Imaging optical lens and system used in night vision goggles

Abstract

The present invention relates to an imaging optical lens and system for use in night vision goggles. The imaging optical lens operates in a wavelength band of 200 nm to 800 nm and comprises, from the object plane to the image plane, a front lens group, a front aperture lens group, a rear aperture lens group, a rear lens group, and an ultraviolet image intensifier. The front lens group includes a first lens with positive focal power, the front aperture lens group includes a second lens with positive focal power, a third lens with negative focal power, and a fourth lens with positive focal power, the rear aperture lens group includes 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 includes an eighth lens with positive focal power. The imaging optical system of the present invention has the characteristics of a large aperture, a wide wavelength band, and high imaging resolution. It can expand the detection wavelength range of night vision goggles to the ultraviolet band. The entire lens is made of quartz and calcium fluoride spherical glass, making it easy to process.

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] Low-light-level night vision goggles can provide essential visual support for activities such as nocturnal wildlife observation and nighttime exploration. One type of night vision goggles is equipped with a near-infrared light source to address extremely low light conditions. These goggles actively illuminate and utilize the near-infrared light reflected by the target animal for observation. These goggles are known as active night vision goggles. While these goggles are not restricted by ambient lighting conditions, the near-infrared light emitted by these goggles produces a red burst phenomenon, making them easily visible to animals and causing them to flee. Most animals cannot perceive ultraviolet light, so using ultraviolet light sources provides a more discreet and less disturbing effect. Therefore, expanding the wavelength range of night vision goggles' imaging optics to include the ultraviolet is highly beneficial.

[0004] Due to the spectral characteristics of night sky light, existing optical lenses for low-light-level night vision goggles are only suitable for use in the visible to near-infrared wavelength range. Directly applying them to the ultraviolet wavelength range would produce unpredictable chromatic aberration, thus affecting image quality. Furthermore, ordinary optical glass strongly absorbs ultraviolet light, making it virtually unsuitable for ultraviolet light reception. Conversely, existing ultraviolet optical lenses mostly cover only the 240nm to 280nm wavelength range, failing to achieve good imaging effects in the visible and near-infrared wavelength ranges. Furthermore, the f-number of imaging optical lenses used in night vision goggles is generally less than 1.3, making it difficult to achieve such a low f-number while maintaining achromatic aberration across a wide wavelength range from the ultraviolet to the 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, wherein the optical lens has a wide operating band, including ultraviolet, visible light and near infrared bands, and the f-number of the imaging optical lens is not higher than

[0006] 1.25, with a field of view of no less than 40°. The entire optical lens consists of only eight lenses, a focal length ratio of no less than 0.58, and an on-axis diffuse spot size of less than 10μm. It is compatible with high-resolution UV image intensifiers and is suitable for use in low-light-level night vision goggles. This optical system can shift the wavelength of the illumination source for active night vision goggles from the near-infrared band to the ultraviolet band, reducing the risk of disturbing the observed animals.

[0007] The technical solution of the present invention is:

[0008] An imaging optical lens for night vision goggles, comprising, 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;

[0009] The front lens group includes a first lens 1 with positive focal power, the front lens group of the aperture 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 rear lens group of the aperture 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;

[0010] 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;

[0011] 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;

[0012] 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;

[0013] 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;

[0014] The full field of view angle of the ultraviolet imaging optical lens is not less than 40 degrees;

[0015] The f-number of the ultraviolet imaging optical lens satisfies the following inequality: 1<f / #<1.25;

[0016] The total optical length of the ultraviolet imaging optical lens is l, which satisfies the following inequality: f / l>0.58;

[0017] 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. 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.

[0018] The present invention also provides an imaging optical system for night vision goggles, comprising an imaging optical lens for night vision goggles and an image intensifier 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.

[0019] The beneficial effects of the present invention include:

[0020] (1) Wide band: The band covers 200nm~800nm, which can shift the illumination light source band of active night vision goggles from the near infrared band to the ultraviolet band;

[0021] (2) Large aperture: f-number ≤ 1.25, which can meet the requirements of night vision goggles;

[0022] (3) The ratio of focal length to length is greater than 0.58, with a compact structure and easy to carry;

[0023] (4) Easy to process, all optical surfaces are spherical. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a light path diagram of the imaging optical system of the present invention applied to night vision goggles; 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.

[0025] Figure 2 It is a point diagram of the imaging optical lens used in night vision goggles of the present invention.

[0026] Figure 3 It is the MTF diagram of the imaging optical lens used in night vision goggles of the present invention.

[0027] Figure 4 This is a vertical axis chromatic aberration diagram of the imaging optical lens used in night vision goggles of the present invention.

[0028] Figure 5 It is a field curvature diagram of the imaging optical lens used in night vision goggles of the present invention.

[0029] Figure 6 This is a distortion diagram of the imaging optical lens used in night vision goggles of the present invention. DETAILED DESCRIPTION

[0030] In order to more clearly understand the above-mentioned objects and features of the present invention, the present invention will be further described below in conjunction with embodiments and drawings.

[0031] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0032] Example 1

[0033] 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.

[0034] The aperture front lens group G2 provides the main optical power and corrects vertical chromatic aberration, while the aperture rear lens group G3 and the rear lens group G4 are responsible for correcting residual aberrations.

[0035] Front lens group G1 includes first lens element 1, which is a meniscus lens with positive optical power. Aperture front lens group G2 includes second lens element 2, third lens element 3, and fourth lens element 4. Second lens element 2 is a meniscus lens with positive optical power, third lens element 3 is a biconcave lens with negative optical power, and fourth lens element 4 is a biconvex lens with positive optical power. Aperture rear lens group G3 includes fifth lens element 5, sixth lens element 6, and seventh lens element 7. Fifth lens element 5 is a meniscus lens with negative optical power, sixth lens element 6 is a biconvex lens with positive optical power, and seventh lens element 7 is a biconcave lens with negative optical power. Aperture rear lens group G4 includes eighth lens element 8, which is a meniscus lens with positive optical power.

[0036] The second lens 2 is in direct contact with the edges of the third lens 3, reducing the need for spacers; the third lens 3 and the fourth lens 4 are double-separated lenses, made of fused quartz and calcium fluoride, respectively, to reduce chromatic aberration; the surface curvature of the front surface of the third lens 3 and the rear surface of the fourth lens 4 are similar, and the aberrations produced thereon compensate for each other; the fifth lens 5 and the sixth lens 6 are another double-separated lens, further reducing chromatic aberration, but introducing monochromatic phase difference, which 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.

[0037] The operating wavelength range of this embodiment is 200nm to 800nm. The calcium fluoride and fused silica used have high transmittance in this wavelength range. The operating wavelength range can also be appropriately widened according to the response wavelength range of the matching image intensifier and is not limited to this embodiment.

[0038] In this embodiment, the effective focal length 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 rear lens group G4 is f4=50.76mm. The lens has a full diagonal field of view of 40°, a diffraction spot of less than 10μm, an on-axis transmission coefficient greater than 0.7 at 40lp, vertical chromatic aberration less than 20μm, distortion less than 0.4%, and a total system length of no more than 40mm.

[0039] The optical system parameter table (unit: mm) is shown in the following table:

[0040] .

[0041] Example 2

[0042] The working wavelength range of this embodiment is 200nm to 800nm.

[0043] In this embodiment, the effective focal length 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 rear lens group G4 is f4=94mm. The lens has a full diagonal field of view of 44°, a diffraction dispersion spot of less than 12μm, an on-axis transmission coefficient greater than 0.5 at 40lp, vertical chromatic aberration less than 30μm, distortion less than 5%, and a total system length of no more than 40mm.

[0044] The optical system parameter table (unit: mm) is shown in the following table:

[0045] .

[0046] Example 3

[0047] An imaging optical system for night vision goggles includes the imaging optical lens for night vision goggles described in the present invention and an image intensifier; 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. An ultraviolet light source is used for illumination.

[0048] As can be seen from the above embodiments, the imaging optical system of the present invention applied to night vision goggles achieves a large aperture that meets the requirements of night vision goggles while ensuring wide-band achromatism. It can expand the detection band of existing low-light-level night vision goggles to the ultraviolet band, change the near-infrared lighting source to an ultraviolet lighting source, and improve 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 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 the main 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; The first lens (1) is a concave-convex lens, with the convex surface of the first lens (1) facing the object plane; the second lens (2) is a concave-convex lens, with the convex surface of the second lens (2) facing 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, with the convex surface of the fifth lens (5) facing 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 concave-convex lens, with the convex surface of the eighth lens (8) facing the seventh lens (7); 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 each other; the fifth lens (5) and the sixth lens (6) are another double-separated lens for further reducing 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) for further reducing the astigmatism of the off-axis field of view; The focal length f of the imaging optical lens and the combined focal length f of the front lens group (G1) G1 Satisfying 1.1f<f G1 <1.3f; the combined focal length f of the imaging optical lens and the aperture front lens group (G2) G2 Satisfying 3f<f G2 <4.2f; the focal length f of the imaging optical lens and the combined focal length f of the rear aperture lens group (G3) G3 Satisfying 2.7f<f G3 <5.5f; the combined focal length f of the imaging optical lens and the rear lens group (G4) G4 Satisfying 4f<f G4 <4.1f; 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; The total optical length l of the imaging optical lens satisfies f / l>0.58; The diffraction dispersion spot of the imaging optical lens is less than 10 μm, the on-axis transmission coefficient is greater than 0.7 at 40 lp, the vertical axis chromatic aberration is less than 20 μm, the distortion is less than 0.4%, and the total length of the system does not exceed 40 mm.

2. The imaging optical lens according to claim 1, wherein: The second lens (2) is in direct contact with the edge of the third lens (3), thereby reducing the use of spacers.

3. The imaging optical lens according to any one of claims 1 to 2, wherein: 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.

4. The imaging optical lens according to any one of claims 1 to 2, wherein: The materials used for the first lens (1), the third lens (3), the fifth lens (5) and the seventh lens (7) are fused quartz, 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.

5. The imaging optical lens according to any one of claims 1 to 2, wherein: 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 rear lens group (G4) is f4=50.76mm; The diagonal full field of view of the imaging optical lens is 40°.

6. An imaging optical system used in night vision goggles, characterized in that: The invention comprises an imaging optical lens for use in a night vision goggle as claimed in any one of claims 1 to 5, 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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