CN114236797A - Catadioptric afocal optical system - Google Patents
Catadioptric afocal optical system Download PDFInfo
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- CN114236797A CN114236797A CN202111621468.9A CN202111621468A CN114236797A CN 114236797 A CN114236797 A CN 114236797A CN 202111621468 A CN202111621468 A CN 202111621468A CN 114236797 A CN114236797 A CN 114236797A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/0836—Catadioptric systems using more than three curved mirrors
- G02B17/084—Catadioptric systems using more than three curved mirrors on-axis systems with at least one of the mirrors having a central aperture
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/02—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of crystals, e.g. rock-salt, semi-conductors
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/30—Collimators
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Abstract
The invention provides a refraction and reflection type afocal optical system, comprising: the first reflector, the second reflector, the third reflector and the fourth reflector. A field lens and a collimating lens group are sequentially arranged behind the third reflector. The light beam passes through the central hole of the fourth reflector after being reflected twice by the first reflector and the second reflector, enters the field lens after being reflected twice by the third reflector and the fourth reflector, is refracted by the field lens to reduce the light beam range, enters the collimating lens group, and is refracted by the collimating lens group to become parallel light for emergence. The invention is simultaneously suitable for visible light and medium wave infrared wave bands, and the imaging quality is close to the diffraction limit in the two wave bands. The optical system provided by the invention has multiple wave bands and common caliber; the structure is compact, and the suitability is good; good imaging quality, small distortion and the like.
Description
Technical Field
The invention relates to the technical field of optics, in particular to a catadioptric afocal optical system.
Background
The afocal optical system is an optical system with plane waves of incident and emergent wave fronts, and is also called a telescope system without converging and diverging the light beam. The afocal optical system can be used as a part of an imaging optical system, in addition to a conventional telescope and laser beam expansion. In particular to an optical system needing image motion compensation or image stabilization, a small-caliber plane Mirror (namely a Fast reflecting Mirror) is arranged between an afocal optical system and an imaging optical system by utilizing the zooming effect of the afocal optical system on light beams, and the relative motion between an object and an image during the exposure period of a detector is eliminated by the rotation of the Fast reflecting Mirror, such as an optical system of a movable platform of a satellite, an airborne vehicle, a vehicle and the like.
When the aperture exceeds 200mm, the optical system is not suitable for being realized in a pure transmission mode due to the limitation of lens materials. By adopting the off-axis reflection type afocal light path, the problems of large caliber, multiband and common aperture can be solved, but the processing and adjusting difficulty is high and the processing cost is high.
For the design of a large-caliber, multiband and common-caliber afocal optical system, the traditional transmission type optical system is limited by materials and coating technology, and has large design difficulty, complex system and larger size. The off-axis reflective light path has the problems of high processing and adjusting difficulty and high processing cost.
Disclosure of Invention
In view of the above problems, the present invention provides a catadioptric afocal optical system. The optical system provided by the invention consists of four reflectors, a field lens and a collimating lens group, can be simultaneously suitable for visible light and medium wave infrared wave bands, and has imaging quality close to the diffraction limit in the two wave bands. The optical system provided by the invention has multiple wave bands and common caliber; the structure is compact, and the suitability is good; good imaging quality, small distortion and the like.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
the invention provides a refraction and reflection type afocal optical system, comprising: the first reflector, the second reflector, the third reflector and the fourth reflector;
the first reflector is provided with a central hole, the second reflector is positioned in front of the first reflector, and the second reflector and the first reflector form a Cassegrain structure;
the third reflector is positioned at the central hole of the first reflector, the reflecting surface of the third reflector has the same direction as that of the reflecting surface of the first reflector, and the third reflector 3 is provided with a central hole;
the fourth reflector is positioned between the second reflector and the third reflector, the reflecting surface of the fourth reflector is opposite to the reflecting surface of the first reflector in direction, and the fourth reflector is provided with a central hole;
a field lens and a collimating lens group are sequentially arranged behind the third reflector.
The light beam passes through the central hole of the fourth reflector after being reflected twice by the first reflector and the second reflector, enters the field lens after being reflected twice by the third reflector and the fourth reflector, is refracted by the field lens to reduce the light beam range, enters the collimating lens group, and is refracted by the collimating lens group to become parallel light for emergence.
Preferably, a first image plane is formed at the central hole of the fourth reflector, a second image plane is formed at the central hole of the first reflector, and the parallel light exits through the real exit pupil.
Preferably, the entrance pupil and the aperture stop of the optical system are located on a first reflecting mirror, the first reflecting mirror is an ellipsoid, the reflecting surface of the first reflecting mirror is a concave surface, the second reflecting mirror is a standard spherical surface, and the reflecting surface of the second reflecting mirror is a convex surface.
Preferably, the third reflector is ellipsoidal and the reflective surface of the third reflector is concave.
Preferably, the fourth reflector is a standard spherical surface, and the reflecting surface of the fourth reflector is a convex surface, a concave surface or a plane mirror.
Preferably, the materials of the first reflector, the second reflector, the third reflector and the fourth reflector are SiC, aluminum, microcrystalline glass or beryllium-aluminum alloy.
Preferably, the first mirror, the second mirror, the third mirror and the fourth mirror are high-order aspheric or free-form surface mirrors.
Preferably, the field lens is a standard spherical lens, the front surface of the field lens is a concave spherical surface, and the rear surface of the field lens is a convex spherical surface; the field lens is made of BaF2。
Preferably, the collimating lens group comprises in sequence from front to back: the device comprises a first collimating mirror, a second collimating mirror, a third collimating mirror and a fourth collimating mirror;
the first collimating lens is a negative lens, the front surface of the first collimating lens is a concave spherical surface, the rear surface of the first collimating lens is a convex spherical surface, and a YAG material is adopted;
the second collimating lens is a negative lens, the front surface is a concave spherical surface, the rear surface is a convex spherical surface, and BaF is adopted2A material;
the third collimating lens is a negative lens, the front surface of the third collimating lens is a concave spherical surface, the rear surface of the third collimating lens is a convex spherical surface, and a ZnS material is adopted;
the fourth collimating lens is a positive lens, the front surface is a convex spherical surface, the rear surface is a convex spherical surface, and BaF is adopted2A material;
the first collimating lens, the second collimating lens, the third collimating lens and the fourth collimating lens are standard spherical lenses.
In the catadioptric afocal optical system provided by the invention, the entrance pupil diameter is D1Diameter of exit pupil D2The beam compression ratio of the optical system provided by the invention is the visual magnification, and is also equal to the angular magnification, and the calculation formula is as follows: gamma-D1/D2. The optical system provided by the invention has the visual magnification satisfying the conditions that: gamma is more than or equal to 8 and less than or equal to 15, and the diameter D of entrance pupil1The conditions are satisfied: d is not less than 200mm1≤1000mm。
Compared with the prior art, the optical system has the advantages that:
1) large caliber, multiband and common caliber;
the optical system provided by the invention is of a coaxial catadioptric optical structure, and can perform high-quality imaging on visible and medium-wave infrared bands simultaneously by utilizing reasonable matching of different optical materials, so that the optical system has the advantages of large caliber, multiple wave bands and common caliber.
2) The structure is compact, and the adaptability is good;
the optical system provided by the invention adopts four reflectors and 5 lenses, is positioned on the same optical axis and has a compact structure; meanwhile, the system has three times of imaging, has a real exit pupil, is easy to assemble and reduces the difficulty in adjusting the system to a great extent.
3) The imaging quality is good, and the distortion is small;
the optical system provided by the invention utilizes reasonable design and matching of the optical lens group to ensure that the imaging quality is close to the diffraction limit in both a visible light wave band and a medium wave infrared wave band; the distortion is small, and the distortion quantity of visible light and infrared wave bands is less than 0.1 percent.
Drawings
Fig. 1 is a schematic structural diagram of a catadioptric afocal optical system according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of an optical transfer function curve of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the visible light band.
Fig. 3 is a schematic diagram of an optical transfer function curve of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in a medium-wave infrared band.
Fig. 4 is a schematic view of field curvature and distortion curves of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the visible light band.
Fig. 5 is a schematic view of field curvature and distortion curves of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the mid-wave infrared band.
Wherein the reference numerals include: the imaging system comprises a first reflector 1, a second reflector 2, a third reflector 3, a fourth reflector 4, a field lens 5, a collimating lens group 6, a first collimating lens 61, a second collimating lens 62, a third collimating lens 63, a fourth collimating lens 64, a first image plane A1, a second image plane A2 and an actual exit pupil A3.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same blocks. In the case of the same reference numerals, their names and functions are also the same. Therefore, detailed description thereof will not be repeated.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention.
The invention provides a refraction-reflection type afocal optical system, which adopts four reflectors, a field lens and a collimating lens group to form a coaxial afocal light path, compresses incident parallel wide light beams from a target into parallel thin light beams, can be used for placing an imaging objective lens behind the afocal optical system to realize imaging of the optical system, and the imaging objective lens can be a single-waveband (visible light or medium-wave infrared) objective lens or a multiband (visible light and medium-wave infrared) objective lens.
Fig. 1 illustrates a structure of a catadioptric afocal optical system provided according to an embodiment of the present invention.
As shown in fig. 1, the catadioptric afocal optical system provided by the embodiment of the present invention includes: the device comprises a first reflector 1, a second reflector 2, a third reflector 3, a fourth reflector 4, a field lens 5 and a collimating lens group 6.
An entrance pupil and an aperture diaphragm of the optical system are both positioned on a first reflector 1, the first reflector 1 is provided with a central hole, a second reflector 2 is positioned in front of the first reflector 1, the direction of the reflecting surface of the second reflector 2 is opposite to that of the reflecting surface of the first reflector 1, and the first reflector 1 and the second reflector 2 form a Cassegrain structure; the first reflector 1 is an ellipsoid, the reflecting surface of the first reflector 1 is a concave surface, the second reflector 2 is a standard spherical surface, and the reflecting surface of the second reflector 2 is a convex surface.
The third reflector 3 is positioned at the central hole of the first reflector 1, the third reflector 3 is provided with a central hole, the direction of the reflecting surface of the third reflector 3 is the same as that of the reflecting surface of the first reflector 1, the third reflector 3 is an ellipsoid, and the reflecting surface of the third reflector 3 is a concave surface.
The fourth reflector 4 is located between the second reflector 2 and the third reflector 3, the fourth reflector 4 is provided with a central hole, the direction of the reflecting surface of the fourth reflector 4 is opposite to that of the reflecting surface of the first reflector 1, the fourth reflector 4 is a standard spherical surface, and the reflecting surface of the fourth reflector 4 is a convex surface, a concave surface or a plane mirror.
The materials of the first reflector 1, the second reflector 2, the third reflector 3 and the fourth reflector 4 are SiC, aluminum, microcrystalline glass or beryllium-aluminum alloy.
A field lens 5 and a collimating lens group 6 are sequentially arranged behind the third reflector 3.
The field lens 5 is a standard spherical lens, the front surface of the field lens 5 is a concave spherical surface, and the rear surface is a convex spherical surface; the field lens 5 is made of BaF2。
The collimating lens group 6 comprises from front to back: a first collimating mirror 61, a second collimating mirror 62, a third collimating mirror 63, and a fourth collimating mirror 64. The lenses in the collimating lens group 6 are all standard spherical lenses. In order to correct chromatic aberration, at least three optical materials, namely, one positive lens and two negative lens materials, are adopted for the collimating lens group 6. In the afocal optical system provided by the embodiment of the invention, the first collimating lens 61 is a negative lens, the front surface is a concave spherical surface, the rear surface is a convex spherical surface, and a YAG material is adopted; the second collimating lens 62 is a negative lens, the front surface is a concave spherical surface, the rear surface is a convex spherical surface, and BaF is adopted2A material; the third collimating lens 63 is a negative lens, the front surface is a concave spherical surface, the rear surface is a convex spherical surface, and ZnS material is adopted; the fourth collimating lens 64 is a positive lens, the front surface is a convex spherical surface, the rear surface is a convex spherical surface, and BaF is adopted2A material.
To reduce central obscuration, the first image plane A1 is located at the central aperture of the fourth mirror 4, the second image plane A2 is located at the central aperture of the third mirror 3, which is located at the central opening of the first mirror.
The real exit pupil a3 is located behind the collimating mirror group.
The incident beam is reflected twice by the first reflector 1 and the second reflector 2, a first image surface A1 is formed at the central hole of the fourth reflector 4, the beam passes through the central hole of the fourth reflector 4 and then is reflected twice by the third reflector 3 and the fourth reflector 4, a second image surface A2 is formed at the central hole of the first reflector 1 and behind the third reflector 3, the beam is refracted by the field lens 5 to narrow the beam range, so that the beam within the narrow range can enter the collimator set 6, the beam within the narrow range is refracted by the collimator set 6 to become parallel light, and the parallel light is emergent from the real exit pupil A3.
The real exit pupil a3 may be the exit pupil of the telephoto lens, and may be used for image motion compensation as a subsequent fast mirror position.
In the catadioptric afocal optical system provided by the invention, imaging of visible light and medium wave infrared bands is not completely confocal, the visible light is plane wave, the medium wave infrared is quasi-plane wave, or the visible light is quasi-plane wave, the medium wave infrared is plane wave, and the former is the former in the embodiment.
The technical indexes of the system are as follows: the working wave band is as follows: visible light wave band is 0.55-0.85 μm, infrared wave band is 3.7-4.8 μm; the entrance pupil diameter is: 250 mm; angle of view Φ: 1.2 degrees; visual magnification: 8.505×(visible); 8.483×(infrared).
The present invention is not limited to the above-described embodiments, and other types of lenses may be used for the field lens 5 and the collimator lens group 6.
The first reflector 1, the second reflector 2, the third reflector 3 and the fourth reflector 4 in the invention can also adopt other kinds of reflectors, such as: high-order aspheric surface and free-form surface reflector to improve imaging quality.
Fig. 2 shows an optical transfer function curve of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the visible light band.
Fig. 3 shows an optical transfer function curve of the catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the mid-wave infrared band.
As shown in fig. 2 and fig. 3, the imaging quality of the catadioptric afocal optical system provided by the embodiment of the present invention reaches the diffraction limit in both the visible light band and the medium wave infrared band,
fig. 4 shows a field curvature and a distortion curve of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the visible light band.
Fig. 5 shows a field curvature and a distortion curve of a catadioptric afocal optical system provided in accordance with an embodiment of the present invention in the mid-wave infrared band.
As shown in fig. 4 and 5, the catadioptric afocal optical system provided by the embodiment of the invention has less imaging distortion in both the visible light band and the medium-wave infrared band.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
The above embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.
Claims (9)
1. A catadioptric afocal optical system, comprising: the first reflector, the second reflector, the third reflector and the fourth reflector;
the first reflector is provided with a central hole, the second reflector is positioned in front of the first reflector, and the second reflector and the first reflector form a Cassegrain structure;
the third reflector is positioned at the central hole of the first reflector, the reflecting surface of the third reflector has the same direction as that of the reflecting surface of the first reflector, and the third reflector 3 is provided with a central hole;
the fourth reflector is positioned between the second reflector and the third reflector, the reflecting surface of the fourth reflector is opposite to the reflecting surface of the first reflector in direction, and the fourth reflector is provided with a central hole;
a field lens and a collimating lens group are sequentially arranged behind the third reflector;
the light beam process first speculum with twice reflection back of second speculum passes the centre bore of fourth speculum, the light beam process the third speculum with get into after twice reflection of fourth speculum the field lens, the light beam process the refraction of field lens is the beam range that contracts, the beam that reduces the scope gets into the collimating mirror group, process become the parallel light outgoing after the refraction of collimating mirror group.
2. The catadioptric afocal optical system according to claim 1, wherein a first image plane is formed at the central aperture of the fourth mirror, a second image plane is formed at the central aperture of the first mirror, and the parallel light exits through the real exit pupil.
3. The catadioptric afocal optical system of claim 2, where the entrance pupil and the aperture stop of the optical system are located on the first mirror, the first mirror is ellipsoidal, the reflective surface of the first mirror is concave, the second mirror is spherical with a standard surface, and the reflective surface of the second mirror is convex.
4. The catadioptric afocal optical system of claim 3, wherein the third mirror is ellipsoidal and the reflective surface of the third mirror is concave.
5. The catadioptric afocal optical system of claim 4, wherein the fourth mirror is a standard spherical surface and the reflective surface of the fourth mirror is a convex surface, a concave surface, or a flat mirror.
6. The catadioptric afocal optical system of claim 5, wherein the material of the first, second, third, and fourth mirrors is SiC, aluminum, microcrystalline glass, or beryllium-aluminum alloy.
7. The catadioptric afocal optical system of claim 6, wherein the first, second, third, and fourth mirrors are high-order aspheric or free-form mirrors.
8. The catadioptric afocal optical system of claim 7, wherein the field lens is a standard spherical lens, the front surface of the field lens is a concave spherical surface, and the rear surface is a convex spherical surface; the field lens is made of BaF2。
9. The catadioptric afocal optical system of claim 8, wherein the set of collimating lenses comprises, in order from front to back: the device comprises a first collimating mirror, a second collimating mirror, a third collimating mirror and a fourth collimating mirror;
the first collimating lens is a negative lens, the front surface of the first collimating lens is a concave spherical surface, the rear surface of the first collimating lens is a convex spherical surface, and a YAG material is adopted;
the second collimating lens is a negative lens, the front surface of the second collimating lens is a concave spherical surface, the rear surface of the second collimating lens is a convex spherical surface, and BaF is adopted2A material;
the third collimating lens is a negative lens, the front surface of the third collimating lens is a concave spherical surface, the rear surface of the third collimating lens is a convex spherical surface, and ZnS material is adopted;
the fourth collimating lens is a positive lens, the front surface of the fourth collimating lens is a convex spherical surface, the rear surface of the fourth collimating lens is a convex spherical surface, and BaF is adopted2A material;
the first collimating lens, the second collimating lens, the third collimating lens and the fourth collimating lens are standard spherical lenses.
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| CN202111621468.9A CN114236797A (en) | 2021-12-28 | 2021-12-28 | Catadioptric afocal optical system |
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| CN202111621468.9A CN114236797A (en) | 2021-12-28 | 2021-12-28 | Catadioptric afocal optical system |
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1114913A (en) * | 1997-06-23 | 1999-01-22 | Kazuo Kosho | Telescope using concave spherical reflector as 1st surface |
| CN101634744A (en) * | 2009-08-06 | 2010-01-27 | 哈尔滨工业大学 | Foldback-type bi-spectral gaze imaging system |
| US20160306149A1 (en) * | 2015-02-02 | 2016-10-20 | Visionmap Ltd. | Cassegrain telescope with angled reflector |
| CN111367066A (en) * | 2018-12-25 | 2020-07-03 | 中国科学院长春光学精密机械与物理研究所 | Coaxial four-reflection optical system |
| CN113805325A (en) * | 2021-09-17 | 2021-12-17 | 航天科工微电子系统研究院有限公司 | Long-focus large-view-field miniaturized active athermal optical system |
-
2021
- 2021-12-28 CN CN202111621468.9A patent/CN114236797A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH1114913A (en) * | 1997-06-23 | 1999-01-22 | Kazuo Kosho | Telescope using concave spherical reflector as 1st surface |
| CN101634744A (en) * | 2009-08-06 | 2010-01-27 | 哈尔滨工业大学 | Foldback-type bi-spectral gaze imaging system |
| US20160306149A1 (en) * | 2015-02-02 | 2016-10-20 | Visionmap Ltd. | Cassegrain telescope with angled reflector |
| CN111367066A (en) * | 2018-12-25 | 2020-07-03 | 中国科学院长春光学精密机械与物理研究所 | Coaxial four-reflection optical system |
| CN113805325A (en) * | 2021-09-17 | 2021-12-17 | 航天科工微电子系统研究院有限公司 | Long-focus large-view-field miniaturized active athermal optical system |
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