Infrared Focal Plane Array cameras have several aberrations and measurement artefacts with different material origins: lenses, sensors, Read-Out-Circuits of the sensors. The authors' goal is to characterize each artefact separately to obtain more versatile correction procedures and improve the correction accuracy. This paper focuses on some radiometric artefacts associated with variations of measured illuminance. It presents a new correction algorithm dedicated to Narcissus and vignetting effects, which is identified and validated for two different lenses. It also proposes an innovative experimental protocol to detect low-level contrast-induced artefacts. Several R&D cameras and lenses are tested and some present such artefacts, which can not be corrected by traditional pixel-to-pixel methods. Their origins are shown to derive either from the optical system or the Read-Out-Circuit.