An underwater laser imaging optical system with pre-pupil

Abstract

The application discloses a kind of underwater laser imaging optical systems of entry pupil preposition, whole system is ten lenses, a protective window, a variable diaphragm and a filter, from object side to image side, it is protective window, front group, rear group and filter in proper order;Wherein: protective window is used to isolate water;Front group includes front group first, second, third and fourth lens four lenses in proper order;Rear group includes rear group first, second, third, fourth, fifth and sixth lens six lenses in proper order;Variable diaphragm is located between rear group third and fourth lens, and variable F number is realized by adjusting diaphragm aperture size, and lens depth of field is promoted;Filter is narrowband filter;Object side imaging beam is imaged once after passing through protective window, front group lens, then pass through rear group lens and filter and be imaged on target surface.The application can realize variable F number by variable diaphragm, promote lens depth of field, and focusing is carried out by last three lenses of rear group, and underwater 3m to infinite distance imaging can be realized.

Description

Technical Field

[0001] This invention belongs to the field of underwater optical systems, specifically relating to an underwater laser imaging optical system with a front-view entrance pupil. Background Technology

[0002] Underwater imaging is an important research direction in underwater optics and marine optics. It is a crucial means and tool for understanding, developing, utilizing, and protecting the ocean, offering advantages such as intuitive target detection, high imaging resolution, and high information content. This technology has been widely used in underwater target reconnaissance / detection / identification, underwater archaeology, marine resource exploration, and biological research. Research shows that blue-green lasers have a strong transmission "window" underwater, allowing them to penetrate seawater effectively. Therefore, lasers with wavelengths around 532nm are generally used for artificial illumination of the imaging space to address the high beam loss caused by the underwater environment.

[0003] Due to the strong scattering of light by water, the illumination window and imaging window of underwater active illumination imaging systems are usually separate, such as the SeeRay underwater laser imaging system from Spartz Corporation in the United States. Research on some co-aperture underwater optical imaging systems has also been conducted. These co-aperture systems often use an aperture mirror for laser emission. To avoid a central black spot in the image caused by the aperture mirror, the pupil of the imaging system needs to be forward-positioned and located at the aperture mirror. Summary of the Invention

[0004] The purpose of this invention is to provide an underwater laser imaging optical system with a front entrance pupil located at the aperture mirror. The system is optimized for cross-medium imaging requirements, resulting in good imaging quality. This system avoids interference from the aperture mirror and can be used in common-aperture underwater laser imaging systems. It has excellent imaging quality and significant economic benefits in fields such as marine resource exploration, underwater target reconnaissance / detection / identification, and underwater archaeology.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] An underwater laser imaging optical system with a front-view entrance pupil comprises ten lenses, a protective window, a variable aperture, and a narrowband filter. From the object side to the image side, the system includes a protective window, a front group, a rear group, and a narrowband filter, wherein:

[0007] The protective window is used to isolate water and air media; the front group includes four lenses: the first, second, third, and fourth lenses; the rear group includes six lenses: the first, second, third, fourth, fifth, and sixth lenses; the last lens is a narrowband filter used to filter out light outside the working wavelength band.

[0008] The beam of light from the target at infinity passes sequentially through the protective window, the four lenses in the front group converge to form an image, and then passes through the six lenses in the rear group to form an image on the target surface.

[0009] Furthermore, the protective window is tempered to withstand high underwater pressure and can isolate water and air media.

[0010] Furthermore, the front group of four lenses adopts a "3+1" structure, where the first three lenses are positive lenses and the fourth lens is a negative lens made of a high-refractive-index material. The rear group consists of six lenses, adopting a "3+3" structure. The first lens in the rear group is a meniscus negative lens with a concave object-side surface, the second lens is a meniscus positive lens, the third lens is a biconvex positive lens, the fourth lens is a biconvex positive lens, the fifth lens is a cemented negative lens, and the sixth lens is a cemented negative lens.

[0011] Furthermore, the optical system operates in the 525–535 nm wavelength range.

[0012] Furthermore, the optical system has a lens focal length of 97mm, a minimum F-number of 2.5, and a variable aperture located between the third and fourth lenses in the rear group. The variable aperture enables variable F-number and improves the depth of field of the lens.

[0013] Furthermore, the entrance pupil is located 210 mm in front of the first lens of the front group.

[0014] Furthermore, a target-surface φ18mm gated camera can be matched, and focusing can be achieved through the last three lenses of the rear group, enabling underwater imaging from 3m to infinity with good image quality.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] The imaging optical system of this invention has an entrance pupil located 210 mm in front of the first lens of the front group. It is optimized for cross-medium imaging requirements, and a filter is added at the end of the system to remove light outside the operating wavelength. A variable aperture is located between the third and fourth lenses of the rear group. Adjusting the aperture size allows for variable F-number, thus improving the depth of field. This system avoids interference from the aperture mirror, and focusing is achieved through the last three lenses of the rear group. It can achieve underwater imaging from 3 meters to infinity, and can be used in common-aperture underwater laser imaging systems, providing excellent image quality. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the optical system of the present invention;

[0018] Figure 2 This is a schematic diagram of the lens and lens surface of the present invention;

[0019] Figure 3 This is a two-dimensional diagram of the optical system of the present invention;

[0020] Figure 4 The MTF diagram of the optical system of the present invention at 50 lp / mm is shown.

[0021] In the diagram: 1-protection window, 2-front group first lens, 3-front group second lens, 4-front group third lens, 5-front group fourth lens, 6-rear group first lens, 7-front and rear group second lenses, 8-rear group third lens, 9-variable aperture, 10-rear group fourth lens, 11-rear group fifth lens, 12-rear group sixth lens, 13-narrow band filter. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] This invention discloses an underwater laser imaging optical system with a front-mounted entrance pupil, employing a secondary imaging structure. The system is used for underwater laser imaging, operating in the 525–535 nm wavelength range. The system consists of a protective window, four lenses in the front group, six lenses in the rear group, and a narrowband filter. A variable aperture is located between the third and fourth lenses in the rear group, and the entrance pupil is located 210 mm in front of the first lens in the front group. The fifth and sixth lenses in the rear group are cemented together and used to correct system aberrations. The optical system of this invention has a focal length of 97 mm, a minimum F-number of 2.5, and is matched with a φ18 mm gated camera. The variable aperture allows for variable F-numbers, improving the depth of field. Focusing is achieved through the last three lenses in the rear group, enabling underwater imaging from 3 m to infinity with excellent image quality.

[0024] like Figure 1As shown, the underwater laser imaging optical system with a front entrance pupil in this embodiment of the invention has a focal length of 97mm and a minimum F-number of 2.5. The entire system consists of ten lenses, a protective window 1, a variable aperture 9, and a narrowband filter 13, which are sequentially composed of the protective window 1, the front group, the rear group, and the narrowband filter 13. Through reasonable material matching, optical power distribution, and the use of cemented components, the system aberration correction is achieved.

[0025] Among them: the protective window 1 is used to isolate water and the lens, the medium on the left is water, and the medium on the right is air; the front group includes the first lens 2, the second lens 3, the third lens 4, and the fourth lens 5; the rear group includes the first lens 6, the second lens 7, the third lens 8, the fourth lens 10, the fifth lens 11, and the sixth lens 12, for a total of six lenses; and the last one is a narrowband filter 13.

[0026] The beam of light from the target at infinity passes sequentially through the protective window 1 and the four lenses in the front group to converge and form an image, and then passes through the six lenses in the rear group and the narrowband filter 13 to form an image on the target surface.

[0027] In this embodiment of the invention, the fifth lens 11 and the sixth lens 12 of the rear group are cemented lenses used to correct system aberrations. The entrance pupil is located 210 mm in front of the first lens 2 of the front group, and is optimized according to the requirements of cross-medium imaging. A narrowband filter 13 is added at the end of the system to filter out light outside the working wavelength. The variable aperture 9 is located between the third lens 8 and the fourth lens 10 of the rear group. Adjusting the aperture of the aperture 9 achieves variable F-number, improving the depth of field. This system avoids interference from the aperture mirror on imaging. Focusing is achieved through the three lenses—the fourth lens 10, the fifth lens 11, and the sixth lens 12—allowing for underwater imaging from 3 m to infinity. It can be used in common-aperture underwater laser imaging systems and has excellent image quality.

[0028] Figure 2 This is a schematic diagram of the lens and lens surface of the present invention. Furthermore, the optical lens materials are all common, high-performance, and readily available visible light glass materials.

[0029] The front group of four lenses adopts a "3+1" structure, where the first three lenses are positive lenses and the fourth lens is a negative lens made of a high-refractive-index material. The rear group has a total of six lenses, adopting a "3+3" structure. The first lens in the rear group is a meniscus negative lens with a concave object-side surface, the second lens is a meniscus positive lens, the third lens is a biconvex positive lens, the fourth lens is a biconvex positive lens, the fifth lens is a cemented negative lens, and the sixth lens is a cemented negative lens.

[0030] To provide a more detailed explanation, the specific parameters of the optical system structure of this invention are given below: Table 1 shows the structural parameters of the entrance pupil front underwater laser imaging optical system (lens curvature radius, thickness, lens spacing and materials).

[0031] Table 1. Structural parameters of the entrance pupil-front underwater laser imaging optical system

[0032]

[0033]

[0034] Figure 3 This is a two-dimensional image of an underwater target at infinity image created by the optical system of the present invention. Figure 4 The MTF diagram of the optical system of the present invention at 50 lp / mm is shown.

[0035] In summary, this invention discloses an underwater laser imaging optical system with a front-mounted entrance pupil, employing a secondary imaging structure. This system is used for underwater laser imaging, operating in the 525–535 nm wavelength range. The system consists of a protective window, four lenses in the front group, six lenses in the rear group, and a narrowband filter. The variable aperture is located between the third and fourth lenses in the rear group, and the entrance pupil is located 210 mm in front of the first lens in the front group. The optical lens of this invention has a focal length of 97 mm and a minimum F-number of 2.5, matched with a φ18 mm gated camera. The variable aperture allows for variable F-numbers, improving the depth of field. Focusing is achieved through the last three lenses in the rear group, enabling underwater imaging from 3 m to infinity with excellent image quality. It has promising application prospects, particularly suitable for underwater common-aperture laser imaging equipment, and can be used in fields such as marine resource exploration, underwater target reconnaissance / detection / identification, and underwater archaeology.

[0036] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0037] Those skilled in the art will readily understand that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An underwater laser imaging optical system with an entrance pupil, characterized in that, The entire system consists of ten lenses, a protective window, a variable aperture, and a filter. From the object side to the image side, the components are the protective window, the front group, the rear group, and the filter. Among them: the protective window is used to isolate water; The front group consists of four lenses in sequence: the first lens, the second lens, the third lens, and the fourth lens. The four lenses in the front group adopt a "3+1" structure, in which the first three lenses are positive lenses and the fourth lens is a negative lens made of a high refractive index material. The rear group consists of six lenses in sequence: the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens. The six lenses in the rear group adopt a "3+3" structure. The first lens is a meniscus negative lens with a concave object-side surface, the second lens is a meniscus positive lens, the third lens is a biconvex positive lens, the fourth lens is a biconvex positive lens, the fifth lens is a cemented negative lens, and the sixth lens is a cemented negative lens. The fifth and sixth lenses are cemented components used to correct system aberrations. The variable aperture is located between the third and fourth lenses in the rear group. The F-number can be adjusted by changing the size of the aperture, thereby increasing the depth of field of the lens. The filter is a narrowband filter; The object-side imaging beam passes sequentially through the protective window and the front lens for one imaging, and then passes through the rear lens and filter to image onto the target surface.

2. The underwater laser imaging optical system with front entrance pupil as described in claim 1, characterized in that, The optical system operates in the 525–535 nm wavelength range.

3. The underwater laser imaging optical system with front entrance pupil as described in claim 1, characterized in that, The entrance pupil is located 210 mm in front of the first lens of the front group.

4. The underwater laser imaging optical system with front entrance pupil as described in claim 1, characterized in that, Focusing is achieved by using the last three lenses in the rear group to capture images from 3 meters underwater to infinity.

5. The underwater laser imaging optical system with front entrance pupil as described in claim 1, characterized in that, The optical system has a focal length of 97mm, a minimum F-number of 2.5, and is matched with a φ18mm gated camera.

6. The underwater laser imaging optical system with front entrance pupil as described in claim 1, characterized in that, The protective window has been tempered.

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