The image quality produced by a thermal camera lenses system depends on its detector and its optical components. The most important parameters for IR detectors used in thermal camera lenses are sensitivity, pixel pitch (pixel-to-pixel distance), and format (number of pixels). In conjunction with the imaging optics, the pixel pitch and format determine the spatial resolution and area of the target to be imaged. Generally, IR detectors for thermal camera lenses are much more expensive than their VIS spectrum counterparts. Consequently, large format detectors with pixel areas of 1024×768 are typically found on higher-end imaging cameras.
Detector sensitivity typically refers to the minimum detectable signal that gives a SNR value of one. The metric used to describe detector sensitivity is the normalized (or specific) detectivity (D*). This value accounts for the impacts of bandwidth and detector area and is intuitive in that larger values represent greater sensitivity. A description of the normalized detectivity, as well as typical values for IR detectors, are given in Radiometric Measurement. In addition to the detector sensitivity, the amount of radiation that reaches the detector ultimately determines the detection range of a thermal camera lenses system. Other factors that contribute to the detection range include the target parameters, e.g., size, temperature, emissivity – the ratio of an object’s radiance to that emitted by a blackbody radiator, and atmospheric transmission.