A short focal length lens suitable for harsh environments

Abstract

The application provides a short focal length lens suitable for a harsh environment, and aims to solve the technical problems that the short focal length lens with high-order aspheric lenses is prone to ghost images in the case of low-illumination bright targets, the aspheric lenses have high requirements for processing, detection and assembly, and the process and economy are poor. The short focal length lens comprises a first lens group, a second lens group and a third lens group, a first spherical lens in the first lens group adopts JGS1, the path of ghost images can be controlled through the design of the curvature radius and the surface type of the first spherical lens, and the appearance of ghost images is avoided; meanwhile, the first spherical lens is matched with the design of each lens, the system aberration correction is participated, the imaging quality is improved, the function of the window glass is considered, the external harsh environment is isolated from the internal lens, the internal lens is protected, and the use requirements in harsh environments such as high temperature, high pressure, humidity and low illumination are met on the basis of ensuring the imaging quality.

Description

Technical Field

[0001] This invention relates to short focal length lenses, and more particularly to a short focal length lens suitable for harsh environments. Background Technology

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

[0003] Currently, short focal length lenses used in harsh environments typically employ a technique of adding a flat window glass (such as quartz glass) with excellent physical and chemical properties in front of a conventional short focal length lens, thereby isolating the external environment from the internal short focal length lens. Since conventional short focal length lenses mainly use multiple lens groups made of different materials, and each lens group uses multiple high-order aspherical lenses to correct aberrations, the overall number of lens groups can be reduced while achieving good image quality. However, a drawback of this type of short focal length lens for harsh environments is that the flat window glass is prone to ghosting under low-light conditions with bright targets, affecting observation. Furthermore, high-order aspherical lenses have high requirements for processing, testing, and assembly, and are relatively difficult to manufacture and cost-effective. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing short focal length lenses using high-order aspherical lenses being prone to ghosting under low-light bright targets, and the high requirements for processing, inspection and assembly of sub-aspherical lenses, as well as their poor manufacturability and economy, and to provide a short focal length lens suitable for harsh environments.

[0005] To achieve the above objectives, 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 mirror 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 mirror group includes a fifth spherical mirror and a sixth spherical mirror arranged coaxially in sequence;

[0009] The third mirror 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 located on the side closer to the image plane.

[0010] The first spherical mirror is a biconvex lens with 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 positive optical power;

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

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

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

[0015] The sixth spherical mirror is a convex flat lens with its convex surface facing the object side, and its optical power is positive.

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

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

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

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

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

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

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

[0023] The second spherical mirror is made of ZK7 material and has a thickness of 3.5mm. The distance between it and the third spherical mirror is 0.4mm.

[0024] The third spherical mirror is made of ZK7 material and has a thickness of 1.4mm. The distance between it and the fourth spherical mirror is 4.2mm.

[0025] The fourth spherical mirror is made of ZK7 material and has a thickness of 2mm. The distance between it and the fifth spherical mirror is 10.64mm.

[0026] The fifth spherical mirror is made of ZK7 material and has a thickness of 3.2mm. The distance between it and the sixth spherical mirror is 0.66mm.

[0027] The sixth spherical mirror is made of ZK7 material and has a thickness of 3.4mm. The distance between it and the seventh spherical mirror is 4.5mm.

[0028] The seventh spherical mirror is made of ZF6 and has a thickness of 2.8 mm. The distance between it and the eighth spherical mirror is 0.6 mm.

[0029] The eighth spherical mirror is made of ZK7 material and has a thickness of 3.8mm. The distance between it and the ninth spherical mirror is 0.4mm.

[0030] The ninth spherical mirror is made of ZF6 and has a thickness of 0.8 mm. The distance between it and the tenth spherical mirror is 1.0 mm.

[0031] The tenth spherical mirror is made of ZK7 material and has a thickness of 1.9mm. The distance between it and the eleventh spherical mirror is 0.3mm.

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

[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 short focal length lens system consisting of the first lens group, the second lens group, and the third lens group has a focal length of 6.2mm, an F-number of F1.8, an image size of Φ7.6mm, a back working distance of 6.16mm, and a field of view of ±31.5°.

[0045] The advantages of this invention compared to the prior art are as follows:

[0046] 1. This invention provides a short focal length lens suitable for harsh environments, comprising a first lens group, a second lens group, and a third lens group. The first spherical lens in the first lens group is made of quartz glass (JGS1) with excellent physical and chemical properties. The design of the curvature radius and surface shape of the first spherical lens can control the ghosting path and avoid the occurrence of ghosting. At the same time, the design of the first spherical lens, together with the design of other lenses, not only participates in the system aberration correction and improves the image quality, but also takes on the role of window glass, isolating the harsh external environment from the internal lens and protecting the internal lens. While ensuring image quality, it meets the requirements for use in harsh environments such as high temperature, high pressure, humidity, and low light.

[0047] 2. Compared with existing short focal length lenses that use 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 lenses, which makes the structure compact. Moreover, the eleven spherical lenses only use three kinds of optical materials (JGS1, ZF7 and ZK6). The design of the spherical lens and the three kinds of optical materials greatly improves the manufacturability and economy of the short focal length lens of the present invention.

[0048] 3. The present invention provides a short focal length lens suitable for harsh environments, which has a large field of view and a large relative aperture. At a spatial frequency of 145 lp / mm, the MTF within a 0.8 field of view is ≥0.4 and the distortion across the entire field of view is ≤2.5%, which has good imaging quality and fully meets the performance requirements of short focal length lenses. Attached Figure Description

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

[0050] Figure 2 The MTF curves of a short focal length lens embodiment suitable for harsh environments according to the present invention are shown in different fields of view.

[0051] Figure 3 This is a distortion curve of the spectrum at different wavelengths in an embodiment of a short focal length lens suitable for harsh environments according to the present invention.

[0052] The specific reference numerals in the attached diagram 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 Implementation

[0053] To make the advantages and features of the present invention clearer, the present invention will be 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-element structure, including a first lens group, a second lens group, and a third lens group arranged coaxially in sequence.

[0055] The first lens group, located at the front of the short focal length lens, comprises four spherical lenses and is primarily used for most distortion and field curvature corrections, as well as auxiliary corrections for other aberrations. Specifically, the first lens group includes a first spherical lens 1, a second spherical lens 2, a third spherical lens 3, and a fourth spherical lens 4, arranged coaxially in sequence. The first spherical lens 1 is located at the very front of the short focal length lens, i.e., on the object side. The first spherical lens 1 is a biconvex lens with positive optical power; the second spherical lens 2 is a biconvex lens with positive optical power; the third spherical lens 3 is a convex-concave lens with negative optical power and its convex surface facing the object side; and the fourth spherical lens is a biconcave lens with negative optical power. The first spherical mirror 1 has a radius of curvature of less than 350 mm for its first surface and a radius of curvature of greater than -670 mm for its second surface. It is made of quartz glass (JGS1) with excellent physical and chemical properties, which not only participates in system aberration correction and improves image quality, but also acts as a window glass, isolating the internal lenses from harsh external environments and protecting them. The inner second spherical mirror 2, third spherical mirror 3, and fourth spherical mirror 4 are all made of crown glass (ZK7).

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

[0057] The third lens group, located after the second lens group, consists of five spherical mirrors. It primarily corrects most of the remaining spherical aberrations, coma, field curvature, distortion, and other aberrations, achieving system aberration balance and image formation at image plane 12. 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. The seventh spherical mirror 7 is located closer to the sixth spherical mirror 6, and the eleventh spherical mirror 11 is located at the rear of the short focal length lens, i.e., closer to image plane 12. The seventh spherical mirror 7 is a convex-concave lens with negative optical power and its convex surface facing the object side; the eighth spherical mirror 8 is a biconvex lens with positive optical power; the ninth spherical mirror 9 is a convex-concave lens with negative optical power and its convex surface facing the object side; the tenth spherical mirror 10 is a convex-concave lens with positive optical power and its convex surface facing the object side; and the eleventh spherical mirror 11 is a biconvex lens with positive optical power. The seventh and ninth spherical mirrors 7 and 9 are both made of lead glass (ZF6), while the eighth, tenth, and eleventh spherical mirrors 8 and 11 are all made of crown glass (ZK7). An aperture stop is positioned between the ninth and tenth spherical mirrors 9 to achieve dimming; in this embodiment, it is positioned on the second surface of the ninth spherical mirror 9.

[0058] It is worth noting that, in this invention, the first surface of each spherical mirror refers to the surface on which it receives the light beam, and the second surface is the surface opposite to the first surface.

[0059] In this embodiment, the short focal length lens has a system focal length of 6.2mm, an F-number of F1.8, an imaging size of Φ7.6mm, a back working distance of 6.16mm, a field of view of ±31.5°, and a relative aperture D / f′ = 1.8 (D represents the entrance pupil diameter, f′ represents the focal length). This achieves the high performance and environmental adaptability requirements of the short focal length lens, making it suitable for a two-megapixel Φ7.6mm inch detector. The optical element parameters of the eleven spherical mirrors are shown in Table 1.

[0060] Table 1 Optical Component Parameters

[0061]

[0062] like Figure 2 , Figure 3 The figures shown are the modulation transfer function (MTF) curves and distortion curves of the short focal length lens in this embodiment under different fields of view. Figure 2The horizontal axis represents spatial frequency (unit: lp / mm), the vertical axis represents modulation transfer function, the black curve represents the diffraction limit curve, the blue curve represents the MTF curves of the meridional and sagittal planes in the 0.00 degree field of view (the two coincide), the two green curves represent the MTF curves of the meridional and sagittal planes in the 15.7 degree field of view, the two red curves represent the MTF curves of the meridional and sagittal planes in the 22 degree field of view, the two yellow curves represent the MTF curves of the meridional and sagittal planes in the 25.2 degree field of view, and the two pink curves represent the MTF curves of the meridional and sagittal planes in the 31.5 degree field of view. Figure 3 The horizontal axis represents percentages, and the vertical axis represents the normalized field of view (the maximum value corresponds to the full field of view, with a normalized value of 1). The blue, green, and red curves represent the spectral distortion at 486.13nm, 587.56nm, and 656.27nm, respectively. It can be seen that the short focal length lens in this embodiment, at a spatial frequency of 145lp / mm, exhibits an MTF ≥ 0.4 within a 0.8 field of view and a full field-of-view distortion ≤ 2.5%, demonstrating good image quality and fully meeting the performance requirements of a short focal length lens.

[0063] The above description is only used to illustrate the technical solutions of the present invention, and is not intended to limit them. For those skilled in the art, modifications can be made to the specific technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A short focal length lens suitable for harsh environments, characterized in that: It consists of a first mirror group, a second mirror group, and a third mirror group arranged coaxially in sequence; The first mirror group consists of a first spherical mirror (1), a second spherical mirror (2), a third spherical mirror (3), and a fourth spherical mirror (4) arranged coaxially in sequence; The second mirror group consists of a fifth spherical mirror (5) and a sixth spherical mirror (6) arranged coaxially in sequence; The third mirror group consists of 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; the eleventh spherical mirror (11) is arranged on the side closer to the image plane (12); The first spherical mirror (1) is a biconvex lens with 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 (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 its convex surface facing the object side, and its optical power is negative; The fourth spherical mirror (4) is a double concave lens with a negative optical power; The fifth spherical mirror (5) is a concave-convex lens with its convex surface facing the image side, and its optical power is positive; The sixth spherical mirror (6) is a convex flat lens with its convex surface facing the object side, and its optical power is positive; The seventh spherical mirror (7) is a convex-concave lens with its 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 its convex surface facing the object side, and its optical power is negative; The tenth spherical mirror (10) is a convex-concave lens with its convex surface facing the object side, and its optical power is positive; The eleventh spherical mirror (11) is a biconvex lens with positive optical power.

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

4. A short focal length lens suitable for harsh environments according to claim 3, characterized in that: The first spherical mirror (1) has a first surface radius of curvature of 116.533 mm and a second surface radius of curvature of -223.624 mm. The radius of curvature of the first surface of the second spherical mirror (2) is 91.705 mm, and the radius of curvature of the second surface is 239.461 mm; The radius of curvature of the first surface of the third spherical mirror (3) is 50.547 mm, and the radius of curvature of the second surface is 9.205 mm; The radius of curvature of the first surface of the fourth spherical mirror (4) is -44.655 mm, and the radius of curvature of the second surface is 11.688 mm; The radius of curvature of the first surface of the fifth spherical mirror (5) is -47.706 mm, and the radius of curvature 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 radius of curvature of the first surface of the seventh spherical mirror (7) is 10.163 mm, and the radius of curvature of the second surface is 5.493 mm; The radius of curvature of the first surface of the eighth spherical mirror (8) is 5.905 mm, and the radius of curvature of the second surface is -30.496 mm; The radius of curvature of the first surface of the ninth spherical mirror (9) is 62.740 mm, and the radius of curvature of the second surface is 5.668 mm; The radius of curvature of the first surface of the tenth spherical mirror (10) is 9.309 mm, and the radius of curvature of the second surface is 68.339 mm; The first surface of the eleventh spherical mirror (11) has a radius of curvature of 24.768 mm, and the second surface has a radius of curvature of -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 system consisting of the first lens group, the second lens group, and the third lens group has a focal length of 6.2mm, an F number of F1.8, an image size of 7.6mm, a back working distance of 6.16mm, and a field of view of ±31.5°.

Images