A large field of view short focal ratio newtonian reflector

Abstract

The application discloses a large-view-field short-focal-ratio Newtonian reflecting telescope and belongs to the technical field of astronomical telescopes. The large-view-field short-focal-ratio Newtonian reflecting telescope comprises a lens barrel, a primary mirror, a secondary mirror, a mounting base, a field lens and a focusing device. The field lens is fixed to the mounting base or the lens barrel, the distance between the field lens and the primary mirror and the secondary mirror is constant, and the focusing device realizes focusing operation by adjusting the distance between a camera sensor and the field lens. The field lens comprises four lenses, the first lens is a concave-convex lens, the second lens is a concave-convex lens, the third lens is a concave-convex lens, and the fourth lens is a double-convex lens. The application solves the problems of mechanical back intercept sensitivity and unstable optical axis in the traditional scheme, and realizes full-frame field of view close to the diffraction limit imaging in the visible light band under the premise of a short focal ratio. The application can be applied to the fields of astronomical observation and celestial photography.

Description

Technical Field

[0001] This invention belongs to the field of astronomical telescope technology, specifically a large field-of-view, short focal ratio Newtonian reflector telescope. Background Technology

[0002] Newtonian reflecting telescopes are commonly used for astrophotography and photography. Their drawback is that image quality is only good along the optical axis; off-axis image quality decreases as the field of view increases, and coma is the dominant off-axis aberration. The traditional solution is to install a coma corrector on the telescope's focusing mechanism. This corrector corrects off-axis aberrations, thereby increasing the usable field of view. In this traditional approach, the camera and other equipment are mounted at the rear of the coma corrector, which is then mounted on the focusing mechanism, which is mounted on the telescope tube. Focusing is achieved by adjusting the coma corrector's back-and-forth movement using the focusing mechanism. The disadvantage of this approach is that the optical and mechanical back-cutoff of the coma corrector are fixed values, with the mechanical back-cutoff typically being 55mm. The total thickness of the camera and other equipment must be exactly 55mm; otherwise, image quality will be severely degraded. However, due to machining and installation errors, it is difficult to ensure that the total thickness of the camera and other equipment exactly matches the mechanical back-cutoff of the coma corrector. Fixing the coma corrector to the focusing mechanism also causes optical axis instability during focusing. In addition, although existing coma correctors correct some aberrations, they still have the problem that the field of view cannot cover the entire frame, and they can only achieve good off-axis aberration correction on long focal ratio Newtonian reflector telescopes. Summary of the Invention

[0003] The purpose of this invention is to propose a design scheme for a large field-of-view, short focal ratio Newtonian reflector telescope to solve the above-mentioned problems.

[0004] The technical solution of the present invention is as follows: A large field of view, short focal ratio Newtonian reflector telescope, comprising a telescope tube (1), a primary mirror (6), a secondary mirror (5), a focuser (3), a mounting base (2), and a field lens (4). The primary mirror (6) is mounted on one side of the telescope tube (1), and the secondary mirror (5) is mounted on the other side of the telescope tube (1). The secondary mirror (5) is used to bend the light converged by the primary mirror (6) by 90 degrees into the field lens (4). The mounting base (2) is fixed on the telescope tube (1), the focuser (3) is fixed on the mounting base (2), and the field lens (4) is fixed on the mounting base (2) or the telescope tube (1).

[0005] The field lens (4) is fixed on the mounting base (2) or the lens barrel (1). When the focuser (3) is focusing, the field lens (4) remains stationary. The focuser (3) achieves focusing by changing the distance from the camera sensor to the field lens.

[0006] Furthermore, the focal ratio of the entire optical system is F3.5, and the effective image size is full-frame, i.e., 36x24mm.

[0007] Furthermore, the primary mirror (6) is parabolic, the secondary mirror (5) is planar, and the field mirror (4) includes four lenses: the first lens (41) is a concave-convex lens with the convex surface facing the object, the second lens (42) is a concave-convex lens with the convex surface facing the object, the third lens (43) is a concave-convex lens with the convex surface facing the object, and the fourth lens (44) is a biconvex lens.

[0008] Furthermore, the effective diameter of the primary mirror (6) is 250 mm, and the surface shape of the primary mirror satisfies the following formula: Where Z represents the sag and r represents the radial distance.

[0009] Furthermore, the first lens (41) of the field lens has a first surface radius of 76.8 mm and a second surface radius of 89.93 mm; the second lens (42) has a first surface radius of 323.89 mm and a second surface radius of 96.09 mm; the third lens (43) has a first surface radius of 105.29 mm and a second surface radius of 60.48 mm; and the fourth lens (44) has a first surface radius of 62.8 mm and a second surface radius of -281.82 mm. The sign of the radius is defined as follows: along the optical axis, with the object side on the left and the image side on the right, the radius is represented by the distance from the vertex of the sphere to the center of the sphere. The radius is positive from left to right and negative from right to left.

[0010] Furthermore, the distance between the first lens (41) and the second lens (42) is 19.558 mm, the distance between the second lens (42) and the third lens (43) is 78.89 mm, the distance between the third lens (43) and the fourth lens (44) is 4 mm, and the optical back cutoff is 75.3 mm.

[0011] Furthermore, the material of the first lens (41) is F1, the material of the second lens (42) is H-ZK9B, the material of the third lens (43) is H-LAF3B, and the material of the fourth lens (44) is H-QK3L.

[0012] The beneficial effects of this invention are as follows: 1. Traditional focusing methods involve fixing the field lens to a focusing device, the camera to the field lens, and the mechanical distance between the camera sensor and the field lens must be a fixed value (otherwise, image quality will degrade). Focusing is achieved by changing the distance between the field lens and the primary and secondary mirrors. In this invention, the field lens is fixed to a mounting base or lens barrel, and the camera to a focusing device. Focusing is achieved by changing the distance between the camera sensor and the field lens. In other words, mechanical backstop is not a concern when mounting the camera, as the focusing device always ensures the camera sensor is in perfect focus. 2. The effective field of view of this invention is full-frame. 3. This invention enables Newtonian reflecting telescopes to achieve a focal ratio as low as F3.5 while still providing near-diffraction-limited image quality. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 A schematic diagram of the overall structure of the large field-of-view, short focal ratio Newtonian reflecting telescope of this invention. Figure 2 Schematic diagram of field lens structure Figure 3 Point diagram of optical system Figure 4 Modulation Transfer Function (MTF) plot of an optical system Figure 5 Axial chromatic aberration diagram of optical system Detailed Implementation

[0015] The following are specific embodiments of the present invention, which, together with the accompanying drawings, will further describe the specific technical solutions of the present invention.

[0016] like Figure 1 As shown, the large field-of-view, short focal ratio Newtonian reflector telescope proposed in this invention includes a telescope tube (1), a mounting base (2), a focusing device (3), a field lens (4), a secondary lens (5), and a primary lens (6). The primary lens (6) is mounted on one side of the telescope tube (1), and the secondary lens (5) is mounted on the other side of the telescope tube (1). The secondary lens is used to rotate the optical axis by 90 degrees, allowing light to enter the field lens (4). The mounting base (2) is fixed to the telescope tube (1). The focusing device (3) is fixed to the mounting base (2). The field lens is fixed to either the mounting base (2) or the telescope tube (1). Cameras and other equipment are directly connected to the rear end of the focusing device. During focusing, the focusing device moves the camera back and forth until the camera sensor reaches the designed focal point to complete focusing.

[0017] The effective diameter of the primary mirror (6) is 250mm, and the surface shape of the primary mirror satisfies the following formula: Where Z represents the sag and r represents the radial distance.

[0018] like Figure 2 As shown, the field lens (4) includes four lenses: the first lens (41) is a concave-convex lens with its convex surface facing the object; the second lens (42) is a concave-convex lens with its convex surface facing the object; the third lens (43) is a concave-convex lens with its convex surface facing the object; and the fourth lens (44) is a biconvex lens. The parameters of the field lens are as follows: 76.8 5.6 F1 70 89.93 19.56 70 323.89 3.5 H-ZK9B 70 96.09 78.89 70 105.29 3.5 H-LAF3B 70 60.48 4 70 62.8 16 H-QK3L 70 -281.82 75.3 70

[0019] like Figure 3As shown, within the full frame and visible light range, the RMS radius of the dot plot is less than or approximately equal to the Airy disk radius. This indicates that the large field-of-view, short focal ratio Newtonian reflection optical system proposed in this invention has excellent image quality, concentrated image spot energy, and clear image quality.

[0020] like Figure 4 As shown, from a spatial frequency of 0 lp / mm up to 120 lp / mm, the modulation transfer function of this optical system is very close to the diffraction-limited MTF, indicating that the image quality of the large field-of-view, short focal ratio Newtonian reflection optical system proposed in this invention is close to the diffraction limit.

[0021] like Figure 5 As shown, the axial chromatic difference of the optical system is within ±0.04mm, indicating that the chromatic difference control of this system is excellent.

[0022] Matters not covered in this invention are common knowledge.

[0023] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A large field-of-view, short focal ratio Newtonian reflecting telescope, characterized in that: It includes a lens barrel (1), a primary lens (6), a secondary lens (5), a mounting base (2), a field lens (4), and a focuser (3). The primary lens (6) is mounted on one side of the lens barrel (1), the secondary lens (5) is mounted on the other side of the lens barrel, the mounting base (2) is fixed on the lens barrel (1), the focuser (3) is fixed on the mounting base (2), and the field lens (4) is fixed on the mounting base (2) or the lens barrel (1).

2. As described in claim 1, characterized in that: The distance between the field lens (4), the primary lens (6), and the secondary lens (5) along the optical axis remains unchanged, and the field lens (4) does not move with the focuser (3) during focusing.

3. As described in claim 1, characterized in that: The field lens (4) includes four lenses: the first lens (41) is a concave-convex lens with the convex surface facing the object; the second lens (42) is a concave-convex lens with the convex surface facing the object; the third lens (43) is a concave-convex lens with the convex surface facing the object; and the fourth lens (44) is a biconvex lens.

4. The field lens (4) according to claim 3, characterized in that: All lenses are spherical.

5. The field lens (4) according to claim 3, characterized in that: The first lens (41) has a positive optical power, the second lens (42) has a negative optical power, the third lens (43) has a negative optical power, and the fourth lens (44) has a positive optical power.

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