An infra-red detection device comprising an infra-red detection section; a plurality of optical elements arranged to direct infra-red radiation to the infrared detection section; and a masking section arranged to partially mask a first optical element of the plurality of optical elements, such that a first part of the first optical element is masked and a second part of the first optical element is not masked, such that the masking section is arranged to attenuate infra-red radiation directed via the first optical element.