RU2411555C1 - Large-aperture lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens consists of three components lying on the beam path. The first component is a positive meniscus made from germanium and the second is a negative meniscus made from zinc selenide, whose concave surface faces the image. The third component is a positive meniscus whose convex surface faces the object. The concave surface of the first component is aspherical. The third component is made from zinc selenide and has refraction index greater than 2.3 and less than 4.1 for wavelength of 10 mcm. Radii of the curvature of the first, third, fourth, fifth and sixth surfaces and the focal distance of the lens are linked by expressions given in the claim.

EFFECT: higher aperture ratio with high image quality.

3 cl, 2 dwg, 3 tbl

Description

The invention relates to optical instrumentation, namely to special lenses operating in the far infrared wavelength range, and can be used in thermal imaging devices.

Known fast lens according to US patent No. 4537464; NKI 350 / 1.4; publ. 1985, which contains three components along the rays, the first of which is the positive meniscus facing the concavity to the image, the second is the negative meniscus facing the concavity to the image, the third is the positive meniscus facing the convex to the object. The lens has a small field of view 2W = 1.6 °, all components are made of silicon and operate in the spectral range from 3.5 to 8 microns. Since all the lenses are made of silicon, the lens cannot work in the far infrared wavelength range from 8 to 12.5 microns.

The closest analogue to the claimed technical solution is a fast lens (Russia Patent No. 2187135; G02B 13/14, 9/14, publ. 2002) containing three components, the first of which (along the rays) is a single positive meniscus, turned concavity to the image, the second is a single negative meniscus, turned concavity to the image and the third is a single positive meniscus, convex to the object. All surfaces in the lens are spherical. In the lens there are relations:

R ₆ > R ₁ ;

R ₃ > R ₁ ;

R ₃ > R ₆ ;

R ₁ / f '= 1.037-1.061;

R ₃ / f '= 17.58-17.62;

R ₄ / f '= 1.68-1.74;

R ₅ / f '= 0.81-0.84;

R ₆ / f '= 1.691-1.74;

where R ₁ , R ₃ , - R ₆ are the radii of curvature of the first, third, fourth, fifth and sixth optical surfaces;

f 'is the focal length of the entire lens.

The lens operates in the wavelength range from 8 to 12.5 μm, all lenses are made of germanium with a refractive index of more than 4, and is designed for the focal length of the lens - 148 mm and 148.39 mm, relative aperture - 1: 1.65, angle field of view - 6 deg., posterior focal segment - 44.06 mm.

By design, the lens is close to the claimed, but has a small relative aperture.

The objective of the invention is the creation of a fast lens with improved performance.

The technical result is an increase in the relative aperture with high image quality.

This is achieved by the fact that in a fast lens consisting of single lenses sequentially located along the rays, the first one is the positive meniscus facing the concavity to the image, the second is the negative meniscus facing the concavity to the image, and the third is the positive meniscus facing the convex to the object wherein the first lens is made of germanium, while the refractive index of the material of the third lens is more than 2.3 and less than 4.1 for a wavelength of 10 μm, in contrast to the known lens, the second lens is made of zinc selenide ka, the second, concave surface of the first lens is aspherical, in addition, the conditions are:

R ₃ <R ₁ ;

R ₃ <R ₆ ;

0.25 <R ₃ / f '<0.5;

0.15 <R ₄ / f '<0.45;

0.3 <R ₅ / f '<0.7;

0.4 <R ₆ / f '<1.3;

where: R ₁ , R ₃ -R ₆ are the radii of curvature of the first, third, fourth, fifth and sixth optical surfaces;

f 'is the focal length of the entire lens;

in addition, the following relations can be fulfilled:

R ₆ <R ₁ ,

0.5 <R ₁ / f '<1,

and the third lens may be made of zinc selenide.

The figure shows the optical scheme of the proposed lens.

The fast lens (see Fig. 2) consists of three components located along the rays of the components, the first of which is the positive meniscus 1 facing the concavity to the image, the second is the negative meniscus 2 facing the concavity to the image and the third is the positive meniscus 3 facing the convex to the subject.

The entrance pupil coincides with the first surface. Behind the meniscus 3 is a plane-parallel plate 4.

The proposed optical system works as a lens collecting from infinity, i.e. the luminous flux from an object located at infinity enters the lens, where it passes through the lenses 1, 2, 3, plane-parallel plate 4 and forms an image of the object in the plane of the best installation in which the optical radiation receiver (not shown) is installed.

In accordance with the proposed solution, two variants of the possible lens design were calculated, corrected in the spectral range from 8 to 12.5 μm.

The design parameters of the lens according to the first embodiment are shown in table 1.

Characteristics of the calculated lens:

focal length f ' 130.22 mm relative hole 1: 1,08 field of view angle 5 deg 20 min back focal length 3,55 mm

The relations are satisfied:

R ₃ / f '= 0.319;

R ₄ / f '= 0.258;

R ₅ / f '= 0.429;

R ₆ / f '= 0.517.

Table 1 Radii, mm Thickness mm Material Refractive index for λ = 10 μm Light diameter mm R ₁ = 144.54 120 d ₁ = 10 Ge 4,0024 R ₂ = 200 ^*) 116.4 d ₂ = 100.2 one R ₃ = 41.5 43.6 d ₃ = 4.2 Znse 2,4067 R ₄ = 33.65 39.2 d ₄ = 17.07 one R ₅ = 55.85 32,4 d ₅ = 4.2 Ge 4,0024 R ₆ = 67.3 30.3 d ₆ = 16.53 one R ₇ = ∞ 16 d ₇ = 1 Ge 4,0024 R ₈ = ∞ 16 ^*) - the equation of the aspherical surface: y ² + z ² -400x + 1.355x ² -0.00114x ³ = 0

The design parameters of the lens according to the second embodiment are shown in table 2.

Characteristics of the calculated lens:

focal length f ' 130.07 mm relative hole 1: 1.4 field of view angle 8 deg 45 min back focal length 3.52 mm

table 2 Radii, mm Thickness mm Material Refractive index for λ = 10 μm Light diameter mm R ₁ = 114.02 90 d ₁ = 7.5 Ge 4,0024 R ₂ = 160.553 ^*) 87.5 d ₂ = 63.67 one R ₃ = 34.04 43.9 d ₃ = 3.9 Znse 2,4067 R ₄ = 27.1 38.9 d ₄ = 29.25 one R ₅ = 82.6 32 d ₅ = 3.9 Znse 2,4067 R ₆ = 132.13 30.9 d ₆ = 17.4 one R ₇ = ∞ 23 d ₇ = 1 Ge 4,0024 R ₈ = ∞ 23 ^*) - the equation of the aspherical surface: y ² + z ² -321.106x + 1.358x ² -0.002x ³ = 0

The relations are satisfied:

R ₃ / f '= 0.262;

R ₄ / f '= 0.208;

R ₅ / f '= 0.635;

R ₆ / f '= 1.016;

R ₁ / f '= 0.877.

Table 3 shows the aberrations for a wavelength of 10 μm of the proposed aperture lens according to the first and second options. Aberrations according to the first embodiment are given for a relative aperture 1: 1.08 and a field of view 2W = 5 deg 20 min; and in the second embodiment, for a relative aperture of 1: 1.4 and a field of view of 2W = 8 degrees 45 minutes.

Table 3 Type of aberration The value of lens aberrations according to the first option, no more according to the second option, no more Transverse spherical aberration for a point on the axis 0.0036 mm 0.014 mm Transverse aberration of a wide inclined beam in the meridional section 0.011 mm 0.024 mm Transverse aberration of a wide inclined beam in a sagittal section 0.0093 mm 0.0023 mm Meridional astigmatic segment X ' _m -0.0067 mm -0.0289 mm Sagittal astigmatic segment X ' _s -0.0066 mm -0.0161 mm Distortion 0.33% 1.1%

The proposed lens has a higher relative aperture (at least 1: 1.4).

The proposed lenses also have high image quality, which follows from table.3.

Thus, as a result of the proposed solutions, a technical result is obtained: a fast lens is created for the spectral range from 8 to 12.5 μm with an increased relative aperture with high image quality.

Claims (3)

1. Aperture lens, consisting of single lenses sequentially located along the rays, the first of which is the positive meniscus facing the concavity to the image, the second is the negative meniscus facing the concavity to the image, the third is the positive meniscus facing the convex to the object, the first is made of Germany, while the refractive index of the material of the third lens is more than 2.3 and less than 4.1 for a wavelength of 10 μm, characterized in that the second lens is made of zinc selenide, the second concave surface of the first lens s is formed aspherical, the following conditions:
R ₃ <R ₁ ;
R ₃ <R ₆ ;
0.2 <R ₃ / f ′ <0.5;
0.15 <R ₄ / f ′ <0.45;
0.3 <R ₅ / f ′ <0.7;
0.4 <R ₆ / f ′ <1.3,
where R ₁ , R ₃ -R ₆ are the radii of curvature of the first, third, fourth, fifth and sixth optical surfaces;
f ′ is the focal length of the entire lens. 2. A fast lens according to claim 1, characterized in that the condition:
R ₆ <R ₁ . 3. A fast lens according to claim 1, characterized in that the third lens is made of zinc selenide, while
0.5 <R ₁ / f ′ <1.

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