CN209879127U - Wavefront coding infrared athermalization continuous zoom lens - Google Patents

Abstract

The utility model belongs to a zoom system, and aims at the technical problems of large volume, high cost and poor reliability in the existing infrared continuous zoom system, and provides a wavefront coded infrared athermalization continuous zoom lens. The optical lens includes a front fixed group, a variable magnification group, a compensation group and a rear fixed group that are coaxially arranged in sequence from left to right along the optical axis. The left side of the front fixed group is the object plane, and the right side of the rear fixed group is the image. The front fixed group is composed of the first lens; the zoom group is composed of the second lens, the compensation group is composed of the third lens, and the rear fixed group is composed of two lenses, from left to right are the fourth lens and the sixth lens A phase plate is set coaxially between the fourth lens and the sixth lens. The zoom group and the compensation group can move toward or away from each other along the optical axis. image plane movement.

Description

A Wavefront Encoded Infrared Athermalized Continuous Zoom Lens

technical field

The utility model belongs to a zoom system, in particular to a wavefront coded infrared athermalization continuous zoom lens.

Background technique

Infrared zoom optics are a distinct class of passive detection optics that search, locate, and continuously track objects and targets that emit infrared light against infrared background radiation and other disturbances. Therefore, it has broad application prospects in target search, early warning detection, security monitoring and other fields.

Since the temperature coefficient of refractive index of infrared materials is 1 to 2 orders of magnitude larger than that of visible light glass, and in the field of high-precision detection and early warning, infrared systems are required to work in the temperature range of -40 to +60°C, so changes in ambient temperature have a great impact on The performance of the infrared system is greatly affected.

At present, the infrared continuous zoom system mostly adopts active compensation measures to keep the imaging performance of the infrared optical system stable in a wide temperature range. Because this kind of zoom lens needs motors, control systems, sensors, moving components and other mechanisms to adjust the temperature, resulting in The overall volume of the system is large and the cost is high; and at high temperature and low temperature, due to the thermal expansion and contraction of the moving component materials, the fit gap changes, and the phenomenon of jamming may occur, resulting in a decrease in system reliability.

Utility model content

The purpose of the utility model is to solve the technical problems of large volume, high cost and poor reliability existing in the existing infrared continuous zoom system, and provides a wavefront coded infrared athermalization continuous zoom lens.

The technical scheme of the utility model is:

A wavefront coded infrared athermalization continuous zoom lens, which is special in that it includes a front fixed group, a zoom group, a compensation group and a rear fixed group arranged coaxially along the optical axis from left to right. The left side of the group is the object plane, and the right side of the rear fixed group is the image plane; the front fixed group is composed of a first lens, and the first lens is a meniscus lens with a positive refractive power bent toward the image side; the variable magnification The group consists of a second lens, which is a biconcave lens with negative power; the compensation group consists of a third lens, which is a biconvex lens with positive power; and the rear fixation group consists of two lenses , from left to right are the fourth lens and the sixth lens, the fourth lens is a meniscus lens with negative refractive power bending toward the object side, and the sixth lens is a meniscus lens with positive refractive power bending toward the object side; A phase plate is coaxially arranged between the fourth lens and the sixth lens; the variable power group and the compensation group can move toward or away from each other along the optical axis, the variable power group is used to realize the continuous change of focal length, and the compensation group is used to compensate Image plane movement caused by focal length change.

Further, from left to right along the optical axis; the distance between the rear surface of the first lens of the front fixed group and the front surface of the second lens of the variable power group is 22.64 mm to 4.55 mm; the rear surface of the second lens of the variable power group The distance from the front surface of the third lens in the compensation group is 1.17mm to 27.81mm; the distance from the back surface of the third lens in the compensation group to the front surface of the fourth lens in the rear fixed group is 11.2mm to 2.65mm; The distance between the rear surface of the fourth lens group and the front surface of the phase plate is 1.17mm; the distance between the rear surface of the phase plate and the front surface of the sixth lens of the rear fixed group is 1.38mm.

Further, the first lens, the second lens, the third lens, the fourth lens and the sixth lens are germanium lenses.

Further, the thickness of the first lens is 8.2mm, its front surface is a spherical surface with a radius of curvature of 63.96; the rear surface is spherical with a radius of curvature of 65.19.

Further, the thickness of the second lens is 7 mm, its front surface is aspherical, its radius of curvature is -179.15, its aspheric coefficients are A=-2.31×10 ^-7 , B=3.61×10 ^-10 ; its rear surface is spherical , the radius of curvature is 420.16.

Further, the thickness of the third lens is 8.98 mm, its front surface is aspherical, its radius of curvature is 116.86, its aspheric coefficients are A=-3.04×10 ^-7 , B=-2.13×10 ^-10 , C=- 1.83×10 ^-13 ; the rear surface is a spherical surface with a radius of curvature of -238.81.

Further, the fourth lens has a thickness of 9.62 mm, its front surface is spherical, and its radius of curvature is -31.17; its rear surface is aspheric, its radius of curvature is -63.04, and its aspheric coefficient A=3.75×10 ^-6 , B =2.59×10 ^-9 .

Further, the phase plate is a third-order phase plate, the thickness of the third-order phase plate is 4mm, and the coefficient of the third-order phase plate is a=7×10 ^-6 .

Further, the sixth lens has a thickness of 15 mm, its front surface is a spherical surface with a radius of curvature of -283.73; the rear surface is a diffractive surface with a radius of curvature of -56.92, and the diffractive surface coefficient C1=-5.45×10-5, C2 = -1.53×10 ^-7 , C3 = 5.81×10 ^-10 .

Compared with the prior art, the utility model has the following technical effects:

1. The wavefront coded infrared athermalized continuous zoom lens provided by the utility model can maintain consistent imaging performance without temperature adjustment within the working temperature range of -40°C to +60°C and the full focal length range of 19mm to 38mm. After decoding, the imaging quality is good and the image plane is stable in the whole focal length range; and there is no need for a temperature-adjusting motor sensor and a control system, the optical system is compact in structure, small in size, high in imaging quality and high in stability.

2. The wavefront coded infrared athermalization continuous zoom lens of this utility model adopts coded forms to eliminate the influence of temperature on the optical system, and has a simple and compact structure, and has the characteristics of high reliability, stability and good maintainability in terms of overall performance , and the cost of this compensation method is low.

Description of drawings

Fig. 1 is the optical path diagram of the telephoto state of the embodiment of the utility model;

Fig. 2 is the optical path diagram of the in-focus state in the embodiment of the utility model;

Fig. 3 is the optical path diagram of the short-focus state of the embodiment of the utility model;

Fig. 4a is the MTF curve diagram of the optical system in the telephoto state with the spatial frequency of 25 lp/mm and the temperature of +20°C in the embodiment of the present utility model;

Fig. 4b is the MTF curve diagram of the optical system in the telephoto state with the spatial frequency of 25 lp/mm and the temperature of -40°C in the embodiment of the present invention;

Fig. 4c is the MTF curve diagram of the optical system in the telephoto state with the spatial frequency of 25 lp/mm and the temperature of +60°C in the embodiment of the present utility model;

Fig. 5a is the MTF curve diagram of the optical system in the middle focus state with the spatial frequency of 25lp/mm and the temperature of +20°C in the embodiment of the present utility model;

Fig. 5b is the MTF curve diagram of the optical system in the middle focus state with the spatial frequency of 25 lp/mm and the temperature of -40°C in the embodiment of the present invention;

Fig. 5c is the MTF curve diagram of the optical system in the middle focus state with the spatial frequency of 25lp/mm and the temperature of +60°C in the embodiment of the present invention;

Fig. 6a is the MTF curve diagram of the optical system in the short-focus state with the spatial frequency of 25 lp/mm and the temperature of +20°C in the embodiment of the present invention;

Fig. 6b is the MTF curve diagram of the optical system in the short-focus state with the spatial frequency of 25 lp/mm and the temperature of -40°C in the embodiment of the present invention;

Fig. 6c is the MTF curve diagram of the optical system in the short-focus state with the spatial frequency of 25 lp/mm and the temperature of +60°C in the embodiment of the present utility model;

Wherein, the reference signs are as follows:

1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-phase plate, 6-sixth lens.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the content of the utility model is described in further detail.

As shown in Figures 1, 2, 3 and Table 1, the 19mm-38mm/F1.2 wavefront coded long-wave infrared athermalized continuous zoom optical system provided by this embodiment adopts a 5-group 6-chip structure, and the focal length range is 19mm～38mm, F-number is 1.2, suitable for long-wave infrared thermal imaging cameras with a resolution of 640×480 and a pixel size of 20μm.

Wavefront coded infrared athermalized continuous zoom lens, including a front fixed group, a zoom group, a compensation group and a rear fixed group coaxially arranged from left to right along the optical axis, the left side of the front fixed group is the object plane, The right side of the rear fixed group is the image plane; the front fixed group is composed of the first lens 1, the first lens 1 is a meniscus single crystal germanium lens with positive refractive power bent to the image side; the zoom group is composed of the second lens 2 Composition, the second lens 2 is a double-concave single-crystal germanium lens with negative dioptric power, which moves axially along the optical axis to realize the connection change of focal length; the compensation group is composed of the third lens 3, and the third lens 3 is a double The convex germanium lens moves regularly along the optical axis to compensate for the image plane movement caused by the change of focal length; the rear fixed group is composed of two lenses, which are the fourth lens 4 and the sixth lens 6 from left to right, and the fourth lens 4 is a The meniscus germanium lens with negative refractive power is bent toward the object side, and the sixth lens 6 is a meniscus germanium lens with positive refractive power bent toward the object side. The rear fixed group converges the light and images it on the target surface of the thermal imager; A phase plate 5 is arranged coaxially between the four lenses 4 and the sixth lens 6. The phase plate 5 is a third-order phase plate, and the third-order phase plate modulates the wavefront to keep images at different temperatures consistent.

The zoom group and the compensation group can move toward or away from each other along the optical axis, the zoom group is used to realize the continuous change of the focal length, and the compensation group is used to compensate the image plane movement caused by the change of the focal length. During the change of the optical system from short focus to long focus, the zoom group moves to the image side, and the compensation group moves to the object side to realize the continuous change of focal length, and the continuous zoom is realized through the interval change. In the process of changing from telephoto to short focus, the direction is opposite to the change from short focus to telephoto, the zoom group is on the object side, and the compensation group is on the image side.

From left to right along the optical axis, the distance between the rear surface of the first lens 1 of the front fixed group and the front surface of the second lens 2 of the variable power group ranges from 22.64 mm to 4.55 mm, and the rear surface of the second lens 2 of the variable power group The distance between the surface and the front surface of the third lens 3 of the compensation group is 1.17 mm to 27.81 mm, and the distance between the front surface of the third lens 3 of the compensation group and the front surface of the fourth lens 4 of the rear fixed group is 11.2 mm ~2.65mm, the distance between the rear surface of the fourth mirror of the rear fixed group and the front surface of the phase plate 5 is 1.17mm, and the distance between the rear surface of the phase plate 5 and the front surface of the sixth lens 6 of the rear fixed group is 1.38mm.

Table 1 Specific parameters of each lens in the optical system of this embodiment (unit: mm)

The continuous zoom system of this embodiment is composed of front fixed group, variable power group, compensation group, phase plate 5 and rear fixed group. The meniscus germanium lens with focal power bent toward the object side) and the sixth lens 6 (a meniscus germanium lens with positive refractive power bent toward the object side) converge the light and image it on the target surface of the thermal imager, and the phase plate 5 pairs the wave Modulate before to keep imaging at different temperatures consistent. In this embodiment, the encoding method is used to eliminate the influence of temperature on the optical system, the structure is simple and compact, the overall performance has the advantages of high reliability and stability, and good maintainability, and the cost of this compensation method is relatively low.

As shown in Figures 4a to 6c, the MTF curve values of the continuous zoom system at the telephoto, medium, and short focal lengths at a spatial frequency of 25 lp/mm can be seen. In the temperature range of ℃～+60℃, the MTF curves are basically consistent, which meets the requirements for decoding the obtained images.

Through experiments, it can be concluded that the continuous zoom system of this embodiment obtains images at different temperatures at long focus, medium focus and short focus, and the imaging consistency at different temperatures is good; After decoding the image, the long-focus, medium-focus, and short-focus images are clear at +20°C, -40°C, and +60°C, and the image quality is good, eliminating the influence of system temperature and realizing the athermalization of the continuous zoom system features.

Claims (9)

1. A wavefront coded infrared athermalization continuous zoom lens is characterized in that: it comprises a front fixed group, a zoom group, a compensation group and a rear fixed group coaxially arranged successively along the optical axis direction from left to right, and the front fixed group The left side of the group is the object plane, and the right side of the rear fixed group is the image plane; The front fixed group is composed of a first lens (1), and the first lens (1) is a meniscus lens with positive refractive power bent toward the image side; The variable power group is composed of a second lens (2), and the second lens (2) is a biconcave lens with negative power; The compensation group is composed of a third lens (3), and the third lens (3) is a biconvex lens with positive refractive power; The rear fixed group is composed of two lenses, the fourth lens (4) and the sixth lens (6) from left to right, the fourth lens (4) is a meniscus with a negative refractive power bent toward the object side Lens, the sixth lens (6) is a meniscus lens with positive refractive power bent toward the object side; A phase plate (5) is coaxially arranged between the fourth lens (4) and the sixth lens (6); The variable magnification group and the compensation group can move toward or opposite to each other along the optical axis, the variable magnification group is used to realize the continuous change of the focal length, and the compensation group is used to compensate the movement of the image plane caused by the change of the focal length. 2. A wavefront encoded infrared athermalization continuous zoom lens according to claim 1, characterized in that: along the optical axis from left to right; The distance between the rear surface of the first lens (1) of the front fixed group and the front surface of the second lens (2) of the zoom group is 22.64mm-4.55mm; The distance between the rear surface of the second lens (2) of the variable power group and the front surface of the third lens (3) of the compensation group is 1.17mm-27.81mm; The distance between the rear surface of the third lens (3) of the compensation group and the front surface of the fourth lens (4) of the rear fixed group is 11.2 mm to 2.65 mm; The distance between the rear surface of the fourth lens (4) of the rear fixed group and the front surface of the phase plate (5) is 1.17 mm; The distance between the rear surface of the phase plate (5) and the front surface of the sixth lens (6) of the rear fixed group is 1.38 mm. 3. A wavefront encoded infrared athermalization continuous zoom lens according to claim 1 or 2, characterized in that: the first lens (1), the second lens (2), and the third lens (3) , the fourth lens (4) and the sixth lens (6) are germanium lenses. 4. A wavefront coded infrared athermalization continuous zoom lens according to claim 3, characterized in that: the thickness of the first lens (1) is 8.2 mm, its front surface is spherical, and its radius of curvature is 63.96 mm. ; The rear surface is spherical with a radius of curvature of 65.19. 5. A kind of wavefront coding infrared athermalization continuous zoom lens according to claim 4, is characterized in that: the thickness of described second lens (2) is 7mm, and its front surface is aspheric surface, and radius of curvature is- 179.15, aspheric coefficient A＝-2.31×10 ^-7 , B＝3.61×10 ^-10 ; The back surface is spherical with a radius of curvature of 420.16. 6. A kind of wavefront coded infrared athermalization continuous zoom lens according to claim 5, is characterized in that: the thickness of described third lens (3) is 8.98mm, and its front surface is aspheric surface, and radius of curvature is 116.86, aspheric coefficient A=-3.04×10 ^-7 , B=-2.13×10 ^-10 , C=-1.83×10 ^-13 ; The back surface is spherical with a radius of curvature of -238.81. 7. A kind of wavefront coding infrared athermalization continuous zoom lens according to claim 6, is characterized in that: the thickness of described fourth lens (4) is 9.62mm, and its front surface is spherical surface, and radius of curvature is- 31.17; The back surface is aspherical, the radius of curvature is -63.04, the aspheric coefficients A=3.75×10 ^-6 , B=2.59×10 ^-9 . 8. A kind of wavefront coding infrared athermalization continuous zoom lens according to claim 7, it is characterized in that: described phase plate (5) is three times phase plate, the thickness of three times phase plate is 4mm, three times phase plate coefficient a=7×10 ⁻⁶ . 9. A wavefront coding infrared athermalization continuous zoom lens according to claim 8, characterized in that: the thickness of the sixth lens (6) is 15 mm, its front surface is spherical, and its radius of curvature is -283.73 ; The rear surface is a diffractive surface with a radius of curvature of -56.92, diffractive surface coefficients C1=-5.45×10-5, C2=-1.53× ^10-7 , C3=5.81× ^10-10 .