A flexible and effective calibration method for fiber viewing camera in multi-object fiber-fed telescope

Abstract The positioning accuracy of the robotic fiber positioners (RFPs) is a crucial issue because incorrect fiber position can significantly affect the spectral quality. The fiber viewing camera is implemented to guide the fiber positioning. However, the current camera calibration methods are inconvenient for the narrow space of the telescope. To solve this problem, a flexible separated calibration method is proposed in this study. Firstly, the initial calibration is completed by traditional Zhang’s method. Secondly, multiple small planar targets (SPTs) are placed on the focal plane to form a spliced large target (SLT) to calibrate the lens aberrations. Then, the home position of the RFPs is used as a variable control point to calibrate the extrinsic parameters. Furthermore, an improved weighted multiple harmonic (WMH) method is proposed to obtain accurate centroids of the deformed light spot. A prototype fiber position detection system is constructed in the laboratory. Physical experiments verify the effectiveness and flexibility of the proposed method, which has practical engineering significance.