RU2281536C1 - Infrared lens with remote entrance pupil - Google Patents

Abstract

FIELD: designed for operation in the far or middle infrared-band, applicable in infra-red imagers.

SUBSTANCE: the lens consists of three elements, the first of which, in the motion of beams, - a single negative meniscus turned by the concavity to the object, the second one - a biconvex lens, the third one - a positive meniscus turned by the concavity to the image. The relations between the radii of the optical surfaces, thickness of the components, distance between the components and the focal length of the lens indicated in the claim are realized in the lens.

EFFECT: enhanced focal length, enhanced remoteness of the entrance pupil, and simplified construction at a high quality of image.

2 cl, 1 dwg

Description

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

Known monochromatic lens with a remote entrance pupil [1], containing three single positive lenses along the rays:

- meniscus facing concavity to the subject;

- biconvex lens;

- meniscus facing concavity to the subject.

This lens has the following characteristics:

focal length f ' 3.29 mm front aperture 0.45 mm image size 0.2 mm removal of the entrance pupil 1 mm

However, this lens has a telecentric path of the main rays in the image space, a small focal length, a small projection of the entrance pupil, a low relative aperture, a small angle of the field of view, and, in addition, since this lens is monochromatic and consists only of positive lenses, it has low image quality in a wide spectral range.

The closest analogue to the claimed technical solution is a fast lens with a remote entrance pupil [2] containing three components, the first of which (along the rays) is a positive meniscus facing concavity to the subject, the second is a single biconvex lens, and the third is a two-lens glued meniscus consisting of biconvex and biconcave lenses; and there are relations:

| R ₁ | / | R ₂ | <1

d ₁ / f '> 0.5,

where R ₁ , R ₂ is the radius of the first and last optical surface along the rays of the first component;

d ₁ is the thickness of the first component;

f 'is the focal length of the entire lens.

This lens has the following characteristics:

focal length f ' 4,5 mm relative hole 1: 1.8 angular field of view 99 degrees removal of the entrance pupil 2 mm

The lens is designed for the near spectral region from 400 nm to 900 nm.

In the lens there is equality:

d ₄ / f '= 0,02222,

where d ₄ is the distance between the second and third components;

f 'is the focal length of the entire lens.

This lens is designed to operate in the visible range of the spectrum, since all the lenses of the lens are made of ordinary optical glass, have a small focal length, a small projection of the entrance pupil and the complexity of the design, since the lens consists of at least four lenses.

The task of the invention is the creation of an infrared lens with a remote entrance pupil for use in thermal imaging optical systems operating in the middle or in the far infrared spectrum with enhanced characteristics.

The technical result is an increase in focal length, an increase in the extension of the entrance pupil and simplification of the design with high image quality.

This is achieved by the fact that in a lens with a remote entrance pupil containing three components, the first of which (along the rays) is a single meniscus facing concavity to the subject, the second is a biconvex single lens, the third is the meniscus facing concavity to the image, and, in addition, there is a ratio:

| R ₁ | / | R ₂ | <1,

where R ₁ , R ₂ is the radius of the first and last optical surface along the rays of the first component;

in contrast to the known component, the first component is negative, the third component is a single positive meniscus, and all three lenses are made of a material that is transparent in the infrared region of the spectrum, while the refractive index of the material of the second and third lenses is at least 2.3, and ratios:

R ₃ / | R ₄ | = 1

0.01 <d ₁ / f '<0.1

0.8 <d ₄ / f '<1.5,

where R ₃ , R ₄ - the radius of the third and fourth optical surface along the rays;

d ₁ is the thickness of the first component;

d ₄ is the distance between the second and third components;

f 'is the focal length of the entire lens.

In addition, the refractive index of the material of the first lens can also be at least 2.3.

The drawing shows an optical diagram of the proposed lens.

The lens consists of three single lenses sequentially located along the rays from the subject: a negative meniscus 1, facing concavity to the subject, a biconvex lens 2, and a positive meniscus 3, facing concavity to the image. Plane-parallel plates can be placed in front of meniscus 1 and behind meniscus 3.

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 and forms an image of the object in the plane of the best setup in which the optical radiation receiver (not shown) is installed.

In accordance with the proposed solution, an infrared lens with a remote entrance pupil, corrected in the spectral range from 8 to 12.5 μm, was calculated.

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

Characteristics of the calculated lens:

focal length 74.55 mm relative hole 1: 2.4 field of view angle 17 deg. back focal length 15.27 mm removal of the entrance pupil 16 mm The lens has the following aberrations for λ = 10 μm: transverse spherical aberration for a point on the axis no more than 0,013 mm lateral aberration of wide inclined beam in the meridional section for field of view 2W = 17 deg. no more than 0,02 mm lateral aberration of wide inclined beam in a sagittal section for the field view 2W = 17 deg. no more than 0,016 mm meridional astigmatic segment X ' _m no more than 0,043 mm sagittal astigmatic segment X ' _s no more than 0,132 mm distortion no more than 0.8%

Table Radii, mm Thickness mm Material Refractive index for λ = 10 μm Light diameter mm R ₁ = -34.59 30,4 d ₁ = 2.9 Znse 2,4067 R ₂ = -38,114 32 d ₂ = 25 one R ₃ = 480.71 34 d ₃ = 2.9 Ge 4,0024 R ₄ = -480.71 34 d ₄ = 74 one R ₅ = 39.167 23.3 d ₅ = 2.5 Znse 2,4067 R ₆ = 44.866 22.4

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

d ₁ / f '= 0.0389,

d ₄ / f '= 0.992,

where d ₁ is the thickness of the first component along the rays;

d ₄ is the distance between the second and third lenses;

f 'is the focal length of the entire lens.

Thus, as a result of the proposed solution, a technical result is obtained: an infrared lens with a remote entrance pupil is created that operates in the middle or far infrared range of the spectrum, with an increased focal length, increased input pupil extension, and with a simplified design with high image quality.

Information sources:

1. Auth. testimonial. USSR No. 1686398, G 02 B 9/16, 11/06, 13/22, publ. 1991 year

2. Russian patent No. 2094833, G 02; 9/20, 13/02, publ. 1997 year

Claims (2)

1. A lens with a remote entrance pupil, containing three components, the first of which (along the rays) is a single meniscus facing concavity to the subject, the second is a biconvex single lens, the third is a meniscus facing concavity to the image, and, in addition, has place ratio | R ₁ | / | R ₂ | <1, where R ₁ , R ₂ is the radius of the first and last along the rays of the optical surface of the first component, characterized in that the first component is negative, the third component is a single positive meniscus, and all three lenses are made of a material that is transparent in the infrared region of the spectrum, and there are relations: R ₃ / | R ₄ | = 1; 0.01 <d ₁ / f '<0.1; 0.8 <d ₄ / f '<1.5, where R ₃ , R ₄ - the radius of the third and fourth optical surface along the rays; d ₁ is the thickness of the first component; d ₄ is the distance between the second and third components; f 'is the focal length of the entire lens, in addition, the refractive indices of the material of the second and third lenses are at least 2.3. 2. The lens with a remote entrance pupil according to claim 1, characterized in that the refractive index of the material of the first lens is at least 2.3.