Design of reflective active zoom systems with four mirrors

The traditional zoom systems usually change the spaces between optical components to realize the variable focal lengths. Based on active optics, a new type of reflective active zoom system with four mirrors is proposed, which is different from the traditional zoom system by changing the spaces between optical components1. The new zoom system consists of an afocal front group with three mirrors, and the fourth mirror used for focusing. The relation among the four mirrors is determined by the Pezval condition. The secondary and third are deformable mirrors, contributing to the transition among different focal lengths by the curvature radius variation controlled by the voltage, with the constraints limiting its' changing rules. According to the designed system characteristics and the practical requirements, based on 3rd-order aberration theory, a set of Seidel aberration coefficient functions are established, with the constraint limitations. Then the initial construction parameters of the optical system can be achieved. The new active zoom system with four mirrors can realize that the zoom rario is 3, the focal lengths vary from 100mm to 300mm, and the field angle of view range is 0.22° -3.6°, and the wide working band is from the visible to the infrared. At the same time, because of the control flexibility, the active optical zoom system has the potential to be widely applied in remote sensing, life medical and other fields.