A Study of Optimization of the Focus in the FAST

FAST will be a Five-hundred-meters Aperture Spherical Telescope built in Guizhou Province, China. The active panels can be simulated to a parabola in time during tracking a source. It is important to choose an optimal focus to ensure a minimum deviation from a spherical panels to the parabola, a minimum relative displacement of panels for the simulating and feasibility of utilization of multi-parabola fitting scheme. An optimal focus could also reduce problems of collision or unnecessarily larger gaps between panels in simulation, realization of multi-beam scheme and decrease errors in programming and adjusting the panels. A study of optimization of focus in the FAST is introduced in this paper.