Stray light analysis and suppression of an ultra-high-magnification zoom endoscopy

Ultra-high-magnification zoom electronic endoscopes are highly susceptible to stray light because compact optomechanical layouts and zoom-dependent optical reconfiguration strongly affect non-imaging light propagation. In compact systems with a small-aperture moving lens group, indiscriminate barrel blackening is not always desirable because coating degradation or peeling may compromise imaging reliability. This study presents a simulation-guided, state-dependent stray light analysis and suppression strategy for a compact ultra-high-magnification zoom endoscope. Monte Carlo ray tracing was performed at different zoom positions to identify the dominant stray light paths in the conventional, low-magnification, and high-magnification modes. The results show that the dominant sources vary significantly with zoom state; as the system moves toward near-focus and high-magnification operation, changes in group position, back focal distance, and ray geometry increase interaction with critical surfaces, leading to stronger ghosting and background stray light. Based on this analysis, targeted suppression measures were implemented at the corresponding critical locations, including reflectance optimization of key optical interfaces, selective blackening of lens edges and mechanical surfaces, and local baffling. Both simulation and experiment confirm that the proposed strategy effectively suppresses ghost artifacts and background stray light while improving image contrast, luminance uniformity, and detail visibility, especially in the high-magnification mode. This work provides a practical framework for state-dependent stray light control in compact ultra-high-magnification zoom endoscopes.