Short-focus lens suitable for severe environment

Abstract

The invention provides a short-focus lens suitable for a severe environment, which is used for solving the technical problems that the existing short-focus lens adopting a high-order aspherical lens is easy to generate ghost images under the condition of a low-illumination bright target, the requirements of the secondary aspherical lens on processing, detection and adjustment are higher, and the manufacturability and the economical efficiency are poor. The short-focus lens comprises a first lens group, a second lens group and a third lens group, a first spherical mirror in the first lens group adopts JGS1, a ghost image path can be controlled through the design of the curvature radius and the surface type of the first spherical mirror, and ghost images are avoided; meanwhile, the first spherical mirror is matched with the design of each lens, so that the system aberration correction is participated, the imaging quality is improved, the function of window glass is also considered, the external severe environment is isolated from the internal lens, the function of protecting the internal lens is achieved, and the imaging quality is improved on the basis of ensuring the imaging quality. And the use requirements in severe environments such as high temperature, high pressure, moisture and low illumination are met.

Description

Technical Field

[0001] The present invention relates to a short - focal - length lens, and particularly to a short - focal - length lens suitable for harsh environments. Background Art

[0002] Short - focal - length lenses are widely used in digital photography and in the fields of monitoring and observation in harsh environments such as high temperature, high pressure, humidity, and low illuminance. In addition to requiring a short focal length, a large relative aperture, high imaging quality, and low distortion, they also need to have good environmental adaptability, good processability, and economy.

[0003] Currently, short - focal - length lenses applied to harsh environments usually adopt a technical route of installing a flat window glass with excellent physical and chemical properties (such as quartz glass) in front of a conventional short - focal - length lens to isolate the external environment from the internal short - focal - length lens. Since conventional short - focal - length lenses mainly adopt a combination of multiple lens groups made of different materials, and each lens group respectively uses multiple high - order aspherical lenses to correct aberration, the overall number of lens groups can be reduced and better imaging quality can be obtained. However, the disadvantage of this short - focal - length lens applied to harsh environments is that the flat window glass is prone to ghost images in the case of a bright target under low illuminance, which affects observation. In addition, high - order aspherical lenses have high requirements for processing, detection, and alignment, and their processability and economy are relatively poor. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems that the short - focal - length lens using high - order aspherical lenses is prone to ghost images in the case of a bright target under low illuminance, and the high - order aspherical lenses have high requirements for processing, detection, and alignment, and their processability and economy are relatively poor, and to provide a short - focal - length lens suitable for harsh environments.

[0005] In order to achieve the above - mentioned purpose, the technical solution provided by the present invention is as follows:

[0006] A short - focal - length lens suitable for harsh environments, characterized in that it includes a first lens group, a second lens group, and a third lens group arranged coaxially in sequence;

[0007] The first lens group includes a first spherical mirror, a second spherical mirror, a third spherical mirror, and a fourth spherical mirror arranged coaxially in sequence;

[0008] The second lens group includes a fifth spherical mirror and a sixth spherical mirror arranged coaxially in sequence;

[0009] The third lens group includes a seventh spherical mirror, an eighth spherical mirror, a ninth spherical mirror, an aperture stop, a tenth spherical mirror, and an eleventh spherical mirror arranged coaxially in sequence; the eleventh spherical mirror is arranged on the side close to the image plane;

[0010] The first spherical mirror is a biconvex lens with a positive optical power. The radius of curvature of its first surface is less than 350 mm, and the radius of curvature of its second surface is greater than -670 mm. The material of the first spherical mirror is JGS1;

[0011] The second spherical mirror is a biconvex lens with a positive optical power;

[0012] The third spherical mirror is a convex-concave lens with its convex surface facing the object side and has a negative optical power;

[0013] The fourth spherical mirror is a biconcave lens with a negative optical power;

[0014] The fifth spherical mirror is a convex-concave lens with its convex surface facing the image side and has a positive optical power;

[0015] The sixth spherical mirror is a convex-plano lens with its convex surface facing the object side and has a positive optical power;

[0016] The seventh spherical mirror is a convex-concave lens with a negative optical power;

[0017] The eighth spherical mirror is a biconvex lens with a positive optical power;

[0018] The ninth spherical mirror is a convex-concave lens with its convex surface facing the object side and has a negative optical power;

[0019] The tenth spherical mirror is a convex-concave lens with its convex surface facing the object side and has a positive optical power;

[0020] The eleventh spherical mirror is a biconvex lens with a positive optical power.

[0021] Further, the aperture stop is arranged on the second surface of the ninth spherical mirror.

[0022] Further, the thickness of the first spherical mirror is 12 mm, and the distance between it and the second spherical mirror is 0.5 mm;

[0023] The material of the second spherical mirror is ZK7, the thickness is 3.5 mm, and the distance between it and the third spherical mirror is 0.4 mm;

[0024] The material of the third spherical mirror is ZK7, the thickness is 1.4 mm, and the distance between it and the fourth spherical mirror is 4.2 mm;

[0025] The material of the fourth spherical mirror is ZK7, the thickness is 2 mm, and the distance between it and the fifth spherical mirror is 10.64 mm;

[0026] The material of the fifth spherical mirror is ZK7, the thickness is 3.2 mm, and the distance between it and the sixth spherical mirror is 0.66 mm;

[0027] The material of the sixth spherical mirror is ZK7, with a thickness of 3.4 mm, and the distance between it and the seventh spherical mirror is 4.5 mm;

[0028] The material of the seventh spherical mirror is ZF6, with a thickness of 2.8 mm, and the distance between it and the eighth spherical mirror is 0.6 mm;

[0029] The material of the eighth spherical mirror is ZK7, with a thickness of 3.8 mm, and the distance between it and the ninth spherical mirror is 0.4 mm;

[0030] The material of the ninth spherical mirror is ZF6, with a thickness of 0.8 mm, and the distance between it and the tenth spherical mirror is 1.0 mm;

[0031] The material of the tenth spherical mirror is ZK7, with a thickness of 1.9 mm, and the distance between it and the eleventh spherical mirror is 0.3 mm;

[0032] The material of the eleventh spherical mirror is ZK7, with a thickness of 2.4 mm, and the distance between it and the image plane is 6.16 mm.

[0033] Furthermore, the radius of curvature of the first surface of the first spherical mirror is 116.533 mm, and the radius of curvature of the second surface is -223.624 mm;

[0034] The radius of curvature of the first surface of the second spherical mirror is 91.705 mm, and the radius of curvature of the second surface is 239.461 mm;

[0035] The radius of curvature of the first surface of the third spherical mirror is 50.547 mm, and the radius of curvature of the second surface is 9.205 mm;

[0036] The radius of curvature of the first surface of the fourth spherical mirror is -44.655 mm, and the radius of curvature of the second surface is 11.688 mm;

[0037] The radius of curvature of the first surface of the fifth spherical mirror is -47.706 mm, and the radius of curvature of the second surface is -15.909 mm;

[0038] The radius of curvature of the first surface of the sixth spherical mirror is 16.436 mm;

[0039] The radius of curvature of the first surface of the seventh spherical mirror is 10.163 mm, and the radius of curvature of the second surface is 5.493 mm;

[0040] The radius of curvature of the first surface of the eighth spherical mirror is 5.905 mm, and the radius of curvature of the second surface is -30.496 mm;

[0041] The radius of curvature of the first surface of the ninth spherical mirror is 62.740 mm, and the radius of curvature of the second surface is 5.668 mm;

[0042] The radius of curvature of the first surface of the tenth spherical mirror is 9.309 mm, and the radius of curvature of the second surface is 68.339 mm;

[0043] The radius of curvature of the first surface of the eleventh spherical mirror is 24.768 mm, and the radius of curvature of the second surface is -24.483 mm.

[0044] Furthermore, the system focal length of the short focal length lens formed by the first lens group, the second lens group, and the third lens group is 6.2 mm, the F-number is F1.8, the imaging size is Φ7.6 mm, the back working distance is 6.16 mm, and the field of view is ±31.5°.

[0045] The beneficial effects of the present invention compared with the prior art are as follows:

[0046] 1. A short focal length lens applicable to harsh environments provided by the present invention includes a first lens group, a second lens group, and a third lens group. The first spherical mirror in the first lens group uses fused silica (JGS1) with excellent physical and chemical properties. The ghost image path can be controlled by designing the radius of curvature and surface shape of the first spherical mirror to avoid the appearance of ghost images. At the same time, the design of the first spherical mirror in cooperation with each lens not only participates in the system aberration correction to improve the imaging quality but also takes into account the role of the window glass, isolating the external harsh environment from the internal lens and protecting the internal lens. On the basis of ensuring the imaging quality, it meets the usage requirements in harsh environments such as high temperature, high pressure, humidity, and low illuminance.

[0047] 2. Compared with the existing short focal length lenses using high-order aspherical lenses, although the short focal length lens of the present invention also adopts a combination of multiple lens groups, all eleven lenses in the three lens groups of the present invention are spherical mirrors, with a compact structure. Moreover, only three optical materials (JGS1, ZF7, and ZK6) are used for the eleven spherical mirrors. The design of all spherical surfaces and three optical materials greatly improves the processability and economy of the short focal length lens of the present invention.

[0048] 3. A short focal length lens applicable to harsh environments provided by the present invention has a large field of view and a large relative aperture. When the spatial frequency is 145 lp / mm, the MTF within 0.8 field of view is ≥0.4, and the full field of view distortion is ≤2.5%, with good imaging quality, fully meeting the performance requirements of short focal length lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic optical path diagram of an embodiment of a short focal length lens applicable to harsh environments of the present invention.

[0050] Figure 2 It is an MTF curve diagram of an embodiment of a short focal length lens applicable to harsh environments of the present invention at different fields of view.

[0051] Figure 3 The figure is a distortion curve diagram of different wavelength spectra in an embodiment of a short focal length lens suitable for harsh environments of the present invention.

[0052] The specific figure numbers are as follows: 1-first spherical mirror; 2-second spherical mirror; 3-third spherical mirror; 4-fourth spherical mirror; 5-fifth spherical mirror; 6-sixth spherical mirror; 7-seventh spherical mirror; 8-eighth spherical mirror; 9-ninth spherical mirror; 10-tenth spherical mirror; 11-eleventh spherical mirror; 12-image plane. DETAILED DESCRIPTION

[0053] In order to make the advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] like Figure 1 As shown, a short focal length lens suitable for harsh environments adopts a three-group eleven-piece structure, including a first lens group, a second lens group and a third lens group that are coaxially arranged in sequence.

[0055] The first lens group is located at the front end of the short focal length lens, and includes four spherical mirrors, which are mainly used for most distortions, field curvature corrections, and auxiliary corrections of other aberrations. Specifically, the first lens group includes a first spherical mirror 1, a second spherical mirror 2, a third spherical mirror 3, and a fourth spherical mirror 4, which are coaxially arranged in sequence, wherein the first spherical mirror 1 is located at the front end of the short focal length lens, that is, the side close to the object. The first spherical mirror 1 is a biconvex lens with positive optical power, the second spherical mirror 2 is a biconvex lens with positive optical power, the third spherical mirror 3 is a convex-concave lens with negative optical power and the convex surface facing the object, and the fourth spherical mirror is a biconcave lens with negative optical power. Among them, the curvature radius of the first surface of the first spherical mirror 1 needs to be less than 350mm, and the curvature radius of the second surface needs to be greater than -670mm. It uses quartz glass (JGS1) with excellent physical and chemical properties, which not only participates in the system aberration correction and improves the imaging quality, but also takes into account the role of window glass, isolates the external harsh environment from the internal lens, and plays a role in protecting the internal lens. The second spherical mirror 2, the third spherical mirror 3 and the fourth spherical mirror 4 on the inside are all made of crown glass (ZK7).

[0056] The second lens group is located after the first lens group, and includes two spherical mirrors, which are mainly used for partial coma and astigmatism correction and auxiliary correction of other aberrations. Specifically, the second lens group includes a fifth spherical mirror 5 and a sixth spherical mirror 6 which are coaxially arranged in sequence, and the fifth spherical mirror 5 is located on the side close to the fourth spherical mirror 4. The fifth spherical mirror 5 is a concave-convex lens with positive optical power and convex surface facing the image side, and the sixth spherical mirror 6 is a convex-flat lens with positive optical power and convex surface facing the object side. The fifth spherical mirror 5 and the sixth spherical mirror 6 are both made of crown glass (ZK7).

[0057] The third lens group is located behind the second lens group and includes five spherical mirrors, which are mainly used for correcting most of the remaining spherical aberration, coma, field curvature, distortion, and assisting in correcting other aberrations, so as to achieve imaging at the image plane 12 position after the system aberration balance. Specifically, the third lens group includes a seventh spherical mirror 7, an eighth spherical mirror 8, a ninth spherical mirror 9, an aperture stop, a tenth spherical mirror 10, and an eleventh spherical mirror 11 arranged coaxially in sequence. Among them, the seventh spherical mirror 7 is located on the side close to the sixth spherical mirror 6, and the eleventh spherical mirror 11 is located at the rear end of the short focal length lens, that is, on the side close to the image plane 12. The seventh spherical mirror 7 is a convex-concave lens with a negative optical power and a convex surface facing the object side. The eighth spherical mirror 8 is a double-convex lens with a positive optical power. The ninth spherical mirror 9 is a convex-concave lens with a negative optical power and a convex surface facing the object side. The tenth spherical mirror 10 is a convex-concave lens with a positive optical power and a convex surface facing the object side. The eleventh spherical mirror 11 is a double-convex lens with a positive optical power. Among them, both the seventh spherical mirror 7 and the ninth spherical mirror 9 are made of flint glass (ZF6), and the eighth spherical mirror 8, the tenth spherical mirror 10, and the eleventh spherical mirror 11 are all made of crown glass (ZK7). The aperture stop is arranged between the ninth spherical mirror 9 and the tenth spherical mirror 10 for dimming, and in this embodiment, it is arranged at the second surface position of the ninth spherical mirror 9.

[0058] It should be noted that in the present invention, the first surface of each spherical mirror refers to the surface that receives the light beam, and the second surface is the opposite surface of the first surface.

[0059] In this embodiment, the system focal length of the short focal length lens is 6.2 mm, the F number is F1.8, the imaging size is Φ7.6 mm, the back working distance is 6.16 mm, the field of view can reach ±31.5°, and the relative aperture D / f′ = 1.8 (D represents the entrance pupil diameter, f′ represents the focal length), meeting the high-performance and environmental adaptability requirements of the short focal length lens, and can be applied to a two-million-pixel Φ7.6 mm inch detector. The optical element parameters of the eleven spherical mirrors are shown in Table 1:

[0060] Table 1 Optical Element Parameters

[0061]

[0062] As Figure 2 、 Figure 3 shown, they are respectively the modulation transfer function (MTF) curve graph and the distortion curve graph of the short focal length lens in this embodiment under different fields of view. Figure 2The horizontal coordinate represents the spatial frequency (unit: lp / mm), the vertical coordinate represents the modulation transfer function, the black curve represents the diffraction limit curve, the blue curve represents the MTF curves of the meridional plane and the sagittal plane at the 0.00-degree field of view (the two coincide), the two green curves respectively represent the MTF curves of the meridional plane and the sagittal plane at the 15.7-degree field of view, the two red curves respectively represent the MTF curves of the meridional plane and the sagittal plane at the 22-degree field of view, the two yellow curves respectively represent the MTF curves of the meridional plane and the sagittal plane at the 25.2-degree field of view, and the two pink curves respectively represent the MTF curves of the meridional plane and the sagittal plane at the 31.5-degree field of view. Figure 3 The horizontal coordinate represents the percentage, the vertical coordinate represents the normalized field of view (the maximum value corresponds to the full field of view, and the normalized value is 1). The blue curve, the green curve, and the red curve respectively represent the distortion of the spectra of 486.13 nm, 587.56 nm, and 656.27 nm. It can be seen that for the short-focus lens of this embodiment, when the spatial frequency is 145 lp / mm, the MTF ≥ 0.4 within the 0.8 field of view, and the full-field distortion ≤ 2.5%, having good imaging quality and fully meeting the performance requirements of the short-focus lens.

[0063] The above is only used to illustrate the technical solution of the present invention and is not intended to limit it. For those of ordinary skill in the art, the specific technical solution recorded in the above embodiment can be modified, or some of its technical features can be equivalently replaced. However, these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A short focal length lens suitable for harsh environments, characterized by: It comprises a first lens group, a second lens group and a third lens group which are coaxially arranged in sequence; The first mirror group comprises a first spherical mirror (1), a second spherical mirror (2), a third spherical mirror (3) and a fourth spherical mirror (4) which are coaxially arranged in sequence; The second mirror group comprises a fifth spherical mirror (5) and a sixth spherical mirror (6) which are coaxially arranged in sequence; The third mirror group comprises a seventh spherical mirror (7), an eighth spherical mirror (8), a ninth spherical mirror (9), an aperture stop, a tenth spherical mirror (10) and an eleventh spherical mirror (11) which are coaxially arranged in sequence; the eleventh spherical mirror (11) is arranged close to the image plane (12); The first spherical mirror (1) is a biconvex lens with positive optical power, a first surface curvature radius less than 350 mm, and a second surface curvature radius greater than -670 mm; the material of the first spherical mirror (1) is JGS1; The second spherical mirror (2) is a biconvex lens with positive optical power; The third spherical mirror (3) is a convex-concave lens with the convex surface facing the object side, and its optical power is negative; The fourth spherical mirror (4) is a biconcave lens, and its optical power is negative; The fifth spherical mirror (5) is a concave-convex lens with the convex surface facing the image side, and its optical power is positive; The sixth spherical mirror (6) is a convex-planar lens with a convex surface facing the object side, and its optical power is positive; The seventh spherical mirror (7) is a convex-concave lens with the convex surface facing the object side, and its optical power is negative; The eighth spherical mirror (8) is a biconvex lens with positive optical power; The ninth spherical mirror (9) is a convex-concave lens with the convex surface facing the object side, and its optical power is negative; The tenth spherical mirror (10) is a convex-concave lens with the convex surface facing the object side, and its optical power is positive; The eleventh spherical mirror (11) is a biconvex lens with positive focal power.

2. A short focal length lens suitable for harsh environments according to claim 1, characterized in that: The aperture stop is arranged on the second surface of the ninth spherical mirror (9).

3. A short focal length lens suitable for harsh environments according to claim 1 or 2, characterized in that: The thickness of the first spherical mirror (1) is 12 mm, and the distance between the first spherical mirror (1) and the second spherical mirror (2) is 0.5 mm; The second spherical mirror (2) is made of ZK7 and has a thickness of 3.5 mm. The distance between the second spherical mirror (2) and the third spherical mirror (3) is 0.4 mm. The third spherical mirror (3) is made of ZK7 and has a thickness of 1.4 mm. The distance between the third spherical mirror (3) and the fourth spherical mirror (4) is 4.2 mm. The fourth spherical mirror (4) is made of ZK7 and has a thickness of 2 mm. The distance between the fourth spherical mirror (4) and the fifth spherical mirror (5) is 10.64 mm. The fifth spherical mirror (5) is made of ZK7 and has a thickness of 3.2 mm. The distance between the fifth spherical mirror (5) and the sixth spherical mirror (6) is 0.66 mm. The sixth spherical mirror (6) is made of ZK7 and has a thickness of 3.4 mm. The distance between the sixth spherical mirror (6) and the seventh spherical mirror (7) is 4.5 mm. The seventh spherical mirror (7) is made of ZF6 and has a thickness of 2.8 mm. The distance between the seventh spherical mirror (7) and the eighth spherical mirror (8) is 0.6 mm. The eighth spherical mirror (8) is made of ZK7 and has a thickness of 3.8 mm. The distance between the eighth spherical mirror (8) and the ninth spherical mirror (9) is 0.4 mm. The ninth spherical mirror (9) is made of ZF6 and has a thickness of 0.8 mm. The distance between the ninth spherical mirror (9) and the tenth spherical mirror (10) is 1.0 mm. The tenth spherical mirror (10) is made of ZK7 and has a thickness of 1.9 mm. The distance between the tenth spherical mirror (10) and the eleventh spherical mirror (11) is 0.3 mm. The material of the eleventh spherical mirror (11) is ZK7, the thickness is 2.4 mm, and the distance between the eleventh spherical mirror and the image plane (12) is 6.16 mm.

4. The short focal length lens suitable for harsh environments according to claim 3, characterized in that: The first spherical mirror (1) has a first surface with a radius of curvature of 116.533 mm and a second surface with a radius of curvature of -223.624 mm; The curvature radius of the first surface of the second spherical mirror (2) is 91.705 mm, and the curvature radius of the second surface is 239.461 mm; The curvature radius of the first surface of the third spherical mirror (3) is 50.547 mm, and the curvature radius of the second surface is 9.205 mm; The curvature radius of the first surface of the fourth spherical mirror (4) is -44.655 mm, and the curvature radius of the second surface is 11.688 mm; The curvature radius of the first surface of the fifth spherical mirror (5) is -47.706 mm, and the curvature radius of the second surface is -15.909 mm; The radius of curvature of the first surface of the sixth spherical mirror (6) is 16.436 mm; The curvature radius of the first surface of the seventh spherical mirror (7) is 10.163 mm, and the curvature radius of the second surface is 5.493 mm; The curvature radius of the first surface of the eighth spherical mirror (8) is 5.905 mm, and the curvature radius of the second surface is -30.496 mm; The curvature radius of the first surface of the ninth spherical mirror (9) is 62.740 mm, and the curvature radius of the second surface is 5.668 mm; The curvature radius of the first surface of the tenth spherical mirror (10) is 9.309 mm, and the curvature radius of the second surface is 68.339 mm; The curvature radius of the first surface of the eleventh spherical mirror (11) is 24.768 mm, and the curvature radius of the second surface is -24.483 mm.

5. A short focal length lens suitable for harsh environments according to claim 4, characterized in that: The short focal length lens composed of the first lens group, the second lens group and the third lens group has a system focal length of 6.2 mm, an F number of F1.8, an imaging size of Φ7.6 mm, a back working distance of 6.16 mm, and a field of view of ±31.5°.

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