NVST Defocus-Detect System

During the continuous observation in 1-meter New Vacuum Solar Telescope, the solar radiation changes the temperature of the telescope surface, resulting in the thermal deformation on the optical and mechanical structure of the telescope. This results in real-time variation of the telescope focus, which produces the defocus aberration in the observation data. Thus it is of importance for the observation to detect and correct the defocus. This paper describes the design and implementation of a defocus-detect system, based on the optical and mechanical structure of this telescope, and the scanning defocus-detect algorithm is used. Firstly, the variation of defocus causing by temperature change is analyzed and the overall design of the defocus-detect system is given. Then the detailed design and implementation of its hardware and software system is described, subsequently the test results of the repeat position precision and detect error show that this defocus-detect system meets the requirement of the observation. At the last part of this paper, the performance of this system on the telescope with 3-months continuous observation is displayed. And it shows that this system can detect and correct the real-time variation of the telescope defocus, and has a positive influence on the quality of the observation data.