Infrared imagers are important for reorganization and monitoring. This paper discusses the design of an infrared imager. Optical design in medium wavelength infrared (MWIR) and long wavelength infrared (LWIR) bands is different and needs distinct detectors and materials. Reflective systems are not suitable due to their small field of view (FOV) and vignetting. Refractive dual band optical system has been designed with considering both regions assessment and each band detector specifications.