Fixed focal length lens suitable for 4K resolution detector

Abstract

The invention provides a fixed-focal-length lens suitable for a 4K-resolution detector, which is used for solving the technical problems that the existing fixed-focal-length lens adopting a high-order aspherical lens has higher processing requirements, and the high-order aspherical lens has higher requirements on detection and adjustment, so that the manufacturability and the economical efficiency are poor. The invention provides a fixed-focal-length lens suitable for a 4K-resolution detector, which is provided with eight groups, namely ten spherical mirrors, and comprises a first spherical mirror, a second spherical mirror, a third spherical mirror, a first glued mirror group, an aperture diaphragm, a second glued mirror group, an eighth spherical mirror, a ninth spherical mirror and a tenth spherical mirror which are coaxially arranged in sequence; through the structure of the ten spherical mirrors and the focal power design, fixed-focal-length imaging is realized, and the lens structure is greatly simplified on the basis of ensuring the imaging quality; meanwhile, the number and the structure of the optical elements of the front part and the rear part of the aperture diaphragm are approximately symmetrical in form, and the distortion correction effect is further improved.

Description

Technical Field

[0001] The present invention relates to a fixed-focus lens, and in particular to a fixed-focus lens suitable for a 4K resolution detector. Background Art

[0002] The fixed-focus lens for a 4K resolution detector has wide applications in the fields of commercial monitoring, digital video shooting, national defense measurement and control, etc. In addition to requiring a large field of view (≥50°), a large relative aperture (D / f′≥2), good imaging quality (MTF≥0.4), high resolution (suitable for a resolution above 4K), and small distortion (<0.5%), it also needs to have good processability and economy.

[0003] Currently, the fixed-focus lens for a 4K resolution detector mainly adopts a combination method of multiple lens groups made of different materials, and each lens group respectively adopts multiple high-order aspherical lenses for correcting aberrations, so as to reduce the number of lens groups as a whole and obtain good imaging quality. However, the disadvantage of this fixed-focus lens is that the processing requirements are relatively high, and the high-order aspherical lenses also have relatively high requirements for detection and alignment, resulting in relatively poor processability and economy. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that the existing fixed-focus lens using high-order aspherical lenses has relatively high processing requirements, and the high-order aspherical lenses also have relatively high requirements for detection and alignment, resulting in relatively poor processability and economy, and to provide a fixed-focus lens suitable for a 4K resolution detector.

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

[0006] A fixed-focus lens suitable for a 4K resolution detector, characterized in that it includes a first spherical mirror, a second spherical mirror, a third spherical mirror, a first cemented lens group, an aperture stop, a second cemented lens group, an eighth spherical mirror, a ninth spherical mirror, and a tenth spherical mirror arranged coaxially in sequence; the image plane is located behind the tenth spherical mirror;

[0007] The first cemented lens group includes a fourth spherical mirror and a fifth spherical mirror cemented coaxially in sequence, and the fourth spherical mirror is located on the side close to the third spherical mirror; the second cemented lens group includes a sixth spherical mirror and a seventh spherical mirror cemented coaxially in sequence, and the sixth spherical mirror is located on the side close to the fifth spherical mirror;

[0008] The first spherical mirror is a meniscus lens with a convex surface facing the object side, and its optical power is negative;

[0009] The second spherical mirror is a plano-convex lens with a convex surface facing the object side, and its optical power is positive;

[0010] The third spherical mirror is a meniscus lens with its convex surface facing the object side, and its optical power is negative;

[0011] The fourth spherical mirror is a biconvex lens, and its optical power is positive;

[0012] The fifth spherical mirror is a biconcave lens, and its optical power is negative;

[0013] The sixth spherical mirror is a meniscus lens with its convex surface facing the object side, and its optical power is negative;

[0014] The seventh spherical mirror is a biconvex lens, and its optical power is positive;

[0015] The eighth spherical mirror is a meniscus lens with its convex surface facing the object side, and its optical power is negative;

[0016] The ninth spherical mirror is a biconvex lens, and its optical power is positive;

[0017] The tenth spherical mirror is a meniscus lens with its convex surface facing the image side, and its optical power is negative.

[0018] Furthermore, the aperture stop is located 0.17 mm in front of the sixth spherical mirror.

[0019] Furthermore, the material of the first spherical mirror is LaK2, its thickness is 3 mm, and the distance between it and the second spherical mirror is 57.77 mm;

[0020] The material of the second spherical mirror is ZF7, its thickness is 10 mm, and the distance between it and the third spherical mirror is 17.67 mm;

[0021] The material of the third spherical mirror is ZF7, its thickness is 3.2 mm, and the distance between it and the fourth spherical mirror is 3.5 mm;

[0022] The material of the fourth spherical mirror is LaK2, its thickness is 10 mm; the material of the fifth spherical mirror is ZF7, its thickness is 2 mm, and the distance between it and the aperture stop is 13.87 mm;

[0023] The material of the sixth spherical mirror is LaK2, its thickness is 2.2 mm; the material of the seventh spherical mirror is ZF7, its thickness is 5.6 mm, and the distance between it and the eighth spherical mirror is 4.97 mm;

[0024] The material of the eighth spherical mirror is ZF7, its thickness is 3.5 mm, and the distance between it and the ninth spherical mirror is 1.69 mm;

[0025] The material of the ninth spherical mirror is ZF7, its thickness is 2.8 mm, and the distance between it and the tenth spherical mirror is 6.0 mm;

[0026] The material of the tenth spherical mirror is ZF7, with a thickness of 2.5 mm and a distance of 2.5 mm from the image plane.

[0027] Further, the radius of curvature of the first surface of the first spherical mirror is 141.6 mm, and the radius of curvature of the second surface is 44.92 mm;

[0028] The radius of curvature of the first surface of the second spherical mirror is 78.46 mm;

[0029] The radius of curvature of the first surface of the third spherical mirror is 28.81 mm, and the radius of curvature of the second surface is 20.40 mm;

[0030] The radius of curvature of the first surface of the fourth spherical mirror is 31.71 mm, and the radius of curvature of the second surface is -43.11 mm;

[0031] The radius of curvature of the first surface of the fifth spherical mirror is -43.11 mm, and the radius of curvature of the second surface is 80.67 mm;

[0032] The radius of curvature of the first surface of the sixth spherical mirror is 28.95 mm, and the radius of curvature of the second surface is 20.10 mm;

[0033] The radius of curvature of the first surface of the seventh spherical mirror is 20.10 mm, and the radius of curvature of the second surface is -81.38 mm;

[0034] The radius of curvature of the first surface of the eighth spherical mirror is 17.65 mm, and the radius of curvature of the second surface is 14.69 mm;

[0035] The radius of curvature of the first surface of the ninth spherical mirror is 66.72 mm, and the radius of curvature of the second surface is -95.90 mm;

[0036] The radius of curvature of the first surface of the tenth spherical mirror is -13.36 mm, and the radius of curvature of the second surface is -52.95 mm.

[0037] Further, the system focal length of the fixed focal length lens formed by the first spherical mirror, the second spherical mirror, the third spherical mirror, the first cemented lens group, the aperture stop, the second cemented lens group, the eighth spherical mirror, the ninth spherical mirror and the tenth spherical mirror is 23 mm, the F number is F2, the imaging size is Φ23.7 mm, and the total length of the system is 150 mm.

[0038] The beneficial effects of the present invention compared with the prior art are as follows:

[0039] 1. A fixed-focus lens applicable to a 4K resolution detector provided by the present invention is provided with a total of ten spherical mirrors in eight groups. Through the structure and optical power design of the ten spherical mirrors, fixed-focus imaging is achieved, and on the basis of ensuring imaging quality, the lens structure is greatly simplified; at the same time, the number and structure of the optical elements in the front and rear parts of the aperture stop of the present invention are approximately symmetrical in form, further improving the distortion correction effect.

[0040] 2. Compared with the existing fixed-focus lenses using high-order aspherical lenses, although the present invention also adopts a multi-group lens combination method, all ten lenses in the eight lens groups of the present invention are spherical mirrors, with a compact structure, and only two optical materials, LaK2 and ZF7, are used for the ten spherical mirrors. The design of all-spherical lenses and two optical materials greatly improves the processability and economy of the fixed-focus lens of the present invention.

[0041] 3. A fixed-focus lens applicable to a 4K resolution detector provided by the present invention has a large field of view (52.8°), a large relative aperture (D / f′ = 2), a high resolution (applicable to cameras with a pixel size of 3.3 μm and above), a low distortion (≤0.5%), and good imaging quality (MTF ≥ 0.4 when the spatial frequency is 150 lp / mm), fully meeting the performance requirements of a fixed-focus lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic optical path diagram of an embodiment of a fixed-focus lens applicable to a 4K resolution detector of the present invention;

[0043] Figure 2 is an MTF curve diagram of an embodiment of a fixed-focus lens applicable to a 4K resolution detector of the present invention at different fields of view.

[0044] Figure 3 is a distortion curve diagram of different wavelength spectra of an embodiment of a fixed-focus lens applicable to a 4K resolution detector of the present invention.

[0045] The specific reference numerals are as follows:

[0046] 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 - Aperture stop; 12 - Image plane. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] To make the advantages and features of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0048] As Figure 1As shown in the figure, a fixed-focus lens applicable to a 4K resolution detector adopts an eight-group and ten-element structure, including a first spherical mirror 1, a second spherical mirror 2, a third spherical mirror 3, a first cemented lens group, an aperture stop 11, a second cemented lens group, an eighth spherical mirror 8, a ninth spherical mirror 9, and a tenth spherical mirror 10 arranged coaxially in sequence.

[0049] The first spherical mirror 1 is located at the front end of the fixed-focus lens and is a meniscus lens with a negative optical power and a convex surface facing the object side. Its material is LaK2 (lanthanum crown glass) and is mainly used for the auxiliary correction of coma, astigmatism, field curvature, and distortion. The second spherical mirror 2 is a plano-convex lens with a positive optical power and a convex surface facing the object side. Its material is ZF7 (heavy flint glass) and is mainly used for the auxiliary correction of astigmatism, field curvature, and distortion. The third spherical mirror 3 is a meniscus lens with a negative optical power and a convex surface facing the object side. Its material is ZF7 and is mainly used for the auxiliary correction of coma, astigmatism, field curvature, distortion, spherical aberration, and chromatic aberration.

[0050] The first cemented lens group includes a fourth spherical mirror 4 and a fifth spherical mirror 5 arranged coaxially in sequence. The first surface of the fourth spherical mirror 4 is arranged close to the third spherical mirror 3, and the second surface is cemented to the first surface of the fifth spherical mirror 5. The fourth spherical mirror 4 is a biconvex lens with a positive optical power, and its material is LaK2; the fifth spherical mirror 5 is a biconcave lens with a negative optical power, and its material is ZF7. The fourth spherical mirror 4 and the fifth spherical mirror 5 work together and are mainly used for the auxiliary correction of spherical aberration, chromatic aberration, astigmatism, field curvature, and distortion.

[0051] The second cemented lens group includes a sixth spherical mirror 6 and a seventh spherical mirror 7 arranged coaxially in sequence. The first surface of the sixth spherical mirror 6 is arranged close to the fifth spherical mirror 5, and the second surface is cemented to the first surface of the seventh spherical mirror 7. The sixth spherical mirror 6 is a meniscus lens with a negative optical power and a convex surface facing the object side, and its material is LaK2; the seventh spherical mirror 7 is a biconvex lens with a positive optical power, and its material is ZF7. The sixth spherical mirror 6 and the seventh spherical mirror 7 work together and are mainly used for the auxiliary correction of coma, astigmatism, field curvature, distortion, spherical aberration, and chromatic aberration.

[0052] The aperture stop 11 is arranged between the fifth spherical mirror 5 and the sixth spherical mirror 6 for dimming. In this embodiment, the aperture stop 11 is located 0.17 mm in front of the sixth spherical mirror 6.

[0053] The eighth spherical mirror 8 is a meniscus lens with a negative optical power and a convex surface facing the object side. Its material is ZF7, and it is mainly used for correcting astigmatism, distortion in off-axis aberrations, and chromatic aberration in on-axis aberrations. The ninth spherical mirror 9 is a biconvex lens with a positive optical power. Its material is ZF7, and it is mainly used for the auxiliary correction of coma, astigmatism, distortion, and spherical aberration. The tenth spherical mirror 10 is located at the rear end of the fixed-focus lens, that is, it is arranged on the side close to the image plane 12. The tenth spherical mirror 10 is a meniscus lens with a negative optical power and a convex surface facing the image side. Its material is ZF7, and it is mainly used for the auxiliary correction of astigmatism, field curvature, and distortion, and realizes imaging at the position of the image plane 12 after the system aberration is balanced.

[0054] 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.

[0055] In this embodiment, the system focal length of the fixed-focus lens is 23 mm, the F number is F2, the imaging size is Φ23.7 mm, the total system length is 150 mm, the field of view can reach ±52.8°, and the relative aperture D / f′ = 2 (D represents the entrance pupil diameter, f′ represents the focal length), and it can be applicable to cameras with a pixel size of 3.3 μm and above. The optical element parameters of the ten spherical mirrors are shown in Table 1:

[0056] Table 1 Optical Element Parameters

[0057]

[0058]

[0059] As Figure 2 、 Figure 3 shown, they are respectively the modulation transfer function (MTF) curve graph and the distortion curve graph of the fixed-focus lens in this embodiment at different fields of view when the spatial frequency is 150 lp / mm. Figure 2 In Figure 3The abscissa represents the percentage, and the ordinate 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, green curve, and 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 fixed-focus lens of this embodiment, when the spatial frequency is 150 lp / mm, MTF ≥ 0.4, and the distortion of the full field of view ≤ 0.5%, which has good imaging quality, small distortion of the full field of view, and high resolution, fully meeting the performance requirements of the fixed-focus lens.

[0060] As described above, it 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 embodiments can be modified, or some of the technical features can be equivalently replaced. However, these modifications or replacements do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solution protected by the present invention.

Claims

1. A fixed focal length lens suitable for a 4K resolution detector, characterized in that: It comprises a first spherical mirror (1), a second spherical mirror (2), a third spherical mirror (3), a first cemented mirror group, an aperture stop (11), a second cemented mirror group, an eighth spherical mirror (8), a ninth spherical mirror (9), and a tenth spherical mirror (10) which are coaxially arranged in sequence; the image plane (12) is located behind the tenth spherical mirror (10); The first glued mirror group comprises a fourth spherical mirror (4) and a fifth spherical mirror (5) which are coaxially glued in sequence, and the fourth spherical mirror (4) is located on a side close to the third spherical mirror (3); the second glued mirror group comprises a sixth spherical mirror (6) and a seventh spherical mirror (7) which are coaxially glued in sequence, and the sixth spherical mirror (6) is located on a side close to the fifth spherical mirror (5); The first spherical mirror (1) is a meniscus lens with a convex surface facing the object side, and its optical power is negative; The second spherical mirror (2) is a plano-convex lens with a convex surface facing the object side, and its optical power is positive; The third spherical mirror (3) is a meniscus lens with a convex surface facing the object side, and its optical power is negative; The fourth spherical mirror (4) is a biconvex lens with positive optical power; The fifth spherical mirror (5) is a biconcave lens, and its optical power is negative; The sixth spherical mirror (6) is a meniscus lens with a convex surface facing the object side, and its optical power is negative; The seventh spherical mirror (7) is a biconvex lens with positive optical power; The eighth spherical mirror (8) is a meniscus lens with a convex surface facing the object side, and its optical power is negative; The ninth spherical mirror (9) is a biconvex lens with positive focal power; The tenth spherical mirror (10) is a meniscus lens with a convex surface facing the image side, and its optical power is negative.

2. A fixed focal length lens suitable for a 4K resolution detector according to claim 1, characterized in that: The aperture stop (11) is located 0.17 mm in front of the sixth spherical mirror (6).

3. A fixed focal length lens suitable for a 4K resolution detector according to claim 1 or 2, characterized in that: The first spherical mirror (1) is made of LaK2 and has a thickness of 3 mm. The distance between the first spherical mirror (1) and the second spherical mirror (2) is 57.77 mm. The second spherical mirror (2) is made of ZF7 and has a thickness of 10 mm. The distance between the second spherical mirror (2) and the third spherical mirror (3) is 17.67 mm. The third spherical mirror (3) is made of ZF7 and has a thickness of 3.2 mm. The distance between the third spherical mirror (3) and the fourth spherical mirror (4) is 3.5 mm. The fourth spherical mirror (4) is made of LaK2 and has a thickness of 10 mm; the fifth spherical mirror (5) is made of ZF7 and has a thickness of 2 mm, and the distance between the fifth spherical mirror and the aperture stop (11) is 13.87 mm; The sixth spherical mirror (6) is made of LaK2 and has a thickness of 2.2 mm; the seventh spherical mirror (7) is made of ZF7 and has a thickness of 5.6 mm, and the distance between the seventh spherical mirror (7) and the eighth spherical mirror (8) is 4.97 mm; The eighth spherical mirror (8) is made of ZF7, has a thickness of 3.5 mm, and a distance between the eighth spherical mirror (8) and the ninth spherical mirror (9) is 1.69 mm; The ninth spherical mirror (9) is made of ZF7, has a thickness of 2.8 mm, and is spaced 6.0 mm from the tenth spherical mirror (10); The material of the tenth spherical mirror (10) is ZF7, the thickness is 2.5 mm, and the distance between the tenth spherical mirror and the image plane (12) is 2.5 mm.

4. A fixed focal length lens suitable for a 4K resolution detector according to claim 3, characterized in that: The first spherical mirror (1) has a first surface with a radius of curvature of 141.6 mm and a second surface with a radius of curvature of 44.92 mm; The radius of curvature of the first surface of the second spherical mirror (2) is 78.46 mm; The curvature radius of the first surface of the third spherical mirror (3) is 28.81 mm, and the curvature radius of the second surface is 20.40 mm; The curvature radius of the first surface of the fourth spherical mirror (4) is 31.71 mm, and the curvature radius of the second surface is -43.11 mm; The curvature radius of the first surface of the fifth spherical mirror (5) is -43.11 mm, and the curvature radius of the second surface is 80.67 mm; The curvature radius of the first surface of the sixth spherical mirror (6) is 28.95 mm, and the curvature radius of the second surface is 20.10 mm; The curvature radius of the first surface of the seventh spherical mirror (7) is 20.10 mm, and the curvature radius of the second surface is -81.38 mm; The curvature radius of the first surface of the eighth spherical mirror (8) is 17.65 mm, and the curvature radius of the second surface is 14.69 mm; The curvature radius of the first surface of the ninth spherical mirror (9) is 66.72 mm, and the curvature radius of the second surface is -95.90 mm; The curvature radius of the first surface of the tenth spherical mirror (10) is -13.36 mm, and the curvature radius of the second surface is -52.95 mm.

5. A fixed focal length lens suitable for a 4K resolution detector according to claim 4, characterized in that: The fixed-focus lens system composed of the first spherical mirror (1), the second spherical mirror (2), the third spherical mirror (3), the first cemented lens group, the aperture stop (11), the second cemented lens group, the eighth spherical mirror (8), the ninth spherical mirror (9) and the tenth spherical mirror (10) has a focal length of 23 mm, an F number of F2, an imaging size of Φ23.7 mm, and a total length of 150 mm.

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