RU2504808C1 - Objective lens for night vision device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: objective lens has a first positive meniscus whose concave surface faces the second component, a second negative component consisting of a biconvex lens and concave lens glued to each other, a fourth biconvex lens, third and fifth negative menisci whose concave surfaces face the fourth lens. The distance between the first lens and the second component is not less than 0.3 times the focal length of the objective lens. All lenses are made of glass with coefficients of linear expansion in the range of (5-10)·10^-6 deg^-1. The operating temperature range ΔT average temperature change of the refraction index

of the glass of the first lens and the biconvex lens of the second component is in the range of (-2-0)·10^-6 deg^-1 and in the range of (0-4)·10^-6 deg^-1 for the other lenses. Optical power ratios satisfy relationships given in the claim.

EFFECT: high aperture ratio and field angle, reduced weight while maintaining the diameter of the entrance pupil, providing thermal adjustability and high image quality in a wide operating temperature range without additional movements of the objective lens, components thereof or electro-optical converter.

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Description

The invention relates to the field of optical instrumentation, namely to the lenses of night vision devices (NVD), and can be used to work in conjunction with electron-optical converters (EOP) in the NVD for solving problems of detection and recognition of objects at low light. The proposed lens can be used in both passive and active-pulse NVDs, including night vision sights and night afocal mounts for daytime optical sights, in conjunction with 2, 2+ and 3rd generation image intensifiers.

The creation of new and improving the design solutions for NVD lenses is based on a combination of characteristics, including increasing the diameters of the entrance pupils, relative openings, image quality on the axis and field, reducing mass and overall dimensions, etc. Since radiation detectors used in NVDs have if the linear dimensions are certain, then the focal length of the lens and the angular field are inversely proportional. Due to the variety of requirements for NVD lenses, a lot of their circuit solutions are known [Patent No. 2175774, 2001 [1]; Patent No. 2276799, 2006 [2]; Tochpribor, T.1, c.259-260 [3]; Patent No. 2368923, 2009 [4]; Patent No. 3260269, 2009 [5]]. For ease of comparison, information on examples of specific lenses shown in the indicated analogues is summarized in table 1. Moreover, the length along the L axis is indicated from the first surface to the image plane.

, который составлен по следующему принципу: в числителе указаны характеристики, увеличение которых способствует повышению эксплуатационных показателей, в знаменателе - повышение которых ведет к снижению эксплуатационных показателей ПНВ в целом. А именно: чем выше

, тем больше поле зрение прибора; чем выше f', тем больше масштаб изображения на приемнике и угловое увеличение ПНВ при прочих равных условиях; чем выше D_p, тем выше дальность обнаружения объектов; чем выше T_50,ось, тем выше дальность распознавания при использовании современных ЭОПов; чем выше отношение

, тем более равномерным является качество изображения по полю прибора. С другой стороны, чем выше масса, тем ниже эксплуатационные показатели ПНВ; чем выше диафрагменное число, тем ниже освещенность изображения протяженных объектов на фотокатоде ЭОП. При вычислении k в таблице 1 все линейные размеры подставлялись в мм, масса - в граммах. Очевидно, что одночисловым критерием невозможно провести оценку всех объективов ПНВ, но применительно к решаемой предлагаемым изобретением задачи такой критерий, на наш взгляд, может быть правомерным для комплексной оценки совокупности сравниваемых характеристик объективов-аналогов.A comparison of the characteristics of IRP lenses was carried out according to the following criterion k:

, which is composed according to the following principle: the numerator shows the characteristics, the increase of which contributes to an increase in operational performance, in the denominator - the increase of which leads to a decrease in operational performance of the NVD as a whole. Namely: the higher

, the larger the field of vision of the device; the higher f ', the larger the image scale at the receiver and the angular increase in NVD, all other things being equal; the higher D _p , the higher the detection range of objects; the higher the T _{50 axis} , the higher the recognition range when using modern image intensifier tubes; higher ratio

, the more uniform is the image quality across the field of the device. On the other hand, the higher the mass, the lower the performance of the NVD; the higher the aperture value, the lower the illumination of the image of extended objects on the image intensifier tube. When calculating k in table 1, all linear dimensions were substituted in mm, mass - in grams. Obviously, it is impossible to evaluate all the NVD lenses using a single-digit criterion, but as applied to the problem solved by the invention, such a criterion, in our opinion, may be valid for a comprehensive assessment of the totality of the compared characteristics of analog lenses.

The task to be solved by the claimed device is aimed at creating a high-speed NVD lens with high technical and operational characteristics, providing the possibility of pairing with 2, 2+ and 3rd generation image intensifiers to create a small-sized, manual NVD and use it in a wide range of operating temperatures.

The disadvantage of the lens [1] is the small size of the image, which does not allow it to be used with an image intensifier tube with a photocathode diameter of 18 mm, as well as a low relative aperture and low image quality on the axis and in the field, which does not allow to fully realize the capabilities of modern image intensifiers spatial resolution.

The disadvantage of the lens [3] is the low image quality, limiting their use with modern image intensifiers, as well as the large mass of the lens.

The disadvantage of the lens [4] is the large mass and overall dimensions of the lens, which reduce the performance of manual, portable NVD.

The disadvantage of the lens [5] is the large vignetting of oblique beams, low image quality, which allows them to be used only with a zero-generation image intensifier.

Based on the analysis of analogs, the lens for NVD [2], which is the closest to the proposed lens in terms of the combination of characteristics and the design of the optical circuit, was adopted as the closest analogue. Its description and analysis of the shortcomings are given below.

The closest in technical essence to the claimed device analogue - a lens for a night vision device - consists of optically coupled, located along the rays of the first positive lens, the second component glued from a biconvex and biconcave lenses, a third negative lens, a fourth positive lens, and a fifth negative meniscus, while the lens is made of glass with a refractive index above 1.65.

In the closest analogue, the first lens is made convex, the second component is positive, the third lens is made concave, the fourth lens is convex, the fifth negative meniscus is oriented towards the fourth positive lens with its convex surface. The distance along the axis between the third and fourth lenses is 0.5 of the focal length, between the others it is made small. The diameter of the second component is 0.88 of the diameter of the first lens. Between the optical powers of the lenses and components of an example of a specific embodiment of the closest analogue, the following relationships are true:

where φ ₁ , φ ₂ , φ ₃ , φ ₄ , φ ₅ are the relative optical powers of the first lens, second component, third, fourth and fifth lenses, respectively.

стекол первой положительной линзы и двояковыпуклой линзы второго компонента находится в диапазоне (1÷3)·10^-6 градус^-1, остальных линз объектива - в диапазоне (6÷9)·10^-6 градус^-1.The glasses from which the objective lenses are made - the closest analogue have linear expansion coefficients in the range (7 ÷ 8) · 10 ^-6 degrees ^-1 , the magnitude of the temperature change in the refractive index

the glasses of the first positive lens and the biconvex lens of the second component are in the range (1 ÷ 3) · 10 ^-6 degrees ^-1 , the remaining lenses in the range (6 ÷ 9) · 10 ^-6 degrees ^-1 .

The lens has an angular field of 2ω = 9 °, focal length f '= 100 mm, a relative aperture of 1: 2, a mass of 184 g (in light diameters), a length along the axis of 115 mm. The contrast transmission coefficient at a frequency of 30 lines / mm is 0.8 for a point on the axis, and 0.74 for points along the field.

The disadvantages of the closest analogue are: a small relative hole; insufficient value of the angular field; large mass with a pupil diameter of 50 mm; the appearance of thermal defocusing and a decrease in the declared image quality when the operating temperature changes in the temperature range from -40 to + 50 ° C or the need to introduce additional lens movements, its components or image intensifier tubes to compensate for thermal defocusing. In addition, the lens was calculated without taking into account the thickness of the substrate of the photocathode of the image intensifier tube, the presence of which introduces additional aberrations in converging beams of rays.

The technical result achieved in solving the problem lies in increasing the relative aperture, increasing the angular field, reducing the mass while maintaining the diameter of the entrance pupil, providing thermal stability and maintaining high image quality in the operating temperature range from -50 to + 50 ° C without introduction additional movements of the lens, its components or image intensifier tubes. In addition, the calculation of the lens is made taking into account the influence of the substrate of the photocathode of the image intensifier tube.

стекол первой положительной линзы и двояковыпуклой линзы второго компонента находится в диапазоне (-2÷0)·10^-6 градус^-1, остальных линз объектива - в диапазоне (0÷4)·10^-6 градус^-1, и между относительными оптическими силами выполняется соотношение:The problem is solved, and the technical result is achieved in that, in contrast to the closest analogue, the first positive lens is made in the form of a meniscus facing a concave surface toward the second component, the second component is made negative, the third negative lens is made in the form of a meniscus, and the fourth positive lens is made biconvex, with the third and fifth menisci facing their concave refracting surfaces toward the fourth biconvex lens, the distance between the first a positive lens and the second component is at least 0.3 of the focal length of the lens, the distance between the third and fourth lenses is small compared to the focal length of the lens, while all lenses are made of glasses, the linear expansion coefficients of which are in the range (5 ÷ 10 ) · 10 ^-6 degrees ^-1 , the average value for the working temperature range ΔΤ of the temperature change in the refractive index

the glasses of the first positive lens and the biconvex lens of the second component are in the range (-2 ÷ 0) · 10 ^-6 degrees ^-1 , the remaining lenses in the range (0 ÷ 4) · 10 ^-6 degrees ^-1 , and between the relative optical forces the ratio is satisfied:

where φ ₁ , φ ₂ , φ ₃ , φ ₄ , φ ₅ are the relative optical powers of the first lens, second component, third, fourth and fifth lenses, respectively.

The execution of the first positive lens in the form of a meniscus facing a concave surface towards the second component, the second component negative, the third negative lens in the form of a meniscus, the fourth positive lens is biconvex, the orientation of the third and fifth menisci so that they face their concave refracting surfaces to the side the fourth biconvex lens while observing relation (2) allows to increase the relative aperture and angular field while maintaining high quality The images at the same time be included in the calculation (consider) a substrate photocathode.

The distance between the first positive lens and the second component is not less than 0.3 of the focal length of the lens, and the distance between the third and fourth lenses is small compared with the focal length of the lens allows you to reduce the mass of the lens while maintaining the diameter of the entrance pupil, due to the fact that light the diameters of all the lenses and components in the lens, except the first, in this case become smaller than the diameter of the entrance pupil.

стекол первой положительной линзы и двояковыпуклой линзы второго компонента находится в диапазоне (-2÷0)·10^-6 градус^-1, остальных линз объектива - в диапазоне (0÷4)·10^-6 градус^-1, при соблюдении соотношения (2) и выполнении расстояния между первой положительной линзой и вторым компонентом не менее 0,3 фокусного расстояния объектива позволяет обеспечить термонерастраиваемость и сохранение высокого качества изображения в диапазоне температур эксплуатации от -50 до +50°C без введения дополнительных подвижек объектива, его компонентов или ЭОП.The implementation of the lenses of the glass, the linear expansion coefficients of which are in the range (5 ÷ 10) · 10 ^-6 degrees ^-1 , and the average temperature for the operating temperature range ΔT is the temperature change in the refractive index

the glasses of the first positive lens and the biconvex lens of the second component are in the range (-2 ÷ 0) · 10 ^-6 degrees ^-1 , the remaining lenses in the range (0 ÷ 4) · 10 ^-6 degrees ^-1 , subject to the relation (2 ) and the distance between the first positive lens and the second component is at least 0.3 of the focal length of the lens, it is possible to provide thermal stability and preservation of high image quality in the operating temperature range from -50 to + 50 ° C without introducing additional lens movements, its components or image intensifier tubes.

The specified set of features in the device of the NVD lens allows you to create a high-speed NVD lens with high technical and operational characteristics, providing the possibility of pairing with 2, 2+ and 3rd generation image intensifier tubes to create a small-sized, manual NVD and use it in a wide range of operating temperatures.

The proposed solution, in our opinion, has novelty and inventive step. The authors are not aware of NVD lenses in which sets of the indicated features corresponding to the proposed device would be implemented.

The proposed device is illustrated by the following graphic materials:

figure 1 is an optical diagram of the lens NVD;

figure 2 - astigmatic segments for three wavelengths;

figure 3 - scattering spots for various points of the field;

figure 4 - frequency-contrast characteristic (CCK);

5 is a distortion.

стекол линз 1 и 6 находится в диапазоне (-2÷0)·10^-6 градус^-1, а линз 3, 4, 5, 7 - в диапазоне (0÷4)·10^-6 градус^-1. Между относительными оптическими силами линз и компонентов в объективе выполняется соотношение (2).The lens for NVD (Fig. 1) contains optically coupled lenses and components 1-5 located along the rays, of which the first positive meniscus 1 faces a concave surface toward the second component 2, the second negative component 2 is glued from a biconvex lens 6 and a biconcave lens 7, the third negative meniscus 3 and the fifth negative meniscus 5 face their concave surfaces toward the fourth biconvex lens 4. Pos. 8, in the form of a plane-parallel plate, the protective window of the image intensifier tube, which is the substrate of the photocathode, is also shown. Since the translucent photocathode of the image intensifier tube is deposited on the inner side of the substrate, a plane-parallel plate is included in the optical circuit of the NVD lens during its calculation. The distance between the first positive lens 1 and the second component 2 is at least 0.3 of the focal length of the lens, the distance between the third and fourth lenses is made small compared with the focal length of the lens. The lenses of the lens 1, 3, 4, 5, 6, 7 are made of glasses with a refractive index above 1.65. The coefficients of linear expansion of the lens glasses 1, 3, 4, 5, 6, 7 are in the range (5 ÷ 10) · 10 ^-6 degrees ^-1 , the average temperature change of the refractive index for the working temperature range ΔT

lens glasses 1 and 6 are in the range (-2 ÷ 0) · 10 ^-6 degrees ^-1 , and lenses 3, 4, 5, 7 are in the range (0 ÷ 4) · 10 ^-6 degrees ^-1 . The relation (2) is fulfilled between the relative optical powers of the lenses and components in the lens.

The lens for NVD works as follows. Lenses 1, 6, 7, 3, 4, 5 focus the radiation coming from each point of the distant objects within the angular field determined by the dimensions of the image intensifier photocathode and the focal length of the lens, and create a real image of objects in the image plane with which the image intensifier photocathode plane is aligned deposited on the inner surface of the substrate 8, which acts as a protective glass of the image intensifier tube. The lens provides for each point of the object the focus of radiation in the spectral range, determined by the spectral sensitivity of the image intensifier photocathode, into a small spot that provides high values of contrast transfer coefficients for spatial frequencies corresponding to modern 2, 2+ and 3rd generation image intensifiers. The diameters of the lenses and lens components are such that a relative aperture of at least 1: 1.5 is provided. The values of the temperature coefficients of linear expansion and the values of the temperature change of the refractive index of the lens material of the lens are such that when using the materials of the lens body and the intermediate rings traditionally used in optical instrument engineering with changing operating temperature, there is no mutual displacement of the image plane of the lens and the plane of the image intensifier tube (t .e. there is no thermal defocusing and thermal stability is ensured) and, as a result e, at operating temperatures ranging from -50 to + 50 ° C provided high-quality images without introducing additional lens shifts its components or IC.

The implementation of the lens for NVD is confirmed by an example of a specific design, the parameters of which are given in table 2. In table 2, the following notation is used: φ _i is the relative optical power of the ith component or lens in accordance with the position in figure 1; D _i - the diameter of the i-th component or lens in accordance with the position in figure 1; L is the distance from the first surface of the lens pos.1 to the plane of the image of the lens; d is the distance along the optical axis between the i-th and (i + 1) -th component or lens in accordance with the position in figure 1. The values of the design parameters in the rows of table 1, located below the parameter f ' _H , are given when normalizing the equivalent focal length of the lens f' _H = 1.

table 2 Specific Performance Example Parameters Parameter Value f 'mm 75 D: f ' 1: 1,5 2ω, degrees 13.5 2y mm eighteen Δλ, μm 0.6-0.9 Mass g 115 Length mm 99 f ' _n one 2y, rel. 0.24 D ₁ 0.67 φ ₁ 0.73 d ₁ 0.40 D ₂ 0.40 φ ₂ -0.025 d ₂ 0.1 D ₃ 0.32 φ ₃ -1.82 d ₃ 0,07 D ₄ 0.34 φ ₄ 3,51 d ₄ 0,07 D ₅ 0.26 φ ₅ -2.14 d ₅ 0.09 L / f ' 1.32

стекол линз поз.1 и поз.6 составляет -1·10^-6 градус^-1, т.е. попадает в диапазон (-2÷0)·10^-6 градус^-1, а остальных линз 0,2·10^-6 градус^-1 и 2,2·10^-6 градус^-1, т.е. попадает в диапазон (0÷4)·10^-6 градус^-1. Все линзы примера конкретного исполнения имеют сферические преломляющие поверхности.As follows from table 1 and figure 1, the signs of the optical forces and the shape of the lenses and components correspond to the claimed. In the example of a specific embodiment, three grades of glass were used for the objective lenses, the refractive indices of which are 1.67; 1.92 and 1.68, i.e. exceed 1.65. These glasses have a temperature coefficient of linear expansion of 7.6 · 10 ^-6 ; 5.9 · 10 ^-6 and 8 · 10 ^-6 degrees ^-1 , i.e. lie in the range (5 ÷ 10) · 10 ^-6 degrees ^-1 . In this case, the average temperature change of the refractive index for the working temperature range ΔT

lens glasses pos. 1 and pos. 6 is -1 · 10 ^-6 degrees ^-1 , i.e. falls into the range (-2 ÷ 0) · 10 ^-6 degrees ^-1 , and the remaining lenses 0.2 · 10 ^-6 degrees ^-1 and 2.2 · 10 ^-6 degrees ^-1 , i.e. falls into the range (0 ÷ 4) · 10 ^-6 degrees ^-1 . All lenses of a particular embodiment have spherical refractive surfaces.

Due to the fact that the distance d ₁ in the example of a specific embodiment is 0.4 from the focal length of the lens, the light diameters of the lenses 2, 3, 4 and 5 are reduced in comparison with the diameter of the entrance pupil, which led to a decrease in the mass of the lens. With the same size of the entrance pupil compared with the closest analogue, the mass of the lens is reduced by 184/115 = 1.6 times.

To confirm the high image quality of the proposed lens, the following are the characteristics most often used to evaluate image quality in optical systems of a similar purpose.

Figure 2 shows graphs of astigmatic segments, showing that the values of longitudinal aberrations in the image space in the working spectral range of wavelengths for both a point on the axis and for the remaining points of the field do not exceed 0.1 mm, which with a relative aperture of 1: 1.5 provides acceptable scatter spots in the image plane.

Figure 3 shows the shapes and sizes of scattering spots for nine different field points. Under each spot (and, accordingly, in the table), the coordinate y 'is indicated in the image plane to which this spot corresponds. The RMS radius of the scattering spots for all field points does not exceed 0.0065 mm, which ensures high values of the contrast transfer coefficients in the working range of spatial frequencies.

The graphs of the frequency response (along the abscissa axis is the spatial frequency, lin / mm; along the ordinate axis is the contrast transfer coefficient, rel. Units) shown in Fig. 4 show that for the spatial frequency of 30 lines / mm in the image plane, the contrast transfer coefficient for all points within the field does not go beyond 0.73 to 0.77; for a spatial frequency of 50 lines / mm - from 0.50 to 0.56. In Fig. 4, the frequency response curves are shown for three field points: on the axis, for the image point with a coordinate of 6 mm and a point with a coordinate of 9 mm For the remaining points of the field, the frequency response graphs lie between those shown in Fig. 4.

The magnitude of the distortion (figure 5) for an example of a specific performance does not exceed 1.3% for the edge of the field of view.

The graphs in FIGS. 2-5 confirm the high image quality in the specific application example required for NVD lenses that use modern image intensifier tubes. For ease of comparison, table 3 shows the characteristics of an example of a specific design and the closest analogue. At the same time, Table 3 shows the values of the complex criterion k introduced in Table 1 above for comparison of analogues.

As follows from table 3, the value of the criterion k for an example of a specific performance is higher than 2 times, compared with the closest analogue. An increase in the value of the complex criterion k is the result of the fact that, in comparison with the closest analogue, the proposed lens has: a higher relative aperture (1: 1.5 instead of 1: 2 in the closest analogue); a larger angular field (13.5 ° instead of 9 ° in the closest analogue); with the same diameters of the entrance pupil, it has 1.6 times less mass and high image quality.

The following are the results of thermo-optical analysis of an example of a specific design for the operating temperature range from -50 to + 50 ° C. The thermo-optical parameters of the materials used in the lens device in combination with the found ratios of the optical powers of its lenses and components provide the possibility of passive thermal compensation when using structural materials (steel, aluminum alloys, etc.) that are traditionally used in lens construction as body materials and intermediate rings. Moreover, for the considered example of a specific design, various designs of a thermostable lens can be implemented. For example, the gaps between poses 2 and 3.3 and 4.5 and 8 (see figure 1) are made of aluminum alloy (22.6 · 10 ^-6 degrees ^-1 ), the gap between 1 and 2 is made of titanium ( 7 · 10 ^-6 degrees ^-1 ). The second embodiment: all the indicated gaps are made of steel with a coefficient of linear expansion equal to 14 · 10 ^-6 degrees ^-1 . In each of these options, the image quality remains close to that calculated at a nominal temperature of 20 ° C. Table 4 shows the values of the contrast transfer coefficients in the considered example of a specific design at operating temperatures of -50, -30, 0, +20, +40 and + 50 ° C.

Table 4 Image quality at various temperatures Temperature ° C -fifty -thirty 0 twenty 40 fifty Contrast transmission coefficient at a frequency of 50 lines / mm: on axis 0.54 0.54 0.53 0.53 0.52 0.52 across the field, max 0.59 0.58 0.58 0.56 0.58 0.59 across the field, min 0.50 0.50 0.50 0.50 0.52 0.52 Relative change in focal length,% -0.08 -0.05 -0.03 0 0,03 0.04

The results of thermo-optical analysis confirm the preservation of high image quality in the operating temperature range, and as follows from the data in table 4, the image quality is almost the same when the operating temperature changes, while there is no movement of bleaching lenses or the entire lens or receiver. In other words, passive thermal compensation is provided in the lens. At the same time, the magnitude of the focal length remains unchanged in the entire operating temperature range: the error in changing the focal length is less than 0.1%.

Thus, the implementation of the technical advantages of the proposed device allows you to create a high-speed NVD lens with high technical and operational characteristics, providing the possibility of pairing with 2, 2+ and 3rd generation image intensifiers to create a small-sized, manual NVD and use it in a wide range of operating temperatures.

Literature

1. RF patent No. 2175774, 2001.

2. RF patent No. 2276799, 2006.

3. Tochpribor: Monograph: In 3 t. / Ans. ed. V.V. Raspberry - Novosibirsk: Nauka, 2011. - Volume 1: Optical and optoelectronic devices, aiming, reconnaissance and surveillance systems for the ground forces. - 412 p.

4. RF patent No. 2368923, 2009.

5. RF patent No. 3260269, 2009.

Claims (1)

A lens for a night vision device, consisting of optically coupled, located along the rays of the first positive lens, the second component glued from a biconvex and biconcave lenses, a third negative lens, a fourth positive lens, and a fifth negative meniscus, while the lens of the lens is made of glass with refractive indices above 1.65, characterized in that the first positive lens is made in the form of a meniscus facing a concave surface towards the second component, the second component in is full of negative, the third negative lens is made in the shape of a meniscus, the fourth positive lens is biconvex, while the third and fifth menisci face their concave refracting surfaces toward the fourth biconvex lens, the distance between the first positive lens and the second component is at least 0.3 focal length the lens, the distance between the third and fourth lenses is made small compared with the focal length of the lens, while all lenses are made of stack l, the linear expansion coefficients of which are in the range (5 ÷ 10) · 10 ^-6 degrees ^-1 , the average value for the working temperature range ΔТ of the temperature change in the refractive index

the glasses of the first positive lens and the biconvex lens of the second component are in the range (-2 ÷ 0) · 10 ^-6 degrees ^-1 , the remaining lenses in the range (0 ÷ 4) · 10 ^-6 degrees ^-1 , and between the relative optical forces the ratio is satisfied:
φ ₁ : φ ₂ : φ ₃ : φ ₄ : φ ₅ = (0.7 ÷ 0.8) :-( 0.01 ÷ 0.1) :-( 1.5 ÷ 2) :( 2.5 ÷ 4,5) :-( 2 ÷ 3), where φ ₁ , φ ₂ , φ ₃ , φ ₄ , φ ₅ are the relative optical powers of the first lens, second component, third, fourth and fifth lenses, respectively.

Images