Large field of view image plane telecentric underwater visual docking imaging optical system

Abstract

The application discloses a kind of big visual field image side telecentric underwater visual docking imaging optical systems, the optical system includes in sequence: spherical cover window, front group lens, variable diaphragm, rear group lens and filter;Front group lens includes in sequence: front group first lens, front group second lens, front group third lens, front group fourth lens;Rear group lens includes in sequence: rear group first lens, rear group second lens, rear group third lens, rear group fourth lens;Variable diaphragm is located between front group fourth lens and rear group first lens;Object side imaging light beam is imaged on strobe camera target surface in sequence through spherical cover window, front group lens, variable diaphragm, rear group lens and filter.The application has big visual field, short focal length, variable F number and image side telecentricity and the like characteristics, clear imaging is realized by rear group focusing and variable F number, can be used for the close-range underwater visual docking recovery of cross-domain aircraft, ensure that imaging is clear during docking process, and the position solution error caused by image side focusing can be eliminated.

Description

TECHNICAL FIELD

[0001] The present application relates to underwater optical systems, in particular to a large field of view image-side telecentric underwater visual docking imaging optical system. BACKGROUND

[0002] The cross-domain aircraft is an important equipment for underwater and water surface detection, and the underwater docking recovery of the aircraft is an important function thereof, the process comprising two stages of remote underwater acoustic or inertial guidance and close-range underwater visual docking, in the close-range underwater visual docking stage, the underwater photoelectric imaging unit is mainly used for imaging the cooperative target array, extracting the target point array coordinates, and calculating the distance and three-dimensional attitude of the cross-domain aircraft relative to the recovery platform according to the point array mode. Research shows that the blue-green laser is in the transmission 'window' under water, and has strong penetration ability to seawater, so the wavelength of the LED lamp of about 530nm is generally selected as the underwater cooperative target, and the imaging wavelength band of the underwater visual docking imaging lens needs to be matched. The imaging system is used for visual positioning calculation, and needs to have the characteristics of large field of view, large depth of field, fast focusing, image-side telecentricity and the like, so as to ensure that the imaging is clear during the whole docking process, and the calculation error caused by image-side focusing is eliminated.

[0003] Therefore, it is urgent to provide a large field of view image-side telecentric underwater visual docking imaging optical system, which is used for visual positioning calculation, and needs to have the characteristics of large field of view, large depth of field, fast focusing, image-side telecentricity and the like, so as to ensure that the imaging is clear during the whole docking process, and the calculation error caused by image-side focusing is eliminated. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a large field of view image-side telecentric underwater visual docking imaging optical system for the close-range underwater visual docking recovery of the cross-domain aircraft, which is matched with the cooperative target. The imaging system is used for visual positioning calculation, and needs to have the characteristics of large field of view, large depth of field, fast focusing, image-side telecentricity and the like, so as to ensure that the imaging is clear during the whole docking process, and the calculation error caused by image-side focusing is eliminated.

[0005] The technical solution adopted by the present application to solve the technical problem is:

[0006] The present application provides a large field of view image-side telecentric underwater visual docking imaging optical system, which comprises a ball cover window, a front group lens, a variable diaphragm, a rear group lens and a filter in sequence.

[0007] The front group lens comprises a front group first lens, a front group second lens, a front group third lens and a front group fourth lens in sequence, and the rear group lens comprises a rear group first lens, a rear group second lens, a rear group third lens and a rear group fourth lens in sequence, and the variable diaphragm is located between the front group fourth lens and the rear group first lens.

[0008] The object-side imaging beam passes through the dome window, front lens group, variable aperture, rear lens group and filter in sequence and forms an image on the target surface of the gated camera.

[0009] Furthermore, the spherical cover window of the present invention is a tempered concentric spherical cover window, which is used to isolate water and the lens, with the left medium being water and the right medium being air.

[0010] Furthermore, the four lenses of the front lens group of the present invention adopt a "2+2" structure, wherein: the first lens and the second lens of the front lens group are negative lenses made of high refractive index materials, and the third lens and the fourth lens of the front lens group are positive lenses made of low dispersion materials.

[0011] Furthermore, the rear lens group of the present invention has a total of four lenses, the first lens of the rear group is a double cemented negative lens, the second lens of the rear group is a plano-convex positive lens, the third lens of the rear group is a biconvex positive lens, and the fourth lens of the rear group is a double cemented positive lens.

[0012] Furthermore, the working wavelength band of the optical system of the present invention is 505-545 nm, and the filter is used to filter out light in wavelength bands outside the working wavelength band.

[0013] Furthermore, the focal length of the lens of the optical system of the present invention is 8.6 mm, the minimum F number is 2.5, the maximum field of view is 80°, and the variable F number is achieved by adjusting the size of the variable aperture.

[0014] Furthermore, the optical system of the present invention is an image-space telecentric system, and the telecentricity is better than 0.1°.

[0015] Furthermore, the optical system of the present invention performs focusing through the four lenses of the rear lens group to achieve underwater imaging from 0.4m to infinity.

[0016] Furthermore, the structural parameters of the optical system of the present invention are specifically as follows:

[0017] The dome window has a curvature radius of 75° and a thickness of 10° on surface S1; a curvature radius of 65° and a thickness of 17° on surface S2;

[0018] The first lens element in the front group has a curvature radius of 86.5mm on surface S3 and a thickness of 8mm. The curvature radius of surface S4 is 24.62mm and the thickness is 8.4mm.

[0019] The second lens element in the front group has a curvature radius of 1900 on surface S5 and a thickness of 3.6; a curvature radius of 42.53 on surface S6 and a thickness of 22.4.

[0020] The third lens element in the front group has a curvature radius of -95.35 on surface S7 and a thickness of 5 mm; a curvature radius of -41.6 on surface S8 and a thickness of 12.35 mm.

[0021] The fourth lens element in the front group has a curvature radius of 66.2 mm on surface S9 and a thickness of 7 mm. The curvature radius of surface S10 is -66.2 mm and the thickness is 23 mm.

[0022] The curvature radius of the variable aperture is ∞ and the thickness is 9;

[0023] The first lens element in the rear group has a curvature radius of -10.2mm on surface S11 and a thickness of 2.5mm. The curvature radius of surface S12 is -85.45mm and the thickness is 5.5mm. The curvature radius of surface S13 is -14.63mm and the thickness is 0.35mm.

[0024] The second lens element in the rear group has a curvature radius of 2405 on surface S14 and a thickness of 5.2. The curvature radius of surface S15 is -18.65 and the thickness is 1.4.

[0025] The third lens element in the rear group has a curvature radius of 142.55 mm on surface S16 and a thickness of 8.2 mm. The curvature radius of surface S17 is -54.52 mm and the thickness is 0.4 mm.

[0026] The fourth lens element in the rear group has a curvature radius of 43.52mm on surface S18 and a thickness of 8.2mm. The curvature radius of surface S19 is -24.62mm and a thickness of 3mm. The curvature radius of surface S20 is -421.24mm and a thickness of 5.5mm.

[0027] The filter has a curvature radius of ∞ and a thickness of 2 on surface S21; a curvature radius of ∞ and a thickness of 10 on surface S22;

[0028] The unit is mm.

[0029] Furthermore, the adjustment method of the optical system of the present invention includes:

[0030] Utilizing a short focal length and large F-number system, it has a large depth of field when focusing on close objects. From a long distance of 50m to a close distance of 0.4m, the rear lens focusing group is used to focus on 50m targets and 0.8m targets, achieving clear imaging within the range of 50m to 0.4m, and realizing rapid and clear focusing on cooperative targets.

[0031] The outstanding features and significant beneficial effects of the present invention are: the imaging optical system of the present invention has the characteristics of a large field of view, short focal length, variable F-number, and image-space telecentricity. Through rear-group focusing and variable F-number, the system can achieve clear imaging within a range of 50m to 0.4m. It can be used for close-range underwater visual docking and recovery of cross-domain aircraft, ensuring clear imaging throughout the docking process. The image-space telecentric optical path eliminates position resolution errors caused by image-space focusing. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0033] Figure 1 is a schematic diagram of an optical system of the present invention;

[0034] In the figure, 1-protective window, 2-first lens of the front group, 3-second lens of the front group, 4-third lens of the front group, 5-fourth lens of the front group, 6-iris diaphragm, 7-first lens of the rear group, 8-second lens of the rear group, 9-third lens of the rear group, 10-fourth lens of the rear group, 11-filter;

[0035] Figure 2 Schematic diagram of the lens and lens surface of the present invention;

[0036] Figure 3 A two-dimensional diagram of the optical system of the present invention;

[0037] Figure 4 This is the MTF diagram of the optical system of the present invention at 80lp / mm.

[0038] Figure 5 This is the MTF diagram of the optical system of the present invention when it is focused at a close distance of 0.4m and at 80lp / mm. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] Example 1

[0041] like Figure 1 As shown, the embodiment of the present invention has a large field of view, image-side telecentric underwater visual docking imaging optical system, with a focal length of 8.6mm, a minimum F number of 2.5, and a field of view of up to 80°. The embodiment of the present invention is an image-side telecentric system with a telecentricity better than 0.1°. The entire system comprises eight lenses, a ball cover window 1, a variable aperture 6, and a filter 11, and includes the ball cover window 1, a front group, a rear group, and a filter 11 in sequence, wherein: the front group includes a front group first lens 2, a front group second lens 3, a front group third lens 4, and a front group fourth lens 5, a total of four lenses; the rear group includes a rear group first lens 7, a rear group second lens 8, a rear group third lens 9, and a rear group fourth lens 10, a total of four lenses; and the last piece is a filter 11.

[0042] The variable aperture 6 is located between the fourth lens element 5 of the front group and the first lens element 7 of the rear group. The F number can be changed by adjusting the size of the variable aperture 6.

[0043] The dome window 1 used in the embodiment of the present invention is a tempered concentric dome window that can withstand 3 MPa hydrostatic pressure and is used to isolate water and the lens. The medium on the left side is water, and the medium on the right side is air.

[0044] In this embodiment of the present invention, the first and fourth rear lens groups (7 and 10) are cemented lenses, used to correct system aberrations. This embodiment utilizes these four rear lens groups to achieve a telecentric image path and focus adjustment. This embodiment operates within the 505-545nm wavelength range, with the final lens element (11) being a filter that filters out light from other wavelengths.

[0045] The embodiment of the present invention utilizes a short focal length and large F-number system to achieve a large depth of field when focusing on close objects. From a long distance of 50m to a close distance of 0.4m, the focusing group only needs to focus on the 50m target and the 0.8m target to achieve clear imaging within the range of 50m to 0.4m. Using this focusing strategy, rapid and clear focusing of cooperative targets can be achieved.

[0046] Figure 2 Schematic diagram of the lens and lens surface of the present invention. Furthermore, the optical lens materials are all common visible light glass materials with excellent performance and abundant stock.

[0047] The front group of four lenses adopts a "2+2" structure, with the first two lenses made of high-refractive-index negative materials, and the second two lenses made of low-dispersion positive materials. The rear group of four lenses consists of the first lens being a doublet-cemented negative lens, the second lens being a plano-convex positive lens, the third lens being a biconvex positive lens, and the fourth lens being a doublet-cemented positive lens.

[0048] Example 2

[0049] The embodiment of the present invention further provides the specific parameters of the optical system structure of the present invention in more detail based on embodiment 1: Table 1 shows the structural parameters of the entrance pupil pre-underwater laser imaging optical system, including lens curvature radius, thickness, lens spacing, and material;

[0050] Table 1 Structural parameters of the pre-entry pupil underwater laser imaging optical system

[0051]

[0052]

[0053] Figure 3 A two-dimensional image of an underwater infinitely distant target imaged by the optical system of the present invention;

[0054] Figure 4 This is the MTF diagram of the optical system of the present invention at 80lp / mm.

[0055] Figure 5 This is the MTF diagram of the optical system of the present invention when it is focused at a close distance of 0.4m and at 80lp / mm.

[0056] In summary, the application discloses a large-view-field image-side telecentric underwater visual docking imaging optical system, which adopts a one-time imaging structure form, realizes image-side telecentric design, and has a telecentricity better than 0.1°. The system is used for underwater visual docking imaging, and has a working wave band of 505-545 nm. The system is composed of a spherical cover window, a front group of four lenses, a rear group of four lenses, a variable diaphragm and a filter, wherein the variable diaphragm is located between the fourth lens of the front group and the first lens of the rear group, and the first lens of the rear group and the fourth lens of the rear group are both cemented lenses, which are used for aberration correction and realize image-side telecentricity. The optical lens has a focal length of 8.6 mm, a minimum F number of 2.5, and a full field of view of 80°. The variable diaphragm can realize variable F number, and the rear group of four lenses can realize focusing. The system uses a short focal length and large F number system, and when a near distance object is focused clearly, the system also has a large depth of field. In a range from a long distance of 50 m to a near distance of 0.4 m, the focusing group only needs to focus on the 50 m target and the 0.8 m target, so that clear imaging in the range from 50 m to 0.4 m can be realized. The focusing strategy can realize rapid focusing and clear imaging of a cooperative target.

[0057] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the application.

[0058] It should be understood that those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes should belong to the protection scope of the appended claims of the application.

Claims

1. A large field of view telecentric underwater visual docking imaging optical system, characterized in that: The optical system comprises, in sequence: a spherical cover window (1), a front lens group, a variable aperture (6), a rear lens group, and a filter (11); wherein: The front lens group includes, in sequence: a front first lens group (2), a front second lens group (3), a front third lens group (4), and a front fourth lens group (5); the rear lens group includes, in sequence: a rear first lens group (7), a rear second lens group (8), a rear third lens group (9), and a rear fourth lens group (10); the variable aperture (6) is located between the front fourth lens group (5) and the rear first lens group (7); The four lenses of the front lens group adopt a "2+2" structure, wherein: the first lens (2) and the second lens (3) of the front lens group are negative lenses made of high refractive index materials, and the third lens (4) and the fourth lens (5) of the front lens group are positive lenses made of low dispersion materials; The rear lens group comprises four lenses, the first lens (7) of the rear lens group is a double-cemented negative lens, the second lens (8) of the rear lens group is a double-convex positive lens, the third lens (9) of the rear lens group is a double-convex positive lens, and the fourth lens (10) of the rear lens group is a double-cemented positive lens; The object-side imaging light beam passes through the spherical cover window (1), the front lens group, the variable aperture (6), the rear lens group and the filter (11) in sequence and forms an image on the target surface of the gated camera.

2. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The spherical cover window (1) is a tempered concentric spherical cover window used to isolate water and the lens, with the left side medium being water and the right side medium being air.

3. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The working wavelength band of the optical system is 505-545 nm, and the filter (11) is used to filter out light in wavelength bands outside the working wavelength band.

4. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The lens focal length of the optical system is 8.6 mm, the minimum F number is 2.5, the maximum field of view is 80°, and the variable F number can be achieved by adjusting the size of the variable aperture (6).

5. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The optical system is an image-space telecentric system with a telecentricity better than 0.1°.

6. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The optical system focuses through the four lenses of the rear lens group to achieve underwater imaging from 0.4m to infinity.

7. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The structural parameters of the optical system are as follows: The dome window (1) has an object side surface with a curvature radius of 75 and a thickness of 10; an image side surface with a curvature radius of 65 and a thickness of 17; The first lens (2) of the front group has a curvature radius of 86.5 on the object side and a thickness of 8; a curvature radius of 24.62 on the image side and a thickness of 8.4; The second lens (3) of the front group has a curvature radius of 1900 on the object side and a thickness of 3.6; a curvature radius of 42.53 on the image side and a thickness of 22.4; The third lens (4) of the front group has a curvature radius of -95.35 on the object side and a thickness of 5; a curvature radius of -41.6 on the image side and a thickness of 12.35; The fourth lens (5) of the front group has a curvature radius of 66.2 on the object side and a thickness of 7; a curvature radius of -66.2 on the image side and a thickness of 23; The curvature radius of the variable aperture (6) is ∞, and the distance between the aperture and the next lens is 9; The first lens (7) of the rear group has a curvature radius of -10.2 on the object side and a thickness of 2.5; a curvature radius of surface S12 is -85.45 and a thickness of 5.5; a curvature radius of the cemented surface is -14.63 and a cemented thickness of 0.35; The second lens (8) of the rear group has a curvature radius of 2405 on the object side and a thickness of 5.2; a curvature radius of -18.65 on the image side and a thickness of 1.4; The third lens (9) of the rear group has a curvature radius of 142.55 on the object side and a thickness of 8.2; a curvature radius of -54.52 on the image side and a thickness of 0.4; The fourth lens (10) of the rear group has a curvature radius of 43.52 on the object side and a thickness of 8.2; a curvature radius of the cemented surface is -24.62 and a cemented thickness of 3; a curvature radius of the image side surface is -421.24 and a thickness of 5.5; The filter (11) has an object side surface with a curvature radius of ∞ and a thickness of 2; an image side surface with a curvature radius of ∞ and a thickness of 10; The unit is mm.

8. The large field of view image space telecentric underwater visual docking imaging optical system according to claim 1, characterized in that: The adjustment method of the optical system includes: Utilizing a short focal length and large F-number system, it has a large depth of field when focusing on close objects. From a long distance of 50m to a close distance of 0.4m, the rear lens focusing group is used to focus on 50m targets and 0.8m targets, achieving clear imaging within the range of 50m to 0.4m, and realizing rapid and clear focusing on cooperative targets.

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