CN112068296B - Large field of view collimator - Google Patents

Abstract

The invention provides a large field of view collimator light pipe, which includes a mirror group constituting an off-axis reflection optical system. The field of view of the field collimator is a rectangular field of view, the field of view in the X-axis direction is much larger than the field of view in the Y-axis direction, the Y-axis is the vertical direction, and the X-axis is the horizontal direction in the same direction as the rotation axis of the mirror. The large field of view collimator provided by the invention has the characteristics of large field of view, high imaging quality and low manufacturing difficulty, and can realize the testing and calibration of wide field of view, multi-spectral and high-resolution optical systems.

Description

Large field of view collimator

technical field

The invention relates to the technical field of aviation and aerospace optical measurement, in particular to an off-axis reflection type collimator with a large field of view.

Background technique

Modulation transfer function (MTF) is an important index to evaluate the imaging quality of the optical system or the whole camera of aviation and aerospace cameras. The final optical image obtained by the camera is closely related to the MTF of the whole camera. The static MTF test in the laboratory is an important part of the camera development process. The static MTF test of the whole machine is generally completed by the imaging method that the collimator and the target cooperate. The structure type and imaging quality of the collimator directly affect the test accuracy of the MTF test. and test efficiency.

At present, the structural types of collimators used in the laboratory static MTF test of cameras include refraction type, reflection type and catadioptric type. The test efficiency is affected by the optical material. The refraction collimator is not suitable for the static MTF test of the wide-spectrum multispectral camera, while the reflective collimator can achieve full-spectrum imaging. MTF testing has inherent advantages. The reflective collimator includes two types: coaxial reflective and off-axis reflective. The coaxial reflective collimator has a central blocking, which results in limited imaging quality, while the off-axis reflective collimator is parallel to the coaxial type. The light pipe has the characteristics of larger field of view and better imaging quality, which is more conducive to improving the test accuracy and efficiency of the static MTF test of the large field of view multispectral camera.

The Chinese invention patent application with the application number 201611253370.1 proposes a multi-spectral reflection collimator. The collimator adopts an off-axis two-reflection optical system type. The primary mirror and the secondary mirror are horizontally opposite to each other, and the height positions are up and down Stagger the arrangement. This technical solution can meet the application of wide-spectrum multi-spectral testing, but the disadvantage is that the imaging field of view of the system is small (the image height field of view is only ±18mm), and the MTF cutoff frequency is low (20lp/mm), which cannot meet the large field of view. , Static MTF test requirements for high-resolution aerospace camera optical systems.

SUMMARY OF THE INVENTION

The invention aims to solve the problems of small imaging field of view and low MTF cut-off frequency of the existing multi-spectral off-axis reflection type collimator, and provides a large field of view collimator, which rotates the mirror of the off-axis reflection optical system The preset angle arrangement increases the field of view of the collimator, which is beneficial to improve the MTF test efficiency of the multispectral camera with a large field of view.

For achieving the above object, the present invention adopts following concrete technical scheme:

The invention provides a large field of view collimator light pipe, which comprises a mirror group constituting an off-axis reflective optical system. In the mirror group, the mirrors located on both sides of the mirror group are respectively rotated by a preset angle to the opposite side mirrors, and the large field of view is achieved. The field of view of the field collimator is a rectangular field of view, the field of view in the X-axis direction is larger than the field of view in the Y-axis direction, the Y-axis is the vertical direction, and the X-axis is the horizontal direction in the same direction as the rotation axis of the mirror.

Preferably, each reflecting mirror is respectively connected with a light blocking plate for blocking stray light.

Preferably, matte tooth patterns are processed on the surface of the light blocking plate.

Preferably, the material of the light blocking plate is aluminum alloy.

Preferably, the surface of the light blocking plate is blackened.

Preferably, the mirror group includes two mirrors, both of which are rectangular concave spherical mirrors.

Preferably, the two reflectors are a first reflector and a second reflector respectively, and the optical power of the first reflector is smaller than that of the second reflector.

Preferably, the radius of curvature of the first reflector is -3600mm≤r1≤-3200mm, the preset angle of rotation is -3°≤θ _p ≤-2°, and the radius of curvature of the second reflector is -4000mm≤r2≤- 3600mm, the preset rotation angle is 5°≤θ _s ≤6°, and the distance between the first reflector and the second reflector is 800mm to 1200mm.

Preferably, the large field of view collimator further includes a target located at the image plane of the off-axis reflective optical system.

Preferably, the distance between the second mirror and the target is 1000mm˜1500mm.

The present invention can achieve the following technical effects:

(1) Large imaging field of view: the large field of view collimator proposed by the present invention adopts an off-axis reflective optical structure to realize multi-spectral imaging; Significant expansion, which is beneficial to improve the test efficiency of MTF test of large field of view multispectral cameras.

(2) High imaging quality: the present invention achieves a large field of view by rationally distributing the optical power of the mirror, and the imaging quality is close to the diffraction limit, and the relative distortion is better than 0.01%; Further improve the imaging effect.

(3) Low manufacturing difficulty: the reflector of the large field of view collimator proposed by the present invention is a spherical reflector, and the manufacturing difficulty is low.

Description of drawings

1 is a schematic structural diagram of a large field of view collimator according to an embodiment of the present invention;

2 is a schematic diagram of a rotation direction of a mirror group according to an embodiment of the present invention;

3 is a schematic diagram of an MTF test curve according to Embodiment 1 of the present invention;

FIG. 4 is a schematic diagram of a distortion network of a collimator with a large field of view according to Embodiment 1 of the present invention.

The reference signs therein include: a first reflecting mirror 1 , a second reflecting mirror 2 , a target 3 , a first light blocking plate 4 , and a second light blocking plate 5 .

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The large field of view collimator light pipe provided by the embodiments of the present invention will be described in detail below.

FIG. 1 shows the structure of a large field of view collimator according to an embodiment of the present invention.

As shown in FIG. 1, the large field of view collimator light pipe provided by the embodiment of the present invention includes: a mirror group and a target 3. The mirror group forms an off-axis reflective optical system to realize multi-spectral imaging; the target 3 is located off-axis. At the image plane of the reflective optical system, after the target 3 pattern is reflected by the off-axis reflective optical system, an infinite parallel light of the target 3 pattern is formed, which is used for the MTF test of the multi-spectral optical system.

The off-axis reflection optical system can be an off-axis two-reflection type, an off-axis three-reflection type, or an off-axis four-reflection optical system. The present invention does not limit the number of mirror groups, and can be selected according to actual needs.

The mirror group that constitutes an off-axis two-reflection optical system consists of two mirrors, and the mirror group that constitutes an off-axis three-reflection optical system consists of three mirrors that constitute an off-axis four-reflection optical system. Consists of four reflectors. The following takes an off-axis two-reflection optical system as an example for description, and an off-axis three-reflection optical system and an off-axis four-reflection optical system can be obtained in the same way.

The reflector group includes a first reflector 1 and a second reflector 2. In the coordinate system shown in The positions of the mirror 1 and the second reflecting mirror 2 are arranged up and down by a certain distance in the y-axis direction.

In an embodiment of the present invention, the first reflector 1 and the second reflector 2 are concave reflectors whose surface type is spherical, and the concave spherical reflector can reduce the difficulty of manufacturing a collimator with a large field of view.

Since the concave spherical mirror has degrees of freedom such as radius and position, the degrees of freedom such as radius and position of the off-axis two-reflection optical system can be released, thereby increasing the field of view.

Specifically, the first reflecting mirror 1 and the second reflecting mirror 2 may be rectangular concave spherical reflecting mirrors, so the field of view of the off-axis two-reflection optical system is a rectangular field of view.

Of course, the first reflector 1 and the second reflector 2 may also be of aspherical, free-form surface and other surface types.

In order to increase the degree of freedom of the off-axis two-reflection optical system, in addition to the degrees of freedom such as radius and position, the degree of freedom of the rotation angle of the mirror should also be released, which is beneficial to balance off-axis aberrations and realize the vision of the off-axis two-reflection optical system. further expansion of the field.

FIG. 2 shows the rotation direction of the mirror group according to one embodiment of the present invention.

As shown in FIG. 2 , in the coordinate system shown in FIG. 2 , the first reflecting mirror 1 is rotated counterclockwise around the x-axis by a preset angle θ _p , that is, the first reflecting mirror 1 is facing the second reflecting mirror around the x-axis. Rotate _{θ p} in the _direction of The direction of the mirror 1 is rotated by θ _s , the rotation angle of the second mirror 2 is θ _s , and the field of view in the X-axis direction of the large-field collimator is much larger than the field of view in the Y-axis direction.

The range of θ _p is -3°≤θ _p ≤-2°, the range of θ _s is 5°≤θ _s ≤6°, the radius of curvature of the first mirror 1 is -3600mm≤r1≤-3200mm, the second mirror The radius of curvature of 2 is -4000mm≤r2≤-3600mm, the distance between the first reflector 1 and the second reflector 2 is 800mm-1200mm, and the distance between the second reflector 2 and the target 3 is 1000mm-1500mm.

By releasing the rotational degrees of freedom of the first mirror 1 and the second mirror 2, the field of view of the large field of view collimator in the X direction is significantly expanded, which is beneficial to improve the MTF test efficiency of the large field of view multispectral camera.

As a preferred embodiment, the optical power of the first reflecting mirror 1 is smaller than that of the second reflecting mirror 2 . Through the reasonable distribution of the optical power of the first reflecting mirror 1 and the second reflecting mirror 2, while realizing a large field of view, the imaging quality is close to the diffraction limit, and the relative distortion is better than 0.01%.

The first reflecting mirror 1 and the second reflecting mirror 2 can be made of metal alloys, microcrystalline materials and other materials.

Returning to FIG. 1 , after the pattern of the target 3 passes through the second mirror 2 and the first mirror 1 in sequence, the parallel light forming the pattern of the target 3 is infinite, which is used for the MTF test of the multispectral optical system. The graphic of the target 3 is a rectangular pattern, which can be a light and dark stripe pattern of equal or gradual distance, and the long side direction of the stripe pattern is parallel to the X-direction field of view.

In a specific embodiment of the present invention, a first light blocking plate 4 is connected to the first reflecting mirror 1, and the reflected light of the first light blocking plate 4 located between the first reflecting mirror 1 and the second reflecting mirror 2 and the second reflecting light The blank area formed by the reflected light between the mirror 2 and the target 3 does not interfere with the optical path. Similarly, a second light blocking plate 5 is connected to the second reflecting mirror 2, and the second light blocking plate 5 is located between the parallel light formed by the first reflecting mirror 1 and the light between the first reflecting mirror 1 and the second reflecting mirror 2. The blank area formed by the reflected light does not interfere with the optical path. The first reflecting mirror 1, the second reflecting mirror 2, the first light blocking plate 4, and the second light blocking plate 5 are in a closed space. The materials of the first light blocking plate 4 and the second light blocking plate 5 The surfaces of the light blocking plate 4 and the second light blocking plate 5 are processed with matte tooth patterns, and the surfaces of the first light blocking plate 4 and the second light blocking plate 5 are blackened by dyeing or spraying black paint, which can effectively eliminate primary impurities. Astigmatism and suppression of secondary stray light effects.

Example 1

The specific parameters of the large field of view collimator are shown in the following table:

Optical element serial number Radius of curvature (mm) Rotation angle Spacing distance (mm) first mirror 1 -3546 (concave spherical) -2.49 992 (distance from the second mirror 2) second mirror 2 -3821 (concave spherical) 5.872 1321 (distance from target 3)

According to the specific parameters of the above-mentioned large field of view collimator, it can be obtained: the focal length is greater than 3000mm, the X-direction field of view is not less than ±0.72°, the Y-direction field of view is not less than ±0.1°, converted to the image height field of view, the X-direction is not less than ±0.1° 37.7mm, the Y direction is not less than ±5.2mm; the spectrum range is the full spectrum.

The MTF test is carried out using the large field of view collimator with the above parameters. The MTF test curve is shown in Figure 3. It can be seen from the MTF test curve in Figure 3 that the transfer function is close to or equal to the diffraction limit, and the cut-off frequency is 50lp/mm. .

The distortion network of the large field of view collimator is shown in Figure 4. From the distortion grid of Figure 4, it can be seen that the distortion of the large field of view collimator is low, and the relative distortion is better than 0.01%.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

The above specific embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (7)

1. A large field of view collimating light pipe, characterized in that it comprises a mirror group that constitutes an off-axis reflective optical system, and the mirrors located on both sides in the mirror group are respectively preset to the mirrors on the opposite side. angle, and the field of view of the large field of view collimator is a rectangular field of view, the field of view in the X-axis direction is greater than the field of view in the Y-axis direction, the Y-axis is the vertical direction, and the X-axis is the same as the rotation axis of the mirror. to the horizontal direction; The reflecting mirror group includes two reflecting mirrors, both of which are rectangular concave spherical reflecting mirrors; The two reflecting mirrors are respectively a first reflecting mirror and a second reflecting mirror, and the optical power of the first reflecting mirror is smaller than that of the second reflecting mirror; The radius of curvature of the first reflector is -3600mm≤r1≤-3200mm, the preset angle of rotation θ _p is -3° _≤θp ≤-2°, and the radius of curvature of the second reflector is -4000mm≤ r2≤-3600mm, the preset rotation angle is 5° _≤θs≤6 °, and the distance between the first reflecting mirror and the second reflecting mirror is 800mm～1200mm; The specific parameters of the large field of view collimator: X-axis field of view ≤-0.72° or X-axis field of view ≥ 0.72°, Y-axis field of view ≤-0.1° or Y-axis field of view ≥ 0.1°, Converted to a high field of view, X-axis ≤-37.7mm or X-axis ≥37.7mm, Y-axis ≤-5.2mm or Y-axis ≥5.2mm; the spectrum range is the full spectrum. 2 . The large field of view collimator light pipe according to claim 1 , wherein each reflecting mirror is respectively connected with a light blocking plate for blocking stray light. 3 . 3 . The large field of view collimator light pipe according to claim 2 , wherein a matting tooth pattern is processed on the surface of the light blocking plate. 4 . 4 . The large field of view collimator light pipe according to claim 3 , wherein the material of the light blocking plate is aluminum alloy. 5 . 5 . The large field of view collimator light pipe according to claim 2 or 3 , wherein the surface of the light blocking plate is blackened. 6 . 6 . The large field of view collimator according to claim 1 , further comprising a target located at the image plane of the off-axis reflective optical system. 7 . 7 . The large field of view collimator light pipe according to claim 6 , wherein the distance between the second reflecting mirror and the target is 1000 mm˜1500 mm. 8 .

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