Electromagnetic-radiation detection system comprising: a casing defining an enclosure in which a partial vacuum prevails, comprising a window transparent to said electromagnetic radiation; a cold finger having a side wall closed at one end by an end wall situated in line with the window; a sensor, mounted on the end wall, having a flat top surface disposed facing the window comprising detectors sensitive to electromagnetic radiation and cooled by the cold finger, said sensor defining an optical axis perpendicular to the flat top surface and centred with respect thereto; a cold screen surrounding the sensor, substantially in the form of a dome, mounted on the cold finger and generated by rotation about the optical axis, and comprising a top end, disposed between the window and the sensor, defining a circular-shaped diaphragm centred on the optical axis and a side wall connecting a base of the cold screen to the top end having an internal face with its concavity turned towards the optical axis; characterised in that the system comprises: at least one bandpass electromagnetic-radiation filter having a predefined transmission coefficient, each filter being movable and being able to adopt a first position in which it is placed outside the casing facing the window and a second position in which it is placed so as to not filter any electromagnetic radiation received by the system, in said first position each filter has in cross section in any secant plane containing the optical axis a concave form turned towards the sensor having a profile with a conical and/or aspherical base and reflects the focal plane inside the casing; and processing means for evaluating, for each detector of the sensor, a gain and an offset value using a first value supplied by said detector when each filter is in the second position and at least one second value supplied by said detector when a filter among the at least one filter is in the first position. a casing defining an enclosure in which a partial vacuum prevails, comprising a window transparent to said electromagnetic radiation; a cold finger having a side wall closed at one end by an end wall situated in line with the window; a sensor, mounted on the end wall, having a flat top surface disposed facing the window comprising detectors sensitive to electromagnetic radiation and cooled by the cold finger, said sensor defining an optical axis perpendicular to the flat top surface and centred with respect thereto; a cold screen surrounding the sensor, substantially in the form of a dome, mounted on the cold finger and generated by rotation about the optical axis, and comprising a top end, disposed between the window and the sensor, defining a circular-shaped diaphragm centred on the optical axis and a side wall connecting a base of the cold screen to the top end having an internal face with its concavity turned towards the optical axis; characterised in that the system comprises: at least one bandpass electromagnetic-radiation filter having a predefined transmission coefficient, each filter being movable and being able to adopt a first position in which it is placed outside the casing facing the window and a second position in which it is placed so as to not filter any electromagnetic radiation received by the system, in said first position each filter has in cross section in any secant plane containing the optical axis a concave form turned towards the sensor having a profile with a conical and/or aspherical base and reflects the focal plane inside the casing; and processing means for evaluating, for each detector of the sensor, a gain and an offset value using a first value supplied by said detector when each filter is in the second position and at least one second value supplied by said detector when a filter among the at least one filter is in the first position. at least one bandpass electromagnetic-radiation filter having a predefined transmission coefficient, each filter being movable and being able to adopt a first position in which it is placed outside the casing facing the window and a second position in which it is placed so as to not filter any electromagnetic radiation received by the system, in said first position each filter has in cross section in any secant plane containing the optical axis a concave form turned towards the sensor having a profile with a conical and/or aspherical base and reflects the focal plane inside the casing; and processing means for evaluating, for each detector of the sensor, a gain and an offset value using a first value supplied by said detector when each filter is in the second position and at least one second value supplied by said detector when a filter among the at least one filter is in the first position.