RU192401U1 - Luminous Infrared Lens - Google Patents

Abstract

The lens can be used in thermal imaging devices, the receivers of which are sensitive in the infrared region of the spectrum, in particular in the spectrum range of 8-14 microns. The lens contains four menisci, the first is a positive meniscus with a convexity to the image, the second is a positive meniscus convex to the image, the third is the negative meniscus convex to the image, and the fourth is the positive meniscus convex to the object. The radii of curvature R of the lens surfaces and the distance d between the lenses satisfy the conditions: 0.76≤ (R / R) ≤0.8; 0.87≤ (R / R = R / R) ≤0.94; 0.3f'≤d / f'≤0.43f '; 0.93f'≤ (d + d + d) ≤lf ', where d, d, d are the distances between the first and second, second and third, third and fourth lenses, respectively, f' is the focal length of the lens as a whole. The technical result is an increase in the relative aperture to 1: 0.9 while ensuring the required image quality throughout the field. 1 s.p. f-ly, 4 ill.

Description

The proposed utility model relates to the field of optical instrumentation and can be used in thermal imaging devices, the receivers of which are sensitive in the infrared (IR) spectrum, in particular in the spectrum range of 8-14 microns.

The following requirements are imposed on lenses operating in the spectrum range of 8-14 microns:

1. An ultrahigh relative aperture of D: f '= 0.75-l.l.

2. High, close to diffractive, image quality.

3. Image quality characteristics should be constant throughout the image field of the lenses, which implies the absence of field beam vignetting, the value of the energy concentration in the receiver pixel should be at least 65-70%.

4. The minimum number of lens elements to reduce the weight, size, cost and transmission of the lens.

Known fast IR lens [1], consisting of 4 sequentially mounted lenses, the first of which is a positive meniscus facing concavity to the image, the second is the negative meniscus convex to the image, the third is the meniscus convex to the image, and the fourth is positive meniscus convex to the subject.

The lens has a high relative aperture D / f '= 1: 0.8, image quality is high: the energy concentration in a 17 × 17 μm pixel in the center of the field is at least 70%, at the field edge 47%, but its focal length (28 mm) is small and does not allow viewing far away objects.

The closest to the claimed technical solution is a fast IR lens [2]. The lens consists of four lenses, the first of which is a positive meniscus facing concavity to the image, the second is a plano-concave negative lens facing a flat surface to the image, the third lens is a convex plane facing a subject, and the fourth lens is a positive meniscus convex to a subject . All lenses are made from Germany.

The lens has a sufficient focal length that allows you to consider far-distant objects (f '= 51 mm), but its relative aperture is smaller than the required one (1: 1.65) and it does not have a high enough image quality.

The main task to which the proposed utility model is directed is to increase the relative aperture to 1: 0.9 while ensuring the required image quality throughout the field.

To solve this problem, a fast infrared lens is proposed, which, like the prototype, contains four sequentially mounted lenses, the first of which is the positive meniscus facing the concavity to the image, and the fourth is the positive meniscus facing the convexity to the object.

In contrast to the prototype in the proposed lens, the second lens is made in the form of a positive meniscus convex to the image, and the third lens is made in the form of a negative meniscus convex to the image, while the radii of curvature R of the lens surfaces and the distance d between the lenses satisfy the conditions:

0.76≤ (R ₁ / R ₂ ) ≤0.8;

0.87≤ (R ₃ / R ₄ = R ₅ / R ₆₎ ≤0.94;

0.3f'≤d ₁ /f'≤0.43f ':

0.93f'≤ (d ₁ + d ₂ + d ₃ ) ≤lf '

where d ₁ , d ₂ , d ₃ are the distances between the first and second, second and third, third and fourth lenses, respectively,

f 'is the focal length of the lens as a whole.

In addition, the first, third and fourth lenses of the lens are made of germanium, and the second lens is made of zinc selenide.

The essence of the proposed utility model is as follows.

By fulfilling the above conditions, the first positive meniscus introduces small positive spherical aberration, coma and astigmatism, the second positive meniscus partially compensates for spherical aberration and astigmatism, adding a small coma, the third negative meniscus corrects spherical aberration, the fourth positive meniscus compensates for residual spherical and aberration astigmatism.

The implementation of the first, third and fourth lenses from germanium and the second from zinc selenide made it possible to correct the curvature of the image, the chromaticity of the position and magnification. As a result, a result was achieved consisting in increasing the relative aperture and ensuring high image quality throughout the field:

- High relative aperture 1: 0.9 - Energy concentration in a pixel of size (17 × 17) microns

In the center of the field of view ≥ 70%

At the edge of the field of view ≥ 47%.

Obtaining close to the telecentric course of the main rays provided uniform illumination throughout the image field.

The essence of the claimed utility model is illustrated by drawings, where

in FIG. 1 - presents an optical circuit of the lens,

in FIG. 2 - presents graphs of transverse aberrations,

in FIG. 3 - presents the aberration of the main rays,

in FIG. 4 - plots of energy concentration in a square of size (17 × 17) microns.

A fast infrared lens consists of four meniscus lenses 1, 2, 3 and 4, the first of which is made in the form of a positive meniscus 1, facing concavity to the image, the second positive lens is made in the form of a meniscus 2, convex to the image, the third negative lens is made in in the form of a meniscus 3, convex to the image and the fourth lens is made in the form of a meniscus 4, facing the concavity to the image. Moreover, the radii of curvature R of the lens surfaces and the distance d between the lenses satisfy the conditions:

0.76≤ (R ₁ / R ₂ ) ≤0.8;

0.87≤ (R ₃ / R ₄ = R ₅ / R ₆ ) ≤0.94;

0.3f'≤d ₁ /f'≤0.43f ':

0.93f'≤ (d ₁ + d ₂ + d ₃ ) ≤lf '

where d ₁ , d ₂ , d ₃ are the distances between the first and second, second and third, third and fourth lenses, respectively,

f 'is the focal length of the lens as a whole.

The aperture diaphragm AD is located on the first surface of the lens.

The lens operates as follows: a parallel beam of radiation from a distant object is focused in the rear focus of meniscus 1, and then each of menisci 2 and 3 alternately projects into its image plane, and the last meniscus 4 redesigns the intermediate image after the third meniscus into its image plane, which coincides with the focal plane of the entire lens.

An illustration of the proposed utility model is a fast infrared lens for the IR spectral region (λ = 8-12) μm with the following parameters:

- Focal length - 49.7 mm

- Angular field 2w = 15.8 °

- Relative aperture 1: 0.9.

Important advantages of the proposed lens are:

- High relative aperture 1: 0.9

- High image quality:

- The concentration of energy in the pixel (17 × 17) microns

in the center of the field of view - 70%

on the edge of the field of view - 47%

Thus, in the proposed lens, an increase in the relative aperture to 1: 0.9 is achieved while ensuring high image quality throughout the field.

1. Russian Federation, utility model patent No. 170736, IPC: G02B 13/14, 2006

2. Russian Federation, copyright certificate No. 1714562, IPC: G02B 13/14, 1992 - prototype.

Claims (8)

1. A fast infrared lens containing four sequentially mounted lenses, the first of which is a positive meniscus facing a concavity to the image, the fourth is a positive meniscus convex to the object, characterized in that the second lens is made in the form of a positive meniscus convex to the image, and the third lens is made in the form of a negative meniscus convex to the image, while the radii of curvature R of the lens surfaces and the distance d between the lenses satisfy loviyam: 0.76≤ (R ₁ / R ₂ ) ≤0.8; 0.87≤ (R ₃ / R ₄ = R ₅ / R ₆ ) ≤0.94; 0.3f'≤d ₁ /f'≤0.43f ': 0.93f'≤ (d ₁ + d ₂ + d ₃₎ ≤lf ' where d ₁ , d ₂ , d ₃ are the distances between the first and second, second and third, third and fourth lenses, respectively, f 'is the focal length of the lens as a whole. 2. A fast infrared lens according to claim 1, characterized in that the first, third and fourth lenses of the lens are made of germanium, and the second lens is made of zinc selenide.

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