Anamorphic night vision binoculars

Description

[0001] The field of the invention is that of night vision binoculars comprising a light intensifier.

[0002] Generally, as shown in the figure 1 , a night vision binocular consists of two identical bodies CD and CG, parallel to each other and mechanically coupled. Each body has an optical objective 1, a light intensifier tube 2 and an eyepiece 3. In this figure, the optics are represented by double arrows and the path of the rays by thin continuous or dotted lines. The magnification of the binocular is equal to or close to 1. The distance separating the two bodies corresponds to the interpupillary distance d ip between the two eyes Y, or approximately 65 millimeters.

[0003] The monocular fields of view of each body have an angular diameter ϕ G and ϕ D generally close to 40 degrees. If the optical axes of the two binocular bodies are parallel, the binocular field ϕ B is also 40 degrees as seen in the figure 2 It is difficult to increase this field without reducing the resolution of the optical system. Indeed, the larger the fields, the greater the distortion of the optics at the edge of the field and the more the resolution decreases at the edge of the field.

[0004] To increase the binocular field, a possible solution is shown in the figures 3 et 4 . It consists of tilting the two optical axes of each body by a known half-angle θ / 2 as seen in the figure 3 . The monocular field is preserved, but the binocular field, in the tilt direction, is increased by the angle θ. Thus, if the monocular fields are circular and have a diameter of 40 degrees and the tilt angle is 20 degrees, the binocular field ϕ B is 60 degrees in the tilt direction.

[0005] This simple solution has several drawbacks. The distance between the entrance pupils of the two lenses increases significantly, which significantly changes the natural stereoscopic effect. This is true for a diverging field solution as shown in the figure 3 than a convergent field solution. Thus, if each body has a length of approximately 100 mm, the center distance increases by 32 mm, giving a total center distance of 97 mm for a total field increase of 60°. This amounts to increasing the interpupillary distance by 50%.

[0006] To overcome this drawback, patent FR 2 721 719 entitled "Compact night vision binoculars" proposes folding the optics using internal mirrors in order to reduce the distance between the lenses. This optical solution necessarily has its limits.

[0007] The night vision binoculars according to the invention are defined in independent claim 1 and do not have the above disadvantages. They are based on the fact that it is possible to increase the field of view of the objective and the eyepiece in a given direction by means of an anamorphic device. The field of view in this direction can be increased by at least 25% without modifications to the objective or the eyepiece.

[0008] More specifically, the invention relates to night vision binoculars as defined in independent claim 1.

[0009] Advantageously, the optical axes of the two sets make a first angle between them other than zero.

[0010] Advantageously, the two anamorphic planes of the two bodies are parallel.

[0011] Advantageously, the two anamorphic planes of the two bodies make a second angle between them different from zero.

[0012] Advantageously, the first anamorphic device and / or the second anamorphic device comprises at least one prism.

[0013] Advantageously, when the first anamorphic device and / or the second anamorphic device comprises a single prism, said prism operates at minimum deviation.

[0014] Advantageously, the first anamorphic device and / or the second anamorphic device comprises two prisms.

[0015] Advantageously, the two prisms are glued by a common face.

[0016] Advantageously, the optical indices of the first prism and the second prism and the constringencies of the first prism and the second prism are such that the chromatism of the anamorphic device is close to zero in a known spectral band.

[0017] Advantageously, the second anamorphic device comprises a prism associated with a Fresnel prism. Advantageously, the visual fields of the objective and the eyepiece are circular with a diameter equal to 40 degrees, the anamorphosis ratio being equal to 0.8.

[0018] Advantageously, the optical axes of the two bodies make a first angle between them equal to 25 degrees.

[0019] Advantageously, the two anamorphic planes of the two bodies make a second angle between them equal to 30 degrees.

[0020] The invention will be better understood and other advantages will appear on reading the following description given without limitation and thanks to the appended figures among which: There figure 1 represents an embodiment of night vision binoculars according to the prior art; The figure 2 represents the monocular and binocular visual fields of the binoculars of the figure 1 ; There figure 3 represents a variant of the night vision binoculars of the figure 1 ; There figure 4 represents the monocular and binocular visual fields of the binoculars of the figure 3 ; There figure 5 represents a binocular body comprising anamorphic devices according to the invention; The figure 6 represents the different visual fields in the body of the twin figure 5 ; There figure 7 binoculars according to the invention; The figure 8 represents the monocular and binocular visual fields of the binoculars of the figure 7 ; There figure 9 represents a variant of the night vision binoculars of the figure 7 ; There figure 10 represents the binocular visual field of a variant of the binoculars of the figure 7 ; There figure 11 represents an anamorphic prism operating at the minimum deviation angle; The figure 12 represents an anamorphic prism configuration; The figure 13 represents an anamorphic device comprising two prisms arranged head to tail; The figure 14 represents an anamorphic device with two glued prisms arranged in front of the eyepiece; The figure 15 represents an anamorphic device comprising a prism and a Fresnel prism arranged in front of the eyepiece.

[0021] There figure 5 represents a binocular body C according to the invention. It comprises, in this order, a first anamorphic device 10 with prism, an objective 11, a light intensifier device 12, an eyepiece 13 and a second anamorphic device 14 with prisms. In this figure 5 , optics 11 and 13 are represented by double arrows and anamorphic devices 10 and 14 by simple prisms. As we will see, these devices can be more complex.

[0022] The first anamorphic device introduces a first anamorphosis in a given plane with a ratio 1 / X strictly less than 1, the second anamorphic device introduces a second anamorphosis in the same plane with a ratio X.

[0023] This arrangement allows the visual field of the binocular body to be enlarged in one direction by a value equal to the ratio 1 / X. Thus, if the field of view of the non-anamorphic lens is circular, the field perceived through the first anamorphic device is elliptical. The ratio of the major axis of the ellipse to its minor axis is equal to the anamorphic ratio. figure 6 illustrates this operation. It represents the visual fields before the first anamorphic prism, after the first anamorphic prism and after the first ocular prism. If the field after the first prism is circular with a diameter ϕ, before the first anamorphic prism and after the second anamorphic prism, this field is elliptical. The minor axis of the ellipse is ϕ and the major axis is X.ϕ.

[0024] As an order of magnitude, the visual fields of the objective and the eyepiece are circular with a diameter equal to 40 degrees, the anamorphic ratio being equal to 0.8. The visual fields before the first anamorphic lens and after the second anamorphic lens are therefore elliptical, the major axis of the ellipse being 50 degrees and the minor axis 40 degrees.

[0025] A pair of binoculars according to the invention therefore comprises two identical bodies as described above. Such a pair of binoculars is shown in the figure 7 In this figure, the optical axes of the objective-intensifier-eyepiece subassemblies are parallel and the distance separating these two axes is approximately equal to the interpupillary distance of a human being, or approximately 65 millimeters.

[0026] One advantage of this arrangement is that anamorphic devices can be added to conventional night vision binoculars without having to modify the initial optical combination.

[0027] Anamorphic devices have a second characteristic. They introduce a deviation of the optical axis. Thus, the visual fields before the first anamorphic lens and after the second anamorphic lens are deviated and consequently the monocular fields seen by the right eye and the right eye do not completely overlap in the direction of anamorphosis. Only a part of the visual field called the overlap field is seen by both eyes. This is what is illustrated in the figure 8 The total binocular field is then worth, in the anamorphic direction, twice the monocular field minus the overlap field.

[0028] For example, if the monocular field is an ellipse with a major axis of 50 degrees and a minor axis of 40 degrees and if the anamorphic lenses introduce a deviation of the optical axis of 12.5 degrees, in the anamorphic direction, the total binocular field is 75 degrees and 40 degrees in the perpendicular direction, the overlapping field being 25 degrees.

[0029] The deviation of the prism is not constant across the field. It is greater for high incidences than for low incidences. Consequently, the resolution of each binocular body is no longer rotationally symmetrical. Depending on the characteristics of the chosen prism, it is then possible to prioritize resolution within the overlapping field.

[0030] There figure 9 represents a variant of the figure 7 . Compared to the figure 9 , the two binocular bodies are reversed. Thus, the central axes of the monocular fields are reversed. Compared to the arrangement of the figure 7 , the right eye sees what the left eye saw and vice versa. The binocular and overlapping fields are identical in both configurations.

[0031] These panoramic binocular fields, large in the horizontal plane and smaller in the vertical plane, are well suited to human binocular vision. In these configurations, since the anamorphosis is made in a specific plane, the two anamorphosis planes of the two binocular bodies are parallel. It is possible to further optimize the binocular field by playing on the anamorphosis planes. If the two anamorphosis planes of the two bodies make a second angle 2α between them, different from zero, as seen in the figure 10 , then the binocular field has a curved shape that optimally matches human vision. As an example of implementation, if the anamorphic monocular fields are 50 degrees by 40 degrees, the total binocular field is 75 degrees by 40 degrees, with each anamorphic plane being inclined 15 degrees relative to a horizontal plane.

[0032] When the anamorphic device comprises a single prism P, for a given incidence of a light ray on a prism, the deviation of this light ray depends on three factors which are: the angle A at the top of the prism, its optical index n at the wavelength of this light ray and the incidence i of the ray with respect to the normal to the prism. To this incidence i corresponds an inclination B of the rear face of the prism with respect to the optical axis xx of the objective O.

[0033] Several prism sizings lead to the same total field and the same overlap field. One possible solution is to use the minimum deviation property of prisms to maintain the sagittal and tangential focal lengths of the downstream lens at the center of the overlap area.

[0034] With the previous notations and calling im the incidence corresponding to the minimum deviation, this minimum deviation Dm represented in figure 11 is worth: Dm = 2 . i m − A = 2 . Arc sin n . sin A 2 − A In the vicinity of this minimum, we have the relationship: dD di = 0

[0035] For a given lens, the anamorphosis ratio X expressed as a desired percentage between the edge of the panoramic field and the center of the overlap field as well as the ratio 1 / Y of the overlap field for which the lens focal lengths are preserved determine the angle at the top of the prism as well as the inclination of its rear face relative to the optical axis of the lens as shown in the figure. figure 12 . More precisely, these parameters are determined by the numerical resolution of the following system of equations: D B − T − D B + 1 Y T = X . Y + 1 Y T With the following notations: B + 1 Y T = Arc sin n . sin A 2 D B − T = A − B − T + a sin n . sin a sin sin B − T n − A D B + 1 Y T = 2 . Arc sin n . sin A 2 − A

[0036] To correct the chromatism of an anamorphic device, it is necessary to have a set comprising two prisms P and P' mounted head to tail as shown in the figure 13 . Generally, the two prisms are joined together to form a single compact optical assembly. If we denote by n(λ) the index of the prism at wavelength λ and by v its constringency, we have the classical relationship: dn λ dλ = n − 1 ν

[0037] Noting A 1 the angle at the apex of the first prism, A 2 the angle at the apex of the second prism or counter prism, n 1 the optical index of the first prism, n 2 the optical index of the second prism, i 1 the angle of incidence on the first face of the first prism, r 1 the angle refracted on the first face of the first prism, r 2 the angle of incidence on the second face of the first prism, i 2 the angle refracted on the second face of the first prism, i 3 the angle of incidence on the first face of the second prism, r 3 the angle refracted on the first face of the second prism, r 4 the angle of incidence on the second face of the second prism, i 4 the angle refracted on the second face of the second prism, noting D 1 (λ) the angle of deviation of the first prism and D 2 (λ) the angle of deviation of the second prism, we have the relationships: D 1 λ = A 1 − i 1 + a sin n 1 . sin a sin sin i 1 n 1 − A 1 D 2 λ = A 2 − i 3 + a sin n 2 . sin a sin sin i 2 n 2 − A 2

[0038] The achromaticity condition of the set of two prisms is therefore: dD λ dλ = 0 = dD 1 λ dλ + dD 2 λ dλ It is worth: sin A 1 cos i 2 . cos r 1 . n 1 − 1 ν 1 + sin A 2 cos i 4 . cos r 3 . n 2 − 1 ν 2 = 0

[0039] The small angle approximation allows us to define the angles A 1 and A 2 , the optical indices n 1 and n 2 and the constringencies ν 1 and ν 2 in order to fold the lateral chromatism into the privileged resolution zone which corresponds to the linearity zone of the sines, that is to say in the zone where the sine of an angle is assimilated to this angle and where its cosine is taken equal to 1. We then obtain the simple relation: A 1 . n 1 − 1 ν 1 + A 2 . n 2 − 1 ν 2 = 0

[0040] When we deviate from this approximation, the values of the cosines deviating from 1, it is possible to refine the values of A 1 and A 2 by optimization by putting as a constraint the target residual lateral chromatism values.

[0041] As a first non-limiting example of the production of an anamorphic optical assembly corrected for chromatism comprising two glued prisms, the two prisms have the following characteristics: Prism: Material: Reference 497816 according to International Glass Code Optical index: 1.497 Constringence: 81.5 Counter Prism: Material: Reference 923189 according to International Glass Code Optical index: 1.923 Constringence: 18.9 Angle at the top of the prism: 17.5 degrees Angle of inclination of the exit face of the counter prism with respect to the optical axis of the objective: 15 degrees

[0042] This dimensioning allows the extension to + / - 37.5° of dichoptic field of the horizontal field of a binocular night vision binocular with a circular field of + / -20° of field by the addition of anamorphic devices, the optical axes of the two bodies excluding anamorphic devices being parallel. The overlap field is then + / -12.5°.

[0043] As a second non-limiting example of the production of an anamorphic optical assembly corrected for chromatism comprising two glued prisms, the two prisms have the following characteristics: Prism: Material: Reference 497816 according to International Glass Code Optical index: 1.497 Constringence: 81.5 Counter Prism: Material: Reference 923189 according to International Glass Code Optical index: 1.923 Constringence: 18.9 Angle at the top of the prism: 33.3 degrees Angle of inclination of the exit face of the counter prism with respect to the optical axis of the objective: -10 degrees

[0044] This dimensioning allows the extension to + / - 37.5° of dichoptic field of the horizontal field of a binocular night vision binocular with a circular field of + / -20° of field by the addition of anamorphic devices, the optical axes of the two bodies excluding anamorphic devices making an angle of + / - 7 degrees between them. The two bodies can work in convergent or divergent dichoptic. The overlap field is then + / -17.5°. The objective focal lengths in the vicinity of the field equal to -5.5 degrees are retained.

[0045] As a third non-limiting example of the production of a chromatism-corrected anamorphic optical assembly comprising two glued prisms, the two prisms have the following characteristics: Prism: Material: Reference 497816 according to International Glass Code Optical index: 1.497 Constringence: 81.5 Counter Prism: Material: Reference 923189 according to International Glass Code Optical index: 1.923 Constringence: 18.9 Angle at the top of the prism: 30 degrees Angle of inclination of the exit face of the counter prism with respect to the optical axis of the objective: 0 degrees

[0046] This dimensioning allows the extension to + / - 42.5° of dichoptic field of the horizontal field of a binocular night vision binocular with a circular field of + / -20° of field by the addition of anamorphic devices, the optical axes of the two bodies excluding anamorphic devices forming an angle of + / - 10 degrees between them. The two bodies can work in convergent or divergent dichoptic mode. The overlapping field is then + / -17.5°.

[0047] A simple prism necessarily has a relatively wide base. When this prism is placed in front of the eyepiece, it reduces the eye draft T which corresponds to the position of the eye box in relation to the last diopter of the eyepiece as can be seen in the figure 14 .

[0048] This eye pull can be optimized by replacing at least one of the two eyepiece prisms with a thinner but optically equivalent or close equivalent component in terms of optical deviation allowing the compensation of the anamorphosis introduced by the set of prisms at the lens input. This component can for example be sized from the original single prism in several different ways.

[0049] In a first embodiment, the prism P is replaced by a Fresnel prism PF. This embodiment is illustrated in figure 15 . A Fresnel prism PF comprises N identical successive elementary MF patterns. Each elementary pattern reproduces the geometry of the prism but shifts the face by 1 / (N-1) times the height of the prism for each level. The number N of levels is sufficiently low in this case to avoid any phenomenon of parasitic images linked to diffraction by a network effect so that the component can operate over a wide spectrum. The shadowing effect introduced by the risers of the prism is not very troublesome, because the eye integrates each field on a pupil with a diameter greater than 3 millimeters. It is all the less troublesome as the number of levels is high. The enlarged view of the figure 15 represents this shading effect. Only the light rays represented by thin lines are transmitted. The dead zones have a width smaller than the size of the human pupil. The eye draw T' is greater than the draw T in the previous figure.

[0050] Other solutions for reducing size and mass are possible: Use of a locally blazed network in the case of binocular operation on a narrow spectrum; Use of a holographic optical component; Use of optics that de-anamorphose the image from the eyepiece. We will mention the cylindrical lens systems that allow this function to be achieved; Adjustment of the overlap field by orientation of the binocular bodies.

[0051] This solution can also be implemented at the goal level.

Claims

1. Night vision binoculars comprising two optically identical assembled bodies (CD, CG), each body comprising an assembly comprising an objective lens (11), a light intensifier device (12) and an eyepiece (13), characterised in that the night vision binoculars comprise two identical anamorphoser assemblies, with each assembly comprising a first detachable anamorphoser device and a second detachable anamorphoser device, each body comprises the first anamorphoser device (10) with a prism disposed in front of the objective lens, the second anamorphoser device (14) disposed behind the eyepiece, the first anamorphoser device introducing a first anamorphosis in a given plane with a ratio of strictly less than 1, the second anamorphoser device introducing a second anamorphosis in the same plane in the inverse of said ratio, with a visual field before the first anamorphoser device and a visual field after the second anamorphoser device being elliptical and a first angle between optical axes of the two bodies, a second angle between the two anamorphosis planes of the two bodies and said anamorphosis ratio being configured, as a function of the visual field of the objective lens and of the eyepiece, so that a binocular visual field of said night vision binoculars is adapted to that of human vision.

2. The night vision binoculars according to claim 1, characterised in that the optical axes of the two assemblies together form a first angle different from zero.

3. The night vision binoculars according to any of the preceding claims, characterised in that the two anamorphosis planes of the two bodies are parallel.

4. The night vision binoculars according to any of claims 1 to 3, characterised in that, with the visual fields of the objective lens and the eyepiece being circular with a diameter equal to 40 degrees, the anamorphosis ratio being equal to 0.8, the optical axes of the two bodies together form a first angle equal to 25 degrees and the two anamorphosis planes of the two bodies together form a second angle equal to 30 degrees, so as to match the binocular field of human vision.

5. The night vision binoculars according to any of the preceding claims, characterised in that the first anamorphoser device and / or the second anamorphoser device comprise at least one prism (P).

6. The night vision binoculars according to claim 5, characterised in that, when the first anamorphoser device and / or the second anamorphoser device comprise a single prism, said prism operates with minimum deflection.

7. The night vision binoculars according to any of claims 1 to 5, characterised in that the first anamorphoser device and / or the second anamorphoser device comprise two prisms (P, P').

8. The night vision binoculars according to claim 7, characterised in that the two prisms are adhered via a common face.

9. The night vision binoculars according to any of claims 7 or 8, characterised in that the optical indices of the first prism and of the second prism and the constringences of the first prism and of the second prism are such that the chromatism of the anamorphoser device is close to zero in a known spectral band.

10. The night vision binoculars according to any of claims 1 to 5, characterised in that the second anamorphoser device comprises a prism associated with a Fresnel prism (PF), with the Fresnel prism comprising N identical successive elementary patterns, with the number N being low enough to avoid any phenomenon of spurious images and being large enough to avoid any shading effect.

11. The night vision binoculars according to any of the preceding claims, characterised in that the visual fields of the objective lens and of the eyepiece are circular with a diameter equal to 40 degrees, with the anamorphosis ratio being equal to 0.8.

12. The night vision binoculars according to claim 11, characterised in that the optical axes of the two bodies together form a first angle equal to 25 degrees.

13. The night vision binoculars according to one of claims 11 or 12, characterised in that the two anamorphosis planes of the two bodies together form a second angle equal to 30 degrees.