Influence of atmospheric dispersion on image resolution of 4 m telescope and correction method
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摘要: 本文分析研究大气色散对4 m望远镜成像系统分辨率的影响及校正方法。首先计算分析了大气色散对其成像分辨力的影响,计算结果表明,天顶角大于15°时,大气色散开始影响系统成像分辨力,天顶角大于45°时,对系统成像分辨力有着较为严重的影响,需要设置大气色散校正器来进行消除。本文列举了3种大气色散校正器的实现形式,分别比较了它们的优缺点,最后选择了胶合棱镜旋转补偿的形式来消除大气色散对4 m望远镜高分辨力成像系统的影响。基于4 m望远镜高分辨力成像系统的特点,将大气色散校正器放置于成像元件前的平行光路中,并利用光学设计软件对不同天顶角与大气色散校正器的旋转角度进行了仿真分析,该大气色散校正器的最大楔角为9.65°,旋转精度为±0.1°,对系统分辨力影响为1/1 000。分析结果表明,旋转精度完全能够满足系统成像分辨力的要求,证明本文对大气色散的影响分析和大气色散校正器的设计是有效的。Abstract: This paper counts and analyzes the effect of atmospheric dispersion on image resolution of 4 m optical telescope system. It is introduced that atmospheric dispersion will influence image resolution when the zenith angle is larger than 15°. With the zenith angle increasing, especially up to 45°, the image quality would be degraded greatly, so it is quite necessary that the atmospheric dispersion corrector(ADC) is applied to compensate atmospheric dispersion. By comparing the advantages and drawbacks of three modes for ADC:tilt mode, move mode and rotate mode, the glue prism pairs is used to eliminate the influence of atmospheric dispersion for 4 m telescope system, which would rotate with each other when the zenith angle changes. In 4 m telescope optical system, the ADC is positioned in front of imaging elements of collimated optical layout. Then we analyze the relation between zenith angle and rotating angle of ADC. The largest wedge angle of the ADC is 9.65°, and the rotating accuracy is ±0.1°, having an effect of 1/1 000 on resolution. So it is obviously concluded that the results satisfied the request of image resolution, and it is an effective way for the analysis of atmospheric dispersion and the application of ADC.
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Key words:
- atmospheric dispersion corrector /
- telescope /
- resolution /
- optical design
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图 2 大气色散与衍射极限分辨力的对比
Figure 2. Comparison of atmospheric dispersion and diffraction-limited resolution
图 12 H-F2和H-ZK4的折射率曲线
Figure 12. Refractive index changes of H-F2 and H-ZK4 with wavelength
图 13 棱镜旋转角度与天顶角的关系
Figure 13. Relationship between prism pairs rotation and zenith angle
图 14 大气色散校正后的系统点列图
Figure 14. Spot diagram of 4 m optical system after the correction of atmospheric dispersion
表 1 大口径望远镜进行大气色散补偿的参数
Table 1. Parameter of atmospheric dispersion compensation for large aperture telescopes
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