阅读说明：本技术 一种大视场宽波段天文望远镜光学系统 (Optical system of wide-field wide-band astronomical telescope ) 是由 董云芬 王斌 于 2019-09-11 设计创作，主要内容包括：本发明公开了一种大视场宽波段天文望远镜光学系统,包括反射式施密特矫正板、平面折转镜、球面反射镜、焦面；其中,光线依次经过施密特矫正板、平面折转镜、球面反射镜到达焦面；其中,焦面位于平面折转镜的背面。施密特矫正板位于球面反射镜的球心,施密特矫正板为正轴高次非球面。本发明在反射式施密特矫正板与球面镜之间插入折转镜,使焦面位于系统外部,方便目视,同时缩短了筒长,使光学结构更加紧凑；更重要的是,设计的反射式施密特矫正板属于正轴高次非球面,并且设计阶段控制非球面度在易加工检测范围内,使得施密特系统加工成本较低。(The invention discloses a wide-field wide-band astronomical telescope optical system, which comprises a reflective Schmidt correction plate, a plane turning mirror, a spherical reflector and a focal plane, wherein the reflective Schmidt correction plate is arranged on the focal plane; wherein, the light rays sequentially pass through the Schmidt correction plate, the plane turning mirror and the spherical reflector to reach the focal plane; wherein the focal plane is positioned on the back of the plane turning mirror. The Schmidt correction plate is positioned at the spherical center of the spherical reflector, and the Schmidt correction plate is a positive-axis high-order aspheric surface. According to the invention, the folding mirror is inserted between the reflective Schmidt correction plate and the spherical mirror, so that the focal plane is positioned outside the system, the visual observation is convenient, the cylinder length is shortened, and the optical structure is more compact; more importantly, the designed reflective Schmidt correction plate belongs to a positive-axis high-order aspheric surface, and the aspheric degree is controlled within an easy-processing detection range in the design stage, so that the processing cost of a Schmidt system is low.)

1. A wide-field wide-band astronomical telescope optical system is characterized in that: comprises a reflective Schmidt correction plate, a plane turning mirror, a spherical reflector and a focal plane; wherein, the light rays sequentially pass through the Schmidt correction plate, the plane turning mirror and the spherical reflector to reach the focal plane; wherein the focal plane is positioned on the back surface of the plane turning mirror.

2. The large-field-of-view, broadband astronomical telescope optical system of claim 1, wherein: the Schmidt correction plate is positioned at the spherical center of the spherical reflector, and the Schmidt correction plate is a positive-axis high-order aspheric surface.

3. the large-field-of-view, broadband astronomical telescope optical system of claim 1, wherein: the Schmidt correction plate forms an included angle of 10 degrees with the optical axis of incident light.

4. the large-field-of-view, broadband astronomical telescope optical system of claim 1, wherein: the optical surface of the Schmidt correction plate is a non-focal aspheric surface, the surface type is determined by the following formula,

x＝Ay+By+Cy+Dy+····

In the formula, A, B, C, D is a characteristic parameter of the schmidt correction plate, y is the height of the aspheric surface from the optical axis, and x is the height of the aspheric surface.

5. The large-field-of-view, broadband astronomical telescope optical system of claim 1, wherein: the center of the plane turning mirror is provided with an opening through which light passes, and the plane turning mirror and the Schmidt correction plate are arranged in parallel or form an included angle of 45 degrees with an optical axis.

6. The large-field-of-view, broadband astronomical telescope optical system of claim 1, wherein: the Schmidt correction plate and/or the plane turning mirror and/or the spherical reflector are metal or glass reflectors.

Technical Field

The invention belongs to the field of optical instruments, particularly relates to an astronomical telescope optical system with a large field of view, a wide waveband and low cost, and particularly relates to an improved total reflection type Schmidt optical system.

background

An optical astronomical telescope is one of important instruments for observing celestial bodies, and a low-cost and high-performance astronomical telescope is a hot spot of current research and development.

Telescope optical systems can be classified into three categories according to the type of objective lens: refractive systems, reflective systems, and catadioptric systems. The refractive system lens with large aperture and large relative aperture has high material and processing cost, so the price is very high. The common optical system of the reflection type telescope comprises a Newton system, a Cassegrain system, a Gregorian system and the like, and the reflection system has weaker off-axis aberration correction capability and smaller field angle of clear imaging, which is generally less than +/-1 DEG and can not meet the requirement of a large-field telescope. The catadioptric system is based on spherical mirror and adds proper refraction element to correct the spherical aberration outside the axis, so as to obtain good optical quality.

The schmitt system has the advantages of large field of view, good image quality and the like, and is one of the most widely applied catadioptric systems. Conventional schmitt systems consist of a spherical mirror and a schmitt correction plate, which can be either a transmissive element or a reflective element. The correcting plate of the traditional reflective Schmidt system is positioned at the center of a spherical lens, is an off-axis high-order aspheric surface, has higher processing and detecting cost, longer lens cone and huge volume, and the focal plane is positioned in the system and is inconvenient to view, so the correcting plate is rarely applied to the popular science astronomical telescopes produced in batches.

Disclosure of Invention

The invention provides an astronomical telescope optical system with large field of view, wide waveband and low cost.A turning mirror is inserted between a reflective Schmidt correction plate and a spherical mirror, so that a focal plane is positioned outside the system, the visual observation is convenient, and the tube length is shortened at the same time, so that the optical structure is more compact; more importantly, the designed reflective Schmidt correction plate belongs to a positive-axis high-order aspheric surface, and the aspheric degree is controlled within an easy-processing detection range in the design stage, so that the processing cost of a Schmidt system is low.

the invention is realized by the following technical scheme:

An optical system of a wide-field wide-band astronomical telescope comprises a reflective Schmidt correction plate, a plane turning mirror, a spherical reflector and a focal plane; wherein, the light rays sequentially pass through the Schmidt correction plate, the plane turning mirror and the spherical reflector to reach the focal plane; wherein the focal plane is positioned on the back surface of the plane turning mirror.

Further, the schmidt correction plate is located at the center of the sphere of the spherical mirror, and the schmidt correction plate is an orthoaxial high-order aspheric surface.

Further, the schmitt correction plate is at a 10 ° angle to the optical axis of the incident light.

further, the optical surface of the schmitt correction plate is an aspherical surface having no optical power, and the surface shape is determined by the following formula,

x＝Ay+By+Cy+Dy+····

In the formula, A, B, C, D is a characteristic parameter of the schmidt correction plate, y is the height of the aspheric surface from the optical axis, and x is the height of the aspheric surface.

Furthermore, the center of the plane turning mirror is provided with an opening for light to pass through, and the plane turning mirror and the Schmidt correction plate are arranged in parallel or form an included angle of 45 degrees with the optical axis.

Further, the schmidt correction plate and/or the plane turning mirror and/or the spherical mirror is a metal or glass mirror.

The invention has the following technical effects:

1. The invention provides an astronomical telescope optical system with large field of view, wide waveband and low cost, which is a total reflection optical system, has no chromatic aberration caused by the wide waveband and has good imaging quality;

2. The invention adopts three reflectors to perform light path deflection, so that the overall length of the long-focus system is reduced, and the light path structure is more compact;

3. The Schmidt correction plate is a high-order aspheric surface, the processing removal amount of the Schmidt correction plate is accurately controlled in the design process, the maximum aspheric surface is only 0.005mm, the processing period is short, and high-precision detection is easy to realize.

4. compared with the existing three-mirror system with the same caliber, the optical system of the invention improves the view field; the primary mirror, the secondary mirror and the tertiary mirror of the three-mirror system with the same caliber are all aspheric surfaces, the processing period is long, and the cost is high.

drawings

FIG. 1 is a schematic view of an optical structure according to the present invention;

FIG. 2 is a graph of MTF of an optical system according to the present invention;

FIG. 3 is a schematic view of an optical structure according to embodiment 1 of the present invention;

FIG. 4 is a MTF graph of an optical system according to embodiment 1 of the present invention;

The labels in the figure are: 1. a schmidt correction plate; 2. a plane turning mirror; 3. spherical mirror 4, focal plane.

Detailed Description

The invention is further illustrated in example 1 with reference to the accompanying drawings:

The optical system design criteria are as follows:

effective caliber: 400mm

optical field of view: full field of view 4 °

the system focal length: 1700mm

Image quality: MTF greater than 0.3 at Nyquist frequency

The working wave band is as follows: 400 nm-900 nm

the structural schematic diagram of the optical system of the 400mm caliber telescope is shown in fig. 1, and fig. 2 is an MTF curve graph of the optical system provided by the invention. The telescope optical system comprises a Schmidt correction plate 1, a plane turning mirror 2, a spherical reflector 3 and a focal plane 4. Wherein, according to the incident direction of the light, the light is incident from left to right, and the light sequentially passes through the Schmidt correction plate 1, the plane turning mirror 2, the spherical reflector 3 and the focal plane 4. The schmidt correction plate is positioned at the spherical center of the spherical reflector, so that the spherical aberration of the whole system can be well corrected, and the system does not generate coma aberration, astigmatism and distortion but only has field curvature.

The large-field schmitt optical system design parameters are as follows:

Aspheric coefficient of correction plate: 2-order coefficient: a ═ 1.70 × 10-7, 4 th order coefficient: b-3.112 × 10-12, 6-degree term coefficient: c-4.177 × 10-19, 8-degree term coefficient: d is-1.662X 10-25 with a Schmidt correction plate equation of

x＝-1.7×10y+3.112×10y+4.177×10y+(-1.662×10)y

The working spectrum section of the system is 400 nm-900 nm, the focal length of the system is f 1700mm, the field angle 2 omega is 4 degrees, and the effective light-passing aperture is 400 mm. And (3) image quality evaluation: the modulation transfer function MTF of the system at the Nyquist frequency is larger than 0.35 in the full field range, the distortion is smaller than 2.5%, and the imaging quality reaches the diffraction limit. After the optimization design, the maximum deviation between the Schmidt correction plate and the approximate spherical surface is 0.005mm, and the surface shape high-precision detection can be completed by adopting a special compensator and an interferometer. The Schmitt system can provide reference for the development of wide-field wide-band astronomical telescopes.