RU2360269C1 - Objective for night vision device - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: proposed objective can be used with electro-optical transducers, particularly zero generation electro optical transducers, with a spherical cathode. The objective contains, in the beam path, a first element in form of a single plane-convex lens, the convex side of which faces the object, and a second element, made in form of double convex and double concave lenses stuck together, the convex side of which faces the object, and a third element in form of a single positive meniscus, the convex surface of which faces the object and a fourth element in form of a symmetrical double concave lens.

EFFECT: improved quality of image in the region of high space frequencies, with compatibility with zero generation electro optical transducers with a spherical cathode.

6 dwg

Description

The invention relates to optical instrumentation and can be used in night-vision devices with electron-optical converters (image intensifier tubes), in particular with zero-generation image intensifiers having a spherical cathode. The market of night-vision devices has been rapidly developing in recent decades, and demand has increased both for military-grade night-vision devices working with second and third-generation image intensifiers, and for civilian devices, which include not only zero-first-generation amateur devices, but also military systems adapted for the needs of rescue services to provide law enforcement and security personnel, also related to zero-generation devices. Significant in terms of the number of manufactured products is the market for night-vision devices working together with a zero-generation image intensifier tube with a spherical cathode. The possibility of using a zero-generation tube with a spherical cathode was very limited due to defocusing at points remote from the center of the cathode. This problem was solved in principle through the use of lenses having an image curvature that matches the curvature of the cathode, but the optics are complex, consisting of a large number of elements. The use of simpler lenses leads to large distortions at the edges of the image, due to the significant curvature of the field of view. So, the known lens for night vision devices according to patent RU No. 22218585, IPC G02B 13/14, 9/60, 2003, containing positive two-lens gluing, positive single meniscus, negative two-lens gluing and two convex facing meniscus installed along the beam to each other.

This lens can be successfully used in conjunction with the second and third generation image intensifier tubes, but its use together with the zero generation image intensifier tubes with a spherical cathode does not provide high image quality because it gives a clear image only in the center, with distortion and lower resolution at the edges due to the significant curvature of the field of view. Thus, a disadvantage of the known lens when used in conjunction with a zero-generation image intensifier tube having a spherical cathode is the low image quality.

Another disadvantage of the known lens is a large number of lenses and a large range of glass brands used. This disadvantage is also significant, since it is mainly on the use of zero-generation image intensifier tubes with a spherical shape that the market segment of wearable and portable night-vision devices is built.

Closest to the claimed lens by technical nature (prototype) is a lens for night vision devices made in the form of five elements installed along the beam, the first of which is made in the form of a single positive plano-convex lens convex to the object, the second - in the form of gluing from positive biconvex and negative biconcave lenses convex to the subject, and the third is a flat-concave lens facing concavity to the image, the fourth and fifth glossy convex lens and meniscus, respectively, convex to the subject [RU No. 2276799, IPC G02B 13/14, 9/60, 2004].

This lens has a smaller number of elements and a smaller range of glasses relative to the first analogue, however, the image quality when working with a zero-generation image intensifier tube with a spherical cathode remains low for the reasons mentioned above when describing the lens according to patent RU No. 2218585.

Thus, the object of the invention is to provide a lens for night vision devices, which provides high image quality when working together with a zero-generation image intensifier tube having a spherical cathode, and which also has a small number of elements.

This object is achieved by the fact that in the lens for night vision devices containing the first element installed in the direction of the beam in the form of a single positive plano-convex lens convex to the object, the second element in the form of gluing from the positive biconvex and negative biconcave lens, convex to the object, the third element is made in the form of a single positive meniscus, the convex surface of the positive lens facing the object, and the fourth in the form of a symmetrical biconcave th lenses. Thus, the lens contains only four elements.

The invention is illustrated by drawings.

Figure 1 shows the optical diagram of the lens of the night vision device;

figure 2 is a graph of a frequency-contrast characteristic (TSC);

in Fig.3 - graphs of radial aberrations, in Fig.3a are graphs of radial aberrations for the axial beam of rays (ω = 0 °), and Fig.3b and 3c for off-axis bundles of rays of two tilts (ω = 4,5 ° and ω = 6.5 °, respectively);

figure 4 is a graph of curvature and astigmatism;

figure 5 is a graph of distortion;

figure 6 is a graph of longitudinal chromatism.

The lens for the night-vision device (Fig. 1) contains four optical elements, the first of which is made in the form of a single positive plano-convex lens 1, convex to the object, and the second - as a gluing 2 of the positive biconvex and negative biconcave lenses, turned convexity to the object, the third element is made in the form of a single positive meniscus 3, the convex side facing the object, the fourth - in the form of a symmetrical biconcave lens 4.

The optical power of the lens elements are related by the following relationships:

φ ₁ = (0.2 ÷ 0.4) φ ₀ ; φ ₂ = (0.3 ÷ 0.6) φ ₀ ; φ ₃ = - (0.7 ÷ 1.4) φ ₀ ; φ ₄ = - (3 ÷ 6) φ ₀ ,

where φ ₀ is the optical power of the lens;

φ ₁ , φ ₂ , φ ₃ , φ ₄ - the optical power of the lens elements.

The optical power of the lenses of the second element 2 of the lens are connected by the following relationships:

φ ₂₁ = (1.5 ÷ 4) φ ₂ ; φ ₂₂ = - (1.5 ÷ 3.5) φ ₂ ,

where φ ₂ is the optical power of the second element 2 of the lens;

φ ₂₁ , φ ₂₂ - optical power of the lenses of the second element 2 of the lens.

In this case, the radii of curvature of the surface of the third element 3, facing the fourth element 4, and the surfaces of the fourth element 4 are in the following dependence:

R ₇ = -R ₈ = R ₉ .

The lens works as follows. Light from an object located at a great distance from the first element, being refracted, passes through elements 1, 2, 3, 4 and forms an image of the object in the focal plane of the lens.

In accordance with the proposed technical solution, the lens variant was calculated for the focal length f = 70 mm and the input aperture D = 50 mm, the design parameters of which are given in the table.

Surface Radius Thickness Glass mark Diameter STO 119.12 6 Bk8 52 2 ∞ 0.4 52 3 44.06 12 Tk14 fifty four -248.9 4.5 TF10 fifty 5 93.76 55.1 44 6 18.196 12 Tk14 16 7 01/23 2.2 fourteen 8 -23.01 3 Bf27 fourteen 9 01/23 0.3 fifteen 10 thirty 1.2 Lk3 fifteen eleven thirty 16

The lens has an angular field of view of 2ω = 13 °, a relative aperture of 1: 1.4, and high image quality, which is confirmed by the graphs presented in figures 2-6.

On all the mentioned graphs, the curves are presented for four wavelengths - 0.486; 0.587; 0.656; 0.852 μm, while the curves for a wavelength of 0.486 μm are shown by a solid line, for 0.587 μm by a short dotted line, 0.656 μm by a long dotted line, and 0.852 μm by a dash-dotted line. The range of scales along the ordinate axis corresponds to the input diameter of the lens.

As can be seen from the graphs, the lens made in accordance with the invention is characterized by the following parameters:

- chromatic aberration does not exceed 0.02 mm in the entire range of the spectrum and field of view (Fig.6);

- spherical aberration on the pupil area m = 0.707 ΔS ′ <0.025 mm (figure 3);

- meridional curvature ΔX′m <0.05 mm (figure 4);

- sagittal curvature ΔX′s <0.05 mm (figure 4);

- distortion <0.3% (figure 5);

The polychromatic modulation transfer coefficient (KPM) in the image of the sinusoidal world of absolute contrast at a spatial frequency of N = 40 mm ^-1 (FIG. 2) in the spectral range of wavelengths from 486 to 852 nm is:

- for the axial point of the subject - from 0.3 to 0.4;

- for the edge of the field:

- meridional section - from 0.17 to 0.2;

- sagittal section - from 0.17 to 0.2.

As can be seen from a specific example embodiment of the invention, the claimed lens has a high image quality in the field of increased spatial frequencies when working in conjunction with a zero-generation image intensifier having a spherical cathode.

This became possible due to the fact that the calculated image surface of the lens has a spherical shape that matches the shape of the cathode, and this ensures a significant reduction in aberrations and, in particular, eliminates the curvature of the field of view, and also ensures high values of polychromatic frequency-contrast characteristics taking into account spectral efficiency photocathode in the field of increased spatial frequencies. Moreover, the lens according to the invention has a relatively simple optics, including only 4 elements (instead of 5 in the prototype) and fewer lenses (5 instead of 6 in the prototype).

Claims (1)

A lens for night vision devices, containing the first element mounted in the direction of the beam made in the form of a single positive plano-convex lens convex to the object, the second element made in the form of gluing from the positive biconvex and negative biconcave lenses, convex to the object, as well as the third and the fourth element, characterized in that the third element is made in the form of a single positive meniscus with a convex surface facing the object, and the fourth in the form of a symmetry ary biconcave lens.

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