RU140705U1 - LENS FOR IR SPECTRUM - Google Patents

Abstract

1. The lens for the infrared region of the spectrum, containing four menisci, of which the first and fourth menisci along the beam are positive, with their concave surfaces facing the image plane, and the second is negative, the first and fourth menisci being made of germanium, and the third of zinc selenide, characterized in that the second meniscus is made of germanium and faces with a concave surface to the image plane, the third meniscus is negative and faces with a concave surface to the image plane, and between the optical forces The following relationships hold: φ: φ: φ: φ = (1.07 ÷ 1.31) :-( 0.57 ÷ 1.5) :-( 0.41 ÷ 0.68) :( 1.31 ÷ 2.08), where φ, φ, φ, φ are the relative optical powers of the first, second, third, and fourth menisci, respectively. 2. The lens according to claim 1, characterized in that it is arranged to move along the optical axis. 3. The lens according to claim 1, characterized in that the second and third menisci are mounted with the possibility of joint movement along the optical axis. The lens according to claim 1, characterized in that the fourth meniscus is mounted to move along the optical axis.

Description

The utility model relates to the field of optical instrumentation, namely, to lenses for the infrared (IR) region of the spectrum, and can be used in thermal imagers built on the basis of matrix photodetector devices sensitive in the spectral range from 8 to 12 μm, including photodetector devices equipped with curtains.

Known fast lens according to the patent of the Russian Federation No. 2348059 from 10.17.2007, IPC G02B 9/34, G02B 13/14. The lens consists of four components, the first of which is a single positive meniscus, facing concavity to the image. The second is a single negative meniscus convex to the image. The third and fourth components are single positive menisci. The third is convex to the image. The fourth is turned concavity to the image. The first and fourth components are made of Germany. The second and third components are made of zinc selenide. All optical surfaces are spherical and the following conditions are satisfied: | R ₂ | = | R ₅ |; | R ₃ | = | R ₆ | = | R ₈ |; | R ₅ |> | R ₆ |, where: R ₂ , R ₃ , R ₅ , R ₆ , R ₈ are the radii of the second, third, fifth, sixth, eighth optical surfaces, respectively.

For comparison, the specified lens is calculated at a focal length of 75 mm. The lens has a small rear segment, less than 14.5 mm, which makes it difficult to install the shutter of the photodetector, the sensitive elements of which are located inside the mechanical case, usually at a distance of 15-20 mm from the end.

Closest to the claimed technical solution - the prototype - is the lens for the infrared region of the spectrum according to the patent of the Russian Federation No. 115514 of 01/11/2012, IPC G02B 13/14. The lens contains four menisci, of which the second is negative, the rest are positive, the first and fourth menisci are made of germanium and face the image plane with their concave surfaces, the second and third menisci are made of zinc selenide and face the image plane with their convex surfaces, the third and the fourth menisci are installed with the possibility of simultaneous movement along the optical axis, between the relative optical forces of the menisci, the following relations hold: φ ₁ : φ ₂ : φ ₃ : φ ₄ = (0.75 ÷ 0.85) :-( 2.0 ÷ 2.5) :( 1.40 ÷ 1.66) :( 1.7 ÷ 1.9), where φ ₁ , φ ₂ , φ ₃ , φ ₄ are the relative optical powers of the first, second, third and fourth menisci, respectively.

The specified lens has the following disadvantages.

1. Long lens length. With a focal length of 75 mm, the lens length is 100 mm.

2. Insufficient rear segment of the lens, equal to 13.3 mm, which complicates the installation of the shutter of the photodetector.

The objective of the utility model is to achieve the following technical results: reducing the length of the lens and increasing its rear segment to enable the installation of a curtain and convenient pairing of the image plane of the lens with the plane of the sensitive elements of the photodetector matrix.

In special cases of implementation, an additional technical result is achieved: focusing the lens at a finite distance and compensating for the displacement of the image plane in the operating temperature range from minus 40 to 50 ° C.

, где

- фокусное расстояние объектива,

- фокусное расстояние мениска, i - номер мениска.The indicated technical results — a decrease in the length of the lens and an increase in its rear segment — are achieved as follows. In the lens for the infrared region of the spectrum, containing, like the prototype, four menisci, of which the first and fourth menisci along the beam are positive, with their concave surfaces facing the image plane, and the second is negative, and the first and fourth menisci are made of Germany, and the third - from zinc selenide, in contrast to the prototype, the following was done: the second meniscus is made of germanium and faces with a concave surface to the image plane, the third meniscus is negative and faces with a concave surface to the image plane ratio, and between the optical forces of the menisci the following relationships hold: φ ₁ : φ ₂ : φ ₃ : φ ₄ = (1.07 ÷ 1.31) :-( 0.57 ÷ 1.5) :-( 0.41 ÷ 0.68) :( 1.31 ÷ 2.08), where φ ₁ , φ ₂ , φ ₃ , φ ₄ are the relative optical powers of the first, second, third, and fourth menisci, respectively.

where

- the focal length of the lens,

is the focal length of the meniscus, i is the number of the meniscus.

An additional technical result - focusing the lens at a finite distance and compensating for the displacement of the image plane in the range of operating temperatures from minus 40 to 50 ° C - is achieved when moving along the optical axis either the entire lens, or the second and third menisci together, or the fourth meniscus.

An example of a specific implementation of the lens is shown in the drawings.

In FIG. Figure 1 shows the optical scheme of the lens for the infrared region of the spectrum.

In FIG. Figure 2 shows the graphs of the frequency-contrast characteristic (FM) of the lens for various points of the field of view.

In FIG. Figure 3 shows a plot of distortion as a percentage of the field of view (Y ordinate).

In FIG. Figure 4 shows plots of the energy concentration in the scattering circle.

The lens for the infrared region of the spectrum (Fig. 1) contains four meniscus. The meniscus 1 is positive, made of germanium and faces with a concave surface to the image plane. Meniscus 2 is negative, made of germanium and faces with a concave surface to the image plane. Meniscus 3 is negative, made of zinc selenide (ZnSe) and faces with a concave surface to the image plane. The meniscus 4 is positive, made of germanium and faces with a concave surface to the image plane.

To focus the lens at a finite distance and compensate for the displacement of the image plane in the range of operating temperatures from minus 40 to 50 ° C, the entire lens can be moved along the optical axis, either menisci 2 and 3 together, or meniscus 4.

Table 1 shows the characteristics of the lens, considered as an example of the implementation of the inventive lens.

Table 1 Focal length 75 mm Entrance pupil diameter 60 mm Relative hole 1: 1.25 Field of view, hail 7.5 × 5.5 Lens length 85 mm Back focal length 17 mm Operating temperature range minus 40 to 50 ° C

Table 2 shows the relative optical powers, the axial distances between the menisci, the materials and the diameters of the menisci of the lens. The values of the parameters are given when normalizing the focal length f '= 1.

table 2 Lens options Relative optical power Material Axis distance, mm Diameter mm Meniscus 1 1.17 Ge 0.40 0.75 Meniscus 2 -1.08 Ge 0.06 0.44 Meniscus 3 -0.49 Znse 0.27 0.40 Meniscus 4 1.80 Ge 0.23 0.35

As can be seen from table 1, the lens has a 27% larger than the prototype, the rear segment (17 mm) and 15% less overall length (85 mm).

From table 2 it follows that the optical power of the menisci 1-4 considered as an example of the lens are related as follows: φ ₁ : φ ₂ : φ ₃ : φ ₄ = (1.17) :-( 1.08) :-( 0.49) :( 1.80) and satisfy the relations φ ₁ : φ ₂ : φ ₃ : φ ₄ = (1.07 ÷ 1.31) :-( 0.57 ÷ 1.5) :-( 0, 41 ÷ 0.68) :( 1.31 ÷ 2.08), in which the specified technical results are achieved in the inventive lens.

The graphs in FIG. 1-4 are given for a lens with a focal length f '= 75 mm, an entrance pupil diameter of 60 mm, a relative aperture of 1: 1.25, for a field of view of 7.5 × 5.5 degrees.

In FIG. Figure 2 shows the graphs of the frequency response of the lens for the infrared region of the spectrum at a frequency of 40 lines / mm. The abscissa axis shows the values of spatial frequencies assigned to the plane of the image of the lens, the ordinate axis shows the values of the contrast transfer coefficients. The frequency response graphs are shown for meridional (T) and sagittal (S) sections. From the above graphs it can be seen that in the proposed lens retained a high, diffraction-limited image quality comparable with the image quality of the prototype. The high image quality of the lens is confirmed by the graphs of distortion (Fig. 3) and energy concentration in the scattering circle for various points of the field of view (Fig. 4). In FIG. 3 shows that the distortion is less than 0.2%. In FIG. 4, the abscissa axis represents the radius of the scattering circle, and the ordinate axis represents the values of the corresponding energy concentration levels. The specified graph also demonstrates the high image quality of the proposed lens, which, compared with the prototype, has a reduced length and an increased rear segment.

The lens works as follows: infrared radiation in the range of 8-12 μm emitted by a distant object enters the lens, where it passes through menisci 1, 2, 3, 4 and forms a real image of the object in the plane of the best installation of the photodetector (not shown) whose position is determined by the distance to the object (for an infinitely distant object, it practically coincides with the focal plane of the entire lens).

Thus, in comparison with the prototype, the proposed utility model allows to reduce the length of the lens and increase its rear segment. In special cases, to focus the lens at a finite distance and compensate for the displacement of the image plane in the operating temperature range from minus 40 to 50 ° C, either the entire lens, the second and third menisci together, or the fourth meniscus are movable along the optical axis.

Claims (4)

1. The lens for the infrared region of the spectrum, containing four menisci, of which the first and fourth menisci along the beam are positive, with their concave surfaces facing the image plane, and the second is negative, the first and fourth menisci being made of germanium, and the third of zinc selenide, characterized in that the second meniscus is made of germanium and faces with a concave surface to the image plane, the third meniscus is negative and faces with a concave surface to the image plane, and between the optical forces s satisfy the following relations: φ ₁ : φ ₂ : φ ₃ : φ ₄ = (1.07 ÷ 1.31) :-( 0.57 ÷ 1.5) :-( 0.41 ÷ 0.68) :( 1.31 ÷ 2 , 08), where φ ₁ , φ ₂ , φ ₃ , φ ₄ are the relative optical powers of the first, second, third, and fourth menisci, respectively. 2. The lens according to claim 1, characterized in that it is arranged to move along the optical axis. 3. The lens according to claim 1, characterized in that the second and third menisci are mounted with the possibility of joint movement along the optical axis. 4. The lens according to claim 1, characterized in that the fourth meniscus is mounted to move along the optical axis.

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