CN109856785B

CN109856785B - Three-piece type long-wave infrared fixed-focus lens

Info

Publication number: CN109856785B
Application number: CN201910200559.1A
Authority: CN
Inventors: 魏群; 秦建秋; 姜振海; 芮训彬; 丁珺
Original assignee: Nanjing Huaqun Photoelectric Technology Co ltd
Current assignee: Nanjing Huaqun Photoelectric Technology Co ltd
Priority date: 2019-03-16
Filing date: 2019-03-16
Publication date: 2021-10-19
Anticipated expiration: 2039-03-16
Also published as: CN109856785A

Abstract

The invention discloses a three-piece type long-wave infrared prime lens. This camera lens includes first lens, second lens, the third lens that sets gradually from the object space to the image space along the optical axis, wherein: the first lens is a plano-convex lens with a plane front surface and a convex back surface facing the image space; the second lens is a convex lens with a concave front surface and a convex back surface facing the image space; the third lens is a meniscus lens with a convex surface facing the object plane; the system diaphragm is arranged on the front surface of the first lens, and light rays sequentially pass through the first lens, the second lens and the third lens and are finally focused on an image surface. The front surface of the first lens is a plane, the rear surface of the third lens is an aspheric surface, and the rest surfaces are spherical surfaces. The invention adopts the three-piece lens, and has simple structure and reliable performance.

Description

Three-piece type long-wave infrared fixed-focus lens

Technical Field

The invention relates to the technical field of infrared imaging, in particular to a three-piece long-wave infrared prime lens.

Background

The infrared detection technology has the advantages of strong anti-interference capability, good infrared penetrability, capability of working day and night and the like, so that the application field of the long-wave infrared uncooled technology is more and more extensive. However, the long-wave infrared imaging lens has the characteristics of complex structure, expensive used materials and high installation and adjustment requirements, so that the cost of the lens is increased. For example, patent CN103941379A discloses an infrared fixed focus lens, which is composed of three chalcogenide glass lenses, and the imaging effect is ideal by using two aspheric surfaces. However, the aspheric surface is highly required for equipment, and a window protection sheet is additionally required to protect the lens group during adjustment, which leads to cost increase.

Disclosure of Invention

The invention aims to provide a three-piece long-wave infrared prime lens which is simple in structure, easy to install and adjust and low in cost.

The technical solution for realizing the purpose of the invention is as follows: the utility model provides a three formula long wave infrared prime lens, includes first lens, second lens, the third lens that sets up in order from the object space to the image space along the optical axis, wherein:

the first lens is a plano-convex lens with a plane front surface and a convex back surface facing the image space;

the second lens is a convex lens with a concave front surface and a convex back surface facing the image space;

the third lens is a meniscus lens with a convex surface facing the object plane;

the system diaphragm is arranged on the front surface of the first lens, and light rays sequentially pass through the first lens, the second lens and the third lens and are finally focused on an image surface.

Further, the relative aperture of the lens is 1, the focal length of the system is 19mm, and the lens is suitable for an infrared detector with the resolution of 384 x 288 and the pixel size of 20 μm.

Further, the front surface of the first lens is denoted as R1, and the back surface is denoted as R2; the front surface of the second lens is denoted as R3, and the back surface is denoted as R4; the front surface of the third lens is denoted as R5, and the back surface is denoted as R6;

taking the optical axis Z as a central optical axis, the distance D1 from R1 to R2 is 11.000 mm from the object side to the image side along the optical axis Z, the distance D2 from R2 to R3 is 10.156 mm, the distance D3 from R3 to R4 is 15.000 mm, the distance D4 from R4 to R5 is 11.530 mm, the distance D5 from R5 to R6 is 11.927 mm, and the distance D6 from R6 to the image side is 20.000 mm.

Further, the front surface R1 of the first lens is a plane, the rear surface R6 of the third lens is an aspheric surface and has a curvature radius of 210.742 mm, and the remaining surfaces R2 to R5 are all spherical surfaces, wherein the spherical radius of the rear surface R2 of the first lens is-105.530 mm, the spherical radius of the front surface R3 of the second lens is-19.677 mm, the spherical radius of the rear surface R4 of the second lens is-41.645 mm, and the spherical radius of the front surface R5 of the third lens is 52.288 mm.

Further, the rear surface R6 of the third lens is an aspherical surface which satisfies the following formula:

wherein Z (Y) is a rise Sag from the aspheric surface vertex at a position of height Y of the aspheric surface in the optical axis direction; r is curvature radius, and K is a conc coefficient;

A. b, C, D is a high-order aspheric coefficient, and takes the following values:

aspherical surface	K	A	B	C	D
						R6	0	-6.911E-004	2.505E-006	-9.071E-010	2.463E-013

。

Furthermore, the first lens is made of chalcogenide glass, the second lens is made of zinc selenide glass, and the third lens is made of germanium glass.

Compared with the prior art, the invention has the following remarkable advantages: (1) one surface is aspheric, so that the processing difficulty is reduced; (2) the front surface of the first lens is a plane, and a window protection sheet does not need to be additionally installed, so that the installation is convenient; (3) the diaphragm is arranged on the front surface of the first lens, and stray light radiation caused by independent design is avoided.

The specific structure of the present invention is given by the following embodiments and the drawings thereof.

Drawings

FIG. 1 is a schematic structural diagram of a three-piece long-wave infrared fixed-focus lens according to the present invention.

Fig. 2 is a vertical axis aberration graph in the example.

Fig. 3 is an astigmatism graph of an embodiment.

Fig. 4 is a distortion plot of the embodiment.

Fig. 5 is a modulation transfer function graph of an embodiment.

Detailed Description

Referring to fig. 1, the three-piece long-wave infrared fixed-focus imaging lens of the present invention includes a first lens L1, a second lens L2, and a third lens L3 sequentially arranged from an object side to an image side along an optical axis, wherein:

the first lens L1 is a plano-convex lens with a plane front surface and a convex back surface facing the image space;

the second lens L2 is a convex lens with a concave front surface and a convex rear surface facing the image space;

the third lens L3 is a meniscus lens with a convex surface facing the object plane;

the system diaphragm is arranged on the front surface of the first lens L1, and light rays sequentially pass through the first lens L1, the second lens L2 and the third lens L3 and are finally focused on an image plane.

In one embodiment, the relative aperture of the lens is 1, the focal length of the system is 19mm, and the lens is suitable for an infrared detector with the resolution of 384 x 288 and the pixel size of 20 μm.

As a specific embodiment, the front surface of the first lens L1 is denoted as R1, and the rear surface is denoted as R2; the front surface of the second lens L2 is denoted as R3, and the rear surface is denoted as R4; the front surface of the third lens L3 is denoted as R5, and the rear surface is denoted as R6;

In one specific embodiment, the front surface R1 of the first lens L1 is a plane, the rear surface R6 of the third lens L3 is an aspheric surface and has a curvature radius of 210.742 mm, and the remaining surfaces R2 to R5 are all spherical surfaces, wherein the rear surface R2 of the first lens L1 has a spherical radius of-105.530 mm, the front surface R3 of the second lens L2 has a spherical radius of-19.677 mm, the rear surface R4 of the second lens L2 has a spherical radius of-41.645 mm, and the front surface R5 of the third lens L3 has a spherical radius of 52.288 mm.

In a specific embodiment, the first lens L1 is made of chalcogenide glass, the second lens L2 is made of zinc selenide glass, and the third lens L3 is made of germanium glass.

The invention is described in further detail below with reference to the figures and the embodiments.

Examples

In the three-piece long-wave infrared prime lens of the embodiment, from an object side to an image side, the front surface of a first lens L1 is R1, and the rear surface is R2; the front surface of the second lens L2 is R3, and the rear surface is R4; the front surface of the third lens L3 is R5, and the rear surface is R6. Wherein R1 is a plane, R6 is an aspheric surface, and the rest are spherical surfaces.

The optical axis Z is a central optical axis and extends from an object side to an image side along the optical axis, the thickness of the first lens L1 is D1, and the distance between the first lens L1 and the second lens L2 is D2; the thickness of the second lens L2 is D3, and the distance from the third lens L3 is D4; the third lens L3 has a thickness D5 and a distance D6 from the image plane.

The first lens L1 is made of chalcogenide glass; the material used for the second lens L2 is zinc selenide glass; the material used for the third lens is germanium glass.

FIGS. 2 to 5 are optical characteristic curve images of the respective embodiments, wherein FIG. 2 is a vertical axis aberration graph expressed by three wavelengths of 8 μm, 10 μm and 12 μm in mm; FIG. 3 is a graph of astigmatism, again represented by three wavelengths 8 μm, 10 μm, 12 μm, in mm; FIG. 4 is a distortion plot showing distortion in% at different angles of view; fig. 5 is an MTF graph showing the integrated resolution level of the optical system.

The invention has the following specific technical indexes: the relative aperture is 1, the focal length of the system is 19mm, and the system is suitable for an infrared detector with the resolution of 384 x 288 and the pixel size of 20 um.

The parameters of the optical system of the present invention refer to tables 1 and 2:

TABLE 1 optical element parameter table

The aspheric surface satisfies the following expression:

in the formula, when Z is a position where the height of the aspherical surface in the optical axis direction is Y, the rise Sag from the vertex of the aspherical surface, R is the radius of curvature, K is a conic coefficient, and A, B, C, D is a high-order aspherical coefficient.

TABLE 2 aspheric data

Aspherical surface	K	A	B	C	D
						R6	0	-6.911E-004	2.505E-006	-9.071E-010	2.463E-013

One surface of the non-spherical surface is adopted, so that the processing difficulty is reduced; the front surface of the first lens is a plane, and a window protection sheet does not need to be additionally installed, so that the installation is convenient; the diaphragm is arranged on the front surface of the first lens, stray light radiation caused by independent design is avoided, and the diaphragm can be widely applied to the field of security monitoring.

Claims

1. A three-piece long-wave infrared prime lens, comprising a first lens (L1), a second lens (L2), and a third lens (L3) sequentially arranged from an object side to an image side along an optical axis, wherein:

the first lens (L1) is a plano-convex lens with a plane front surface and a convex back surface facing the image space;

the second lens (L2) is a convex lens with a concave front surface and a convex back surface facing the image;

the third lens (L3) is a meniscus lens with a convex surface facing the object plane;

the system diaphragm is arranged on the front surface of the first lens (L1), and light rays sequentially pass through the first lens (L1), the second lens (L2) and the third lens (L3) and are finally focused on an image surface;

the relative aperture of the lens is 1, the focal length of the system is 19mm, and the lens is suitable for an infrared detector with the resolution of 384 x 288 and the pixel size of 20 mu m;

the front surface of the first lens (L1) is recorded as R1, and the back surface is recorded as R2; the front surface of the second lens (L2) is denoted as R3, and the rear surface is denoted as R4; the front surface of the third lens (L3) is denoted as R5, and the rear surface is denoted as R6;

2. The three-piece long-wave infrared prime lens according to claim 1, wherein the front surface R1 of the first lens (L1) is a plane, the rear surface R6 of the third lens (L3) is an aspheric surface and has a radius of curvature of 210.742 mm, and the remaining surfaces R2 to R5 are spherical surfaces, wherein the rear surface R2 of the first lens (L1) has a spherical radius of-105.530 mm, the front surface R3 of the second lens (L2) has a spherical radius of-19.677 mm, the rear surface R4 of the second lens (L2) has a spherical radius of-41.645 mm, and the front surface R5 of the third lens (L3) has a spherical radius of 52.288 mm.

3. The three-piece long-wave infrared prime lens according to claim 1, wherein the rear surface R6 of the third lens (L3) is an aspherical surface satisfying the following formula:

aspherical surface K A B C D R6 0 -6.911E-004 2.505E-006 -9.071E-010 2.463E-013

。

4. The three-piece long-wave infrared prime lens according to claim 3, wherein the first lens (L1) is made of chalcogenide glass, the second lens (L2) is made of zinc selenide glass, and the third lens (L3) is made of germanium glass.