A geometric and radiometric calibration and test apparatus for testing electro-optical thermal-IR instruments, the apparatus being designed to simulate different angularly-extending thermal-IR sources with different geometries and with thermal-IR emissions containing different hot-cold transitions; the geometric and radiometric calibration and test apparatus comprising: : - an IR collimator having an optical axis ( Z ), a focal plane ( F ), and a focal length ( f ); - a thermal-IR source mounted to be controllably movable relative to the collimator , to be arrangeable and displaceable in the focal plane ( F ) of the collimator , and to be operable to radiate towards the collimator thermal-IR radiations, - a kit of masks individually interchangeably arrangeable between the thermal-IR source and the collimator so as to integrally move with the thermal-IR source to provide the wavefront of the thermal-IR radiations from the thermal-IR source with geometric and radiometric properties such as to cause calibration or test patterns containing different hot-cold transitions to be reproduced on the electro-optical instrument to be calibrated or tested; means for measuring ambient temperature; a computer; and means for moving the thermal-IR source and mask ; the thermal-IR source together with the mask , being movable by the means for moving under control of the computer along the optical axis (Z) of the IR collimator to compensate for variations in the focal length (f) of the IR collimator due to ambient temperature changes. the geometric and radiometric calibration and test apparatus comprising: : - an IR collimator having an optical axis ( Z ), a focal plane ( F ), and a focal length ( f ); - a thermal-IR source mounted to be controllably movable relative to the collimator , to be arrangeable and displaceable in the focal plane ( F ) of the collimator , and to be operable to radiate towards the collimator thermal-IR radiations, - a kit of masks individually interchangeably arrangeable between the thermal-IR source and the collimator so as to integrally move with the thermal-IR source to provide the wavefront of the thermal-IR radiations from the thermal-IR source with geometric and radiometric properties such as to cause calibration or test patterns containing different hot-cold transitions to be reproduced on the electro-optical instrument to be calibrated or tested; - an IR collimator having an optical axis ( Z ), a focal plane ( F ), and a focal length ( f ); - a thermal-IR source mounted to be controllably movable relative to the collimator , to be arrangeable and displaceable in the focal plane ( F ) of the collimator , and to be operable to radiate towards the collimator thermal-IR radiations, - a kit of masks individually interchangeably arrangeable between the thermal-IR source and the collimator so as to integrally move with the thermal-IR source to provide the wavefront of the thermal-IR radiations from the thermal-IR source with geometric and radiometric properties such as to cause calibration or test patterns containing different hot-cold transitions to be reproduced on the electro-optical instrument to be calibrated or tested; means for measuring ambient temperature; a computer; and means for moving the thermal-IR source and mask ; the thermal-IR source together with the mask , being movable by the means for moving under control of the computer along the optical axis (Z) of the IR collimator to compensate for variations in the focal length (f) of the IR collimator due to ambient temperature changes. <EOS>