For detecting exoplanets with high precision, using the angular distance between the two stars to detect the periodic motion of the star will be a better choice. This approach can avoid importing the position error of the reference catalog in the process that using the traditional photographic plate to derive the star position. At the precision level of microarcseconds, the error caused by optical axis deviation is not negligible. In this paper, we evaluate the impact of the stability of the optical axis on the relative angular distance measurement from the aspects of theoretical analysis and numerical simulation. When the angular distance error limit of 1~microarcsecond is given, the upper limit of optical axis deviation is estimated to be 68~milliarcsecond. In addition, when limiting the deviation of the optical axis, we give the corresponding error allowance of angular distance measurement. Moreover, we also discuss the way to resolve the problem of CCD distortion and focal length change on the measurement of angular distance. The work in this paper is of guiding significance to the design of the telescope.

Atmosphere turbulence often degrades image quality in long range infrared imaging system due to intensity fluctuations, distortion, and blur effects. In this work, long range infrared imaging through anisotropic turbulence is simulated, which combines the theoretical turbulence effects models of optical waves (the angle of arrival fluctuations of optical wave and the modulation transfer function) under anisotropic non-Kolmogorov turbulence and the imaging processing algorithms (image convolution and interpolation methods). This simulation technique allows the performance assessment of a long range infrared imaging system under various anisotropic atmosphere turbulence conditions to be done in a cost efficient manner. Simulation uses single image containing no turbulence effects as an input and produces image sequences degraded by specified turbulence. Imaging distance, optics diameter, wavelength, anisotropic factor, general spectral power law, and turbulence strength are included. The influence of anisotropic non-Kolmogorov turbulence on the long range infrared imaging system is analyzed.