Optical design of off-axis reflective zoom imaging system based on wave-aberration control and focal-length approximation

Reflective zoom systems can be used in many areas owing to their characteristics of simplified layout, good imaging performance, and wide spectrum. In this paper, we propose a design method for off-axis reflective zoom optical systems (ORZOS) based on wave-aberration control and focal-length approximation. In the proposed method, the optical system is processed linearly when it is perturbed slightly. On the premise of linearity, the change rate of wave aberration can be predicted based on the rays tracing data of the unperturbed system, the type of perturbation, and the location changes of chief rays after adding perturbation. The constraint matrix for suitable parameter combination is then constructed and solved. In this process, the required focal length of the zoom system can be gradually approached through several iterations. To verify the feasibility of this method, an off-axis three-mirror zoom imaging optical system is designed. The F number is 5, and the zoom ratio is 4 times. The modulation transfer function of different focal lengths and fields of view all exceed 0.49 at 100 cycles/mm and is close to that of the diffraction limit imaging, thereby proving the effectiveness of the proposed method.