RU2421764C1 - Objective lens for visible and near infrared spectrum - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: first component has on the beam path a biconvex lens 1 whose more convex surface faces the object space, a positive meniscus 2 whose convex surface faces the object space, and a biconcave lens 3 whose more gentle surface faces the object space. The second component is in form of biconvex lens 4 whose more gentle surface faces the image space. The third component is in form of a plane-concave lens 5 whose flat surface faces the image space. The refraction index of lenses 1, 2 and 4 is greater than 1.65, and that of lens 3 is not less than 1.8 and that of lens 5 is equal to approximately 1.5. The aperture diaphragm lies on the concave surface of the third lens of the second component. The second component can be displaced along an optical axis. ^ EFFECT: simple design, high field-of-view angle, high image quality owing to higher light transmission, reduced vignetting and high transfer constant of modulation, wider working spectral range of the objective lens. ^ 2 cl, 7 dwg, 2 tbl

Description

The invention relates to optical instrumentation, and in particular to lenses for the visible and near infrared spectral range, and can be used in conjunction with electron-optical converters (EOPs) in night vision devices and in modern digital devices designed to detect and identify objects of observation at low light.

Known lens for night vision devices according to patent RU No. 2218585, IPC G02B 13/14, 9/60, 2003, containing two components installed along the beam, the first of which includes a positive two-lens gluing, a positive single meniscus and a negative two-lens gluing, and the second component is made in the form of two menisci, convex to each other, and a parallel plate. The refractive indices of materials for lenses exceed 1.65. The main disadvantage of this lens is a large number of lenses and a large range of glass brands used.

The closest to the claimed lens by technical nature (prototype) is a lens for the near infrared region of the spectrum, made in the form of two components installed along the beam, the first of which consists of a single positive plano-convex lens convex to the object, gluing from a positive biconvex and a negative biconcave lens convex to the object, and a flat-concave lens facing concavity to the image. The second component includes a plano-convex lens and meniscus, convex to the subject [RU No. 2276799, IPC G02B 13/14, 9/60, 2004].

Thus, the prototype has 5 elements, including one gluing. This lens has in relation to the first analogue fewer elements and a smaller range of glasses. The disadvantage of the prototype is the insufficient angle of view, low image quality due to low light transmission, a drop in the illumination of the image when moving from the center to the edge of the field of view and a low value of modulation transmission coefficients, as well as a low spectral range.

The objective of the invention is to simplify the design, increase the angle of the field of view, improve image quality by improving light transmission, reducing vignetting and increasing the transmission modulation, expanding the working spectral range of the lens.

The problem is achieved in that in the lens for the visible and near infrared spectral region, containing in series the first component comprising three elements and the second component mounted in series on the optical axis, the first element in the first component is made in the form of a positive biconvex lens facing a more convex surface to the space of objects, the second element is made in the form of a positive meniscus facing a convex surface to the space of objects, and the third element is made in the form of a negative in two ways ognutoy lens facing a flat surface of the space objects, the second component is in the form of asymmetrical biconvex lens 4 facing a flat surface of the space image and lens introduced the third component formed as a negative ploskokovognutoy lens facing planar surface of the space of images. The lenses of the first and second elements of the first component and the lens of the second component are made of glass with a refractive index not exceeding 1.65, the third lens of the first component is made of glass with a refractive index of at least 1.8, and the lens of the third component is made of glass with a refractive index equal to about 1.5. The aperture diaphragm is located on the concave surface of the third element of the first component.

Another feature of the inventive lens is that the second component is mounted with the possibility of its movement along the optical axis for internal adjustment to the exact distance to the object.

The invention is illustrated by drawings:

figure 1 shows the optical diagram of the inventive lens,

figure 2 is a graph of curvature,

figure 3 is a graph of distortion,

figure 4 is a graph of longitudinal spherical aberration,

Figures 5, 6, 7 show graphs of the frequency-contrast characteristic (FM) of the lens at a distance of ∞, 10 m and 5 m from the object, respectively.

In Fig.2, the curves are presented for wavelengths: 486 nm, 656 nm and 852 nm, and in Fig.4 for wavelengths of 486 nm, 588 nm and 852 nm. In this case, the curves for wavelength 486 are shown to them by a dashed line, the curves for wavelengths of 656 nm and 588 nm are shown by a solid line, the curves for wavelengths of 852 nm are shown by a dashed line. The letters M and S in FIGS. 2, 5, 6, 7 indicate a meridional (M) and sagittal (S) section. 5, 6, 7, the curves are presented for wavelengths: 486-852 nm.

The lens for the visible and near infrared spectral region (figure 1) contains three components. The first component includes three optical elements, the first of which along the beam is made in the form of a positive biconvex lens 1, facing a more convex surface to the space of objects, the second - in the form of a positive meniscus 2, facing a convex surface to the space of objects, and the third - in the form of a negative biconcave lens 3, facing a flatter surface to the space of objects. The second component is made in the form of an asymmetric biconvex lens 4 facing a flatter surface to the image space. This component is installed with the possibility of its movement along the optical axis. The third component is made in the form of a negative plano-concave lens 5, facing a flat surface to the image space.

Lenses 1, 2 and 4 are made of glass with a refractive index not exceeding 1.65. Lens 3 is made of glass with a refractive index of at least 1.8, lens 5 is made of glass with a refractive index of approximately 1.5. Said components are arranged such that the aperture diaphragm is located on the concave surface of the lens 3 of the first component.

Thus, the inventive lens, although it contains, like the prototype, five elements, it does not have a glued lens. All elements used are single lenses. This leads to a simplification of the lens design and determines a sufficiently high light transmission coefficient.

In addition, the second component in the form of a positive biconvex lens 4 in the inventive lens design is capable of performing the function of a focusing and compensating element at the same time and, therefore, is able to provide an internal adjustment of the lens to the exact distance to the object in the entire range of distances from the object (from ∞ to 5 m) at which the image of the object will be the clearest and sharpest.

In accordance with the proposed technical solution, the lens variant for the focal length f = 80 mm is calculated, the design parameters of which are given in table 1.

Table 1 Surface Radius Thickness Glass Diameter An object ∞ ∞ Nd Vd one 64.9 10 1.623 58.2 54.7 2 -379.6 0.3 53.3 3 46.85 8 1.623 58.2 46.3 four 210.8 2.26 43.3 5 -651.6 four 1.805 25.4 41.9 6 52.12 3.24 36.5 Aperture diaphragm ∞ 37.32 36.5 8 61.03 5 1.623 58.2 23.5 9 -91.22 13.65 22.8 10 -26.14 3 1.516 64.1 18.1 eleven ∞ 7.78 18.1 Image plane ∞ 18.3

The lens works as follows. Light from an object located at a great distance from the first element, refracting, passes through elements 1, 2, 3, 4, 5 and forms an image of the object in the focal plane of the lens.

The internal adjustment of the lens to the exact distance to the object is carried out by moving the second component (lens 4). The position of the lens 4 when setting the distance to the object ∞, 10 m and 5 m are shown in table 2.

table 2 Distance ∞ 10 m 5 m d7 37.32 36.92 36.34 d9 13.71 14.11 14.69

In this table: d7 are the distances between the surfaces of the lenses 3 and 4, and d9 are the distances between the surfaces of the lenses 4 and 5.

The proposed lens has a field of view angle of 2ω = 13 °, distortion is less than 1%, the relative aperture is 1: 1.6. The total length of the lens is approximately 1.2 f. The lens provides high image quality, which is confirmed by the frequency-contrast characteristic shown in Figures 5, 6, 7. From these graphs it follows that the lens has a high modulation transmission coefficient at frequencies up to 100 mm ^-1 over the entire field of view, which determines it high resolution, which, along with the lack of vignetting, ensures equally uniform image quality across the entire field of view. At the same time, the working spectral range was significantly expanded (486 ... 852 nm versus 660 ... 920 nm in the prototype). From the graphs presented it also follows that the inventive lens has a lower distortion with respect to the prototype (less than 1% instead of 2% in the prototype). In addition, in the lens made in accordance with the invention, in comparison with the prototype, the field of view angle is increased (2ω = 13 °, in the prototype 2ω = 9 °) and the relative aperture (1: 1.6 instead of 1: 2 in the prototype) .

It is known that for lenses that work with image intensifiers, the parameters characterizing the image quality are a wide spectral region (from 500 to 900 nm), a large relative aperture, and a high modulation transmission coefficient at a frequency determined by the sensitivity of the image intensifier. The inventive lens meets these requirements.

At the same time, high resolution allows the use of the inventive lens in modern digital devices based on CCD, in which the pixel size <10 um. The prototype for these purposes cannot be applied.

Simplicity (only 5 lenses and only one meniscus-shaped lens and one flint glass lens with a refractive index> 1.8 versus two prototype flint lenses) provides a lighter and cheaper lens design with better light transmission.

Another advantage of the inventive lens is the possibility of internal focusing at the exact distance to the object at a distance of 5 m to ∞. In the prototype, such focusing (by one component) will obviously lead to an unacceptable deterioration in image quality.

Claims (2)

1. The lens for the visible and near infrared region of the spectrum, containing the first component installed in series on the optical axis, including three elements, and the second component, characterized in that in the first component the first element is made in the form of a positive biconvex lens, facing a more convex surface to to the space of objects, the second element is made in the form of a positive meniscus facing a convex surface to the space of objects, and the third element is made in the form of a negative biconcave lens, with a flatter surface to the space of objects, the second component is made in the form of an asymmetric biconvex lens facing a flatter surface to the image space, and a third component is introduced into the lens, made in the form of a negative plane-concave lens, facing a flat surface to the image space, and the lenses of the first and the second element of the first component and the lens of the second component are made of glass with a refractive index not exceeding 1.65, the third lens of the first component is ying glass with a refractive index of at least 1.8, the third lens component made of a glass with a refractive index of about 1.5, while the lens aperture diaphragm is located on the concave surface of the third element of the first component. 2. The lens according to claim 1, characterized in that the second component is mounted to move along the optical axis to provide internal focusing of the lens.

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