Design method for large zoom ratio freeform reflective zoom systems based on initial configuration optimization using global algorithms

Reflective zoom optical systems are characterized by lightweight design and intrinsic achromaticity, making them highly adaptable to complex environmental conditions. However, due to constraints such as the feasible solution space of the zoom equation and physical collisions during the zoom process, achieving a large zoom ratio in reflective zoom optical systems has remained a significant challenge. Recognizing the critical role of the initial configuration in enabling a large zoom ratio in reflective zoom systems, we propose what we believe to be a novel design method for large zoom ratio off-axis reflective zoom optical systems. The proposed method begins by deriving the zoom equations and aberration characteristics of mechanically compensated reflective zoom systems. Based on these derivations, a global merit function <i>G</i> is constructed, integrating zoom ratio and imaging quality as evaluation metrics. Utilizing this merit function, a global optimization algorithm is employed to perform a comprehensive search across the design space, yielding an initial configuration with the potential for a large zoom ratio. Finally, this initial configuration is further refined by incorporating freeform surfaces and other complex optical geometries, culminating in the successful realization of a large zoom ratio off-axis three-mirror reflective zoom optical system. This method offers what we feel is a novel approach for designing reflective zoom optical systems with large zoom ratios.