Influence of fabrication errors on imaging performance for the 2.5m telescope primary mirror

The primary scientific objectives of the Purple Mountain Observatory's (PMO) 2.5-meter Multi-Terminal Universal Telescope are high-precision astrometry of solar system objects and lunar laser ranging. To ensure the telescope's ultimate measurement accuracy, exceptional optical quality is required, imposing stringent specifications on the surface figure of the primary mirror. However, during the primary mirror fabrication process, it was observed that the impact of various residual manufacturing errors (e.g., surface figure errors, mid-to-high-frequency errors) on final imaging quality remains inadequately characterized under diffraction-limited constraints. Therefore, this paper systematically analyzes the influence of primary mirror surface errors on imaging quality under diffraction-limited requirements. It investigates characterization methods for primary mirror surface figure errors, aiming to establish clear control specifications—including permissible amplitudes, spatial frequency spectra, and distribution patterns—for optical surface errors across different bandwidths. This will enable the development of an optimized surface quality evaluation methodology. The outcomes of this work will not only directly guide the fabrication of the primary mirror for the 2.5-meter Multi-Terminal Universal Telescope but also provide significant insights for the manufacturing of future large-aperture primary mirrors.