A step-zoom and reimaging structure were utilized to construct a dual field-of-view optical design for high-magnification switching in the 3-5 microm spectral band. The design has a flexible optomechanical layout, which means it can be utilized for multipurpose applications. The effects of the surrounding environmental temperature and axial gradient temperature are analyzed using the concept of thermal resistance, and the thermal compensation is discussed. A description of the zooming mechanism and optomechanical control is offered.