RU2586273C1 - High-aperture lens - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: invention can be used in imaging devices. Lens is composed of four single meniscus facing concave to the image. First meniscus - a positive, second and third - negative, the fourth - a positive. First, second and fourth meniscus formed of germanium, the third - zinc selenide. Radius of the second optical surface along the beam modulo can be equal to the radius of the sixth optical surface. Radius of the third optical surface along the ray path in modulus can be equal to the radius of the fifth optical surface.

EFFECT: image enhancement and downsizing.

3 cl, 1 dwg, 3 tbl

Description

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

Known fast lens described in patent RU, No. 2386155; IPC G02B 9/34, 13/14, published in 2010, consisting of four single lenses 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 negative the meniscus, convex to the image and the fourth, the positive meniscus, convex to the object, while the radius of curvature of the first optical surface of the fourth lens is less than the radius of curvature of the second optical surface of the fourth lens, in addition, Vai and fourth lenses made of germanium, and the second and third lenses are made of oxygen-free infrared optical glass with a refractive index for a wavelength of 10 microns greater than 2.5 and less than 3.1 and that the conditions:

| 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 optical surfaces along the rays. In addition, in this lens, the ratio of the magnitude of the first air gap to the focal length of the entire lens is 0.108. This lens works in the wavelength range from 8 to 12.5 microns.

Lens Specifications: 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 protective glass 18.7 mm

This lens is close in design to the claimed, but has a small relative aperture of 1: 1.4.

The closest analogue to the claimed technical solution is a fast aperture lens of the infrared region of the spectrum, described in patent RU, No. 2506616; IPC G02B 9/34, 11/22, 13/14, published in 2014, consisting of four components along the rays: the first component is a single positive meniscus facing concavity to the image, the second component is a single positive meniscus facing convex to image, the third component is a single negative meniscus facing concavity to the image, and the fourth component is a single positive meniscus facing concavity to the image, in addition, the first and fourth components are made of germanium, the second and third components are from zinc selenide, while the focal lengths of the components satisfy the necessary conditions stated in the patent, and, in addition, the following conditions

| R ₃ | = | R ₈ |

| R ₄ | = | R ₅ |

where R ₃ , R ₄ , R ₅ , R ₈ are the radii of the third, fourth, fifth and eighth optical surfaces, respectively.

This lens can operate in the wavelength range from 8 to 12.5 microns.

Lens Specifications:

focal length 40 mm relative hole 1: 0.84 field of view angle 12 deg. back focal length 6.7 mm

This lens is close in design to the claimed one, however, calculated at a focal length of 130 mm with a relative aperture of 1: 1.08 and with an angular field of view of 2w = 6 degrees, it has insufficient image quality and large dimensions (for example, longitudinal aberrations for a point on the axes are - 0.17 mm in the Gauss plane and - 0.072 mm in the plane of the best installation, and the distance from the first optical surface to the image plane is 223.58 mm).

The task of the invention is the creation of a fast lens with improved optical and technical characteristics.

The technical result is an increase in image quality and a reduction in size.

This is achieved by the fact that in a fast lens consisting of four single lenses located along the rays: the first is the positive meniscus facing the concavity to the image, the second is the meniscus, the third is the negative meniscus facing the concavity to the image, and the fourth a positive meniscus facing concavity to the image, with the first and fourth lenses made of germanium, and the third lens made of zinc selenide, in contrast to the known one, the second lens is presented as a negative meniscus facing nutostyu to an image made of germanium.

In addition, the following conditions may be met:

| R ₂ | = | R ₆ |.

| R ₃ | = | R ₅ |.

where R ₂ , R ₃ , R ₅ , R ₆ are the radii of curvature of the second, third, fifth and sixth optical surfaces along the rays.

The drawing shows an optical diagram of the proposed lens.

A fast lens consists of four single lenses along the rays: the first lens is a positive meniscus 1, facing concavity to the image, the second lens is a negative meniscus 2, facing concavity to the image, the third lens is a negative meniscus 3, facing concavity to the image, and the fourth lens is positive meniscus 4, facing concavity to the image. Lenses 1, 2 and 4 are made of Germany, lens 3 - of zinc selenide. The radius of the second optical surface along the rays can be equal in absolute value to the radius of the sixth optical surface along the rays, and the radius of the third along the rays of the optical surface can be equal to the radius of the fifth optical surface along the rays. Behind the meniscus 4 is a plane-parallel plate 5, which can be made in the form of a protective glass in front of the optical radiation receiver (not shown).

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 the lenses 1, 2, 3, 4 and plane-parallel plate 5 and forms an image of the object in the plane of the best setup in which the optical radiation receiver is installed (not shown).

In accordance with the proposed solution, two variants of a specific design of the fast lens 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.

The characteristics of the calculated lens in the first embodiment:

focal length 130 mm relative hole 1: 1,08 field of view angle 6 deg back focal length 0.93 mm back focal length excluding protective glass 27.58 mm

The entrance pupil is located on the first optical surface.

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

The characteristics of the calculated lens in the second embodiment:

focal length 130.03 mm relative hole 1: 1,08 field of view angle 6 deg back focal length 0.844 mm back focal length excluding protective glass 27.5 mm

The entrance pupil is located on the first optical surface.

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

| R ₂ | = | R ₆ | = 274.2;

| R ₃ | = | R ₅ | = 381.9

In the table. 3 shows aberrations in the Gaussian plane for a wavelength of 10 μm of the closest analogue, calculated at a focal length of 130 mm and the proposed fast lens according to the first and second versions.

The proposed lens according to the first and second versions has a higher image quality, which follows from the table. 3, and reduced dimensions, as it has a distance from the first optical surface to the image plane for the first embodiment is 173.44 mm, and for the second embodiment is 173.53 mm.

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 microns with improved image quality and reduced dimensions.

Claims (3)

1. A fast lens consisting of four single lenses located along the rays: the first one is the positive meniscus facing the concavity to the image, the second is the meniscus, the third is the negative meniscus facing the concavity to the image, and the fourth is the positive meniscus facing concavity to the image, while the first and fourth lenses are made of germanium, and the third is made of zinc selenide, characterized in that the second lens is presented in the form of a negative meniscus facing the concavity to the image, made wow from Germany. 2. A fast lens according to claim 1, characterized in that the radius of the second optical surface along the rays of the modulus is equal to the radius of the sixth optical surface located along the rays. 3. A fast lens according to claim 2, characterized in that the radius of the third optical surface along the rays of the modulus is equal to the radius of the fifth optical surface located along the rays.