Imaging optical lens and system applied to night vision goggles

Abstract

The invention relates to an imaging optical lens and system applied to night vision goggles, the working wave band of the imaging optical lens is 200nm-800nm, and the imaging optical lens sequentially comprises a front lens group, a diaphragm front lens group, a diaphragm rear lens group, a rear lens group and an ultraviolet image intensifier from an object plane to an image plane; the front lens group comprises a first lens with positive focal power, the diaphragm front lens group comprises a second lens with positive focal power, a third lens with negative focal power and a fourth lens with positive focal power, and the diaphragm rear lens group comprises a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with negative focal power. And the rear lens group comprises an eighth lens with positive focal power. The imaging optical system has the advantages of being large in caliber, wide in wave band and high in imaging resolution, the detection wave band range of the night vision goggles can be expanded to the ultraviolet wave band, and the whole lens is made of quartz and calcium fluoride spherical glass and is easy to machine.

Description

Technical Field

[0001] The present invention relates to the technical field of optical instruments, and in particular to an imaging optical lens and system used in night vision goggles. Background Art

[0002] Low-light-level night vision goggles use image intensifiers to enhance the faint target image illuminated by night sky light, making it a clear picture for observation.

[0003] In nighttime wildlife observation, night exploration and other activities, low-light night vision goggles can provide necessary visual assistance. There is a type of night vision goggles equipped with near-infrared light sources to cope with extremely weak lighting conditions. They are called active night vision goggles, which are used to observe by actively irradiating and using the near-infrared light reflected by the target animal. Although active night vision goggles are not restricted by ambient lighting conditions, the light emitted by their near-infrared light sources will produce a red storm phenomenon, which can easily be discovered by animals and cause them to escape. Most animals cannot perceive light in the ultraviolet band. If ultraviolet light sources are used for lighting, it will be more concealed and will not disturb the animals. Therefore, it is of positive significance to expand the band range of the imaging optical system of night vision goggles to ultraviolet.

[0004] According to the spectral characteristics of night sky light, the optical lenses of existing low-light night vision goggles can only be applied to the visible light to near-infrared band. Directly applying them to the ultraviolet band will produce unpredictable chromatic aberrations and affect the image quality. In addition, ordinary optical glass has strong absorption of ultraviolet light and can hardly be used for receiving ultraviolet light. In contrast, most existing ultraviolet optical lenses only cover the 240nm to 280nm band and cannot achieve good imaging effects in the visible light band and near-infrared band. In addition, the f-number of imaging optical lenses for night vision goggles is generally less than 1.3. It is difficult for imaging lenses to achieve such a small f-number while achromatizing in a wide band from ultraviolet to near-infrared. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide an imaging optical lens and system for night vision goggles. The optical lens has a wide working band range, including ultraviolet, visible light and near-infrared bands, and the f-number of the imaging optical lens is not higher than 1.25, the field of view is not less than 40°, the entire optical lens includes only 8 lenses, the focal length ratio is not less than 0.58, the axial dispersion spot is less than 10μm, and it can be adapted to a high-resolution ultraviolet image intensifier and applied to low-light night vision goggles. The optical system can migrate the illumination light source band of active night vision goggles from the near-infrared band to the ultraviolet band, reducing the disturbance of the night vision goggles light source to the observed animals.

[0006] The technical solution of the present invention is:

[0007] An imaging optical lens used in night vision goggles, including, in order from the object plane to the image plane along the optical axis direction: a front lens group G1, an aperture front lens group G2, an aperture rear lens group G3, and a rear lens group G4;

[0008] The front lens group includes a first lens 1 with positive focal power, the aperture front lens group includes a second lens 2 with positive focal power, a third lens 3 with negative focal power, and a fourth lens 4 with positive focal power, the aperture rear lens group includes a fifth lens 5 with negative focal power, a sixth lens 6 with positive focal power, and a seventh lens 7 with negative focal power, and the rear lens group includes an eighth lens 8 with positive focal power;

[0009] The focal length of the imaging optical lens is f, and the combined focal length of the front lens group is f G1 , f and fG1 have the same sign and satisfy the following inequality: 1.1f<f G1 <1.3f;

[0010] The combined focal length of the lens group before the aperture is f G2 , f and f G2 The signs are the same and the following inequality is satisfied: 3f<f G2 <4.2f;

[0011] The combined focal length of the lens group behind the aperture is f G3 , f and f G3 The signs are opposite and the following inequality is satisfied: 2.7f<f G3 <5.5f;

[0012] The combined focal length of the rear lens group is f G4 , f and f G4 The signs are the same and the following inequality is satisfied: 4f<f G4 <4.1f;

[0013] The full field of view of the ultraviolet imaging optical lens is not less than 40 degrees;

[0014] The f-number of the ultraviolet imaging optical lens satisfies the following inequality: 1<f / #<1.25;

[0015] The total optical length of the ultraviolet imaging optical lens is l, which satisfies the following inequality: f / l>0.58;

[0016] The optical surfaces of the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7 and the eighth lens 8 are all spherical surfaces, wherein the material used for the first lens 1, the third lens 3, the fifth lens 5 and the seventh lens 7 is fused silica, and the material used for the second lens 2, the fourth lens 4, the sixth lens 6 and the eighth lens 8 is calcium fluoride;

[0017] The present invention also provides an imaging optical system for night vision goggles, comprising an imaging optical lens and an image intensifier for night vision goggles as described in the present invention; the photocathode surface of the image intensifier is located on the focal plane of the imaging optical system, and the photocathode surface is encapsulated with protective glass 9.

[0018] The beneficial effects of the present invention include:

[0019] (1) Wide band: The band covers 200nm to 800nm, which can shift the illumination light source band of active night vision goggles from the near-infrared band to the ultraviolet band;

[0020] (2) Large aperture: f number ≤ 1.25, which can meet the requirements of night vision goggles;

[0021] (3) The ratio of focal length to length is greater than 0.58, with a compact structure and easy to carry;

[0022] (4) Easy to process, all optical surfaces are spherical. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is an optical path diagram of the imaging optical system applied to night vision goggles of the present invention; wherein: G1-front lens group, G2-aperture front lens group, G3-aperture rear lens group, G4-rear lens group; 1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-fifth lens, 6-sixth lens, 7-seventh lens, 8-eighth lens, 9-image intensifier protection glass.

[0024] Figure 2 It is a point arrangement diagram of the imaging optical lens used in night vision goggles of the present invention.

[0025] Figure 3 It is the MTF diagram of the imaging optical lens applied to the night vision goggle of the present invention.

[0026] Figure 4 It is a vertical axis chromatic aberration diagram of the imaging optical lens used in night vision goggles of the present invention.

[0027] Figure 5 It is a field curvature diagram of the imaging optical lens applied to night vision goggles of the present invention.

[0028] Figure 6 It is a distortion diagram of the imaging optical lens used in night vision goggles of the present invention. DETAILED DESCRIPTION

[0029] In order to more clearly understand the above-mentioned objects and features of the present invention, the present invention is further described below in conjunction with embodiments and drawings.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from the description. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0031] Example 1

[0032] An imaging optical system used in night vision goggles, such as Figure 1 As shown, along the optical axis direction from the object plane to the image plane, it includes: front lens group G1, aperture front lens group G2, aperture rear lens group G3, rear lens group G4 and image intensifier. The front lens group G1 and the aperture front lens group G2 provide the main focal power and correct the vertical axis chromatic aberration, and the aperture rear lens group G3 and the rear lens group G4 are responsible for correcting the residual aberration.

[0033] The front lens group G1 includes a first lens 1, which is a concave-convex lens with positive focal power. The aperture front lens group G2 includes a second lens 2, a third lens 3 and a fourth lens 4. The second lens 2 is a concave-convex lens with positive focal power, the third lens 3 is a biconcave lens with negative focal power, and the fourth lens 4 is a biconvex lens with positive focal power. The aperture rear lens group G3 includes a fifth lens 5, a sixth lens 6 and a seventh lens 7. The fifth lens 5 is a concave-convex lens with negative focal power, the sixth lens 6 is a biconvex lens with positive focal power, and the seventh lens 7 is a biconcave lens with negative focal power. The rear lens group G4 includes an eighth lens 8, which is a concave-convex lens with positive focal power.

[0034] The second lens 2 is in direct contact with the edge of the third lens 3, reducing the use of spacers; the third lens 3 and the fourth lens 4 are double-separated lenses, and the materials are fused quartz and calcium fluoride, respectively, to reduce chromatic aberration; the surface curvatures of the front surface of the third lens 3 and the rear surface of the fourth lens 4 are close, and the aberrations produced thereon compensate each other; the fifth lens 5 and the sixth lens 6 are another double-separated lens, which further reduces chromatic aberration, but introduces monochromatic phase difference, which is compensated by the seventh lens 7; the eighth lens 8 adopts a meniscus lens, combined with a protective glass 9, to further reduce the astigmatism of the off-axis field of view.

[0035] The working band of this embodiment is 200nm-800nm, and the calcium fluoride and fused quartz used have high transmittance in this band. The working band range can also be appropriately widened according to the response band of the matching image intensifier, and is not limited by this embodiment.

[0036] The effective focal length of this embodiment is f=26mm, the effective focal length of the front lens group G1 is f1=461.9mm, the effective focal length of the aperture front lens group G2 is f2=36mm, the effective focal length of the aperture rear lens group G3 is f3=-62.35mm, and the effective focal length of the aperture rear lens group G4 is f4=50.76mm. The diagonal full field of view of the lens is 40°, the diffraction dispersion spot is less than 10μm, the on-axis transmission function is greater than 0.7 at 40lp, the vertical axis chromatic aberration is less than 20um, the distortion is less than 0.4%, and the total length of the system does not exceed 40mm.

[0037] The optical system parameter table (unit: mm) is shown in the following table:

[0038] Surface number lens Curvature radius (mm) Thickness(mm) lens Net diameter (mm) 1 First lens 32 1.5 Fused Silica 16.67 2 37.15 0.1 15.86 3 Second lens 14.39 3.38 Calcium Fluoride 14.8 4 125.47 1.51 13.5 5 The third lens -17.57 1.5 Fused Silica 13.4 6 8.14 0.26 11.2 7 The fourth lens 8.46 7.50 Calcium Fluoride 11.2 8 -13.94 0.2 9.6 9 Fifth lens 12.29 1.4 Fused Silica 10.6 10 9.17 0.15 10.6 11 The sixth lens 9.50 5 Calcium Fluoride 10.6 12 -17.69 0.96 10.6 13 Seventh lens -10.99 1 Fused Silica 10.5 14 10.41 0.91 11.1 15 The eighth lens 10.87 5.0 Calcium Fluoride 12.9 16 18.50 3.81 13 17 Protective glass endless 6 Quartz glass 18 18 endless 0 18 19 Image plane endless 0 18

[0039] Example 2

[0040] The working wavelength range of this embodiment is 200nm to 800nm.

[0041] The effective focal length of this embodiment is f=23.5mm, the effective focal length of the front lens group G1 is f1=30.55mm, the effective focal length of the aperture front lens group G2 is f2=100.91mm, the effective focal length of the aperture rear lens group G3 is f3=-130.44mm, and the effective focal length of the aperture rear lens group G4 is f4=94mm. The diagonal full field angle of the lens is 44°, the diffraction dispersion spot is less than 12μm, the axial transmission function is greater than 0.5 at 40lp, the vertical axis chromatic aberration is less than 30um, the distortion is less than 5%, and the total length of the system does not exceed 40mm. The optical system parameter table (unit: mm) is shown in the following table:

[0042] Surface number lens Curvature radius (mm) Thickness(mm) lens Net diameter (mm) 1 First lens 16.22 3.42 Fused Silica 16.67 2 -103.87 1.37 15.86 3 Second lens -14.97 1.58 Calcium Fluoride 14.8 4 -12.95 0.13 13.5 5 The third lens -12.78 1.5 Fused Silica 13.4 6 7.31 0.18 11.2 7 The fourth lens 7.6 6.08 Calcium Fluoride 11.2 8 -11.65 0.2 9.6 9 Fifth lens 16.3 1.4 Fused Silica 10.6 10 8.44 0.31 10.6 11 The sixth lens 9.67 4.99 Calcium Fluoride 10.6 12 -15.54 0.27 10.6 13 Seventh lens -12.64 2.70 Fused Silica 10.5 14 19.83 0.09 11.1 15 The eighth lens 12.31 5 Calcium Fluoride 12.9 16 15.41 4.11 13 17 Protective glass endless 6 Quartz glass 18 18 endless 0 18 19 Image plane endless 0 18

[0043] Example 3

[0044] An imaging optical system applied to night vision goggles comprises an imaging optical lens and an image intensifier applied to night vision goggles as described in the present invention; the photocathode surface of the image intensifier is located on the focal plane of the imaging optical system, and the photocathode surface is encapsulated with protective glass 9; and an ultraviolet light source is used for illumination.

[0045] It can be seen from the above embodiments that the imaging optical system applied to night vision goggles of the present invention achieves a large aperture that meets the requirements for the use of night vision goggles while ensuring wide-band achromatism, and can expand the detection band of existing low-light night vision goggles to the ultraviolet band, and change the near-infrared lighting source to an ultraviolet lighting source, thereby improving the concealment when using night vision goggles.

Claims

1. An imaging optical lens used in night vision goggles, characterized in that: Along the optical axis direction from the object plane to the image plane, the imaging optical lens is composed of a front lens group (G1), an aperture front lens group (G2), an aperture rear lens group (G3) and a rear lens group (G4) in sequence; the front lens group (G1) and the aperture front lens group (G2) are used to provide optical power and correct vertical axis chromatic aberration, and the aperture rear lens group (G3) and the rear lens group (G4) are used to correct residual aberration; The front lens group (G1) is composed of a first lens (1) with positive focal power, the aperture front lens group (G2) is composed of a second lens (2) with positive focal power, a third lens (3) with negative focal power, and a fourth lens (4) with positive focal power in sequence, the aperture rear lens group (G3) is composed of a fifth lens (5) with negative focal power, a sixth lens (6) with positive focal power, and a seventh lens (7) with negative focal power in sequence, and the rear lens group (G4) is composed of an eighth lens (8) with positive focal power; The working wavelength band of the imaging optical lens is 200nm-800nm.

2. The imaging optical lens according to claim 1, characterized in that: The first lens (1) is a concave-convex lens, and the convex surface of the first lens (1) faces the object plane; The second lens (2) is a concave-convex lens, and the convex surface of the second lens (2) faces the first lens (1) or the third lens (3); The third lens (3) is a biconcave lens; The fourth lens (4) is a biconvex lens; The fifth lens (5) is a concave-convex lens, and the convex surface of the fifth lens (5) faces the fourth lens (4); The sixth lens (6) is a biconvex lens; The seventh lens (7) is a biconcave lens; The eighth lens (8) is a meniscus lens, and the convex surface of the eighth lens (8) faces the seventh lens (7).

3. The imaging optical lens according to claim 2, characterized in that: The second lens (2) is in direct contact with the edge of the third lens (3), so as to reduce the use of a spacer; The third lens (3) and the fourth lens (4) are double-separated lenses for reducing chromatic aberration; The surface curvatures of the front surface of the third lens (3) and the rear surface of the fourth lens (4) are close, and the aberrations generated thereon compensate for each other; The fifth lens (5) and the sixth lens (6) are another double-separated lens, which further reduces chromatic aberration, and the introduced monochromatic aberration is compensated by the seventh lens (7); The eighth lens (8) is a meniscus lens combined with a protective glass (9) to further reduce the astigmatism of the off-axis field of view.

4. The imaging optical lens according to claim 2, characterized in that: The focal length f of the imaging optical lens and the combined focal length f of the front lens group (G1) G1 Satisfy 1.1f<f G1 <1.3f; The focal length f of the imaging optical lens and the combined focal length f of the aperture front lens group (G2) G2 Satisfy 3f<f G2 <4.2f; The focal length f of the imaging optical lens and the combined focal length f of the rear lens group (G3) after the aperture are G3 Satisfy 2.7f<f G3 <5.5f; The focal length f of the imaging optical lens and the combined focal length f of the rear lens group (G4) G4 Satisfying 4f<f G4 <4.1f.

5. The imaging optical lens according to claim 4, characterized in that: The full field angle of the imaging optical lens is greater than or equal to 40 degrees; The f-number of the imaging optical lens satisfies 1<f / #<1.

25.

6. The imaging optical lens according to claim 5, characterized in that: The total optical length l of the imaging optical lens satisfies f / l>0.

58.

7. The imaging optical lens according to any one of claims 1 to 6, characterized in that: The optical surfaces of the first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6), the seventh lens (7) and the eighth lens (8) are all spherical surfaces.

8. The imaging optical lens according to any one of claims 1 to 6, characterized in that: The materials used for the first lens (1), the third lens (3), the fifth lens (5) and the seventh lens (7) are fused silica, and the materials used for the second lens (2), the fourth lens (4), the sixth lens (6) and the eighth lens (8) are calcium fluoride.

9. The imaging optical lens according to any one of claims 1 to 6, characterized in that: The effective focal length of the imaging optical lens is f=26mm, the effective focal length of the front lens group (G1) is f1=461.9mm, the effective focal length of the aperture front lens group (G2) is f2=36mm, the effective focal length of the aperture rear lens group (G3) is f3=-62.35mm, and the effective focal length of the aperture rear lens group (G4) is f4=50.76mm; The lens has a diagonal full field of view of 40°, a diffraction dispersion spot of less than 10 μm, an on-axis transmission function greater than 0.7 at 40 lp, a vertical axis chromatic aberration less than 20 μm, a distortion less than 0.4%, and a total system length not exceeding 40 mm.

10. An imaging optical system used in night vision goggles, characterized in that: The invention comprises an imaging optical lens for night vision goggles as claimed in any one of claims 1 to 9, and also comprises an image intensifier, wherein the photocathode surface of the image intensifier is located on the focal plane of the imaging optical lens, and the photocathode surface is encapsulated with protective glass (9).

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