RU2386155C1 - Large-aperture lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: objective can be used for operation in the far-infrared range in thermal imaging devices. The objective has four lenses along the beam path: the first is a single positive meniscus whose concave surface faces the image, the second is a single negative meniscus whose concave surface faces the image, the third is a single negative meniscus whose convex surface faces the image, the fourth is a single positive meniscus whose convex surface faces the object. The modulus of the radius of curvature of the first optical surface of the fourth lens is less than that of the second optical surface. The first and fourth lenses are made from germanium, the second and third are made from optical oxygen-free infrared glass with refraction index for wavelength 10 mcm greater than 2.5 and less than 3.1. Radii of curvature of the lenses are linked by relationships given in the formula of invention.

EFFECT: improved technological effectiveness and transmission, increased focal distance and aperture ratio with high image quality.

1 dwg, 2 tbl

Description

The present 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 [patent of Russia No. 2183340; G02B 13/14, 9/34; publ. 2002], containing four lenses along the rays, the first of which is a positive meniscus, facing a concavity to the image; the second is a concave lens facing the image with a plane; the third is a plano-convex lens, facing the subject with a plane, and the fourth is a positive meniscus, convex to the subject. This lens works in the wavelength range from 8 to 12.5 microns. The lens is designed for the focal length of the lens - 51.14 mm, the relative aperture - 1: 1.65, the angle of the field of view - 18 degrees., The rear focal segment - 45.23 mm. All of his lenses are made of Germany with a refractive index of more than 4.

This lens is close in design to the claimed, but has a small focal length and relative aperture.

The closest analogue to the claimed technical solution is a fast lens [Russia, utility model certificate No. 26664; G02B 13/14, 9/34, 9/56, 3/02, publ. 2002], containing four lenses, the first of which (along the rays) is the positive meniscus facing the concavity to the image, the second is the negative meniscus facing the concavity to the object, the third and fourth are positive menisci facing the convex to the subject. The second, concave surface of the first lens is aspherical, the radius of curvature of the first optical surface of the fourth lens is less in magnitude than the radius of the second optical surface of the fourth lens, and the following relations hold:

| R ₅ | <| R ₆ |,

| R ₃ | <| R ₆ |,

d ₃ ≤0.01R ₅ ,

where R ₃ , R ₅ , R ₆ are the radii of curvature of the third, fifth and sixth along the rays of the optical surfaces;

d ₃ is the thickness of the third component.

In addition, there is equality:

R ₅ / R ₆ = 0.1192.

The ratio of the size of the third air gap to the focal length of the entire lens is 0.00323.

This lens works in the wavelength range from 8 to 12.5 microns and is designed for the focal length of the lens - 62 mm, relative aperture - 1: 2, field of view - 16 degrees, rear focal length - 52.78 mm. All lenses are made of Germany with a refractive index of more than 4.

This lens is close in design to the claimed one, however, it has a small focal length and relative aperture, as well as insufficient manufacturability, as it contains an aspherical optical surface, the manufacture of which is more time-consuming than spherical. In addition, all the radii modulo are different, which does not allow the unification of reference test glasses. All lenses of this lens are made of germanium, which has a reduced transmission for wavelengths greater than 10 microns.

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

The technical result is an increase in manufacturability and transmittance, an increase in focal length and relative aperture with high image quality.

This is achieved by the fact that in a fast lens consisting of four single lenses along the rays: the first is the positive meniscus facing the concavity to the image, the second is the negative meniscus, the third is the meniscus facing the convex to the object, and the radius of curvature of the first optical surface of the fourth lens is less in magnitude than the radius of curvature of the second optical surface of the fourth lens, in addition, the first and fourth lenses are made of germanium, and the second and third lenses are made of the same material, unlike the known one, the second lens is turned concavity to the image, the third lens is negative and convex to the image, all optical surfaces of the fast lens are made spherical, and the second and third lenses are made of optical oxygen-free infrared glass with a refractive index for length waves of 10 microns more than 2.5 and less than 3.1 and the conditions are:

| R ₅ | = | R ₇ |,

| R ₃ |> | R ₆ |,

0.8 <R ₅ / R ₆ <0.97,

where R ₃ , R ₅ , R ₆ , R ₇ are the radii of curvature of the third, fifth, sixth and seventh along the rays of the optical surfaces.

The drawing shows an optical diagram of the proposed lens.

A fast lens consists of four lenses along the rays: the first lens is a single positive meniscus 1, facing concavity to the image, the second lens is a single negative meniscus 2, facing concavity to the image, the third lens is a single negative meniscus 3, facing convex to the image, and the fourth lens is a single positive meniscus 4, convex to the subject. Behind the meniscus 4, a plane-parallel plate or plates may be located.

The proposed optical system works like a lens collecting from infinity.

The lens works as follows: the light flux from an object located at infinity enters the lens, where it passes through lenses 1, 2, 3, 4 and forms an image of the object in the plane of the best setting in which the optical radiation receiver (not shown) is installed.

In accordance with the proposed solution, an aperture lens is calculated, corrected in the spectral range from 8 to 12.5 microns.

The design parameters of the lens are shown in table 1.

Characteristics of the calculated lens:

focal length 130 mm relative hole 1: 1.4 field of view angle 9 deg. back focal length 9.45 mm back focal length excluding safety glass 18.7 mm

the aperture diaphragm is located behind the lens 2 at a distance of 36.8 mm

Table 1 Radii, mm Thickness mm Material Refractive index for λ = 10 μm Light diameter mm R ₁ = 25.31 90 d ₁ = 6 Ge 4,0024 R ₂ = 176.2 88.2 d ₂ = 14 one R ₃ = 552.1 80.92 d ₃ = 5.5 IKS25 2.7675 R ₄ = 406.4 78.9 d ₄ = 102.54 one R ₅ = -35.48 31.72 d ₅ = 2.7 IKS25 2.7675 R ₆ = -37.84 33.1 d ₆ = 0.3 one R ₇ = 35.48 30.8 d ₇ = 2.7 Ge 4,0024 R ₈ = 36.64 29th d ₈ = 9 one R ₉ = ∞ thirty d ₉ = 1 Ge 4,0024 R ₁₀ = ∞ thirty

In the proposed embodiment of the invention, there are equalities:

| R ₅ | = | R ₇ | = 35.48

R ₅ / R ₆ = 0.9376,

where R ₅ , R ₆ , R ₇ are the radii of curvature of the fifth, sixth and seventh along the rays of the optical surfaces.

In addition, the refractive index of the material of the second and third lenses for a wavelength of 10 μm is 2.7675, and the second and third lenses are made of optical oxygen-free infrared glass of the IKS25 brand.

Table 2 shows the aberrations for a wavelength of 10 μm of the proposed aperture lens.

table 2 Type of aberration Proposed lens (no more) Transverse spherical aberration for a point on the axis with a relative aperture of 1: 1.4 0.012 mm Transverse aberration of a wide inclined beam in the meridional section for the field of view 2W = 9 deg. 0.006 mm Transverse aberration of a wide inclined beam in a sagittal section for a field of view 2W = 9 deg. 0.016 mm The meridional astigmatic segment X ' _m for the field of view 2W = 9 degrees. 0.033 mm Sagittal astigmatic segment X ' _s for the field of view 2W = 9 degrees. -0.029 mm Distortion for the field of view 2W = 9 deg. -0.018%

The proposed lens contains only spherical optical surfaces and the radii of curvature of the spherical optical surfaces are equal in absolute value for two surfaces, which provides it with a higher manufacturability. In addition, the proposed lens has a focal length of 130 mm and high image quality, which follows from table 2. In the proposed lens, the second and third components are made of optical oxygen-free infrared glass brand IKS25, which provides greater transmission.

Thus, as a result of the proposed solution, a technical result is obtained: a high-aperture lens is created for the spectral range from 8 to 12.5 μm with increased manufacturability and transmission, increased focal length and relative aperture with high image quality.

Claims (1)

A fast lens consisting of four single lenses along the rays: the first one is the positive meniscus facing the concavity of the image, the second is the negative meniscus, the third is the meniscus and the convex meniscus is convex to the object, and the radius of curvature of the first optical surface the fourth lens is less in magnitude than the radius of curvature of the second optical surface of the fourth lens, in addition, the first and fourth lenses are made of germanium, and the second and third lenses are made of the same material, characterized in that the second lens is concave toward the image, the third lens is negative and convex towards the image, all optical surfaces of the fast lens are made spherical, and the second and third lenses are made of optical oxygen-free infrared glass with a refractive index for a wavelength of 10 μm or more 2.5 and less than 3.1 and the following conditions apply:
| R ₅ | = | R ₇ |,
| R ₃ |> | R ₆ |,
0.8 <R ₅ / R ₆ <0.97,
where R ₃ , R ₅ , R ₆ , R ₇ are the radii of curvature of the third, fifth, sixth and seventh along the rays of the optical surfaces.