Design method for the off-axis four-mirror imaging system with a real ray tracing model and the distance constraint between adjacent mirrors

With the development of optical manufacturing and alignment technologies, the off-axis four-mirror imaging system plays an increasingly important role in achieving high performance. The initial structure, which includes more constraints, can significantly reduce the dependence on the experience of optical designers. In this paper, a design method with a real ray tracing model and the distance constraint between adjacent mirrors is proposed to design the off-axis four-mirror imaging system. First, in the local coordinate systems of each mirror, the parameters of each mirror are calculated separately according to the marginal ray and the lateral and longitudinal distance constraints between the adjacent mirrors. Then, the decenter and tilt of each mirror will be calculated through the real ray tracing model. Finally, by iterating the above process, the reasonable unobscured off-axis initial structure, which can be taken as a good starting point for further optimization, will be calculated. An off-axis four-mirror imaging system with high performance in the visible band was designed to demonstrate the feasibility of the proposed method.