The design of a triple-field-of-view optical system for 3- to 5-μm infrared focal-plane arrays is described. Preliminary calculations are done to determine the first-order parameters of the narrow-, medium-, and wide-field-of-view modes. An optical configuration based on the combination of axial motion of a lens group and the rotate-in motion of two separated lens groups is used. Diffractive and aspheric surfaces are employed to control the color and monochromatic aberrations, thereby decreasing the total number of lenses used. Paraxial and real-ray modeling of the narcissus effect, which plays an important role in the optical design of infrared systems, is explained. The final optical designs along with their aberrations curves and polychromatic modulation transfer function plots are presented, showing acceptable performance in all fields of view.