One reverse type common-bore three-stage zoom optical system

Abstract

The application provides a catadioptric co-caliber three-grade zoom optical system, which can eliminate the vignetting of a transmission zoom system, compress the structure size of a long focal length, and improve the target energy collection capacity by using a large caliber. The optical system realizes three-grade zoom of a Cassegrain primary mirror as a diaphragm, eliminates the vignetting of the transmission zoom system, compresses the structure size of the long focal length, and improves the target energy collection capacity by using the large caliber. Even in low-illumination weather conditions, the target surface illumination can be ensured, and a high target surface irradiance can still be realized in the long focal length mode. The co-caliber zoom structure integrates a part of the long focal length mode of continuous zoom, so that the structure of a small focal length and large field of view zoom system used in cooperation is more compact, and the weight and space pressure of the overall load are reduced. Meanwhile, the three-grade zoom structure can realize rapid switching of the focal length, and eliminates the zoom delay in the continuous zoom case.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical systems, and particularly relates to a catadioptric common-aperture three-grade zoom optical system. BACKGROUND

[0002] With the rapid development of visible light imaging systems in the field of aviation, the visible light imaging systems now have multiple grades of zoom, continuous zoom, large-aperture long focus, large field of view fixed focus and other system forms, and have become an important part of aviation loads. At present, the front fixed group of the multiple grades of zoom or continuous zoom is generally a transmissive lens, which can meet the needs of continuous change of large field of view and small field of view, although there is a certain vignetting at the edge of the field of view. For example, the patent number CN201510147959 "compact three-group large zoom ratio continuous zoom lens" and the patent number CN201510481734 "a large target surface continuous zoom optical system", the front fixed group is a refractive lens group. This type of zoom lens is simple to assemble and adjust, but the long-focus lens generally has a large volume.

[0003] At present, the visible light system with multiple grades and continuous zoom generally exists in a coaxial transmissive system, and the front fixed group is a transmissive lens group with positive focal length. Although this type of zoom system is simple to assemble and has a large zoom ratio, it has the problem of long system size. Due to the limitation of the aperture, there is vignetting at the edge of the field of view, which will result in low energy collected by the target surface and low contrast in low-illumination weather conditions.

[0004] The long-focus system generally uses a Cassegrain incident aperture to effectively compress the size of the structure while realizing target recognition with long focus, and to collect target energy with a large aperture. However, the optical system with Cassegrain reflection structure is generally a long-focus fixed-focus lens. On the one hand, it is necessary to compress the structure size, and on the other hand, it is necessary to collect target energy with a large aperture because the scene in the field of view is far away. Therefore, it is generally used in combination with a transmissive zoom lens, which will increase the weight and volume of the flight load. SUMMARY

[0005] Therefore, the present application provides a catadioptric common-aperture three-grade zoom optical system, which can eliminate the vignetting of the transmissive zoom system, compress the structure size of the long focal length, and improve the collection ability of target energy with a large aperture.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] The present application discloses a catadioptric common-aperture three-grade zoom optical system, which sequentially comprises a primary imaging group, a front fixed lens group, a variable lens group, a compensation lens group and a rear fixed lens group from the object side to the image side, and the optical power distribution of the five lens groups is positive, positive, positive, negative and positive in sequence.

[0008] The primary mirror of the Cassegrain structure is a parabolic mirror, and the secondary mirror is a hyperboloidal mirror.

[0009] The aperture stop is arranged on the primary mirror.

[0010] The front fixed lens group is composed of two single lenses and one cemented lens, the first single lens is a convex moon-shaped positive focal length single lens with the convex surface facing the image side, the second single lens is a double-cemented negative lens with the convex surface facing the object side, and the third single lens is a positive lens with the convex surface facing the image side.

[0011] The variable lens group is composed of one double-cemented lens and two single lenses, the first single lens is a double-cemented negative lens with the convex surface facing the object side, the second single lens is a positive lens with the convex surface facing the image side, and the third single lens is a positive lens with the convex surface facing the object side.

[0012] The compensation lens group is composed of one double-cemented lens and one single lens, and the compensation lens group moves between the variable lens group and the rear fixed group to compensate for the image surface movement of the catadioptric common-aperture three-grade zoom optical system during zooming.

[0013] The rear fixed group is composed of a single lens and a double cemented lens, from the object side to the image side, the first lens is a double-convex positive focal length single lens, and the second lens is a double cemented negative lens with a convex surface facing the object surface, and the interval between the compensation lens group and the rear fixed group ranges from 12mm to 58.8mm.

[0014] Beneficial effects:

[0015] The optical system of the application realizes three-grade zooming of the Cassegrain primary mirror as a diaphragm, eliminates vignetting of the transmission type zooming system, compresses the structure size of the long focal length, and improves the target energy collection capacity by using a large aperture. The optical system of the application compresses the size in the long focal length mode to the greatest extent. Meanwhile, the aperture diaphragm is arranged on the primary mirror, the system does not have vignetting in the short focal length mode, and the full aperture of the Cassegrain structure primary mirror is used for imaging in the three-grade different focal length modes. Even in low-illumination weather conditions, the target surface illumination can be ensured, and high target surface irradiance can still be realized in the long focal length mode. The co-aperture zooming structure integrates a part of the long focal length mode of continuous zooming, so that the structure of the small focal length and large field of view zooming system used in cooperation is more compact, and the weight and space pressure of the overall load are reduced. Meanwhile, the three-grade zooming structure can realize rapid switching of the focal length, and eliminates the zooming delay in the continuous zooming case.

[0016] The co-aperture three-grade zooming optical system of the application adopts an image side telecentric optical path design on the image side, relaxes the tolerance, and uniformly illuminates the target surface with scene energy. With the change of the aperture required by different engineering projects, the system can also be scaled proportionally and simply optimized, so that different design requirements can be met. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic view of the optical structure of the catadioptric co-aperture three-grade zooming optical system;

[0018] Figure 2 is a schematic view of the positional relationship of the catadioptric co-aperture three-grade zooming optical system in the short focal length state;

[0019] Figure 3 is a schematic view of the positional relationship of the catadioptric co-aperture three-grade zooming optical system in the mid focal length state;

[0020] Figure 4 is a schematic view of the positional relationship of the catadioptric co-aperture three-grade zooming optical system in the long focal length state;

[0021] Figure 5 is a transfer function of 0 field of view in the short focal length state of the catadioptric co-aperture three-grade zooming optical system;

[0022] Figure 6is a transfer function of a 0.7 field of view in a short-focus state of the catadioptric co-axial three-stage zoom optical system;

[0023] Figure 7 is a transfer function of an edge field of view in the short-focus state of the catadioptric co-axial three-stage zoom optical system;

[0024] Figure 8 is a transfer function of a 0 field of view in a mid-focus state of the catadioptric co-axial three-stage zoom optical system;

[0025] Figure 9 is a transfer function of a 0.7 field of view in the mid-focus state of the catadioptric co-axial three-stage zoom optical system;

[0026] Figure 10 is a transfer function of an edge field of view in the mid-focus state of the catadioptric co-axial three-stage zoom optical system;

[0027] Figure 11 is a transfer function of a 0 field of view in a long-focus state of the catadioptric co-axial three-stage zoom optical system;

[0028] Figure 12 is a transfer function of a 0.7 field of view in the long-focus state of the catadioptric co-axial three-stage zoom optical system;

[0029] Figure 13 is a transfer function of an edge field of view in the long-focus state of the catadioptric co-axial three-stage zoom optical system;

[0030] Figure 14 is a field curvature distortion map in the short-focus state of the catadioptric co-axial three-stage zoom optical system;

[0031] Figure 15 is a field curvature distortion map in the mid-focus state of the catadioptric co-axial three-stage zoom optical system;

[0032] Figure 16 is a field curvature distortion map in the long-focus state of the catadioptric co-axial three-stage zoom optical system;

[0033] Figure 17 is a point spread function map in the short-focus state of the catadioptric co-axial three-stage zoom optical system;

[0034] Figure 18 is a point spread function map in the mid-focus state of the catadioptric co-axial three-stage zoom optical system;

[0035] Figure 19 is a point spread function map in the long-focus state of the catadioptric co-axial three-stage zoom optical system. DETAILED DESCRIPTION

[0036] The present application will be described in detail below with reference to the drawings and embodiments.

[0037] In order to solve the problems of the aperture vignetting, the size of the long-focus mode being too long and the target surface illumination being limited in the visible light zoom system at present, the catadioptric common-aperture three-grade zoom optical system is considered from the angles of system lightening and the development trend of the aviation load, and the catadioptric common-aperture three-grade zoom optical system comprises, from the object side to the image side, a primary imaging group, a front fixed lens group, a variable magnification lens group, a compensation lens group and a rear fixed lens group, the focal power distribution of the five lens groups is positive, positive, positive, negative and positive in turn, the zoom function of the catadioptric common-aperture three-grade zoom optical system is realized by the axial movement of the variable magnification lens group and the compensation lens group, and the primary image surface is corrected by the aberration of the front fixed lens group, the variable magnification lens group, the compensation lens group and the rear fixed lens group and finally imaged on the detector target surface in the telecentric light path.

[0038] In view of the problems of the aperture vignetting, the size of the long-focus mode being too long and the target surface illumination being limited in the visible light zoom system, the catadioptric common-aperture three-grade zoom optical system is realized by using the Cassegrain structure and the zoom optical theory, the one-way movement of the variable magnification lens group and the compensation lens group along the optical axis, the full-aperture imaging of the Cassegrain structure main mirror is utilized for the three-grade focal lengths, the target surface can receive sufficient energy when the long-focus and short-focus structures are imaged, and there is no vignetting, the design of the telecentric light path on the image side enables the scene energy to be uniformly distributed on the target surface, the catadioptric common-aperture three-grade zoom optical system comprises a Cassegrain mirror group and a piece of cemented lens as the primary imaging group of the three-grade zoom system, and the rear is sequentially provided with the front fixed lens group, the variable magnification lens group, the compensation lens group and the rear fixed lens group, the zoom is realized by the axial movement of the variable magnification lens group and the compensation lens group, and then the switching of different fields of view is realized, the system structure can compress the system size to the maximum extent in the long-focus mode, the aperture stop is arranged on the main mirror, the system does not have vignetting in the short-focus mode, the target surface illumination is improved to the maximum extent due to the large aperture in the low-illumination weather condition, the high target surface illumination can still be realized in the long-focus mode, the common-aperture zoom structure integrates a part of the long-focus mode of the continuous zoom, and the volume and weight of the load are compressed.

[0039] Meanwhile, the three-grade zoom structure can realize the rapid switching of the focal length, and the zoom delay in the continuous zoom condition is avoided, in addition, the telecentric light path on the image side is designed in the common-aperture three-grade zoom optical system, the tolerance is relaxed, and the scene energy uniformly illuminates the target surface.

[0040] The catadioptric common-aperture three-grade zoom optical system is designed by using the Chengdu Guangming Glass Library glass, and can be applied to a 1920*1080 pixel image element 5.5 mu detector and a visible light detector with the same target surface size.

[0041] Wherein, the lens F number is 4.6-10-14, the three gear focal lengths are 700mm, 1500mm and 2100mm respectively, the entrance pupil diameter is 150mm, and the optical size is less than 340mm.

[0042] Taking the application in the visible light detector as an example, the target surface is 1920*1080 pixels, and the pixel size is 5.5μm, Figure 2 、 Figure 3 and Figure 4 respectively are optical system schematic diagrams of the catadioptric co-axial three-gear zoom optical system at the short-focus, medium-focus and long-focus positions. From the object plane (left side) to the image plane (right side) are in turn a primary imaging group, a front fixed lens group A, a variable magnification lens group B, a compensation lens group C and a rear fixed lens group D, and the power distribution of the four lens groups is positive, positive, negative and positive respectively. The catadioptric co-axial three-gear zoom optical system relies on the axial movement of the variable magnification lens group B and the compensation lens group C to realize the zoom function of the system.

[0043] Specifically, the primary imaging group is realized by a Cassegrain structure and a double cemented lens. The primary mirror of the Cassegrain structure is a parabolic mirror with an aperture of 150mm, and the secondary mirror is a hyperboloidal mirror with an aperture of 37mm. The Cassegrain structure realizes the convergence of the light beam, and then a double cemented lens with negative power is used to realize the primary imaging. In the zoom process of the catadioptric co-axial three-gear zoom optical system, the position of the primary image plane does not change and is always between the primary imaging group and the front fixed group. However, due to the change of the field of view range in the zoom process, the size of the primary image will change accordingly.

[0044] The front fixed lens group A is composed of two single lenses and a cemented lens. The first piece is a meniscus positive focal length single lens with the convex surface facing the image plane, and the material is H-LAK8B; the second piece is a double cemented negative lens with the convex surface facing the object plane, and the material is H-ZBAF3 and ZF2; and the third piece is a positive lens with the convex surface facing the image plane, and the material is H-ZBAF21. The front fixed lens group A does not change in position during the entire zoom process.

[0045] The variable magnification lens group B is composed of a double cemented lens and two single lenses. The first piece is a double cemented negative lens with the convex surface facing the object plane, and the material is H-ZK21 and ZF8 in turn; the second piece is a positive lens with the convex surface facing the image plane, and the material is H-LAK8A; and the third piece is a positive lens with the convex surface facing the object plane, and the material is H-BAK7. The entire variable magnification lens group B moves axially between the front fixed lens group A and the compensation lens group C to change the focal length of the catadioptric co-axial three-gear zoom optical system. When the system changes from short focus to long focus, the variable magnification lens group B moves in one direction towards the front fixed group A, and the spacing range between the variable magnification lens group B and the front fixed lens group A is 7-71.6mm.

[0046] The compensation lens group C is composed of a doublet and a single lens, and moves between the variable lens group B and the rear fixed group D, and is used for compensating the image surface movement of the catadioptric three-stage variable focal length optical system during zooming. The first lens near the object surface of the compensation lens group C is a doublet with a double concave shape, and is made of H-ZF5 and H-QF14. The second lens is a single lens with a convex shape towards the image surface, and is made of H-ZLAF53B. When the catadioptric three-stage variable focal length optical system changes from a short focal length to a long focal length, the compensation lens group C moves towards the front fixed group A along the optical axis, and the moving direction is consistent with that of the variable lens group B. The interval between the compensation lens group C and the variable lens group B changes in the range of 12-29.8mm.

[0047] The rear fixed group D is composed of a single lens and a doublet, and the first lens is a doublet with a double convex shape, and is made of H-LAK2A. The second lens is a doublet with a convex shape towards the object surface, and is made of H-LAF10LA and ZF51. The interval between the compensation lens group C and the rear fixed group D changes in the range of 12-58.8mm.

[0048] The front fixed group A, the variable lens group B, the compensation lens group C and the rear fixed group D re-image the primary image surface of the primary imaging group on the target surface of the detector.

[0049] The change process of the system from a short focal length to a long focal length is as follows: when the system is in a short focal length state, the variable lens group B is farthest from the front fixed group A, the compensation lens group C is closest to the rear fixed group D, and the distance between the variable lens group B and the compensation lens group C is also the shortest. As the system changes from a short focal length to a long focal length, the variable lens group B gradually approaches the front fixed group A, and the compensation lens group C gradually moves away from the rear fixed group D. The moving direction of the variable lens group B is consistent with that of the compensation lens group C. Due to different moving curves, the interval between the variable lens group B and the compensation lens group C gradually increases during the change process of the system from a short focal length to a long focal length.

[0050] The technical indexes of the three-stage variable focal length realized by the catadioptric three-stage variable focal length optical system are as follows: the working waveband is 0.5-0.7μm, the focal length is 700-1500-2100mm, the corresponding F number is 4.6, 10 and 14, and the system is suitable for a visible light detector with 1920×1080 image elements and a 5.5μm image element size.

[0051] In the embodiment, the change process of the system from a short focal length to a long focal length is taken as an example. When the system is in a short focal length of 700mm, the distance between the variable lens group B and the front fixed group A is the farthest, which is 71.6mm. The distance between the compensation lens group C and the rear fixed group D is the closest, which is 12mm. The distance between the variable lens group B and the compensation lens group C is the shortest, which is 12mm.

[0052] During the movement of the system from short to long focal length, the variable lens group B moves gradually forward to the front fixed group A, and the compensation lens group C moves gradually away from the rear fixed group D. When the distance between the variable lens group B and the compensation lens group C reaches 19.8mm, the system reaches the intermediate focal length position, and the focal length is 1500mm. The interval between the variable lens group B and the front fixed group A is 22.2mm, and the interval between the compensation lens group C and the rear fixed group D is 53.7mm.

[0053] The variable lens group B continues to move forward to the front fixed group A, and the compensation lens group C further moves away from the rear fixed group D. When the interval between the variable lens group B and the compensation lens group C is 29.8mm, the system reaches the long focal length position, and the focal length is 2100mm. The interval between the variable lens group B and the front fixed group A is 7mm, and the interval between the compensation lens group C and the rear fixed group D is 58.8mm.

[0054] Similarly, when the catadioptric three-stage variable focal length optical system changes from long to short focal length, the variable lens group B moves in a single direction of axial movement away from the front fixed group A, and the compensation lens group moves in a single direction of axial movement close to the rear fixed group D. The parameter table of the optical system is as shown in Table 1.

[0055] Table 1 Lens parameters of the catadioptric three-stage variable focal length optical system

[0056]

[0057]

[0058] Lenses 2, 3 and 4 form the front fixed group A; lenses 5, 6 and 7 form the variable lens group B, lenses 8 and 9 form the compensation lens group C, and lenses 10 and 11 form the rear fixed group D. T1, T2 and T3 are the air intervals between the groups during the zooming process.

[0059] Table 2 Interval of variable focal length size

[0060] Tele Mid Short T1 71.6 22.2 7 T2 12 19.8 29.8 T3 12 53.7 58.8

[0061] The designed catadioptric co-caliber three-grade zoom optical system is based on visible light zoom theory and combines with Cassegrain reflection structure to realize secondary imaging of visible light. The system is suitable for 1920*1080 pixels, pixel size 5.5 μm and visible light detector with the same target surface size, lens F number 4.6-10-14, corresponding to three grades of focal length 700 mm, 1500 mm and 2100 mm. The main mirror aperture size is 150 mm. The optical axial size is less than 340 mm. The F number of three grades of focal length of the system is 4.6, 10 and 14, corresponding to three grades of focal length 700 mm, 1500 mm and 2100 mm. The total length of the system is less than 340 mm. The system is suitable for 1920*1080 pixels, pixel size 5.5 μm and visible light detector with the same target surface size.

[0062] To sum up, the above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A catadioptric three-stop zoom optical system with common aperture, characterized in that, From the object side to the image side, the five lenses are arranged in sequence: a primary imaging group, a front fixed lens group, a zoom lens group, a compensation lens group, and a rear fixed lens group. The optical power distribution of these five lens groups is positive, positive, positive, negative, and positive, respectively. The zoom function of the catadioptric three-stop zoom optical system is achieved by axial movement of the zoom lens group and the compensation lens group. The primary image plane undergoes aberration correction by the front fixed lens group, the zoom lens group, the compensation lens group, and the rear fixed lens group, and is finally imaged onto the detector target surface via a telecentric optical path. The primary imaging group includes a Cassegrain mirror group and a cemented mirror. The front fixed lens group consists of two single lenses and a cemented mirror. The zoom lens group consists of a cemented doublet and two single lenses. The compensation lens group consists of a cemented doublet and a single lens. The rear fixed lens group consists of a single lens and a cemented doublet.

2. The system as described in claim 1, characterized in that, The primary mirror of the Cassegrain reflector assembly is a parabolic reflector, and the secondary mirror is a hyperboloid reflector.

3. The system as described in claim 2, characterized in that, An aperture stop is mounted on the primary mirror.

4. The system according to any one of claims 1-3, characterized in that, In the front fixed lens group, the first element is a meniscus positive focal length single lens with its convex surface facing the image plane; the second element is a cemented doublet negative lens with its convex surface facing the object plane; and the third element is a positive lens with its convex surface facing the image plane. The position of the front fixed lens group remains unchanged throughout the zoom process.

5. The system according to any one of claims 1-3, characterized in that, In the zoom lens group, the first lens is a cemented doublet negative lens with its convex surface facing the object plane; the second lens is a positive lens with its convex surface facing the image plane; and the third lens is a positive lens with its convex surface facing the object plane. The entire zoom lens group moves axially between the front fixed lens group and the compensation lens group to change the focal length of the catadioptric three-stop zoom optical system. When the system changes from short focal length to long focal length, the zoom lens group moves in one direction to the front fixed lens group, and the interval between the zoom lens group and the front fixed lens group is 7 to 71.6 mm.

6. The system according to any one of claims 1-3, characterized in that, The compensation lens group moves between the zoom lens group and the rear fixed group to compensate for the image plane movement of the catadioptric three-stop zoom optical system during zooming. The first lens of the compensation lens group near the object plane is a double concave cemented doublet lens, and the second lens is a meniscus single lens with its convex surface facing the image plane. When the catadioptric three-stop zoom optical system changes from short focal length to long focal length, the compensation lens group moves forward to the fixed group along the optical axis, in the same direction as the zoom lens group. The interval between the compensation lens group and the zoom lens group varies from 12 to 29.8 mm.

7. The system according to any one of claims 1-3, characterized in that, In the rear fixed group, from the object side to the image side, the first lens is a biconvex positive focal length single lens, and the second lens is a cemented doublet negative lens with the convex surface facing the object surface. The interval between the compensation lens group and the rear fixed group is 12 to 58.8 mm.

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