Thermal imagers based on an uncooled microbolometer detector are finding many applications in short-range devices because of cost effectiveness. A typical application for such a system is firefighting, by providing visibility through smoke and absolute darkness. The design of an objective lens for an infrared (IR) camera to be utilized in firefighting is described. Because of the relatively poor responsivity of the thermal detector, the objective lens is to be operated at fast f-numbers (typically f/1 or faster). The proposed camera lens is simple and lightweight, able to operate under harsh ambient conditions, gives acceptable image quality for various object distances as well as operating temperatures without any focus adjustment, and has a wide field of view and an auto-iris facility. The design constraints of such lenses are also discussed. The performance evaluation curves of the lens of the camera and a few photographs taken with the camera in a fire situation are presented. Experimental results are in accordance with the predicted values.
"Optical design and salient features of an objective for a firefighting camera," Optical Engineering 46(8), 083001 (1 August 2007). https://doi.org/10.1117/1.2768080