Optical structure of main focus type large aperture large field of view telescope

Abstract

The present application relates to the field of telescope technology, and more particularly to a main focus type large aperture and large field of view telescope optical structure, comprising a main reflector and a correction lens group coaxially arranged, the correction lens group comprising a first lens to a fourth lens arranged in sequence along the reflection direction of the main reflector, the first lens and the second lens are made of the same optical lens material, the third lens and the fourth lens are made of different optical lens materials and are different from the optical lens material of the first lens; the focal length of the first lens is 45-55m, the focal length of the second lens is 0.5-0.7m, the focal length of the third lens is 0.3-0.5m, and the focal length of the fourth lens is 0.1-0.3m. The present application optimizes and improves the correction lens group, achieves basically the same optical performance and detection capability as patent CN117666094A by using only four lenses without changing the parameters of the main reflector, thereby reducing the complexity and processing difficulty of the correction lens group.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of telescopes, and particularly relates to a main focal point type large-aperture large-field-of-view telescope optical structure. BACKGROUND

[0002] A large-aperture large-field-of-view optical telescope is an important means for detecting dark and weak space targets. A main focal point type telescope is a relatively common structural form of a meter-level large-aperture large-field-of-view optical telescope, which is usually composed of a main mirror and a corrector lens group. Compared with a Mason-Schmidt type telescope, an RC type telescope and an off-axis three-mirror type telescope, the main focal point type telescope has the advantages of small central obstruction, good imaging quality and simple assembly and adjustment.

[0003] The chromatic aberration of the main focal point optical system and the off-axis field aberration are corrected by the corrector lens group. The correction of the aberration requires the combination of multiple different types of transmission glass materials with different transmittance and dispersion coefficients. Generally, the correction of the aberration of the corrector lens group of a meter-level main focal point large-field-of-view telescope requires sufficient degrees of freedom, so the number of lenses in the corrector lens group is usually large, and the aperture is also large.

[0004] A Chinese invention patent with the publication number CN117666094A proposes a meter-level large-aperture large-field-of-view main focal point telescope optical system, which is composed of a main mirror and a corrector lens group. The main mirror is an elliptical concave mirror, and the corrector lens group is composed of six spherical lenses, which contain three different glass materials, and the maximum lens aperture is 400 mm. The working waveband of the system is 400 nm-800 nm, and the performance is good within an optical field of view of 10 square degrees. However, the corrector lens group requires a large number of lenses with large apertures, which increases the complexity and processing difficulty of the corrector lens group. SUMMARY

[0005] Therefore, the present application aims to provide a main focal point type large-aperture large-field-of-view telescope optical structure to solve the technical problems of high complexity and great processing difficulty of the corrector lens group in the patent CN117666094A.

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

[0007] The application discloses an optical structure of a primary focus type large-aperture large-field-of-view telescope, which comprises a primary mirror and a correction lens group coaxially arranged, wherein the correction lens group comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence along a reflection direction of the primary mirror; wherein the first lens and the second lens are made of a first optical lens material, the third lens is made of a second optical lens material, and the fourth lens is made of a third optical lens material; the focal length of the first lens is 45000mm-55000mm, the focal length of the second lens is -700mm--500mm, the focal length of the third lens is -500mm--300mm, and the focal length of the fourth lens is -300mm--100mm.

[0008] Further, the refractive index Nd and the Abbe number Vd of the first optical lens material satisfy 1.50≤Nd≤1.60 and 60≤Vd≤70.

[0009] Further, the refractive index Nd and the Abbe number Vd of the second optical lens material satisfy 1.55≤Nd≤1.65 and 40≤Vd≤50.

[0010] Further, the refractive index Nd and the Abbe number Vd of the third optical lens material satisfy 1.45≤Nd≤1.55 and 75≤Vd≤85.

[0011] Further, the optical power of the first lens is positive, and both sides are spherical surfaces; the optical power of the second lens is negative, and both sides are spherical surfaces; the optical power of the third lens is negative, and both sides are spherical surfaces; and the optical power of the fourth lens is negative, one side close to the primary mirror is a spherical surface, and the other side away from the primary mirror is an even aspheric surface, and the conic coefficient is less than -1.

[0012] Further, the aperture of the first lens is 300mm-320mm, and the thickness is 70mm-80mm; the aperture of the second lens is 240mm-250mm, and the thickness is 40mm-50mm; the aperture of the third lens is 135mm-145mm, and the thickness is 25mm-35mm; the aperture of the fourth lens is 110mm-130mm, and the thickness is 25mm-35mm; the interval between the first lens and the second lens is 40mm-50mm; the interval between the second lens and the third lens is 145mm-155mm; and the interval between the third lens and the fourth lens is 3mm-8mm.

[0013] Further, the expression of the even aspheric surface of the fourth lens is as follows:

[0014] ;

[0015] wherein, z is the sag of the curved surface, k is the conic coefficient, c is the radius of curvature at a fixed point,r is a radial radius, α is a radial coordinate term coefficient.

[0016] Further, the F number of the main focus type large-aperture large-field-of-view telescope optical structure is 1.1-1.4, and the working waveband is 400nm-800nm.

[0017] Further, the optical field of view of the main focus type large-aperture large-field-of-view telescope optical structure is 10 square degrees.

[0018] Compared with the prior art, the application can achieve the following beneficial effects:

[0019] On the basis of the patent CN117666094A, the correction lens group is optimized and improved, without changing the parameters of the main reflector, by redesigning the correction lens group, only four lenses are used, including three spherical lenses and one even aspheric lens, the maximum aperture of the three spherical lenses is only 320mm, and the aperture of the even aspheric lens is only 110mm, while the optical performance and detection capability are basically the same as those of the patent CN117666094A, the complexity and processing difficulty of the correction lens group are reduced. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application illustrated in the drawings are presented to explain the present application and not intended to limit the present application. In the drawings:

[0021] Figure 1 is a structural schematic diagram of the main focus type large-aperture large-field-of-view telescope optical structure according to the embodiment of the application.

[0022] Legend: main reflector 1, first lens 2, second lens 3, third lens 4, fourth lens 5, image plane 6. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and do not limit the application.

[0024] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict.

[0025] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0026] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0028] As shown in Figure 1 The present application provides a main focus type large aperture and large field of view telescope optical structure, which comprises a main reflector 1 and a correction lens group. The light beam of a space target is incident on the main reflector 1 from infinity, is reflected by the main reflector 1, and then passes through the correction lens group to reach an image plane 6. The correction lens group is responsible for completing the correction of chromatic aberration and off-axis field aberration of the system.

[0029] The main reflector 1 is a meter-level elliptical concave spherical reflector, the conic coefficient is less than 0 and greater than -1, which is an elliptical concave surface, and the F number of the main reflector 1 is 2-4.

[0030] The correction lens group comprises a first lens 2, a second lens 3, a third lens 4 and a fourth lens 5. After the light passes through the main reflector 1, it passes through the first lens 2, the second lens 3, the third lens 4 and the fourth lens 5 in turn to reach the image plane 6. The central axes of the first lens 2 to the fourth lens 5 and the main reflector 1 are all coincident with the optical axis of the system.

[0031] The first lens 2 has positive optical power, both sides are spherical surfaces, the aperture is 300mm-320mm, the thickness is 70mm-80mm, the focal length is 45000mm-55000mm, the refractive index Nd and the Abbe number Vd of the optical lens material satisfy: 1.50≤Nd≤1.60, 60≤Vd≤70; the interval between the first lens 2 and the second lens 3 is 40-50mm.

[0032] The second lens 3 has negative optical power, both sides are spherical surfaces, the aperture is 240mm-250mm, the thickness is 40mm-50mm, the focal length is -700mm--500mm, the optical lens material is the same as the first lens 2, the refractive index Nd and the Abbe number Vd satisfy: 1.50≤Nd≤160, 60≤Vd≤70; the interval between the second lens 3 and the third lens 4 is 145-155mm.

[0033] The third lens 4 has negative optical power, both sides are spherical surfaces, the aperture is 135mm-145mm, the thickness is 25mm-35mm, the focal length is -500mm--300mm, the refractive index Nd and the Abbe number Vd of the optical lens material satisfy: 1.55≤Nd≤1.65, 40≤Vd≤50; the interval between the third lens 4 and the fourth lens 5 is 3-8mm.

[0034] The fourth lens 5 has negative optical power, the side close to the main reflector is a spherical surface, the side away from the main reflector is an even aspheric surface, the conical surface coefficient is less than -1, the aperture is 110mm-130mm, the thickness is 25mm-35mm, the focal length is -300mm--100mm, the refractive index Nd and the Abbe number Vd of the optical lens material satisfy: 1.45≤Nd≤1.55, 75≤Vd≤85.

[0035] The expression of the even aspheric surface on the side of the fourth lens 5 away from the main reflector 1 is:

[0036] ;

[0037] wherein, z is the sag of the curved surface, k is the conical surface coefficient, c is the radius of curvature at the fixed point, r is the radial radius, α is the coefficient of each radial coordinate term.

[0038] In the process of optical design optimization, it can be found that as the aspheric surface order set as a variable is increased to a certain order, the optimization time is greatly increased, and the effect changes are not obvious, so the aspheric surface order is not selected r 10 The above parameters are not selected as variables, and the α 2、 α 3、α 4 as a variable participates in optimization.

[0039] The correction lens group realizes third-order correction for system chromatic aberration and off-axis field aberration, first-order correction is performed on the system chromatic aberration and off-axis field aberration by the first lens 2 and the second lens 3 in the spherical lens with a medium refractive index and a medium Abbe number, second-order correction is performed on the system chromatic aberration and off-axis field aberration by the third lens 4 with a high refractive index and a low Abbe number, and third-order correction is performed on the system chromatic aberration and off-axis field aberration by the fourth lens 5 with a low refractive index and a high Abbe number.

[0040] The main focal point type large-aperture large-field-of-view telescope optical structure disclosed by the application has the same optical structure as that of the patent CN117666094A, the working waveband is 400nm-800nm, the optical field of view can reach 10 square degrees, the F number is 1.1-1.4, and the optical performance is good, so that starlight collection and imaging detection of an infinite remote “dark and weak” target can be realized.

[0041] In the main focal point type large-aperture large-field-of-view telescope optical structure disclosed by the application, the main reflector 1 is a meter-level elliptical concave spherical reflector, which has the same parameters as the main reflector in the patent CN117666094A and does not need to be additionally processed; the correction lens group is composed of four lenses, including three spherical lenses and one lens using an even-order aspheric surface (one surface is an even-order aspheric surface, and the other surface is a spherical surface), the aperture of the largest one of the three spherical lenses is only 320mm, and the aperture of the lens using the even-order aspheric surface is only 110mm, so that the structure of the correction lens group is simplified, the machining and adjustment are easy, the manufacturing difficulty of the entire optical system is reduced, the structure is simpler, and the aperture is smaller compared with the patent CN117666094A. On the premise that the optical performance and detection capability are basically the same as those of the patent CN117666094A, the complexity and machining difficulty of the correction lens group are reduced, and the original scheme is effectively and reasonably replaced.

[0042] It should be further explained that the fewer the number of lenses in the correction lens group, the lower the machining and adjustment difficulty and the lower the cost, but the system needs to meet the optical imaging quality requirements. The correction lens group in the patent CN117666094A adopts a six-lens structure, and the spot diagram of the system is controlled within two image elements of the detector. In order to reduce the machining difficulty, adjustment difficulty and cost, the number of lenses in the correction lens group is reduced through optical structure design, and under the premise of using the same detector and the same image element size, the optical performance of the four-lens structure in the application is the same as that of the patent CN117666094A, and the optical imaging quality is basically the same as that of the patent CN117666094A.

[0043] The correction lens group adopts 4 lenses, which has reached the limit of optical performance, if the correction lens group adopts 3 lenses, the correction lens group has insufficient degrees of freedom, that is, the optimization variables are insufficient, so the required imaging quality cannot be achieved; if the correction lens group adopts 5 lenses, although the required imaging quality can be achieved, the machining difficulty, assembly and adjustment difficulty and cost of the correction lens group cannot be reduced by further reducing the number of lenses, therefore the correction lens group is composed of 3 spherical lenses and 1 lens with an even aspheric surface on one side.

[0044] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, each step described in the present disclosure can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, which is not limited herein.

[0045] The above detailed description does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A primary focus large aperture large field of view telescope optical structure comprising a primary mirror and a corrector lens group coaxially arranged, characterized in that, The correction lens set comprises a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the reflection direction of the main mirror; wherein the first lens and the second lens are made of a first optical lens material, the third lens is made of a second optical lens material, and the fourth lens is made of a third optical lens material; the focal length of the first lens is 45000mm-55000mm, the focal length of the second lens is -700mm--500mm, the focal length of the third lens is -500mm--300mm, and the focal length of the fourth lens is -300mm--100mm.

2. The prime-focus large-aperture wide-field telescope optical structure according to claim 1, characterized in that, The refractive index Nd and the Abbe number Vd of the first optical lens material satisfy 1.50≤Nd≤1.60 and 60≤Vd≤70.

3. The prime-focus large-aperture wide-field telescope optical structure according to claim 1, characterized in that, The refractive index Nd and the Abbe number Vd of the second optical lens material satisfy 1.55≤Nd≤1.65 and 40≤Vd≤50.

4. The prime-focus large-aperture wide-field telescope optical structure according to claim 1, characterized in that, The refractive index Nd and the Abbe number Vd of the third optical lens material satisfy 1.45≤Nd≤1.55 and 75≤Vd≤85.

5. The prime-focus large-aperture wide-field telescope optical structure according to any one of claims 1-4, characterized in that, The optical power of the first lens is positive, and both sides are spherical surfaces; the optical power of the second lens is negative, and both sides are spherical surfaces; the optical power of the third lens is negative, and both sides are spherical surfaces; the optical power of the fourth lens is negative, and the side close to the main mirror is a spherical surface, and the side away from the main mirror is an even aspheric surface with a conical surface coefficient less than -1.

6. The prime-focus large-aperture wide-field telescope optical structure according to claim 5, characterized in that, The aperture of the first lens is 300mm-320mm, and the thickness is 70mm-80mm; the aperture of the second lens is 240mm-250mm, and the thickness is 40mm-50mm; the aperture of the third lens is 135mm-145mm, and the thickness is 25mm-35mm; the aperture of the fourth lens is 110mm-130mm, and the thickness is 25mm-35mm; the interval between the first lens and the second lens is 40mm-50mm; the interval between the second lens and the third lens is 145mm-155mm; and the interval between the third lens and the fourth lens is 3mm-8mm.

7. The prime-focus large-aperture wide-field telescope optical structure according to claim 5, characterized in that, The expression of the even aspheric surface of the fourth lens is: ； wherein z is the sag of the surface, k is the conic constant, c is the radius of curvature at the point, r is the radial radius, α is the coefficient of each radial coordinate term.

8. The prime-focus large-aperture wide-field telescope optical structure according to claim 1, characterized in that, The F number of the optical structure of the main focus type large-aperture large-field-of-view telescope is 1.1-1.4, and the working waveband is 400nm-800nm.

9. The prime-focus large-aperture wide-field telescope optical structure according to claim 1, characterized in that, The optical field of view is 10 square degrees.

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