aberration correction is insufficient.

12A and 12B are cross-sectional views of the imaging optical system 10F and the like of the sixth embodiment. Specifically, FIG. 12A is a cross-sectional view of the imaging optical system 10F incorporating the in-air auxiliary lens SL, and FIG. 12B is a cross-sectional view of the imaging optical system 10F incorporating the underwater auxiliary lens SL. is there. The imaging optical system 10F substantially includes a main lens ML and an in-air or underwater auxiliary lens SL. The main lens ML includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, an aperture stop (or stop) ST, a positive fourth lens L4, and a positive fifth lens. The lens substantially includes a lens L5, a negative sixth lens L6, and a positive seventh lens L7. The auxiliary lens SL substantially consists of one negative lens. A filter F having an appropriate thickness is disposed between the seventh lens L7 of the main lens ML and the image sensor 51. The filter F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the image sensor 51, and the like.

FIGS. 13A and 13B are aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10F incorporating the in-air auxiliary lens SL of Example 6. FIG. 13C and 13D show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system 10F in which the underwater auxiliary lens SL of Example 6 is incorporated. 13E and 13F show aberration diagrams (spherical aberration and astigmatism) of the imaging optical system including only the main lens ML of Comparative Example 6.

Table 37 below summarizes the values of Examples 1 to 6 corresponding to the conditional expressions (1) to (6) for reference.
[Table 37]

As described above, in the actual lens measurement scene, the radius of curvature of the lens surface referred to in the present application is a shape measurement value in the vicinity of the center of the lens (specifically, a central region within 10% of the lens outer diameter). This is the approximate radius of curvature when fitting with the least squares method. For example, when a secondary aspheric coefficient is used, the reference radius of curvature of the aspheric definition formula also includes a curvature radius that takes into account the secondary aspheric coefficient.

As described above, the imaging optical system 10 and the like have been described according to the embodiment. However, the imaging optical system 10 according to the present invention is not limited to the above-described embodiment or example, and various modifications can be made.

In the above-described embodiment, the main lens ML and the auxiliary lens SL are fixed to the lens barrel 41. However, the main lens ML and the auxiliary lens SL can be appropriately moved for focusing or the like.

In the above-described embodiment, the imaging optical system 10 including one main lens ML and one auxiliary lens SL has been described. However, a combination of one main lens ML and one auxiliary lens SL is combined into one unit. As an example, an imaging optical system in which two units are combined to face each other on the imaging element 51 side may be used. In this case, the entire 360 ° circumference can be photographed.

Claims (16)

1. Consisting essentially of a main lens and an auxiliary lens for aqueous media or air,
   In the state of the main lens alone, the imaging position is on the object side of the imaging surface,
   The main lens is composed of a plurality of lenses,
   The auxiliary lens consists of one negative lens,
   Desired imaging performance is obtained in a state where the main lens and the auxiliary lens are combined,
   An imaging optical system that satisfies the following conditional expression.
   −42 ≦ fA / fM ≦ −17 (1)
   here,
   fA: focal length of the auxiliary lens fM: focal length of the main lens
2. The main lens includes a negative first lens, a negative second lens, a positive third lens, a diaphragm, a positive fourth lens, a positive fifth lens, a negative sixth lens, and a positive lens in order from the object side. The imaging optical system according to claim 1, substantially consisting of:
3. The imaging optical system according to any one of claims 1 and 2, wherein the auxiliary lens for either the aqueous medium or in the air is detachable from the main lens.
4. The imaging optical system according to any one of claims 1 to 3, wherein the auxiliary lens is attached to the object side from the main lens.
5. The imaging optical system according to any one of claims 1 to 4, which satisfies the following conditional expression.
   −42 ≦ fAA / fM ≦ −28 (2)
   here,
   fAA: focal length of the auxiliary lens for air fM: focal length of the main lens
6. The imaging optical system according to any one of claims 1 to 5, which satisfies the following conditional expression.
   −31 ≦ fAW / fM ≦ −17 (3)
   here,
   fAW: focal length of the auxiliary lens in an aqueous medium fM: focal length of the main lens
7. The imaging optical system according to any one of claims 1 to 6, wherein the object side surface of the auxiliary lens has a convex surface facing the object side.
8. The imaging optical system according to any one of claims 1 to 7, which satisfies the following conditional expression.
   −6 ≦ (R2AA + R1AA) / (R2AA−R1AA) ≦ −3 (4)
   here,
   R1AA: radius of curvature of the object side surface of the auxiliary lens for air R2AA: radius of curvature of the image side surface of the auxiliary lens for air
9. The imaging optical system according to any one of claims 1 to 8, which satisfies the following conditional expression.
   −9 ≦ (R2AW + R1AW) / (R2AW−R1AW) ≦ −3 (5)
   here,
   R1AW: radius of curvature of the object side surface of the auxiliary lens in the aqueous medium R2AW: radius of curvature of the image side surface of the auxiliary lens in the aqueous medium
10. The imaging optical system according to any one of claims 1 to 9, which satisfies the following conditional expression.
    0.5 ≦ fAW / fAA ≦ 0.9 (6)
    here,
    fAW: focal length of the auxiliary lens for aqueous medium fAA: focal length of the auxiliary lens for air
11. The main lens is substantially composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, and a seventh lens in order from the object side.
    The imaging optical system according to any one of claims 1 to 10, wherein the object side surface of the first lens has a meniscus shape with a convex surface facing the object side.
12. The main lens is substantially composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, and a seventh lens in order from the object side.
    The imaging optical system according to any one of claims 1 to 11, wherein the image side surface of the second lens has a concave surface that is stronger on the image side than the object side surface of the second lens.
13. The main lens is substantially composed of a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a sixth lens, and a seventh lens in order from the object side.
    The imaging optical system according to any one of claims 1 to 12, wherein the fifth and sixth lenses are cemented lenses.
14. The imaging optical system according to any one of claims 1 to 13, which is used both in air and in an aqueous medium.
15. The imaging optical system according to any one of claims 1 to 14,
    A lens barrel holding the imaging optical system;
    A lens unit.
16. The imaging optical system according to any one of claims 1 to 14,
    An image sensor for detecting an image obtained from the imaging optical system;
    An imaging apparatus comprising:

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