Off-axis guiding device for telescopes with a focuser

Abstract

The utility model discloses a kind of astronomical telescope off-axis star guide device with zoom lens, including telescope, reflector, main detector system, zoom lens group, star guide detector etc.The utility model has realized telescope off-axis large field of view star guide, star guide system shares telescope main light path, light collection ability and stability are stronger than external star guide mirror, zoom lens device improves star guide detection field of view, it is favorable to find suitable reference star.The utility model also discloses the calculation method of star guide offset, star guide transmits the image photographed in certain period to program processing, program calculates the WCS coordinate (world coordinate system) of image by the way of star map matching, and then extract the right ascension and declination information of image reference point.The offset of center point is obtained by comparing with historical data and is fed back to telescope motion system to be corrected, to realize long time high-precision observation to target celestial body.

Description

Technical Field

[0001] This utility model relates to the field of astronomical observation technology, specifically to an off-axis guiding device for astronomical telescopes, and in particular a guiding system with a zoom mechanism, which can significantly expand the guiding field of view while ensuring guiding accuracy. Background Technology

[0002] When conducting long-exposure observations, astronomical telescopes require high-precision guiding systems to compensate for tracking errors caused by the Earth's rotation. Currently, there are two main types of guiding techniques:

[0003] The first approach is an external guide telescope solution, which uses a separate small-aperture guide telescope mechanically connected to the main telescope. The advantage of this approach is its ease of installation and adjustment. However, because the guide telescope's optical path is separate from the main telescope's optical path, relative position and angular errors inevitably occur during long-term operation, affecting the telescope's guiding and tracking accuracy. Furthermore, guide telescopes typically have a short focal length, resulting in limited position detection accuracy.

[0004] The second method is the off-axis guiding scheme, which extracts edge field rays from the telescope's main optical path for guiding. Chinese patent CN202210467570A discloses a main optical path guiding device for a telescope, where the guiding detector is installed near the telescope's main focal detector, sharing the same focal plane and optical path. While this scheme reduces errors caused by optical path separation, it has significant drawbacks: astronomical telescopes are mostly long-focal-length systems, resulting in a very small field of view for the guiding camera, and significant edge field-of-view aberrations, making it difficult to find suitable guiding targets. Furthermore, such schemes often use simple bright star pairing methods to calculate the offset, which can easily lead to matching errors when new bright stars appear in the field of view.

[0005] Existing methods for calculating guide star offsets typically employ a pairing approach using the brightest stars. For example, CN202210467570A discloses a method that selects a predetermined number of the brightest stars as guide stars in the first frame of image data, and then performs pairing and offset calculations in subsequent frames. This method has significant limitations: when new, brighter stars appear in the field of view, it can lead to pairing errors, resulting in incorrect offset calculations. Furthermore, this method relies on a small number of bright stars, and in sparsely populated areas of the sky, it may be difficult to find sufficient guide star targets.

[0006] Compared with CN202210467570A, this utility model has the following significant differences:

[0007] Structurally: This invention introduces a special five-piece zoomer in the off-axis guiding star optical path, which effectively expands the guiding star field of view and improves edge aberrations. In contrast, CN202210467570A simply places the guiding star detector near the main focal plane, without solving the problems of small field of view and large aberrations.

[0008] In terms of methodology: This invention employs a WCS calculation method based on full-image star map matching, which does not rely on a few bright stars, thus improving anti-interference capability and accuracy. In contrast, CN202210467570A uses a method of selecting the brightest star for pairing, which is prone to matching errors due to the appearance of new bright stars.

[0009] In terms of application effects: This utility model expands the guiding star field of view by about 10 times through the zoom unit. Combined with the WCS algorithm, it can find sufficient guiding star targets under various sky conditions, which significantly improves the reliability of the system. Therefore, there is an urgent need in this field for a new technology solution that can maintain the guiding star accuracy advantage of the main optical path, effectively expand the guiding star field of view, improve image quality and improve the reliability of offset calculation. Utility Model Content

[0010] (I) Purpose of the utility model

[0011] The primary objective of this invention is to provide an off-axis guiding device for astronomical telescopes with a zoom mechanism, thereby solving the problems of small field of view and large edge aberrations in existing off-axis guiding technologies.

[0012] The second objective of this invention is to provide a high-precision method for calculating guide star offsets, which utilizes star map matching and the World Coordinate System (WCS) to calculate offsets, thereby improving the reliability and accuracy of guide star data.

[0013] (II) Technical Solution

[0014] This invention provides an off-axis guiding device for an astronomical telescope with a zoom function, comprising an astronomical telescope, a main detector system, and an off-axis guiding system. The astronomical telescope is used to gather celestial signals; the main detector system is aligned with the optical axis of the astronomical telescope and is used to collect signals from the target celestial object; the off-axis guiding system is at an angle to the optical axis of the astronomical telescope and collects edge field-of-view signals for guiding.

[0015] The off-axis guiding system includes a zoom unit and a guiding detector D1. The zoom unit consists of five lenses G1, G2, G3, G4, and G5, arranged sequentially along the optical path, used to zoom in on the edge field of view signal and correct aberrations. The guiding detector is an area array detector, located at the image plane of the zoom unit, used to receive the zoomed-in optical signal and convert it into image data.

[0016] Preferably, the off-axis guiding system also includes optical path folding elements, such as mirrors or prisms, to prevent mechanical interference between the off-axis guiding system and the main detector system.

[0017] The five lenses of the zoom unit meet the following conditions:

[0018] At least two lenses have a refractive index greater than 1.9 and less than 2.0;

[0019] At least one lens has a refractive index greater than 1.5 and less than 1.6;

[0020] At least two lenses have an Abbe number greater than 15 and less than 20;

[0021] At least two lenses have an Abbe number greater than 50 and less than 70.

[0022] In one specific embodiment, the zoom unit is configured to reduce the focal ratio of the astronomical telescope from F#8 to F#2.5, and the equivalent focal length from 19200mm to 5760mm, thereby increasing the usable field of view for guiding stars by approximately 10 times.

[0023] (III) Beneficial Effects

[0024] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0025] 1. The guiding system utilizes the edge field of view light of the astronomical telescope, which is the same optical path as the main optical path, thus avoiding errors caused by asynchronous deformation of the telescope's mechanical structure.

[0026] 2. A five-lens focusing system was adopted, which improved image quality, reduced the equivalent focal length of the guiding system, and effectively expanded the field of view of the sky captured by the guiding detector, which is beneficial to the calculation of the WCS coordinates (world coordinate system) of the image.

[0027] 3. This utility model also discloses an algorithm program for guiding star offset. During continuous exposure, the guiding star detector calculates the offset by comparing the changes in right ascension and declination of the reference point between subsequent images and the first image. This offset is then fed back to the telescope's control system to guide it in correcting its pointing, thus achieving closed-loop control.

[0028] 4. This utility model uses star map matching to calculate the WCS coordinates of the image, which can make full use of the position information of all detected celestial bodies on the guide star image. Compared with the method of selecting a number of bright stars to calculate the guide star offset, it has higher accuracy and stronger anti-interference ability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the off-axis guiding device for an astronomical telescope with a zoom mechanism, according to this utility model.

[0030] Figure 2 This is an image captured by a guide camera in one embodiment, corresponding to a sky field of view of 10 arcminutes × 7.3 arcminutes.

[0031] Figure 3 yes Figure 2 A schematic diagram of celestial targets identified in the image that can be used to calculate offsets is shown, marked with red circles.

[0032] Figure labeling: 1: Astronomical telescope, 2: Main detector system, 3: Off-axis guiding system, M1: Mirror (optical path folding element), G1-G5: First to fifth lenses, D1: Guiding detector Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0034] Example

[0035] Please refer to Figure 1 This embodiment provides an off-axis guiding device for an astronomical telescope with a zoom, including an astronomical telescope (1), a main detector system (2) and an off-axis guiding system (3).

[0036] The astronomical telescope is pointed at the target area in the sky, and the main detector system is aligned with the optical axis of the telescope to collect signals from the target celestial object. The off-axis guiding system collects signals from the edge of the telescope's field of view.

[0037] In some embodiments, a reflector M1 can be added to fold the optical path to avoid mechanical interference between the main detector system and the off-axis guiding system.

[0038] The focusing system consists of five lenses, arranged sequentially from the object side to the image side: first lens G1, second lens G2, third lens G3, fourth lens G4, and fifth lens G5.

[0039] The first lens G1 is a positive lens with its convex surface facing the object direction, including a first convex spherical surface and a second concave spherical surface;

[0040] The second lens G2 is a negative lens with its convex surface facing the object direction, and includes a third convex spherical surface and a fourth concave spherical surface;

[0041] The third lens G3 is a positive lens with its convex surface facing the object direction, and includes a fifth convex spherical surface and a sixth concave spherical surface;

[0042] The fourth lens G4 is a positive lens with its concave surface facing the object direction, including a seventh concave spherical surface and an eighth convex spherical surface;

[0043] The fifth lens G5 is a positive lens with its convex surface facing the object direction, and includes a ninth convex spherical surface and a tenth convex spherical surface. Specifically, all of the first lenses G1 to the fifth lens G5 are made of glass, and all use spherical glass to correct various aberrations, which can effectively control lens costs.

[0044] In some embodiments, the first lens G1 is made of a material with a refractive index greater than 1.8 to achieve rapid focusing of light rays at the edge of a large field of view and control the volume of subsequent lens groups.

[0045] In some embodiments, the first lens G1 and the second lens G2 are respectively made of materials with Abbe numbers greater than 50 and less than 20 to achieve achromaticity.

[0046] In its practical application, this invention was used on the Lijiang 2.4-meter telescope at the Yunnan Astronomical Observatory of the Chinese Academy of Sciences. The Lijiang 2.4-meter telescope has a focal ratio of F#8 and a focal length of 19200 mm. After passing through the off-axis guiding focusing system, the focal ratio becomes F#2.5, with an equivalent focal length of 5760 mm, and the usable field of view for guiding the star is increased by approximately 10 times. The parameter selection for each lens is shown in Table 1.

[0047] First lens (1) -43.37 -14.95 H-ZLAF68N 31.00 First lens (2) -89.13 -35.30 AIR 27.00 Second lens (1) -21.06 -15.00 H-ZF72A 14.00 Second lens (2) -6.89 -3.00 AIR 6.00 Third lens (1) -25.74 -15.00 H-ZF72A 8.50 Third lens (2) -39.90 -0.64 AIR 6.20 Fourth lens (1) 195.98 -5.60 H-ZPK7 6.20 Fourth lens (2) 10.48 -1.42 AIR 8.00 Fifth lens (1) -27.24 -6.58 H-LAK52 11.00 Fifth lens (2) 61.94 -16.50 AIR 11.00

[0048] Appendix Figure 2 These are images acquired by the off-axis guiding star system detector, corresponding to a sky field of view of 10 arcminutes * 7.3 arcminutes. After data processing, celestial targets that can be used to calculate the offset are marked with red circles. Figure 3 In addition to the guiding optics for the main optical path, this invention also involves a specific algorithm for guiding star offset. The astronomical telescope 1 is pointed at the celestial object to be observed, and the main detector system 2 begins a long exposure.

[0049] The D1 guide star detector continuously acquires images using a single image exposure time of 10 seconds. The first image is named REF.fits. The WCS coordinate information of REF.fits is calculated using the astrometry.net astronomical automatic star map matching software. Then, the right ascension RA_01 and declination DEC_01 information of the reference point (usually the image center) are extracted using the astropy package in Python.

[0050] The second image acquired by the guide star detector was named OBS01.fits. The right ascension RA_02 and declination DEC_02 of the reference point were extracted. The guide star offsets (RA_02-RA_01) and (DEC_02-DEC_01) were calculated respectively, and the results were fed back to the control system of the astronomical telescope 1 for pointing correction.

[0051] Following the above method, OBS02.fits, OBS03.fits, ... are processed sequentially, and the offset from the REF.fits reference point is calculated and fed back to the control system of the astronomical telescope (1) to achieve reliable closed-loop control. Finally, the main detector system (2) obtains a clear image of the target celestial body.

[0052] The above are merely preferred embodiments of this utility model. The protection scope of this utility model is not limited to the above embodiments. All technical solutions falling within the scope of this utility model's concept are within its protection scope. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of this utility model should be considered within its protection scope.

Claims

1. An off-axis guiding device for an astronomical telescope with a zoom mechanism, characterized in that, include: Astronomical telescopes are used to collect signals from celestial bodies; The main detector system, which is aligned with the optical axis of the astronomical telescope, is used to collect signals from the target celestial body. An off-axis guiding system, which is at an angle to the optical axis of the astronomical telescope, is used to collect signals from the edge field of view of the astronomical telescope for guiding; The off-axis guiding system includes a zoom unit and a guiding detector; The zoom unit consists of five lenses (G1, G2, G3, G4, G5) arranged sequentially along the optical path, used to zoom the edge field of view signal and correct aberrations; The guide detector is positioned at the image plane of the zoom unit to receive the zoomed-in optical signal and convert it into image data.

2. The apparatus according to claim 1, characterized in that, The off-axis guiding system also includes an optical path folding element, which is a mirror or prism, used to avoid mechanical interference between the off-axis guiding system and the main detector system.

3. The apparatus according to claim 1, characterized in that, The five lenses of the zoom unit satisfy at least one of the following conditions: At least two lenses have a refractive index greater than 1.9 and less than 2.0; At least one lens has a refractive index greater than 1.5 and less than 1.6; At least two lenses have an Abbe number greater than 15 and less than 20; At least two lenses have an Abbe number greater than 50 and less than 70.

4. The apparatus according to claim 1, characterized in that, The guide detector is a CCD or CMOS area array sensor.

5. The apparatus according to claim 1, characterized in that, The zoom reducer is configured to reduce the focal ratio of the astronomical telescope from F#8 to F#2.5, and the equivalent focal length from 19200mm to 5760mm.

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