CN109283671B - A light, small, large field of view and low distortion quasi-coaxial five-mirror optical system - Google Patents

Abstract

A light, small, large field of view and low distortion quasi-coaxial five-mirror optical system relates to the field of aerospace optical remote sensors. A light, small, large field of view and low distortion quasi-coaxial five-mirror optical system of the present invention includes an aperture diaphragm, a primary mirror, a secondary mirror, a third mirror, a fourth mirror, a five mirror and a plane reflector, and light passes through the primary mirror in sequence. , secondary mirror, plane mirror, three mirrors, four mirrors, and five mirrors are imaged on the image plane; the aperture stop is located on the primary mirror; the primary mirror is inclined relative to the optical axis of the light incident on the primary mirror; the plane mirror, The third, fourth and fifth mirrors are all located behind the primary mirror; the primary mirror is a quadratic surface; the secondary mirror, the third mirror, the fourth mirror, and the fifth mirror are all high-order spherical surfaces; the primary mirror and the secondary mirror form a concave mirror group. The invention has the characteristics of small size, low cost, low distortion, large field of view, wide spectral range, no obscuration, long focal length, etc., can realize high-precision ground detection and mapping, and is especially suitable as a small-volume and low-cost micro-nano High-resolution cameras for satellites.

Description

A light, small, large field of view and low distortion quasi-coaxial five-mirror optical system

technical field

The invention relates to the technical field of aerospace optical remote sensors, in particular to a quasi-coaxial five-mirror optical system with a light and small size, large field of view and low distortion.

Background technique

With the continuous development of science and technology and the increasing demand for high-resolution remote sensing images, space cameras with high spatial resolution have become an important development trend. On the other hand, in order to improve the image acquisition speed of sensitive areas, the revisit capability of the satellite is required, which requires stronger wide-format imaging capability. However, limited by the satellite's field of view, the ground width will not be too large, so using small satellites to form a network has become the most effective way. Therefore, the design of a small-volume high-precision space camera suitable for micro-nano satellites has also been put on the agenda.

The optical system forms of space cameras that have been successfully launched at present mainly include transmission type, off-axis reflection type and coaxial reflection type. For high-resolution long focal length cameras, the transmissive type is not suitable as an optical system for space cameras due to volume, weight constraints and temperature control issues. Therefore, the current spatial high-resolution telephoto cameras are mainly reflective optical systems. Among them, the off-axis reflective optical system has not many applications due to the long development cycle, which is often more than 5 years. In addition, because the off-axis reflective type is extremely difficult to process and assemble when the focal length is large, most off-axis reflective space cameras are generally less than 500mm in focal length, so high-resolution space cameras are not suitable for using off-axis reflective optical systems. Space cameras for micro-nano satellites are especially unsuitable for use. Therefore, the coaxial reflection optical system has become the only choice.

The current coaxial reflective optical cameras often use a cassette system structure, which has good engineering realization and is easy to achieve high-precision temperature control, so it is widely used. However, its field of view is small, the full field of view is only about 1 degree, and the second mirror blocks the light, and the modulation transfer function of the optical system will drop significantly in the mid-range. Therefore, it is imperative to design a coaxial reflective optical system with long focal length, short barrel length, large field of view and high image quality.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a light, small, large field of view and low distortion quasi-coaxial five-mirror optical system, which can achieve long focal length, short barrel length, large field of view and high image quality, and is suitable for small volume high-resolution space optics camera.

The technical scheme adopted by the present invention for solving the technical problem is as follows:

The invention provides a light, small, large field of view and low distortion quasi-coaxial five-mirror optical system, comprising: an aperture diaphragm, a primary mirror, a secondary mirror, a third mirror, a fourth mirror, a five mirror and a plane reflection mirror. Mirror, secondary mirror, plane mirror, third mirror, fourth mirror, and five mirrors are imaged on the image plane;

the aperture stop is located on the primary mirror;

The primary mirror is inclined relative to the optical axis where the light incident on the primary mirror is located;

The plane mirror, the third mirror, the fourth mirror and the fifth mirror are all located behind the main mirror;

The primary mirror is a quadratic surface;

The secondary mirror, the third mirror, the fourth mirror and the fifth mirror are all high-order spherical surfaces;

The primary mirror and the secondary mirror form a concave mirror group.

Further, the primary mirror is a conical surface with a quadratic term coefficient ranging from -2 to 0.

Further, the quadratic term coefficients of the primary mirror, the secondary mirror, the third mirror, the fourth mirror and the fifth mirror are -1.19, -21.09, 3.43, -2.65, and -12.35, respectively.

Further, the reflection surfaces of the primary mirror, the secondary mirror, the plane mirror, the third mirror, the fourth mirror and the fifth mirror are all coated with a high reflectivity reflective film.

Further, the plane reflection mirror is located between the secondary mirror and the third mirror, and the optical axis is turned by 65 degrees through the plane reflection mirror to realize optical path compression.

Further, the image plane is inclined with respect to the optical axis of the light incident on the image plane.

Further, the image plane is a linear array CCD or COMS.

The beneficial effects of the present invention are as follows:

1. The present invention is a long focal length optical system with the characteristics of small size, low cost, low distortion, large field of view, wide spectral range, and no occlusion, which can realize high-precision ground detection and mapping. On the basis of ensuring small volume and long focal length, the invention can also realize the characteristics of large field of view and low distortion, and is especially suitable as a high-resolution camera for small-volume and low-cost micro-nano satellites.

2. The entire optical system of the present invention has a compact structure, and the three mirrors, four mirrors, five mirrors and plane mirrors are all located behind the main mirror. When the focal length is 7 meters, the total length of the system is less than 0.2 times the focal length. It is light and has little processing difficulty, and is especially suitable for the high-resolution space optical camera optical system of micro-nano satellites for earth observation.

Description of drawings

FIG. 1 is a schematic structural diagram of a light, small, large field of view and low distortion quasi-coaxial five-mirror optical system according to the present invention.

FIG. 2 is a modulation transfer function curve diagram of the optical system of the present invention.

FIG. 3 is a distortion grid diagram of the optical system of the present invention.

In the figure: 1. Primary mirror, 2. Secondary mirror, 3. Plane mirror, 4. Third mirror, 5. Fourth mirror, 6. Fifth mirror, 7. Image plane.

Detailed ways

The present invention will be further elaborated below in conjunction with the accompanying drawings.

As shown in FIG. 1, a light, small, large field of view and low distortion quasi-coaxial five-mirror optical system of the present invention mainly includes: a primary mirror 1, a secondary mirror 2, a third mirror 4, a fourth mirror 5, a five mirror 6 and a In the plane mirror 3 , the light rays pass through the primary mirror 1 , the secondary mirror 2 , the plane mirror 3 , the third mirror 4 , the fourth mirror 5 , and the fifth mirror 6 in sequence, and finally form an image on the image plane 7 .

The aperture stop is located on the main mirror 1 and on both sides of the edge of the main mirror 1, and the main mirror 1 is slightly offset and inclined (the offset and inclination mentioned here refer to: the reflective surface of the main mirror 1 and the incident The optical axis of the light on the main mirror 1 has a certain angle, as for the size of the angle does not need to be limited, it can be about 5 degrees), the function of offset and tilt is to deflect the light path, the purpose is to make the optical system The light is not blocked by the secondary mirror 2, which improves the MTF value in the mid-frequency range.

The primary mirror 1 is deformed from the primary mirror in the cassette system. Specifically, the upper half of the primary mirror in the cassette system is removed, and the light-transmitting area of the lower portion is retained, thereby forming the primary mirror 1 in the present invention, The main function of the primary mirror 1 is to enable light with a large field of view to enter the optical system without significantly decreasing the transfer function curve of the optical system.

The main mirror 1 and the secondary mirror 2 form a concave mirror group, whose function is to compress the optical path. Mirror 3, three mirrors 4, four mirrors 5, five mirrors 6 of the optical path) growth adverse effects.

In the optical system, the primary mirror 1 is a quadratic surface. Specifically, the primary mirror is a conical surface with a quadratic term coefficient of -2 to 0. The secondary mirror 2, the third mirror 4, the fourth mirror 5, and the fifth mirror 6 are all high-order. The design of spherical surface, primary mirror 1 and secondary mirror 2, third mirror 4, fourth mirror 5, and fifth mirror 6 can reduce the difficulty of processing the lens. The primary aberrations of the optical system are corrected by the assignment of their quadratic coefficients and curvatures. The quadratic coefficient of the primary mirror 1 is -1.19, and the quadratic coefficients of the secondary mirror 2, the third mirror 4, the fourth mirror 5, and the fifth mirror 6 are -21.09, 3.43, -2.65, and -12.35, respectively.

The plane mirror 3 , the third mirror 4 , the fourth mirror 5 and the fifth mirror 6 are all located behind the main mirror 1 . The plane mirror 3 is located between the secondary mirror 2 and the third mirror 4, and its function is to compress the optical path, so as to reduce the length of the optical system. The installation position of the plane mirror 3 is located behind the main mirror 1 and does not obstruct the optical paths of the third mirror 4 and the fourth mirror 5 . The plane mirror 3 turns the optical axis by 65 degrees (that is to say, the angle between the light incident on the plane mirror 3 and the light emitted from the plane mirror 3 is 65 degrees), the purpose is to compress the optical path and reduce the optical system. The overall size of the three-mirror 4 can also be reduced.

In the optical system, the secondary mirror 2, the third mirror 4, the fourth mirror 5, and the fifth mirror 6 all have a certain degree of offset and inclination (for example, the reflective surface of the secondary mirror 2 is different from the optical axis of the light incident on the secondary mirror 2. A certain included angle, the size of the included angle does not need to be limited, it can be greater than about 5 degrees. The reflection surface of the three mirrors 4 and the optical axis of the light incident on the three mirrors 4 have a certain included angle, as for the size of the included angle There is no need to limit, it can be more than 5 degrees. The reflection surface of the four mirror 5 has a certain angle with the optical axis of the light incident on the four mirror 5. As for the size of the angle, there is no need to limit it, and it can be more than about 5 degrees. The reflective surface of the five mirrors 6 has a certain angle with the optical axis of the light incident on the five mirrors 6. As for the size of the angle, it does not need to be limited, it can be greater than about 5 degrees), through the secondary mirror 2, the third mirror 4 , four mirrors 5, five mirrors 6 aspheric coefficients and eccentricity and inclination to correct the residual aberration of the optical system and optimize the image quality. In this way, more optimization degrees of freedom are introduced while reducing the processing difficulty of the primary mirror 1, so that the optical system can achieve ultra-low distortion while ensuring high imaging quality.

In the optical system, the primary mirror 1, the secondary mirror 2 and the third mirror 4 bear most of the optical power, which is a deformed structure of the cassette system. The combination of the primary mirror 1 and the secondary mirror 2 is used to share the focal length and shorten the length of the optical system. .

In the optical system, the reflective surfaces of the primary mirror 1, the secondary mirror 2, the plane mirror 3, the third mirror 4, the fourth mirror 5 and the fifth mirror 6 are all coated with a high reflectivity reflective film.

In the optical system, the image plane 7 is a linear CCD or COMS, and the image plane 7 is inclined relative to the optical axis (the optical axis refers to the optical axis where the light incident on the image plane 7 is located).

As shown in FIG. 2 , it is the MTF curve of the optical system of the present invention. It can be seen from the figure that the MTF curve of the optical system is close to the diffraction limit, and the image quality is good.

As shown in FIG. 3 , it is the distortion grid diagram of the optical system of the present invention. It can be seen from the figure that the maximum distortion value of the optical system is less than 0.012%, which meets the requirement of low distortion.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (7)

1. A light, small, large-field-of-view and low-distortion coaxial five-mirror optical system is characterized by comprising: the aperture diaphragm, the primary mirror (1), the secondary mirror (2), the third mirror (4), the fourth mirror (5), the fifth mirror (6) and the plane reflector (3), and light rays sequentially pass through the primary mirror (1), the secondary mirror (2), the plane reflector (3), the third mirror (4), the fourth mirror (5) and the fifth mirror (6) to be imaged on an image surface (7);

the aperture diaphragm is positioned on the primary mirror (1);

the primary mirror (1) is inclined relative to the optical axis of the light incident on the primary mirror (1);

the plane reflector (3), the three mirrors (4), the four mirrors (5) and the five mirrors (6) are all positioned behind the main mirror (1);

the primary mirror (1) is a quadric surface;

the secondary mirror (2), the third mirror (4), the fourth mirror (5) and the fifth mirror (6) are high-order spherical surfaces;

the primary mirror (1) and the secondary mirror (2) form a concave reflector group;

the main mirror (1) is formed by removing the upper half part of the main mirror in the card system and reserving the light-passing area of the lower part;

the secondary mirror (2), the third mirror (4), the fourth mirror (5) and the fifth mirror (6) are offset and inclined to a certain degree.

2. The light, small, large-field-of-view and low-distortion quasi-coaxial five-mirror optical system according to claim 1, wherein the primary mirror (1) is a conical surface with a quadratic coefficient of-2-0.

3. The light, small, large-field-of-view and low-distortion coaxial five-mirror optical system according to claim 1, wherein the coefficients of the second order terms of the primary mirror (1), the secondary mirror (2), the tertiary mirror (4), the quaternary mirror (5) and the quinary mirror (6) are respectively-1.19, -21.09, 3.43, -2.65 and-12.35.

4. The light, small, large, visual field and low distortion quasi-coaxial five-mirror optical system according to claim 1, wherein the reflecting surfaces of the primary mirror (1), the secondary mirror (2), the plane reflecting mirror (3), the three mirrors (4), the four mirrors (5) and the five mirrors (6) are all plated with high-reflectivity reflecting films.

5. The light, small, large, visual field and low distortion quasi-coaxial five-mirror optical system as claimed in claim 1, wherein the plane mirror (3) is located between the secondary mirror (2) and the tertiary mirror (4), and the optical axis is turned by 65 degrees through the plane mirror (3) to realize optical path compression.

6. The light, small, large, field-of-view and low distortion quasi-coaxial penta-reflecting optical system as claimed in claim 1, characterized in that said image plane (7) is tilted with respect to the optical axis of the light incident on the image plane (7).

7. The light, small, large-field-of-view and low-distortion quasi-coaxial five-mirror optical system as claimed in claim 1, wherein the image plane (7) is a linear array CCD or COMS.

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